Osteocalcin modulates Abeta42 aggregation to aid in amyloid reduction in mouse models of Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by overexpression of amyloid-beta in the brain, particularly the toxic Abeta-42 form. Recent studies have identified osteocalcin, a peptide traditionally associated with bone, to modulate cognitive function in the AD brain. Osteocalcin exists in two forms: the undercarboxylated (uOC) and carboxylated (cOC) forms. This study investigates the role of uOC in modulating Abeta42 aggregation and its potential therapeutic implications for AD. Administration of uOC, but not cOC, improved both spatial learning and exploratory behavior of 5xFAD transgenic Alzheimer mice. Further investigation showed that uOC reduced the level of insoluble Abeta42 in the brain and increased the level of soluble Abeta42. There was increase in mRNA levels of CD36 in uOC treated 5xFAD transgenic brain alongside upregulation of neuroprotectants like Adipoq and Ahsg (fetuin). We explored the mechanisms underlying the influence of uOC on Aβ42 dynamics and understood that uOC interacts with Glu residues to form non-toxic early tube-like intermediates (A-O) before advancing to late mature Abeta42 fibrils. These intermediates enable Abeta42 uptake by glial cells by upregulating the cell surface expression of CD36 and reducing TNF-alpha production. Collectively, the study sheds light on the fact that uOC modulates Abeta42 dynamics and this interaction is warranted for Abeta42 uptake and clearance. The study provides a novel dimension for the treatment of amyloid disorders like AD.