Long-Term Contribution of Human Bone Marrow Mesenchymal Stromal Cells to Skeletal Muscle Regeneration in Mice

Abstract

Mesenchymal stromal cells (MSCs) are attractive for cellular therapy of muscular dystrophies as they are easy to procure, can be greatly expanded ex vivo, and contribute to skeletal muscle repair in vivo. However, detailed information about the contribution of bone marrow (BM)-derived human MSCs (BM-hMSCs) to skeletal muscle regeneration in vivo is very limited. Here, we present the results of a comprehensive study of the fate of LacZ-tagged BM-hMSCs following implantation in cardiotoxin (CTX)-injured tibialis anterior muscles (TAMs) of immunodeficient mice. β-Galactosidase-positive (β-gal(+)) human-mouse hybrid myofibers (HMs) were counted in serial cross sections over the full length of the treated TAMs of groups of mice at monthly intervals. The number of human cells was estimated using chemiluminescence assays. While the number of human cells declined gradually to about 10% of the injected cells at 60 days after transplantation, the number of HMs increased from day 10 onwards, reaching 104 ± 39.1 per TAM at 4 months postinjection. β-gal(+) cells and HMs were distributed over the entire muscle, indicating migration of the former from the central injection site to the ends of the TAMs. The identification of HMs that stained positive for human spectrin suggests myogenic reprogramming of hMSC nuclei. In summary, our findings reveal that BM-hMSCs continue to participate in the regeneration/remodeling of CTX-injured TAMs, resulting in ±5% HMs at 4 months after damage induction. Moreover, donor-derived cells were shown to express genetic information, both endogenous and transgenic, in recipient myofibers.

Trends in Mesenchymal Stem Cells' Applications for Skeletal Muscle Repair and Regeneration

“…Today, based on the acquired evidence, the scientific community tends toward the fusion theory. As mentioned earlier, MSCs have been demonstrated to successfully fuse to host cells and contribute with genetic information, leading to the expression of human-derived genes and gene products [2,79,88]. Fusion efficiency seems to differ among MSCs sources, and AT-MSCs appear more prone to in vivo formation of hybrid myotubes, surpassing BM-MSCs and SM-MSCs [74].…”

“…It is set that the engraftment potential of MSCs into a damaged tissue is not absolute. The numbers or percent of cells identified at different time points following injection invariably decreases [76,85,87,88], down to nearly as little as 10% of the initially delivered numbers in a couple of months [88].…”

“…As suggested by some authors, the different engraftment potential might be due to the distinct MSC sources reported [35,74], but it may also relate to the chosen disease model: dystrophic muscle models seem to better adopt exogenous cells than non-dystrophic-induced lesion models [88]. Although some disease models, especially of degenerative nature, seem to display sex-related differences, physical models of skeletal muscle lesions appear to respond similarly, at least in terms of functional recuperation.…”

“…SM-MSCs are detectable integrated within host tissue for up to 6 months after either local or systemic delivery, demonstrating their preferential homing ability to the injured tissues since greater numbers were harbored by the injured muscle, although they could seldom be identified in other body systems [2]. At longer terms after BM-MSC [88] or UC-MSC [76] administration, about 5% of myofibers were of hybrid nature and could be identified along the whole muscle length [88]. The hybrids' formations seem to be a progressive process since hybrid myofibers represent a much smaller fraction (under 1%) in the regenerating muscle at shorter time points [74].…”

“…Nonmuscular sources seem to behave closer to MPCs in terms of niche replenishment. Based on the location of the remaining delivered cells not associated to hybrid fibers, some authors suggest that these residual donor-derived cells might have also contributed to the resident SCs pool, and that they can effectively contribute to skeletal muscle regeneration in the events of a new injury [2,35,76,88]. Alike exogenous SCs and MPCs integrated into the resident quiescent pool, other sources of engrafted cells are amenable of activation upon reinjury of the muscle [2,35] and can be reisolated [35] and also originate primary myoblast cultures in vitro [2].…”