Sirtuin 1 is a negative regulator of parathyroid hormone stimulation of matrix metalloproteinase 13 expression in osteoblastic cells: role of sirtuin 1 in the action of PTH on osteoblasts

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.

Epigenetic regulators controlling osteogenic lineage commitment and bone formation

Bone formation and homeostasis are controlled by environmental factors and endocrine regulatory cues that initiate intracellular signaling pathways capable of modulating gene expression in the nucleus. Bone-related gene expression is controlled by nucleosome-based chromatin architecture that limits the accessibility of lineage-specific gene regulatory DNA sequences and sequence-specific transcription factors. From a developmental perspective, bone-specific gene expression must be suppressed during the early stages of embryogenesis to prevent the premature mineralization of skeletal elements during fetal growth in utero. Hence, bone formation is initially inhibited by gene suppressive epigenetic regulators, while other epigenetic regulators actively support osteoblast differentiation. Prominent epigenetic regulators that stimulate or attenuate osteogenesis include lysine methyl transferases (e.g., EZH2, SMYD2, SUV420H2), lysine deacetylases (e.g., HDAC1, HDAC3, HDAC4, HDAC7, SIRT1, SIRT3), arginine methyl transferases (e.g., PRMT1, PRMT4/CARM1, PRMT5), dioxygenases (e.g., TET2), bromodomain proteins (e.g., BRD2, BRD4) and chromodomain proteins (e.g., CBX1, CBX2, CBX5). This narrative review provides a broad overview of the covalent modifications of DNA and histone proteins that involve hundreds of enzymes that add, read, or delete these epigenetic modifications that are relevant for self-renewal and differentiation of mesenchymal stem cells, skeletal stem cells and osteoblasts during osteogenesis.

PTH and the Regulation of Mesenchymal Cells within the Bone Marrow Niche

Parathyroid hormone (PTH) plays a pivotal role in maintaining calcium homeostasis, largely by modulating bone remodeling processes. Its effects on bone are notably dependent on the duration and frequency of exposure. Specifically, PTH can initiate both bone formation and resorption, with the outcome being influenced by the manner of PTH administration: continuous or intermittent. In continuous administration, PTH tends to promote bone resorption, possibly by regulating certain genes within bone cells. Conversely, intermittent exposure generally favors bone formation, possibly through transient gene activation. PTH's role extends to various aspects of bone cell activity. It directly influences skeletal stem cells, osteoblastic lineage cells, osteocytes, and T cells, playing a critical role in bone generation. Simultaneously, it indirectly affects osteoclast precursor cells and osteoclasts, and has a direct impact on T cells, contributing to its role in bone resorption. Despite these insights, the intricate mechanisms through which PTH acts within the bone marrow niche are not entirely understood. This article reviews the dual roles of PTH-catabolic and anabolic-on bone cells, highlighting the cellular and molecular pathways involved in these processes. The complex interplay of these factors in bone remodeling underscores the need for further investigation to fully comprehend PTH's multifaceted influence on bone health.

Ginsenoside Rh2 and its octyl ester derivative inhibited invasion and metastasis of hepatocellular carcinoma via the c-Jun/COX2/PGE2 pathway

BACKGROUND

Liver cancer is a topical global health issue. The treatment of liver cancer meets significant challenges in the high recurrence rate and invasive incidence. Therefore, the treatment strategies that target epithelial-mesenchymal transition (EMT) induced by cyclooxygenase 2 (COX2)/ prostaglandin E2 (PGE2) pathway have become epidemic. Ginsenoside Rh2 has been proved to inhibit the EMT. However, the underlying mechanisms remain unclear. Moreover, the octyl ester derivative of Rh2 (Rh2-O) exhibited superior anti-proliferative and immunomodulatory effects than Rh2 in our previous researches, which indicated that Rh2-O might also exert inhibitory effects on invasion and metastasis.

PURPOSE

The aim of current study is to explore the inhibitory effects of Rh2 and Rh2-O on invasion and metastasis of hepatocellular carcinoma, and to investigate whether these effects are dependent on the c-Jun/COX2/PGE2 pathway.

STUDY DESIGN

The Huh-7 liver cancer cells and the H22 tumor-bearing mice were treated with Rh2 and Rh2-O.

METHOD

In this paper, the inhibitory effects of Rh2 and Rh2-O on invasion and metastasis were tested by wound healing, trans-well assay and tumor-bearing mice, and the involvement of c-Jun/COX2/PGE2 pathway were verified by exogenous PGE2, activation of COX2 and overexpression of c-Jun.

RESULTS

The results showed that Rh2 and Rh2-O could efficiently inhibit the invasion and metastasis in a dose-dependent manner (p < 0.05). And the Rh2-O showed stronger effects than Rh2. Moreover, the exogenous PGE2, activation of COX2 by exogenous LPS and the overexpression of c-Jun by transfection all reversed the inhibitory effects of Rh2 and Rh2-O on metastasis or EMT (p < 0.05).

CONCLUSION

Rh2 and Rh2-O could inhibit the invasion and metastasis of hepatocellular carcinoma via restraining the EMT, which was mediated by c-Jun/COX2/PGE2 pathway.

Pathophysiology of bone disease in chronic kidney disease: from basics to renal osteodystrophy and osteoporosis

Chronic kidney disease (CKD) is a highly prevalent disease that has become a public health problem. Progression of CKD is associated with serious complications, including the systemic CKD-mineral and bone disorder (CKD-MBD). Laboratory, bone and vascular abnormalities define this condition, and all have been independently related to cardiovascular disease and high mortality rates. The "old" cross-talk between kidney and bone (classically known as "renal osteodystrophies") has been recently expanded to the cardiovascular system, emphasizing the importance of the bone component of CKD-MBD. Moreover, a recently recognized higher susceptibility of patients with CKD to falls and bone fractures led to important paradigm changes in the new CKD-MBD guidelines. Evaluation of bone mineral density and the diagnosis of "osteoporosis" emerges in nephrology as a new possibility "if results will impact clinical decisions". Obviously, it is still reasonable to perform a bone biopsy if knowledge of the type of renal osteodystrophy will be clinically useful (low versus high turnover-bone disease). However, it is now considered that the inability to perform a bone biopsy may not justify withholding antiresorptive therapies to patients with high risk of fracture. This view adds to the effects of parathyroid hormone in CKD patients and the classical treatment of secondary hyperparathyroidism. The availability of new antiosteoporotic treatments bring the opportunity to come back to the basics, and the knowledge of new pathophysiological pathways [OPG/RANKL (LGR4); Wnt-ß-catenin pathway], also affected in CKD, offers great opportunities to further unravel the complex physiopathology of CKD-MBD and to improve outcomes.

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.

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.

SIRT1, a promising regulator of bone homeostasis

Sirtuin 1 (SIRT1), a nicotinamide adenine dinucleotide-dependent deacetylase, epigenetically regulates various cell metabolisms, including inflammation, tumorigenesis, and bone metabolism. Many clinical studies have found the potential of SIRT1 in predicting and treating bone-related disorders, such as osteoporosis and osteonecrosis, suggesting that SIRT1 might be a regulator of bone homeostasis. In order to identify the mechanisms that underlie the pivotal role of SIRT1 in bone homeostasis, many studies revealed that SIRT1 could maintain the balance between bone formation and absorption via regulating the ratio of osteoblasts to osteoclasts. SIRT1 controls the differentiation of mesenchymal stem cells (MSCs) and bone marrow-derived macrophages, increasing osteogenesis and reducing osteoclastogenesis. Besides, SIRT1 can enhance bone-forming cells' viability, including MSCs and osteoblasts under adverse conditions by resisting senescence, suppressing apoptosis, and promoting autophagy in favor of osteogenesis. Furthermore, the effect on bone vasculature homeostasis enables SIRT1 to become a valuable strategy for ischemic osteonecrosis and senile osteoporosis. The review systemically discusses SIRT1 pathways and the critical role in bone homeostasis and assesses whether SIRT1 is a potential target for manipulation and therapy, to lay a solid foundation for further researches in the future.

Cartilage -specific knockout of Sirt1 significantly reduces bone quality and catch-up growth efficiency

BACKGROUND

Spontaneous catch-up (CU) growth occurs when a growth-restricting factor is resolved. However, its efficiency is sometimes inadequate and growth deficits remain permanent. The therapeutic toolbox for short stature is currently very limited, thus, finding new regulatory pathways is important for the development of novel means of treatment. Our previous studies using a nutrition-induced CU growth model showed that the level of sirtuin-1 (Sirt1) was significantly increased in food-restricted animals and decreased during CU growth.

AIM

This study sought to investigate the role of Sirt1 in modulating the response of the epiphyseal growth plate (EGP) to nutritional manipulation.

METHOD

Collagen type II-specific Sirt1 knockout (CKO) mice were tested for response to our CU growth model consisting of a period of food restriction followed by re-feeding.

RESULTS

The transgenic CKO mice weighed more than the control (CTL) mice, their EGP was higher and less organized, specifically at the resting and proliferative zones, leading to shorter bones. Ablation of Sirt1 in the chondrocytes was found to have a dramatic effect on bone mineralization on micro-CT analysis. The CKO mice were less responsive to the nutritional manipulation, and their CU growth was less efficient. They remained shorter than the CTL mice who corrected the food restriction-induced growth deficit during the re-feeding period.

CONCLUSIONS

Sirt1 appears to be important for normal regulation of the EGP. In its absence, the EGP is less organized and CU growth is less efficient. These results suggest that SIRT1 may serve as a novel therapeutic target for short stature.

Decreased SIRT1 expression in the peripheral blood of patients with Graves' disease

SIRT1, a class III histone/protein deacetylase (HDAC), has been associated with autoimmune diseases. There is a paucity of data about the role of SIRT1 in Graves' disease. The aim of this study was to investigate the role of SIRT1 in the pathogenesis of GD. Here, we showed that SIRT1 expression and activity were significantly decreased in GD patients compared with healthy controls. The NF-κB pathway was activated in the peripheral blood of GD patients. The reduced SIRT1 levels correlated strongly with clinical parameters. In euthyroid patients, SIRT1 expression was markedly upregulated and NF-κB downstream target gene expression was significantly reduced. SIRT1 inhibited the NF-κB pathway activity by deacetylating P65. These results demonstrate that reduced SIRT1 expression and activity contribute to the activation of the NF-κB pathway and may be involved in the pathogenesis of GD.

SIRT1 protects against aortic dissection by regulating AP-1/decorin signaling-mediated PDCD4 activation

Medial degeneration of aorta wall is the principal feature of aortic dissection (AD). Sirtuin 1 (SIRT1) plays essential protective effect on many aortic-associated disease. However, it is still unclear whether SIRT1participates in the process of medial degeneration-mediated AD. The purpose of this study is to explore the association between SIRT1 and AD process. qRT-PCR was used to evaluate the transcriptional level of genes involved in study. Protein levels and acetylation detection were measured by Western blotting. The regulatory relations between AP-1 and decorin was assessed by luciferase reporter gene assay. Acute aortic dissection (AAD) mice model was constructed by feeding with β-aminopropionitrile monofumarate (BAPN). Haematoxylin and eosin (HE) and Mallory staining were performed for pathological analysis. In clinical aorta tissue of thoracic aortic dissection (TAD), the expression of SIRT1, activator protein 1 (AP-1) and decorin were in accordant trend. AP-1 expression which acts on Decorin promoter region is possibly regulated in a SIRT1-mediated deacetylation dependent manner. Resveratrol or SRT1720-initiated SIRT1 activation ameliorated BAPN-induced AAD symptoms accompanied by the activation of AP-1/decorin signaling and decorin-mediated programmed cell death 4 (PDCD4) expression by inhibiting miR-21 and miR-181b. These data suggest that SIRT1/AP-1/decorin signal cascades possibly play a part role in the process of AD. Our research demonstrate that activation of SIRT1 protects against AAD symptoms by enhancing AP-1-mediated decorin expression and downstream PDCD4 signaling pathway. Possibly, SIRT1 is served as a protective factor of AD and targeting SIRT1 therapy might be an attractive therapeutic approaches for AD treatment.

Survival and Clinicopathological Significance of SIRT1 Expression in Cancers: A Meta-Analysis

Background: Silent information regulator 2 homolog 1 (SIRT1) is an evolutionarily conserved enzymes with nicotinamide adenine dinucleotide (NAD)⁺-dependent deacetylase activity. SIRT1 is involved in a large variety of cellular processes, such as genomic stability, energy metabolism, senescence, gene transcription, and oxidative stress. SIRT1 has long been recognized as both a tumor promoter and tumor suppressor. Its prognostic role in cancers remains controversial. Methods: A meta-analysis of 13,138 subjects in 63 articles from PubMed, EMBASE, and Cochrane Library was performed to evaluate survival and clinicopathological significance of SIRT1 expression in various cancers. Results: The pooled results of meta-analysis showed that elevated expression of SIRT1 implies a poor overall survival (OS) of cancer patients [Hazard Ratio (HR) = 1.566, 95% CI: 1.293-1.895, P < 0.0001], disease free survival (DFS) (HR = 1.631, 95% CI: 1.250-2.130, P = 0.0003), event free survival (EFS) (HR = 2.534, 95% CI: 1.602-4.009, P = 0.0001), and progress-free survival (PFS) (HR = 3.325 95% CI: 2.762-4.003, P < 0.0001). Elevated SIRT1 level was associated with tumor stage [Relative Risk (RR) = 1.299, 95% CI: 1.114-1.514, P = 0.0008], lymph node metastasis (RR = 1.172, 95% CI: 1.010-1.360, P = 0.0363), and distant metastasis (RR = 1.562, 95% CI: 1.022-2.387, P = 0.0392). Meta-regression and subgroup analysis revealed that ethnic background has influence on the role of SIRT1 expression in predicting survival and clinicopathological characteristics of cancers. Overexpression of SIRT1 predicted a worse OS and higher TNM stage and lymphatic metastasis in Asian population especially in China. Conclusion: Our data suggested that elevated expression of SIRT1 predicted a poor OS, DFS, EFS, PFS, but not for recurrence-free survival (RFS) and cancer-specific survival (CCS). SIRT1 overexpression was associated with higher tumor stage, lymph node metastasis, and distant metastasis. SIRT1-mediated molecular events and biological processes could be an underlying mechanism for metastasis and SIRT1 is a therapeutic target for inhibiting metastasis, leading to good prognosis.

Regulation of Bone Remodeling by Parathyroid Hormone

Parathyroid hormone (PTH) exerts profound effects on skeletal homeostasis through multiple cellular and molecular mechanisms. Continuous hyperparathyroidism causes net loss of bone mass, despite accelerating bone formation by osteoblasts. Intermittent treatment with PTH analogs represents the only Food and Drug Administration (FDA)-approved bone anabolic osteoporosis treatment strategy. Functional PTH receptors are present on cells of the osteoblast lineage, ranging from early skeletal stem cells to matrix-embedded osteocytes. In addition, bone remodeling by osteoclasts liberates latent growth factors present within bone matrix. Here, we will provide an overview of the multiple cellular and molecular mechanisms through which PTH influences bone homeostasis. Notably, net skeletal effects of continuous versus intermittent can differ significantly. Where possible, we will highlight mechanisms through which continuous hyperparathyroidism leads to bone loss, and through which intermittent hyperparathyroidism boosts bone mass. Given the therapeutic usage of intermittent PTH (iPTH) treatment for osteoporosis, particular attention will be paid toward mechanisms underlying the bone anabolic effects of once daily PTH administration.

Distinct effects of SIRT1 in cancer and stromal cells on tumor promotion

The lysyl deacetylase SIRT1 acts as a metabolic sensor in adjusting metabolic imbalance. To explore the role of SIRT1 in tumor-stroma interplay, we designed an in vivo tumor model using SIRT1-transgenic mice. B16F10 mouse melanoma grew more quickly in SIRT1-transgenic mice than in wild-type mice, whereas SIRT1-overexpressing one grew slowly in both mice. Of human tumors, SIRT1 expression in stromal fibroblasts was found to correlate with poor prognosis in ovarian cancer. B16F10 and human ovarian cancer (SKOV3 and SNU840) cells were more proliferative in co-culture with SIRT1-overexpressiong fibroblasts. In contrast, SIRT1 within cancer cells has a negative effect on cell proliferation. In conditioned media from SIRT1-overexpressing fibroblasts, matrix metalloproteinase-3 (MMP3) was identified in cytokine arrays to be secreted from fibroblasts SIRT1-dependently. Fibroblast-derived MMP3 stimulated cancer cell proliferation, and such a role of MMP3 was also demonstrated in cancer/fibroblast co-grafts. In conclusion, SIRT1 plays differential roles in cancer and stromal cells. SIRT1 in stromal cells promotes cancer growth by producing MMP3, whereas SIRT1 in cancer cells inhibits growth via an intracellular event. The present study provides a basis for setting new anticancer strategies targeting SIRT1.

SIRT1/HERC4 Locus Associated With Bisphosphonate-Induced Osteonecrosis of the Jaw: An Exome-Wide Association Analysis

Osteonecrosis of the jaw (ONJ) is a rare, but serious drug side effect, mainly associated with the use of intravenous (iv) bisphosphonates (BPs). The purpose of this study was to identify genetic variants associated with ONJ in patients of European ancestry treated with iv BPs using whole-exome sequencing (WES). The WES phase 1 included 44 multiple myeloma patients (22 ONJ cases and 22 controls) and WES phase 2 included 17 ONJ patients with solid tumors. Multivariable logistic regression analysis was performed to estimate the odds ratios (ORs) and 95% confidence intervals (CI), adjusting for age, sex, and principal components for ancestry. Meta-analysis of WES phase 1 and 2 was performed to estimate the combined ORs. In silico analyses were then performed to identify expression quantitative loci (eQTL) single-nucleotide polymorphisms (SNPs) that are in high linkage disequilibrium (LD) with the top SNPs. The associations of the potentially functional SNPs were replicated and validated in an independent case-control study of 48 patients of European ancestry treated with iv BPs (19 ONJ cases and 29 controls). The top SNPs in the exome-wide association meta-analysis were two SNPs on chromosome 10: SIRT1 SNP rs7896005 and HERC4 SNP rs3758392 with identical OR of 0.07 (0.01-0.46; p = 3.83 × 10^-5 ). In the in silico functional analyses, two promoter region SNPs (rs7894483 and rs3758391) were identified to be in high LD with the index SNPs and are eQTLs for SIRT1 gene in whole blood in the GTEx database. The ORs were 0.30 (0.10-0.88), 0.26 (0.12-0.55), and 0.26 (0.12-0.55) for the WES top SNP rs7896005 and two promoter SNPs rs7894483 and rs3758391, respectively, in the replication sample. In summary, we identified the SIRT1/HERC4 locus on chromosome 10 to be associated with iv BP-induced ONJ and two promoter SNPs that might be the potential genetic markers for this association. © 2017 The Authors.Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Antcin-H Isolated from Antrodia cinnamomea Inhibits Renal Cancer Cell Invasion Partly through Inactivation of FAK-ERK-C/EBP-β/c-Fos-MMP-7 Pathways

Antcin-H, a natural triterpene, is purified from a famous anticancer medicinal mushroom, Antrodia cinnamomea, in Taiwan. This study showed that antcin-H inhibited the growth of human renal carcinoma 786-0 cells; the IC₅₀ value (for 48 h) was 170 μM. Besides, the migration and invasion of 786-0 cells were suppressed by antcin-H under noncytotoxic concentrations (<100 μM); these events were accompanied by inhibition of FAK and Src kinase activities, decrease of paxillin phosphorylation, impairment of lamellipodium formation, and upregulation of TIMPs and downregulation of MMPs, especially MMP-7 expression. Luciferase reporter assay showed that antcin-H repressed the MMP-7 promoter activity, in parallel to inhibiting c-Fos/AP-1 and C/EBP-β transactivation abilities. Moreover, antcin-H suppressed the activity of ERK1/2 and decreased the binding ability of C/EBP-β and c-Fos on the upstream/enhancer region of MMP-7 promoter. Overall, this study demonstrated that the anti-invasive effect of antcin-H in human renal carcinoma 786-0 cells might be at least in part by abrogating focal adhesion complex and lamellipodium formation through inhibiting the Src/FAK-paxillin signaling pathways and decreasing MMP-7 expression through suppressing the ERK1/2-AP-1/c-Fos and C/EBP-β signaling axis. Our findings provide the evidence that antcin-H may be an active component existing in A. cinnamomea with anticancer effect.

MEF2C Interacts With c-FOS in PTH-Stimulated Mmp13 Gene Expression in Osteoblastic Cells

Parathyroid hormone (PTH) regulates the transcription of many genes in the osteoblast. One of these genes is Mmp13, which is involved in bone remodeling and early stages of endochondral bone formation. Previously, we reported that PTH induces Mmp13 transcription by regulating the dissociation of histone deacetylase 4 (HDAC4) from runt-related transcription factor 2 (Runx2), and the association of the HATs, p300, and p300/CREB binding protein (CBP)-associated factor. It is known that, in addition to Runx2, HDAC4 binds to the transcription factor, myocyte-specific enhancer factor 2c (MEF2C), and represses its activity. In this work, we investigated whether MEF2C participates in PTH-stimulated Mmp13 gene expression in osteoblastic cells and how it does so. Knockdown of Mef2c in UMR 106-01 cells repressed Mmp13 messenger RNA expression and promoter activity with or without PTH treatment. Chromatin immunoprecipitation (ChIP) assays showed that MEF2C associated with the Mmp13 promoter; this increased after 4 hours of PTH treatment. ChIP-reChIP results indicate that endogenous MEF2C associates with HDAC4 on the Mmp13 promoter; after PTH treatment, this association decreased. From gel shift, ChIP, and promoter-reporter assays, MEF2C was found to associate with the activator protein-1 (AP-1) site without directly binding to DNA and had its stimulatory effect through interaction with c-FOS. In conclusion, MEF2C is necessary for Mmp13 gene expression at the transcriptional level and participates in PTH-stimulated Mmp13 gene expression by increased binding to c-FOS at the AP-1 site in the Mmp13 promoter. The observation of MEF2C interacting with a member of the AP-1 transcription factor family provides knowledge of the functions of HDAC4, c-FOS, and MEF2C.

The Histone-Deacetylase-Inhibitor Suberoylanilide Hydroxamic Acid Promotes Dental Pulp Repair Mechanisms Through Modulation of Matrix Metalloproteinase-13 Activity

Direct application of histone-deacetylase-inhibitors (HDACis) to dental pulp cells (DPCs) induces chromatin changes, promoting gene expression and cellular-reparative events. We have previously demonstrated that HDACis (valproic acid, trichostatin A) increase mineralization in dental papillae-derived cell-lines and primary DPCs by stimulation of dentinogenic gene expression. Here, we investigated novel genes regulated by the HDACi, suberoylanilide hydroxamic acid (SAHA), to identify new pathways contributing to DPC differentiation. SAHA significantly compromised DPC viability only at relatively high concentrations (5 μM); while low concentrations (1 μM) SAHA did not increase apoptosis. HDACi-exposure for 24 h induced mineralization-per-cell dose-dependently after 2 weeks; however, constant 14d SAHA-exposure inhibited mineralization. Microarray analysis (24 h and 14 days) of SAHA exposed cultures highlighted that 764 transcripts showed a significant >2.0-fold change at 24 h, which reduced to 36 genes at 14 days. 59% of genes were down-regulated at 24 h and 36% at 14 days, respectively. Pathway analysis indicated SAHA increased expression of members of the matrix metalloproteinase (MMP) family. Furthermore, SAHA-supplementation increased MMP-13 protein expression (7 d, 14 days) and enzyme activity (48 h, 14 days). Selective MMP-13-inhibition (MMP-13i) dose-dependently accelerated mineralization in both SAHA-treated and non-treated cultures. MMP-13i-supplementation promoted expression of several mineralization-associated markers, however, HDACi-induced cell migration and wound healing were impaired. Data demonstrate that short-term low-dose SAHA-exposure promotes mineralization in DPCs by modulating gene pathways and tissue proteases. MMP-13i further increased mineralization-associated events, but decreased HDACi cell migration indicating a specific role for MMP-13 in pulpal repair processes. Pharmacological inhibition of HDAC and MMP may provide novel insights into pulpal repair processes with significant translational benefit. J. Cell. Physiol. 231: 798-816, 2016. © 2015 Wiley Periodicals, Inc.

Sirtuin 1 regulates matrix metalloproteinase-13 expression induced by Porphyromonas endodontalis lipopolysaccharide via targeting nuclear factor-κB in osteoblasts

Porphyromonas endodontalis lipopolysaccharide (P.e LPS) is an important initiating factor for periapical inflammation and bone destruction. Matrix metalloproteinase-13 (MMP-13) has been shown to participate in the formation and diffusion of periapical bone lesion in chronic apical periodontitis. Sirtuin 1 (SIRT1) is a key regulator of inflammation in mammalian cells which suppresses the release of inflammatory mediators. This study aimed to explore the role of SIRT1 in regulating MMP-13 expression induced by P.e LPS in osteoblasts. P.e LPS stimulated MMP-13 expression in MC3T3-E1 cells. Knockdown of SIRT1 reinforced the increase of MMP-13mRNA expression induced by P.e LPS. SIRT1 activator resveratrol significantly reduced the expression of MMP-13 and SIRT1 inhibitor EX-527 enhanced the expression of MMP-13. Moreover, SIRT1 activation with resveratrol inhibited acetylation of NF-κB p65 and NF-κB transcriptional activity, which were enhanced by P.e LPS. In addition, NF-κB p65 was involved in P.e LPS-induced MMP-13 expression via directly binding to the MMP-13 promoter. However, SIRT1 activation significantly interfered with this binding. These findings strongly suggest that P.e LPS induces MMP-13 expression in osteoblasts, and SIRT1 suppresses this expression of MMP-13 through targeting NF-κB p65. This provides new insights into understanding the actions of SIRT1 on anti-inflammatory and anti-bone resorption activity.

The protective effects of resveratrol, H2S and thermotherapy on the cell apoptosis induced by CdTe quantum dots

Quantum dots (QDs) could be used in the field of biology and medicine as excellent nano-scale fluorescent probes due to their unique optical properties, but the adverse effects of QDs are always the obstruction for its usage in living organisms. In this study, we observed that CdTe QDs exposure decreased the cell viability while increased the apoptosis rates in the L929 cells. Apart from QD-induced oxidative stress indicated by excessive ROS generation, three signal transductions, including Akt, p38 and JNK, played important roles on the regulation of cell apoptosis by CdTe QDs exposure as well. In order to reduce the toxicity of CdTe QDs, we explored the protective effects of three treatments, i.e. resveratrol, H₂S and thermotherapy at 43°C, against the cell apoptosis elicited by CdTe QDs. The results showed that resveratrol, H₂S and thermotherapy at 43°C were capable of attenuating cell apoptosis and intercellular ROS production through inhibiting signal pathways of Akt, p38 and JNK, respectively. As there is only limited number of exogenous treatments reported to diminish the toxicity of QDs, our findings will provide a novel insight for researchers who try to reduce or even eliminate the adverse health effects of QDs.

PTH Signaling and Epigenetic Control of Bone Remodeling

As our understanding of the mechanisms that govern bone development advance, the role of epigenetic modifications in these processes become increasingly evident. Interestingly, in parathyroid hormone (PTH)-induced bone metabolism and remodeling, recent evidence shows that PTH signaling employs a particular facet of the epigenetic machinery to elicit its desired effects. In this review, we briefly discuss the known epigenetic events occurring in cells of the osteoblast lineage. More specifically, we elaborate on current findings that reveal the utilization of histone deacetylating enzymes (HDACs) in PTH-regulated modulation of gene expression in bone.