Interaction of bone and brain: osteocalcin and cognition

Osteocalcin: Beyond Bones

Apart from basic roles such as supporting the body, protecting internal organs, and storing calcium, the skeletal system also performs hormonal functions. In recent years, several reports have been published on proteins secreted by bones and their impact on the homeostasis of the entire body. These proteins include fibroblast growth factor 23, sclerostin, lipocalin 2, and osteocalcin. Osteocalcin, the most abundant non-collagenous protein in bone tissue, is routinely measured as a clinical marker for diagnosing bone metabolism disorders. Its molecule undergoes numerous transformations, with decarboxylation being the critical process. Decarboxylation occurs in the acidic environment typical of bone resorption, facilitating the release of the molecule into the bloodstream and enabling its hormonal action. Decarboxylated osteocalcin promotes insulin secretion and stimulates the proliferation of pancreatic islet β-cells. It also plays a role in reducing the accumulation of visceral fat and decreasing fat storage in the liver. Furthermore, decarboxylated osteocalcin levels are inversely correlated with fasting serum glucose levels, total body fat, visceral fat area, and body mass index. Apart from its role in energy metabolism, osteocalcin affects testosterone production and the synthesis of glucagon-like peptide-1. It is also actively involved in muscle-bone crosstalk and influences cognitive function.

Approximation of bone mineral density and subcutaneous adiposity using T1-weighted images of the human head

Bones and brain are intricately connected and scientific interest in their interaction is growing. This has become particularly evident in the framework of clinical applications for various medical conditions, such as obesity and osteoporosis. The adverse effects of obesity on brain health have long been recognised, but few brain imaging studies provide sophisticated body composition measures. Here we propose to extract the following bone- and adiposity-related measures from T1-weighted MR images of the head: an approximation of skull bone mineral density (BMD), skull bone thickness, and two approximations of subcutaneous fat (i.e., the intensity and thickness of soft non-brain head tissue). The measures pertaining to skull BMD, skull bone thickness, and intensi-ty-based adiposity proxy proved to be reliable ( r =.93/.83/.74, p <.001) and valid, with high correlations to DXA-de-rived head BMD values (rho=.70, p <.001) and MRI-derived abdominal subcutaneous adipose volume (rho=.62, p <.001). Thickness-based adiposity proxy had only a low retest reliability ( r =.58, p <.001).The outcomes of this study constitute an important step towards extracting relevant non-brain features from available brain scans.

Low bone mineral density is associated with gray matter volume decrease in UK Biobank

Objectives

Previous research has found an association of low bone mineral density (BMD) and regional gray matter (GM) volume loss in Alzheimer's disease (AD). We were interested whether BMD is associated with GM volume decrease in brains of a healthy elderly population from the UK Biobank.

Materials and methods

T1-weighted images from 5,518 women (MAge = 70.20, SD = 3.54; age range: 65-82 years) and 7,595 men (MAge = 70.84, SD = 3.68; age range: 65-82 years) without neurological or psychiatric impairments were included in voxel-based morphometry (VBM) analysis in CAT12 with threshold-free-cluster-enhancement (TFCE) across the whole brain.

Results

We found a significant decrease of GM volume in women in the superior frontal gyri, middle temporal gyri, fusiform gyri, temporal poles, cingulate gyri, precunei, right parahippocampal gyrus and right hippocampus, right ventral diencephalon, and right pre- and postcentral gyrus. Only small effects were found in men in subcallosal area, left basal forebrain and entorhinal area.

Conclusion

BMD is associated with low GM volume in women but less in men in regions afflicted in the early-stages of AD even in a sample without neurodegenerative diseases.

Mechanisms of the Beneficial Effects of Exercise on Brain-Derived Neurotrophic Factor Expression in Alzheimer's Disease

Brain-derived neurotrophic factor (BDNF) is a key molecule in promoting neurogenesis, dendritic and synaptic health, neuronal survival, plasticity, and excitability, all of which are disrupted in neurological and cognitive disorders such as Alzheimer's disease (AD). Extracellular aggregates of amyloid-β (Aβ) in the form of plaques and intracellular aggregates of hyperphosphorylated tau protein have been identified as major pathological insults in the AD brain, along with immune dysfunction, oxidative stress, and other toxic stressors. Although aggregated Aβ and tau lead to decreased brain BDNF expression, early losses in BDNF prior to plaque and tangle formation may be due to other insults such as oxidative stress and contribute to early synaptic dysfunction. Physical exercise, on the other hand, protects synaptic and neuronal structure and function, with increased BDNF as a major mediator of exercise-induced enhancements in cognitive function. Here, we review recent literature on the mechanisms behind exercise-induced BDNF upregulation and its effects on improving learning and memory and on Alzheimer's disease pathology. Exercise releases into the circulation a host of hormones and factors from a variety of peripheral tissues. Mechanisms of BDNF induction discussed here are osteocalcin, FNDC5/irisin, and lactate. The fundamental mechanisms of how exercise impacts BDNF and cognition are not yet fully understood but are a prerequisite to developing new biomarkers and therapies to delay or prevent cognitive decline.

To investigate the association of serum osteocalcin with cognitive functional status in patients with type 2 diabetes: A systematic review with meta-analysis

BACKGROUND

To systematically evaluate the correlation between serum osteocalcin levels and cognitive function status in type 2 diabetes mellitus (T2D) patients.

METHODS

This review was conducted according to the PRISMA guidelines, and was developed and submitted to PROSPERO (CRD42022339295). We comprehensively searched PubMed, EMBASE, Web of Science, Scopus, ProQuest, and Chinese Databases (China National Knowledge Infrastructure, Wan Fang, Chinese Science and Technology Periodical Database, and China Biology Medicine) up to 1 June 2023. 3 investigators performed independent literature screening and data extraction of the included literature, and 2 investigators performed an independent quality assessment of case-control studies using the Newcastle-Ottawa-Scale tool. Data analysis was performed using Review Manager 5.4 software. For continuous various outcomes, mean difference (MD) or standardized MD with 95% confidence intervals (CIs) was applied for assessment by fixed-effect or random-effect model analysis. The heterogeneity test was performed by the Q statistic and quantified using I2, and publication bias was evaluated using a funnel plot.

RESULTS

9 studies with T2D were included (a total of 1310 subjects). Meta-analysis results indicated that cognitive function was more impaired in patients with lower serum osteocalcin levels [MD = 9.91, 95% CI (8.93, -10.89), I2 = 0%]. Serum osteocalcin levels were also significantly different between the 2 groups of T2D patients based on the degree of cognitive impairment [MD = -0.93, 95% CI (-1.09, -0.78), I2 = 41%]. It summarized the statistical correlation between serum osteocalcin and cognitive function scores in patients with T2D at r = 0.43 [summary Fisher's Z = 0.46, 95% CI (0.39, -0.50), I2 = 41%). After sensitivity analysis, the heterogeneity I2 decreased to 0%, indicating that the results of the meta-analysis are more reliable.

CONCLUSION SUBSECTIONS

Based on a meta-analysis of included studies, we concluded that there is a moderately strong positive correlation between serum osteocalcin levels and patients' cognitive function in T2D. An intervention to increase serum osteocalcin levels can contribute to delaying and improving cognitive decline in patients with T2D.

Osteocalcin and Its Potential Functions for Preventing Fatty Liver Hemorrhagic Syndrome in Poultry

Osteocalcin (OCN) is synthesized and secreted by differentiating osteoblasts. In addition to its role in bone, OCN acts as a hormone in the pancreas, liver, muscle, fat, and other organs to regulate multiple pathophysiological processes including glucose homeostasis and adipic acid metabolism. Fat metabolic disorder, such as excessive fat buildup, is related to non-alcoholic fatty liver disease (NAFLD) in humans. Similarly, fatty liver hemorrhage syndrome (FLHS) is a metabolic disease in laying hens, resulting from lipid accumulation in hepatocytes. FLHS affects hen health with significant impact on poultry egg production. Many studies have proposed that OCN has protective function in mammalian NAFLD, but its function in chicken FLHS and related mechanism have not been completely clarified. Recently, we have revealed that OCN prevents laying hens from FLHS through regulating the JNK pathway, and some pathways related to the disease progression have been identified through both in vivo and vitro investigations. In this view, we discussed the current findings for predicting the strategy for using OCN to prevent or reduce FLHS impact on poultry production.

Brief Report: Undercarboxylated Osteocalcin Is Associated With Cognition in Women With and Without HIV

INTRODUCTION

Bone loss and cognitive impairment are common in women living with HIV (WLWH) and are exacerbated by menopause. Bone-derived undercarboxylated osteocalcin (ucOCN) and sclerostin appear to influence cognition. The current study investigated whether the circulating levels of these 2 proteins are associated with cognition in midlife WLWH and demographically similar HIV seronegative women.

METHODS

Plasma samples from women enrolled in a musculoskeletal substudy within the Women's Interagency HIV Study were used to measure ucOCN and sclerostin. A neuropsychological (NP) test battery assessing executive function, processing speed, attention/working memory, learning, memory, verbal fluency, and motor function was administered within 6 months of musculoskeletal enrollment and every 2 years after (1-4 follow-up visits per participant). A series of generalized estimating equations were conducted to examine the association between biomarkers and NP performance at the initial assessment and over time in the total sample and in WLWH only. Primary predictors included biomarkers, time, and biomarker by time interactions. If the interaction terms were not significant, models were re-run without interactions.

RESULTS

Neither biomarker predicted changes in NP performance over time in the total sample or in WLWH. ucOCN was positively associated with executive function in the total sample and in WLWH and with motor skills in WLWH. ucOCN was negatively associated with attention/working memory in the total sample. There were no significant associations between sclerostin and NP performance.

CONCLUSION

The current study suggests an association between bone-derived ucOCN and cognition in women with and without HIV infection.

Rethinking Fragility Fractures in Type 2 Diabetes: The Link between Hyperinsulinaemia and Osteofragilitas

Patients with type 2 diabetes mellitus (T2DM) and/or cardiovascular disease (CVD), conditions of hyperinsulinaemia, have lower levels of osteocalcin and bone remodelling, and increased rates of fragility fractures. Unlike osteoporosis with lower bone mineral density (BMD), T2DM bone fragility "hyperinsulinaemia-osteofragilitas" phenotype presents with normal to increased BMD. Hyperinsulinaemia and insulin resistance positively associate with increased BMD and fragility fractures. Hyperinsulinaemia enforces glucose fuelling, which decreases NAD+-dependent antioxidant activity. This increases reactive oxygen species and mitochondrial fission, and decreases oxidative phosphorylation high-energy production capacity, required for osteoblasto/cytogenesis. Osteocytes directly mineralise and resorb bone, and inhibit mineralisation of their lacunocanalicular space via pyrophosphate. Hyperinsulinaemia decreases vitamin D availability via adipocyte sequestration, reducing dendrite connectivity, and compromising osteocyte viability. Decreased bone remodelling and micropetrosis ensues. Trapped/entombed magnesium within micropetrosis fossilisation spaces propagates magnesium deficiency (MgD), potentiating hyperinsulinaemia and decreases vitamin D transport. Vitamin D deficiency reduces osteocalcin synthesis and favours osteocyte apoptosis. Carbohydrate restriction/fasting/ketosis increases beta-oxidation, ketolysis, NAD+-dependent antioxidant activity, osteocyte viability and osteocalcin, and decreases excess insulin exposure. Osteocalcin is required for hydroxyapatite alignment, conferring bone structural integrity, decreasing fracture risk and improving metabolic/endocrine homeodynamics. Patients presenting with fracture and normal BMD should be investigated for T2DM and hyperinsulinaemia.