Splicing factor SRSF1 limits IFN-γ production via RhoH and ameliorates experimental nephritis.

OBJECTIVE: CD4 T helper 1 (Th1) cells producing IFN-γ contribute to inflammatory responses in the pathogenesis of SLE and lupus nephritis. Moreover, elevated serum type II IFN levels precede the appearance of type I IFNs and autoantibodies in patient years before clinical diagnosis. However, the molecules and mechanisms that control this inflammatory response in SLE remain unclear. Serine/arginine-rich splicing factor 1 (SRSF1) is decreased in T cells from SLE patients, and restrains T cell hyperactivity and systemic autoimmunity. Our objective here was to evaluate the role of SRSF1 in IFN-γ production, Th1 differentiation and experimental nephritis. METHODS: T cell-conditional Srsf1-knockout mice were used to study nephrotoxic serum-induced nephritis and evaluate IFN-γ production and Th1 differentiation by flow cytometry. RNA sequencing was used to assess transcriptomics profiles. RhoH was silenced by siRNA transfections in human T cells by electroporation. RhoH and SRSF1 protein levels were assessed by immunoblots. RESULTS: Deletion of Srsf1 in T cells led to increased Th1 differentiation and exacerbated nephrotoxic serum nephritis. The expression levels of RhoH are decreased in Srsf1-deficient T cells, and silencing RhoH in human T cells leads to increased production of IFN-γ. Furthermore, RhoH expression was decreased and directly correlated with SRSF1 in T cells from SLE patients. CONCLUSION: Our study uncovers a previously unrecognized role of SRSF1 in restraining IFN-γ production and Th1 differentiation through the control of RhoH. Reduced expression of SRSF1 may contribute to pathogenesis of autoimmune-related nephritis through these molecular mechanisms.

Splicing factor SRSF1 controls T cell homeostasis and its decreased levels are linked to lymphopenia in systemic lupus erythematosus.

OBJECTIVE: Lymphopenia is a frequent clinical manifestation and risk factor for infections in SLE, but the underlying mechanisms are not fully understood. We previously identified novel roles for the RNA-binding protein serine arginine-rich splicing factor 1 (SRSF1) in the control of genes involved in signalling and cytokine production in human T cells. SRSF1 is decreased in T cells from patients with SLE and associates with severe disease. Because SRSF1 controls the expression of apoptosis-related genes, we hypothesized that SRSF1 controls T cell homeostasis and, when reduced, leads to lymphopenia. METHODS: We evaluated SRSF1 expression in T cells from SLE patients by immunoblots and analysed its correlation with clinical parameters. T cell conditional Srsf1 knockout mice were used to evaluate lymphoid cells and apoptosis by flow cytometry. Quantitative PCR and immunoblots were used to assess Bcl-xL mRNA and protein expression. SRSF1 overexpression was performed by transient transfections by electroporation. RESULTS: We found that low SRSF1 levels correlated with lymphopenia in SLE patients. Selective deletion of Srsf1 in T cells in mice led to T cell lymphopenia, with increased apoptosis and decreased expression of the anti-apoptotic Bcl-xL. Lower SRSF1 expression correlated with low Bcl-xL levels in T cells and lower Bcl-xL levels associated with lymphopenia in SLE patients. Importantly, overexpression of SRSF1 rescued survival of T cells from patients with SLE. CONCLUSION: Our studies uncovered a previously unrecognized role for SRSF1 in the control of T cell homeostasis and its reduced expression as a molecular defect that contributes to lymphopenia in systemic autoimmunity.

Estrogen-Induced hsa-miR-10b-5p Is Elevated in T Cells From Patients With Systemic Lupus Erythematosus and Down-Regulates Serine/Arginine-Rich Splicing Factor 1.

OBJECTIVE: Autoimmune diseases affect women disproportionately more than men. Estrogen is implicated in immune cell dysfunction, yet its precise molecular roles are not fully known. We recently identified new roles for serine/arginine-rich splicing factor 1 (SRSF1) in T cell function and autoimmunity. SRSF1 levels are decreased in T cells from patients with systemic lupus erythematosus (SLE) and are associated with active disease and comorbidity. However, the molecular mechanisms that control SRSF1 expression are unknown. Srsf1 messenger RNA (mRNA) has a long 3'-untranslated region (3'-UTR), suggesting posttranscriptional control. This study was undertaken to investigate the role of estrogen and posttranscriptional mechanisms of SRSF1 regulation in T cells and SLE. METHODS: In silico bioinformatics analysis of Srsf1-3'-UTR revealed multiple microRNA (miRNA; miR)-binding sites. Additional screening and literature searches narrowed down hsa-miR-10b-5p for further study. Peripheral blood T cells from healthy individuals and SLE patients were evaluated for mRNA and miRNA expression by quantitative reverse transcription-polymerase chain reaction, and SRSF1 protein levels were assessed by immunoblotting. T cells were cultured with ß-estradiol, and transient transfections were used to overexpress miRNAs. Luciferase assays were used to measure 3'-UTR activity. RESULTS: We demonstrated that estrogen increased hsa-miR-10b-5p expression in human T cells, and hsa-miR-10b-5p down-regulated SRSF1 protein expression. Mechanistically, hsa-mir-10b-5p regulated SRSF1 posttranscriptionally via control of its 3'-UTR activity. Importantly, hsa-miR-10b-5p expression levels were elevated in T cells from healthy women compared to healthy men and also elevated in T cells from SLE patients. CONCLUSION: We identified a previously unrecognized molecular link between estrogen and gene regulation in immune cells, with potential relevance to systemic autoimmune disease.