Arterial aging results in a progressive reduction in elasticity of the vessel wall and an impaired ability of aged blood vessels to control local blood flow and pressure. Recently, a new concept has emerged that the stiffness and decreased contractility of vascular smooth muscle (VSM) cells are important contributors to age-induced arterial dysfunction. This study investigated the hypothesis that aging alters integrin function in a matrix stiffness-dependent manner, which contributes to decreased VSM contractility in aged soleus muscle feed arteries (SFA). The effect of RGD-binding integrins on contractile function of cannulated SFA isolated from young (4 months) and old (24 months) Fischer 344 rats was assessed by measuring constrictor responses to norepinephrine, phenylephrine, and angiotensin II. Results indicated that constrictor responses in presence of RGD were impaired in old compared to young SFA. VSM cells isolated from young and old SFA were used for functional experiments using atomic force microscopy and high-resolution imaging. Aging was associated with a modulation of integrin β1 recruitment at cell-matrix adhesions that was matrix and substrate stiffness dependent. Our data showed that substrate stiffening drives altered integrin β1 expression in aging, while soft substrates abolish age-induced differences in overall integrin β1 expression. In addition, substrate stiffness and matrix composition contribute to the modulation of SMα-actin cytoskeleton architecture with soft substrates reducing age effects. Our results provide new insights into age-induced structural changes at VSM cell level that translates to decreased functionality of aged resistance soleus feed arteries.
Introduction
Previous data have shown that aging impairs vasomotor function and alters vascular smooth muscle cell (VSMC) properties. Integrins play an important role in regulating many cellular functions including arterial contractility. However, how aging affects integrin function, and their contribution to impaired constriction in aged arteries has not yet been elucidated. Thus, the purpose of this study was to investigate the age‐induced alteration of integrin function in isolated VSMC and in intact soleus muscle resistance arteries.
Methods
Soleus muscle feed arteries (SFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats, cannulated with glass micropipettes and pressurized at 90cm H2O. Endothelial cells were removed (denuded) by passing 5 ml of air through the artery lumen. Vasoconstrictor responses were assessed by adding of norepinephrine (NE; 10‐9‐10‐4M), angiotensin II (Ang II; 10‐11‐10‐7 M), or phenylephrine (PE; 10‐9‐10‐4 M) in the presence or absence of RGD, an integrin inhibitory peptide. RGE, a non‐inhibitory peptide was used as control. To investigate changes in integrin expression and recruitment at focal adhesions with age, RT‐qPCR, cell adhesion assays, and total internal reflection fluorescence (TIRF) imaging were performed using VSMC isolated from young and old SFA.
Results
Old denuded SFA had reduced vasoconstrictor responses to NE, PE, and Ang II. In the presence of the RGD‐inhibitory peptide, constrictor responses to Ang II were significantly inhibited in denuded old vs. young SFA. Constrictor responses to NE and PE were not significantly altered by RGD. Constrictor responses to NE, PE, and Ang II were also not affected by RGE. Gene expression of specific integrins expressed by VSMC were downregulated in old VSMC compared to young. In addition, RGD‐treated VSMC showed decreased adhesion to fibronectin in both young and old VSMC compared to RGE non‐inhibitory peptide. Quantitative analysis of TIRF images showed that recruitment of integrin α5 and β3 was diminished in old VSMC while β1 was not altered with age.
Conclusions
Taken together, these data suggest that aging leads to integrin dysfunction, which contributes to decreased contractile properties of vascular smooth muscle in SFA.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.