Cathepsin D-driven IL2RG-JAK2 signal hijacking disrupts hepatic insulin action: mechanism-grounded proof that targeting cathepsin D prevents prediabetes.

BACKGROUND: Hepatic insulin resistance (HIR), an early feature of prediabetic, plays a pivotal role in disrupting glucose homeostasis. Clarifying the mechanisms underlying HIR is critical for diabetes prevention. Our previous study has discovered the positive correlations between plasma cathepsin D (CTSD) activity and the degree of HIR in people with obesity. Accordingly, this study investigates the roles of CTSD in the underlying mechanisms involving HIR and impaired glucose homeostasis. METHODS: The samples from people/mice with obesity/MASLD (metabolic dysfunction- associated steatotic liver disease) and HIR cellular models were used for assessing mRNA expression/protein expressions/activity of CTSD. RNA sequencing data from hepatocytes were then performed to disclose the potential mechanism of CTSD-induced HIR. Next, the plasmids of CTSD overexpression and CTSD knockdown were constructed to verify the effects and mechanisms of CTSD in HIR. Lastly, the CTSD inhibitor Pepstatin A (PepA) was administrated to mice with obesity/MASLD to explore the preventive effect of targeting CTSD on prediabetes. RESULTS: Significant increases in mRNA expression, protein levels, and activity of CTSD were observed in individuals and mice with obesity/MASLD, as well as in HIR cell models, compared with controls. Furthermore, we found that increased CTSD or overexpressing CTSD could trigger HIR mediated by the IL2RG-JAK2 axis, thus disturbing hepatic insulin signaling transduction. Inhibiting CTSD with PepA or knocking down CTSD markedly improved HIR and rebalanced glucose metabolism in mice with obesity/MASLD and HIR cell models. CONCLUSION: Altogether, these current findings implicate that increased CTSD suppresses hepatic insulin sensitivity via activating the IL2RG-JAK2-STAT3 axis, highlighting CTSD inhibition as an attractive preventative strategy for prediabetes. CTSD-centered IL2RG-JAK2 axis interruption as a precision strategy to rescue hepatic insulin signaling and halt prediabetes progression.