Myogenic fusion of human bone marrow stromal cells, but not hematopoietic cells

Abstract

IntroductionRecent reports suggest that bone marrow-derived cells can be detected in regenerated muscle tissue of mice. [1][2][3][4] In addition, bone marrow transplantation in the dystrophin mutant (mdx) mouse, a model for Duchenne muscular dystrophy (DMD), resulted in the detection of donor cell-derived dystrophin in affected muscle fibers. 5,6 The presence of donor cells in muscle fibers was also observed in a patient with DMD who received an allogeneic marrow transplantation at one year of age. 7 However, in both the mdx mouse and the patient with DMD, the contribution of donor cells to affected muscle was very low and did not impact muscle function. 7,8 Whether this low frequency event represents transdifferentiation of marrow stem cells into muscle or rare fusion events remains controversial. [9][10][11] Resolving this controversy is critical for understanding the real potential and limitations of marrow transplantation. In addition, understanding how marrow cells contribute, even as rare events, to myogenesis is an important step toward developing strategies to increase the frequency of these events. We hypothesized that, regardless of the mechanism, bone marrowderived cells could be therapeutically valuable if a higher frequency of donor cell contribution to myogenesis could be achieved. This concept is supported by studies in which wild-type mesoangioblast cells were shown to rescue the ␣-sarcoglycan null dystrophic mice through myogenic fusion. 12 To identify human marrow cells with myogenic fusion potential we investigated the ability of human cells to contribute to myogenesis using first a xenogeneic in vitro model combining mouse C2C12 myoblasts with various subsets of human marrow cells, and second using an in vivo regeneration model. C2C12 cells represent an early stage of muscle differentiation. Depending on the culture conditions, they can either proliferate as myoblasts or differentiate into myotubes. 13 Previous studies have shown that coculturing C2C12 cells with dermal fibroblasts resulted in cell fusion and the subsequent correction of the dysgenic membrane in regenerating muscle. [14][15][16] The myogenic potential of neural stem cells was also demonstrated by coculture with C2C12 cells. 17,18 In this report we cocultured human hematopoietic and nonhematopoietic bone marrow cells with C2C12 and found that stromal cells have a significantly greater potential to contribute to myotube formation than enriched populations of hematopoietic progenitor cells, and that this contribution is due to cell fusion. Human stromal cells also contributed to regenerating muscle in vivo in the nonobese diabetic-severe combined immunodeficient (NOD/SCID) ␤2m Ϫ/Ϫ mouse. Materials and methods Human cell preparationsHuman CD34 ϩ cells from cadaveric marrow were provided by the Cellular Therapy Laboratory, Fred Hutchinson Cancer Research Center (FHCRC). Flow sorting was used to prepare CD34 ϩ and CD34 ϩ /CD38 Ϫ populations, both more than 95% pure. A more differentiated CD33 ϩ population was expanded from the CD34...

Splenic CD19−CD35+B220+ cells function as an inducer of follicular dendritic cell network formation

“…Spontaneous cell fusion can also take place in stem cells and cancer cells in vivo and in vitro and is attributed to the possible plasticity of these cells. 19,[41][42][43] Our observation is also consistent with previous findings that freshly isolated FDCs as well as long-term cultured FDC-like cells show the double-nuclear phenotype. 44,45 Nevertheless, most of the FDCs found in splenic white pulp as well as the reticular cells that differentiated from CD35 ϩ B220 ϩ cells have a single nucleus.…”

Multipotent adult progenitor cells sustain function of ischemic limbs in mice

“…Despite the presence of skeletal muscle precursors in BM (18), mBMCs also failed to differentiate in situ into SkMBs. This is in agreement with the observation that cells with high fusion capability mainly reside in the stromal fraction, while only a small fraction of the hematopoietic lineage is fusigenic (34). Other nonmuscle-derived cell types have shown the potential to contribute to SkMBs in ischemic muscle, e.g., CD34 + or CD34 + KDR + cord blood cells (10,13), the immortalized CD34 -R26 cell line generated from peripheral blood (35), or ADSCs (36).…”

Satellite Cells and the Muscle Stem Cell Niche

“…It was also demonstrated that Mac-1 low bone marrow SP cells, particularly those c-Kit ϩ /CD11b Ϫ immature cells, were able to generate myofibers (147,382). On the other hand, mesenchymal stem cells were able to incorporate into myofibers in injured muscles (140,488) and gave rise to Pax7 ϩ satellite cells, which can support multiple rounds of muscle regeneration (140). Interestingly, the high myofiber turnover rate induced by muscle stress and injury seems to facilitate bone marrow cell engraftment into regenerating muscles (1,68,287,460,487).…”