Abstract
Background and Aims
Pro-inflammatory cytokines are one of several factors which contribute to the progression of diabetic kidney disease (DKD), a condition characterized by chronic kidney inflammation which results in the tubulointerstitial fibrosis which contributes to the progression of DKD. Interleukin 1 (IL-1) two main agonists IL-1α and IL-1β activate a pro-inflammatory cascade in response to different inflammatory stimuli, including hyperglycemia. It was previously shown that a deficiency of NLRP3 which is required for the conversion of IL-1 to its active state, protects mice from the development and progression of DKD. We hypothesize that the chronic hyperglycemia in diabetic patients triggers the activation and release of IL1α and/or IL-1β from renal tubular cells and that this activation leads to the tissue fibrosis. We aim to assess Il-1 and fibronectin expression in an immortalized proximal tubule epithelial cell line from normal adult human kidney (HK-2). In addition, we evaluate the influence of Anakinra™, a pharmaceutical inhibitor of the Il-1 receptor, currently indicated mainly for rheumatoid diseases, on the levels of fibronectin expression in this model.
Methods
HK-2 cells were cultured and treated with either physiological glucose concentration (5.5mM), high glucose (30mM) or 30mM mannitol as osmotic control for 24 hours to evaluate their effects on Il-1 expression and fibronectin expression. mRNA levels of IL-1α, IL-1β and fibronectin were assessed in q-PCR, and protein expression levels were quantified by western blotting. Immunofluorescence was used to visually demonstrate the presence of IL-1α and IL-1β upon stimulation. Finally, Anakinra™ was added to the tissue cultures in a range of physiologic prescribed concentrations and its effect on cell fibrosis was assessed by the measurement of fibronectin expression 24 hours later by western blotting.
Results
mRNA and protein expression of IL-1α but mostly IL-1β was elevated in HK-2 cells under hyperglycemic conditions but not in physiological glucose environment or under high osmotic conditions. Fibronectin levels were elevated in the high glucose treated cells compared with control. Finally, Anakinra™ was found to attenuate fibronectin expression under high glucose conditions, compared with the untreated cells.
Conclusion
Proinflammatory IL-1α and IL-1β cytokines are expressed by HK-2 cells upon stimulation with glucose and result in the fibrosis on the cells measured by the production of fibronectin. The addition of Anakinra™, an IL-1 receptor blocker, to the cell culture attenuate the expression of fibronectin by the tubular cells. Our research is the first to describe a causation between hyperglycemia, IL-1 elevated levels and fibrosis in HK-2 cells, as demonstrated by the beneficial effect of Anakinra™ on lowering fibronectin expression.
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