LTK deficiency induces macrophage M2 polarization and ameliorates Sjogren's syndrome by reducing chemokine CXCL13

Abstract

Background

Sjogren's syndrome (SS) is an autoimmune disease involving macrophage infiltration of the exocrine glands. LTK, a receptor tyrosine kinase, is involved in many autoimmune diseases, such as lupus erythematosus. The objectives of this study was to explore the impact of LTK on autophagy in SS.

Methods

The NCBI Gene Expression Omnibus (GEO) database was used to screen for differentially expressed genes (DEGs) in SS patients and validated by quantitative reverse transcription PCR (RT-qPCR) in A253 cells with EGF and IFN-γ. Meanwhile, lentiviral vectors were used to transfect A253 cells for stable LTK silencing. CCK-8, flow cytometry, and transmission electron microscopy (TEM), Western blotting (WB) was employed to assess proliferation, apoptosis, autophagy, and autoimmune antigens (Ro52/SSA and La/SSB) in A253 cells. Then, macrophages were treated with 100 ng/ml of LPS to induce the polarization of macrophages towards the M1 phenotype, while macrophages were treated with IL-4 to activate the macrophage M2 phenotype. LTK-silenced A253 cells were co-cultured with macrophages. WB as well as flow cytometry were used to assess macrophage polarization markers. Furthermore, protein-antibody microarrays were utilized to analyze downstream proteins regulated by LTK. Finally, the functionality of LTK was confirmed in NOD/ShiLtJ mice.

Results

LTK expression in the GEO database was increased in SS patients. And LTK was also significantly increased by EGF and IFN-γ. Knockdown of LTK increased proliferation and autophagy in A253 cells. While LTK deficiency inhibited the expression of Ro52/SSA and La/SSB, and apoptosis in A253 cells. Furthermore, LTK-silenced A253 cells promoted polarization of macrophages towards the M2 phenotype, which is associated with the pathogenesis of SS. Knockdown of LTK resulted in reduced expression of CXCL13, which in turn triggered macrophage M2 polarization. Additionally, LTK deficiency ameliorated submandibular gland tissue damage and inhibited autoimmune antigens secretion in NOD/ShiLtJ mice. In addition, the expression of autophagy markers and M2 polarization markers in the submandibular gland tissue was increased by shLTK.

Conclusion

LTK could promote progressive SS pathogenesis via CXCL13. This discovery indicates that targeting LTK/CXCL13 could be a potential therapeutic strategy for the clinical management of SS.