Reduced growth factor responses in vascular smooth muscle cells derived from 12/15-lipoxygenase-deficient mice

Biochemical and genetic evidence support the involvement of leukocyte- type 12/15-lipoxygenase enzyme and its products in the atherogenic process. We recently showed that products of the 12/15-lipoxygenase pathway play an important role in mediating hypertrophy, matrix protein production, and inflammatory gene expression in vascular smooth muscle cells (VSMC) through activation of mitogen activated protein kinases and key transcription factors. The current study is aimed at establishing the in vivo role of 12/15-lipoxygenase in VSMC by comparing growth factor-induced responses in VSMC derived from 12/15-lipoxygenase knockout mice versus genetic control wild-type mice. In the lipoxygenase knockout cells, 12/15-lipoxygenase protein was not expressed, and levels of its product, 12(S)-hydroxyeicosatetraenoic acid, were reduced (51% of wild type). Knockout cells exhibited significantly lower rates of growth factor-induced migration, fibronectin production, and incorporation of H-3-thymidine and H-3-leucine (54%, 55%, 61%, and 57% of wild type, respectively). Growth factor-induced superoxide production and p38 mitogen-activated protein kinase activation were also reduced in knockout cells. Serum-stimulated AP-1 transcription factor activation was markedly reduced (50% of wild type), whereas cAMP response element binding protein activation was abrogated in knockout cells. Furthermore, growth factor-induced mRNA expression of immediate early genes and fibronectin were also greatly reduced. These results suggest that the modulation of specific signaling pathways and growth-responsive genes may be responsible for the altered growth factor responses in the lipoxygenase knockout cells. They also demonstrate the important in vivo role of vascular 12/15-lipoxygenase in VSMC growth, migration, and matrix responses associated with hypertension, atherosclerosis, and restenosis.