Mechanisms of norepinephrine induced Ca ²⁺ responses in perivascular adipose tissue

Structural changes in microcirculation are often considered the first signs of vascular damage due to hypertension. A key tissue type emerging as a regulator of vascular tone is perivascular adipose tissue (PVAT). PVAT is a complex collection of adipocytes, immune cells, nerves, collagen fibers, and capillaries that surround most blood vessels. Norepinephrine (NE) is an important catecholamine that has emerged as a key driver of PVAT anticontractile factors. The release of anticontractile factors such as nitric oxide (NO) and adiponectin counteract smooth muscle contraction and limit vasoconstriction. NE stimulates adrenergic receptors such as β3, β2, and α1a leading to the activation of Gs and Gq signal transduction cascades. Despite the importance of NE in promoting PVAT vasoactive functions, the cellular signal transduction mechanisms that underlie this effect remain unknown. Here, we used Ca²⁺ and NO imaging, selective drugs, and immunofluorescence to investigate mechanisms of NE-induced Ca²⁺ responses in PVAT. Our findings demonstrate that NE-induced Ca²⁺ signaling in PVAT is mediated by α1a, β2, and β3 adrenergic receptors, with depot-specific differences. Ca²⁺ responses in mesenteric PVAT, aortic PVAT, and white adipose tissue originate largely from internal ER stores. Selective agonism used in Ca²⁺ and NO imaging supports the role of adrenergic receptors as major mediators of NE-induced responses with depot specific differences. Immunofluorescence confirmed that all three receptor subtypes are present on the adipocyte membrane and the vasculature. Together, these results highlight the complexity of adrenergic signaling in PVAT.