Abstract 654: XBP1 Splicing is Involved in Endothelial and Smooth Muscle Cells Interaction

Abstract

Background: The X-box binding protein 1 (XBP1) is a stress inducible transcription factors, essential for cell survival under stress conditions. Our previous studies have revealed that XBP1 participates in endothelial cell (EC) proliferation, autophagic response and survival and in smooth muscle cell (SMC) proliferation. Whether XBP1 is involved in EC/SMC interaction remains unclear. Methods and Results: In this study, we first performed hindlimb ischemia model in XBP1loxP/loxP and SM22-Cre+/XBP1loxP/loxP mice. The XBP1 deficiency in SMCs significantly attenuated the recovery of foot blood perfusion in ischemic mice. Immunofluorescence staining revealed that ECs lost contact to each other in XBP1 deficient mice, suggesting that XBP1 in SMCs may contribute to EC/SMC interaction. The conditioned medium from Ad-XBP1s-infected SMCs increased EC migration and proliferation. The conditioned medium from Ad-XBP1s-infected ECs also increased SMC migration but suppressed SMC proliferation. The migration effect could be attenuated by depletion with anti-col4A1 antibody. Proteomics analysis and Western blot assays demonstrated that over-expression of the spliced XBP1 in SMCs increased the secretion of a 50KD band of collagen IVα1. RT-PCR analysis indicated that this 50KD band might be derived from an unconventional splicing, in which exon 4 and exon 42 directly joins together, resulting in a 533 amino acid peptide with the internal part shortened. Further experiments with immunohistological staining revealed that a functional XBP1 was essential to collagen IVα1 expression during embryonic development. Very little amount of collagen IV could be observed in XBP1-/- embryos. Conclusion: XBP1 in SMCs may modulate EC-SMC interaction via regulation of collagen IV expression and splicing, which may contribute to vasculature remodelling.