Abstract 10741: Lamin-Associated Protein 2a (Lap2a) is a Novel Regulatory Switch for the Vascular Smooth Muscle Cell Contractile Gene Program
LAP2α is a nucleoplasmic protein that interacts with A-type lamins. LAP2α is known to affect the E2F/retinoblastoma pathway and thus, controls the proliferation/differentiation balance of early progenitor cells. Accordingly, we hypothesized that LAP2α plays a key role in modulating the phenotype of vascular smooth muscle cells (VSMCs), especially in the regulation of differentiation and proliferative phenotypes. Isolation of mouse aortic SMCs revealed LAP2α expression (mRNA and protein) and an upregulation (50±6%) in initial phases of growth culture and proliferation. To induce differentiation we maintained VSMCs in Basal Medium (48h); to induce de-differentiation we then stimulated with PDGFbb (25ng/mL, 24h) or 10% Serum (24h). VSMCs from LAP2α-/- mice proliferated in Basal Medium. Proliferation, as indicated by EdU staining, showed a 1015±160% increase in LAP2α-/- compared to WT. Immunostaining revealed LAP2α-/- VSMCs have positive nuclear ERK1/2 and E2F1 during differentiation with Basal Medium, which is consistent with the signaling events in progenitor cells that control the phenotype. We next analyzed gene expression of known E2F1 target genes. qRT-PCR revealed 150±13% increase in proliferation and migration-related genes (Cdc25, Ctgf, Mmp2) compared to WT. A Boyden Chamber assay confirmed that LAP2α-/- cells migrate 118±71% more in comparison with WT under Basal Medium conditions. Surprisingly, the evaluation of Myocardin and Contractile SM markers (MHC, SM-α-actin) revealed that their expression is 40±11% upregulated in LAP2α-/- VSMCs (compared to WT VSMCs) in Basal Medium, even though these cells functionally proliferate and migrate more than WT. This upregulation is maintained in all other cell culture conditions. In summary, LAP2α-/- mouse primary VSMCs have an atypical phenotype in that these cells express markers of a contractile phenotype (Myocardin, SM-α-actin, MHC) during proliferation. This identifies LAP2α as a new regulator of VSMC phenotype and suggests that a contractile phenotype is not mutually exclusive from a proliferative/synthetic phenotype in vascular smooth muscle.
- © 2013 by American Heart Association, Inc.