Habitual Exercise Modulates Neuroimmune Interaction to Mitigate Aortic Stiffness.

Background: Exercise augments hemodynamic shear to activate mechano-sensitive molecular transducers in the vascular endothelium. Recently, the central nervous system has been reported to mediate neuroimmune interactions in the aortic adventitia (AA). Whether exercise modulates sympathetic nerve interactions with the immune cells to mitigate aortic stiffness remains unknown.

Methods: C57BL/6 mice infused with angiotensin II (Ang II) were subjected to voluntary wheel running (VWR) for four weeks. Sympathetic activation was assessed by tyrosine hydroxylase (TH) expression, norepinephrine (NE) levels, and colocalization of synapsin with CD68. Sympathetic denervation was performed by performing celiac ganglionectomy or administration of 6-hydroxydopamine. Single-cell RNA sequencing was analyzed to profile immune and vascular cell populations. Circulating macrophage depletion was achieved with Ki20227 or Ccr2 knock-out (Ccr2) mice. Terbutaline, a β2-adrenergic receptor (β2-AR) agonist, was administered to assess β2-AR underlying VWR -mediated arterial effects.

Results: Ang II increased TH and synapsin expression, NE levels, and colocalization of synapsin with macrophages in AA, accompanied by vascular fibrosis and elevated pulse wave velocity (PWV). Ang II increased Ccr2CD80 circulating macrophages in the AA. VWR mitigated Ang II-induced Ccr2CD80 macrophage accumulation and extracellular matrix (ECM) deposition. Macrophage depletion reduced Ang II-mediated synapsin macrophages, AA thickness, TH expression, and PWV. Terbutaline treatment attenuated the VWR-mediated protective effects , implicating β2-AR-positive macrophages in Ang II-mediated neuro-immune interaction. Col1a1-tdT mice supported that Ang II-mediated sympathetic nerves colocalized with macrophages, but not fibroblasts. Cell-cell communication analysis revealed Ang II enhanced interleukin-1β signaling from macrophages to fibroblasts, and NE-treated macrophage media up-regulated profibrotic genes in fibroblasts. Ang II further upregulated synapse organization, neurotropic and attractive axon guidance genes in fibroblasts, whereas VWR attenuated these transcriptional changes.

Conclusions: Exercise mitigates Ang II-mediated sympathetic nerve interactions with macrophages to activate fibroblasts via inflammation in AA, leading to ECM deposition and aortic stiffness.