Role of extracellular vesicles in pathogenesis and therapy of renal ischemia-reperfusion injury

A lectin affinity plasmapheresis device removes extracellular vesicles and microRNAs from renal perfusates following controlled oxygenated rewarming of discarded donor kidneys

Kidney transplantation is considered the benchmark treatment for end-stage kidney disease patients, yet the scarcity of suitable kidneys poses a significant hindrance for patients and healthcare providers. One approach is to extend the criteria for the use of kidneys from deceased brain death and deceased circulatory death donors. Use of these organs, especially from these extended criteria donors, is associated with ischemia reperfusion injury and resultant delayed graft function as well as increased rates of allograft rejection. To lessen these complications as well as increase the time of organ viability assessment, machine perfusion has been evaluated on recovered kidneys. In this study we examined the immunogenic molecular content of perfusates from discarded organs that had undergone Controlled Oxygenated Rewarming (COR). Perfusates were analyzed for extracellular vesicles (EVs), DNA (Deoxyribonucleic acid), and microRNAs. These perfusates were then pumped over a plasma separator containing a lectin affinity resin. Following treatment, a significant diminution in extracellular vesicles, dsDNA (double-stranded DNA) associated with EVs, and microRNAs (miRNA) were observed. Specifically, in three out of the four renal perfusates analyzed there was significant removal of small EVs (<200 nm) and vesicles loaded with dsDNA (p < 0.05). Notably, depletion of larger EVs (100-500 nm) was found to be significant in all treated perfusates (p < 0.01). NanoString analysis of miRNA found 5 species potentially involved in renal dysfunction (hsa-let 7a-5p, hsa-miR-148b-3p, hsa-miR-148a-3p, hsa-miR-29b-3pb and hsa-miR-99a5p) to be significantly depleted in treated renal perfusates (p ≤ 0.05). These results support a future study incorporating this treatment method into a dynamic machine perfusion circuit to explore if reduction of these mediators is associated with improved function of retrieved kidneys.

FOXC1 Aggravates the Ischemia-Reperfusion Induced Injury in Renal Tubular Epithelial Cells by Activating NF-κB/NLRP3 Signaling

Renal ischemia-reperfusion injury (RIRI) is a condition characterized by inflammation and cell damage in the kidneys following a period of ischemia and subsequent reperfusion, which lacks effective treating method in the clinic. Exploring molecular mechanisms holds profound significance in guiding the clinical prevention and treatment of RIRI. Herein, the potential function of Forkhead box C1 (FOXC1), a protein belongs to FOX family, in I/R-induced injury in renal tubular epithelial cells (RTECs) was studied to explore potential targets for RIRI. FOXC1 was upregulated in RIRI rats, expressions of which were elevated as time prolonged. FOXC1-overexpressed or knockdown HK-2 cells were constructed, followed by I/R stimulation. FOXC1 was found markedly upregulated in I/R-stimulated HK-2 cells. Notably repressed cell viability, enhanced apoptosis, increased release of inflammatory cytokines, boosted reactive oxygen species (ROS) and malondialdehyde (MDA) levels, and inactivated superoxide dismutase (SOD) enzyme were observed in I/R-stimulated HK-2 cells, which were sharply reversed by silencing FOXC1 and aggravated by overexpression FOXC1. Furthermore, largely increased levels of NLRP3, caspase-1, GSDMD-N, IL-18, IL-1β, and p-p65/p65 were observed in I/R-stimulated HK-2 cells, which were notably suppressed by silencing FOXC1 and further elevated by overexpression FOXC1. Additionally, FOXC1-overexpressed HK-2 cells were stimulated by I/R with or without 10 μM MCC950, an inhibitor of NLRP3. The enhanced apoptosis, triggered inflammation, and facilitated ROS by FOXC1 overexpression in I/R-stimulated HK-2 cells were remarkably abolished by the coculture of MCC950, accompanied by an inhibition on the NF-κB/NLRP3 signaling. Collectively, FOXC1 aggravated the I/R induced injury in RTECs by activating NF-κB/NLRP3 signaling.

METTL3 promotes renal ischemia-reperfusion injury by modulating miR-374b-5p/SRSF7 axis

Renal ischemia-reperfusion injury (IRI) is a prevalent cause of acute kidney injury, however, the regulatory mechanisms of miR-374b-5p in renal IRI remain poorly understood. We established hypoxia/reoxidation (H/R)-induced renal injury models using HK-2 and TCMK-1 cells, as well as an ischemia-reperfusion (I/R)-induced mouse model. Renal tubular epithelial cells (RTECs) viability and apoptosis were assessed using CCK-8, flow cytometry, and TUNEL assays. The targeting relationship between miR-374b-5p and SRSF7 was analyzed using dual luciferase reporter assays. The interaction between METTL3 and miR-374b-5p was confirmed through methylated RNA immunoprecipitation (MeRIP) and co-immunoprecipitation (Co-IP) assays. We found that miR-374b-5p levels were significantly upregulated in H/R-induced HK-2 and TCMK-1 cells. Furthermore, miR-374b-5p promoted H/R-induced RTEC injury by suppressing cell viability and exacerbating apoptosis. SRSF7 was identified as a downstream target of miR-374b-5p, inhibition of SRSF7 reversed the inhibitory effects of miR-374b-5p inhibitors on RTEC injury. Additionally, METTL3 interacted with the microprocessor protein DGCR8 and modulated the processing of pri-miR-374b-5p in an m6A-dependent manner. In the renal IRI model, METTL3 and miR-374b-5p levels were upregulated, and knockdown of METTL3 inhibited apoptosis in H/R-induced HK-2 and TCMK-1 cells. Conversely, miR-374b-5p reversed the protective effects of METTL3 knockdown on renal IRI. Our findings provide novel insights into the role of m6A methylation in the development of renal IRI, demonstrating that METTL3 promotes renal IRI by modulating the miR-374b-5p/SRSF7 axis.

Bilirubin-Modified Chondroitin Sulfate-Mediated Multifunctional Liposomes Ameliorate Acute Kidney Injury by Inducing Mitophagy and Regulating Macrophage Polarization

Acute kidney injury (AKI) is a dynamic process associated with inflammation, oxidative stress, and lipid peroxidation, in which mitochondrial mitophagy and macrophage polarization play a critical role in the pathophysiology. Based on the expression of the CD44 receptor on renal tubular epithelial cells (RTECs) and activated M1 macrophages being abnormally increased, accompanied by up-regulation of reactive oxygen species (ROS) during AKI, the conjugates of bilirubin (BR), an endogenous antioxidant which has the property of anti-inflammation, and chondroitin sulfate (CS) with CD44-targeting property could be a promising therapeutic carrier. In this study, we develop a CD44-targeted/ROS-responsive CS-BR-mediated multifunctional liposome loading celastrol (CS-BR@CLT) for the targeted therapy of AKI. CS-BR@CLT is shown to selectively accumulate in AKI mouse kidneys via targeting of CD44 receptors. Treatment with CS-BR@CLT significantly ameliorates acute kidney injury caused by ischemia-reperfusion and protects renal function. Mechanistically, CS-BR@CLT inhibits apoptosis, protects mitochondria, promotes autophagy, regulates macrophage polarization, and alleviates interstitial inflammation. Overall, our study demonstrates that CS-BR@CLT could be a promising strategy to ameliorate acute kidney injury.

RAS protein activator-like 2 (RASAL2) initiates peritubular capillary rarefaction in hypoxic renal interstitial fibrosis

The progression of chronic kidney disease (CKD) often involves renal interstitial fibrosis (RIF) and subsequent loss of peritubular capillaries (PTCs), which enhances disease severity. Despite advancements in our understanding of fibrosis, effective interventions for reversing capillary loss remain elusive. Notably, RIF exhibits reduced capillary density, whereas renal cell carcinoma (RCC) shows robust angiogenesis under hypoxic conditions. Using RNA sequencing and bioinformatics, we identified differentially expressed genes (DEGs) in hypoxic human renal tubular epithelial cells (HK-2) and renal cancer cells (786-0). Analysis of altered Ras and PI3K/Akt pathways coupled with hub gene investigation revealed RAS protein activator-like 2 (RASAL2) as a key candidate. Subsequent in vitro and in vivo studies confirmed RASAL2's early-stage response in RIF, which reduced with fibrosis progression. RASAL2 suppression in HK-2 cells enhanced angiogenesis, as evidenced by increased proliferation, migration, and branching of human umbilical vein endothelial cells (HUVECs) co-cultured with HK-2 cells. In mice, RASAL2 knockdown improved Vascular endothelial growth factor A (VEGFA) and Proliferating cell nuclear antigen (PCNA) levels in unilateral ureteral occlusion (UUO)-induced fibrosis (compared to wild type). Hypoxia-inducible factor 1 alpha (HIF-1α) emerged as a pivotal mediator, substantiated by chromatin immunoprecipitation (ChIP) sequencing, with its induction linked to activation. Hypoxia increased the production of RASAL2-enriched extracellular vesicles (EVs) derived from tubular cells, which were internalized by endothelial cells, contributing to the exacerbation of PTC loss. These findings underscore RASAL2's role in mediating reduced angiogenesis in RIF and reveal a novel EV-mediated communication between hypoxic tubular- and endothelial cells, demonstrating a complex interplay between angiogenesis and fibrosis in CKD pathogenesis.

ROS-responsive MSC-derived Exosome Mimetics Carrying MHY1485 Alleviate Renal Ischemia Reperfusion Injury through Multiple Mechanisms

Renal ischemia reperfusion (IR) injury is a prevalent inflammatory nephropathy in surgeries such as renal transplantation or partial nephrectomy, damaging renal function through inducing inflammation and cell death in renal tubules. Mesenchymal stromal/stem cell (MSC)-based therapies, common treatments to attenuate inflammation in IR diseases, fail to exhibit satisfying effects on cell death in renal IR. In this study, we prepared MSC-derived exosome mimetics (EMs) carrying the mammalian target of the rapamycin (mTOR) agonist to protect kidneys in proinflammatory environments under IR conditions. The thioketal-modified EMs carried the mTOR agonist and bioactive molecules in MSCs and responsively released them in kidney IR areas. MSC-derived EMs and mTOR agonists protected kidneys synergistically from IR through alleviating inflammation, apoptosis, and ferroptosis. The current study indicates that MSC-TK-MHY1485 EMs (MTM-EM) are promising therapeutic biomaterials for renal IR injury.