Aging Alters Integrin‐mediated Vascular Smooth Muscle Function in Soleus Feed Arteries

Abstract

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.