Abstract MP22: GRP78 Protects Against Angiotensin II-induced Protein Aggregation, Profibrotic VSMC Phenotype, And Vascular Remodeling

Abstract

Arterial stiffening is a critical risk factor contributing to the development of cardiovascular disease and end organ damage. Vascular smooth muscle cell (VSMC) hypercontractility, vessel fibrosis, and proinflammatory responses are involved. The renin angiotensin system plays critical roles in the development of VSMC stiffness phenotype, as well as CVD pathophysiology. Angiotensin II (Ang II) stimulation induces these stiffness-promoting mechanisms, however, the involvement of dysfunctional proteostasis governing Ang II contribution to vascular stiffness remains underdefined. While endoplasmic reticulum (ER) stress has been implicated in the development of arterial stiffness and hypertension, it is unknown whether the protein aggregation potentially due to maladapted unfolded protein response (UPR) in VSMCs is involved. We hypothesize AngII induced ER stress initiates protein misfolding and effects VSMC stiffness phenotype. We identify a significant increase in protein aggregate size (P<0.001: from 1,000 to 4,500 pixel/aggregate) and number per cell (P<0.01: from 20 to 100 aggregate #/cell) in rat VSMCs stimulated with AngII, which is attenuated with adenoviral overexpression of resident ER chaperone, GRP78 (P<0.01: 2000 pixels/aggregate and P<0.05: 25 aggregate #/cell). Furthermore, UPRosome associated IRE1α phosphorylation induced at 3 and 6 h following AngII stimulation is reduced in GRP78 overexpressing VSMCs (P<0.05), which may contribute to reduced monocyte adhesion (P<0.001), assessed utilizing THP-1 cells. In mice, pharmacological chaperone 3-HNA reduced AngII induced vascular hypertrophy (P=0.056), cardiac perivascular fibrosis (P=0.065), and pulse propagation velocity from 0.35 m/s to 0.23 m/s (P<0.05). A trend in pre-amyloid oligomer accumulation was seen in the medial layer of thoracic aortas following 2 weeks of AngII infusion, which was reduced with 3-HNA treatment. Similar findings were investigated in a SM22α cre-GRP78 mouse model, where a trend in reduction of these parameters are also seen. Overall, GRP78 regulation over VSMC proteostasis influences vascular stiffness phenotype and therefore, these findings may elude new pharmacological intervention for arterial stiffness and aging associated CVD.