Systemic Lupus Erythematosus (SLE), or lupus, is an autoimmune disease that affects multiple organs and tissues, including skin, heart, kidneys and connective tissues. SLE pathology indicates that CD4+ T cells and B cells lose self-tolerance resulting in autoantibody production. Because CD4+ T cells play such a crucial role in SLE pathogenesis, they are a common therapeutic target. Activated T cells require more energy than quiescent T cells and display increased glycolysis and mitochondrial metabolism. A fascinating new report in Science Translational Medicine (Yin et al. 2015) demonstrates that normalizing CD4+ T cell metabolism reduces disease in mouse models of lupus and proposes an exciting new therapeutic approach for treating this disease.
B6.NZM-Sle1NZM2410/Aeg Sle2NZM2410/Aeg Sle3NZM2410/Aeg/LmoJ (007228) mice carry three lupus susceptibility loci derived from the lupus-prone NZM2410/J (002676) mouse model backcrossed into the C57BL/6J (000664) background. These triple congenic (TC) mice develop systemic autoimmunity with fatal glomerulonephritis by one year of age and exhibit many signs that resemble those observed in human lupus patients, including heavy proteinuria, elevated blood urea nitrogen, and anti-double-stranded DNA (dsDNA) antibodies.
Cellular glycolysis and mitochondrial oxidative phosphorylation can be measured by extracellular acidification (ECAR) and oxygen consumption (OCR) rates, respectively. In the Yin et al. study, CD4+ T cells collected from TC mice at 2 months (prior to lupus onset) displayed both increased ECAR and OCR compared to CD4+ T cells collected from C57BL/6J control mice. These metabolic indicators were even higher in CD4+ T cells from 9 month-old triple congenic mice with overt disease. In addition, CD4+ T cells from 9 month-old TC mice showed significantly higher spare respiratory capacity (an indicator of increased cellular energy stores), elevated mTORC1 activity (a sensor for cellular energy), and increased expression of genes in the glycolytic, fatty acid oxidation, and amino acid metabolic pathways. These data demonstrate that cellular metabolism in CD4+ T cells from triple congenic mice is significantly elevated and that targeting cell metabolism might be a novel therapeutic approach to treating lupus.
To determine whether targeting glycolysis or mitochondrial metabolism offered a valid therapeutic approach for treating lupus, Yin et al. treated activated CD4+ T cells from triple congenic mice in vitro with either 2-deoxy-D-glucose (2DG), a glucose metabolism inhibitor, or metformin, a mitochondrial electron transport inhibitor. The addition of 2DG reduced ECAR of the activated CD4+ T cells in a dose-dependent manner, and lowered the cells’ OCR. Adding metformin to the activated TC-derived CD4+ T cells also resulted in a dose-dependent reduction in OCR. Further, both 2DG and metformin dramatically reduced interferon-γ production, which is higher in TC-derived CD4+ T cells as compared to C57BL/6J control-derived T cells. In addition, metformin increased IL-2 production (which is defective in T cells from lupus patients) in activated, TC-derived CD4+ T cells in a dose-dependent fashion. These data demonstrate that inhibiting either glycolysis with 2DG or mitochondrial metabolism with metformin can partially normalize the metabolic profile of activated CD4+ T cells from triple congenic mice in vitro.
The promising data described above inspired Yin et al. to test whether targeting glycolysis and mitochondrial metabolism concurrently could be even more effective at reducing lupus-related signs in triple congenic mice than either treatment separately. Treating early disease-stage TC mice with a combination of metformin and 2DG (Met + 2DG) for 3 months dramatically reduced both ECAR and OCR in CD4+ T cells to nearly the levels observed in CD4+ T cells from either treated or untreated C57BL/6J control mice. (CD4+ T cells from normal C57BL/6J mice are not affected by this treatment.) The Met + 2DG combination therapy produced additional pleiotropic and beneficial effects in triple congenic mice, including:
As mentioned above, Met + 2DG treatment had minimal effects on control C57BL/6J mice, indicating that the treatment selectively targets the more metabolically active CD4+ T cells in triple congenic mice. Additionally, the Met + 2DG treatment reversed the lupus phenotype in both the NZBWF1/J (100008) and chronic graft-versus-host disease mouse models of lupus, demonstrating more widespread efficacy.
As in mice, CD4+ T cells collected from SLE patients display greater ECAR, OCR, and spare respiratory capacity as compared to CD4+ T cells from unaffected patients. The exciting results published in Yin et al. demonstrating that normalizing CD4+ T cell metabolism effectively reverses disease phenotypes in multiple SLE mouse models offers a promising and novel therapeutic strategy for treating human lupus patients.