Caveolin-1 knockout mice exhibit airway hyperreactivity

Abstract

Although caveolins have been found in endothelium and epithelium (where they regulate nitric oxide synthase activity), their role in smooth muscle is still under investigation. We and others have previously shown that caveolae of human airway smooth muscle (ASM), which express caveolin-1, contain Ca 2ϩ and force regulatory proteins and are involved in mediating the effects of inflammatory cytokines such as TNF-␣ on intracellular Ca 2ϩ concentration responses to agonist. Accordingly, we tested the hypothesis that in vivo, absence of caveolin-1 leads to reduced airway hyperresponsiveness, using a knockout (KO) (Cav1 KO) mouse and an ovalbumin-sensitized/challenged (OVA) model of allergic airway hyperresponsiveness. Surprisingly, airway responsiveness to methacholine, tested by use of a FlexiVent system, was increased in Cav1 KO control (CTL) as well as KO OVA mice, which could not be explained by a blunted immune response to OVA. In ASM of wild-type (WT) OVA mice, expression of caveolin-1, the caveolar adapter proteins cavins 1-3, and caveolae-associated Ca 2ϩ and force regulatory proteins such as Orai1 and RhoA were all increased, effects absent in Cav1 KO CTL and OVA mice. However, as with WT OVA, both CTL and OVA Cav1 KO airways showed signs of enhanced remodeling, with high expression of proliferation markers and increased collagen. Separately, epithelial cells from airways of all three groups displayed lower endothelial but higher inducible nitric oxide synthase and arginase expression. Arginase activity was also increased in these three groups, and the inhibitor nor-NOHA (N-omega-nor-L-arginine) enhanced sensitivity of isolated tracheal rings to ACh, especially in Cav1 KO mice. On the basis of these data disproving our original hypothesis, we conclude that caveolin-1 has complex effects on ASM vs. epithelium, resulting in airway hyperreactivity in vivo mediated by altered airway remodeling and bronchodilation. Overall, in vitro data clearly demonstrate an important role for caveolin-1 in enhanced airway contractility relevant to asthma. However, the effect of altered caveolin-1 expression or function in vivo has not been examined and was the focus of this study. Based on previous work, our hypothesis was that reduced caveolin-1 results in airway hyporesponsiveness. To this end we employed the mouse lacking caveolin-1 (Cav1 KO) as a model, with ovalbumin (OVA) sensitization and challenge as a model of allergic airway hyperresponsiveness to test our hypothesis. Cav1 KO mice are known to develop pulmonary fibrosis (9,15,60), and a single study showed that these mice have reduced lung compliance and increased elastance by 3 mo of age (28), with evidence of progressively greater deposition of collagen within airways and parenchyma. Whether such changes are associated with altered airway contractility and the specific role of ASM per se have not been examined. In the present study, we compared airway structure and function in wild-type (WT) vs. Cav1 KO mice that were either unsensitized [control (CTL)] or sensitiz...

Airway smooth muscle in airway reactivity and remodeling: what have we learned?

“…Thus it could be reasoned that caveolin-1 contributes to the balance between contractile vs. proliferative phenotype of ASM in the context of inflammation but in either fashion enhance airway changes in asthma for example. Unfortunately, this distinction may not be as clear cut, as evidenced by a recent report that airways of caveolin-1 knockout mice are actually more responsive to methacholine challenge, a feature exacerbated with ovalbumin sensitization and challenge (7). However, airway thickness as well as markers of cell proliferation are increased in caveolin-1 KO mice, consistent with other in vitro data on cell proliferation.…”

“…Furthermore, signaling mechanisms within ASM itself could be involved. For example, caveolin-1 can inhibit proliferation (7,89,92), whereas the SOCE mechanisms STIM1 and Orai1 can enhance TGF-␤1-induced proliferation (79) (Fig. 5).…”

“…However, airway thickness as well as markers of cell proliferation are increased in caveolin-1 KO mice, consistent with other in vitro data on cell proliferation. Although the reasons for discrepancies between in vitro [Ca 2ϩ ] i /contractility and in vivo airway reactivity remain to be determined, the potential contribution of airway epithelial caveolin-1 itself should be considered (7,103,161,281). Certainly, caveolin-1 is associated with endothelial NOS, and, if epithelial NO is important in regulation of airway tone, then dysfunction due to lack of caveolin-1 may be contributory.…”

Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca2+ regulation in airway smooth muscle (ASM)

“…This effect on ASM force generation and contractility is mimicked in animal models following airway sensitization (Stephens et al 2003; Aravamudan et al 2012), or following cytokine exposure in ASM muscle strips (Fig. 2), or in lung slice preparations (Fig.…”

Synergistic Effects of Matrix Nanotopography and Stiffness on Vascular Smooth Muscle Cell Function

“…Notably, caveolin-1 suppression has been associated with the proliferative airway smooth muscle phenotype. 50 Of particular relevance to this study is also the fact that caveolin-1 has been shown to confer cell polarity, 51 which makes our finding that caveolin-1 is upregulated in more polarized cells, specifically those on soft ANFS, interesting. Finally, we also found that the levels of profilin-2 were upregulated in cells on nanopatterned substrata (Fig.…”