Abstract Body: Introduction: Aortic stiffness is a major determinant of systolic hypertension and aging-associated cardiovascular disease. We previously showed that Angiotensin II (Ang II)-induced sympathetic innervation activates adventitial macrophages (MΦ) via norepinephrine, thereby promoting fibroblast activation, extracellular matrix (ECM) deposition, and aortic stiffening. In our scRNA-seq dataset, Ang II increased the expression of the β2-adrenergic receptor (AR) gene (Adrb2) in adventitial myeloid cells, suggesting a candidate exercise-responsive pathway. However, whether myeloid β2-AR signaling contributes to Ang II-induced MΦ activation, adventitial remodeling, and aortic stiffness remains unknown.

Hypothesis: Myeloid-specific β2-AR signaling is required for Ang II-induced adventitial collagen/ECM deposition and remodeling.

Methods: We generated a myeloid-specific Adrb2 knockout (KO) mouse line (LysM-Cre^ERT2; Adrb2^fl/fl). WT (Adrb2^fl/fl) and KO mice received tamoxifen followed by a 2-week washout, then were infused with Vehicle (Veh) or Ang II for 4 weeks (WT+Veh, WT+Ang II, KO+Veh, KO+Ang II; both sexes; n=7-8/group). Aortic stiffness was assessed by pulse wave velocity (PWV); adventitial ECM remodeling by Picrosirius Red, Masson Trichrome, and Verhoeff-Van Gieson staining; and MΦ subsets and neuro-immune phenotypes by immunostaining.

Results: In WT mice, Ang II increased PWV, expanded Ccr2⁺ MΦ (circulating), reduced Lyve1⁺ MΦ (resident), and increased adventitial thickness and ECM/collagen accumulation (p<0.05). In KO+Ang II mice, the Ang II-induced increase in the proportion of Ccr2⁺ MΦ and decrease in the proportion of Lyve1⁺ MΦ in the adventitia were preserved; however, PWV and adventitial ECM remodeling were reduced (p<0.05), indicating that myeloid β2-AR signaling is a mediator of adventitial remodeling and aortic stiffness. Ang II increased adventitial tyrosine hydroxylase (TH) expression, a sympathetic axon marker, whereas TH⁺ axons were reduced in KO+Ang II mice (p<0.05), indicating interruption of the sympathetic-myeloid interaction in the adventitia. Overall, these phenotypic effects were comparable between males and females.

Conclusions: Myeloid β2-AR signaling promotes Ang II-induced adventitial collagen/ECM accumulation, adventitia remodeling, and aortic stiffness, suggesting myeloid β2-AR as a mechanistic exercise-mimic target in large artery stiffness.