The Role of Endoplasmic Reticulum Stress in Metabolic Diseases.

The endoplasmic reticulum (ER), the center of protein folding, also controls the cell's life-and-death signaling mechanisms. ER stress caused by unfolded or misfolded proteins leads to the activation of the unfolded protein response (UPR) in the cell. The UPR utilizes three main signaling pathways to restore disrupted ER homeostasis. These signaling pathways are protein kinase R-like endoplasmic reticulum kinase, inositol-requiring enzyme 1, and activating transcription factor 6. Studies have reported that ER stress (ERS) plays a role in the pathogenesis of metabolic disorders such as diabetes, obesity, atherosclerosis, and nonalcoholic liver disease. This review will briefly discuss the ERS response in these metabolic diseases.

Impaired kynurenine metabolism in patients with primary Sjögren's syndrome.

OBJECTIVES: Primary Sjögren's syndrome (pSS) is an autoinflammatory disease characterized by inflammation of the exocrine glands. Elevated inflammation causes an increase in kynurenine pathway (KP) metabolite levels by activating indoleamine 2,3-dioxygenase (IDO). The aim of this study was to measure serum KP metabolite concentrations in patients with pSS and to evaluate the relationship between these metabolites with disease activity score and clinical manifestations. DESIGN & METHODS: A total of 80 patients with pSS and 80 healthy controls were enrolled in this study. Serum tryptophan (TRP), kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxyanthranilic acid (3HAA), 3-hydroxykynurenine (3HK), quinolinic acid (QUIN) concentrations were quantified with liquid chromatography with tandem mass spectrometry (LC-MS/MS). Demographic characteristics, clinical manifestations and disease activity score (ESSDAI) of the participants were recorded. RESULTS: The serum level of KYN and QUIN were significantly higher in patients with pSS with low and moderate activity compared those healthy controls, while the serum level of TRP, KYNA/KYN and 3HK/KYN were lower. In addition, the significant difference for the serum level of KYNA was only in patients with moderate activity from healthy controls, and the difference was higher in favor of pSS patients. Moreover, the KYN/TRP levels were significantly increased with disease activity. The ESSDAI score was positively correlated with KYN/TRP ratio, but negatively correlated with KYNA/KYN ratio. CONCLUSIONS: These findings indicated that KP metabolites may play a role in the etiopathogenesis, activation and progression of pSS.