Osteocalcin ameliorates cognitive dysfunctions in a mouse model of Alzheimer's Disease by reducing amyloid β burden and upregulating glycolysis in neuroglia.

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by the accumulation of amyloid β peptides (Aβ) and impaired glucose metabolism in the brain. Osteocalcin (OCN), an osteoblast-derived protein, has been shown to modulate brain functions but whether it has any effect on AD is undetermined. In this study, daily intraperitoneal injection of OCN for 4 weeks ameliorated the anxiety-like behaviors and cognitive dysfunctions in the APP/PS1 transgenic AD mice model, as shown in the increased entries into the central area in open field test, the increased time and entries into open arms in elevated plus maze test, the increased time spent in the light chamber in light-dark transition test, as well as the reduced escape latency and the increased preference for target quadrant in Morris water maze test. Aβ burden in the hippocampus and cortex of AD mice was ameliorated by OCN. Besides, OCN improved the neural network function of the brain, mainly in the enhanced power of high gamma band in the medial prefrontal cortex of AD mice. The proliferation of astrocytes in the hippocampus in AD mice was also inhibited by OCN as demonstrated by immunofluorescence. Furthermore, OCN enhanced glycolysis in astrocytes and microglia, as evidenced by elevated glucose consumption, lactate production, and increased extracellular acidification rate. Such an effect was abolished when the receptor of OCN - Gpr158 was knockdown in astrocytes. Our study revealed OCN as a novel therapeutic factor for AD potentially through reducing Aβ burden and upregulation of glycolysis in neuroglia.