Abstract Body: Perivascular adipose tissue (PVAT) is recognized as an endocrine organ that secretes a variety of adipokines, which negatively regulate vascular contraction. Progranulin (PGRN), a glycoprotein encoded by the GRN gene, is highly expressed in adipocytes, and is implicated in inflammation, cellular proliferation, and repair mechanisms. The relationship between PGRN and PVAT remains unclear. We hypothesized that the lack of PGRN negatively affects PVAT quality. We used male C57BL/6J wild-type (WT) and global PGRN knockout (KO) mice, aged 10-12 weeks. Energy expenditure was analyzed via the Comprehensive Lab Animal Monitoring System (CLAMS). Vascular function was studied in endothelium-intact aortae with PVAT [PVAT(+)] and without PVAT [PVAT(-)]. Additionally, 3T3-L1 cells were used to evaluate the molecular mechanisms. The KO mice showed a decreased respiratory exchange ratio (RER) and a whitening phenotype of PVAT, which was accompanied by a loss of anti-contractile effects [(mN) WT_PVAT(-): 5.2±0.3 vs PVAT(+): 3.4±0.5*, *P<0.05 and KO_PVAT(-): 6.1±0.7 vs KO_PVAT(+): 5.7±0.4]. Additionally, PVAT from KO displayed a significant reduction in nitric oxide production [(RFU) WT_PVAT: 223.1± 12.3 vs KO_PVAT: 67.3±9.1*, *P<0.05] and endothelial NO synthase phosphorylation. Additionally, the lack of PGRN attenuated the expression of mitochondrial complexes [(AU) WT_PVAT: 1.3± 0.03 vs KO_PVAT: 0.6±0.06*, *P<0.05] measured by the OXPHOS cocktail antibody. Via high-resolution respirometry, we found that isolated mitochondria from KO_PVAT showed impaired succinate-driven respiration or complex II activity. To understand if the whitening phenotype of PVAT was leading to its dysfunction, we induced a browning phenotype of PVAT by treating the mice with a β3-agonist for 7 days (CL 316243, 1mg/kg/day). This treatment increased RER restored the PVAT phenotype, and improved PVAT anti-contractile effect and mitochondrial respiration. Using 3T3-L1 cells, we engineered the overexpression and knockdown of PGRN via lentivirus (LV) infection and siRNA, respectively. Suppression of PGRN increased mRNA of whitening markers (1.5-fold increase vs scramble siRNA), while overexpression elevated mRNA of browning and mitochondrial markers (1.3-fold increase vs scramble LV). In summary, our findings reveal that PGRN is crucial for maintaining the phenotype and anti-contractile function of PVAT and highlight PGRN as a pharmacological target for vascular outcomes in cardiometabolic conditions.