Mechanisms of norepinephrine-induced Ca2+ 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 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.NEW & NOTEWORTHY Norepinephrine (NE)-induced Ca2+ signaling in PVAT is mediated by adrenergic receptors with depot-specific roles. All three receptor subtypes contribute in mPVAT and aPVAT, whereas α1a predominates in white adipose tissue. Internal Ca2+ stores are the primary Ca2+ source for NE-induced signaling across depots. Ca2+ imaging with selective agonists supports α1a's role, and NO imaging highlights depot diversity. Immunofluorescence data confirm receptor expression on adipocytes and vasculature, indicating complex signaling pathways in adipose tissues studied here across depots.