Claude A. Dechesne

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.

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−/−γc−/− 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. STEM CELLS 2010;28:753–764

Hierarchization of Myogenic and Adipogenic Progenitors Within Human Skeletal Muscle

Skeletal muscle cells constitute a heterogeneous population that maintains muscle integrity through a high myogenic regenerative capacity. More unexpectedly, this population is also endowed with an adipogenic potential, even in humans, and intramuscular adipocytes have been found to be present in several disorders. We tested the distribution of myogenic and adipogenic commitments in human muscle‐derived cells to decipher the cellular basis of the myoadipogenic balance. Clonal analysis showed that adipogenic progenitors can be separated from myogenic progenitors and, interestingly, from myoadipogenic bipotent progenitors. These progenitors were isolated in the CD34+ population on the basis of the expression of CD56 and CD15 cell surface markers. In vivo, these different cell types have been found in the interstitial compartment of human muscle. In vitro, we show that the proliferation of bipotent myoadipogenic CD56+CD15+ progenitors gives rise to myogenic CD56+CD15− progenitors and adipogenic CD56−CD15+ progenitors. A cellular hierarchy of muscle and fat progenitors thus occurs within human muscle. These results provide cellular bases for adipogenic differentiation in human skeletal muscle, which may explain the fat development encountered in different muscle pathological situations. STEM CELLS 2010;28:2182–2194

Mouse model of skeletal muscle adiposity: A glycerol treatment approach

Fat cell accumulation in skeletal muscle is a major characteristic of various disorders, such as obesity, sarcopenia and dystrophies. Moreover, these fat cells could be involved in muscle homeostasis regulation as previously described for adipocytes in bone marrow. Despite recent advances on the topic, no clearly characterized mouse model is currently available to study fat accumulation within skeletal muscle. Here, we report a detailed characterization of a mouse model of skeletal muscle fat cell accumulation after degeneration induced by intra-muscular injection of glycerol. Information is provided on the kinetics of degeneration/fat deposition, including the quantity of fat deposited based on various parameters such as glycerol concentration, age, sex and strain of mice. Finally, these fat cells are characterized as true white adipocytes morphologically and molecularly. Our study shows that the mouse adipocyte accumulation within skeletal muscle after glycerol degeneration is a reproducible, transposable and easy model to use. This mouse model should allow a more comprehensive understanding of the impact of adipocyte accumulation in skeletal muscle pathophysiology.

Stem Cells from Human Adipose Tissue: A New Tool for Pharmacological Studies and for Clinical Applications

Multipotent adult stem cells constitute an unlimited source of differentiated cells that could be used in pharmacological studies and in medicine. The presence of stem cells in different tissues, such as bone marrow, skin, muscle, has been reported. However, stem cells are rare in these tissues, are difficult to isolate and to maintain ex vivo. As adipose tissue allows extraction of a large volume of tissue with limited morbidity, this tissue could be an exciting alternative stem cell source. We have recently identified and isolated multipotent stem cells from adipose tissue of young donors. These cells, named human Multipotent Adipose-Derived Stem (hMADS) cells, exhibit features of stem cells, i.e. a high ability to self-renew and the capacity to differentiate in different lineages at the single cell level. The adipocyte differentiation of hMADS cells has been thoroughly studied and differentiated cells exhibit the unique characteristics of human adipocytes. The effects of HIV drugs on the development of hMADS cells into adipocytes will be discussed. Finally, the therapeutic potential of hMADS cells has been revealed after their transplantation into muscles of mdx mice, an animal model of Duchenne muscular dystrophy. Therefore, hMADS cells provides a powerful cellular model for drug screenings and their regenerative properties suggest that these cells could be an important tool for cell-mediated therapy.

Adipose-Derived Stem Cells and Skeletal Muscle Repair

Treatments for muscular dystrophies constitute the goal of a very active field of research, and the characteristics of mesenchymal stem cells make them promising alternative candidates for cell-based therapy. In this context, adipose-derived stem cells (ADSCs) present very interesting intrinsic features in terms of abundance and easy access. Their myogenic potential has been investigated since the early 2000s. A synthesis of the findings is presented in this chapter. In fact, ADSCs harbor a limited autonomous myogenic differentiation potential. However, this capacity is increased when ADSCs are engrafted in a regenerating muscle. Very recently, it has been reported that an explanation for the relatively modest myogenic potential of ADSCs is that only a small perivascular cell subfraction carries an efficient myogenic potential. From a clinical perspective, significant results have been obtained by genetic modification of the whole ADSC population. Human ADSCs modified with MyoD, a master gene of embryonic myogenesis, have been shown in vitro and in vivo to be as myogenic as genuine myoblasts, and these cells are now being studied in animal models of dystrophic muscles.