This 2020 review subject was brain-bone crosstalk:
“Multiple stress, mood and neurodegenerative brain disorders are associated with osteoporosis. Skeletal diseases display impaired brain development and function.
Along with brain and bone pathologies, trauma events highlight strong interaction of both organs. While brain-derived molecules affecting bone include central regulators – transmitters of the sympathetic, parasympathetic and sensory nervous system – bone-derived mediators altering brain function are released from bone cells and marrow.
Osteoblast-derived hormone osteocalcin (OCN) exerts neuroprotective effects. Studies revealed a bidirectional dependence of brain and bone through bone cell-derived modulators that directly affect behavioral and cognitive function.
The main bone-derived mediator affecting the brain is OCN, which is exclusively synthesized by osteoblasts. OCN was recently discovered to transverse the BBB to enter the CNS, where it promotes spatial learning and memory while preventing anxiety-like behavior or even depression.
Cognitive function and circulating levels of OCN are proposed to inversely correlate with age. Maternal osteocalcin regulates embryonic brain development by enhancing monoamine neurotransmitters and their synthesis.
Clinical observations provide key evidence for a bidirectional communication between brain and bone tissue, which is strongly supported by experimental studies that unraveled underlying mechanistic pathways and identified molecular mediators involved in this crosstalk.”
https://www.mdpi.com/1422-0067/21/14/4946/htm “Crosstalk of Brain and Bone-Clinical Observations and Their Molecular Bases”
The first paper of Vitamin K2 – What can it do? said:
“Osteocalcin γ-carboxylation is the main mechanism of action through which Vitamin K2 improves bone health.”
This paper didn’t mention Matrix Gla Protein (MGP) carboxylation, and said a contrary:
“Undercarboxylated, bioactive OCN, initially considered as an inhibitor of bone mineralization, participates in systemic body regulation and homeostasis.”
The 2019 paper cited was Osteocalcin‑GPRC6A: An update of its clinical and biological multi‑organic interactions (Review):
“Osteocalcin is a small protein present in two forms: Carboxylated (cOC) and undercarboxylated (ucOC). Only ucOC can signal as a hormone while cOC cannot.”
It went on to downplay cOC, and also didn’t mention MGP carboxylation.
I think it’s a question of balance. cOC stays in your bones. Carboxylated MGP influences calcium to go into your bones instead of your blood vessel walls. Two good things.