Inhibition of GCKIII kinases STK25 and MST3 mitigates organ lipotoxicity and enhances metabolic resilience under nutritional stress.

Background: Obesity has reached pandemic proportions, highlighting the urgent need for continued research to uncover the molecular mechanisms governing lipid homeostasis and ectopic fat deposition in overnutrition. Our recent translational studies demonstrated that STE20-type kinases STK25 and MST3 associate with intracellular lipid droplets and play a pivotal role in regulating the dynamic balance between fat storage and utilization. This study aimed to assess the in vivo effects of the combined inhibition of STK25 and MST3 in obese mice.

Methods: We performed phenotypic characterization in three cohorts of mice fed a high-fat diet: (1) mice with genetic ablation of Stk25, (2) mice treated with Mst3-targeting antisense oligonucleotide (ASO), and (3) mice depleted of both STK25 and MST3 by injecting Stk25^-/- mice with Mst3 ASO. Whole-body metabolic physiology and organ lipotoxicity were examined in the STK25- and/or MST3-deficient mice compared with their respective controls by using histological assessments, immunofluorescence microscopy, molecular profiling, and biochemical assays.

Results: We found that the inactivation of STK25 and MST3, either individually or in combination, provided equal protection against ectopic fat accumulation and associated lipotoxic damage in the liver, kidney, and skeletal muscle of obese mice. Strikingly, high-fat diet-fed STK25/MST3-deficient mice, but not mice lacking only one kinase, displayed reduced body and fat mass gain, which was accompanied by markedly increased abundance of thermogenesis markers in the brown adipose tissue (BAT).

Conclusions: Dual inhibition of STK25 and MST3 in mice mitigates obesity-triggered lipotoxic injury to metabolic tissues and elevates indicators of BAT thermogenic capacity.