Abstract Body (Do not enter title and authors here): Notch3 is important in vasculogenesis and vascular function. Notch3 mutations cause CADASIL (small vessel disease) and aberrant Notch3 signaling is associated with vascular dysfunction and remodeling of resistance arteries, similar to the vascular phenotype in hypertension. Notch receptors, including Notch3, also play a role in adipose biology. Based on our previous findings that aberrant Notch3 signaling leads to vascular injury, and that perivascular adipose tissue influences vascular function we investigated a potential role for Notch3 in the vascular-adipose interactome. We characterized adipose tissue (AT) [brown AT (BAT) and white AT (WAT)] and vascular function in mice overexpressing Notch3 (N3) and in mice harboring the R169C gain of function Notch3 mutation (RC). We evaluated expression of Notch3, and its target transcription factors, BAT markers (UCP-1, OTOP-1), and production of adiponectin and IL-6. Isolated arteries from control mice were exposed to BAT conditioned medium (CM) and vascular function assessed by myography. We did not observe any changes in body weight, but BAT (N3: 115.4±7.1; RC: 115.3±8.2; WT: 154±12.1 mg, p<0.05) and WAT (N3: 309.7±39; RC: 370.4±41; WT: 618.1±73 mg, p<0.05) were decreased in N3 and RC mice. Expression of Notch3 target genes (Heyl, Hes5) was increased in BAT from N3 and RC mice. This was associated with increased production of adiponectin (N3: 25.1±0.4; RC: 25.8±0.6; WT: 23.6±0.4 pg/µg of tissue, p<0.05) and IL-6 (N3: 45.3±5.6; RC: 51.6±5.1; WT: 33.7±2.1 pg/µg of tissue, p<0.05) (by ELISA). UCP-1 expression was increased in WAT from Notch3 mice versus wildtype. Vascular contraction to U46619 was reduced by BAT CM from WT mice (EMax: 158.5±9.7% vs control 183.6±6%). This effect was enhanced with BAT CM from Notch3 (N3 and RC) mice. WAT CM from N3 and RC mice reduced vascular sensitivity to contraction (logEC50: N3=7.2±0.17M; RC=7.2±0.1M; WT: 7.7±0.1M, p<0.05). In summary, at the molecular level, Notch3 regulates adipose tissue, with increased production of adiponectin in BAT and increased expression of browning markers in WAT. Functionally BAT from Notch3 mice attenuates vasoconstriction in WT mice. Our data suggest a putative role for Notch3 in the vasoprotective effects of BAT. These novel findings suggest an important role for Notch3 in the vascular:adipose interactome. Notch3 activation may influence vascular function, in part, by regulating perivascular BAT/WAT.