gms | German Medical Science

Objective: Osteocalcin (OC), the bone-derived hormone is important in the regulation of brain development and aging. In the brainstem and hippocampus, OC promotes the synthesis of neurotransmitters, which contribute to cognition and anxiety. OC expression in the brain is contradictory: some reporting its synthesis in the brain and some explaining its brain presence by blood delivery. Presence of OC in the brain would give an opportunity to modulate its level and therefore also the cognition by certain drugs. Here we examined two brain regions, after treatment with an anti-inflammatory drug zileuton, for the OC peptide presence.

Methods: mRNA expression level of OC gene was analyzed using qRT-PCR from hypothalamic and hippocampal brain regions of ovariectomized rat treated with/without zileuton. For the peptide analysis, neuronal (4DIV), as well as neuronal stem cell (7DIV) cultures were developed from hypothalamic and hippocampal regions and protein extracts were made. Targeted mass spectrometry using parallel reaction monitoring (PRM) was used in order to detect and quantify OC.

Results: Level of OC mRNA in different brain regions varies after zileuton treatment. Cloning and sequencing of these amplified fragments detected an OC sequence, confirming the mRNA expression oscillation. Synthetic heavy isotope-labeled peptide was chosen as a probe for the detection and absolute quantification of OC. Targeted mass spectrometry using PRM and heavy isotope-labeled standards did not detect endogenous peptide down to a detection limit of 1 fmol, where the spiked heavy-labeled peptide was always detected.

Conclusion: This data support OC’s blood delivery to the brain. The variations in the expression level of OC should undergo further study, like e.g. screening for the potentially homologues molecule(s) in the brain. Even more important is broader picture of OC: 1) how extracellular cues coming from the periphery-bones can affect brain function(s), 2) could the decrease in cognition during aging, be due to the reduction in circulating levels of OC, 3) can we reduce cognitive decline by OC supplementation.