Publications by authors named "Jarrod Call"

52 Publications

Lifelong Ulk1-Mediated Autophagy Deficiency in Muscle Induces Mitochondrial Dysfunction and Contractile Weakness.

Int J Mol Sci 2021 Feb 16;22(4). Epub 2021 Feb 16.

Department of Kinesiology, University of Georgia, Athens, GA 30602, USA.

The accumulation of damaged mitochondria due to insufficient autophagy has been implicated in the pathophysiology of skeletal muscle aging. Ulk1 is an autophagy-related kinase that initiates autophagosome assembly and may also play a role in autophagosome degradation (i.e., autophagy flux), but the contribution of Ulk1 to healthy muscle aging is unclear. Therefore, the purpose of this study was to investigate the role of Ulk1-mediated autophagy in skeletal muscle aging. At age 22 months (80% survival rate), muscle contractile and metabolic function were assessed using electrophysiology in muscle-specific Ulk1 knockout mice (MKO) and their littermate controls (LM). Specific peak-isometric torque of the ankle dorsiflexors (normalized by tibialis anterior muscle cross-sectional area) and specific force of the fast-twitch extensor digitorum longus muscles was reduced in MKO mice compared to LM mice ( < 0.03). Permeabilized muscle fibers from MKO mice had greater mitochondrial content, yet lower mitochondrial oxygen consumption and greater reactive oxygen species production compared to fibers from LM mice ( ≤ 0.04). Alterations in neuromuscular junction innervation patterns as well as changes to autophagosome assembly and flux were explored as possible contributors to the pathological features in Ulk1 deficiency. Of primary interest, we found that Ulk1 phosphorylation (activation) to total Ulk1 protein content was reduced in older muscles compared to young muscles from both human and mouse, which may contribute to decreased autophagy flux and an accumulation of dysfunctional mitochondria. Results from this study support the role of Ulk1-mediated autophagy in aging skeletal muscle, reflecting Ulk1's dual role in maintaining mitochondrial integrity through autophagosome assembly and degradation.
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http://dx.doi.org/10.3390/ijms22041937DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7919824PMC
February 2021

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition).

Autophagy 2021 Jan 8;17(1):1-382. Epub 2021 Feb 8.

University of Crete, School of Medicine, Laboratory of Clinical Microbiology and Microbial Pathogenesis, Voutes, Heraklion, Crete, Greece; Foundation for Research and Technology, Institute of Molecular Biology and Biotechnology (IMBB), Heraklion, Crete, Greece.

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.
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http://dx.doi.org/10.1080/15548627.2020.1797280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7996087PMC
January 2021

Mitochondria-cytokine crosstalk following skeletal muscle injury and disuse: a mini-review.

Am J Physiol Cell Physiol 2021 05 10;320(5):C681-C688. Epub 2021 Feb 10.

Department of Kinesiology, University of Georgia, Athens, Georgia.

Skeletal muscle mitochondria are highly adaptable, highly dynamic organelles that maintain the functional integrity of the muscle fiber by providing ATP for contraction and cellular homeostasis (e.g., Na/K ATPase). Emerging as early modulators of inflammation, mitochondria sense and respond to cellular stress. Mitochondria communicate with the environment, in part, by release of physical signals called mitochondrial-derived damage-associated molecular patterns (mito-DAMPs) and deviation from routine function (e.g., reduced ATP production, Ca overload). When skeletal muscle is compromised, mitochondria contribute to an acute inflammatory response necessary for myofibril regeneration; however, exhaustive signaling associated with altered or reduced mitochondrial function can be detrimental to muscle outcomes. Here, we describe changes in mitochondrial content, structure, and function following skeletal muscle injury and disuse and highlight the influence of mitochondria-cytokine crosstalk on muscle regeneration and recovery. Although the appropriate therapeutic modulation following muscle stressors remains unknown, retrospective gene expression analysis reveals that interleukin-6 (IL-6), interleukin-1β (IL-1β), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1) are significantly upregulated following three unique muscle injuries. These cytokines modulate mitochondrial function and execute bona fide pleiotropic roles that can aid functional recovery of muscle, however, when aberrant, chronically disrupt healing partly by exacerbating mitochondrial dysfunction. Multidisciplinary efforts to delineate the opposing regulatory roles of inflammatory cytokines in the muscle mitochondrial environment are required to modulate regenerative behavior following skeletal muscle injury or disuse. Future therapeutic directions to consider include quenching or limited release of mito-DAMPs and cytokines present in cytosol or circulation.
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http://dx.doi.org/10.1152/ajpcell.00462.2020DOI Listing
May 2021

Mitochondria-cytokine crosstalk following skeletal muscle injury and disuse: a mini-review.

Am J Physiol Cell Physiol 2021 05 10;320(5):C681-C688. Epub 2021 Feb 10.

Department of Kinesiology, University of Georgia, Athens, Georgia.

Skeletal muscle mitochondria are highly adaptable, highly dynamic organelles that maintain the functional integrity of the muscle fiber by providing ATP for contraction and cellular homeostasis (e.g., Na/K ATPase). Emerging as early modulators of inflammation, mitochondria sense and respond to cellular stress. Mitochondria communicate with the environment, in part, by release of physical signals called mitochondrial-derived damage-associated molecular patterns (mito-DAMPs) and deviation from routine function (e.g., reduced ATP production, Ca overload). When skeletal muscle is compromised, mitochondria contribute to an acute inflammatory response necessary for myofibril regeneration; however, exhaustive signaling associated with altered or reduced mitochondrial function can be detrimental to muscle outcomes. Here, we describe changes in mitochondrial content, structure, and function following skeletal muscle injury and disuse and highlight the influence of mitochondria-cytokine crosstalk on muscle regeneration and recovery. Although the appropriate therapeutic modulation following muscle stressors remains unknown, retrospective gene expression analysis reveals that interleukin-6 (IL-6), interleukin-1β (IL-1β), chemokine C-X-C motif ligand 1 (CXCL1), and monocyte chemoattractant protein 1 (MCP-1) are significantly upregulated following three unique muscle injuries. These cytokines modulate mitochondrial function and execute bona fide pleiotropic roles that can aid functional recovery of muscle, however, when aberrant, chronically disrupt healing partly by exacerbating mitochondrial dysfunction. Multidisciplinary efforts to delineate the opposing regulatory roles of inflammatory cytokines in the muscle mitochondrial environment are required to modulate regenerative behavior following skeletal muscle injury or disuse. Future therapeutic directions to consider include quenching or limited release of mito-DAMPs and cytokines present in cytosol or circulation.
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http://dx.doi.org/10.1152/ajpcell.00462.2020DOI Listing
May 2021

Spatial frequency metrics for analysis of microscopic images of musculoskeletal tissues.

Connect Tissue Res 2021 Jan 7;62(1):4-14. Epub 2020 Oct 7.

Regenerative Bioscience Center, Rhodes Center for ADS, University of Georgia , Athens, GA, USA.

Imaging-based metrics for analysis of biological tissues are powerful tools that can extract information such as shape, size, periodicity, and many other features to assess the requested qualities of a tissue. Muscular and osseous tissues consist of periodic structures that are directly related to their function, and so analysis of these patterns likely reflects tissue health and regeneration. A method for assessment of periodic structures is by analyzing them in the spatial frequency domain using the Fourier transform. In this paper, we present two filters which we developed in the spatial frequency domain for the purpose of analyzing musculoskeletal structures. These filters provide information about 1) the angular orientation of the tissues and 2) their periodicity. We explore periodic structural patterns in the mitochondrial network of skeletal muscles that are reflective of muscle metabolism and myogenesis; and patterns of collagen fibers in the bone that are reflective of the organization and health of bone extracellular matrix. We present an analysis of mouse skeletal muscle in healthy and injured muscles. We used a transgenic mouse that ubiquitously expresses fluorescent protein in their mitochondria and performed 2-photon microscopy to image the structures. To acquire the collagen structure of the bone we used non-linear SHG microscopy of mouse flat bone. We analyze and compare juvenile versus adult mice, which have different structural patterns. Our results indicate that these metrics can quantify musculoskeletal tissues during development and regeneration.
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http://dx.doi.org/10.1080/03008207.2020.1828381DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7718369PMC
January 2021

Mitochondrial dysfunction in skeletal muscle of fukutin-deficient mice is resistant to exercise- and 5-aminoimidazole-4-carboxamide ribonucleotide-induced rescue.

Exp Physiol 2020 10 10;105(10):1767-1777. Epub 2020 Sep 10.

Department of Kinesiology, University of Georgia, Athens, GA, USA.

New Findings: What is the central question of this study? Does fukutin deficiency in skeletal muscle cause mitochondrial dysfunction, and if so, can AMP-activated protein kinase (AMPK) stimulation via 5-aminoimidazole-4-carboxamide ribonucleotide attenuate this through regulation of mitochondrial biogenesis and autophagy? What is the main finding and its importance? Mitochondrial dysfunction is associated with fukutin deficiency and AMPK stimulation may benefit muscle contractility to a greater extent than mitochondrial function.

Abstract: Disruptions in the dystrophin-glycoprotein complex (DGC) are clearly the primary basis underlying various forms of muscular dystrophies and dystroglycanopathies, but the cellular consequences of DGC disruption are still being investigated. Mitochondrial abnormalities are becoming an apparent consequence and contributor to dystrophy disease pathology. Herein, we demonstrate that muscle-specific deletion of the fukutin gene (Myf5/fktn-KO mice (Fktn KO)), a model of secondary dystroglycanopathy, results in ∼30% lower muscle strength (P < 0.001) and 16% lower mitochondrial respiratory function (P = 0.002) compared to healthy littermate controls (LM). We also observed ∼80% lower expression of the gene for peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) (P = 0.004), a primary transcription factor for mitochondrial biogenesis, in Fktn KO mice that likely contributes to the mitochondrial defects. PGC-1α is post-translationally regulated via phosphorylation by AMP-activated protein kinase (AMPK). Treatment with the AMPK agonist 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) failed to rescue mitochondrial deficits in Fktn KO mice (P = 0.458) but did have beneficial (∼30% greater) effects on recovery of muscle contractility following injury in both LM and Fktn KO mice compared to saline treatment (P = 0.006). The beneficial effects of AMPK stimulation via AICAR on muscle contractile function may be partially explained by AMPK's other role of regulating skeletal muscle autophagy, a cellular process critical for clearance of damaged and/or dysfunctional organelles. Two primary conclusions can be drawn from this data: (1) fukutin deletion produces intrinsic muscular metabolic defects that likely contribute to dystroglycanopathy disease pathology, and (2) AICAR treatment accelerates recovery of muscle contractile function following injury suggesting AMPK signalling as a possible target for therapeutic strategies.
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http://dx.doi.org/10.1113/EP088812DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7953326PMC
October 2020

Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses.

J Equine Vet Sci 2020 08 29;91:103103. Epub 2020 Apr 29.

Department of Animal and Dairy Science, University of Georgia, Athens, GA.

Vitamin E is an essential antioxidant that may benefit athletes by reducing oxidative stress and influencing cytokine expression. Supplements can be derived from natural or manufactured synthetic sources. This study aimed to determine (1) if supplemental vitamin E is beneficial to exercising horses and (2) if there is a benefit of natural versus synthetic vitamin E. After 2 weeks on the control diet (vitamin E-deficient grain and hay), 18 horses were divided into three groups and fed the control diet plus (1) 1000 IU/d synthetic α-tocopherol (SYN-L), (2) 4000 IU/d synthetic α-tocopherol (SYN-H), or (3) 4000 IU/d RRR-α-tocopherol (natural source [NAT]). On day 7, horses began a 6-week training protocol, with standard exercise tests (SETs) performed before and after the 6-week protocol. Venous blood samples were collected on days 0, 7, 29, and 49. Horses fed NAT had higher α-tocopherol (P < .05) at post-SET1 through post-SET2. Plasma thiobarbituric acid-reactive substance levels were lower in NAT versus SYN-L horses after SET2 (P = .02). Serum aspartate aminotransferase was lower after exercise in NAT horses versus SYN-L and SYN-H (P = .02), and less reduction in stride duration was seen after exercise in NAT as compared with SYN-L and SYN-H (P = .02). Gene expression of tumor necrosis factor α was lower in NAT compared with SYN-H (P = .01) but not SYN-L. In conclusion, feeding higher levels of natural vitamin E source resulted in higher serum α-tocopherol levels as well as some improvement in oxidative and inflammatory response and improved functional outcomes in response to an exercise test.
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http://dx.doi.org/10.1016/j.jevs.2020.103103DOI Listing
August 2020

Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses.

J Equine Vet Sci 2020 08 29;91:103103. Epub 2020 Apr 29.

Department of Animal and Dairy Science, University of Georgia, Athens, GA.

Vitamin E is an essential antioxidant that may benefit athletes by reducing oxidative stress and influencing cytokine expression. Supplements can be derived from natural or manufactured synthetic sources. This study aimed to determine (1) if supplemental vitamin E is beneficial to exercising horses and (2) if there is a benefit of natural versus synthetic vitamin E. After 2 weeks on the control diet (vitamin E-deficient grain and hay), 18 horses were divided into three groups and fed the control diet plus (1) 1000 IU/d synthetic α-tocopherol (SYN-L), (2) 4000 IU/d synthetic α-tocopherol (SYN-H), or (3) 4000 IU/d RRR-α-tocopherol (natural source [NAT]). On day 7, horses began a 6-week training protocol, with standard exercise tests (SETs) performed before and after the 6-week protocol. Venous blood samples were collected on days 0, 7, 29, and 49. Horses fed NAT had higher α-tocopherol (P < .05) at post-SET1 through post-SET2. Plasma thiobarbituric acid-reactive substance levels were lower in NAT versus SYN-L horses after SET2 (P = .02). Serum aspartate aminotransferase was lower after exercise in NAT horses versus SYN-L and SYN-H (P = .02), and less reduction in stride duration was seen after exercise in NAT as compared with SYN-L and SYN-H (P = .02). Gene expression of tumor necrosis factor α was lower in NAT compared with SYN-H (P = .01) but not SYN-L. In conclusion, feeding higher levels of natural vitamin E source resulted in higher serum α-tocopherol levels as well as some improvement in oxidative and inflammatory response and improved functional outcomes in response to an exercise test.
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http://dx.doi.org/10.1016/j.jevs.2020.103103DOI Listing
August 2020

Autophagy: an essential but limited cellular process for timely skeletal muscle recovery from injury.

Autophagy 2020 07 17;16(7):1344-1347. Epub 2020 Apr 17.

Department of Kinesiology, University of Georgia , Athens, GA, USA.

Macroautophagy/autophagy induction, i.e., the formation of autophagosomes, is robust following many forms of muscle injury. Autophagy inhibition studies strongly indicate that autophagy is necessary for successful muscle fiber recovery. Now, there are accumulating pieces of evidence indicating that autophagosome clearance, i.e., autophagy flux, does not increase to match the burden of accumulating damaged proteins and organelles after muscle fiber damage, creating a bottleneck effect. Some potential consequences of the bottleneck effect are reduced regenerative capacity marked by the inadequate activation of muscle stem cells (i.e., satellite cells) and a lesser commitment toward differentiation due to a deficiency in energetic substrates and/or molecular signaling pathways. These findings highlight an emerging area of investigation for both autophagy and muscle regeneration fields. The identification of the molecular mechanisms governing autophagy and autophagy flux may serve as targets for future therapies to enhance the recovery of its function in healthy and diseased muscle.

Abbreviations: BNIP3: BCL2/adenovirus E1B interacting protein 3; CQ: chloroquine; DMD: Duchenne muscular dystrophy; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; ULK1: unc-51 like kinase 1.
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http://dx.doi.org/10.1080/15548627.2020.1753000DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7469477PMC
July 2020

Musculoskeletal Regeneration, Rehabilitation, and Plasticity Following Traumatic Injury.

Int J Sports Med 2020 Jul 2;41(8):495-504. Epub 2020 Apr 2.

Department of Kinesiology, University of Georgia, Athens, United States.

The musculoskeletal system has an integral role throughout life, including structural support to the body, protection, and allowing a range of fine to complex movements for daily living to elite sporting events. At various times, injuries to the musculoskeletal system occur resulting in varying levels of impact to the person both acutely and chronically. Specifically, there is a spectrum of complexity in orthopedic injuries, with some such as common muscle strains, that while burdensome will have no impact on life-long functional ability, and others that can result in long lasting disability. Focusing on extremity injuries, this review highlights: )the current impact of orthopedic injuries in sport and daily life; ) the foundation of bone and skeletal muscle repair and regeneration; and ) the disruptions in regenerative healing due to traumatic orthopedic injuries. This review seeks to maximize the broad and collective research impact on sport and traumatic orthopedic injuries in search of promoting ongoing innovation for treatment and rehabilitation approaches aimed to improve musculoskeletal health throughout life.
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http://dx.doi.org/10.1055/a-1128-7128DOI Listing
July 2020

Musculoskeletal Regeneration, Rehabilitation, and Plasticity Following Traumatic Injury.

Int J Sports Med 2020 Jul 2;41(8):495-504. Epub 2020 Apr 2.

Department of Kinesiology, University of Georgia, Athens, United States.

The musculoskeletal system has an integral role throughout life, including structural support to the body, protection, and allowing a range of fine to complex movements for daily living to elite sporting events. At various times, injuries to the musculoskeletal system occur resulting in varying levels of impact to the person both acutely and chronically. Specifically, there is a spectrum of complexity in orthopedic injuries, with some such as common muscle strains, that while burdensome will have no impact on life-long functional ability, and others that can result in long lasting disability. Focusing on extremity injuries, this review highlights: )the current impact of orthopedic injuries in sport and daily life; ) the foundation of bone and skeletal muscle repair and regeneration; and ) the disruptions in regenerative healing due to traumatic orthopedic injuries. This review seeks to maximize the broad and collective research impact on sport and traumatic orthopedic injuries in search of promoting ongoing innovation for treatment and rehabilitation approaches aimed to improve musculoskeletal health throughout life.
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http://dx.doi.org/10.1055/a-1128-7128DOI Listing
July 2020

Mitochondrial-specific autophagy linked to mitochondrial dysfunction following traumatic freeze injury in mice.

Am J Physiol Cell Physiol 2020 02 13;318(2):C242-C252. Epub 2019 Nov 13.

Department of Kinesiology, University of Georgia, Athens, Georgia.

The objective of this study was to interrogate the link between mitochondrial dysfunction and mitochondrial-specific autophagy in skeletal muscle. C57BL/6J mice were used to establish a time course of mitochondrial function and autophagy induction after fatigue ( = 12), eccentric contraction-induced injury ( = 20), or traumatic freeze injury (FI, = 28); only FI resulted in a combination of mitochondrial dysfunction, i.e., decreased mitochondrial respiration, and autophagy induction. Moving forward, we tested the hypothesis that mitochondrial-specific autophagy is important for the timely recovery of mitochondrial function after FI. Following FI, there is a significant increase in several mitochondrial-specific autophagy-related protein contents including dynamin-related protein 1 (Drp1), BCL1 interacting protein (BNIP3), Pink1, and Parkin (~2-fold, < 0.02). Also, mitochondrial-enriched fractions from FI muscles showed microtubule-associated protein light chain B1 (LC3)II colocalization suggesting autophagosome assembly around the damaged mitochondrial. Unc-51 like autophagy activating kinase (Ulk1) is considered necessary for mitochondrial-specific autophagy and herein we utilized a mouse model with Ulk1 deficiency in adult skeletal muscle (). While Ulk1 knockouts had contractile weakness compared with littermate controls (-27%, < 0.02), the recovery of mitochondrial function was not different, and this may be due in part to a partial rescue of Ulk1 protein content within the regenerating muscle tissue of knockouts from differentiated satellite cells in which Ulk1 was not genetically altered via . Lastly, autophagy flux was significantly less in injured versus uninjured muscles (-26%, < 0.02) despite the increase in autophagy-related protein content. This suggests autophagy flux is not upregulated to match increases in autophagy machinery after injury and represents a potential bottleneck in the clearance of damaged mitochondria by autophagy.
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http://dx.doi.org/10.1152/ajpcell.00123.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7052610PMC
February 2020

Five-dimensional two-photon volumetric microscopy of in-vivo dynamic activities using liquid lens remote focusing.

Biomed Opt Express 2019 Jul 26;10(7):3591-3604. Epub 2019 Jun 26.

Regenerative Bioscience Center, Rhodes Center for ADS, University of Georgia, Athens, GA 30602, USA.

Multi-photon scanning microscopy provides a robust tool for optical sectioning, which can be used to capture fast biological events such as blood flow, mitochondrial activity, and neuronal action potentials. For many studies, it is important to visualize several different focal planes at a rate akin to the biological event frequency. Typically, a microscope is equipped with mechanical elements to move either the sample or the objective lens to capture volumetric information, but these strategies are limited due to their slow speeds or inertial artifacts. To overcome this problem, remote focusing methods have been developed to shift the focal plane axially without physical movement of the sample or the microscope. Among these methods is liquid lens technology, which adjusts the focus of the lens by changing the wettability of the liquid and hence its curvature. Liquid lenses are inexpensive active optical elements that have the potential for fast multi-photon volumetric imaging, hence a promising and accessible approach for the study of biological systems with complex dynamics. Although remote focusing using liquid lens technology can be used for volumetric point scanning multi-photon microscopy, optical aberrations and the effects of high energy laser pulses have been concerns in its implementation. In this paper, we characterize a liquid lens and validate its use in relevant biological applications. We measured optical aberrations that are caused by the liquid lens, and calculated its response time, defocus hysteresis, and thermal response to a pulsed laser. We applied this method of remote focusing for imaging and measurement of multiple in-vivo specimens, including mesenchymal stem cell dynamics, mouse tibialis anterior muscle mitochondrial electrical potential fluctuations, and mouse brain neural activity. Our system produces 5 dimensional (x,y,z,λ,t) data sets at the speed of 4.2 volumes per second over volumes as large as 160 x 160 x 35 µm.
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http://dx.doi.org/10.1364/BOE.10.003591DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640832PMC
July 2019

PGC-1α overexpression partially rescues impaired oxidative and contractile pathophysiology following volumetric muscle loss injury.

Sci Rep 2019 03 11;9(1):4079. Epub 2019 Mar 11.

Department of Kinesiology, University of Georgia, Athens, GA, 30602, USA.

Volumetric muscle loss (VML) injury is characterized by a non-recoverable loss of muscle fibers due to ablative surgery or severe orthopaedic trauma, that results in chronic functional impairments of the soft tissue. Currently, the effects of VML on the oxidative capacity and adaptability of the remaining injured muscle are unclear. A better understanding of this pathophysiology could significantly shape how VML-injured patients and clinicians approach regenerative medicine and rehabilitation following injury. Herein, the data indicated that VML-injured muscle has diminished mitochondrial content and function (i.e., oxidative capacity), loss of mitochondrial network organization, and attenuated oxidative adaptations to exercise. However, forced PGC-1α over-expression rescued the deficits in oxidative capacity and muscle strength. This implicates physiological activation of PGC1-α as a limiting factor in VML-injured muscle's adaptive capacity to exercise and provides a mechanistic target for regenerative rehabilitation approaches to address the skeletal muscle dysfunction.
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http://dx.doi.org/10.1038/s41598-019-40606-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6411870PMC
March 2019

Voluntary running protects against neuromuscular dysfunction following hindlimb ischemia-reperfusion in mice.

J Appl Physiol (1985) 2019 01 15;126(1):193-201. Epub 2018 Nov 15.

Department of Medicine, Robert M. Berne Cardiovascular Research Center, University of Virginia School of Medicine , Charlottesville, Virginia.

Ischemia-reperfusion (IR) due to temporary restriction of blood flow causes tissue/organ damages under various disease conditions, including stroke, myocardial infarction, trauma, and orthopedic surgery. In the limbs, IR injury to motor nerves and muscle fibers causes reduced mobility and quality of life. Endurance exercise training has been shown to increase tissue resistance to numerous pathological insults. To elucidate the impact of endurance exercise training on IR injury in skeletal muscle, sedentary and exercise-trained mice (5 wk of voluntary running) were subjected to ischemia by unilateral application of a rubber band tourniquet above the femur for 1 h, followed by reperfusion. IR caused significant muscle injury and denervation at neuromuscular junction (NMJ) as early as 3 h after tourniquet release as well as depressed muscle strength and neuromuscular transmission in sedentary mice. Despite similar degrees of muscle atrophy and oxidative stress, exercise-trained mice had significantly reduced muscle injury and denervation at NMJ with improved regeneration and functional recovery following IR. Together, these data suggest that endurance exercise training preserves motor nerve and myofiber structure and function from IR injury and promote functional regeneration. NEW & NOTEWORTHY This work provides the first evidence that preemptive voluntary wheel running reduces neuromuscular dysfunction following ischemia-reperfusion injury in skeletal muscle. These findings may alter clinical practices in which a tourniquet is used to modulate blood flow.
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http://dx.doi.org/10.1152/japplphysiol.00358.2018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6383643PMC
January 2019

Early rehabilitation for volumetric muscle loss injury augments endogenous regenerative aspects of muscle strength and oxidative capacity.

BMC Musculoskelet Disord 2018 May 29;19(1):173. Epub 2018 May 29.

Department of Kinesiology, University of Georgia, Athens, GA, 30602, USA.

Background: Volumetric muscle loss (VML) injuries occur due to orthopaedic trauma or the surgical removal of skeletal muscle and result in debilitating long-term functional deficits. Current treatment strategies do not promote significant restoration of function; additionally appropriate evidenced-based practice physical therapy paradigms have yet to be established. The objective of this study was to develop and evaluate early rehabilitation paradigms of passive range of motion and electrical stimulation in isolation or combination to understand the genetic and functional response in the tissue remaining after a multi-muscle VML injury.

Methods: Adult male mice underwent an ~ 20% multi-muscle VML injury to the posterior compartment (gastrocnemius, soleus, and plantaris muscle) unilaterally and were randomized to rehabilitation paradigm twice per week beginning 2 days post-injury or no treatment.

Results: The most salient findings of this work are: 1) that the remaining muscle tissue after VML injury was adaptable in terms of improved muscle strength and mitigation of stiffness; but 2) not adaptable to improvements in metabolic capacity. Furthermore, biochemical (i.e., collagen content) and gene (i.e., gene arrays) assays suggest that functional adaptations may reflect changes in the biomechanical properties of the remaining tissue due to the cellular deposition of non-contractile tissue in the void left by the VML injury and/or differentiation of gene expression with early rehabilitation.

Conclusions: Collectively this work provides evidence of genetic and functional plasticity in the remaining skeletal muscle with early rehabilitation approaches, which may facilitate future evidenced-based practice of early rehabilitation at the clinical level.
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http://dx.doi.org/10.1186/s12891-018-2095-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5975473PMC
May 2018

Aggregate mesenchymal stem cell delivery ameliorates the regenerative niche for muscle repair.

J Tissue Eng Regen Med 2018 08 25;12(8):1867-1876. Epub 2018 Jun 25.

Department of Kinesiology, University of Georgia, Athens, GA, USA.

Duchenne muscular dystrophy is a severe muscle wasting disease due to the absence of the dystrophin protein from the muscle cell membrane, which renders the muscle susceptible to continuous damage. In Duchenne muscular dystrophy patients, muscle weakness, together with cycles of degeneration/regeneration and replacement with noncontractile tissue, limit mobility and lifespan. Because the loss of dystrophin results in loss of polarity and a reduction in the number of self-renewing satellite cells, it is postulated that these patients could achieve an improved quality of life if delivered cells could restore satellite cell function. In this study, we used both an established myotoxic injury model in wild-type (WT) mice and mdx mice alone (spontaneous muscle damage). Single (SC) and aggregated (AGG) mesenchymal stem cells (MSCs) were injected into the gastrocnemius muscles 4 hr after injury (WT mice). The recovery of peak isometric torque was longitudinally assessed over 5 weeks, with earlier takedowns for histological assessment of healing (fibre cross-section area and central nucleation) and MSC retention. AGG-treated WT mice had significantly greater torque recovery at Day 14 than SC or saline-treated mice and a greater CSA at Day 10, compared with SC/saline. AGG-treated mdx mice had a greater peak isometric torque compared with SC/saline. In vitro immunomodulatory factor secretion of AGG-MSCs was higher than SC-MSCs for all tested growth factors with the largest difference observed in hepatocyte growth factor. Future studies are necessary to pair immunomodulatory factor secretion with functional attributes, to better predict the potential therapeutic value of MSC treatment modalities.
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http://dx.doi.org/10.1002/term.2707DOI Listing
August 2018

Transient HIF2A inhibition promotes satellite cell proliferation and muscle regeneration.

J Clin Invest 2018 06 30;128(6):2339-2355. Epub 2018 Apr 30.

Department of Biochemistry and Molecular Biology.

The remarkable regeneration capability of skeletal muscle depends on the coordinated proliferation and differentiation of satellite cells (SCs). The self-renewal of SCs is critical for long-term maintenance of muscle regeneration potential. Hypoxia profoundly affects the proliferation, differentiation, and self-renewal of cultured myoblasts. However, the physiological relevance of hypoxia and hypoxia signaling in SCs in vivo remains largely unknown. Here, we demonstrate that SCs are in an intrinsic hypoxic state in vivo and express hypoxia-inducible factor 2A (HIF2A). HIF2A promotes the stemness and long-term homeostatic maintenance of SCs by maintaining their quiescence, increasing their self-renewal, and blocking their myogenic differentiation. HIF2A stabilization in SCs cultured under normoxia augments their engraftment potential in regenerative muscle. Conversely, HIF2A ablation leads to the depletion of SCs and their consequent regenerative failure in the long-term. In contrast, transient pharmacological inhibition of HIF2A accelerates muscle regeneration by increasing SC proliferation and differentiation. Mechanistically, HIF2A induces the quiescence and self-renewal of SCs by binding the promoter of the Spry1 gene and activating Spry1 expression. These findings suggest that HIF2A is a pivotal mediator of hypoxia signaling in SCs and may be therapeutically targeted to improve muscle regeneration.
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http://dx.doi.org/10.1172/JCI96208DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5983316PMC
June 2018

Effect of exercise intensity on circulating microparticles in men and women.

Exp Physiol 2018 05 26;103(5):693-700. Epub 2018 Mar 26.

Department of Kinesiology, University of Georgia, Athens, GA, USA.

New Findings: What is the central question of this study? What is the effect of exercise intensity on circulating microparticle populations in young, healthy men and women? What is the main finding and its importance? Acute, moderate-intensity continuous exercise and high-intensity interval exercise altered distinct microparticle populations during and after exercise in addition to a sex-specific response in CD62E microparticles. The microparticles studied contribute to cardiovascular disease progression, regulate vascular function and facilitate new blood vessel formation. Thus, characterizing the impact of intensity on exercise-induced microparticle responses advances our understanding of potential mechanisms underlying the beneficial vascular adaptations to exercise.

Abstract: Circulating microparticles (MPs) are biological vectors of information within the cardiovascular system that elicit both deleterious and beneficial effects on the vasculature. Acute exercise has been shown to alter MP concentrations, probably through a shear stress-dependent mechanism, but evidence is limited. Therefore, we investigated the effect of exercise intensity on plasma levels of CD34 and CD62E MPs in young, healthy men and women. Blood samples were collected before, during and after two energy-matched bouts of acute treadmill exercise: interval exercise (10 × 1 min intervals at ∼95% of maximal oxygen uptake V̇O2max) and continuous exercise (65% V̇O2max). Continuous exercise, but not interval exercise, reduced CD62E MP concentrations in men and women by 18% immediately after exercise (from 914.5 ± 589.6 to 754.4 ± 390.5 MPs μl ; P < 0.05), suggesting that mechanisms underlying exercise-induced CD62E MP dynamics are intensity dependent. Furthermore, continuous exercise reduced CD62E MPs in women by 19% (from 1030.6 ± 688.1 to 829.9 ± 435.4 MPs μl ; P < 0.05), but not in men. Although interval exercise did not alter CD62E MPs per se, the concentrations after interval exercise were higher than those observed after continuous exercise (P < 0.05). Conversely, CD34 MPs did not fluctuate in response to short-duration acute continuous or interval exercise in men or women. Our results suggest that exercise-induced MP alterations are intensity dependent and sex specific and impact MP populations differentially.
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http://dx.doi.org/10.1113/EP086644DOI Listing
May 2018

Two-photon deep-tissue spatially resolved mitochondrial imaging using membrane potential fluorescence fluctuations.

Biomed Opt Express 2018 Jan 19;9(1):254-259. Epub 2017 Dec 19.

Regenerative Bioscience Center, Rhodes Center for ADS, University of Georgia, Athens, GA 30602, USA.

Cell metabolism and viability are directly reflected in their mitochondria. Imaging-based analysis of mitochondrial morphological structure, size and dynamic characteristics can therefore provide critical insight into cell function. However, mitochondria are often very abundant, and due to their close to diffraction-limit size, it is often non-trivial to distinguish a tubular or large mitochondrion from an ensemble of punctate mitochondria. In this paper, we use membrane potential dependent fluorescence fluctuations of individual mitochondria to resolve them using an approach similar to single molecule localization microscopy. We use 2-photon microscopy to image mitochondrial intensity fluctuations at 200 μm deep inside an intact in-vivo mouse soleus muscle. By analyzing the acquired images, we can reconstruct images with an extra layer of information about individual mitochondria, separated from their ensemble. Our analysis shows a factor of 14 improvement in detection of mitochondria.
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http://dx.doi.org/10.1364/BOE.9.000254DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5772580PMC
January 2018

Impact of volumetric muscle loss injury on persistent motoneuron axotomy.

Muscle Nerve 2018 05 23;57(5):799-807. Epub 2018 Jan 23.

Extremity Trauma and Regenerative Medicine Task Area, United States Army Institute of Surgical Research, 3698 Chambers Pass, BHT1, Fort Sam Houston, Texas, 78234, USA.

Introduction: Volumetric muscle loss (VML) occurs following significant traumatic injury or surgical removal of skeletal muscle, resulting in nonrecoverable loss of tissue and long-term dysfunction. Perhaps less recognized is that VML injuries inherently disrupt the neuromuscular unit, resulting in fiber denervation and presumptive motor unit rearrangement, expansion, and/or loss. To characterize neural dysfunction we quantified motoneuron axotomy, in efforts to understand how this relates to the temporal coordination of neuromuscular and morphological alterations due to injury.

Methods: In an established rat tibialis anterior (TA) VML injury model, we examined the motoneuron, skeletal muscle, and maximal isometric torque at 3, 7, 14, and 21 days postinjury.

Results: Significant axotomy of 57-79% of all TA muscle motoneurons was observed through 21 days postinjury, which was coupled with a 45-90% TA maximal torque deficit.

Discussion: A ∼20% partial ablation of the TA muscle causes disproportionate damage across the motor unit acutely postinjury. Muscle Nerve 57: 799-807, 2018.
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http://dx.doi.org/10.1002/mus.26016DOI Listing
May 2018

Muscle-derived extracellular superoxide dismutase inhibits endothelial activation and protects against multiple organ dysfunction syndrome in mice.

Free Radic Biol Med 2017 12 2;113:212-223. Epub 2017 Oct 2.

Center for Skeletal Muscle Research at Robert Berne Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908, USA; Departments of Medicine, University of Virginia, Charlottesville, VA 22908, USA; Departments of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA; Departments of Molecular Physiology & Biological Physics, University of Virginia, Charlottesville, VA 22908, USA. Electronic address:

Multiple organ dysfunction syndrome (MODS) is a detrimental clinical complication in critically ill patients with high mortality. Emerging evidence suggests that oxidative stress and endothelial activation (induced expression of adhesion molecules) of vital organ vasculatures are key, early steps in the pathogenesis. We aimed to ascertain the role and mechanism(s) of enhanced extracellular superoxide dismutase (EcSOD) expression in skeletal muscle in protection against MODS induced by endotoxemia. We showed that EcSOD overexpressed in skeletal muscle-specific transgenic mice (TG) redistributes to other peripheral organs through the circulation and enriches at the endothelium of the vasculatures. TG mice are resistant to endotoxemia (induced by lipopolysaccharide [LPS] injection) in developing MODS with significantly reduced mortality and organ damages compared with the wild type littermates (WT). Heterogenic parabiosis between TG and WT mice conferred a significant protection to WT mice, whereas mice with R213G knock-in mutation, a human single nucleotide polymorphism leading to reduced binding EcSOD in peripheral organs, exacerbated the organ damages. Mechanistically, EcSOD inhibits vascular cell adhesion molecule 1 expression and inflammatory leukocyte adhesion to the vascular wall of vital organs, blocking an early step of the pathology in organ damage under endotoxemia. Therefore, enhanced expression of EcSOD in skeletal muscle profoundly protects against MODS by inhibiting endothelial activation and inflammatory cell adhesion, which could be a promising therapy for MODS.
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http://dx.doi.org/10.1016/j.freeradbiomed.2017.09.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5740866PMC
December 2017

Exercise leads to unfavourable cardiac remodelling and enhanced metabolic homeostasis in obese mice with cardiac and skeletal muscle autophagy deficiency.

Sci Rep 2017 08 11;7(1):7894. Epub 2017 Aug 11.

Department of Health & Human Physiology, Obesity Research and Educational Initiative, Fraternal Order of Eagles Diabetes Research Center, University of Iowa, Iowa City, IA, United States.

Autophagy is stimulated by exercise in several tissues; yet the role of skeletal and cardiac muscle-specific autophagy on the benefits of exercise training remains incompletely understood. Here, we determined the metabolic impact of exercise training in obese mice with cardiac and skeletal muscle disruption of the Autophagy related 7 gene (Atg7). Muscle autophagy deficiency did not affect glucose clearance and exercise capacity in lean adult mice. High-fat diet in sedentary mice led to endoplasmic reticulum stress and aberrant mitochondrial protein expression in autophagy-deficient skeletal and cardiac muscles. Endurance exercise training partially reversed these abnormalities in skeletal muscle, but aggravated those in the heart also causing cardiac fibrosis, foetal gene reprogramming, and impaired mitochondrial biogenesis. Interestingly, exercise-trained Atg7 mice were better protected against obesity and insulin resistance with increased circulating fibroblast growth factor 21 (FGF21), elevated Fgf21 mRNA and protein solely in the heart, and upregulation of FGF21-target genes involved in thermogenesis and fatty acid oxidation in brown fat. These results indicate that autophagy is essential for the protective effects of exercise in the heart. However, the atypical remodelling elicited by exercise in the autophagy deficient cardiac muscle enhances whole-body metabolism, at least partially, via a heart-brown fat cross-talk involving FGF21.
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http://dx.doi.org/10.1038/s41598-017-08480-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5554260PMC
August 2017

A putative lysophosphatidylinositol receptor GPR55 modulates hippocampal synaptic plasticity.

Hippocampus 2017 09 27;27(9):985-998. Epub 2017 Jun 27.

Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah, 84602.

GPR55, an orphan G-protein coupled receptor, is activated by lysophosphatidylinositol (LPI) and the endocannabinoid anandamide, as well as by other compounds including THC. LPI is a potent endogenous ligand of GPR55 and neither GPR55 nor LPIs' functions in the brain are well understood. While endocannabinoids are well known to modulate brain synaptic plasticity, the potential role LPI could have on brain plasticity has never been demonstrated. Therefore, we examined not only GPR55 expression, but also the role its endogenous ligand could play in long-term potentiation, a common form of synaptic plasticity. Using quantitative RT-PCR, electrophysiology, and behavioral assays, we examined hippocampal GPR55 expression and function. qRT-PCR results indicate that GPR55 is expressed in hippocampi of both rats and mice. Immunohistochemistry and single cell PCR demonstrates GPR55 protein in pyramidal cells of CA1 and CA3 layers in the hippocampus. Application of the GPR55 endogenous agonist LPI to hippocampal slices of GPR55 mice significantly enhanced CA1 LTP. This effect was absent in GPR55 mice, and blocked by the GPR55 antagonist CID 16020046. We also examined paired-pulse ratios of GPR55 and GPR55 mice with or without LPI and noted significant enhancement in paired-pulse ratios by LPI in GPR55 mice. Behaviorally, GPR55 and GPR55 mice did not differ in memory tasks including novel object recognition, radial arm maze, or Morris water maze. However, performance on radial arm maze and elevated plus maze task suggests GPR55 mice have a higher frequency of immobile behavior. This is the first demonstration of LPI involvement in hippocampal synaptic plasticity.
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http://dx.doi.org/10.1002/hipo.22747DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5568947PMC
September 2017

Experimental intermittent ischemia augments exercise-induced inflammatory cytokine production.

J Appl Physiol (1985) 2017 Aug 1;123(2):434-441. Epub 2017 Jun 1.

Department of Kinesiology, University of Georgia, Athens, Georgia;

Acute exercise-induced inflammation is implicated in mediating the beneficial adaptations to regular exercise. Evidence suggests that reduced oxygen and/or blood flow to contracting muscle alters cytokine appearance. However, the acute inflammatory responses to hypoxic/ischemic exercise have been documented with inconsistent results and may not accurately reflect the ischemia produced during exercise in patients with ischemic cardiovascular diseases. Therefore, we determined the extent to which local inflammation is involved in the response to ischemic exercise. Fourteen healthy males performed unilateral isometric forearm contractions for 30 min with and without experimental ischemia. Blood was drawn at baseline, 5 and 10 min into exercise, at the end of exercise, and 30, 60, and 120 min after exercise. Oxygen saturation levels, as measured by near-infrared spectroscopy, were reduced by 10% and 41% during nonischemic and ischemic exercise, respectively. Nonischemic exercise did not affect cytokine values. Ischemia enhanced concentrations of basic fibroblast growth factor, interleukin (IL)-6, IL-10, tumor necrosis factor-alpha, and vascular endothelial growth factor during exercise, but IL-8 was not influenced by ischemic exercise. In conclusion, the present study demonstrates that ischemic, small-muscle endurance exercise elicits local inflammatory cytokine production compared with nonischemic exercise. We demonstrate that ischemic, small-muscle endurance exercise elicits local inflammatory cytokine production compared with nonischemic exercise. The present study advances our knowledge of the inflammatory response to exercise in a partial ischemic state, which may be relevant for understanding the therapeutic effects of exercise training for people with ischemic cardiovascular disease-associated comorbidities.
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http://dx.doi.org/10.1152/japplphysiol.01006.2016DOI Listing
August 2017

Ulk1-mediated autophagy plays an essential role in mitochondrial remodeling and functional regeneration of skeletal muscle.

Am J Physiol Cell Physiol 2017 Jun 29;312(6):C724-C732. Epub 2017 Mar 29.

Department of Medicine, University of Virginia, Charlottesville, Virginia;

Autophagy is a conserved cellular process for degrading aggregate proteins and dysfunctional organelle. It is still debatable if autophagy and mitophagy (a specific process of autophagy of mitochondria) play important roles in myogenic differentiation and functional regeneration of skeletal muscle. We tested the hypothesis that autophagy is critical for functional regeneration of skeletal muscle. We first observed time-dependent increases (3- to 6-fold) of autophagy-related proteins (Atgs), including Ulk1, Beclin1, and LC3, along with reduced p62 expression during C2C12 differentiation, suggesting increased autophagy capacity and flux during myogenic differentiation. We then used cardiotoxin (Ctx) or ischemia-reperfusion (I/R) to induce muscle injury and regeneration and observed increases in Atgs between and in adult skeletal muscle followed by increased autophagy flux after Since Ulk1 has been shown to be essential for mitophagy, we asked if Ulk1 is critical for functional regeneration in skeletal muscle. We subjected skeletal muscle-specific knockout mice (MKO) to Ctx or I/R. MKO mice had significantly impaired recovery of muscle strength and mitochondrial protein content post-Ctx or I/R. Imaging analysis showed that MKO mice have significantly attenuated recovery of mitochondrial network at 7 and 14 days post-Ctx. These findings suggest that increased autophagy protein and flux occur during muscle regeneration and Ulk1-mediated mitophagy is critical for recovery for the mitochondrial network and hence functional regeneration.
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http://dx.doi.org/10.1152/ajpcell.00348.2016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5494591PMC
June 2017

Skeletal muscle metabolic adaptations to endurance exercise training are attainable in mice with simvastatin treatment.

PLoS One 2017 16;12(2):e0172551. Epub 2017 Feb 16.

Department of Kinesiology, University of Georgia, Athens, Georgia, United States of America.

We tested the hypothesis that a 6-week regimen of simvastatin would attenuate skeletal muscle adaptation to low-intensity exercise. Male C57BL/6J wildtype mice were subjected to 6-weeks of voluntary wheel running or normal cage activities with or without simvastatin treatment (20 mg/kg/d, n = 7-8 per group). Adaptations in in vivo fatigue resistance were determined by a treadmill running test, and by ankle plantarflexor contractile assessment. The tibialis anterior, gastrocnemius, and plantaris muscles were evaluated for exercised-induced mitochondrial adaptations (i.e., biogenesis, function, autophagy). There was no difference in weekly wheel running distance between control and simvastatin-treated mice (P = 0.51). Trained mice had greater treadmill running distance (296%, P<0.001), and ankle plantarflexor contractile fatigue resistance (9%, P<0.05) compared to sedentary mice, independent of simvastatin treatment. At the cellular level, trained mice had greater mitochondrial biogenesis (e.g., ~2-fold greater PGC1α expression, P<0.05) and mitochondrial content (e.g., 25% greater citrate synthase activity, P<0.05), independent of simvastatin treatment. Mitochondrial autophagy-related protein contents were greater in trained mice (e.g., 40% greater Bnip3, P<0.05), independent of simvastatin treatment. However, Drp1, a marker of mitochondrial fission, was less in simvastatin treated mice, independent of exercise training, and there was a significant interaction between training and statin treatment (P<0.022) for LC3-II protein content, a marker of autophagy flux. These data indicate that whole body and skeletal muscle adaptations to endurance exercise training are attainable with simvastatin treatment, but simvastatin may have side effects on muscle mitochondrial maintenance via autophagy, which could have long-term implications on muscle health.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0172551PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5313210PMC
September 2017

Eccentric Contraction-Induced Muscle Injury: Reproducible, Quantitative, Physiological Models to Impair Skeletal Muscle's Capacity to Generate Force.

Methods Mol Biol 2016 ;1460:3-18

Programs in Physical Therapy and Rehabilitation Science, Department of Physical Medicine and Rehabilitation Medical School, University of Minnesota, Minneapolis, MN, 55455, USA.

In order to investigate the molecular and cellular mechanisms of muscle regeneration an experimental injury model is required. Advantages of eccentric contraction-induced injury are that it is a controllable, reproducible, and physiologically relevant model to cause muscle injury, with injury being defined as a loss of force generating capacity. While eccentric contractions can be incorporated into conscious animal study designs such as downhill treadmill running, electrophysiological approaches to elicit eccentric contractions and examine muscle contractility, for example before and after the injurious eccentric contractions, allows researchers to circumvent common issues in determining muscle function in a conscious animal (e.g., unwillingness to participate). Herein, we describe in vitro and in vivo methods that are reliable, repeatable, and truly maximal because the muscle contractions are evoked in a controlled, quantifiable manner independent of subject motivation. Both methods can be used to initiate eccentric contraction-induced injury and are suitable for monitoring functional muscle regeneration hours to days to weeks post-injury.
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http://dx.doi.org/10.1007/978-1-4939-3810-0_1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5832429PMC
January 2018

Mitochondrial maintenance via autophagy contributes to functional skeletal muscle regeneration and remodeling.

Am J Physiol Cell Physiol 2016 08 8;311(2):C190-200. Epub 2016 Jun 8.

Department of Kinesiology, University of Georgia, Athens, Georgia; Regenerative Bioscience Center, University of Georgia, Athens, Georgia;

The primary objective of this study was to determine whether alterations in mitochondria affect recovery of skeletal muscle strength and mitochondrial enzyme activity following myotoxic injury. 3-Methyladenine (3-MA) was administered daily (15 mg/kg) to blunt autophagy, and the creatine analog guanidionpropionic acid (β-GPA) was administered daily (1% in chow) to enhance oxidative capacity. Male C57BL/6 mice were randomly assigned to nontreatment (Con, n = 6), 3-MA-treated (n = 6), and β-GPA-treated (n = 8) groups for 10 wk. Mice were euthanized at 14 days after myotoxic injury for assessment of mitochondrial remodeling during regeneration and its association with the recovery of muscle strength. Expression of several autophagy-related proteins, e.g., phosphorylated Ulk1 (∼2- to 4-fold, P < 0.049) was greater in injured than uninjured muscles, indicating a relationship between muscle regeneration/remodeling and autophagy. By 14 days postinjury, recovery of muscle strength (18% less, P = 0.03) and mitochondrial enzyme (e.g., citrate synthase) activity (22% less, P = 0.049) were significantly lower in 3-MA-treated than Con mice, suggesting that the autophagy process plays an important role during muscle regeneration. In contrast, muscle regeneration was nearly complete in β-GPA-treated mice, i.e., muscle strength recovered to 93% of baseline vs. 78% for Con mice. Remarkably, 14 days allowed sufficient time for a near-complete recovery of mitochondrial function in β-GPA-treated mice (e.g., no difference in citrate synthase activity between injured and uninjured, P = 0.49), indicating a robust mitochondrial remodeling process during muscle regeneration. In conclusion, autophagy is likely activated following muscle injury and appears to play an important role in functional muscle regeneration.
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http://dx.doi.org/10.1152/ajpcell.00066.2016DOI Listing
August 2016