Myosin, Transgelin, and Myosin Light Chain Kinase

Abstract

Rationale: Airway smooth muscle (SM) of patients with asthma exhibits a greater velocity of shortening (Vmax) than that of normal subjects, and this is thought to contribute to airway hyperresponsiveness. A greater Vmax can result from increased myosin activation. This has been reported in sensitized human airway SM and in models of asthma. A faster Vmax can also result from the expression of specific contractile proteins that promote faster cross-bridge cycling. This possibility has never been addressed in asthma. Objectives: We tested the hypothesis that the expression of genes coding for SM contractile proteins is altered in asthmatic airways and contributes to their increased Vmax. Methods: We quantified the expression of several genes that code for SM contractile proteins in mild allergic asthmatic and control human airway endobronchial biopsies. The function of these contractile proteins was tested using the in vitro motility assay. Measurements and Main Results:We observed an increased expression of the fast myosin heavy chain isoform, transgelin, and myosin light chain kinase in patients with asthma. Immunohistochemistry demonstrated the expression of these genes at the protein level. To address the functional significance of this overexpression, we purified tracheal myosin from the hyperresponsive Fisher rats, which also overexpress the fast myosin heavy chain isoform as compared with the normoresponsive Lewis rats, and found a faster rate of actin filament propulsion. Conversely, transgelin did not alter the rate of actin filament propulsion. Conclusions: Selective overexpression of airway smooth muscle genes in asthmatic airways leads to increased Vmax, thus contributing to the airway hyperresponsiveness observed in asthma.

Gene expression in asthmatic airway smooth muscle: a mixed bag

“…Isoforms of MYH11, including SMA, SMB, and SM2 were shown to be upregulated at the gene level in asthmatics when compared with non-asthmatics (Léguillette et al 2009) and were negatively correlated with PC 20 values; however, these findings did not agree with the results of previous studies (Ammit et al 2000;Ma et al 2002;Woodruff et al 2004). Ma et al did not detect SMB in their samples, only SMA (Ma et al 2002).…”

“…Interestingly, there was a further increase in the levels of smMLCK in severe asthmatics compared with those with milder disease. Leguillette et al showed increased expression of smMLCK mRNA by quantitative PCR in biopsies from mild to moderate asthmatics (Léguillette et al 2009). The expression of smMLCK protein in the ASM was verified by IHC but not quantified.…”

“…It has been postulated that increased expression of ␣-SMA or cytoskeletal actins may contribute to the lack of effect of deep inspiration seen in asthmatics (Scichilone et al 2000) by increasing stiffness and making the muscle more resistant to the force reduction caused by oscillating strain (Wang et al 2000;Chin et al 2012). However, to date no difference in the expression of ␣-SMA in ASM from asthmatics and non-asthmatics has been reported (Woodruff et al 2004;Léguillette et al 2009). …”

“…There is little knowledge about the function of TAGLN in ASM, and whether it is over-expressed in the ASM of asthmatics is debated (Woodruff et al 2004;Léguillette et al 2009). While Léguillette et al were able to show an increase in TAGLN mRNA expression in asthmatic airway biopsies, Woodruff et al did not detect a difference in their sample of asthmatics, although it should be noted that this was a small sample size.…”

Suppression of Eosinophil Integrins Prevents Remodeling of Airway Smooth Muscle in Asthma

“…Non-canonical Wnt signaling activated via WNT-5a ligand is involved in adult tissue homeostasis (Logan and Nusse, 2004; Clevers, 2006). ASM remodeling is mainly characterized by increased muscle mass because of cell hyperplasia and hypertrophy, but increased production of specific types of ECM proteins is also an important step in ASM abnormalities in asthma, as the ASM bundle thickens and expresses more ECM and contractile proteins compared with healthy people (Woodruff et al, 2004; Léguillette et al, 2009; James et al, 2012). In the current study, we sought to better understand and to control eosinophil-induced ASM remodeling caused by altered ASM cell proliferation and ECM protein production.…”