Novel osmotin inhibits SREBP2 via the AdipoR1/AMPK/SIRT1 pathway to improve Alzheimer's disease neuropathological deficits

Extensive evidence has indicated that a high rate of cholesterol biogenesis and abnormal neuronal energy metabolism play key roles in Alzheimer's disease (AD) pathogenesis. Here, for we believe the first time, we used osmotin, a plant protein homolog of mammalian adiponectin, to determine its therapeutic efficacy in different AD models. Our results reveal that osmotin treatment modulated adiponectin receptor 1 (AdipoR1), significantly induced AMP-activated protein kinase (AMPK)/Sirtuin 1 (SIRT1) activation and reduced SREBP2 (sterol regulatory element-binding protein 2) expression in both in vitro and in vivo AD models and in Adipo(-/-) mice. Via the AdipoR1/AMPK/SIRT1/SREBP2 signaling pathway, osmotin significantly diminished amyloidogenic A beta production, abundance and aggregation, accompanied by improved pre- and post-synaptic dysfunction, cognitive impairment, memory deficits and, most importantly, reversed the suppression of long-term potentiation in AD mice. Interestingly, AdipoR1, AMPK and SIRT1 silencing not only abolished osmotin capability but also further enhanced AD pathology by increasing SREBP2, amyloid precursor protein (APP) and beta-secretase (BACE1) expression and the levels of toxic A beta production. However, the opposite was true for SREBP2 when silenced using small interfering RNA in APPswe/ind-transfected SH-SY5Y cells. Similarly, osmotin treatment also enhanced the non-amyloidogenic pathway by activating the alpha-secretase gene that is, ADAM10, in an AMPK/SIRT1-dependent manner. These results suggest that osmotin or osmotin-based therapeutic agents might be potential candidates for AD treatment.