Smooth Muscle Stiffness Sensitivity is Driven by Soluble and Insoluble ECM Chemistry

Abstract

Smooth muscle cell (SMC) invasion into plaques and subsequent proliferation is a major factor in the progression of atherosclerosis. During disease progression, SMCs experience major changes in their microenvironment, such as what integrin-binding sites are exposed, the portfolio of soluble factors available, and the elasticity and modulus of the surrounding vessel wall. We have developed a hydrogel biomaterial platform to examine the combined effect of these changes on SMC phenotype. We were particularly interested in how the chemical microenvironment affected the ability of SMCs to sense and respond to modulus. To our surprise, we observed that integrin binding and soluble factors are major drivers of several critical SMC behaviors, such as motility, proliferation, invasion, and differentiation marker expression, and these factors modulated the effect of stiffness on proliferation and migration. Overall, modulus only modestly affected behaviors other than proliferation, relative to integrin binding and soluble factors. Surprisingly, pathological behaviors (proliferation, motility) are not inversely related to SMC marker expression, in direct conflict with previous studies on substrates coupled with single extracellular matrix (ECM) proteins. A high-throughput bead-based ELISA approach and inhibitor studies revealed that differentiation marker expression is mediated chiefly via focal adhesion kinase (FAK) signaling, and we propose that integrin binding and FAK drive the transition from a migratory to a proliferative phenotype. We emphasize the importance of increasing the complexity of in vitro testing platforms to capture these subtleties in cell phenotypes and signaling, in order to better recapitulate important features of in vivo disease and elucidate potential context-dependent therapeutic targets.

Zwitterionic PEG-PC Hydrogels Modulate the Foreign Body Response in a Modulus-Dependent Manner

“…Recently, we synthesized hydrogels composed of both PEG and PC, which have an increased range of stiffnesses, and reduced protein adsorption in vitro compared to PEG-only hydrogels 26 . These PEG-PC hydrogels can be used for cell culture scaffolds of varying stiffness and biochemical complexity 27–29 . We hypothesized that PEG-PC hydrogels would have a reduced inflammatory response because of minimal protein adsorption, making them potentially advantageous for long-term in vivo implants.…”

Biomechanics and Mechanobiology of Saphenous Vein Grafts

“…While the potential effects of compliance on vascular grafts is typically considered in terms of the difference between the graft and host artery, it might be useful to consider potential impacts from the temporal change in compliance within the saphenous vein as it moves from the lower pressure venous circulation to the higher pressure arterial circulation and the accompanying ten fold decrease in compliance. Change in material stiffness, which would be inversely related to compliance, regulates the function of many cell types including endothelial [156][157][158] and smooth muscle cells [159,160].…”

Micromechanical Properties of Microstructured Elastomeric Hydrogels

“…Microindentation and puncture studies require minimum sample volume, provide ease of implementation, and have been used to successfully characterize a variety of synthetic polymer hydrogels and biological tissues. [19,[34][35][36][37][38][39][40] In addition, a manual indentation system was designed on a confocal microscope that allowed real time observation of the deformation of RLP-PEG_25 hydrogels prior to puncture with a spherically tipped indenter providing unique information about the local deformation of domains subjected to failure under pointed loads.…”