Ischemia-reperfusion injury in renal transplantation: 3 key signaling pathways in tubular epithelial cells

MELATONIN ATTENUATES RENAL ISCHEMIA-REPERFUSION INJURY BY REGULATING MITOCHONDRIAL DYNAMICS AND AUTOPHAGY THROUGH AMPK/DRP1

ABSTRACT

Ischemia-reperfusion injury (IRI) often stems from an imbalance between mitochondrial dynamics and autophagy. Melatonin mitigates IRI by regulating mitochondrial dynamics. However, the precise molecular mechanism underlying the role of melatonin in reducing IRI through modulating mitochondrial dynamics remains elusive. The objective of this study was to investigate whether pretreatment with melatonin before IRI confers protective effects by modulating mitochondrial dynamics and mitophagy. Melatonin pretreatment was administered to HK-2 cells and live rats before subjecting them to hypoxia-reoxygenation or IRI, respectively. Cells and rat kidney models were evaluated for markers of oxidative stress, autophagy, mitochondrial dynamics, and the expression of adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) and phospho-AMPKα (P-AMPK). After renal IRI, increased mitochondrial fission and autophagy were observed, accompanied by exacerbated cellular oxidative stress injury and aggravated mitochondrial dysfunction. Nevertheless, melatonin pretreatment inhibited mitochondrial fission, promoted mitochondrial fusion, and attenuated autophagy levels. This intervention was correlated with a notable reduction in oxidative stress injury and remarkable restoration of mitochondrial functionality. Ischemia-reperfusion injury led to a decline in P-AMPK levels, whereas melatonin pretreatment increased the level of P-AMPK levels. Silencing AMPK with small interfering RNA exacerbated mitochondrial damage, and in this context, melatonin pretreatment did not alleviate mitochondrial fission or autophagy levels but resulted in sustained oxidative stress damage. Collectively, these findings indicate that melatonin pretreatment shields the kidneys from IRI by mitigating excessive mitochondrial fission, moderating autophagy levels, and preserving appropriate mitochondrial fission, all in an AMPK-dependent manner.

A20 in Kidney Transplantation and Autoimmunity

A20, the central inhibitor of NFκB, has multiple anti-inflammatory properties, making it an interesting target in kidney autoimmune disease and transplant biology. It has been shown to be able to inhibit inflammatory functions in macrophages, dendritic cells, T cells, and B cells in various ways, leading to less tissue damage and better graft outcomes. In this review, we will discuss the current literature regarding A20 in kidney transplantation and autoimmunity. Future investigations on animal models and in existing immunosuppressive therapies are needed to establish A20 as a therapeutic target in kidney transplantation and autoimmunity. Cell-based therapies, modified viruses or RNA-based therapies could provide a way for A20 to be utilized as a promising mediator of inflammation and tissue damage.

Renoprotective effects of laxative linaclotide: Inhibition of acute kidney injury and fibrosis in a rat model of renal ischemia-reperfusion

Ischemia-reperfusion (I/R) leads to tissue damage in transplanted kidneys, resulting in acute kidney injury (AKI) and chronic graft dysfunction, which critically compromises transplant outcomes, such as graft loss. Linaclotide, a guanylate cyclase C agonist clinically approved as a laxative, has recently been identified to exhibit renoprotective effects in a chronic kidney disease (CKD) model. This study evaluates the therapeutic effects of linaclotide on AKI triggered by I/R in a rat model with an initial comparison with other laxatives. Here, we show that linaclotide administration resulted in substantial reduction in serum creatinine levels, reflective of enhanced renal function. Histological examination revealed diminished tubular damage, and Sirius Red staining confirmed less collagen deposition, collectively indicating preserved structural integrity and mitigation of fibrosis. Further analysis demonstrated lowered expression of TGF-β and associated fibrotic markers, α-SMA, MMP2, and TIMP1, implicating the downregulation of the fibrogenic TGF-β pathway by linaclotide. Furthermore, one day after I/R insult, linaclotide profoundly diminished macrophage infiltration and suppressed critical pro-inflammatory cytokines such as TNF, IL-1β, and IL-6, signifying its potential to disrupt initial inflammatory mechanisms integral to AKI pathology. These findings suggest that linaclotide, with its established safety profile, could extend its benefits beyond gastrointestinal issues and potentially serve as a therapeutic intervention for organ transplantation. Additionally, it could provide immediate and practical insights into selecting laxatives for managing patients with AKI or CKD, regardless of the cause, and for those receiving dialysis or transplant therapy.

Targeted Restoration of GPX3 Attenuates Renal Ischemia/Reperfusion Injury by Balancing Selenoprotein Expression and Inhibiting ROS-mediated Mitochondrial Apoptosis

BACKGROUND

Renal ischemia/reperfusion (IR) injury is the leading cause of acute kidney injury in both autologous and transplanted kidneys. Low-level glutathione peroxidase 3 (GPX3) is associated with renal IR injury. The exact mechanism of targeted GPX3 restoration in renal IR injury has yet to be determined.

METHODS

The distribution of GPX3 in different tissues and organs of the body was investigated. The level of GPX3 in renal IR injury was assessed. To confirm the action of GPX3 and its mechanisms, IR models were used to introduce adeno-associated virus 9 containing GPX3, as well as hypoxia/reoxygenation-exposed normal rat kidney cells that consistently overexpressed GPX3. Reverse molecular docking was used to confirm whether GPX3 was a target of ebselen.

RESULTS

GPX3 is abundant in the kidneys and decreases in expression during renal IR injury. GPX3 overexpression reduced renal IR injury and protected tubular epithelial cells from apoptosis. Proteomics analysis revealed a strong link between GPX3 and mitochondrial signaling, cellular redox state, and different expression patterns of selenoproteins. GPX3 inhibited reactive oxygen species-induced mitochondrial apoptosis and balanced the disordered expression of selenoproteins. GPX3 was identified as a stable selenoprotein that interacts with ebselen. Ebselen enhanced the level of GPX3 and reduced IR-induced mitochondrial damage and renal dysfunction.

CONCLUSIONS

Targeted restoration of GPX3 attenuates renal IR injury by balancing selenoprotein expression and inhibiting reactive oxygen species-mediated mitochondrial apoptosis, indicating that GPX3 could be a potential therapeutic target for renal IR injury.

The SP1/SIRT1/ACLY signaling axis mediates fatty acid oxidation in renal ischemia-reperfusion-induced renal fibrosis

BACKGROUND

Renal ischemia-reperfusion is the primary cause of acute kidney injury (AKI). Clinically, most patients who experience ischemia-reperfusion injury eventually progress gradually to renal fibrosis and chronic kidney disease (CKD). However, the underlying mechanism for AKI to CKD transition remain absent. Our study demonstrated that the downregulation of sirtuin 1 (Sirt1)-mediated fatty acid oxidation (FAO) facilitates IRI-induced renal fibrosis.

METHODS

The IRI animal model was established, and ribonucleic acid (RNA) sequencing was used to explore potential differentially expressed genes (DEGs) and pathways. The SIRT1 knockout mice were generated, and a recombinant adeno-associated virus that overexpresses SIRT1 was injected into mice to explore the function of SIRT1 in renal fibrosis induced by renal IRI. In vitro, hypoxia/reoxygenation (H/R) was used to establish the classical model of renal IRI and overexpression or knockdown of SIRT1 to investigate the SIRT1 function through lentiviral plasmids. The underlying molecular mechanism was explored through RNA sequencing, bioinformatics analysis, and chromatin immunoprecipitation assay.

RESULTS

RNA sequencing analysis and western blot demonstrated that the expression of SIRT1 was significantly decreased in IRI mice. Overexpression of SIRT1 improved renal function and reduced lipid deposition and renal fibrosis. On the contrary, knockout of SIRT1 aggravated kidney injury and renal fibrosis. RNA sequencing, bioinformatics analysis, and chromatin immunoprecipitation assay mechanistically revealed that SIRT1 impairs the acetylation of histone H3K27 on the promoter region of ACLY, thereby impeding FAO activity and promoting renal fibrosis. Additionally, SP1 regulated FAO by directly modulating SIRT1 expression.

CONCLUSION

Our findings highlight that downregulation of SIRT1-modulated FAO facilitated by the SP1/SIRT1/ACLY axis in the kidney increases IRI, suggesting SIRT1 to be a potential therapeutic target for renal fibrosis induced by renal IRI.

The emerging role of regulated cell death in ischemia and reperfusion-induced acute kidney injury: current evidence and future perspectives

Renal ischemia‒reperfusion injury (IRI) is one of the main causes of acute kidney injury (AKI), which is a potentially life-threatening condition with a high mortality rate. IRI is a complex process involving multiple underlying mechanisms and pathways of cell injury and dysfunction. Additionally, various types of cell death have been linked to IRI, including necroptosis, apoptosis, pyroptosis, and ferroptosis. These processes operate differently and to varying degrees in different patients, but each plays a role in the various pathological conditions of AKI. Advances in understanding the underlying pathophysiology will lead to the development of new therapeutic approaches that hold promise for improving outcomes for patients with AKI. This review provides an overview of the recent research on the molecular mechanisms and pathways underlying IRI-AKI, with a focus on regulated cell death (RCD) forms such as necroptosis, pyroptosis, and ferroptosis. Overall, targeting RCD shows promise as a potential approach to treating IRI-AKI.

1-Phosphate receptor agonists: A promising therapeutic avenue for ischemia-reperfusion injury management

Ischemia-reperfusion injury (IRI) - a complex pathological condition occurring when blood supply is abruptly restored to ischemic tissues, leading to further tissue damage - poses a significant clinical challenge. Sphingosine-1-phosphate receptors (S1PRs), a specialized set of G-protein-coupled receptors comprising five subtypes (S1PR1 to S1PR5), are prominently present in various cell membranes, including those of lymphocytes, cardiac myocytes, and endothelial cells. Increasing evidence highlights the potential of targeting S1PRs for IRI therapeutic intervention. Notably, preconditioning and postconditioning strategies involving S1PR agonists like FTY720 have demonstrated efficacy in mitigating IRI. As the synthesis of a diverse array of S1PR agonists continues, with FTY720 being a prime example, the body of experimental evidence advocating for their role in IRI treatment is expanding. Despite this progress, comprehensive reviews delineating the therapeutic landscape of S1PR agonists in IRI remain limited. This review aspires to meticulously elucidate the protective roles and mechanisms of S1PR agonists in preventing and managing IRI affecting various organs, including the heart, kidney, liver, lungs, intestines, and brain, to foster novel pharmacological approaches in clinical settings.

Exploration of the shared gene signatures and biological mechanisms between ischemia-reperfusion injury and antibody-mediated rejection in renal transplantation

BACKGROUND

Antibody-mediated rejection (ABMR) plays a crucial role in graft loss during allogeneic renal transplantation. In renal transplantation, ischemia-reperfusion injury (IRI) is unavoidable, serves as a major contributor to acute rejection, and is linked to graft loss. However, the mechanisms underlying IRI and ABMR are unclear. Therefore, this study aimed to investigate the shared genetic characteristics and biological mechanisms between IRI and ABMR.

METHODS

Gene expressions for IRI (GSE43974) and ABMR (GSE129166 and GSE36059) were retrieved from the Gene Expression Omnibus database. The shared differentially expressed genes (DEGs) of IRI and ABMR were identified, and subsequent functional enrichment analysis was performed. Immune cell infiltration in ABMR and its relationship with the shared DEGs were investigated using the CIBERSORT method. Random forest analysis, a protein-protein interaction network, and Cytoscape were used to screen hub genes, which were subsequently subjected to gene set enrichment analysis, miRNA prediction, and transcription factors analysis. The survival analysis was performed through Kaplan-Meier curves. Finally, drug compound prediction was performed on the shared DEGs using the Drug Signature Database.

RESULTS

Overall, 27 shared DEGs were identified between the renal IRI and ABMR groups. Among these, 24 genes exhibited increased co-expression, whereas none showed decreased co-expression. The shared DEGs were primarily enriched in the inflammation signaling pathways. Notably, CD4 memory T cells were identified as potential critical mediators of IRI, leading to ABMR. Tumor necrosis factor alpha-induced protein 3 (TNFAIP3), interferon regulatory factor 1 (IRF1), and early growth response 2 (EGR2) were identified as key components in the potential mechanism that link IRI and ABMR. Patients undergoing renal transplantation with higher expression levels of TNFAIP3, IRF1, and EGR2 exhibited decreased survival rates compared to those with lower expression levels.

CONCLUSION

Inflammation is a key mechanism that links IRI and ABMR, with a potential role played by CD4 memory T cells. Furthermore, TNFAIP3, IRF1, and EGR2 are implicated in the underlying mechanism between IRI and ABMR.

Ferroptosis in organ ischemia-reperfusion injuries: recent advancements and strategies

Ferroptosis is a newly discovered type of regulated cell death participated in multiple diseases. Different from other classical cell death programs such as necrosis and apoptosis, ferroptosis involving iron-catalyzed lipid peroxidation is characterized by Fe2+ accumulation and mitochondria alterations. The phenomenon of oxidative stress following organ ischemia-reperfusion (I/R) has recently garnered attention for its connection to the onset of ferroptosis and subsequent reperfusion injuries. This article provides a comprehensive overview underlying the mechanisms of ferroptosis, with a further focus on the latest research progress regarding interference with ferroptotic pathways in organ I/R injuries, such as intestine, lung, heart, kidney, liver, and brain. Understanding the links between ferroptosis and I/R injury may inform potential therapeutic strategies and targeted agents.

Comprehensive molecular and cellular characterization of endoplasmic reticulum stress-related key genes in renal ischemia/reperfusion injury

Background

Renal ischemia-reperfusion injury (RIRI) is an inevitable complication in the process of kidney transplantation and lacks specific therapy. The study aims to determine the underlying mechanisms of RIRI to uncover a promising target for efficient renoprotection.

Method

Four bulk RNA-seq datasets including 495 renal samples of pre- and post-reperfusion were collected from the GEO database. The machine learning algorithms were utilized to ascertain pivotal endoplasmic reticulum stress genes. Then, we incorporated correlation analysis and determined the interaction pathways of these key genes. Considering the heterogeneous nature of bulk-RNA analysis, the single-cell RNA-seq analysis was performed to investigate the mechanisms of key genes at the single-cell level. Besides, 4-PBA was applied to inhibit endoplasmic reticulum stress and hence validate the pathological role of these key genes in RIRI. Finally, three clinical datasets with transcriptomic profiles were used to assess the prognostic role of these key genes in renal allograft outcomes after RIRI.

Results

In the bulk-RNA analysis, endoplasmic reticulum stress was identified as the top enriched pathway and three endoplasmic reticulum stress-related genes (PPP1R15A, JUN, and ATF3) were ranked as top performers in both LASSO and Boruta analyses. The three genes were found to significantly interact with kidney injury-related pathways, including apoptosis, inflammatory response, oxidative stress, and pyroptosis. For oxidative stress, these genes were more strongly related to oxidative markers compared with antioxidant markers. In single-cell transcriptome, the three genes were primarily upregulated in endothelium, distal convoluted tubule cells, and collecting duct principal cells among 12 cell types of renal tissues in RIRI. Furthermore, distal convoluted tubule cells and collecting duct principal cells exhibited pro-inflammatory status and the highest pyroptosis levels, suggesting their potential as main effectors of three key genes for mediating RIRI-associated injuries. Importantly, inhibition of these key genes using 4-phenyl butyric acid alleviated functional and histological damage in a mouse RIRI model. Finally, the three genes demonstrated highly prognostic value in predicting graft survival outcomes.

Conclusion

The study identified three key endoplasmic reticulum stress-related genes and demonstrated their prognostic value for graft survival, providing references for individualized clinical prevention and treatment of postoperative complications after renal transplantation.

Macrophage Ontogeny, Phenotype, and Function in Ischemia Reperfusion-Induced Injury and Repair

AKI is characterized by a sudden, and usually reversible, decline in kidney function. In mice, ischemia-reperfusion injury (IRI) is commonly used to model the pathophysiologic features of clinical AKI. Macrophages are a unifying feature of IRI as they regulate both the initial injury response as well as the long-term outcome following resolution of injury. Initially, macrophages in the kidney take on a proinflammatory phenotype characterized by the production of inflammatory cytokines, such as CCL2 (monocyte chemoattractant protein 1), IL-6, IL-1 β , and TNF- α . Release of these proinflammatory cytokines leads to tissue damage. After resolution of the initial injury, macrophages take on a reparative role, aiding in tissue repair and restoration of kidney function. By contrast, failure to resolve the initial injury results in prolonged inflammatory macrophage accumulation and increased kidney damage, fibrosis, and the eventual development of CKD. Despite the extensive amount of literature that has ascribed these functions to M1/M2 macrophages, a recent paradigm shift in the macrophage field now defines macrophages on the basis of their ontological origin, namely monocyte-derived and tissue-resident macrophages. In this review, we focus on macrophage phenotype and function during IRI-induced injury, repair, and transition to CKD using both the classic (M1/M2) and novel (ontological origin) definition of kidney macrophages.

Necroptosis-related genes allow novel insights into predicting graft loss and diagnosing delayed graft function in renal transplantation

Ischemia-reperfusion injury (IRI) is an inevitable pathophysiological phenomenon in kidney transplantation. Necroptosis is an undoubtedly important contributing mechanism in renal IRI. We first screened differentially expressed necroptosis-related genes (DENRGs) from public databases. Eight DENRGs were validated by independent datasets and verified by qRT-PCR in a rat IRI model. We used univariate and multivariate Cox regression analyses to establish a prognostic signature, and graft survival analysis was performed. Immune infiltrating landscape analysis and gene set enrichment analysis (GSEA) were performed to understand the underlying mechanisms of graft loss, which suggested that necroptosis may aggravate the immune response, resulting in graft loss. Subsequently, a delayed graft function (DGF) diagnostic signature was constructed using the Least Absolute Shrinkage and Selection Operator (LASSO) and exhibited robust efficacy in validation datasets. After comprehensively analyzing DENRGs during IRI, we successfully constructed a prognostic signature and DGF predictive signature, which may provide clinical insights for kidney transplant.

Role of Renal Venous Oxygen Pressure for Renal Function Monitoring After Related Living-Donor Kidney Transplantation: Cohort Study

BACKGROUND

Monitoring of renal function after kidney transplantation (KT) is performed by measuring serum creatinine (SCr), urine volumes (UV), and glomerular filtration rate (GFR). Other methods based on oxygen metabolism, such as the renal venous oxygen pressure (PrvO2), may be useful. The aim of this study was to explore the correlation between PrvO2 and SCr, UV, and GFR 5 days after KT (SCr5, UV5, and GFR5, respectively).

METHODS

We conducted a prospective cohort study in adults scheduled for living donor KT. A venous blood sample was taken from the renal vein after declamping the renal artery, and blood gas determinations were made. Correlation analyses between PrvO2 and SCr5, UV5, and GFR5 were done by calculating Spearman's correlation coefficient with generalized linear models (GLM). A Spearman's correlation analysis was performed between the percentage decrease in SCr (%ΔSCr) and PrvO2. A GLM was also performed to determine the association of PrvO2 with slow graft function (SGF).

RESULTS

The study included 42 patients, of whom 67% were men. The median age was 31 years (IQR, 27-43.5). PrvO2 was negatively correlated with SCr5 (ρ = -0.53, P = .003), and positively correlated with GFR5 (ρ = 0.49, P = .001) and %ΔSCr (ρ = 0.47, P = .002). A higher PrvO2 was associated with an increase in GFR in univariable (β = 1.24, 95% CI, 0.56-1.93, P = .001) and multivariable (β = 1.24, 95% CI, 0.53-1.94, P = .001) analyses. No association was found between PrvO2 and SGF.

CONCLUSION

PrvO2 could be used to monitor renal function in the first 5 days after related living-donor KT, given its good correlation with SCr and GFR.

Mechanistic Implications of GSK and CREB Crosstalk in Ischemia Injury

Ischemia-reperfusion (IR) injury is a damage to an organ when the blood supply is less than the demand required for normal functioning, leading to exacerbation of cellular dysfunction and death. IR injury occurs in different organs like the kidney, liver, heart, brain, etc., and may not only involve the ischemic organ but also cause systemic damage to distant organs. Oxygen-glucose deprivation in cells causes oxidative stress, calcium overloading, inflammation, and apoptosis. CREB is an essential integrator of the body's various physiological systems, and it is widely accepted that dysfunction of CREB signaling is involved in many diseases, including ischemia-reperfusion injury. The activation of CREB can provide life to a cell and increase the cell's survival after ischemia. Hence, GSK/CREB signaling pathway can provide significant protection to cells of different organs after ischemia and emerges as a futuristic strategy for managing ischemia-reperfusion injury. Different signaling pathways such as MAPK/ERK, TLR4/MyD88, RISK, Nrf2, and NF-κB, get altered during IR injury by the modulation of GSK-3 and CREB (cyclic AMP response element (CRE)-binding protein). GSK-3 (protein kinase B) and CREB are the downstream targets for fulfilling the roles of various signaling pathways. Calcium overloading during ischemia increases the expression of calcium-calmodulin-dependent protein kinase (CaMK), which subsequently activates CREB-mediated transcription, thus promoting the survival of cells. Furthermore, this review highlights the crosstalk between GSK-3 and CREB, promoting survival and rendering the cells resistant to subsequent severe ischemia.

Potassium canrenoate in brain-dead organ donors: a randomised controlled clinical trial protocol (CANREO-PMO)

INTRODUCTION

Ischaemia/reperfusion injuries (IRIs) are associated with poorer survival of kidney grafts from expanded criteria donors. Preclinical studies have shown that mineralocorticoid receptor antagonists (MRAs) prevent acute and chronic post-ischaemic renal dysfunction by limiting IRI. However, data concerning the safety of MRAs in brain-dead donor patients are scarce. We seek to investigate the tolerance of MRAs on the haemodynamics in this population.

METHODS AND ANALYSIS

CANREO-PMO is a randomised, controlled, single-centre, double-blind study. Brain-dead organ donors hospitalised in intensive care are randomised 1:1 after consent to receive 200 mg potassium canrenoate or its matching placebo every 6 hours until organ procurement. The primary outcome is a hierarchical composite endpoint that includes: (1) cardiocirculatory arrest, (2) the impossibility of kidney procurement, (3) the average hourly dose of norepinephrine/epinephrine between randomisation and departure to the operating room, and (4) the average hourly volume of crystalloids and/or colloids received. Thirty-six patients will be included. The secondary endpoints evaluated among the graft recipients are the: (1) vital status of the kidney graft recipients and serum creatinine level with estimated glomerular filtration rate (GFR) according to Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) at 3 months after renal transplantation, (2) percentage of patients dependent on dialysis and/or with an estimated GFR <20 mL/min/1.73 m2 at 3 months, (3) vital status of the kidney graft recipients at 3 months, and (4) vital status of the kidney graft recipients and creatinine levels (in μmol/L), with the estimated GFR according to CKD-EPI (in mL/min/1.73 m2), at 1 year, 3 years and 10 years after transplantation.

ETHICS AND DISSEMINATION

This trial has full ethical approval (Comité de Protection des Personnes: CPP Ouest II-ANGERS, France), and the written consent of relatives will be obtained. Results will be reported at conferences, peer-reviewed publications and using social media channels.

TRIAL REGISTRATION NUMBER

NCT04714710.

Reno-protective effects of perioperative dexmedetomidine in kidney transplantation: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND AND OBJECTIVE

There is currently no FDA-approved medical therapy for delayed graft function (DGF). Dexmedetomidine (DEX) has multiple reno-protective effects preventing ischemic reperfusion injury, DGF, and acute kidney injury. Therefore, we aimed to evaluate the reno-protective effects of perioperative DEX during renal transplantation.

METHODS

A systematic review and meta-analysis synthesizing randomized controlled trials (RCTs) from WOS, SCOPUS, EMBASE, PubMed, and CENTRAL until June 8th, 2022. We used the risk ratio (RR) for dichotomous outcomes and the mean difference for continuous outcomes; both presented with the corresponding 95% confidence interval (CI). We registered our protocol in PROSPERO with ID: CRD42022338898.

RESULTS

We included four RCTs with 339 patients. Pooled risk ratio found no difference between DEX and placebo in reducing DGF (RR: 0.58 with 95% CI [0.34, 1.01], p = 0.05) and acute rejection (RR: 0.88 with 95% CI [0.52, 1.49], p = 0.63). However, DEX improved short-term creatinine on day 1 (MD: - 0.76 with 95% CI [- 1.23, - 0.3], p = 0.001) and day 2 (MD: - 0.28 with 95% CI [- 0.5, - 0.07], p = 0.01); and blood urea nitrogen on day 2 (MD: - 10.16 with 95% CI [- 17.21, - 3.10], p = 0.005) and day 3 (MD: - 6.72 with 95% CI [- 12.85, - 0.58], p = 0.03).

CONCLUSION

Although there is no difference between DEX and placebo regarding reducing DGF and acute rejection after kidney transplantation, there may be some evidence that it has reno-protective benefits because we found statistically significant improvement in the short-term serum creatinine and blood urea nitrogen levels. More trials are required to investigate the long-term reno-protective effects of DEX.

Inhibition of pyruvate dehydrogenase kinase 4 ameliorates kidney ischemia-reperfusion injury by reducing succinate accumulation during ischemia and preserving mitochondrial function during reperfusion

Ischemia-reperfusion (IR) injury, a leading cause of acute kidney injury (AKI), is still without effective therapies. Succinate accumulation during ischemia followed by its oxidation during reperfusion leads to excessive reactive oxygen species (ROS) and severe kidney damage. Consequently, the targeting of succinate accumulation may represent a rational approach to the prevention of IR-induced kidney injury. Since ROS are generated primarily in mitochondria, which are abundant in the proximal tubule of the kidney, we explored the role of pyruvate dehydrogenase kinase 4 (PDK4), a mitochondrial enzyme, in IR-induced kidney injury using proximal tubule cell-specific Pdk4 knockout (Pdk4ptKO) mice. Knockout or pharmacological inhibition of PDK4 ameliorated IR-induced kidney damage. Succinate accumulation during ischemia, which is responsible for mitochondrial ROS production during reperfusion, was reduced by PDK4 inhibition. PDK4 deficiency established conditions prior to ischemia resulting in less succinate accumulation, possibly because of a reduction in electron flow reversal in complex II, which provides electrons for the reduction of fumarate to succinate by succinate dehydrogenase during ischemia. The administration of dimethyl succinate, a cell-permeable form of succinate, attenuated the beneficial effects of PDK4 deficiency, suggesting that the kidney-protective effect is succinate-dependent. Finally, genetic or pharmacological inhibition of PDK4 prevented IR-induced mitochondrial damage in mice and normalized mitochondrial function in an in vitro model of IR injury. Thus, inhibition of PDK4 represents a novel means of preventing IR-induced kidney injury, and involves the inhibition of ROS-induced kidney toxicity through reduction in succinate accumulation and mitochondrial dysfunction.

miR-147 Represses NDUFA4, Inducing Mitochondrial Dysfunction and Tubular Damage in Cold Storage Kidney Transplantation

SIGNIFICANCE STATEMENT

Cold storage-associated transplantation (CST) injury occurs in renal transplant from deceased donors, the main organ source. The pathogenesis of CST injury remains poorly understood, and effective therapies are not available. This study has demonstrated an important role of microRNAs in CST injury and revealed the changes in microRNA expression profiles. Specifically, microRNA-147 (miR-147) is consistently elevated during CST injury in mice and in dysfunctional renal grafts in humans. Mechanistically, NDUFA4 (a key component of mitochondrial respiration complex) is identified as a direct target of miR-147. By repressing NDUFA4, miR-147 induces mitochondrial damage and renal tubular cell death. Blockade of miR-147 and overexpression of NDUFA4 reduce CST injury and improve graft function, unveiling miR-147 and NDUFA4 as new therapeutic targets in kidney transplantation.

BACKGROUND

Kidney injury due to cold storage-associated transplantation (CST) is a major factor determining the outcome of renal transplant, for which the role and regulation of microRNAs remain largely unclear.

METHODS

The kidneys of proximal tubule Dicer (an enzyme for microRNA biogenesis) knockout mice and their wild-type littermates were subjected to CST to determine the function of microRNAs. Small RNA sequencing then profiled microRNA expression in mouse kidneys after CST. Anti-microRNA-147 (miR-147) and miR-147 mimic were used to examine the role of miR-147 in CST injury in mouse and renal tubular cell models.

RESULTS

Knockout of Dicer from proximal tubules attenuated CST kidney injury in mice. RNA sequencing identified multiple microRNAs with differential expression in CST kidneys, among which miR-147 was induced consistently in mouse kidney transplants and in dysfunctional human kidney grafts. Anti-miR-147 protected against CST injury in mice and ameliorated mitochondrial dysfunction after ATP depletion injury in renal tubular cells in intro . Mechanistically, miR-147 was shown to target NDUFA4, a key component of the mitochondrial respiration complex. Silencing NDUFA4 aggravated renal tubular cell death, whereas overexpression of NDUFA4 prevented miR-147-induced cell death and mitochondrial dysfunction. Moreover, overexpression of NDUFA4 alleviated CST injury in mice.

CONCLUSIONS

microRNAs, as a class of molecules, are pathogenic in CST injury and graft dysfunction. Specifically, miR-147 induced during CST represses NDUFA4, leading to mitochondrial damage and renal tubular cell death. These results unveil miR-147 and NDUFA4 as new therapeutic targets in kidney transplantation.

GADD45A and GADD45B as Novel Biomarkers Associated with Chromatin Regulators in Renal Ischemia-Reperfusion Injury

Chromatin regulators (CRs) are essential upstream regulatory factors of epigenetic modification. The role of CRs in the pathogenesis of renal ischemia-reperfusion injury (IRI) remains unclear. We analyzed a bioinformatic analysis on the differentially expressed chromatin regulator genes in renal IRI patients using data from public domains. The hub CRs identified were used to develop a risk prediction model for renal IRI, and their expressions were also validated using Western blot, qRT-PCR, and immunohistochemistry in a murine renal IRI model. We also examined the relationships between hub CRs and infiltrating immune cells in renal IRI and used network analysis to explore drugs that target hub CRs and their relevant downstream microRNAs. The results of machine learning methods showed that five genes (DUSP1, GADD45A, GADD45B, GADD45G, HSPA1A) were upregulated in renal IRI, with key roles in the cell cycle, p38 MAPK signaling pathway, p53 signaling pathway, FoxO signaling pathway, and NF-κB signaling pathway. Two genes from the network, GADD45A and GADD45B (growth arrest and DNA damage-inducible protein 45 alpha and beta), were chosen for the renal IRI risk prediction model. They all showed good performance in the testing and validation cohorts. Mice with renal IRI showed significantly upregulated GADD45A and GADD45B expression within kidneys compared to sham-operated mice. GADD45A and GADD45B showed correlations with plasmacytoid dendritic cells (pDCs) in infiltrating immune cell analysis and enrichment in the MAPK pathway based on the weighted gene co-expression network analysis (WGCNA) method. Candidate drugs that target GADD45A and GADD45B include beta-escin, sertraline, primaquine, pimozide, and azacyclonol. The dysregulation of GADD45A and GADD45B is related to renal IRI and the infiltration of pDCs, and drugs that target GADD45A and GADD45B may have therapeutic potential for renal IRI.

Sufentanil inhibits Pin1 to attenuate renal tubular epithelial cell ischemia-reperfusion injury by activating the PI3K/AKT/FOXO1 pathway

BACKGROUND

Renal ischemia-reperfusion injury (RIRI) has become a great concern in clinical practice with high morbidity and mortality rates. Sufentanil has protective effects on IRI-induced organ injury. Herein, the effects of sufentanil on RIRI were investigated.

METHODS

RIRI cell model was established by hypoxia/reperfusion (H/R) stimulation. The mRNA and protein expressions were assessed using qRT-PCR and western blot. TMCK-1 cell viability and apoptosis were assessed using MTT assay and flow cytometry, respectively. The mitochondrial membrane potential and ROS level were detected by JC-1 mitochondrial membrane potential fluorescent probe and DCFH-DA fluorescent probe, respectively. LDH, SOD, CAT, GSH and MDA levels were determined by the kits. The interaction between FOXO1 and Pin1 promoter was analyzed using dual luciferase reporter gene and ChIP assays.

RESULTS

Our results revealed that sufentanil treatment attenuated H/R-induced cell apoptosis, mitochondrial membrane potential (MMP) dysfunction, oxidative stress, inflammation and activated PI3K/AKT/FOXO1 associated proteins, while these effects were reversed by PI3K inhibitor, suggesting that sufentanil attenuated RIRI via activating the PI3K/AKT/FOXO1 signaling pathway. We subsequently found that FOXO1 transcriptionally activated Pin1 in TCMK-1 cells. Pin1 inhibition ameliorated H/R-induced TCMK-1 cell apoptosis, oxidative stress and inflammation. In addition, as expected, the biological effects of sufentanil on H/R-treated TMCK-1 cells were abrogated by Pin1 overexpression.

CONCLUSION

Sufentanil reduced Pin1 expression through activation of the PI3K/AKT/FOXO1 signaling to suppress cell apoptosis, oxidative stress and inflammation in renal tubular epithelial cells during RIRI development.

Identification and verification of hub genes associated with ferroptosis in ischemia and reperfusion injury during renal transplantation

Ferroptosis is involved in ischemia and reperfusion injury (IRI) of transplanted kidney. Understanding the molecular mechanisms of ferroptosis is essential to elucidate the pathogenesis of IRI. 1307 differentially expressed genes (DEGs) were obtained by GSE90861 retrieved from the GEO database. 29 ferroptosis-related DEGs were obtained from the intersection with FerrDb database, which were subjected to enrichment analysis and cytoHubba plugin for selecting the top three (IL6, ATF3 and JUN) as hub genes. Next, ROC analysis of hub genes showed good diagnostic prospects in both GSE90861 and GSE126805. Given the close link between ferroptosis and immunity, immunological analysis of CIBERSORTx revealed that the proportions of 10 cell types out of 22 immune cells in the transplanted kidney significantly changed after reperfusion. To study the relationship between IRI and ferroptosis, 15 male C57BL/6j mice were randomly divided into three groups: control (C), ischemia and reperfusion (IR), and IR + Fer-1 (IF) groups. The IRI mouse model not only developed significant histological damage changes, but also exhibited mitochondrial damage, iron accumulation, increased MDA, and decreased GSH. The ferroptosis inhibitor, Fer-1, ameliorated renal IRI, as demonstrated by rise of GPX4 and decline of TFRC, PTGS2 and ACSL4. In addition, hub genes were further confirmed by significant increase in IRI mouse model the same as the GEO database. In brief, ferroptosis-related hub genes (IL-6, ATF3 and JUN) screened were closely relevant to immune response and might be diagnostic biomarkers and therapeutic targets for IRI during renal transplantation, which could prevent renal allograft dysfunction.

Evaluation of renal cold ischemia-reperfusion injury with intravoxel incoherent motion diffusion-weighted imaging and blood oxygenation level-dependent MRI in a rat model

Purpose: Cold ischemia-reperfusion injury (CIRI) is one of the most serious complications following renal transplantation. The current study investigated the feasibility of Intravoxel Incoherent Motion (IVIM) imaging and blood oxygenation level-dependent (BOLD) in the evaluation of different degrees of renal cold ischemia-reperfusion injury in a rat model. Methods: Seventy five rats were randomly divided into three groups (N = 25 for each group): T0: sham-operated group, T2/T4: CIRI groups with different cold ischemia hours (2, 4 h, respectively). The rat model of CIRI group was established by left kidney cold ischemia with right nephrectomy. All the rats received a baseline MRI before the surgery. Five rats in each group were randomly selected to undergo an MRI examination at 1 h, day 1, day 2 and day 5 after CIRI. The IVIM and BOLD parameters were studied in the renal cortex (CO), the outer stripe of the outer medulla (OSOM), and the inner stripe of the outer medulla (ISOM) followed by histological analysis to examine Paller scores, peritubular capillary (PTC) density, apoptosis rate and biochemical indicators to obtain the contents of serum creatinine (Scr), blood urea nitrogen (BUN), superoxide dismutase (SOD) and malondialdehyde (MDA). Results: The D, D*, PF and T2* values in the CIRI groups were lower than those in the sham-operated group at all timepoints (all p < 0.05). The prolonged cold ischemia times resulted in gradually lower D, D*, PF and T2* values (all p < 0.05). The D and T2* values of cortex and OSOM in Group T0 and T2 returned to the baseline level (all p > 0.05) except Group T4. The D* and PF values of cortex, OSOM and ISOM in Group T2 and T4 still remained below the normal levels (all p < 0.05) except Group T0. D, D*, PF and T2* values were strongly correlated with histopathological (Paller scores, PTC density and apoptosis rate) and the biochemistry indicators (SOD and MDA) (|r|>0.6, p < 0.001). D*, PF and T2* values were moderately to poorly correlated with some biochemistry indicators (Scr and BUN) (|r|<0.5, p < 0.05). Conclusion: IVIM and BOLD can serve as noninvasive radiologic markers for monitoring different degrees of renal impairment and recovery after renal CIRI.

miRNA155-5P participated in DDX3X targeted regulation of pyroptosis to attenuate renal ischemia/reperfusion injury

BACKGROUND

Renal ischemia/reperfusion injury (IRI) induced pathological damage to renal microvessels and tubular epithelial cells through multiple factors. However, studies investigated whether miRNA155-5P targeted DDX3X to attenuate pyroptosis were scarce.

RESULTS

The expression of pyroptosis-related proteins (caspase-1, interleukin-1β (IL-1β), NOD-like receptor family pyrin domain containing 3 (NLRP3), and IL-18) were up-regulated in the IRI group. Additionally, miR-155-5p was higher in the IRI group comparing with the sham group. The DDX3X was inhibited by the miR-155-5p mimic more than in the other groups. DEAD-box Helicase 3 X-Linked (DDX3X), NLRP3, caspase-1, IL-1β, IL-18, LDH, and pyroptosis rates were higher in all H/R groups than in the control group. These indicators were higher in the miR-155-5p mimic group than in the H/R and the miR-155-5p mimic negative control (NC) group.

CONCLUSIONS

Current findings suggested that miR-155-5p decreased the inflammation involved in pyroptosis by downregulating the DDX3X/NLRP3/caspase-1 pathway.

METHODS

Using the models of IRI in mouse and the hypoxia-reoxygenation (H/R)-induced injury in human renal proximal tubular epithelial cells (HK-2 cells), we analyzed the changes in renal pathology and the expression of factors correlated with pyroptosis and DDX3X. Real-time reverse transcription polymerase chain reaction (RT-PCR) detected miRNAs and enzyme-linked immunosorbent assay (ELISA) was used to detect lactic dehydrogenase activity. The StarBase and luciferase assays examined the specific interplay of DDX3X and miRNA155-5P. In the IRI group, severe renal tissue damage, swelling, and inflammation were examined.

The impact of the cytoplasmic ubiquitin ligase TNFAIP3 gene variation on transcription factor NF-κB activation in acute kidney injury

Nuclear factor κB (NF-κB) activation is a deleterious molecular mechanism that drives acute kidney injury (AKI) and manifests in transplanted kidneys as delayed graft function. The TNFAIP3 gene encodes A20, a cytoplasmic ubiquitin ligase and a master negative regulator of the NF- κB signaling pathway. Common population-specific TNFAIP3 coding variants that reduce A20's enzyme function and increase NF- κB activation have been linked to heightened protective immunity and autoimmune disease, but have not been investigated in AKI. Here, we functionally identified a series of unique human TNFAIP3 coding variants linked to the autoimmune genome-wide association studies single nucleotide polymorphisms of F127C; namely F127C;R22Q, F127C;G281E, F127C;W448C and F127C;N449K that reduce A20's anti-inflammatory function in an NF- κB reporter assay. To investigate the impact of TNFAIP3 hypomorphic coding variants in AKI we tested a mouse Tnfaip3 hypomorph in a model of ischemia reperfusion injury (IRI). The mouse Tnfaip3 coding variant I325N increases NF- κB activation without overt inflammatory disease, providing an immune boost as I325N mice exhibit enhanced innate immunity to a bacterial challenge. Surprisingly, despite exhibiting increased intra-kidney NF- κB activation with inflammation in IRI, the kidney of I325N mice was protected. The I325N variant influenced the outcome of IRI by changing the dynamic expression of multiple cytoprotective mechanisms, particularly by increasing NF- κB-dependent anti-apoptotic factors BCL-2, BCL-XL, c-FLIP and A20, altering the active redox state of the kidney with a reduction of superoxide levels and the enzyme super oxide dismutase-1, and enhancing cellular protective mechanisms including increased Foxp3⁺ T cells. Thus, TNFAIP3 gene variants represent a kidney and population-specific molecular factor that can dictate the course of IRI.

Selenoprotein Gene mRNA Expression Evaluation During Renal Ischemia-Reperfusion Injury in Rats and Ebselen Intervention Effects

Effects of selenoproteins on many renal diseases have been reported. However, their role in renal ischemia-reperfusion (I/R) injury is unclear. The present study was performed to investigate the impact of ebselen and renal I/R injury on the expression of selenoproteins. Sprague-Dawley rats were pretreated with or without ebselen (10 mg/kg) through a daily single oral administration from 3 days before renal I/R surgery. RT-qPCR (real-time quantitative PCR) was performed to determine the mRNA expression of 25 selenoprotein genes in the renal tissues. The expression levels of two selenoproteins, including GPX3 (glutathione peroxidase 3) and DIO1 (iodothyronine deiodinase 1), were evaluated by Western blot or/and IHF (immunohistofluorescence) assays. Furthermore, renal function, renal damage, oxidative stress, and apoptosis were assessed. The results showed that in renal I/R injury, the mRNA levels of 15 selenoprotein genes (GPX1, GPX3, GPX4, DIO1, DIO2, TXNRD2, TXNRD3, SEPHS2, MSRB1, SELENOF, SELENOK, SELENOO, SELENOP, SELENOS, and SELENOT) were decreased, whereas those of eight selenoprotein genes (GPX2, GPX6, DIO3, TXNRD1, SELENOH, SELENOM, SELENOV, and SELENOW) were increased. I/R also induced a reduction in the expression levels of GPX3 and DIO1 proteins. In addition, our results indicated that ebselen reversed the changes in those selenoprotein genes, excluding SELENOH, SELENOM, SELENOP, and SELENOT, in renal I/R injury and alleviated I/R-induced renal dysfunction, tissue damage, oxidative stress, and apoptosis. To our knowledge, this is the first study to investigate the changes of 25 mammalian selenoprotein genes in renal I/R injury kidneys. The present study also provided more evidence for the roles of ebselen against renal I/R injury.

Overexpression of miR-92a attenuates kidney ischemia-reperfusion injury and improves kidney preservation by inhibiting MEK4/JNK1-related autophagy

BACKGROUND

Kidney ischemia-reperfusion injury is inevitable in kidney transplantation, and is essential for primary graft dysfunction and delayed graft function. Our previous study has proved that miR-92a could ameliorate kidney ischemia-reperfusion injury, but the mechanism has not been studied.

METHODS

This study conducted further research on the role of miR-92a in kidney ischemia-reperfusion injury and organ preservation. In vivo, mice models of bilateral kidney ischemia (30 min), cold preservation after ischemia (cold preservation time of 6, 12, and 24 h), and ischemia-reperfusion (reperfusion time of 24, 48, and 72 h) were established. Before or after modeling, the model mice were injected with miR-92a-agomir through the caudal vein. In vitro, the hypoxia-reoxygenation of HK-2 cells was used to simulate ischemia-reperfusion injury.

RESULTS

Kidney ischemia and ischemia-reperfusion significantly damaged kidney function, decreased the expression of miR-92a, and increased apoptosis and autophagy in kidneys. miR-92a agomir tail vein injection significantly increased the expression of miR-92a in kidneys, improved kidney function, and alleviated kidney injury, and the intervention before modeling achieved a better effect than after. Moreover, miR-92a agomir significantly reduced the apoptosis and autophagy in HK-2 cells induced by hypoxia, hypoxia-reoxygenation, and rapamycin, while miR-92a antagomir had opposite effects. Furthermore, mitogen-activated protein kinase, c-Jun NH (2) terminal kinase, caspase 3, Beclin 1, and microtubule-associated protein 1 light chain 3B were inhibited by overexpression of miR-92a both in vivo and in vitro, which in turn reduced apoptosis and autophagy.

CONCLUSIONS

Our results prove that overexpression of miR-92a attenuated kidney ischemia-reperfusion injury and improved kidney preservation, and intervention before ischemia-reperfusion provides better protection than after.

How to Best Protect Kidneys for Transplantation-Mechanistic Target

The increasing number of patients on the kidney transplant waiting list underlines the need to expand the donor pool and improve kidney graft utilization. By protecting kidney grafts adequately from the initial ischemic and subsequent reperfusion injury occurring during transplantation, both the number and quality of kidney grafts could be improved. The last few years have seen the emergence of many new technologies to abrogate ischemia-reperfusion (I/R) injury, including dynamic organ preservation through machine perfusion and organ reconditioning therapies. Although machine perfusion is gradually making the transition to clinical practice, reconditioning therapies have not yet progressed from the experimental setting, pointing towards a translational gap. In this review, we discuss the current knowledge on the biological processes implicated in I/R injury and explore the strategies and interventions that are being proposed to either prevent I/R injury, treat its deleterious consequences, or support the reparative response of the kidney. Prospects to improve the clinical translation of these therapies are discussed with a particular focus on the need to address multiple aspects of I/R injury to achieve robust and long-lasting protective effects on the kidney graft.

Hypoxia-Inducible Factor 2α Attenuates Renal Ischemia-Reperfusion Injury by Suppressing CD36-Mediated Lipid Accumulation in Dendritic Cells in a Mouse Model

BACKGROUND

Hypoxia and hypoxia-inducible factors (HIFs) play essential and multiple roles in renal ischemia-reperfusion injury (IRI). Dendritic cells (DCs) comprise a major subpopulation of the immunocytes in the kidney and are key initiators and effectors of the innate immune responses after IRI. The role of HIF-2α in DCs remains unclear in the context of renal IRI.

METHODS

To investigate the importance of HIF-2α in DCs upon renal IRI, we examined the effects of DC-specific HIF-2α ablation in a murine model. Bone marrow-derived DCs (BMDCs) from DC-specific HIF-2α-ablated mice and wild-type mice were used for functional studies and transcriptional profiling.

RESULTS

DC-specific ablation of HIF-2α led to hyperactivation of natural killer T (NKT) cells, ultimately exacerbating murine renal IRI. HIF-2α deficiency in DCs triggered IFN-γ and IL-4 production in NKT cells, along with upregulation of type I IFN and chemokine responses that were critical for NKT cell activation. Mechanistically, loss of HIF-2α in DCs promoted their expression of CD36, a scavenger receptor for lipid uptake, increasing cellular lipid accumulation. Furthermore, HIF-2α bound directly to a reverse hypoxia-responsive element (rHRE) in the CD36 promoter. Importantly, CD36 blockade by sulfo-N-succinimidyl oleate (SSO) reduced NKT cell activation and abolished the exacerbation of renal IRI elicited by HIF-2α knockout.

CONCLUSIONS

Our study reveals a previously unrecognized role of the HIF-2α/CD36 regulatory axis in rewiring DC lipid metabolism under IRI-associated hypoxia. These findings suggest a potential therapeutic target to resolve long-standing obstacles in treatment of this severe complication.

Effects of perioperative dexmedetomidine infusion on renal function and microcirculation in kidney transplant recipients: a randomised controlled trial

OBJECTIVE

Ischemia-reperfusion injury affects postoperative transplanted kidney function in kidney transplant recipients. Dexmedetomidine was reported to attenuate ischemia-reperfusion injury and improve microcirculation, but its propensity to cause bradycardia and hypotension may adversely affect microcirculation. This study investigated the effect of dexmedetomidine on postoperative renal function and sublingual microcirculation in kidney recipients.

METHODS

The enrolled kidney transplant recipients were randomly allocated to the control group or dexmedetomidine group. After anaesthesia induction, patients in the dexmedetomidine group received dexmedetomidine infusion until 2 h after surgery. Sublingual microcirculation was recorded using an incident dark-field video microscope and analysed. The primary outcomes were the creatinine level on a postoperative day 2 and total vessel density at 2 h after surgery.

RESULTS

A total of 60 kidney recipients were analysed, and the creatinine levels on postoperative day 2 were significantly lower in the dexmedetomidine group than in the control group (1.5 (1.1-2.4) vs. 2.2 (1.7-3.0) mg/dL, median difference -0.6 (95% CI, -0.7 to -0.5) mg/dL, p = .018). On a postoperative day 7, the creatinine levels did not differ significantly between the two groups. Total vessel density at 2 h after surgery did not differ significantly between the two groups.

CONCLUSION

We found that early postoperative renal function was better in kidney transplant recipients receiving dexmedetomidine infusion, but total vessel density was not significantly different between the intervention and control groups. Key messagesIschemia-reperfusion injury affects postoperative transplanted kidney function, and dexmedetomidine was reported to attenuate ischemia-reperfusion injury and improve microcirculation in other clinical conditions.This study showed that early postoperative renal function was better in kidney transplant recipients receiving dexmedetomidine.Dexmedetomidine's side effect of bradycardia and hypotension may affect microcirculation, our results revealed that the perioperative sublingual microcirculation did not differ significantly in kidney transplant recipients receiving dexmedetomidine.

Identification of renal ischemia reperfusion injury subtypes and predictive strategies for delayed graft function and graft survival based on neutrophil extracellular trap-related genes

Background

Ischemia reperfusion injury (IRI) is an inevitable process in renal transplantation, which is closely related to serious postoperative complications such as delayed graft function (DGF), acute rejection and graft failure. Neutrophil extracellular traps (NETs) are extracellular DNA structures decorated with various protein substances released by neutrophils under strong signal stimulation. Recently, NETs have been found to play an important role in the process of IRI. This study aimed to comprehensively analyze the expression landscape of NET-related genes (NRGs) during IRI, identify clusters with different degrees of IRI and construct robust DGF and long-term graft survival predictive strategies.

Methods

The microarray and RNA-seq datasets were obtained from the GEO database. Differentially expressed NRGs (DE-NRGs) were identified by the differential expression analysis, and the NMF algorithm was used to conduct a cluster analysis of IRI samples. Machine learning algorithms were performed to screen DGF-related hub NRGs, and DGF and long-term graft survival predictive strategies were constructed based on these hub NRGs. Finally, we verified the expression of Cxcl1 and its effect on IRI and NETs generation in the mouse IRI model.

Results

This study revealed two IRI clusters (C1 and C2 clusters) with different molecular features and clinical characteristics. Cluster C1 was characterized by active metabolism, mild inflammation and lower incidence of DGF, while Cluster C2 was inflammation activated subtype with a higher incidence of DGF. Besides, based on DGF-related hub NRGs, we successfully constructed robust DGF and long-term graft survival predictive strategies. The mouse renal IRI model verified that Cxcl1 was significantly upregulated in renal tissues after IRI, and using a CXCL8/CXCL1 inhibitor could significantly improve renal function, alleviate renal tubular necrosis, tissue inflammatory response, and NET formation.

Conclusion

This study identified two distinct IRI clusters based on DE-NRGs and constructed robust prediction methods for DGF and graft survival, which can provide references for early prevention and individualized treatment of various postoperative complications after renal transplantation.

Next-Generation REBOA (Resuscitative Endovascular Balloon Occlusion of the Aorta) Device Precisely Achieves Targeted Regional Optimization in a Porcine Model of Hemorrhagic Shock

INTRODUCTION

Limitations such as time-dependent distal ischemia have slowed the adoption of resuscitative endovascular balloon occlusion of the aorta (REBOA) for noncompressible hemorrhage. Next-generation REBOA technologies may allow for controlled partial flow, known as targeted regional optimization, to reduce distal ischemia. We aimed to characterize the efficacy of one such catheter in a porcine model of lethal hemorrhagic shock.

METHODS

Noncompressible hemorrhage from an iliac injury was induced in anesthetized swine (Sus scrofa) (70-90 kg), targeting 30% total blood volume. Animals were then randomized to partial aortic occlusion (PO) with targeted distal mean arterial pressure (MAP) of 35-40 mm of mercury (mm Hg) and complete aortic occlusion (CO) (n = 8 per group) for 90 min. All groups were then resuscitated during a two-h critical care (CC) phase, with flow rate and MAP recorded continuously at the distal infrarenal aorta and proximal carotid artery, and analyzed with two-way repeated measures analysis of variance with S-N-K post-hoc test.

RESULTS

During aortic occlusion, MAP distal to the balloon was consistently maintained at 35.8 ± 0.3 mm Hg in the PO group compared to 27.1 ± 0.3 mm Hg in the CO group (P < 0.05), which also corresponded to higher flow rates (202.9 ± 4.8 mL/min PO versus 25.9 ± 0.8 mL/min CO; P < 0.05). MAP proximal to the balloon was significantly higher with CO versus PO (109.2 ± 2.3 mm Hg versus 85.2 ± 2.3 mm Hg; P < 0.05). During the CC phase, distal aortic flow and MAP were not significantly different between groups. However, creatinine returned to baseline levels by the end of the study in the PO group, but not the CO group. One animal died in the CO group, whereas none died in the PO group.

CONCLUSIONS

This is the first examination of the next-generation pREBOA-PRO in a porcine model of lethal hemorrhagic shock. We show technical feasibility of this technique to precisely achieve targeted regional optimization without device failure or complication. The ability to titrate balloon inflation and thus distal flow/pressure may extend the therapeutic window of REBOA by mitigating distal ischemia.

The Role of Innate Immune Cells in the Prediction of Early Renal Allograft Injury Following Kidney Transplantation

Background: Despite recent advances and refinements in perioperative management of kidney transplantation (KT), early renal graft injury (eRGI) remains a critical problem with serious impairment of graft function as well as short- and long-term outcome. Serial monitoring of peripheral blood innate immune cells might be a useful tool in predicting post-transplant eRGI and graft outcome after KT. Methods: In this prospective study, medical data of 50 consecutive patients undergoing KT at the University Hospital of Leipzig were analyzed starting at the day of KT until day 10 after the transplantation. The main outcome parameter was the occurrence of eRGI and other outcome parameters associated with graft function/outcome. eRGI was defined as graft-related complications and clinical signs of renal IRI (ischemia reperfusion injury), such as acute tubular necrosis (ATN), delayed graft function (DGF), initial nonfunction (INF) and graft rejection within 3 months following KT. Typical innate immune cells including neutrophils, natural killer (NK) cells, monocytes, basophils and dendritic cells (myeloid, plasmacytoid) were measured in all patients in peripheral blood at day 0, 1, 3, 7 and 10 after the transplantation. Receiver operating characteristics (ROC) curves were performed to assess their predictive value for eRGI. Cutoff levels were calculated with the Youden index. Significant diagnostic immunological cutoffs and other prognostic clinical factors were tested in a multivariate logistic regression model. Results: Of the 50 included patients, 23 patients developed eRGI. Mean levels of neutrophils and monocytes were significantly higher on most days in the eRGI group compared to the non-eRGI group after transplantation, whereas a significant decrease in NK cell count, basophil levels and DC counts could be found between baseline and postoperative course. ROC analysis indicated that monocytes levels on POD 7 (AUC: 0.91) and NK cell levels on POD 7 (AUC: 0.92) were highly predictive for eRGI after KT. Multivariable analysis identified recipient age (OR 1.53 (95% CI: 1.003−2.350), p = 0.040), recipient body mass index > 25 kg/m2 (OR 5.6 (95% CI: 1.36−23.9), p = 0.015), recipient cardiovascular disease (OR 8.17 (95% CI: 1.28−52.16), p = 0.026), donor age (OR 1.068 (95% CI: 1.011−1.128), p = 0.027), <0.010), deceased-donor transplantation (OR 2.18 (95% CI: 1.091−4.112), p = 0.027) and cold ischemia time (CIT) of the renal graft (OR 1.005 (95% CI: 1.001−1.01), p = 0.019) as clinically relevant prognostic factors associated with increased eRGI following KT. Further, neutrophils > 9.4 × 103/μL on POD 7 (OR 16.1 (95% CI: 1.31−195.6), p = 0.031), monocytes > 1150 cells/ul on POD 7 (OR 7.81 (95% CI: 1.97−63.18), p = 0.048), NK cells < 125 cells/μL on POD 3 (OR 6.97 (95% CI: 3.81−12.7), p < 0.01), basophils < 18.1 cells/μL on POD 10 (OR 3.45 (95% CI: 1.37−12.3), p = 0.02) and mDC < 4.7 cells/μL on POD 7 (OR 11.68 (95% CI: 1.85−73.4), p < 0.01) were revealed as independent biochemical predictive variables for eRGI after KT. Conclusions: We show that the combined measurement of immunological innate variables (NK cells and monocytes on POD 7) and specific clinical factors such as prolonged CIT, increased donor and recipient age and morbidity together with deceased-donor transplantation were significant and specific predictors of eRGI following KT. We suggest that intensified monitoring of these parameters might be a helpful clinical tool in identifying patients at a higher risk of postoperative complication after KT and may therefore help to detect and—by diligent clinical management—even prevent deteriorated outcome due to IRI and eRGI after KT.

Cellular senescence in ischemia/reperfusion injury

Ischemia/reperfusion (IR) injury, a main reason of mortality and morbidity worldwide, occurs in many organs and tissues. As a result of IR injury, senescent cells can accumulate in multiple organs. Increasing evidence shows that cellular senescence is the underlying mechanism that transforms an acute organ injury into a chronic one. Several recent studies suggest senescent cells can be targeted for the prevention or elimination of acute and chronic organ injury induced by IR. In this review, we concisely introduce the underlying mechanism and the pivotal role of premature senescence in the transition from acute to chronic IR injuries. Special focus is laid on recent advances in the mechanisms as well as on the basic and clinical research, targeting cellular senescence in multi-organ IR injuries. Besides, the potential directions in this field are discussed in the end. Together, the recent advances reviewed here will act as a comprehensive overview of the roles of cellular senescence in IR injury, which could be of great significance for the design of related studies, or as a guide for potential therapeutic target.

Lactobacillus rhamnosus GG ameliorates DON-induced intestinal damage depending on the enrichment of beneficial bacteria in weaned piglets

BACKGROUND

Deoxynivalenol (DON) is one of the most common environmental pollutants that induces intestinal inflammation and microbiota dysbiosis. Lactobacillus rhamnosus GG (LGG) is a probiotic that not only has anti-inflammatory effects, but also shows protective effect on the intestinal barrier. However, it is still unknown whether LGG exerts beneficial effects against DON-induced intestinal damage in piglets. In this work, a total of 36 weaned piglets were randomized to one of four treatment groups for 21 d. The treatment groups were CON (basal diet); LGG (basal diet supplemented with 1.77 × 10¹¹ CFU/kg LGG); DON (DON-contaminated diet) and LGG + DON (DON-contaminated diet supplemented with 1.77 × 10¹¹ CFU/kg LGG).

RESULT

Supplementation of LGG can enhance growth performance of piglets exposed to DON by improving intestinal barrier function. LGG has a mitigating effect on intestinal inflammation induced by DON exposure, largely through repression of the TLR4/NF-κB signaling pathway. Furthermore, supplementation of LGG increased the relative abundances of beneficial bacteria (e.g., Collinsella, Lactobacillus, Ruminococcus_torques_group and Anaerofustis), and decreased the relative abundances of harmful bacteria (e.g., Parabacteroides and Ruminiclostridium_6), and also promoted the production of SCFAs.

CONCLUSIONS

LGG ameliorates DON-induced intestinal damage, which may provide theoretical support for the application of LGG to alleviate the adverse effects induced by DON exposure.

Gut microbial sodium butyrate alleviates renal ischemia-reperfusion injury by regulating HES1/PPARα

This study investigated the effect of gut microbial sodium butyrate (NaB) on renal ischemia-reperfusion injury (IRI) and its mechanism using a rat model of renal IRI and a HK-2 cell model of hypoxia-reoxygenation (HR) injury. The activity of malondialdehyde, superoxide dismutase, glutathione peroxidase, and catalase in kidney tissues and HK-2 cells was detected. ELISA was performed to measure the concentrations of TNF-α, IL-1β, and IL-6 in serum and cell culture supernatant. TUNEL staining and flow cytometry were used to assess apoptosis in kidney tissues and HK-2 cells, respectively. UCSC and JASPAR predicted the binding sites between HES1 and PPARα promoter, followed by experimental verification of the binding. NaB pretreatment inhibited oxidative stress, inflammation, and apoptosis following renal IRI in vivo and in vitro. NaB suppressed the expression of HES1 and promoted that of PPARα. Overexpression of HES1 or knockdown of PPARα in HR-treated HK-2 cells inhibited the protective effects of NaB. HES1 repressed the expression of PPARα by binding PPARα promoter. In conclusion, NaB may alleviate renal IRI by promoting the transcription of PPARα via downregulation of HES1.

Ceria nanoparticles prophylactic used for renal ischemia-reperfusion injury treatment by attenuating oxidative stress and inflammatory response

Renal ischemia-reperfusion (IR) injury (RIRI) is the leading cause of acute kidney injury (AKI), a common disease with high morbidity and mortality. However, due to the lack of effective diagnostic and therapeutic tools, patients have to resort to conservative treatment. To address this issue, we have developed a novel prophylactic strategy that involves the pre-treatment use of ceria nanoparticles (CNPs) before surgery. Based on our careful study of the three different sizes of CNPs that we synthesized, 46 nm (NP46), 81 nm (NP81), and 118 nm (NP118), we have found that NP118 can be used as effective prophylactic agents against RIRI and subsequent renal fibrosis. In our experiments, the CNPs exhibited excellent antioxidant and anti-inflammatory activities in vitro and effectively protected the kidney against RIRI and renal fibrosis in vivo, as proved by the decreases in renal lesions, serum creatinine, blood urea nitrogen, apoptotic cell, KIM-1 expression, and fibrotic area in CNPs treated samples relative to RIRI group. Mechanistically, not only did the CNPs reduce oxidative stress by regulating the Nrf2 pathway, but they also attenuated RIRI induced inflammatory response by decreasing macrophage infiltration and polarization to M1 phenotype, and reducing pro-inflammatory cytokine and chemokine production. In vitro results further confirmed that CNPs pre-treatment not only dramatically decreased intracellular ROS production in renal tubular epithelial cells and vascular endothelial cells, but also effectively attenuated lipopolysaccharide-induced inflammation in RAW264.7 cells. In addition, we found that one fourth of the NP118 persisted for more than 21 days in IR kidneys, and that out of the three sizes of CNPs, NP118 achieved the best results in all our experiments. Our study provides new insights into the usage and majorization of CNPs as a potential therapy to treat or prevent RIRI and renal fibrosis.

The Potential Diagnostic Value of Immune-Related Genes in Interstitial Fibrosis and Tubular Atrophy after Kidney Transplantation

Background

Inflammation within areas of interstitial fibrosis and tubular atrophy (IF/TA) is associated with kidney allograft failure. The aim of this study was to reveal new diagnostic markers of IF/TA based on bioinformatics analysis.

Methods

Raw data of IF/TA samples after kidney transplantation and control samples after kidney transplantation were extracted from the Gene Expression Omnibus (GEO) database (GSE76882 and GSE120495 datasets), and genes that were differentially expressed between the two groups (DEGs) were screened. Gene Set Enrichment Analysis (GSEA), ESTIMATE and single sample GSEA (ssGSEA), least absolute shrinkage and selection operator (LASSO) regression analysis, and competing endogenous RNA (ceRNA) network were used to analyze the data.

Results

The results of GSEA revealed that multiple immune-related pathways were enriched in the IF/TA group, and subsequent immune landscape analysis also showed that the IF/TA group had higher immune and stromal scores and up to 15 types of immune cells occupied them, such as B cells, cytotoxic cells, and T cells. LASSO regression analysis selected 6 (including ANGPTL3, APOH, LTF, FCGR2B, HLA-DQA2, and EGF) out of 14 DE-IRGs as diagnostic genes to construct a diagnostic model. Then, receiver operating characteristic (ROC) curve analysis showed the powerful diagnostic value of the model, and the area under the curve (AUC) of a single diagnostic gene was greater than 0.75. The results of ingenuity pathway analysis (IPA) also indicated that DEGs were involved in the immune system and kidney disease-related pathways. Finally, we found multiple miRNAs that could regulate diagnostic genes from the ceRNA network.

Conclusion

This study identified 6 IF/TA-related genes, which might be used as a new diagnosis model in the clinical practice.

Diacylglycerol kinase epsilon protects against renal ischemia/reperfusion injury in mice through Krüppel-like factor 15/klotho pathway

Although recent studies have indicated that mutations in the gene encoding diacylglycerol kinase epsilon (DGKE) result in some proteinuria related hereditary kidney diseases, the DGKE expression pattern in the kidney and its contribution to acute kidney injury (AKI) remain unknown. Therefore, the present study was designed to detect the role of DGKE in mice with AKI. DGKE expression was time-dependently altered in the kidneys of mice with renal ischemia/reperfusion injury (IRI). Compared with wild-type (WT) mice, DGKE- overexpressing mice (Rosa26-Dgke^+/+) exhibited protective effects against renal IRI, including reduced serum creatinine, blood urea concentration, tubular cell death and inflammatory responses as well as improved morphological injuries. Consistently, in vitro, DGKE overexpression in human renal proximal tubule (HK-2) cells also protected against oxygen-glucose deprivation (OGD)/reoxygenation-induced cell death. Mechanistically, DGKE regulated Klotho expression, at least partly via the transcription factor Krüppel-like factor (KLF) 15. Moreover, a significant reduction in DGKE was also found in kidneys from patients with ischemia-associated acute tubular necrosis (ATN). Collectively, our studies demonstrate that DGKE protects against AKI in mice at least partly through KLF15/Klotho signaling pathway, indicating that DGKE may present an innovative therapeutic strategy for treating patients with AKI.

Plants with Therapeutic Potential for Ischemic Acute Kidney Injury: A Systematic Review

Acute kidney injury (AKI) is a complex condition which has an intricate pathology mostly involving hemodynamic, inflammatory, and direct toxic effects at the cellular level with high morbidity and mortality ratios. Renal ischemic reperfusion injury (RIRI) is the main factor responsible for AKI, most often observed in different types of shock, kidney transplantation, sepsis, and postoperative procedures. The RIRI-induced AKI is accompanied by increased reactive oxygen species generation together with the activation of various inflammatory pathways. In this context, plant-derived medicines have shown encouraging nephroprotective properties. Evidence provided in this systemic review leads to the conclusion that plant-derived extracts and compounds exhibit nephroprotective action against renal ischemic reperfusion induced-AKI by increasing endogenous antioxidants and decreasing anti-inflammatory cytokines. However, there is no defined biomarker or target which can be used for treating AKI completely. These plant-derived extracts and compounds are only tested in selected transgenic animal models. To develop the results obtained into a therapeutic entity, one should apply them in proper vertebrate multitransgenic animal models prior to further validation in humans.

Sevoflurane activates MEF2D-mediated Wnt/β-catenin signaling pathway via microRNA-374b-5p to affect renal ischemia/reperfusion injury

BACKGROUND

The inhaled sevoflurane (Sev) has been demonstrated to protect multiple organs against ischemia/reperfusion injury (IRI). However, the mechanisms of Sev in renal IRI remain largely unknown. This study intends to explore the effect of Sev on renal IRI and the molecular mechanism behind.

METHODS

Following Sev preconditioning, a mouse model with renal IRI was established. The effects of Sev on IRI in mice were assessed by BUN, Scr, MDA and SOD kits, Western blot, HE staining, and TUNEL. Subsequently, we performed microarray analysis on renal tissues from mice with Sev to identify differentially expressed microRNAs (miRNAs). Then, the mice were treated with agomiR-374b-5p combined with Sev to observe the renal histopathology after IRI. The targeting mRNA of miR-374b-5p was verified using bioinformatics analysis and dual-luciferase assay, followed by KEGG enrichment analysis. Rescue experiments were implemented with simultaneous miR-374b-5p and MEF2D overexpression to detect renal histopathology and Wnt/β-catenin pathway activity in the mice.

RESULTS

Sev significantly reduced the levels of BUN and Scr in mouse serum, prevented cell apoptosis, decreased MDA content and increased SOD levels in renal tissues. Moreover, Sev downregulated the miR-374b-5p expression in the renal tissues. Overexpression of miR-374b-5p attenuated the protective effects of Sev on mouse renal tissues. miR-374b-5p targeted MEF2D and blocked the Wnt/β-catenin pathway. Overexpression of MEF2D activated the Wnt/β-catenin pathway and attenuated the supporting effects of miR-374b-5p on renal IRI.

CONCLUSION

Sev promotes MEF2D and activates the Wnt/β-catenin pathway through inhibition of miR-374b-5p expression to affect renal IRI.

MicroRNA antagonist therapy during normothermic machine perfusion of donor kidneys

Normothermic machine perfusion (NMP) is a novel clinical approach to overcome the limitations of traditional hypothermic organ preservation. NMP can be used to assess and recondition organs prior to transplant and is the subject of clinical trials in solid organ transplantation. In addition, NMP provides an opportunity to deliver therapeutic agents directly to the organ, thus avoiding many limitations associated with systemic treatment of the recipient. We report the delivery of oligonucleotide-based therapy to human kidneys during NMP, in this case to target microRNA function (antagomir). An antagomir targeting mir-24-3p localized to the endothelium and proximal tubular epithelium. Endosomal uptake during NMP conditions facilitated antagomir co-localization with proteins involved in the RNA-induced silencing complex (RISC) and demonstrated engagement of the miRNA target. This pattern of uptake was not seen during cold perfusion. Targeting mir-24-3p action increased expression of genes controlled by this microRNA, including heme oxygenase-1 and sphingosine-1-phosphate receptor 1. The expression of genes not under the control of mir-24-3p was unchanged, indicating specificity of the antagomir effect. In summary, this is the first report of ex vivo gymnotic delivery of oligonucleotide to the human kidney and demonstrates that NMP provides the platform to bind and block detrimental microRNAs in donor kidneys prior to transplantation.

Chronic intermittent hypoxia induces the pyroptosis of renal tubular epithelial cells by activating the NLRP3 inflammasome

Obstructive sleep apnea syndrome (OSAS) is a respiratory disorder and chronic intermittent hypoxia (CIH) is an important pathological characteristic of OSAS. Injuries on renal tubular epithelial cells were observed under the condition of CIH. Pyroptosis is a programmed mode of cell death following cell apoptosis and cell necrosis, which is mediated by NLRP3 signaling. The present study aims to investigate the effects of CIH on the pyroptosis of renal tubular epithelial cells and the underlying mechanism. Firstly, CIH was induced in two renal tubular epithelial cell lines, HK-2 cells and TCMK-1 cells. As the aggravation of hypoxia, an increasing trend of elevated apoptotic rate was observed in HK-2 cells and TCMK-1 cells, accompanied by the excessive release of ROS and LDH, and upregulation of NLRP3. Subsequently, the CIH model was established on rats. The pathological analysis results indicated that in CIH rats, the glomerular bottom membrane and mesangium were slightly thickened and edema was observed in the renal tubule epithelium. More serious injury was observed in the moderate intermittent hypoxia group. The expression level of IL-1β and IL-18 was promoted as the aggravation of hypoxia, accompanied by the elevated production of LDH and ROS. The expression level of cleaved Caspase-1, Caspase-1, GSDMD, TLR4, MyD88, NF-κB, p-NF-κB, and NLRP3 was found significantly upregulated as the aggravation of hypoxia. Lastly, the pathological changes in rats induced by CIH were dramatically abolished by MCC950, a specific inhibitor of NLRP3. Collectively, CIH triggered the pyroptosis of renal tubular epithelial cells by activating the NLRP3 inflammasome.

rhADAMTS13 reduces oxidative stress by cleaving VWF in ischaemia/reperfusion-induced acute kidney injury

AIMS

Acute kidney injury (AKI), a major health burden, lacks effective therapy. Anti-inflammatory actions of a disintegrin and metalloproteinase with a thrombospondin type 1 motif member 13 (ADAMTS13) may provide a new treatment option for AKI. Along with inflammation, oxidative stress is critical for AKI development, yet the impact of ADAMTS13 on oxidative stress in AKI remains to be fully elucidated.

METHODS

We assess recombinant human ADAMTS13 (rhADAMTS13) actions on oxidative stress in a murine ischaemia/reperfusion (IR) model. Antioxidant stress-enzyme activities, renal morphology, kidney function markers and vascular function of isolated afferent arterioles are quantified.

RESULTS

rhADAMTS13 provided after IR, reduces blood urea nitrogen (BUN) by 33% and serum creatinine (Scr) by 73% in 24 hours post-IR. rhADAMTS13 reduces BUN (40.03 ± 20.34 mmol/L vs 72.35 ± 18.74 mmol/L, P < .01), Scr (75.67 ± 51.19 μmol/L vs 176.17 ± 55.38 μmol/L, P < .01) and proteinuria by 41% in 48 hours post-IR as well. Moreover, rhADAMTS13 administration decreases malondialdehyde (MDA) and increases the activity of antioxidant stress enzymes, and attenuates reactive oxygen species production. rhADAMTS13 also upregulates nuclear factor-erythroid-2-related factor 2/haem oxygenase-1, enhances antioxidant enzymes activity and alleviates endothelial dysfunction. Finally, treatment with rhADAMTS13 mitigates severe functional and morphological injury present in IR mice. Extracellular signal-regulated kinase (ERK) phosphorylation is limited by rhADAMTS13 and PPARγ expression is partly restored in ischaemic kidneys. Co-administration of von Willebrand factor (VWF) impairs rhADAMTS13's antioxidant capacity and its protective role in IR.

CONCLUSION

rhADAMTS13 alleviates renal IR injury through antioxidant effects by cleaving VWF.

Identification of Subtypes and a Delayed Graft Function Predictive Signature Based on Ferroptosis in Renal Ischemia-Reperfusion Injury

Renal ischemia-reperfusion injury (IRI) is an inevitable process in kidney transplantation, leading to acute kidney injury, delayed graft function (DGF), and even graft loss. Ferroptosis is an iron-dependent regulated cell death in various diseases including IRI. We aimed to identify subtypes of renal IRI and construct a robust DGF predictive signature based on ferroptosis-related genes (FRGs). A consensus clustering analysis was applied to identify ferroptosis-associated subtypes of 203 renal IRI samples in the GSE43974 dataset. The FRG-associated DGF predictive signature was constructed using the Least Absolute Shrinkage and Selection Operator (LASSO), and its robustness was further verified in the validation set GSE37838. The present study revealed two ferroptosis-related patient clusters (pBECN1 and pNF2 cluster) in renal IRI samples based on distinct expression patterns of BECN1 and NF2 gene clusters. Cluster pBECN1 was metabolically active and closely correlated with less DGF, while pNF2 was regarded as the metabolic exhausted subtype with higher incidence of DGF. Additionally, a six-gene (ATF3, SLC2A3, CXCL2, DDIT3, and ZFP36) ferroptosis-associated signature was constructed to predict occurrence of DGF in renal IRI patients and exhibited robust efficacy in both the training and validation sets. High-risk patients tended to have more infiltration of dendritic cells, macrophages, and T cells, and they had significantly enriched chemokine-related pathway, WNT/β-catenin signaling pathway, and allograft rejection. Patients with low risks of DGF were associated with ferroptosis-related pathways such as glutathione and fatty acid metabolism pathways. In conclusion, patient stratification with distinct metabolic activities based on ferroptosis may help distinguish patients who may respond to metabolic therapeutics. Moreover, the DGF predictive signature based on FRGs may guide advanced strategies toward prevention of DGF in the early stage.

Urolithin A alleviates acute kidney injury induced by renal ischemia reperfusion through the p62-Keap1-Nrf2 signaling pathway

Acute kidney injury (AKI) induced by renal ischemia reperfusion (RIR) is typically observed in renal surgeries and is a leading cause of renal failure. However, there is still an unmet medical need currently in terms of clinical treatments. Herein, we report the effect of Urolithin A (UA) in a mouse RIR model, wherein we demonstrated its underlying mechanism both in vitro and in vivo. The expression levels of p62 and Keap1 significantly decreased, while that of nuclear Nrf2 increased in vitro in a hypoxia cell model after UA treatment. Furthermore, the apoptosis of tubular cells was attenuated and the reactive oxygen species (ROS) levels were reduced in the kidneys in a mouse RIR model after UA administration. In this study, we demonstrated that UA can alleviate oxidative stress and promote autophagy by activating the p62-Keap1-Nrf2 signaling pathway, which could protect the kidneys from ischemia reperfusion injury.

Protective Effect of Melatonin for Renal Ischemia-Reperfusion Injury: A Systematic Review and Meta-Analysis

Background: Renal ischemia-reperfusion (I/R) injury is one of the major causes related to acute kidney damage. Melatonin has been shown as a powerful antioxidant, with many animal experiments have been designed to evaluate the therapeutic effect of it to renal I/R injury.

Objectives: This systematic review aimed to assess the therapeutic effect of melatonin for renal I/R injury in animal models.

Methods and Results: The PubMed, Web of Science, Embase, and Science Direct were searched for animal experiments applying melatonin to treat renal I/R injury to February 2021. Thirty-one studies were included. The pooled analysis showed a greater reduction of blood urea nitrogen (BUN) (21 studies, weighted mean difference (WMD) = −30.00 [−42.09 to −17.91], p < 0.00001), and serum creatinine (SCr) (20 studies, WMD = −0.91 [−1.17 to −0.66], p < 0.00001) treated with melatonin. Subgroup analysis suggested that multiple administration could reduce the BUN compared with control. Malondialdehyde and myeloperoxidase were significantly reduced, meanwhile, melatonin significantly improved the activity of glutathione, as well as superoxide dismutase. The possible mechanism for melatonin to treat renal I/R injury is inhibiting endoplasmic reticulum stress, apoptosis, inflammation, autophagy, and fibrillation in AKI to chronic kidney disease.

Conclusions: From the available data of small animal studies, this systematic review demonstrated that melatonin could improve renal function and antioxidative effects to cure renal I/R injury through, then multiple administration of melatonin might be more appropriate. Nonetheless, extensive basic experiments are need to study the mechanism of melatonin, then well-designed randomized controlled trials to explore the protective effect of melatonin.

Renal ischemia/reperfusion injury in rats is probably due to the activation of the 5-HT degradation system in proximal renal tubular epithelial cells

AIMS

To explore the relationship between renal ischemia/reperfusion injury (RIRI) and the activation of the renal 5-HT degradation system, including 5-HT_2A receptor (5-HT_2AR), 5-HT synthases and monoamine oxidase-A (MAO-A).

MAIN METHODS

Rat RIRI was induced by removing the right kidney, causing ischemia of the left kidney for 45 min and reperfusion for different times. RIRI model (ischemia for 45 min and reperfusion for 24 h) was pretreated with 5-HT_2AR antagonist sarpogrelate hydrochloride (SH) and the 5-HT synthase inhibitor carbidopa. In HK-2 cells, cellular damage was induced by hypoxia (24 h)/reoxygenation (12 h) (H/R) and treated with SH, carbidopa or the MAO-A inhibitor clorgyline. Hematoxylin-eosin, immunohistochemistry, TUNEL and fluorescent probe staining, RT-qPCR, western blotting, ELISA, etc. were used in the tests.

KEY FINDINGS

The development of RIRI and the emergence of the RIRI peak were consistent with renal 5-HT degradation system activation. The highest expression regions of the 5-HT degradation system overlapped with those of the most severe lesions in the kidney, which were in proximal renal tubules. Rat RIRI and HK-2 cell damage, including oxidative stress, inflammation and apoptosis, could be almost abolished by synergistic inhibition of SH and carbidopa. Clorgyline also abolished the cellular damage induced by H/R. H/R-induced production of mitochondrial ROS in HK-2 cells was due to MAO-A-catalyzed 5-HT degradation, and 5-HT_2AR was involved by mediating the expression of 5-HT synthases and MAO-A.

SIGNIFICANCE

These findings revealed a close association between RIRI and activation of the renal 5-HT degradation system.

Circulating RNA Profiling in Postreperfusion Plasma From Kidney Transplant Recipients

BACKGROUND

Ischemia/reperfusion injury (IRI) is inevitable in kidney transplantation (KT) and may lead to impaired tubular epithelial cell function and reduce graft function and survival. Renal IRI is a complex cellular and molecular event; therefore, investigating the genetic or molecular pathways associated with the early phase of KT would improve our understanding of IRI in KT. MicroRNAs (miRNAs) play a critical role in various pathologic events associated with IRI.

METHODS

We compared the expression profile of miRNAs extracted from 2 blood plasma samples, 1 from periphery and the other form gonadal veins immediately after reperfusion, in a total 5 cases of KT.

RESULTS

We observed that the total RNA yield was higher in postreperfusion plasma and that a subset of miRNAs was upregulated (miR-let-7a-3p, miR-143-3p, and miR-214-3p) or downregulated (let-7d-3p, let-7d-3p, miR-1246, miR-1260b, miR-1290, and miR-130b-3p) in postreperfusion plasma. Gene ontology analyses revealed that these subsets target different biological functions. Twenty-four predicted genes were commonly targeted by the upregulated miRNAs, and gene ontology enrichment and pathway analyses revealed that these were associated with various cellular activities such as signal transduction or with components such as exosomes and membranous organelles.

CONCLUSION

We present 2 subsets of miRNAs that were differentially upregulated or downregulated in postreperfusion plasma. Our findings may enhance our understanding of miRNA-mediated early molecular events related to IRI in KT.

Treprostinil alleviates hepatic mitochondrial injury during rat renal ischemia-reperfusion injury

BACKGROUND

Renal ischemia-reperfusion injury (IRI) causes acute kidney injury as well as liver injury. Renal IRI depletes hepatic antioxidants, promotes hepatic inflammation and dysfunction through Tlr9 upregulation. There is no treatment available for liver injury during renal IRI. This study examines the hepatoprotective role of treprostinil, a prostacyclin analog, during renal IRI.

METHODS

Male Sprague-Dawley rats were divided into four groups: control, sham, IRI-placebo, or IRI-treprostinil and subjected to bilateral ischemia (45 min) followed by reperfusion (1-72 h). Placebo or treprostinil (100 ng/kg/min) was administered subcutaneously via an osmotic minipump.

RESULTS

Treprostinil significantly reduced peak serum creatinine, BUN, ALT and AST levels vs. IRI-placebo. Treprostinil also restored hepatic levels of superoxide dismutase, glutathione, catalase, and Gclc expression to baseline, while reducing lipid peroxidation vs. IRI-placebo. Additionally, treprostinil significantly reduced elevated hepatic Tlr9, Il-1β, Ccl2, Vcam1, and Serpine1 mRNA expression. Renal IRI increased hepatic apoptosis which was inhibited by treprostinil through reduced cytochrome c and cleaved caspase-3 protein expression. Treprostinil enhanced hepatic ATP concentrations and mitochondrial DNA copy number and improved mitochondrial dynamics by restoring Pgc-1α expression and significantly upregulating Mfn1, Mfn2, and Sirt3 levels, while reducing Drp-1 protein vs. IRI-placebo. Non-targeted semi-quantitative proteomics showed improved oxidative stress indices and ATP subunits in the IRI-treprostinil group.

CONCLUSIONS

Treprostinil improved hepatic function and antioxidant levels, while suppressing the inflammatory response and alleviating Tlr9-mediated apoptotic injury during renal IRI. Our study provides evidence of treprostinil's hepatoprotective effect, which supports the therapeutic potential of treprostinil in reducing hepatic injury during renal IRI.