MYOBLAST SURVIVAL ENHANCEMENT AND TRANSPLANTATION SUCCESS IMPROVEMENT BY HEAT-SHOCK TREATMENT IN MDX MICE

Hyperthermia increases HSP production in human PDMCs by stimulating ROS formation, p38 MAPK and Akt signaling, and increasing HSF1 activity

Background

Human placenta-derived multipotent cells (hPDMCs) are isolated from a source uncomplicated by ethical issues and are ideal for therapeutic applications because of their capacity for multilineage differentiation and proven immunosuppressive properties. It is known that heat shock preconditioning induces the upregulation of heat shock proteins (HSPs), which enhance survival and engraftment of embryonic stem cells (ESCs) during transplantation in live animal models, although whether heat shock preconditioning has the same effects in hPDMCs is unclear.

Methods

The hPDMCs were isolated from placenta of healthy donors. The cells were treated with heat shock (43 °C, 15 min), followed by evaluation of cell viability. Furthermore, the HSPs expression was assessed by Western blot, qPCR. The reactive oxygen species (ROS) production and signal pathway activation were determined by flow cytometry and Western blot, respectively. The regulatory pathways involved in HSPs expression were examined by pretreatment with chemical inhibitors, and siRNAs of MAPK, Akt, and heat shock factor 1 (HSF1), followed by determination of HSPs expression.

Results

This study demonstrates that heat shock treatment induced ROS generation and HPSs expression in hPDMCs. Heat shock stimulation also increased p38 MAPK and Akt phosphorylation. These effects were reduced by inhibitors of ROS, p38 MAPK and Akt. Moreover, we found that heat shock treatment enhanced nuclear translocation of the HSF1 in hPDMCs, representing activation of HSF1. Pretreatment of hPDMCs with ROS scavengers, SB203580 and Akt inhibitors also reduced the translocation of HSF1 induced by heat shock.

Conclusions

Our data indicate that heat shock acts via ROS to activate p38 MAPK and Akt signaling, which subsequently activates HSF1, leading to HSP activation and contributing to the protective role of hPDMCs.

Muscle stem cell adaptations to cellular and environmental stress

Background

Lifelong regeneration of the skeletal muscle is dependent on a rare population of resident skeletal muscle stem cells, also named ‘satellite cells’ for their anatomical position on the outside of the myofibre and underneath the basal lamina. Muscle stem cells maintain prolonged quiescence, but activate the myogenic programme and the cell cycle in response to injury to expand a population of myogenic progenitors required to regenerate muscle. The skeletal muscle does not regenerate in the absence of muscle stem cells.

Main body

The notion that lifelong regeneration of the muscle is dependent on a rare, non-redundant population of stem cells seems contradictory to accumulating evidence that muscle stem cells have activated multiple stress response pathways. For example, muscle stem cell quiescence is mediated in part by the eIF2α arm of the integrated stress response and by negative regulators of mTORC1, two translational control pathways that downregulate protein synthesis in response to stress. Muscle stem cells also activate pathways to protect against DNA damage, heat shock, and environmental stress. Here, we review accumulating evidence that muscle stem cells encounter stress during their prolonged quiescence and their activation. While stress response pathways are classically described to be bimodal whereby a threshold dictates cell survival versus cell death responses to stress, we review evidence that muscle stem cells additionally respond to stress by spontaneous activation and fusion to myofibres.

Conclusion

We propose a cellular stress test model whereby the prolonged state of quiescence and the microenvironment serve as selective pressures to maintain muscle stem cell fitness, to safeguard the lifelong regeneration of the muscle. Fit muscle stem cells that maintain robust stress responses are permitted to maintain the muscle stem cell pool. Unfit muscle stem cells are depleted from the pool first by spontaneous activation, or in the case of severe stress, by activating cell death or senescence pathways.

Adipose Tissue-Derived Stromal Cells in Matrigel Impacts the Regeneration of Severely Damaged Skeletal Muscles

In case of large injuries of skeletal muscles the pool of endogenous stem cells, i.e., satellite cells, might be not sufficient to secure proper regeneration. Such failure in reconstruction is often associated with loss of muscle mass and excessive formation of connective tissue. Therapies aiming to improve skeletal muscle regeneration and prevent fibrosis may rely on the transplantation of different types of stem cell. Among such cells are adipose tissue-derived stromal cells (ADSCs) which are relatively easy to isolate, culture, and manipulate. Our study aimed to verify applicability of ADSCs in the therapies of severely injured skeletal muscles. We tested whether 3D structures obtained from Matrigel populated with ADSCs and transplanted to regenerating mouse gastrocnemius muscles could improve the regeneration. In addition, ADSCs used in this study were pretreated with myoblasts-conditioned medium or anti-TGFβ antibody, i.e., the factors modifying their ability to proliferate, migrate, or differentiate. Analyses performed one week after injury allowed us to show the impact of 3D cultured control and pretreated ADSCs at muscle mass and structure, as well as fibrosis development immune response of the injured muscle.

Myoblast Therapy: From Bench to Bedside

Myoblasts are defined as stem cells containing skeletal muscle cell precursors. A decade of experimental work has revealed many properties of myoblasts, including the stability of resulting hybrid myofibers without immune suppression, the persistence of transgene expression, and the lack of tumorigenicity. Early phase clinical trials also showed that myoblast-based therapy is a promising approach for many intractable clinical conditions, including both muscle-related and non-muscle-related diseases. The potential application of myoblast therapy may be in the treatment of genetic muscle diseases, cardiomyocyte damaged heart diseases, and urinary incontinence. This review will provide an overview of myoblast biology, along with discussion of the potential application in clinical medicine. In addition, problems in current myoblast therapy and possible future improvements will be addressed.

1,25-Dihydroxyvitamin D3 Increases the Transplantation Success of Human Muscle Precursor Cells in SCID Mice

Human muscle precursor cell (hMPC) transplantation is a potential therapy for severe muscle trauma or myopathies. Some previous studies demonstrated that 1,25-dihydroxyvitamin-D3 (1,25-D3) acted directly on myoblasts, regulating their proliferation and fusion. 1,25-D3 is also involved in apoptosis modulation of other cell types and may thus contribute to protect the transplanted hMPCs. We have therefore investigated whether 1,25-D3 could improve the hMPC graft success. The 1,25-D3 effects on hMPC proliferation, fusion, and survival were initially monitored in vitro. hMPCs were also grafted in the tibialis anterior of SCID mice treated or not with 1,25-D3 to determine its in vivo effect. Graft success, proliferation, and viability of transplanted hMPCs were evaluated. 1,25-D3 enhanced proliferation and fusion of hMPCs in vitro and in vivo. However, 1,25-D3 did not protect hMPCs from various proapoptotic factors (in vitro) or during the early posttransplantation period. 1,25-D3 enhanced hMPC graft success because the number of muscle fibers expressing human dystrophin was significantly increased in the TA sections of 1,25-D3-treated mice (166.75 ± 20.64) compared to the control mice (97.5 ± 16.58). This result could be partly attributed to the improvement of the proliferation and differentiation of hMPCs in the presence of 1,25-D3. Thus, 1,25-D3 administration could improve the clinical potential of hMPC transplantation currently developed for muscle trauma or myopathies.

The Effects of Thermal Preconditioning on Oncogenic and Intraspinal Cord Growth Features of Human Glioma Cells

The adult rodent spinal cord presents an inhibitory environment for donor cell survival, impeding efficiency for xenograft-based modeling of gliomas. We postulated that mild thermal preconditioning may influence the fate of the implanted tumor cells. To test this hypothesis, high-grade human astrocytoma G55 and U87 cells were cultured under 37C and 38.5C to mimic regular experimental or core body temperatures of rodents, respectively. In vitro, the 38.5C-conditioned cells, relative to 37C, grew slightly faster. Compared to U87 cells, G55 cells demonstrated a greater response to the temperature difference. Hyperthermal culture markedly increased production of Hsp27 in most G55 cells, but only promoted transient expression of cancer stem cell marker CD133 in a small cell subpopulation. We subsequently transplanted G55 cells following 37C or 38.5C culture into the C2 or T10 spinal cord of adult female immunodeficient rats (3 rats/each locus/per temperature; total: 12 rats). Systematic analyses revealed that 38.5C-preconditioned G55 cells grew more malignantly at either C2 or T10 as determined by tumor size, outgrowth profile, resistance to bolus intratumor administration of 5-fluorouracil (0.1 mol), and posttumor survival (p0.05; n=6/group). Therefore, thermal preconditioning of glioma cells may be an effective way to influence the in vitro and in vivo oncological contour of glioma cells. Future studies are needed for assessing the potential oncogenic modifying effect of hyperthermia regimens on glioma cells.

Hyperglycemia induced expression, phosphorylation, and translocation of αB-crystallin in rat skeletal muscle

αB-Crystallin (αBC) is a member of the small heat shock protein family that responds to a variety of stress and prevents the aggregation of partially unfolded proteins. Chronic hyperglycemia created during diabetes results in skeletal muscle atrophy and leads to diabetic myopathy. The aim of this study was to investigate the role of αBC under chronic hyperglycemia in rat skeletal muscle. Diabetes was induced in Wistar rats by a single i.p injection of streptozotocin and maintained for a period of 12 weeks at the end of which the animals were sacrificed and the muscle was collected. The protein levels of αBC and its phosphorylation status in gastrocnemius muscle were analyzed by immunoblotting. The translocation of phosphorylated αBC was analyzed by detergent solubility assay, co-immunoprecipitation (Co-IP), and immunohistochemistry. The cell death was analyzed by TUNEL assay and by apoptotic markers. The interaction of αBC with Bax was analyzed by Co-IP. Chronic hyperglycemia significantly increased the protein levels of αBC and its phosphorylation at S59 by activation of p38 mitogen-activated protein kinase (p38MAPK) and at S45 by activation of the extracellular regulated protein kinase 1/2 (ERK1/2). Further, phosphorylated αBC translocated and interacted with desmin indicating that phosphorylated αBC forms might be involved in protection of sarcomere structures from disruption in chronic hyperglycemia. Further, Co-IP studies showed an impaired interaction of αBC with Bax which could be one of the possible factors for increased cell death as evidenced by TUNEL assay in diabetic muscle. These results suggest that an increased expression, phosphorylation, translocation of αBC, and its involvement in apoptosis might play a significant role in maintenance of cytoskeletal architecture and protection of cells from apoptosis in diabetic skeletal muscle.

Recent progress in satellite cell/myoblast engraftment -- relevance for therapy

There is currently no cure for muscular dystrophies, although several promising strategies are in basic and clinical research. One such strategy is cell transplantation with satellite cells (or their myoblast progeny) to repair damaged muscle and provide dystrophin protein with the aim of preventing subsequent myofibre degeneration and repopulating the stem cell niche for future use. The present review aims to cover recent advances in satellite cell/myoblast therapy and to discuss the challenges that remain for it to become a realistic therapy.

Low Molecular Weight Dextran Sulfate Binds to Human Myoblasts and Improves their Survival after Transplantation in Mice

Myoblast transplantation represents a promising therapeutic strategy in the treatment of several genetic muscular disorders including Duchenne muscular dystrophy. Nevertheless, such an approach is impaired by the rapid death, limited migration, and rejection of transplanted myoblasts by the host. Low molecular weight dextran sulfate (DXS), a sulfated polysaccharide, has been reported to act as a cytoprotectant for various cell types. Therefore, we investigated whether DXS could act as a “myoblast protectant” either in vitro or in vivo after transplantation in immunodeficient mice. In vitro, DXS bound human myoblasts in a dose dependent manner and significantly inhibited staurosporine-mediated apoptosis and necrosis. DXS pretreatment also protected human myoblasts from natural killer cell-mediated cytotoxicity. When human myoblasts engineered to express the renilla luciferase transgene were transplanted in immunodeficient mice, bioluminescence imaging analysis revealed that the proportion of surviving myoblasts 1 and 3 days after transplantation was two times higher when cells were preincubated with DXS compared to control (77.9 ± 10.1% vs. 39.4 ± 4.9%, p = 0.0009 and 38.1 ± 8.5% vs. 15.1 ± 3.4%, p = 0.01, respectively). Taken together, we provide evidence that DXS acts as a myoblast protectant in vitro and is able in vivo to prevent the early death of transplanted myoblasts.

Macrophages improve survival, proliferation and migration of engrafted myogenic precursor cells into MDX skeletal muscle

Transplantation of muscle precursor cells is of therapeutic interest for focal skeletal muscular diseases. However, major limitations of cell transplantation are the poor survival, expansion and migration of the injected cells. The massive and early death of transplanted myoblasts is not fully understood although several mechanisms have been suggested. Various attempts have been made to improve their survival or migration. Taking into account that muscle regeneration is associated with the presence of macrophages, which are helpful in repairing the muscle by both cleansing the debris and deliver trophic cues to myoblasts in a sequential way, we attempted in the present work to improve myoblast transplantation by coinjecting macrophages. The present data showed that in the 5 days following the transplantation, macrophages efficiently improved: i) myoblast survival by limiting their massive death, ii) myoblast expansion within the tissue and iii) myoblast migration in the dystrophic muscle. This was confirmed by in vitro analyses showing that macrophages stimulated myoblast adhesion and migration. As a result, myoblast contribution to regenerating host myofibres was increased by macrophages one month after transplantation. Altogether, these data demonstrate that macrophages are beneficial during the early steps of myoblast transplantation into skeletal muscle, showing that coinjecting these stromal cells may be used as a helper to improve the efficiency of parenchymal cell engraftment.

Restricted Myogenic Potential of Mesenchymal Stromal Cells Isolated from Umbilical Cord

Nonhematopoietic cord blood cells and mesenchymal cells of umbilical cord Wharton's jelly have been shown to be able to differentiate into various cell types. Thus, as they are readily available and do not raise any ethical issues, these cells are considered to be a potential source of material that can be used in regenerative medicine. In our previous study, we tested the potential of whole mononucleated fraction of human umbilical cord blood cells and showed that they are able to participate in the regeneration of injured mouse skeletal muscle. In the current study, we focused at the umbilical cord mesenchymal stromal cells isolated from Wharton's jelly. We documented that limited fraction of these cells express markers of pluripotent and myogenic cells. Moreover, they are able to undergo myogenic differentiation in vitro, as proved by coculture with C2C12 myoblasts. They also colonize injured skeletal muscle and, with low frequency, participate in the formation of new muscle fibers. Pretreatment of Wharton's jelly mesenchymal stromal cells with SDF-1 has no impact on their incorporation into regenerating muscle fibers but significantly increased muscle mass. As a result, transplantation of mesenchymal stromal cells enhances the skeletal muscle regeneration.

Heat shock attenuates VEGF expression in three-dimensional myoblast sheets deteriorating therapeutic efficacy in heart failure

Background

Myoblast sheet transplantation is a promising novel treatment for ischemic heart failure. The aim of this study was to test the hypothesis that heat shock (HS) pre-treatment affects the angiogenic properties of myoblast sheets in vivo and in vitro.

Material/Methods

We studied HS preconditioning of L6 myoblast sheets in relation to their apoptosis, proliferation, and vascular endothelial growth factor (VEGF)-associated responses under normoxia and under hypoxia in vitro. In vivo evaluation of their therapeutic effect was performed with 60 male Wistar rats divided into 3 groups (20 each): sole left anterior descending (LAD) ligation (control); LAD ligation and non-conditioned sheet transplantation (L6 No-Shock); and LAD ligation and L6-heat shock conditioned sheet transplantation (L6 Heat-Shock). Left ventricular function was evaluated by echocardiography after 3, 10, and 28 days.

Results

Expression of HSP70/72 was strongly induced 24 hours after HS, and thereafter it decreased notably during 72 hours in hypoxia. Under normal growth conditions, HSP70/72 expression remained stable. HS delayed apoptosis-associated caspase-3 expression during 24-hour hypoxia compared to non-treated controls. However, VEGF expression reduced significantly in the heat shock pretreated sheets. Ejection fraction of the L6-myoblast HS pre-treatment group (L6 Heat-Shock) decreased gradually during follow-up, in the same pattern as the controls. However, these functional parameters improved in the L6-myoblast normal sheet group (L6 No-Shock) at the tenth day and remained significantly better.

Conclusions

HS protects myoblast sheets from hypoxia-associated apoptosis in vitro, but reduces VEGF expression of the sheet, leading to lower therapeutic effect in heart failure.

Fibrin Gel Improves the Survival of Transplanted Myoblasts

Duchenne muscular dystrophy (DMD) is the most frequent muscular dystrophy in children and young adults. Currently, there is no cure for the disease. The transplantation of healthy myoblasts is an experimental therapeutic strategy, since it could restore the expression of dystrophin in DMD muscles. Nevertheless, this cellular therapy is limited by immune reaction, low migration of the implanted cells, and high early cell death that could be at least partially due to anoikis. To avoid the lack of attachment of the cells to an extracellular matrix after the transplantation, which is the cause of anoikis, we tested the use of a fibrin gel for myoblast transplantation. In vitro, three concentrations of fibrinogen were compared (3, 20, and 50 mg/ml) to form a fibrin gel. A stiffer fibrin gel leads to less degradability and less proliferation of the cells. A concentration of 3 mg/ml fibrin gel enhanced the differentiation of the myoblasts earlier as a culture in monolayer. Human myoblasts were also transplanted in muscles of Rag/mdx mice in a fibrin gel or in a saline solution (control). The use of 3 mg/ml fibrin gel for cell transplantation increased not only the survival of the cells as measured after 5 days but also the number of fibers expressing dystrophin after 21 days, compared to the control. Moreover, the fibrin gel was also compared to a prosurvival cocktail. The survival of the myoblasts at 5 days was increased in both conditions compared to the control but the efficacy of the prosurvival cocktail was not significantly higher than the fibrin gel.

Role of heat shock proteins in stem cell behavior

Stress response is well appreciated to induce the expression of heat shock proteins (Hsps) in the cell. Numerous studies have demonstrated that Hsps function as molecular chaperones in the stabilization of intracellular proteins, repairing damaged proteins, and assisting in protein translocation. Various kinds of stem cells (embryonic stem cells, adult stem cells, or induced pluripotent stem cells) have to maintain their stemness and, under certain circumstances, undergo stress. Therefore, Hsps should have an important influence on stem cells. Actually, numerous studies have indicated that some Hsps physically interact with a number of transcription factors as well as intrinsic and extrinsic signaling pathways. Importantly, alterations in Hsp expression have been demonstrated to affect stem cell behavior including self-renewal, differentiation, sensitivity to environmental stress, and aging. This chapter summarizes recent findings related to (1) the roles of Hsps in maintenance of stem cell dormancy, proliferation, and differentiation; (2) the expression signature of Hsps in embryonic/adult stem cells and differentiated stem cells; (3) the protective roles of Hsps in transplanted stem cells; and (4) the possible roles of Hsps in stem cell aging.

Aldehyde dehydrogenase activity promotes survival of human muscle precursor cells

Aldehyde dehydrogenases (ALDH) are a family of enzymes that efficiently detoxify aldehydic products generated by reactive oxygen species and might therefore participate in cell survival. Because ALDH activity has been used to identify normal and malignant cells with stem cell properties, we asked whether human myogenic precursor cells (myoblasts) could be identified and isolated based on their levels of ALDH activity. Human muscle explant-derived cells were incubated with ALDEFLUOR, a fluorescent substrate for ALDH, and we determined by flow cytometry the level of enzyme activity. We found that ALDH activity positively correlated with the myoblast-CD56⁺ fraction in those cells, but, we also observed heterogeneity of ALDH activity levels within CD56-purified myoblasts. Using lentiviral mediated expression of shRNA we demonstrated that ALDH activity was associated with expression of Aldh1a1 protein. Surprisingly, ALDH activity and Aldh1a1 expression levels were very low in mouse, rat, rabbit and non-human primate myoblasts. Using different approaches, from pharmacological inhibition of ALDH activity by diethylaminobenzaldehyde, an inhibitor of class I ALDH, to cell fractionation by flow cytometry using the ALDEFLUOR assay, we characterized human myoblasts expressing low or high levels of ALDH. We correlated high ALDH activity ex vivo to resistance to hydrogen peroxide (H₂O₂)-induced cytotoxic effect and in vivo to improved cell viability when human myoblasts were transplanted into host muscle of immune deficient scid mice. Therefore detection of ALDH activity, as a purification strategy, could allow non-toxic and efficient isolation of a fraction of human myoblasts resistant to cytotoxic damage.

Exacerbation of pathology by oxidative stress in respiratory and locomotor muscles with Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the most devastating type of muscular dystrophy, leading to progressive weakness of respiratory (e.g. diaphragm) and locomotor muscles (e.g. gastrocnemius). DMD is caused by X-linked defects in the gene that encodes for dystrophin, a key scaffolding protein of the dystroglycan complex (DCG) within the sarcolemmal cytoskeleton. As a result of a compromised dystroglycan complex, mechanical integrity is impaired and important signalling proteins (e.g. nNOS, caveolin-3) and pathways are disrupted. Disruption of the dystroglycan complex leads to high susceptibility to injury with repeated, eccentric contractions as well as inflammation, resulting in significant damage and necrosis. Chronic damage and repair cycling leads to fibrosis and weakness. While the link between inflammation with damage and weakness in the DMD diaphragm is unresolved, elevated oxidative stress may contribute to damage, weakness and possibly fibrosis. While utilization of non-specific antioxidant interventions has yielded inconsistent results, recent data suggest that NAD(P)H oxidase could play a pivotal role in elevating oxidative stress via integrated changes in caveolin-3 and stretch-activated channels (SACs). Oxidative stress may act as an amplifier, exacerbating disruption of the dystroglycan complex, upregulation of the inflammatory transcription factor NF-B, and thus functional impairment of force-generating capacity.

Isolation of a highly myogenic CD34-negative subset of human skeletal muscle cells free of adipogenic potential

The differentiation of multipotent cells into undesirable lineages is a significant risk factor when performing cell therapy. In muscular diseases, myofiber loss can be associated with progressive fat accumulation that is one of the primary factors leading to decline of muscular strength. Therefore, to avoid any contribution of injected multipotent cells to fat deposition, we have searched for a highly myogenic but nonadipogenic muscle-derived cell population. We show that the myogenic marker CD56, which is the gold standard for myoblast-based therapy, was unable to separate muscle cells into myogenic and adipogenic fractions. Conversely, using the stem cell marker CD34, we were able to sort two distinct populations, CD34(+) and CD34(-), which have been thoroughly characterized in vitro and in vivo using an immunodeficient Rag2(-/-)gamma(c) (-/-) mouse model of muscle regeneration with or without adipose deposition. Our results demonstrate that both populations have equivalent capacities for in vitro amplification. The CD34(+) cells and CD34(-) cells exhibit equivalent myogenic potential, but only the CD34(-) population fails to differentiate into adipocytes in vitro and in vivo after transplantation into regenerative fat muscle. These data indicate that the muscle-derived cells constitute a heterogeneous population of cells with various differentiation potentials. The simple CD34 sorting allows isolation of myogenic cells with no adipogenic potential and therefore could be of high interest for cell therapy when fat is accumulated in diseased muscle.

Comparison of the response of human embryonic stem cells and their differentiated progenies to oxidative stress

OBJECTIVE

To investigate effects of oxidative stress on human embryonic stem cells (hESC) and their spontaneously differentiated fibroblastic progenies (at passage 5).

BACKGROUND DATA

In ischemic disease models, high levels of free radicals and reactive oxygen species are critical factors in decreasing survivability and engraftment of transplanted/transfused cells. Hence, it is imperative to characterize response of hESC and their differentiated progenies to oxidative stress.

METHODS

Oxidative stress was induced either by (i) varying durations (0 to 40 min) of photodynamic treatment (diode laser, 664 nm, 30 mW) in the presence of 10 microM methylene blue as a photosensitizer, or by (ii) exposure to varying concentrations of hydrogen peroxide (0 to 50 microM) for a fixed duration of 40 min. Additionally, the effects of heat shock and mild oxidative stress preconditioning on oxidative stress response was also investigated.

RESULTS

Consistently higher survivability (MTT assay) of hESC was observed compared to their differentiated fibroblastic progenies, upon exposure to equivalent levels of oxidative stress. Further experiments demonstrated that heat-shock pretreatment (42 degrees C for 90 min) did not enhance the resistance of either hESC or their differentiated progenies to oxidative stress (photodynamic treatment), but in fact had a slightly detrimental effect on their survivability upon subsequent exposure to oxidative stress. Similarly, preconditioning of both undifferentiated hESC and their differentiated progenies with low levels of oxidative stress also did not enhance cellular survivability upon subsequent exposure to much higher levels of oxidative stress induced by photodynamic treatment.

CONCLUSIONS

Undifferentiated hESC are intrinsically more resistant to oxidative stress compared to their spontaneously differentiated fibroblastic progenies.

Non-canonical role for the TRAIL receptor DR5/FADD/caspase pathway in the regulation of MyoD expression and skeletal myoblast differentiation

We report herein that the TRAIL receptor DR5/FADD/caspase pathway plays a role in skeletal myoblast differentiation through modulation of the expression of the muscle regulatory transcription factor MyoD. Specifically, treatment with the selective caspase 3 inhibitor DEVD-fmk or the selective caspase 8 inhibitor IETD-fmk in growth media (GM), prior to culture in differentiation media (DM), inhibited differentiation. Further, this treatment resulted in decreased levels of MyoD message and protein. We next explored a role for the TRAIL receptor DR5/FADD pathway. We found that expression of either dominant negative (dn) FADD or dominant negative (dn) DR5 also resulted in decreased levels of MyoD mRNA and protein and blocked differentiation. This decreased level of MyoD mRNA was not a consequence of altered stability. Treatment with TSA, an inhibitor of histone deacetylases (HDACs), allowed MyoD expression in myoblasts expressing dnDR5. Finally, acetylation of histones associated with the distal regulatory region (DRR) enhancer of MyoD was decreased in myoblasts expressing dnDR5. Thus, our data suggests a non-canonical role for the TRAIL receptor/FADD pathway in the regulation of MyoD expression and skeletal myoblast differentiation.

Enhancement of myogenic and muscle repair capacities of human adipose-derived stem cells with forced expression of MyoD

Muscle disorders such as Duchenne muscular dystrophy (DMD) still need effective treatments, and mesenchymal stem cells (MSCs) may constitute an attractive cell therapy alternative because they are multipotent and accessible in adult tissues. We have previously shown that human multipotent adipose-derived stem (hMADS) cells were able to restore dystrophin expression in the mdx mouse. The goal of this work was to improve the myogenic potential of hMADS cells and assess the impact on muscle repair. Forced expression of MyoD in vitro strongly induced myogenic differentiation while the adipogenic differentiation was inhibited. Moreover, MyoD-expressing hMADS cells had the capacity to fuse with DMD myoblasts and to restore dystrophin expression. Importantly, transplantation of these modified hMADS cells into injured muscles of immunodepressed Rag2(-/-)gammaC(-/-) mice resulted in a substantial increase in the number of hMADS cell-derived fibers. Our approach combined the easy access of MSCs from adipose tissue, the highly efficient lentiviral transduction of these cells, and the specific improvement of myogenic differentiation through the forced expression of MyoD. Altogether our results highlight the capacity of modified hMADS cells to contribute to muscle repair and their potential to deliver a repairing gene to dystrophic muscles.

Heat shock treatment increases engraftment of transplanted human myoblasts into immunodeficient mice

Myoblast transfer therapy (MTT) is a strategy that has been proposed to treat some striated muscle pathologies. However, the first therapeutic trials using this technique were unsuccessful due to the limited migration and early cell death of the injected myoblasts. Various strategies have been considered to increase myoblast survival in the host muscle after MTT. Overexpression of heat shock proteins (HSPs) in mouse myoblasts has been shown to improve cell resistance against apoptosis in vitro and in vivo. Our objective was to determine whether heat shock (HS) treatment increased the survival of human myoblasts leading to better participation of the injected cells in muscle regeneration. For this study, HS-treated human myoblasts were injected into the tibialis anterior (TA) muscles of immunodeficient RAG-/- gammaC-/- mice. TA muscles were excised at 24 hour and at 1 month after injection. Our results showed that HS treatment increased the expression of the hsp70 protein and protected the cells from apoptosis in vitro. HS treatment dramatically increased the number of human fibers present at 1 month after injection when compared with nontreated cells. Interestingly, HS treatment decreased apoptosis at 24 hour after human myoblast injection, but no differences were observed concerning proliferation, suggesting that the increased fiber formation among the HS-treated group was probably due to decreased cell death. These data suggested that HS treatment might be used in the clinical context to improve the success of MTT.

Increased expression of the pro-apoptotic Bcl2 family member PUMA is required for mitochondrial release of cytochrome C and the apoptosis associated with skeletal myoblast differentiation

We have previously shown that when skeletal myoblasts are cultured in differentiation medium (DM), roughly 30% undergo caspase 3-dependent apoptosis rather than differentiation. Herein, we investigate the molecular mechanism responsible for the activation of caspase 3 and the ensuing apoptosis. When 23A2 myoblasts are cultured in DM, caspase 9 activity is increased and pharmacological abrogation of caspase 9 activation impairs caspase 3 activation and apoptosis. Further, we detect a time dependent release of mitochondrial cytochrome C into the cytosol in roughly 30% of myoblasts. Inclusion of cycloheximide inhibits the release of cytochrome C, the activation of caspase 9 and apoptosis. These data indicate that the mitochondrial pathway plays a role in this apoptotic process and that engagement of this pathway relies on de novo protein synthesis. Through RT-PCR and immunoblot analysis, we have determined that the expression level of the pro-apoptotic Bcl2 family member PUMA is elevated when 23A2 myoblasts are cultured in DM. Further, silencing of PUMA inhibits the release of cytochrome C and apoptosis. Signaling by the transcription factor p53 is not responsible for the increased level of PUMA. Finally, myoblasts rescued from apoptosis by either inhibition of elevated caspase 9 activity or silencing of PUMA are competent for differentiation. These results indicate a critical role for PUMA in the apoptosis associated with skeletal myoblast differentiation and that a p53-independent mechanism is responsible for the increased expression of PUMA in these cells.

Lentivirus mediated HO-1 gene transfer enhances myogenic precursor cell survival after autologous transplantation in pig

Cell therapy for Duchenne muscular dystrophy and other muscle diseases is limited by a massive early cell death following injections. In this study, we explored the potential benefit of heme oxygenase-1 (HO-1) expression in the survival of porcine myogenic precursor cells (MPCs) transplanted in pig skeletal muscle. Increased HO-1 expression was assessed either by transient hyperthermia or by HO-1 lentiviral infection. One day after the thermic shock, we observed a fourfold and a threefold increase in HSP70/72 and HO-1 levels, respectively. This treatment protected 30% of cells from staurosporine-induced apoptosis in vitro. When porcine MPC were heat-shocked prior to grafting, we improved cell survival by threefold at 5 days after autologous transplantation (26.3 +/- 5.5% surviving cells). After HO-1 lentiviral transduction, almost 60% of cells expressed the transgene and kept their myogenic properties to proliferate and fuse in vitro. Apoptosis of HO-1 transduced cells was reduced by 50% in vitro after staurosporine induction. Finally, a fivefold enhancement in cell survival was observed after transplantation of HO-1-group (47.5 +/- 9.1% surviving cells) as compared to the nls-LacZ-group or control group. These results identify HO-1 as a protective gene against early MPC death post-transplantation.

A synthetic mechano growth factor E Peptide enhances myogenic precursor cell transplantation success

Myogenic precursor cell (MPC) transplantation is a good strategy to introduce dystrophin expression in muscles of Duchenne muscular dystrophy (DMD) patients. Insulin-like growth factor (IGF-1) promotes MPC activities, such as survival, proliferation, migration and differentiation, which could enhance the success of their transplantation. Alternative splicing of the IGF-1 mRNA produces different muscle isoforms. The mechano growth factor (MGF) is an isoform, especially expressed after a mechanical stress. A 24 amino acids peptide corresponding to the C-terminal part of the MGF E domain (MGF-Ct24E peptide) was synthesized. This peptide had been shown to enhance the proliferation and delay the terminal differentiation of C(2)C(12) myoblasts. The present study showed that the MGF-Ct24E peptide improved human MPC transplantation by modulating their proliferation and differentiation. Indeed, intramuscular or systemic delivery of this synthetic peptide significantly promoted engraftment of human MPCs in mice. In vitro experiments demonstrated that the MGF-Ct24E peptide enhanced MPC proliferation by a different mechanism than the binding to the IGF-1 receptor. Moreover, MGF-Ct24E peptide delayed human MPC differentiation while having no outcome on survival. Those combined effects are probably responsible for the enhanced transplantation success. Thus, the MGF-Ct24E peptide is an interesting agent to increase MPC transplantation success in DMD patients.

Aging skeletal muscle shows a drastic increase in the small heat shock proteins αB-crystallin/HspB5 and cvHsp/HspB7

Most heat shock proteins operate as molecular chaperones and play a central role in the maintenance of normal cellular function. In skeletal muscle, members of the alpha-crystallin domain-containing family of small heat shock proteins are believed to form a cohort of essential stress proteins. Since alphaB-crystallin (alphaBC/HspB5) and the cardiovascular heat shock protein (cvHsp/HspB7) are both implicated in the molecular response to fibre transformation and muscle wasting, it was of interest to investigate the fate of these stress proteins in young adult versus aged muscle. The age-related loss of skeletal muscle mass and strength, now generally referred to as sarcopenia, is one of the most striking features of the senescent organism. In order to better understand the molecular pathogenesis of age-related muscle wasting, we have performed a two-dimensional gel electrophoretic analysis, immunoblotting and confocal microscopy study of aged rat gastrocnemius muscle. Fluorescent labelling of the electrophoretically separated soluble muscle proteome revealed an overall relatively comparable protein expression pattern of young adult versus aged fibres, but clearly an up-regulation of alphaBC and cvHsp. This was confirmed by immunofluorescence microscopy and immunoblot analysis, which showed a dramatic age-induced increase in these small heat shock proteins. Immunodecoration of other major stress proteins showed that they were not affected or less drastically changed in their expression in aged muscle. These findings indicate that the increase in muscle-specific small heat shock proteins constitutes an essential cellular response to fibre aging and might therefore be a novel therapeutic option to treat sarcopenia of old age.

Proteomic profiling of animal models mimicking skeletal muscle disorders

Over the last few decades of biomedical research, animal models of neuromuscular diseases have been widely used for determining pathological mechanisms and for testing new therapeutic strategies. With the emergence of high-throughput proteomics technology, the identification of novel protein factors involved in disease processes has been decisively improved. This review outlines the usefulness of the proteomic profiling of animal disease models for the discovery of new reliable biomarkers, for the optimization of diagnostic procedures and the development of new treatment options for skeletal muscle disorders. Since inbred animal strains show genetically much less interindividual differences as compared to human patients, considerably lower experimental repeats are capable of producing meaningful proteomic data. Thus, animal model proteomics can be conveniently employed for both studying basic mechanisms of molecular pathogenesis and the effects of drugs, genetic modifications or cell-based therapies on disease progression. Based on the results from comparative animal proteomics, a more informed decision on the design of clinical proteomics studies could be reached. Since no one animal model represents a perfect pathobiochemical replica of all of the symptoms seen in complex human disorders, the proteomic screening of novel animal models can also be employed for swift and enhanced protein biochemical phenotyping.

Heat shock pretreatment enhances porcine myoblasts survival after autotransplantation in intact skeletal muscle

Myoblast transplantation (MT) is a cell-based gene therapy treatment, representing a potential treatment for Duchenne muscular dystrophy (DMD), cardiac failure and muscle trauma. The rapid and massive death of transplanted cells after MT is considered as a major hurdle which limits the efficacy of MT treatment. Heat shock proteins (HSPs) are overexpressed when cells undergo various insults. HSPs have been described to protect cells in vivo and in vitro against diverse insults. The aim of our study is to investigate whether HSP overexpression could increase myoblast survival after autotransplantation in pig intact skeletal muscle. HSP expression was induced by warming the cells at 42 degrees C for 1 h. HSP70 expression was quantified by Western blot and flow cytometry 24 h after the treatment. To investigate the myogenic characteristics of myoblasts, desmin and CD56 were analysed by Western blot and flow cytometry; and the fusion index was measured. We also quantified cell survival after autologous transplantation in pig intact skeletal muscle and followed cell integration. Results showed that heat shock treatment of myoblasts induced a significative overexpression of the HSP70 (P < 0.01) without loss of their myogenic characteristics as assessed by FACS and fusion index. In vivo (n=7), the myoblast survival rate was not significantly different at 24 h between heat shock treated and nontreated cells (67.69% +/- 8.35% versus 58.79% +/- 8.35%, P > 0.05). However, the myoblast survival rate in the heat shocked cells increased by twofold at 48 h (53.32% +/- 8.22% versus 28.27% +/- 6.32%, P < 0.01) and more than threefold at 120 h (26.33% +/- 5.54% versus 8.79% +/- 2.51%, P < 0.01). Histological analysis showed the presence of non-heat shocked and heat shocked donor myoblasts fused with host myoblasts. These results suggested that heat shock pretreatment increased the HSP70 expression in porcine myoblasts, and improved the survival rate after autologous transplantation. Therefore, heat shock pretreatment of myoblast in vitro is a simple and effective way to enhance cell survival after transplantation in pig. It might represent a potential method to overcome the limitations of MT treatment.

Induction of Anoikis following myoblast transplantation into SCID mouse muscles requires the Bit1 and FADD pathways

Seventy-five percent of the myoblasts transplanted in the mouse muscle die during the first 4 days following transplantation. The purpose of this study was to determine if anoikis plays a role in this phenomenon. Survival and proliferation of myoblasts in vitro were determined by Hoescht-PI labeling and cell counts respectively. In vivo cell survival and proliferation were quantified by injecting human male myoblasts labeled with (14)C-thymidine in SCID mouse muscles. Survival and proliferation of the transplanted myoblasts were evaluated by scintigraphy and quantitative PCR of human Y chromosomal DNA. Inclusion of the extracellular matrix protein fibronectin enhanced transplanted myoblast survival by 1.7-fold while vitronectin improved their proliferation by 1.8-fold. Reductions in FADD and Bit1 expression reduced anoikis in vitro and improved the injected myoblast survival in vivo. Ectopic expression of the anti-apoptotic protein Bcl-2 completely abolished myoblast anoikis in vitro and enhanced cell survival by 3.1-fold in vivo. Cell death following transplantation appears to me mediated in part by anoikis. Inclusion of extracellular matrix proteins enhanced both survival and proliferation. Reduced expression of the proapoptotic proteins Bit1 and FADD or overexpression of Bcl-2 improved myoblast survival.

Signaling through the TRAIL receptor DR5/FADD pathway plays a role in the apoptosis associated with skeletal myoblast differentiation

Apoptosis rather than differentiation is a physiological process during myogenesis and muscle regeneration. When cultured myoblasts were induced to differentiate, we detected an increase in caspase 8 activity. Pharmacological inhibition of caspase 8 activity decreased apoptosis. Expression of a dominant-negative mutant of the adapter protein FADD also abrogated apoptosis, implicating a death ligand pathway. Treatment with TRAIL, but not Fas, induced apoptosis in these myoblasts. Accordingly, treatment with a soluble TRAIL decoy receptor or expression of a dominant-negative mutant of the TRAIL receptor DR5 abrogated apoptosis. While TRAIL expression levels remained unaltered in apoptotic myoblasts, DR5 expression levels increased. Finally, we also detected a reduction in FLIP, a death-receptor effector protein and caspase 8 competitive inhibitor, to undetectable levels in apoptotic myoblasts. Thus, our data demonstrate an important role for the TRAIL/DR5/FADD/caspase 8 pathway in the apoptosis associated with skeletal myoblast differentiation. Identifying the functional apoptotic pathways in skeletal myoblasts may prove useful in minimizing the myoblast apoptosis that contributes pathologically to a variety of diseases and in minimizing the apoptosis of transplanted myoblasts to treat these and other disease states.

Proteome analysis of the dystrophin-deficient MDX diaphragm reveals a drastic increase in the heat shock protein cvHSP

Duchenne muscular dystrophy is the most commonly inherited neuromuscular disorder in humans. Although the primary genetic deficiency of dystrophin in X-linked muscular dystrophy is established, it is not well-known how pathophysiological events trigger the actual fibre degeneration. We have therefore performed a DIGE analysis of normal diaphragm muscle versus the severely affected x-linked muscular dystrophy (MDX) diaphragm, which represents an established animal model of dystrophinopathy. Out of 2398 detectable 2-D protein spots, 35 proteins showed a drastic differential expression pattern, with 21 proteins being decreased, including Fbxo11-protein, adenylate kinase, beta-haemoglobin and dihydrolipoamide dehydrogenase, and 14 proteins being increased, including cvHSP, aldehyde reductase, desmin, vimentin, chaperonin, cardiac and muscle myosin heavy chain. This suggests that lack of sarcolemmal integrity triggers a generally perturbed protein expression pattern in dystrophin-deficient fibres. However, the most significant finding was the dramatic increase in the small heat shock protein cvHSP, which was confirmed by 2-D immunoblotting. Confocal fluorescence microscopy revealed elevated levels of cvHSP in MDX fibres. An immunoblotting survey of other key heat shock proteins showed a differential expression pattern in MDX diaphragm. Stress response appears to be an important cellular mechanism in dystrophic muscle and may be exploitable as a new approach to counteract muscle degeneration.

Stem cell based therapies to treat muscular dystrophy

Muscular dystrophies comprise a heterogeneous group of neuromuscular disorders, characterized by progressive muscle wasting, for which no satisfactory treatment exists. Multiple stem cell populations, both of adult or embryonic origin, display myogenic potential and have been assayed for their ability to correct the dystrophic phenotype. To date, many of these described methods have failed, underlying the need to identify the mechanisms controlling myogenic potential, homing of donor populations to the musculature, and avoidance of the immune response. Recent results focus on the fresh isolation of satellite cells and the use of multiple growth factors to promote mesangioblast migration, both of which promote muscle regeneration. Throughout this chapter, various stem cell based therapies will be introduced and evaluated based on their potential to treat muscular dystrophy in an effective and efficient manner.

Can cold or heat shock improve skeletal myoblast engraftment in infarcted myocardium?

OBJECTIVE

Cell death remains a major limitation of skeletal myoblast (SM) transplantation but the patterns of cell survival and proliferation in heart and their potential modulation by thermic stresses like heat shock (HS) and cryopreservation (Cryo) are still incompletely characterized.

METHODS

To track SMs in situ, we developed a dual-marker system based on the semiconservative expression of the foreign soluble protein, beta-Galactosidase (beta-Gal) and the constitutive expression of the Y chromosome in a myocardial infarction model. Control medium or Lewis male rat SMs (fresh or subjected to Cryo or HS) were injected in Lewis female rats.

RESULTS

There was a massive cell loss early after transplantation in the fresh group, which was only partially compensated for by a subsequent proliferation. Conversely, both Cryo and HS significantly improved early cell survival but blunted subsequent proliferation so that, at 15 days posttransplantation, the total number of engrafted donor-derived Y-positive cells did not differ significantly between the three groups. Most of them expressed a skeletal muscle phenotype.

CONCLUSIONS

These data confirm the high death rate of in-scar transplanted myoblasts, demonstrate the ability of those that survive to proliferate and differentiate along the myogenic pathway but do not support the efficacy of either Cryo or HS for increasing the ultimate magnitude of myoblast engraftment.

Real-time imaging of myoblast transplantation using the human sodium iodide symporter

The quantification of the graft success is a key element to evaluate the efficiency of cellular therapies for several pathologies such as Duchenne muscular dystrophy. This study describes an approach to evaluate the success of myoblast transplantation (i.e., survival of the transplanted cells and the muscle fibers formed) by real-time imaging. C2C12 myoblasts were first transfected with a plasmid containing the human sodium iodide symporter (hNIS) gene. Specific uptake of the radioactive sodium pertechnetate (Na99mTcO4) by the hNIS-positive myoblasts was demonstrated in vitro, while only background level of Na99mTcO4 was observed within the control cells. The cells were then transplanted into the tibialis anterior (TA) muscle of mdx (X-linked dystrophic) mice. Following intraperitoneal administration of Na99mTcO4, scintigraphies were performed to detect hNIS-dependent Na99mTcO4 uptake within the TA. This approach permitted to evaluate the progression of the transplantation and the graft success without having to biopsy the animals during the follow-up period.