Background/Purpose:

Systemic lupus erythematosus (SLE) is a potentially fatal autoimmune disease that involves all organs of the body. Without a known cure, a detailed understanding of pathogenesis is vital for development of new treatments. The polymorphic Rab4a locus has been associated with genetic susceptibility and protection from lung disease in patients with SLE (Arthritis Rheum 58: 532-540). Rab4a is overexpressed in T cells of patients and mice with SLE (J Immunol 182: 2063-73). To determine the role of Rab4a in pathogenesis, its impact on intra-alveolar hemorrhage (IAH), a fatal complication of pulmonary involvement, was investigated in Rab4A-KO^CD4Cre (KO) mice lacking expression of Rab4a in T cells relative to wild-type (WT) controls. Additionally, the role of Rab4a in T-cell lineage specification and underlying metabolic pathways was investigated in mice and human T-cell lines with modulated Rab4a activity.

Methods:

Mice matched for age and gender were injected intraperitoneally with 0.5 ml per 20 g of body weight of pristane and evaluated for pulmonary capillaritis. 14 days after injection, spleen and lung tissues were harvested and examined for lineage specification within the adaptive and innate arms of the immune system by flow cytometry. CD4⁺CD25⁺ T cells were analyzed for regulatory T cell (Treg) function. Metabolic studies were completed using the Seahorse Metabolic Flux Analyzer.

Results:

Pulmonary vasculitis scores were increased in Rab4A-KO^CD4Cre mice relative to WT controls, which was underlain by 5.7-fold (p=0.0003) expansion of Gr-1⁺ neutrophils in the lung of KO mice. Among infiltrating T lymphocytes, CD4⁺ cells were increased by 42% (p=0.0018) and CD8⁺ cells were depleted by 45% (p=0.0037). T_H1 cells, CD4⁺CD25⁺ and CD8⁺CD25⁺ Tregs were expanded by 9.4-fold (p=0.002), 4.6 fold (p=0.0009) and 2.6-fold (p=0.017), respectively. mTORC1 activities were decreased in all CD4⁺ T cells and CD4⁺CD25⁺ Tregs of the KO mice by 45% (p=0.01) and 29% (p=0.027), respectively. CD4⁺CD25⁺ FoxP3⁺/Akt^– Tregs were depleted by 45% (p=0.02). The suppressor activity of CD4⁺CD25⁺ Tregs was diminished 3.8-fold (±0.05, p=0.04) in KO mice. Glycolysis in CD4⁺ T_H1 cells and Tregs of Rab4A-KO^CD4Cre mice was diminished by 27% (p=0.02) and 35% (p=0.029). Along this line, glycolysis was also reduced by 22% in Jurkat T cells overexpressing dominant negative Rab4a^S27N (p=0.004). In contrast, overexpression of wild-type Rab4a enhanced glycolysis in Jurkat cells by 72% (p=5.41E-06). 1 mg/kg of rapamycin, which blocked nephritis in lupus-prone mice (Ann Rheum Dis 73: 1888-97), failed to prevent pristane-induced IAH.

Conclusion:

Rab4a controls metabolic fitness and mTORC1-dependent expansion and function of Tregs, and thus it protects against IAH in a mouse model of SLE.

« Back to 2017 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/rab4a-control-over-glycolytic-metabolism-and-t-cell-lineage-specification-protects-from-intra-alveolar-hemorrhage-in-mouse-model-of-sle/