Myogenic Potential of Muscle Side and Main Population Cells after Intravenous Injection into Sub-lethally IrradiatedmdxMice

Abstract

S U M M A R YMuscle side population (SP) cells have demonstrated hematopoietic and myogenic activities in vivo upon intravenous (IV) injection into lethally irradiated mdx mice. In contrast, muscle main population (MP) cells were unable to rescue the bone marrow of lethally irradiated mice and, consequently, their in vivo myogenic potential could not be assessed using this method. In the current study, muscle SP or MP cells derived from syngeneic wild-type male mice were delivered to sub-lethally irradiated mdx female mice by single or serial IV injections. Recipient mice were euthanized 12 weeks after transplantation at which time the quadriceps and diaphragm muscles were analyzed for the presence of donor-derived cells. Mice injected with 10 4 muscle SP cells or with 10 6 MP cells appeared to have similar numbers of dystrophin-positive myofibers containing fused donor nuclei. Analysis of the remaining tissue via real-time quantitative PCR indicated that mice injected with muscle SP cells had a higher percentage of donor-derived Y-DNA in the quadriceps than mice injected with MP cells, suggesting that muscle SP cells may be enriched for progenitors able to engraft dystrophic skeletal muscles from the circulation. Although the overall engraftment did not reach therapeutically significant levels, these results indicate that further optimization of cell delivery techniques may lead to improved efficacy of cellmediated therapy using muscle SP cells.

Satellite Cells and the Muscle Stem Cell Niche

“…Importantly, when introduced intravenously into mdx mice, muscle SP cells from wild-type mice incorporate into host myofibers and restore their dystrophin expression (27,210), suggesting these cells are able to migrate to regenerating muscles through the bloodstream. Indeed, compared with satellite cells and their derivatives, muscle SP cells are much more efficient at engrafting into mdx hosts after systemic delivery (368). Interestingly, the systemic delivery of wild-type SP cells into mdx mice can also repopulate the bone marrow of an irradiated host, although at lower efficacy compared with bone marrow-derived SP cells (210).…”

AML1/Runx1 Negatively Regulates Quiescent Hematopoietic Stem Cells in Adult Hematopoiesis

“…Chimerism assays using real-time PCR were done as previously described (23). Briefly, male bone marrow cells were serially diluted with female bone marrow cells (to contain 0, 0.1, 0.3, 1, 3, 10, 30, and 100% of male cells) for establishing standard curves, and the genomic DNA was subjected for real-time PCR amplification for Zfy2 (primers 5Ј-TGG AGA GCC ACA AGC TAA CCA-3Ј and 5Ј-TCC CAG CAT GAG AAA GAT TCT TC-3Ј) and GAPDH (primers 5Ј-GGA GAT TGT TGC CAT CAA CG-3Ј and 5Ј-GTC TCG CTC CTG GAA GAT GG-3Ј) using the SYBR Green PCR reagent kit (Invitrogen Life Technologies) and Applied Biosystems 7000 Sequence Detector.…”

“…At 4 mo after transplantation, genomic DNA was purified from the bone marrow cells. Donor cell chimerism was assayed using quantitative real-time genomic PCR targeted for the Zfy locus, which is specific for the Y chromosome (23). Mice with Ն1% test cell chimerism were treated as positive for donor cell engraftment, and CRUs were evaluated using proportions of engrafted mice and numbers of transplanted cells (28).…”

Myogenic stem cells.

“…From the other side, intravenous administration of male-derived unfractionated bone marrow cells into female mdx mice resulted in formation of dystrophinexpressing Y-chromosome-positive muscle fibers already after 8 weeks [42]. Following analogous injection of the same number of bone marrow main population (BMMP) and bone marrow side population (BMSP) the regeneration of muscle was 100 fold more effective in the case of BMSP transplantation [52]. This suggests that stem cells finding niche in skeletal muscle during postnatal life are derived mainly from bone marrow side population.…”