Abstract
Type 2 diabetes is a complex multifactorial metabolic disease characterized by elevate glucose blood levels. Among genetic factors, hyperglycemia and hyperlipidemia can trigger and exacerbate diabetogenesis. There are several reports describing how chronically elevated glucose and fatty acids lead to a gradual loss of pancreatic β-cell mass and function (Rhodes, 2005; Mathis, Vence, & Benoist, 2005). Increased metabolic stress results in activation of proinflammatory signalling pathways, which ultimately lead to β-cell death. Recent high-density microarray experiments, on the INS-1 pancreatic β-cell transcriptome (Mark D. Turner, unpublished data), have identified genes and proteins whose expression is most sensible to the glucolipotoxic environment. Among 10% of genes found to show two-fold increase in expression (following exposure to glucolipotoxicity), the strongest candidate linked to islet inflammation and β-cell death was found to be TNFRSF5 (encoding CD40/TNFR5). This data was confirmed by independent quantitative PCR analysis (Mark D. Turner, unpublished data) showing a 3.62 fold change in TNFRSF5 expression, induced by high glucose and fatty acid environment.
CD40/TNFR5 protein expression was examined in detail through a combination of Western Blot and confocal microscopy. Moreover, CD40 molecular function was confirmed using an RNA interference strategy in order to knock-down CD40 and subsequently, studying the effects of knock-down on molecules likely to have a major role in CD40 signalling. These included TRAF2, TRAF3, TRAF6, STAT1 and NF-kB.
These studies show that, among all the genes most likely related to inflammation and apoptosis, CD40 is the most upregulated. Furthermore, TRAF2, TRAF3, TRAF6 and STAT1 show upregulation in the same experimental conditions.
A similar pattern of CD40 upregulation was also described in isolated mouse islets, high fat-fed mice and human islets (donated post-mortem); therefore, this may be a possible conserved pathway of cellular death, triggered by glucolipotoxicity.
