Dual Role of Mitogen-Activated Protein Kinase 8 Interacting Protein-1 in Inflammasome and Pancreatic beta-Cell Function

Inflammasomes have been implicated in the pathogenesis of type 2 diabetes (T2D). However, their expression and functional importance in pancreatic beta-cells remain largely unknown. Mitogen-activated protein kinase 8 interacting protein-1 (MAPK8IP1) is a scaffold protein that regulates JNK signaling and is involved in various cellular processes. The precise role of MAPK8IP1 in inflammasome activation in beta-cells has not been defined. To address this gap in knowledge, we performed a set of bioinformatics, molecular, and functional experiments in human islets and INS-1 (832/13) cells. Using RNA-seq expression data, we mapped the expression pattern of proinflammatory and inflammasome-related genes (IRGs) in human pancreatic islets. Expression of MAPK8IP1 in human islets was found to correlate positively with key IRGs, including the NOD-like receptor (NLR) family pyrin domain containing 3 (NLRP3), Gasdermin D (GSDMD) and Apoptosis-associated speck-like protein containing a CARD (ASC), but correlate inversely with Nuclear factor kappa beta 1 (NF-kappa beta 1), Caspase-1 (CASP-1), Interleukin-18 (IL-18), Interleukin-1 beta (IL-1 beta) and Interleukin 6 (IL-6). Ablation of Mapk8ip1 by siRNA in INS-1 cells down-regulated the basal expression levels of Nlrp3, NLR family CARD domain containing 4 (Nlrc4), NLR family CARD domain containing 1 (Nlrp1), Casp1, Gsdmd, Il-1 beta, Il-18, Il-6, Asc, and Nf-kappa beta 1 at the mRNA and/or protein level and decreased palmitic acid (PA)-induced inflammasome activation. Furthermore, Mapk8ip1-silened cells substantially reduced reactive oxygen species (ROS) generation and apoptosis in palmitic acid-stressed INS-1 cells. Nonetheless, silencing of Mapk8ip1 failed to preserve beta-cell function against inflammasome response. Taken together, these findings suggest that MAPK8IP1 is involved in regulating beta-cells by multiple pathways.