The mouse osteocalcin gene cluster contains three genes with two separate spatial and temporal patterns of expression

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.

Current knowledge of bone-derived factor osteocalcin: its role in the management and treatment of diabetes mellitus, osteoporosis, osteopetrosis and inflammatory joint diseases

Osteocalcin (OC) is the most abundant non-collagenous and osteoblast-secreted protein in bone. It consists of two forms such as carboxylated OC (cOC) and undercarboxylated OC (ucOC). While cOC promotes bone mineralization and increases bone strength, ucOC is regarded an endocrinologically active form that may have several functions in multiple end organs and tissues. Total OC (tOC) includes both of these forms (cOC and ucOC) and is considered a marker of bone turnover in clinical settings. Most of the data on OC is limited to preclinical studies and therefore may not accurately reflect the situation in clinical conditions. For the stated reason, the aim of this review was not only to summarize current knowledge of all forms of OC and characterize its role in diabetes mellitus, osteoporosis, osteopetrosis, inflammatory joint diseases, but also to provide new interpretations of its involvement in the management and treatment of aforementioned diseases. In this context, special emphasis was placed on available clinical trials. Significantly lower levels of tOC and ucOC could be associated with the risk of type 2 diabetes mellitus. On the contrary, tOC level does not seem to be a good indicator of high bone turnover status in postmenopausal osteoporosis, osteoarthritis and rheumatoid arthritis. The associations between several pharmacological drugs used to treat all disorders mentioned above and OC levels have also been provided. From this perspective, OC may serve as a medium through which certain medications can influence glucose metabolism, body weight, adiponectin secretion, and synovial inflammation.

Osteocalcin: A Multifaceted Bone-Derived Hormone

Together, loss- and gain-of-function experiments have identified the bone-derived secreted molecule osteocalcin as a hormone with a broad reach in rodents and primates. Following its binding to one of three receptors, osteocalcin exerts a profound influence on various aspects of energy metabolism as well as steroidogenesis, neurotransmitter biosynthesis and thereby male fertility, electrolyte homeostasis, cognition, the acute stress response, and exercise capacity. Although this review focuses mostly on the regulation of energy metabolism by osteocalcin, it also touches on its other functions. Lastly, it proposes what could be a common theme between the functions of osteocalcin and between these functions and the structural functions of bone.

Triple-gene deletion for osteocalcin significantly impairs the alignment of hydroxyapatite crystals and collagen in mice

Osteocalcin (Ocn), also known as bone Gla protein, is synthesized by osteoblasts and thought to regulate energy metabolism, testosterone synthesis and brain development. However, its function in bone is not fully understood. Mice have three Ocn genes: Bglap, Bglap2 and Bglap3. Due to the long span of these genes in the mouse genome and the low expression of Bglap3 in bone, researchers commonly use Bglap and Bglap2 knockout mice to investigate the function of Ocn. However, it is unclear whether Bglap3 has any compensatory mechanisms when Bglap and Bglap2 are knocked out. Considering the controversy surrounding the role of Ocn in bone, we constructed an Ocn-deficient mouse model by knocking out all three genes (Ocn−/−) and analyzed bone quality by Raman spectroscopy (RS), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and MicroCT (μCT). The RS test showed that the alignment of hydroxyapatite crystals and collagen fibers was significantly poorer in Ocn−/− mice than in wild-type (WT) mice. Ocn deficiency resulted in a looser surface structure of bone particles and a larger gap area proportion. FTIR analysis showed few differences in bone mineral index between WT and Ocn−/− mice, while μCT analysis showed no significant difference in cortical and trabecular regions. However, under tail-suspension simulating bone loss condition, the disorder of hydroxyapatite and collagen fiber alignment in Ocn−/− mice led to more obvious changes in bone mineral composition. Collectively, our results revealed that Ocn is necessary for regulating the alignment of minerals parallel to collagen fibrils.

TRIM28 promotes luminal cell plasticity in a mouse model of prostate cancer

The Tripartite motif-containing 28 (TRIM28) transcriptional cofactor is significantly upregulated in high-grade and metastatic prostate cancers. To study the role of TRIM28 in prostate cancer progression in vivo, we generated a genetically-engineered mouse model, combining prostate-specific inactivation of Trp53, Pten and Trim28. Trim28 inactivated NPp53T mice developed an inflammatory response and necrosis in prostate lumens. By conducting single-cell RNA sequencing, we found that NPp53T prostates had fewer luminal cells resembling proximal luminal lineage cells, which are cells with progenitor activity enriched in proximal prostates and prostate invagination tips in wild-type mice with analogous populations in human prostates. However, despite increased apoptosis and reduction of cells expressing proximal luminal cell markers, we found that NPp53T mouse prostates evolved and progressed to invasive prostate carcinoma with a shortened overall survival. Altogether, our findings suggest that TRIM28 promotes expression of proximal luminal cell markers in prostate tumor cells and provides insights into TRIM28 function in prostate tumor plasticity.

A one-step multiplex PCR assay for the detection and differentiation of four species of Clarireedia causing dollar spot on turfgrass

BACKGROUND

Dollar spot (DS) is one of the most destructive and economically important diseases of cool- and warm-season turfgrasses worldwide. A total of six species causing DS disease in the genus Clarireedia have been described, and four of them have been reported to be distributed countrywide in China. Identification of different species of Clarireedia is a prerequisite for the effective management of DS disease.

RESULTS

Here we report a novel polymerase chain reaction (PCR)-based method for the detection and differentiation of the four species of Clarireedia associated with DS on turfgrass in China: C. jacksonii, C. paspali, C. monteithiana and C. hainanense. Species-specific genes were identified for each species by comparative genomics analysis. Four primer pairs were designed and mixed to amplify species-specific PCR fragments with differential sizes for the four species of Clarireedia in a single multiplex PCR assay. No PCR products were generated from the DNA templates of other common fungal pathogens associated with multiple turfgrass diseases. The multiplex PCR method developed can be used for the rapid and accurate detection and differentiation of the four species of Clarireedia from pure cultures as well as from infected turfgrass blades with DS symptoms.

CONCLUSION

The study developed a one-step multiplex PCR assay for the detection and differentiation of four species of Clarireedia causing DS on turfgrass in China, which will have important implications for DS management in China and worldwide. © 2022 Society of Chemical Industry.

Structural role of osteocalcin and its modification in bone fracture

Osteocalcin (OC), an abundant non-collagenous protein in bone extracellular matrix, plays a vital role in both its biological and mechanical function. OC undergoes post-translational modification, such as glycation; however, it remains unknown whether glycation of OC affects bone's resistance to fracture. Here, for the first time, we demonstrate the formation of pentosidine, an advanced glycation end-product (AGE) cross-link on mouse OC analyzed by ultra-performance liquid chromatography. Next, we establish that the presence of OC in mouse bone matrix is associated with lower interlamellar separation (distance) and thicker bridges spanning the lamellae, both of which are critical for maintaining bone's structural integrity. Furthermore, to determine the impact of modification of OC by glycation on bone toughness, we glycated bone samples in vitro from wild-type (WT) and osteocalcin deficient (Oc-/-) mice, and compared the differences in total fluorescent AGEs and fracture toughness between the Oc -/- glycated and control mouse bones and the WT glycated and control mouse bones. We determined that glycation resulted in significantly higher AGEs in WT compared to Oc-/- mouse bones (delta-WT > delta-OC, p = 0.025). This observed change corresponded to a significant decrease in fracture toughness between WT and Oc-/- mice (delta-WT vs delta-OC, p = 0.018). Thus, we propose a molecular deformation and fracture mechanics model that corroborates our experimental findings and provides evidence to support a 37%-90% loss in energy dissipation of OC due to formation of pentosidine cross-link by glycation. We anticipate that our study will aid in elucidating the effects of a major non-collagenous bone matrix protein, osteocalcin, and its modifications on bone fragility and help identify potential therapeutic targets for maintaining skeletal health.

Recent advances in the crosstalk between adipose, muscle and bone tissues in fish

Control of tissue metabolism and growth involves interactions between organs, tissues, and cell types, mediated by cytokines or direct communication through cellular exchanges. Indeed, over the past decades, many peptides produced by adipose tissue, skeletal muscle and bone named adipokines, myokines and osteokines respectively, have been identified in mammals playing key roles in organ/tissue development and function. Some of them are released into the circulation acting as classical hormones, but they can also act locally showing autocrine/paracrine effects. In recent years, some of these cytokines have been identified in fish models of biomedical or agronomic interest. In this review, we will present their state of the art focusing on local actions and inter-tissue effects. Adipokines reported in fish adipocytes include adiponectin and leptin among others. We will focus on their structure characteristics, gene expression, receptors, and effects, in the adipose tissue itself, mainly regulating cell differentiation and metabolism, but in muscle and bone as target tissues too. Moreover, lipid metabolites, named lipokines, can also act as signaling molecules regulating metabolic homeostasis. Regarding myokines, the best documented in fish are myostatin and the insulin-like growth factors. This review summarizes their characteristics at a molecular level, and describes both, autocrine effects and interactions with adipose tissue and bone. Nonetheless, our understanding of the functions and mechanisms of action of many of these cytokines is still largely incomplete in fish, especially concerning osteokines (i.e., osteocalcin), whose potential cross talking roles remain to be elucidated. Furthermore, by using selective breeding or genetic tools, the formation of a specific tissue can be altered, highlighting the consequences on other tissues, and allowing the identification of communication signals. The specific effects of identified cytokines validated through in vitro models or in vivo trials will be described. Moreover, future scientific fronts (i.e., exosomes) and tools (i.e., co-cultures, organoids) for a better understanding of inter-organ crosstalk in fish will also be presented. As a final consideration, further identification of molecules involved in inter-tissue communication will open new avenues of knowledge in the control of fish homeostasis, as well as possible strategies to be applied in aquaculture or biomedicine.

ROS-induced PADI2 downregulation accelerates cellular senescence via the stimulation of SASP production and NFκB activation

Cellular senescence is closely related to tissue aging including bone. Bone homeostasis is maintained by the tight balance between bone-forming osteoblasts and bone-resorbing osteoclasts, but it undergoes deregulation with age, causing age-associated osteoporosis, a main cause of which is osteoblast dysfunction. Oxidative stress caused by the accumulation of reactive oxygen species (ROS) in bone tissues with aging can accelerate osteoblast senescence and dysfunction. However, the regulatory mechanism that controls the ROS-induced senescence of osteoblasts is poorly understood. Here, we identified Peptidyl arginine deiminase 2 (PADI2), a post-translational modifying enzyme, as a regulator of ROS-accelerated senescence of osteoblasts via RNA-sequencing and further functional validations. PADI2 downregulation by treatment with H₂O₂ or its siRNA promoted cellular senescence and suppressed osteoblast differentiation. CCL2, 5, and 7 known as the elements of the senescence-associated secretory phenotype (SASP) which is a secretome including proinflammatory cytokines and chemokines emitted by senescent cells and a representative feature of senescence, were upregulated by H₂O₂ treatment or Padi2 knockdown. Furthermore, blocking these SASP factors with neutralizing antibodies or siRNAs alleviated the senescence and dysfunction of osteoblasts induced by H₂O₂ treatment or Padi2 knockdown. The elevated production of these SASP factors was mediated by the activation of NFκB signaling pathway. The inhibition of NFκB using the pharmacological inhibitor or siRNA effectively relieved H₂O₂ treatment- or Padi2 knockdown-induced senescence and osteoblast dysfunction. Together, our study for the first time uncover the role of PADI2 in ROS-accelerated cellular senescence of osteoblasts and provide new mechanistic and therapeutic insights into excessive ROS-promoted cellular senescence and aging-related bone diseases.

Osteocalcin and the Physiology of Danger

Bone biology has long been driven by the question as to what molecules affect cell differentiation or the functions of bone. Exploring this issue has been an extraordinarily powerful way to improve our knowledge of bone development and physiology. More recently, a second question has emerged: does bone have other functions besides making bone? Addressing this conundrum revealed that the bone-derived hormone osteocalcin affects a surprisingly large number of organs and physiological processes, including acute stress response. This review will focus on this emerging aspect of bone biology taking osteocalcin as a case study and will show how classical and endocrine functions of bone help to define a new functional identity for this tissue.

Insights into Mechanisms of Tumorigenesis in Neuroendocrine Neoplasms

Genomic studies have identified some of the most relevant genetic players in Neuroendocrine Neoplasm (NEN) tumorigenesis. However, we are still far from being able to draw a model that encompasses their heterogeneity, elucidates the different biological effects consequent to the identified molecular events, or incorporates extensive knowledge of molecular biomarkers and therapeutic targets. Here, we reviewed recent insights in NEN tumorigenesis from selected basic research studies on animal models, highlighting novel players in the intergenic cooperation and peculiar mechanisms including splicing dysregulation, chromatin stability, or cell dedifferentiation. Furthermore, models of tumorigenesis based on composite interactions other than a linear progression of events are proposed, exemplified by the involvement in NEN tumorigenesis of genes regulating complex functions, such as MEN1 or DAXX. Although limited by interspecies differences, animal models have proved helpful for the more in-depth study of every facet of tumorigenesis, showing that the identification of driver mutations is only one of the many necessary steps and that other mechanisms are worth investigating.

Endothelium-specific depletion of LRP1 improves glucose homeostasis through inducing osteocalcin

The vascular endothelium is present within metabolic organs and actively regulates energy metabolism. Here we show osteocalcin, recognized as a bone-secreted metabolic hormone, is expressed in mouse primary endothelial cells isolated from heart, lung and liver. In human osteocalcin promoter-driven green fluorescent protein transgenic mice, green fluorescent protein signals are enriched in endothelial cells lining aorta, small vessels and capillaries and abundant in aorta, skeletal muscle and eye of adult mice. The depletion of lipoprotein receptor-related protein 1 induces osteocalcin through a Forkhead box O -dependent pathway in endothelial cells. Whereas depletion of osteocalcin abolishes the glucose-lowering effect of low-density lipoprotein receptor-related protein 1 depletion, osteocalcin treatment normalizes hyperglycemia in multiple mouse models. Mechanistically, osteocalcin receptor-G protein-coupled receptor family C group 6 member A and insulin-like-growth-factor-1 receptor are in the same complex with osteocalcin and required for osteocalcin-promoted insulin signaling pathway. Therefore, our results reveal an endocrine/paracrine role of endothelial cells in regulating insulin sensitivity, which may have therapeutic implications in treating diabetes and insulin resistance through manipulating vascular endothelium.

Associations of Osteocalcin Forms With Metabolic Syndrome and Its Individual Components in Older Men: The Health In Men Study

CONTEXT

The osteoblast-derived polypeptide, osteocalcin (OC), has been associated with lower risk of type 2 diabetes and metabolic syndrome (MetS) in several epidemiological studies. Animal studies have indicated the undercarboxylated form of OC (ucOC) drives its association with metabolic outcomes.

OBJECTIVE

We compared associations of ucOC and carboxylated OC (cOC) with MetS and its components in older men.

METHODS

A cross-sectional analysis of 2575 men aged ≥70 years and older resident in Perth, Western Australia. ucOC was assayed using a hydroxyapatite-binding method, and cOC calculated by subtracting ucOC from total OC. Main outcome measures were MetS and its components.

RESULTS

Both lower serum ucOC and cOC levels, and the proportion of cOC (%cOC) were associated with less favorable metabolic parameters (higher waist circumference, triglyceride, glucose, blood pressure, and lower high-density lipoprotein cholesterol), whereas inverse associations were found with %ucOC. Men in the lowest quintile of ucOC had higher risk of MetS compared to men in the highest quintile (Q1 ≤ 7.7 vs Q5 > 13.8 ng/mL; OR = 2.4; 95% CI, 1.8-3.2). Men in the lowest quintile of cOC had higher risk of MetS compared to those in the highest quintile (≤ 5.8 vs > 13.0 ng/mL; OR = 2.4; 95% CI, 1.8-3.2).

CONCLUSION

Lower concentrations of serum ucOC or cOC were associated with less favorable metabolic parameters and a higher risk of MetS. In contrast, a lower proportion of ucOC was associated with better metabolic parameters and lower MetS risk. Further research is warranted to determine whether ucOC and cOC are suitable biomarkers for cardiometabolic risk in men.

Overexpression of miR-125b in Osteoblasts Improves Age-Related Changes in Bone Mass and Quality through Suppression of Osteoclast Formation

We recently reported an unexpected role of osteoblast-derived matrix vesicles in the delivery of microRNAs to bone matrix. Of such microRNAs, we found that miR-125b inhibited osteoclast formation by targeting Prdm1 encoding a transcriptional repressor of anti-osteoclastogenesis factors. Transgenic (Tg) mice overexpressing miR-125b in osteoblasts by using human osteocalcin promoter grow normally but exhibit high trabecular bone mass. We have now further investigated the effects of osteoblast-mediated miR-125b overexpression on skeletal morphogenesis and remodeling during development, aging and in a situation of skeletal repair, i.e., fracture healing. There were no significant differences in the growth plate, primary spongiosa or lateral (periosteal) bone formation and mineral apposition rate between Tg and wild-type (WT) mice during early bone development. However, osteoclast number and medial (endosteal) bone resorption were less in Tg compared to WT mice, concomitant with increased trabecular bone mass. Tg mice were less susceptible to age-dependent changes in bone mass, phosphate/amide I ratio and mechanical strength. In a femoral fracture model, callus formation progressed similarly in Tg and WT mice, but callus resorption was delayed, reflecting the decreased osteoclast numbers associated with the Tg callus. These results indicate that the decreased osteoclastogenesis mediated by miR-125b overexpression in osteoblasts leads to increased bone mass and strength, while preserving bone formation and quality. They also suggest that, in spite of the fact that single miRNAs may target multiple genes, the miR-125b axis may be an attractive therapeutic target for bone loss in various age groups.

Oral biosciences: The annual review 2020

BACKGROUND

The Journal of Oral Biosciences is devoted to the advancement and dissemination of fundamental knowledge concerning every aspect of oral biosciences.

HIGHLIGHT

This review featured the review articles in the fields of "Microbiology," "Palate," "Stem Cells," "Mucosal Diseases," "Bone Cell Biology," "MicroRNAs," "TRPV1 Cation Channels," and "Interleukins" in addition to the review article by prize-winners of the "Rising Members Award" ("DKK3 expression and function in head and neck squamous cell carcinoma and other cancers"), presented by the Japanese Association for Oral Biology.

CONCLUSION

These reviews in the Journal of Oral Biosciences have inspired the readers of the journal to broaden their knowledge regarding the various aspects of oral biosciences. The current editorial review introduces these exciting review articles.

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.

Sensitive detection of Cre-mediated recombination using droplet digital PCR reveals Tg(BGLAP-Cre) and Tg(DMP1-Cre) are active in multiple non-skeletal tissues

In humans, somatic activating mutations in PIK3CA are associated with skeletal overgrowth. In order to determine if activated PI3K signaling in bone cells causes overgrowth, we used Tg(BGLAP-Cre) and Tg(DMP1-Cre) mouse strains to somatically activate a disease-causing conditional Pik3ca allele (Pik3ca^H1047R) in osteoblasts and osteocytes. We observed Tg(BGLAP-Cre);Pik3ca^H1047R/+ offspring were born at the expected Mendelian frequency. However, these mice developed cutaneous lymphatic malformations and died before 7 weeks of age. In contrast, Tg(DMP1-Cre);Pik3ca^H1047R/+ offspring survived and had no cutaneous lymphatic malformations. Assuming that Cre-activity outside of the skeletal system accounted for the difference in phenotype between Tg(BGLAP-Cre);Pik3ca^H1047R/+ and Tg(DMP1-Cre);Pik3ca^H1047R/+ mice, we developed sensitive and specific droplet digital PCR (ddPCR) assays to search for and quantify rates of Tg(BGLAP-Cre)- and Tg(DMP1-Cre)-mediated recombination in non-skeletal tissues. We observed Tg(BGLAP-Cre)-mediated recombination in several tissues including skin, muscle, artery, and brain; two CNS locations, hippocampus and cerebellum, exhibited Cre-mediated recombination in >5% of cells. Tg(DMP1-Cre)-mediated recombination was also observed in muscle, artery, and brain. Although we cannot preclude that differences in phenotype between mice with Tg(BGLAP-Cre)- and Tg(DMP1-Cre)-mediated PIK3CA activation are due to Cre-recombination being induced at different stages of osteoblast differentiation, differences in recombination at non-skeletal sites are the more likely explanation. Since unanticipated sites of recombination can affect the interpretation of data from experiments involving conditional alleles, we recommend ddPCR as a good first step for assessing efficiency, leakiness, and off-targeting in experiments that employ Cre-mediated or Flp-mediated recombination.

Functions of Osteocalcin in Bone, Pancreas, Testis, and Muscle

Osteocalcin (Ocn), which is specifically produced by osteoblasts, and is the most abundant non-collagenous protein in bone, was demonstrated to inhibit bone formation and function as a hormone, which regulates glucose metabolism in the pancreas, testosterone synthesis in the testis, and muscle mass, based on the phenotype of Ocn^-/- mice by Karsenty's group. Recently, Ocn^-/- mice were newly generated by two groups independently. Bone strength is determined by bone quantity and quality. The new Ocn^-/- mice revealed that Ocn is not involved in the regulation of bone formation and bone quantity, but that Ocn regulates bone quality by aligning biological apatite (BAp) parallel to the collagen fibrils. Moreover, glucose metabolism, testosterone synthesis and spermatogenesis, and muscle mass were normal in the new Ocn^-/- mice. Thus, the function of Ocn is the adjustment of growth orientation of BAp parallel to the collagen fibrils, which is important for bone strength to the loading direction of the long bone. However, Ocn does not play a role as a hormone in the pancreas, testis, and muscle. Clinically, serum Ocn is a marker for bone formation, and exercise increases bone formation and improves glucose metabolism, making a connection between Ocn and glucose metabolism.

Osteocalcin and measures of adiposity: a systematic review and meta-analysis of observational studies

Osteocalcin, the osteoblast-derived protein, has been shown to be modulated in patients with problematic glucose metabolism. Our systematic review and meta-analysis found that in humans, higher blood osteocalcin level is associated with lower body indices of fat.

PURPOSE/INTRODUCTION

Osteocalcin (OC) was found to be inversely correlated with measures of glucose and energy metabolism, with some groups suggesting the undercarboxylated form (ucOC) to be metabolically active, although the link is not clear, especially in humans. Given obesity is a major risk factor for metabolic disorders, we aimed to assess the correlation between OC and two measures of body weight: body mass index (BMI) and percentage body fat (%BF).

METHODS

MEDLINE and EMBASE were searched to identify observational studies in adult populations that reported the crude correlation coefficients (r) between OC and BMI and %BF. Pool r were obtained using random-effects models.

RESULTS

Fifty-one publications were included in this analysis. Both total OC (TOC) (pooled r = - 0.151, 95% CI - 0.17, - 0.130; I² = 52%) and ucOC (pooled r = - 0.060, 95% CI - 0.103, - 0.016; I² = 54%) were inversely correlated with BMI. The pooled r between TOC and BMI in Caucasian-and-other-regions (r = - 0.187) were stronger than those in Asian populations (r = - 0.126; intra-group p = 0.002; R² = 0.21). The mean/median BMI of the reported cohort was the major contributor to between-study heterogeneity in correlation between TOC/ucOC and BMI (R² = 0.28 and 0.77, respectively). Both TOC and ucOC were also inversely correlated with %BF (TOC: pooled r = - 0.185, 95% CI - 0.257 to - 0.112; ucOC: pooled r = - 0.181, 95% CI - 0.258 to - 0.101).

CONCLUSION

Higher OC and ucOC were correlated with lower BMI and %BF. The inverse correlations between TOC/ucOC and BMI appear to be affected by ethnicity and obesity status.

Daxx maintains endogenous retroviral silencing and restricts cellular plasticity in vivo

Tumor sequencing studies have emphasized the role of epigenetics and altered chromatin homeostasis in cancer. Mutations in DAXX, which encodes a chaperone for the histone 3.3 variant, occur in 25% of pancreatic neuroendocrine tumors (PanNETs). To advance our understanding of physiological functions of Daxx, we developed a conditional Daxx allele in mice. We demonstrate that Daxx loss is well tolerated in the pancreas but creates a permissive transcriptional state that cooperates with environmental stress (inflammation) and other genetic lesions (Men1 loss) to alter gene expression and cell state, impairing pancreas recovery from inflammatory stress in vivo. The transcriptional changes are associated with dysregulation of endogenous retroviral elements (ERVs), and dysregulation of endogenous genes near ERVs is also observed in human PanNETs with DAXX mutations. Our results reveal a physiologic function of DAXX, provide a mechanism associated with impaired tissue regeneration and tumorigenesis, and expand our understanding of ERV regulation in somatic cells.

What is the function of osteocalcin?

BACKGROUND

Osteocalcin is the most abundant non-collagenous protein in bone and is specifically expressed in osteoblasts. Previous studies using osteocalcin-deficient (Ocn^-/-) mice demonstrated that osteocalcin inhibits bone formation, and serum uncarboxylated osteocalcin functions as a hormone that improves glucose metabolism, induces testosterone synthesis in the testes, and maintains muscle mass. Furthermore, the relationship between serum osteocalcin and glucose metabolism or cardiovascular risk in humans has been reported. However, new Ocn^-/- mice exhibited different phenotypes.

HIGHLIGHT

Bone volume, formation, and resorption were normal in the new Ocn^-/- mice. The orientation of collagen fibers was parallel to the bone longitudinal direction and the size of apatite crystals was normal, but the c-axis of apatite crystals was random and bone strength was reduced in new Ocn^-/- mice. Glucose metabolism, testosterone synthesis, and muscle mass were normal in new Ocn^-/- mice. Exercise improved glucose metabolism and increased bone formation, leading to an increase in the serum osteocalcin level, which is a marker for bone formation.

CONCLUSION

Contrary to previous findings, new Ocn^-/- mice revealed that osteocalcin has no function in the regulation of bone quantity, but instead, functions to direct the parallel alignment of the c-axis of apatite crystals with collagen fibrils. Moreover, it has no physiological function as a hormone that regulates glucose metabolism, testosterone synthesis, or muscle mass. These controversial phenotypes require further investigation. The relationship of serum osteocalcin with glucose metabolism or cardiovascular risk suggests the importance of exercise for their improvement.

Osteocalcin is necessary for the alignment of apatite crystallites, but not glucose metabolism, testosterone synthesis, or muscle mass

The strength of bone depends on bone quantity and quality. Osteocalcin (Ocn) is the most abundant noncollagenous protein in bone and is produced by osteoblasts. It has been previously claimed that Ocn inhibits bone formation and also functions as a hormone to regulate insulin secretion in the pancreas, testosterone synthesis in the testes, and muscle mass. We generated Ocn-deficient (Ocn^–/–) mice by deleting Bglap and Bglap2. Analysis of Ocn^–/–mice revealed that Ocn is not involved in the regulation of bone quantity, glucose metabolism, testosterone synthesis, or muscle mass. The orientation degree of collagen fibrils and size of biological apatite (BAp) crystallites in the c-axis were normal in the Ocn^–/–bone. However, the crystallographic orientation of the BAp c-axis, which is normally parallel to collagen fibrils, was severely disrupted, resulting in reduced bone strength. These results demonstrate that Ocn is required for bone quality and strength by adjusting the alignment of BAp crystallites parallel to collagen fibrils; but it does not function as a hormone.

The strength of bone depends on both its quantity and quality. Osteocalcin (Ocn) is the most abundant non-collagenous protein in bone, but its function remains unclear. Earlier studies by other investigators have suggested that Ocn decreases the quantity of bone by decreasing bone formation; and in addition it works as a hormone to regulate glucose metabolism, testosterone synthesis, and muscle mass in distant tissues. We have generated Ocn-deficient mice and show herein that Ocn is not required for bone formation. It is, however, required for optimal bone quality and strength. Specifically, we show that in the Ocn-deficient mice collagen fibers align normally, but apatite crystallites align randomly against collagen, resulting in disorganized mineralization and reduced bone strength. Furthermore, we show that glucose metabolism, testosterone synthesis, and muscle mass are normal in the Ocn-deficient mice. We conclude that Ocn acts in bone to optimize its quality and strength, but not quantity. And, in contrast to earlier claims, it does not work as a hormone to control glucose metabolism, testosterone synthesis, and muscle mass.

Delayed tooth movement in Runx2+/- mice associated with mTORC2 in stretch-induced bone formation

Runt-related transcription factor 2 (Runx2) is an essential transcription factor for osteoblast differentiation, and is activated by mechanical stress to promote osteoblast function. Cleidocranial dysplasia (CCD) is caused by mutations of RUNX2, and CCD patients exhibit malocclusion and often need orthodontic treatment. However, treatment is difficult because of impaired tooth movement, the reason of which has not been clarified. We examined the amount of experimental tooth movement in Runx2^+/− mice, the animal model of CCD, and investigated bone formation on the tension side of experimental tooth movement in vivo. Continuous stretch was conducted to bone marrow stromal cells (BMSCs) as an in vitro model of the tension side of tooth movement. Compared to wild-type littermates the Runx2^+/− mice exhibited delayed experimental tooth movement, and osteoid formation and osteocalcin (OSC) mRNA expression were impaired in osteoblasts on the tension side of tooth movement. Runx2 heterozygous deficiency delayed stretch-induced increase of DNA content in BMSCs, and also delayed and reduced stretch-induced alkaline phosphatase (ALP) activity, OSC mRNA expression, and calcium content of BMSCs in osteogenic medium. Furthermore Runx2^+/− mice exhibited delayed and suppressed expression of mammalian target of rapamycin (mTOR) and rapamycin-insensitive companion of mTOR (Rictor), essential factors of mTORC2, which is regulated by Runx2 to phosphorylate Akt to regulate cell proliferation and differentiation, in osteoblasts on the tension side of tooth movement in vivo and in vitro. Loss of half Runx2 gene dosage inhibited stretch-induced PI3K dependent mTORC2/Akt activity to promote BMSCs proliferation. Furthermore, Runx2^+/− BMSCs in osteogenic medium exhibited delayed and suppressed stretch-induced expression of mTOR and Rictor. mTORC2 regulated stretch-elevated Runx2 and ALP mRNA expression in BMSCs in osteogenic medium. We conclude that Runx2^+/− mice present a useful model of CCD patients for elucidation of the molecular mechanisms in bone remodeling during tooth movement, and that Runx2 plays a role in stretch-induced proliferation and osteogenesis in BMSCs via mTORC2 activation.

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Experimental tooth movement is delayed in Runx2^+/− mice compared with wild-type mice.

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Runx2 plays a role in stretch-induced proliferation and differentiation of BMSCs via mTORC2 activation.

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Runx2^+/− mice are useful model to clarify the mechanical stress-induced bone remodeling in CCD patients.

Effect of vitamin K2 on type 2 diabetes mellitus: A review

Type 2 diabetes mellitus (T2DM) continue to be a major public health problem around the world that frequently presents with microvascular and macrovascular complications. Individuals with T2DM are not only suffering from significant emotional and physical misery, but also at increased risk of dying from severe complications. In recent years, evidence from prospective observational studies and clinical trials has shown T2DM risk reduction with vitamin K2 supplementation. We thus did an overview of currently available studies to assess the effect of vitamin K2 supplementation on insulin sensitivity, glycaemic control and reviewed the underlying mechanisms. We proposed that vitamin K2 improved insulin sensitivity through involvement of vitamin K-dependent-protein osteocalcin, anti-inflammatory properties, and lipid-lowering effects. Vitamin K2 had a better effect than vitamin K1 on T2DM. The interpretation of this review will increase comprehension of the development of a therapeutic strategy to prevent and treat T2DM.

Interaction between bone and glucose metabolism [Review]

Accumulating evidence has shown that bone and glucose metabolism are closely associated with each other. Since the risk of osteoporotic fractures is increased in patients with diabetes mellitus (DM), osteoporosis is recently recognized as one of diabetic complications, called DM-induced bone fragility. Previous studies showed that collagen cross-links of advanced glycation end products (AGEs) and dysfunctions of osteoblast and osteocyte are involved in DM-induced bone fragility. Circulating levels of AGEs and homocysteine are increased in patients with DM, and they directly impair the functions of osteoblast and osteocyte, resulting in decreased bone formation and bone remodeling. On the other hand, bone is recently recognized as an endocrine organ. Previous studies based on in vitro and animal studies showed that osteocalcin, which is specifically expressed in osteoblasts and secreted into the circulation, may regulate glucose homeostasis. Although several clinical studies reported the relationship between osteocalcin and glucose metabolism, further large-scale and intervention studies are necessary to confirm the beneficial effects of osteocalcin on glucose metabolism in human. It has been shown that adenosine monophosphate-activated protein kinase (AMPK), an intracellular energy sensor, is involved in bone metabolism. Adiponectin and metformin stimulate osteocalcin expression and the differentiation of osteoblasts via AMPK activation. Also, AMPK activation protects against oxidative stress-induced apoptosis of osteocytes. These findings suggest that AMPK in osteoblasts and osteocytes may be a therapeutic target for DM-induced bone fragility.

Altered Ethanol Consumption in Osteocalcin Null Mutant Mice

Osteocalcin (OC) is an abundant extracellular calcium-binding protein synthesized by osteoblasts. Although most OC is bound to hydroxyapatite mineral during bone formation, a consistent amount is released directly to circulation. Plasma OC (pOC) levels are highly sensitive to stressful stimuli that alter stress-responsive hormones, such as glucocorticoids (cortisol or corticosterone) and the catecholamines norepinephrine and epinephrine. To gain a better understanding of the apparent relationship of OC to the effects of ethanol (EtOH) and the stress responses, we compared mice that have OC (WT [OC+/+] and HET [OC+/-]) with OC null mutants (KO [OC-/-]), which have no OC in either plasma or in bone. One experiment included chronic unpredictable stress, a second was conducted in the absence of any known stressors other than EtOH, while a third imposed a more severe acute immobilization stress in addition to EtOH consumption. The data obtained confirmed significant differences in EtOH consumption in mice that previously experienced various stressful stimuli. We also determined that adrenal tyrosine-hydroxylase expression was inversely proportional to EtOH consumption and tended to be lower in KO than in WT. Data suggest that OC possesses the ability to modulate the adrenal gene expression of the catecholamine synthetic pathway. This modulation may be responsible for differences in EtOH consumption under stress.

Bone Cell Bioenergetics and Skeletal Energy Homeostasis

The rising incidence of metabolic diseases worldwide has prompted renewed interest in the study of intermediary metabolism and cellular bioenergetics. The application of modern biochemical methods for quantitating fuel substrate metabolism with advanced mouse genetic approaches has greatly increased understanding of the mechanisms that integrate energy metabolism in the whole organism. Examination of the intermediary metabolism of skeletal cells has been sparked by a series of unanticipated observations in genetically modified mice that suggest the existence of novel endocrine pathways through which bone cells communicate their energy status to other centers of metabolic control. The recognition of this expanded role of the skeleton has in turn led to new lines of inquiry directed at defining the fuel requirements and bioenergetic properties of bone cells. This article provides a comprehensive review of historical and contemporary studies on the metabolic properties of bone cells and the mechanisms that control energy substrate utilization and bioenergetics. Special attention is devoted to identifying gaps in our current understanding of this new area of skeletal biology that will require additional research to better define the physiological significance of skeletal cell bioenergetics in human health and disease.

Bone-Derived Factors: A New Gateway to Regulate Glycemia

Type 2 diabetes mellitus (T2DM) and osteoporosis are two major disorders which prevalence increases with aging and is predicted to worsen in the coming years. Preclinical investigations suggest common mechanisms implicated in the pathogenesis of both disorders. Recent evidence has established that there is a clear link between glucose and bone metabolism. The emergence of bone as an endocrine regulator through FGF23 and osteocalcin has led to the re-evaluation of the role of bone cells and bone-derived factors in the development of metabolic diseases such as T2DM. The development of bone morphogenetic proteins, fibroblast growth factor 23, and osteoprotegerin-deficient mice has allowed to elucidate their role in bone homeostasis, as well as revealed their potential important function in glucose homeostasis. This review proposes emerging perspectives for several bone-derived factors that may regulate glycemia through the activation or inhibition of bone remodeling or directly by regulating function of key organs such as pancreatic beta cell proliferation, insulin expression and secretion, storage and release of glucose from the liver, skeletal muscle contraction, and browning of the adipose tissue. Connections between organs including bone-derived factors should further be explored to understand the pathophysiology of glucose metabolism and diabetes.

Increased trabecular bone and improved biomechanics in an osteocalcin-null rat model created by CRISPR/Cas9 technology

Osteocalcin, also known as bone γ-carboxyglutamate protein (Bglap), is expressed by osteoblasts and is commonly used as a clinical marker of bone turnover. A mouse model of osteocalcin deficiency has implicated osteocalcin as a mediator of changes to the skeleton, endocrine system, reproductive organs and central nervous system. However, differences between mouse and human osteocalcin at both the genome and protein levels have challenged the validity of extrapolating findings from the osteocalcin-deficient mouse model to human disease. The rat osteocalcin (Bglap) gene locus shares greater synteny with that of humans. To further examine the role of osteocalcin in disease, we created a rat model with complete loss of osteocalcin using the CRISPR/Cas9 system. Rat osteocalcin was modified by injection of CRISPR/Cas9 mRNA into the pronuclei of fertilized single cell Sprague-Dawley embryos, and animals were bred to homozygosity and compound heterozygosity for the mutant alleles. Dual-energy X-ray absorptiometry (DXA), glucose tolerance testing (GTT), insulin tolerance testing (ITT), microcomputed tomography (µCT), and a three-point break biomechanical assay were performed on the excised femurs at 5 months of age. Complete loss of osteocalcin resulted in bones with significantly increased trabecular thickness, density and volume. Cortical bone volume and density were not increased in null animals. The bones had improved functional quality as evidenced by an increase in failure load during the biomechanical stress assay. Differences in glucose homeostasis were observed between groups, but there were no differences in body weight or composition. This rat model of complete loss of osteocalcin provides a platform for further understanding the role of osteocalcin in disease, and it is a novel model of increased bone formation with potential utility in osteoporosis and osteoarthritis research.

Summary: A complete null of osteocalcin, generated by the CRISPR/Cas9 system, results in an increase in trabecular bone, increased bone strength and altered glucose homeostasis in Sprague-Dawley rats.

New insights into the biology of osteocalcin

Osteocalcin is among the most abundant proteins in bone and is produced exclusively by osteoblasts. Initially believed to be an inhibitor of bone mineralization, recent studies suggest a broader role for osteocalcin that extends to the regulation of whole body metabolism, reproduction, and cognition. Circulating undercarboxylated osteocalcin, which is regulated by insulin, acts in a feed-forward loop to increase β-cell proliferation as well as insulin production and secretion, while skeletal muscle and adipose tissue respond to osteocalcin by increasing their sensitivity to insulin. Osteocalcin also acts in the brain to increase neurotransmitter production and in the testes to stimulate testosterone production. At least one putative receptor for osteocalcin, Gprc6a, is expressed by adipose, skeletal muscle, and the Leydig cells of the testes and appears to mediate osteocalcin's effects in these tissues. In this review, we summarize these new discoveries, which suggest that the ability of osteocalcin to function both locally in bone and as a hormone depends on a novel post-translational mechanism that alters osteocalcin's affinity for the bone matrix and bioavailability. This article is part of a Special Issue entitled Bone and diabetes.

Histone demethylase JMJD3 is required for osteoblast differentiation in mice

JMJD3 (KDM6B) is an H3K27me3 demethylases and emerges as an important player in developmental processes. Although some evidence indicated the involvement of JMJD3 in osteoblast differentiation in vitro, its role as a whole in osteoblast differentiation and bone formation in vivo remains unknown. Here we showed that homozygous deletion of Jmjd3 resulted in severe delay of osteoblast differentiation and bone ossification in mice. By biochemical and genetical methods, we demonstrated that JMJD3 mediated RUNX2 transcriptional activity and cooperated with RUNX2 to promote osteoblast differentiation and bone formation in vivo. These results strongly demonstrated that JMJD3 is required for osteoblast differentiation and bone formation in mice.

Comprehensive Assessment of Host Responses to 5-Fluorouracil-Induced Oral Mucositis through Transcriptomic Analysis

Background

Chemotherapy plays an important role in current cancer therapy; however, several problems remain unsolved on the issue of host-therapeutics interaction. The purpose of this study was to investigate the host responses after 5-flurouracil (5-FU) administration and to find the target genes and their relationship with other cytokines in the 5-FU-induced oral mucositis (OM) mouse model through transcriptomic analysis.

Materials and Methods

Thirty-six 6 to 8 week-old male BALB/c mice were randomly divided into the control group and 5-FU-treated group. In the 5-FU group, mice received 5-FU (100 mg/kg, intraperitoneally) on day 1, day 8, day 15, day 22, and day 29, respectively. We evaluated the oral mucosal change under macroanalysis and histological examination at indicated periods, and then applied transcriptomic analysis of gene expression profile and Immunohistochemical stain to identify the target molecules related to 5-FU-induced OM.

Results

The most prominent histological change in this model was observed in the fifth week. The gene expression of Bone gamma-carboxyglutamate protein, related sequence 1 (Bglap-rs1) (–12.69-fold) and Chitinase 3-like 4 (Chi3l4) (–6.35-fold) were significantly down-regulated in this phase. The quantitative real-time PCR results also revealed the expression levels were 0.62-fold in Bglap-rs1 and 0.13-fold in Chi3l4 compared with the control group. Immunohistochemical stain showed significant expression of cluster of differentiation 11b (p<0.01), interleukin-1β (p<0.001) and tumor necrosis factor-α (p<0.05), and down-regulation of Bglap-rs1 (p<0.01) compared with the control group. By Kyoto Encyclopedia of Genes and Genomes pathway analysis, there were twenty-three pathways significantly participated in this study (p<0.05).

Conclusions

Through comprehensively transcriptomic analysis and IHC stain, we discovered several valuable pathways, verified the main pro-inflammatory cytokines, and revealed two significantly down-regulated genes in the 5-FU-induced OM model. These findings highlighted the way of seeking effective therapeutic agents for chemotherapy-induced OM in future.

An overview of the metabolic functions of osteocalcin

A recent unexpected development of bone biology is that bone is an endocrine organ regulating a growing number of physiological processes. One of the functions regulated by bone through the hormone osteocalcin is glucose homeostasis. In this overview, we will explain why we hypothesized that bone mass and energy metabolism should be subjected to a coordinated endocrine regulation. We will then review the experiments that revealed the endocrine function of osteocalcin and the cell biology events that allow osteocalcin to become a hormone. We will also illustrate the importance of this regulation to understand whole-body glucose homeostasis in the physiological state and in pathological conditions. Lastly, we will mention epidemiological and genetic evidence demonstrating that this function of osteocalcin is conserved in humans.

An overview of the metabolic functions of osteocalcin

A recent unexpected development of bone biology is that bone is an endocrine organ contributing to the regulation of a number of physiological processes. One of the functions regulated by bone through osteocalcin, an osteoblast specific hormone, is glucose homeostasis. In this overview, we explain the rationale why we hypothesized that there should be a coordinated endocrine regulation between bone mass and energy metabolism. We then review the experiments that identified the endocrine function of osteocalcin and the cell biology events that allow osteocalcin to become a hormone. We also demonstrate the importance of this regulation to understand whole-body glucose homeostasis in the physiological state and in pathological conditions. Lastly we discuss the epidemiological and genetic evidence demonstrating that this function of osteocalcin is conserved in humans.

Deletion of connexin43 in osteoblasts/osteocytes leads to impaired muscle formation in mice

It is well-established that muscle forces are necessary for bone development as well as proper bone modeling and remodeling. Recent work has also suggested that bone acts as an endocrine organ that can influence the development of other organs. Connexin43 (Cx43), a gap junction protein that transduces mechanical signals, is an important determinant of cortical bone modeling. Using an osteoblast/osteocyte-specific ablation of the Cx43 gene (Gja1) driven by the 2.3-kb Col1 α1 promoter (cKO) in the mouse, in this study we confirmed reduced cortical bone thickness and density with expanded bone marrow cavity in the cKO humerus. Surprisingly, Gja1 deletion in bone cells also affected skeletal muscle development, resulting in lower fast muscle weight, grip strength, and maximum absolute and specific tetanic forces (60% to 80%, 85%, and 50%, respectively, of WT mice). The normally fast twitch extensor digitorum longus (EDL) muscle exhibited increased slow twitch fibers in cKO mice. These muscle defects were accompanied by a 40% to 60% reduction in mRNA abundance for genes encoding osteocalcin in the humerus, relative to WT mice. Accordingly, both carboxylated and undercarboxylated isoforms of osteocalcin were reduced by over 30% in the circulation of cKO mice. Moreover, the active, undercarboxylated isoform of osteocalcin (glu-OC) promoted myotube formation in C2C12 myoblast cultures, and glu-OC injections to cKO mice rescued EDL muscle cross-sectional area and grip strength in vivo. These findings demonstrate that Cx43 in osteoblasts/osteocytes indirectly modulates skeletal muscle growth and function, potentially via an endocrine effect of glu-OC.

A melting method for RNA extraction from the mucosal membrane of the mouse middle ear

PURPOSE

There is much confusion surrounding the methods of RNA extraction from the middle ear mucosa of mice. In this study, we worked to develop a "melting method," which is faster, purer, and more reliable than other methods in common use.

MATERIALS AND METHODS

Thirty-two ears were used for this study. Light microscopy with hematoxylin-eosin staining of the bullae, scanning electron microscopy (SEM), spectrophotometer analysis, and reverse transcription polymerase chain reaction were performed before and after melting the half lateral bullae, which were detached from the temporal bone by using a lateral retroauricular approach.

RESULTS

Each resected half bulla contained a well distributed mucosal membrane. After a TRIzol melting duration of 10-30 minutes, only mucosal marker (MUC5AC) was expressed without bony marker (total osteocalcin). The same results were determined from SEM.

CONCLUSION

This melting method, compared with stripping and irrigation methods, is effective and offers an easier, more robust approach to extracting RNA from the middle ear mucosal membranes of mice.

A whole genome SNP genotyping by DNA microarray and candidate gene association study for kidney stone disease

BACKGROUND

Kidney stone disease (KSD) is a complex disorder with unknown etiology in majority of the patients. Genetic and environmental factors may cause the disease. In the present study, we used DNA microarray to genotype single nucleotide polymorphisms (SNP) and performed candidate gene association analysis to determine genetic variations associated with the disease.

METHODS

A whole genome SNP genotyping by DNA microarray was initially conducted in 101 patients and 105 control subjects. A set of 104 candidate genes reported to be involved in KSD, gathered from public databases and candidate gene association study databases, were evaluated for their variations associated with KSD.

RESULTS

Altogether 82 SNPs distributed within 22 candidate gene regions showed significant differences in SNP allele frequencies between the patient and control groups (P < 0.05). Of these, 4 genes including BGLAP, AHSG, CD44, and HAO1, encoding osteocalcin, fetuin-A, CD44-molecule and glycolate oxidase 1, respectively, were further assessed for their associations with the disease because they carried high proportion of SNPs with statistical differences of allele frequencies between the patient and control groups within the gene. The total of 26 SNPs showed significant differences of allele frequencies between the patient and control groups and haplotypes associated with disease risk were identified. The SNP rs759330 located 144 bp downstream of BGLAP where it is a predicted microRNA binding site at 3'UTR of PAQR6 - a gene encoding progestin and adipoQ receptor family member VI, was genotyped in 216 patients and 216 control subjects and found to have significant differences in its genotype and allele frequencies (P = 0.0007, OR 2.02 and P = 0.0001, OR 2.02, respectively).

CONCLUSIONS

Our results suggest that these candidate genes are associated with KSD and PAQR6 comes into our view as the most potent candidate since associated SNP rs759330 is located in the miRNA binding site and may affect mRNA expression level.

The negative impact of single prolonged stress (SPS) on bone development in mice

Posttraumatic stress disorder (PTSD) disrupts hypothalamic-pituitary-adrenal (HPA) axis function. Given the established role of HPA axis hormones in regulating bone metabolism, we tested the hypothesis that traumatic stress has a negative impact on bone development. We employed a variant single prolonged stress (SPS) model in which several stressors were applied to three week old C57BL/6J mice. Compared to the controls, the stressed mice showed increased freezing behavior reminiscent of PTSD symptoms. At two weeks, bone mineral content (BMC), bone area (B area) and bone mineral density (BMD) in total body based on dual-energy X-ray absorptiometry (DXA) analysis were reduced by 10.2%, 7.0% and 3.6%, respectively. Micro-CT analysis of the metaphyseal region of the excised tibia revealed that SPS caused a deterioration of trabecular architecture with trabecular number (Tb.N), BV/TV, connectivity density (Conn-Den) decreasing 12.0%, 18.9%, 23.3% and trabecular spacing (Tb.Sp), structure model index (SMI) increasing 13.9%, 21.8%, respectively. Mechanical loading increased the cross-sectional area in the mid-shaft region of the loaded right versus unloaded left tibia by 7.6% in the controls, and 10.0% in the stressed mice. Therefore, SPS applied to pre-pubertal young mice produced strong negative impact on both bone mass acquisition and trabecular architecture. Mechanical loading can be employed to increase bone size, a parameter related to bone strength, in normal as well as stressed conditions.

Inactivation of anoctamin-6/Tmem16f, a regulator of phosphatidylserine scrambling in osteoblasts, leads to decreased mineral deposition in skeletal tissues

During vertebrate skeletal development, osteoblasts produce a mineralized bone matrix by deposition of hydroxyapatite crystals in the extracellular matrix. Anoctamin6/Tmem16F (Ano6) belongs to a conserved family of transmembrane proteins with chloride channel properties. In addition, Ano6 has been linked to phosphatidylserine (PS) scrambling in the plasma membrane. During skeletogenesis, Ano6 mRNA is expressed in differentiating and mature osteoblasts. Deletion of Ano6 in mice results in reduced skeleton size and skeletal deformities. Molecular analysis revealed that chondrocyte and osteoblast differentiation are not disturbed. However, mutant mice display increased regions of nonmineralized, Ibsp-expressing osteoblasts in the periosteum during embryonic development and increased areas of uncalcified osteoid postnatally. In primary Ano6(-/-) osteoblasts, mineralization is delayed, indicating a cell autonomous function of Ano6. Furthermore, we demonstrate that calcium-dependent PS scrambling is impaired in osteoblasts. Our study is the first to our knowledge to reveal the requirement of Ano6 in PS scrambling in osteoblasts, supporting a function of PS exposure in the deposition of hydroxyapatite.

The role of osteocalcin in human glucose metabolism: marker or mediator?

Increasing evidence supports an association between the skeleton and energy metabolism. These interactions are mediated by a variety of hormones, cytokines and nutrients. Here, the evidence for a role of osteocalcin in the regulation of glucose metabolism in humans is reviewed. Osteocalcin is a bone matrix protein that regulates hydroxyapatite size and shape through its vitamin-K-dependent, γ-carboxylated form. The concentration of osteocalcin in the circulation is a measure of bone formation. The undercarboxylated form of osteocalcin is active in glucose metabolism in mice. Total serum osteocalcin concentrations in humans are inversely associated with measures of glucose metabolism; however, human data are inconclusive with regard to the role of uncarboxylated osteocalcin in glucose metabolism because most studies do not account for the influence of vitamin K on the proportion of undercarboxylated osteocalcin or differentiate between the total and uncarboxylated forms of osteocalcin. Furthermore, most human studies do not concomitantly measure other bone turnover markers to isolate the role of osteocalcin as a measure of bone formation from its effect on glucose metabolism. Carefully designed studies are required to define the role of osteocalcin and its carboxylated or undercarboxylated forms in the regulation of glucose metabolism in humans.

Distinct patterns of notochord mineralization in zebrafish coincide with the localization of Osteocalcin isoform 1 during early vertebral centra formation

BACKGROUND

In chondrichthyans, basal osteichthyans and tetrapods, vertebral bodies have cartilaginous anlagen that subsequently mineralize (chondrichthyans) or ossify (osteichthyans). Chondrocytes that form the vertebral centra derive from somites. In teleost fish, vertebral centrum formation starts in the absence of cartilage, through direct mineralization of the notochord sheath. In a second step, the notochord is surrounded by somite-derived intramembranous bone. In several small teleost species, including zebrafish (Danio rerio), even haemal and neural arches form directly as intramembranous bone and only modified caudalmost arches remain cartilaginous. This study compares initial patterns of mineralization in different regions of the vertebral column in zebrafish. We ask if the absence or presence of cartilaginous arches influences the pattern of notochord sheath mineralization.

RESULTS

To reveal which cells are involved in mineralization of the notochord sheath we identify proliferating cells, we trace mineralization on the histological level and we analyze cell ultrastructure by TEM. Moreover, we localize proteins and genes that are typically expressed by skeletogenic cells such as Collagen type II, Alkaline phosphatase (ALP) and Osteocalcin (Oc). Mineralization of abdominal and caudal vertebrae starts with a complete ring within the notochord sheath and prior to the formation of the bony arches. In contrast, notochord mineralization of caudal fin centra starts with a broad ventral mineral deposition, associated with the bases of the modified cartilaginous arches. Similar, arch-related, patterns of mineralization occur in teleosts that maintain cartilaginous arches throughout the spine.Throughout the entire vertebral column, we were able to co-localize ALP-positive signal with chordacentrum mineralization sites, as well as Collagen II and Oc protein accumulation in the mineralizing notochord sheath. In the caudal fin region, ALP and Oc signals were clearly produced both by the notochord epithelium and cells outside the notochord, the cartilaginous arches. Based on immunostaining, real time PCR and oc2:gfp transgenic fish, we identify Oc in the mineralizing notochord sheath as osteocalcin isoform 1 (Oc1).

CONCLUSIONS

If notochord mineralization occurs prior to arch formation, mineralization of the notochord sheath is ring-shaped. If notochord mineralization occurs after cartilaginous arch formation, mineralization of the notochord sheath starts at the insertion point of the arches, with a basiventral origin. The presence of ALP and Oc1, not only in cells outside the notochord, but also in the notochord epithelium, suggests an active role of the notochord in the mineralization process. The same may apply to Col II-positive chondrocytes of the caudalmost haemal arches that show ALP activity and Oc1 accumulation, since these chondrocytes do not mineralize their own cartilage matrix. Even without cartilaginous preformed vertebral centra, the cartilaginous arches may have an inductive role in vertebral centrum formation, possibly contributing to the distinct mineralization patterns of zebrafish vertebral column and caudal fin vertebral fusion.

Effect of alginate hydrogel containing polyproline-rich peptides on osteoblast differentiation

Polyproline-rich synthetic peptides have previously been shown to induce bone formation and mineralization in vitro and to decrease bone resorption in vivo. Alginate hydrogel formulations containing these synthetic peptides (P2, P5, P6) or Emdogain® (EMD) were tested for surface coating of bone implants. In an aqueous environment, the alginate hydrogels disclosed a highly compact structure suitable for cell adhesion and proliferation. Lack of cytotoxicity of the alginate-gel coating containing peptides was tested in MC3T3-E1 cell cultures. In the present study, relative mRNA expression levels of integrin alpha 8 were induced by P5 compared to untreated alginate gel, and osteopontin mRNA levels were increased after 21 days of culture by treatment with synthetic peptides or EMD compared to control. Further, in agreement with previous results when the synthetic peptides were administered in the culture media, osteocalcin mRNA was significantly upregulated after long-term treatment with the formulated synthetic peptides compared to untreated and EMD alginate gel. These results indicate that the alginate gel is a suitable carrier for the delivery of synthetic peptides, and that the formulation is promising as biodegradable and biocompatible coating for bone implants.

Correlation between molecular signals and bone bonding to titanium implants

OBJECTIVES

A better understanding of the biological processes controlling osseointegration at the bone-to-implant interface is needed. The aim of this study was to examine which are the molecular and biochemical variables that are significantly related to osseointegration, using multiple regression analysis.

MATERIALS AND METHODS

Titanium coins were placed into the tibial cortical bone of New Zealand White rabbits and evaluated using pull-out test after 4 and 8 weeks of healing. Correlations between pull-out and several markers from tissue fluid (Lactate dehydrogenase [LDH] and Alkaline phosphatase [ALP] activities and total protein content) and peri-implant bone tissue (total protein, RNA and DNA content, implant area covered with bone and gene expression of osteoblast, osteoclast and inflammation markers) were used to assess the importance of these parameters in bone healing and in relation to implant performance.

RESULTS

Our results showed a negative correlation between the content of DNA, RNA and total protein at the peri-implant bone tissue and the pull-out force, indicating that as bone matures and implant becomes more osseointegrated, the organic content of bone decreases. The negative correlation found between pull-out force and ALP activity pointed to a delayed healing in implants with lower pull-out values and primary mineralization still ongoing. LDH activity and total protein content in the tissue fluid were as well negatively correlated with the pull-out force. Finally, a positive correlation was observed between the pull-out force and the expression of the osteoblast and the bone resorption markers, being osteocalcin and collagen-I the best predictive markers for osseointegration after 4 and 8 weeks of healing respectively.

CONCLUSIONS

These results suggest that the evaluation of these markers could be relevant for the assessment of new implant surfaces for rapid bone healing and improved implant performance.

Multiligand specificity and wide tissue expression of GPRC6A reveals new endocrine networks

Emerging evidence supports the hypothesis that the skeleton is an endocrine organ that regulates energy metabolism through the release of the osteoblast-derived hormone, osteocalcin (Ocn). This bone-pancreas endocrine network is controversial because important gaps remain to be filled in our knowledge of the physiological effects of Ocn in multiple organs and the complex alterations in other hormonal networks induced by Ocn administration. A key step toward understanding the integrative regulation of energy metabolism by bone is the identification of GPCR family C group 6 member A (GPRC6A) as the Ocn receptor. GPRC6A is an amino acid-sensing G protein-coupled receptor highly expressed in β-cells and is activated by recombinant Ocn in vitro and in vivo but that is widely expressed in tissues other than the pancreas and is capable of sensing multiple structurally unrelated ligands, including l-amino acids, cations, and anabolic steroids in addition to Ocn. The broad expression and multiligand specificity of GPRC6A is identifying both systemic and paracrine regulation of seemingly disparate biological processes, ranging from energy metabolism, sexual reproduction, hypothalamic-pituitary function, bone formation, and prostate cancer. Consistent with the existence of more complex endocrine networks, ablation of GPRC6A in Gprc6a(-/-) mice results in complex metabolic abnormalities, including obesity, glucose intolerance, hepatic steatosis, insulin resistance, hyperphosphatemia, osteopenia, plus several hormonal abnormalities, including decreased circulating testosterone, IGF-I, and insulin and increased estradiol, LH, GH, and leptin. Recombinant Ocn also regulates testosterone production by the testes and male fertility through a GPRC6A-dependent mechanism, and testosterone regulation of LH secretion is abnormal in Gprc6a(-/-) mice. Thus, GPRC6A, as the biologically relevant receptor for Ocn, defines not only a molecular mechanism for linking bone metabolism with metabolic regulation of β-cells and sexual reproduction but also as a receptor shared by testosterone and dietary factors, and it is also involved in multiple endocrine networks integrating the functions of pancreas, muscle, liver, fat, testes, bone, and the hypothalamic-pituitary axis with alterations in both environmental and endogenous ligands.

Decreased sensory responses in osteocalcin null mutant mice imply neuropeptide function

Osteocalcin, the most abundant member of the family of extracellular mineral binding gamma-carboxyglutamic acid proteins is synthesized primarily by osteoblasts. Its affinity for calcium ions is believed to limit bone mineralization. Several of the numerous hormones that regulate synthesis of osteocalcin, including glucocorticoids and parathyroid hormone, are also affected by stressful stimuli that require energy for an appropriate response. Based on our observations of OC responding to stressful sensory stimuli, the expression of OC in mouse and rat sensory ganglia was confirmed. It was thus hypothesized that the behavioral responses of the OC knockout mouse to stressful sensory stimuli would be abnormal. To test this hypothesis, behaviors related to sensory aspects of the stress response were quantified in nine groups of mice, aged 4-14 months, comparing knockout with their wild-type counterparts in six distinctly different behavioral tests. Resulting data indicated the following statistically significant differences: open field grooming frequency following saline injection, wild-type > knockout; paw stimulation with Von Frey fibers, knockout < wild-type; balance beam, knockout mobility < WT; thermal sensitivity to heat (tail flick), knockout < wild-type; and cold, knockout < wild-type. Insignificant differences in hanging wire test indicate that these responses are unrelated to reduced muscle strength. Each of these disparate environmental stimuli provided data indicating alterations of responses in knockout mice that suggest participation of osteocalcin in transmission of information about those sensory stimuli.