Splicing regulatory proteins and vascular smooth muscle diversity in development and disease

Abstract

The rat portal vein (PV) is a prototypical phasic smooth muscle (SM) and develops this phenotype in the neonatal period. Aorta and other large vessels contain tonic SM, while the small resistance arteries are of an intermediate phenotype. In several models of vascular disease the phasic SM reverts to the embryonic tonic phenotype. Much of the phenotypic diversity is generated by alternative splicing of exons for which the control mechanisms are mostly unknown. We are using the myosin phosphatase targeting subunit 1 (MYPT1) alternative exons, the splicing of which are highly regulated, to address this question. We used computational database analysis and gene expression analysis to identify the cis and trans regulators of MYPT1 alternative exon splicing. Splicing factors TIA, Raver-1 and a potentially novel PTB co-factor were repressed by 5–10 fold as the PV acquired the phasic phenotype. They were re-induced in a model of portal hypertension (PHT) in which the PV reverts to the embryonic tonic phenotype. In contrast, TRA2β, a SR protein family member was induced ~10 fold during PV development and repressed in PHT PV. Expression of other splicing regulators including SR family proteins and PTB were unchanged. We conclude that the transcription program that alters the expression of specific splicing factors may determine the vascular smooth muscle phenotype via the control of splicing of alternative exons in development and disease.