Publications by authors named "María Laura Messi"

36 Publications

The emerging role of the sympathetic nervous system in skeletal muscle motor innervation and sarcopenia.

Ageing Res Rev 2021 May 18;67:101305. Epub 2021 Feb 18.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, USA.

Examining neural etiologic factors'role in the decline of neuromuscular function with aging is essential to our understanding of the mechanisms underlying sarcopenia, the age-dependent decline in muscle mass, force and power. Innervation of the skeletal muscle by both motor and sympathetic axons has been established, igniting interest in determining how the sympathetic nervous system (SNS) affect skeletal muscle composition and function throughout the lifetime. Selective expression of the heart and neural crest derivative 2 gene in peripheral SNs increases muscle mass and force regulating skeletal muscle sympathetic and motor innervation; improving acetylcholine receptor stability and NMJ transmission; preventing inflammation and myofibrillar protein degradation; increasing autophagy; and probably enhancing protein synthesis. Elucidating the role of central SNs will help to define the coordinated response of the visceral and neuromuscular system to physiological and pathological challenges across ages. This review discusses the following questions: (1) Does the SNS regulate skeletal muscle motor innervation? (2) Does the SNS regulate presynaptic and postsynaptic neuromuscular junction (NMJ) structure and function? (3) Does sympathetic neuron (SN) regulation of NMJ transmission decline with aging? (4) Does maintenance of SNs attenuate aging sarcopenia? and (5) Do central SN group relays influence sympathetic and motor muscle innervation?
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http://dx.doi.org/10.1016/j.arr.2021.101305DOI Listing
May 2021

Heart and neural crest derivative 2-induced preservation of sympathetic neurons attenuates sarcopenia with aging.

J Cachexia Sarcopenia Muscle 2021 Feb 30;12(1):91-108. Epub 2020 Nov 30.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, USA.

Background: Sarcopenia, or age-dependent decline in muscle force and power, impairs mobility, increasing the risk of falls, institutionalization, co-morbidity, and premature death. The discovery of adrenoceptors, which mediate the effects of the sympathetic nervous system (SNS) neurotransmitter norepinephrine on specific tissues, sparked the development of sympathomimetics that have profound influence on skeletal muscle mass. However, chronic administration has serious side effects that preclude their use for muscle-wasting conditions. Interventions that can adjust neurotransmitter release to changing physiological demands depend on understanding how the SNS affects neuromuscular transmission, muscle motor innervation, and muscle mass.

Methods: We examined age-dependent expression of the heart and neural crest derivative 2 (Hand2), a critical transcription factor for SN maintenance, and we tested the possibility that inducing its expression exclusively in sympathetic neurons (SN) will prevent (i) motor denervation, (ii) impaired neuromuscular junction (NMJ) transmission, and (iii) loss of muscle mass and function in old mice. To test this hypothesis, we delivered a viral vector carrying Hand2 expression or an empty vector exclusively in SNs by vein injection in 16-month-old C57BL/6 mice that were sacrificed 6 months later. Techniques include RNA-sequencing, real-time PCR, genomic DNA methylation, viral vector construct, tissue immunohistochemistry, immunoblot, confocal microscopy, electrophysiology, and in vivo mouse physical performance.

Results: Hand2 expression declines throughout life, but inducing its expression increased (i) the number and size of SNs, (ii) muscle sympathetic innervation, (iii) muscle weight and force and whole-body strength, (iv) myofiber size but not muscle fibre-type composition, (v) NMJ transmission and nerve-evoked muscle force, and (vi) motor innervation in old mice. Additionally, the SN controls a set of genes to reduce inflammation and to promote transcription factor activity, cell signalling, and synapse in the skeletal muscle. Hand2 DNA methylation may contribute, at least partially, to gene silencing.

Conclusions: Selective expression of Hand2 in the mouse SNs from middle age through old age increases muscle mass and force by (i) regulating skeletal muscle sympathetic and motor innervation; (ii) improving acetylcholine receptor stability and NMJ transmission; (iii) preventing inflammation and myofibrillar protein degradation; (iv) increasing autophagy; and (v) probably enhancing protein synthesis.
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http://dx.doi.org/10.1002/jcsm.12644DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7890150PMC
February 2021

Aging Blunts Sympathetic Neuron Regulation of Motoneurons Synaptic Vesicle Release Mediated by β1- and α2B-Adrenergic Receptors in Geriatric Mice.

J Gerontol A Biol Sci Med Sci 2020 07;75(8):1473-1480

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.

This study was designed to determine whether and how the sympathetic nervous system (SNS) regulates motoneuron axon function and neuromuscular transmission in young (3-4-month) and geriatric (31-month) mice. Our approach included sciatic-peroneal nerve immunolabeling coregistration, and electrophysiological recordings in a novel mouse ex-vivo preparation, the sympathetic-peroneal nerve-lumbricalis muscle (SPNL). Here, the interaction between the motoneuron and SNS at the neuromuscular junction (NMJ) and muscle innervation reflect the complexity of the living mouse. Our data show that electrical stimulation of the sympathetic neuron at the paravertebral ganglia chain enhances motoneuron synaptic vesicle release at the NMJ in young mice, while in geriatric mice, this effect is blunted. We also found that blocking β-AR prevents the sympathetic neuron from increasing NMJ transmission. Immunofluorescence coexpression analysis of immunolabeled ARs with choline acetyltransferase-, tyrosine hydroxylase-, or calcitonin gene-related peptide immunoreactive axons showed that α2B-AR is found mainly in sympathetic neurons, β1-AR in sympathetic- and motor-neurons, and both decline significantly with aging. In summary, this study unveils the molecular substrate accounting for the influence of endogenous sympathetic neurons on motoneuron-muscle transmission in young mice and its decline with aging.
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http://dx.doi.org/10.1093/gerona/glaa022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7357579PMC
July 2020

Sympathomimetics regulate neuromuscular junction transmission through TRPV1, P/Q- and N-type Ca channels.

Mol Cell Neurosci 2019 03 11;95:59-70. Epub 2019 Feb 11.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC, United States of America; Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC, United States of America. Electronic address:

Increasing evidence indicates that, first, the sympathetic nervous system interacts extensively with both vasculature and skeletal muscle fibers near neuromuscular junctions (NMJs) and, second, its neurotransmitter, noradrenaline, influences myofiber molecular composition and function and motor innervation. Since sympathomimetic agents have been reported to improve NMJ transmission, we examined whether two in clinical use, salbutamol and clenbuterol, affect the motor axon terminal via extracellular Ca and molecular targets, such as TRPV1 and P/Q- and N-type voltage-activated Ca channels. Electrophysiological recordings in ex-vivo preparations of peroneal nerves and lumbricalis muscles from young adult mice focused on spontaneous miniature end-plate potentials and singly and repetitively evoked end-plate potentials. Adding one dose of salbutamol or clenbuterol to the nerve/muscle preparation or repeatedly administering salbutamol to a mouse for 4 weeks increased spontaneous and evoked synaptic vesicle release but induced a steep decline in EPP amplitude in response to repetitive nerve stimulation. These effects were mediated primarily by ω-agatoxin IVA-sensitive P/Q-type and secondarily by ω-conotoxin GVIA-sensitive N-type Ca channels. Presynaptic arvanil-sensitive TRPV1 channels seem to regulate Ca at the motor neuron terminal at rest, while putative presynaptic β-adrenergic receptors may mediate sympathomimetic and catecholamine effects on presynaptic Ca channels during NMJ activation.
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http://dx.doi.org/10.1016/j.mcn.2019.01.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6394868PMC
March 2019

Troponin T3 associates with DNA consensus sequence that overlaps with p53 binding motifs.

Exp Gerontol 2018 07 27;108:35-40. Epub 2018 Mar 27.

Departments of Internal Medicine, Section of Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, NC 27157, United States. Electronic address:

We recently reported that in addition to its classical cytoplasmic location, the fast skeletal muscle Troponin T3 (TnT3) shuttles to the nucleus, where it appears to perform nonclassical transcription regulatory functions. Importantly, changes in the composition of the nucleus-localized pool of TnT3 and its fragments contribute to age-dependent muscle damage and wasting. Here, using ChIP-Seq, we demonstrate that TnT3 associates with DNA consensus sequences including the TGCCT motif, which is required for p53 binding to the promoter area of p53-related genes. Gene set enrichment analysis further demonstrated that the p53 pathway was the most significantly enriched pathway among genes annotated to the TnT3 ChIP-Seq peaks. We further demonstrated a strong correlation (r = 0.78, P = 1 × 10) between the expression levels of TNNT3 and TP53-inducible ribonucleotide reductase regulatory subunit M2B (RRM2B) in skeletal muscle tissue of 21 lean non-diabetic human subjects and a significant (P < 0.05) reduction in the levels of both gene transcripts in the third age-tertile group [42.3-70 years of age (yoa)] as compared to the second age-tertile (31.3-42.3 yoa). Of note, both TNNT3 and RRM2B expression levels negatively associated with total body fat mass (each with r = 0.49, P < 0.05), whereas RRM2B positively correlated with pancreatic β cell function (r = 0.47, P = 0.047). This work suggests that reduced TNNT3 gene expression is another mechanism leading to reduced TnT3 and excitation-contraction coupling with aging. Consequently, TnT3 appears to contribute to age-related sarcopenia and possibly other age-related deficiencies such as muscle insulin resistance and β cell dysfunction by interacting with TnT3-binding sequences in the promoter area of p53-related genes, among others, and consequently modulating the transcriptional regulation of these target genes.
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http://dx.doi.org/10.1016/j.exger.2018.03.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5994179PMC
July 2018

Relationship of Physical Function to Single Muscle Fiber Contractility in Older Adults: Effects of Resistance Training With and Without Caloric Restriction.

J Gerontol A Biol Sci Med Sci 2019 02;74(3):412-419

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, North Carolina.

Background: Previous studies support beneficial effects of both resistance exercise training (RT) and caloric restriction (CR) on skeletal muscle strength and physical performance. The goal of this study was to determine the effects of adding CR to RT on single-muscle fiber contractility responses to RT in older overweight and obese adults.

Methods: We analyzed contractile properties in 1,253 single myofiber from muscle biopsies of the vastus lateralis, as well as physical performance and thigh muscle volume, in 31 older (65-80 years), overweight or obese (body mass index = 27-35 kg/m2) men (n = 19) and women (n = 12) who were randomly assigned to a standardized, progressive RT intervention with CR (RT+CR; n = 15) or without CR (RT; n = 16) for 5 months.

Results: Both interventions evoked an increase in force normalized to cross-sectional area (CSA), in type-I and type-II fibers and knee extensor quality. However, these improvements were not different between intervention groups. In the RT group, changes in total thigh fat volume inversely correlated with changes in type-II fiber force (r = -.691; p = .019). Within the RT+CR group, changes in gait speed correlated positively with changes in type-I fiber CSA (r = .561; p = .030). In addition, increases in type-I normalized fiber force were related to decreases in thigh intermuscular fat volume (r = -0.539; p = .038).

Conclusion: Single muscle fiber force and knee extensor quality improve with RT and RT+CR; however, CR does not enhance improvements in single muscle fiber contractility or whole muscle in response to RT in older overweight and obese men and women.
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http://dx.doi.org/10.1093/gerona/gly047DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6376083PMC
February 2019

Novel Peripherally Derived Neural-Like Stem Cells as Therapeutic Carriers for Treating Glioblastomas.

Stem Cells Transl Med 2017 02 14;6(2):471-481. Epub 2016 Sep 14.

Department of Radiology, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA.

Glioblastoma (GBM), an aggressive grade IV astrocytoma, is the most common primary malignant adult brain tumor characterized by extensive invasiveness, heterogeneity, and angiogenesis. Standard treatment options such as radiation and chemotherapy have proven to be only marginally effective in treating GBM because of its invasive nature. Therefore, extensive efforts have been put forth to develop tumor-tropic stem cells as viable therapeutic vehicles with potential to treat even the most invasive tumor cells that are harbored within areas of normal brain. To this end, we discovered a newly described NG2-expressing cell that we isolated from a distinct pericyte subtype found abundantly in cultures derived from peripheral muscle. In this work, we show the translational significance of these peripherally derived neural-like stem cells (NLSC) and their potential to migrate toward tumors and act as therapeutic carriers. We demonstrate that these NLSCs exhibit in vitro and in vivo GBM tropism. Furthermore, NLSCs did not promote angiogenesis or transform into tumor-associated stromal cells, which are concerns raised when using other common stem cells, such as mesenchymal stem cells and induced neural stem cells, as therapeutic carriers. We also demonstrate the potential of NLSCs to express a prototype therapeutic, tumor necrosis factor α-related apoptosis-inducing ligand and kill GBM cells in vitro. These data demonstrate the therapeutic potential of our newly characterized NLSC against GBM. Stem Cells Translational Medicine 2017;6:471-481.
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http://dx.doi.org/10.5966/sctm.2016-0007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5442817PMC
February 2017

BDA-410 Treatment Reduces Body Weight and Fat Content by Enhancing Lipolysis in Sedentary Senescent Mice.

J Gerontol A Biol Sci Med Sci 2017 Aug;72(8):1045-1053

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina.

Loss of muscle mass and force with age leads to fall risk, mobility impairment, and reduced quality of life. This article shows that BDA-410, a calpain inhibitor, induced loss of body weight and fat but not lean mass or skeletal muscle proteins in a cohort of sedentary 23-month-old mice. Food and water intake and locomotor activity were not modified, whereas BDA-410 treatment decreased intramyocellular lipid and perigonadal fat, increased serum nonesterified fatty acids, and upregulated the genes mediating lipolysis and oxidation, lean phenotype, muscle contraction, muscle transcription regulation, and oxidative stress response. This finding is consistent with our recent report that lipid accumulation in skeletal myofibers is significantly correlated with slower fiber-contraction kinetics and diminished power in obese older adult mice. A proteomic analysis and immunoblot showed downregulation of the phosphatase PPP1R12B, which increases phosphorylated myosin half-life and modulates the calcium sensitivity of the contractile apparatus. This study demonstrates that BDA-410 exerts a beneficial effect on skeletal muscle contractility through new, alternative mechanisms, including enhanced lipolysis, upregulation of "lean phenotype-related genes," downregulation of the PP1R12B phosphatase, and enhanced excitation-contraction coupling. This single compound holds promise for treating age-dependent decline in muscle composition and strength.
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http://dx.doi.org/10.1093/gerona/glw192DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5861946PMC
August 2017

Resistance Training Enhances Skeletal Muscle Innervation Without Modifying the Number of Satellite Cells or their Myofiber Association in Obese Older Adults.

J Gerontol A Biol Sci Med Sci 2016 10 7;71(10):1273-80. Epub 2015 Oct 7.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine and J Paul Sticht Center on Aging, Wake Forest School of Medicine, Winston-Salem, North Carolina.

Studies in humans and animal models provide compelling evidence for age-related skeletal muscle denervation, which may contribute to muscle fiber atrophy and loss. Skeletal muscle denervation seems relentless; however, long-term, high-intensity physical activity appears to promote muscle reinnervation. Whether 5-month resistance training (RT) enhances skeletal muscle innervation in obese older adults is unknown. This study found that neural cell-adhesion molecule, NCAM+ muscle area decreased with RT and was inversely correlated with muscle strength. NCAM1 and RUNX1 gene transcripts significantly decreased with the intervention. Type I and type II fiber grouping in the vastus lateralis did not change significantly but increases in leg press and knee extensor strength inversely correlated with type I, but not with type II, fiber grouping. RT did not modify the total number of satellite cells, their number per area, or the number associated with specific fiber subtypes or innervated/denervated fibers. Our results suggest that RT has a beneficial impact on skeletal innervation, even when started late in life by sedentary obese older adults.
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http://dx.doi.org/10.1093/gerona/glv176DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5018557PMC
October 2016

Troponin T3 regulates nuclear localization of the calcium channel Cavβ1a subunit in skeletal muscle.

Exp Cell Res 2015 Aug 15;336(2):276-86. Epub 2015 May 15.

Department of Internal Medicine-Gerontology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA; Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA. Electronic address:

The voltage-gated calcium channel (Cav) β1a subunit (Cavβ1a) plays an important role in excitation-contraction coupling (ECC), a process in the myoplasm that leads to muscle-force generation. Recently, we discovered that the Cavβ1a subunit travels to the nucleus of skeletal muscle cells where it helps to regulate gene transcription. To determine how it travels to the nucleus, we performed a yeast two-hybrid screening of the mouse fast skeletal muscle cDNA library and identified an interaction with troponin T3 (TnT3), which we subsequently confirmed by co-immunoprecipitation and co-localization assays in mouse skeletal muscle in vivo and in cultured C2C12 muscle cells. Interacting domains were mapped to the leucine zipper domain in TnT3 COOH-terminus (160-244 aa) and Cavβ1a NH2-terminus (1-99 aa), respectively. The double fluorescence assay in C2C12 cells co-expressing TnT3/DsRed and Cavβ1a/YFP shows that TnT3 facilitates Cavβ1a nuclear recruitment, suggesting that the two proteins play a heretofore unknown role during early muscle differentiation in addition to their classical role in ECC regulation.
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http://dx.doi.org/10.1016/j.yexcr.2015.05.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4522384PMC
August 2015

Type-1 pericytes accumulate after tissue injury and produce collagen in an organ-dependent manner.

Stem Cell Res Ther 2014 Nov 6;5(6):122. Epub 2014 Nov 6.

Introduction: Fibrosis, or scar formation, is a pathological condition characterized by excessive production and accumulation of collagen, loss of tissue architecture, and organ failure in response to uncontrolled wound healing. Several cellular populations have been implicated, including bone marrow-derived circulating fibrocytes, endothelial cells, resident fibroblasts, epithelial cells, and recently, perivascular cells called pericytes. We previously demonstrated pericyte functional heterogeneity in skeletal muscle. Whether pericyte subtypes are present in other tissues and whether a specific pericyte subset contributes to organ fibrosis are unknown.

Methods: Here, we report the presence of two pericyte subtypes, type-1 (Nestin-GFP-/NG2-DsRed+) and type-2 (Nestin-GFP+/NG2-DsRed+), surrounding blood vessels in lungs, kidneys, heart, spinal cord, and brain. Using Nestin-GFP/NG2-DsRed transgenic mice, we induced pulmonary, renal, cardiac, spinal cord, and cortical injuries to investigate the contributions of pericyte subtypes to fibrous tissue formation in vivo.

Results: A fraction of the lung's collagen-producing cells corresponds to type-1 pericytes and kidney and heart pericytes do not produce collagen in pathological fibrosis. Note that type-1, but not type-2, pericytes increase and accumulate near the fibrotic tissue in all organs analyzed. Surprisingly, after CNS injury, type-1 pericytes differ from scar-forming PDGFRβ + cells.

Conclusions: Pericyte subpopulations respond differentially to tissue injury, and the production of collagen by type-1 pericytes is organ-dependent. Characterization of the mechanisms underlying scar formation generates cellular targets for future anti-fibrotic therapeutics.
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http://dx.doi.org/10.1186/scrt512DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4445991PMC
November 2014

Pericytes at the intersection between tissue regeneration and pathology.

Clin Sci (Lond) 2015 Jan;128(2):81-93

‡Department of Neurosurgery, Wake Forest School of Medicine, Winston-Salem, North Carolina, Medical Center Boulevard, Winston Salem, NC 27157, U.S.A.

Perivascular multipotent cells, pericytes, contribute to the generation and repair of various tissues in response to injury. They are heterogeneous in their morphology, distribution, origin and markers, and elucidating their molecular and cellular differences may inform novel treatments for disorders in which tissue regeneration is either impaired or excessive. Moreover, these discoveries offer novel cellular targets for therapeutic approaches to many diseases. This review discusses recent studies that support the concept that pericyte subtypes play a distinctive role in myogenesis, neurogenesis, adipogenesis, fibrogenesis and angiogenesis.
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http://dx.doi.org/10.1042/CS20140278DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4200531PMC
January 2015

The Cavβ1a subunit regulates gene expression and suppresses myogenin in muscle progenitor cells.

J Cell Biol 2014 Jun 16;205(6):829-46. Epub 2014 Jun 16.

Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157Department of Internal Medicine-Gerontology, Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, NC 27157

Voltage-gated calcium channel (Cav) β subunits are auxiliary subunits to Cavs. Recent reports show Cavβ subunits may enter the nucleus and suggest a role in transcriptional regulation, but the physiological relevance of this localization remains unclear. We sought to define the nuclear function of Cavβ in muscle progenitor cells (MPCs). We found that Cavβ1a is expressed in proliferating MPCs, before expression of the calcium conducting subunit Cav1.1, and enters the nucleus. Loss of Cavβ1a expression impaired MPC expansion in vitro and in vivo and caused widespread changes in global gene expression, including up-regulation of myogenin. Additionally, we found that Cavβ1a localizes to the promoter region of a number of genes, preferentially at noncanonical (NC) E-box sites. Cavβ1a binds to a region of the Myog promoter containing an NC E-box, suggesting a mechanism for inhibition of myogenin gene expression. This work indicates that Cavβ1a acts as a Cav-independent regulator of gene expression in MPCs, and is required for their normal expansion during myogenic development.
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http://dx.doi.org/10.1083/jcb.201403021DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4068134PMC
June 2014

Type-2 pericytes participate in normal and tumoral angiogenesis.

Am J Physiol Cell Physiol 2014 Jul 30;307(1):C25-38. Epub 2014 Apr 30.

Department of Internal Medicine-Gerontology, Wake Forest School of Medicine, Winston-Salem, North Carolina; Neuroscience Program, Wake Forest School of Medicine, Winston-Salem, North Carolina;

Tissue growth and function depend on vascularization, and vascular insufficiency or excess exacerbates many human diseases. Identification of the biological processes involved in angiogenesis will dictate strategies to modulate reduced or excessive vessel formation. We examine the essential role of pericytes. Their heterogeneous morphology, distribution, origins, and physiology have been described. Using double-transgenic Nestin-GFP/NG2-DsRed mice, we identified two pericyte subsets. We found that Nestin-GFP(-)/NG2-DsRed(+) (type-1) and Nestin-GFP(+)/NG2-DsRed(+) (type-2) pericytes attach to the walls of small and large blood vessels in vivo; in vitro, type-2, but not type-1, pericytes spark endothelial cells to form new vessels. Matrigel assay showed that only type-2 pericytes participate in normal angiogenesis. Moreover, when cancer cells were transplanted into Nestin-GFP/NG2-DsRed mice, type-1 pericytes did not penetrate the tumor, while type-2 pericytes were recruited during its angiogenesis. As inhibition of angiogenesis is a promising strategy in cancer therapy, type-2 pericytes may provide a cellular target susceptible to signaling and pharmacological manipulation in treating malignancy. This work also reports the potential of type-2 pericytes to improve blood perfusion in ischemic hindlimbs, indicating their potential for treating ischemic illnesses.
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http://dx.doi.org/10.1152/ajpcell.00084.2014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4080181PMC
July 2014

Type-1 pericytes participate in fibrous tissue deposition in aged skeletal muscle.

Am J Physiol Cell Physiol 2013 Dec 25;305(11):C1098-113. Epub 2013 Sep 25.

Department of Internal Medicine-Gerontology, Wake Forest School of Medicine, Winston-Salem, North Carolina;

In older adults, changes in skeletal muscle composition are associated with increased fibrosis, loss of mass, and decreased force, which can lead to dependency, morbidity, and mortality. Understanding the biological mechanisms responsible is essential to sustaining and improving their quality of life. Compared with young mice, aged mice take longer to recover from muscle injury; their tissue fibrosis is more extensive, and regenerated myofibers are smaller. Strong evidence indicates that cells called pericytes, embedded in the basement membrane of capillaries, contribute to the satellite-cell pool and muscle growth. In addition to their role in skeletal muscle repair, after tissue damage, they detach from capillaries and migrate to the interstitial space to participate in fibrosis formation. Here we distinguish two bona fide pericyte subtypes in the skeletal muscle interstitium, type-1 (Nestin-GFP(-)/NG2-DsRed(+)) and type-2 (Nestin-GFP(+)/NG2-DsRed(+)), and characterize their heretofore unknown specific roles in the aging environment. Our in vitro results show that type-1 and type-2 pericytes are either fibrogenic or myogenic, respectively. Transplantation studies in young animals indicate that type-2 pericytes are myogenic, while type-1 pericytes remain in the interstitial space. In older mice, however, the muscular regenerative capacity of type-2 pericytes is limited, and type-1 pericytes produce collagen, contributing to fibrous tissue deposition. We conclude that in injured muscles from aging mice, the pericytes involved in skeletal muscle repair differ from those associated with scar formation.
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http://dx.doi.org/10.1152/ajpcell.00171.2013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3882385PMC
December 2013

Role of pericytes in skeletal muscle regeneration and fat accumulation.

Stem Cells Dev 2013 Aug 27;22(16):2298-314. Epub 2013 Apr 27.

Department of Internal Medicine-Gerontology, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157, USA.

Stem cells ensure tissue regeneration, while overgrowth of adipogenic cells may compromise organ recovery and impair function. In myopathies and muscle atrophy associated with aging, fat accumulation increases dysfunction, and after chronic injury, the process of fatty degeneration, in which muscle is replaced by white adipocytes, further compromises tissue function and environment. Some studies suggest that pericytes may contribute to muscle regeneration as well as fat formation. This work reports the presence of two pericyte subpopulations in the skeletal muscle and characterizes their specific roles. Skeletal muscle from Nestin-GFP/NG2-DsRed mice show two types of pericytes, Nestin-GFP-/NG2-DsRed+ (type-1) and Nestin-GFP+/NG2-DsRed+ (type-2), in close proximity to endothelial cells. We also found that both Nestin-GFP-/NG2-DsRed+ and Nestin-GFP+/NG2-DsRed+ cells colocalize with staining of two pericyte markers, PDGFRβ and CD146, but only type-1 pericyte express the adipogenic progenitor marker PDGFRα. Type-2 pericytes participate in muscle regeneration, while type-1 contribute to fat accumulation. Transplantation studies indicate that type-1 pericytes do not form muscle in vivo, but contribute to fat deposition in the skeletal muscle, while type-2 pericytes contribute only to the new muscle formation after injury, but not to the fat accumulation. Our results suggest that type-1 and type-2 pericytes contribute to successful muscle regeneration which results from a balance of myogenic and nonmyogenic cells activation.
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http://dx.doi.org/10.1089/scd.2012.0647DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3730538PMC
August 2013

Enhanced dihydropyridine receptor calcium channel activity restores muscle strength in JP45/CASQ1 double knockout mice.

Nat Commun 2013 ;4:1541

Department of Experimental and Diagnostic Medicine, General Pathology section, University of Ferrara, Via Borsari 46, Ferrara 44121, Italy.

Muscle strength declines with age in part due to a decline of Ca(2+) release from sarcoplasmic reticulum calcium stores. Skeletal muscle dihydropyridine receptors (Ca(v)1.1) initiate muscle contraction by activating ryanodine receptors in the sarcoplasmic reticulum. Ca(v)1.1 channel activity is enhanced by a retrograde stimulatory signal delivered by the ryanodine receptor. JP45 is a membrane protein interacting with Ca(v)1.1 and the sarcoplasmic reticulum Ca(2+) storage protein calsequestrin (CASQ1). Here we show that JP45 and CASQ1 strengthen skeletal muscle contraction by modulating Ca(v)1.1 channel activity. Using muscle fibres from JP45 and CASQ1 double knockout mice, we demonstrate that Ca(2+) transients evoked by tetanic stimulation are the result of massive Ca(2+) influx due to enhanced Ca(v)1.1 channel activity, which restores muscle strength in JP45/CASQ1 double knockout mice. We envision that JP45 and CASQ1 may be candidate targets for the development of new therapeutic strategies against decay of skeletal muscle strength caused by a decrease in sarcoplasmic reticulum Ca(2+) content.
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http://dx.doi.org/10.1038/ncomms2496DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4856057PMC
June 2013

Skeletal muscle pericyte subtypes differ in their differentiation potential.

Stem Cell Res 2013 Jan 29;10(1):67-84. Epub 2012 Sep 29.

Department of Internal Medicine-Gerontology, Wake Forest School of Medicine, Winston-Salem, North Carolina, Medical Center Boulevard, Winston Salem, NC 27157, USA.

Neural progenitor cells have been proposed as a therapy for central nervous system disorders, including neurodegenerative diseases and trauma injuries, however their accessibility is a major limitation. We recently isolated Tuj1+ cells from skeletal muscle culture of Nestin-GFP transgenic mice however whether they form functional neurons in the brain is not yet known. Additionally, their isolation from nontransgenic species and identification of their ancestors is unknown. This gap of knowledge precludes us from studying their role as a valuable alternative to neural progenitors. Here, we identified two pericyte subtypes, type-1 and type-2, using a double transgenic Nestin-GFP/NG2-DsRed mouse and demonstrated that Nestin-GFP+/Tuj1+ cells derive from type-2 Nestin-GFP+/NG2-DsRed+/CD146+ pericytes located in the skeletal muscle interstitium. These cells are bipotential as they generate either Tuj1+ cells when cultured with muscle cells or become "classical" α-SMA+pericytes when cultured alone. In contrast, type-1 Nestin-GFP-/NG2-DsRed+/CD146+ pericytes generate α-SMA+pericytes but not Tuj1+ cells. Interestingly, type-2 pericyte derived Tuj1+ cells retain some pericytic markers (CD146+/PDGFRβ+/NG2+). Given the potential application of Nestin-GFP+/NG2-DsRed+/Tuj1+ cells for cell therapy, we found a surface marker, the nerve growth factor receptor, which is expressed exclusively in these cells and can be used to identify and isolate them from mixed cell populations in nontransgenic species for clinical purposes.
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http://dx.doi.org/10.1016/j.scr.2012.09.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3781014PMC
January 2013

Skeletal muscle neural progenitor cells exhibit properties of NG2-glia.

Exp Cell Res 2013 Jan 20;319(1):45-63. Epub 2012 Sep 20.

Department of Internal Medicine-Gerontology, Wake Forest School of Medicine, Winston Salem, NC 27157, United States.

Reversing brain degeneration and trauma lesions will depend on cell therapy. Our previous work identified neural precursor cells derived from the skeletal muscle of Nestin-GFP transgenic mice, but their identity, origin, and potential survival in the brain are only vaguely understood. In this work, we show that Nestin-GFP+ progenitor cells share morphological and molecular markers with NG2-glia, including NG2, PDGFRα, O4, NGF receptor (p75), glutamate receptor-1(AMPA), and A2B5 expression. Although these cells exhibit NG2, they do not express other pericyte markers, such as α-SMA or connexin-43, and do not differentiate into the muscle lineage. Patch-clamp studies displayed outward potassium currents, probably carried through Kir6.1 channels. Given their potential therapeutic application, we compared their abundance in tissues and concluded that skeletal muscle is the richest source of predifferentiated neural precursor cells. We found that these cells migrate toward the neurogenic subventricular zone displaying their typical morphology and nestin-GFP expression two weeks after brain injection. For translational purposes, we sought to identify these neural progenitor cells in wild-type species by developing a DsRed expression vector under Nestin-Intron II control. This approach revealed them in nonhuman primates and aging rodents throughout the lifespan.
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http://dx.doi.org/10.1016/j.yexcr.2012.09.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3597239PMC
January 2013

Endogenously determined restriction of food intake overcomes excitation-contraction uncoupling in JP45KO mice with aging.

Exp Gerontol 2012 Apr 25;47(4):304-16. Epub 2012 Jan 25.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, United States.

The decline in muscular strength with age is disproportionate to the loss in total muscle mass that causes it. Knocking out JP45, an integral protein of the junctional face membrane of the skeletal muscle sarcoplasmic reticulum (SR), results in decreased expression of the voltage-gated Ca(2+) channel, Ca(v)1.1; excitation-contraction uncoupling (ECU); and loss of muscle force (Delbono et al., 2007). Here, we show that Ca(v)1.1 expression, charge movement, SR Ca(2+) release, in vitro contractile force, and sustained forced running remain stable in male JP45KO mice at 12 and 18 months. They also exhibit the level of ECU reported for 3-4-month mice (Delbono et al., 2007). No further decline at later ages was recorded. Preserved ECC was not related to increased expression of any protein that directly or indirectly interacts with JP45 at the triad junction. However, maintained muscle force and physical performance were associated with ablation of JP45 expression in the brain, spontaneous and significantly diminished food intake and less tendency toward obesity when exposed to a high-fat diet compared to WT. We propose that (1) endogenously generated restriction in food intake overcomes the deleterious effects of JP45 ablation on ECC and skeletal muscle force mainly through downregulation of neuropeptide-Y expression in the hypothalamic arcuate nucleus; and (2) the JP45KO mouse constitutes an invaluable model to examine the mechanisms controlling food intake as well as skeletal muscle function with aging.
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http://dx.doi.org/10.1016/j.exger.2012.01.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3307889PMC
April 2012

Residual sarcoplasmic reticulum Ca2+ concentration after Ca2+ release in skeletal myofibers from young adult and old mice.

Pflugers Arch 2012 Apr 17;463(4):615-24. Epub 2012 Jan 17.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, 1 Medical Center Boulevard, Winston-Salem, NC, 27157, USA.

Contrasting information suggests either almost complete depletion of sarcoplasmic reticulum (SR) Ca(2+) or significant residual Ca(2+) concentration after prolonged depolarization of the skeletal muscle fiber. The primary obstacle to resolving this controversy is the lack of genetically encoded Ca(2+) indicators targeted to the SR that exhibit low-Ca(2+) affinity, a fast biosensor: Ca(2+) off-rate reaction, and can be expressed in myofibers from adult and older adult mammalian species. This work used the recently designed low-affinity Ca(2+) sensor (Kd = 1.66 mM in the myofiber) CatchER (calcium sensor for detecting high concentrations in the ER) targeted to the SR, to investigate whether prolonged skeletal muscle fiber depolarization significantly alters residual SR Ca(2+) with aging. We found CatchER a proper tool to investigate SR Ca(2+) depletion in young adult and older adult mice, consistently tracking SR luminal Ca(2+) release in response to brief and repetitive stimulation. We evoked SR Ca(2+) release in whole-cell voltage-clamped flexor digitorum brevis muscle fibers from young and old FVB mice and tested the maximal SR Ca(2+) release by directly activating the ryanodine receptor (RyR1) with 4-chloro-m-cresol in the same myofibers. Here, we report for the first time that the Ca(2+) remaining in the SR after prolonged depolarization (2 s) in myofibers from aging (~220 μM) was larger than young (~132 μM) mice. These experiments indicate that SR Ca(2+) is far from fully depleted under physiological conditions throughout life, and support the concept of excitation-contraction uncoupling in functional senescent myofibers.
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http://dx.doi.org/10.1007/s00424-012-1073-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3319114PMC
April 2012

Troponin T nuclear localization and its role in aging skeletal muscle.

Age (Dordr) 2013 Apr 22;35(2):353-70. Epub 2011 Dec 22.

Department of Internal Medicine-Gerontology and Geriatric Medicine, Wake Forest School of Medicine, 1 Medical Center Blvd., Winston-Salem, NC 27157, USA.

Troponin T (TnT) is known to mediate the interaction between Tn complex and tropomyosin (Tm), which is essential for calcium-activated striated muscle contraction. This regulatory function takes place in the myoplasm, where TnT binds Tm. However, recent findings of troponin I and Tm nuclear translocation in Drosophila and mammalian cells imply other roles for the Tn-Tm complex. We hypothesized that TnT plays a nonclassical role through nuclear translocation. Immunoblotting with different antibodies targeting the NH2- or COOH-terminal region uncovered a pool of fast skeletal muscle TnT3 localized in the nuclear fraction of mouse skeletal muscle as either an intact or fragmented protein. Construction of TnT3-DsRed fusion proteins led to the further observation that TnT3 fragments are closely related to nucleolus and RNA polymerase activity, suggesting a role for TnT3 in regulating transcription. Functionally, overexpression of TnT3 fragments produced significant defects in nuclear shape and caused high levels of apoptosis. Interestingly, nuclear TnT3 and its fragments were highly regulated by aging, thus creating a possible link between the deleterious effects of TnT3 and sarcopenia. We propose that changes in nuclear TnT3 and its fragments cause the number of myonuclei to decrease with age, contributing to muscle damage and wasting.
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http://dx.doi.org/10.1007/s11357-011-9368-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3592954PMC
April 2013

Nestin-GFP transgene reveals neural precursor cells in adult skeletal muscle.

PLoS One 2011 Feb 3;6(2):e16816. Epub 2011 Feb 3.

Department of Internal Medicine-Gerontology, Wake Forest University School of Medicine, Winston-Salem, North Carolina, USA.

Background: Therapy for neural lesions or degenerative diseases relies mainly on finding transplantable active precursor cells. Identifying them in peripheral tissues accessible for biopsy, outside the central nervous system, would circumvent the serious immunological and ethical concerns impeding cell therapy.

Methodology/principal Findings: In this study, we isolated neural progenitor cells in cultured adult skeletal muscle from transgenic mice in which nestin regulatory elements control GFP expression. These cells also expressed the early neural marker Tuj1 and light and heavy neurofilament but not S100β, indicating that they express typical neural but not Schwann cell markers. GFP+/Tuj1+ cells were also negative for the endothelial and pericyte markers CD31 and α-smooth muscle actin, respectively. We established their a) functional response to glutamate in patch-clamp recordings; b) interstitial mesenchymal origin; c) replicative capacity; and d) the environment necessary for their survival after fluorescence-activated cell sorting.

Conclusions/significance: We propose that the decline in nestin-GFP expression in muscle progenitor cells and its persistence in neural precursor cells in muscle cultures provide an invaluable tool for isolating a population of predifferentiated neural cells with therapeutic potential.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0016816PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3033412PMC
February 2011

Sarcoplasmic reticulum Ca2+ depletion in adult skeletal muscle fibres measured with the biosensor D1ER.

Pflugers Arch 2010 Apr 13;459(5):725-35. Epub 2010 Jan 13.

Department of Internal Medicine, Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

The endoplasmic/sarcoplasmic reticulum (ER/SR) plays a crucial role in cytoplasmic signalling in a variety of cells. It is particularly relevant to skeletal muscle fibres, where this organelle constitutes the main Ca2+ store for essential functions, such as contraction. In this work, we expressed the cameleon biosensor D1ER by in vivo electroporation in the mouse flexor digitorum brevis (FDB) muscle to directly assess SR Ca2+ depletion in response to electrical and pharmacological stimulation. The main conclusions are: (1) D1ER is expressed in the SR of FDB fibres according to both di-8-(amino naphthyl ethenyl pyridinium) staining experiments and reductions in the Förster resonance energy transfer signal consequent to SR Ca2+ release; (2) the amplitude of D1ER citrine/cyan fluorescent protein (CFP) ratio evoked by either 4-chloro-m-cresol (4-CmC) or electrical stimulation is directly proportional to the basal citrine/CFP ratio, which indicates that SR Ca2+ modulates ryanodine-receptor-isoform-1-mediated SR Ca2+ release in the intact muscle fibre; (3) SR Ca2+ release, measured as D1ER citrine/CFP signal, is voltage-dependent and follows a Boltzmann function; and (4) average SR Ca2+ depletion is 20% in response to 4-CmC and 6.4% in response to prolonged sarcolemmal depolarization. These results indicate that significantly depleting SR Ca2+ content under physiological conditions is difficult.
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http://dx.doi.org/10.1007/s00424-009-0778-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2864504PMC
April 2010

Role of Ca2+, membrane excitability, and Ca2+ stores in failing muscle contraction with aging.

Exp Gerontol 2009 Apr 10;44(4):261-73. Epub 2008 Oct 10.

Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

Excitation-contraction (EC) coupling in a population of skeletal muscle fibers of aged mice becomes dependent on the presence of external Ca(2+) ions (Payne, A.M., Zheng, Z., Gonzalez, E., Wang, Z.M., Messi, M.L., Delbono, O., 2004b. External Ca(2+)-dependent excitation - contraction coupling in a population of aging mouse skeletal muscle fibers. J. Physiol. 560, 137-155.). However, the mechanism(s) underlying this process remain unknown. In this work, we examined the role of (1) extracellular Ca(2+); (2) voltage-induced influx of external Ca(2+) ions; (3) sarcoplasmic reticulum (SR) Ca(2+) depletion during repeated contractions; (4) store-operated Ca(2+) entry (SOCE); (5) SR ultrastructure; (6) SR subdomain localization of the ryanodine receptor; and (7) sarcolemmal excitability in muscle force decline with aging. These experiments show that external Ca(2+), but not Ca(2+) influx, is needed to maintain force upon repetitive fiber electrical stimulation. Decline in fiber force is associated with depressed SR Ca(2+) release. SR Ca(2+) depletion, SOCE, and the putative segregated Ca(2+) release store do not play a significant role in external Ca(2+)-dependent contraction. More importantly, a significant number of action potentials fail in senescent mouse muscle fibers subjected to a stimulation frequency. These results indicate that failure to generate action potentials accounts for decreased intracellular Ca(2+) mobilization and tetanic force in aging muscle exposed to a Ca(2+)-free medium.
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http://dx.doi.org/10.1016/j.exger.2008.09.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3082867PMC
April 2009

Loss of skeletal muscle strength by ablation of the sarcoplasmic reticulum protein JP45.

Proc Natl Acad Sci U S A 2007 Dec 5;104(50):20108-13. Epub 2007 Dec 5.

Departments of Anaesthesia and Research, Basel University Hospital, Hebelstrasse 20, 4031 Basel, Switzerland.

Skeletal muscle constitutes approximately 40% of the human body mass, and alterations in muscle mass and strength may result in physical disability. Therefore, the elucidation of the factors responsible for muscle force development is of paramount importance. Excitation-contraction coupling (ECC) is a process during which the skeletal muscle surface membrane is depolarized, causing a transient release of calcium from the sarcoplasmic reticulum that activates the contractile proteins. The ECC machinery is complex, and the functional role of many of its protein components remains elusive. This study demonstrates that deletion of the gene encoding the sarcoplasmic reticulum protein JP45 results in decreased muscle strength in young mice. Specifically, this loss of muscle strength in JP45 knockout mice is caused by decreased functional expression of the voltage-dependent Ca(2+) channel Ca(v)1.1, which is the molecule that couples membrane depolarization and calcium release from the sarcoplasmic reticulum. These results point to JP45 as one of the molecules involved in the development or maintenance of skeletal muscle strength.
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http://dx.doi.org/10.1073/pnas.0707389104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2148430PMC
December 2007

The lack of effect of specific overexpression of IGF-1 in the central nervous system or skeletal muscle on pathophysiology in the G93A SOD-1 mouse model of ALS.

Exp Neurol 2007 Sep 2;207(1):52-63. Epub 2007 Jun 2.

Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

The ability of insulin like growth factor 1 (IGF-1) to prevent the pathophysiology associated with amyotrophic lateral sclerosis (ALS) is currently being explored with animal models and in clinical trials with patients. Several studies have reported positive effects of IGF-1 in reducing motor neuron death, delaying the onset of motor performance decline, and increasing life span, in SOD-1 mouse models of ALS and in one clinical trial. However, a second clinical trial produced no positive results raising questions about the therapeutic efficacy of IGF-1. To investigate the effect of specific and sustained IGF-1 expression in skeletal muscle or central nervous system on motor performance, life span, and motor neuron survival, human-IGF-1 transgenic mice were crossed with the G93A SOD-1 mutant model of ALS. No significant differences were found in onset of motor performance decline, life span, or motor neuron survival in the spinal cord, between SOD+/IGF-1+ and SOD+/IGF-1- hybrid mice. IGF-1 concentration levels, measured by radioimmunoassay, were found to be highly increased throughout life in the central nervous system (CNS) and skeletal muscle of IGF-1 transgenic hybrid mice. Additionally, increased CNS weight in SOD+ mice crossbred with CNS IGF-1 transgenic mice demonstrates that IGF-1 overexpression is biologically active even after the disease is fully developed. Taken together, these results raise questions concerning the therapeutic value of IGF-1 and indicate that further studies are needed to examine the relationship between methods of IGF-1 administration and its potential therapeutic value.
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http://dx.doi.org/10.1016/j.expneurol.2007.05.016DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2043146PMC
September 2007

Role of sustained overexpression of central nervous system IGF-I in the age-dependent decline of mouse excitation-contraction coupling.

J Membr Biol 2006 28;212(3):147-61. Epub 2007 Feb 28.

Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC, 27157, USA.

We investigated the effects of exclusive and sustained transgenic overexpression of insulin-like growth factor (IGF)-I in the central nervous system (CNS) on the age-dependent decline in muscle strength, excitation-contraction coupling, muscle innervation and neuromuscular junction postterminal architecture. We found that (1) transgenic IGF-I overexpression in the CNS does not modify the decline in extensor digitorum longus (EDL) and soleus muscle weight with aging and (2) strength significantly decreases in transgenic (Tg) compared to wild-type mice. The latter finding is consistent with (3) the decreased absolute and specific force measured in the EDL muscle in vitro and (4) the decreased charge movement and peak intracellular Ca(2+) mobilization in individual muscle fibers from old IGF-I Tg mice compared to young wild-type mice, which also is associated with (5) decreased dihydropyridine receptor alpha(1)-subunit expression in old compared to young IGF-I Tg mice. (6) Tg IGF-I prevents a change in muscle fiber type that is associated with (7) improved muscle innervation and postterminal neuromuscular structure. (8) IGF-I is expressed extensively across the spinal cord gray matter and the lateral motor column. Our results raise questions about the timing and cell location of CNS IGF-I overexpression necessary to prevent or to ameliorate age-dependent alterations in the structure and function of skeletal muscle.
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http://dx.doi.org/10.1007/s00232-006-0044-zDOI Listing
August 2007

Motor neuron targeting of IGF-1 attenuates age-related external Ca2+-dependent skeletal muscle contraction in senescent mice.

Exp Gerontol 2007 Apr 14;42(4):309-19. Epub 2006 Dec 14.

Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

A population of fast muscle fibers from aging mice is dependent on external Ca(2+) to maintain tetanic force during repeated contractions. We hypothesized that age-related denervation in muscle fibers plays a role in initiating this contractile deficit, and that prevention of denervation by IGF-1 overexpression would prevent external Ca(2+)-dependent contraction in aging mice. IGF-1 overexpression in skeletal muscle prevents age-related denervation, and prevented external Ca(2+)-dependent contraction in this work. To determine if the effects of IGF-1 overexpression are on muscle or nerve, aging mice were injected with a tetanus toxin fragment-C (TTC) fusion protein that targets IGF-1 to spinal cord motor neurons. This treatment prevented external Ca(2+)-dependent contraction. We also show evidence that injections of the IGF-1-TTC fusion protein prevent age-related alterations to the nerve terminals at the neuromuscular junctions. We conclude that the slow age-related denervation of fast muscle fibers underlies dependence on external Ca(2+) to maintain tetanic force in a population of muscle fibers from senescent mice.
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http://dx.doi.org/10.1016/j.exger.2006.11.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2063746PMC
April 2007

Motor neurone targeting of IGF-1 prevents specific force decline in ageing mouse muscle.

J Physiol 2006 Jan 17;570(Pt 2):283-94. Epub 2005 Nov 17.

Department of Physiology and Pharmacology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

IGF-1 is a potent growth factor for both motor neurones and skeletal muscle. Muscle IGF-1 is known to provide target-derived trophic effects on motor neurones. Therefore, IGF-1 overexpression in muscle is effective in delaying or preventing deleterious effects of ageing in both tissues. Since age-related decline in muscle function stems partly from motor neurone loss, a tetanus toxin fragment-C (TTC) fusion protein was created to target IGF-1 to motor neurones. IGF-1-TTC retains IGF-1 activity as indicated by [(3)H]thymidine incorporation into L6 myoblasts. Spinal cord motor neurones effectively bound and internalized the IGF-1-TTC in vitro. Similarly, IGF-1-TTC injected into skeletal muscles was taken up and retrogradely transported to the spinal cord in vivo, a process prevented by denervation of injected muscles. Three monthly IGF-1-TTC injections into muscles of ageing mice did not increase muscle weight or muscle fibre size, but significantly increased single fibre specific force over aged controls injected with saline, IGF-1, or TTC. None of the injections changed muscle fibre type composition, but neuromuscular junction post-terminals were larger and more complex in muscle fibres injected with IGF-1-TTC, compared to the other groups, suggesting preservation of muscle fibre innervation. This work demonstrates that induced overexpression of IGF-1 in spinal cord motor neurones of ageing mice prevents muscle fibre specific force decline, a hallmark of ageing skeletal muscle.
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http://dx.doi.org/10.1113/jphysiol.2005.100032DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1464304PMC
January 2006