Expression of TGF-β Signaling Regulator RBPMS (RNA-Binding Protein With Multiple Splicing) Is Regulated by IL-1β and TGF-β Superfamily Members, and Decreased in Aged and Osteoarthritic Cartilage

Emerging roles of RNA binding proteins in intervertebral disc degeneration and osteoarthritis

The etiology of intervertebral disc degeneration (IDD) and osteoarthritis (OA) is complex and multifactorial. Both predisposing genes and environmental factors are involved in the pathogenesis of IDD and OA. Moreover, epigenetic modifications affect the development of IDD and OA. Dysregulated phenotypes of nucleus pulposus (NP) cells and OA chondrocytes, including apoptosis, extracellular matrix disruption, inflammation, and angiogenesis, are involved at all developmental stages of IDD and OA. RNA binding proteins (RBPs) have recently been recognized as essential post-transcriptional regulators of gene expression. RBPs are implicated in many cellular processes, such as proliferation, differentiation, and apoptosis. Recently, several RBPs have been reported to be associated with the pathogenesis of IDD and OA. This review briefly summarizes the current knowledge on the RNA-regulatory networks controlled by RBPs and their potential roles in the pathogenesis of IDD and OA. These initial findings support the idea that specific modulation of RBPs represents a promising approach for managing IDD and OA.

TGF-β as A Master Regulator of Aging-Associated Tissue Fibrosis

Fibrosis is the abnormal accumulation of extracellular matrix proteins such as collagen and fibronectin. Aging, injury, infections, and inflammation can cause different types of tissue fibrosis. Numerous clinical investigations have shown a correlation between the degree of liver and pulmonary fibrosis in patients and telomere length and mitochondrial DNA content, both of which are signs of aging. Aging involves the gradual loss of tissue function over time, which results in the loss of homeostasis and, ultimately, an organism's fitness. A major feature of aging is the accumulation of senescent cells. Senescent cells abnormally and continuously accumulate in the late stages of life, contributing to age-related fibrosis and tissue deterioration, among other aging characteristics. Furthermore, aging generates chronic inflammation, which results in fibrosis and decreases organ function. This finding suggests that fibrosis and aging are closely related. The transforming growth factor-beta (TGF-β) superfamily plays a crucial role in the physiological and pathological processes of aging, immune regulation, atherosclerosis, and tissue fibrosis. In this review, the functions of TGF-β in normal organs, aging, and fibrotic tissues is discussed: TGF-β signalling is altered with age and is an indicator of pathology associated with tissue fibrosis. In addition, this review discusses the potential targeting of noncoding.

RNA-binding proteins that are highly expressed and enriched in healthy cartilage but suppressed in osteoarthritis

Objectives: RNA-binding proteins (RBPs) have diverse and essential biological functions, but their role in cartilage health and disease is largely unknown. The objectives of this study were (i) map the global landscape of RBPs expressed and enriched in healthy cartilage and dysregulated in osteoarthritis (OA); (ii) prioritize RBPs for their potential role in cartilage and in OA pathogenesis and as therapeutic targets. Methods: Our published bulk RNA-sequencing (RNA-seq) data of healthy and OA human cartilage, and a census of 1,542 RBPs were utilized to identify RBPs that are expressed in healthy cartilage and differentially expressed (DE) in OA. Next, our comparison of healthy cartilage RNA-seq data to 37 transcriptomes in the Genotype-Tissue Expression (GTEx) database was used to determine RBPs that are enriched in cartilage. Finally, expression of RBPs was analyzed in our single cell RNA-sequencing (scRNA-seq) data from healthy and OA human cartilage. Results: Expression of RBPs was higher than nonRBPs in healthy cartilage. In OA cartilage, 188 RBPs were differentially expressed, with a greater proportion downregulated. Ribosome biogenesis was enriched in the upregulated RBPs, while splicing and transport were enriched in the downregulated. To further prioritize RBPs, we selected the top 10% expressed RBPs in healthy cartilage and those that were cartilage-enriched according to GTEx. Intersecting these criteria, we identified Tetrachlorodibenzodioxin (TCDD) Inducible Poly (ADP-Ribose) Polymerase (TIPARP) as a candidate RBP. TIPARP was downregulated in OA. scRNA-seq data revealed TIPARP was most significantly downregulated in the "pathogenic cluster". Conclusion: Our global analyses reveal expression patterns of RBPs in healthy and OA cartilage. We also identified TIPARP and other RBPs as novel mediators in OA pathogenesis and as potential therapeutic targets.

Deciphering the role of lipoproteins and lipid metabolic alterations in ageing and ageing-associated renal fibrosis

Fibrosis is the ultimate pathological feature of many chronic diseases, and ageing a major risk factor for fibrotic diseases. Current therapies are limited to those that reduce the rate of functional decline in patients with mild to moderate disease, but few interventions are available to specifically target the pathogenesis of fibrosis. In this context, new treatments that can significantly improve survival time and quality of life for these patients are urgently needed. In this review, we outline both the synthesis and metabolism of lipids and lipoproteins associated with ageing-associated renal fibrosis and the prominent contribution of lipids and lipidomics in the discovery of biomarkers that can be used for the prevention, diagnosis, and treatment of renal ageing and fibrosis. Next, we describe the effect of dyslipidaemia on ageing-related renal fibrosis and the pathophysiological changes in the kidney caused by dyslipidaemia. We then summarize the enzymes, transporters, transcription factors, and RNAs that contribute to dysregulated lipid metabolism in renal fibrosis and discuss their role in renal fibrosis in detail. We conclude by discussing the progress in research on small molecule therapeutic agents that prevent and treat ageing and ageing-associated renal fibrosis by modulating lipid metabolism. A growing number of studies suggest that restoring aberrant lipid metabolism may be a novel and promising therapeutic strategy to combat ageing and ageing-associated renal fibrosis.

Increased Expression of the RBPMS Splice Variants Inhibits Cell Proliferation in Ovarian Cancer Cells

RNA-Binding Protein with Multiple Splicing (RBPMS) is a member of family proteins that bind to nascent RNA transcripts and regulate their splicing, localization, and stability. Evidence indicates that RBPMS controls the activity of transcription factors associated with cell growth and proliferation, including AP-1 and Smads. Three major RBPMS protein splice variants (RBPMSA, RBPMSB, and RBPMSC) have been described in the literature. We previously reported that reduced RBPMS levels decreased the sensitivity of ovarian cancer cells to cisplatin treatment. However, little is known about the biological role of the RBPMS splice variants in ovarian cancer cells. We performed RT-PCR and Western blots and observed that both RBPMSA and RBPMSC are reduced at the mRNA and protein levels in cisplatin resistant as compared with cisplatin sensitive ovarian cancer cells. The mRNA and protein levels of RBPMSB were not detectable in any of the ovarian cancer cells tested. To better understand the biological role of each RBPMSA and RBPMSC, we transfected these two splice variants in the A2780CP20 and OVCAR3CIS cisplatin resistant ovarian cancer cells and performed cell proliferation, cell migration, and invasion assays. Compared with control clones, a significant reduction in the number of colonies, colony size, cell migration, and invasion was observed with RBPMSA and RBPMSC overexpressed cells. Moreover, A2780CP20-RBPMSA and A2780CP20-RBPMSC clones showed reduced senescence-associated β-galactosidase (β-Gal)-levels when compared with control clones. A2780CP20-RBPMSA clones were more sensitive to cisplatin treatment as compared with A2780CP20-RBPMSC clones. The A2780CP20-RBPMSA and A2780CP20-RBPMSC clones subcutaneously injected into athymic nude mice formed smaller tumors as compared with A2780CP20-EV control group. Additionally, immunohistochemical analysis showed lower proliferation (Ki67) and angiogenesis (CD31) staining in tissue sections of A2780CP20-RBPMSA and A2780CP20-RBPMSC tumors compared with controls. RNAseq studies revealed many common RNA transcripts altered in A2780CP20-RBPMSA and A2780CP20-RBPMSC clones. Unique RNA transcripts deregulated by each RBPMS variant were also observed. Kaplan-Meier (KM) plotter database information identified clinically relevant RBPMSA and RBPMSC downstream effectors. These studies suggest that increased levels of RBPMSA and RBPMSC reduce cell proliferation in ovarian cancer cells. However, only RBPMSA expression levels were associated with the sensitivity of ovarian cancer cells to cisplatin treatment.

RNA binding proteins in osteoarthritis

Osteoarthritis (OA) is a common chronic degenerative joint disease worldwide. The pathological features of OA are the erosion of articular cartilage, subchondral bone sclerosis, synovitis, and metabolic disorder. Its progression is characterized by aberrant expression of genes involved in inflammation, proliferation, and metabolism of chondrocytes. Effective therapeutic strategies are limited, as mechanisms underlying OA pathophysiology remain unclear. Significant research efforts are ongoing to elucidate the complex molecular mechanisms underlying OA focused on gene transcription. However, posttranscriptional alterations also play significant function in inflammation and metabolic changes related diseases. RNA binding proteins (RBPs) have been recognized as important regulators in posttranscriptional regulation. RBPs regulate RNA subcellular localization, stability, and translational efficiency by binding to their target mRNAs, thereby controlling their protein expression. However, their role in OA is less clear. Identifying RBPs in OA is of great importance to better understand OA pathophysiology and to figure out potential targets for OA treatment. Hence, in this manuscript, we summarize the recent knowledge on the role of dysregulated RBPs in OA and hope it will provide new insight for OA study and targeted treatment.

Divalent Metal Transporter 1 Knock-Down Modulates IL-1β Mediated Pancreatic Beta-Cell Pro-Apoptotic Signaling Pathways through the Autophagic Machinery

Pro-inflammatory cytokines promote cellular iron-import through enhanced divalent metal transporter-1 (DMT1) expression in pancreatic β-cells, consequently cell death. Inhibition of β-cell iron-import by DMT1 silencing protects against apoptosis in animal models of diabetes. However, how alterations of signaling networks contribute to the protective action of DMT1 knock-down is unknown. Here, we performed phosphoproteomics using our sequential enrichment strategy of mRNA, protein, and phosphopeptides, which enabled us to explore the concurrent molecular events in the same set of wildtype and DMT1-silenced β-cells during IL-1β exposure. Our findings reveal new phosphosites in the IL-1β-induced proteins that are clearly reverted by DMT1 silencing towards their steady-state levels. We validated the levels of five novel phosphosites of the potential protective proteins using parallel reaction monitoring. We also confirmed the inactivation of autophagic flux that may be relevant for cell survival induced by DMT1 silencing during IL-1β exposure. Additionally, the potential protective proteins induced by DMT1 silencing were related to insulin secretion that may lead to improving β-cell functions upon exposure to IL-1β. This global profiling has shed light on the signal transduction pathways driving the protection against inflammation-induced cell death in β-cells after DMT1 silencing.

Epigenetic analysis of Paget's disease of bone identifies differentially methylated loci that predict disease status

Paget's disease of bone (PDB) is characterized by focal increases in disorganized bone remodeling. This study aims to characterize PDB-associated changes in DNA methylation profiles in patients' blood. Meta-analysis of data from the discovery and cross-validation set, each comprising 116 PDB cases and 130 controls, revealed significant differences in DNA methylation at 14 CpG sites, 4 CpG islands, and 6 gene-body regions. These loci, including two characterized as functional through expression quantitative trait-methylation analysis, were associated with functions related to osteoclast differentiation, mechanical loading, immune function, and viral infection. A multivariate classifier based on discovery samples was found to discriminate PDB cases and controls from the cross-validation with a sensitivity of 0.84, specificity of 0.81, and an area under curve of 92.8%. In conclusion, this study has shown for the first time that epigenetic factors contribute to the pathogenesis of PDB and may offer diagnostic markers for prediction of the disease.

Maturity-dependent cartilage cell plasticity and sensitivity to external perturbation

OBJECTIVE

Articular cartilage undergoes biological and morphological changes throughout maturation. The prevalence of osteoarthritis in the aged population suggests that maturation predisposes cartilage to degradation and/or impaired regeneration, but this process is not fully understood. Therefore, the objective of this study was to characterize the cellular and genetic profile of cartilage, as well as biological plasticity in response to mechanical and culture time stimuli, as a function of animal maturity.

METHODS/DESIGN

Porcine articular cartilage explants were harvested from stifle joints of immature (2-4 weeks), adolescent (5-6 months), and mature (1-5 years) animals. Half of all samples were subjected to a single compressive mechanical load. Loaded samples were paired with unloaded controls for downstream analyses. Expression of cartilage progenitor cell markers CD105, CD44, and CD29 were determined via flow cytometry. Expression of matrix synthesis genes Col1, Col2, Col10, ACAN, and SOX9 were determined via qPCR. Tissue morphology and matrix content were examined histologically. Post-loading assays were performed immediately and following 7 days in culture.

RESULTS

CD105 and CD29 expression decreased with maturity, while CD44 expression was upregulated in cartilage from mature animals. Expression of matrix synthesis genes were generally upregulated in cartilage from mature animals, and adolescent animals showed the lowest expression of several matrix synthesizing genes. Culture time and mechanical loading analyses revealed greater plasticity to mechanical loading and culture time in cartilage from younger animals. Histology confirmed distinct structural and biochemical profiles across maturity.

CONCLUSION

This study demonstrates differential, nonlinear expression of chondroprogenitor markers and matrix synthesis genes as a function of cartilage maturity, as well as loss of biological plasticity in aged tissue. These findings have likely implications for age-related loss of regeneration and osteoarthritis progression.

Long Noncoding RNA HUPCOS Promotes Follicular Fluid Androgen Excess in PCOS Patients via Aromatase Inhibition

CONTEXT

Androgen excess is a key feature of polycystic ovary syndrome (PCOS), but the underlying molecular mechanism remains unclear.

OBJECTIVE

To determine the role and mechanism of novel long noncoding RNA (lncRNA) highly up-regulated in PCOS (HUPCOS) in the androgen excess of PCOS patients.

DESIGN

The lncRNA expression profile in granulosa cells derived from PCOS and non-PCOS women were analyzed by using microarray assay. Human granulosa cell line KGN was used for mechanism investigation.

SETTING

This was a university-based study.

PATIENTS

Thirty-eight PCOS and 38 control patients were recruited: 8 PCOS and 8 control samples used for microarray discovery, the remaining 30 PCOS cases and 30 controls for quantitative RT-PCR validation.

MAIN OUTCOME MEASURES

The aberrant expression lncRNA profile of PCOS patients was measured using microarray. The relationship of HUPCOS and follicular fluid testosterone was measured. Aromatase expression were analyzed after HUPCOS downregulation. HUPCOS interaction protein was confirmed by RNA pull-down.

RESULTS

The significantly elevated lncRNA in PCOS granulosa cells was named HUPCOS, which was positively correlated with follicular fluid testosterone of PCOS patients. HUPCOS downregulation increased aromatase expression and promoted conversion of androgen to estrogen. RNA-binding protein with multiple splicing (RBPMS) was the most likely protein that combined with HUPCOS.

CONCLUSIONS

Our findings suggested that HUPCOS mediated androgen excess in follicular fluid of PCOS patients by suppressing aromatase expression via interaction with RBPMS.

7,8-Dihydroxyflavone activates Nrf2/HO-1 signaling pathways and protects against osteoarthritis

The aim of the present study was to investigate the effect of 7,8-dihydroxyflavone (7,8-DHF) against osteoarthritis (OA) and examine its regulatory role in the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway in chondrocytes. Primary mouse chondrocytes were treated with 7,8-DHF to examine the expression of Nrf2 and downstream heme oxygenase 1 (HO-1). The surgical destabilization of the medial meniscus model was used to assess the effectiveness of 7,8-DHF in protecting the cartilage from damage, with knee cartilage harvested from mice for histological analysis. The results revealed that 7,8-DHF activated the Nrf2 signaling pathway in primary chondrocytes. Cartilage degradation in the 7,8-DHF-treated group was reduced significantly compared with that in the vehicle-treated group, according to histological evaluation. The gene expression of matrix metalloproteinase (MMP)1, MMP3, MMP13, interleukin (IL)-1β, IL-6 and tumor necrosis factor-α were reduced in the cartilage of OA mice following 7,8-DHF treatment. Genetic and protein analyses indicated that the expression levels of HO-1 were upregulated in the cartilage of the knee with OA, and 7,8-DHF treatment further promoted the induction of HO-1. These results suggest that 7,8-DHF may serve as a potential therapeutic agent in OA.

Aberrant activation of latent transforming growth factor-β initiates the onset of temporomandibular joint osteoarthritis

There is currently no effective medical treatment for temporomandibular joint osteoarthritis (TMJ-OA) due to a limited understanding of its pathogenesis. This study was undertaken to investigate the key role of transforming growth factor-β (TGF-β) signalling in the cartilage and subchondral bone of the TMJ using a temporomandibular joint disorder (TMD) rat model, an ageing mouse model and a Camurati–Engelmann disease (CED) mouse model. In the three animal models, the subchondral bone phenotypes in the mandibular condyles were evaluated by µCT, and changes in TMJ condyles were examined by TRAP staining and immunohistochemical analysis of Osterix and p-Smad2/3. Condyle degradation was confirmed by Safranin O staining, the Mankin and OARSI scoring systems and type X collagen (Col X), p-Smad2/3a and Osterix immunohistochemical analyses. We found apparent histological phenotypes of TMJ-OA in the TMD, ageing and CED animal models, with abnormal activation of TGF-β signalling in the condylar cartilage and subchondral bone. Moreover, inhibition of TGF-β receptor I attenuated TMJ-OA progression in the TMD models. Therefore, aberrant activation of TGF-β signalling could be a key player in TMJ-OA development.

Blocking the activity of a critical growth factor could help treat degenerative disease of the jaw joint, according to experiments in three rodent models. Xuedong Zhou from Sichuan University in Chengdu, China, examined the cartilage and adjoining layer of bone found at the ends of the jawbone in a rat model of temporomandibular joint disorder and in two related mouse models. In all three, the researchers observed tissue abnormalities consistent with what’s seen in humans with osteoarthritis of the jaw joint, a condition with no effective therapeutic options. They showed that transforming growth factor-β, a master regulatory protein, displayed aberrant signalling patterns in these tissues and that blocking this protein’s receptor with a drug attenuated the disease process. The findings help explain what drives jaw joint osteoarthritis — and point to a strategy for treating it.

Aging and osteoarthritis: Central role of the extracellular matrix

Osteoarthritis (OA), is a major cause of severe joint pain, physical disability and quality of life impairment in the aging population across the developed and developing world. Increased catabolism in the extracellular matrix (ECM) of the articular cartilage is a key factor in the development and progression of OA. The molecular mechanisms leading to an impaired matrix turnover have not been fully clarified, however cellular senescence, increased expression of inflammatory mediators as well as oxidative stress in association with an inherently limited regenerative potential of the tissue, are all important contributors to OA development. All these factors are linked to and tend to be maximized by aging. Nonetheless the role of aging in compromising joint stability and function in OA has not been completely clarified yet. This review will systematically analyze cellular and structural changes taking place in the articular cartilage and bone in the pathogenesis of OA which are linked to aging. A particular emphasis will be placed on age-related changes in the phenotype of the articular chondrocytes.

Glutaredoxin 1 (GRX1) inhibits oxidative stress and apoptosis of chondrocytes by regulating CREB/HO-1 in osteoarthritis

GRX1 (glutaredoxin1), a sulfhydryl disulfide oxidoreductase, is involved in many cellular processes, including anti-oxidation, anti-apoptosis, and regulation of cell differentiation. However, the role of GRX1 in the oxidative stress and apoptosis of osteoarthritis chondrocytes remains unclear, prompting the current study. Protein and mRNA expressions were measured by Western blot and RT-qPCR. Oxidative stress was detected by the measurement of MDA and SOD contents. Cells apoptosis were detected by Annexin V-FITC/PI and caspase-3 activity assays. We found that the mRNA and protein expressions of GRX1 were significantly down-regulated in osteoarthritis tissues and cells. GRX1 overexpression increased the mRNA and protein expression of CREB and HO-1. Meanwhile, GRX1 overexpression inhibited oxidative stress and apoptosis in osteoarthritis chondrocytes. Furthermore, we found that GRX1 overexpression regulated HO-1 by increasing CREB, and that HO-1 regulated oxidative stress and apoptosis in osteoarthritis chondrocytes. Thus, GRX1 overexpression constrains oxidative stress and apoptosis in osteoarthritis chondrocytes by regulating CREB/HO-1, providing a novel insight into the molecular mechanism and potential treatment of osteoarthritis.