Regulation of contractile signaling and matrix remodeling by T-cadherin in vascular smooth muscle cells: constitutive and insulin-dependent effects

Abstract

Expression of GPI-anchored T-cadherin (T-cad) on vascular smooth muscle cells (VSMC) is elevated in vascular disorders such as atherosclerosis and restenosis which are associated with insulin resistance. Functions for T-cad and signal transduction pathway utilization by T-cad in VSMC are unknown. The present study examines the consequences of altered T-cad expression on VSMC for constitutive and insulin-induced Akt/mTOR axis signaling and contractile competence. Using viral vectors rat (WKY and SHR) and human aortic VSMCs were variously transduced with respect to T-cad-overexpression (Tcad+-VSMC) or T-cad-deficiency (shT-VSMC) and compared with their respective control transductants (E-VSMC or shC-VSMC). Tcad+-VSMC exhibited elevated constitutive levels of phosphorylated Akt(ser473), GSK3β(ser9), S6RP(ser235/236) and IRS-1(ser636/639). Total IRS-1 levels were reduced. Contractile machinery was constitutively altered in a manner indicative of reduced intrinsic contractile competence, namely decreased phosphorylation of MYPT1(thr696 or thr853) and MLC20(thr18/ser19), reduced RhoA activity and increased iNOS expression. Tcad+-VSMC-populated collagen lattices exhibited greater compaction which was due to increased collagen fibril packing/reorganization. T-cad+-VSMC exhibited a state of insulin insensitivity as evidenced by attenuation of the ability of insulin to stimulate Akt/mTOR axis signaling, phosphorylation of MLC20 and MYPT1, compaction of free-floating lattices and collagen fibril reorganization in unreleased lattices. The effects of T-cad-deficiency on constitutive characteristics and insulin responsiveness of VSMC were opposite to those of T-cad-overexpression. The study reveals novel cadherin-based modalities to modulate VSMC sensitivity to insulin through Akt/mTOR axis signaling as well as vascular function and tissue architecture through the effects on contractile competence and organization of extracellular matrix.

Keywords: Insulin resistance; Remodeling; Signal transduction; T-cadherin; Vascular smooth muscle cells.