Sex- and stressor-dependent effects of metformin on cardiac fibrosis in plasminogen activator inhibitor-1 deficiency.

Heart failure arises when persistent cardiac stress drives maladaptive remodeling and fibrosis. Plasminogen activator inhibitor-1 (SERPINE1/PAI-1) acts as a repressor of cardiac fibrosis (CF). While complete human PAI-1 deficiency is rare, individuals carrying loss-of-function PAI-1 mutations and genetic loss of PAI-1 in mice accelerates CF following cardiac stress and with age. Here, we used this model to investigate sex-specific mechanisms underlying CF in PAI-1 deficiency and an effective intervention to prevent its progression. Our transcriptomic profiling identified Serpine1/SERPINE1-positive fibroblasts primed for activation, inflammatory chemokine signaling, and ECM remodeling, establishing PAI-1 as a marker of a stress-responsive fibroblast state. We then examined whether metformin, a glucose-lowering drug with known anti-fibrotic effects through inhibition of TGF-β1 signaling, could attenuate CF in male and female PAI-1-/- mice subjected to angiotensin II (AngII) infusion or surgical injury. Echocardiographic and molecular analyses revealed that PAI-1-/- mice exhibited exaggerated fibrotic remodeling, particularly following AngII stress. Notably, metformin improved cardiac function and reduced fibrosis in a sex- and stressor-dependent manner, modestly benefiting males after surgery and markedly protecting females following AngII insult. In vitro, metformin suppressed AngII-induced Tgfb1 expression exclusively in cardiac fibroblasts isolated from female PAI-1-/- mice. These findings reveal context-dependent fibrotic mechanisms, and identify metformin as a promising therapy for PAI-1 deficiency-associated CF.