T-cadherin promotes vascular smooth muscle cell dedifferentiation via a GSK3β-inactivation dependent mechanism.

Participation of the cadherin superfamily of adhesion molecules in smooth muscle cell (SMC) phenotype modulation is poorly understood. Immunohistochemical analyses of arterial lesions indirectly suggest upregulated expression of atypical glycosylphosphatidylinositol-anchored T-cadherin on vascular SMCs as a molecular indicator of the dedifferentiated/proliferative phenotype. This study investigated the role of T-cadherin in SMC phenotypic modulation. Morphological, molecular and functional SMC-signature characteristics of rat, porcine and human arterial SMCs stably transduced with respect to T-cadherin upregulation (Tcad+) or T-cadherin-deficiency (shTcad) were compared with their respective control transductants (E-SMCs or shC-SMCs). Tcad+-SMCs displayed several characteristics of the dedifferentiated phenotype including loss of spindle morphology, reduced/disorganized stress fiber formation, decay of SMC-differentiation markers (smooth muscle α-actin, smooth muscle myosin heavy chain, h-caldesmon), gain of SMC-dedifferentiation marker calmodulin, reduced levels of myocardin, nuclear-to-cytoplasmic redistribution of the myocardin related transcription factors MRTFA/B and increased proliferative and migratory capacities. T-cadherin depletion enforced features of the differentiated SMC phenotype. PI3K/Akt is a major signal pathway utilized by T-cadherin in SMCs and we investigated mTORC1/S6K1 and GSK3β axes as mediators of T-cadherin-induced dedifferentiation. Inhibition of mTORC1/S6K1 signalling by rapamycin suppressed proliferation in both E-SMCs and Tcad+-SMCs but failed to restore expression of contractile protein markers in Tcad+-SMCs. Ectopic adenoviral-mediated co-expression of constitutively active GSK3β mutant S9A in Tcad+-SMCs restored the morphological and molecular marker characteristics of differentiated SMCs and normalized rate of proliferation to that in control SMCs. In conclusion our study demonstrates that T-cadherin promotes acquisition of the dedifferentiated phenotype via a mechanism that is dependent on GSK3β inactivation.