Evidence that increased 12-lipoxygenase activity induces apoptosis in fibroblasts

The 12-lipoxygenase (LO) enzyme has been implicated in playing a role in pa ncreatic beta cell inflammatory damage and atherosclerosis. 12-LO reacts wi th fatty acids to form hydroperoxides which may alter cellular growth. In t his study we investigated the direct effect of mouse leukocyte type 12-LO c DNA overexpression on apoptosis in Chinese hamster ovary fibroblast cells t hat also stably overexpress the angiotensin II type 1a receptor. CHO-AT1a c ells expressing background levels of 12-LO exhibited clear increases in gro wth in response to angiotensin II. in contrast, the new 12-LO transfected c ells (CHO-AT1 a/ML12-LO cells) displayed reduced basal and angiotensin II-i nduced growth compared to CHO-AT1a cells. Furthermore, serum-deprivation re sulted in a significantly greater number of non-viable cells in clones havi ng the greatest magnitude of 12-LO overexpression. These results suggested that reduction of the proliferation rate of CHO-AT1a/ML12-LO cells was due to an increasing rate of cell death. To determine whether the increase in c ell death was due to apoptosis, we evaluated nuclear DNA fragmentation, cel l morphologic changes, and activation of caspase-3. Cells overexpressing 12 -LO cDNA displayed all these changes characteristic of apoptosis. In additi on the 12-LO product, 12-hydroperoxyeicosatetraenoic acid(12-HPETE), direct ly induced apoptosis in CHO-AT1a cells. These results demonstrate for the f irst time that 12-LO activation can lead to apoptosis in fibroblasts, sugge sting a role of 12-LO in leading to inflammatory mediated cellular damage. (C) 2001 Wiley-Liss Inc.