Loss Of Satellite Cells Research Articles

Amyotrophic lateral sclerosis as a disease model of sarcopenia

Abstract Sarcopenia, the progressive decline of muscle mass and function, has traditionally been viewed as an age-related process leading to a broad range of adverse outcomes. However, it has been widely reported that sarcopenia can occur earlier in life in association with various conditions (i.e. disease-related sarcopenia), including neuromuscular disorders. As early as 2010, the European Working Group on Sarcopenia in Older People included neurodegenerative diseases characterised by motor neuron loss among the mechanisms underlying sarcopenia. Despite some differences in pathogenetic mechanisms, both amyotrophic lateral sclerosis (ALS) and age-related sarcopenia share common characteristics, such as the loss of motor units and muscle fibre atrophy, oxidative stress, mitochondrial dysfunction and inflammation. The histology of older muscle shows fibre size heterogeneity, fibre grouping and a loss of satellite cells, similar to what is observed in ALS patients. Regrettably, the sarcopenic process in ALS patients has been largely overlooked, and literature on the condition in this patient group is very scarce. Some instruments used for the assessment of sarcopenia in older people could also be applied to ALS patients. At this time, there is no approved specific pharmacological treatment to reverse damage to motor neurons or cure ALS, just as there is none for sarcopenia. However, some agents targeting the muscle, like myostatin and mammalian target of rapamycin inhibitors, are under investigation both in the sarcopenia and ALS context. The development of new therapeutic agents targeting the skeletal muscle may indeed be beneficial to both ALS patients and older people with sarcopenia.

P66Shc signaling and autophagy impact on C2C12 myoblast differentiation during senescence

During aging, muscle regenerative capacities decline, which is concomitant with the loss of satellite cells that enter in a state of irreversible senescence. However, what mechanisms are involved in myogenic senescence and differentiation are largely unknown. Here, we showed that early-passage or “young” C2C12 myoblasts activated the redox-sensitive p66Shc signaling pathway, exhibited a strong antioxidant protection and a bioenergetic profile relying predominantly on OXPHOS, responses that decrease progressively during differentiation. Furthermore, autophagy was increased in myotubes. Otherwise, late-passage or “senescent” myoblasts led to a highly metabolic profile, relying on both OXPHOS and glycolysis, that may be influenced by the loss of SQSTM1/p62 which tightly regulates the metabolic shift from aerobic glycolysis to OXPHOS. Furthermore, during differentiation of late-passage C2C12 cells, both p66Shc signaling and autophagy were impaired and this coincides with reduced myogenic capacity. Our findings recognized that the lack of p66Shc compromises the proliferation and the onset of the differentiation of C2C12 myoblasts. Moreover, the Atg7 silencing favored myoblasts growth, whereas interfered in the viability of differentiated myotubes. Then, our work demonstrates that the p66Shc signaling pathway, which highly influences cellular metabolic status and oxidative environment, is critical for the myogenic commitment and differentiation of C2C12 cells. Our findings also support that autophagy is essential for the metabolic switch observed during the differentiation of C2C12 myoblasts, confirming how its regulation determines cell fate. The regulatory roles of p66Shc and autophagy mechanisms on myogenesis require future attention as possible tools that could predict and measure the aging-related state of frailty and disability.

Targeting STAT6 to mitigate sepsis-induced muscle atrophy and weakness: Modulation of mitochondrial dysfunction, ferroptosis, and CHI3L1-Mediated satellite cell loss

Sepsis-induced muscle weakness is a debilitating consequence of prolonged critical illness, often associated with a poor prognosis. While recent research has shown that STAT6 functions as an inhibitor of myogenesis, its role in sepsis-induced muscle weakness remains unclear. In this study, we hypothesized that inhibiting STAT6 could attenuate sepsis-induced muscle atrophy and weakness, and we explored the underlying mechanisms. Leveraging a microarray dataset from sepsis patients, we identified significant enrichment of genes related to muscle function, ferroptosis, and the p53 signalling pathway in muscle tissue from sepsis patients. Using a murine sepsis model induced by cecum ligation and puncture (CLP), we explore the multifaceted role of STAT6 inhibition. Our findings demonstrate that STAT6 inhibition effectively attenuates muscle atrophy, enhances grip strength, preserves mitochondrial integrity, and modulates ferroptosis in septic mice. Additionally, we identify elevated levels of CHI3L1 in septic muscle tissue, which are significantly reduced by STAT6 inhibition. In-depth analysis of primary muscle satellite cells reveals that CHI3L1 overexpression is associated with increased expression of key regulators of satellite cell myogenicity, while negatively impacting cell viability. Silencing CHI3L1 expression mitigates satellite cell injury and loss, highlighting its pivotal role in sepsis-induced muscle damage. In summary, this study unveils the potential of STAT6 as a therapeutic target for mitigating sepsis-induced muscle atrophy and weakness. Our findings underscore the regulation of mitochondrial dysfunction, ferroptosis, and CHI3L1-mediated satellite cell damage by STAT6, offering promising avenues for therapeutic intervention in the management of sepsis-induced muscle weakness.

Mitochondrial dynamics maintain muscle stem cell regenerative competence throughout adult life by regulating metabolism and mitophagy.

Skeletal muscle regeneration depends on the correct expansion of resident quiescent stem cells (satellite cells), a process that becomes less efficient with aging. Here, we show that mitochondrial dynamics are essential for the successful regenerative capacity of satellite cells. The loss of mitochondrial fission in satellite cells-due to aging or genetic impairment-deregulates the mitochondrial electron transport chain (ETC), leading to inefficient oxidative phosphorylation (OXPHOS) metabolism and mitophagy and increased oxidative stress. This state results in muscle regenerative failure, which is caused by the reduced proliferation and functional loss of satellite cells. Regenerative functions can be restored in fission-impaired or aged satellite cells by the re-establishment of mitochondrial dynamics (by activating fission or preventing fusion), OXPHOS, or mitophagy. Thus, mitochondrial shape and physical networking controls stem cell regenerative functions by regulating metabolism and proteostasis. As mitochondrial fission occurs less frequently in the satellite cells in older humans, our findings have implications for regeneration therapies in sarcopenia.

Satellite cell depletion does not affect diaphragm adaptations to hypoxia.

The diaphragm is the main skeletal muscle responsible for inspiration and is susceptible to age-associated decline in function and morphology. Satellite cells in diaphragm fuse into unperturbed muscle fibers throughout life, yet their role in adaptations to hypoxia in diaphragm is unknown. Given their continual fusion, we hypothesize that satellite cell depletion will negatively impact adaptations to hypoxia in the diaphragm, particularly with aging. We used the Pax7CreER/CreER:R26RDTA/DTA genetic mouse model of inducible satellite cell depletion to investigate diaphragm responses to hypoxia in adult (6 mo) and aged (22 mo) male mice. The mice were subjected to normobaric hypoxia at 10% [Formula: see text] or normoxia for 4 wk. We showed that satellite cell depletion had no effect on diaphragm muscle fiber cross-sectional area, fiber-type distribution, myonuclear density, or regulation of extracellular matrix in either adult or aged mice. Furthermore, we showed lower muscle fiber cross-sectional area with hypoxia and age (main effects), while extracellular matrix content was higher and satellite cell abundance was lower with age (main effect) in diaphragm. Lastly, a greater number of Pax3-mRNA+ cells was observed in diaphragm muscle of satellite cell-depleted mice independent of hypoxia (main effect), potentially as a compensatory mechanism for the loss of satellite cells. We conclude that satellite cells are not required for diaphragm muscle adaptations to hypoxia in either adult or aged mice.NEW & NOTEWORTHY Satellite cells show consistent fusion into diaphragm muscle fibers throughout life, suggesting a critical role in maintaining homeostasis. Here, we report identical diaphragm adaptations to hypoxia with and without satellite cells in adult and aged mice. In addition, we propose that the higher number of Pax3-positive cells in satellite cell-depleted diaphragm muscle acts as a compensatory mechanism.

Muscle Stem Cell Depletion Blunts Skeletal Muscle Adaptation to Weighted Wheel Running

Satellite cells, the resident muscle stem cell, are not required for short term skeletal muscle hypertrophy in mice when subjected to mechanical overload via synergist ablation, however, long term growth is blunted. This study aimed to further investigate the effect of satellite cell depletion on muscle adaptation using Progressive Weighted Wheel Running (PoWeR). We hypothesized that satellite cell depletion would reduce the adaptive response of skeletal muscle to the training stimulus. The Pax7‐DTA mouse model was used to deplete satellite cell content in adult skeletal muscle. PoWeR training involved adding weight to the running wheel of the mice incrementally over the 8‐week training period. Hindlimb muscles were excised at the 8‐week time point, and the plantaris was immunohistochemically analyzed. PoWeR induced an oxidative shift in fiber type distribution and increased muscle fiber cross sectional area (CSA). However, this increase in fiber CSA was blunted in mice without satellite cells. To investigate the blunted growth in satellite cell‐depleted mice, the plantaris was analyzed for extracellular matrix content and capillarization. We found that neither extracellular matrix buildup nor capillary density differed between satellite cell replete and depleted groups following PoWeR. These findings suggest that loss of satellite cells reduces the capacity for hypertrophy in response to PoWeR, but this was not due to excessive extracellular matrix accumulation. Further, satellite cells were not required for a robust fiber type shift in response to PoWeR training.Support or Funding InformationThis work was funded by the American Physiological Society’s UGSRF program and a grant from the National Institute of Health to Dr. Charlotte Peterson and Dr. John McCarthy (AR060701).

Expression rate of myogenic regulatory factors and muscle growth factor after botulinum toxin A injection in the right masseter muscle of dystrophin deficient (mdx) mice.

The mdx mouse, the most approved animal model for basic research in Duchenne muscular dystrophy (DMD), has the ability to compensate muscle degeneration by regeneration process, which is obvious at approx. 3 months of age. Hence, this mouse model is only temporarily suitable to proof craniofacial changes which are usually evident in humans with the progression of the disease. The purpose of our study was to examine the impact of botulinum toxin A (BTX-A) in influencing muscle regeneration in the masticatory muscles of healthy and mdx mice. Chemo-denervation of the right masseter muscle was induced in 100-day-old, healthy and dystrophic mice by a specific intramuscular BTX-A injection. Gene expression and protein content of myogenic regulatory factors and muscle growth factor (MyoD1, myogenin and myostatin) in the right and left masseter, temporal and the tongue muscle were determined 4 and 21 days after injection, respectively, using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot technique. The 4 day and 21 day interval proved significant but varying changes of mRNA expression in both control and mdx mice. At the protein level, myogenin expression was increased in the temporal and masseter muscle on the injection side in controls, whereas dystrophic mice showed the same effect for MyoD1 expression. Additionally, increased protein expression of all studied genes could be found in dystrophic mice compared to controls, except the left temporal and the tongue muscle. Muscle regeneration is not constant in BTX-A injected mdx masticatory muscles, presumably due to the already exhausted capacity or functional loss of satellite cells caused by dystrophin deficiency, and, therefore, disturbed regeneration potential of myofibrils. Botulinum toxin A injection cannot fully break down regulatory processes at molecular level in 100-day-old mdx mice. Further investigations are necessary to fully understand the regeneration process following BTX-A injection into dystrophic muscles.

A POGLUT1 mutation causes a muscular dystrophy with reduced Notch signaling and satellite cell loss.

Skeletal muscle regeneration by muscle satellite cells is a physiological mechanism activated upon muscle damage and regulated by Notch signaling. In a family with autosomal recessive limb‐girdle muscular dystrophy, we identified a missense mutation in POGLUT1 (protein O‐glucosyltransferase 1), an enzyme involved in Notch posttranslational modification and function. In vitro and in vivo experiments demonstrated that the mutation reduces O‐glucosyltransferase activity on Notch and impairs muscle development. Muscles from patients revealed decreased Notch signaling, dramatic reduction in satellite cell pool and a muscle‐specific α‐dystroglycan hypoglycosylation not present in patients' fibroblasts. Primary myoblasts from patients showed slow proliferation, facilitated differentiation, and a decreased pool of quiescent PAX7+ cells. A robust rescue of the myogenesis was demonstrated by increasing Notch signaling. None of these alterations were found in muscles from secondary dystroglycanopathy patients. These data suggest that a key pathomechanism for this novel form of muscular dystrophy is Notch‐dependent loss of satellite cells.

S.O.4 - A POGLUT1 mutation causes a muscular dystrophy with reduced notch signaling and satellite cell loss

S.O.4 - A POGLUT1 mutation causes a muscular dystrophy with reduced notch signaling and satellite cell loss

Notch Signaling Rescues Loss of Satellite Cells Lacking Pax7 and Promotes Brown Adipogenic Differentiation.

Pax7 is a nodal transcription factor that is essential for regulating the maintenance, expansion, and myogenic identity of satellite cells during both neonatal and adult myogenesis. Deletion of Pax7 results in loss of satellite cells and impaired muscleregeneration. Here, we show that ectopic expression of the constitutively active intracellular domain of Notch1 (NICD1) rescues the loss of Pax7-deficient satellite cells and restores their proliferative potential. Strikingly NICD1-expressing satellite cells do not undergo myogenic differentiation and instead acquire a brown adipogenic fate both invivo and invitro. NICD-expressing Pax7(-/-) satellite cells fail to upregulate MyoD and instead express the brown adipogenic marker PRDM16. Overall, these results show that Notch1 activation compensates for the loss of Pax7 in the quiescent state and acts as a molecular switch topromote brown adipogenesis in adult skeletal muscle.

Inactivation of PPARβ/δ adversely affects satellite cells and reduces postnatal myogenesis.

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a ubiquitously expressed gene with higher levels observed in skeletal muscle. Recently, our laboratory showed (Bonala S, Lokireddy S, Arigela H, Teng S, Wahli W, Sharma M, McFarlane C, Kambadur R. J Biol Chem 287: 12935-12951, 2012) that PPARβ/δ modulates myostatin activity to induce myogenesis in skeletal muscle. In the present study, we show that PPARβ/δ-null mice display reduced body weight, skeletal muscle weight, and myofiber atrophy during postnatal development. In addition, a significant reduction in satellite cell number was observed in PPARβ/δ-null mice, suggesting a role for PPARβ/δ in muscle regeneration. To investigate this, tibialis anterior muscles were injured with notexin, and muscle regeneration was monitored on days 3, 5, 7, and 28 postinjury. Immunohistochemical analysis revealed an increased inflammatory response and reduced myoblast proliferation in regenerating muscle from PPARβ/δ-null mice. Histological analysis confirmed that the regenerated muscle fibers of PPARβ/δ-null mice maintained an atrophy phenotype with reduced numbers of centrally placed nuclei. Even though satellite cell numbers were reduced before injury, satellite cell self-renewal was found to be unaffected in PPARβ/δ-null mice after regeneration. Previously, our laboratory had showed (Bonala S, Lokireddy S, Arigela H, Teng S, Wahli W, Sharma M, McFarlane C, Kambadur R. J Biol Chem 287: 12935-12951, 2012) that inactivation of PPARβ/δ increases myostatin signaling and inhibits myogenesis. Our results here indeed confirm that inactivation of myostatin signaling rescues the atrophy phenotype and improves muscle fiber cross-sectional area in both uninjured and regenerated tibialis anterior muscle from PPARβ/δ-null mice. Taken together, these data suggest that absence of PPARβ/δ leads to loss of satellite cells, impaired skeletal muscle regeneration, and postnatal myogenesis. Furthermore, our results also demonstrate that functional antagonism of myostatin has utility in rescuing these effects.

RNA Transcription and Maturation in Skeletal Muscle Cells are Similarly Impaired in Myotonic Dystrophy and Sarcopenia: The Ultrastructural Evidence.

OPINION article Front. Aging Neurosci., 30 July 2014Sec. Neuroinflammation and Neuropathy Volume 6 - 2014 | https://doi.org/10.3389/fnagi.2014.00196

Notch signaling deficiency underlies age-dependent depletion of satellite cells in muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a devastating disease characterized by muscle wasting, loss of mobility and death in early adulthood. Satellite cells are muscle-resident stem cells responsible for the repair and regeneration of damaged muscles. One pathological feature of DMD is the progressive depletion of satellite cells, leading to the failure of muscle repair. Here, we attempted to explore the molecular mechanisms underlying satellite cell ablation in the dystrophin mutant mdx mouse, a well-established model for DMD. Initial muscle degeneration activates satellite cells, resulting in increased satellite cell number in young mdx mice. This is followed by rapid loss of satellite cells with age due to the reduced self-renewal ability of mdx satellite cells. In addition, satellite cell composition is altered even in young mdx mice, with significant reductions in the abundance of non-committed (Pax7+ and Myf5−) satellite cells. Using a Notch-reporter mouse, we found that the mdx satellite cells have reduced activation of Notch signaling, which has been shown to be necessary to maintain satellite cell quiescence and self-renewal. Concomitantly, the expression of Notch1, Notch3, Jag1, Hey1 and HeyL are reduced in the mdx primary myoblast. Finally, we established a mouse model to constitutively activate Notch signaling in satellite cells, and show that Notch activation is sufficient to rescue the self-renewal deficiencies of mdx satellite cells. These results demonstrate that Notch signaling is essential for maintaining the satellite cell pool and that its deficiency leads to depletion of satellite cells in DMD.

Satellite cells regulate the skeletal muscle environment by inhibiting fibroblast function

Interaction between satellite cells and the skeletal muscle extracellular matrix (ECM) has been demonstrated, but a role for satellite cells in regulating the ECM during hypertrophy has not been defined. We utilized mouse primary myoblasts and fibroblasts in co‐culture in addition to a genetically modified mouse model (Pax7‐DTA) to investigate the role of satellite cells in the regulation of muscle ECM. The Pax7‐DTA mouse allows for the conditional depletion of satellite cells in adult muscle following tamoxifen administration. Vehicle/tamoxifen treated animals were randomized to sham or synergist ablation surgery, leading to overload of the plantaris muscle for 1 and 8 weeks. Microarray analysis after 1 week of surgery showed the loss of satellite cells was associated with increased expression of numerous collagens and ECM structural genes. Depletion of satellite cells also led to attenuated hypertrophy and fibrosis of the plantaris with increases in both ECM deposition and fibroblast number following 8 weeks of overload. Co‐culturing mouse myoblasts with fibroblasts led to decreased mRNA expression of Col Ia2, IIIa1, VIa2 and Fibronectin compared to fibroblasts cocultured with fibroblasts, suggesting a paracrine role of myoblasts that inhibits fibroblast ECM production. We conclude that a novel function of satellite cells both at rest and during hypertrophy is to regulate muscle fibroblasts and the ECM.Funding: NIAMS R01AR060701, R21AG34453 and the Jeane B. Kempner Postdoctoral Award.

Isolation, characterization, and molecular regulation of muscle stem cells

Skeletal muscle has great regenerative capacity which is dependent on muscle stem cells, also known as satellite cells. A loss of satellite cells and/or their function impairs skeletal muscle regeneration and leads to a loss of skeletal muscle power; therefore, the molecular mechanisms for maintaining satellite cells in a quiescent and undifferentiated state are of great interest in skeletal muscle biology. Many studies have demonstrated proteins expressed by satellite cells, including Pax7, M-cadherin, Cxcr4, syndecan3/4, and c-met. To further characterize satellite cells, we established a method to directly isolate satellite cells using a monoclonal antibody, SM/C-2.6. Using SM/C-2.6 and microarrays, we measured the genes expressed in quiescent satellite cells and demonstrated that Hesr3 may complement Hesr1 in generating quiescent satellite cells. Although Hesr1- or Hesr3-single knockout mice show a normal skeletal muscle phenotype, including satellite cells, Hesr1/Hesr3-double knockout mice show a gradual decrease in the number of satellite cells and increase in regenerative defects dependent on satellite cell numbers. We also observed that a mouse's genetic background affects the regenerative capacity of its skeletal muscle and have established a line of DBA/2-background mdx mice that has a much more severe phenotype than the frequently used C57BL/10-mdx mice. The phenotype of DBA/2-mdx mice also seems to depend on the function of satellite cells. In this review, we summarize the methodology of direct isolation, characterization, and molecular regulation of satellite cells based on our results. The relationship between the regenerative capacity of satellite cells and progression of muscular disorders is also summarized. In the last part, we discuss application of the accumulating scientific information on satellite cells to treatment of patients with muscular disorders.

No role of muscle satellite cells in hypertrophy: further evidence of a mistaken identity?

No role of muscle satellite cells in hypertrophy: further evidence of a mistaken identity?

Skeletal muscle fibroblast collagen expression is negatively regulated by satellite cells

Interaction between satellite cells and components of the extracellular matrix (ECM) of skeletal muscle has been demonstrated, and recent evidence suggests that satellite cells may regulate ECM remodeling following overload in muscle. We utilized mouse primary myoblasts and fibroblasts in co‐culture in addition to a genetically modified mouse model (Pax7‐DTA) to investigate the role of satellite cells in regulation of skeletal muscle ECM. The Pax7‐DTA mouse allows for the conditional ablation of >90% of satellite cells in adult mice following the administration of tamoxifen. Control/tamoxifen treated animals were randomized to sham or synergist ablation surgery, leading to overload of the plantaris muscle for 2 weeks. Microarray analysis was performed to determine if the loss of satellite cells altered plantaris gene expression. The loss of satellite cells under rest and overload conditions was associated with increased expression of a number of different collagens, as well as ECM structural and remodeling genes. Co‐culturing mouse myoblasts with fibroblasts led to a 40% decrease in the mRNA expression of Col VIa2 and Fibronectin compared to fibroblasts co‐cultured with fibroblasts. These results suggest that satellite cells are involved in the regulation and maintenance of the ECM both under rest and during muscle hypertrophy.Funding: NIAMS R01AR060701 and the Jeane B. Kempner Postdoctoral Fellowship.

Pax7-expressing satellite cells are indispensable for adult skeletal muscle regeneration

Distinct cell populations with regenerative capacity have been reported to contribute to myofibres after skeletal muscle injury, including non-satellite cells as well as myogenic satellite cells. However, the relative contribution of these distinct cell types to skeletal muscle repair and homeostasis and the identity of adult muscle stem cells remain unknown. We generated a model for the conditional depletion of satellite cells by expressing a human diphtheria toxin receptor under control of the murine Pax7 locus. Intramuscular injection of diphtheria toxin during muscle homeostasis, or combined with muscle injury caused by myotoxins or exercise, led to a marked loss of muscle tissue and failure to regenerate skeletal muscle. Moreover, the muscle tissue became infiltrated by inflammatory cells and adipocytes. This localised loss of satellite cells was not compensated for endogenously by other cell types, but muscle regeneration was rescued after transplantation of adult Pax7(+) satellite cells alone. These findings indicate that other cell types with regenerative potential depend on the presence of the satellite cell population, and these observations have important implications for myopathic conditions and stem cell-based therapeutic approaches.

Satellite cell loss and impaired muscle regeneration in selenoprotein N deficiency

Selenoprotein N (SelN) deficiency causes a group of inherited neuromuscular disorders termed SEPN1-related myopathies (SEPN1-RM). Although the function of SelN remains unknown, recent data demonstrated that it is dispensable for mouse embryogenesis and suggested its involvement in the regulation of ryanodine receptors and/or cellular redox homeostasis. Here, we investigate the role of SelN in satellite cell (SC) function and muscle regeneration, using the Sepn1(-/-) mouse model. Following cardiotoxin-induced injury, SelN expression was strongly up-regulated in wild-type muscles and, for the first time, we detected its endogenous expression in a subset of mononucleated cells by immunohistochemistry. We show that SelN deficiency results in a reduced basal SC pool in adult skeletal muscles and in an imperfect muscle restoration following a single injury. A dramatic depletion of the SC pool was detected after the first round of degeneration and regeneration that totally prevented subsequent regeneration of Sepn1(-/-) muscles. We demonstrate that SelN deficiency affects SC dynamics on isolated single fibres and increases the proliferation of Sepn1(-/-) muscle precursors in vivo and in vitro. Most importantly, exhaustion of the SC population was specifically identified in muscle biopsies from patients with mutations in the SEPN1 gene. In conclusion, we describe for the first time a major physiological function of SelN in skeletal muscles, as a key regulator of SC function, which likely plays a central role in the pathophysiological mechanism leading to SEPN1-RM.

P74. Age-related changes in prospectively isolated muscle satellite cells

Sarcopenia is the loss of skeletal muscle mass and strength with age. The causes of sarcopenia are probably manifold and remain to be completely elucidated. One of the possible causes could be the decline of stem cell function. Satellite cell is muscle-specific stem cell and is responsible for the postnatal muscle maintenance, growth and regeneration. We showed that muscle regenerative potential of aged mice (24–30 months old) remarkably declined compared with that of young mice (2–3 months old) after injection with cardiotoxin (CTX). To study age-related changes of satellite cells, we prospectively isolated satellite cells from limb muscles of aged mice (aged satellite cells) and young mice (young satellite cells) by FACS using a monoclonal antibody SM/C-2.6. Satellite cells remarkably decreased in both number/g muscle weight and number/muscle cross section with age. To clarify the molecular mechanisms leading to loss of satellite cells with age, we performed DNA microarray analysis using freshly isolated aged and young satellite cells. Compared with young satellite cells, 95 genes were down-regulated (<1/4-fold) in aged satellite cells. In contrast, 85 genes were up-regulated (>4-fold) in aged satellite cells. Detailed analyses of some identified genes will be reported. On the other hand, when evaluated myogenic potential in vitro, there was no difference in proliferation and differentiation ability between residual aged satellite cells and young satellite cells. In vivo intramuscular transplantation experiment also showed that muscle reconstitution ability of aged satellite cells was similar to that of young satellite cells. To elucidate whether the decline of regenerative potential in aged muscle results at least from deterioration of aged muscle environment, we transplanted satellite cells freshly isolated from young GFP-Tg mice into CTX-injected young and aged muscle. The muscle reconstitution ability in aged host significantly decreased compared with that in young host. Therefore, it is thought that the decline of muscle regenerative potential in sarcopenia is attributed to decrease in satellite cell number and deterioration of aged muscle environment.