Metabolic changes in synovial cells in early inflammation: Involvement of CREB phosphorylation in the anti-inflammatory effect of 2-deoxyglucose

Role of mitochondrial dysfunction in the pathogenesis of rheumatoid arthritis: Looking closely at fibroblast- like synoviocytes

Rheumatoid arthritis (RA) is a chronic, autoimmune, and inflammatory disease that primarily targets the joints, leading to cartilage and bone destruction.Fibroblast-like synoviocytes (FLS) are specialized cells of the synovial lining in the joint that plays a fundamental role in the development of RA. Particularly, FLS of RA patients (RA-FLS) in the joint exhibit specific characteristics like higher invading and immunogenic properties, hyperproliferation, and reduced apoptotic capacity, suggesting a dysfunctional mitochondrial pool in these cells. Mitochondria are emerging as a potential organelle that can decide cellular immunometabolism, invasion properties, and cell death. Accordingly, multiplestudies established that mitochondria are crucial in establishing RA. However, the underlying mechanism of impaired mitochondrial function in RA remains poorly understood. This review will provide an overview of the mitochondrial role in the progression of RA, specifically in the context of FLS biology. We will also outline how mitochondria-centric therapeutics can be achieved that would yield novel avenues of research in pathological mediation and prevention.

Sirtuin 6 ameliorates arthritis through modulating cyclic AMP-responsive element binding protein/CCN1/cyclooxygenase 2 pathway in osteoblasts

INTRODUCTION

CCN1 is an immediate-early gene product pivotal for arthritis progression. We have previously shown that sirtuin 6 (SIRT6) inhibited hypoxia-induced CCN1 expression in osteoblasts. Herein we examined the contribution of cyclic AMP-responsive element binding protein (CREB)/CRE to this suppressive action and the influence of CCN1 on cyclooxygenase (COX) 2 synthesis.

MATERIALS AND METHODS

MC3T3-E1 murine osteoblasts were cultured under normoxia (21% oxygen) or hypoxia (2% oxygen). Expressions of CCN1, phospho-CREB (Ser133), COX2 and relevant kinases were assessed by Western blot. SIRT6 was overexpressed in cultured osteoblasts and arthritic joints by a lentiviral-based technique. Activities of CCN1 gene promoter constructs were examined by luciferase reporter assay. Interaction between CREB and CCN1 promoter was assessed by chromatin immunoprecipitation (ChIP). Collagen-induced arthritis (CIA) was established in 20 rats to evaluate the effects of SIRT6 therapy on osteoblastic expressions of phospho-CREB, CCN1 and COX2.

RESULTS

SIRT6 suppressed hypoxia-enhanced CCN1 expression and CREB phosphorylation. Attenuation of calcium/calmodulin-dependent protein kinase II (CaMKII) may be responsible for SIRT6-induced CREB inhibition. CRE at - 286 bp upstream of the ATG start codon was essential for CCN1 expression under hypoxia and SIRT6 reduced hypoxia-stimulated CREB/CRE interaction. Forced expression of CREB rescued SIRT6-suppressed CCN1 synthesis. CCN1 induced COX2 expression in osteoblasts. In rat CIA, the therapeutic effect of SIRT6 was accompanied by decreases in osteoblastic expressions of phospho-CREB, CCN1 and COX2.

CONCLUSION

Our study indicated that the benefits of SIRT6 to inflammatory arthritis and bone resorption are at least partially derived from its modulation of CREB/CCN1/COX2 pathway in osteoblasts.

In Situ Growth Intercalation Structure MXene@Anatase/Rutile TiO2 Ternary Heterojunction with Excellent Phosphoprotein Detection in Sweat

Abnormal protein phosphorylation may relate to diseases such as Alzheimer's, schizophrenia, and Parkinson's. Therefore, the real-time detection of phosphoproteins in sweat was of great significance for the early knowledge, detection, and treatment of neurological diseases. In this work, anatase/rutile TiO₂ was in situ grown on the MXene surface to constructing the intercalation structure MXene@anatase/rutile TiO₂ ternary heterostructure as a sensing platform for detecting phosphoprotein in sweat. Here, the intercalation structure of MXene acted as electron and diffusion channels for phosphoproteins. The in situ grown anatase/rutile TiO₂ with n-n-type heterostructure provided specific adsorption sites for the phosphoproteins. The determination of phosphoprotein covered concentrations in sweat, with linear range from 0.01 to 1 mg/mL, along with a low LOD of 1.52 μM. It is worth noting that, since the macromolecular phosphoprotein was adsorbed on the surface of the material, the electrochemical signal gradually decreased with the increase of phosphoprotein concentration. In addition, the active sites in the MXene@anatase/rutile TiO₂ ternary heterojunction and synergistic effect of the heterojunction were verified by first-principle calculations to further realize the response to phosphoproteins. Additionally, the effective diffusion capacity and mobility of phosphoprotein molecules in the ternary heterojunction structure were studied by molecular dynamics simulation. Furthermore, the constructed sensing platform showed high selectivity, repeatability, reproducibility, and stability, and this newly developed sensor can detect for phosphoprotein in actual sweat samples. This satisfactory sensing strategy could be promoted to realize the noninvasive and continuous detection of sweat.

Rheumatoid arthritis and mitochondrial homeostasis: The crossroads of metabolism and immunity

Rheumatoid arthritis is an autoimmune disease characterized by chronic symmetric synovial inflammation and erosive bone destruction. Mitochondria are the main site of cellular energy supply and play a key role in the process of energy metabolism. They possess certain self-regulatory and repair capabilities. Mitochondria maintain relative stability in number, morphology, and spatial structure through biological processes, such as biogenesis, fission, fusion, and autophagy, which are collectively called mitochondrial homeostasis. An imbalance in the mitochondrial homeostatic environment will affect immune cell energy metabolism, synovial cell proliferation, apoptosis, and inflammatory signaling. These biological processes are involved in the onset and development of rheumatoid arthritis. In this review, we found that in rheumatoid arthritis, abnormal mitochondrial homeostasis can mediate various immune cell metabolic disorders, and the reprogramming of immune cell metabolism is closely related to their inflammatory activation. In turn, mitochondrial damage and homeostatic imbalance can lead to mtDNA leakage and increased mtROS production. mtDNA and mtROS are active substances mediating multiple inflammatory pathways. Several rheumatoid arthritis therapeutic agents regulate mitochondrial homeostasis and repair mitochondrial damage. Therefore, modulation of mitochondrial homeostasis would be one of the most attractive targets for the treatment of rheumatoid arthritis.

Glycolysis in Innate Immune Cells Contributes to Autoimmunity

Autoimmune diseases (AIDs) refer to connective tissue inflammation caused by aberrant autoantibodies resulting from dysfunctional immune surveillance. Most of the current treatments for AIDs use non-selective immunosuppressive agents. Although these therapies successfully control the disease process, patients experience significant side effects, particularly an increased risk of infection. There is a great need to study the pathogenesis of AIDs to facilitate the development of selective inhibitors for inflammatory signaling to overcome the limitations of traditional therapies. Immune cells alter their predominant metabolic profile from mitochondrial respiration to glycolysis in AIDs. This metabolic reprogramming, known to occur in adaptive immune cells, i.e., B and T lymphocytes, is critical to the pathogenesis of connective tissue inflammation. At the cellular level, this metabolic switch involves multiple signaling molecules, including serine-threonine protein kinase, mammalian target of rapamycin, and phosphoinositide 3-kinase. Although glycolysis is less efficient than mitochondrial respiration in terms of ATP production, immune cells can promote disease progression by enhancing glycolysis to satisfy cellular functions. Recent studies have shown that active glycolytic metabolism may also account for the cellular physiology of innate immune cells in AIDs. However, the mechanism by which glycolysis affects innate immunity and participates in the pathogenesis of AIDs remains to be elucidated. Therefore, we reviewed the molecular mechanisms, including key enzymes, signaling pathways, and inflammatory factors, that could explain the relationship between glycolysis and the pro-inflammatory phenotype of innate immune cells such as neutrophils, macrophages, and dendritic cells. Additionally, we summarize the impact of glycolysis on the pathophysiological processes of AIDs, including systemic lupus erythematosus, rheumatoid arthritis, vasculitis, and ankylosing spondylitis, and discuss potential therapeutic targets. The discovery that immune cell metabolism characterized by glycolysis may regulate inflammation broadens the avenues for treating AIDs by modulating immune cell metabolism.

Glycolysis Rate-Limiting Enzymes: Novel Potential Regulators of Rheumatoid Arthritis Pathogenesis

Rheumatoid arthritis (RA) is a classic autoimmune disease characterized by uncontrolled synovial proliferation, pannus formation, cartilage injury, and bone destruction. The specific pathogenesis of RA, a chronic inflammatory disease, remains unclear. However, both key glycolysis rate-limiting enzymes, hexokinase-II (HK-II), phosphofructokinase-1 (PFK-1), and pyruvate kinase M2 (PKM2), as well as indirect rate-limiting enzymes, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), are thought to participate in the pathogenesis of RA. In here, we review the latest literature on the pathogenesis of RA, introduce the pathophysiological characteristics of HK-II, PFK-1/PFKFB3, and PKM2 and their expression characteristics in this autoimmune disease, and systematically assess the association between the glycolytic rate-limiting enzymes and RA from a molecular level. Moreover, we highlight HK-II, PFK-1/PFKFB3, and PKM2 as potential targets for the clinical treatment of RA. There is great potential to develop new anti-rheumatic therapies through safe inhibition or overexpression of glycolysis rate-limiting enzymes.