Ventricular septal defects in mice targeted deletion of versican in vascular smooth muscle cells

Abstract

Purpose: To determine the function of versican (Vcan) in the cardiovascular system in vivo, we generated the versican conditional knockout mice, in which the Vcan gene was selectively ablated in vascular smooth muscle cells (SMCs). Versican is a large secreted chondroitin sulfate proteoglycan, which is important for cardiac development, and is also implicated in adult cardiovascular disease. Four splice variants of versican (V0, V1, V2, V3) have been identified, each containing two invariant domains, an N-terminal G1 domain that interact with hyaluronan, and a C-terminal G3 domain that interact with other extracellular matrix (ECM) molecules. As it has been reported that versican knockout mice died of cardiac defects at E10.5, the role of versican in cardiac development and disease has not been completely elucidated. Methods: SM22-Cre+:Vcanflox/flox conditional knockout mice were generated by combining Cre/loxP with a Flp/FRT system. In brief, a targeting vector harboring the Vcan flox allele was constructed by franking exon2 including start codon with loxP sites in the combination of a PGK-neoR cassette flanked by the FRT sequence. After obtaining Vcanflox/flox mice, they crossbred with SM22-Cre Tg mice, and the Vcan gene was selectively ablated in SMCs. The expression of different cardiac markers and ECM molecules were analyzed using histological and biochemical methods. Results: SM22-Cre+:Vcanflox/flox mice were viable and fertile, and they can reach their lifespan. The hearts in SM22-Cre+:Vcanflox/flox newborn mice showed normal cardiac looping; however, exhibited dilated heart and ventricular septal defects (VSD). The expressions of the a-actinin in their ventricular wall, which is a marker of cardiac muscle cell, decreased compared to wild type. Furthermore, though their arterial walls were thinner than wild type, elastic lamina was formed. Conclusions: Previously we generated the versican mutant mice (VcanΔ3/Δ3) whose versican lacked the A-subdomain of the G1 domain. The VcanΔ3/Δ3 mice died at neonatal period day 0, exhibiting the dilated heart and VSD. In this study, the targeted deletion of versican in SMCs leads to moderate cardiovascular defects with the dilated heart and VSD. SMCs transduce a variety of signals from a highly structured ECM that modulate cellular differentiation, migration, and proliferation. Our results suggest that the versican expression from SMCs is important for the cardiovascular development, and this study can lead to the treatment for congenital cardiovascular disease.