Direct evidence for tumor necrosis factor-α signaling in arteriogenesis

Background - Arteriogenesis serves as an efficient mechanism for flow restoration after arterial occlusion. This process is associated with inflammatory mediators such as tumor necrosis factor-α (TNF-α), although their role in arteriogenesis remains unclear. We hypothesized that arteriogenesis is reduced in mice lacking functional TNF-α or p55 receptor. To test this hypothesis, we developed a novel microsphere -based murine model of hindlimb perfusion measurement. Methods and Results - Unilateral femoral arteries of nude (n=9), TNF-α^-/- (n=9), TNF-α receptor p55^-/- (n=8), and p75^-/- (n=8) mice as well as their appropriate genetic background controls were occluded. The nude mice underwent laser Doppler hindlimb flux measurements preoperatively, postoperatively, and after 7 days. Seven days after ligation, all animals underwent tissue perfusion determinations using fluorescent microspheres. Laser Doppler findings confirmed acute decrease in flux with falsely normal values after 1 week. Microsphere results from control mice showed perfusion restoration to values ≈50% of normal within 7 days. TNF-α^-/- mice demonstrated a significant reduction (45.1%) in collateral artery perfusion compared with controls (TNF-α^-/- 22.4±5.1% versus B6x129 49.7±9.3%; P<0.01). p55^-/- mice exhibited an almost identical 45.8% reduction in collateral artery formation (p55^-/- 28.3±4.3% versus C57BL/6J 61.8±9.1%; P<0.01), whereas p75^-/- mice were equivalent to controls (p75^-/- 54.5±5.5%; P=0.13). Conclusions - Microsphere techniques in mice offer a tool for the molecular dissection of arteriogenesis mechanisms. These results suggest that TNF-α positively modulates arteriogenesis probably via signaling through its p55 receptor.