Reduced expression of let‐7f activates TGF ‐β/ ALK 5 pathway and leads to impaired ischaemia‐induced neovascularization after cigarette smoke exposure

This study sought to determine the potential role of microRNAs (mi RNA s) in the detrimental effects of cigarette smoke on angiogenesis and neovascularization. Using large‐scale mi RNA profiling and qRT ‐ PCR analyses, we identified let‐7f as a pro‐angiogenic mi RNA which expression is significantly reduced in HUVEC s treated with cigarette smoke extracts ( CSE ), and in the ischemic muscles of mice that are exposed to cigarette smoke ( MES ). In a mouse model of hindlimb ischaemia, intramuscular injection of let‐7f mimic restored ischaemia‐induced neovascularization in MES . Doppler flow ratios and capillary density in ischemic muscles were significantly improved in MES treated with let‐7f mimic. Clinically, this was associated with reduced ambulatory impairment and hindlimb ischaemic damage. Treatment with let‐7f mimic could also rescue pro‐angiogenic cell ( PAC ) number and function (attachment, proliferation, migration) in MES . ALK 5 ( TGF ‐βR1), an important modulator of angiogenesis, is a target of let‐7f. Here we show that ALK 5 is increased in HUVEC s exposed to CSE and in the ischaemic muscles of MES . This is associated with a downstream activation of the anti‐angiogenic factors SMAD 2/3 and PAI ‐1. Importantly, treatment with let‐7f mimic reduces the expression of ALK 5, SMAD 2/3 and PAI ‐1 both in vitro and in vivo . Moreover, let‐7f overexpression or ALK 5 inhibition can rescue angiogenesis in HUVEC s exposed to CSE . Cigarette smoke exposure is associated with reduced expression of let‐7f and activation of the anti‐angiogenic TGF ‐β/ ALK 5 pathway. Overexpression of let‐7f using a mi RNA mimic could constitute a novel therapeutic strategy to improve ischaemia‐induced neovascularization in pathological conditions.