Deletion of SA β‐Gal+ cells using senolytics improves muscle regeneration in old mice

Abstract

Systemic deletion of senescent cells leads to robust improvements in cognitive, cardiovascular, and whole‐body metabolism, but their role in tissue reparative processes is incompletely understood. We hypothesized that senolytic drugs would enhance regeneration in aged skeletal muscle. Young (3 months) and old (20 months) male C57Bl/6J mice were administered the senolytics dasatinib (5 mg/kg) and quercetin (50 mg/kg) or vehicle bi‐weekly for 4 months. Tibialis anterior (TA) was then injected with 1.2% BaCl2 or PBS 7‐ or 28 days prior to euthanization. Senescence‐associated β‐Galactosidase positive (SA β‐Gal+) cell abundance was low in muscle from both young and old mice and increased similarly 7 days following injury in both age groups, with no effect of D+Q. Most SA β‐Gal+ cells were also CD11b+ in young and old mice 7‐ and 14 days following injury, suggesting they are infiltrating immune cells. By 14 days, SA β‐Gal+/CD11b+ cells from old mice expressed senescence genes, whereas those from young mice expressed higher levels of genes characteristic of anti‐inflammatory macrophages. SA β‐Gal+ cells remained elevated in old compared to young mice 28 days following injury, which were reduced by D+Q only in the old mice. In D+Q‐treated old mice, muscle regenerated following injury to a greater extent compared to vehicle‐treated old mice, having larger fiber cross‐sectional area after 28 days. Conversely, D+Q blunted regeneration in young mice. In vitro experiments suggested D+Q directly improve myogenic progenitor cell proliferation. Enhanced physical function and improved muscle regeneration demonstrate that senolytics have beneficial effects only in old mice.

Removal of p16INK4 Expressing Cells in Late Life has Moderate Beneficial Effects on Skeletal Muscle Function in Male Mice

“…Our experiments showed no difference in overall inflammatory profiles between saline treated controls (GCV − ) and GCV + mice (both male and female). Although somewhat surprising, these data are consistent with findings from two independent studies that found no change in serum/plasma cytokine levels with p16 + cell ablation and treatment with senolytics (Farr et al, 2017;Dungan et al, 2021). Similarly, we found no differences in expression of TNFα or IL-6 mRNA between GCV + and GCV − GTN muscles.…”

Cellular senescence in neuroinflammatory disease: new therapies for old cells?

“…Muscle regeneration was measured by fiber cross-sectional area. Interestingly, DQ did not improve muscle regeneration in young mice, suggesting that the framework in which senolytics are effective is affected by age in skeletal muscle [96]. Although limited to mice, these findings underline the importance of understanding how muscle tissue responds to cellular stress, and how senescence is implicated in this process.…”

“…Interestingly, treatment of old mice with the senolytic DQ resulted in enhanced muscle and muscle fiber size as well as improvements in functional testing [95,96]. In response to chemical muscle injury induced by barium chloride, muscle regeneration was improved by DQ treatment, as compared to vehicle, in old mice [96]. Muscle regeneration was measured by fiber cross-sectional area.…”

Short-term senolytic treatment: a paradigm to promote fracture repair during aging

“…Thus, proper timing and/or duration in the delivery of senotherapeutics may limit potential off-target effects, such as injury to other cell types that share markers with senescent cells. For instance, D+Q treatment improves skeletal muscle regeneration and repair after injury in aged mice, whereas it is ineffective in young mice ( 11 ). One week after muscle injury, immune-related senescence-associated cells emerge in the damaged environment, as indicated by senescence-associated β-gal (SA–β-gal), and are depleted in response to D+Q treatment ( 11 ).…”

“…For instance, D+Q treatment improves skeletal muscle regeneration and repair after injury in aged mice, whereas it is ineffective in young mice ( 11 ). One week after muscle injury, immune-related senescence-associated cells emerge in the damaged environment, as indicated by senescence-associated β-gal (SA–β-gal), and are depleted in response to D+Q treatment ( 11 ).…”