4.4 ARTERIAL PHENOTYPE MODULATION AND REGULATION OF VASCULAR FIBROSIS IN MICE BY CONDITIONAL INACTIVATION OF INTEGRIN AV SUBUNIT IN VASCULAR SMOOTH MUSCLE CELLS

Abstract

Integrin αv functions as a receptor for adhesion proteins and is expressed at high density in vascular smooth muscle cells (VSMC)1,2,3,4,5 whose phenotypic modulation plays a crucial role in arterial ageing and atherosclerosis.6,7. Our aim was to define the arterial phenotype in mice conditionally inactivated for the integrin αv subunit in VSMC8,9,10(αv SMKO) and its role in angiotensin II (AngII)-induced arterial fibrosis. Transgenic mice αv SMKO and their control littermates (WT) were treated with two doses of AngII, low (0.3 mg/kg/day) and high (1.5 mg/kg/day), for 4 weeks. At baseline, blood pressure was lower in αvSMKO compared to WT mice. Carotid distensibility was increased in αv SMKO mice (13.3±0.7 vs 10.3±0.6 mmHg−1.10−3). With low dose AngII isobaric distensibility remained higher in αvSMKOmice (12.4±1.2 vs 10.7±1.0 mmHg−1.10−3).With high dose AngII the increase in collagen content in carotid media was lower in αvSMKOthan in WT (19 vs 35%) for a similar increase in blood pressure (30 mmHg) and arterial wall hypertrophy. Collagen immunostaining and fluorescence measurements (multiphoton microscopy second harmonic generation) confirmed that high dose AngII induced lower increases in collagen content in αvSMKO mice versus WT (8.9±1.7 vs 14.2±1.4 greyscale mean/pixel). The combination of similar arterial wall hypertrophy with less fibrosis in mutant mice explains an increased distensibility in response to AngII. The αv subunit regulates AngII-induced arterial fibrosis as determined by collagen staining, immunostaining and fluorescence. Pharmacological targeting of vascular αv integrin may have clinical applications in the treatment of patients with fibrosis associated with hypertension and atherosclerosis.