Strain increases airway smooth muscle contractile and cytoskeletal proteins in vitro

Abstract

Mechanical stress contributes to lung development and the progression of some lung diseases, although its effects on individual lung cells are unknown. Because increased airway smooth muscle (ASM) is found in lung diseases where abnormal stress is present, we determined if strain (change in resting length) causes ASM hypertrophy independently of other in vivo influences. Cultured canine ASM cells were subjected to two levels of cyclic deformational strain for 14 days and compared with nonstrained cells by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. Cells subjected to 16-30% strain demonstrated increases in total cellular protein, myosin, myosin light chain kinase (MLCK), and desmin, whereas the cellular contents of actin, vimentin, and tubulin were similar. Changes in myosin appeared mostly due to the smooth muscle isoform, whereas nonmuscle myosin was unchanged. The increases in myosin and MLCK were disproportionate to increases in total protein, suggesting selective changes in contractile proteins. These relative increases in content of proteins were not as pronounced with 0-16% strain, suggesting a graded response. These data suggest that strain per se can increase the contractile proteins of ASM cells independently of other in vivo factors and modulates cultured cell phenotype to a more differentiated state, since it increases smooth muscle-specific proteins, such as smooth muscle myosin isoforms and desmin.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma

“…These observations are consistent with decreased Rho activation, which is in contrast to the increased Rho-A activation observed in response to predominantly uniaxial strain [231] and would appear to represent anticontractile effects of strain rather than pro-contractile effects of strain as occurring with primarily uniaxial strain. Furthermore, increases in amount of myosin light chain kinase after 11 days of strain seem to occur primarily in uniaxially strained cells [243,246]. Interestingly, proliferation is reduced in cells grown on laminin and subjected to lower strains of 4% compared with cells grown on collagen with either 0 or 4% strain.…”

“…These changes depend on strain magnitude and orientation, as discussed in sections below. In several studies, SMITH and coworkers [230,[242][243][244] have demonstrated that a predominantly uniaxial (stretch in one direction) strain of ,10% applied for several days in culture increases proliferation, force generation, expression of contractile proteins, calcium sensitivity and cytoskeletal stiffness with contractile activation. Perhaps the most dramatic changes they have been shown are a doubling in shortening capacity and shortening velocity [245].…”

“…After 2-4 days, the cells in the region of predominantly uniaxial strain re-orient, forming a ring of cells aligned circumferentially, while cells in the central region do not show any particular preferred direction. Thus, over most of the dish, stretch is primarily across the ''waists'' of the cells, with very little stretch occurring along the cell's long axis [242,243]. This is illustrated in figure 3.…”

Mechanical strain increases cell stiffness through cytoskeletal filament reorganization

“…To determine GЈ using OMTC, we grew cells to ϳ90% confluence and then changed them to serum-free media supplemented with insulin and transferrin as previously described (21). After a rinse with PBS, membranes were cut from the six-well plates with a scalpel and placed in serumfree media.…”

Παράγοντες Που Επηρεάζουν Την Απελευθέρωση Του Μονοξειδίου Του Αζώτου (NO) Στους Αεραγωγούς

“…Οι ΛΜΙ αλλάζουν μήκος και φορτίο κατά τη διάρκεια της εισπνοής και της εκπνοής και οι μεταβολές αυτές του μήκους επηρεάζουν τη διάμετρο των αεραγωγών και κατά συνέπεια τη ροή του αέρα προς τους πνεύμονες. Αυτές οι μεταβολές του μήκους επιφέρουν αλλαγές στην τάση (ενεργή και παθητική) που αναπτύσουν οι ΛΜΙ [48,49] . Η παθητική τάση η οποία αναπτύσσουν οι ΛΜΙ είναι ένας σημαντικός παράγοντας για τον καθορισμό της ανταποκρισιμότητας των ΛΜΙ των αεραγωγών στην επίδραση συσπαστικών παραγόντων και φαίνεται να εμπλέκεται στην παθογένεση των αποφρακτικών νόσων των αεραγωγών όπως είναι η χρόνια αποφρακτική πνευμονοπάθεια και το άσθμα [9] .…”