Neuraminidase 1 activates insulin receptor and reverses insulin resistance in obese mice

Abstract Objectives Neuraminidase 1 ( NEU1) cleaves terminal sialic acids of glycoconjugatesduring lysosomal catabolism. It also modulates the structure and activity of cellular surface receptors affecting diverse pathways. Previously we demonstrated that NEU1activates the insulin receptor (IR) and that NEU1-deficient CathA S190A-Neo mice (hypomorph of the NEU1activator protein, cathepsin A/CathA) on a high-fat diet (HFD) develop hyperglycaemia and insulin resistancefaster than wild-type animals. The major objective of the current work was to reveal the molecular mechanism by which NEU1desialylation activates the IR and to test if increase of NEU1activity in insulin target tissues reverses insulin resistanceand glucose intolerance. Methods To test if desialylation causes a conformational change in the IR dimer we measured interaction between the receptor subunits by Bioluminescence Resonance Energy Transfer in the HEK293T cells either overexpressing NEU1or treated with the NEU1inhibitor. The influence of NEU1overexpression on insulin resistancewas studied in vitro in palmitate-treated HepG2 cells transduced with NEU1-expressing lentivirusand in vivo in C57Bl6 mice treated with HFD and either pharmacological inducer of NEU1, Ambroxolor NEU1-expressing adenovirus. NEU1-deficient CathA S190A-Neo mice were used as a control. Results By desialylation of IR, NEU1induced formation of its active dimer leading to insulin signaling. Overexpression of NEU1in palmitate-treated HepG2 cells restored insulin signaling, suggesting that increased NEU1levels may reverse insulin resistance. Five-day treatment of glycemic C57Bl6 mice receiving HFD with the activator of the lysosomal gene network, Ambroxol, increased NEU1expression and activity in muscle tissue, normalized fasting glucose levels, and improved physiological and molecular responses to glucose and insulin. Ambroxoldid not improve insulin sensitivity in obese insulin-resistantCathA S190A-Neo mice indicating that the Ambroxoleffect is mediated through NEU1induction. Sustained increase of liver NEU1activity through adenovirus-based gene transfer failed to attenuate insulin resistancemost probably due to negative feedback regulation of IR expression. Conclusion Together our results demonstrate that increase of NEU1activity in insulin target tissues reverses insulin resistanceand glucose intolerance suggesting that a pharmacological modulation of NEU1activity may be potentially explored for restoring insulin sensitivity and resolving hyperglycemia associated with T2DM.