Effects of short chain fatty acid, sodium butyrate, on osteoblastic cells and osteoclastic cells

Protective effects of sodium butyrate on fluorosis in rats by regulating bone homeostasis and serum metabolism

Fluorosis due to high fluoride levels in drinking water profoundly affects the development of human skeletal and dental structures. Sodium butyrate (NaB) has been found to regulate overall bone mass and prevent pathological bone loss. However, the mechanism of NaB action on fluorosis remains unclear. In this study, a rat model of fluorosis induced by 100 mg/L sodium fluoride was used to investigate the impact of NaB on bone homeostasis and serum metabolomics. It was found that NaB significantly reduced the levels of bone resorption markers CTX-Ⅰ and TRACP-5B in fluorosis rats. Moreover, NaB increased calcium and magnesium levels in bone, while decreasing phosphorus levels. In addition, NaB improved various bone microstructure parameters, including bone mineral density (BMD), trabecular thickness (Tb. Th), trabecular bone separation (Tb. SP), and structural model index (SMI) in the femur. Notably, NaB intervention also enhanced the antioxidant capacity of plasma in fluorosis rats. Furthermore, a comprehensive analysis of serum metabolomics by LC-MS revealed a significant reversal trend of seven biomarkers after the intervention of NaB. Finally, pathway enrichment analysis based on differential metabolites indicated that NaB exerted protective effects on fluorosis by modulating arginine and proline metabolic pathways. These findings suggest that NaB has a beneficial effect on fluorosis and can regulate bone homeostasis by ameliorating metabolic disorders.

Microbiota metabolites in bone: Shaping health and Confronting disease

The intricate interplay between the gut microbiota and bone health has become increasingly recognized as a fundamental determinant of skeletal well-being. Microbiota-derived metabolites play a crucial role in dynamic interaction, specifically in bone homeostasis. In this sense, short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, indirectly promote bone formation by regulating insulin-like growth factor-1 (IGF-1). Trimethylamine N-oxide (TMAO) has been found to increase the expression of osteoblast genes, such as Runt-related transcription factor 2 (RUNX2) and bone morphogenetic protein-2 (BMP2), thus enhancing osteogenic differentiation and bone quality through BMP/SMADs and Wnt signaling pathways. Remarkably, in the context of bone infections, the role of microbiota metabolites in immune modulation and host defense mechanisms potentially affects susceptibility to infections such as osteomyelitis. Furthermore, ongoing research elucidates the precise mechanisms through which microbiota-derived metabolites influence bone cells, such as osteoblasts and osteoclasts. Understanding the multifaceted influence of microbiota metabolites on bone, from regulating homeostasis to modulating susceptibility to infections, has the potential to revolutionize our approach to bone health and disease management. This review offers a comprehensive exploration of this evolving field, providing a holistic perspective on the impact of microbiota metabolites on bone health and diseases.

Sodium butyrate enhances titanium nail osseointegration in ovariectomized rats by inhibiting the PKCα/NOX4/ROS/NF-κB pathways

BACKGROUND

Elevated levels of oxidative stress as a consequence of estrogen deficiency serve as a key driver of the onset of osteoporosis (OP). In addition to increasing the risk of bone fractures, OP can reduce the bone volume proximal to titanium nails implanted to treat these osteoporotic fractures, thereby contributing to titanium nail loosening. Sodium butyrate (NaB) is a short-chain fatty acid produced by members of the gut microbiota that exhibits robust antioxidant and anti-inflammatory properties.

METHODS

OP fracture model rats parameters including bone mineral density (BMD), new bone formation, and the number of bonelets around the implanted nail were analyzed via micro-CT scans, H&E staining, and Masson's staining. The protective effects of NaB on such osseointegration and the underlying mechanisms were further studied in vitro using MC3T3-E1 cells treated with carbonyl cyanide m-chlorophenylhydrazone (CCCP) to induce oxidative stress. Techniques including Western immunoblotting, electron microscopy, flow cytometry, alkaline phosphatase (ALP) staining, and osteoblast mineralization assays were employed to probe behaviors such as reactive oxygen species production, mineralization activity, ALP activity, protein expression, and the ability of cells to attach to and survive on titanium plates.

RESULTS

NaB treatment was found to enhance ALP activity, mineralization capacity, and Coll-I, BMP2, and OCN expression levels in CCCP-treated MC3T3-E1 cells, while also suppressing PKC and NF-κB expression and enhancing Nrf2 and HO-1 expression in these cells. NaB further suppressed intracellular ROS production and malondialdehyde levels within the cytosol while enhancing superoxide dismutase activity and lowering the apoptotic death rate. In line with these results, in vivo work revealed an increase in BMD in NaB-treated rats that was associated with enhanced bone formation surrounding titanium nails.

CONCLUSION

These findings indicate that NaB may represent a valuable compound that can be postoperatively administered to aid in treating OP fractures through the enhancement of titanium nail osseointegration.

Bone loss is ameliorated by fecal microbiota transplantation through SCFA/GPR41/ IGF1 pathway in sickle cell disease mice

Bone loss is common in sickle cell disease (SCD), but the molecular mechanisms is unclear. Serum insulin-like growth factor 1 (IGF1) was low in SCD subjects and SCD mice. To determine if decreased IGF1 associated with low bone mass in SCD is due to reduced SCFA production by gut microbiota, we performed reciprocal fecal microbiota transplantation (FMT) between healthy control (Ctrl) and SCD mice. uCT and histomorphometry analysis of femur showed decreased bone volume/total volume (BV/TV), trabecular number (Tb.N), osteoblast surface/bone surface (Ob.S/BS), mineralizing surface/ bone surface (MS/BS), inter-label thickness (Ir.L.Th) in SCD mice were significantly improved after receiving Ctrl feces. Bone formation genes Alp, Col1, Runx2, and Dmp1 from SCD mice were significantly decreased and were rescued after FMT from Ctrl feces. Transplantation of Ctrl feces increased the butyrate, valerate, and propionate levels in cecal content of SCD mice. Decreased G-coupled protein receptors 41 and 43 (GPR41 and GPR43) mRNA in tibia and lower IGF1 in bone and serum of SCD mice were partially restored after FMT from Ctrl feces. These data indicate that the healthy gut microbiota of Ctrl mice is protective for SCD bone loss through regulating IGF1 in response to impaired bacterial metabolites SCFAs.

The possible role of increased consumption of ultra-processed food products in the development of frailty: a threat for healthy ageing?

Frailty, a multifactorial ageing-related syndrome characterised by reduced resistance to stressors and possibly associated with low-grade systemic inflammation, results in negative health outcomes and compromises healthy ageing. There is a growing body of evidence on the relationship between dietary habits, low-grade systemic inflammation and the risk of frailty. Consumption of dietary ultra-processed products (UPP) could negatively contribute to these conditions. In this article, we intend to (i) discuss the role that UPP might have on the development of frailty considering the inflammatory potential of this type of food and (ii) to raise awareness on deleterious effects of excess UPP intake in the development of adverse health outcomes, in particular, frailty and compromised healthy ageing. UPP are industrial formulations whose nutrient profile has been associated with inflammation and altered gut microbiota. Besides, diets with a greater presence of unprocessed foods and antioxidants have been linked to the reduction of oxidative stress and the expression of inflammatory biomarkers. Because inflammation is believed to be a contributing factor in the development of frailty, it is possible that UPP would contribute to the onset or increase of this condition. Importantly, the increasing consumption of UPP in younger populations might pose a greater risk to the development of compromised healthy ageing in the long term.

The short-chain fatty acid butyrate accelerates vascular calcification via regulation of histone deacetylases and NF-κB signaling

Recent studies have shown that short-chain fatty acids (SCFAs), primarily acetate, propionate and butyrate, play a crucial role in the pathogenesis of cardiovascular disease. Whether SCFAs regulate vascular calcification, a common pathological change in cardiovascular tissues, remains unclear. This study aimed to investigate the potential role of SCFAs in vascular calcification. Using cellular and animal models of vascular calcification, we showed that butyrate significantly enhanced high phosphate (Pi)-induced calcification and osteogenic transition of vascular smooth muscle cells (VSMC) in vitro, whereas acetate and propionate had no effects. Subsequent studies confirmed that butyrate significantly promoted high Pi-induced aortic ring calcification ex vivo and high dose vitamin D₃ (vD₃)-induced mouse vascular calcification in vivo. Mechanistically, butyrate significantly inhibited histone deacetylase (HDAC) expression in VSMCs, and a pan HDAC inhibitor Trichostatin A showed similar inductive effects on calcification and osteogenic transition of VSMCs to butyrate. In addition, the SCFA sensing receptors Gpr41 and Gpr109a were primarily expressed by VSMCs, and butyrate induced the rapid activation of NF-κB, Wnt and Akt signaling in VSMCs. Intriguingly, the NF-κB inhibitor SC75741 significantly attenuated butyrate-induced calcification and the osteogenic gene Msx2 expression in VSMCs. We showed that knockdown of Gpr41 but not Gpr109a attenuated butyrate-induced VSMC calcification. This study reveals that butyrate accelerates vascular calcification via its dual effects on HDAC inhibition and NF-κB activation. Our data provide novel insights into the role of microbe-host interaction in vascular calcification, and may have implications for the development of potential therapy for vascular calcification.

Gut-Bone Axis: A Non-Negligible Contributor to Periodontitis

Periodontitis is a polymicrobial infectious disease characterized by alveolar bone loss. Systemic diseases or local infections, such as diabetes, postmenopausal osteoporosis, obesity, and inflammatory bowel disease, promote the development and progression of periodontitis. Accumulating evidences have revealed the pivotal effects of gut microbiota on bone health via gut-alveolar-bone axis. Gut pathogens or metabolites may translocate to distant alveolar bone via circulation and regulate bone homeostasis. In addition, gut pathogens can induce aberrant gut immune responses and subsequent homing of immunocytes to distant organs, contributing to pathological bone loss. Gut microbial translocation also enhances systemic inflammation and induces trained myelopoiesis in the bone marrow, which potentially aggravates periodontitis. Furthermore, gut microbiota possibly affects bone health via regulating the production of hormone or hormone-like substances. In this review, we discussed the links between gut microbiota and periodontitis, with a particular focus on the underlying mechanisms of gut-bone axis by which systemic diseases or local infections contribute to the pathogenesis of periodontitis.

Fermentation of Pleurotus ostreatus and Ganoderma lucidum mushrooms and their extracts by the gut microbiota of healthy and osteopenic women: potential prebiotic effect and impact of mushroom fermentation products on human osteoblasts

Recent data have highlighted the role of the gut microbiota and its several metabolites in maintaining bone health. Thus, gut microbiota manipulation, e.g., by prebiotics, might offer a plausible target in the fight against bone degenerative diseases. This study aimed (a) to investigate the in vitro prebiotic potential of Ganoderma lucidum and Pleurotus ostreatus mushrooms in healthy and osteopenic women and (b) to explore the impact of mushroom fermentation products on human osteoblasts. G. lucidum LGAM 9720 and P. ostreatus IK 1123 lyophilized mushroom-powders (2% w/v) and their hot-water extracts (1% w/v) were fermented in a 24 h static batch culture model by using faecal inocula from healthy (n = 3) or osteopenic (n = 3) donors. Gut microbiota analysis (qPCR) and measurement of short chain fatty acids (SCFAs) were performed during fermentation, and 24 h-prebiotic indexes were calculated. Evaluation of the effects of fermentation products on bone metabolism parameters (OPG: osteoprotegerin; and RANKL: receptor activator of nuclear factor kappa B ligand) in osteoblast cultures was also performed. Our data suggest that the origin of the gut microbiota inoculum plays a major role in the viability of osteoblasts. The treatments using P. ostreatus mushroom-powder and G. lucidum mushroom-extract had positive effects based on gut microbiota and SCFA analyses. Both mushrooms exhibited lower RANKL levels compared to controls, whereas their extracts tended to enhance the osteoblastic activity. In conclusion, mushrooms that are rich in beta-glucans may exert beneficial in vitro effects on bone physiology by alterations in the gut microbiota and/or SCFA production.

Immunomodulatory roles of microbiota-derived short-chain fatty acids in bacterial infections

In recent years, an overwhelming amount of evidence has positively recommended a significant role of microbiota in human health and disease. Microbiota also plays a crucial role in the initiation, preparation, and function of the host immune response. Recently, it has been shown that short-chain fatty acids (SCFAs) are the primary metabolites of the intestinal microbiota produced by anaerobic fermentation, which contributes to the host-pathogen interaction. SCFAs, such as propionate, acetate, and butyrate, are bacterial metabolites with immunomodulatory activity, and they are indispensable for the maintenance of homeostasis. Some evidence indicates that they are involved in the development of infections. In the present study, we provide the latest findings on the role of SCFAs in response to bacterial infections.

Regulation of Bone Cell Differentiation and Activation by Microbe-Associated Molecular Patterns

Gut microbiota has emerged as an important regulator of bone homeostasis. In particular, the modulation of innate immunity and bone homeostasis is mediated through the interaction between microbe-associated molecular patterns (MAMPs) and the host pattern recognition receptors including Toll-like receptors and nucleotide-binding oligomerization domains. Pathogenic bacteria such as Porphyromonas gingivalis and Staphylococcus aureus tend to induce bone destruction and cause various inflammatory bone diseases including periodontal diseases, osteomyelitis, and septic arthritis. On the other hand, probiotic bacteria such as Lactobacillus and Bifidobacterium species can prevent bone loss. In addition, bacterial metabolites and various secretory molecules such as short chain fatty acids and cyclic nucleotides can also affect bone homeostasis. This review focuses on the regulation of osteoclast and osteoblast by MAMPs including cell wall components and secretory microbial molecules under in vitro and in vivo conditions. MAMPs could be used as potential molecular targets for treating bone-related diseases such as osteoporosis and periodontal diseases.

LIN28B induces a differentiation program through CDX2 in colon cancer

Most colorectal cancers (CRCs) are moderately differentiated or well differentiated, a status that is preserved even in metastatic tumors. However, the molecular mechanisms underlying CRC differentiation remain to be elucidated. Herein, we unravel a potentially novel posttranscriptional regulatory mechanism via a LIN28B/CDX2 signaling axis that plays a critical role in mediating CRC differentiation. Owing to a large number of mRNA targets, the mRNA-binding protein LIN28B has diverse functions in development, metabolism, tissue regeneration, and tumorigenesis. Our RNA-binding protein IP (RIP) assay revealed that LIN28B directly binds CDX2 mRNA, which is a pivotal homeobox transcription factor in normal intestinal epithelial cell identity and differentiation. Furthermore, LIN28B overexpression resulted in enhanced CDX2 expression to promote differentiation in subcutaneous xenograft tumors generated from CRC cells and metastatic tumor colonization through mesenchymal-epithelial transition in CRC liver metastasis mouse models. A ChIP sequence for CDX2 identified α-methylacyl-CoA racemase (AMACR) as a potentially novel transcriptional target of CDX2 in the context of LIN28B overexpression. We also found that AMACR enhanced intestinal alkaline phosphatase activity, which is known as a key component of intestinal differentiation, through the upregulation of butyric acid. Overall, we demonstrated that LIN28B promotes CRC differentiation through the CDX2/AMACR axis.

Role of histone deacetylases in bone development and skeletal disorders

Bone cells must constantly respond to hormonal and mechanical cues to change gene expression programs. Of the myriad of epigenomic mechanisms used by cells to dynamically alter cell type-specific gene expression, histone acetylation and deacetylation has received intense focus over the past two decades. Histone deacetylases (HDACs) represent a large family of proteins with a conserved deacetylase domain first described to deacetylate lysine residues on histone tails. It is now appreciated that multiple classes of HDACs exist, some of which are clearly misnamed in that acetylated lysine residues on histone tails is not the major function of their deacetylase domain. Here, we will review the roles of proteins bearing deacetylase domains in bone cells, focusing on current genetic evidence for each individual HDAC gene. While class I HDACs are nuclear proteins whose primary role is to deacetylate histones, class IIa and class III HDACs serve other important cellular functions. Detailed knowledge of the roles of individual HDACs in bone development and remodeling will set the stage for future efforts to specifically target individual HDAC family members in the treatment of skeletal diseases such as osteoporosis.

Epigenetic therapies of osteoporosis

The study of epigenetics reaches its 50th anniversary, however, its clinical application is gradually coming into the clinical setting. Osteoporosis is one of the major and widely diffused bone diseases. Pathogenic mechanisms at the epigenetic level may interfere with bone remodeling occurring during osteoporosis. Preclinical models were used to understand whether such events may interfere with the disease. Besides, observational clinical trials investigated epigenetic-related biomarkers. This effort leads to some epigenetic-related therapies in clinical trials for the treatment of osteoporosis. Bisphosphonates (BPs), target therapy blocking RANK/RANKL pathway, and anti-sclerostin antibody (SOST) are the main therapeutic approaches. However, future large trials will reveal whether epigenetic therapies of osteoporosis will remain a work in progress or data will become more robust in the real-world management of these frailty patients.

Enterococcus faecium Modulates the Gut Microbiota of Broilers and Enhances Phosphorus Absorption and Utilization

Modern broiler chickens have ongoing bone health problems. Phosphorus (P) plays an important role in bone development and increased understanding of P metabolism should improve the skeletal health of broilers. Enterococcus faecium has been widely used as a probiotic in broiler production and is shown to improve skeletal health of rats, but its effect on the bones of broilers remains unclear. This study investigated the effect of E. faecium on P absorption and utilization in broilers and the associated changes in the gut microbiota using 16S rDNA sequencing. Dietary supplementation with E. faecium improved P absorption through upregulation of the expression of intestinal NaP-IIb mRNA and increased the concentration of serum alkaline phosphatase. These actions increased P retention and bone mineralization in E. faecium-treated broilers. The positive effects of E. faecium on P metabolism were associated with changes in the populations of the intestinal microbiota. There was increased relative abundance of the following genera, Alistipes, Eubacterium, Rikenella and Ruminococcaceae and a decrease in the relative abundance of Faecalibacterium and Escherichia-Shigella. Dietary supplementation with E. faecium changed gut microbiota populations of broilers, increased the relative abundance of SCFA (short-chain fatty acid)-producing bacteria, improved intestinal P absorption and bone forming metabolic activities, and decreased P excretion. E. faecium facilitates increased utilisation of P in broilers.

The epigenetic reader Brd4 is required for osteoblast differentiation

Transcription networks and epigenetic mechanisms including DNA methylation, histone modifications, and noncoding RNAs control lineage commitment of multipotent mesenchymal progenitor cells. Proteins that read, write, and erase histone tail modifications curate and interpret the highly intricate histone code. Epigenetic reader proteins that recognize and bind histone marks provide a crucial link between histone modifications and their downstream biological effects. Here, we investigate the role of bromodomain-containing (BRD) proteins, which recognize acetylated histones, during osteogenic differentiation. Using RNA-sequencing (RNA-seq) analysis, we screened for BRD proteins (n = 40) that are robustly expressed in MC3T3 osteoblasts. We focused functional follow-up studies on Brd2 and Brd4 which are highly expressed in MC3T3 preosteoblasts and represent "bromodomain and extra terminal domain" (BET) proteins that are sensitive to pharmacological agents (BET inhibitors). We show that small interfering RNA depletion of Brd4 has stronger inhibitory effects on osteoblast differentiation than Brd2 loss as measured by osteoblast-related gene expression, extracellular matrix deposition, and alkaline phosphatase activity. Similar effects on osteoblast differentiation are seen with the BET inhibitor +JQ1, and this effect is reversible upon its removal indicating that this small molecule has no lasting effects on the differentiation capacity of MC3T3 cells. Mechanistically, we find that Brd4 binds at known Runx2 binding sites in promoters of bone-related genes. Collectively, these findings suggest that Brd4 is recruited to osteoblast-specific genes and may cooperate with bone-related transcription factors to promote osteoblast lineage commitment and maturation.

The gut-bone axis: how bacterial metabolites bridge the distance

The gut microbiome is a key regulator of bone health that affects postnatal skeletal development and skeletal involution. Alterations in microbiota composition and host responses to the microbiota contribute to pathological bone loss, while changes in microbiota composition that prevent, or reverse, bone loss may be achieved by nutritional supplements with prebiotics and probiotics. One mechanism whereby microbes influence organs of the body is through the production of metabolites that diffuse from the gut into the systemic circulation. Recently, short-chain fatty acids (SCFAs), which are generated by fermentation of complex carbohydrates, have emerged as key regulatory metabolites produced by the gut microbiota. This Review will focus on the effects of SCFAs on the musculoskeletal system and discuss the mechanisms whereby SCFAs regulate bone cells.

Harnessing the HDAC-histone deacetylase enzymes, inhibitors and how these can be utilised in tissue engineering

There are large knowledge gaps regarding how to control stem cells growth and differentiation. The limitations of currently available technologies, such as growth factors and/or gene therapies has led to the search of alternatives. We explore here how a cell’s epigenome influences determination of cell type, and potential applications in tissue engineering. A prevalent epigenetic modification is the acetylation of DNA core histone proteins. Acetylation levels heavily influence gene transcription. Histone deacetylase (HDAC) enzymes can remove these acetyl groups, leading to the formation of a condensed and more transcriptionally silenced chromatin. Histone deacetylase inhibitors (HDACis) can inhibit these enzymes, resulting in the increased acetylation of histones, thereby affecting gene expression. There is strong evidence to suggest that HDACis can be utilised in stem cell therapies and tissue engineering, potentially providing novel tools to control stem cell fate. This review introduces the structure/function of HDAC enzymes and their links to different tissue types (specifically bone, cardiac, neural tissues), including the history, current status and future perspectives of using HDACis for stem cell research and tissue engineering, with particular attention paid to how different HDAC isoforms may be integral to this field.

Exercise prevents high fat diet-induced bone loss, marrow adiposity and dysbiosis in male mice

High fat diets can have detrimental effects on the skeleton as well as cause intestinal dysbiosis. Exercise prevents high fat (HF) diet-induced obesity and also improves bone density and prevents the intestinal dysbiosis that promotes energy storage. Previous studies indicate a link between intestinal microbial balance and bone health. Therefore, we examined whether exercise could prevent HF-induced bone pathology in male mice and determined whether benefits correlate to changes in host intestinal microbiota. Male C57Bl/6 mice were fed either a low fat diet (LF; 10 kcal% fat) or a HF diet (60 kcal% fat) and put under sedentary or voluntary exercise conditions for 14 weeks. Our results indicated that HF diet reduced trabecular bone volume, when corrected for differences in body weight, of both the tibia (40% reduction) and vertebrae (25% reduction) as well and increased marrow adiposity (44% increase). More importantly, these effects were prevented by exercise. Exercise also had a significant effect on several cortical bone parameters and enhanced bone mechanical properties in LF but not HF fed mice. Microbiome analyses indicated that exercise altered the HF induced changes in microbial composition by reducing the Firmicutes/Bacteriodetes ratio. This ratio negatively correlated with bone volume as did levels of Clostridia and Lachnospiraceae. In contrast, the abundance of several Actinobacteria phylum members (i.e., Bifidobacteriaceae) were positively correlated with bone volume. Taken together, exercise can prevent many of the negative effects of a high fat diet on male skeletal health. Exercise induced changes in microbiota composition could represent a novel mechanism that contributes to exercise induced benefits to bone health.

Sodium butyrate-modified sulfonated polyetheretherketone modulates macrophage behavior and shows enhanced antibacterial and osteogenic functions during implant-associated infections

Prevention of implant-associated infections and insufficient bone tissue integration is critical to exploit the immunomodulatory properties and antibacterial effects of implant materials, which have attracted considerable attention.

Butyrate Stimulates Histone H3 Acetylation, 8-Isoprostane Production, RANKL Expression, and Regulated Osteoprotegerin Expression/Secretion in MG-63 Osteoblastic Cells

Butyric acid as a histone deacetylase (HDAC) inhibitor is produced by a number of periodontal and root canal microorganisms (such as Porphyromonas, Fusobacterium, etc.). Butyric acid may affect the biological activities of periodontal/periapical cells such as osteoblasts, periodontal ligament cells, etc., and thus affect periodontal/periapical tissue destruction and healing. The purposes of this study were to study the toxic effects of butyrate on the matrix and mineralization marker expression in MG-63 osteoblasts. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Cellular apoptosis and necrosis were analyzed by propidium iodide/annexin V flow cytometry. The protein and mRNA expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-B ligand (RANKL) were analyzed by Western blotting and reverse transcriptase-polymerase chain reaction (RT-PCR). OPG, soluble RANKL (sRANKL), 8-isoprostane, pro-collagen I, matrix metalloproteinase-2 (MMP-2), osteonectin (SPARC), osteocalcin and osteopontin (OPN) secretion into culture medium were measured by enzyme-linked immunosorbant assay. Alkaline phosphatase (ALP) activity was checked by ALP staining. Histone H3 acetylation levels were evaluated by immunofluorescent staining (IF) and Western blot. We found that butyrate activated the histone H3 acetylation of MG-63 cells. Exposure of MG-63 cells to butyrate partly decreased cell viability with no marked increase in apoptosis and necrosis. Twenty-four hours of exposure to butyrate stimulated RANKL protein expression, whereas it inhibited OPG protein expression. Butyrate also inhibited the secretion of OPG in MG-63 cells, whereas the sRANKL level was below the detection limit. However, 3 days of exposure to butyrate (1 to 8 mM) or other HDAC inhibitors such as phenylbutyrate, valproic acid and trichostatin stimulated OPG secretion. Butyrate stimulated 8-isoprostane, MMP-2 and OPN secretion, but not procollagen I, or osteocalcin in MG-63 cells. Exposure to butyrate (2⁻4 mM) for 3 days markedly stimulated osteonectin secretion and ALP activity. In conclusion, higher concentrations of butyric acid generated by periodontal and root canal microorganisms may potentially induce bone destruction and impair bone repair by the alteration of OPG/RANKL expression/secretion, 8-isoprostane, MMP-2 and OPN secretion, and affect cell viability. However, lower concentrations of butyrate (1⁻4 mM) may stimulate ALP, osteonectin and OPG. These effects are possibly related to increased histone acetylation. These events are important in the pathogenesis and repair of periodontal and periapical destruction.

HDAC6 regulates dental mesenchymal stem cells and osteoclast differentiation

Background

Dental and periodontal tissue development is a complicated process involving a finely regulated network of communication among various cell types. Understanding the mechanisms involved in regulating dental mesenchymal stem cells (MSCs) and osteoclast cell differentiation is critical. However, it is still unclear whether histone deacetylase HDAC6 is involved in dental MSCs fate determination and osteoclast differentiation.

Methods

We used shRNA and siRNA knockdown to explore the role of HDAC6 in dental MSCs odontogenic differentiation and osteoclasts maturation.

Results

Based on HDAC6 knockdown dental MSCs, our data suggest that HDAC6 knockdown significantly increases alkaline phosphate activity and mineralized nodules formation. Additionally, mRNA expression of odontogenic marker genes (OSX, OCN, and OPN) was induced by HDAC6 knockdown. By using HDAC6 siRNA, we knocked down HDAC6 in osteoclast precursor RAW 264.7 cells. Our data suggests that HDAC6 knockdown significantly inhibited osteoclasts differentiation. Additionally, mRNA expression of osteoclast marker genes Trap, Mmp9, and Ctsk was decreased by HDAC6 knockdown.

Conclusions

Our study demonstrated that HDAC6 plays an important role in regulating dental MSCs and osteoclasts differentiation.

The impact of the intestinal microbiome on bone health

Intestinal microbial flora, known as the second gene pool of the human body, play an important role in immune function, nutrient uptake, and various activities of host cells, as well as in human disease. Intestinal microorganisms are involved in a variety of mechanisms that affect bone health. Gut microbes are closely related to genetic variation, and gene regulation plays an important part in the development of bone-related diseases such as osteoporosis. Intestinal microorganisms can disrupt the balance between bone formation and resorption by indirectly stimulating or inhibiting osteoblasts and osteoclasts. In addition, intestinal microorganisms affect bone metabolism by regulating growth factors or altering bone immune status and can also alter the metabolism of serotonin, cortisol, and sex hormones, thereby affecting bone mass in mice. Moreover, probiotics, antibiotics, and diet can change the composition of the intestinal microbial flora, thus affecting bone health and also potentially helping to treat bone disease. Studying the relationship between intestinal flora and osteoblasts, osteoclasts, and bone marrow mesenchymal stem cells may provide a basis for preventing and treating bone diseases. This paper reviews recent advances in the study of the relationship between intestinal microflora and bone disease.

Effects of probiotic supplementation on performance traits, bone mineralization, cecal microbial composition, cytokines and corticosterone in laying hens

Recent researches have showed that probiotics promote bone health in humans and rodents. The objective of this study was to determine if probiotics have the similar effects in laying hens. Ninety-six 60-week-old White Leghorn hens were assigned to four-hen cages based on their BW. The cages were randomly assigned to 1 of 4 treatments: a layer diet mixed with a commercial probiotic product (containing Enterococcus faecium, Pediococcus acidilactici, Bifidobacterium animalis and Lactobacillus reuteri) at 0, 0.5, 1.0 or 2.0 g/kg feed (Control, 0.5×, 1.0× and 2.0×) for 7 weeks. Cecal Bifidobacterium spp. counts were higher in all probiotic groups (P0.05). In addition, the plasma concentrations of cytokines (interleukin-1β, interleukin-6, interleukin-10, interferon-γ and tumor necrosis factor-α) and corticosterone as well as the levels of heterophil to lymphocyte ratio were similar between the 2.0× group and the control group (P>0.05). In line with these findings, no differences of cecal tonsil mRNA expressions of interleukin-1β, interleukin-6 and lipopolysaccharide-induced tumor necrosis factor-α factor were detected between these two groups (P>0.05). These results suggest that immune cytokines and corticosterone may not involve in the probiotic-induced improvement of eggshell quality and bone mineralization in laying hens. In conclusion, the dietary probiotic supplementation altered cecal microbiota composition, resulting in reduced shell-less egg production and improved bone mineralization in laying hens; and the dietary dose of the probiotic up to 2.0× did not cause negative stress reactions in laying hens.

Short-chain fatty acids regulate systemic bone mass and protect from pathological bone loss

Microbial metabolites are known to modulate immune responses of the host. The main metabolites derived from microbial fermentation of dietary fibers in the intestine, short-chain fatty acids (SCFA), affect local and systemic immune functions. Here we show that SCFA are regulators of osteoclast metabolism and bone mass in vivo. Treatment of mice with SCFA as well as feeding with a high-fiber diet significantly increases bone mass and prevents postmenopausal and inflammation-induced bone loss. The protective effects of SCFA on bone mass are associated with inhibition of osteoclast differentiation and bone resorption in vitro and in vivo, while bone formation is not affected. Mechanistically, propionate (C3) and butyrate (C4) induce metabolic reprogramming of osteoclasts resulting in enhanced glycolysis at the expense of oxidative phosphorylation, thereby downregulating essential osteoclast genes such as TRAF6 and NFATc1. In summary, these data identify SCFA as potent regulators of osteoclast metabolism and bone homeostasis.

Short-chain fatty acids (SCFA) are a main class of metabolites derived from fermentation of dietary fibre in the intestine. Here, the authors show that dietary administration of SCFA is associated with inhibition of osteoclast differentiation, increased bone mass, and reduced pathological bone loss in mice.

Evaluation of MC3T3 Cells Proliferation and Drug Release Study from Sodium Hyaluronate-1,4-butanediol Diglycidyl Ether Patterned Gel

A pattern gel has been fabricated using sodium hyaluronate (HA) and 1,4-butanediol diglycidyl ether (BDDGE) through the micro-molding technique. The cellular behavior of osteoblast cells (MC3T3) in the presence and absence of dimethyloxalylglycine (DMOG) and sodium borate (NaB) in the pattern gel (HA-BDDGE) has been evaluated for its potential application in bone regeneration. The Fourier transform infrared spectroscopy (FTIR), 13C-nuclear magnetic resonance spectroscopy (13C NMR), and thermogravimetric analysis (TGA) results implied the crosslinking reaction between HA and BDDGE. The scanning electron microscopy (SEM) analysis confirmed the formation of pattern on the surface of HA-BDDGE. The gel property of the crosslinked HA-BDDGE has been investigated by swelling study in distilled water at 37 °C. The HA-BDDGE gel releases DMOG in a controlled way for up to seven days in water at 37 °C. The synthesized gel is biocompatible and the bolus drug delivery results indicated that the DMOG containing patterned gel demonstrates a better cell migration ability on the surface than NaB. For local delivery, the pattern gel with 300 µM NaB or 300 µM DMOG induced cell clusters formation, and the gel with 150 µM NaB/DMOG showed high cell proliferation capability only. The vital role of NaB for bone regeneration has been endorsed from the formation of cell clusters in presence of NaB in the media. The in vitro results indicated that the pattern gel showed angiogenic and osteogenic responses with good ALP activity and enhanced HIF-1α, and Runx2 levels in the presence of DMOG and NaB in MC3T3 cells. Hence, the HA-BDDGE gel could be used in bone regeneration application.

Mechanisms of gut microbiota-mediated bone remodeling

The mechanisms underlying the systemic effects mediated by gut microbiota are under active investigation. In addition to local, direct effects of gut microbiota on the host, metabolic products from microbiota may act peripherally, reaching distal organs through the circulation. In our recent publication we demonstrated that gut microbiota influence bone remodeling distally, promoting both bone resorption and formation. We proposed that these effects are mediated, at least in part, by the induction of insulin like growth factor (IGF-1) by the microbiota metabolite short chain fatty acids (SCFA). Here we explore additional mechanisms by which microbial metabolites could directly or indirectly alter host bone remodeling. We discuss whether SCFA directly modulate bone resorption by their actions on osteoclasts, and test the possibility that serotonin is another gut microbiota derived long-distance mediator of effects on bone remodeling. A detailed understanding of the mechanisms of microbiota effect on bone remodeling could help establish potential therapeutic strategies to promote bone health.

Gut Microbiome and Bone: to Build, Destroy, or Both?

PURPOSE OF REVIEW

The gut microbiota can be considered a hidden organ that plays essential roles in host homeostasis. Exploration of the effects of microbiota on bone has just begun. Complimentary studies using germ-free mice, antibiotic, and probiotic treatments reveal a complicated relationship between microbiota and bone. Here, we review recent reports addressing the effect of gut microbiota on bone health, discuss potential reasons for discrepant findings, and explore potential mechanisms for these effects.

RECENT FINDINGS

Manipulation of microbiota by colonization of germ-free mice, antibiotics, or probiotic supplementation significantly alters bone remodeling, bone development and growth, as well as bone mechanical strength. Different experimental models reveal context-dependent effects of gut microbiota on bone. By examining phenotypic effects, experimental context, and proposed mechanisms, revealed by recent reports, we hope to provide comprehensive and fresh insights into the many facets of microbiota and bone interactions.

Histone deacetylases (HDAC) in physiological and pathological bone remodelling

Histone deacetylases (HDACs)² play important roles in the epigenetic regulation of gene expression in cells and are emerging therapeutic targets for treating a wide range of diseases. HDAC inhibitors (HDACi)³ that act on multiple HDAC enzymes have been used clinically to treat a number of solid and hematological malignancies. HDACi are also currently being studied for their efficacy in non-malignant diseases, including pathologic bone loss, but this has necessitated a better understanding of the roles of individual HDAC enzymes, particularly the eleven zinc-containing isozymes. Selective isozyme-specific inhibitors currently being developed against class I HDACs (1, 2, 3 and 8) and class II HDACs (4, 5, 6, 7, 9 and 10) will be valuable tools for elucidating the roles played by individual HDACs in different physiological and pathological settings. Isozyme-specific HDACi promise to have greater efficacy and reduced side effects, as required for treating chronic disease over extended periods of time. This article reviews the current understanding of roles for individual HDAC isozymes and effects of HDACi on bone cells, (osteoblasts, osteoclasts and osteocytes), in relation to bone remodelling in conditions characterised by pathological bone loss, including periodontitis, rheumatoid arthritis and myeloma bone disease.

Profiling of human epigenetic regulators using a semi-automated real-time qPCR platform validated by next generation sequencing

Epigenetic mechanisms control phenotypic commitment of mesenchymal stromal/stem cells (MSCs) into osteogenic, chondrogenic or adipogenic lineages. To investigate enzymes and chromatin binding proteins controlling the epigenome, we developed a hybrid expression screening strategy that combines semi-automated real-time qPCR (RT-qPCR), next generation RNA sequencing (RNA-seq), and a novel data management application (FileMerge). This strategy was used to interrogate expression of a large cohort (n>300) of human epigenetic regulators (EpiRegs) that generate, interpret and/or edit the histone code. We find that EpiRegs with similar enzymatic functions are variably expressed and specific isoforms dominate over others in human MSCs. This principle is exemplified by analysis of key histone acetyl transferases (HATs) and deacetylases (HDACs), H3 lysine methyltransferases (e.g., EHMTs) and demethylases (KDMs), as well as bromodomain (BRDs) and chromobox (CBX) proteins. Our results show gender-specific expression of H3 lysine 9 [H3K9] demethylases (e.g., KDM5D and UTY) as expected and upregulation of distinct EpiRegs (n>30) during osteogenic differentiation of MSCs (e.g., HDAC5 and HDAC7). The functional significance of HDACs in osteogenic lineage commitment of MSCs was functionally validated using panobinostat (LBH-589). This pan-deacetylase inhibitor suppresses osteoblastic differentiation as evidenced by reductions in bone-specific mRNA markers (e.g., ALPL), alkaline phosphatase activity and calcium deposition (i.e., Alizarin Red staining). Thus, our RT-qPCR platform identifies candidate EpiRegs by expression screening, predicts biological outcomes of their corresponding inhibitors, and enables manipulation of the human epigenome using molecular or pharmacological approaches to control stem cell differentiation.

Epigenetic regulation of bone cells

Bone is a major organ in the skeletal system that supports and protects muscles and other organs, facilitates movement and hematopoiesis, and forms a reservoir of minerals including calcium. The cells in the bone, such as osteoblasts, osteoclasts, and osteocytes, orchestrate sequential and balanced regulatory mechanisms to maintain bone and are capable of differentiating in bones. Bone development and remodeling require a precise regulation of gene expressions in bone cells, a process governed by epigenetic mechanisms such as histone modification, DNA methylation, and chromatin structure. Importantly, lineage-specific transcription factors can determine the epigenetic regulation of bone cells. Emerging data suggest that perturbation of epigenetic programs can affect the function and activity of bone cells and contributes to pathogenesis of bone diseases, including osteoporosis. Thus, understanding epigenetic regulations in bone cells would be important for early diagnosis and future therapeutic approaches.

Maternal Dietary Supplementation with Oligofructose-Enriched Inulin in Gestating/Lactating Rats Preserves Maternal Bone and Improves Bone Microarchitecture in Their Offspring

Nutrition during pregnancy and lactation could exert a key role not only on maternal bone, but also could influence the skeletal development of the offspring. This study was performed in rats to assess the relationship between maternal dietary intake of prebiotic oligofructose-enriched inulin and its role in bone turnover during gestation and lactation, as well as its effect on offspring peak bone mass/architecture during early adulthood. Rat dams were fed either with standard rodent diet (CC group), calcium-fortified diet (Ca group), or prebiotic oligofructose-enriched inulin supplemented diet (Pre group), during the second half of gestation and lactation. Bone mineral density (BMD) and content (BMC), as well as micro-structure of dams and offspring at different stages were analysed. Dams in the Pre group had significantly higher trabecular thickness (Tb.Th), trabecular bone volume fraction (BV/TV) and smaller specific bone surface (BS/BV) of the tibia in comparison with CC dams. The Pre group offspring during early adulthood had an increase of the lumbar vertebra BMD when compared with offspring of CC and Ca groups. The Pre group offspring also showed significant increase versus CC in cancellous and cortical structural parameters of the lumbar vertebra 4 such as Tb.Th, cortical BMD and decreased BS/BV. The results indicate that oligofructose-enriched inulin supplementation can be considered as a plausible nutritional option for protecting against maternal bone loss during gestation and lactation preventing bone fragility and for optimizing peak bone mass and architecture of the offspring in order to increase bone strength.

Epigenetic Mechanisms Regulating Mesenchymal Stem Cell Differentiation

Human Mesenchymal Stem Cells (hMSCs) have emerged in the last few years as one of the most promising therapeutic cell sources and, in particular, as an important tool for regenerative medicine of skeletal tissues. Although they present a more restricted potency than Embryonic Stem (ES) cells, the use of hMCS in regenerative medicine avoids many of the drawbacks characteristic of ES cells or induced pluripotent stem cells. The challenge in using these cells lies into developing precise protocols for directing cellular differentiation to generate a specific cell lineage. In order to achieve this goal, it is of the upmost importance to be able to control de process of fate decision and lineage commitment. This process requires the coordinate regulation of different molecular layers at transcriptional, posttranscriptional and translational levels. At the transcriptional level, switching on and off different sets of genes is achieved not only through transcriptional regulators, but also through their interplay with epigenetic modifiers. It is now well known that epigenetic changes take place in an orderly way through development and are critical in the determination of lineage-specific differentiation. More importantly, alteration of these epigenetic changes would, in many cases, lead to disease generation and even tumour formation. Therefore, it is crucial to elucidate how epigenetic factors, through their interplay with transcriptional regulators, control lineage commitment in hMSCs.

Dynamic and distinct histone modifications of osteogenic genes during osteogenic differentiation

Many skeletal diseases have common pathological phenotype of defective osteogenesis of bone marrow stromal cells (BMSCs), in which histone modifications play an important role. However, few studies have examined the dynamics of distinct histone modifications during osteogenesis. In this study, we examined the dynamics of H3K9/K14 and H4K12 acetylation; H3K4 mono-, di- and tri-methylation; H3K9 di-methylation and H3K27 tri-methylation in osteogenic genes, runt-related transcription factor 2 (Runx2), osterix (Osx), alkaline phosphatase, bone sialoprotein and osteocalcin, during C3H10T1/2 osteogenesis. H3 and H4 acetylation and H3K4 di-methylation were elevated, and H3K9 di-methylation and H3K27 tri-methylation were reduced in osteogenic genes during C3H10T1/2 osteogenesis. C3H10T1/2 osteogenesis could be modulated by altering the patterns of H3 and H4 acetylation and H3K27 tri-methylation. In a glucocorticoid-induced osteoporosis mouse model, we observed the attenuation of osteogenic potential of osteoporotic BMSCs in parallel with H3 and H4 hypo-acetylation and H3K27 hyper-tri-methylation in Runx2 and Osx genes. When H3 and H4 acetylation was elevated, and H3K27 tri-methylation was reduced, the attenuated osteogenic potential of osteoporotic BMSCs was rescued effectively. These observations provide a deeper insight into the mechanisms of osteogenic differentiation and the pathophysiology of osteoporosis and can be used to design new drugs and develop new therapeutic methods to treat skeletal diseases.

The intestinal microbiome and skeletal fitness: Connecting bugs and bones

Recent advances have dramatically increased our understanding of how organ systems interact. This has been especially true for immunology and bone biology, where the term "osteoimmunology" was coined to capture this relationship. The importance of the microbiome to the immune system has also emerged as a driver of health and disease. It makes sense therefore to ask the question: how does the intestinal microbiome influence bone biology and does dysbiosis promote bone disease? Surprisingly, few studies have analyzed this connection. A broader interpretation of this question reveals many mechanisms whereby the microbiome may affect bone cells. These include effects of the microbiome on immune cells, including myeloid progenitors and Th17 cells, as well as steroid hormones, fatty acids, serotonin and vitamin D. As mechanistic interactions of the microbiome and skeletal system are revealed within and without the immune system, novel strategies to optimize skeletal fitness may emerge.

Histone deacetylase inhibition destabilizes the multi-potent state of uncommitted adipose-derived mesenchymal stromal cells

Human adipose-derived mesenchymal stromal cells (AMSCs) grown in platelet lysate are promising agents for therapeutic tissue regeneration. Here, we investigated whether manipulation of epigenetic events by the clinically relevant histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) alters differentiation of AMSCs. The multipotency of AMSCs was validated by their ability to differentiate into osteogenic, chondrogenic, and adipogenic lineages. High-throughput RNA sequencing and RT-qPCR established that human histone deacetylases (HDAC1 to HDAC11, and SIRT1 to SIRT7) are differentially expressed in AMSCs. SAHA induces hyper-acetylation of histone H3 and H4, stimulates protein expression of the HDAC-responsive gene SLC9A3R1/NHERF1 and modulates the AKT/FOXO1 pathway. Biologically, SAHA interferes with osteogenic, chondrogenic and adipogenic lineage commitment of multipotent AMSCs. Mechanistically, SAHA-induced loss of differentiation potential of uncommitted AMSCs correlates with multiple changes in the expression of principal transcription factors that control mesenchymal or pluripotent states. We propose that SAHA destabilizes the multi-potent epigenetic state of uncommitted human AMSCs by hyper-acetylation and perturbation of key transcription factor pathways. Furthermore, AMSCs grown in platelet lysate may provide a useful biological model for screening of new HDAC inhibitors that control the biological fate of human mesenchymal stromal cells.

Histone deacetylase 8 suppresses osteogenic differentiation of bone marrow stromal cells by inhibiting histone H3K9 acetylation and RUNX2 activity

Bone marrow stromal cells (BMSCs) are multipotent progenitor cells with capacities to differentiate into the various cell types and hold great promise in regenerative medicine. The regulatory roles of histone deacetylases (HDACs) in osteoblast differentiation process have been increasingly recognized; however, little is known about the precise roles of HDAC8 in the osteogenic differentiation of BMSCs. Herein we aimed to investigate the roles of HDAC8 in the osteogenic differentiation of rat BMSCs by pharmacological and genetic manipulations in vitro. During osteogenic differentiation of BMSCs, pharmacological inhibition of HDAC8 by HDAC inhibitor valproic acid (VPA) promoted the level of histone H3 lysine 9 acetylation (H3K9Ac) and significantly enhanced the expression of osteogenesis-related genes Runx2, Osterix, osteocalcin (OCN), osteopontin (OPN) and alkaline phosphatase (ALP). Similarly, knockdown of HDAC8 using short interfering RNA triggered H3K9Ac and enhanced osteogenic differentiation of BMSCs, largely phenocopied the effects of VPA-mediated HDAC8 depletion. However, enforced expression of HDAC8 significantly reduced the level of H3K9Ac and inhibited osteogenic differentiation of BMSCs, which can be attenuated by VPA addition. Mechanistically, HDAC8 suppressed osteogenesis-related genes expression by removing the acetylation of histone H3K9, thus leading to transcriptional inhibition during osteogenic differentiation of BMSCs. Importantly, we found that HDAC8 physically associated with Runx2 to repress its transcriptional activity and this association decreased when BMSCs underwent osteogenic differentiation. Taken together, these results indicate that epigenetic regulation of Runx2 by HDAC8-mediated histone H3K9 acetylation is required for the proper osteogenic differentiation of BMSCs.

(+)-Vitisin A inhibits osteoclast differentiation by preventing TRAF6 ubiquitination and TRAF6-TAK1 formation to suppress NFATc1 activation

We recently reported that oral administration of a (+)-vitisin A-enriched product prepared from Vitis thunbergii obviously ameliorated bone loss in ovariectomized mice and (+)-vitisin A was able to inhibit receptor activator of NF-κB ligand (RANKL)-induced osteoclast differentiation in RAW264.7 cells. Here we further clarified the mechanism(s) by which (+)-vitisin A targets osteoclastic differentiation and activity. Osteoclast-characteristic enzyme activity was determined using gel zymography or spectroflurometric-based assay. Expression of signal molecules was analyzed via Western blot or immunoprecipitation. Results showed that (+)-vitisin A suppressed RANKL-induced multinuclear cells (MNCs) formation and bone resorption which was accompanied with reduction in β3 integrin, osteoclast stimulatory transmembrane protein (OC-STAMP), matrix metalloproteinase-9 (MMP-9) and cathepsin K proteins expression. (+)-Vitisin A also down-regulated the proteolytic activities of MMP-9 and cathepsin K via targeting at the late stage function. (+)-Vitisin A prominently abrogated RANKL-triggered nuclear translocations of NF-κB, AP-1 (c-Fos/c-Jun dimer) and associated induction and nuclear accumulation of nuclear factor of activated T cells c1 (NFATc1). The upstream IκB degradation as well as ERK and JNK phosphorylation were also substantially repressed. Transfection with siRNA targeting tumor necrosis factor receptor associated factor 6 (TRAF6) clearly restrained RANKL-induced MNCs formation and NFATc1 induction. Interesting, RANKL triggered poly-ubiquitination of TRAF6 and associated TRAF6-TAK1 (transforming growth factor β-activated kinase 1) complex formation was prominently attenuated by (+)-vitisin A. Furthermore, the interaction between c-src tyrosine kinase (c-Src) and β3 was markedly induced by RANKL stimulation. (+)-Vitisin A significantly attenuated this interaction when concomitant treated with RANKL in RAW264.7 cells, but failed to affect c-Src/β3 complex formation when post-cultured with MNCs. Taken together, (+)-vitisin A suppressed bone resorption possibly via interruption of RANKL-induced TRAF6 ubiquitination and associated downstream signaling pathways. Furthermore, action through negative regulation of the proteolytic activity of MMP-9 and cathepsin K might also contribute to the anti-resorption effect of (+)-vitisin A.

Histone deacetylase inhibition promotes osteoblast maturation by altering the histone H4 epigenome and reduces Akt phosphorylation

Bone has remarkable regenerative capacity, but this ability diminishes during aging. Histone deacetylase inhibitors (HDIs) promote terminal osteoblast differentiation and extracellular matrix production in culture. The epigenetic events altered by HDIs in osteoblasts may hold clues for the development of new anabolic treatments for osteoporosis and other conditions of low bone mass. To assess how HDIs affect the epigenome of committed osteoblasts, MC3T3 cells were treated with suberoylanilide hydroxamic acid (SAHA) and subjected to microarray gene expression profiling and high-throughput ChIP-Seq analysis. As expected, SAHA induced differentiation and matrix calcification of osteoblasts in vitro. ChIP-Seq analysis revealed that SAHA increased histone H4 acetylation genome-wide and in differentially regulated genes, except for the 500 bp upstream of transcriptional start sites. Pathway analysis indicated that SAHA increased the expression of insulin signaling modulators, including Slc9a3r1. SAHA decreased phosphorylation of insulin receptor β, Akt, and the Akt substrate FoxO1, resulting in FoxO1 stabilization. Thus, SAHA induces genome-wide H4 acetylation and modulates the insulin/Akt/FoxO1 signaling axis, whereas it promotes terminal osteoblast differentiation in vitro.

Butyrate stimulates the early process of the osteogenic differentiation but inhibits the biomineralization in dental follicle cells (DFCs)

Dental stem cells, especially dental follicle cells (DFCs) as precursor cells for the periodontium have interesting prospects for regenerative dentistry. During periodontitis, butyrate as a bacterial metabolite and inflammatory agent is often found in millimolar concentrations in periodontal pockets. This study evaluates the effects of butyrate on the proliferation and osteogenic differentiation of DFCs. We assessed cell viability/proliferation (BCA assay) and osteogenic differentiation (ALP activity, alizarin staining and RT PCR) of DFCs in vitro after butyrate supplementation. Butyrate concentrations of 20 mM or higher are toxic for DFCs. At a non-toxic concentration, butyrate promotes the expression of alkaline phosphatase and collagen type-1 but inhibits the formation of calcified nodules and the induction of RUNX2 and osteocalcin under osteogenic differentiation conditions. In conclusion, DFCs are resistant to physiological high concentrations of butyrate. Butyrate facilitates the osteogenic differentiation of DFCs in early stages but inhibits calcification at later stages of the differentiation process.

CD99/MIC2 Constitutes a Differentiation Antigen of a Human Osteoblast Cell Line

BACKGROUND

The histological origin of the Ewing's family of tumors (EFT) is still not clear. Since these small cell bone tumors may originate from osteogenic stem cells, the presence of the CD99/MIC2 antigen, known to be overexpressed in EFT, was studied in a human osteoblast cell line in response to differentiation inducers.

METHODS

The HBA-71 monoclonal antibody directed to the CD99/MIC2 antigen was used to stain a human osteoblast cell line as well as the two EFT cell lines KAL and EW-2 after pretreatment of the cells with the differentiation inducers calcitriol and the histone deacetylase (HDAC) inhibitors sodium butyrate (NaB), sodium phenylacetate (NaPA) as well as N, N'-hexamethylen-bis-acetamide (HMBA). Alkaline phosphatase (ALP) levels were determined as cellular differentiation marker.

RESULTS

Significant expression of the CD99/MIC2 antigen, yielding a molecular weight of 32 kD in Western blotting, was found in the human osteoblast cell line. Pretreatment of the osteoblasts with calcitriol and HMBA increased ALP content and suppressed the CD99/MIC2 antigen. Calcitriol had no major effect on CD99/MIC2 expression of both EFT cell lines, but HMBA enhanced ALP activity in KAL cells and downregulated CD99/MIC2. EW-2 cells exhibited reduced levels of both CD99/MIC2 and ALP.

CONCLUSIONS

This study supports the role of CD99/MIC2 as differentiation antigen of osteoblasts and a Ewing's sarcoma cell line with neuroectodermal phenotype. Response to calcitriol is absent or low in the two EFT cell lines tested.

Suberoylanilide hydroxamic acid (SAHA; vorinostat) causes bone loss by inhibiting immature osteoblasts

Histone deacetylase (Hdac) inhibitors are used clinically to treat cancer and epilepsy. Although Hdac inhibition accelerates osteoblast maturation and suppresses osteoclast maturation in vitro, the effects of Hdac inhibitors on the skeleton are not understood. The purpose of this study was to determine how the pan-Hdac inhibitor, suberoylanilide hydroxamic acid (SAHA; a.k.a. vorinostat or Zolinza(TM)) affects bone mass and remodeling in vivo. Male C57BL/6J mice received daily SAHA (100mg/kg) or vehicle injections for 3 to 4weeks. SAHA decreased trabecular bone volume fraction and trabecular number in the distal femur. Cortical bone at the femoral midshaft was not affected. SAHA reduced serum levels of P1NP, a bone formation marker, and also suppressed tibial mRNA levels of type I collagen, osteocalcin and osteopontin, but did not alter Runx2 or osterix transcripts. SAHA decreased histological measures of osteoblast number but interestingly increased indices of osteoblast activity including mineral apposition rate and bone formation rate. Neither serum (TRAcP 5b) nor histological markers of bone resorption were affected by SAHA. P1NP levels returned to baseline in animals which were allowed to recover for 4weeks after 4weeks of daily SAHA injections, but bone density remained low. In vitro, SAHA suppressed osteogenic colony formation, decreased osteoblastic gene expression, induced cell cycle arrest, and caused DNA damage in bone marrow-derived adherent cells. Collectively, these data demonstrate that bone loss following treatment with SAHA is primarily due to a reduction in osteoblast number. Moreover, these decreases in osteoblast number can be attributed to the deleterious effects of SAHA on immature osteoblasts, even while mature osteoblasts are resistant to the harmful effects and demonstrate increased activity in vivo, indicating that the response of osteoblasts to SAHA is dependent upon their differentiation state. These studies suggest that clinical use of SAHA and other Hdac inhibitors to treat cancer, epilepsy or other conditions may potentially compromise skeletal structure and function.

Histone deacetylases in skeletal development and bone mass maintenance

The skeleton is a multifunctional and regenerative organ. Dynamic activities within the bone microenvironment necessitate and instigate rapid and temporal changes in gene expression within the cells (osteoclasts, osteoblasts, and osteocytes) responsible for skeletal maintenance. Regulation of gene expression is controlled, in part, by histone deacetylases (Hdacs), which are intracellular enzymes that directly affect chromatin structure and transcription factor activity. Key roles for several Hdacs in bone development and biology have been elucidated though in vitro and in vivo models. Recent findings suggest that clinical usage of small molecule Hdac inhibitors for conditions like epilepsy, bipolar disorder, cancer, and a multitude of other ailments may have unintended effects on bone cell populations. Here we review the progress that has been made in the last decade in understanding how Hdacs contribute to bone development and maintenance.

Sodium butyrate induces the production of cyclooxygenases and prostaglandin E₂ in ROS 17/2.8 osteoblastic cells

OBJECTIVE

Sodium butyrate (butyric acid; BA) is a major metabolic by-product of the anaerobic periodontopathic bacteria present in subgingival plaque. We examined the effects of BA and/or indomethacin on cell proliferation, the expression of cyclooxygenases (COXs), prostaglandin (PG) receptors (EP1-4), extracellular matrix proteins, such as type I collagen and osteopontin, and PGE(2) production, using ROS17/2.8 cells as osteoblasts.

METHODS

The rat clonal cell line ROS 17/2.8 was cultured with 0, 10(-5), 10(-4), and 10(-3)M BA in the presence or absence of 0.5 μM indomethacin, for up to 7 days. The expression of COX-1, COX-2, EP1, EP2, EP3, EP4, type I collagen, and osteopontin was examined at the mRNA and protein levels using real-time PCR and Western blotting, respectively. The amount of PGE(2) in the culture medium was measured by ELISA.

RESULTS

Proliferation of ROS 17/2.8 cells was not affected by the addition of BA. However, PGE(2) production and the expression of COX-1 and COX-2 increased with the addition of BA. In contrast, indomethacin, an inhibitor of COX, blocked the stimulatory effect of BA. Furthermore, EP2 expression increased with BA treatment, whereas EP1 expression was not affected and the expression of EP3 and EP4 was not detected. The addition of BA also increased the expression of type I collagen and osteopontin. Indomethacin blocked about 50% of the stimulatory effect of BA on type I collagen, whereas it did not block the effect on osteopontin.

CONCLUSIONS

These results suggest that BA induces PGE(2) production by increasing the expression of COX-1 and COX-2 in osteoblasts, and that an autocrine action of the produced PGE(2), via EP1 or BA-induced EP2, is related to an increase in type I collagen expression by BA.

Hdac-mediated control of endochondral and intramembranous ossification

Histone deacetylases (Hdacs) remove acetyl groups (CH3CO-) from ε-amino groups in lysine residues within histones and other proteins. This posttranslational (de) modification alters protein stability, protein-protein interactions, and chromatin structure. Hdac activity plays important roles in the development of all organs and tissues, including the mineralized skeleton. Bone is a dynamic tissue that forms and regenerates by two processes: endochondral and intramembranous ossification. Chondrocytes and osteoblasts are responsible for producing the extracellular matrices of skeletal tissues. Several Hdacs contribute to the molecular pathways and chromatin changes that regulate tissue-specific gene expression during chondrocyte and osteoblast specification, maturation, and terminal differentiation. In this review, we summarize the roles of class I and class II Hdacs in chondrocytes and osteoblasts. The effects of small molecule Hdac inhibitors on the skeleton are also discussed.

Histone deacetylase 3 depletion in osteo/chondroprogenitor cells decreases bone density and increases marrow fat

Histone deacetylase (Hdac)3 is a nuclear enzyme that contributes to epigenetic programming and is required for embryonic development. To determine the role of Hdac3 in bone formation, we crossed mice harboring loxP sites around exon 7 of Hdac3 with mice expressing Cre recombinase under the control of the osterix promoter. The resulting Hdac3 conditional knockout (CKO) mice were runted and had severe deficits in intramembranous and endochondral bone formation. Calvarial bones were significantly thinner and trabecular bone volume in the distal femur was decreased 75% in the Hdac3 CKO mice due to a substantial reduction in trabecular number. Hdac3-CKO mice had fewer osteoblasts and more bone marrow adipocytes as a proportion of tissue area than their wildtype or heterozygous littermates. Bone formation rates were depressed in both the cortical and trabecular regions of Hdac3 CKO femurs. Microarray analyses revealed that numerous developmental signaling pathways were affected by Hdac3-deficiency. Thus, Hdac3 depletion in osterix-expressing progenitor cells interferes with bone formation and promotes bone marrow adipocyte differentiation. These results demonstrate that Hdac3 inhibition is detrimental to skeletal health.

Histone deacetylases in control of skeletogenesis

Skeletogenesis occurs continuously during the lifespan of vertebrate organisms. In development, the skeleton is patterned and modeled until each bone achieves its optimal shape and full size. During adults, the skeleton is remodeled to maintain strength and release calcium. The bone-resorbing and bone-forming activities of osteoclasts and osteoblasts, respectively, are tightly coupled to maintain optimal skeletal health; however, during aging and disease, these cells can become uncoupled, adversely affecting skeletal health and strength. Histone deacetylases have emerged as important regulators of endochondral bone formation, osteoblast maturation and osteoclast survival. Histone deacetylases are inhibited by small molecules that are approved and/or in clinical trials as cancer therapeutic drugs or anti-epileptic agents. In this article, the roles of histone deacetylases and effects of histone deacetylase inhibitors on bone and cartilage cells are reviewed.

Gene profile analysis of osteoblast genes differentially regulated by histone deacetylase inhibitors

Background

Osteoblast differentiation requires the coordinated stepwise expression of multiple genes. Histone deacetylase inhibitors (HDIs) accelerate the osteoblast differentiation process by blocking the activity of histone deacetylases (HDACs), which alter gene expression by modifying chromatin structure. We previously demonstrated that HDIs and HDAC3 shRNAs accelerate matrix mineralization and the expression of osteoblast maturation genes (e.g. alkaline phosphatase, osteocalcin). Identifying other genes that are differentially regulated by HDIs might identify new pathways that contribute to osteoblast differentiation.

Results

To identify other osteoblast genes that are altered early by HDIs, we incubated MC3T3-E1 preosteoblasts with HDIs (trichostatin A, MS-275, or valproic acid) for 18 hours in osteogenic conditions. The promotion of osteoblast differentiation by HDIs in this experiment was confirmed by osteogenic assays. Gene expression profiles relative to vehicle-treated cells were assessed by microarray analysis with Affymetrix GeneChip 430 2.0 arrays. The regulation of several genes by HDIs in MC3T3-E1 cells and primary osteoblasts was verified by quantitative real-time PCR. Nine genes were differentially regulated by at least two-fold after exposure to each of the three HDIs and six were verified by PCR in osteoblasts. Four of the verified genes (solute carrier family 9 isoform 3 regulator 1 (Slc9a3r1), sorbitol dehydrogenase 1, a kinase anchor protein, and glutathione S-transferase alpha 4) were induced. Two genes (proteasome subunit, beta type 10 and adaptor-related protein complex AP-4 sigma 1) were suppressed. We also identified eight growth factors and growth factor receptor genes that are significantly altered by each of the HDIs, including Frizzled related proteins 1 and 4, which modulate the Wnt signaling pathway.

Conclusion

This study identifies osteoblast genes that are regulated early by HDIs and indicates pathways that might promote osteoblast maturation following HDI exposure. One gene whose upregulation following HDI treatment is consistent with this notion is Slc9a3r1. Also known as NHERF1, Slc9a3r1 is required for optimal bone density. Similarly, the regulation of Wnt receptor genes indicates that this crucial pathway in osteoblast development is also affected by HDIs. These data support the hypothesis that HDIs regulate the expression of genes that promote osteoblast differentiation and maturation.