MicroRNA-21 Is Required for Local and Remote Ischemic Preconditioning in Multiple Organ Protection Against Sepsis*

Objective: Sepsis, triggered by microbial infection, is a common and life-threatening systemic illness, often leads to impaired function of vital organs. Ischemic preconditioning induced by transient brief episodes of ischemia is a powerful innate mechanism of organ protection. We have reported that a 15-minute renal ischemic preconditioning substantially attenuated subsequent renal ischemia-reperfusion injury. Here, we investigate whether a brief ischemia and reperfusion in kidney can provide protection at local and remote sites against sepsis-induced organ injury, and whether this protection is microRNA-21 dependent. Design: Laboratory study. Setting: University laboratory. Subjects: Mouse renal tubular epithelial cells, C57BL/6 J wildtype (Animal Center of Fudan University, Shanghai, China) and microRNA-21–/– mice (B6.129-Mir21atm1Smoc, Shanghai Biomodel Organism Science & Technology Development Co. Shanghai, China). Interventions: Mouse renal tubular epithelial cells were treated with hypoxia (2% oxygen). Renal ischemic preconditioning was induced by bilateral renal pedicle clamping for 15 minutes, and sepsis was induced by a single intraperitoneal injection of lipopolysaccharide at a dose of 20 mg/kg or cecal ligation and puncture in mice. Measurements and Main Results: Mice treated with renal ischemic preconditioning were protected from endotoxemia or polymicrobial sepsis-induced multiple organ injury, including kidneys, heart, liver, and lungs. Renal ischemic preconditioning induced activation of hypoxia-inducible factor-1α in kidneys, which up-regulated microRNA-21 at transcriptional level, subsequently, leading to increased expression of microRNA-21 in serum exosomes and remote organs, resulting in decreased apoptosis and reduced proinflammatory cytokines production in these organs. In vivo knockdown of microRNA-21 or genetic deletion of microRNA-21 abrogated the organoprotective effects conferred by renal ischemic preconditioning. Mechanistically, we discovered that knockdown of microRNA-21 increased programmed cell death protein 4 expression and nuclear factor-kappa B activity, decreased expression of anti-apoptotic B-cell lymphoma-2. Conclusion: MicroRNA-21 is required for local and remote ischemic preconditioning in multiple organ protection against sepsis, and up-regulation of miR-21 may be a potential therapy for sepsis.

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