The Sirt1 Activators SRT2183 and SRT3025 Inhibit RANKL-Induced Osteoclastogenesis in Bone Marrow-Derived Macrophages and Down-Regulate Sirt3 in Sirt1 Null Cells

Sirt1: An Increasingly Interesting Molecule with a Potential Role in Bone Metabolism and Osteoporosis

Osteoporosis (OP) is a common metabolic bone disease characterized by low bone mass, decreased bone mineral density, and degradation of bone tissue microarchitecture. However, our understanding of the mechanisms of bone remodeling and factors affecting bone mass remains incomplete. Sirtuin1 (SIRT1) is a nicotinamide adenine dinucleotide-dependent deacetylase that regulates a variety of cellular metabolisms, including inflammation, tumorigenesis, and bone metabolism. Recent studies have emphasized the important role of SIRT1 in bone homeostasis. This article reviews the role of SIRT1 in bone metabolism and OP and also discusses therapeutic strategies and future research directions for targeting SIRT1.

Sirtuins: exploring next-gen therapeutics in the pathogenesis osteoporosis and associated diseases

OBJECTIVE

Osteoporosis poses a substantial public health challenge due to an ageing population and the lack of adequate treatment options. The condition is marked by a reduction in bone mineral density, resulting in an elevated risk of fractures. The reduction in bone density and strength, as well as musculoskeletal issues that come with aging, present a significant challenge for individuals impacted by these conditions, as well as the healthcare system worldwide.

METHODS

Literature survey was conducted until May 2023 using databases such as Web of Science, PubMed, Scopus, and Google Scholar.

RESULT

Sirtuins 1-7 (SIRT1-SIRT7), which are a group of Nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, possess remarkable capabilities to increase lifespan and combat diseases related to aging. Research has demonstrated that these proteins play an important role in regular skeletal development and maintenance by directly impacting bone cells. Their dysfunction could be a factor in various bone conditions. Studies conducted on animals before clinical trials have shown that administering Sirtuins agonists to mice provides a safeguard against osteoporosis resulting from aging, menopause, and immobilization. These findings imply that Sirtuins may be a viable target for addressing the irregularity in bone remodeling and treating osteoporosis and other skeletal ailments.

CONCLUSION

The purpose of this review was to present a thorough and current evaluation of the existing knowledge on Sirtuins biology, with a particular emphasis on their involvement in maintaining bone homeostasis and contributing to osteoporosis. Additionally, the review examines potential pharmacological interventions targeting Sirtuins for the treatment of osteoporosis.

Exploring epigenetic strategies for the treatment of osteoporosis

The worldwide trend toward an aging population has resulted in a higher incidence of chronic conditions, such as osteoporosis. Osteoporosis, a prevalent skeletal disorder characterized by decreased bone mass and increased fracture risk, encompasses primary and secondary forms, each with distinct etiologies. Mechanistically, osteoporosis involves an imbalance between bone resorption by osteoclasts and bone formation by osteoblasts. Current pharmacological interventions for osteoporosis, such as bisphosphonates, denosumab, and teriparatide, aim to modulate bone turnover and preserve bone density. Hormone replacement therapy and lifestyle modifications are also recommended to manage the condition. While current medications offer therapeutic options, they are not devoid of limitations. Recent studies have highlighted the importance of epigenetic mechanisms, including DNA methylation and histone modifications, in regulating gene expression during bone remodeling. The use of epigenetic drugs, or epidrugs, to target these mechanisms offers a promising avenue for therapeutic intervention in osteoporosis. In this review, we comprehensively examine the recent advancements in the application of epidrugs for treating osteoporosis.

Redox signaling and antioxidant defense in osteoclasts

Bone remodeling is essential for the repair and replacement of damaged or aging bones. Continuous remodeling is necessary to prevent the accumulation of bone damage and to maintain bone strength and calcium balance. As bones age, the coupling mechanism between bone formation and absorption becomes dysregulated, and bone loss becomes dominant. Bone development and repair rely on interaction and communication between osteoclasts and surrounding cells. Osteoclasts are specialized cells that are accountable for bone resorption and degradation, and any abnormalities in their activity can result in notable alterations in bone structure and worsen disease symptoms. Recent findings from transgenic mouse models and bone analysis have greatly enhanced our understanding of the origin, differentiation pathway, and activation stages of osteoclasts. In this review, we explore osteoclasts and discuss the cellular and molecular events that drive their generation, focusing on intracellular oxidative and antioxidant signaling. This knowledge can help develop targeted therapies for diseases associated with osteoclast activation.

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.

A Review of Proposed Mechanisms in Rheumatoid Arthritis and Therapeutic Strategies for the Disease

Rheumatoid arthritis (RA) is characterized by synovial edema, inflammation, bone and cartilage loss, and joint degradation. Patients experience swelling, stiffness, pain, limited joint movement, and decreased mobility as the condition worsens. RA treatment regimens often come with various side effects, including an increased risk of developing cancer and organ failure, potentially leading to mortality. However, researchers have proposed mechanistic hypotheses to explain the underlying causes of synovitis and joint damage in RA patients. This review article focuses on the role of synoviocytes and synoviocytes resembling fibroblasts in the RA synovium. Additionally, it explores the involvement of epigenetic regulatory systems, such as microRNA pathways, silent information regulator 1 (SIRT1), Peroxisome proliferatoractivated receptor-gamma coactivator (PGC1-α), and protein phosphatase 1A (PPM1A)/high mobility group box 1 (HMGB1) regulators. These mechanisms are believed to modulate the function of receptors, cytokines, and growth factors associated with RA. The review article includes data from preclinical and clinical trials that provide insights into potential treatment options for RA.

SRT2183 and SRT1720, but not Resveratrol, Inhibit Osteoclast Formation and Resorption in the Presence or Absence of Sirt1

Background

Osteoclastic bone resorption markedly increases with aging, leading to osteoporosis characterized by weak and fragile bones. Mice exhibit greater bone resorption and poor bone mass when Sirt1 is removed from their osteoclasts. Here we investigated the ex vivo impacts of putative Sirt1 activators, Resveratrol (RSV), SRT2183, and SRT1720, on osteoclast formation and activity in primary mouse bone marrow cells (BMCs) derived from wild-type (WT) and osteoclast specific Sirt1 knockout (OC-Sirt1KO) mice and in the RAW264.7 mouse macrophage cell line.

Results

We found that SRT2183 and SRT1720 inhibit the formation of osteoclasts and actin belts in BMCs and RAW264.7 cells, whereas RSV does not. We also observed that the OC-Sirt1KO mice exhibited less bone mineral density, and the BMCs harvested from these mice yielded more osteoclasts than BMCs harvested from littermate controls. Interestingly, both SRT2183 and SRT1720 reduced osteoclast and actin belt formation in BMCs from OC-Sirt1KO mice. SRT2183 and SRT1720 also significantly disrupted actin belts of mature osteoclasts generated from BMCs of WT mice, within 3 and 6 hours of administration, respectively. Furthermore, these compounds inhibited the resorption activity of mature osteoclasts, while RSV did not.

Conclusion

Our findings suggest SRT2183 and SRT1720 impede bone resorption by disrupting actin belts of mature osteoclasts, inhibit actin belt formation, and inhibit osteoclastogenesis even in the absence of Sirt1. Thus, the mechanism of action of these compounds appears to extend beyond Sirt1 activation and possibly pave the way for potential new therapies in alleviating osteoporosis associated bone loss.

Activation of the sirtuin silent information regulator 1 pathway inhibits pathological myocardial remodeling

Myocardial remodeling refers to structural and functional disorders of the heart caused by molecular biological changes in the cardiac myocytes in response to neurological and humoral factors. A variety of heart diseases, such as hypertension, coronary artery disease, arrhythmia, and valvular heart disease, can cause myocardial remodeling and eventually lead to heart failure. Therefore, counteracting myocardial remodeling is essential for the prevention and treatment of heart failure. Sirt1 is a nicotinamide adenine dinucleotide⁺-dependent deacetylase that plays a wide range of roles in transcriptional regulation, energy metabolism regulation, cell survival, DNA repair, inflammation, and circadian regulation. It positively or negatively regulates myocardial remodeling by participating in oxidative stress, apoptosis, autophagy, inflammation, and other processes. Taking into account the close relationship between myocardial remodeling and heart failure and the involvement of SIRT1 in the development of the former, the role of SIRT1 in the prevention of heart failure via inhibition of myocardial remodeling has received considerable attention. Recently, multiple studies have been conducted to provide a better understanding of how SIRT1 regulates these phenomena. This review presents the progress of research involving SIRT1 pathway involvement in the pathophysiological mechanisms of myocardial remodeling and heart failure.

Oxidative Stress and Natural Antioxidants in Osteoporosis: Novel Preventive and Therapeutic Approaches

This review reports in detail the cellular and molecular mechanisms which regulate the bone remodeling process in relation to oxidative stress (OS), inflammatory factors, and estrogen deficiency. OS is considered an important pathogenic factor of osteoporosis, inducing osteocyte apoptosis and varying levels of specific factors, such as receptor activator κB ligand (RANKL), sclerostin, and, according to recent evidence, fibroblast growth factor 23, with consequent impairment of bone remodeling and high bone resorption. Bone loss increases the risk of fragility fractures, and the most commonly used treatments are antiresorptive drugs, followed by anabolic drugs or those with a double effect. In addition, recent data show that natural antioxidants contained in the diet are efficient in preventing and reducing the negative effects of OS on bone remodeling and osteocytes through the involvement of sirtuin type 1 enzyme. Indeed, osteocytes and some of their molecular factors are considered potential biological targets on which antioxidants can act to prevent and reduce bone loss, as well as to promote bone anabolic and regenerative processes by restoring physiological bone remodeling. Several data suggest including antioxidants in novel therapeutic approaches to develop better management strategies for the prevention and treatment of osteoporosis and OS-related bone diseases. In particular, anthocyanins, as well as resveratrol, lycopene, oleuropein, some vitamins, and thiol antioxidants, could have protective and therapeutic anti-osteoporotic effects.

Novel Role of the SIRT1 in Endocrine and Metabolic Diseases

Silent information regulator 1 (SIRT1), a highly conserved NAD⁺-dependent deacetylase, is a cellular regulator that has received extensive attention in recent years and regarded as a sensor of cellular energy and metabolism. The accumulated evidence suggests that SIRT1 is involved in the development of endocrine and metabolic diseases. In a variety of organisms, SIRT1 regulates gene expression through the deacetylation of histone, transcription factors, and lysine residues of other modified proteins including several metabolic and endocrine signal transcription factors, thereby enhancing the therapeutic effects of endocrine and metabolic diseases. These evidences indicate that targeting SIRT1 has promising applications in the treatment of endocrine and metabolic diseases. This review focuses on the role of SIRT1 in endocrine and metabolic diseases. First, we describe the background and structure of SIRT1. Then, we outline the role of SIRT1 in endocrine and metabolic diseases such as hyperuricemia, diabetes, hypertension, hyperlipidemia, osteoporosis, and polycystic ovarian syndrome. Subsequently, the SIRT1 agonists and inhibitors in the above diseases are summarized and future research directions are proposed. Overall, the information presents here may highlight the potential of SIRT1 as a future biomarker and therapeutic target for endocrine and metabolic diseases.

Reversing the imbalance in bone homeostasis via sustained release of SIRT-1 agonist to promote bone healing under osteoporotic condition

The imbalance of bone homeostasis is the root cause of osteoporosis. However current therapeutic approaches mainly focus on either anabolic or catabolic pathways, which often fail to turn the imbalanced bone metabolism around. Herein we reported that a SIRT-1 agonist mediated molecular therapeutic strategy to reverse the imbalance in bone homeostasis by simultaneously regulating osteogenesis and osteoclastogenesis via locally sustained release of SRT2104 from mineral coated acellular matrix microparticles. Immobilization of SRT2104 on mineral coating (MAM/SRT) harnessing their electrostatic interactions resulted in sustained release of SIRT-1 agonist for over 30 days. MAM/SRT not only enhanced osteogenic differentiation and mineralization, but also attenuated the formation and function of excessive osteoclasts via integrating multiple vital upstream signals (β-catenin, FoxOs, Runx2, NFATc1, etc.) in vitro. Osteoporosis animal model also validated that it accelerated osteoporotic bone healing and improved osseointegration of the surrounding bone. Overall, our work proposes a promising strategy to treat osteoporotic bone defects by reversing the imbalance in bone homeostasis using designated small molecule drug delivery systems.

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A mineral coated acellular matrix microcarriers sustainably release SIRT2104 more than 30 days.

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This drug delivery system regulates osteogenesis and osteoclastogenesis.

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It can accelerate osteoporotic bone healing by reversing the imbalance in bone homeostasis.

Regulation of sclerostin by the SIRT1 stabilization pathway in osteocytes

Osteocytes play a critical role in bone remodeling through the secretion of paracrine factors regulating the differentiation and activity of osteoblasts and osteoclasts. Sclerostin is a key osteocyte-derived factor that suppresses bone formation and promotes bone resorption, therefore regulators of sclerostin secretion are a likely source of new therapeutic strategies for treatment of skeletal disorders. Here, we demonstrate that protein kinase CK2 (casein kinase 2) controls sclerostin expression in osteocytes via the deubiquitinase ubiquitin-specific peptidase 4 (USP4)-mediated stabilization of Sirtuin1 (SIRT1). Deletion of CK2 regulatory subunit, Csnk2b, in osteocytes (Csnk2b^Dmp1) results in low bone mass due to elevated levels of sclerostin. This phenotype in Csnk2b^Dmp1 mice was partly reversed when sclerostin expression was downregulated by a single intravenous injection with bone-targeting adeno-associated virus 9 (AAV9) carrying an artificial-microRNA that targets Sost. Mechanistically, CK2-induced phosphorylation of USP4 is important for stabilization of SIRT1 by suppressing ubiquitin-dependent proteasomal degradation. Upregulated expression of SIRT1 inhibits sclerostin transcription in osteocytes. Collectively, the CK2-USP4-SIRT1 pathway is crucial for the regulation of sclerostin expression in osteocytes to maintain bone homeostasis.

Osteonecrosis development by tooth extraction in zoledronate treated mice is inhibited by active vitamin D analogues, anti-inflammatory agents or antibiotics

Invasive dental treatment such as tooth extraction following treatment with strong anti-bone resorptive agents, including bisphosphonates and denosumab, reportedly promotes osteonecrosis of the jaw (ONJ) at the extraction site, but strategies to prevent ONJ remain unclear. Here we show that in mice, administration of either active vitamin D analogues, antibiotics or anti-inflammatory agents can prevent ONJ development induced by tooth extraction during treatment with the bisphosphonate zoledronate. Specifically, tooth extraction during treatment with zoledronate induced osteonecrosis in mice, but administration of either 1,25(OH)2D3 or ED71, both active vitamin D analogues, significantly antagonized osteonecrosis development, even under continuous zoledronate treatment. 1,25(OH)2D3 or ED71 administration also significantly inhibited osteocyte apoptosis induced by tooth extraction and bisphosphonate treatment. Administration of either active vitamin D analogue significantly inhibited elevation of serum inflammatory cytokine levels in mice in response to injection of lipopolysaccharide, an infection mimetic. Furthermore, administration of either anti-inflammatory or antibiotic reagents significantly blocked ONJ development following tooth extraction and zoledronate treatment. These findings suggest that administration of active vitamin D, anti-inflammatory agents or antibiotics could prevent ONJ development induced by tooth extraction in patients treated with zoledronate.

Regulation of Sirt1 on energy metabolism and immune response in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease. Synovial hyperplasia and persistent inflammation serve as its typical pathological manifestations, which ultimately lead to joint destruction and function loss. Both clinical observations and metabolomics studies have revealed the prevalence of metabolic disorders in RA. In inflammatory immune microenvironments, energy metabolism is profoundly changed. Increasingly evidences suggest that this abnormality is involved in the occurrence and development of RA-related inflammation. Unsurprisingly, many energy metabolism sensors have been confirmed with immunoregulatory properties. As a representative, silent information regulator type 1 (Sirt1) controls many aspects of immune cells, such as cell lifespan, polarization, and secretion by functioning as a transcriptional regulator. Because of the profound clinical implication, researches on Sirt1 in the regulation of energy metabolism and immune functions under RA conditions have gradually gained momentum. This signaling balances glycolysis, lipid metabolism and insulin secretion orchestrating with other metabolism sensors, and consequently affects immune milieu through a so-called metabolism-immune feedback mechanism. This article reviews the involvement of Sirt1 in RA by discussing its impacts on energy metabolism and immune functions, and specially highlights the potential of Sirt1-targeting anti-rheumatic regimens. It also provides a theoretical basis for clarifying the mystery about the high incidence of metabolic complications in RA patients and identifying new anti-rheumatic reagents.

Role of Silent Information Regulator 1 (SIRT1) in Regulating Oxidative Stress and Inflammation

Silent information regulator 1 (SIRT1) is a ubiquitously expressed protein and has an intricate role in the pathology, progression, and treatment of several diseases. SIRT1 is a NAD+-dependent deacetylase and regulates gene expression by histone deacetylation. Deletion of SIRT1 in the liver, pancreas, and brain significantly increases the reactive oxygen species (ROS) and inflammatory response. Literature survey on SIRT1 shows the evidence for its role in preventing oxidative stress and inflammation. Oxidative stress and inflammation are closely related pathophysiological processes and are involved in the pathogenesis of a number of chronic disorders such as fatty liver diseases, diabetes, and neurodegenerative diseases. Both oxidative stress and inflammation alter the expression of several genes such as nuclear factor E2 related factor (Nrf2), nuclear factor E2 related factor 2 (Nef2), nuclear factor kappa B (NF-kB), pancreatic and duodenal homeobox factor 1 (PDX1), interleukin-1 (IL1), forkhead box class O (FOXO), and tumour necrosis factor alpha (TNF-α). By annotating this knowledge, we can conclude that modulating the expression of SIRT1 might prevent the onset of diseases inexorably linked to the liver, pancreas, and brain. Graphical Abstract Role of silent information regulator 1 (SIRT1) in the pancreas, brain, and liver.

miR-9-5p promotes wear-particle-induced osteoclastogenesis through activation of the SIRT1/NF-κB pathway

To explore the potential function of miR-9-5p in wear-particle-induced osteoclastogenesis, we examined the expression of SIRT1 and miR-9-5p in particle-induced osteolysis (PIO) mice calvariae and polyethylene (PE)-induced RAW 264.7 cells and found that SIRT1 expression was downregulated while miR-9-5p expression was upregulated in both models. We then verified that miR-9-5p targets SIRT1. miR-9-5p was found to promote PE-induced osteoclast formation from RAW 264.7 cells by tartrate-resistant acid phosphatase staining and detection of osteoclast markers, and miR-9-5p activation of the SIRT1/NF-kB signaling pathway was found in cells by detecting the expression of SIRT1/NF-kB pathway-related proteins and rescue assays. In conclusion, we found that miR-9-5p activated the SIRT1/NF-κB pathway to promote wear-particle-induced osteoclastogenesis. miR-9-5p may be a useful therapeutic target for PIO remission and treatment.

Tooth extraction in mice administered zoledronate increases inflammatory cytokine levels and promotes osteonecrosis of the jaw

INTRODUCTION

Osteonecrosis of the jaw (ONJ) occurring after invasive dental treatment often adversely affects patients' activities of daily living. Long-term administration of strong anti-bone resorptive agents such as bisphosphonates prior to invasive dental treatment is considered an ONJ risk factor; however, pathological mechanisms underlying ONJ development remain unclear.

MATERIALS AND METHODS

We developed an ONJ mouse model in which a tooth is extracted during treatment with the bisphosphonate zoledronate.

RESULTS

We observed induction of apoptosis in osteocytes, resulting in formation of empty lacunae in jaw bones at sites of tooth extraction but not in other bones of the same mice. We also observed elevated levels of inflammatory cytokines such as TNFα, IL-6 and IL-1 in jaw bone at the extraction site relative to other sites in zoledronate-treated mice. We also report that treatment in vitro with either zoledronate or an extract from Porphyromonas gingivalis, an oral bacteria, promotes expression of inflammatory cytokines in osteoclast progenitor cells. We demonstrate that gene-targeting of either TNFα, IL-6 or IL-1 or treatment with etanercept, a TNFα inhibitor, or a neutralizing antibody against IL-6 can antagonize ONJ development caused by combined tooth extraction and zoledronate treatment.

CONCLUSIONS

Taken together, the cytokine storm induced by invasive dental treatment under bisphosphonate treatment promotes ONJ development due to elevated levels of inflammatory cytokine-producing cells. Our work identifies novel targets potentially useful to prevent ONJ.

The Roles of Epigenetics Regulation in Bone Metabolism and Osteoporosis

Osteoporosis is a metabolic disease characterized by decreased bone mineral density and the destruction of bone microstructure, which can lead to increased bone fragility and risk of fracture. In recent years, with the deepening of the research on the pathological mechanism of osteoporosis, the research on epigenetics has made significant progress. Epigenetics refers to changes in gene expression levels that are not caused by changes in gene sequences, mainly including DNA methylation, histone modification, and non-coding RNAs (lncRNA, microRNA, and circRNA). Epigenetics play mainly a post-transcriptional regulatory role and have important functions in the biological signal regulatory network. Studies have shown that epigenetic mechanisms are closely related to osteogenic differentiation, osteogenesis, bone remodeling and other bone metabolism-related processes. Abnormal epigenetic regulation can lead to a series of bone metabolism-related diseases, such as osteoporosis. Considering the important role of epigenetic mechanisms in the regulation of bone metabolism, we mainly review the research progress on epigenetic mechanisms (DNA methylation, histone modification, and non-coding RNAs) in the osteogenic differentiation and the pathogenesis of osteoporosis to provide a new direction for the treatment of bone metabolism-related diseases.

SRT2183 impairs ovarian cancer by facilitating autophagy

The 5-year survival rate of ovarian cancer patients is only 47%, and developing novel drugs for ovarian cancer is needed. Herein, we evaluated if and how SRT2183, a sirtuin-1 activator, impairs the ovarian cancer cells. OVCAR-3 and A2780 cells were treated with SRT2183. Cell viability was measured by cell counting kit-8 assay and clonogenic assay. Apoptosis was determined by flow cytometry with Annexin V and propidium iodide. The level of autophagy was evaluated by western blot and immunofluorescence. The activities of AKT/mTOR/70s6k and MAPK signaling pathway were measured by immunoblot. SRT2183 inhibited the growth of ovarian cancer cells, increased the accumulation of BAX, cleaved-caspase 3 and cleaved-PARP, and decreased the level of anti-apoptotic Bcl-2 and Mcl-1. SRT2183 increased the LC3II level, and enhanced the degradation of p62/SQSTM1. SRT2183 increased the formation of GFP-LC3 puncta and induced the maturation of autophagosome. Interestingly, knockdown of autophagy related 5 and 7 significantly impaired the anti-carcinoma activity of SRT2183, implying that SRT2183 impaired the ovarian cancer cells by inducing autophagy. SRT2183 decreased the accumulation of p-Akt, p-mTOR and p-70s6k, and activated the p38 MAPK signaling pathway. This indicated that Akt/mTOR/70s6k and p38 MAPK signaling pathway might be involved in the SRT2183-mediated autophagy and apoptosis.

The road ahead for health and lifespan interventions

Aging is a modifiable risk factor for most chronic diseases and an inevitable process in humans. The development of pharmacological interventions aimed at delaying or preventing the onset of chronic conditions and other age-related diseases has been at the forefront of the aging field. Preclinical findings have demonstrated that species, sex and strain confer significant heterogeneity on reaching the desired health- and lifespan-promoting pharmacological responses in model organisms. Translating the safety and efficacy of these interventions to humans and the lack of reliable biomarkers that serve as predictors of health outcomes remain a challenge. Here, we will survey current pharmacological interventions that promote lifespan extension and/or increased healthspan in animals and humans, and review the various anti-aging interventions selected for inclusion in the NIA's Interventions Testing Program as well as the ClinicalTrials.gov database that target aging or age-related diseases in humans.

Blueberry Juice Antioxidants Protect Osteogenic Activity against Oxidative Stress and Improve Long-Term Activation of the Mineralization Process in Human Osteoblast-Like SaOS-2 Cells: Involvement of SIRT1

Diets rich in fruits and vegetables with many antioxidants can be very important in the prevention and treatment of osteoporosis. Studies show that oxidative stress, often due to lack of antioxidants, is involved in alteration of bone remodeling and reduction in bone density. This study demonstrates in human osteoblast-like SaOS-2 cells that blueberry juice (BJ), containing 7.5 or 15 μg∙mL^-1 total soluble polyphenols (TSP), is able to prevent the inhibition of osteogenic differentiation and the mineralization process due to oxidative stress induced by glutathione depletion. This situation mimics a metabolic condition of oxidative stress that may occur during estrogen deficiency. The effect of BJ phytochemicals occurs through redox- and non-redox-regulated mechanisms. BJ protects from oxidative damage factors related to bone remodeling and bone formation, such as alkaline phosphatase and Runt-related transcription factor 2. It upregulates these factors by activation of sirtuin type 1 deacetylase expression, a possible molecular target for anti-osteoporotic drugs. Quantitative analysis of TSP in BJ shows high levels of anthocyanins with high antioxidant capacity and bioavailability. These novel data may be important to elucidate the molecular and cellular beneficial effects of blueberry polyphenols on bone regeneration, and they suggest their use as a dietary supplement for osteoporosis prevention and therapies.

Mitochondrial Deacetylase Sirt3 Reduces Vascular Dysfunction and Hypertension While Sirt3 Depletion in Essential Hypertension Is Linked to Vascular Inflammation and Oxidative Stress

RATIONALE

Hypertension represents a major risk factor for stroke, myocardial infarction, and heart failure and affects 30% of the adult population. Mitochondrial dysfunction contributes to hypertension, but specific mechanisms are unclear. The mitochondrial deacetylase Sirt3 (Sirtuin 3) is critical in the regulation of metabolic and antioxidant functions which are associated with hypertension, and cardiovascular disease risk factors diminish Sirt3 level.

OBJECTIVE

We hypothesized that reduced Sirt3 expression contributes to vascular dysfunction in hypertension, but increased Sirt3 protects vascular function and decreases hypertension.

METHODS AND RESULTS

To test the therapeutic potential of targeting Sirt3 expression, we developed new transgenic mice with global Sirt3OX (Sirt3 overexpression), which protects from endothelial dysfunction, vascular oxidative stress, and hypertrophy and attenuates Ang II (angiotensin II) and deoxycorticosterone acetate-salt induced hypertension. Global Sirt3 depletion in Sirt3^-/- mice results in oxidative stress due to hyperacetylation of mitochondrial superoxide dismutase (SOD2), increases HIF1α (hypoxia-inducible factor-1), reduces endothelial cadherin, stimulates vascular hypertrophy, increases vascular permeability and vascular inflammation (p65, caspase 1, VCAM [vascular cell adhesion molecule-1], ICAM [intercellular adhesion molecule-1], and MCP1 [monocyte chemoattractant protein 1]), increases inflammatory cell infiltration in the kidney, reduces telomerase expression, and accelerates vascular senescence and age-dependent hypertension; conversely, increased Sirt3 expression in Sirt3OX mice prevents these deleterious effects. The clinical relevance of Sirt3 depletion was confirmed in arterioles from human mediastinal fat in patients with essential hypertension showing a 40% decrease in vascular Sirt3, coupled with Sirt3-dependent 3-fold increases in SOD2 acetylation, NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) activity, VCAM, ICAM, and MCP1 levels in hypertensive subjects compared with normotensive subjects.

CONCLUSIONS

We suggest that Sirt3 depletion in hypertension promotes endothelial dysfunction, vascular hypertrophy, vascular inflammation, and end-organ damage. Our data support a therapeutic potential of targeting Sirt3 expression in vascular dysfunction and hypertension.

MicroRNA-506 upregulation contributes to sirtuin 1 inhibition of osteoclastogenesis in bone marrow stromal cells induced by TNF-α treatment

As a deacetylase relying on NAD, sirtuin 1 (SIRT1) has been proven to inhibit osteoclastogenesis directly by repressing reactive oxygen species (ROS) production and TRPV1 channel stimulation modulated by TNF-α. MicroRNAs do not have coding functions, but they influence the expression of particular genes after transcription. Nevertheless, the current understanding of the impact of SIRT1 on osteoclastogenesis is insufficient. Our research explored whether and how miRNAs contributed to osteoclast differentiation modulated by SIRT1 in vitro. In osteoclastogenesis induced by RANKL in bone marrow-derived macrophages (BMMs), repression of SIRT1 expression and enhancement of miR-506 expression were discovered. Transfection with an miR-506 inhibitor repressed miR-506 concentration in BMMs treated with RANKL. Additional research revealed that BMMs with repressed miR-506 treated with RANKL displayed phenotypes with suppressed osteoclastogenesis, as demonstrated by TRAP staining, reduced function, decreased expression of osteoclast markers and correlated genes, and reduced multinuclear cell quantity. Bioinformatics prediction outcomes and the dual-luciferase reporter test suggested that miR-506 targeted the SIRT1 3'-UTR for silencing. Decreased miR-506 in BMMs induced by RANKL caused SIRT1 upregulation. Additionally, treatment with EX-527 (SIRT1 repressor) or SIRT1 silencing attenuated repression caused by miR-506 depletion in BMMs treated with RANKL. Furthermore, TNF-α was repressed via miR-506 inhibition but was enhanced following EX-527 incubation as well as SIRT1 depletion. TRPV1 channel stimulation and ROS generation, which was related to osteoclastogenesis, were reduced via miR-506 depletion. miR-506 modulated osteoclastogenesis by targeting SIRT1 expression in part through modulation of the TRPV1 channel, ROS production, and TNF-α.

Sirtuin1 activator SRT2183 suppresses glioma cell growth involving activation of endoplasmic reticulum stress pathway

Background

Glioblastoma (GBM) is an extremely deadly form of brain cancer with limited treatment options and thus novel therapeutic modalities are necessary. Histone deacetylase inhibitors (HDACi) have demonstrated clinical and preclinical activities against GBM. (Silent mating type information regulation 2 homolog, Sirt1) abbreviated as Sirtuin 1, has been implicated in GBM. We explored the activity of the Sirt1 activator SRT2183 in glioma cell lines in terms of biological response.

Methods

The effects of SRT2183 on glioma cell growth and neurosphere survival were evaluated in vitro using the CCK-8, clonogenic and neurosphere assays, respectively. Glioma cell cycle arrest and apoptosis were determined by flow cytometry. SRT2183-induced autophagy was investigated by detection of GFP-microtubule-associated protein 1 light chain 3 (GFP-LC3) puncta, conversion of the nonlipidated form of LC3 (LC3-I) to the phosphatidylethanolamine-conjugated form (LC3-II). Acetylation of STAT3 and NF-κB in SRT2183-treated glioma cells was examined using immunoprecipitation. The expression levels of anti-apoptotic proteins were assayed by immunoblotting.

Results

SRT2183 suppressed glioma cell growth and destroyed neurospheres in vitro. Furthermore, SRT2183 induced glioma cell cycle arrest and apoptosis, accompanying by upregulation of the pro-apoptotic Bim and downregulation of Bcl-2 and Bcl-xL. Notably, ER stress was triggered in glioma cells upon exposure to SRT2183 while the pre-exposure to 4-PBA, an ER stress inhibitor, significantly antagonized SRT2183-mediated growth inhibition in glioma cells. In addition, SRT2183 induced autophagy in glioma cells and pharmacological modulation of autophagy appeared not to affect SRT2183-inhibited cell growth. Of interest, the acetylation and phosphorylation of p65 NF-κB and STAT3 in glioma cells were differentially affected by SRT2183.

Conclusions

Our data suggest the ER stress pathway is involved in SRT2183-mediated growth inhibition in glioma. Further investigation in vivo is needed to consolidate the data.

Blueberry juice protects osteocytes and bone precursor cells against oxidative stress partly through SIRT1

Oxidative stress and abnormal osteocyte apoptosis are often related to dysregulation of bone turnover and chronic bone loss, and so fruit and vegetables with high antioxidant potential may play an important role in the prevention and/or management of osteoporosis. Osteocytes are the main regulators of bone remodelling. For the first time, we demonstrate here that blueberry juice (BJ), obtained from Vaccinium myrtillus, rich in polyphenols, shows antioxidant and antiosteoclastogenic properties in MLO‐Y4 osteocytes. We report that BJ prevents oxidative stress‐induced apoptosis and reverses the increase in receptor activator of nuclear factor κB ligand and sclerostin expression, crucial factors for osteoclast activation and bone resorption. BJ is also able to prevent oxidative stress‐induced cell cytotoxicity in bone marrow mesenchymal stromal cells (MSCs), which are considered to be an important tool for cell therapy in bone disorders. No significant difference in preventing these events was observed between BJ and blueberry dry extract containing equal amounts of total soluble polyphenols. We have also shown that blueberry acts as both an antioxidant and an activator of sirtuin type 1, a class III histone deacetylase involved in cell death regulation and considered a molecular target for blocking bone resorption without affecting osteoclast survival. Overall, these novel data obtained in osteocytes and MSCs may help us clarify the mechanisms by which blueberry counteracts oxidative stress‐induced damage in bone remodelling and osteogenesis at the cellular and molecular level. Our findings are consistent with the reported beneficial effects of blueberry on bone tissue reported in animal studies, which suggest that blueberry may be a useful supplement for the prevention and/or management of osteoporosis and osteogenic process.

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.

Sirt1 Promotes a Thermogenic Gene Program in Bone Marrow Adipocytes: From Mice to (Wo)Men

Bone marrow adipose tissue (MAT) is influenced by nutritional cues, and participates in whole body energy metabolism. To investigate the role of Sirtuin1 (Sirt1), a key player in metabolism, in MAT, marrow adiposity was evaluated in inbred 5-month-old 129/Sv Sirt1 haplo-insufficient (Sirt1 ^Δ/+) and wild type (WT) mice. Decreased expression of the thermogenic genes: Prdm16, Pgc1α, Foxc2, Dio2, and β3AR was detected in whole tibiae derived from Sirt1 ^Δ/+ compared to WT female mice. Similarly, decreased expression of Prdm16 and Pgc1α was observed in primary bone marrow mesenchymal stem cell (BM-MSC) cultures obtained from Sirt1 ^Δ/+ compared to WT female mice, suggesting a cell autonomous effect of Sirt1 in BM-MSCs. In vitro, Sirt1 over-expression in the mesenchymal embryonic fibroblast stem cell line C3HT101/2 increased Pgc1α and Prdm16 protein level. Similarly, pharmacologic activation of Sirt1 by SRT3025 increased Foxc2, Pgc1α, Dio2, Tfam, and Cyc1 expression while inhibition of Sirt1 by EX527 down-regulated UCP1 in C3HT101/2 cells. Importantly, in human femoral BM-MSCs obtained from female patients undergoing hip operations for fracture or osteoarthritis, Sirt1 activation by SRT3025 increased PGC1α mRNA and protein level. Blocking sclerostin, an inhibitor of the WNT pathway and a Sirt1 target, by the monoclonal humanized antibody (Sc-AbII), stimulated β3AR, PRDM16, and UCP1 gene expression, and increased PGC1α protein level. These results show that Sirt1 stimulates a thermogenic gene program in marrow adipocytes in mice and humans via PGC1α activation and sclerostin inhibition. The implications of these findings to bone health, hematopoiesis and whole body energy metabolism remain to be investigated.

Sirtuin 1 inhibits TNF-α-mediated osteoclastogenesis of bone marrow-derived macrophages through both ROS generation and TRPV1 activation

Sirtuin 1 (SIRT1), also known as NAD-dependent deacetylase, has been reported to increase in vivo osteoclast-mediated bone resorption. However, its effects on osteoclastogenesis or bone loss in vitro have not been widely examined. Therefore, the effects and underlying mechanism of SIRT1 on osteoclast differentiation in mice in vitro were studied. During RANKL-induced osteoclastogenesis in differentiated bone marrow-derived macrophages (BMMs), SIRT1 downregulation was observed. The use of resveratrol (SIRT1 activator) and SIRT1 overexpression was found to inhibit osteoclastogenesis, which was confirmed by TRAP staining and activity loss, reduced expression of osteoclast markers and related genes, and a decrease in the number of multinuclear cells. In contrast, treatment with EX-527 (SIRT1 inhibitor) as well as SIRT1 silencing promoted osteoclastogenesis. Furthermore, the tumor necrosis factor (TNF)-α level was reduced by resveratrol treatment and SIRT1 overexpression but increased following EX-527 incubation and SIRT1 depletion. TNF-α silencing blocked the osteoclastogenesis of BMMs promoted by SIRT1 depletion. Moreover, transient receptor potential vanilloid 1 (TRPV1) channel activation and reactive oxygen species (ROS) production, which are associated with osteoclastogenesis, were impaired by TNF-α silencing. These data demonstrate that SIRT1 directly inhibits osteoclastogenesis by inhibiting ROS generation and TRPV1 channel activation under mediation of TNF-α.

Sirt1/Foxo Axis Plays a Crucial Role in the Mechanisms of Therapeutic Effects of Erzhi Pill in Ovariectomized Rats

Background. Erzhi pill (EZP), a traditional Chinese herbal formula, has been widely used to treat postmenopausal osteoporosis (PMOP) in China. However, its molecular mechanisms remain unclear. The aim of the present study is to investigate the antiosteoporotic effect of EZP on an ovariectomized rat model of PMOP. We performed the biomarkers of bone metabolism disorder, bone morphology, bone mineral density (BMD), and bone biomechanics to confirm the successful establishment of the PMOP model. We then investigated the expression of biomarkers related to the Sirt1/Foxo axis. We also examined microRNA-132 (miR-132), a regulator in the Sirtuin1 (Sirt1) expression. The bone metabolism disorder, bone morphology, BMD, and bone biomechanics in ovariectomized rats were improved by EZP administration. The antiosteoporotic effect of EZP was confirmed. We also found that the expressions of Sirt1, Runx2, Foxo1, and Foxo3a were downregulated in ovariectomized rats, while being then upregulated by EZP administration. And the expression of PPAR-γ and miR-132 was upregulated in ovariectomized rats and then downregulated by EZP administration. These results provided evidence that Sirt1/Foxo axis related mechanism may play a crucial role in the therapeutic effects of EZP, indicating that Sirt1/Foxo axis can be considered as a potential therapeutic target for PMOP in the future.

SIRT1 is a positive regulator of in vivo bone mass and a therapeutic target for osteoporosis

Overexpression or pharmacological activation of SIRT1 has been shown to extend the lifespan of mice and protect against aging-related diseases. Here we show that pharmacological activation of SIRT1 protects in two models of osteoporosis. Ovariectomized female mice and aged male mice, models for post-menopausal and aging-related osteoporosis, respectively, show significant improvements in bone mass upon treatment with SIRT1 agonist, SRT1720. Further, we find that calorie restriction (CR) results in a two-fold upregulation of sirt1 mRNA expression in bone tissue that is associated with increased bone mass in CR mice. Reciprocally, SIRT1 whole-body knockout (KO) mice, as well as osteoblast and osteoclast specific KOs, show a low bone mass phenotype; though double knockout mice (containing SIRT1 deleted in both osteoblasts and osteoclasts) do not show a more severe phenotype. Altogether, these findings provide strong evidence that SIRT1 is a positive regulator of bone mass and a promising target for the development of novel therapeutics for osteoporosis.

Sirt3 Impairment and SOD2 Hyperacetylation in Vascular Oxidative Stress and Hypertension

RATIONALE

Clinical studies have shown that Sirt3 (Sirtuin 3) expression declines by 40% by 65 years of age paralleling the increased incidence of hypertension and metabolic conditions further inactivate Sirt3 because of increased NADH (nicotinamide adenine dinucleotide, reduced form) and acetyl-CoA levels. Sirt3 impairment reduces the activity of a key mitochondrial antioxidant enzyme, superoxide dismutase 2 (SOD2) because of hyperacetylation.

OBJECTIVE

In this study, we examined whether the loss of Sirt3 activity increases vascular oxidative stress because of SOD2 hyperacetylation and promotes endothelial dysfunction and hypertension.

METHODS AND RESULTS

Hypertension was markedly increased in Sirt3-knockout (Sirt3^-/-) and SOD2-depleted (SOD2^+/-) mice in response to low dose of angiotensin II (0.3 mg/kg per day) compared with wild-type C57Bl/6J mice. Sirt3 depletion increased SOD2 acetylation, elevated mitochondrial O₂^· -, and diminished endothelial nitric oxide. Angiotensin II-induced hypertension was associated with Sirt3 S-glutathionylation, acetylation of vascular SOD2, and reduced SOD2 activity. Scavenging of mitochondrial H₂O₂ in mCAT mice expressing mitochondria-targeted catalase prevented Sirt3 and SOD2 impairment and attenuated hypertension. Treatment of mice after onset of hypertension with a mitochondria-targeted H₂O₂ scavenger, mitochondria-targeted hydrogen peroxide scavenger ebselen, reduced Sirt3 S-glutathionylation, diminished SOD2 acetylation, and reduced blood pressure in wild-type but not in Sirt3^-/- mice, whereas an SOD2 mimetic, (2-[2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino]-2-oxoethyl) triphenylphosphonium (mitoTEMPO), reduced blood pressure and improved vasorelaxation both in Sirt3^-/- and wild-type mice. SOD2 acetylation had an inverse correlation with SOD2 activity and a direct correlation with the severity of hypertension. Analysis of human subjects with essential hypertension showed 2.6-fold increase in SOD2 acetylation and 1.4-fold decrease in Sirt3 levels, whereas SOD2 expression was not affected.

CONCLUSIONS

Our data suggest that diminished Sirt3 expression and redox inactivation of Sirt3 lead to SOD2 inactivation and contributes to the pathogenesis of hypertension.

SIRT1 is a positive regulator of the master osteoblast transcription factor, RUNX2

Activation of SIRT1 has previously been shown to protect mice against osteoporosis through yet ill-defined mechanisms. In this study, we outline a role for SIRT1 as a positive regulator of the master osteoblast transcription factor, RUNX2. We find that ex vivo deletion of sirt1 leads to decreased expression of runx2 downstream targets, but not runx2 itself, along with reduced osteoblast differentiation. Reciprocally, treatment with a SIRT1 agonist promotes osteoblast differentiation, as well as the expression of runx2 downstream targets, in a SIRT1-dependent manner. Biochemical and luciferase reporter assays demonstrate that SIRT1 interacts with and promotes the transactivation potential of RUNX2. Intriguingly, mice treated with the SIRT1 agonist, resveratrol, show similar increases in the expression of RUNX2 targets in their calvaria (bone tissue), validating SIRT1 as a physiologically relevant regulator of RUNX2.