Expression of adrenomedullin and its receptor by chondrocyte phenotype cells

The role of apoptosis in the pathogenesis of osteoarthritis

PURPOSE

Apoptosis is an important physiological process, making a great difference to development and tissue homeostasis. Osteoarthritis (OA) is a chronic joint disease characterized by degeneration and destruction of articular cartilage and bone hyperplasia. This purpose of this study is to provide an updated review of the role of apoptosis in the pathogenesis of osteoarthritis.

METHODS

A comprehensive review of the literature on osteoarthritis and apoptosis was performed, which mainly focused on the regulatory factors and signaling pathways associated with chondrocyte apoptosis in osteoarthritis and other pathogenic mechanisms involved in chondrocyte apoptosis.

RESULTS

Inflammatory mediators such as reactive oxygen species (ROS), nitric oxide (NO), IL-1β, tumor necrosis factor-α (TNF-α), and Fas are closely related to chondrocyte apoptosis. NF-κB signaling pathway, Wnt signaling pathway, and Notch signaling pathway activate proteins and gene targets that promote or inhibit the progression of osteoarthritis disease, including chondrocyte apoptosis and ECM degradation. Long non-coding RNAs (LncRNAs) and microRNAs (microRNAs) have gradually replaced single and localized research methods and become the main research approaches. In addition, the relationship between cellular senescence, autophagy, and apoptosis was also briefly explained.

CONCLUSION

This review offers a better molecular delineation of apoptotic processes that may help in designing new therapeutic options for OA treatment.

Candidate Marker Genes for Diagnosis of Osteoarthritis and Prediction of Their Regulatory Mechanisms

We have screened candidate marker genes for the diagnosis of osteoarthritis and predicted their regulatory mechanisms. Six expression chips of tissue samples and one expression chip of peripheral blood mononuclear cell (PMBC) samples were obtained from the GEO database. Differential analysis, GSEA, and WGCNA were performed on the integra-ted tissue sample data with batch correction. Can-didate genes were obtained from the intersection of the genes significantly related to osteoarthritis in the WGCNA and the differentially expressed genes. ROC analysis was performed on the candidate genes in the tissue and PMBC samples. Genes with AUC values greater than 0.6 were retained as final candidates, and their upstream regulatory miRNAs were predicted. A total of 106 genes with differential expression were found in osteoarthritis tissue samples, which were mainly enriched in cell cycle and p53 signalling pathways. WGCNA selected a gene module significantly correlated with the occurrence of osteoarthritis. Fourteen candidate genes were obtained from the intersection of the genes in the module and the differentially expressed genes. ROC analysis showed that among these 14 candidate genes, only ADM, CX3CR1 and GADD45A had AUC values greater than 0.6 in both tissue and PMBC samples. The AUC values of the gene set of these three genes were greater than 0.7. Multiple miRNAs were predicted to be regulators of these three genes. ADM, CX3CR1 and GADD45A have potential as diagnostic marker genes for osteoarthritis and may be regulated by multiple miRNAs.

A Novel Hypoxia Related Marker in Blood Link to Aid Diagnosis and Therapy in Osteoarthritis

Osteoarthritis (OA) is a common chronic degenerative arthritis. Its treatment options are very limited. At present, hypoxia is a prominent factor in OA. This study aimed to re-explore the mechanism between hypoxia and OA, which provides new insights into the diagnosis and therapy of OA. We acquired the OA-related expression profiles of GSE48556, GSE55235, and GSE55457 for our analysis. Using gene set variation analysis (GSVA), we found significant differences in hypoxia. These differences result from multiple pathways, such as the p53 signaling pathway, cell senescence, the NF-kappa B signaling pathway, Ubiquitin-mediated proteolysis, and apoptosis. Meanwhile, the single-sample gene set enrichment analysis (ssGSEA) showed that hypoxia was significantly associated with the level of immune cell infiltration in the immune microenvironment. Thus, we believe that hypoxia is useful for the diagnosis and treatment of OA. We successfully constructed a novel hypoxia-related index (HRI) based on seven hypoxia-related genes (ADM, CDKN3, ENO1, NDRG1, PGAM1, SLC2A1, VEGFA) by least absolute shrinkage and binary logistic regression of the generalized linear regression. HRI showed potential for improving OA diagnosis through receiver operation characteristic (ROC) analysis (AUC training cohort = 0.919, AUC testing cohort = 0.985). Moreover, we found that celastrol, droxinostat, torin-2, and narciclasine may be potential therapeutic compounds for OA based on the Connectivity Map (CMap). In conclusion, hypoxia is involved in the development and progression of OA. HRI can improve diagnosis and show great potential in clinical application. Celastrol, droxinostat, torin-2, and narciclasine may be potential compounds for the treatment of OA patients.

Adrenergic signalling in osteoarthritis

Adrenoceptors (ARs) mediate the effects of the sympathetic neurotransmitters norepinephrine (NE) and epinephrine (E) in the human body and play a central role in physiologic and pathologic processes. Therefore, ARs have long been recognized as targets for therapeutic agents, especially in the field of cardiovascular medicine. During the past decades, the contribution of the sympathetic nervous system (SNS) and particularly of its major peripheral catecholamine NE to the pathogenesis of osteoarthritis (OA) attracted growing interest. OA is the most common degenerative joint disorder worldwide and a disease of the whole joint. It is characterized by progressive degradation of articular cartilage, synovial inflammation, osteophyte formation, and subchondral bone sclerosis mostly resulting in chronic pain. The subchondral bone marrow, the periosteum, the synovium, the vascular meniscus and numerous tendons and ligaments are innervated by tyrosine hydroxylase-positive (TH+) sympathetic nerve fibers that release NE into the synovial fluid and cells of all abovementioned joint tissues express at least one out of nine AR subtypes. During the past decades, several in vitro studies explored the AR-mediated effects of NE on different cell types in the joint. So far, only a few studies used animal OA models to investigate the contribution of distinct AR subtypes to OA pathogenesis in vivo. This narrative review shortly summarizes the current background knowledge about ARs and their signalling pathways at first. In the second part, we focus on recent findings in the field of NE-induced AR-mediated signalling in different joint tissues during OA pathogenesis and at the end, we will delineate the potential of targeting the adrenergic signalling for OA prevention or treatment. We used the PubMed bibliographic database to search for keywords such as 'joint' or 'cartilage' or 'synovium' or 'bone' and 'osteoarthritis' and/or 'trauma' and 'sympathetic nerve fibers' and/or 'norepinephrine' and 'adrenergic receptors / adrenoceptors' as well as 'adrenergic therapy'.

Adrenomedullin and truncated peptide adrenomedullin(22-52) affect chondrocyte response to apoptotis in vitro: downregulation of FAS protects chondrocyte from cell death

Chondrocyte apoptosis may have a pivotal role in the development of osteoarthritis. Interest has increased in the use of anti-apoptotic compounds to protect against osteoarthritis development. In this work, we investigated the effect of adrenomedullin (AM), a 52 amino-acid hormone peptide, and a 31 amino-acid truncated form, AM(22-52), on chondrocyte apoptosis. Bovine articular chondrocytes (BACs) were cultured under hypoxic conditions to mimic cartilage environment and then treated with Fas ligand (Fas-L) to induce apoptosis. The expression of AM and its calcitonin receptor-like receptor (CLR)/receptor activity-modifying protein (RAMP) (receptor/co-receptor) was assessed by immunostaining. We evaluated the effect of AM and AM(22-52) on Fas-L-induced chondrocyte apoptosis. FAS expression was appreciated by RT-qPCR and immunostainings. The expression of hypoxia-inducible factor 1α (HIF-1α), CLR and one co-receptor (RAMP2) was evidenced. With BACs under hypoxia, cyclic adenosine monophosphate production increased dose-dependently with AM stimulation. AM significantly decreased caspase-3 activity (mean 35% decrease; p = 0.03) as a marker of Fas-L-induced apoptosis. Articular chondrocytes treated with AM showed significantly reduced cell death, along with downregulated Fas expression and production, as compared with AM(22-52). AM decreased articular chondrocyte apoptosis by downregulating a Fas receptor. These findings may pave the way for novel therapeutic approaches in osteoarthritis.

Norepinephrine modulates osteoarthritic chondrocyte metabolism and inflammatory responses

OBJECTIVE

Norepinephrine (NE) was measured in synovial fluid of trauma patients and sympathetic nerve fibers were detected in healthy and osteoarthritic (OA) joint tissues indicating that cartilage pathophysiology might be influenced by sympathetic neurotransmitters. The aim of this study was to elucidate the mostly unknown role of NE in OA chondrocyte metabolism and inflammatory responses.

METHODS

Articular cartilage was received after total knee replacement surgery from OA patients. Expression of adrenergic receptors (AR) and tyrosine hydroxylase (TH) was tested with end point polymerase chain reaction (PCR) and immunohistochemistry. 3-dimensional (3D) cell cultures were employed to analyze effects of NE on chondrocyte cell metabolism and the expression of interleukins (ILs), matrix metalloproteases (MMPs), tissue inhibitor of metalloproteases (TIMPs), glycosaminoglycan (GAG) and collagen II under non- and inflammatory conditions. Chondrocyte monolayer cultures were used to specify AR subtypes, to analyze cell cycle distribution and to determine catecholamines in cell culture supernatants.

RESULTS

AR subtypes and TH were detected in chondrocytes, whereas NE was not released in measurable amounts. 10(-6) M NE reversed IL-1β induced changes in IL-8, MMP-13, GAG and collagen II expression/production indicating for β-AR signaling. Additionally, NE caused cell cycle slow down and decreased proliferation via β-AR signaling. 10(-8) M NE increased the number of proliferating cells and induced apoptosis via α1-AR signaling.

CONCLUSIONS

NE affects chondrocytes from OA cartilage regarding inflammatory response and its cell metabolism in a dose dependent manner. The sympathetic nervous system (SNS) may have a dual function in OA pathology with preserving a stable chondrocyte phenotype via β-AR signaling and OA pathogenesis accelerating effects via α-AR signaling.

Adrenomedullin(22-52) combats inflammation and prevents systemic bone loss in murine collagen-induced arthritis

OBJECTIVE

Adrenomedullin(22-52) is a truncated peptide derived from adrenomedullin, a growth factor with antiapoptotic and immunoregulatory properties. It can act as an agonist or an antagonist depending on cell type. Its in vivo effects are unknown, but adrenomedullin(22-52) could possess immunomodulatory properties. This study was undertaken to evaluate the effect of adrenomedullin(22-52) in a mouse model of arthritis.

METHODS

DBA/1 mice with collagen-induced arthritis (CIA) were treated with 1.2 μg/gm adrenomedullin(22-52) , adrenomedullin, or saline at arthritis onset. Bone mineral density was measured at the beginning of the experiment and when mice were killed. Mouse joints were processed for histologic analysis and protein studies, and spleens were examined for Treg cell expression. Cytokine expression was studied in mouse joint tissue and serum.

RESULTS

In mice with CIA, adrenomedullin and adrenomedullin(22-52) reduced clinical and histologic arthritis scores and shifted the pattern of articular and systemic cytokine expression from Th1 to Th2, as compared to untreated mice with CIA (controls). Tumor necrosis factor α, interleukin-6 (IL-6), and IL-17A levels were significantly decreased in the joints of mice with CIA treated with adrenomedullin or adrenomedullin(22-52) as compared to controls, whereas IL-4 and IL-10 levels were increased. Adrenomedullin(22-52) was more effective than adrenomedullin in modulating cytokine content and enhanced Treg cell function without changing Treg cell expression compared to controls. Adrenomedullin receptor binding and transcriptional adrenomedullin receptor expression were markedly increased in joints from controls, whereas adrenomedullin receptor binding was considerably decreased in treated animals. Mice with CIA treated with adrenomedullin or adrenomedullin(22-52) had considerably fewer apoptotic chondrocytes and diminished cartilage degradation. Adrenomedullin(22-52) completely prevented systemic bone loss by preserving osteoblastic activity, but without changes in osteoclastic activity.

CONCLUSION

Our findings indicate that adrenomedullin(22-52) , which has no vasoactive or tumor-inducing effects, is a potent antiinflammatory and bone-protective agent in this arthritis model.

A critical role for adrenomedullin-calcitonin receptor-like receptor in regulating rheumatoid fibroblast-like synoviocyte apoptosis

Rheumatoid arthritis (RA) is characterized by fibroblast-like synoviocyte (FLS) hyperplasia, which is partly ascribable to decreased apoptosis. In this study, we show that adrenomedullin (ADM), an antiapoptotic peptide, is constitutively secreted in larger amounts by FLS from joints with RA (RA-FLS) than with osteoarthritis (OA-FLS). ADM secretion was regulated by TNF-alpha. Peptidylglycine alpha-amidating monooxygenase, the ADM-processing enzyme, was expressed at the mRNA level by both RA-FLS and OA-FLS. Constituents of the ADM heterodimeric receptor calcitonin receptor-like receptor (CRLR)/receptor activity-modifying protein (RAMP)-2 were up-regulated at the mRNA and protein levels in cultured RA-FLS compared with OA-FLS. ADM induced rapid intracellular cAMP production in FLS and reduced caspase-3 activity, DNA fragmentation, and chromatin condensation in RA-FLS exposed to apoptotic conditions, indicating that CRLR/RAMP-2 was fully functional. ADM-induced cAMP production was less marked in OA-FLS than in RA-FLS, suggesting differences in receptor regulation and expression. ADM dose-dependently inhibited RA-FLS apoptosis, and this effect was reversed by the 22-52 ADM antagonist peptide. ADM inhibited RA-FLS apoptosis triggered by extrinsic and intrinsic pathways. Our data suggest that ADM may prevent or reduce RA-FLS apoptosis, via up-regulation of its functional receptor CRLR/RAMP-2. Regulation of ADM secretion and/or CRLR/RAMP-2 activation may constitute new treatment strategies for RA.

Activation of genes for growth factor and cytokine pathways late in chondrogenic differentiation of ATDC5 cells

The mouse embryonal carcinoma cell line ATDC5 provides an excellent model system for chondrogenesis in vitro. To understand better the molecular mechanisms of endochondral bone formation, we investigated gene expression profiles during the differentiation course of ATDC5 cells, using an in-house microarray harboring full-length-enriched cDNAs. For 28 days following chondrogenic induction, 507 genes were up- or down-regulated at least 1.5-fold. These genes were classified into five clusters based on their expression patterns. Genes for growth factor and cytokine pathways were significantly enriched in the cluster characterized by increases in expression during late stages of chondrocyte differentiation. mRNAs for decorin and osteoglycin, which have been shown to bind to transforming growth factors-beta and bone morphogenetic proteins, respectively, were found in this cluster and were detected in hypertrophic chondrocytes of developing mouse bones by in situ hybridization analysis. Taken together with assigned functions of individual genes in the cluster, interdigitated interaction between a number of intercellular signaling molecules is likely to take place in the late chondrogenic stage for autocrine and paracrine regulation among chondrocytes, as well as for chemoattraction and stimulation of progenitor cells of other lineages.

GPCR modulation by RAMPs

Our conceptual understanding of the molecular architecture of G-protein coupled receptors (GPCRs) has transformed over the last decade. Once considered as largely independent functional units (aside from their interaction with the G-protein itself), it is now clear that a single GPCR is but part of a multifaceted signaling complex, each component providing an additional layer of sophistication. Receptor activity-modifying proteins (RAMPs) provide a notable example of proteins that interact with GPCRs to modify their function. They act as pharmacological switches, modifying GPCR pharmacology for a particular subset of receptors. However, there is accumulating evidence that these ubiquitous proteins have a broader role, regulating signaling and receptor trafficking. This article aims to provide the reader with a comprehensive appraisal of RAMP literature and perhaps some insight into the impact that their discovery has had on those who study GPCRs.