Abstract 305: Tumor Necrosis Factor-α p75 Receptor, Satellite-Cell Survival, Activation and Muscle Regeneration
Aging is a risk factor for ischemic diseases. TNF-α, a pro-inflammatory cytokine, is expressed in ischemic tissues and is known to modulate angiogenesis. Little is known about the role of TNF-α receptors (TNFR1/p55 and TNFR2/p75) in angiogenic signaling and muscle regeneration. We studied neovascularization in the hind limb ischemia (HLI) model in young and old TNFR2/p75 knockout (p75KO) and wild type (WT) age-matched controls. Between days 7–10 post-HL surgery 100% of old p75KOs experienced auto-amputation of the operated limbs, whereas none of the age-matched WT mice exhibited HL necrosis. Poor blood flow recovery in p75KOs was associated with decreased capillary density and significant reduction in the expression of VEGF mRNA transcripts in ischemic tissue. Compared to presurgery, on days 1–10 post-HL surgery there was 6–10-fold increase in the number of satellite-cells (embrionic NCAM staining) in WT mice, whereas in p75KOs after day 1 through day 10 satellite cells were not detecable. Indeed, p75KO tissue showed increased and prolonged (via day 10) inflammation - neutrophil (MPO-1) and macrophage (F/480) infiltration. Transplantation of WT/GFP (+) BM mononuclear cells into γ-irradiated p75KOs one month prior to HL surgery prevented limb loss, suggesting that ischemia-induced neovascularization and mobilization of BM-derived cells is mediated, at least in part, via TNFR2/p75 expressed in BM-derived cells. In the same BM transplantation model we evaluated the rate of proliferation (Ki67 + cells) of resident GFP (−) vs BM-derived GFP (+) cells. We found that in both WT and p75KO ischemic tissue Ki67 (+) cells almost exclusively were GFP (+), indicating that only BM-derived cells proliferate in the ischemic tissue. Interestingly, Ki67/GFP (+) cells started to appear in WT tissue by day 3 through day 21, whereas in p75KO tissue first proliferative activity was detected on day 28, suggesting extremely delayed recovery and regenaration in p75KO tissue. Our study suggests that, signaling through p75 receptor is required for collateral vessel development in ischemia-induced neovascularization as well as plays a critical role in muscle regeneration and suggest a potential gene target, which could be used to improve the repair of ischemic tissue in adults.