The effects of leukocyte-type 12/15-lipoxygenase on Id3-mediated vascular smooth muscle cell growth

Objective - 12/15-Lipoxygenase (12/15-LO) has been implicated in the pathogenesis of vascular disease. Vascular smooth muscle cell (VSMC) proliferation is a key component of the response to injury in vascular disease. The role of 12/15-LO in regulating VSMC proliferation is poorly understood. Id3 has been shown to regulate growth in various cell types and is expressed in VSMCs within atherosclerotic and restenotic lesions. This study examines the role of Id3 in 12/15-LO-mediated VSMC proliferation. Methods and Results - Primary aortic VSMCs from leukocyte-type 12/15-LO transgenic, leukocyte-type 12/15-LO knockout (KO), and control mice were plated in equal densities and assayed for growth, Id3 protein expression, and Id3 transcription. Results demonstrated that 12/15-LO transgenic VSMCs grew faster, whereas 12/15-LO KO VSMCs grew slower relative to control VSMCs. Further, pharmacological and molecular inhibition of 12/15-LO resulted in decreased VSMC growth. Western blots demonstrated increased Id3 protein in 12/15-LO transgenic VSMCs, whereas luciferase promoter reporter assays revealed increased Id3 transcription. In addition, overexpression of 12/15-LO increased growth in control cells but not in Id3 KO cells. 12/15-LO transgenic VSMCs demonstrated increased protein kinase C (PKC) activity. Consistent with these data, PKC inhibition decreased Id3 promoter activation. Conclusions - 12/15-LO is an important mediator of VSMC growth. The growth-promoting effects of 12/15-LO are at least partially mediated through induction of Id3 transcription.