Regulation of actin dynamics by WNT-5A: Implications for human airway smooth muscle contraction

Abstract

A defining feature of asthma is airway hyperresponsiveness (AHR), which underlies the exaggerated bronchoconstriction response of asthmatics. The role of the airway smooth muscle (ASM) in AHR has garnered increasing interest over the years, but how asthmatic ASM differs from healthy ASM is still an active topic of debate. WNT-5A is increasingly expressed in asthmatic ASM and has been linked with Th2-high asthma. Due to its link with calcium and cytoskeletal remodelling, we propose that WNT-5A may modulate ASM contractility. We demonstrated that WNT-5A can increase maximum isometric tension in bovine tracheal smooth muscle strips. In addition, we show that WNT-5A is preferentially expressed in contractile human airway myocytes compared to proliferative cells, suggesting an active role in maintaining contractility. Furthermore, WNT-5A treatment drives actin polymerisation, but has no effect on intracellular calcium flux. Next, we demonstrated that WNT-5A directly regulates TGF-β1-induced expression of α-SMA via ROCK-mediated actin polymerization. These findings suggest that WNT-5A modulates fundamental mechanisms that affect ASM contraction and thus may be of relevance for AHR in asthma.Asthma is a disease characterized by chronic inflammation of the large and small airways, and estimated to affect 235 million people worldwide 1 . A defining feature of asthma is airway hyperresponsiveness (AHR), which underlies the exaggerated bronchoconstriction response of asthmatics. While it is clear that the airway smooth muscle (ASM) is essential in mediating airway constriction typical of AHR in asthma, there remains much debate concerning the root cause of altered ASM contraction and AHR. The mass of ASM is generally greater in the airway wall of asthmatics due to cellular hyperplasia or hypertrophy, but whether or not the ASM behaves differently in terms of contractility is still controversial. Asthmatic ASM does not appear to produce more force per cell [2][3][4] , but evidence from isolated human ASM cells suggests that asthmatic ASM exhibits greater shortening capacity [5][6][7] . Not all studies have reproduced this finding in whole ASM tissue 2,4,8 , suggesting that the mechanical properties of the surrounding extracellular tissue matrix may also be altered in asthma. In this regard it is notable that the ASM of asthmatics does appear to respond differently to strain induced by tidal breathing. In healthy individuals, deep inspiration causes a bronchodilatory effect that can prevent or alleviate airway narrowing, whereas this response is largely absent in asthmatics [9][10][11][12][13] . Insights into the mechanisms that may underpin altered contractility of ASM are diverse and not fully conclusive. Some studies 5,14,15 , but not all 6,16 , show increased expression of myosin light chain kinase (MLCK) in ASM samples from asthmatics. Similarly, there may be increased abundance of myosin heavy chain in asthmatic ASM 15 , however not all studies prove this to be the case 5,16 . Other changes in asthmatic ASM cells may r...

Smooth-muscle-derived WNT5A augments allergen-induced airway remodelling and Th2 type inflammation

“…Alternatively, the high endogenous expression of WNT5A in smooth muscle may have obscured potential effects. We found that basal expression levels of WNT5A in airway smooth muscle and elastic arteries were already very high and our previous studies have shown that WNT5A in freshly isolated human ASM is higher than that in cultured human ASM cells 16 . Moreover, whereas our previous studies showed effects of WNT5A knockdown on TGF-β-induced matrix protein and α-SMA expression, recombinant WNT5A by itself did not have such effects 16 .…”

“…We found that basal expression levels of WNT5A in airway smooth muscle and elastic arteries were already very high and our previous studies have shown that WNT5A in freshly isolated human ASM is higher than that in cultured human ASM cells 16 . Moreover, whereas our previous studies showed effects of WNT5A knockdown on TGF-β-induced matrix protein and α-SMA expression, recombinant WNT5A by itself did not have such effects 16 . Collectively, these previous studies and our current findings may point towards a role of WNT5A as a facilitator, rather than instigator of airway remodelling, and that WNT5A is required but not sufficient to promote the asthmatic pathology.…”

“…2B). As we have previously shown a role for WNT5A in the TGF-β-mediated production of α-SMA and matrix proteins in human ASM 15,16 , we initially focused our attention on these parameters of airway remodelling. As expected, mice treated with OVA showed a clear trend towards thickening of smooth muscle around the airways, which appeared further elevated in the transgenic animals when assessed by immunohistochemistry ( Fig.…”

“…WNT5A increases ECM turnover in human ASM through functional interactions with TGF-β 15 . Similarly, human ASM cells require WNT5A for the TGF-β-mediated induction of alpha-smooth-muscle-actin (α-SMA) 16 . Treatment of human ASM with recombinant WNT5A promotes formation of actin filaments and increases contractility 16 .…”

“…Similarly, human ASM cells require WNT5A for the TGF-β-mediated induction of alpha-smooth-muscle-actin (α-SMA) 16 . Treatment of human ASM with recombinant WNT5A promotes formation of actin filaments and increases contractility 16 . In addition, we have shown that WNT5A is more abundantly expressed in ASM cells isolated from mild to moderate asthmatics compared to healthy controls 15 .…”