Compromised regulation of tissue perfusion and arteriogenesis limit, in an AT₁R-independent fashion, recovery of ischemic tissue in Cx40^-/- mice

Recently, we reported that recovery of tissue perfusion in the ischemic hindlimb was reduced, inflammatory response increased, and survival of distal limb tissue compromised in connexin 40 (Cx40)-deficient (Cx40^-/-) mice. Here we evaluate whether genotype-specific differences in tissue perfusion, native vascular density, arteriogenesis, blood pressure, and chronic ANG II type 1 receptor (AT₁R) activation contribute to poor recovery of ischemic hindlimb tissue in Cx40^-/- mice. Hindlimb ischemia was induced in wild-type (WT), Cx40^-/-, and losartan-treated Cx40^-/- mice by using surgical procedures that either maintained (mild surgery) or compromised (severe surgery) perfusion of major collateral vessels supplying the distal limb. Preand postsurgical hindlimb perfusion was evaluated, and tissue survival, microvascular density, and macrophage infiltration were documented during recovery. Hindlimb perfusion was compromised in presurgical Cx40^-/- versus WT mice despite comparable native microvascular density. Hindlimb perfusion 24 h postsurgery in Cx40^-/- and WT mice was comparable after mild surgery (collateral vessels maintained), but compromised arteriogenesis in Cx40^-/- animals nevertheless limited subsequent recovery of tissue perfusion and compromised tissue survival. Prolonged pre- and postsurgical treatment of Cx40^-/- mice with losartan (an AT₁R antagonist) normalized blood pressure but did not improve tissue perfusion or survival, despite reduced macrophage infiltration. Thus it appears Cx40 is necessary for normal tissue perfusion and for recovery of perfusion, arteriogenesis, and tissue survival in the ischemic hindlimb. Our data suggest that Cx40^-/- mice are at significantly greater risk for poor recovery from ischemic insult due to compromised regulation of tissue perfusion, vascular remodeling, and prolonged inflammatory response.