Association between osteocalcin and cognitive performance in healthy older adults

Acute effects of high-intensity interval exercise plus whole-body vibration on bone turnover markers, BDNF, irisin, and neurocognitive performance in postmenopausal women

The acute effects of exercise can elucidate the molecular and psychophysiological mechanisms underlying exercise's benefits in several systems (e.g., the brain, muscle, and bone). In this study, a single 30-minute session of high-intensity interval aerobic exercise (HIIAE) administered in conjunction with isometric resistance exercise on a whole-body vibration (WBV) platform (HIIAE+WBV) was compared with HIIAE alone in their effects on molecular and neurocognitive indices among 63 sedentary, healthy postmenopausal women who were randomly assigned to HIIAE (n = 20), HIIAE+WBV (n = 20), and Control (n = 23) groups. The assessed molecular indices were serum levels of osteocalcin (OC), uncarboxylated OC (ucOC), carboxylated OC (cOC), brain-derived neurotrophic factor (BDNF), and irisin, and the assessed neurocognitive indices were the accuracy rate (AR), reaction time (RT), and electroencephalography event-related potentials (ERPs) of P2 and P3 components in a visuospatial working memory task. Data on these indices before versus after an acute bout of HIIAE or HIIAE+WBV or after a resting session were compared. An HIIAE or HIIAE+WBV intervention yielded no significant change in ERP P2 latency/amplitude and P3 latency but yielded significantly higher ARs, shorter RTs, larger ERP P3 amplitudes, and higher OC, cOC, BDNF, and irisin levels in the postmenopausal women. HIIAE+WBV outperformed HIIAE alone in AR, ucOC, and BDNF. However, the changes in these molecular and neurocognitive indices induced by the two exercise modes did not show any significant correlations in the present study. The present findings suggest that HIIAE and HIIAE+WBV have the potential to acutely influence markers of bone and brain health, with HIIAE+WBV showing greater effectiveness than HIIAE alone. These interventions should be further investigated in future randomized controlled trials involving postmenopausal women.

Ginkgolide B increases healthspan and lifespan of female mice

Various anti-aging interventions show promise in extending lifespan, but many are ineffective or even harmful to healthspan. Ginkgolide B (GB), derived from Ginkgo biloba, reduces aging-related morbidities such as osteoporosis, yet its effects on healthspan and longevity have not been fully understood. In this study, we found that continuous oral administration of GB to female mice beginning at 20 months of age extended median survival and median lifespan by 30% and 8.5%, respectively. GB treatment also decreased tumor incidence; enhanced muscle quality, physical performance and metabolism; and reduced systemic inflammation and senescence. Single-nucleus RNA sequencing of skeletal muscle tissue showed that GB ameliorated aging-associated changes in cell type composition, signaling pathways and intercellular communication. GB reduced aging-induced Runx1+ type 2B myonuclei through the upregulation of miR-27b-3p, which suppresses Runx1 expression. Using functional analyses, we found that Runx1 promoted senescence and cell death in muscle cells. Collectively, these findings suggest the translational potential of GB to extend healthspan and lifespan and to promote healthy aging.

The potential link between the development of Alzheimer's disease and osteoporosis

Alzheimer's disease (AD) and osteoporosis (OP) pose distinct but interconnected health challenges, both significantly impacting the aging population. AD, a neurodegenerative disorder characterized by memory impairment and cognitive decline, is primarily associated with the accumulation of abnormally folded amyloid beta (Aβ) peptides and neurofibrillary tangles in the brain. OP, a skeletal disorder marked by low bone mineral density, involves dysregulation of bone remodeling and is associated with an increased risk of fractures. Recent studies have revealed an intriguing link between AD and OP, highlighting shared pathological features indicative of common regulatory pathophysiological pathways. In this article, we elucidate the signaling mechanisms that regulate the pathology of AD and OP and offer insights into the intricate network of factors contributing to these conditions. We also examine the role of bone-derived factors in the progression of AD, underscoring the plausibility of bidirectional communication between the brain and the skeletal system. The presence of amyloid plaques in the brain of individuals with AD is akin to the accumulation of brain Aβ in vascular dementia, pointing towards the need for further investigation of shared molecular mechanisms. Moreover, we discuss the role of bone-derived microRNAs that may regulate the pathological progression of AD, providing a novel perspective on the role of skeletal factors in neurodegenerative diseases. The insights presented here should help researchers engaged in exploring innovative therapeutic approaches targeting both neurodegenerative and skeletal disorders in aging populations.

Brain aging rejuvenation factors in adults with genetic and sporadic neurodegenerative disease

The largest risk factor for dementia is age. Heterochronic blood exchange studies have uncovered age-related blood factors that demonstrate 'pro-aging' or 'pro-youthful' effects on the mouse brain. The clinical relevance and combined effects of these factors for humans is unclear. We examined five previously identified brain rejuvenation factors in cerebrospinal fluid of adults with autosomal dominant forms of frontotemporal dementia and sporadic Alzheimer's disease. Our frontotemporal dementia cohort included 100 observationally followed adults carrying autosomal dominant frontotemporal dementia mutations (Mage = 49.6; 50% female; 43% C9orf72, 24% GRN, 33% MAPT) and 62 non-carriers (Mage = 52.6; 45% female) with cerebrospinal fluid analysed on Somascan, and longitudinal (Mvisits = 3 years, range 1-7 years) neuropsychological and functional assessments and plasma neurofilament light chain. Our Alzheimer's disease cohort included 35 adults with sporadic Alzheimer's disease (Mage = 69.4; 60% female) and 56 controls (Mage = 68.8, 50% female) who completed the same cerebrospinal fluid and clinical outcome measures cross-sectionally. Levels of C-C motif chemokine ligand 11, C-C motif chemokine ligand 2, beta-2-micorglobulin, bone gamma-carboxyglutamate protein (aka Osteocalcin) and colony stimulating factor 2 in cerebrospinal fluid were linearly combined into a composite score, with higher values reflecting 'pro-youthful' levels. In genetic frontotemporal dementia, higher baseline cerebrospinal fluid rejuvenation proteins predicted slower decline across cognitive, functional, and neurofilament light chain trajectories; estimates were similar across genotypes. In transdiagnostic analyses, higher cerebrospinal fluid rejuvenation proteins associated with better functional, cognitive, and neurofilament light chain outcomes in adults with sporadic Alzheimer's disease. Proteins with pre-clinical evidence for brain rejuvenation show translational clinical relevance in adults with Alzheimer's disease and related dementias and warrant further investigation.

Comparing the effect of high-intensity interval exercise and voluntary exercise training on cognitive functions in rats

It is known that exercise increases brain-derived neurotrophic factor (BDNF) levels in the hippocampus, the brain region responsible for learning and memory, resulting in improved cognitive functions and learning processes. However, it is claimed that different types of exercise cause different responses in the brain. It is thought that lactate and osteocalcin secreted in response to exercise are associated with an increase in BDNF levels. However, there are not enough studies on this subject. This study aimed to compare the effects of high-intensity interval training (HIIT) and voluntary exercise training on cognitive performance and molecular connections. Male rats were randomly divided into control, voluntary exercise training and HIIT groups. The voluntary exercise group had free access to the voluntary wheel for 8 weeks. The HIIT group performed HIIT on the treadmill 3 days a week for 8 weeks. The rats underwent open field (OF), elevated plus maze (EPM) and Morris water maze (MWM) tests 24 h after the last exercise training. Then, after blood was drawn under anesthesia, the rats were sacrificed and their hippocampus tissues were separated. Glucocorticoid and BDNF levels in the blood were evaluated by enzyme-linked immunosorbent assay (ELISA), and osteocalcin and BDNF expressions in the hippocampus were evaluated by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). Neither voluntary exercise training nor HIIT had any significant effect on behavioral parameters assessed by OF, EPM and MWM tests. However, BDNF expression in hippocampus tissue was higher in the HIIT group than in the control group. In addition, osteocalcin expression in hippocampus tissue was higher in the HIIT and voluntary exercise groups than in the control group. In conclusion, according to the findings we obtained from this study, although it does not have a significant effect on cognitive functions, the effect of HIIT on brain functions seems to be more effective than voluntary exercise.

Unraveling of Molecular Mechanisms of Cognitive Frailty in Chronic Kidney Disease: How Exercise Makes a Difference

As our population ages, the medical challenges it faces become increasingly acute, with chronic kidney disease (CKD) becoming more prevalent among older adults. Frailty is alarmingly more common in CKD patients than in the general populace, putting the elderly at high risk of both physical and cognitive decline. CKD not only accelerates physical deterioration, but also heightens vascular dysfunction, calcification, arterial rigidity, systemic inflammation, oxidative stress, and cognitive impairment. Cognitive frailty, a distinct syndrome marked by cognitive deficits caused by physiological causes (excluding Alzheimer's and other dementias), is a critical concern. Although cognitive impairment has been well-studied, the molecular mechanisms driving cognitive frailty remain largely uncharted. Comprehensive interventions, including cutting-edge pharmaceuticals and lifestyle changes, are pivotal and effective, especially in the early stages of CKD. Recent research suggests that systematic exercise could counteract cognitive decline by improving brain blood flow, boosting neuroplasticity through the brain-derived neurotrophic factor (BDNF), and by triggering the release of neurotrophic factors such as insulin-like growth factor (IGF-1). This review delves into the molecular pathways of cognitive frailty in CKD, identifies key risk factors, and highlights therapeutic approaches, particularly the potent role of exercise in enhancing cognitive health.

Roles of osteocalcin in the central nervous system

BACKGROUND

Bone-derived protein osteocalcin, which has beneficial effects on brain function, may be a future research direction for neurological disorders. A growing body of evidence suggests a link between osteocalcin and neurological disorders, but the exact relationship is contradictory and unclear.

SCOPE OF REVIEW

The aim of this review is to summarize the current research on the interaction between osteocalcin and the central nervous system and to propose some speculative future research directions.

MAJOR CONCLUSIONS

In the normal central nervous system, osteocalcin is involved in neuronal structure, neuroprotection, and the regulation of cognition and anxiety. Studies on osteocalcin-related abnormalities in the central nervous system are divided into animal model studies and human studies, depending on the subject. In humans, the link between osteocalcin and brain function is inconsistent. These conflicting data may be due to methodological inconsistencies. By reviewing the related literature on osteocalcin, some comorbidities of the bone and nervous system and future research directions related to osteocalcin are proposed.

Crosstalk between bone and brain in Alzheimer's disease: Mechanisms, applications, and perspectives

Alzheimer's disease (AD) is a neurodegenerative disease that involves multiple systems in the body. Numerous recent studies have revealed bidirectional crosstalk between the brain and bone, but the interaction between bone and brain in AD remains unclear. In this review, we summarize human studies of the association between bone and brain and provide an overview of their interactions and the underlying mechanisms in AD. We review the effects of AD on bone from the aspects of AD pathogenic proteins, AD risk genes, neurohormones, neuropeptides, neurotransmitters, brain-derived extracellular vesicles (EVs), and the autonomic nervous system. Correspondingly, we elucidate the underlying mechanisms of the involvement of bone in the pathogenesis of AD, including bone-derived hormones, bone marrow-derived cells, bone-derived EVs, and inflammation. On the basis of the crosstalk between bone and the brain, we propose potential strategies for the management of AD with the hope of offering novel perspectives on its prevention and treatment. HIGHLIGHTS: The pathogenesis of AD, along with its consequent changes in the brain, may involve disturbing bone homeostasis. Degenerative bone disorders may influence the progression of AD through a series of pathophysiological mechanisms. Therefore, relevant bone intervention strategies may be beneficial for the comprehensive management of AD.

Research progress in Alzheimer's disease and bone-brain axis

Alzheimer's disease (AD) is the most common type of cognitive impairment. AD is closely related to orthopedic diseases, such as osteoporosis and osteoarthritis, in terms of epidemiology and pathogenesis. Brain and bone tissues can regulate each other in different manners through bone-brain axis. This article reviews the research progress of the relationship between AD and orthopedic diseases, bone-brain axis mechanisms of AD, and AD therapy by targeting bone-brain axis, in order to deepen the understanding of bone-brain communication, promote early diagnosis and explore new therapy for AD patients.

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.

Impact of menopause-associated frailty on traumatic brain injury

Navigating menopause involves traversing a complex terrain of hormonal changes that extend far beyond reproductive consequences. Menopausal transition is characterized by a decrease in estradiol-17β (E2), and the impact of menopause resonates not only in the reproductive system but also through the central nervous system, musculoskeletal, and gastrointestinal domains. As women undergo menopausal transition, they become more susceptible to frailty, amplifying the risk and severity of injuries, including traumatic brain injury (TBI). Menopause triggers a cascade of changes leading to a decline in muscle mass, accompanied by diminished tone and excitability, thereby restricting the availability of irisin, a crucial hormone derived from muscles. Concurrently, bone mass undergoes reduction, culminating in the onset of osteoporosis and altering the dynamics of osteocalcin, a hormone originating from bones. The diminishing levels of E2 during menopause extend their influence on the gut microbiota, resulting in a reduction in the availability of tyrosine, tryptophan, and serotonin metabolites, affecting neurotransmitter synthesis and function. Understanding the interplay between menopause, frailty, E2 decline, and the intricate metabolisms of bone, gut, and muscle is imperative when unraveling the nuances of TBI after menopause. The current review underscores the significance of accounting for menopause-associated frailty in the incidence and consequences of TBI. The review also explores potential mechanisms to enhance gut, bone, and muscle health in menopausal women, aiming to mitigate frailty and improve TBI outcomes.

Causal effect of blood osteocalcin on the risk of Alzheimer's disease and the mediating role of energy metabolism

Growing evidence suggests an association between osteocalcin (OCN), a peptide derived from bone and involved in regulating glucose and lipid metabolism, and the risk of Alzheimer's disease (AD). However, the causality of these associations and the underlying mechanisms remain uncertain. We utilized a Mendelian randomization (MR) approach to investigate the causal effects of blood OCN levels on AD and to assess the potential involvement of glucose and lipid metabolism. Independent instrumental variables strongly associated (P < 5E-08) with blood OCN levels were obtained from three independent genome-wide association studies (GWAS) on the human blood proteome (N = 3301 to 35,892). Two distinct summary statistics datasets on AD from the International Genomics of Alzheimer's Project (IGAP, N = 63,926) and a recent study including familial-proxy AD patients (FPAD, N = 472,868) were used. Summary-level data for fasting glucose (FG), 2h-glucose post-challenge, fasting insulin, HbA1c, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, total cholesterol (TC), and triglycerides were incorporated to evaluate the potential role of glucose and lipid metabolism in mediating the impact of OCN on AD risk. Our findings consistently demonstrate a significantly negative correlation between genetically determined blood OCN levels and the risk of AD (IGAP: odds ratio [OR, 95%CI] = 0.83[0.72-0.96], P = 0.013; FPAD: OR = 0.81 [0.70-0.93], P = 0.002). Similar estimates with the same trend direction were obtained using other statistical approaches. Furthermore, employing multivariable MR analysis, we found that the causal relationship between OCN levels and AD was disappeared after adjustment of FG and TC (IGAP: OR = 0.97[0.80-1.17], P = 0.753; FPAD: OR = 0.98 [0.84-1.15], P = 0.831). There were no apparent instances of horizontal pleiotropy, and leave-one-out analysis showed good stability of the estimates. Our study provides evidence supporting a protective effect of blood OCN levels on AD, which is primarily mediated through regulating FG and TC levels. Further studies are warranted to elucidate the underlying physio-pathological mechanisms.

Insulin resistance and osteocalcin associate with the incidence and severity of postoperative delirium in elderly patients undergoing joint replacement

AIM

While insulin sensitivity plays an important role in maintaining glucose metabolic homeostasis and cognitive function, its impact on postoperative delirium (POD) remains unclear. This study aimed to investigate the association between POD and indicators of insulin sensitivity, including insulin resistance and osteocalcin.

METHODS

A total of 120 elderly patients undergoing joint replacement were recruited and divided into delirium and non-delirium groups. Plasma and cerebrospinal fluid (CSF) samples were collected for the analysis of biomarkers, including insulin, uncarboxylated osteocalcin (ucOC), total osteocalcin (tOC), and glucose. Insulin resistance was assessed through the homeostatic model assessment of insulin resistance (HOMA-IR).

MAIN RESULTS

Out of the total, 28 patients (23.3%) experienced POD within 5 days after surgery. Patients with delirium exhibited higher levels of preoperative HOMA-IR and ucOC in CSF and plasma, and of tOC in CSF (P = 0.028, P < 0.001, P = 0.005, P = 0.019). After adjusting for variables, including age, Mini-Mental State Examination score, surgical site and preoperative fracture, only preoperative ucOC in CSF and HOMA-IR were significantly linked to the incidence of delirium (OR = 5.940, P = 0.008; OR = 1.208, P = 0.046, respectively), both of which also correlated with the severity of delirium (P = 0.007, P < 0.001). Receiver operating curve analysis indicated that preoperative HOMA-IR and ucOC in CSF might partly predict POD (area under the curve [AUC] = 0.697, 95% confidence interval [CI] = 0.501-0.775, AUC = 0.745, 95% CI = 0.659-0.860).

CONCLUSIONS

We observed that preoperative elevated HOMA-IR and ucOC in CSF were associated with the incidence and severity of POD. While these preliminary results need confirmation, they suggest a potential involvement of insulin resistance and osteocalcin in the pathological mechanism of POD. Geriatr Gerontol Int 2024; 24: 421-429.

Association of bone turnover markers and cognitive function in Chinese chronic schizophrenia patients with or without vitamin D insufficiency

BACKGROUND

Increasing evidence shows that bone turnover markers (BTMs) and vitamin D can affect human cognitive function. However, there are few studies that have investigated the association between BTMs and cognitive function in chronic schizophrenia patients. The aim of this study was to investigate the relationship between BTMs and cognitive function in chronic schizophrenia patients with or without vitamin D insufficiency (VDI).

METHODS

In all, 118 chronic schizophrenia patients were enrolled in this cross-sectional study. Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was applied to evaluate the cognitive function of the subjects. Blood analysis included bone turnover markers, vitamin D levels, and glycolipid levels.

RESULTS

Relative to 72 vitamin D-sufficient (VDS) patients, 46 VDI patients had higher bone resorption markers levels and lower bone formation markers levels. Regression analysis showed that, in the total sample, CTX and language function exhibited independent positive correlation (p = 0.027, R2 change = 0.042), and in the VDS group, procollagen type I N-terminal propeptide (PINP) was independently negatively correlated with language function (p = 0.031, R2 change = 0.065), while the positive correlation between osteopontin (OPN) and delayed memory remained in the VDI group (p = 0.036, R2 change = 0.083).

CONCLUSION

Our study showed an association between the levels of BTMs and cognitive function among chronic schizophrenia patients. This correlation may have different mechanisms of action at different vitamin D levels.

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.

Investigation of the causal relationship between osteocalcin and dementia: A Mendelian randomization study

Objective

Basic medical studies have reported an improved effect of osteocalcin on cognition. We explored the causal link between osteocalcin and dementia via the implementation of Mendelian randomization methodology.

Methods

Genome-wide association studies were employed to identify single nucleotide polymorphisms (SNPs) showing significant correlations with osteocalcin. Subsequently, A two-sample Mendelian randomization analysis was conducted utilizing the inverse-variance-weighted (IVW) technique to assess the causal relationship between osteocalcin and various types of dementia, including Alzheimer's disease (AD), Parkinson's disease (PD), Lewy body dementia (LBD), and vascular dementia (VD). This approach aimed to minimize potential sources of confounding bias and provide more robust results. Multivariable MR (MVMR) analysis was conducted to adjust for potential genetic pleiotropy.

Results

The study employed three SNPs, namely rs71631868, rs9271374, and rs116843408, as genetic tools to evaluate the causal association of osteocalcin with dementia. The IVW analysis indicated that osteocalcin may have a potential protective effect against AD with an odds ratio (OR) of 0.790 (95 % CI: 0.688-0.906; P < 0.001). However, no significant relationship was observed between osteocalcin and other types of dementia. Furthermore, the MVMR analysis indicated that the impact of osteocalcin on AD remained consistent even after adjusting for age-related macular degeneration and Type 2 diabetes with an OR of 0.856 (95 % CI: 0.744-0.985; P = 0.030).

Conclusions

Our findings provide important insights into the role of osteocalcin in the pathogenesis of AD. Future research is required to clarify the underlying mechanisms and their clinical applications.

Positive associations between sex hormones, bone metabolism and cognitive impairment in Chinese oldest-old females

PURPOSE

With a rapid increase in older adults, progressive impairment in cognitive function has become an increasing concern owing to high social and economic burdens. The current study was designed to investigate the associations of sex hormones and bone metabolism with cognitive impairment (CI) in Chinese oldest-old females.

METHODS

There were 396 oldest-old females from the China Hainan Oldest-old Cohort Study (CHOCS). Following standardized procedures, Mini Mental State Examination was effectively completed, and sex hormones and bone metabolism were assessed in these females.

RESULTS

The median age of all females was 101 years (range: from 80 to 116). There were 340 females (86%) with CI. Participants with CI had significantly higher levels of age, progesterone, prolactin and estradiol than those without CI (P < 0.05 for all). Total type I collagen N-terminal elongation peptide [hazard ratio (HR): 1.018, 95%CI: 1.001-1.035] and prolactin (HR: 1.065, 95%CI: 1.005-1.129) levels were positively and significantly associated with CI (P < 0.05 for all).

CONCLUSIONS

Prolactin and total type I collagen N-terminal elongation peptide had positive associations with CI in Chinese oldest-old females. Thus, a balance in sex hormones and bone metabolism may have significant effects on cognitive function during the aging process.

Targeting aging with the healthy skeletal system: The endocrine role of bone

Aging is an inevitable biological process, and longevity may be related to bone health. Maintaining strong bone health can extend one's lifespan, but the exact mechanism is unclear. Bone and extraosseous organs, including the heart and brain, have complex and precise communication mechanisms. In addition to its load bearing capacity, the skeletal system secretes cytokines, which play a role in bone regulation of extraosseous organs. FGF23, OCN, and LCN2 are three representative bone-derived cytokines involved in energy metabolism, endocrine homeostasis and systemic chronic inflammation levels. Today, advanced research methods provide new understandings of bone as a crucial endocrine organ. For example, gene editing technology enables bone-specific conditional gene knockout models, which allows the study of bone-derived cytokines to be more precise. We systematically evaluated the various effects of bone-derived cytokines on extraosseous organs and their possible antiaging mechanism. Targeting aging with the current knowledge of the healthy skeletal system is a potential therapeutic strategy. Therefore, we present a comprehensive review that summarizes the current knowledge and provides insights for futures studies.

Alzheimer's Disease and Impaired Bone Microarchitecture, Regeneration and Potential Genetic Links

Alzheimer's Disease (AD) and osteoporosis are both age-related degenerative diseases. Many studies indicate that these two diseases share common pathogenesis mechanisms. In this review, the osteoporotic phenotype of AD mouse models was discussed, and shared mechanisms such as hormonal imbalance, genetic factors, similar signaling pathways and impaired neurotransmitters were identified. Moreover, the review provides recent data associated with these two diseases. Furthermore, potential therapeutic approaches targeting both diseases were discussed. Thus, we proposed that preventing bone loss should be one of the most important treatment goals in patients with AD; treatment targeting brain disorders is also beneficial for osteoporosis.

Degradation of Bone Quality in a Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) patients present with symptoms such as impairment of insulin signaling, chronic inflammation, and oxidative stress. Furthermore, there are comorbidities associated with AD progression. For example, osteoporosis is common with AD wherein patients exhibit reduced mineralization and a risk for fragility fractures. However, there is a lack of understanding on the effects of AD on bone beyond loss of bone density. To this end, we investigated the effects of AD on bone quality using the 5XFAD transgenic mouse model in which 12-month-old 5XFAD mice showed accumulation of amyloid-beta (Aβ42) compared with wild-type (WT) littermates (n = 10/group; 50% female, 50% male). Here, we observed changes in cortical bone but not in cancellous bone quality. Both bone mass and bone quality, measured in femoral samples using imaging (micro-CT, confocal Raman spectroscopy, X-ray diffraction [XRD]), mechanical (fracture tests), and chemical analyses (biochemical assays), were altered in the 5XFAD mice compared with WT. Micro-CT results showed 5XFAD mice had lower volumetric bone mineral density (BMD) and increased endocortical bone loss. XRD results showed decreased mineralization with smaller mineral crystals. Bone matrix compositional properties, from Raman, showed decreased crystallinity along with higher accumulation of glycoxidation products and glycation products, measured biochemically. 5XFAD mice also demonstrated loss of initiation and maximum toughness. We observed that carboxymethyl-lysine (CML) and mineralization correlated with initiation toughness, whereas crystal size and pentosidine (PEN) correlated with maximum toughness, suggesting bone matrix changes predominated by advanced glycation end products (AGEs) and altered/poor mineral quality explained loss of fracture toughness. Our findings highlight two pathways to skeletal fragility in AD through alteration of bone quality: (i) accumulation of AGEs; and (ii) loss of crystallinity, decreased crystal size, and loss of mineralization. We observed that the accumulation of amyloidosis in brain correlated with an increase in several AGEs, consistent with a mechanistic link between elevated Aβ42 levels in the brain and AGE accumulation in bone. © 2022 American Society for Bone and Mineral Research (ASBMR).

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.

Exerkines and long-term synaptic potentiation: Mechanisms of exercise-induced neuroplasticity

Physical exercise may improve cognitive function by modulating molecular and cellular mechanisms within the brain. We propose that the facilitation of long-term synaptic potentiation (LTP)-related pathways, by products induced by physical exercise (i.e., exerkines), is a crucial aspect of the exercise-effect on the brain. This review summarizes synaptic pathways that are activated by exerkines and may potentiate LTP. For a total of 16 exerkines, we indicated how blood and brain exerkine levels are altered depending on the type of physical exercise (i.e., cardiovascular or resistance exercise) and how they respond to a single bout (i.e., acute exercise) or multiple bouts of physical exercise (i.e., chronic exercise). This information may be used for designing individualized physical exercise programs. Finally, this review may serve to direct future research towards fundamental gaps in our current knowledge regarding the biophysical interactions between muscle activity and the brain at both cellular and system levels.

Traditional Japanese apricot (Prunus mume) induces osteocalcin in osteoblasts

The fruit of Prunus mume (ume, also known as Japanese apricot) has been used as a functional food in Japan since ancient times. We previously reported that ume stimulates the differentiation of preosteoblastic cells. Osteocalcin (OCN) is secreted by osteoblasts, and there is known association with glucolipid metabolism and cognitive function. This study sought to clarify the relationship between ume extracts and OCN production both in vitro and in vivo. Alkaline phosphatase activity and OCN level in the ethyl acetate extracts of ume-treated extracts were significantly increased in preosteoblast MC3T3-E1 cells compared with the control group. In human study, serum OCN level was significantly higher in the high ume intake group than in the low intake group in community-dwelling participants over 60 years old. These results suggest that ume has the potential to upregulated OCN production both in vitro and in vivo.

Inorganic Polyphosphate, Mitochondria, and Neurodegeneration

With an aging population, the presence of aging-associated pathologies is expected to increase within the next decades. Regrettably, we still do not have any valid pharmacological or non-pharmacological tools to prevent, revert, or cure these pathologies. The absence of therapeutical approaches against aging-associated pathologies can be at least partially explained by the relatively lack of knowledge that we still have regarding the molecular mechanisms underlying them, as well as by the complexity of their etiopathology. In fact, a complex number of changes in the physiological function of the cell has been described in all these aging-associated pathologies, including neurodegenerative disorders. Based on multiple scientific manuscripts produced by us and others, it seems clear that mitochondria are dysfunctional in many of these aging-associated pathologies. For example, mitochondrial dysfunction is an early event in the etiopathology of all the main neurodegenerative disorders, and it could be a trigger of many of the other deleterious changes which are present at the cellular level in these pathologies. While mitochondria are complex organelles and their regulation is still not yet entirely understood, inorganic polyphosphate (polyP) could play a crucial role in the regulation of some mitochondrial processes, which are dysfunctional in neurodegeneration. PolyP is a well-preserved biopolymer; it has been identified in every organism that has been studied. It is constituted by a series of orthophosphates connected by highly energetic phosphoanhydride bonds, comparable to those found in ATP. The literature suggests that the role of polyP in maintaining mitochondrial physiology might be related, at least partially, to its effects as a key regulator of cellular bioenergetics. However, further research needs to be conducted to fully elucidate the molecular mechanisms underlying the effects of polyP in the regulation of mitochondrial physiology in aging-associated pathologies, including neurodegenerative disorders. With a significant lack of therapeutic options for the prevention and/or treatment of neurodegeneration, the search for new pharmacological tools against these conditions has been continuous in past decades, even though very few therapeutic approaches have shown potential in treating these pathologies. Therefore, increasing our knowledge about the molecular mechanisms underlying the effects of polyP in mitochondrial physiology as well as its metabolism could place this polymer as a promising and innovative pharmacological target not only in neurodegeneration, but also in a wide range of aging-associated pathologies and conditions where mitochondrial dysfunction has been described as a crucial component of its etiopathology, such as diabetes, musculoskeletal disorders, and cardiovascular disorders.

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.

Bone-Derived Modulators That Regulate Brain Function: Emerging Therapeutic Targets for Neurological Disorders

Bone has traditionally been regarded as a structural organ that supports and protects the various organs of the body. Recent studies suggest that bone also acts as an endocrine organ to regulate whole-body metabolism. Particularly, homeostasis of the bone is shown to be necessary for brain development and function. Abnormal bone metabolism is associated with the onset and progression of neurological disorders. Recently, multiple bone-derived modulators have been shown to participate in brain function and neurological disorders, including osteocalcin, lipocalin 2, and osteopontin, as have bone marrow-derived cells such as mesenchymal stem cells, hematopoietic stem cells, and microglia-like cells. This review summarizes current findings regarding the roles of these bone-derived modulators in the brain, and also follows their involvement in the pathogenesis of neurological disorders. The content of this review may aide in the development of promising therapeutic strategies for neurological disorders via targeting bone.

Bone-to-Brain: A Round Trip in the Adaptation to Mechanical Stimuli

Besides the classical ones (support/protection, hematopoiesis, storage for calcium, and phosphate) multiple roles emerged for bone tissue, definitively making it an organ. Particularly, the endocrine function, and in more general terms, the capability to sense and integrate different stimuli and to send signals to other tissues, has highlighted the importance of bone in homeostasis. Bone is highly innervated and hosts all nervous system branches; bone cells are sensitive to most of neurotransmitters, neuropeptides, and neurohormones that directly affect their metabolic activity and sensitivity to mechanical stimuli. Indeed, bone is the principal mechanosensitive organ. Thanks to the mechanosensing resident cells, and particularly osteocytes, mechanical stimulation induces metabolic responses in bone forming (osteoblasts) and bone resorbing (osteoclasts) cells that allow the adaptation of the affected bony segment to the changing environment. Once stimulated, bone cells express and secrete, or liberate from the entrapping matrix, several mediators (osteokines) that induce responses on distant targets. Brain is a target of some of these mediator [e.g., osteocalcin, lipocalin2, sclerostin, Dickkopf-related protein 1 (Dkk1), and fibroblast growth factor 23], as most of them can cross the blood-brain barrier. For others, a role in brain has been hypothesized, but not yet demonstrated. As exercise effectively modifies the release and the circulating levels of these osteokines, it has been hypothesized that some of the beneficial effects of exercise on brain functions may be associated to such a bone-to-brain communication. This hypothesis hides an interesting clinical clue: may well-addressed physical activities support the treatment of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s diseases?

The small molecule DIPQUO promotes osteogenic differentiation via inhibition of glycogen synthase kinase 3-beta signaling

Bone fractures are common impact injuries typically resolved through natural processes of osteogenic regeneration and bone remodeling, restoring the biological and mechanical function. However, dysfunctionality in bone healing and repair often arises in the context of aging-related chronic disorders, such as Alzheimer's disease (AD). There is unmet need for effective pharmacological modulators of osteogenic differentiation and an opportunity to probe the complex links between bone biology and cognitive disorders. We previously discovered the small molecule DIPQUO, which promotes osteoblast differentiation and bone mineralization in mouse and human cell culture models, and in zebrafish developmental and regenerative models. Here, we examined the detailed function of this molecule. First, we used kinase profiling, cellular thermal shift assays, and functional studies to identify glycogen synthase kinase 3-beta (GSK3-β) inhibition as a mechanism of DIPQUO action. Treatment of mouse C2C12 myoblasts with DIPQUO promoted alkaline phosphatase expression and activity, which could be enhanced synergistically by treatment with other GSK3-β inhibitors. Suppression of the expression or function of GSK3-β attenuated DIPQUO-dependent osteogenic differentiation. In addition, DIPQUO synergized with GSK3-β inhibitors to stimulate expression of osteoblast genes in human multipotent progenitors. Accordingly, DIPQUO promoted accumulation and activation of β-catenin. Moreover, DIPQUO suppressed activation of tau microtubule-associated protein, an AD-related effector of GSK3-β signaling. Therefore, DIPQUO has potential as both a lead candidate for bone therapeutic development and a pharmacological modulator of GSK3-β signaling in cell culture and animal models of disorders including AD.

Bone-Derived Factors as Potential Biomarkers for Parkinson's Disease

Background: Parkinson’s disease (PD) and osteoporosis are both common aging diseases. It is reported that PD has a close relationship with osteoporosis and bone secretory proteins may be involved in disease progression.

Objectives: To detect the bone-derived factors in plasma and cerebrospinal fluid (CSF) of patients with PD and evaluate their correlations with C-reaction protein (CRP) level, motor impairment, and Hoehn-Yahr (HY) stage of the disease.

Methods: We included 250 PD patients and 250 controls. Levels of osteocalcin (OCN), osteopontin (OPN), osteoprotegerin (OPG), Sclerostin (SO), Bone morphogenetic protein 2 (BMP2), and Dickkopf-1 (DKK-1) in plasma and CSF were measured by custom protein antibody arrays. Data were analyzed using Mann–Whitney U-test and Spearman’s receptor activator of NF-κB (RANK) correlation.

Results: Plasma levels of OCN and OPN were correlated with CRP levels and HY stage and motor impairment of PD. Furthermore, the plasma assessment with CSF detection may enhance their potential prediction on PD.

Conclusions: OCN and OPN may serve as potential biomarkers for PD. The inflammation response may be involved in the cross-talk between the two factors and PD.

Sclerostin and Osteocalcin: Candidate Bone-Produced Hormones

In addition to its structural role, the skeleton serves as an endocrine organ that controls mineral metabolism and energy homeostasis. Three major cell types in bone - osteoblasts, osteoclasts, and osteocytes - dynamically form and maintain bone and secrete factors with systemic activity. Osteocalcin, an osteoblast-derived factor initially described as a matrix protein that regulates bone mineralization, has been suggested to be an osteoblast-derived endocrine hormone that regulates multiple target organs including pancreas, liver, muscle, adipose, testes, and the central and peripheral nervous system. Sclerostin is predominantly produced by osteocytes, and is best known as a paracrine-acting regulator of WNT signaling and activity of osteoblasts and osteoclasts on bone surfaces. In addition to this important paracrine role for sclerostin within bone, sclerostin protein has been noted to act at a distance to regulate adipocytes, energy homeostasis, and mineral metabolism in the kidney. In this article, we aim to bring together evidence supporting an endocrine function for sclerostin and osteocalcin, and discuss recent controversies regarding the proposed role of osteocalcin outside of bone. We summarize the current state of knowledge on animal models and human physiology related to the multiple functions of these bone-derived factors. Finally, we highlight areas in which future research is expected to yield additional insights into the biology of osteocalcin and sclerostin.

The Associations of Serum Osteocalcin and Cortisol Levels With the Psychological Performance in Primary Hyperparathyroidism Patients

OBJECTIVES

The aim of this study was to investigate factors responsible for the psychological performance in primary hyperparathyroidism (PHPT) patients.

METHODS

A group of 38 PHPT patients receiving questionnaires, including Beck Depression Inventory (BDI), State-Trait Anxiety Inventory (STAI), and 36-Item Short Form Survey (SF-36), was evaluated. The relationships between scores of questionnaires and clinical biomarkers were examined. Collinearity and linear regression model were applied to examine variables determining the scores of the questionnaire. In 192 PHPT patients, bivariate and partial correlation were used to analyze the relationships between serum concentrations of parathyroid hormone (PTH), calcium, osteocalcin (OCN), and cortisol.

RESULTS

Among 38 patients receiving questionnaire tests, 50% (19/38) of the patients developed state anxiety, 60.5% (23/38) of the patients had the trait of developing anxiety. In addition, 18.4% (7/38) of the patients developed mild to severe depression. Serum cortisol at 8:00 was negatively and significantly correlated with social function (r = -0.389, p = 0.041) after controlling for age, sex, disease duration, serum PTH, calcium, phosphorus, and 25-hydroxyvitamin D [25(OH)D] concentration. OCN was significantly and negatively correlated with score of STAI-S (r = -0.426, p = 0.027). In the linear regression model for BDI score, variables with statistical significance were serum OCN (β = -0.422, p = 0.019) and cortisol at 0:00 (β = 0.371, p = 0.037). In 192 PHPT patients, the serum concentration of OCN (r = 0.373, p = 0.000) was positively correlated with PTH level. After controlling for age, sex, disease duration, serum 25(OH)D, phosphorus, and calcium concentration, the positive correlation between OCN and PTH was still statistically significant (r = 0.323, p = 0.000). The serum concentration of cortisol at 0:00 was significantly and positively correlated with serum calcium (r = 0.246, p = 0.001) in bivariate correlation analysis. After controlling for age, sex, disease duration, serum PTH, 25(OH)D, and phosphorus concentration, serum cortisol at 0:00 was still positively and significantly correlated with serum calcium (r = 0.245, p = 0.001).

CONCLUSION

Serum levels of OCN and cortisol, rather than PTH and calcium, are associated with the development of anxiety and depression symptoms in PHPT patients.

Dysregulation of BDNF in Prefrontal Cortex in Alzheimer's Disease

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is essential for neurogenesis and has been implicated in Alzheimer's disease (AD). However, few studies have investigated together the epigenetic, transcriptional, and translational regulation of this peptide in the brain in relation to AD.

OBJECTIVE

To investigate mechanisms underlying how BDNF is possibly dysregulated in the brain in relation to aging and AD neuropathology.

METHODS

Prefrontal cortex tissues were acquired from the Manchester Brain Bank (N = 67). BDNF exon I, and exon IV-containing transcripts and total long 3' transcript gene expression were determined by quantitative PCR and bisulfite pyrosequencing was used to quantify DNA methylation within promoters I and IV. Protein concentrations were quantified via ELISA.

RESULTS

BDNF exon IV and total long 3' isoform gene expression levels negatively associated with donor's age at death (IV: r = -0.291, p = 0.020; total: r = -0.354, p = 0.004). Expression of BDNF exon I- containing isoform was significantly higher in Met-carriers of the rs6265 variant, compared to Val-homozygotes, when accounting for donor ages (F = 6.455, p = 0.014). BDNF total long 3' transcript expression was significantly lower in those with early AD neuropathology, compared to those without any neuropathology (p = 0.021). There were no associations between BDNF promoter I and IV methylation or protein levels with ages, rs6265 genotype or AD neuropathology status.

CONCLUSION

Prefrontal cortex BDNF gene expression is associated with aging, rs6265 carrier status, and AD neuropathology in a variant-specific manner that seems to be independent of DNA methylation influences.

Crosstalk of Brain and Bone-Clinical Observations and Their Molecular Bases

As brain and bone disorders represent major health issues worldwide, substantial clinical investigations demonstrated a bidirectional crosstalk on several levels, mechanistically linking both apparently unrelated organs. While multiple stress, mood and neurodegenerative brain disorders are associated with osteoporosis, rare genetic skeletal diseases display impaired brain development and function. Along with brain and bone pathologies, particularly trauma events highlight the strong interaction of both organs. This review summarizes clinical and experimental observations reported for the crosstalk of brain and bone, followed by a detailed overview of their molecular bases. 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 the bone marrow. Although the main pathways of the brain-bone crosstalk remain ‘efferent’, signaling from brain to bone, this review emphasizes the emergence of bone as a crucial ‘afferent’ regulator of cerebral development, function and pathophysiology. Therefore, unraveling the physiological and pathological bases of brain-bone interactions revealed promising pharmacologic targets and novel treatment strategies promoting concurrent brain and bone recovery.

Protective actions of exercise-related FNDC5/Irisin in memory and Alzheimer's disease

The proportion of elderly populations is rapidly booming, and human lifespan has considerably increased in the past century because of scientific and medical advances. However, the winds of change brought by the 21st century made sedentarism one of the factors that renders the brain vulnerable to age-related chronic diseases, such as Alzheimer's disease (AD). Conversely, physical exercise has been shown to stimulate molecular mechanisms beneficial to cognition. Here, we review evidence showing the positive effects of physical exercise in the brain. We further discuss recent evidence that irisin, a myokine stimulated by physical exercise derived from fibronectin type III domain-containing protein 5 (FNDC5) transmembrane protein, has neuroprotective actions in the brain. Lastly, we highlight the importance of the crosstalk between the periphery and the brain in cognition and the therapeutic potential of FNDC5/irisin in AD.

Interaction of bone and brain: osteocalcin and cognition

INTRODUCTION

Bone has conventionally been considered to be a passive organ that only receives external control, but according to recent findings, it has become clear that bone is an endocrine organ that actively regulates systemic metabolism through osteocalcin (OC).

METHODS

We focus on the relationship between the brain and bone and summarize the effects of OC on cognitive function as well as the association between OC and improved cognitive function through exercise.

RESULTS

The findings suggest that the decrease in OC produced by bone is responsible for the decrease in cognitive function associated with aging. Furthermore, positive effect of improving cognitive function can generally be recognized in exercise interventions conducted for healthy elderly people and those with MCI, and moderate exercise is particularly effective for dementia prevention.

CONCLUSION

The improving bone health with aging may exert beneficial effects on cognition.

Associations of Bone Turnover Markers with Cognitive Function in Patients Undergoing Hemodialysis

BACKGROUND

Patients undergoing hemodialysis experience a greater risk of cognitive impairment than the general population, but limited data elucidates the biomarkers on this. We evaluated the association of bone turnover markers on cognitive function among 251 prevalent hemodialysis enrollees in a cross-sectional study.

METHODS

251 hemodialysis patients (median age = 57.8, 55% men) and 37 control subjects (mean age = 61.2, 56% men) without a prior stroke or dementia diagnosis were enrolled. Serum concentrations of 8 bone markers were analyzed as the association of cognitive function (Montreal Cognitive Assessment (MoCA) and Cognitive Abilities Screening Instrument (CASI)) using linear regression analysis.

RESULTS

A lower cognitive function was noted in hemodialysis patients compared to control subjects. The receptor activator of nuclear factor kappa-B ligand (RANKL) was the only bone marker found to be associated with cognitive function (MoCA and CASI tests) in hemodialysis patients without a prior stroke or dementia diagnosis. In stepwise multiple linear regression analysis, the association remained significant in MoCA (β = 1.14, 95% CI 0.17 to 2.11) and CASI (β = 3.06, 95% CI 0.24 to 5.88). Short-term memory (β = 0.52, 95% CI 0.01 to 1.02), mental manipulation (β = 0.51, 95% CI 0.05 to 0.96), and abstract thinking (β = 0.57, 95% CI 0.06 to 1.09) were the significant subdomains in the CASI score related to RANKL.

CONCLUSIONS

Serum RANKL levels were potentially associated with better cognitive function in hemodialysis patients. Further large-scale and prospective studies are needed to confirm our findings.

Viewpoint on the role of tissue maintenance in ageing: focus on biomarkers of bone, cartilage, muscle, and brain tissue maintenance

Specific hallmarks are thought to underlie the ageing process and age-related functional decline. In this viewpoint, we put forward the hypothesis that disturbances in the process of tissue maintenance are an important common denominator that may lie in between specific hallmarks of ageing (i.e. damage and responses to damage) and their ultimate (patho)physiological consequences (i.e. functional decline and age-related disease). As a first step towards verifying or falsifying this hypothesis, it will be important to measure biomarkers of tissue maintenance in future studies in different study populations. The main aim of the current paper is to discuss potential biomarkers of tissue maintenance that could be used in such future studies. Among the many tissues that could have been chosen to explore our hypothesis, to keep the paper manageable, we chose to focus on a selected number of tissues, namely bone, cartilage, muscle, and the brain, which are important for mobility and cognition and affected in several common age-related diseases, including osteoporosis, osteoarthritis, sarcopenia, and neurodegenerative diseases. Furthermore, we discuss the advantages and limitations of potential biomarkers for use in (pre)clinical studies. The proposed biomarkers should be validated in future research, for example by measuring these in humans with different rates of ageing.

Elevated parathyroid hormone levels and cognitive function: A systematic review

OBJECTIVE

To systematically estimate the association between elevated parathyroid hormone (PTH) levels and cognitive function.

METHODS

This review was conducted on ten papers identified through database searches from inception to 31 October 2018. The quality of studies was assessed using the Downs and Black checklist.

RESULTS

There is a low volume of data reporting on the impact of elevated PTH levels on cognitive impairment. The quality of the identified studies ranged from poor (37 %) to good (76 %). Although the results from studies were mixed, one cross-sectional study and one prospective study suggested a link between elevated PTH levels and a decrease in the Mini-Mental State Examination (MMSE) score. Three cross-sectional studies that assessed other cognitive domain in specific domains, such as language, memory and executive function provided mixed results for an association between elevated PTH levels and cognitive function. Two studies showed mixed evidence for a link between elevated PTH levels and poor executive function. One prospective study, one cross-sectional study and three case-control studies provide mixed evidence for an association between higher PTH levels and Alzheimer´s disease (AD). Two studies showed limited evidence for an association between elevated PTH levels and vascular dementia.

CONCLUSION

This review presented that the level of evidence available to support an association between elevated PTH levels and cognitive function was generally weak and inconsistent. Future studies with more better methodological quality are needed.

Circulating Dkk1 and TRAIL Are Associated With Cognitive Decline in Community-Dwelling, Older Adults With Cognitive Concerns

Background

Osteoporosis and Alzheimer's disease are common diseases of aging that would seem to be unrelated, but may be linked through the influence of bone-derived signals on brain function. The aim of the current study is to investigate the relationship between circulating levels of bone-related biomarkers and cognition.

Methods

The population included 103 community-dwelling older individuals with memory concerns but without cognitive impairment. A global cognition summary measure was collected at baseline and 6, 12, and 18 months post-enrollment by converting raw scores from 19 cognitive function tests to z-scores and averaging. Baseline plasma concentrations of bone-related biomarkers, including undercarboxylated, carboxylated, and total osteocalcin, parathyroid hormone, C-terminal telopeptide of collagen 1 (CTX-1), procollagen type 1 amino-terminal propeptide, osteoprotegrin, osteopontin, Dickkopf WNT signaling pathway inhibitor 1 (Dkk1), sclerostin, and amyloid β peptides (Aβ40 and Aβ42), were measured.

Results

Using sex, age, and education-adjusted mixed-effects models, we found that baseline levels of TNF-related apoptosis-inducing ligand (TRAIL; p < .001), Dkk1 (p = .014), and CTX-1 (p = .046) were related to the annual rate of change of global cognition over the 18 month follow-up. In cognitive domain-specific analysis, baseline TRAIL was found to be positively related to the annual rate of change in episodic (p < .001) and working memory (p = .016), and baseline Dkk1 was positively related to semantic memory (p = .027) and negatively related to working memory (p = .016).

Conclusions

These results further confirm the link between bone and brain health and suggest that circulating levels of bone-related biomarkers may have diagnostic potential to predict worsening cognition.

The Endocrine Function of Osteocalcin Regulated by Bone Resorption: A Lesson from Reduced and Increased Bone Mass Diseases

Bone is a peculiar tissue subjected to a continuous process of self-renewal essential to assure the integrity of the skeleton and to explicate the endocrine functions. The study of bone diseases characterized by increased or reduced bone mass due to osteoclast alterations has been essential to understand the great role played by osteocalcin in the endocrine functions of the skeleton. The ability of osteoclasts to regulate the decarboxylation of osteocalcin and to control glucose metabolism, male fertility, and cognitive functions was demonstrated by the use of animal models. In this review we described how diseases characterized by defective and increased bone resorption activity, as osteopetrosis and osteoporosis, were essential to understand the involvement of bone tissue in whole body physiology. To translate this knowledge into humans, recently published reports on patients were described, but further studies should be performed to confirm this complex hormonal regulation in humans.

Potential exerkines for physical exercise-elicited pro-cognitive effects: Insight from clinical and animal research

A sedentary lifestyle is now known as a critical risk factor for accelerated aging-related neurodegenerative disorders. In contract, having regular physical exercise has opposite effects. Clinical findings have suggested that physical exercise can promote brain plasticity, particularly the hippocampus and the prefrontal cortex, that are important for learning and memory and mood regulations. However, the underlying mechanisms are still unclear. Animal studies reveal that the effects of physical exercise on promoting neuroplasticity could be mediated by different exerkines derived from the peripheral system and the brain itself. This book chapter summarizes the recent evidence from clinical and pre-clinical studies showing the emerging mediators for exercise-promoted brain health, including myokines secreted from skeletal muscles, adipokines from adipose tissues, and other factors secreted from the bone and liver.

Roles for osteocalcin in brain signalling: implications in cognition- and motor-related disorders

It is now generally accepted that the extra-skeleton functionalities of bone are multifaceted. Its endocrine functions came first to light when it was realized that osteoblasts, the bone forming cells, maintain energy homeostasis by improving glucose metabolism, insulin sensitivity and energy expenditure through osteocalcin, a multipurpose osteokine secreted by osteoblasts. Recently, the emerging knowledge on the functional aspects of this osteokine expanded to properties including adult and maternal regulation of cognitive functions. Therapeutic potential of this osteokine has also been recently reported in experimental Parkinson’s disease models. This review highlights such findings on the functions of osteocalcin in the brain and emphasizes on exploring and analyzing much more in-depth basic and clinical studies.

The 24-hour serum profiles of bone markers in healthy older men and women

The process of bone turnover displays variations over 24 h, with C-terminal cross-linked telopeptide of type 1 collagen (CTX) and osteocalcin exhibiting a nadir in the afternoon and a peak in the night. In contrast, N-terminal propeptide of type 1 procollagen (P1NP) did not display an apparent 24-hour rhythm. Other emerging novel biomarkers of bone, sclerostin and Dickkopf-related protein 1 (DKK1), are markers of osteocyte activity with limited data available regarding their 24-hour profiles. In this study, we aimed to extend available data on 24-hour profiles of CTX, osteocalcin, and P1NP and to assess the 24-hour profiles of sclerostin and DKK1 in healthy older men and women and to compare these between men and women. We measured these five bone markers in EDTA plasma collected every 4 h during 24 h in 37 healthy older men and women (range 52-76 years). Differences between time points were determined using repeated measures ANOVA and cosinor analyses were performed to determine circadian rhythmicity. The circadian rhythm of CTX was confirmed by the cosinor model, with women showing larger amplitude compared to men. Osteocalcin showed higher levels during nighttime compared to daytime in both men and women. For P1NP levels we observed a small but significant increase in the night in men. Sclerostin and DKK1 did not show a circadian rhythm, but sclerostin levels differed between time points. Because of the large intraindividual variation, DKK1 as measured in this study cannot be considered a reliable marker for diagnostic or research purposes. In conclusion, when measuring CTX, osteocalcin, P1NP, or sclerostin either in clinical practice or in a research setting, one should consider the 24-hour profiles of these bone markers.

Osteocalcin‑GPRC6A: An update of its clinical and biological multi‑organic interactions (Review)

Osteocalcin is no longer regarded as a molecule exclusive to bone remodeling and osteogenesis, but as a hormone with manifold functions. The discovery of the interaction of osteocalcin with the G protein‑coupled receptor family C group 6‑member A (GPRC6A) receptor has accompanied the characterization of several roles that this peptide serves in body regulation and homeostasis. These roles include the modulation of memory in the brain, fertility in the testis, fat accumulation in the liver, incretins release in the intestine and adaptation to exercise in muscle, in addition to the well‑known effects on β‑cell proliferation, insulin release and adiponectin secretion. The aim of the present review was to provide a practical update of the multi‑organ effects that osteocalcin exerts through its interaction with GPRC6A and the clinical implications of this.

Involvement of Bone in Systemic Endocrine Regulation

The skeleton shows an unconventional role in the physiology and pathophysiology of the human organism, not only as the target tissue for a number of systemic hormones, but also as endocrine tissue modulating some skeletal and extraskeletal systems. From this point of view, the principal cells in the skeleton are osteocytes. These cells primarily work as mechano-sensors and modulate bone remodeling. Mechanically unloaded osteocytes synthetize sclerostin, the strong inhibitor of bone formation and RANKL, the strong activator of bone resorption. Osteocytes also express hormonally active vitamin D (1,25(OH)2D) and phosphatonins, such as FGF23. Both 1,25(OH)2D and FGF23 have been identified as powerful regulators of the phosphate metabolism, including in chronic kidney disease. Further endocrine cells of the skeleton involved in bone remodeling are osteoblasts. While FGF23 targets the kidney and parathyroid glands to control metabolism of vitamin D and phosphates, osteoblasts express osteocalcin, which through GPRC6A receptors modulates beta cells of the pancreatic islets, muscle, adipose tissue, brain and testes. This article reviews some knowledge concerning the interaction between the bone hormonal network and phosphate or energy homeostasis and/or male reproduction.

Head Transplantation: The Immune System, Phantom Sensations, and the Integrated Mind

The principal focus of this paper is to consider the implications of head and neck transplantation surgery on the issue of personal identity. To this end, it is noted that the immune system has not only been established to impose a level of self-identity on bodily cells, it has also been implicated in mental development and the regulation of mental state. In this it serves as a paradigm for the mind as the product of cephalic and extracephalic systems. The importance of bodily systems in identity is then discussed in relation to phantom tissue syndrome. The data strongly indicate that, even if surgically successful, head and neck transplantation will result in the loss of the continuity of personal identity.

Osteocalcin in the brain: from embryonic development to age-related decline in cognition

A remarkable, unexpected aspect of the bone-derived hormone osteocalcin is that it is necessary for both brain development and brain function in the mouse, as its absence results in a profound deficit in spatial learning and memory and an exacerbation of anxiety-like behaviour. The regulation of cognitive function by osteocalcin, together with the fact that its circulating levels decrease in midlife compared with adolescence in all species tested, raised the prospect that osteocalcin might be an anti-geronic hormone that could prevent age-related cognitive decline. As presented in this Review, recent data indicate that this is indeed the case and that osteocalcin is necessary for the anti-geronic activity recently ascribed to the plasma of young wild-type mice. The diversity and amplitude of the functions of osteocalcin in the brain, during development and postnatally, had long called for the identification of its receptor in the brain, which was also recently achieved. This Review presents our current understanding of the biology of osteocalcin in the brain, highlighting the bony vertebrate specificity of the regulation of cognitive function and pointing toward where therapeutic opportunities might exist.

[Osteocalcin, a key molecule for bone endocrine functions]

The maintenance of our physiological functions and their adaptive response to environmental changes depend on precise crosstalk between organs. Recent advances in mouse genetics have helped demonstrate that this holistic view of physiology extends to the skeletal system, where many unexpected signaling axes are found to play essential roles affecting numerous organs. After being long regarded as a static tissue, functioning merely as a structural support system, the skeleton has seen its image evolve into a much more complex picture. The skeleton reveals itself as a key endocrine organ for the homeostasis of our body, both by its central position in our body, but also by the large number of physiological functions it influences. In this review, we discuss the multiple endocrine roles of osteocalcin, an osteoclast-derived molecule (Ocn), where its functional importance has steadily increased over the last 15 years.