Background/Purpose:

Lymphopenia is one of the most common clinical features in patients with systemic lupus erythematosus (SLE), and associates with severe disease and comorbidities such as infections. However, the mechanisms of lymphopenia in SLE are still unclear. T cells from SLE patients exhibit numerous defects in gene expression, including altered expression the Bcl-2 family genes, which have pro- and anti-apoptotic alternative splice isoforms. By discovery approaches we previously identified the serine arginine-rich splicing factor 1 (SRSF1) in human T cells and showed that it is an important regulator of signaling and cytokine genes. SRSF1 expression levels are decreased in T cells from SLE patients, and this decrease associates with severe disease. Because SRSF1 is an important survival factor known to regulate alternative splicing of Bcl-2 genes, we evaluated the role of SRSF1 in T cell homeostasis and correlation with lymphopenia in patients with SLE.

Methods:

To delete Srsf1 selectively in T cells, we crossed Srsf1-flox mice with d.Lck.Cre transgenic mice to generate Srsf1conditional knockout (Srsf1-cko) mice, and analyzed lymphoid tissues (spleen and lymph nodes). Apoptosis was assessed in splenocytes ex vivo or after crosslinking with anti-CD95 (Fas), and flow cytometry staining for 7AAD and Annexin V. Apoptosis associated genes were analyzed by RT-qPCR. Naïve CD4 T cells from Srsf1-wt and -cko mice were stimulated with anti-CD3 and anti-CD28 antibodies for 72hrs, and total RNA was subjected to RNA-sequencing. Peripheral blood was collected from 42 SLE patients, and age-, race- and gender-matched healthy individuals. T cells were isolated by negative selection, and SRSF1 protein levels assessed by western blots. Clinical and lab tests for all patients were recorded. SLE patients were divided into lymphopenic (<1000/μL) and non-lymphopenic groups, and correlations were assessed with relative SRSF1 expression levels.

Results:

Peripheral T cell lymphopenia was observed in the Srsf1-ckomice. Lymphopenia was evident in young mice compared with aged mice, and was more profound in CD8 than CD4 T cells. Crosslinking with anti-CD95 (Fas) antibody led to increased apoptosis in T cells from Srsf1-cko mice. Gene set enrichment analysis (GSEA) of RNA-sequencing data from effector CD4 T cells of Srsf1-cko mice showed aberrant expression of genes in the apoptosis and cell cycle pathways. We validated expression levels of the Bcl-x gene and found that its anti-apoptotic long (L) isoform was decreased in spleen cells from Srsf1-cko mice. In parallel, examination of SRSF1 levels in T cells from SLE patients revealed that reduced SRSF1 protein levels correlated positively with lymphopenia in SLE patients.

Conclusion:

These results suggest that SRSF1 controls expression of survival/apoptosis-related genes in T cells andis a vital regulator of T lymphocyte homeostasis in vivo, and its reduced expression levels associate with lymphopenia in SLE patients. Therefore, the deficiency of SRSF1 may represent a molecular defect that contributes to the pathophysiology of autoimmune disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/serine-arginine-rich-splicing-factor-1-srsf1-is-essential-for-t-lymphocyte-homeostasis-and-decreased-levels-of-srsf1-correlate-with-lymphopenia-in-sle-patients/