The ␣7␤1 integrin is a laminin receptor that has been implicated in muscle disease and the development of neuromuscular and myotendinous junctions. Studies have shown the ␣7␤1 integrin is also expressed in nonskeletal muscle tissues. To identify the expression pattern of the ␣7 integrin in these tissues during embryonic development, ␣7 integrin chain knockout mice were generated by a LacZ knockin strategy. In these mice, expression from the ␣7 promoter is reported by ␤-galactosidase. From embryonic day (ED) 11.5 to ED14.5, ␤-galactosidase was detected in the developing central and peripheral nervous systems and vasculature. The loss of the ␣7 integrin gene resulted in partial embryonic lethality. Several ␣7 null embryos were identified with cerebrovascular hemorrhages and showed reduced vascular smooth muscle cells and cerebral vascularization. The ␣7 null mice that survived to birth exhibited vascular smooth muscle defects, including hyperplasia and hypertrophy. In addition, altered expression of ␣5 and ␣6B integrin chains was detected in the cerebral arteries of ␣7 null mice, which may contribute to the vascular phenotype. Our results demonstrate for the first time that the ␣7␤1 integrin is important for the recruitment or survival of cerebral vascular smooth muscle cells and that this integrin plays an important role in vascular development and integrity. Developmental Dynamics 234:11-21, 2005.

Abstract-VascularV ascular smooth muscle cell (VSMC) proliferation and migration are major underlying factors in the development and progression of various forms of cardiovascular disease, including atherosclerosis, postangioplasty restenosis, transplant arteriopathy, and pulmonary hypertension. 1 Vascular remodeling during disease or injury involves altered expression of extracellular matrix proteins and cell surface integrins. 2-4 After arterial injury, laminin expression is reduced and fibronectin accumulates around VSMCs. 5,6 These changes coincide with a phenotypic switch in which contractile VSMCs adopt a proliferative phenotype, possibly as part of a developmental program associated with wound repair. 2,4 Integrins are transmembrane mechanosensors that relay signals from the extracellular matrix to the cell cytoskeleton and/or cell signaling pathways to modulate cell shape, adhesion, differentiation, proliferation, and contraction. 7 Various integrins modulate cell proliferation, usually by crosstalk with proliferative cell signaling pathways or in cooperation with growth factor receptors. 8 The ␣7␤1 integrin is a major laminin-binding receptor in VSMCs, and expression of this integrin increases after differentiation. 9 Previous studies using blocking antibodies and peptides have demonstrated that the ␣7␤1 integrin mediates adhesion of VSMCs to laminin in vitro. 9,10 Expression of this integrin has also been shown to be modulated by chemically induced injury and platelet-derived growth factor in cultured rat VSMCs. 10,11 We have previously demonstrated that embryonic loss of the ␣7 integrin results in vascular defects and partial embryonic lethality, whereas in adult mice, loss of the ␣7 integrin results in VSMC hyperplasia. 12 Loss of the ␣7␤1 integrin in VSMCs leads to altered expression of other integrin chains, which may contribute to the vascular phenotype observed in ␣7 integrin-null mice. 12 These observations have led to the hypothesis that the ␣7␤1 integrin promotes the contractile phenotype of VSMCs, but the mechanism of this regulation is unclear.Activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase signaling Original

Background— Recent evidence suggests that chloride channels may be involved in ischemic preconditioning (IPC). In this study, we tested whether the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channels, which are expressed in the heart and activated by protein kinase A and protein kinase C, are important for IPC in isolated heart preparations from wild-type (WT) and CFTR knockout (CFTR −/− ) mice. Methods and Results— Hearts were isolated from age-matched WT or CFTR −/− (B6.129P2-Cftr tm1Unc and STOCKCftr tm1Unc -TgN 1Jaw) mice and perfused in the Langendorff or working-heart mode. All hearts were allowed to stabilize for 10 minutes before they were subjected to 30 or 45 minutes of global ischemia followed by 40 minutes of reperfusion (control group) or 3 cycles of 5 minutes of ischemia and reperfusion (IPC group) before 30 or 45 minutes of global ischemia and 40 minutes of reperfusion. Hemodynamic indices were recorded to evaluate cardiac functions. Release of creatine phosphate kinase (CPK) in the samples of coronary effluent and infarct size of the ventricles were used to estimate myocardial tissue injury. In WT adult hearts, IPC protected cardiac function during reperfusion and significantly decreased ischemia-induced CPK release and infarct size. A selective CFTR channel blocker, gemfibrozil, abrogated the protective effect of IPC. Furthermore, targeted inactivation of the CFTR gene in 2 different strains of CFTR −/− mice also prevented IPC’s protection of cardiac function and myocardial injury against sustained ischemia. Conclusions— CFTR Cl − channels may serve as novel and crucial mediators in mouse heart IPC.

1. ClC-3 has been proposed as a molecular candidate responsible for volume-sensitive outwardly rectifying anion channels (VSOAC) in cardiac and smooth muscle cells. To further test this hypothesis, we produced a novel line of transgenic mice with cardiac-specific overexpression of the human short ClC-3 isoform (hsClC-3). 2. Northern and western blot analyses demonstrated that mRNA and protein levels of the short isoform (sClC-3) in the heart were significantly increased in hsClC-3-overexpressing (OE) mice compared with wild-type (WT) mice. Heart weight : bodyweight ratios for OE mice were significantly smaller compared with age-matched WT mice. 3. Electrocardiogram recordings indicated no difference at rest, whereas echocardiographic recordings revealed consistent reductions in left ventricular diastolic diameter, left ventricular posterior wall thickness at end of diastole and interventricular septum thickness in diastole in OE mice. 4. The VSOAC current densities in atrial cardiomyocytes were significantly increased by ClC-3 overexpression compared with WT cells. No differences in VSOAC current properties in OE and WT atrial myocytes were observed in terms of outward rectification, anion permeability (I(-) > Cl(-) > Asp(-)) and inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid and glibenclamide. The VSOAC in atrial myocytes from both groups were totally abolished by phorbol-12,13-dibutyrate (a protein kinase C activator) and by intracellular dialysis of an N-terminal anti-ClC-3 antibody. 5. Cardiac cell volume measurements revealed a significant acceleration of the rate of regulatory volume decrease (RVD) in OE myocytes compared with WT. 6. In conclusion, enhanced VSOAC currents and acceleration of the time-course of RVD in atrial myocytes of OE mice is strong evidence supporting an essential role of sClC-3 in native VSOAC function in mouse atrial myocytes.