Metabolic dysfunction and inflammatory disease: the role of stromal fibroblasts

Immunomodulation and fibroblast dynamics driving nociceptive joint pain within inflammatory synovium: Unravelling mechanisms for therapeutic advancements in osteoarthritis

OBJECTIVE

Synovitis is a widely accepted sign of osteoarthritis (OA), characterised by tissue hyperplasia, where increased infiltration of immune cells and proliferation of resident fibroblasts adopt a pro-inflammatory phenotype, and increased the production of pro-inflammatory mediators that are capable of sensitising and activating sensory nociceptors, which innervate the joint tissues. As such, it is important to understand the cellular composition of synovium and their involvement in pain sensitisation to better inform the development of effective analgesics.

METHODS

Studies investigating pain sensitisation in OA with a focus on immune cells and fibroblasts were identified using PubMed, Web of Science and SCOPUS.

RESULTS

In this review, we comprehensively assess the evidence that cellular crosstalk between resident immune cells or synovial fibroblasts with joint nociceptors in inflamed OA synovium contributes to peripheral pain sensitisation. Moreover, we explore whether the elucidation of common mechanisms identified in similar joint conditions may inform the development of more effective analgesics specifically targeting OA joint pain.

CONCLUSION

The concept of local environment and cellular crosstalk within the inflammatory synovium as a driver of nociceptive joint pain presents a compelling opportunity for future research and therapeutic advancements.

Cardiac fibrogenesis: an immuno-metabolic perspective

Cardiac fibrosis is a major and complex pathophysiological process that ultimately culminates in cardiac dysfunction and heart failure. This phenomenon includes not only the replacement of the damaged tissue by a fibrotic scar produced by activated fibroblasts/myofibroblasts but also a spatiotemporal alteration of the structural, biochemical, and biomechanical parameters in the ventricular wall, eliciting a reactive remodeling process. Though mechanical stress, post-infarct homeostatic imbalances, and neurohormonal activation are classically attributed to cardiac fibrosis, emerging evidence that supports the roles of immune system modulation, inflammation, and metabolic dysregulation in the initiation and progression of cardiac fibrogenesis has been reported. Adaptive changes, immune cell phenoconversions, and metabolic shifts in the cardiac nonmyocyte population provide initial protection, but persistent altered metabolic demand eventually contributes to adverse remodeling of the heart. Altered energy metabolism, mitochondrial dysfunction, various immune cells, immune mediators, and cross-talks between the immune cells and cardiomyocytes play crucial roles in orchestrating the transdifferentiation of fibroblasts and ensuing fibrotic remodeling of the heart. Manipulation of the metabolic plasticity, fibroblast-myofibroblast transition, and modulation of the immune response may hold promise for favorably modulating the fibrotic response following different cardiovascular pathological processes. Although the immunologic and metabolic perspectives of fibrosis in the heart are being reported in the literature, they lack a comprehensive sketch bridging these two arenas and illustrating the synchrony between them. This review aims to provide a comprehensive overview of the intricate relationship between different cardiac immune cells and metabolic pathways as well as summarizes the current understanding of the involvement of immune-metabolic pathways in cardiac fibrosis and attempts to identify some of the previously unaddressed questions that require further investigation. Moreover, the potential therapeutic strategies and emerging pharmacological interventions, including immune and metabolic modulators, that show promise in preventing or attenuating cardiac fibrosis and restoring cardiac function will be discussed.

Reflecting on the cardiac toxicity in non-small cell lung cancer in the era of immune checkpoint inhibitors therapy combined with thoracic radiotherapy

In recent years, immune checkpoint inhibitors (ICIs) have become a widely used treatment for non-small cell lung cancer (NSCLC), and the combination with traditional radiotherapy (RT) has shown significant potential in prolonging patient survival. However, both thoracic RT and ICIs can lead to cardiac toxicity, including radiation-induced heart damage (RIHD) and immunotherapy-related heart damage (IRHD). It still remains uncertain whether the combination of thoracic RT and immunotherapy will exacerbate acute or late cardiovascular (CV) toxicity and incidence. In this review, we summarize safety data from relevant clinical studies regarding CV toxicity for the combination therapy in NSCLC patients, explore the underlying synergetic mechanisms and common risk factors, and proposed treatment and management strategies. We hope to increase emphasis on the long-term assessment of CV toxicity risks associated with the combination therapy, and reduce the incidence of CV deaths resulting from such regimens.

Dual inhibition of glycolysis and glutaminolysis for synergistic therapy of rheumatoid arthritis

BACKGROUND

Synovial fibroblasts in rheumatoid arthritis (RAFLS) exhibit a pathological aberration of glycolysis and glutaminolysis. Henceforth, we aimed to investigate if dual inhibition of these pathways by phytobiological compound c28MS has the potential of synergistic therapy for arthritis by targeting both glucose and glutamine metabolism.

METHODS

The presence of HK2 and GLS across various cell types and associated gene expression in human synovial cells and a murine model of arthritis was evaluated by scRNA-seq. The metabolic profiling of RAFLS cells was done using H1-nuclear magnetic resonance spectroscopy under glycolytic and glutaminolytic inhibitory conditions by incubating with 3-bromopyruvate, CB839, or dual inhibitor c28MS. FLS functional analysis was conducted under similar conditions. ELISA was employed for the quantification of IL-6, CCL2, and MMP3. K/BxN sera was administered to mice to induce arthritis for in vivo arthritis experiments.

RESULTS

scRNA-seq analysis revealed that many fibroblasts expressed Hk2 along with Gls with several genes including Ptgs2, Hif1a, Timp1, Cxcl5, and Plod2 only associated with double-positive fibroblasts, suggesting that dual inhibition can be an attractive target for fibroblasts. Metabolomic and functional analysis revealed that c28MS decreased the aggressive behavior of RAFLS by targeting both upregulated glycolysis and glutaminolysis. c28MS administered in vivo significantly decreased the severity of arthritis in the K/BxN model.

CONCLUSION

Our findings imply that dual inhibition of glycolysis and glutaminolysis could be an effective approach for the treatment of RA. It also suggests that targeting more than one metabolic pathway can be a novel treatment approach in non-cancer diseases.

Oligonucleotide Therapeutics for Age-Related Musculoskeletal Disorders: Successes and Challenges

Age-related disorders of the musculoskeletal system including sarcopenia, osteoporosis and arthritis represent some of the most common chronic conditions worldwide, for which there remains a great clinical need to develop safer and more efficacious pharmacological treatments. Collectively, these conditions involve multiple tissues, including skeletal muscle, bone, articular cartilage and the synovium within the joint lining. In this review, we discuss the potential for oligonucleotide therapies to combat the unmet clinical need in musculoskeletal disorders by evaluating the successes of oligonucleotides to modify candidate pathological gene targets and cellular processes in relevant tissues and cells of the musculoskeletal system. Further, we discuss the challenges that remain for the clinical development of oligonucleotides therapies for musculoskeletal disorders and evaluate some of the current approaches to overcome these.

Dysregulated energy metabolism impairs chondrocyte function in osteoarthritis

OBJECTIVES

Metabolic pathways are a series of chemical reactions by which cells take in nutrient substrates for energy and building blocks needed to maintain critical cellular processes. Details of chondrocyte metabolism and how it rewires during the progression of osteoarthritis (OA) are unknown. This research aims to identify what changes in the energy metabolic state occur in OA cartilage.

METHODS

Patient matched OA and non-OA cartilage specimens were harvested from total knee replacement patients. Cartilage was first collected for metabolomics, proteomics, and transcriptomics analyses to study global alterations in OA metabolism. We then determined the metabolic routes by tracking [U-¹³C] isotope with liquid chromatography-mass spectrometry (LC-MS). We further evaluated cellular bioenergetic profiles by measuring oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) and investigated the effects of low-dose and short-term effects of 2-deoxyglucose (2DG) on chondrocytes.

RESULTS

OA chondrocytes showed increased basal ECAR and more lactate production compared to non-OA chondrocytes. [U-¹³C] glucose labelling revealed that less glucose-derived carbon entered the tricarboxylic acid (TCA) cycle. On the other hand, mitochondrial respiratory rates were markedly decreased in the OA chondrocytes compared to non-OA chondrocytes. These changes were accompanied by decreased cellular ATP production, mitochondrial membrane potential and disrupted mitochondrial morphology. We further demonstrated in vitro that short-term inhibition of glycolysis suppressed matrix degeneration gene expression in chondrocytes and bovine cartilage explants cultured under inflammatory conditions.

CONCLUSION

This study represents the first comprehensive comparative analysis of metabolism in OA chondrocytes and lays the groundwork for therapeutic targeting of metabolism in OA.

Increased stromal PFKFB3-mediated glycolysis in inflammatory bowel disease contributes to intestinal inflammation

Inflammatory bowel disease (IBD) is a chronic relapsing inflammation of the intestinal tract with currently not well-understood pathogenesis. In addition to the involvement of immune cells, increasing studies show an important role for fibroblasts in the pathogenesis of IBD. Previous work showed that glycolysis is the preferred energy source for fibroblasts in fibrotic diseases. 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3) is a key kinase supporting glycolysis. Increased expression of PFKFB3 in several cancers and inflammatory diseases has been previously reported, but the metabolic status of fibroblasts and the role of PFKFB3 in patients with IBD are currently unknown. Therefore, in this study, we evaluated the role of glycolysis and PFKFB3 expression in IBD. Single-sample gene set enrichment analysis (ssGSEA) revealed that glycolysis was significantly higher in IBD intestinal samples, compared to healthy controls, which was confirmed in the validation cohorts of IBD patients. Single-cell sequencing data indicated that PFKFB3 expression was higher in IBD-derived stromal cells. In vitro, PFKFB3 expression in IBD-derived fibroblasts was increased after the stimulation with pro-inflammatory cytokines. Using seahorse real-time cell metabolic analysis, inflamed fibroblasts were shown to have a higher extracellular acidification rate and a lower oxygen consumption rate, which could be reversed by inhibition of JAK/STAT pathway. Furthermore, increased expression of pro-inflammatory cytokines and chemokines in fibroblasts could be reverted by PFK15, a specific inhibitor of PFKFB3. In vivo experiments showed that PFK15 reduced the severity of dextran sulfate sodium (DSS)- and Tcell transfer induced colitis, which was accompanied by a reduction in immune cell infiltration in the intestines. These findings suggest that increased stromal PFKFB3 expression contributes to inflammation and the pathological function of fibroblasts in IBD. Inhibition of PFKFB3 suppressed their inflammatory characteristics.

Differential Metabotypes in Synovial Fibroblasts and Synovial Fluid in Hip Osteoarthritis Patients Support Inflammatory Responses

Changes in cellular metabolism have been implicated in mediating the activated fibroblast phenotype in a number of chronic inflammatory disorders, including pulmonary fibrosis, renal disease and rheumatoid arthritis. The aim of this study was therefore to characterise the metabolic profile of synovial joint fluid and synovial fibroblasts under both basal and inflammatory conditions in a cohort of obese and normal-weight hip OA patients. Furthermore, we sought to ascertain whether modulation of a metabolic pathway in OA synovial fibroblasts could alter their inflammatory activity. Synovium and synovial fluid was obtained from hip OA patients, who were either of normal-weight or obese and were undergoing elective joint replacement surgery. The synovial fluid metabolome was determined by 1H NMR spectroscopy. The metabolic profile of isolated synovial fibroblasts in vitro was characterised by lactate secretion, oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) using the Seahorse XF Analyser. The effects of a small molecule pharmacological inhibitor and siRNA targeted at glutaminase-1 (GLS1) were assessed to probe the role of glutamine metabolism in OA synovial fibroblast function. Obese OA patient synovial fluid (n = 5) exhibited a different metabotype, compared to normal-weight patient fluid (n = 6), with significantly increased levels of 1, 3-dimethylurate, N-Nitrosodimethylamine, succinate, tyrosine, pyruvate, glucose, glycine and lactate, and enrichment of the glutamine-glutamate metabolic pathway, which correlated with increasing adiposity. In vitro, isolated obese OA fibroblasts exhibited greater basal lactate secretion and aerobic glycolysis, and increased mitochondrial respiration when stimulated with pro-inflammatory cytokine TNFα, compared to fibroblasts from normal-weight patients. Inhibition of GLS1 attenuated the TNFα-induced expression and secretion of IL-6 in OA synovial fibroblasts. These findings suggest that altered cellular metabolism underpins the inflammatory phenotype of OA fibroblasts, and that targeted inhibition of glutamine-glutamate metabolism may provide a route to reducing the pathological effects of joint inflammation in OA patients who are obese.

Changes in Thyroid Hormone Signaling Mediate Cardiac Dysfunction in the Tg197 Mouse Model of Arthritis: Potential Therapeutic Implications

Background Rheumatoid Arthritis (RA) patients show a higher risk of heart failure. The present study investigated possible causes of cardiac dysfunction related to thyroid hormone (TH) signaling in a RA mouse model. Methods A TNF-driven mouse model of RA[TghuTNF (Tg197)] was used. Cardiac function was evaluated by echocardiography. SERCA2a and phospholamban protein levels in left ventricle (LV) tissue, thyroid hormone levels in serum, TH receptors in LV and TH-related kinase signaling pathways were measured. T3 hormone was administered in female Tg197 mice. Results We show LV and atrial dilatation with systolic dysfunction in Tg197 animals, accompanied by downregulated SERCA2a. We suggest an interaction of pro-inflammatory and thyroid hormone signaling indicated by increased p38 MAPK and downregulation of TRβ1 receptor in Tg197 hearts. Interestingly, female Tg197 mice showed a worse cardiac phenotype related to reduced T3 levels and Akt activation. T3 supplementation increased Akt activation, restored SERCA2a expression and improved cardiac function in female Tg197 mice. Conclusions TNF overexpression of Tg197 mice results in cardiac dysfunction via p38 MAPK activation and downregulation of TRβ1. Gender-specific reduction in T3 levels could cause the worse cardiac phenotype observed in female mice, while T3 administration improves cardiac function and calcium handling via modified Akt activation.

Oligonucleotide Therapies in the Treatment of Arthritis: A Narrative Review

Osteoarthritis (OA) and rheumatoid arthritis (RA) are two of the most common chronic inflammatory joint diseases, for which there remains a great clinical need to develop safer and more efficacious pharmacological treatments. The pathology of both OA and RA involves multiple tissues within the joint, including the synovial joint lining and the bone, as well as the articular cartilage in OA. In this review, we discuss the potential for the development of oligonucleotide therapies for these disorders by examining the evidence that oligonucleotides can modulate the key cellular pathways that drive the pathology of the inflammatory diseased joint pathology, as well as evidence in preclinical in vivo models that oligonucleotides can modify disease progression.

Recent advances and future avenues in understanding the role of adipose tissue cross talk in mediating skeletal muscle mass and function with ageing

Sarcopenia, broadly defined as the age-related decline in skeletal muscle mass, quality, and function, is associated with chronic low-grade inflammation and an increased likelihood of adverse health outcomes. The regulation of skeletal muscle mass with ageing is complex and necessitates a delicate balance between muscle protein synthesis and degradation. The secretion and transfer of cytokines, long non-coding RNAs (lncRNAs) and microRNAs (miRNAs), both discretely and within extracellular vesicles, have emerged as important communication channels between tissues. Some of these factors have been implicated in regulating skeletal muscle mass, function, and pathologies and may be perturbed by excessive adiposity. Indeed, adipose tissue participates in a broad spectrum of inter-organ communication and obesity promotes the accumulation of macrophages, cellular senescence, and the production and secretion of pro-inflammatory factors. Pertinently, age-related sarcopenia has been reported to be more prevalent in obesity; however, such effects are confounded by comorbidities and physical activity level. In this review, we provide evidence that adiposity may exacerbate age-related sarcopenia and outline some emerging concepts of adipose-skeletal muscle communication including the secretion and processing of novel myokines and adipokines and the role of extracellular vesicles in mediating inter-tissue cross talk via lncRNAs and miRNAs in the context of sarcopenia, ageing, and obesity. Further research using advances in proteomics, transcriptomics, and techniques to investigate extracellular vesicles, with an emphasis on translational, longitudinal human studies, is required to better understand the physiological significance of these factors, the impact of obesity upon them, and their potential as therapeutic targets in combating muscle wasting.