EHHADH Delays Articular Cartilage Degeneration By Promoting Fatty Acid β-oxidation In Chondrocytes

ObjectiveOsteoarthritis(OA)is the most common degenerative joint disease and has become one of the three major killers threatening human health.In the past ten years,OA has been a research hotspot,but its pathogenesis has not yet been elucidated.Chondrocytes are the only cell type of mature articular cartilage,and the disorder of lipid metabolism in chondrocytes is an important pathogenic factor of OA.Previous studies have found that abnormal fatty acid metabolism in OA articular cartilage is associated with insufficient βoxidation.Ehhadh in peroxisomes is an important bifunctional enzyme that regulates fatty acid β-oxidation in cells.However,the role of Ehhadh in fatty acid β-oxidation in OA chondrocytes and the upstream and downstream regulatory mechanisms have not yet been elucidated.This study will use clinical samples,gene knockout mouse models and cell models to deeply explore the relationship between fatty acid metabolism and osteoarthritis,and provide new potential targets for the prevention and treatment of OA.MethodCollect articular cartilage samples from clinical OA patients,collect 3 months and 18 months old mouse knee joint samples,and collect DMM-OA model knee joint samples at 4 and 8 weeks after operation.Construct Ehhadh transgenic mice specifically knocked out in embryonic chondrocytes to study the relationship among Ehhadh,peroxisomes,and fatty acid metabolism in articular chondrocytes.Safranin O fixed green histological staining was performed on the above specimens,and the pathological degree of knee OA was evaluated based on the OARSI scoring system;immunofluorescence detection of Catalase and ABCD3 reflected the function of chondrocyte peroxisomes;immunohistochemical detection of Col2a1,Aggrecan,Sox9,and MMP13 reflect the synthesis and catabolism of chondrocytes;Bodipy staining marks intracellular lipid droplets to evaluate fatty acid metabolism in chondrocytes;overexpression of lentivirus Ehhadh and PPARa agonist fenofibrate are used to intervene articular chondrocytes in vivo,To observe the effect of enhanced Ehhadh expression in chondrocytes on osteoarthritis.mRNA sequencing of knee articular cartilage of transgenic mice and their littermate controls was performed to explore the specific mechanism of Ehhadh regulating fatty acid metabolism in chondrocytes.ResultsFatty acid metabolism is an important factor leading to osteoarthritis.Osteoarthritis can cause down-regulation of Ehhadh expression in articular chondrocytes and downregulation of peroxisome-related functional proteins Ctalase and ABCD3.The study found that Ehhadh knockout mice in chondrocytes showed a more obvious OA phenotype after DMM,and Ehhadh deletion in chondrocytes would cause structural and functional abnormalities of peroxisomes and mitochondria,promote intracellular lipid deposition and Apoptosis,together they can induce the disorder of cartilage matrix metabolism and accelerate the occurrence and development of OA.In the process of OA,the intra-articular injection of overexpressed lentivirus and intragastric administration of fenofibrate can both increase the expression level of Ehhadh in chondrocytes,thereby promoting the anabolism of chondrocytes,ensuring the stability of peroxisome function and delaying osteoarthritis.inflammation.MCAD is the downstream interacting protein of Ehhadh,and Ehhadh participates in osteoarthritis by regulating the expression of MCAD and affecting the fatty acid metabolism of chondrocytes.ConclusionEhhadh deletion plays a crucial role in mediating osteoarthritis-induced disturbance of fatty acid metabolism in chondrocytes and is associated with peroxisome dysfunction.Targeted regulation of Ehhadh may provide a new therapeutic approach for OA.