MECHANICAL STRAIN INDUCES CONSTITUTIVE AND REGULATED SECRETION OF GLYCOSAMINOGLYCANS AND PROTEOGLYCANS IN FETAL LUNG-CELLS

We have previously shown that an intermittent strain regimen, which si mulates fetal breathing movements, enhanced mixed fetal rat lung cell proliferation in organotypic culture. As glycosaminoglycans (GAGs) and proteoglycans (PGs) may modulate growth factor activities, we investi gated the effect of intermittent strain on the formation and secretion of GAGs and PGs. Mechanical strain increased the incorporation of [H- 3]glucosamine and (SO4)-S-35 into GAGs and promoted the release of GAG s into the medium. The composition of the individual GAC molecules was not altered by strain. Mixed fetal lung cells subjected to strain sec reted more [S-35]biglycan into the medium than static controls but big lycan mRNA expression was not significantly altered. As mechanical str ain primarily affected the secretion of GAGs and PGs, we then investig ated which secretory pathways were stimulated by strain. Fetal lung ce lls secreted GAGs mainly through a constitutive (basal) pathway which was stimulated by strain. In contrast to static cultures, strain-induc ed constitutive secretion was partially blocked by the cytoskeletal di srupters colchicine and cytochalasin B, but not by the small G-protein inhibitors N-acetyl-S-farnesyl-L-cysteine and perillic acid.This resu lt suggests that strain-induced constitutive export of GAGs depends on the functional integrity of the cytoskeleton. Strain also triggered t he regulated secretion of GAGs. The strain-induced regulatory pathway in fetal lung cells was blocked by ionomycin, BAPTA/AM and gadolinium, suggesting that strain stimulated the regulatory pathway hy inducing a rapid calcium influx via a stretch-activated ion channel. We conclud e that mechanical strain of mixed fetal lung cells stimulates GAG and PG exocytosis via activation of both the regulated and constitutive pa thways.