Leptin modulates T cells responses in autoimmune arthritis

Abstract

Leptin, a protein hormone encoded by obese (ob) gene, is mainly produced by adipocytes. Leptin plays an important role in regulating neuroendocrine function and energy metabolism. As a cytokine, leptin is involved in modulating the hematopoiesis and lymphopoiesis. Although leptin has been found to promote T cells activation, it is largely unclear whether and how leptin regulates T cell differentiation and function.

Leptin has been associated with disease severity in rheumatoid arthritis (RA). Elevated leptin levels have been detected in the sera and synovial fluid of active RA patients. Th17 cells play key roles in synovitis and joint damage during arthritis development. However, the role of leptin on Th17 cells has not been investigated so far. In culture, leptin promoted Th17 cells differentiationfrom naïve 〖CD4〗^+ T cells via upregulating ROR-γt expression. Moreover, Th17 cells and IL-17 levels were significantly increased in leptin-treated naïve CD4+ T cells. Moreover, this study found that synoviocytes and chondrocytes produced large amounts of leptin especially during acute and chronic stages of mice with collagen-induced arthritis (CIA). Furthermore, leptin levels, Th17 cells in the joint and IL-17 levels in the synovial fluid were closely related to disease activity. Leptin intraarticular injection led to earlier onset of disease, higher clinical score, and more severe joint destruction compared with PBS-treated control mice. Importantly, leptin-injected mice had higher percentages of Th17 cells and cell numbers, elevated IL-17 levels in the synovial fluid, and increased infiltration of Th17 cells in the inflamed joint tissues compared with PBS-treated mice.

T follicular helper (Tfh) cells are indispensible for pathogenic autoantibodies production. However, whether leptin receptor (ObR) signaling has a role on Tfh cells and its implication in CIA remain elusive. Upon a T cell-dependent antigen TNP-KLH immunization, germinal center (GC) response, plasma cells (PCs) and memory B cells formation were impaired in db/db mice compared with wild-type (WT) controls. In coculture of Tfh cells from db/db and WT mice with WT GC B cells, anti-TNP IgGs titers in supernatants of db/db Tfh cells were significantly reduced. Intravenously transfer of naïve CD4+ T cells from db/db and WT mice to BoyJ recipient mice, donor CD4+ T cells from db/db mice showed impaired Tfh cells generation in spleens of BoyJ recipient mice compared with mice received with WT CD4+ T cells. These data indicated that ObR-mediated signaling intrinsically modulate Tfh cells generation. In culture, leptin promoted Tfh cells differentiation via inducing Bcl6 expression, and increased IL-21 production in Tfh cells in a dose-dependent manner. Leptin significantly enhanced the phosphorylation of STAT3, upregulated Bcl6 expression, and increased p-STAT3 binding to the Il21 promoter in CD4+ T cells with leptin receptor b (Ob-Rb) overexpression. Upon CIA induction, db/db mice exhibited ameliorated disease severity with impaired Tfh cells response. However, WT Tfh cells transfer to db/db mice restored GC responses, PCs formation, antibody production, and exacerbated synovium inflammation and joint damage in db/db recipient mice.

Together, these findings demonstrate that leptin modulates arthritis development via enhancement of Th17 and Tfh cells responses.