Abstract 220: Role of ECM Stiffness in Microvascular Inflammation
Nitric oxide (NO) produced by endothelial nitric oxide synthase (eNOS) is a critical regulator of inflammation as it inhibits leukocyte adhesion to vessel endothelium. Notably, reduced eNOS activity/NO bioavailability and chronic inflammation are key features, and often major determinants, of atherosclerosis and diabetic cardiovascular complications. Past approaches aimed at normalizing eNOS activity have focused primarily on the role of soluble, genetic or shear stress-mediated physical factors. However, extracellular matrix (ECM) mechanics also plays a crucial role in endothelial cell (EC) activation and function. Importantly, tissue mechanics is altered in both atherosclerosis and diabetes that are marked by chronic inflammation and impaired eNOS activity. Thus, we investigated whether there exists a causal relationship between ECM stiffness and eNOS/NO-dependent endothelial inflammation. To test this hypothesis, we cultured ECs on fibronectin-coated elastic substrates of varying stiffness (220 Pa/soft, 1000 Pa/intermediate and 4000 Pa/stiff). EC mechanosensitivity was first confirmed by quantifying the density of actin cytoskeletal filaments, which increased with increasing ECM stiffness. EC-leukocyte adhesion (inflammation) on these substrates, however, followed a biphasic trend where ECs on both 220 Pa (soft) and 4000 Pa (stiff) substrates exhibited greater leukocyte adhesion than those cultured on intermediate 1000 Pa substrates. This biphasic effect of ECM stiffness on endothelial inflammation correlated inversely with levels of eNOS-activation and NO production on these substrates. Consistent with these data, NF-kB activation was enhanced on 220 Pa and 4000 Pa while being suppressed on 1000 Pa substrates. Preliminary data implicate differential levels of calcium influx via mechanosensitive calcium ion channels in this ECM stiffness-dependent eNOS activation and endothelial inflammation. These new findings can potentially lead to superior cardiovascular disease management as they identify ECM stiffness both as a novel therapeutic target for immunomodulatory strategies as well as a key physical design criterion for the development of instructive biomaterials for cardiovascular tissue engineering.
- © 2013 by American Heart Association, Inc.