New insights into TNFα/PTP1B and PPARγ pathway through RNF213- a link between inflammation, obesity, insulin resistance and Moyamoya disease

Diabetic patients are always at a higher risk of ischemic diseases like coronary artery diseases. One such ischemic carotid artery disease is Moyamoya. Moyamoya disease (MMD) has been associated with diabetes Type-I and II and the causality was unclear. RNF213 is the major susceptible gene for MMD. To understand the association between diabetes mellitus and MMD we chose the major players from both the anomalies, insulin and RNF213. But before establishing a role of RNF213 in insulin regulating pathway we had to understand the involvement of RNF213 within different biological systems. For this we have adopted a preliminary computational approach to understand the prominent interactions of RNF213. Our first objective was to construct an interactome for RNF213. We have analyzed several curated databases and adapted a list of RNF213 interacting partners to develop its interactome. Then to understand the involvement of this interactome in biological functions we have analyzed major biological pathways, biological processes and prominent clusters related to this interactome through computational approach. Then to develop a pathway that might give clue for RNF213 involvement in insulin regulatory pathway we have validated the intercluster and intracluster predictions and identified a regulatory pathway for RNF213. RNF213 interactome was observed to be involved in adaptive immunity with 4 major clusters; one of the cluster involved TNFα. Immune system involves several pathways, and therefore at this point we have chosen an event-based strategy to obtain an explicit target. Immunity is mediated by many pro-inflammatory cytokines like TNFα. TNFα-mediated inflammation, obesity and insulin resistance are associated. Therefore we chose to explore the role of RNF213 in TNFα-mediated inflammation in macrophages and inflammation-mediated insulin-resistance in adipocytes. We have observed an enhancement of RNF213 gene expression by LPS mediated pro-inflammatory stimuli and suppression by PPARγ-mediated anti-inflammatory, insulin sensitizing stimuli in macrophages. A more significant response was observed in adipocytes as well. Administration of the pro-inflammatory cytokine TNFα was able to impede the reduction in RNF213 expression during adipogenesis and this effect was observed to be mediated by PTP1B. Inactivation of PTP1B abolished RNF213 expression which in turn enhanced the adipogenesis process through enhanced PPARγ. Constitutive expression of RNF213 suppressed the adipocyte differentiation by the inhibition of PPARγ. We could show the expression of RNF213 has been regulated by TNFα/PTP1B pathway and PPARγ. The constitutive expression of RNF213 during adipogenesis appears to be an adipostatic measure that obese patients acquire to inhibit further adipogenesis. This is verified in silico by analyzing the gene expression data obtained from Gene Expression Omnibus database, which showed a higher expression of RNF213 in adipose tissue samples of obese people. Overall this study gives new insights in the TNFα-mediated pathway in adipogenesis and suggests a role of RNF213 in adipogenesis via this pathway.