Phenotypic research on senile osteoporosis caused by SIRT6 deficiency

Epigenetically rewiring metabolic genes via SIRT6 orchestrates MSC fate determination

SIRT6 owns versatile types of enzymatic activities as a multitasking protein, including ribosyltransferase and deacetylase. To investigate the epigenetic regulations of SIRT6 on MSC fate determination via histone deacetylation, we used allosteric small molecules specifically controlling its histone 3 deacetylation activities. Results showed that enhanced deacetylation of SIRT6 promoted the ossific lineage commitment of MSC and finally achieved anabolic effects on hard tissues. Mechanistically, H3K9ac and H3K56ac, governed by SIRT6, in MSC orchestrated the transcriptions of crucial metabolic genes, mediating MSC fate determination. Most importantly, our data evidenced that modulating the epigenetic regulations of SIRT6, specifically via enhancing its deacetylation of H3K9ac and H3K56ac, was a promising choice to treat bone loss diseases and promote dentin regeneration. In this study, we revealed the specific roles of SIRT6's histone modification in MSC fate determination. These findings endow us with insights on SIRT6 and the promising therapeutic choices through SIRT6's epigenetic functions for hard tissues regeneration.

Study on the Bioactivity Response of the Newly Developed Zn-Cu-Mn/Mg Alloys for Biodegradable Implant Application

Scaffolds play a crucial role in bone tissue engineering to support the defect area through bone regeneration and defect reconstruction. Promising tissue regeneration without negative repercussions and avoidance of the lifelong presence inside the body make bioresorbable metals prosper in the field of regenerative medicine. Recently, Zn and its alloys have emerged as promising biodegradable materials for their moderate degradation rate and satisfactory biocompatibility. Nevertheless, it is very challenging for cells to adhere and grow over the Zn surface alone, which influences the tissue-implant integration. In this study, an attempt has been made to systematically investigate the bioactivity responses in terms of in vitro hemocompatibility, cytotoxicity, antibacterial activity, and in vivo biocompatibility of newly developed Zn-2Cu-0.5Mn/Mg alloy scaffolds with different surface roughness. The rough surface of Zn-2Cu-0.5Mg shows the highest degradation rate of 0.16 mm/yr. The rough surface exhibits a prominent role in the adsorption of protein, further enhancing cell adhesion. Concentration-dependent alloy extract shows the highest cell proliferation for 12.5% of the extract with a maximum cell viability of 101% in Zn-2Cu-0.5Mn and 108% in Zn-2Cu-0.5Mg after 3 d. Acceptable hemolysis percentages (less than 5%) with promising anticoagulation properties are observed for all of the conditions. Enhanced antibacterial (Staphylococcus aureus and Escherichia coli) activity due to a significant effect of ions illustrates the maximum killing effect on the bacterial colony for the rough Zn-2Cu-0.5Mg alloy. In addition, it is observed that for rough Zn-2Cu-0.5Mn/Mg alloys, the inflammatory response is minimal after subcutaneous implantation, and neo-bone tissue forms in the defect areas of the rat femur with satisfactory biosafety response. The osseointegration property of the Zn-2Cu-0.5Mg alloy is comparable to that of the Zn-2Cu-0.5Mn alloy. Therefore, the rough surface of the Zn-2Cu-0.5Mg alloy has the potential to enhance biocompatibility and promote better osseointegration activity with host tissues for various biomedical applications.

Research advances on silence information regulator 6 as a potential therapeutic target for bone regeneration and repair

Segmental bone defects and nonunion of fractures caused by trauma, infection, tumor or systemic diseases with limited osteogenesis and prolonged bone healing cycles are challenging issues in orthopedic clinical practice. Therefore, identifying regulatory factors for bone tissue regeneration and metabolism is crucial for accelerating bone repair and reconstructing defective areas. Silence information regulator 6 (SIRT6), functioning as a deacetylase and nucleotide transferase, is extensively involved in the regulation of differentiation, apoptosis, metabolism, and inflammation in bone cells including osteoblasts and osteoclasts, and is considered to be an important factor in regulating bone metabolism. SIRT6 forms a complex with B lymphocyte-induced maturation protein 1 (Blimp1), down-regulates the expression of the nuclear factor κB (NF-κB) pathway, and promotes the expression of the ERα-FasL axis signal to inhibit osteoclast formation and maturation differentiation, thereby hindering bone resorption and increasing bone mass. In addition, SIRT6 activates the Akt-mTOR pathway to regulate the autophagy level and osteogenesis of bone marrow mesenchymal stem cells, inhibits glycolysis and reactive oxygen production in osteoblasts, promotes osteoblast differentiation through the CREB/CCN1/COX2 pathway and the bone morphogenetic protein (BMP) signaling pathway, enhances bone formation, and accelerates bone regeneration and repair of skeletal tissue. This article provides an overview of the research progress on SIRT6 in the pathophysiology of bone regeneration, revealing its potential as a novel therapeutic target for bone tissue repair to alleviate the progression of skeletal pathological diseases.

Skeletal phenotypes and molecular mechanisms in aging mice

Aging is an inevitable physiological process, often accompanied by age-related bone loss and subsequent bone-related diseases that pose serious health risks. Research on skeletal diseases caused by aging in humans is challenging due to lengthy study durations, difficulties in sampling, regional variability, and substantial investment. Consequently, mice are preferred for such studies due to their similar motor system structure and function to humans, ease of handling and care, low cost, and short generation time. In this review, we present a comprehensive overview of the characteristics, limitations, applicability, bone phenotypes, and treatment methods in naturally aging mice and prematurely aging mouse models (including SAMP6, POLG mutant, LMNA, SIRT6, ZMPSTE24, TFAM, ERCC1, WERNER, and KL/KL-deficient mice). We also summarize the molecular mechanisms of these aging mouse models, including cellular DNA damage response, senescence-related secretory phenotype, telomere shortening, oxidative stress, bone marrow mesenchymal stem cell (BMSC) abnormalities, and mitochondrial dysfunction. Overall, this review aims to enhance our understanding of the pathogenesis of aging-related bone diseases.

Sirt6 protects retinal ganglion cells and optic nerve from degeneration during aging and glaucoma

Glaucoma is characterized by the progressive degeneration of retinal ganglion cells (RGCs) and their axons, and its risk increases with aging. Yet comprehensive insights into the complex mechanisms are largely unknown. Here, we found that anti-aging molecule Sirt6 was highly expressed in RGCs. Deleting Sirt6 globally or specifically in RGCs led to progressive RGC loss and optic nerve degeneration during aging, despite normal intraocular pressure (IOP), resembling a phenotype of normal-tension glaucoma. These detrimental effects were potentially mediated by accelerated RGC senescence through Caveolin-1 upregulation and by the induction of mitochondrial dysfunction. In mouse models of high-tension glaucoma, Sirt6 level was decreased after IOP elevation. Genetic overexpression of Sirt6 globally or specifically in RGCs significantly attenuated high tension-induced degeneration of RGCs and their axons, whereas partial or RGC-specific Sirt6 deletion accelerated RGC loss. Importantly, therapeutically targeting Sirt6 with pharmacological activator or AAV2-mediated gene delivery ameliorated high IOP-induced RGC degeneration. Together, our studies reveal a critical role of Sirt6 in preventing RGC and optic nerve degeneration during aging and glaucoma, setting the stage for further exploration of Sirt6 activation as a potential therapy for glaucoma.

Osteoclasts and osteoarthritis: Novel intervention targets and therapeutic potentials during aging

Osteoarthritis (OA), a chronic degenerative joint disease, is highly prevalent among the aging population, and often leads to joint pain, disability, and a diminished quality of life. Although considerable research has been conducted, the precise molecular mechanisms propelling OA pathogenesis continue to be elusive, thereby impeding the development of effective therapeutics. Notably, recent studies have revealed subchondral bone lesions precede cartilage degeneration in the early stage of OA. This development is marked by escalated osteoclast-mediated bone resorption, subsequent imbalances in bone metabolism, accelerated bone turnover, and a decrease in bone volume, thereby contributing significantly to the pathological changes. While the role of aging hallmarks in OA has been extensively elucidated from the perspective of chondrocytes, their connection with osteoclasts is not yet fully understood. There is compelling evidence to suggest that age-related abnormalities such as epigenetic alterations, proteostasis network disruption, cellular senescence, and mitochondrial dysfunction, can stimulate osteoclast activity. This review intends to systematically discuss how aging hallmarks contribute to OA pathogenesis, placing particular emphasis on the age-induced shifts in osteoclast activity. It also aims to stimulate future studies probing into the pathological mechanisms and therapeutic approaches targeting osteoclasts in OA during aging.

Sirtuins mediate mitochondrial quality control mechanisms: a novel therapeutic target for osteoporosis

Mitochondria plays a role in cell differentiation and apoptosis processes. Maintaining mitochondrial function is critical, and this involves various aspects of mitochondrial quality control such as protein homeostasis, biogenesis, dynamics, and mitophagy. Osteoporosis, a metabolic bone disorder, primarily arises from two factors: the dysregulation between lipogenic and osteogenic differentiation of aging bone marrow mesenchymal stem cells, and the imbalance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. Mitochondrial quality control has the potential to mitigate or even reverse the effects. Among the Sirtuin family, consisting of seven Sirtuins (SIRT1-7), SIRT1-SIRT6 play a crucial role in maintaining mitochondrial quality control. Additionally, SIRT1, SIRT3, SIRT6, and SIRT7 are directly involved in normal bone development and homeostasis by modulating bone cells. However, the precise mechanism by which these Sirtuins exert their effects remains unclear. This article reviews the impact of various aspects of mitochondrial quality control on osteoporosis, focusing on how SIRT1, SIRT3, and SIRT6 can improve osteoporosis by regulating mitochondrial protein homeostasis, biogenesis, and mitophagy. Furthermore, we provide an overview of the current state of clinical and preclinical drugs that can activate Sirtuins to improve osteoporosis. Specific Sirtuin-activating compounds are effective, but further studies are needed. The findings of this study may offer valuable insights for future research on osteoporosis and the development of clinical prevention and therapeutic target strategies.

Insights into the Mechanism of Osteoporosis and the Available Treatment Options

Osteoporosis, one of the most prevalent bone illnesses, majorly affects postmenopausal women and men over 50 years of age. Osteoporosis is associated with an increased susceptibility to fragility fractures and can result in persistent pain and significant impairment in affected individuals. The primary method for diagnosing osteoporosis involves the assessment of bone mineral density (BMD) through the utilisation of dual energy x-ray absorptiometry (DEXA). The integration of a fracture risk assessment algorithm with bone mineral density (BMD) has led to significant progress in the diagnosis of osteoporosis. Given that osteoporosis is a chronic condition and multiple factors play an important role in maintaining bone mass, comprehending its underlying mechanism is crucial for developing more effective pharmaceutical interventions for the disease. The effective management of osteoporosis involves the utilisation of appropriate pharmacological agents in conjunction with suitable dietary interventions and lifestyle modifications. This review provides a comprehensive understanding of the types of osteoporosis and elucidates the currently available pharmacological treatment options and their related mechanism of action and usage.

Development of Zn-2Cu-xMn/Mg Alloys for Orthopedic Applications: Mechanical Performance to In Vitro Degradation under Different Physiological Environments

Zinc (Zn) and its alloys are considered futuristic biodegradable materials for their acceptable mechanical properties, suitable corrosion rate, and good biocompatibility. In this study, we report newly developed biodegradable Zn-2Cu-xMn/Mg (x = 0, 0.1, and 0.5) alloys, aiming to achieve good mechanical strength with excellent elongation, desirable wear resistance, and suitable corrosion rate. The effect of Mn/Mg addition on the structural, mechanical, wear, and degradation behaviors of the Zn-2Cu-xMn/Mg alloys was thoroughly investigated. Degradation and tribological behaviors of the alloys were explored in the presence of simulated body fluid (SBF), Dulbecco's modified Eagle medium (DMEM), and DMEM with a 10% fetal bovine serum (FBS) solution. Alloy elements and hot rolling improve their mechanical properties significantly due to precipitation hardening, grain refinement, and solid solution strengthening owing to the formation of MnZn13 and Mg2Zn11 phases. Among all the alloys, the Zn-2Cu-0.5Mn alloy achieved the highest ultimate tensile strength (UTS) of ∼405 MPa and yield strength (YS) of ∼293 MPa with an excellent elongation of ∼51%. The corrosion behavior of the alloys as determined by a potentiodynamic polarization study under different solutions follows the sequence Zn-2Cu < Zn-2Cu-0.5Mn < Zn-2Cu-0.1Mn < Zn-2Cu-0.1Mg < Zn-2Cu-0.5Mg. The corrosion rate by immersion testing for 30 and 90 days also follows the same sequence. The corrosion rate in different solutions follows the order SBF > DMEM + 10%FBS > DMEM. The addition of Mn/Mg also improves the wear resistance and slows the wear rate under wet conditions. The bending test results also indicate the highest bending strength of ∼375 MPa for the Zn-2Cu-0.5Mn alloy, among all the alloys. The bending and tensile strengths deteriorate continuously after the immersion for 30 and 90 days in the solution of SBF, DMEM, and DMEM + 10%FBS. Therefore, the Zn-2Cu-xMn/Mg (x = 0.1 and 0.5) alloys can be considered potential biodegradable implant materials.

Assessment of Awareness and Knowledge about Osteoporosis in Relation to Health Prevention among Patients Treated in Osteoporosis Clinics

The increasing incidence of osteoporosis indicates that the disease is a serious public health problem, with about 200 million people being affected worldwide. The aims of this research are to assess the awareness and knowledge about osteoporosis in relation to risk factors, health condition, supplementation used, socio-demographic factors and other variables among osteoporosis patients. The study was conducted in 2016-2018 in osteoporosis clinics in Poland. The study involved 312 patients with a diagnosis of osteoporosis. In the diagnostic survey method, the authors' own questionnaire was used. The results indicate that the more frequent the symptoms associated with the disease, the lower the general self-assessment of the health condition of the respondents (rho = -0.682, p < 0.001). In addition, almost half of the respondents stated that their knowledge of osteoporosis is negligible. Moreover, the use of dietary supplements significantly differentiated respondents in terms of health self-assessed (p < 0.001), and it is noteworthy that users of dietary supplements assessed their health significantly better. We also saw a statistically significant relationship between the self-assessment of knowledge about osteoporosis and the use of dietary supplements (p < 0.001). Accordingly, significantly more respondents rating their knowledge as good or very good used dietary supplements. The conducted study demonstrates the need to educate patients and implement educational programs at central and provincial levels to improve patient knowledge concerning the disease. Supporting adaptation to chronic diseases and appropriate therapeutic management may contribute to improved osteoporosis treatment and enhanced patient quality of life.

Oxidative stress and inflammation regulation of sirtuins: New insights into common oral diseases

Sirtuins are a family of nicotinamide adenine dinucleotide (NAD)⁺-dependent histone deacetylases, comprising seven members SIRT1-SIRT7. Sirtuins have been extensively studied in regulating ageing and age-related diseases. Sirtuins are also pivotal modulators in oxidative stress and inflammation, as they can regulate the expression and activation of downstream transcriptional factors (such as Forkhead box protein O3 (FOXO3a), nuclear factor erythroid 2-related factor 2 (Nrf2) and nuclear factor-kappa B (NF-κB)) as well as antioxidant enzymes, through epigenetic modification and post-translational modification. Most importantly, studies have shown that aberrant sirtuins are involved in the pathogenesis of infectious and inflammatory oral diseases, and oral cancer. In this review, we provide a comprehensive overview of the regulatory patterns of sirtuins at multiple levels, and the essential roles of sirtuins in regulating inflammation, oxidative stress, and bone metabolism. We summarize the involvement of sirtuins in several oral diseases such as periodontitis, apical periodontitis, pulpitis, oral candidiasis, oral herpesvirus infections, dental fluorosis, and oral cancer. At last, we discuss the potential utilization of sirtuins as therapeutic targets in oral diseases.

Krüppel-like factor 5 -mediated Sirtuin6 promotes osteogenic differentiation and inhibits inflammatory injury of lipopolysaccharide-induced periodontal membrane stem cells by inhibiting nuclear factor kappa-B pathway

Periodontitis is a chronic infectious disease that causes inflammation and immune response and has an ultimate impact on the health of the whole body. Sirtuin6 (SIRT6) and Krüppel-like factor 5 (KLF5) have been reported to regulate the inflammatory response and play an important role in the development of periodontitis. LPS was adopted to induce periodontal ligament stem cells (PDLSCs) to construct a periodontitis cell model. SIRT6 expression was assayed through RT-qPCR and Western blot. Subsequently, after SIRT6 was overexpressed, CCK8 was to appraise cell viability. ELISA analysis was used to estimate inflammatory response. ALP staining, ARS staining, and Western blot were used to detect osteogenic differentiation. The JASPAR website then predicts the binding of transcription factor KLF5 to SIRT6 promoter. The interaction between KLF5 and SIRT6 was verified by a luciferase reporter and ChIP assays. Additionally, the osteogenic differentiation and inflammation in LPS-induced PDLSCs transfected with Ov-SIRT6 and si-KIF5 were also explored. Finally, the protein levels of the nuclear factor kappa-B (NF-κB) pathway-related factors were detected by Western blot to further explore the mechanism. There was a marked decrease in SIRT6 expression in LPS-induced PDLSCs. SITR6 overexpression prevented LPS-induced cell viability loss and inflammation, while promoting osteogenic differentiation. In addition, KLF5 could transcriptionally activate SIRT6. Further, KLF5 knockdown reversed the impacts of SIRT6 on the proliferation, inflammation, and osteogenic differentiation of LPS-induced PDLSCs via mediating NF-κB pathway. Overall, KLF5-mediated SIRT6 promoted the viability and osteogenic differentiation, while inhibiting the inflammatory response of LPS-induced PDLSCs by inhibiting NF-κB pathway.

Role of sirtuins in bone biology: Potential implications for novel therapeutic strategies for osteoporosis

The decline in bone mass and bone strength and musculoskeletal problems associated with aging constitute a major challenge for affected individuals and the healthcare system globally. Sirtuins 1-7 (SIRT1-SIRT7) are a family of nicotinamide adenine dinucleotide-dependent deacetylases with remarkable abilities to promote longevity and counteract age-related diseases. Sirtuin knockout and transgenic models have provided novel insights into the function and signaling of these proteins in bone homeostasis. Studies have revealed that sirtuins play a critical role in normal skeletal development and homeostasis through their direct action on bone cells and that their dysregulation might contribute to different bone diseases. Preclinical studies have demonstrated that mice treated with sirtuin agonists show protection against age-related, postmenopausal, and immobilization-induced osteoporosis. These findings suggest that sirtuins could be potential targets for the modulation of the imbalance in bone remodeling and treatment of osteoporosis and other bone disorders. The aim of this review was to provide a comprehensive updated review of the current knowledge on sirtuin biology, focusing specifically on their roles in bone homeostasis and osteoporosis, and potential pharmacological interventions targeting sirtuins for the treatment of osteoporosis.

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.

Clinical effect of Zoledronic Acid in the treatment of Senile Osteoporosis

Objective:

To investigate the clinical efficacy of zoledronic acid in the treatment of senile osteoporosis.

Methods:

One hundred and six cases of senile osteoporosis who visited to our hospital from August 2017 to December 2018 for treatment were selected and randomly divided into a control group and an observation group. The control group was treated with conventional therapy, while the observation group was treated with zoledronic acid in addition to the treatment of the control group. Bone mineral density, pain degree, therapeutic effect and adverse reactions of the two groups were compared.

Results:

The total effective rate of the observation group was 96.67%, higher than 80.00% of the control group (P<0.05); the bone mineral density of lumbar vertebrae, femoral neck and Ward’ area in the two groups increased after 6 months of treatment, and the bone mineral density of the observation group increased more than that of the control group (P<0.05); the pain degree of the observation group was lower than that of the control group after 6 months of treatment, and the difference was significant (P<0.05). There was no significant difference in the occurrence of adverse reactions between the two groups (P>0.05).

Conclusion:

Zoledronic acid is helpful to alleviate clinical symptoms, reduce the degree of bone pain, and promote the increase of bone mass, and has high safety in the treatment of senile osteoporosis, which is worth promotion.

A biodegradable Zn-1Cu-0.1Ti alloy with antibacterial properties for orthopedic applications

Zinc (Zn) alloys are receiving increasing attention in the field of biodegradable implant materials due to their unique combination of suitable biodegradability and good biological functionalities. However, the currently existing industrial Zn alloys are not necessarily biocompatible, nor sufficiently mechanically strong and wear-resistant. In this study, a Zn-1Cu-0.1Ti alloy is developed with enhanced mechanical strength, corrosion wear property, biocompatibility, and antibacterial ability for biodegradable implant material applications. HR and HR + CR were performed on the as-cast alloy and its microstructure, mechanical properties, frictional and wear behaviors, corrosion resistance, in vitro cytocompatibility, and antibacterial ability were systematically assessed. The microstructures of the Zn-1Cu-0.1Ti alloy after different deformation conditions included a η-Zn phase, a ε-CuZn₅ phase, and an intermetallic phase of TiZn₁₆. The HR+CR sample of Zn-1Cu-0.1Ti exhibited a yield strength of 204.2 MPa, an ultimate tensile strength of 249.9 MPa, and an elongation of 75.2%; significantly higher than those of the HR alloy and the AC alloy. The degradation rate in Hanks' solution was 0.029 mm/y for the AC alloy, 0.032 mm/y for the HR+CR alloy, and 0.034 mm/y for the HR alloy. The HR Zn-1Cu-0.1Ti alloy showed the best wear resistance, followed by the AC alloy and the alloy after HR + CR. The extract of the AC Zn-1Cu-0.1Ti alloy showed over 80% cell viability with MC3T3-E1 pre-osteoblast and MG-63 osteosarcoma cells at a concentration of ≤ 25%. The as-cast Zn-1Cu-0.1Ti alloy showed good blood compatibility and antibacterial ability. STATEMENT OF SIGNIFICANCE: This work repots a Zn-1Cu-0.1Ti alloy with enhanced mechanical strength, corrosion wear property, biocompatibility, and antibacterial ability for biodegradable implant applications. Our findings showed that Zn-1Cu-0.1Ti after hot-rolling plus cold-rolling exhibited a yield strength of 204.2 MPa, an ultimate tensile strength of 249.9 MPa, an elongation of 75.2%, and a degradation rate of 0.032 mm/y in Hanks' Solution. The hot-rolled Zn-1Cu-0.1Ti showed the best wear resistance. The extract of the as-cast alloy at a concentration of ≤ 25% showed over 80% cell viability with MC3T3-E1 and MG-63 cells. The Zn-1Cu-0.1Ti alloy showed good hemocompatibility and antibacterial ability.

Fructus Ligustri Lucidi preserves bone quality through the regulation of gut microbiota diversity, oxidative stress, TMAO and Sirt6 levels in aging mice

Gut dysbiosis and oxidative stress may trigger senile osteoporosis. Fructus Ligustri Lucidi (FLL) has bone-preserving properties and affects the intestinal microecology. However, the mechanism of the anti-osteoporotic effect of FLL and its link to the gut microbiota remains to be elucidated. Here, we demonstrated that sustained exposure of ICR mice to D-galactose / sodium nitrite for 90 days causes aging-related osteoporosis and reduced cognitive performance. The aging phenotype is also characterized by increased oxidative stress in serum. This is likely triggered by abnormal changes in the gut microbiota population of Bifidobacterium and the ratio of Firmicutes/ Bacteroidetes that resulted in increased levels of flavin-containing monooxygenase-3 and trimethylamine-N-oxide (TMAO). Moreover, the increased oxidative stress further accelerated aging by increasing tumor necrosis factor-α levels in serum and reducing Sirtuin 6 (Sirt6) expression in long bones, which prompted nuclear factor kappa-B acetylation as well as over-expression and activation of cathepsin K. FLL-treated aging mice revealed a non-osteoporotic bone phenotype and an improvement on the cognitive function. The mechanism underlying these effects may be linked to the regulation of gut microbiota diversity, antioxidant activity, and the levels of TMAO and Sirt6. FLL may represent a potential source for identifying anti-senile osteoporotic drug candidates.

Inhibitory Effect of Sirtuin6 (SIRT6) on Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

BACKGROUND The imbalance between bone resorption and formation is the basic mechanism underlying osteoporosis in the elderly. Osteogenesis is the differentiation of human mesenchymal stem cells (hMSCs) into osteoblasts. Sirtuin6 (SIRT6) regulates various biological functions, including differentiation. Transient receptor potential cation channel subfamily V member 1 (TRPV1) is a non-selective cation channel that can be activated by physical and chemical stimulation. However, experimental data supporting the role of SIRT6 in osteogenic differentiation (OD) of hMSCs are lacking. MATERIAL AND METHODS Differentiation of hMSCs was induced. The expressions of SIRT6, TRPV1, and CGRP were detected by Q-PCR, Western blot, and ELISA, respectively. SIRT6 was overexpressed in hMSCs by transfection. ALP activity and Alizarin Red staining were utilized to detect the effect of SIRT6 on hMSC OD. Then, capsaicin and capsazepine, the TRPV1 agonist and antagonist, respectively, were administrated to assess the role of TRPV1. RESULTS SIRT6 expression was downregulated during hMSC differentiation. SIRT6 overexpression was accompanied by reduced expression of specific genes and alkaline phosphatase (ALP) activity in osteoblasts. Furthermore, TRPV1 channel was also reduced by SIRT6 overexpression via ubiquitinating TRPV1. Capsaicin was utilized in SIRT6-overexpressed cells. Capsaicin therapy counteracted the effect of SIRT6 overexpression on OD, and markedly decreased OD. CONCLUSIONS The SIRT6-TRPV1-CGRP signal axis is the key to regulating OD in hMSCs, which could be a potential therapeutic target for osteoporosis and bone loss-related diseases.

Role of APD-Ribosylation in Bone Health and Disease

The transfer of adenosine diphosphate (ADP)-ribose unit(s) from nicotinamide adenine dinucleotide (NAD⁺) to acceptor proteins is known as ADP-ribosylation. This post-translational modification (PTM) unavoidably alters protein functions and signaling networks, thereby impacting cell behaviors and tissue outcomes. As a ubiquitous mechanism, ADP-ribosylation affects multiple tissues, including bones, as abnormal ADP-ribosylation compromises bone development and remodeling. In this review, we describe the effects of ADP-ribosylation in bone development and maintenance, and highlight the underlying mechanisms.

Associations of IDUA and PTCH1 with Bone Mineral Density, Bone Turnover Markers, and Fractures in Chinese Elderly Patients with Osteoporosis

Introduction

Osteoporosis (OP) is a common polygenic disorder in the aging population, and several single nucleotide polymorphisms (SNPs) in the alpha-L-iduronidase (IDUA) gene and patched homolog 1 (PTCH1) gene regulate bone metabolism and affect bone mass. The study aimed at investigating the relationships of rs3755955 and rs6831280 in the IDUA gene and rs28377268 in the PTCH1 gene with bone mineral density (BMD), bone turnover markers (BTMs), and fractures in the elderly Chinese subjects with OP.

Materials and Methods

A cohort of 328 unrelated senile osteoporosis (SOP) patients with or without osteoporotic fractures was recruited. rs3755955, rs6831280, and rs28377268 polymorphisms were identified using SNaPshot technology. BTM levels were determined by electrochemiluminescence (ECL). Bone mineral densities (BMDs) at the lumbar spine (LS) and proximal femur sites were measured by dual-energy X-ray absorptiometry (DEXA) in all subjects. The Hardy-Weinberg equilibrium (HWE) test was performed. HWE P values and comparisons of genotype frequencies were estimated using the chi-square test. Analysis of covariance (ANCOVA) adjusted for confounding factors was performed to investigate associations of SNPs with BMDs and BTMs in subgroups.

Results

The chi-square test indicated that genotype distributions in the control group conformed to HWE (P > 0.05). The distributions of allele and genotype frequencies of rs6831280 between fracture and osteoporotic participants were significantly different (P-allele = 0.002 and P-genotype = 0.012, respectively). Concerning rs6831280, ANCOVA found BMDs at LS 2-4 (L2-4) and total hip (TH) among the study subjects suffering from SOP with GA genotype were lower than in those carrying GG or AA (P-L2-4 = 0.004 and P-TH = 0.027, respectively).

Conclusions

IDUA rs6831280 is associated with BMDs at L2-4 and TH in the elderly Chinese population with SOP and may serve as a marker for the genetic susceptibility to osteoporotic fractures.

Sirtuins and FoxOs in osteoporosis and osteoarthritis

The sirtuin family of NAD⁺-dependent protein deacetylases promotes longevity and counteracts age-related diseases. One of the major targets of Sirtuins are the FoxO family of transcription factors. FoxOs play a major role in the adaptation of cells to a variety of stressors such as oxidative stress and growth factor deprivation. Studies with murine models of cell-specific loss- or gain-of-function of Sirtuins or FoxOs and with Sirtuin1 stimulators have provided novel insights into the function and signaling of these proteins on the skeleton. These studies have revealed that both Sirtuins and FoxOs acting directly in cartilage and bone cells are critical for normal skeletal development, homeostasis and that their dysregulation might contribute to skeletal disease. Deacetylation of FoxOs by Sirt1 in osteoblasts and osteoclasts stimulates bone formation and inhibits bone resorption, making Sirt1 ligands promising therapeutic agents for diseases of low bone mass. While a similar link has not been established in chondrocytes, Sirt1 and FoxOs both have chondroprotective actions, suggesting that Sirt1 activators may have similar efficacy in preventing cartilage degeneration due to aging or injury. In this review we summarize these advances and discuss their implications for the pathogenesis of age-related osteoporosis and osteoarthritis.

Current understanding and future perspectives of the roles of sirtuins in the reprogramming and differentiation of pluripotent stem cells

In mammalian cells, there are seven members of the sirtuin protein family (SIRT1-7). SIRT1, SIRT6, and SIRT7 catalyze posttranslational modification of proteins in the nucleus, SIRT3, SIRT4, and SIRT5 are in the mitochondria and SIRT2 is in the cytosol. SIRT1 can deacetylate the transcription factor SOX2 and regulate induced pluripotent stem cells (iPSCs) reprogramming through the miR-34a-SIRT1-p53 axis. SIRT2 can regulate the function of pluripotent stem cells through GSK3β. SIRT3 can positively regulate PPAR gamma coactivator 1-alpha (PGC-1α) expression during the differentiation of stem cells. SIRT4 has no direct role in regulating reprogramming but may have the potential to prevent senescence of somatic cells and to facilitate the reprogramming of iPSCs. SIRT5 can deacetylate STAT3, which is an important transcription factor in regulating pluripotency and differentiation of stem cells. SIRT6 can enhance the reprogramming efficiency of iPSCs from aged skin fibroblasts through miR-766 and increase the expression levels of the reprogramming genes including Sox2, Oct4, and Nanog through acetylation of histone H3 lysine 56. SIRT7 plays a regulatory role in the process of mesenchymal-to-epithelial transition (MET), which has been suggested to be a crucial process in the generation of iPSCs from fibroblasts. In this review, we summarize recent findings of the roles of sirtuins in the metabolic reprogramming and differentiation of stem cells and discuss the bidirectional changes in the gene expression and activities of sirtuins in the commitment of differentiation of mesenchymal stem cells (MSCs) and reprogramming of somatic cells to iPSCs, respectively. Thus, understanding the molecular basis of the interplay between different sirtuins and mitochondrial function will provide new insights into the regulation of differentiation of stem cells and iPSCs formation, respectively, and may help design effective stem cell therapies for regenerative medicine. Impact statement This is an extensive review of the recent advances in our understanding of the roles of some members of the sirtuins family, such as SIRT1, SIRT2, SIRT3, and SIRT6, in the regulation of intermediary metabolism during stem cell differentiation and in the reprogramming of somatic cells to form induced pluripotent stem cells (iPSCs). This article provides an updated integrated view on the mechanisms by which sirtuins-mediated posttranslational protein modifications regulate mitochondrial biogenesis, bioenergetics, and antioxidant defense in the maintenance and differentiation of stem cells and in iPSCs formation, respectively.

SIRT6 inhibits proliferation and invasion in osteosarcoma cells by targeting N-cadherin

SIRT6, is a member of the NAD-dependent sirtuin family of enzymes, and has been reported as a novel tumor suppressor gene or oncogene, dependent on the type of cancer. However, the role of SIRT6 in osteosarcoma has not been investigated. The present study demonstrated that the expression of SIRT6 was downregulated in osteosarcoma tissues and osteosarcoma cell lines when compared with adjacent tissues or osteoblastic cell lines. Kaplan-Meier analysis was performed to evaluate the prognostic significance of SIRT6. The overall survival of patients with higher expression of SIRT6 was significantly longer than patients with lower expression. Subsequently, MTT and invasion assays were performed to detect the biological functions of SIRT6 in osteosarcoma cells in vitro. The results revealed that overexpression of SIRT6 inhibited SAOS-2 and MG-63 cell proliferation and invasion. Knockdown of SIRT6 enhanced cell ability for the proliferation and invasion. A qChIP assay, luciferase reporter assay, reverse transcription-quantitative polymerase chain reaction and western blotting confirmed that CDH2 (N-cadherin) was a target of SIRT6. SIRT6 overexpression suppressed N-cadherin on the mRNA and protein levels. In addition, it was confirmed that the promotional effect of Si-SIRT6 on OS cell growth and invasion was suppressed by downregulating N-cadherin. The present study suggested that SIRT6 may serve as a tumor suppressor during the development of osteosarcoma. In addition, N-cadherin may be a promising therapeutic target for osteosarcoma.

Evidence for excessive osteoclast activation in SIRT6 null mice

SIRT6 is a NAD-dependent histone 3 deacetylase. SIRT6 null mice have been reported suffering osteopenia. However, the role of SIRT6 in bone resorption is still not well understood. In this study, we focused on the role of SIRT6 in osteoclast. We performed histological analysis on the femur, spine, alveolar bone and even tail of mutant mice, and found the bone mass is sharply decreased while the osteoclast activity is significantly increased. These phenotypes were further demonstrated by the osteoclast differentiation in cell-cultures with TRAP staining and Pit Resorption Assay. We next found the proliferation activity of mutant osteoclast precursors was increased, which might account for the enhanced osteoclast formation. The concentration of tartrate-resistant acid phosphatase 5b, a marker of osteoclast differentiation, was significantly higher in the mutant mice than control. Besides, the osteoclastogenic and NF-κB signaling related genes were significantly up-regulated. Moreover, osteoblast/osteoclast co-culture demonstrated that SIRT6 regulated osteoclast mainly through osteoblast paracrine manner, rather than osteoclast-autonomous behavior. Together, the enhanced osteoclast activation in SIRT6 null mice might be regulated by the hyperactive NF-κB signaling and the enhanced proliferation activity of osteoclast precursors through osteoblast paracrine manner at the cellular level.

Sirt6 deficiency results in progression of glomerular injury in the kidney

Aging is associated with an increased incidence and prevalence of renal glomerular diseases. Sirtuin (Sirt) 6, a nicotinamide adenine dinucleotide (NAD)-dependent histone deacetylase, has been shown to protect against multiple age-associated phenotypes; however it is unknown whether Sirt6 has a direct pathophysiologic role in the kidney. In the present study, we demonstrate that Sirt6 is expressed in the kidney and aging Sirt6-deficient mice exhibit renal hypertrophy with glomerular enlargement. Sirt6 deletion induces podocyte injury, including decreases in slit diaphragm proteins, foot process effacement, and cellular loss, resulting in proteinuria. Knockdown of Sirt6 in cultured primary murine podocytes induces shape changes with loss of process formation and cell apoptosis. Moreover, Sirt6 deficiency results in progressive renal inflammation and fibrosis. Collectively, these data provide compelling evidence that Sirt6 is important for podocyte homeostasis and maintenance of glomerular function, and warrant further investigation into the role of Sirt6 in age-associated kidney dysfunction.

The Sirt6 gene: Does it play a role in tooth development?

Dental Mesenchymal Cells (DMCs) are known to play a role in tooth development as well as in the repair and regeneration of dental tissue. A large number of signaling molecules regulate the proliferation and differentiation of DMC, though the underlying mechanisms are still not fully understood. Sirtuin-6 (SIRT6), a key regulator of aging, can exert an impact on embryonic stem cell (ESC) differentiation. The experimental deletion of Sirt6 in mouse bone marrow cells has been found to have an inhibiting impact on the bone mineral density and the osteogenic differentiation of these cells. The possible role of Sirt6 in tooth development, however, has at present remained largely unexplored. In the present study, we found that SIRT6 had no effect on tooth development before birth. However, Sirt6 gene deletion in knockout mice did have two post-natal impacts: a delay in tooth eruption and sluggishness in the development of dental roots. We propose an explanation of the possible molecular basis of the changes observed in Sirt6-/- mice. SIRT6 is expressed in mouse odontoblasts. Sirt6 deletion enhanced the proliferation of DMCs, as well as their capacity for adipogenic differentiation. On the other hand, it inhibited their capacity for in vitro osteogenic/chondrogenic differentiation. Further studies suggested that other factors may mediate the role of Sirt6 in odontogenesis. These include the nuclear factor kappa B (NF-κB), p38 mitogen-activated protein kinase (p38-MAPK), extracellular regulated MAP kinase (ERK) pathways and the mitochondrial energy. We demonstrated that Sirt6 plays a role in tooth root formation and confirmed that SIRT6 is necessary for DMC differentiation as well as for the development of the tooth root and for eventual tooth eruption. These results establish a new link between SIRT6 and tooth development.