Down-Regulation of Adiponectin Receptors in Osteoarthritic Chondrocytes

Adipokines as potential pharmacological targets for immune inflammatory rheumatic diseases: Focus on rheumatoid arthritis, osteoarthritis, and intervertebral disc degeneration

Adipokines are a heterogeneous group of signalling molecules secreted prevalently by adipose tissue. Initially considered as regulators of energy metabolism and appetite, adipokines have been recognized for their substantial involvement in musculoskeletal disorders, including osteoarthritis, rheumatoid arthritis, and many others. Understanding the role of adipokines in rheumatic inflammatory and autoimmune diseases, as well as in other musculoskeletal diseases such as intervertebral disc degeneration, is crucial for the development of novel therapeutic strategies. Targeting adipokines, or their signalling pathways, may offer new opportunities for the treatment and management of these conditions. By modulating adipokines levels or activity, it may be possible to regulate inflammation, to maintain bone health, and preserve muscle mass, thereby improving the outcomes and quality of life for individuals affected by musculoskeletal diseases. The aim of this review article is to update the reader on the multifaceted role of adipokines in the main rheumatic diseases such as osteoarthritis and rheumatoid arthritis and to unravel the complex interplay among adipokines, cartilage metabolism, bone remodelling and muscles, which will pave the way for innovative therapeutic intervention in the future. For completeness, the role of adipokines in intervertebral disc degeneration will be also addressed.

Adipokines as targets in musculoskeletal immune and inflammatory diseases

Adipokines are the principal mediators in adipose signaling. Nevertheless, besides their role in energy storage, these molecules can be produced by other cells, such as immune cells or chondrocytes. Given their pleiotropic effects, research over the past few years has also focused on musculoskeletal diseases, showing that these adipokines might have relevant roles in worsening the disease or improving the treatment response. In this review, we summarize recent advances in our understanding of adipokines and their role in the most prevalent musculoskeletal immune and inflammatory disorders.

Chondrocytes from osteoarthritic cartilage of obese patients show altered adiponectin receptors expression and response to adiponectin

Obesity and osteoarthritis (OA) are well-known comorbidities and their precise molecular interactions are still unidentified. Adiponectin, a major adipokine, known to have an anti-inflammatory effect in atherosclerosis or Type 2 Diabetes Mellitus (T2DM), has also been postulated to be pro-inflammatory in OA. This dual role of adiponectin is still not explained. The precise mechanism by which adiponectin affects cartilage and chondrocytes remains to be elucidated. In the present observational study chondrocytes from 30 patients with OA (18 females and 12 males) undergoing total knee replacement (TKR) were isolated. Expression of adiponectin receptors 1 and 2 (ADIPOR1 and ADIPOR2) was examined both at gene and protein levels in chondrocytes. The difference in adiponectin receptor expression between lean and obese patients with OA and the role of adiponectin in regulating pro-inflammatory genes (MCP-1, IL-6, and VCAM-1, MMP-1, MMP-2, and TIMP-1) has been investigated. We found that ADIPOR1 represented the most abundant adiponectin receptor in primary OA chondrocytes. ADIPOR1 and ADIPOR2 genes and ADIPOR1 protein were differently expressed in OA chondrocytes obtained from obese compared with lean patients with OA. Adiponectin induced gene expression of MCP-1, IL-6, and MMP-1 in all OA patients' chondrocytes. In contrast, VCAM-1 and MMP-2 were differently regulated by adiponectin depending on the patient's body mass index. This study suggests that adiponectin and ADIPOR1 may have important roles in the pathogenesis of cartilage degeneration in OA of obese subjects.

Osteoarthritis and type 2 diabetes: From pathogenetic factors to therapeutic intervention

Over the last decades, osteoarthritis (OA) and type 2 diabetes (T2D) prevalence increased due to the global ageing population and the pandemic obesity. They currently affect a substantial part of the Western world population and are characterized by enhancing the risk of disability and reduction of quality of life. OA is a multifactorial condition whose development derives from the interaction between individual and environmental factors: The best known primarily include age, female gender, genetic determinants, articular biomechanics, and obesity (OB). Given the high prevalence of OA and T2D and their association with OB and inflammation, several studies have been conducted to investigate the causative role of biological characteristics proper to T2D on the development of OA. This review aims to analyse the relationship between of OA and T2D, in order to explain the pathophysiological drivers of the degenerative process and to delineate possible targets to which appropriate treatments may be addressed in the near future.

Genome-wide meta-analysis and replication studies in multiple ethnicities identify novel adolescent idiopathic scoliosis susceptibility loci

Adolescent idiopathic scoliosis (AIS) is the most common musculoskeletal disorder of childhood development. The genetic architecture of AIS is complex, and the great majority of risk factors are undiscovered. To identify new AIS susceptibility loci, we conducted the first genome-wide meta-analysis of AIS genome-wide association studies, including 7956 cases and 88 459 controls from 3 ancestral groups. Three novel loci that surpassed genome-wide significance were uncovered in intragenic regions of the CDH13 (P-value_rs4513093 = 1.7E-15), ABO (P-value_ rs687621 = 7.3E-10) and SOX6 (P-value_rs1455114 = 2.98E-08) genes. Restricting the analysis to females improved the associations at multiple loci, most notably with variants within CDH13 despite the reduction in sample size. Genome-wide gene-functional enrichment analysis identified significant perturbation of pathways involving cartilage and connective tissue development. Expression of both SOX6 and CDH13 was detected in cartilage chondrocytes and chromatin immunoprecipitation sequencing experiments in that tissue revealed multiple HeK27ac-positive peaks overlapping associated loci. Our results further define the genetic architecture of AIS and highlight the importance of vertebral cartilage development in its pathogenesis.

Adiponectin Downregulates TNF-α Expression in Degenerated Intervertebral Discs

STUDY DESIGN

Given the results of previous in vitro investigations of the expression patterns of adiponectin and its receptors in healthy and degenerated intervertebral discs (IVDs), we studied the effects of adiponectin on tumor necrosis factor-alpha (TNF-α) production in degenerated nucleus pulposus (NP) cells and analyzed the association between adiponectin levels in IVD tissues and IVD Pfirrmann grades.

OBJECTIVE

The aim of this study was to investigate the potential role of adiponectin in the pathogenesis of IVD degeneration.

SUMMARY OF BACKGROUND DATA

Adiponectin has been reported to be involved in physiologic and pathologic processes associated with bone and cartilage diseases. However, the expression profiles of adiponectin and its receptors in human IVD tissues and the function of adiponectin in the pathogenesis of IVD degeneration remain unknown.

METHODS

Real-time polymerase chain reaction, immunohistochemistry, and western blotting were performed to examine the expression levels of adiponectin, adiponectin receptors, and TNF-α in IVD tissues and isolated NP cells. The effects of adiponectin on TNF-α production in degenerated NP cells were detected by enzyme linked immunosorbent assay.

RESULTS

Adiponectin expression levels were downregulated, while adiponectin receptor 1 (adipoR1) and adipoR2 expression levels were upregulated in degenerated IVD tissues and degenerated NP cells compared with those in healthy IVD tissues and healthy NP cells. Moreover, we confirmed that TNF-α production by degenerated NP cells was downregulated by adiponectin administration in a dose- and time-dependent manner. Furthermore, our data showed that adiponectin levels in degenerated IVD tissues were inversely correlated with IVD Pfirrmann grades.

CONCLUSION

These results indicated that adiponectin may play an anti-inflammatory role with respect to the maintenance of IVD homeostasis by downregulating TNF-α production.

LEVEL OF EVIDENCE

N/A.

Inter-relations between osteoarthritis and metabolic syndrome: A common link?

Osteoarthritis (OA) is a degenerative disorder of the joint, principally occurring during aging, and characterized by a focal degradation of cartilage. It is the most prevalent rheumatic disease in industrialized countries and represents the second cause of disability in France. However, the etiology of OA remains unclear. There is only one cell type found in cartilage, chondrocyte, which is responsible for its repair and the synthesis of the elements of the extra-cellular matrix. A dysfunction of these cells results in an imbalance between repair and degradation in cartilage, leading to its destruction. Recently, a link between OA and metabolic syndrome (MetS) has been suggested, introducing a notion of metabolic OA, and a new vision of the disease. MetS is characterized by a cluster of factors (insulin resistance, hypertension, dyslipidemia, visceral obesity), although there is still no clear definition of it. During the 20th century, MetS dramatically increased with changes in population lifestyle, becoming a major health issue in industrialized countries. MetS concerns 10-30% of the worldwide population, but is prevalent in 59% of OA patients. Patients with both OA and MetS have more severe symptoms, occurring sooner than in the general population. Indeed, OA is generally a disease concerning the population over 65 years old, but with an associated MetS the target population is around 50 years old. In this review, we will focus on common factors in OA and MetS, such as hypertension, obesity, dyslipidemia, mitochondrial dysfunction and hyperglycemia, linking one disease to the other.