Central role of SREBP-2 in the pathogenesis of osteoarthritis

The impact of sericin on inflammation, oxidative stress, and lipid metabolism in female rats with experimental knee osteoarthritis

OBJECTIVE

This study investigated the effects of sericin on inflammation, oxidative stress, and lipid metabolism in female rats with experimental knee osteoarthritis (KOA), focusing on evaluating its effectiveness via the sterol regulatory protein (SREBP)-1C and SREBP-2 pathways.

METHODS

The rats were randomly assigned to three experimental groups: the C group (control), the KOA group (KOA control), and the sericin group (KOA + sericin). The KOA model was created by injecting monosodium iodoacetate (MIA) into the knee joint. Sericin was administered intra-articularly to rats on days 1, 7, 14, and 21 (0.8 g/kg/mL, 50 µL). After 21 days, the rats were sacrificed, and serum samples were analyzed using an ELISA to measure tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-10, SREBP-1c, SREBP-2, acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), cholesterol, triglyceride, and total oxidant-antioxidant status (TOS-TAS) levels.

RESULTS

The KOA group exhibited higher serum TNF-α, IL-1β, TOS, SREBP-1C, ACC, FAS, triglyceride, SREBP-2, and cholesterol levels than the C group (P < 0.05). However, the levels of these cytokines, except cholesterol, were significantly lower in the sericin group than in the KOA group. The KOA group exhibited significantly lower serum TAS and IL-10 levels than the C group (P < 0.05). In the sericin group, there was a statistically significant increase (P < 0.05).

CONCLUSION

Sericin shows promising potential for reducing inflammation, oxidative stress, and lipid metabolism in experimental models of KOA in rats. However, further clinical research is necessary to validate the potential of sericin as a therapeutic agent for treating KOA. Key Points • Sericin can reduce knee osteoarthritis (KOA) symptoms in an experimental rat model. • In particular, in the serum of an experimental KOA rat model, sericin specifically reduces the levels of proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β), and increases the levels of anti-inflammatory cytokines, such as IL-10. • Sericin reduced lipid metabolism via the sterol regulatory protein (SREBP)-1C and SREBP-2 pathways and oxidative stress in the serum of the experimental KOA rat model. • The intra-articular administration of sericin has been shown to significantly reduce lipid metabolism, oxidative stress, and inflammation, as supported by biochemical analysis. These findings suggest its promising potential as an alternative treatment option for KOA.

Eliglustat exerts anti-fibrotic effects by activating SREBP2 in TGF-β1-treated myofibroblasts derived from patients with idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive chronic lung disease. Myofibroblasts play a critical role in fibrosis. These cells produce the extracellular matrix (ECM), which contributes to tissue regeneration; however, excess ECM production can cause fibrosis. Transforming growth factor-β (TGF-β)/Smad signaling induces ECM production by myofibroblasts; therefore, the inhibition of TGF-β/Smad signaling may be an effective strategy for IPF treatment. We recently reported that miglustat, an inhibitor of glucosylceramide synthase (GCS), ameliorates pulmonary fibrosis by inhibiting the nuclear translocation of Smad2/3. In the present study, we examined the anti-fibrotic effects of another GCS inhibitor, eliglustat, a clinically approved drug for treating Gaucher disease type 1, in myofibroblasts derived from patient with IPF (IPF-MyoFs). We found that eliglustat exerted anti-fibrotic effects independent of GCS inhibition, and inhibited TGF-β1-induced expression of α-smooth muscle actin, a marker of fibrosis, without suppressing the phosphorylation and nuclear translocation of Smad2/3. RNA sequencing analysis of eliglustat-treated human lung fibroblasts identified sterol regulatory element-binding protein 2 (SREBP2) activation. Transient overexpression of SREBP2 attenuated the TGF-β1-induced increase in the expression of Smad target genes in IPF-MyoFs, and SREBP2 knockdown nullified the inhibitory effect of eliglustat on TGF-β1-induced expression of α-SMA. These results suggested that eliglustat exerts its anti-fibrotic effects through SREBP2 activation. The findings of this study may contribute to the development of novel therapeutic strategies for IPF treatment.

Dysregulation of Cholesterol Homeostasis in Ovarian Cancer

Cholesterol plays an essential role in maintaining the rigidity of cell membranes and signal transduction. Various investigations confirmed empirically that the dysregulation of cholesterol homeostasis positively correlates with tumor progression. More specifically, recent studies suggested the distinct role of cholesterol in ovarian cancer cell proliferation, metastasis and chemoresistance. In this review, we summarize the current findings that suggest the contribution of cholesterol homeostasis dysregulation to ovarian cancer progression and resistance to anti-cancer agents. We also discuss the therapeutic implications of cholesterol-lowering drugs in ovarian cancer.

Resveratrol Improves the Progression of Osteoarthritis by Regulating the SIRT1-FoxO1 Pathway-Mediated Cholesterol Metabolism

Osteoarthritis (OA) is considered a metabolic disorder. This study investigated the effect of resveratrol (RES) on cholesterol accumulation in osteoarthritic articular cartilage via the silent information regulator 1 (SIRT1)/forkhead transcription factor (FoxO1) pathway. Interleukin (IL)-1β-treated chondrocytes that mimic OA chondrocytes were used in in vitro experiments. The optimal RES concentration was selected based on the results of chondrocyte proliferation in the Cell Counting Kit-8 assay. Western blotting, immunofluorescence, and reverse transcription-quantitative polymerase chain reaction were performed. For the animal experiments, mice were randomly divided into the RES group (n = 15), medial meniscus destabilization group (n = 15), and sham group (n = 15), and each group received the same dose of RES or saline. Articular cartilage tissue was obtained eight weeks after surgery for relevant histological analysis. Clinical tissue test results suggest that downregulation of the SIRT1/FoxO1 pathway is associated with cholesterol buildup in OA chondrocytes. For the in vitro studies, RES increased the expression of SIRT1 and phosphorylation of FoxO1 in IL-1β-treated chondrocytes, promoted the expression of cholesterol efflux factor liver X receptor alpha (LXRα), and inhibited the expression of cholesterol synthesis-associated factor sterol-regulatory element binding proteins 2 (SREBP2). This reduced IL-1β-induced chondrocytes cholesterol accumulation. SIRT1 inhibition prevented the RES-mediated reduction in cholesterol buildup. Inhibiting FoxO1 but not SIRT1 reduced FoxO1 phosphorylation and increased cholesterol buildup in cultured chondrocytes. Additionally, in vivo experiments have shown that RES can alleviate cholesterol buildup and pathological changes in OA cartilage. Our findings suggest that RES regulates cholesterol buildup in osteoarthritic articular cartilage via the SIRT1/FoxO1 pathway, thereby improving the progression of OA.

Metformin mitigates cholesterol accumulation via the AMPK/SIRT1 pathway to protect osteoarthritis chondrocytes

In this study, we aim to investigate the effect of metformin on cholesterol synthesis and efflux-related genes in chondrocytes during osteoarthritis (OA) and explore the underlying mechanisms. Primary chondrocytes were harvested from Wistar rat cartilage and divided into control and treatment groups. Chondrocytes in the treatment group were treated with interleukin-1β (IL-1β) mimicking the inflammatory environment of osteoarthritis. Subsequently, RT-qPCR, Western blotting, immunofluorescence staining, and Cell Counting Kit-8 (CCK-8) were conducted. Significant reductions in phosphorylated AMP-activated protein kinase (p-AMPK) and silent information regulator 1 (SIRT1) protein expression were observed in both human OA chondrocytes and cultured primary murine chondrocytes treated with IL-1β, while AMP-activated protein kinase (AMPK) was not inhibited. Moreover, in the presence of IL-1β, metformin significantly increased the expression of p-AMPK and SIRT1 at the protein and mRNA level. Meanwhile, metformin could reverse IL-1β-induced cartilage extracellular matrix degradation in chondrocytes from the rat model of OA (treated by IL-β) by activating the AMPK/SIRT1 pathway. Moreover, metformin activated AMPK and SIRT1, mediated by the activation of SREBP-2 and HMGCR in OA chondrocytes. Inhibiting AMPK/SIRT1 activity by its specific inhibitor could suppress IL-1β-induced expression of LXRα, ABCA1 and ApoA1 and cholesterol efflux. Thus, metformin inhibits cholesterol synthesis and promotes cholesterol efflux by activating the AMPK/SIRT1 pathway in OA chondrocytes. This study improves our understanding of the effect of metformin on cholesterol accumulation in OA chondrocytes.

Lipid Metabolism in Cartilage Development, Degeneration, and Regeneration

Lipids affect cartilage growth, injury, and regeneration in diverse ways. Diet and metabolism have become increasingly important as the prevalence of obesity has risen. Proper lipid supplementation in the diet contributes to the preservation of cartilage function, whereas excessive lipid buildup is detrimental to cartilage. Lipid metabolic pathways can generate proinflammatory substances that are crucial to the development and management of osteoarthritis (OA). Lipid metabolism is a complicated metabolic process involving several regulatory systems, and lipid metabolites influence different features of cartilage. In this review, we examine the current knowledge about cartilage growth, degeneration, and regeneration processes, as well as the most recent research on the significance of lipids and their metabolism in cartilage, including the extracellular matrix and chondrocytes. An in-depth examination of the involvement of lipid metabolism in cartilage metabolism will provide insight into cartilage metabolism and lead to the development of new treatment techniques for metabolic cartilage damage.

Hyperlipidemia does not influence clinical outcome in arthroscopic treatment of femoroacetabular impingement syndrome

Background

Cholesterol can trigger degenerative processes in the chondrocytes. The internal layer of the hip labral consists of cartilage-specific type II collagen-positive fibrocartilage. The purpose of this study was to compare outcomes after arthroscopy labral repair in FAIS patients with preoperative hyperlipidemia to a control group with no hyperlipidemia.

Methods

Data were prospectively collected and retrospectively reviewed for FAIS patients who had arthroscopy 2019. Patients with hyperlipidemia were 1:1 propensity-score matched to patients without hyperlipidemia. Patient-reported outcomes (HOS-ADL, iHOT-12, mHHS), VAS scores, radiographic measures, performed procedures, complications, and revision surgery were compared and analyzed for both groups.

Results

A total of 41 patients with hyperlipidemia and 41 patients without hyperlipidemia were found using propensity-score matching. When compared to preoperative levels, both groups demonstrated significant improvements in PROs and VAS scores at the final follow-up. Besides, there were no significant differences in preoperative scores and final outcome scores between the groups. Besides, there were no other differences in revision rate and the rate of meeting the PASS and MCID between the study and the control groups.

Conclusion

It was demonstrated in this study that FAIS patients with hyperlipidemia can expect to experience similar good short-term patient-reported outcomes as compared with patients without hyperlipidemia.

Level of evidence

Case-series study; Level of Evidence: Level III.

Anti-fibrotic mechanism of SPP1 knockdown in atrial fibrosis associates with inhibited mitochondrial DNA damage and TGF-β/SREBP2/PCSK9 signaling

Atrial fibrosis occurs frequently with structural heart disease and is considered as a major cause of arrhythmia. Microarray-based profiling predicted the differential expression of SPP1 in atrial fibrosis. Herein, we aimed to analyze the role of shRNA-mediated SPP1 knockdown in the progression of atrial fibrosis as well as the downstream mechanism. In vivo model in mice and in vitro HL-1 cell model of atrial fibrosis were developed by the angiotensin II (Ang II) method, where SPP1 expression was validated by RT-qPCR. Gain- and loss-of-function experiments were performed in Ang II-induced mice and HL-1 cells to evaluate the effect of the SPP1/TGF-β/SREBP2/PCSK9 axis on cell viability, apoptosis, collagen production and mitochondrial DNA (mtDNA) damage in atrial fibrosis. Expression of SPP1, TGF-β, SREBP2 and PCSK9 was increased in Ang II-induced mice and HL-1 cells. Silencing of SPP1 inhibited the occurrence of atrial fibrosis, as reflected by attenuated cell viability and collagen production as well as increased cell apoptosis. Conversely, upregulated SPP1 enhanced atrial fibrosis, which was related to upregulation of TGF-β. In addition, TGF-β elevated the expression of SREBP2, which promoted mtDNA damage and the consequent atrial fibrosis by augmenting the expression of PCSK9. This study uncovers previously unrecognized pro-fibrotic activities of SPP1 in atrial fibrosis, which is achieved through activation of the TGF-β/SREBP2/PCSK9 signaling pathway and promotion of mtDNA damage.

Retinoic Acid Grafted to Hyaluronic Acid Activates Retinoid Gene Expression and Removes Cholesterol from Cellular Membranes

All-trans-retinoic acid (atRA) is a potent ligand that regulates gene expression and is used to treat several skin disorders. Hyaluronic acid (HA) was previously conjugated with atRA (HA-atRA) to obtain a novel amphiphilic compound. HA-atRA forms micelles that incorporate hydrophobic molecules and facilitate their transport through the skin. The aim of this study was to determine the influence of HA-atRA on gene expression in skin cells and to compare it with that of unbound atRA. Gene expression was investigated using microarrays and a luciferase system with a canonical atRA promoter. HA-atRA upregulated gene expression similarly to atRA. However, HA-atRA activated the expression of cholesterol metabolism genes, unlike atRA. Further investigation using HPLC and filipin III staining suggested that the treated cells induced cholesterol synthesis to replenish the cholesterol removed from the cells by HA-atRA. HA modified with oleate (HA-C18:1) removed cholesterol from the cells similarly to HA-atRA, suggesting that the cholesterol removal stemmed from the amphiphilic nature of the two derivatives. HA-atRA induces retinoid signaling. Thus, HA-atRA could be used to treat skin diseases, such as acne and psoriasis, where the combined action of atRA signaling and anti-inflammatory cholesterol removal may be potentially beneficial.

LncRNA MEG3 Inhibits the Degradation of the Extracellular Matrix of Chondrocytes in Osteoarthritis via Targeting miR-93/TGFBR2 Axis

BACKGROUND

As a degenerative joint disease, osteoarthritis (OA) is characterized by articular cartilage degradation. Long noncoding RNAs (lncRNAs) act critical roles in the regulation of OA development, including affecting the proliferation, apoptosis, extracellular matrix (ECM) degradation, and inflammatory response of chondrocytes. The current study's aim was to investigate the regulatory function and the underlying molecular mechanism of lncRNA MEG3 in ECM degradation of chondrocytes in OA.

METHODS

In the current study, chondrocytes were induced by interleukin-1β (IL-1β) to simulate OA condition, and further assessed cell viability, lncRNA MEG3 and miR-93 expression levels. Overexpression or knockdown of lncRNA MEG3 in chondrocytes treated with IL-1β were performed to investigate the function of MEG3 in regulating cell proliferation, apoptosis and ECM degradation using EdU assay, flow cytometry, quantitative reverse transcription polymerase chain reaction (qRT-PCR), and Western blot. The interaction between MEG3 and miR-93 was assessed using qRT-PCR. Furthermore, overexpression of miR-93 was performed as recovery experiment to explore the functional mechanism of MEG3.

RESULTS

MEG3 was significantly downregulated in chondrocytes treated with IL-1β, whereas miR-93 was upregulated concomitantly. Overexpression of MEG3 induced the proliferation, suppressed the apoptosis, and relieved the degradation of ECM in IL-1β-induced chondrocytes. By contrast, knockdown of MEG3 suppressed the proliferation, promoted the apoptosis, and aggravated ECM degradation in IL-1β induced chondrocytes. In addition, MEG3 was found to relieve the inhibitive expression of TGFBR2 as a competitive endogenous RNA (ceRNA) of miR-93, and then activated transforming growth factor-β (TGF-β) signaling pathway, regulated chondrocytes ECM degradation in IL-1β induced chondrocytes subsequently.

CONCLUSION

LncRNA MEG3 targeted miR-93/TGFBR2 axis, regulated the proliferation, apoptosis and ECM degradation of chondrocytes in OA.

Metabolites as drivers and targets in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by neovascularization, immune cell infiltration, and synovial hyperplasia, which leads to degradation of articular cartilage and bone, and subsequent functional disability. Dysregulated angiogenesis, synovial hypoxia, and immune cell infiltration result in a ‘bioenergetic crisis’ in the inflamed joint which further exacerbates synovial invasiveness. Several studies have examined this vicious cycle between metabolism, immunity, and inflammation and the role metabolites play in these interactions. To add to this complexity, the inflamed synovium is a multicellular tissue with many cellular subsets having different metabolic requirements. Metabolites can shape the inflammatory phenotype of immune cell subsets during disease and act as central signalling hubs. In the RA joint, the increased energy demand of stromal and immune cells leads to the accumulation of metabolites such as lactate, citrate, and succinate as well as adipocytokines which can regulate downstream signalling pathways. Transcription factors such as HIF1ɑ and mTOR can act as metabolic sensors to activate synovial cells and drive pro-inflammatory effector function, thus perpetuating chronic inflammation further. These metabolic intermediates may be potential therapeutic targets and so understanding the complex interplay between metabolites and synovial cells in RA may allow for identification of novel therapeutic strategies but also may provide significant insight into the underlying mechanisms of disease pathogenesis.

Stigmasterol alleviates interleukin-1beta-induced chondrocyte injury by down-regulatingsterol regulatory element binding transcription factor 2 to regulateferroptosis

Stigmasterol (STM), one of the main active components of Achyranthes bidentata, has been shown to effectively inhibit proinflammatory factors and matrix degradation in chondrocytes. However, the effect of STM on interleukin (IL)-1β-induced chondrocytes and its specific mechanism remain unclear. The purpose of the present study was to explore the effect and mechanism of sterol regulatory element binding transcription factor 2 (SREBF2) on IL-1β induced chondrocytes in the presence of STM. CCK-8 was used to detect the effect of STM on the cell viability of mouse chondrogenic cells (ATDC5). After ATDC5 cells were induced by IL-1β, the expression of SREBF2 in osteoarthritis cells was detected by RT-qPCR. The content of iron ion in the cells was detected by using an iron colorimetric assay kit. After further transfection of a SREBF2 overexpressing vector (Oe-SREBF2) or addition of a ferroptosis inhibitor, the expression levels of inflammation and matrix degradation-related proteins were detected via Western blotting. The levels of oxidative stress in cells were determined by using an ELISA kit. The results revealed that STM had no significant effect on the viability of ATDC5 cells. STM reduced IL-1β-induced ATDC5 cell damage and ferroptosis through SREBF2 and enhanced the inhibitory effect of ferroptosis inhibitors on IL-1β-induced ATDC5 cell injury. The present data suggest that STM attenuated chondrocyte injury induced by IL-1β by regulating ferroptosis via down-regulation of SREBF2, and may have potential as a novel therapeutic method for knee osteoarthritis.

Cholesterol metabolism related genes in osteoarthritis

Cholesterol homeostasis plays a significant role in skeletal development and the dysregulation of cholesterol-related mechanism has been shown to be involved in the development of cartilage diseases including osteoarthritis (OA). Epidemiological studies have shown an association between elevated serum cholesterol levels and OA. Furthermore, abnormal lipid accumulation in chondrocytes as a result of abnormal regulation of cholesterol homeostasis has been demonstrated to be involved in the development of OA. Although, many in vivo and in vitro studies support the connection between cholesterol and cartilage degradation, the mechanisms underlying the complex interactions between lipid metabolism, especially HDL cholesterol metabolism, and OA remain unclear. The current review aims to address this problem and focuses on key molecular players of the HDL metabolism pathway and their role in ΟΑ pathogenesis. Understanding the complexity of biological processes implicated in OA pathogenesis, such as cholesterol metabolism, may lead to new targets for drug therapy of OA patients.

Cholesterol-induced toxicity: An integrated view of the role of cholesterol in multiple diseases

High levels of cholesterol are generally considered to be associated with atherosclerosis. In the past two decades, however, a number of studies have shown that excess cholesterol accumulation in various tissues and organs plays a critical role in the pathogenesis of multiple diseases. Here, we summarize the effects of excess cholesterol on disease pathogenesis, including liver diseases, diabetes, chronic kidney disease, Alzheimer's disease, osteoporosis, osteoarthritis, pituitary-thyroid axis dysfunction, immune disorders, and COVID-19, while proposing that excess cholesterol-induced toxicity is ubiquitous. We believe this concept will help broaden the appreciation of the toxic effect of excess cholesterol, and thus potentially expand the therapeutic use of cholesterol-lowering medications.

Pravastatin ameliorated osteoarthritis susceptibility in male offspring rats induced by prenatal ethanol exposure

Osteoarthritis (OA) is a disease associated with a disorder of cholesterol metabolism. Our previous studies showed that prenatal ethanol exposure (PEE) caused cholesterol accumulation in articular cartilage and increased the susceptibility to OA in offspring. However, we did not determine whether pravastatin, a cholesterol-lowering agent, could rescue PEE-induced susceptibility to OA. Here, fetal rats were divided into a PEE group and a control group during pregnancy. At postnatal week (PW) 8, sixteen male offspring rats from both groups were injected papain through the articular cavity. Eight of them from each group were treated with pravastatin (20 mg/kg·d) by gavage for four weeks simultaneously. We found that pravastatin ameliorated papain-induced high expression of inflammatory factors [interleukin (IL)-1, IL-6], matrix degradation enzymes [matrix metalloproteinase (MMP)-3, MMP-13], and apoptosis factors (caspase-3 and caspase-8) in the cartilage of the PEE group. Also, pravastatin significantly reduced the content of TCH in the blood and cartilage of the PEE offspring and improved cholesterol efflux pathway. Our in vitro findings further confirmed that pravastatin partially reversed cholesterol-induced inflammation and apoptosis of chondrocytes. In conclusion, pravastatin effectively reduced inflammation and matrix degradation, and thus ameliorate OA susceptibility in articular cartilage by relieving cholesterol accumulation in chondrocyte.

Lipid metabolism in cartilage and its diseases: a concise review of the research progress

The homeostasis of the vertebrate body depends on anabolic and catabolic activities that are closely linked the inside and outside of the cell. Lipid metabolism plays an essential role in these metabolic activities. Although a large amount of evidence shows that normal lipid metabolism guarantees the conventional physiological activities of organs in the vertebrate body and that abnormal lipid metabolism plays an important role in the occurrence and deterioration of cardiovascular-related diseases, such as obesity, atherosclerosis, and type II diabetes, little is known about the role of lipid metabolism in cartilage and its diseases. This review aims to summarize the latest advances about the function of lipid metabolism in cartilage and its diseases including osteoarthritis, rheumatoid arthritis, and cartilage tumors. With the gradual in-depth understanding of lipid metabolism in cartilage, treatment methods could be explored to focus on this metabolic process in various cartilage diseases.

Vaspin regulated cartilage cholesterol metabolism through miR155/LXRα and participated in the occurrence of osteoarthritis in rats

AIMS

This study intends to explore the role of Vaspin and cholesterol metabolism in the process of osteoarthritis (OA) and its mechanism in vitro and in vivo.

MAIN METHODS

In vitro, chondrocytes were treated with interleukin-1β (IL-1β, 20 ng/mL) in combination with Vaspin at different concentrations for 48 h. The expressions of Aggrecan (ACAN), Collagen 2a1 (Col2a1), A Disintegrin And Metalloproteinase with Thrombo Spondin type 1 motifs 5 (ADAMTS 5), and Matrix metalloproteinase 13 (MMP13) were detected. In vivo, the expression of liver X receptor (LXRα) and other Cholesterol efflux related genes were detected in the rat OA knee cartilage-induced by papain.

KEY FINDINGS

In vitro, in a concentration-dependent manner, Vaspin reversed the decreased expression of ACAN and Col2a1, and the increased expression of ADAMTS 5 and MMP13 caused by IL-1β. Besides, Vaspin promoted the expression of LXRα and other Cholesterol efflux related genes in a concentration-dependent manner in chondrocytes. However, miR155 mimics reversed the Vaspin-induced expression changes of cholesterol efflux pathway in chondrocytes. In vivo, the expression of LXRα and other Cholesterol efflux related genes were decreased in the rat OA knee cartilage-induced by papain. Besides, the level of Vaspin was reduced and the miroRNA155 (miR155) expression was increased in OA knee cartilage of rats.

SIGNIFICANCE

In conclusion, the decreased expression of Vaspin inhibited the expression of Cholesterol efflux pathway via miR155/LXRα. Finally, the inhibited Cholesterol efflux pathway led to the cholesterol accumulation and OA in cartilage.

MicroRNA-194 inactivates hepatic stellate cells and alleviates liver fibrosis by inhibiting AKT2

BACKGROUND

Activation of hepatic stellate cells (HSCs) is a pivotal event in the onset and progression of liver fibrosis. Loss of microRNA-194 (miR-194) has been reported in activated HSCs, but the actual role of miR-194 in liver fibrosis remains uncertain.

AIM

To explore the role and potential mechanism of miR-194-mediated regulation of liver fibrosis in vitro and in vivo.

METHODS

The expression of miR-194 was examined in human fibrotic liver tissues, activated HSCs, and a carbon tetrachloride (CCl₄) mouse model by qPCR. The effects of AKT2 regulation by miR-194 on the activation and proliferation of HSCs were assessed in vitro. For in vivo experiments, we reintroduced miR-194 in mice using a miR-194 agomir to investigate the functions of miR-194 in liver fibrosis.

RESULTS

MiR-194 expression was notably lacking in activated HSCs from both humans and mice. Overexpression of miR-194 (OV-miR-194) inhibited α-smooth muscle actin (α-SMA) and type I collagen (Col I) expression and suppressed cell proliferation in HSCs by causing cell cycle arrest in G0/G1 phase. AKT2 was predicted to be a target of miR-194. Notably, the effects of miR-194 knockdown in HSCs were almost blocked by AKT2 deletion, indicating that miR-194 plays a role in HSCs via regulation of AKT2. Finally, miR-194 agomir treatment dramatically ameliorated liver fibrosis in CCl₄-treated mice.

CONCLUSION

We revealed that miR-194 plays a protective role by inhibiting the activation and proliferation of HSCs via AKT2 suppression. Our results further propose miR-194 as a potential therapeutic target for liver fibrosis.

DNA methylation regulates miR-140-5p and miR-146a expression in osteoarthritis

AIMS

Previous studies have demonstrated that transcriptional silencing of miRNAs due to DNA hypermethylation is associated with different pathologies. It has also been reported that abnormal expression of miR-140-5p and miR-146a is linked to osteoarthritis (OA) progression. In this study, we investigated the role of DNA methylation on miR-140-5p and miR-146a expression in OA.

MAIN METHODS

miR-140-5p and miR-146a expression was investigated by qRT-PCR. The methylation status of miR-140 and miR-146a regulatory regions was analyzed using qMSP and bisulfite sequencing analysis. SMAD-3 and NF-kB binding to miR-140 and miR-146a regulatory regions was assessed by ChIP assay and knockdown experiments. OA-related genes' expression was evaluated in 5-AzadC, miRNAs inhibitor and 5-AzadC/miRNAs inhibitor-treated cells.

KEY FINDINGS

Hypermethylation of specific CpG sites in miR-140 and miR-146a regulatory regions was associated with downregulation of miR-140-5p and miR-146a in OA chondrocytes and synoviocytes, respectively. 5-AzadC-induced miR-140-5p and miR-146a upregulation was observed in OA chondrocytes and synoviocytes. Moreover, we found decreased binding affinity of SMAD-3 and NF-kB transcription factors on the hypermethylated miR-140-5p and miR-146a regulatory regions, respectively. Downregulation of MMP-13 and ADAMTS-5 in 5-AzadC-treated OA chondrocytes was prevented by miR-140-5p inhibitor transfection. Similarly, 5-AzadC-treated OA synoviocytes showed decreased expression of IRAK-1, IL1Β and IL-6, which was reversed following 5-AzadC-/miR-146a inhibitor treatment.

SIGNIFICANCE

Our results strongly suggest the impact of DNA methylation on miR-140-5p and miR-146a suppression in OA chondrocytes and synoviocytes, contributing to OA pathogenesis.

Role of SREBP2 gene polymorphism on knee osteoarthritis in the South Indian Hyderabad Population: A hospital based study with G595C variant

Introduction

Osteoarthritis (OA) is a multifactorial disease with genetic factors playing a crucial role, and it has been associated with a family history of obesity. G595C polymorphism in the sterol regulatory element-binding protein 2 (SREBP2) gene has demonstrated an association with knee osteoarthritis (KOA) patients. However, this polymorphism has been never explored in an Indian population. Hence, the current study aimed to examine whether G595C (rs2228314) polymorphism in SREBP2 gene was associated with KOA susceptibility in the South Indian Hyderabad population.

Methods

G595C polymorphism was genotyped with 200 KOA cases and 200 healthy controls using polymerase chain reaction-restriction fragment length polymorphism analysis.

Results

A significant association was observed between age, body mass index (BMI), and family histories in KOA cases and controls (p < 0.05). The current allele (C vs G; OR-2.8 [95%CI = 2.1-3.7]; p < 0.0001) and genotype analysis confirms the significant association with (GC + CC vs GG; OR-3.5 [95%CI = 2.3-5.3]; p < 0.0001 & GC vs GG + CC; OR-1.7 [95%CI = 1.0-2.9]; p = 0.02) KOA vs. control subjects. On stratification analysis, genotype CC and C allele were associated with KOA. Gender association failed to demonstrate positive genotype frequencies (p > 0.05). Multifactor-dimensionality reduction (MDR) analysis showed a positive association with BMI and G595C genotypes (p < 0.05); 51% of the homozygous variant CC genotypes were present in obesity subjects.

Conclusion

In conclusion, our findings suggest that G595C polymorphism in SREBP2 gene is associated with KOA in the South Indian Hyderabad population and presents scope for further investigation of the gene's function in KOA.

Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy to diagnose osteoarthritis in equine serum

BACKGROUND

Reliable and validated biomarkers for osteoarthritis (OA) are currently lacking.

OBJECTIVES

To develop an accurate and minimally invasive method to assess OA-affected horses and provide potential spectral markers indicative of disease.

STUDY DESIGN

Observational, cross-sectional study.

METHODS

Our cohort consisted of 15 horses with OA and 48 without clinical signs of the disease, which were used as controls. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy was used to investigate serum samples (50 μL) collected from these horses. Spectral processing and multivariate analysis revealed differences and similarities, allowing for detection of spectral biomarkers that discriminated between the two cohorts. A supervised classification algorithm, namely principal component analysis coupled with quadratic discriminant analysis (PCA-QDA), was applied to evaluate the diagnostic accuracy.

RESULTS

Segregation between the two different cohorts, OA-affected and controls, was achieved with 100% sensitivity and specificity. The six most discriminatory peaks were attributed to proteins and lipids. Four of the spectral peaks were elevated in OA horses, which could be potentially due to an increase in lipids, protein expression levels and collagen, all of which have been previously reported in OA. Two peaks were found decreased and were tentatively assigned to the reduction of proteoglycan content that is observed during OA.

MAIN LIMITATIONS

The control group had a wide range of ages and breeds. Presymptomatic OA cases were not included. Therefore, it remains unknown whether this test could also be used as an early diagnostic tool.

CONCLUSIONS

This spectrochemical approach could provide an accurate and cost-effective blood test, facilitating point-of-care diagnosis of equine OA.

What is the evidence for a role for diet and nutrition in osteoarthritis?

As current treatment options in OA are very limited, OA patients would benefit greatly from some ability to self-manage their condition. Since diet may potentially affect OA, we reviewed the literature on the relationship between nutrition and OA risk or progression, aiming to provide guidance for clinicians. For overweight/obese patients, weight reduction, ideally incorporating exercise, is paramount. The association between metabolic syndrome, type-2 diabetes and OA risk or progression may partly explain the apparent benefit of dietary-lipid modification resulting from increased consumption of long-chain omega-3 fatty-acids from oily fish/fish oil supplements. A strong association between OA and raised serum cholesterol together with clinical effects in statin users suggests a potential benefit of reduction of cholesterol by dietary means. Patients should ensure that they meet the recommended intakes for micronutrients such as vitamin K, which has a role in bone/cartilage mineralization. Evidence for a role of vitamin D supplementation in OA is unconvincing.

Site-1 protease regulates skeletal stem cell population and osteogenic differentiation in mice

Site-1 protease (S1P) is a proprotein convertase with essential functions in the conversion of precursor proteins to their active form. In earlier studies, we demonstrated that S1P ablation in the chondrocyte lineage results in a drastic reduction in endochondral bone formation. To investigate the mechanistic contribution of S1P to bone development we ablated S1P in the osterix lineage in mice. S1P ablation in this lineage results in osteochondrodysplasia and variable degrees of early postnatal scoliosis. Embryonically, even though Runx2 and osterix expression are normal, S1P ablation results in a delay in vascular invasion and endochondral bone development. Mice appear normal when born, but by day 7 display pronounced dwarfism with fragile bones that exhibit significantly reduced mineral density, mineral apposition rate, bone formation rate and reduced osteoblasts indicating severe osteopenia. Mice suffer from a drastic reduction in bone marrow mesenchymal progenitors as analyzed by colony-forming unit-fibroblast assay. Fluorescence-activated cell sorting analysis of the skeletal mesenchyme harvested from bone marrow and collagenase-digested bone show a drastic reduction in hematopoietic lineage-negative, endothelial-negative, CD105⁺ skeletal stem cells. Bone marrow mesenchymal progenitors are unable to differentiate into osteoblasts in vitro, with no effect on adipogenic differentiation. Postnatal mice have smaller growth plates with reduced hypertrophic zone. Thus, S1P controls bone development directly by regulating the skeletal progenitor population and their differentiation into osteoblasts.

This article has an associated First Person interview with the first author of the paper.

Summary: S1P governs a fundamental aspect of skeletal development and homeostasis, mainly the maintenance and osteogenic differentiation of skeletogenic stem cells that are a source of osteoblast and chondrocyte lineages.

Emerging Players at the Intersection of Chondrocyte Loss of Maturational Arrest, Oxidative Stress, Senescence and Low-Grade Inflammation in Osteoarthritis

The prevalence of Osteoarthritis (OA) is increasing because of the progressive aging and unhealthy lifestyle. These risk factors trigger OA by removing constraints that keep the tightly regulated low turnover of the extracellular matrix (ECM) of articular cartilage, the correct chondrocyte phenotype, and the functionality of major homeostatic mechanisms, such as mitophagy, that allows for the clearance of dysfunctional mitochondria, preventing increased production of reactive oxygen species, oxidative stress, and senescence. After OA onset, the presence of ECM degradation products is perceived as a “danger” signal by the chondrocytes and the synovial macrophages that release alarmins with autocrine/paracrine effects on the same cells. Alarmins trigger innate immunity in the joint, with important systemic crosstalks that explain the beneficial effects of dietary interventions and improved lifestyle. Alarmins also boost low-grade inflammation: the release of inflammatory molecules and chemokines sustained by continuous triggering of NF-κB within an altered cellular setting that allows its higher transcriptional activity. Chemokines exert pleiotropic functions in OA, including the recruitment of inflammatory cells and the induction of ECM remodeling. Some chemokines have been successfully targeted to attenuate structural damage or pain in OA animal models. This represents a promising strategy for the future management of human OA.

Association of SREBP2 gene polymorphisms with the risk of osteonecrosis of the femoral head relates to gene expression and lipid metabolism disorders

Although lipid metabolism disorders have been recognized as a primary factor of osteonecrosis of the femoral head (ONFH), the molecular pathogenesis remains unclear. Sterol regulatory element‑binding protein 2 (SREBP2) specifically regulates cholesterol and fatty acid metabolism to maintain lipid homeostasis. To explore the roles of the SREBP2 gene in the development of ONFH, the authors analyzed the gene polymorphism and gene expression of three tag single nucleotide polymorphisms of the SREBP2 gene, the serum lipids levels, and their associations with ONFH development in 182 ONFH patients and 179 healthy controls. The results demonstrated that the stage IV proportions of ONFH patients carrying the rs2267439CT or CC genotype were significantly higher and lower than the stage III proportions of ONFH patients (P=0.039), respectively. The serum triglyceride, low‑density lipoprotein (LDL)‑c levels, and LDL‑C/high‑density lipoprotein (HDL)‑C ratio in the ONFH group were significantly increased compared to those in the control group (P=0.01, P=0.005, P=0.0001) while the HDL‑C level of ONFH group was remarkably lower than that of the control group (P=0.0001). Association analysis further revealed that the LDL‑c levels of the rs226744 GG and AG genotype carriers were statistically higher than that of the AA genotype carriers (P=0.039, P=0.05). These results demonstrated that the gene polymorphism of SREBP2 not only significantly associated with the clinical phenotypes of ONFH but also closely related to lipid metabolism disorder. The results indicated that SREBP2 gene polymorphism and function may play key roles in the development of ONFH.

The Role of miRNAs in Common Inflammatory Arthropathies: Osteoarthritis and Gouty Arthritis

MicroRNAs (miRNAs) are small, non-coding RNA species that are highly evolutionarily conserved, from higher invertebrates to man. Up to 1000 miRNAs have been identified in human cells thus far, where they are key regulators of the expression of numerous targets at the post-transcriptional level. They are implicated in various processes, including cell differentiation, metabolism, and inflammation. An expanding list of miRNAs is known to be involved in the pathogenesis of common, non-autoimmune inflammatory diseases. Interestingly, osteoarthritis (OA) is now being conceptualized as a metabolic disease, as there is a correlation among hyperuricemia and metabolic syndrome (MetS). Experimental evidence suggests that metabolic deregulation is a commonality between these different pathological entities, and that miRNAs are key players in the modulation of metabolic routes. In light of these findings, this review discusses the role of miRNAs in OA and gouty arthritis, as well as the possible therapeutic targetability of miRNAs in these diseases.

Bicoronal and metopic craniosynostosis in association with a de novo unbalanced t(2;7) chromosomal translocation

We report the case of a developmentally appropriate infant male with a de novo unbalanced chromosome translocation involving bands 2q32.1 and 7p21.3. The child was noted to have metopic and bicoronal craniosynostosis with closely spaced eyes, turricephaly, and flattening of the forehead. © 2016 Wiley Periodicals, Inc.

Effects of SIRT1 gene knock-out via activation of SREBP2 protein-mediated PI3K/AKT signaling on osteoarthritis in mice

This study investigated the effects of SIRT1 gene knock-out on osteoarthritis in mice, and the possible roles of SREBP2 protein and the PI3K/AKT signaling pathway in the effects. Mice were randomly divided into a normal group and a SIRT1 gene knock-out group (6 mice in each group). In these groups, one side of the knee anterior cruciate ligament was traversed, and the ipsilateral medial meniscus was cut to establish an osteoarthritis model of knee joint. The countralateral synovial bursa was cut out, serving as controls. The knee joint specimens were then divided into four groups: SIRT1+/+ control group (group A, n=6); SIRT1+/+ osteoarthritis group (group B, n=6); SIRT1-/- control group (group C, n=6); SIRT1-/- osteoarthritis group (group D, n=6). HE staining, Masson staining, Safranin O-Fast Green staining and Van Gieson staining were used to observe the morphological changes in the articular cartilage of the knee. Immunohistochemical staining was employed to detect the expression of SIRT1, SREBP2, VEGF, AKT, HMGCR and type II collagen proteins. SA-β-gal staining was utilized to evaluate chondrocyte aging. The results showed clear knee joint cartilage destruction and degeneration in the SIRT1-/- osteoarthritis group. The tidal line was twisted and displaced anteriorly. Type II collagen was destroyed and distributed unevenly. Compared with the SIRT1+/+ osteoarthritis group and SIRT1-/- control group, SIRT1 protein expression was not obviously changed in the SIRT1-/- osteoarthritis group (P>0.05), while the expression levels of the SREBP2, VEGF and HMGCR proteins were significantly increased (P<0.05) and the levels of AKT and type II collagen proteins were significantly decreased (P<0.05). SIRT1 gene knock-out may aggravate cartilage degeneration in osteoarthritis by activating the SREBP2 protein-mediated PI3K/AKT signalling pathway, suggesting that SIRT1 gene may play a protective role against osteoarthritis.

The Role of MicroRNAs and Their Targets in Osteoarthritis

Micro ribonucleic acid (microRNA) regulation and expression has become an emerging field in determining the mechanisms regulating a variety of inflammation-mediated diseases. Several studies have focused on specific microRNAs that are differentially expressed in cases of osteoarthritis. Furthermore, several targets of these miRNAs important in disease progression have also been identified. In this review, we focus on microRNA biogenesis, regulation, detection, and quantification with an emphasis on cellular localization and how these concepts may be linked to disease processes such as osteoarthritis. Next, we review the relationships of specific microRNAs to certain features and risk factors associated with osteoarthritis such as inflammation, obesity, autophagy, and cartilage homeostasis. We also identify certain microRNAs that are differentially expressed in osteoarthritis but have unidentified targets and functions in the disease state. Lastly, we identify the potential use of microRNAs for therapeutic purposes and also mention certain remedies that regulate microRNA expression.

Regulation of Cholesterol Homeostasis by Hedgehog Signaling in Osteoarthritic Cartilage

Objective

With no effective therapies to attenuate cartilage degeneration in osteoarthritis (OA), the result is pain and disability. Activation of hedgehog (HH) signaling causes changes related to the progression of OA, with higher levels of Gli‐mediated transcriptional activation associated with increased disease severity. To elucidate the mechanism through which this occurs, this study sought to identify genes regulated by HH signaling in human OA chondrocytes.

Methods

Using human OA cartilage samples, microarray analyses were performed to detect changes in gene expression when the HH pathway was modulated. Results were analyzed for differentially expressed genes, grouped into functional networks, and validated in independent samples. To investigate the effects of chondrocyte‐specific sterol accumulation, we generated mice lacking Insig1 and Insig2, which are major negative regulators of cholesterol homeostasis, under Col2a1 regulatory elements.

Results

HH signaling was found to regulate genes that govern cholesterol homeostasis, and this led to alterations in cholesterol accumulation in chondrocytes. A higher level of Gli‐mediated transcription resulted in accumulation of intracellular cholesterol. In genetically modified mice, chondrocyte‐specific cholesterol accumulation was associated with an OA phenotype. Reducing cholesterol accumulation attenuated the severity of OA in mice in vivo and decreased the expression of proteases in human OA cartilage in vitro.

Conclusion

HH signaling regulates cholesterol homeostasis in chondrocytes, and intracellular cholesterol accumulation contributes to the severity of OA. Our findings have therapeutic implications, since reduction of HH signaling reversed cholesterol accumulation and statin treatment attenuated cartilage degeneration.

Identification of novel osteochondrosis--Associated genes

During the early stages of articular osteochondrosis, cartilage is retained in subchondral bone, but the pathophysiology of this condition of growing humans and domestic animals is poorly understood. A subtractive hybridization study was undertaken to compare gene expression between the cartilage of early experimentally induced equine osteochondrosis lesions and control cartilage. Of the many putative differentially expressed genes identified, eight were confirmed by quantitative PCR analysis as differentially expressed, in addition to those already known to be associated with early lesions. Genes encoding vacuolar H(+)-ATPase V0 subunit d2 (ATP6V0D2), cathepsin K, integrin-binding sialoprotein, integrin αV, low density lipoprotein receptor-related protein 4, lumican, osteopontin, and thymosin β4 (TMSB4) were expressed at higher levels in lesions than in control cartilage. These genes included 34 genes not previously identified in cartilage. Some genes identified as associated with early lesions are known chondrocyte hypertrophy-associated genes, and in transmission electron microscopy studies normal hypertrophic chondrocytes were observed in lesions. Differential expression of ATP6V0D2 and TMSB4 in the cartilage of early naturally occurring osteochondrosis lesions was confirmed by immunohistochemistry. These results identify novel osteochondrosis-associated genes and provide evidence that articular osteochondrosis does not necessarily result from failure of chondrocytes to undergo hypertrophy.

Prenatal caffeine exposure induces a poor quality of articular cartilage in male adult offspring rats via cholesterol accumulation in cartilage

Epidemiological investigations indicate that osteoarthritis is associated with intrauterine growth retardation (IUGR) and abnormal cholesterol metabolism. Our previous studies showed that prenatal caffeine exposure (PCE) induced chondrogenesis retardation in IUGR offspring rats. The current study sought to investigate the effects of PCE on male IUGR offspring rats’ articular cartilage, and the mechanisms associated with abnormal cholesterol metabolism. Based on the results from both male fetal and adult fed a high-fat diet (HFD) studies of rats that experienced PCE (120 mg/kg.d), the results showed a poor quality of articular cartilage and cholesterol accumulation in the adult PCE group. Meanwhile, the serum total cholesterol and low-density lipoprotein-cholesterol concentrations were increased in adult PCE offspring. We also observed lower expression of insulin-like growth factor1 (IGF1) and impaired cholesterol efflux in adult articular cartilage. Furthermore, the expression of cartilage functional genes, components of the IGF1 signaling pathway and cholesterol efflux pathway related genes were decreased in PCE fetal cartilage. In conclusion, PCE induced a poor quality of articular cartilage in male adult offspring fed a HFD. This finding was shown to be due to cholesterol accumulation in the cartilage, which may have resulted from intrauterine reduced activity of the IGF1 signaling pathway.

Association between single nucleotide polymorphisms of sterol regulatory element binding protein-2 and liver X receptor α gene and risk of polycystic ovary syndrome in a Chinese Han population

To investigate associations of single nucleotide polymorphisms (SNPs) rs2228314 of sterol regulatory element-binding protein-2 (SREBP-2) or rs11039155 of liver X receptor α (LXRα) with susceptibility to polycystic ovary syndrome (PCOS) in a Chinese Han population. SREBP-2 rs2228314 and LXRα rs11039155 polymorphisms were genotyped in patients with PCOS and age- and sex-matched PCOS-free controls from a Chinese Han population. A total of 605 patients with PCOS and 615 controls were recruited in this study. We found that GC and CC genotypes of rs2228314, and variant C, were associated with a significantly increased risk of PCOS. In addition, GA and AA genotypes of rs11039155, as well as variant A, were also associated with a significantly increased risk of PCOS. Our results showed that SREBP-2 rs2228314 G to C change and variant C genotype as well as LXRα rs11039155 G to A change and variant A may contribute to PCOS in Chinese Han population.

Comparative proteomic analysis of hypertrophic chondrocytes in osteoarthritis

Background

Osteoarthritis (OA) is a multi-factorial disease leading progressively to loss of articular cartilage and subsequently to loss of joint function. While hypertrophy of chondrocytes is a physiological process implicated in the longitudinal growth of long bones, hypertrophy-like alterations in chondrocytes play a major role in OA. We performed a quantitative proteomic analysis in osteoarthritic and normal chondrocytes followed by functional analyses to investigate proteome changes and molecular pathways involved in OA pathogenesis.

Methods

Chondrocytes were isolated from articular cartilage of ten patients with primary OA undergoing knee replacement surgery and six normal donors undergoing fracture repair surgery without history of joint disease and no OA clinical manifestations. We analyzed the proteome of chondrocytes using high resolution mass spectrometry and quantified it by label-free quantification and western blot analysis. We also used WebGestalt, a web-based enrichment tool for the functional annotation and pathway analysis of the differentially synthesized proteins, using the Wikipathways database. ClueGO, a Cytoscape plug-in, is also used to compare groups of proteins and to visualize the functionally organized Gene Ontology (GO) terms and pathways in the form of dynamical network structures.

Results

The proteomic analysis led to the identification of a total of ~2400 proteins. 269 of them showed differential synthesis levels between the two groups. Using functional annotation, we found that proteins belonging to pathways associated with regulation of the actin cytoskeleton, EGF/EGFR, TGF-β, MAPK signaling, integrin-mediated cell adhesion, and lipid metabolism were significantly enriched in the OA samples (p ≤10⁻⁵). We also observed that the proteins GSTP1, PLS3, MYOF, HSD17B12, PRDX2, APCS, PLA2G2A SERPINH1/HSP47 and MVP, show distinct synthesis levels, characteristic for OA or control chondrocytes.

Conclusion

In this study we compared the quantitative changes in proteins synthesized in osteoarthritic compared to normal chondrocytes. We identified several pathways and proteins to be associated with OA chondrocytes. This study provides evidence for further testing on the molecular mechanism of the disease and also propose proteins as candidate markers of OA chondrocyte phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-015-9085-6) contains supplementary material, which is available to authorized users.

Emerging targets in osteoarthritis therapy

Osteoarthritis (OA) is a destructive joint disease in which the initiation may be attributed to direct injury and mechanical disruption of joint tissues, but the progressive changes are dependent on active cell-mediated processes that can be observed or inferred during the generally long time-course of the disease. Based on clinical observations and experimental studies, it is now recognized a that it is possible for individual patients to exhibit common sets of symptoms and structural abnormalities due to distinct pathophysiological pathways that act independently or in combination. Recent research that has focused on the underlying mechanisms involving biochemical cross talk among the cartilage, synovium, bone, and other joint tissues within a background of poorly characterized genetic factors will be addressed in this review.

MicroRNA-33a regulates cholesterol synthesis and cholesterol efflux-related genes in osteoarthritic chondrocytes

Introduction

Several studies have shown that osteoarthritis (OA) is strongly associated with metabolism-related disorders, highlighting OA as the fifth component of the metabolic syndrome (MetS). On the basis of our previous findings on dysregulation of cholesterol homeostasis in OA, we were prompted to investigate whether microRNA-33a (miR-33a), one of the master regulators of cholesterol and fatty acid metabolism, plays a key role in OA pathogenesis.

Methods

Articular cartilage samples were obtained from 14 patients with primary OA undergoing total knee replacement surgery. Normal cartilage was obtained from nine individuals undergoing fracture repair surgery. Bioinformatics analysis was used to identify miR-33a target genes. miR-33a and sterol regulatory element-binding protein 2 (SREBP-2) expression levels were investigated using real-time PCR, and their expression was also assessed after treatment with transforming growth factor-β1 (TGF-β1) in cultured chondrocytes. Akt phosphorylation after treatment with both TGF-β1 and miR-33a inhibitor or TGF-β1 and miR-33a mimic was assessed by Western blot analysis. Furthermore, we evaluated the effect of miR-33a mimic and miR-33a inhibitor on Smad7, a negative regulator of TGF-β signaling, on cholesterol efflux-related genes, ATP-binding cassette transporter A1 (ABCA1), apolipoprotein A1 (ApoA1) and liver X receptors (LXRα and LXRβ), as well as on matrix metalloproteinase-13 (MMP-13), using real-time PCR.

Results

We found that the expression of miR-33a and its host gene SREBP-2 was significantly elevated in OA chondrocytes compared with normal chondrocytes. Treatment of cultured chondrocytes with TGF-β1 resulted in increased expression of both miR-33a and SREBP-2, as well as in rapid induction of Akt phosphorylation, whereas TGF-β-induced Akt phosphorylation was enhanced by miR-33a and suppressed by inhibition of miR-33a, as a possible consequence of Smad7 regulation by miR-33a. Moreover, treatment of normal chondrocytes with miR-33a resulted in significantly reduced ABCA1 and ApoA1 mRNA expression levels and significantly elevated MMP-13 expression levels, promoting the OA phenotype, whereas miR-33a’s suppressive effect was reversed using its inhibitor.

Conclusions

Our findings suggest, for the first time to our knowledge, that miR-33a regulates cholesterol synthesis through the TGF-β1/Akt/SREBP-2 pathway, as well as cholesterol efflux-related genes ABCA1 and ApoA1, in OA chondrocytes, pointing to its identification as a novel target for ameliorating the OA phenotype.

Association of MMP-1 -1607 1G/2G (rs1799750) polymorphism with primary knee osteoarthritis in the Greek population

Osteoarthritis is the most common form of arthritis with still unknown pathogenic etiology and considerable contribution of genetic factors. One of the mechanisms of cartilage degradation in osteoarthritis is enzymatic proteolysis of the extracellular matrix by metalloproteinases. MMP-1, produced by chondrocytes and synovial cells, is a major proteinase of the MMPs family. The present study aims at evaluating the association of MMP1 gene -1607 1G/2G (rs1799750) polymorphism with primary knee osteoarthritis in the Greek population. One hundred fifty five patients with primary symptomatic knee osteoarthritis participated in the study along with 139 controls. Genotypes were determined using PCR-RLFP technique. Allelic and genotypic frequencies were compared between both study groups. There was no significant association between MMP1 -1607 1G/2G polymorphism and knee osteoarthritis, in crude analysis; however, after multiple logistic regression analysis, 1G/2G was associated with reduced odds of knee osteoarthritis by 75% in males, compared to genotypes 1G/1G + 2G/2G, adjusting for age and BMI (adjusted OR: 0.25, 95% CI: 0.069, 0.910, p = 0.035). The present study shows that MMP1 -1607 1G/2G (rs1799750) polymorphism might be a risk factor for knee osteoarthritis susceptibility in the Greek population. Further investigations are needed to confirm this association in the pathogenesis of osteoarthritis.

Assessment of osteoarthritis candidate genes in a meta-analysis of nine genome-wide association studies

Objective

To assess candidate genes for association with osteoarthritis (OA) and identify promising genetic factors and, secondarily, to assess the candidate gene approach in OA.

Methods

A total of 199 candidate genes for association with OA were identified using Human Genome Epidemiology (HuGE) Navigator. All of their single-nucleotide polymorphisms (SNPs) with an allele frequency of >5% were assessed by fixed-effects meta-analysis of 9 genome-wide association studies (GWAS) that included 5,636 patients with knee OA and 16,972 control subjects and 4,349 patients with hip OA and 17,836 control subjects of European ancestry. An additional 5,921 individuals were genotyped for significantly associated SNPs in the meta-analysis. After correction for the number of independent tests, P values less than 1.58 × 10⁻⁵ were considered significant.

Results

SNPs at only 2 of the 199 candidate genes (COL11A1 and VEGF) were associated with OA in the meta-analysis. Two SNPs in COL11A1 showed association with hip OA in the combined analysis: rs4907986 (P = 1.29 × 10⁻⁵, odds ratio [OR] 1.12, 95% confidence interval [95% CI] 1.06−1.17) and rs1241164 (P = 1.47 × 10⁻⁵, OR 0.82, 95% CI 0.74−0.89). The sex-stratified analysis also showed association of COL11A1 SNP rs4908291 in women (P = 1.29 × 10⁻⁵, OR 0.87, 95% CI 0.82−0.92); this SNP showed linkage disequilibrium with rs4907986. A single SNP of VEGF, rs833058, showed association with hip OA in men (P = 1.35 × 10⁻⁵, OR 0.85, 95% CI 0.79−0.91). After additional samples were genotyped, association at one of the COL11A1 signals was reinforced, whereas association at VEGF was slightly weakened.

Conclusion

Two candidate genes, COL11A1 and VEGF, were significantly associated with OA in this focused meta-analysis. The remaining candidate genes were not associated.

An intron polymorphism of the fibronectin gene is associated with end-stage knee osteoarthritis in a Han Chinese population: two independent case-control studies

Background

Knee osteoarthritis (OA) is a complex disease involving both biomechanical and metabolic factors that alter the tissue homeostasis of articular cartilage and subchondral bone. The catabolic activities of extracellular matrix degradation products, especially fibronectin (FN), have been implicated in mediating cartilage degradation. Chondrocytes express several members of the integrin family which can serve as receptors for FN including integrins α5β1, αvβ3, and αvβ5. The purpose of this study was to determine whether polymorphisms in the FN (FN-1) and integrin genes are markers of susceptibility to, or severity of, knee OA in a Han Chinese population.

Methods

Two independent case–control studies were conducted on 928 patients with knee OA and 693 healthy controls. Ten single nucleotide polymorphisms (SNPs) of FN-1 and the integrin αV gene (ITGAV) were detected using the ABI 7500 real-time PCR system.

Results

The AT heterozygote in FN-1 (rs940739A/T) was found to be significantly associated with knee OA (adjusted OR = 1.44; 95% CI = 1.16–1.80) in both stages of the study. FN-1 rs6725958C/A and ITGAV rs10174098A/G SNPs were only associated with knee OA when both study groups were combined. Stratifying the participants by Kellgren-Lawrence (KL) score identified significant differences in the FN-1 rs6725958C/A and rs940739 A/T genotypes between patients with grade 4 OA and controls. Haplotype analyses revealed that TGA and TAA were associated with a higher risk of OA, and that TAG conferred a lower risk of knee OA in the combined population.

Conclusions

Our study suggests that the FN-1 rs940739A/T polymorphism may be an important risk factor of genetic susceptibility to knee OA in the Han Chinese population.

Association between single nucleotide polymorphisms of sterol regulatory element binding protein-2 gene and risk of knee osteoarthritis in a Chinese Han population

OBJECTIVE

To investigate associations between single nucleotide polymorphisms (SNPs) rs2228314 and rs2267443 in the sterol regulatory element binding protein-2 gene (SREBP-2) and knee osteoarthritis (OA) susceptibility in a Chinese Han population.

METHODS

SREBP-2 rs2228314 and rs2267443 polymorphisms were genotyped in patients with knee OA and age- and sex-matched OA-free controls from a Chinese Han population.

RESULTS

A total of 402 patients with knee OA and 410 controls were enrolled in the study. GC and CC genotypes of rs2228314, and variant C, were associated with a significantly increased risk of knee OA. On stratification analysis, the association between the risk of OA and rs2228314 GC heterozygotes compared with GG homozygotes was stronger in females and those aged >65 years. In contrast, the GA and AA genotypes of rs2267443 were not significantly associated with the risk of knee OA, even after further stratification analysis according to age or sex.

CONCLUSIONS

SREBP-2 rs2228314 G to C change and variant C genotype may contribute to knee OA risk in a Chinese Han population.

Profibrotic effect of miR-33a with Akt activation in hepatic stellate cells

MicroRNAs (miRNAs) attract more attention in the pathophysiology of liver fibrosis and miR-33a has been previously demonstrated as involved in the regulation of cholesterol and lipid metabolism. Transforming growth factor-beta1 (TGF-β1) is generally accepted to be the main stimulating factor in the hepatic stellate cells (HSCs) activation, which plays an important role in hepatic fibrosis. However, the involvement and underlying mechanism of miR-33a and its role in TGF-β1-induced hepatic fibrogenesis remains unknown. Here, we investigate the role of miR-33a in the activation of immortalized human HSCs, Lx-2 cells. Our findings have shown that the expression of miR-33a with its host gene sterol regulatory element-binding protein 2 (SREBP2) was more highly expressed in activation of Lx-2 cells than in quiescent cells. The expression of miR-33a on TGF-β1-induced HSCs activation may be modulated via the activation of PI3K/Akt pathway. In addition, miR-33a significantly correlated with TGF-β1-induced expression of α1 (I) collagen (Col1A1) and α-SMA in HSCs. Bioinformatics analyses predict that peroxisome proliferator activated receptor-alpha (PPAR-α) is the potential target of miR-33a. We further found that anti-miR-33a significantly increases target gene PPAR-α mRNA and protein level, suggesting that miR-33a involved in HSCs function might be modulated by targeting PPAR-α. Finally, our results indicate that the expression of miR-33a increased with the progression of liver fibrosis. These results suggested that anti-miR-33a inhibit activation and extracellular matrix production, at least in part, via the activation of PI3K/Akt pathway and PPAR-α and anti sense of miR-33a may be a novel potential therapeutic approach for treating hepatic fibrosis in the future.

Osteoarthritis year 2013 in review: genetics and genomics

Progress in genetic research has delivered important highlights in the last year. One of the widest impact is the publication of the Encyclopedia of DNA Elements (ENCODE) project showing the impressive complexity of the human genome and providing information useful for all areas of genetics. More specific of osteoarthritis (OA) has been the incorporation of DOT1-like, histone H3 methyltransferase (DOT1L) to the list of 11 OA loci with genome-wide significant association, the demonstration of significant overlap between OA genetics and height or body mass index (BMI) genetics, and the tentative prioritization of HMG-box transcription factor 1 (HBP1) in the 7q22 locus based on functional analysis. In addition, the first large scale analysis of DNA methylation has found modest differences between OA and normal cartilage, but has identified a subgroup of OA patients with a very differentiated phenotype. The role of DNA methylation in regulation of NOS2, SOX9, MMP13 and IL1B has been further clarified. MicroRNA expression studies in turn have shown some replication of differences between OA and control cartilage from previous profiling studies and have identified potential regulators of TGFβ signaling and of IL1β effects. In addition, non-coding RNAs showed promising results as serum biomarkers of cartilage damage. Gene expression microarray studies have found important differences between studies of hip or knee OA that reinforce the idea of joint specificity in OA. Expression differences between articular cartilage and other types of cartilage highlighted the WNT pathway whose regulation is proposed as critical for maintaining the articular cartilage phenotype. Many of these results need confirmation but they signal the exciting progress that is taking place in all areas of OA genetics, indicate questions requiring more study and augur further interesting discoveries.

Osteoarthritis year 2013 in review: biomarkers; reflecting before moving forward, one step at a time

In 2010, in Osteoarthritis and Cartilage, we published a comprehensive systematic review applying the consensus BIPED criteria (Burden of Disease, Investigative, Prognostic, Efficacy of Intervention and Diagnostic) criteria on serum and urinary biochemical markers for knee and hip osteoarthritis (OA) using publications that were available at that time. It appeared that none of the biochemical markers at that time were sufficiently discriminating to allow diagnosis and prognosis of OA in individual or limited numbers of patients, nor performed so consistently that they could function as primary outcome parameters in clinical trials. Also at present, almost 3 years later, this ultimate goal has not been reached (yet). Frankly, it might be questioned whether we are making the most adequate steps ahead and maybe we have to take a step back to reconsider our approaches. Some reflections are made and discussed: A critical review of molecular metabolism in OA and validation of currently investigated marker molecules in this may be vital and may lead to new and better markers. Creating cohorts in which synovial fluid (SF) is obtained in a systematic way, together with serum and urine, may also bring the field a further step ahead. Thirdly, better understanding of different phenotypes (subtypes) of OA may facilitate identification and validation of biochemical markers. Finally, the systems biology approach as discussed in the last years OA in review on biomarkers, although very complex, might provide steps forward. Looking ahead, we are optimistic but realistic in our expectations, we believe that the field can be brought forward by critically and cautiously reconsidering our approaches, and making changes forward, one step at a time.

The genetics and functional analysis of primary osteoarthritis susceptibility

Recent genome-wide association scans (GWASs) along with several adequately powered candidate gene studies have yielded a number of risk alleles for osteoarthritis (OA). This number is now sufficiently large to allow conclusions to be drawn regarding the nature of genetic susceptibility, including the fact that the risk alleles have variable effects depending on sex, ethnicity and on the skeletal site of the disease. Several of the alleles that have emerged from the GWASs are within or close to highly plausible candidate genes, including RUNX2 and CHST11. However, the majority of risk alleles do not map to genes previously reported to play a role in musculoskeletal biology, indicating that the GWAS datasets are telling us something new about the OA disease process. Functional studies have so far revealed that effects on gene expression are likely to be one of the main mechanisms through which OA susceptibility is acting. Epigenetic mechanisms such as DNA methylation also influence OA risk, and integration of genetic, transcriptomic and epigenetic data will allow us to use the genetic discoveries for informed development of new OA biological treatments.

Migfilin's elimination from osteoarthritic chondrocytes further promotes the osteoarthritic phenotype via β-catenin upregulation

Osteoarthritis (OA) is a debilitating disease of the joints characterized by cartilage degradation but to date there is no available pharmacological treatment to inhibit disease progression neither is there any available biomarker to predict its development. In the present study, we examined the expression level and possible involvement of novel cell-ECM adhesion-related molecules such as Iintegrin Linked Kinase (ILK), PINCH, parvin, Mig-2 and Migfilin in OA pathogenesis using primary human articular chondrocytes from healthy individuals and OA patients. Our findings show that only ILK and Migfilin were upregulated in OA compared to the normal chondrocytes. Interestingly, Migfilin silencing in OA chondrocytes rather exacerbated than ameliorated the osteoarthritic phenotype, as it resulted in even higher levels of catabolic and hypertrophic markers while at the same time induced reduction in ECM molecules such as aggrecan. Furthermore, we also provide a link between Migfilin and β-catenin activation in OA chondrocytes, showing Migfilin to be inversely correlated with β-catenin. Thus, the present study emphasizes for the first time to our knowledge the role of Migfilin in OA and highlights the importance of cell-ECM adhesion proteins in OA pathogenesis.