Abstract Body: Introduction:
Sorbs2 is a cytoskeletal adaptor protein that is dysregulated in cardiovascular diseases (CVD) and is highly expressed in vascular smooth muscle cells (VSMCs). Our objective is to understand the role of Sorbs2 in vascular biology.

Hypothesis:
Sorbs2 regulates VSMC contraction and mechanotransduction responses.

Methods and Results:
To test if Sorbs2 knockout in VSMCs is associated with CVD phenotypes, we created a smooth muscle specific Sorbs2-KO (smKO) mouse. Blood pressure radio telemeters were installed, and mice were treated with Angiotensin II (AngII) at 400 ng/kg/min for 10 days to induce hypertension. Sorbs2-smKOs showed a reduced change in mean arterial blood pressure (dMAP) after AngII administration relative to WT. However, after 5 days post-AngII administration, smKOs increased in dMAP relative to WT, potentially through compensatory mechanisms.

To test if Sorbs2 knockout affects vascular tone in arteries, we performed wire myography experiments. Force of contraction in aortas isolated from WT and global Sorbs2-KO (KO) mice was measured in response to increasing phenylephrine (PE) dose. KO aortas showed increased PE-induced contractility compared to WT (n=6). In passive length-tension relationships, KO aortas showed lower passive tension and higher elasticity than WT. The higher contractility and lower passive tension of KO aortas suggest Sorbs2 plays a role in maintaining the VSMC structural cytoskeleton.

To examine Sorbs2’s role in VSMC cytoskeletal dynamics, primary, aorta-derived WT or KO VSMCs were plated on collagen-coated elastic membranes at static conditions, or with 10% bicyclic stretch at 1 hz for 24 hours. After, cells were lysed for protein and RNA expression analysis via western blots or RNA sequencing. Sorbs2 KO showed dysregulation of Calponin1 and Integrin beta-5 protein expression and significant upregulation of phosphorylated ERK1/2 with no change in total ERK expression (n=6, p<0.05). RNA sequencing of static KO vs WT showed an increase in genes involved in contractile and focal adhesion pathways (Z=5.8, p<0.0001). Under stretch, KO VSMCs continued to show compensatory upregulation of genes associated in focal adhesion (Z=4.9, p<0.001) compared to WT.

Conclusion:
Our results suggest Sorbs2 regulates vascular tone and VSMC mechanotransduction by regulating the VSMC structural cytoskeleton. We think this is achieved by mediating focal adhesion protein expression, actin cytoskeletal dynamics, and microtubule stability.