Haematopoietic stem cells participate in muscle regeneration

Skeletal Muscle Regeneration in Cardiotoxin-Induced Muscle Injury Models

Skeletal muscle injuries occur frequently in daily life and exercise. Understanding the mechanisms of regeneration is critical for accelerating the repair and regeneration of muscle. Therefore, this article reviews knowledge on the mechanisms of skeletal muscle regeneration after cardiotoxin-induced injury. The process of regeneration is similar in different mouse strains and is inhibited by aging, obesity, and diabetes. Exercise, microcurrent electrical neuromuscular stimulation, and mechanical loading improve regeneration. The mechanisms of regeneration are complex and strain-dependent, and changes in functional proteins involved in the processes of necrotic fiber debris clearance, M1 to M2 macrophage conversion, SC activation, myoblast proliferation, differentiation and fusion, and fibrosis and calcification influence the final outcome of the regenerative activity.

Disturbance of calcium homeostasis and myogenesis caused by TET2 deletion in muscle stem cells

Skeletal muscle myogenesis is a sophisticated process controlled by genetic and epigenetic regulators. In animals, one of the key enzymes for the DNA demethylation of 5-methylcytosine is TET2. Although TET2 is essential for muscle development, the mechanisms by which TET2 regulates myogenesis, particularly the implication for muscle stem cells, remains unclear. In the present study, we employed the TET2 knockout mouse model to investigate the function of TET2 in muscle development and regeneration. We observed that TET2 deficiency caused impaired muscle stem cell proliferation and differentiation, resulting in the reduction in both myofiber number and muscle tissue size. Specifically, TET2 maintains calcium homeostasis in muscle stem cells by controlling the DNA methylation levels of the calcium pathway genes. Forced expression of the sodium/calcium exchanger protein SLC8A3 could rescue the myogenic defects in TET2 knockout cells. Our data not only illustrated the vital function of TET2 during myogenesis but also identified novel targets that contribute to calcium homeostasis for enhancing muscle function.

Adult stem cell sources for skeletal and smooth muscle tissue engineering

INTRODUCTION

Tissue engineering is an innovative field with enormous developments in recent years. These advances are not only in the understanding of how stem cells can be isolated, cultured and manipulated but also in their potential for clinical applications. Thus, tissue engineering when applied to skeletal and smooth muscle cells is an area that bears high benefit for patients with muscular diseases or damage. Most of the recent research has been focused on use of adult stem cells. These cells have the ability to rejuvenate and repair damaged tissues and can be derived from different organs and tissue sources. Recently there are several different types of adult stem cells, which have the potential to function as a cell source for tissue engineering of skeletal and smooth muscles. However, to build neo-tissues there are several challenges which have to be addressed, such as the selection of the most suitable stem cell type, isolation techniques, gaining control over its differentiation and proliferation process.

CONCLUSION

The usage of adult stem cells for muscle engineering applications is promising. Here, we summarize the status of research on the use of adult stem cells for cell transplantation in experimental animals and humans. In particular, the application of skeletal and smooth muscle engineering in pre-clinical and clinical trials will be discussed.

Bone Marrow-Derived Cells Participate in Composition of the Satellite Cell Niche in Intact and Regenerating Mouse Skeletal Muscle

The cellular components of the satellite cell niche participate in the regulation of skeletal muscle regeneration. Beside myogenic cells at different developmental stages, this niche is formed by cells of the immune system, the interstitial connective tissue and the vascular system. Unambiguous determination of the origin of these cell types could contribute to optimization of the cell-based therapy of skeletal muscle disorders. In our work, we intravenously transplanted mouse GFP+ unseparated bone marrow cells into whole-body lethally irradiated immunocompetent mice four weeks before cardiotoxin-induced injury of the recipients' skeletal muscles. Seven and 28 days after the toxin injection, the injured regenerating and contralateral intact muscles were examined for identification of GFP+ bone marrow-derived cells by direct fluorescence, protein immunohistochemistry and immunogold transmission electron microscopy. In both the intact and injured muscles, GFP positivity was determined in immune cells, mainly in macrophages, and in interstitial spindleshaped cells. Moreover, in the injured muscles, rare GFP+ endothelial cells of the blood vessels and newly formed myotubes and muscle fibres were present. Our results confirmed the ability of bone marrowderived cells to contribute to the cellular component of the satellite cell niche in the intact and regenerating skeletal muscle. These cells originated not only from haematopoietic stem cells, but obviously also from other stem or progenitor cells residing in the bone marrow, such as multipotent mesenchymal stromal cells and endothelial progenitors.

Role of transplanted bone marrow cells in development of rotator cuff muscle fatty degeneration in mice

BACKGROUND

Rotator cuff muscle fatty degeneration after a chronic tendon tear is an irreversible pathologic change associated with poor clinical outcomes of tendon repair, and its exact pathogenesis remains unknown. We sought to investigate the role of transplanted bone marrow cells in the development of fatty degeneration, specifically in adipocyte accumulation, using a mouse model.

METHODS

Fourteen mice were divided into 2 bone marrow chimeric animal groups: bone marrow transplantation (BMT) group and reverse BMT group. For the BMT group, C57BL/6J wild-type mice underwent whole body irradiation followed by BMT into the retro-orbital sinus from green fluorescent protein (GFP)-transgenic donor mice. For the reverse BMT group, GFP-transgenic mice received BMT from C57BL/6J wild-type donor mice after irradiation. The supraspinatus tendon, infraspinatus tendon, and suprascapular nerve were surgically transected 3 weeks after transplantation. The rotator cuff muscles were harvested 13 weeks after transplantation for histologic analysis and GFP immunohistochemistry.

RESULTS

On histologic examination, both groups showed substantial fatty degeneration, fibrosis, and atrophy of the cuff muscles. The BMT group showed no noticeable GFP immunostaining, whereas the reverse BMT group showed significantly stronger GFP staining in most adipocytes (P < .001). However, both groups also showed that a small number of adipocytes originated from transplanted bone marrow cells. A small number of myocytes showed a large cytoplasmic lipid vacuole resembling adipocytes.

CONCLUSIONS

This study's findings suggest that most adipocytes in fatty degeneration of the rotator cuff muscles originate from sources other than bone marrow-derived stem cells, and there may be more than 1 source for the adipocytes.

Surgical and immune reconstitution murine models in bone marrow research: Potential for exploring mechanisms in sepsis, trauma and allergy

Bone marrow, the vital organ which maintains lifelong hemopoiesis, currently receives considerable attention, as a source of multiple cell types which may play important roles in repair at distant sites. This emerging function, distinct from, but closely related to, bone marrow roles in innate immunity and inflammation, has been characterized through a number of strategies. However, the use of surgical models in this endeavour has hitherto been limited. Surgical strategies allow the experimenter to predetermine the site, timing, severity and invasiveness of injury; to add or remove aggravating factors (such as infection and defects in immunity) in controlled ways; and to manipulate the context of repair, including reconstitution with selected immune cell subpopulations. This endows surgical models overall with great potential for exploring bone marrow responses to injury, inflammation and infection, and its roles in repair and regeneration. We review three different murine surgical models, which variously combine trauma with infection, antigenic stimulation, or immune reconstitution, thereby illuminating different aspects of the bone marrow response to systemic injury in sepsis, trauma and allergy. They are: (1) cecal ligation and puncture, a versatile model of polymicrobial sepsis; (2) egg white implant, an intriguing model of eosinophilia induced by a combination of trauma and sensitization to insoluble allergen; and (3) ectopic lung tissue transplantation, which allows us to dissect afferent and efferent mechanisms leading to accumulation of hemopoietic cells in the lungs. These models highlight the gain in analytical power provided by the association of surgical and immunological strategies.

Bone marrow cell migration to the heart in a chimeric mouse model of acute chagasic disease

BACKGROUND

Chagas disease is a public health problem caused by infection with the protozoan Trypanosoma cruzi. There is currently no effective therapy for Chagas disease. Although there is some evidence for the beneficial effect of bone marrow-derived cells in chagasic disease, the mechanisms underlying their effects in the heart are unknown. Reports have suggested that bone marrow cells are recruited to the chagasic heart; however, studies using chimeric mouse models of chagasic cardiomyopathy are rare.

OBJECTIVES

The aim of this study was to investigate the migration of bone marrow cells to the heart after T. cruzi infection in a model of chagasic disease in chimeric mice.

METHODS

To obtain chimerical mice, wild-type (WT) C57BL6 mice were exposed to full body irradiation (7 Gy), causing bone marrow ablation. Then, bone marrow cells from green fluorescent protein (GFP)-transgenic mice were infused into the mice. Graft effectiveness was confirmed by flow cytometry. Experimental mice were divided into four groups: (i) infected chimeric (iChim) mice; (ii) infected WT (iWT) mice, both of which received 3 × 104 trypomastigotes of the Brazil strain; (iii) non-infected chimeric (Chim) mice; and (iv) non-infected WT mice.

FINDINGS

At one-month post-infection, iChim and iWT mice showed first degree atrioventricular block with decreased heart rate and treadmill exercise parameters compared to those in the non-infected groups.

MAIN CONCLUSIONS

iChim mice showed an increase in parasitaemia, myocarditis, and the presence of amastigote nests in the heart tissue compared to iWT mice. Flow cytometry analysis did not detect haematopoietic progenitor cells in the hearts of infected mice. Furthermore, GFP+ cardiomyocytes were not detected in the tissues of chimeric mice.

Effect of mesenchymal stem cells on induced skeletal muscle chemodenervation atrophy in adult male albino rats

The present research was conducted to evaluate the effect of bone marrow derived mesenchymal stem cells (BM-MSCs) as a potential therapeutic tool for improvement of skeletal muscle recovery after induced chemodenervation atrophy by repeated local injection of botulinum toxin-A in the right tibialis anterior muscle of adult male albino rats. Forty five adult Wistar male albino rats were classified into control and experimental groups. Experimental group was further subdivided into 3 equal subgroups; induced atrophy, BM-MSCs treated and recovery groups. Biochemical analysis of serum LDH, CK and Real-time PCR for Bcl-2, caspase 3 and caspase 9 was measured. Skeletal muscle sections were stained with H and E, Mallory trichrome, and Immunohistochemical reaction for Bax and CD34. Improvement in the skeletal muscle histological structure was noticed in BM-MSCs treated group, however, in the recovery group, some sections showed apparent transverse striations and others still affected. Immunohistochemical reaction of Bax protein showed strong positive immunoreaction in the cytoplasm of muscle fibers in the induced atrophy group. BM-MSCs treated group showed weak positive reaction while the recovery group showed moderate reaction in the cytoplasm of muscle fibers. Immunohistochemical reaction for CD34 revealed occasional positive CD34 stained cells in the induced atrophy group. In BM-MSCs treated group, multiple positive CD34 stained cells were detected. However, recovery group showed some positive CD34 stained cells at the periphery of the muscle fibers. Marked improvement in the regenerative capacity of skeletal muscles after BM-MSCs therapy. Hence, stem cell therapy provides a new hope for patients suffering from myopathies and severe injuries.

Intrinsic ability of adult stem cell in skeletal muscle: an effective and replenishable resource to the establishment of pluripotent stem cells

Adult stem cells play an essential role in mammalian organ maintenance and repair throughout adulthood since they ensure that organs retain their ability to regenerate. The choice of cell fate by adult stem cells for cellular proliferation, self-renewal, and differentiation into multiple lineages is critically important for the homeostasis and biological function of individual organs. Responses of stem cells to stress, injury, or environmental change are precisely regulated by intercellular and intracellular signaling networks, and these molecular events cooperatively define the ability of stem cell throughout life. Skeletal muscle tissue represents an abundant, accessible, and replenishable source of adult stem cells. Skeletal muscle contains myogenic satellite cells and muscle-derived stem cells that retain multipotent differentiation abilities. These stem cell populations have the capacity for long-term proliferation and high self-renewal. The molecular mechanisms associated with deficits in skeletal muscle and stem cell function have been extensively studied. Muscle-derived stem cells are an obvious, readily available cell resource that offers promise for cell-based therapy and various applications in the field of tissue engineering. This review describes the strategies commonly used to identify and functionally characterize adult stem cells, focusing especially on satellite cells, and discusses their potential applications.

Sdf-1 (CXCL12) improves skeletal muscle regeneration via the mobilisation of Cxcr4 and CD34 expressing cells

BACKGROUND INFORMATION

The regeneration of skeletal muscles involves satellite cells, which are muscle-specific precursor cells. In muscles, injured either mechanically or as a consequence of a disease, such as muscular dystrophy, local release of the growth factors and cytokines leads to satellite cells activation, proliferation and differentiation of the resulting myoblasts, followed by the formation of new myofibres. Various cell types, such as stem and progenitor cells, originating from other tissues different than the muscle, are also able to follow a myogenic program. Participation of these cells in the repair process depends on their precise mobilisation to the site of the injury.

RESULTS

In this study, we showed that stromal-derived factor-1 (Sdf-1) impacts on the mobilisation of CXC chemokine receptor (Cxcr)4-positive cells and improves skeletal muscle regeneration. Analysis of isolated and in vitro cultured satellite cells showed that Sdf-1 did not influence myoblasts proliferation and expression of myogenic regulatory transcription factors but induced migration of the myoblasts in Cxcr4-dependent ways. This phenomenon was also associated with the increased activity of crucial extracellular matrix modifiers, i.e. metalloproteases Mmp-2 and Mmp-9.

CONCLUSIONS

Thus, positive impact of Sdf-1 on muscle regeneration is related to the mobilisation of endogenous cells, that is satellite cells and myoblasts, as well as non-muscle stem cells, expressing Cxcr4 and CD34.

Endogenous erythropoietin signaling facilitates skeletal muscle repair and recovery following pharmacologically induced damage

Erythropoietin acts by binding to its cell surface receptor on erythroid progenitor cells to stimulate erythrocyte production. Erythropoietin receptor expression in nonhematopoietic tissue, including skeletal muscle progenitor cells, raises the possibility of a role for erythropoietin beyond erythropoiesis. Mice with erythropoietin receptor restricted to hematopoietic tissue were used to assess contributions of endogenous erythropoietin to promote skeletal myoblast proliferation and survival and wound healing in a mouse model of cardiotoxin induced muscle injury. Compared with wild-type controls, these mice had fewer skeletal muscle Pax-7(+) satellite cells and myoblasts that do not proliferate in culture, were more susceptible to skeletal muscle injury and reduced maximum load tolerated by isolated muscle. In contrast, mice with chronic elevated circulating erythropoietin had more Pax-7(+) satellite cells and myoblasts with increased proliferation and survival in culture, decreased muscle injury, and accelerated recovery of maximum load tolerated by isolated muscle. Skeletal muscle myoblasts also produced endogenous erythropoietin that increased at low O(2). Erythropoietin promoted proliferation, survival, and wound recovery in myoblasts via the phosphoinositide 3-kinase/AKT pathway. Therefore, endogenous and exogenous erythropoietin contribute to increasing satellite cell number following muscle injury, improve myoblast proliferation and survival, and promote repair and regeneration in this mouse induced muscle injury model independent of its effect on erythrocyte production.

Skeletal Muscle-derived Hematopoietic Stem Cells: Muscular Dystrophy Therapy by Bone Marrow Transplantation

For postnatal growth and regeneration of skeletal muscle, satellite cells, a self-renewing pool of muscle stem cells, give rise to daughter myogenic precursor cells that contribute to the formation of new muscle fibers. In addition to this key myogenic cell class, adult skeletal muscle also contains hematopoietic stem cell and progenitor cell populations which can be purified as a side population (SP) fraction or as a hematopoietic marker CD45-positive cell population. These muscle-derived hematopoietic stem/progenitor cell populations are surprisingly capable of differentiation into hematopoietic cells both after transplantation into irradiated mice and during in vitro colony formation assay. Therefore, these muscle-derived hematopoietic stem/progenitor cells appear to have characteristics similar to classical hematopoietic stem/progenitor cells found in bone marrow. This review outlines recent findings regarding hematopoietic stem/progenitor cell populations residing in adult skeletal muscle and discusses their myogenic potential along with their role in the stem cell niche and related cell therapies for approaching treatment of Duchenne muscular dystrophy.

Regeneration of skeletal muscle

Skeletal muscle has a robust capacity for regeneration following injury. However, few if any effective therapeutic options for volumetric muscle loss are available. Autologous muscle grafts or muscle transposition represent possible salvage procedures for the restoration of mass and function but these approaches have limited success and are plagued by associated donor site morbidity. Cell-based therapies are in their infancy and, to date, have largely focused on hereditary disorders such as Duchenne muscular dystrophy. An unequivocal need exists for regenerative medicine strategies that can enhance or induce de novo formation of functional skeletal muscle as a treatment for congenital absence or traumatic loss of tissue. In this review, the three stages of skeletal muscle regeneration and the potential pitfalls in the development of regenerative medicine strategies for the restoration of functional skeletal muscle in situ are discussed.

A mouse model of yellow fluorescent protein (YFP) expression in hematopoietic cells to assess leukocyte-endothelial interactions in the microcirculation

In this study, we describe the use of intravital microscopy in a transgenic mouse model expressing yellow fluorescent protein (YFP) under the control of a monocyte specific promoter c-fms (CD115) to track and quantify specific leukocyte subsets. Flow cytometry on peripheral and bone marrow leukocytes revealed that YFP was predominantly expressed by CD11a(+), CD11b(+), and CD14(+) monocytes. In the bone marrow, 67+/-4% of Ly6C(high) F4/80(+) cells were YFP(high) while 55+/-1% of Ly6C(low) F4/80(+) cells were YFP(low) supporting the use of c-fms(YFP) expression as a marker of monocyte lineage. 70+/-7% of CD11b(+) F4/80(+) Ly6C(+) ("triple positive") cells expressed YFP. To assess leukocyte-endothelial interactions in YFP(+) cells in c-fms(YFP+) mice, we evaluated leukocyte adhesion, rolling and local shear stress responses in the cremasteric endothelium 4 h following administration of TNFalpha. TNFalpha resulted in a five-fold increase in adhesion of YFP(+) cells to the endothelium and provided superior discriminative ability in assessing rolling and adhesion events when compared with bright field microscopy. Additionally, when compared with Rhodamine-6G labeled leukocytes or GFP(+) cells in mice transplanted with green fluorescent protein (GFP) positive bone marrow, the level of detail observed in the c-fms(YFP+) was greater, with both GFP(+) and YFP(+) cells demonstrating superior signal to noise compared to bright field microscopy. A weak positive linear correlation between wall shear stress and YFP(+) cell adhesion (r(2)=0.20, p<0.05) was seen in the cremasteric microcirculation. Taken together, these data demonstrate the use of c-fms(YFP+) mice in identifying distinct monocyte subsets and highlight the potential of this model for real-time monocyte-endothelial interactions using intravital microscopy.

Cellular therapy for repair of cardiac damage after acute myocardial infarction

Cardiovascular diseases, particularly acute myocardial infarction, are the leading causes of death worldwide. Important advances have been made in the secondary treatment for cardiovascular diseases such as heart transplantation and medical and surgical therapies. Although these therapies alleviate symptoms, and may even improve survival, none can reverse the disease process and directly repair the lasting damage. Thus, the cure of cardiovascular diseases remains a major unmet medical need. Recently, cellular therapy has been proposed as a candidate treatment for this. Many stem and progenitor cell populations have each been suggested as a potential basis for such therapy. This review assesses some of the more notable exogenous adult cell candidates and provides insights into the mechanisms by which they may mediate improvement in cardiac function following acute myocardial infarction. Research into the cellular therapy field is of great importance for the further planning of clinical trials for cardiac cellular myoplasty.

Transdifferentiation of stem cells: a critical view

Recently a large amount of new data on the plasticity of stem cells of various lineages have emerged, providing new perspectives especially for the therapeutic application of adult stem cells. Previously unknown possibilities of cell differentiation beyond the known commitment of a given stem cell have been described using keywords such as "blood to liver," or "bone to brain." Controversies on the likelihood, as well as the biological significance, of these conversions almost immediately arose within this young field of stem cell biology. This chapter will concentrate on these controversies and focus on selected examples demonstrating the technical aspects of stem cell transdifferentiation and the evaluation of the tools used to analyze these events.

Hematopoietic contribution to skeletal muscle regeneration in acid alpha-glucosidase knockout mice

Recent studies have shown that cells from bone marrow (BM) can give rise to differentiated skeletal muscle fibers. However, the mechanisms and identities of the cell types involved remain unknown. We performed BM transplantation in acid alpha-glucosidase (GAA) knockout mice, a model of glycogen storage disease type II, and our observations suggested that the BM cells contribute to skeletal muscle fiber formation. Furthermore, we showed that most CD45+:Sca1+ cells have a donor character in regenerating muscle of recipient mice. Based on these findings, CD45+:Sca1+ cells were sorted from regenerating muscles. The cell number was increased with granulocyte colony-stimulating factor after cardiotoxin injury, and the cells were transplanted directly into the tibialis anterior (TA) muscles of GAA knockout mice. Sections of the TA muscles stained with anti-laminin-alpha2 antibody showed that the number of CD45+:Sca1+ cells contributing to muscle fiber formation and glycogen levels were decreased in transplanted muscles. Our results indicated that hematopoietic stem cells, such as CD45+:Sca1+ cells, are involved in skeletal muscle regeneration.