BACKGROUND: Obesity predisposes individuals to multiple pathologies, including metabolic dysfunction–associated steatotic liver disease and diabetes. Although it is known that accumulation of proinflammatory macrophages within adipose tissues drives adiposity and provokes obesity-linked sequelae, the molecular mechanisms that provoke macrophage dysfunction in obesity remain elusive. Macrophages express high levels of uPA (urokinase plasminogen activator), and uPA has been implicated in leukocyte migration. METHODS: Human adipose tissues from patients receiving bariatric surgery were collected and analyzed for uPA protein levels. To determine the impact of uPA in adipose tissue and subsequent high-fat diet (HFD)–induced weight gain and metabolic diseases, a novel mouse model with a conditional knockout of uPA ( Plau fl /fl ) was generated. Plau WT/WT , Plau KO/KO (global uPA deficiency), and Plau fl/fl /LysM Cre+ (conditional uPA deficiency in macrophages) mice were fed low-fat diet or HFD for up to 20 weeks. RESULTS: Protein levels of visceral adipose tissue uPA positively correlated with body mass index in patients with obesity, and uPA levels decreased in adipose tissue 2 years after bariatric surgery. The expression and activity of uPA also increased in the adipose tissue of HFD-fed control mice. Plau KO/KO mice displayed reduced weight gain and metabolic sequelae through 14 weeks on a HFD compared with Plau WT/WT mice, but not with prolonged HFD feeding. Interestingly, Plau fl/fl /LysM Cre+ mice developed HFD-induced metabolic pathologies equivalently to Plau WT/WT mice. CONCLUSIONS: Our findings suggest that global uPA deletion, but not selective deletion of uPA in LysM+ myeloid cells, attenuates the development of early-stage HFD-driven obesity and pathologies consistent with metabolic syndrome.
Hur et al. (Thu,) studied this question.