Mitochondrial Control of Proteasomal Psmb5 Drives the Differentiation of Tissue‐Resident Memory T Cells in Patients with Rheumatoid Arthritis

Objective To explore T cell‐intrinsic mechanisms underpinning the mal‐differentiation of tissue‐resident memory T (Trm) cells in patients with rheumatoid arthritis (RA). Methods Circulating T cells from patient with RA and healthy individuals were used for Trm cell differentiation. The role of Hobit in Trm differentiation was investigated through targeted silencing experiments. Psmb5 expression regulation was explored by identifying BRD2 as a key transcription factor, with the interaction validated through chromatin immunoprecipitation‐quantitative polymerase chain reaction. The impact of BRD2 succinylation on Trm differentiation was examined by manipulating succinyl‐CoA levels in T cells. Humanized NSG chimeras representing synovitis provided insights into Trm infiltration in RA synovitis and were used for translational experiments. Results In patients with RA, a notable predisposition of CD4+ T cells toward differentiation into Trm cells was observed, demonstrating a positive correlation with the disease activity score 28. Remarkably, Hobit was a pivotal facilitator in the formation of RA CD4+ Trm cells. Mechanistic studies unveiled the dysregulation of proteasomal Psmb5 in T cells of patients with RA as the key factor contributing to elevated Hobit protein levels. The deficiency of proteasomal Psmb5 was intricately linked to BRD2, with succinylation exerting a significant impact on Psmb5 transcription and Trm cell differentiation. This heightened BRD2 succinylation was attributed to elevated levels of mitochondrial succinyl‐CoA in RA T cells. Consequently, targeting succinyl‐CoA within CD4+ T cells controlled the inflammation of synovial tissues in humanized chimeras. Conclusion Mitochondrial succinyl‐CoA fosters the succinylation of BRD2, resulting in compromised transcription of proteasomal Psmb5 and the differentiation of Trm cells in RA.