Valproic Acid Suppresses Interleukin-1ß-induced Microsomal Prostaglandin E2 Synthase-1 Expression in Chondrocytes Through Upregulation of NAB1

Microsomal prostaglandin E2 synthase-1 and its inhibitors: Molecular mechanisms and therapeutic significance

Inflammation is closely linked to the abnormal phospholipid metabolism chain of cyclooxygenase-2/microsomal prostaglandin E₂ synthase-1/prostaglandin E₂ (COX-2/mPGES-1/PGE₂). In clinical practice, non-steroidal anti-inflammatory drugs (NSAIDs) as upstream COX-2 enzyme activity inhibitors are widely used to block COX-2 cascade to relieve inflammatory response. However, NSAIDs could also cause cardiovascular and gastrointestinal side effects due to its inhibition on other prostaglandins generation. To avoid this, targeting downstream mPGES-1 instead of upstream COX is preferable to selectively block overexpressed PGE₂ in inflammatory diseases. Some mPGES-1 inhibitor candidates including synthetic compounds, natural products and existing anti-inflammatory drugs have been proved to be effective in in vitro experiments. After 20 years of in-depth research on mPGES-1 and its inhibitors, ISC 27864 have completed phase II clinical trial. In this review, we intend to summarize mPGES-1 inhibitors focused on their inhibitory specificity with perspectives for future drug development.

Cytokines and pregnancy: Potential regulation by histone deacetylases

Cytokines are important regulators of pregnancy and parturition. Aberrant expression of proinflammatory cytokines during pregnancy contributes towards preterm labor, pre-eclampsia, and gestational diabetes mellitus. The regulation of cytokine expression in human cells is highly complex, involving interactions between environment, transcription factors, and feedback mechanisms. Recent developments in epigenetic research have made tremendous advancements in exploring histone modifications as a key epigenetic regulator of cytokine expression and the effect of their signaling molecules on various organ systems in the human body. Histone acetylation and subsequent deacetylation by histone deacetylases (HDACs) are major epigenetic regulators of protein expression in the human body. The expression of various proinflammatory cytokines, their role in normal and abnormal pregnancy, and their epigenetic regulation via HDACs will be discussed in this review.

Valproic Acid Protects Chondrocytes from LPS-Stimulated Damage via Regulating miR-302d-3p/ITGB4 Axis and Mediating the PI3K-AKT Signaling Pathway

Background: Osteoarthritis (OA) is one of the most common degenerative joint diseases characterized by increased apoptosis and autophagy deficiency. The investigation was performed to examine the effect of valproic acid (VPA) and molecular mechanism related to miR-302d-3p/ITGB4 axis in OA. Methods: The OA clinical samples were obtained from the GEO database to analyze differentially expressed genes. An in vitro OA model was mimicked by LPS in CHON-001 cells. Autophagy-related genes were downloaded from the HADb website, and potential drugs were mined using the CTD website. The upstream factors of ITGB4 were predicted with bioinformatics analysis, which was validated by luciferase activity assay and RIP assay. Cell viability and apoptosis were evaluated using CCK-8 and flow cytometry. The expression levels, including ITGB4, miR-302d-3p, and autophagy-/PI3K-AKT pathway-related markers, were measured by qRT-PCR or/and western blot. Results: Our results showed that miR-302d-3p inhibited cell viability and promoted apoptosis of LPS-treated CHON-001 cells by targeting ITGB4. VPA treatment remarkably alleviated LPS-stimulated injury in CHON-001 cells. The inhibitory effect of VPA on LPS-stimulated damage in CHON-001 cells was weakened by miR-302d-3p overexpression, while it was intensified because of ITGB4 upregulation. Mechanistically, VPA treatment induced a significant decrease in the levels of p-PI3K and p-AKT in LPS-stimulated CHON-001 cells through regulating miR-302d-3p/ITGB4 axis. Conclusion: Overall, VPA treatment may ameliorate LPS-induced injury on chondrocytes via the regulation of miR-302d-3p/ITGB4 pair and the inactivation of the PI3K-AKT pathway.

The Role of HDACs and HDACi in Cartilage and Osteoarthritis

Epigenetics plays an important role in the pathogenesis and treatment of osteoarthritis (OA). In recent decades, HDAC family members have been associated with OA. This paper aims to describe the different role of HDACs in the pathogenesis of OA through interaction with microRNAs and the regulation of relevant signaling pathways. We found that HDACs are involved in cartilage and chondrocyte development but also play a crucial role in OA. However, the distinct HDAC mechanism in the pathogenesis and treatment of OA require further investigation. Furthermore, HDAC inhibitors (HDACi) can protect cartilage from disease, which may represent a potential therapeutic approach against OA.

Tumor cells hijack enteric glia to activate colon cancer stem cells and stimulate tumorigenesis

BACKGROUND

Colon cancer stem cells (CSCs), considered responsible for tumor initiation and cancer relapse, are constantly exposed to regulatory cues emanating from neighboring cells present in the tumor microenvironment. Among these cells are enteric glial cells (EGCs) that are potent regulators of the epithelium functions in a healthy intestine. However, whether EGCs impact CSC-driven tumorigenesis remains unknown.

METHODS

Impact of human EGC primary cultures or a non-transformed EGC line on CSCs isolated from human primary colon adenocarcinomas or colon cancer cell lines with different p53, MMR system and stemness status was determined using murine xenograft models and 3D co-culture systems. Supernatants of patient-matched human primary colon adenocarcinomas and non-adjacent healthy mucosa were used to mimic tumor versus healthy mucosa secretomes and compare their effects on EGCs.

FINDINGS

Our data show that EGCs stimulate CSC expansion and ability to give rise to tumors via paracrine signaling. Importantly, only EGCs that were pre-activated by tumor epithelial cell-derived soluble factors increased CSC tumorigenicity. Pharmacological inhibition of PGE2 biosynthesis in EGCs or IL-1 knockdown in tumor epithelial cells prevented EGC acquisition of a pro-tumorigenic phenotype. Inhibition of PGE2 receptor EP4 and EGFR in CSCs inhibited the effects of tumor-activated EGCs.

INTERPRETATION

Altogether, our results show that EGCs, once activated by the tumor, acquire a pro-tumorigenic phenotype and stimulate CSC-driven tumorigenesis via a PGE2/EP4/EGFR-dependent pathway.

FUNDING

This work was supported by grants from the French National Cancer Institute, La Ligue contre le Cancer, the 'Région des Pays de la Loire' and the UNC Lineberger Comprehensive Cancer Center.

Histone Deacetylases in Bone Development and Skeletal Disorders

Histone deacetylases (Hdacs) are conserved enzymes that remove acetyl groups from lysine side chains in histones and other proteins. Eleven of the 18 Hdacs encoded by the human and mouse genomes depend on Zn(2+) for enzymatic activity, while the other 7, the sirtuins (Sirts), require NAD2(+). Collectively, Hdacs and Sirts regulate numerous cellular and mitochondrial processes including gene transcription, DNA repair, protein stability, cytoskeletal dynamics, and signaling pathways to affect both development and aging. Of clinical relevance, Hdacs inhibitors are United States Food and Drug Administration-approved cancer therapeutics and are candidate therapies for other common diseases including arthritis, diabetes, epilepsy, heart disease, HIV infection, neurodegeneration, and numerous aging-related disorders. Hdacs and Sirts influence skeletal development, maintenance of mineral density and bone strength by affecting intramembranous and endochondral ossification, as well as bone resorption. With few exceptions, inhibition of Hdac or Sirt activity though either loss-of-function mutations or prolonged chemical inhibition has negative and/or toxic effects on skeletal development and bone mineral density. Specifically, Hdac/Sirt suppression causes abnormalities in physiological development such as craniofacial dimorphisms, short stature, and bone fragility that are associated with several human syndromes or diseases. In contrast, activation of Sirts may protect the skeleton from aging and immobilization-related bone loss. This knowledge may prolong healthspan and prevent adverse events caused by epigenetic therapies that are entering the clinical realm at an unprecedented rate. In this review, we summarize the general properties of Hdacs/Sirts and the research that has revealed their essential functions in bone forming cells (e.g., osteoblasts and chondrocytes) and bone resorbing osteoclasts. Finally, we offer predictions on future research in this area and the utility of this knowledge for orthopedic applications and bone tissue engineering.

Histone deacetylase 4 alters cartilage homeostasis in human osteoarthritis

BACKGROUND

Osteoarthritis (OA) is the most common degenerative joint disorder, and a major cause of pain and disability among the elderly. Histone deacetylase 4 (HDAC4) has been shown to be a key regulator of chondrocyte hypertrophy during skeletogenesis. The aims of present study were to investigate the expression of HDAC4 in normal and OA cartilage and its potential roles during OA pathogenesis.

METHODS

The knee cartilage specimen (a total of 18, 12 female and 6 male) were obtained from primary OA patients undergoing total knee arthroplasty (TKA) and normal donors. By using immunohistochemistry staining, we detected the expression patterns of HDAC4 in OA cartilage and normal cartilage respectively. To assess the potential roles of HDAC4, HDAC4 expression in human chondrosarcoma cells (SW1353) was down-regulated by transfecting small interference RNA (siRNA), thereafter, cells were treated with IL-1β or TNF-α, and the expressions of several matrix-degrading enzymes and anabolic factors were examined by using quantitative PCR.

RESULTS

The expression of HDAC4 was observed in the OA cartilage, whereas it was barely detected in the normal cartilage. The extent of HDAC4 expression had a statistically negative correlation with OA severity. We further explored that the reduction of HDAC4 level led to a significant repression of proinflammation cytokines induced up-regulated expressions of matrix-degrading enzymes (MMP1 (Matrix metalloproteinase 1), MMP3 (Matrix metalloproteinase 3) , MMP13 (Matrix metalloproteinase 13), ADAMTS4 (aggrecanase 1) and ADAMTS5 (aggrecanase 2)) in SW1353 in vitro. Moreover, knockdown of HDAC4 inhibited the expression of some anabolic genes (such as aggrecan).

CONCLUSIONS

In this study, our findings suggest that the abnormal expression of HDAC4 in osteoarthritic cartilage might be implicated in promoting catabolic activity of chondrocyte, which is associated with OA pathogenesis. Thus, our findings give a new insight into the mechanism of articular cartilage damage, and indicate that HDAC4 might be a potential target for the therapeutic interventions of OA.

Epigenetic mechanisms in cartilage and osteoarthritis: DNA methylation, histone modifications and microRNAs

Osteoarthritis (OA) is a complex multifactorial disease with a strong genetic component. Several studies have suggested or identified epigenetic events that may play a role in OA progression and the gene expression changes observed in diseased cartilage. The aim of this review is to inform about current research in epigenetics and epigenetics in OA. Epigenetic mechanisms include DNA methylation, histone modifications, and microRNAs. Collectively, these enable the cell to respond quickly to environmental changes and can be inherited during cell division. However, aberrant epigenetic modifications are associated with a number of pathological conditions, including OA. Advancements in epigenetic research suggests that global analysis of such modifications in OA are now possible, however, with the exception of microRNAs, it will be a significant challenge to demonstrate how such events impact on the disease.

Regulation of human microsomal prostaglandin E synthase-1 by IL-1β requires a distal enhancer element with a unique role for C/EBPβ

The studies of PGE2 (prostaglandin E2) biosynthesis have focused primarily on the role of cyclo-oxygenases. Efforts have shifted towards the specific PGE2 terminal synthases, particularly mPGES-1 (microsomal PGE synthase 1), which has emerged as the crucial inducible synthase with roles in pain, cancer and inflammation. mPGES-1 is induced by pro-inflammatory cytokines with studies focusing on the proximal promoter, mediated specifically through Egr-1 (early growth-response factor 1). Numerous studies demonstrate that the mPGES-1 promoter (PTGES) alone cannot account for the level of IL-1β (interleukin 1β) induction. We identified two DNase I-hypersensitive sites within the proximal promoter near the Egr-1 element and a novel distal site near −8.6 kb. Functional analysis of the distal site revealed two elements that co-operate with basal promoter expression and a stimulus-dependent enhancer. A specific binding site for C/EBPβ (CCAAT/enhancer-binding protein β) in the enhancer was directly responsible for inducible enhancer activity. ChIP (chromatin immunoprecipitation) analysis demonstrated constitutive Egr-1 binding to the promoter and induced RNA polymerase II and C/EBPβ binding to the promoter and enhancer respectively. Knockout/knockdown studies established a functional role for C/EBPβ in mPGES-1 gene regulation and the documented interaction between Egr-1 and C/EBPβ highlights the proximal promoter co-operation with a novel distal enhancer element in regulating inducible mPGES-1 expression.