HYPOXIA REGULATES BASAL AND INDUCED DNA-SYNTHESIS AND COLLAGEN TYPE-IPRODUCTION IN HUMAN CARDIAC FIBROBLASTS - EFFECTS OF TRANSFORMING-GROWTH-FACTOR BETA(1), THYROID-HORMONE, ANGIOTENSIN-II AND BASIC FIBROBLAST GROWTH-FACTOR

Analysis of post-infarct ventricular remodeling consistently shows the accumulation of collagen in failing heart. The goal of this study was to gain insights into the underlying mechanisms of this event. We det ermined the effect of hypoxia, caused as the result of ischemia, on bi ological responses including cell viability, basal and growth factor-s timulated proliferative capacity and collagen type I production in car diac fibroblasts obtained from adult human heart. The cell viability, as examined by light microscopy and analysis of DNA, did not change by hypoxia (2% oxygen), Basal level of protein synthesis, as determined by measuring the incorporation of H-3-leucine, decreased (30%, P<0.05) under hypoxia, Transforming growth factor-beta (TGF-beta(1))-and thyr oid hormone (T-3)-induced increases in protein synthesis did not chang e under hypoxia. In contrast, basic fibroblast growth factor (bFGF)-st imulated protein synthesis enhanced significantly under hypoxia, Angio tensin II (Ang II)-treatment, which did not induce significant changes in protein synthesis under ambient conditions, led to moderate but si gnificant increase under hypoxia, Basal level of DNA synthesis, as det ermined by measuring the incorporation of H-3-thymidine into DNA, decr eased (32%, P<0.05) under hypoxia. The TGF-beta(1)-induced inhibition of DNA synthesis which was observed under ambient conditions was rever sed [61% (P<0.005) increase under hypoxia]. Under ambient conditions, T-3, Ang II and bFGF stimulated DNA synthesis and their effects were e nhanced under hypoxia, Northern analysis showed a 46% (P<0.05) increas e in the level of pro alpha(1)(l) collagen mRNA under hypoxia, The TGF -beta(1)-induced increase in the level of pro alpha(1)(l) collagen mRN A, under ambient conditions, was not observed under hypoxia. On the ot her hand, the T-3-induced decrease in pro alpha(1)(l) collagen mRNA wa s reversed under hypoxia, Ang II- and bFGF-treatment of human cardiac fibroblasts did not cause detectable changes in the level of pro alpha (1)(l) collagen mRNA under ambient conditions or hypoxia. At the prote in level, the amount of immunoreactive collagen type I, as determined by immunoslot blot analysis, was increased (33%, P<0.05) under hypoxia . Treatment of human cardiac fibroblasts with TGF-beta(1) and T-3 unde r ambient conditions led to diminished level of collagen type I, Under hypoxia, however, effect of both factors was reversed. The level of i mmunoreactive collagen type I in Ang II- and bFGF-treated cells, which was comparable to that in untreated cells under ambient conditions, r emained unchanged under hypoxia, Together, these results provide evide nce that hypoxia regulates growth, proliferative capacity and collagen type I production in human cardiac fibroblasts, and that although hyp oxia alone may not be a stimulus for human cardiac fibroblast prolifer ation, it enhances growth factor-induced DNA synthesis in those cells. Furthermore, hypoxia bg increasing the basal levels of collagen type I and by reversing the TGF-beta(1)- and T-3-induced inhibition of coll agen type I gene expression in human cardiac fibroblasts can enhance o verall collagen type I production. Combinatorial effects of hypoxia on proliferation and collagen type I production in cardiac fibroblasts c ontribute to the post-infarct remodeling of the collagen matrix in fai ling human heart. (C) 1997 Academic Press Limited.