ANGIOTENSIN II-INDUCED ER STRESS RESPONSE CONTRIBUTES TO PROFIBROTIC VSMC PHENOTYPE AND SUBSEQUENT HYPERTENSIVE ARTERIAL STIFFNESS

Abstract

Objective: The renin-angiotensin-aldosterone system is known to play a pivotal role in human hypertension, and specifically angiotensin II (Ang II) is believed to mediate arterial stiffness through maladaptive responses from vascular smooth muscle cells (VSMCs). The objective of this study was to elucidate Ang II activation of the endoplasmic reticulum unfolded protein response (ER UPR) in VSMCs, how this contributes to hypertrophic and fibrotic responses, and how inhibition of ER UPR may mitigate increased aortic pulse propagation velocity (PPV, a surrogate measurement for aortic stiffness). Design and method: ApoE-/- mice were infused with 1 ug/kg/min angiotensin II for 14 days with or without 1 mg/mL 4-PBA For in vitro studies, rat VSMCs were explanted and used from P4-P8. 4-PBA 30 min pretreatment at 1 mM before Ang II 48 hr stimulation or adeno GRP78 infection used to assess chaperoning effect on sirius red collagen assay, THP-1 adhesion, and protein aggregate accumulation. Results: Chronic 14 day infusion of Ang II in apoE-/- mice leads to increased PPV from 0.06 m/s to 0.12 m/s, whereas supplementing drinking water with 1 mg/mL chemical ER chaperone 4-PBA mitigates this induction (PPV = 0.055 m/s), P = 0.039. Fibrosis of the heart, kidney and aorta were reduced with 4-PBA treatment as well. ER stress markers pIRE1a and XBP1S were activated in the thoracic aorta by Ang II infusion and inhibited by 4-PBA. Preamyloid oligomer accumulation induced by Ang II in the aorta was also reduced by 4-PBA. Rat VSMCs stimulated with Ang II were stained with aggregate dye Proteostat, which was increased with 48 hour Ang II treatment, and inhibited with 4-PBA pretreatment (P < 0.05). To evaluate VSMC stiffness promoting phenotype, collagen production and immune cell adhesion were assessed by Sirius Red assay and THP-1 adhesion, respectively. Both inductions by Ang II were decreased by 4-PBA. Overexpression of GRP78 significantly mitigated aggregate formation (P < 0.05) and immune cell infiltration (P < 0.05). Conclusions: Ang II induced pulse pressure and vascular amyloid deposition is decreased by chaperoning nascent protein folding. Targeting GRP78 to reduce ER UPR activation and subsequent disturbances in proteostasis may be a therapeutic strategy for aortic stiffness.