BACKGROUND: Remote ischemic preconditioning (RIPC) has 2 time windows for organ protection: acute and delayed. Previous studies have mainly focused on the organoprotective effects of acute RIPC. We aimed to determine whether delayed RIPC can reduce the occurrence of acute kidney injury (AKI) and postoperative complications in patients undergoing cardiac surgery. METHODS: This prospective, single-center, double-blind, randomized controlled trial involved 509 patients at high risk for AKI who were scheduled for elective cardiac surgery requiring cardiopulmonary bypass. Patients were randomized to receive RIPC (4 cycles of 5-minute inflation and 5-minute deflation on 1 upper arm with a blood pressure cuff) 24 hours before surgery or a sham condition (control group) that was induced by 4 cycles of 5-minute inflation to a pressure of 20 mm Hg followed by 5-minute cuff deflation. The primary end point was the incidence of AKI within the prior 7 days after cardiac surgery. The secondary end points included renal replacement therapy during hospitalization, change in urinary biomarkers of AKI and markers of myocardial injury, duration of intensive care unit stay and mechanical ventilation, and occurrence of nonfatal myocardial infarction, stroke, and all-cause mortality by day 90. RESULTS: A total of 509 patients (mean age, 65.2±8.2 years; 348 men [68.4%]) were randomly assigned to the RIPC group (n=254) or control group (n=255). AKI was significantly reduced in the RIPC group compared with the control group (69/254 [27.2%] versus 90/255 [35.3%]; odds ratio, 0.68 [95% CI, 0.47–1.00]; P =0.048). There were no significant between-group differences in the secondary end points of perioperative myocardial injury (assessed by the concentrations of cardiac troponin T, creatine kinase myocardial isoenzyme, and NT-proBNP [N-terminal pro-brain natriuretic peptide]), duration of stay in the intensive care unit and hospital, and occurrence of nonfatal myocardial infarction, stroke, and all-cause mortality by day 90. CONCLUSIONS: Among high-risk patients undergoing cardiac surgery, delayed RIPC significantly reduced the occurrence of AKI. REGISTRATION: URL: https://www.chictr.org.cn ; Unique identifier: ChiCTR2000035568.

Increasing evidence demonstrates that long noncoding RNAs (lncRNAs) play an important role in several pathogenic processes of the kidney. However, functions of lncRNAs in ischemic acute kidney injury (AKI) remain undefined. In this study, global lncRNA profiling indicated that many lncRNA transcripts were deregulated in kidney after ischemia reperfusion (IR). Among them, we identified IRAR (ischemia-reperfusion injury associated RNA) as a potential lncRNA candidate, which was mostly expressed by the tubular epithelial cells (TECs) after IR, involved in the development of AKI. GapmeR-mediated silencing and viral-based overexpression of IRAR were carried out to assess its function and contribution to IR-induced AKI. The results revealed that in vivo silencing of IRAR significantly reduced IR-induced proinflammatory cells infiltration and AKI. IRAR overexpression induced chemokine CCL2, CXCL1 and CXCL2 expression both in mRNA and protein levels in TECs, while, silencing of IRAR resulted in downregulation of these chemokines. RNA immunoprecipitation and RNA pulldown assay validated the association between IRAR and CCL2, CXCL1/2. Further examination revealed that specific ablation of CCL2 in TECs reduced macrophages infiltration and proinflammatory cytokine production, attenuated renal dysfunction in IR mice. Inhibition of CXC chemokine receptor 2 (receptor of CXCL1/2) reduced neutrofils infiltration, but had no overt effect on kidney function. To explore the mechanism of IRAR upregulation in kidney during IR, we analyzed promoter region of IRAR and predicted a potential binding site for transcription factor C/EBP β on IRAR promoter. Silencing of C/EBP β reduced IRAR expression in TECs. A dual-luciferase reporter assay and chromatin immunoprecipitation (ChIP) confirmed that IRAR was a transcriptional target of the C/EBP β. Altogether, our findings identify IRAR as a new player in the development of ischemic AKI through regulating chemokine production and immune cells infiltration, suggesting that IRAR is a potential target for prevention and/or attenuation of AKI.

Renal ischemia-reperfusion (I/R) can induce oxidative stress and injury via the generation of reactive oxygen species (ROS). Renal proximal tubular cells are susceptible to oxidative stress, and the dysregulation of renal proximal tubular cellular homeostasis can damage cells via apoptotic pathways. A recent study showed that the generation of ROS can increase perilipin 2 (Plin2) expression in HepG2 cells. Some evidence has also demonstrated the association between Plin2 expression and renal tumors. However, the underlying mechanism of Plin2 in I/R-induced acute kidney injury (AKI) remains elusive. Here, using a mouse model of I/R-induced AKI, we found that ROS generation was increased and the expression of Plin2 was significantly upregulated. An in vitro study further revealed that the expression of Plin2, and the generation of ROS were significantly upregulated in primary tubular cells treated with hydrogen peroxide. Accordingly, Plin2 knockdown decreased apoptosis in renal proximal tubular epithelial cells treated with hydrogen peroxide, which depended on the activation of peroxisome proliferator-activated receptor α (PPARα). Overall, the present study demonstrated that Plin2 is involved in AKI; knockdown of this marker might limit apoptosis via the activation of PPARα. Consequently, the downregulation of Plin2 could be a novel therapeutic strategy for AKI.

Acute kidney injury (AKI), characterized by inflammation and oxidative stress, is a life‐threatening clinical presentation. We previously demonstrated the role of miR‐382 in the progression of chronic kidney disease (CKD). However, the role of miR‐382 in AKI is unknown. Genetic depletion of miR‐382 exacerbated renal dysfunction, histologic lesions, apoptosis of epithelial cells, and oxidative stress in kidneys in ischemia‐reperfusion (I/R)‐ and sepsis‐induced AKI. In vitro, downregulation of miR‐382 accompanied with activation of phosphorylation of signal transducer and activator of transcription 1 (STAT1) were induced in mouse renal tubular epithelial cells (mTECs) with hypoxia/reoxygenation (H/R) and lipopolysaccharide (LPS) treatments. Colocalization of phosphorylated STAT1 (p‐STAT1) and Lotus tetragonolobus lectin (LTL) suggested the activation of STAT1 signaling in renal epithelial after I/R injury (IRI). Overexpression of miR‐382 in mTECs abrogated phosphorylation of STAT1, generation of interleukin‐6 ( Il-6 ), tumor necrosis factor‐ α ( Tnf-α ), and Il-1β as well as reactive oxygen species (ROS) and apoptosis after H/R‐ and LPS treatments. Additionally, loss of miR‐382 was found in isolated macrophages from kidney during I/R‐induced AKI. Upregulation of miR‐382 in Raw264.7 cells inactivated STAT1 signaling and hindered polarization of M1 macrophages inhibiting Il-6 and inducible nitric oxide synthase ( iNos ). Inhibition of STAT1 pharmacologically reduced Il-1β , Il-6 , and Tnf-α in Raw264.7 after H/R. Taken together, these results demonstrated the protective role of miR‐382 in I/R‐ and sepsis‐induced AKI, suggesting miR‐382 as a novel therapeutic strategy for AKI.