Pathogenesis of lupus nephritis: RIP3 dependent necroptosis and NLRP3 inflammasome activation
Introduction
Necroptosis is a regulated cell necrosis process sharing characteristics unique to necrosis and apoptosis [1]. With the inhibition of caspase-8, receptor interacting protein kinase 1 (RIP1) and RIP3 are recruited and auto-phosphorylated [2]. The RIP1-RIP3 complex recruits the mixed lineage kinase domain like pseudokinase (MLKL) and promotes its phosphorylation [2]. The phosphorylated MLKL inserts itself into the plasma membrane, compromising its integrity of the plasma membrane [2]. This mechanism may lead to cell death [3]. NLRP3 inflammasome activation is often accompanied with the necroptosis pathway activation [4]. RIP3 is the essential molecule for both necroptosis pathway and NLRP3 inflammasome activation [5]. Although the NLRP3 inflammasome activation was initially thought to be dependent on the necroptotic pathway activation, RIP3 dependent NLRP3 inflammasome activation has been shown to be independent of necroptotic cell death [5].
Cell death has been considered a major contributing factor in the pathogenesis of SLE and lupus nephritis (LN) [6,7]. Of all the mechanisms that lead to cell death, necroptosis has been the least interrogated regarding its contribution in LN. In this study, the RIP3 dependent necroptosis pathway and NLRP3 inflammasome activation are shown to be present in the kidneys of patients with LN and in the kidneys of lupus-prone mice. In addition, inhibition of RIP3 kinase is effective in treating LN in mice, suggesting that RIP3 is a target for the treatment of lupus and LN.
Section snippets
Animals
Female 10-week-old MRL/lpr mice were purchased from SLAC Laboratory Animal Company (Shanghai, China). Both MRL/lpr and NZM2328 [8] were maintained in a specific pathogen-free condition at the Experimental Animal Center of Sun Yat-sen University. The study protocol was approved by the Ethics Committee of Sun Yat-sen University and all experiments were performed in accordance with the National Institutes of Health Guide for Care and Use of Animals. Only female mice were used in this study.
GSK872 treatment
A RIP3
Activation of RIP3 and the necroptosis pathway in podocytes of class IV LN
In order to demonstrate the activation of RIP3 and the necroptosis pathway in podocytes, we took advantage of the availability of Abs to p-RIP3 and p-MLKL, which are the phosphorylated active forms of RIP3 and MLKL. As shown in Fig. 1A and B, Abs to p-RIP3 and p-MLKL stained the glomeruli from a patient with Class IV LN. With anti-synaptopodin Ab to identify podocytes, the staining of p-RIP3 and p-MLKL were localized in the podocytes. From the staining patterns by the anti-synatopodin Ab and
Discussion
Since the discovery of necroptosis, its roles in various kidney diseases have been studied. Mulay et al. reported that the necroptosis pathway was activated and the pharmacological inhibition of RIP3 or MLKL or specific gene knockout of RIP3 or MLKL exerted protective effects and limited tissue injury and organ failure in a crystal induced acute kidney injury (AKI) model [17]. The necroptosis pathway has also been identified in tubular cells in renal ischemia/reperfusion injury [18] and in
Conclusion
Our results demonstrate that RIP3 dependent necroptosis and NLRP3 inflammasome pathways are activated in podocytes during LN. IgG from diseased lupus-prone mice induced both necroptosis and NLRP3 inflammasome pathways activation in a podocyte cell line and this activation was blocked by GSK872, a RIP3 inhibitor. Inhibition of RIP3 kinase may be a novel therapeutic approach to treat LN and SLE.
Acknowledgement
All authors were involved in drafting and revising the article, and all authors approved the final version to be published. Dr. Yang had full access to all of the data in the study and took responsibility for the integrity of the data and the accuracy of the data analysis.
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These authors contributed equally to this work.