Regenerative Capacity of Old Muscle Stem Cells Declines without Significant Accumulation of DNA Damage
Figure 2
Assessment of satellite cell radiosensitivity and DNA repair pathways with age.
(A–B) The expression of major proteins involved in homologous recombination and non-homologous end joining were detected using western blotting. Protein nuclear extracts were prepared from activated satellite cells 72 hours post muscle injury. Lamin B was used as an internal loading control. (A) Representative images of western blots. (B) Quantification using Image J software. Data represent the mean +/− SEM, n = 3 to 5 (n = a pool of muscles from 3 mice), two-tailed unpaired Student's t-test, no significant difference. (C) Graphical representation of data from Table S1. Gene expression of old relative to young satellite cells are presented as fold change with a 95 percent confidence interval for the 12 genes with a statistically significant relative expression, n = 3 mice per group, two-tailed unpaired Student's t-test, *: p value<0.05. The dotted line represents the young level. BER: Base Excision Repair, NER: Nucleotide-Excision Repair; MR: Mismatch Repair, DRR: DNA Repair Related. (D–E) Satellite cells were freshly isolated from uninjured (D) or 72 hours after injury (E) muscle of C57BL/6 young and old mice, and of young SCID mice. Cells were plated at low density, irradiated at indicated Gray (Gy) doses, and cultured for 10 days. Myogenic colonies formed by irradiated cells were quantified and represented relative to their respective non-irradiated controls. On average, 178, 77, and 228 myogenic colonies were scored per mouse for young, old, and SCID uninjured non-irradiated respectively and 67, 34, and 91 myogenic colonies were scored per mouse for young, old, and SCID injured non-irradiated respectively. Data represent the mean +/− SEM, n = 3 to 4 mice per group, two-tailed unpaired Student's t-test, a, b or c: p value<0.05, (a: young vs old, b: young vs SCID, c: old versus SCID).