Abstract
Background and Aims
Renal inflammation is a protective response to several types of renal insults. Resolution is the ideal outcome of acute inflammation, however fail in resolution leads to chronic inflammation, progressive renal fibrosis and finally to end-stage renal failure. Recently is has been established that resolution of inflammation is mediated not only by disappearance of pro-inflammatory signals (including lipid mediators such as leukotrienes and prostaglandins) but also by activation of specialized pro-resolving mediators (SPM) including lipid mediators such as protectins (PD) and resolvins (Rvs) derived from omega-3 fatty acids precursors.
Several authors have explored the role of different SPM in the treatment of experimental nephropathies. In the experimental model of bilateral ischemia/reperfusion pro-resolving mediators such as RvDs and PD1 were endogenously produced in the kidney in response to the injury. In this model, administration of RvD1 or PD1 before the ischemia or after the reperfusion showed a renoprotective effect. Moreover in the unilateral ureteral obstruction model RvE1 and RvD1administration inhibited interstitial fibrosis.
One of the key mediators of renal injury is Angiotensin II (AngII) that participates in the pathogenesis of renal diseases through the regulation of two key processes, inflammation and fibrosis. Therefore, the aim of this study was to investigate the effect of the pro-resolving mediator Resolvin D2 (RvD2) in AngII-induced renal injury
Method
We used C57BL/6 mice that were infused with AngII (1440 µg/kg/day o 1000 ng/Kg/min). After 7 days of AngII treatment, when hypertension was already established, mice were treated with RvD2 (100ng/mouse ip) every two days for additional 7 days. At day 14 mice were sacrificed and kidneys were removed for protein and gene expression analysis and for histological examination.
Results
In our experimental model RvD2 ameliorated renal injury assessed by expression of NGAL both at mRNA and protein levels. In addition AngII-treated mice presented significant reduction in glomerular size that was increased by RvD2 treatment reaching values comparable to control. In addition, RvD2 inhibited the activation of inflammatory markers including COX-2, IL-6 and MCP-1 induced by AngII and reduced the number of F4/80+ infiltrated macrophages. We next evaluated the effect of RvD2 in the activation of NFκB, a key signaling pathway in inflammation. We observed that RvD2 inhibited AngII-induced NFkB activation. Moreover, RT-PCR analysis indicated that Ang II increased the expression of Tenascin C, a component of the fibrogenic niche in kidney fibrosis, as well as Type-I Collagen and Fibronectin and these levels were significantly reduced by the treatment with RvD2. These results were also confirmed by Masson-Goldner trichrome staining. Importantly, these effects were independent of changes in blood pressure. We finally studied whether the effects of RvD2 might be related to the modulation of RvDs endogenous biosynthesis pathway or RvD2 receptor GPR-18. mRNA analysis showed that AngII did not modified the expression levels of RvD2 biosynthesis enzymes including LOX-5 and LOX-15 nor GPR-18. However, RvD2 treatment increased the expression of LOX-15 and GPR-18 and downregulated LOX-5 indicating a possible auto-regulatory mechanism of RvD2
Conclusion
Our results evidence a dual beneficial effect of the pro-resolvin mediator RvD2 in Ang II-induced renal injury as RvD2 treatment reversed not only renal inflammation but also tubulo-interstitial fibrosis. Hence, synthetic pro-resolving mediators would be an interesting therapeutic option for renal diseases.
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