Mechanical strain induces a persistent upregulation of syndecan-1 expression in smooth muscle cells

Syndecan-1 belongs to a family of transmembrane proteoglycans, acts as a coreceptor for growth factor binding, as well as cell-matrix and cell-cell interactions, and is induced in smooth muscle cells (SMCs) following balloon catheter injury. In this report, we investigated syndecan-1 expression in SMCs in response to several distinct biomechanical force profiles and the related syndecan shedding response. Syndecan-1 mRNA expression increased in response to 5% and 10% cyclic strain (24 h: 206 +/- 40% and 278 +/- 33%, respectively, P < 0.05) when compared to unstrained controls. When subjected to 10% cyclic strain for periods of up to 48 h, syndecan-1 mRNA levels remained elevated at 294 +/- 31%. Notably, the SMC mechanosensor mechanism remained responsive after an initial 24 h "preconditioning" period, as evident by a fivefold increase in syndecan-1 gene expression following a change in cyclic stress from 10% to 20% (48 h: 516 +/- 55%, P < 0.05). Of note, similar behavior was not observed in an analysis of syndecan-2 mRNA levels. Commensurate with mRNA responses, mechanical stress induced an increase in cell-associated syndecan-1 protein levels with an associated increase in protein shedding. Given the varied functions of syndecan-1, stress-induced effects on SMC syndecan-1 expression and shedding may represent an additional component of the pro-inflammatory, growth-stimulating pathways that are activated in response to changes in the mechanical microenvironment of the vascular wall. Syndecan-1 expression is uniquely influenced by changes in the phase and magnitude of the local stress field.