Age-Related Intimal Stiffening Enhances Endothelial Permeability and Leukocyte Transmigration

Abstract

Age is the most significant risk factor for atherosclerosis; however, the link between age and atherosclerosis is poorly understood. During both aging and atherosclerosis progression, the blood vessel wall stiffens owing to alterations in the extracellular matrix. Using in vitro and ex vivo models of vessel-wall stiffness and aging, we show that stiffening of extracellular matrix within the intima promotes endothelial cell permeability—a hallmark of atherogenesis. When cultured on hydrogels fabricated to match the elasticity of young and aging intima, endothelial monolayers exhibit increased permeability and disrupted cell-cell junctions on stiffer matrices. In parallel experiments, we showed a corresponding increase in cell-cell junction width with age in ex vivo aortas from young (10 weeks) and old (21 to 25 months) healthy mice. To investigate the mechanism by which matrix stiffening alters monolayer integrity, we found that cell contractility increases with increased matrix stiffness, mechanically destabilizing cell-cell junctions. This increase in endothelial permeability results in increased leukocyte extravasation, which is a critical step in atherosclerotic plaque formation. Mild inhibition of Rho-dependent cell contractility using Y-27632, an inhibitor of Rho-associated kinase, or siRNA restored monolayer integrity in vitro and in vivo. Our results suggest that extracellular matrix stiffening alone, which occurs during aging, can lead to endothelial monolayer disruption and atherosclerosis pathogenesis. Because previous therapeutics designed to decrease vascular stiffness have been met with limited success, our findings could be the basis for the design of therapeutics that target the Rho-dependent cellular contractile response to matrix stiffening, rather than stiffness itself, to more effectively prevent atherosclerosis progression.

Control of lung vascular permeability and endotoxin-induced pulmonary oedema by changes in extracellular matrix mechanics

“…Various diseases, such as cancer and fibrosis, that are accompanied by abnormal vascular permeability also exhibit altered tissue mechanics (for example, increased stiffness) 4,13,[18][19][20] . We, therefore, explored whether changes in mechanical interactions between cells and ECM might regulate vascular permeability by culturing lung human microvascular endothelial (L-HMVE) cells on fibronectin-coated polyacrylamide gels with different stiffness (Young's moduli of 150-35,000 Pa) (ref.…”

“…Strikingly, the potent effects of endotoxin on pulmonary vascular permeability can be prevented by manipulating ECM structure, and hence, this mechanical control pathway could potentially lead to new approaches to clinical therapy in the future, in addition to providing greater insight into how changes in pulmonary microvascular structure influence organ pathophysiology. Changes in LOX activity levels that alter tissue structure and ECM mechanics contribute to many pathological processes that are characterized by abnormal vascular permeability, including fibrotic disorders 33,39 and cancer progression 13,37 , as well as cardiovascular diseases 20,40,41 . Our results show that ECM mechanics need to be regulated tightly to maintain optimal cell-cell junctional integrity and pulmonary vascular function in normal lung.…”

“…Changes in ECM structure can normalize tumour microvessels 17 , which are known to be hyperpermeable 4 , and bleomycin-induced pulmonary fibrosis is accompanied by increases in both lung stiffness 18 and vascular permeability 19 . Stiffening of ECM within the vascular intima also promotes endothelial cell permeability during atherosclerosis progression 20 . Taken together, these observations raised the intriguing possibility that physical changes in ECM mechanics might actively regulate lung vascular permeability.…”

Tissue Stiffness Dictates Development, Homeostasis, and Disease Progression

“…A previous study by Choi et al has shown that using hydrogels to mimic the stiffness of young and aging intima demonstrates that the aging process increases the permeability of an endothelial cell monolayer and disrupts cell-cell junctions by activating the Rho-dependent signaling pathway to upregulate cell contractility. 64 …”

Vascular Permeability in Cerebral Cavernous Malformations

“…Beyond CCM disease, endothelial ROCK activity has been postulated as a central mechanism in the aging brain. 33 Thus, our studies of brain permeability optimized and clarified in CCM patients may motivate future research and find broader biomedical applications in the clinical setting.…”