Central role of nitric oxide in the pathogenesis of rheumatoid arthritis and systemic lupus erythematosus

Abstract

Nitric oxide (NO) has been shown to regulate T cell functions under physiological conditions, but overproduction of NO may contribute to T lymphocyte dysfunction. NO-dependent tissue injury has been implicated in a variety of rheumatic diseases, including systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). Several studies reported increased endogenous NO synthesis in both SLE and RA, and recent evidence suggests that NO contributes to T cell dysfunction in both autoimmune diseases. The depletion of intracellular glutathione may be a key factor predisposing patients with SLE to mitochondrial dysfunction, characterized by mitochondrial hyperpolarization, ATP depletion and predisposition to death by necrosis. Thus, changes in glutathione metabolism may influence the effect of increased NO production in the pathogenesis of autoimmunity.

Figure 1

Schematic diagram of T cell activation, nitric oxide production, and mitochondrial hyperpolarization. Nitric oxide (NO) is produced in the cytosol, the mitochondrial membrane, and at the immunological synapse of T cells. Localized NO production has been linked to targeting of endothelial NO synthase (eNOS) to the outer mitochondrial membrane and to the T-cell synapse. NO regulates many steps of T cell activation, the production of cytokines, such as IL-2, and mitochondrial hyperpolarization and mitochondrial biogenesis. NO regulates mammalian target of rapamycin (mTOR) activity. NO dependent mTOR activation induces the loss of TCRζ in lupus T cells through HRES-1/Rab4. Mitochondrial hyperpolarization is associated with depletion of ATP, which predisposes T cells to necrosis. In turn, necrotic materials released from T cells activate monocytes and dendritic cells. Solid arrows indicate processes upregulated by NO, while broken lines indicate processes down-regulated by NO. APC, antigen-presenting cell; DAG, diacylglycerol; IP₃, inositol-1,4,5-triphosphate; LAT, linker for activation of T cells; MHC, major histocompatibility complex; PIP2, phosphatidylinositol 4,5-biphosphate; PLC, phospholipase C.