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

Abstract

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.

Combined – whole blood and skin fibroblasts- transcriptomic analysis in Psoriatic Arthritis reveals molecular signatures of activity, resistance and early response to treatment

“…Skin is an important target tissue in PsA and therefore, we sought to explore the contribution of dermal fibroblasts -the main regulators of ECM homeostasis- in disease pathogenesis. Our transcriptomic analysis revealed that PsA fibroblasts exhibited greater proliferation and increased mitochondrial respiration compared to fibroblasts from HI, which could underpin their activated phenotype ( 49 , 50 ). Notably, PsA fibroblasts also displayed decreased expression of transcripts involved in TNFα signaling and IFN response, possibly shaping a counteracting immunosuppressive adaptation to the inflammatory microenvironment of the psoriatic skin.…”

Analysis of contact pressure in a 3D model of dual-mobility hip joint prosthesis under a gait cycle

“…Second, in actual conditions, hip joint implants are lubricated with synovial fluid, which is a natural human joint lubricant. Unfortunately, the current model still maintains dry contact by negating the influence of the synovial fluid 45,46 . Next, the materials used-SS 316L and UHMWPE-are assumed to be linearly elastic.…”

Obesity defined molecular endotypes in the synovium of patients with osteoarthritis provides a rationale for therapeutic targeting of fibroblast subsets

“…Synovial joint tissue ( n = 32) was collected peri‐operatively and used to isolate and characterise primary SF as previously described. 16 , 24 , 25 Each joint sample collected was from an independent patient undergoing arthroscopy at a single anatomical joint, see Supplementary Materials (SM. 1 ) for the summary of patient characteristics.…”