Abstract 234: MyD88 and TRIF Mediate Divergent Responses Following Skeletal Muscle Ischemia
Introduction: We have shown that TLR2 mediates muscle regeneration and angiogenesis after muscle ischemia, independent of TLR4. Downstream signaling of TLR2 and TLR4 include MyD88 (TLR2 and 4) and TRIF (TLR4 and 3) pathways. We hypothesize that MyD88 is required for normal angiogenesis and muscle regeneration following ischemia while TRIF is not.
Methods: MyD88 -/- (KO), TRIF KO and control C57B6 mice (WT) (N=4-7) underwent femoral artery ligation on the right hindlimb, and sham operation on the left. LDPI was performed at day 14 and anterior tibialis muscle was collected to quantify muscle necrosis and regeneration. Vascular structures were identified with CD31 staining.
Results: MyD88 KO and WT mice demonstrated partial perfusion recovery by 14 days while TRIF KO had minimal recovery. Despite this, there were significantly fewer vascular structures in MyD88 KO mice while TRIF KO had the greatest (17.9±1.5 MyD88 KO; 55.3±6.8 WT; 69.1±5.2 TRIF KO; p<0.01). TRIF KO exhibited marked muscle necrosis (43.1±19.9%) while WT and MyD88 KO had none (p<0.01) (Figure). Instead, WT had large areas of regenerating myocytes (95.8 ± 0.96%; p <0.01). Strikingly, MyD88 KO had almost no histologic evidence of ischemic injury with essentially normal muscle (85.3±12.6%, p<0.01).
Conclusions: Contrary to our hypothesis, TRIF appears to be required for normal muscle regeneration and functional angiogenesis after ischemia, while MyD88 is an important mediator of hypoxic injury. These results, along with our prior findings that muscle regeneration is independent of TLR4, suggest that TLR3 may play a key role in ischemic muscle recovery independent of angiogenesis.
- © 2012 by American Heart Association, Inc.