Sepsis is a common and life-threatening systemic disorder, often leading to acute injury of multiple organs. Here, we show that remote ischemic preconditioning (rIPC), elicited by brief episodes of ischemia and reperfusion in femoral arteries, provides protective effects against sepsis-induced acute kidney injury (AKI). Methods: Limb rIPC was conducted on mice in vivo 24 h before the onset of cecal ligation and puncture (CLP), and serum exosomes derived from rIPC mice were infused into CLP-challenged recipients. In vitro , we extracted and identified exosomes from differentiated C2C12 cells (myotubes) subjected to hypoxia and reoxygenation (H/R) preconditioning, and the exosomes were administered to lipopolysaccharide (LPS)-treated mouse tubular epithelial cells (mTECs) or intravenously injected into CLP-challenged miR-21 knockout mice for rescue experiments. Results: Limb rIPC protected polymicrobial septic mice from multiple organ dysfunction, systemic accumulation of inflammatory cytokines and accelerated parenchymal cell apoptosis through upregulation of miR-21 in a hypoxia-inducible factor 1α (HIF-1α)-dependent manner in the ischemic limbs of mice. However, in miR-21 knockout mice or mice that received HIF-1α siRNA injection into hind limb muscles, the organ protection conferred by limb rIPC was abolished. Mechanistically, we discovered that miR-21 was transported from preischemic limbs to remote organs via serum exosomes. In kidneys, the enhanced exosomal miR-21 derived from cultured myotubes with H/R or the serum of mice treated with rIPC integrated into renal tubular epithelial cells and then targeted the downstream PDCD4/NF-κB and PTEN/AKT pathways, exerting anti-inflammatory and anti-apoptotic effects and consequently attenuating sepsis-induced renal injury both in vivo and in vitro . Conclusion: This study demonstrates a critical role for exosomal miR-21 in renoprotection conferred by limb rIPC against sepsis and suggests that rIPC and exosomes might serve as the possible therapeutic strategies for sepsis-induced kidney injury.

Background: Uncoupling protein 1 (UCP1) is predominantly found in brown adipose tissue mitochondria, and mediates energy dissipation to generate heat rather than ATP via functional mitochondrial uncoupling. However, little is known about its expression and function in kidney. Methods: We carried out a mRNA microarray analysis in mice kidneys with ischemia reperfusion (IR) injury. The most dramatically downregulated gene UCP1 after IR was identified, and its role in generation of mitochondrial reactive oxygen species (ROS) and oxidative stress injury was assessed both in vitro and in vivo. Genetic deletion of UCP1 was used to investigate the effects of UCP1 on ischemia or cisplatinindued acute kidney injury (AKI) in mice. Findings: UCP1 was located in renal tubular epithelial cells in kidney and downregulated in a timedependent manner during renal IR. Deletion of UCP1 increased oxidative stress in kidneys and aggravated ischemia or cisplatin induced AKI in mice.Viral-based overexpression of UCP1 reduced mitochondrial ROS generation and apoptosis in hypoxia-treated tubular epithelial cells. Furthermore, UCP1 expression was regulated by peroxisome proliferator-activator receptor (PPAR) γ in kidneys during renal IR. Overexpression of PPAR-γ resembled UCP1-overexpression phenotype in vitro. Treatment with PPAR-γ agonist could induce UCP1 upregulation and provide protective effect against renal IR injury in UCP1 + / + mice, but not in UCP1 −/ − mice. Interpretation: UCP1 protects against AKI likely by suppressing oxidative stress, and activation of UCP1 represents a potential therapeutic strategy for AKI.

One of the challenges for extrusion bioprinting using low-viscosity bioinks is the fast gravity-driven sedimentation of cells. Cells in a hydrogel bioink that features low viscosity tend to settle to the bottom of the bioink reservoir, and as such, their bioprintability is hindered by association with the inhomogeneous cellularized structures that are deposited. This is particularly true in cases where longer periods are required to print complex or larger tissue constructs. Increasing the bioink’s viscosity efficiently retards sedimentation but gives rise to cell membranolysis or functional disruption due to increased shear stress on the cells during the extrusion process. Inspired by the rainbow cocktail, we report the development of a multilayered modification strategy for gelatin methacryloyl (GelMA) bioink to manipulate multiple liquid interfaces, providing interfacial retention to retard cell sedimentation in the bioink reservoir. Indeed, the interfacial tension in our layer-by-layer bioink system, characterized by the pendant drop method, was found to be exponentially higher than the sedimental pull (ΔGravity‑Buoyancy = ∼10–9 N) of cells, indicating that the interfacial retention is crucial for preventing cell sedimentation across the adjacent layers. It was demonstrated that the encapsulated cells displayed better dispersibility in constructs bioprinted using the multilayered GelMA bioink system than that of pristine GelMA where the index of homogeneity of the cell distribution in the multilayered bioink was 4 times that of the latter.

Dendritic cells (DCs) play an important role in the pathophysiology of renal ischemia‐reperfusion injury (IRI). The mechanisms underlying DCs phenotypic modulation and their function are not fully understood. In this study, we examined the effect of miR‐21 on the phenotypic modulation of DCs in vitro and in vivo, and further investigated the impact of miR‐21‐overexpression DC or miR‐21‐deficient DC on renal IRI. We found that treatment with hypoxia/reoxygenation (H/R) suppressed miR‐21 expression in bone marrow‐derived dendritic cells (BMDCs), and significantly increased the percentage of mature DCs (CD11c+/MHC‐II+/CD80+). Using a selection of microRNA mimics, we successfully induced the upregulation of miR‐21 in BMDCs, which induced immature DC phenotype and an anti‐inflammatory DC response. However, deletion of miR‐21 in BMDCs promoted maturation of DCs under H/R. Adoptive transfer of miR‐21‐overexpression BMDCs could alleviate renal IR‐induced pro‐inflammatory cytokines production and acute kidney injury (AKI). Mice with miR‐21 deficiency in DCs subjected to renal IR showed more severe renal dysfunction and inflammatory response compared with wild‐type mice. In addition, chemokine C receptor 7 (CCR7), a surface marker of mature DC, was a target gene of miR‐21, and silencing of CCR7 in BMDCs led to reduced mature DCs under H/R. In conclusion, our findings highlight miR‐21 as a key regulator of DCs subset phenotype and a potential therapeutic target in renal IRI.