Smooth Myocytes - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 390

8.4 Airway Smooth Myocytes

8.4.1 Mechanical Loading-Induced Cytoskeleton Remodeling

Airway smooth myocyte (aSMC) is able to modify its shape, stiffness, and contrac-
tility in response to mechanical loading after adaptation of actomyosin interaction
and integrins at adhesion junctions [ 718 ].
In the tracheal muscle, strains elevate phosphorylation level of both focal
adhesion kinase and paxillin. Once phosphorylated by focal adhesion kinase, ad-
hesion complex component paxillin couples to neuronal Wiskott-Aldrich syndrome
protein (nWASP) via CRK adaptor to launch nWASP activation by activated CDC42
GTPase that binds to recruited nWASP (Vol. 1 - Chaps. 6. Cell Cytoskeleton
and 7. Plasma Membrane). The latter stimulates the ARP2-ARP3 complex that
polymerizes actin filaments.
Integrin-linked kinase and its binding partners coordinate cytoskeleton
remodeling, especially formation of structural links between integrins and the actin
cytoskeleton. Integrin-linked kinase tethers to

β 1 -integrins and can then transduce
signals from integrin receptors to regulate actin polymerization. This scaffold forms
a heterotrimer with LIMS1 adaptor (or PINCH) and -parvin that binds to actin

filaments. Enzyme ILK also connects to paxillin. In addition, LIMS1 adaptor may
couple to nWASP via NCK adaptor.

α

8.4.2 Contractile and Proliferative Phenotype

Airway smooth myocyte can evolve from a contractile to a proliferative phenotype.
When aSMCs proliferate, the content in smooth muscle -actin, high-molecular-

weight caldesmon hMW isoform, calponin, desmin, smooth muscle myosin heavy
chain, myosin light chain kinase, and

α

-tropomyosin decays. On the other hand, the
content of non-muscle myosin heavy chain, low-molecular-weight caldesmon lMW ,
vimentin, protein kinase-C

β

, and CD44 heightens (1-6 fold) when cells
divide [ 719 ]. The content in cytoskeletal proteins is greater in the trachealis muscle
than that in the media of the pulmonary artery [ 719 ]. Airway smooth myocytes
shorten faster than arterial ones.

α and -C β

8.4.3 Calcium Influx

Plasma membrane depolarization activates Ca V channels. Subsequent Ca 2 + entry
causes rapidly (in a few milliseconds) local Ca 2 + release through ryanodine