Abstract

Vascular smooth muscle cells (VSMCs) convert from a non-proliferative, contractile phenotype to a migratory phenotype depending on the tissue context. This phenotypic switching is important for normal vascular development and in vascular pathologies. Therefore, our goal has been to understand these mechanisms. Plexin B2 (PlxnB2) is a transmembrane receptor involved in migration and axon targeting in neurons, and is expressed in VSMCs.  We hypothesize it may be involved in conversion to a migratory phenotype in VSMCs. PlxnB2 was knocked down in rat VSMCs using lentivirus carrying PlxnB2 or control shRNA.  Cells were treated with PDGF to induce the phenotypic switch. We analyzed expression of SM22 and MMP-2 (markers for the contractile/proliferative state) by qRT-PCR, quantified focal adhesions, measured cell proliferation by EdU assay, and performed migration assays. Knockdown of PlxnB2 in VSMCs resulted in 50% fewer EdU positive cells after 24 hours of PDGF treatment compared to controls, and resulted in a 56% reduction in PDGF-induced migration. PlxnB2 knockdown also partially blocked PDGF-induced upregulation of MMP2 and downregulation of SM22.  Analysis of focal adhesions is ongoing. These data support our hypothesis that PlxnB2 plays a role in phenotypic switching in VSMCs, and suggest that PlxnB2 is important for the conversion to a migratory phenotype.  Future work will focus on understanding molecular pathways tying PlxnB2 to cell migration and down-regulation of the contractile gene program.