Abstract 431: The Novel Small Leucin Rich Repeat Protein Podocan Regulates Smooth Muscle Cell Function via the Wnt Pathway
SMC function determines the clinical course of vascular disease in patients. Excessive SMC activation is associated with restenosis post PCI whereas insufficient SMC activity can result in weakening of the fibrous cap and plaque rupture. We tested the effect of the novel small leucin rich repeat protein podocan on SMC function in vitro and in vivo using a podocan deficient mouse and an arterial injury model. In addition, we examined the role of podocan in human vascular disease and its relationship with SMC growth regulatory pathways. Podocan was selectively expressed in injured arteries of WT mice during extra-cellular matrix synthesis of neointima beyween 2 and 4 weeks after injury and in SMC of human arterial lesions (n=18 human atherectomy specimens and n=8 human carotid lesions. No podocan expression was detected in non-injured arteries. Analyzing the time course of arterial repair (1, 2, and 4 week time points) we found that arterial lesion formation was accelerated in podocan −/− mice (n=21) compared to WT littermates (n=20) at 4 weeks after arterial injury (P<0.05). SMC proliferation as measured by BRDU incorporation and Ki 67 expression was increased in injured arteries of podocan −/− mice at 4 weeks (P<0.05. In vitro, proliferative and migratory activity in SMC derived from aortic explant culture was increased with podocan −/− genotype and was normalized by transfection with WT podocan gene (P<0.05. Of note, Wnt-pathway upregulation was found in podocan −/− SMC both in vitro and in vivo measuring the ratio between phosphorylated and non-phosphorylated beta-catenin and using a TOPflash reporter assay for nuclear beta-catenin/Tcf/Lef-1 transcriptional activity. Wnt inhibition normalized the proliferation of podocan −/− SMC similar to WT podocan gene transfer. Wnt-pathway activation was also observed in human coronary restenotic tissue and was associated with SMC hyperplasia and absence of extra-cellular podocan. These findings point to podocan as a novel and potent physiologic inhibitor of SMC function and implicate a possible interaction with the Wnt-pathway in mouse and human SMC in vitro and in vivo.