Visceral fat-specific regulation of plasminogen activator inhibitor-1 in aged septic mice

Elevated plasma levels of plasminogen activator inhibitor-1 (PAI-1) are documented in patients with sepsis and levels positively correlate with disease severity and mortality. Our previous work demonstrated that visceral adipose tissues (VAT) are a major source of PAI-1, especially in the aged (murine endotoxemia), that circulating PAI-1 protein levels match the trajectory of PAI-1 transcript levels in VAT (clinical sepsis), and that PAI-1 in both VAT and plasma are positively associated with acute kidney injury (AKI) in septic patients. In the current study utilizing preclinical sepsis models, PAI-1 tissue distribution was examined and cellular sources, as well as mechanisms mediating PAI-1 induction in VAT, were identified. In aged mice with sepsis, PAI-1 gene expression was significantly higher in VAT than in other major organs. VAT PAI-1 gene expression correlated with PAI-1 protein levels in both VAT and plasma. Moreover, VAT and plasma levels of PAI-1 were positively associated with AKI markers, modeling our previous clinical data. Using explant cultures of VAT, we determined that PAI-1 is secreted robustly in response to recombinant transforming growth factor β (TGFβ) and tumor necrosis factor α (TNFα) treatment; however, neutralization was effective only for TNFα indicating that TGFβ is not an endogenous modulator of PAI-1. Within VAT, TNFα was localized to neutrophils and macrophages. PAI-1 protein levels were fourfold higher in stromal vascular fraction (SVF) cells compared with mature adipocytes, and among SVF cells, both immune and nonimmune compartments expressed PAI-1 in a similar fashion. PAI-1 was localized predominantly to macrophages within the immune compartment and preadipocytes and endothelial cells within the nonimmune compartment. Collectively, these results indicate that induction and secretion of PAI-1 from VAT is facilitated by a complex interaction among immune and nonimmune cells. As circulating PAI-1 contributes to AKI in sepsis, understanding PAI-1 regulation in VAT could yield novel strategies for reducing systemic consequences of PAI-1 overproduction.