Background/Purpose: Pro-inflammatory T-cell development underlies the pathogenesis of systemic lupus erythematosus (SLE). Activation of the mechanistic target of rapamycin (mTOR) plays a central role in T-cell lineage specification both under physiological conditions and during inflammation in SLE. Persistent mitochondrial hyperpolarization (MHP) and the accumulation of mitochondria underlie mTOR activation which serves as a biomarker of pathogenesis and target for treatment in SLE (Nat Rev Rheumatol 2016; 12: 169-82). HRES-1/Rab4, a small GTPase enzyme regulating endosomal trafficking, is overexpressed in lupus T cells and triggers the accumulation of mitochondrial mass and the activation of mTOR. Therefore, understanding metabolic consequences of HRES-1/Rab4 overexpression is expected to shed light on the mechanisms of proinflammatory T cell lineage development in SLE.

Methods: To study the effects of Rab4A expression and mTOR pathway activity in T cells, a site-specific Cre/Lox recombinase system was used to knock down Rab4A expression in lupus-prone triple congenic SLE 1.2.3 mice. The mice were treated with 3 mg/kg intraperitoneal rapamycin three times weekly or solvent control or 10 g/l N-acetylcysteine (NAC) in the drinking water for 14 weeks starting at 27 weeks of age. The metabolic flux was characterized by feeding ¹³C-stable isotope labeled nutrients, such as glucose or glutamine, to cells in culture and subsequently measuring isotope labeled metabolites using liquid chromatography-mass spectrometry (LC-MS) after the preparation of cell extracts.

Results: Activation of Rab4A in triple congenic SLE 1.2.3 (B6.TC/ Rab4A^Q72L) mice carrying constitutively active Rab4A^Q72L alleles had earlier and more severe onset of glomerulonephritis (GN), ANA production and proteinuria than parental lupus-prone controls (B6.TC). In turn, deletion of Rab4A in T cells blocked GN, ANA production and proteinuria. Rapamycin and NAC reduced disease activity in B6.TC/ Rab4A^Q72L mice. Rapamycin decreased metabolic flux in CD8+ T cells from ¹³C -labeled glutamine into mitochondrial tricarboxylic cycle metabolites, such as alfa-ketoglutarate (38% decrease, p=0.005), citrate (37% decrease, p=0.0018) and malate (20% decrease, p=0.025). NAC increased the metabolic flux derived from ¹³C-labeled glutamine in CD8+ T cells into alfa-ketoglutarate (66% increase, p=0.046), citrate (53% increase, p=0.048) and malate (51% increase, p=0.032). T cell-specific deletion of Rab4A increased ¹³C-labeled glucose flux into the non-oxidative pentose phosphate pathway (PPP) metabolite, sedoheptulose-7-phosphate (180% increase, p=0.002) and glycolysis intermediates glucose-6-phosphate/fructose-6-phosphate (61% increase, p=0.034) in CD4+ T cells. Rab4A deletion increased glutathione concentration in CD4+ T cells (101% increase, P=0.014).

Conclusion: mTOR pathway blockade and Rab4A inactivation may provide therapeutic targets for correcting pro-inflammatory metabolic dysfunction of T cells in SLE.

« Back to ACR Convergence 2020

ACR Meeting Abstracts - https://acrabstracts.org/abstract/mtor-signaling-pathway-blockade-and-rab4-expression-affects-metabolism-of-lupus-t-cells/