Autoinflammation in the TNF Receptor-Associated Periodic Syndrome (TRAPS): Pathophysiology and Implications for Treatment

• Main Author: Bulua, Ariel C
• Format: Dissertation
• Language: English
• Subjects: health sciences, immunology
• ISBN: 1124916172; 9781124916170

Tumor necrosis factor receptor-associated periodic syndrome (TRAPS) is an autosomal dominantly inherited autoinflammatory disease characterized by recurrent fevers, abdominal pain, migratory rash, and inflammation. The disorder is caused by missense mutations in the type 1 TNF receptor (TNFR1). TRAPS associated mutant receptors do not bind TNF, do not traffic to the cell surface, and instead are retained at high levels in the endoplasmic reticulum. Accumulation of the mutant receptor leads to elevated activation of p38 and JNK MAP kinases (MAPKs) and enhanced production of inflammatory cytokines, but the signaling pathways responsible for these effects remain unknown.
In this work, I have investigated how the abnormal TNFR1 protein leads to enhanced inflammatory responses in TRAPS. Reactive oxygen species (ROS) can negatively regulate MAPK phosphatases and promote MAPK activation, similar to what is observed in TRAPS. Thus, we sought to determine whether ROS play a role in disease pathogenesis and to elucidate the cellular source of ROS underlying these effects. Using both mouse embryonic fibroblasts from knock-in mice and human immune cells, we show elevated baseline ROS in TRAPS. In addition, antioxidant treatment decreases the sustained MAPK phosphorylation and inflammatory cytokine production in TRAPS cells. gp91phox and p22 phox NADPH oxidase subunits are dispensable for inflammatory cytokine production, indicating that NADPH oxidases are not the source of pro-inflammatory ROS. TNFR1 mutant cells exhibit altered mitochondrial function with enhanced oxidative capacity and mitochondrial ROS generation, and pharmacological blockade of mitochondrial ROS efficiently reduces inflammatory cytokine production after lipopolysaccharide (LPS) stimulation in cells from TRAPS patients and healthy controls. These findings suggest that mitochondrial ROS may be a novel therapeutic target for TRAPS and other inflammatory diseases. I have also studied antigen presentation to T cells in dendritic cells from mice harboring TNFR1 mutations associated with TRAPS. The results show no enhancement of costimulatory molecules or antigen presentation in TNFR1 mutant cells, providing a possible explanation for the purely autoinflammatory and not autoimmune features of TRAPS. Finally, I have analyzed and conducted long-term follow-up in a clinical trial testing the efficacy of etanercept, a soluble TNF-receptor-2 immunoglobulin fusion protein, in patients with TRAPS.