Publications by authors named "Ulrik Frandsen"

27 Publications

  • Page 1 of 1

Assessment of functional sit-to-stand muscle power: Cross-sectional trajectories across the lifespan.

Exp Gerontol 2021 Sep 9;152:111448. Epub 2021 Jun 9.

Geriatric Research Unit, Geriatric Department, Bispebjerg University Hospital, Copenhagen, Denmark; Department of Clinical Physiology, Nuclear Medicine & PET, Rigshospitalet-Glostrup University Hospital, Copenhagen, Denmark; Geriatric Research Unit, Department of Internal Medicine, Herlev-Gentofte University Hospital, Copenhagen, Denmark. Electronic address:

Background: The 30-s sit-to-stand (STS) muscle power test is a valid test to assess muscle power in older people; however, whether it may be used to assess trajectories of lower-limb muscle power through the adult lifespan is not known. This study evaluated the pattern and time course of variations in relative, allometric and specific STS muscle power throughout the lifespan.

Methods: Subjects participating in the Copenhagen Sarcopenia Study (729 women and 576 men; aged 20 to 93 years) were included. Lower-limb muscle power was assessed with the 30-s version of the STS muscle power test. Allometric, relative and specific STS power were calculated as absolute STS power normalized to height squared, body mass and leg lean mass as assessed by DXA, respectively.

Results: Relative STS muscle power tended to increase in women (0.08 ± 0.05 W·kg·yr; p = 0.082) and increased in men (0.14 ± 0.07 W·kg·yr; p = 0.046) between 20 and 30 years, followed by a slow decline (-0.05 ± 0.05 W·kg·yr and -0.06 ± 0.08 W·kg·yr, respectively; both p > 0.05) between 30 and 50 years. Then, relative STS power declined at an accelerated rate up to oldest age in men (-0.09 ± 0.02 W·kg·yr) and in women until the age of 75 (-0.09 ± 0.01 W·kg·yr) (both p < 0.001). A lower rate of decline was observed in women aged 75 and older (-0.04 ± 0.02 W·kg·yr; p = 0.039). Similar age-related patterns were noted for allometric and specific STS power.

Conclusions: The STS muscle power test appears to provide a feasible and inexpensive tool to monitor cross-sectional trajectories of muscle power throughout the lifespan.
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http://dx.doi.org/10.1016/j.exger.2021.111448DOI Listing
September 2021

Exercise-induced fluid shifts are distinct to exercise mode and intensity: a comparison of blood flow-restricted and free-flow resistance exercise.

J Appl Physiol (1985) 2021 06 29;130(6):1822-1835. Epub 2021 Apr 29.

Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, grid.4973.9Copenhagen University Hospital, Copenhagen, Denmark.

MRI can provide fundamental tools in decoding physiological stressors stimulated by training paradigms. Acute physiological changes induced by three diverse exercise protocols known to elicit similar levels of muscle hypertrophy were evaluated using muscle functional magnetic resonance imaging (mfMRI). The study was a cross-over study with participants ( = 10) performing three acute unilateral knee extensor exercise protocols to failure and a work matched control exercise protocol. Participants were scanned after each exercise protocol; 70% 1 repetition maximum (RM) (FF70); 20% 1RM (FF20); 20% 1RM with blood flow restriction (BFR20); free-flow (FF) control work matched to BFR20 (FF20). Post exercise mfMRI scans were used to obtain interleaved measures of muscle R2 (indicator of edema), R2' (indicator of deoxyhemoglobin), muscle cross sectional area (CSA) blood flow, and diffusion. Both BFR20 and FF20 exercise resulted in a larger acute decrease in R2, decrease in R2', and expansion of the extracellular compartment with slower rates of recovery. BFR20 caused greater acute increases in muscle CSA than FF20 and FF70. Only BFR20 caused acute increases in intracellular volume. Postexercise muscle blood flow was higher after FF70 and FF20 exercise than BFR20. Acute changes in mean diffusivity were similar across all exercise protocols. This study was able to differentiate the acute physiological responses between anabolic exercise protocols. Low-load exercise protocols, known to have relatively higher energy contributions from glycolysis at task failure, elicited a higher mfMRI response. Noninvasive mfMRI represents a promising tool for decoding mechanisms of anabolic adaptation in muscle. Using muscle functional MRI (mfMRI), this study was able to differentiate the acute physiological responses following three established hypertrophic resistance exercise strategies. Low-load exercise protocols performed to failure, with or without blood flow restriction, resulted in larger changes in R (i.e. greater T-shifts) with a slow rate of return to baseline indicative of myocellular fluid shifts. These data were cross evaluated with interleaved measures of macrovascular blood flow, water diffusion, muscle cross sectional area (i.e. acute macroscopic muscle swelling), and intracellular water fraction measured using MRI.
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http://dx.doi.org/10.1152/japplphysiol.01012.2020DOI Listing
June 2021

Subcellular localization- and fibre type-dependent utilization of muscle glycogen during heavy resistance exercise in elite power and Olympic weightlifters.

Acta Physiol (Oxf) 2021 02 4;231(2):e13561. Epub 2020 Oct 4.

Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense M, Denmark.

Aim: Glycogen particles are found in different subcellular localizations, which are utilized heterogeneously in different fibre types during endurance exercise. Although resistance exercise typically involves only a moderate use of mixed muscle glycogen, the hypothesis of the present study was that high-volume heavy-load resistance exercise would mediate a pattern of substantial glycogen depletion in specific subcellular localizations and fibre types.

Methods: 10 male elite weightlifters performed resistance exercise consisting of four sets of five (4 × 5) repetitions at 75% of 1RM back squats, 4 × 5 at 75% of 1RM deadlifts and 4 × 12 at 65% of 1RM rear foot elevated split squats. Muscle biopsies (vastus lateralis) were obtained before and after the exercise session. The volumetric content of intermyofibrillar (between myofibrils), intramyofibrillar (within myofibrils) and subsarcolemmal glycogen was assessed by transmission electron microscopy.

Results: After exercise, biochemically determined muscle glycogen decreased by 38 (31:45)%. Location-specific glycogen analyses revealed in type 1 fibres a large decrement in intermyofibrillar glycogen, but no or only minor changes in intramyofibrillar or subsarcolemmal glycogen. In type 2 fibres, large decrements in glycogen were observed in all subcellular localizations. Notably, a substantial fraction of the type 2 fibres demonstrated near-depleted levels of intramyofibrillar glycogen after the exercise session.

Conclusion: Heavy resistance exercise mediates a substantial utilization of glycogen from all three subcellular localization in type 2 fibres, while mostly taxing intermyofibrillar glycogen stores in type 1 fibres. Thus, a better understanding of the impact of resistance training on myocellular metabolism and performance requires a focus on compartmentalized glycogen utilization.
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http://dx.doi.org/10.1111/apha.13561DOI Listing
February 2021

Physiological responses of human skeletal muscle to acute blood flow restricted exercise assessed by multimodal MRI.

J Appl Physiol (1985) 2020 10 27;129(4):748-759. Epub 2020 Aug 27.

Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark.

Important physiological quantities for investigating muscle hypertrophy include blood oxygenation, cell swelling, and changes in blood flow. The purpose of this study was to compare the acute changes of these parameters in human skeletal muscle induced by low-load (20% 1-RM) blood flow-restricted (BFR-20) knee extensor exercise compared with free-flow work-matched (FF-20) and free-flow 50% 1-RM (FF-50) knee extensor exercise using multimodal magnetic resonance imaging (MRI). Subjects ( = 11) completed acute exercise sessions for each exercise mode in an MRI scanner, where interleaved measures of muscle (indicator of edema), [Formula: see text] (indicator of deoxyhemoglobin), macrovascular blood flow, and diffusion were performed before, between sets, and after the final set for each exercise protocol. BFR-20 exercise resulted in larger acute decreases in R and greater increases in cross-sectional area than FF-20 and FF-50 ( < 0.01). Blood oxygenation decreased between sets during BFR-20, as indicated by a 13.6% increase in [Formula: see text] values ( < 0.01)), whereas they remained unchanged for FF-20 and decreased during FF-50 exercise. Quadriceps blood flow between sets was highest for the heavier load (FF-50), averaging 305 mL/min, and lowest for BFR-20 at 123 ± 73 mL/min until post-exercise cuff release, where blood flow rates in BFR-20 exceeded both FF protocols ( < 0.01). Acute changes in diffusion rates were similar for all exercise protocols. This study was able to differentiate the acute exercise response of selected physiological factors associated with skeletal muscle hypertrophy. Marked differences in these parameters were found to exist between BFR and FF exercise conditions, which contribute to explain the anabolic potential of low-load blood flow restricted muscle exercise. Acute changes in blood flow, diffusion, blood oxygenation, cross-sectional area, and the "T shift" are evaluated in human skeletal muscle in response to blood flow-restricted (BFR) and conventional free-flow knee extensor exercise performed in an MRI scanner. The acute physiological response to exercise was dependent on the magnitude of load and the application of BFR. Physiological variables changed markedly and established a steady state rapidly after the first of four exercise sets.
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http://dx.doi.org/10.1152/japplphysiol.00171.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7654733PMC
October 2020

Skeletal Muscle Microvascular Changes in Response to Short-Term Blood Flow Restricted Training-Exercise-Induced Adaptations and Signs of Perivascular Stress.

Front Physiol 2020 12;11:556. Epub 2020 Jun 12.

Department of Sports Science and Clinical Biomechanics and SDU Muscle Research Cluster, Faculty of Health Sciences, University of Southern Denmark, Odense, Denmark.

Previous reports suggest that low-load muscle exercise performed under blood flow restriction (BFR) may lead to endurance adaptations. However, only few and conflicting results exist on the magnitude and timing of microvascular adaptations, overall indicating a lack of angiogenesis with BFR training. The present study, therefore, aimed to examine the effect of short-term high-frequency BFR training on human skeletal muscle vascularization. Participants completed 3 weeks of high-frequency (one to two daily sessions) training consisting of either BFR exercise [(BFRE) = 10, 22.8 ± 2.3 years; 20% one-repetition maximum (1RM), 100 mmHg] performed to concentric failure or work-matched free-flow exercise [(CON) = 8, 21.9 ± 3.0 years; 20% 1RM]. Muscle biopsies [vastus lateralis (VL)] were obtained at baseline, 8 days into the intervention, and 3 and 10 days after cessation of the intervention to examine capillary and perivascular adaptations, as well as angiogenesis-related protein signaling and gene expression. Capillary per myofiber and capillary area (CA) increased 21-24 and 25-34%, respectively, in response to BFRE ( < 0.05-0.01), while capillary density (CD) remained unchanged. Overall, these adaptations led to a consistent elevation (15-16%) in the capillary-to-muscle area ratio following BFRE ( < 0.05-0.01). In addition, evaluation of perivascular properties indicated thickening of the perivascular basal membrane following BFRE. No or only minor changes were observed in CON. This study is the first to show that short-term high-frequency, low-load BFRE can lead to microvascular adaptations (i.e., capillary neoformation and changes in morphology), which may contribute to the endurance effects previously documented with BFR training. The observation of perivascular membrane thickening suggests that high-frequency BFRE may be associated with significant vascular stress.
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http://dx.doi.org/10.3389/fphys.2020.00556DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7303802PMC
June 2020

Age- and Sex-Specific Changes in Lower-Limb Muscle Power Throughout the Lifespan.

J Gerontol A Biol Sci Med Sci 2020 06;75(7):1369-1378

Geriatric Research Unit, Geriatric Department, Bispebjerg University Hospital, Copenhagen, Denmark.

Background: Our main goal was to evaluate the pattern and time course of changes in relative muscle power and its constituting components throughout the life span.

Methods: A total of 1,305 subjects (729 women and 576 men; aged 20-93 years) participating in the Copenhagen Sarcopenia Study took part. Body mass index (BMI), leg lean mass assessed by dual-energy X-ray absorptiometry (DXA), and leg extension muscle power (LEP) assessed by the Nottingham power rig were recorded. Relative muscle power (normalized to body mass) and specific muscle power (normalized to leg lean mass) were calculated. Segmented regression analyses were used to identify the onset and pattern of age-related changes in the recorded variables.

Results: Relative muscle power began to decline above the age of 40 in both women and men, with women showing an attenuation of the decline above 75 years. Relative muscle power decreased with age due to (i) the loss of absolute LEP after the fourth decade of life and (ii) the increase in BMI up to the age of 75 years in women and 65 years in men. The decline in absolute LEP was caused by a decline in specific LEP up to the age of 75 in women and 65 in men, above which the loss in relative leg lean mass also contributed.

Conclusions: Relative power decreased (i) above 40 years by the loss in absolute power (specific power only) and the increase in body mass, and (ii) above ~70 years by the loss in absolute power (both specific power and leg lean mass).
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http://dx.doi.org/10.1093/gerona/glaa013DOI Listing
June 2020

The immune system in sporadic inclusion body myositis patients is not compromised by blood-flow restricted exercise training.

Arthritis Res Ther 2019 12 18;21(1):293. Epub 2019 Dec 18.

Department of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC), University of Southern Denmark, Odense, Denmark.

Background: Sporadic inclusion body myositis (sIBM) is clinically characterised by progressive proximal and distal muscle weakness and impaired physical function while skeletal muscle tissue displays abnormal cellular infiltration of T cells, macrophages, and dendritic cells. Only limited knowledge exists about the effects of low-load blood flow restriction exercise in sIBM patients, and its effect on the immunological responses at the myocellular level remains unknown. The present study is the first to investigate the longitudinal effects of low-load blood flow restriction exercise on innate and adaptive immune markers in skeletal muscle from sIBM patients.

Methods: Twenty-two biopsy-validated sIBM patients were randomised into either 12 weeks of low-load blood flow restriction exercise (BFRE) or no exercise (CON). Five patients from the control group completed 12 weeks of BFRE immediately following participation in the 12-week control period leading to an intervention group of 16 patients. Muscle biopsies were obtained from either the m. tibialis anterior or the m. vastus lateralis for evaluation of CD3-, CD8-, CD68-, CD206-, CD244- and FOXP3-positive cells by three-colour immunofluorescence microscopy and Visiopharm-based image analysis quantification. A linear mixed model was used for the statistical analysis.

Results: Myocellular infiltration of CD3/CD8 expressing natural killer cells increased following BFRE (P < 0.05) with no changes in CON. No changes were observed for CD3/CD8 or CD3/CD8 T cells in BFRE or CON. CD3/CD244 T cells decreased in CON, while no changes were observed in BFRE. Pronounced infiltration of M1 pro-inflammatory (CD68/CD206) and M2 anti-inflammatory (CD68/CD206) macrophages were observed at baseline; however, no longitudinal changes in macrophage content were observed for both groups.

Conclusions: Low-load blood flow restriction exercise elicited an upregulation in CD3/CD8 expressing natural killer cell content, which suggests that 12 weeks of BFRE training evokes an amplified immune response in sIBM muscle. However, the observation of no changes in macrophage or T cell infiltration in the BFRE-trained patients indicates that patients with sIBM may engage in this type of exercise with no risk of intensified inflammatory activity.
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http://dx.doi.org/10.1186/s13075-019-2036-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6921522PMC
December 2019

The Copenhagen Sarcopenia Study: lean mass, strength, power, and physical function in a Danish cohort aged 20-93 years.

J Cachexia Sarcopenia Muscle 2019 12 16;10(6):1316-1329. Epub 2019 Aug 16.

Department of Clinical Physiology and Nuclear Medicine, Bispebjerg-Frederiksberg University Hospital, Copenhagen, Denmark.

Background: Despite no international consensus on the diagnostic criteria for sarcopenia, low lean mass, muscle strength, and physical function are important risk factors for disability, frailty, and mortality in older individuals, as well as in a wide range of patients with muscle loss. Here, we provide a population-based reference material of total and regional lean body mass, muscle strength/power parameters, and physical function in a healthy cohort of Danish men and women across the lifespan.

Methods: Volunteers aged 20-93 years from the Copenhagen City Heart Study were invited to establish a Danish reference material (Copenhagen Sarcopenia Study) on lean mass characteristics [appendicular lean mass (ALM), iDXA, GE Lunar], muscle function [handgrip strength (HGS), Jamar dynamometer and leg extension power (LEP), Nottingham Power Rig], and physical function [30 s sit-to-stand test (STS), 10-m maximal and habitual gait speed (GS)].

Results: A total of 1305 participants [729 women (age: 56.4 ± 18.9 years, height: 1.66 ± 0.01 m, body mass index: 24.6 ± 4.3 kg/m and 576 men, age: 57.0 ± 17.5 years, height: 1.80 ± 0.07 m, body mass index: 26.0 ± 3.9 kg/m ] completed all measurements and were included in the present analysis. Lean mass characteristics (TLM, ALM, and ALM/h ) decreased with increasing age in both men and women (P < 0.001). Men demonstrated larger absolute and relative total ALM and higher HGS and LEP compared with women at all age intervals (P < 0.001). HGS and LEP decreased progressively with age in both men and women (P < 0.01); 30 s STS performance, habitual GS, and maximal GS decreased at an accellerated rate of decline with increasing age in both men and women (P < 0.001). Habitual GS was reduced in men and women aged ≥70 years, while maximal GS was reduced from the age of ≥60 years compared with young adults (P < 0.001). Regardless of sex, 30 s STS was reduced from the age of ≥50 years compared with the young reference group (P < 0.001) CONCLUSIONS: While the power-based measurements (LEP and 30 s STS) started to decline already at age +50 years, less power-based parameters (GS and HGS) and lean mass characteristics (TLM, ALM, and ALM/h ) remained unaltered until after the age of +70 years. Notably, the cut-off thresholds derived in the present study differed from earlier reference data, which underlines the importance of obtaining updated and local reference materials.
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http://dx.doi.org/10.1002/jcsm.12477DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6903448PMC
December 2019

Fundamental constraints in synchronous muscle limit superfast motor control in vertebrates.

Elife 2017 11 22;6. Epub 2017 Nov 22.

Department of Biology, University of Southern Denmark, Odense, Denmark.

Superfast muscles (SFMs) are extremely fast synchronous muscles capable of contraction rates up to 250 Hz, enabling precise motor execution at the millisecond time scale. SFM phenotypes have been discovered in most major vertebrate lineages, but it remains unknown whether all SFMs share excitation-contraction coupling pathway adaptations for speed, and if SFMs arose once, or from independent evolutionary events. Here, we demonstrate that to achieve rapid actomyosin crossbridge kinetics bat and songbird SFM express myosin heavy chain genes that are evolutionarily and ontologically distinct. Furthermore, we show that all known SFMs share multiple functional adaptations that minimize excitation-contraction coupling transduction times. Our results suggest that SFM evolved independently in sound-producing organs in ray-finned fish, birds, and mammals, and that SFM phenotypes operate at a maximum operational speed set by fundamental constraints in synchronous muscle. Consequentially, these constraints set a fundamental limit to the maximum speed of fine motor control.
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http://dx.doi.org/10.7554/eLife.29425DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5699865PMC
November 2017

Blood flow restricted training leads to myocellular macrophage infiltration and upregulation of heat shock proteins, but no apparent muscle damage.

J Physiol 2017 07 23;595(14):4857-4873. Epub 2017 Jun 23.

Department of Sports Science and Clinical Biomechanics, and SDU Muscle Research Cluster (SMRC), University of Southern Denmark, Odense, Denmark.

Key Points: Muscular contractions performed using a combination of low external loads and partial restriction of limb blood flow appear to induce substantial gains in muscle strength and muscle mass. This exercise regime may initially induce muscular stress and damage; however, the effects of a period of blood flow restricted training on these parameters remain largely unknown. The present study shows that short-term, high-frequency, low-load muscle training performed with partial blood flow restriction does not induce significant muscular damage. However, signs of myocellular stress and inflammation that were observed in the early phase of training and after the training intervention, respectively, may be facilitating the previously reported gains in myogenic satellite cell content and muscle hypertrophy. The present results improve our current knowledge about the physiological effects of low-load muscular contractions performed under blood flow restriction and may provide important information of relevance for future therapeutic treatment of muscular atrophy.

Abstract: Previous studies indicate that low-load muscle contractions performed under local blood flow restriction (BFR) may initially induce muscle damage and stress. However, whether these factors are evoked with longitudinal BFR training remains unexplored at the myocellular level. Two distinct study protocols were conducted, covering 3 weeks (3 wk) or one week (1 wk). Subjects performed BFR exercise (100 mmHg, 20% 1RM) to concentric failure (BFRE) (3 wk/1 wk), while controls performed work-matched (LLE) (3 wk) or high-load (HLE; 70% 1RM) (1 wk) free-flow exercise. Muscle biopsies (3 wk) were obtained at baseline (Pre), 8 days into the intervention (Mid8), and 3 and 10 days after training cessation (Post3, Post10) to examine macrophage (M1/M2) content as well as heat shock protein (HSP27/70) and tenascin-C expression. Blood samples (1 wk) were collected before and after (0.1-24 h) the first and last training session to examine markers of muscle damage (creatine kinase), oxidative stress (total antibody capacity, glutathione) and inflammation (monocyte chemotactic protein-1, interleukin-6, tumour necrosis factor α). M1-macrophage content increased 108-165% with BFRE and LLE at Post3 (P < 0.05), while M2-macrophages increased (163%) with BFRE only (P < 0.01). Membrane and intracellular HSP27 expression increased 60-132% at Mid8 with BFRE (P < 0.05-0.01). No or only minor changes were observed in circulating markers of muscle damage, oxidative stress and inflammation. The amplitude, timing and localization of the above changes indicate that only limited muscle damage was evoked with BFRE. This study is the first to show that a period of high-frequency, low-load BFR training does not appear to induce general myocellular damage. However, signs of tissue inflammation and focal myocellular membrane stress and/or reorganization were observed that may be involved in the adaptation processes evoked by BFR muscle exercise.
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http://dx.doi.org/10.1113/JP273907DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5509865PMC
July 2017

Physical function and muscle strength in sporadic inclusion body myositis.

Muscle Nerve 2017 Dec 10;56(6):E50-E58. Epub 2017 Apr 10.

Department of Rheumatology, Odense University Hospital, Odense, Denmark.

Introduction: In this study, self-reported physical function, functional capacity, and isolated muscle function were investigated in sporadic inclusion body myositis (sIBM) patients.

Methods: The 36-item Short Form (SF-36) Health Survey and 2-min walk test (2MWT), timed up & go test (TUG), and 30-s chair stand performance were evaluated. In addition, patients were tested for knee extensor muscle strength (isokinetic dynamometer) and leg extension power (Nottingham power rig).

Results: TUG performance was the strongest predictor of self-reported physical function (r = 0.56, P < 0.05). Knee extension strength and between-limb strength asymmetry were the strongest multi-regression indicators of TUG performance (r = 0.51, P < 0.05). Strength asymmetry showed the strongest single-factor (negative) association with 2MWT performance (r = 0.49, P < 0.05).

Discussion: TUG assessment appears to sensitively predict self-perceived physical function in sIBM patients. Notably, between-limb asymmetry in lower limb muscle strength had a substantial negative impact on motor tasks involving gait function. Muscle Nerve 56: E50-E58, 2017.
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http://dx.doi.org/10.1002/mus.25603DOI Listing
December 2017

Delayed Effect of Blood Flow-restricted Resistance Training on Rapid Force Capacity.

Med Sci Sports Exerc 2017 06;49(6):1157-1167

1Department of Sports Science and Clinical Biomechanics and SDU Muscle Research Cluster (SMRC), University of Southern Denmark, Odense, DENMARK; 2Department of Orthopedic Surgery, Odense University Hospital, Odense, DENMARK; 3Department of Orthopedic Surgery, Rigshospitalet, University of Copenhagen, Copenhagen, DENMARK; and 4Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet Glostrup, University of Copenhagen, Copenhagen, DENMARK.

Purpose: The aim of the present study was to investigate the effect and time course of high-frequent low-load blood flow-restricted (BFR) resistance training on rapid force capacity (i.e., rate of torque development [RTD]).

Materials And Methods: Ten male subjects (22.8 ± 2.3 yr) performed four sets of knee extensor exercise (20% one-repetition maximum) to concentric failure during concurrent BFR of the thigh (100 mm Hg), and eight work-matched controls (21.9 ± 3.0 yr) trained without BFR (CON). Twenty-three training sessions were performed within 19 d. Maximal slow and fast knee joint velocity muscle strength and rapid force capacity (e.g., RTD) and evoked twitch contractile parameters were assessed before (Pre) and 5 and 12 d after (Post5 and Post12) training. Muscle biopsies were obtained Pre, after 8 d (Mid8), and 3 and 10 d after (Post3 and Post10) training to examine changes in myofiber area and expression of myocellular proteins known to be modified by cellular stress (CaMKII, annexin A6, SNO-CYS).

Results: RTD remained unchanged after BFR training at Post5, while increasing 15%-20% Post12 (P < 0.01). Evoked muscle twitch parameters showed a general decline Post5 (P < 0.01) while returning to baseline levels at Post12. All contractile parameters essentially remained unchanged in CON. Elevated CaMKII was observed with BFR training at Post3 (57%) and Post10 (71%) (P < 0.05), whereas SNO-CYS increased in CON at Mid8 (P < 0.05).

Conclusion: This study is the first to show that low-load resistance exercise performed with BFR leads to marked increases in rapid force capacity (RTD). However, a general delayed adaptive response was observed for voluntary contractile parameters (including RTD) in parallel with a decline and subsequent recovery in evoked contractile properties, suggesting the delayed gain in rapid force capacity mainly have a peripheral origin.
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http://dx.doi.org/10.1249/MSS.0000000000001208DOI Listing
June 2017

Effects of a multi-component camp-based intervention on inflammatory markers and adipokines in children: A randomized controlled trial.

Prev Med 2015 Dec 3;81:367-72. Epub 2015 Oct 3.

Center of Research in Childhood Health (RICH), Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark; Department of Sports Medicine, Norwegian School of Sport Sciences, Oslo, Norway.

Objective: To examine the effects of a multi-component camp-based intervention on inflammatory markers and adipokines in children.

Methods: One hundred and fifteen children were recruited in Odense, Denmark (2012-2014). The participants were randomly allocated to either the day camp intervention arm (DCIA) or the standard intervention arm (SIA). The intervention for the DCIA consisted of a 6-week camp-based intervention and a 46-week family-based intervention. The SIA was offered one weekly physical activity session for 6 weeks and one educational meeting. C-reactive protein (CRP), monocyte chemoattractant protein-1 (MCP1), leptin, and adiponectin were measured in serum at baseline, 6 weeks and 52 weeks.

Results: In comparison with the SIA, the reductions in CRP (P=0.003) and leptin (p<0.001) were larger in the DCIA at 6 weeks. The intervention effects on leptin were significantly mediated by the changes in body fat mass. No intervention effects on CRP and leptin were seen at 52 weeks. No between-group differences in changes in MCP1 and adiponectin were observed at 6 weeks or 52 weeks.

Conclusions: The 6-week camp intervention resulted in reductions in CRP and leptin. The intervention effects did not persist to 52 weeks. The intervention effect on leptin was explained by changes in body fat mass.
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http://dx.doi.org/10.1016/j.ypmed.2015.09.014DOI Listing
December 2015

Carbohydrate restricted recovery from long term endurance exercise does not affect gene responses involved in mitochondrial biogenesis in highly trained athletes.

Physiol Rep 2015 Feb 12;3(2). Epub 2015 Feb 12.

Institute of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster, University of Southern Denmark, Odense, Denmark.

The aim was to determine if the metabolic adaptations, particularly PGC-1α and downstream metabolic genes were affected by restricting CHO following an endurance exercise bout in trained endurance athletes. A second aim was to compare baseline expression level of these genes to untrained. Elite endurance athletes (VO2max 66 ± 2 mL·kg(-1)·min(-1), n = 15) completed 4 h cycling at ~56% VO2max. During the first 4 h recovery subjects were provided with either CHO or only H2O and thereafter both groups received CHO. Muscle biopsies were collected before, after, and 4 and 24 h after exercise. Also, resting biopsies were collected from untrained subjects (n = 8). Exercise decreased glycogen by 67.7 ± 4.0% (from 699 ± 26.1 to 239 ± 29.5 mmol·kg(-1)·dw(-1)) with no difference between groups. Whereas 4 h of recovery with CHO partly replenished glycogen, the H2O group remained at post exercise level; nevertheless, the gene expression was not different between groups. Glycogen and most gene expression levels returned to baseline by 24 h in both CHO and H2O. Baseline mRNA expression of NRF-1, COX-IV, GLUT4 and PPAR-α gene targets were higher in trained compared to untrained. Additionally, the proportion of type I muscle fibers positively correlated with baseline mRNA for PGC-1α, TFAM, NRF-1, COX-IV, PPAR-α, and GLUT4 for both trained and untrained. CHO restriction during recovery from glycogen depleting exercise does not improve the mRNA response of markers of mitochondrial biogenesis. Further, baseline gene expression of key metabolic pathways is higher in trained than untrained.
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http://dx.doi.org/10.14814/phy2.12184DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4393183PMC
February 2015

Muscle glycogen content modifies SR Ca2+ release rate in elite endurance athletes.

Med Sci Sports Exerc 2014 Mar;46(3):496-505

1Institute of Sports Science and Clinical Biomechanics, SDU Muscle Research Cluster (SMRC), University of Southern Denmark, Odense, DENMARK; 2Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Östersund, SWEDEN; and 3The Åstrand Laboratory, Swedish School of Sport and Health Sciences, Stockholm, SWEDEN.

Purpose: The aim of the present study was to investigate the influence of muscle glycogen content on sarcoplasmic reticulum (SR) function and peak power output (Wpeak) in elite endurance athletes.

Methods: Fourteen highly trained male triathletes (VO2max = 66.5 ± 1.3 mL O2·kg·min), performed 4 h of glycogen-depleting cycling exercise (HRmean = 73% ± 1% of maximum). During the first 4 h of recovery, athletes received either water (H2O) or carbohydrate (CHO), separating alterations in muscle glycogen content from acute changes affecting SR function and performance. Thereafter, all subjects received CHO-enriched food for the remaining 20-h recovery period.

Results: Immediately after exercise, muscle glycogen content and SR Ca release rate was reduced to 32% ± 4% (225 ± 28 mmol·kg dw) and 86% ± 2% of initial levels, respectively (P < 0.01). Glycogen markedly recovered after 4 h of recovery with CHO (61% ± 2% of preexercise) and SR Ca release rate returned to preexercise level. However, in the absence of CHO during the first 4 h of recovery, glycogen and SR Ca release rate remained depressed, with the normalization of both parameters at the end of the 24 h of recovery after receiving a CHO-enriched diet. Linear regression demonstrated a significant correlation between SR Ca release rate and muscle glycogen content (P < 0.01, r = 0.30). The 4 h of cycling exercise reduced Wpeak by 5.5%-8.9% at different cadences (P < 0.05), and Wpeak was normalized after 4 h of recovery with CHO, whereas Wpeak remained depressed (P < 0.05) after water provision. Wpeak was fully recovered after 24 h in both the H2O and the CHO group.

Conclusion: In conclusion, the present results suggest that low muscle glycogen depresses muscle SR Ca release rate, which may contribute to fatigue and delayed recovery of Wpeak 4 h postexercise.
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http://dx.doi.org/10.1249/MSS.0000000000000132DOI Listing
March 2014

Aging affects the transcriptional regulation of human skeletal muscle disuse atrophy.

PLoS One 2012 19;7(12):e51238. Epub 2012 Dec 19.

Institute of Sports Medicine and Center for Healthy Aging, University of Copenhagen, Bispebjerg Hospital, Copenhagen, Denmark.

Important insights concerning the molecular basis of skeletal muscle disuse-atrophy and aging related muscle loss have been obtained in cell culture and animal models, but these regulatory signaling pathways have not previously been studied in aging human muscle. In the present study, muscle atrophy was induced by immobilization in healthy old and young individuals to study the time-course and transcriptional factors underlying human skeletal muscle atrophy. The results reveal that irrespectively of age, mRNA expression levels of MuRF-1 and Atrogin-1 increased in the very initial phase (2-4 days) of human disuse-muscle atrophy along with a marked reduction in PGC-1α and PGC-1β (1-4 days) and a ~10% decrease in myofiber size (4 days). Further, an age-specific decrease in Akt and S6 phosphorylation was observed in young muscle within the first days (1-4 days) of immobilization. In contrast, Akt phosphorylation was unchanged in old muscle after 2 days and increased after 4 days of immobilization. Further, an age-specific down-regulation of MuRF-1 and Atrogin-1 expression levels was observed following 2 weeks of immobilization, along with a slowing atrophy response in aged skeletal muscle. Neither the immediate loss of muscle mass, nor the subsequent age-differentiated signaling responses could be explained by changes in inflammatory mediators, apoptosis markers or autophagy indicators. Collectively, these findings indicate that the time-course and regulation of human skeletal muscle atrophy is age dependent, leading to an attenuated loss in aging skeletal muscle when exposed to longer periods of immobility-induced disuse.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0051238PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3526599PMC
June 2013

Four days of muscle disuse impairs single fiber contractile function in young and old healthy men.

Exp Gerontol 2013 Feb 3;48(2):154-61. Epub 2012 Dec 3.

SDU Muscle Research Cluster, Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.

The purpose of the study was to investigate the effects of 4 days of disuse (knee brace) on contractile function of isolated vastus lateralis fibers (n=486) from 11 young (24.3±0.9 yrs) and 11 old (67.2±1.0 yrs) healthy men having comparable levels of physical activity. Prior to disuse single fiber specific force (maximal Ca(2+)-activated force per cross-sectional area) was lower in MHC I vs. IIa fibers (p<0.05) both in young (44%) and old (32%), and specific force of MHC IIa fibers was lower in old vs. young (19%, p<0.05). Further, Ca(2+) sensitivity was higher in MHC I vs. IIa fibers (p<0.05) in both age groups. Following disuse single fiber specific force decreased (p<0.05) in MHC I fibers in young (-19%) and old (-17%), and in MHC IIa fibers in young (-21%) but not in old (-11%; ns). The extent of these decreases did not differ between young and old. Ca(2+) sensitivity decreased (p<0.05) in MHC I fibers in old (-0.11 pCa units) but not in young (-0.08 pCa units; ns). The extent of these decreases was greater in old vs. young (p<0.05). In conclusion, 4 days of lower limb disuse led to marked impairments in single muscle fiber specific force independently of age, while changes in Ca(2+) sensitivity were dependent on age and MHC isoform composition. The present findings stress the importance of determining and implementing effective preventive and rehabilitative approaches for old individuals exposed to as little as 4 days of disuse.
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http://dx.doi.org/10.1016/j.exger.2012.11.005DOI Listing
February 2013

Proliferation of myogenic stem cells in human skeletal muscle in response to low-load resistance training with blood flow restriction.

J Physiol 2012 Sep 16;590(17):4351-61. Epub 2012 Jul 16.

Institute for Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark.

Low-load resistance training with blood flow restriction has been shown to elicit substantial increases in muscle mass and muscle strength; however, the effect on myogenic stem cells (MSCs) and myonuclei number remains unexplored. Ten male subjects (22.8 ± 2.3 years)performed four sets of knee extensor exercise (20% 1RM) to concentric failure during bloodflow restriction (BFR) of the proximal thigh (100 mmHg), while eight work-matched controls(21.9 ± 3.0 years) trained without BFR (control, CON). Twenty-three training sessions were performed within 19 days. Maximal isometric knee extensor strength (MVC) was examined pre- and post-training, while muscle biopsies were obtained at baseline (Pre), after 8 days intervention(Mid8) and 3 (Post3) and 10 days (Post10) post training to examine changes in myofibre area (MFA), MSC and myonuclei number. MVC increased by 7.1% (Post5) and 10.6% (Post12)(P <0.001) with BFR training, while type I and II MFA increased by 38% (Mid8), 35 – 37%(Post3) and 31 – 32% (Post10) (P <0.001). MSCs per myofibre increased with BFR training from 0.10 ± 0.01 (Pre) to 0.38 ± 0.02 (Mid8), 0.36 ± 0.04 (Post3) and 0.25 ± 0.02 (Post10) (P <0.001). Likewise, myonuclei per myofibre increased from 2.49 ± 0.07 (Pre) to 3.30 ± 0.22(Mid8), 3.20 ± 0.16 (Post3) and 3.11 ± 0.11 (Post10), (P<0.01). Although MFA increased in CON at Mid8, it returned to baseline at Post3. No changes in MSC or myonuclei number were observed in CON. This study is the first to show that short-term low-load resistance exercise performed with partial blood flow restriction leads to marked proliferation of myogenic stem cells and resulting myonuclei addition in human skeletal muscle, which is accompanied by substantial myofibre hypertrophy.
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http://dx.doi.org/10.1113/jphysiol.2012.237008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3473290PMC
September 2012

Strength training increases the size of the satellite cell pool in type I and II fibres of chronically painful trapezius muscle in females.

J Physiol 2011 Nov 26;589(Pt 22):5503-15. Epub 2011 Sep 26.

Institute of Sports Medicine, Department of Orthopaedic Surgery M, Bispebjerg Hospital, and Centre for Healthy Ageing, Faculty of Health Sciences,University of Copenhagen, Denmark.

While strength training has been shown to be effective in mediating hypertrophy and reducing pain in trapezius myalgia, responses at the cellular level have not previously been studied. This study investigated the potential of strength training targeting the affected muscles (SST, n = 18) and general fitness training (GFT, n = 16) to augment the satellite cell (SC) and macrophage pools in the trapezius muscles of women diagnosed with trapezius myalgia. A group receiving general health information (REF, n = 8) served as a control. Muscle biopsies were collected from the trapezius muscles of the 42 women (age 44 ± 8 years; mean ± SD) before and after the 10 week intervention period and were analysed by immunohistochemistry for SCs, macrophages and myonuclei. The SC content of type I and II fibres was observed to increase significantly from baseline by 65% and 164%, respectively, with SST (P < 0.0001), together with a significant correlation between the baseline number of SCs and the extent of hypertrophy (r = -0.669, P = 0.005). SST also resulted in a 74% enhancement of the trapezius macrophage content (P < 0.01), accompanied by evidence for the presence of an increased number of actively dividing cells (Ki67(+)) post-SST (P < 0.001). GFT resulted in a significant 23% increase in the SC content of type II fibres, when expressed relative to myonuclear number only (P < 0.05). No changes in the number of myonuclei per fibre or myonuclear domain were detected in any group. These findings provide strong support at the cellular level for the potential of SST to induce a strong myogenic response in this population.
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http://dx.doi.org/10.1113/jphysiol.2011.217885DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3240887PMC
November 2011

Distribution of myogenic progenitor cells and myonuclei is altered in women with vs. those without chronically painful trapezius muscle.

J Appl Physiol (1985) 2010 Dec 7;109(6):1920-9. Epub 2010 Oct 7.

Institute of Sports Medicine Copenhagen, Bispebjerg Hospital, Bldg. 8, Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark.

It is hypothesized that repeated recruitment of low-threshold motor units is an underlying cause of chronic pain in trapezius myalgia. This study investigated the distribution of satellite cells (SCs), myonuclei, and macrophages in muscle biopsies from the trapezius muscle of 42 women performing repetitive manual work, diagnosed with trapezius myalgia (MYA; 44 ± 8 yr; mean ± SD) and 20 matched healthy controls (CON; 45 ± 9 yr). Our hypothesis was that muscle of MYA, in particular type I fibers, would demonstrate higher numbers of SCs, myonuclei, and macrophages compared with CON. SCs were identified on muscle cross sections by combined immunohistochemical staining for Pax7, type I myosin, and laminin, allowing the number of SCs associated with type I and II fibers to be determined. We observed a pattern of SC distribution in MYA previously only reported for individuals above 70 yr of age. Compared with CON, MYA demonstrated 19% more SCs per fiber associated with type I fibers (MYA 0.098 ± 0.039 vs. CON 0.079 ± 0.031; P < 0.05) and 40% fewer SCs associated with type II fibers (MYA 0.047 ± 0.017 vs. CON 0.066 ± 0.035; P < 0.05). The finding of similar numbers of macrophages between the two groups was not in line with our hypothesis and suggests that the elevated SC content of MYA was not due to heightened inflammatory cell contents, but rather to provide new myonuclei. The findings of greater numbers of SCs in type I fibers of muscle subjected to repeated low-intensity work support our hypothesis and provide new insight into stimuli capable of regulating SC content.
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http://dx.doi.org/10.1152/japplphysiol.00789.2010DOI Listing
December 2010

Isolation and differentiation of chondrocytic cells derived from human embryonic stem cells using dlk1/FA1 as a novel surface marker.

Stem Cell Rev Rep 2009 Dec;5(4):353-68

Molecular Endocrinology laboratory (KMEB), Medical Biotechnology Centre, Odense University Hospital, University of South Denmark, DK-5000 Odense C, Denmark.

Few surface markers are available to monitor lineage differentiation during chondrogenesis. Recently, delta-like1/fetal antigen1 (dlk1/FA1), a transmembrane protein of the Notch/Delta/Serrata family, was shown to be essential for inducing early chondrogenesis. Thus, we investigated the possible use of dlk1/FA1 as a novel surface marker for chondroprogenitor cells during hESC differentiation. We found that, Dlk1/FA1 is expressed specifically in cells undergoing transition from proliferating to prehypertrophic chondrocytes during endochondral ossification of the mouse limb. In hESC cells, dlk1/FA1 was not expressed by undifferentiated hESC, but expressed during in vitro embryoid bodies (hEBs) formation upon down-regulation of undifferentiated markers e.g. Oct 3/4. Similarly, dlk1/FA1 was expressed in chondrocytic cells during in vivo teratoma formation. Interestingly, treatment of hEBs with Activin B, a member of TGF-ss family, markedly increased Dlk1 expression in association with up-regulation of the mesoderm-specific markers (e.g. FOXF1, KDR and VE-cadherin) and SOX9. dlk1/FA1(+) cells isolated by fluorescence activated cell sorting (FACS) were capable of differentiating into chondrocytic cells when cultured as micromass pellets in a xeno-free system containing TGFbeta1. In conclusion, we identified dlk1/FA1 as a novel marker of chondroprogenitor cells that undergo embryonic lineage progression from proliferation to the prehypertrophic stage. Tracking dlk1/FA1 expression as a mesoderm/chondroprogenitor surface marker provides a novel strategy for designing clinically relevant protocols to direct the differentiation of hESC into chondrocytes.
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http://dx.doi.org/10.1007/s12015-009-9099-4DOI Listing
December 2009

Distinct GAGE and MAGE-A expression during early human development indicate specific roles in lineage differentiation.

Hum Reprod 2008 Oct 8;23(10):2194-201. Epub 2008 Jul 8.

Medical Biotechnology Center, University of Southern Denmark, Winsloewparken 25, DK-5000 Odense C, Denmark.

Background: Expression of cancer/testis-associated proteins (CTAs) has traditionally been considered to be restricted to germ cells in normal tissues and to different types of malignancies. We have evaluated the potential role of CTAs in early human development.

Methods: Using immunohistochemistry and RT-PCR, we investigated the expression of CTAs in differentiated human embryonic stem cells (hESC) and in late embryos and early fetuses.

Results: We found that melanoma antigen A (MAGE-A) family members were expressed during differentiation of hESC to embryoid bodies and in teratomas, and overlapped with expression of the neuroectodermal markers beta-tubulin 3, Pax6 and nestin. A widespread expression of MAGE-A was also observed in neurons of the early developing central nervous system and peripheral nerves. G antigen (GAGE) expression was present in the early ectoderm of embryos, including cells of the ectodermal ring and apical epidermal ridge. Neuroectodermal cells in the floor plate and adjacent processes and endfeet of radial glial cells also expressed GAGE. In addition, GAGE family members were expressed in the peripheral adrenal cortex of 6-9-week-old embryos and fetuses, which specifically correlated with massive cellular proliferation and establishment of the definitive and fetal zones. Overlapping expression of MAGE-A and GAGE proteins occurred in migrating primordial germ cells.

Conclusions: Our results show that CTAs, in addition to their role in germ cells, may be involved in early development of various types of somatic cells, and suggest that they are implicated in specific differentiation processes.
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http://dx.doi.org/10.1093/humrep/den262DOI Listing
October 2008

Teratoma formation by human embryonic stem cells is site dependent and enhanced by the presence of Matrigel.

Stem Cells Dev 2009 Jan-Feb;18(1):47-54

Molecular Endocrinology Laboratory (KMEB), Department of Endocrinology and Metabolism, University Hospital of Odense and Medical Biotechnology Center, University of Southern Denmark, Winsløwparken, Odense, Denmark.

When implanted into immunodeficient mice, human embryonic stem cells (hESCs) give rise to teratoma, tumor-like formations containing tissues belonging to all three germ layers. The ability to form teratoma is a sine qua non characteristic of pluripotent stem cells. However, limited data are available regarding the effects of implantation site and the methods employed for implantation on the success rate of teratoma formation. In this study, the rate of teratoma formation in immunodeficient mice was site dependent: subcutaneous (25-100%), intratesticular (60%), intramuscular (12.5%), and under the kidney capsule (100%). Co-injecting the hESCs with Matrigel increased subcutaneous teratoma formation efficiency from 25-40% to 80-100%. We did not observe site-specific differences in the teratoma composition at the histological level. However, subcutaneous teratomas were quite distinct, easy to remove, and caused minimal discomfort to the mice. Also, subcutaneous teratomas displayed larger proportion of solid tissues as opposed to cyst formation that dominated the teratomas formed at the other sites. Interestingly, a chromosomally abnormal hESCs with trisomy 20 formed teratomas where the ratio of differentiated to undifferentiated tissues was significantly decreased suggesting defective pluripotency of the cells. In conclusion, subcutaneous implantation of hESCs in presence of Matrigel appears to be the most efficient, reproducible, and the easiest approach for teratoma formation by hESCs. Also, teratoma formation can be employed to study the development defects exhibited by the chromosomally abnormal hESC lines.
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http://dx.doi.org/10.1089/scd.2007.0266DOI Listing
October 2010

Activin B mediated induction of Pdx1 in human embryonic stem cell derived embryoid bodies.

Biochem Biophys Res Commun 2007 Oct 15;362(3):568-74. Epub 2007 Aug 15.

KMEB Laboratory, Medical Biotechnology Center, Winslevparken 25.1, DK-5000 Odense C, Denmark.

Human embryonic stem cells (hESCs) have the potential to provide alternative sources for pancreatic islet grafts. In the present study we have investigated the influence of Activin A and Activin B on the expression of the pancreas marker gene Pdx1 in hESCs differentiated as embryoid bodies (EBs). We report here that Activin B in a dose depend manner markedly up-regulates Pdx1 expression as compared to Activin A and untreated cultures. Pdx1(+) cells co-express FOXA2 but lacks, however, co-expression with nkx6.1, a marker combination that in the present study is shown precisely to identify embryonic and fetal pancreas anlage in humans. Pdx1(+) cells are found in cell clusters also expressing Serpina1 and FABP1, suggesting activation of intestinal/liver developmental programs. Moreover, Activin B up-regulates Sonic Hedgehog (Shh) and its target Gli1, which during normal development is suppressed in the pancreatic anlage. In conclusion, Activin B is a potent inducer of Pdx1 as well as Shh in differentiating hESCs. The data suggest that additional suppression of Shh signaling may be required to allow for proper specification of pancreatic cell lineages in hESCs.
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http://dx.doi.org/10.1016/j.bbrc.2007.07.200DOI Listing
October 2007

EGF-induced proliferation of adult human pancreatic duct cells is mediated by the MEK/ERK cascade.

Lab Invest 2005 Jan;85(1):65-74

The JDRF Center for Beta Cell Therapy in Europe, University of Florence, Italy.

Human postnatal pancreatic duct cells are a potential source of new beta cells. Factors regulating proliferation of human pancreatic duct cells in vitro are unknown. In several other cell types, this process is influenced by ligands of the ErbB receptor family. The expression and functionality of the ErbB family members and their possible role in duct cell proliferation were determined. In cultured adult human pancreatic duct cells the different members of the ErbB family (ErbB1-4) were present at transcript and protein level. Stimulation of the duct cells with epidermal growth factor (EGF) and betacellulin results in Tyr-phosphorylation of ErbB1 and ErbB2, followed by activation of Shc, MEK1/2 and ERK1/2. Duct cells with activated ErbB signaling changed morphology and motility. EGF induced proliferation of a fraction of the duct cells and treatment with PD98059 prevented Ki67 expression in EGF-supplemented cells. When transduced with recombinant adenovirus expressing constitutively activated MEK1, duct cells proliferate and spread even in the absence of EGF. Importantly, the adult human duct cells retain their capacity to recapitulate ngn3-induced embryonic (neuro)endocrine differentiation after proliferation. Therefore, the present data support a possible role for human adult pancreatic duct cells, following expansion and transdifferentiation, as a source of insulin by transplantation to type I diabetes patients.
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http://dx.doi.org/10.1038/labinvest.3700204DOI Listing
January 2005

Artifactual insulin release from differentiated embryonic stem cells.

Diabetes 2004 Oct;53(10):2603-9

Department of Developmental Biology, Hagedorn Research Institute, Niels Steensens vej 6, DK-2820 Gentofte, Denmark.

Several recent reports claim the generation of insulin-producing cells from embryonic stem cells via the differentiation of progenitors that express nestin. Here, we investigate further the properties of these insulin-containing cells. We find that although differentiated cells contain immunoreactive insulin, they do not contain proinsulin-derived C-peptide. Furthermore, we find variable insulin release from these cells upon glucose addition, but C-peptide release is never detected. In addition, many of the insulin-immunoreactive cells are undergoing apoptosis or necrosis. We further show that cells cultured in the presence of a phosphoinositide 3-kinase inhibitor, which previously was reported to facilitate the differentiation of insulin(+) cells, are not C-peptide immunoreactive but take up fluorescein isothiocyanate-labeled insulin from the culture medium. Together, these data suggest that nestin(+) progenitor cells give rise to a population of cells that contain insulin, not as a result of biosynthesis but from the uptake of exogenous insulin. We conclude that C-peptide biosynthesis and secretion should be demonstrated to claim insulin production from embryonic stem cell progeny.
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http://dx.doi.org/10.2337/diabetes.53.10.2603DOI Listing
October 2004

Unspecific labeling of pancreatic islets by antisera against fibroblast growth factors and their receptors.

J Histochem Cytochem 2003 Mar;51(3):397-400

Department of Developmental Biology, Hagedorn Research Institute, Gentofte, Denmark.

Six distinct fibroblast growth factors (FGFs) have been detected in pancreatic islets by immunohistochemistry (IHC) using commercially available antisera. We show here that these antisera are useful for Western blotting but that only two are suited for IHC. By Western blotting, these antisera detect recombinant FGFs. Detection can be eliminated by preabsorption with immunizing peptide but not with irrelevant peptide. By IHC we find specific labeling of islets with anti-FGF1 and anti-FGF2 antisera. Labeling can be abolished by preabsorption with the immunizing peptides. In contrast, prominent staining of islets by anti-FGF4, -FGF5, -FGF7, and -FGF10 antisera is unspecific because the staining cannot be competed by preabsorption with the immunizing peptides.
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http://dx.doi.org/10.1177/002215540305100314DOI Listing
March 2003
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