The endothelial cell in ischemic acute kidney injury: implications for acute and chronic function

A bioprinted and scalable model of human tubulo-interstitial kidney fibrosis

Chronic kidney disease (CKD) affects more than 10% of the global population. As kidney function negatively correlates with the presence of interstitial fibrosis, the development of new anti-fibrotic therapies holds promise to stabilize functional decline in CKD patients. The goal of the study was to generate a scalable bioprinted 3-dimensional kidney tubulo-interstitial disease model of kidney fibrosis. We have generated novel human PDGFRβ+ pericytes, CD10+ epithelial and CD31+ endothelial cell lines and compared their transcriptomic signature to their in vivo counterpart using bulk RNA sequencing in comparison to human kidney single cell RNA-sequencing datasets. This comparison indicated that the novel cell lines still expressed kidney cell specific genes and shared many features with their native cell-state. PDGFRβ+ pericytes showed three-lineage differentiation capacity and differentiated towards myofibroblasts following TGFβ treatment. We utilized a fibrinogen/gelatin-based hydrogel as bioink and confirmed a good survival rate of all cell types within the bioink after printing. We then combined all three cells in a bioprinted model using separately printed compartments for tubule epithelium, and interstitial endothelium and pericytes. We confirmed that this 3D printed model allows to recapitulate key disease driving epithelial-mesenchymal crosstalk mechanisms of kidney fibrosis since injury of epithelial cells prior to bioprinting resulted in myofibroblast differentiation and fibrosis driven by pericytes after bioprinting. The bioprinted model was also scalable up to a 96-well format.

Association between EASIX and acute kidney injury in critically ill cancer patients

BACKGROUND

To analyze the relationship between endothelial activation and stress index (EASIX) and the occurrence of acute kidney injury (AKI) in critically ill cancer patients.

METHODS

Critically ill cancer patients were selected from the Medical Information Mart for Intensive Care IV (MIMIC-IV). Multivariate logistic regression was used to analyze the association between EASIX and the occurrence of AKI in critically ill cancer patients.

RESULTS

One thousand forty-one cancer patients were retrospectively included, including 607 men and 434 women with mean age of 64.86 ± 13.67 years. Univariate analysis showed that high EASIX levels were associated with an increased risk of AKI occurrence in intensive care unit (ICU) cancer patients (OR: 1.47,95% CI: 1.13-1.91, P < 0.05). After adjusting for other confounders, high EASIX levels remained an independent risk factor predicting the development of AKI (OR: 1.42,95% CI: 1.08-1.88, P < 0.05). Trends in effect sizes were generally consistent across all subgroups in the prespecified subgroup analyses.

CONCLUSION

EASIX is an independent risk factor for AKI in critically ill cancer patients. More prospective studies are needed to validate the effect of EASIX on the occurrence of AKI in critically ill cancer patients in the future.

Current and emerging tools for simultaneous assessment of infection and rejection risk in transplantation

Infection and rejection are major complications that impact transplant longevity and recipient survival. Balancing their risks is a significant challenge for clinicians. Current strategies aimed at interrogating the degree of immune deficiency or activation and their attendant risks of infection and rejection are imprecise. These include immune (cell counts, function and subsets, immunoglobulin levels) and non-immune (drug levels, viral loads) markers. The shared risk factors between infection and rejection and the bidirectional and intricate relationship between both entities further complicate transplant recipient care and decision-making. Understanding the dynamic changes in the underlying net state of immunity and the overall risk of both complications in parallel is key to optimizing outcomes. The allograft biopsy is the current gold standard for the diagnosis of rejection but is associated with inherent risks that warrant careful consideration. Several biomarkers, in particular, donor derived cell-free-DNA and urinary chemokines (CXCL9 and CXCL10), show significant promise in improving subclinical and clinical rejection risk prediction, which may reduce the need for allograft biopsies in some situations. Integrating conventional and emerging risk assessment tools can help stratify the individual's short- and longer-term infection and rejection risks in parallel. Individuals identified as having a low risk of rejection may tolerate immunosuppression wean to reduce medication-related toxicity. Serial monitoring following immunosuppression reduction or escalation with minimally invasive tools can help mitigate infection and rejection risks and allow for timely diagnosis and treatment of these complications, ultimately improving allograft and patient outcomes.

Metabolic Chaos in Kidney Disease: Unraveling Energy Dysregulation

BACKGROUND

Acute kidney injury (AKI) and chronic kidney disease (CKD) share a fundamental disruption: metabolic dysfunction.

METHODS

A literature review was performed to determine the metabolic changes that occur in AKI and CKD as well as potential therapeutic targets related to these changes.

RESULTS

In AKI, increased energy demand in proximal tubular epithelial cells drives a shift from fatty acid oxidation (FAO) to glycolysis. Although this shift offers short-term support, it also heightens cellular vulnerability to further injury. As AKI progresses to CKD, metabolic disruption intensifies, with both FAO and glycolysis becoming downregulated, exacerbating cellular damage and fibrosis. These metabolic alterations are governed by shifts in gene expression and protein signaling pathways, which can now be precisely analyzed through advanced omics and histological methods.

CONCLUSIONS

This review examines these metabolic disturbances and their roles in disease progression, highlighting therapeutic interventions that may restore metabolic balance and enhance kidney function. Many metabolic changes that occur in AKI and CKD can be utilized as therapeutic targets, indicating a need for future studies related to the clinical utility of these therapeutics.

Evaluation of Neutrophil Gelatinase-Associated Lipocalin Levels in Children With Febrile Seizures: A Case-Control Study

Febrile seizure (FS) is a common pediatric neurological disorder, which may be associated with hypoxia and kidney injury. We aimed to investigate serum levels of neutrophil gelatinase-associated lipocalin (NGAL) in children with FS. This case-control study included 50 children with FS, 50 febrile controls (FCs), and 50 healthy controls (HCs). We measured serum NGAL levels using a human enzyme-linked immunosorbent assay. Serum NGAL/creatinine values showed significant differences within and between study groups with the highest levels for the FS group (1382 ± 215), the middle for FCs (1133 ± 129), and the lowest for HCs (857 ± 97). None of the study participants had abnormal serum creatinine levels, and their values were comparable among the 3 study groups. In conclusion, children with FS may have increased serum NGAL levels despite normal serum creatinine, indicating that FS could contribute to subclinical renal injury without significant loss of excretory kidney function.

The Need to Identify Novel Markers for Early Renal Injury in Cardiorenal Syndrome

The term "Cardiorenal Syndrome" (CRS) refers to the complex interplay between heart and kidney dysfunction. First described by Robert Bright in 1836, CRS was brought to its modern view by Ronco et al. in 2008, who defined it as one organ's primary dysfunction leading to secondary dysfunction in the other, a view that led to the distinction of five different types depending on the organ of primary dysfunction and the temporal pattern (acute vs. chronic). Their pathophysiology is intricate, involving various hemodynamic, neurohormonal, and inflammatory processes that result in damage to both organs. While traditional biomarkers have been utilized for diagnosing and prognosticating CRS, they are inadequate for the early detection of acute renal damage. Hence, there is a pressing need to discover new biomarkers to enhance clinical outcomes and treatment approaches.

Utilizing pathophysiological concepts of ischemia-reperfusion injury to design renoprotective strategies and therapeutic interventions for normothermic ex vivo kidney perfusion

Normothermic machine perfusion (NMP) has emerged as a promising tool for the preservation, viability assessment, and repair of deceased-donor kidneys prior to transplantation. These kidneys inevitably experience a period of ischemia during donation, which leads to ischemia-reperfusion injury when NMP is subsequently commenced. Ischemia-reperfusion injury has a major impact on the renal vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis. With an increased understanding of the underlying pathophysiological mechanisms, renoprotective strategies and therapeutic interventions can be devised to minimize additional injury during normothermic reperfusion, ensure the safe implementation of NMP, and improve kidney quality. This review discusses the pathophysiological alterations in the vasculature, metabolism, oxygenation, electrolyte balance, and acid-base homeostasis of deceased-donor kidneys and delineates renoprotective strategies and therapeutic interventions to mitigate renal injury and improve kidney quality during NMP.

miR-486-5p protects against rat ischemic kidney injury and prevents the transition to chronic kidney disease and vascular dysfunction

AIM

Acute kidney injury (AKI) increases the risk for progressive chronic kidney disease (CKD). MicroRNA (miR)-486-5p protects against kidney ischemia-reperfusion (IR) injury in mice, although its long-term effects on the vasculature and development of CKD are unknown. We studied whether miR-486-5p would prevent the AKI to CKD transition in rat, and affect vascular function.

METHODS

Adult male rats were subjected to bilateral kidney IR followed by i.v. injection of liposomal-packaged miR-486-5p (0.5 mg/kg). Kidney function and histologic injury were assessed after 24 h and 10 weeks. Kidney endothelial protein levels were measured by immunoblot and immunofluorescence, and mesenteric artery reactivity was determined by wire myography.

RESULTS

In rats with IR, miR-486-5p blocked kidney endothelial cell increases in intercellular adhesion molecule-1 (ICAM-1), reduced neutrophil infiltration and histologic injury, and normalized plasma creatinine (P<0.001). However, miR-486-5p attenuated IR-induced kidney endothelial nitric oxide synthase (eNOS) expression (P<0.05). At 10 weeks, kidneys from rats with IR alone had decreased peritubular capillary density and increased interstitial collagen deposition (P<0.0001), and mesenteric arteries showed impaired endothelium-dependent vasorelaxation (P<0.001). These changes were inhibited by miR-486-5p. Delayed miR-486-5p administration (96 h, 3 weeks after IR) had no impact on kidney fibrosis, capillary density, or endothelial function.

CONCLUSION

In rats, administration of miR-486-5p early after kidney IR prevents injury, and protects against CKD development and systemic endothelial dysfunction. These protective effects are associated with inhibition of endothelial ICAM-1 and occur despite reduction in eNOS. miR-486-5p holds promise for the prevention of ischemic AKI and its complications.

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.

Recent Update on Acute Kidney Injury-to-Chronic Kidney Disease Transition

Acute kidney injury (AKI) is characterized by an abrupt decline of excretory kidney function. The incidence of AKI has increased in the past decades. Patients diagnosed with AKI often undergo diverse clinical trajectories, such as early or late recovery, relapses, and even a potential transition from AKI to chronic kidney disease (CKD). Although recent clinical studies have demonstrated a strong association between AKI and progression of CKD, our understanding of the complex relationship between AKI and CKD is still evolving. No cohort study has succeeded in painting a comprehensive picture of these multi-faceted pathways. To address this lack of understanding, the idea of acute kidney disease (AKD) has recently been proposed. This presents a new perspective to pinpoint a period of heightened vulnerability following AKI, during which a patient could witness a substantial decline in glomerular filtration rate, ultimately leading to CKD transition. Although AKI is included in a range of kidney conditions collectively known as AKD, spanning from mild and self-limiting to severe and persistent, AKD can also occur without a rapid onset usually seen in AKI, such as when kidney dysfunction slowly evolves. In the present review, we summarize the most recent findings about AKD, explore the current state of biomarker discovery related to AKD, discuss the latest insights into pathophysiological underpinnings of AKI to CKD transition, and reflect on therapeutic challenges and opportunities that lie ahead.

Serum Nostrin-A risk factor of death, kidney replacement therapy and acute kidney disease in acute kidney injury

BACKGROUND

The prediction of Acute Kidney Injury (AKI)-related outcomes remains challenging. Persistent kidney excretory dysfunction for longer than 7 days has been defined as Acute Kidney Disease (AKD). In this study, we prospectively quantified serum Nostrin, an essential regulator of endothelial NO metabolism, in hospitalized patients with AKI.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In-hospital subjects with AKI of various etiology were identified through the in-hospital AKI alert system of the Brandenburg University Hospital. Serum Nostrin, and serum NGAL and KIM-1 were measured within a maximum of 48 hours from the timepoint of initial diagnosis of AKI. The following endpoints were defined: in-hospital death, need of kidney replacement therapy (KRT), recovery of kidney function (ROKF) until discharge.

RESULTS

AKI patients had significantly higher serum Nostrin levels compared to Controls. The level of serum Nostrin increased significantly with the severity of AKI. Within the group of AKI patients (n = 150) the in-hospital mortality was 16.7%, KRT was performed in 39.3%, no ROKF occurred in 28%. Patients who required KRT had significantly higher levels of serum Nostrin compared to patients who did not require KRT. Significantly higher levels of serum Nostrin were also detected in AKI patients without ROKF compared to patients with ROKF. In addition, low serum Nostrin levels at the timepoint of AKI diagnosis were predictive of in-hospital survival. For comparison, the serum concentrations of NGAL and KIM-1 were determined in parallel to the Nostrin concentrations and the results confirm the prognostic properties of serum Nostrin in AKI.

CONCLUSIONS

The current study suggests serum Nostrin as novel biomarker of AKI-associated mortality, KRT and Acute Kidney Disease.

Efficacy of metamizole to prevent kidney injury after renal-ischaemic reperfusion injury in Wistar rats

Background

Renal ischaemia-reperfusion injury (RIRI) is a common kidney procedure complication due to temporary blood flow interruption, leading to kidney injuries. This study aimed to analyze the effect of metamizole on the levels of interleukin-18 (IL-18), neutrophil-gelatinase-associated lipocalin (NGAL), myeloperoxidase (MPO), and histopathological changes in rats with RIRI.

Materials and methods

Animal pre-clinical design study was used. Thirty-two male Wistar rats (Rattus norvegicus) were divided into four groups: negative control, positive control, M100, and M200. Blood samples were collected by intracardiac puncture, followed by bilateral nephrectomy and analyzed histopathologically.

Results

Significant difference in IL-18 levels between positive control vs negative control (114.1 + 12.07 vs. 94.0 + 11.4; P = 0.019) and positive control vs M100 (114.1 + 12.07 vs. 86.9 + 8.34; P = 0.007). There was no difference in NGAL. M100 group had the lowest serum MPO levels (14.78+2.01), there was a significant difference in MPO levels in all pairwise analyses. There was a difference in cumulative EGTI scores among the study groups [positive 10.5 (8-11) vs. negative 9 (7-10) vs. M100 9 (7-10) vs. M200 9 (7-11); P = 0.021].

Conclusion

Metamizole 100 mg/kgBW can reduce IL-18 and MPO levels in RIRI, giving more optimal results without affecting NGAL levels. Metamizole administration can reduce cumulative EGTI scores in RIRI, both at doses of 100 mg/kgBW and 200 mg/kgBW. This study shows that Metamizole can be used to prevent kidney injury caused by RIRI. IL-18 and MPO can be biomarkers in predicting kidney injury in RIRI.

The AKI-to-CKD Transition: The Role of Uremic Toxins

After acute kidney injury (AKI), renal function continues to deteriorate in some patients. In a pro-inflammatory and profibrotic environment, the proximal tubules are subject to maladaptive repair. In the AKI-to-CKD transition, impaired recovery from AKI reduces tubular and glomerular filtration and leads to chronic kidney disease (CKD). Reduced kidney secretion capacity is characterized by the plasma accumulation of biologically active molecules, referred to as uremic toxins (UTs). These toxins have a role in the development of neurological, cardiovascular, bone, and renal complications of CKD. However, UTs might also cause CKD as well as be the consequence. Recent studies have shown that these molecules accumulate early in AKI and contribute to the establishment of this pro-inflammatory and profibrotic environment in the kidney. The objective of the present work was to review the mechanisms of UT toxicity that potentially contribute to the AKI-to-CKD transition in each renal compartment.

Acute kidney disease: an overview of the epidemiology, pathophysiology, and management

Acute kidney injury (AKI) increases the risk of chronic kidney disease (CKD), and AKI and CKD are seen as interconnected syndromes. Acute kidney disease (AKD) is defined as subacute damage and/or loss of kidney function occurring 7 to 90 days after AKI, during which period key interventions may be initiated to hinder the development of CKD. While AKD is usually under-recognized, it is associated with high morbidity and mortality globally. This review article aims to summarize the current knowledge concerning the epidemiology, pathophysiology, and management of AKD with the aim to develop monitoring strategies and therapeutic agents of AKD. Generally, AKD tends to occur more frequently in the elderly and those with chronic diseases, such as hypertension, diabetes mellitus, and metabolic syndrome. In addition, the severity, duration, and frequency of AKI are independent risk factors for AKD. Investigations of several mechanisms of AKD, such as renal tubular epithelium cell-cycle arrest, epigenetic change, chronic inflammation, mitochondria dysfunction, failed regeneration of tubular cells, metabolic reprogramming, and renin-angiotensin system (RAS) activation, have identified additional potential pharmacotherapy targets. Management of AKD includes prevention of repeated AKI, early and regular follow-up by a nephrologist, resumption and adjustment of essential medication, optimization of blood pressure control and nutrition management, and development of new pharmaceutical agents including RAS inhibitors. Finally, we outline a care bundle for AKD patients based on important lessons learned from studies and registries and identify the need for clinical trials of RAS inhibitors or other novel agents to impede ensuing CKD development.

cGAS-STING signaling pathway promotes hypoxia-induced renal fibrosis by regulating PFKFB3-mediated glycolysis

Hypoxia has long been considered to play an active role in the progression of fibrosis in chronic kidney disease, but its specific mechanism is not fully understood. The stimulator of interferon genes (STING) has been a research hotspot in the fields of tumor, immunity, and infection in recent years, and its role in immune and inflammatory responses related to kidney disease has gradually attracted attention. This study mainly explores the role and mechanism of STING in hypoxia-related renal fibrosis. To address this issue, we stimulated human proximal tubular epithelial (HK-2) cells with hypoxia for 48 h to construct cell models. Meanwhile, C57BL/6J male mice were used to establish a renal fibrosis model induced by renal ischemia-reperfusion injury (IRI). In our present study, we found that the GMP-AMP synthase (cGAS)-STING signaling pathway can promote the progression of renal fibrosis after hypoxic exposure, and this effect is closely related to 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 3 (PFKFB3)-mediated glycolysis. Furthermore, inhibition of both STING and its downstream interferon regulatory factor 3 (IRF3) reversed elevated PFKFB3 expression, thereby attenuating hypoxia-induced renal fibrosis. Taken together, our data suggest that the cGAS-STING-IRF3-PFKFB3 signaling pathway activated under hypoxia may provide new ideas and targets for the treatment of early renal fibrosis.

Long-term kidney follow-up after pediatric acute kidney support therapy for children less than 15 kg

BACKGROUND

In small children, acute dialysis (pediatric acute kidney support therapy (paKST)) is increasingly used; however, it is challenging for many reasons. We compared clinical characteristics and predictors of long-term outcomes of patients < 15 kg on peritoneal dialysis (PD), hemodialysis (HD), and continuous kidney replacement therapy (CKRT).

METHODS

Patients with history of paKST (CKRT, HD, PD) weighing < 15 kg and ≥ 6 months of follow-up at Hacettepe University were included. Surviving patients were evaluated at last visit.

RESULTS

109 patients (57 females) were included. Median age at paKST was 10.1 months (IQR: 2-27 months). In total, 43 (39.4%) patients received HD, 37 (34%) PD, and 29 (26.6%) CKRT. 64 (58.7%) patients died a median 3 days (IQR: 2-9.5 days) after paKST. Percentages of patients using vasopressor agents, with sepsis, and undergoing mechanical ventilation were lower in those who survived. After mean follow-up of 2.9 ± 2.1 years, 34 patients were evaluated at mean age 4.7 ± 2.4 years. Median spot urine protein/creatinine was 0.19 (IQR: 0.13-0.37) and 12 patients (35.3%) had non-nephrotic proteinuria. Three patients had estimated glomerular filtration rate (eGFR) < 90 mL/min/1.73m2 and 2 (6%) had hyperfiltration. In total 22 patients (64.7%) had ≥ 1 kidney risk factor (elevated blood pressure/hypertension, hyperfiltration, eGFR < 90 ml/min/1.73m2, and/or proteinuria) at last visit. Among 28 patients on paKST < 32 months, 21 had ≥ 1 risk factor (75%), whereas among 6 patients who had paKST ≥ 32 months, one patient had ≥ 1 risk factor (16.7%), (p = 0.014).

CONCLUSIONS

Patients on paKST who undergo mechanical ventilation and vasopressor treatment should be followed-up more closely. After surviving the acute period, patients on paKST need to be followed-up closely during the chronic stage. A higher resolution version of the Graphical abstract is available as Supplementary information.

A single administration of FGF2 after renal ischemia-reperfusion injury alleviates post-injury interstitial fibrosis

BACKGROUND

Despite lack of clinical therapy in acute kidney injury (AKI) or its progression to chronic kidney disease (CKD), administration of growth factors shows great potential in the treatment of renal repair and further fibrosis. At an early phase of AKI, administration of exogenous fibroblast growth factor 2 (FGF2) protects against renal injury by inhibition of mitochondrial damage and inflammatory response. Here, we investigated whether this treatment attenuates the long-term renal interstitial fibrosis induced by ischemia-reperfusion (I/R) injury.

METHODS

Unilateral renal I/R with contralateral nephrectomy was utilized as an in vivo model for AKI and subsequent CKD. Rats were randomly divided into four groups: Sham-operation group, I/R group, I/R-FGF2 group and FGF2-3D group. These groups were monitored for up to 2 months. Serum creatinine, inflammatory response and renal histopathology changes were detected to evaluate the role of FGF2 in AKI and followed renal interstitial fibrosis. Moreover, the expression of vimentin, α-SMA, CD31 and CD34 were examined.

RESULTS

Two months after I/R injury, the severity of renal interstitial fibrosis was significantly attenuated in both of I/R-FGF2 group and FGF2-3D group, compared with the I/R group. The protective effects of FGF2 administration were associated with the reduction of high-mobility group box 1 (HMGB1)-mediated inflammatory response, the inhibition of transforming growth factor beta (TGF-β1)/Smads signaling-induced epithelial-mesenchymal transition and the maintenance of peritubular capillary structure.

CONCLUSIONS

A single dose of exogenous FGF2 administration 1 h or 3 days after reperfusion inhibited renal fibrogenesis and thus blocked the transition of AKI to CKD. Our findings provided novel insight into the role of FGF signaling in AKI-to-CKD progression and underscored the potential of FGF-based therapy for this devastating disease.

Endothelial cell activation and glycocalyx shedding - potential as biomarkers in patients with lupus nephritis

Lupus nephritis (LN) is a common and severe manifestation of systemic lupus erythematosus and an important cause of acute and chronic kidney injury. Early diagnosis of LN and preventing relapses are key to preserving renal reserve. However, due to the complexity and heterogeneity of the disease, clinical management remains challenging. Kidney biopsy remains the gold standard for confirming the diagnosis of LN and subsequent assessment of kidney histopathology, but it is invasive and cannot be repeated frequently. Current clinical indicators of kidney function such as proteinuria and serum creatinine level are non-specific and do not accurately reflect histopathological changes, while anti-dsDNA antibody and C3 levels reflect immunological status but not kidney injury. Identification of novel and specific biomarkers for LN is prerequisite to improve management. Renal function deterioration is associated with changes in the endothelial glycocalyx, a delicate gel-like layer located at the interface between the endothelium and bloodstream. Inflammation induces endothelial cell activation and shedding of glycocalyx constituents into the circulation. This review discusses the potential role of soluble glycocalyx components as biomarkers of active LN, especially in patients in whom conventional serological and biochemical markers do not appear helpful.

Post-ischemic inactivation of HIF prolyl hydroxylases in endothelium promotes maladaptive kidney repair by inducing glycolysis

Ischemic acute kidney injury (AKI) is common in hospitalized patients and increases the risk for chronic kidney disease (CKD). Impaired endothelial cell (EC) functions are thought to contribute in AKI to CKD transition, but the underlying mechanisms remain unclear. Here, we identify a critical role for endothelial oxygen sensing prolyl hydroxylase domain (PHD) enzymes 1-3 in regulating post-ischemic kidney repair. In renal endothelium, we observed compartment-specific differences in the expression of the three PHD isoforms in both mice and humans. We found that post-ischemic concurrent inactivation of endothelial PHD1, PHD2, and PHD3 but not PHD2 alone promoted maladaptive kidney repair characterized by exacerbated tissue injury, fibrosis, and inflammation. Single-cell RNA-seq analysis of the post-ischemic endothelial PHD1, PHD2 and PHD3 deficient (PHDTiEC) kidney revealed an endothelial glycolytic transcriptional signature, also observed in human kidneys with severe AKI. This metabolic program was coupled to upregulation of the SLC16A3 gene encoding the lactate exporter monocarboxylate transporter 4 (MCT4). Strikingly, treatment with the MCT4 inhibitor syrosingopine restored adaptive kidney repair in PHDTiEC mice. Mechanistically, MCT4 inhibition suppressed pro-inflammatory EC activation reducing monocyte-endothelial cell interaction. Our findings suggest avenues for halting AKI to CKD transition based on selectively targeting the endothelial hypoxia-driven glycolysis/MCT4 axis.

The Role of Vascular Biomarkers in Outcomes of Patients with Kidney Disease

BACKGROUND

Vascular biomarkers may explain the link between acute kidney injury (AKI) and poor long-term outcomes such as cardiovascular disease (CVD). Vessel injury is exceedingly common in AKI and contributes to the development of kidney fibrosis and CVD. As prominent determinants of vessel stability in the body, angiopoietins and other prominent vascular biomarkers may explain this biological link.

SUMMARY

Angiopoietin-1 (Angpt-1) promotes vessel stability by decreasing inflammation, apoptosis, and vessel permeability. By contrast, angiopoietin-2 (Angpt-2) blocks the binding of Angpt-1 to its receptor and thus contributes to vessel instability and permeability. Based on our findings, higher levels of Angpt-1 relative to Angpt-2 were strongly associated with less risk of kidney disease progression, heart failure, and death in hospitalized patients with AKI. In chronic kidney disease patients, it has been shown that endothelial damage in glomerular vasculature triggers Angpt-2 secretion, leading to poor outcomes such as CVD and mortality. Furthermore, in kidney transplant recipients, Angpt-2 levels significantly decrease after transplantation suggesting that transplantation may reduce Angpt-2 levels and decrease rates of poor outcomes. Other vascular health pathways - such as vascular endothelial growth factor and placental growth factor - were associated with improved rates of survival after cardiac surgery in participants with and without AKI.

KEY MESSAGES

Vascular health biomarkers provide actionable pathways for clinical intervention in reducing CVD and mortality for AKI patients. There is great need for future research that focuses on developing robust prognostic vascular biomarker panels in order to help identify high-risk AKI survivors who may benefit from targeted follow-up and therapy, with the intention to prevent kidney and cardiac complications.

Zinc finger protein 24-dependent transcription factor SOX9 up-regulation protects tubular epithelial cells during acute kidney injury

Transcriptional profiling studies have identified several protective genes upregulated in tubular epithelial cells during acute kidney injury (AKI). Identifying upstream transcriptional regulators could lead to the development of therapeutic strategies augmenting the repair processes. SOX9 is a transcription factor controlling cell-fate during embryonic development and adult tissue homeostasis in multiple organs including the kidneys. SOX9 expression is low in adult kidneys; however, stress conditions can trigger its transcriptional upregulation in tubular epithelial cells. SOX9 plays a protective role during the early phase of AKI and facilitates repair during the recovery phase. To identify the upstream transcriptional regulators that drive SOX9 upregulation in tubular epithelial cells, we used an unbiased transcription factor screening approach. Preliminary screening and validation studies show that zinc finger protein 24 (ZFP24) governs SOX9 upregulation in tubular epithelial cells. ZFP24, a Cys2-His2 (C2H2) zinc finger protein, is essential for oligodendrocyte maturation and myelination; however, its role in the kidneys or in SOX9 regulation remains unknown. Here, we found that tubular epithelial ZFP24 gene ablation exacerbated ischemia, rhabdomyolysis, and cisplatin-associated AKI. Importantly, ZFP24 gene deletion resulted in suppression of SOX9 upregulation in injured tubular epithelial cells. Chromatin immunoprecipitation and promoter luciferase assays confirmed that ZFP24 bound to a specific site in both murine and human SOX9 promoters. Importantly, CRISPR/Cas9-mediated mutation in the ZFP24 binding site in the SOX9 promoter in vivo led to suppression of SOX9 upregulation during AKI. Thus, our findings identify ZFP24 as a critical stress-responsive transcription factor protecting tubular epithelial cells through SOX9 upregulation.

Activation of Angiopoietin-Tie2 Signaling Protects the Kidney from Ischemic Injury by Modulation of Endothelial-Specific Pathways

SIGNIFICANCE STATEMENT

Ischemia-reperfusion AKI (IR-AKI) is common and causes significant morbidity. Effective treatments are lacking. However, preclinical studies suggest that inhibition of angiopoietin-Tie2 vascular signaling promotes injury, whereas activation of Tie2 is protective. We show that kidney ischemia leads to increased levels of the endothelial-specific phosphatase vascular endothelial protein tyrosine phosphatase (VE-PTP; PTPRB), which inactivates Tie2. Activation of Tie2 through VE-PTP deletion, or delivery of a novel angiopoietin mimetic (Hepta-ANG1), abrogated IR-AKI in mice. Single-cell RNAseq analysis showed Tie2 activation promotes increased Entpd1 expression, downregulation of FOXO1 target genes in the kidney vasculature, and emergence of a new subpopulation of glomerular endothelial cells. Our data provide a molecular basis and identify a candidate therapeutic to improve endothelial integrity and kidney function after IR-AKI.

BACKGROUND

Ischemia-reperfusion AKI (IR-AKI) is estimated to affect 2%-7% of all hospitalized patients. The significant morbidity and mortality associated with AKI indicates urgent need for effective treatments. Previous studies have shown activation of the vascular angiopoietin-Tie2 tyrosine kinase signaling pathway abrogates ischemia-reperfusion injury (IRI). We extended previous studies to (1) determine the molecular mechanism(s) underlying kidney injury and protection related to decreased or increased activation of Tie2, respectively, and (2) to test the hypothesis that deletion of the Tie2 inhibitory phosphatase vascular endothelial protein tyrosine phosphatase (VE-PTP) or injection of a new angiopoietin mimetic protects the kidney from IRI by common molecular mechanism(s).

METHODS

Bilateral IR-AKI was performed in VE-PTP wild-type or knockout mice and in C57BL/6J mice treated with Hepta-ANG1 or vehicle. Histologic, immunostaining, and single-cell RNA sequencing analyses were performed.

RESULTS

The phosphatase VE-PTP, which negatively regulates the angiopoietin-Tie2 pathway, was upregulated in kidney endothelial cells after IRI, and genetic deletion of VE-PTP in mice protected the kidney from IR-AKI. Injection of Hepta-ANG1 potently activated Tie2 and protected the mouse kidney from IRI. Single-cell RNAseq analysis of kidneys from Hepta-ANG1-treated and vehicle-treated mice identified endothelial-specific gene signatures and emergence of a new glomerular endothelial subpopulation associated with improved kidney function. Overlap was found between endothelial-specific genes upregulated by Hepta-ANG1 treatment and those downregulated in HUVECs with constitutive FOXO1 activation, including Entpd1 / ENTPD1 that modulates purinergic receptor signaling.

CONCLUSIONS

Our data support a key role of the endothelium in the development of IR-AKI, introduce Hepta-ANG1 as a putative new therapeutic biologic, and report a model to explain how IRI reduces Tie2 signaling and how Tie2 activation protects the kidney.

PODCAST

This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/JASN/2023_05_23_JSN_Ang_EP23_052323.mp3.

Mitochondrial Oxidative Metabolism: An Emerging Therapeutic Target to Improve CKD Outcomes

Chronic kidney disease (CKD) predisposes one toward end-stage renal disease (ESRD) and its associated morbidity and mortality. Significant metabolic perturbations in conjunction with alterations in redox status during CKD may induce increased production of reactive oxygen species (ROS), including superoxide (O₂^●-) and hydrogen peroxide (H₂O₂). Increased O₂^●- and H₂O₂ may contribute to the overall progression of renal injury as well as catalyze the onset of comorbidities. In this review, we discuss the role of mitochondrial oxidative metabolism in the pathology of CKD and the recent developments in treating CKD progression specifically targeted to the mitochondria. Recently published results from a Phase 2b clinical trial by our group as well as recently released data from a ROMAN: Phase 3 trial (NCT03689712) suggest avasopasem manganese (AVA) may protect kidneys from cisplatin-induced CKD. Several antioxidants are under investigation to protect normal tissues from cancer-therapy-associated injury. Although many of these antioxidants demonstrate efficacy in pre-clinical models, clinically relevant novel compounds that reduce the severity of AKI and delay the progression to CKD are needed to reduce the burden of kidney disease. In this review, we focus on the various metabolic pathways in the kidney, discuss the role of mitochondrial metabolism in kidney disease, and the general involvement of mitochondrial oxidative metabolism in CKD progression. Furthermore, we present up-to-date literature on utilizing targets of mitochondrial metabolism to delay the pathology of CKD in pre-clinical and clinical models. Finally, we discuss the current clinical trials that target the mitochondria that could potentially be instrumental in advancing the clinical exploration and prevention of CKD.

HDAC9-mediated epithelial cell cycle arrest in G2/M contributes to kidney fibrosis in male mice

Renal tubular epithelial cells (TECs) play a key role in kidney fibrosis by mediating cycle arrest at G2/M. However, the key HDAC isoforms and the underlying mechanism that are involved in G2/M arrest of TECs remain unclear. Here, we find that Hdac9 expression is significantly induced in the mouse fibrotic kidneys, especially in proximal tubules, induced by aristolochic acid nephropathy (AAN) or unilateral ureter obstruction (UUO). Tubule-specific deletion of HDAC9 or pharmacological inhibition by TMP195 attenuates epithelial cell cycle arrest in G2/M, then reduces production of profibrotic cytokine and alleviates tubulointerstitial fibrosis in male mice. In vitro, knockdown or inhibition of HDAC9 alleviates the loss of epithelial phenotype in TECs and attenuates fibroblasts activation through inhibiting epithelial cell cycle arrest in G2/M. Mechanistically, HDAC9 deacetylates STAT1 and promotes its reactivation, followed by inducing G2/M arrest of TECs, finally leading to tubulointerstitial fibrosis. Collectively, our studies indicate that HDAC9 may be an attractive therapeutic target for kidney fibrosis.

Salt-sensitive hypertension after reversal of unilateral ureteral obstruction

The incidence of ureter obstruction is increasing and patients recovering from this kidney injury often progress to chronic kidney injury. There is evidence that a long-term consequence of recovery from ureter obstruction is an increased risk for salt-sensitive hypertension. A reversal unilateral ureteral obstruction (RUUO) model was used to study long-term kidney injury and salt-sensitive hypertension. In this model, we removed the ureteral obstruction at day 10 in mice. Mice were divided into four groups: (1) normal salt diet, (2) high salt diet, (3) RUUO normal salt diet, and (4) RUUO high salt diet. At day 10, the mice were fed a normal or high salt diet for 4 weeks. Blood pressure was measured, and urine and kidney tissue collected. There was a progressive increase in blood pressure in the RUUO high salt diet group. RUUO high salt group had decreased sodium excretion and glomerular injury. Renal epithelial cell injury was evident in RUUO normal and high salt mice as assessed by neutrophil gelatinase-associated lipocalin (NGAL). Kidney inflammation in the RUUO high salt group involved an increase in F4/80 positive macrophages; however, CD3+ positive T cells were not changed. Importantly, RUUO normal and high salt mice had decreased vascular density. RUUO was also associated with renal fibrosis that was further elevated in RUUO mice fed a high salt diet. Overall, these findings demonstrate long-term renal tubular injury, inflammation, decreased vascular density, and renal fibrosis following reversal of unilateral ureter obstruction that could contribute to impaired sodium excretion and salt-sensitive hypertension.

Endothelial cells overexpressing CXCR1/2 are renoprotective in rats with acute kidney injury

Inflammation that develops with the release of chemokines and cytokines during acute kidney injury (AKI) has been shown to participate in functional renal recovery. Although a major research focus has been on the role of macrophages, the family of C-X-C motif chemokines that promote neutrophil adherence and activation also increases with kidney ischemia-reperfusion (I/R) injury. This study tested the hypothesis that intravenous delivery of endothelial cells (ECs) that overexpress (C-X-C motif) chemokine receptors 1 and 2 (CXCR1 and CXCR2, respectively) improves outcomes in kidney I/R injury. Overexpression of CXCR1/2 enhanced homing of endothelial cells to I/R-injured kidneys and limited interstitial fibrosis, capillary rarefaction, and tissue injury biomarkers (serum creatinine concentration and urinary kidney injury molecule-1) following AKI and also reduced expression of P-selectin and the rodent (C-X-C motif) chemokine cytokine-induced neutrophil chemoattractant (CINC)-2β as well as the number of myeloperoxidase-positive cells in the postischemic kidney. The serum chemokine/cytokine profile, including CINC-1, showed similar reductions. These findings were not observed in rats given endothelial cells transduced with an empty adenoviral vector (null-ECs) or a vehicle alone. These data indicate that extrarenal endothelial cells that overexpress CXCR1 and CXCR2, but not null-ECs or vehicle alone, reduce I/R kidney injury and preserve kidney function in a rat model of AKI.NEW & NOTEWORTHY Inflammation facilitates kidney ischemia-reperfusion (I/R) injury. Endothelial cells (ECs) that were modified to overexpress (C-X-C motif) chemokine receptor (CXCR)1/2 (CXCR1/2-ECs) were injected immediately following kidney I/R injury. The interaction of CXCR1/2-ECs, but not ECs transduced with an empty adenoviral vector, with injured kidney tissue preserved kidney function and reduced production of inflammatory markers, capillary rarefaction, and interstitial fibrosis. The study highlights a functional role for the C-X-C chemokine pathway in kidney damage following I/R injury.

A refined protocol for the isolation and monoculture of primary mouse renal peritubular endothelial cells

During an episode of acute kidney injury (AKI), a sudden and rapid decline in renal function is often accompanied by a persistent reduction in mitochondrial function, microvasculature dysfunction/rarefaction, and tubular epithelial injury/necrosis. Additionally, patients who have experienced an AKI are at an elevated risk of developing other progressive renal, cardiovascular, and cardiorenal related diseases. While restoration of the microvasculature is imperative for oxygen and nutrient delivery/transport during proper renal repair processes, the mechanism(s) by which neovascularization and/or inhibition of microvascular dysfunction improves renal recovery remain understudied. Interestingly, pharmacological stimulation of mitochondrial biogenesis (MB) post-AKI has been shown to restore mitochondrial and renal function in mice. Thus, targeting MB pathways in microvasculature endothelial cell (MV-EC) may provide a novel strategy to improve renal vascular function and repair processes post-AKI. However, limitations to studying such mechanisms include a lack of commercially available primary renal peritubular MV-ECs, the variability in both purity and outgrowth of primary renal MV-EC in monoculture, the tendency of primary renal MV-ECs to undergo phenotypic loss in primary monoculture, and a limited quantity of published protocols to obtain primary renal peritubular MV-ECs. Thus, we focused on refining the isolation and phenotypic retention of mouse renal peritubular endothelial cells (MRPEC) for future physiological and pharmacological based studies. Here, we present a refined isolation method that augments the purity, outgrowth, and phenotypic retention of primary MRPEC monocultures by utilizing a collagenase type I enzymatic digestion, CD326+ (EPCAM) magnetic microbead epithelial cell depletion, and two CD146+ (MCAM) magnetic microbead purification cycles to achieve a monoculture MRPEC purity of ≅ 91-99% by all markers evaluated.

Predictive Value of N-Terminal Pro B-Type Natriuretic Peptide for Contrast-Induced Nephropathy Non-Recovery and Poor Outcomes Among Patients Undergoing Percutaneous Coronary Intervention

BACKGROUND

Contrast-induced nephropathy (CIN) is a frequent complication in patients undergoing percutaneous coronary intervention (PCI). The degree of recovery of renal function from CIN may affect long-term prognosis. N-terminal pro B-type natriuretic peptide (NT-proBNP) is a simple but useful biomarker for predicting CIN. However, the predictive value of preprocedural NT-proBNP for CIN non-recovery and long-term outcomes in patients undergoing PCI remains unclear.

METHODS AND RESULTS

This study prospectively enrolled 550 patients with CIN after PCI between January 2012 and December 2018. CIN non-recovery was defined as persistent serum creatinine >25% or 0.5 mg/dL over baseline from 1 week to 12 months after PCI in patients who developed CIN. CIN non-recovery was observed in 40 (7.3%) patients. Receiver operating characteristic analysis indicated that the best NT-proBNP cut-off value for detecting CIN non-recovery was 876.1 pg/mL (area under the curve 0.768; 95% confidence interval [CI] 0.731-0.803). After adjusting for potential confounders, multivariable analysis indicated that NT-proBNP >876.1 pg/mL was an independent predictor of CIN non-recovery (odds ratio 1.94; 95% CI 1.03-3.75; P=0.0042). Kaplan-Meier curves showed higher rates of long-term mortality among patients with CIN non-recovery than those with CIN recovery (Chi-squared=14.183, log-rank P=0.0002).

CONCLUSIONS

Preprocedural NT-proBNP was associated with CIN non-recovery among patients undergoing PCI. The optimal cut-off value for NT-proBNP to predict CIN non-recovery was 876.1 pg/mL.

Renal Endothelial Cell-Targeted Extracellular Vesicles Protect the Kidney from Ischemic Injury

Endothelial cell injury plays a critical part in ischemic acute kidney injury (AKI) and participates in the progression of AKI. Targeting renal endothelial cell therapy may ameliorate vascular injury and further improve the prognosis of ischemic AKI. Here, P-selectin as a biomarker of ischemic AKI in endothelial cells is identified and P-selectin binding peptide (PBP)-engineered extracellular vesicles (PBP-EVs) with imaging and therapeutic functions are developed. The results show that PBP-EVs exhibit a selective targeting tendency to injured kidneys, while providing spatiotemporal information for the early diagnosis of AKI by quantifying the expression of P-selectin in the kidneys by molecular imaging. Meanwhile, PBP-EVs reveal superior nephroprotective functions in the promotion of renal repair and inhibition of fibrosis by alleviating inflammatory infiltration, improving reparative angiogenesis, and ameliorating maladaptive repair of the renal parenchyma. In conclusion, PBP-EVs, as an ischemic AKI theranostic system that is designed in this study, provide a spatiotemporal diagnosis in the early stages of AKI to help guide personalized therapy and exhibit superior nephroprotective effects, offering proof-of-concept data to design EV-based theranostic strategies to promote renal recovery and further improve long-term outcomes following AKI.

Gender and Renal Insufficiency: Opportunities for Their Therapeutic Management?

Acute kidney injury (AKI) is a major clinical problem associated with increased morbidity and mortality. Despite intensive research, the clinical outcome remains poor, and apart from supportive therapy, no other specific therapy exists. Furthermore, acute kidney injury increases the risk of developing chronic kidney disease (CKD) and end-stage renal disease. Acute tubular injury accounts for the most common intrinsic cause of AKI. The main site of injury is the proximal tubule due to its high workload and energy demand. Upon injury, an intratubular subpopulation of proximal epithelial cells proliferates and restores the tubular integrity. Nevertheless, despite its strong regenerative capacity, the kidney does not always achieve its former integrity and function and incomplete recovery leads to persistent and progressive CKD. Clinical and experimental data demonstrate sexual differences in renal anatomy, physiology, and susceptibility to renal diseases including but not limited to ischemia-reperfusion injury. Some data suggest the protective role of female sex hormones, whereas others highlight the detrimental effect of male hormones in renal ischemia-reperfusion injury. Although the important role of sex hormones is evident, the exact underlying mechanisms remain to be elucidated. This review focuses on collecting the current knowledge about sexual dimorphism in renal injury and opportunities for therapeutic manipulation, with a focus on resident renal progenitor stem cells as potential novel therapeutic strategies.

Plasma proteomic characterization of the development of acute kidney injury in early sepsis patients

Acute kidney injury (AKI) develops frequently in the course of patients with sepsis and strongly associates with in-hospital mortality. However, diagnosing AKI involves a considerable lag-time because it depends on assessing an increase in serum creatinine, and offers no insight in the underlying pathophysiology. Consequently, identifying a set of proteins reflecting the development of AKI may improve earlier recognition of AKI and the understanding of its pathophysiology. A targeted plasma proteomic approach was performed in early sepsis patients with and without subsequent AKI development in a matched pair design (n = 19 each). Principal component analysis identified 53 proteins associated with development of AKI, which were further analysed using Enrichr gene ontology and pathway analysis. Nine differentially expressed proteins from the targeted proteomics were increased among patients who subsequently developed AKI and correlated with principal components, namely CALCA, CALR, CA12, CLEC1A, PTK7, KIM-1, NPPC, NUCB2 and PGF. We demonstrated the biological insight in the development of AKI in early sepsis compared to non-AKI sepsis.

From AKI to CKD: Maladaptive Repair and the Underlying Mechanisms

Acute kidney injury (AKI) is defined as a pathological condition in which the glomerular filtration rate decreases rapidly over a short period of time, resulting in changes in the physiological function and tissue structure of the kidney. An increasing amount of evidence indicates that there is an inseparable relationship between acute kidney injury and chronic kidney disease (CKD). With the progress in research in this area, researchers have found that the recovery of AKI may also result in the occurrence of CKD due to its own maladaptation and other potential mechanisms, which involve endothelial cell injury, inflammatory reactions, progression to fibrosis and other pathways that promote the progress of the disease. Based on these findings, this review summarizes the occurrence and potential mechanisms of maladaptive repair in the progression of AKI to CKD and explores possible treatment strategies in this process so as to provide a reference for the inhibition of the progression of AKI to CKD.

Pathophysiology of Acute Kidney Injury in Critical Illness: A Narrative Review

Acute kidney injury (AKI) is a syndrome that entails a rapid decline in kidney function with or without injury. The consequences of AKI among acutely ill patients are dire and lead to higher mortality, morbidity, and healthcare cost. To prevent AKI and its short and long-term repercussions, understanding its pathophysiology is essential. Depending on the baseline kidney histology and function reserves, the number of kidney insults, and the intensity of each insult, the clinical presentation of AKI may differ. While many factors are capable of inducing renal injury, they can be categorized into a few processes. The three primary processes reported in the literature are hemodynamic changes, inflammatory reactions, and nephrotoxicity. The majority of patients with AKI will suffer from more than one during their development and/or progression of AKI. Moreover, the development of one usually leads to the instigation of another. Thus, the interactions and progression between these mechanisms may determine the severity and duration of the AKI. Other factors such as organ crosstalk and how our concurrent therapies interact with these mechanisms complicate the pathophysiology of the progression of the AKI even further. In this narrative review article, we describe these three main pathophysiological processes that lead to the development and progression of AKI. © 2022 American Physiological Society. Compr Physiol 12: 1-14, 2022.

Inflammation in kidney repair: Mechanism and therapeutic potential

The kidney has a remarkable ability of repair after acute kidney injury (AKI). However, when injury is severe or persistent, the repair is incomplete or maladaptive and may lead to chronic kidney disease (CKD). Maladaptive kidney repair involves multiple cell types and multifactorial processes, of which inflammation is a key component. In the process of inflammation, there is a bidirectional interplay between kidney parenchymal cells and the immune system. The extensive and complex crosstalk between renal tubular epithelial cells and interstitial cells, including immune cells, fibroblasts, and endothelial cells, governs the repair and recovery of the injured kidney. Further research in this field is imperative for the discovery of biomarkers and promising therapeutic targets for kidney repair. In this review, we summarize the latest progress in the immune response and inflammation during maladaptive kidney repair, analyzing the interaction between immune cells and intrinsic kidney cells, pointing out the potentialities of inflammation-related pathways as therapeutic targets, and discussing the challenges and future research prospects in this field.

Single-cell analysis highlights differences in druggable pathways underlying adaptive or fibrotic kidney regeneration

The kidney has tremendous capacity to repair after acute injury, however, pathways guiding adaptive and fibrotic repair are poorly understood. We developed a model of adaptive and fibrotic kidney regeneration by titrating ischemic injury dose. We performed detailed biochemical and histological analysis and profiled transcriptomic changes at bulk and single-cell level (> 110,000 cells) over time. Our analysis highlights kidney proximal tubule cells as key susceptible cells to injury. Adaptive proximal tubule repair correlated with fatty acid oxidation and oxidative phosphorylation. We identify a specific maladaptive/profibrotic proximal tubule cluster after long ischemia, which expresses proinflammatory and profibrotic cytokines and myeloid cell chemotactic factors. Druggability analysis highlights pyroptosis/ferroptosis as vulnerable pathways in these profibrotic cells. Pharmacological targeting of pyroptosis/ferroptosis in vivo pushed cells towards adaptive repair and ameliorates fibrosis. In summary, our single-cell analysis defines key differences in adaptive and fibrotic repair and identifies druggable pathways for pharmacological intervention to prevent kidney fibrosis.

Persistent vascular congestion in male spontaneously hypertensive rats contributes to delayed recovery of renal function following ischemia-reperfusion compared to females

Acute kidney injury (AKI) is a serious and frequent clinical complication with mortality rates up to 80%. Vascular congestion in the renal outer medulla occurs early after ischemia reperfusion (IR) injury, and congestion has been linked to worsened outcomes following IR. There is evidence implicating both male sex and preexisting hypertension as risk factors for poor outcomes following IR. The present study tested the hypothesis that male spontaneously hypertensive rats (SHR) have greater vascular congestion and impaired renal recovery following renal IR vs. female SHR and normotensive male Sprague-Dawley rats (SD). 13 wk old male and female SHR and SD were subjected to sham surgery or 30 minutes of warm bilateral ischemia followed by reperfusion. Rats were euthanized 24 hours or 7 days post-IR. IR increased renal injury in all groups vs. sham controls at 24 hours. At 7 days post-IR, injury remained elevated only in male SHR. Histological examination of SD and SHR kidneys 24 hours post-IR showed vascular congestion in males and females. Vascular congestion was sustained only in male SHR 7 days post-IR. To assess the role of vascular congestion on impaired recovery following IR, additional male and female SHR were pretreated with heparin (200 U/kg) prior to IR. Heparin pre-treatment reduced IR-induced congestion and improved renal function in male SHR 7 days post-IR. Interestingly, preventing increases in BP in male SHR did not alter sustained vascular congestion. Our data demonstrate that IR-induced vascular congestion is a major driving factor for impaired renal recovery in male SHR.

Lipopolysaccharide from Rhodobacter spheroids modulate toll-like receptors expression and tissue damage in an animal model of bilateral renal ischemic reperfusion injury

Ischemic reperfusion injury (IRI) of the kidneys is a direct sequela of surgical procedures associated with the interruption of blood supply. The pathophysiology of IRI is complicated, and several inflammatories, apoptosis, and oxidative stress pathways are implicated. Among the major receptors directly involved in renal IRI are the toll-like receptors (TLRs), specifically TLR2 and TLR4. In this study, we investigated the effects of Lipopolysaccharide from Rhodobacter Sphaeroides (TLR2 and TLR4 antagonist, LPS-RS) and the ultrapure form (pure TLR4 antagonist, ULPS-RS) on the histopathological changes and TLRs expression in an animal model of bilateral renal IRI. Forty-eight adult male rats were allocated into six groups (N=8) as follows: sham group (negative control without IRI), control group (rats underwent bilateral renal ischemia for 30 minutes and 2 hours of reperfusion), vehicle group (IRI+ vehicle), LPS-RS group (IRI+ 0.5 mg/kg of LPS-RS), ULPS-RS group (IRI+ 0.1 mg/kg of ULPS-RS), ULPS-RSH group (IRI+ 0.2 mg/kg of ULPS-RS). Significant improvement in the histopathological damages induced by renal IRI was found in the ULPS-RS treated groups at both doses compared with the control group. The protective effect of ULPS-RS was associated with significantly reduced TLR4 expression without affecting TLR2. Regarding LPS-RS, the tested dose adversely affected the renal tissues as manifested by the histopathological findings, although it similarly affected TLRs expression as ULPS-RS. Our results demonstrated that ULPS-RS was renoprotective while LPS-RS had no protective effect against the tissue damages induced by renal IRI.

The effects of exercise on kidney injury: the role of SIRT1

In patients with kidney injury, muscle mass and strength decrease with altered muscle protein synthesis and degradation along with complications such as inflammation and low physical activity. A treatment strategy to maintain muscle metabolism in kidney injury is important. One of the proposed strategies in this regard is exercise, which in addition to inducing muscle hypertrophy, reducing plasma creatinine and urea and decreasing the severity of tubal injuries, can boost immune function and has anti-inflammatory effects. One of the molecules that have been considered as a target in the treatment of many diseases is silent information regulator 1 (SIRT1). Exercise increases the expression of SIRT1 and improves its activity. Therefore, studies that examined the effect of exercise on kidney injury considering the role of SIRT1 in this effect were reviewed to determine the direction of kidney injury research in future regarding to its prevalence, especially following diabetes, and lack of definitive treatment. In this review, we found that SIRT1 can be one of renoprotective target pathways of exercise. However, further studies are needed to determine the role of SIRT1 in different kidney injuries following exercise according to the type and severity of exercise, and the type of kidney injury.

Nanotechnology in Kidney and Islet Transplantation: An Ongoing, Promising Field

Organ transplantation has evolved rapidly in recent years as a reliable option for patients with end-stage organ failure. However, organ shortage, surgical risks, acute and chronic rejection reactions and long-term immunosuppressive drug applications and their inevitable side effects remain extremely challenging problems. The application of nanotechnology in medicine has proven highly successful and has unique advantages for diagnosing and treating diseases compared to conventional methods. The combination of nanotechnology and transplantation brings a new direction of thinking to transplantation medicine. In this article, we provide an overview of the application and progress of nanotechnology in kidney and islet transplantation, including nanotechnology for renal pre-transplantation preservation, artificial biological islets, organ imaging and drug delivery.

Long-term follow-up of patients after acute kidney injury in the neonatal period: abnormal ambulatory blood pressure findings

Background

Data on the long-term effects of neonatal acute kidney injury (AKI) are limited.

Methods

We invited 302 children who had neonatal AKI and survived to hospital discharge; out of 95 patients who agreed to participate in the study, 23 cases were excluded due to primary kidney, cardiac, or metabolic diseases. KDIGO definition was used to define AKI. When a newborn had no previous serum creatinine, AKI was defined as serum creatinine above the mean plus two standard deviations (SD) (or above 97.5^th percentile) according to gestational age, weight, and postnatal age. Clinical and laboratory features in the neonatal AKI period were recorded for 72 cases; at long-term evaluation (2–12 years), kidney function tests with glomerular filtration rate (eGFR) by the Schwartz formula, microalbuminuria, office and 24-h ambulatory blood pressure monitoring (ABPM), and kidney ultrasonography were performed.

Results

Forty-two patients (58%) had stage I AKI during the neonatal period. Mean age at long-term evaluation was 6.8 ± 2.9 years (range: 2.3–12.0); mean eGFR was 152.3 ± 26.5 ml/min/1.73 m². Office hypertension (systolic and/or diastolic BP ≥ 95^th percentile), microalbuminuria (> 30 mg/g creatinine), and hyperfiltration (> 187 ml/min/1.73 m²) were present in 13.0%, 12.7%, and 9.7% of patients, respectively. ABPM was performed on 27 patients, 18.5% had hypertension, and 40.7% were non-dippers; 48.1% had abnormal findings. Female sex was associated with microalbuminuria; low birth weight (< 1,500 g) and low gestational age (< 32 weeks) were associated with hypertension by ABPM. Twenty-three patients (33.8%) had at least one sign of microalbuminuria, office hypertension, or hyperfiltration. Among 27 patients who had ABPM, 16 (59.3%) had at least one sign of microalbuminuria, abnormal ABPM (hypertension and/or non-dipping), or hyperfiltration.

Conclusion

Even children who experienced stage 1 and 2 neonatal AKI are at risk for subclinical kidney dysfunction. Non-dipping is seen in four out of 10 children. Long-term follow-up of these patients is necessary.

Endothelial cells: potential novel regulators of renal inflammation

Substantial evidence has supported the role of endothelial cell (EC) activation and dysfunction in the development of hypertension, chronic kidney disease (CKD), and lupus nephritis (LN). In both humans and experimental models of hypertension, CKD, and LN, ECs become activated and release potent mediators of inflammation including cytokines, chemokines, and reactive oxygen species that cause EC dysfunction, tissue damage, and fibrosis. Factors that activate the endothelium include inflammatory cytokines, mechanical stretch, and pathological shear stress. These signals can activate the endothelium to promote upregulation of adhesion molecules, such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, which promote leukocyte adhesion and migration to the activated endothelium. More importantly, it is now recognized that some of these signals may in turn promote endothelial antigen presentation through major histocompatibility complex II. In this review, we will consider in-depth mechanisms of endothelial activation and the novel mechanism of endothelial antigen presentation. Moreover, we will discuss these proinflammatory events in renal pathologies and consider possible new therapeutic approaches to limit the untoward effects of endothelial inflammation in hypertension, CKD, and LN.

Interfering TUG1 Attenuates Cerebrovascular Endothelial Apoptosis and Inflammatory injury After Cerebral Ischemia/Reperfusion via TUG1/miR-410/FOXO3 ceRNA Axis

Background Emerging studies illustrate that long non-coding RNA TUG1 (TUG1) participates in neuron death after ischemia. However, the role of TUG1 in cerebral ischemia/reperfusion (CI/R) injury through cerebrovascular pathology was undetermined yet. Methods Expression of TUG1, miRNA-410-3p (miR-410), and forkhead box O3 (FOXO3) was detected by RT-qPCR and western blot. Neural function, apoptosis, and inflammatory damage were assessed by triphenyltetrazolium chloride straining, modified neurological severity score, fluorescence-activated cell sorting method, and western blot. The relationship among TUG1, miR-410, and FOXO3 was identified by dual-luciferase reporter assay, RNA pull-down, and RNA immunoprecipitation. Results TUG1 was upregulated in middle cerebral artery occlusion/reperfusion (MCAO/R) mice and oxygen-glucose deprivation/reoxygenation (OGD/R)-induced mouse brain microvascular endothelial cells (BMECs) in a certain of time-dependent manner. Blockage of TUG1 decreased infarct volume and increased neurological score in MCAO/R mice, accompanied with elevated Bcl-2 expression and declined expression of IL-1β, IL-6, TNF-α, Bax, and cleaved caspase 3. Abovementioned proteins were similarly expressed in OGD/R-induced BMECs with TUG1 knockdown, paralleled with diminished apoptosis rate. Either, miR-410 overexpression and FOXO3 interference could suppress OGD/R-induced inflammatory and apoptotic responses. Of note, TUG1 and FOXO3 are competing endogenous RNAs (ceRNAs) for miR-410 via target binding. Depleting miR-410 counteracted the role of TUG1 exhaustion, and reinforcing FOXO3 abated the effect of miR-410 overexpression. Conclusion Exhausting TUG1 could alleviate CI/R-induced inflammatory injury and apoptosis in brain tissues and BMECs via targeting miR-410/FOXO3 axis, suggesting an innovative perspective from cerebrovascular endothelial cells in the pathogenesis and treatment of CI/R.

Bioactive Flavonoids Icaritin and Icariin Protect against Cerebral Ischemia-Reperfusion-Associated Apoptosis and Extracellular Matrix Accumulation in an Ischemic Stroke Mouse Model

Stroke, which is the second leading cause of mortality in the world, is urgently needed to explore the medical strategies for ischemic stroke treatment. Both icariin (ICA) and icaritin (ICT) are the major active flavonoids extracted from Herba epimedii that have been regarded as the neuroprotective agents in disease models. In this study, we aimed to investigate and compare the neuroprotective effects of ICA and ICT in a middle cerebral artery occlusion (MCAO) mouse model. Male ICR mice were pretreated with both ICA and ICT, which ameliorated body weight loss, neurological injury, infarct volume, and pathological change in acute ischemic stroke mice. Furthermore, administration of both ICA and ICT could also protect against neuronal cell apoptotic death, oxidative and nitrosative stress, lipid peroxidation, and extracellular matrix (ECM) accumulation in the brains. The neuroprotective effects of ICT are slightly better than that of ICA in acute cerebral ischemic stroke mice. These results suggest that pretreatment with both ICA and ICT improves the neuronal cell apoptosis and responses of oxidative/nitrosative stress and counteracts the ECM accumulation in the brains of acute cerebral ischemic stroke mice. Both ICA and ICT treatment may serve as a useful therapeutic strategy for acute ischemic stroke.

The Protective Role of Prolyl Oligopeptidase (POP) Inhibition in Kidney Injury Induced by Renal Ischemia-Reperfusion

Ischemia/reperfusion injury (IRI) is a complex pathophysiological process characterized by blood circulation disorder caused by various factors, such as traumatic shock, surgery, organ transplantation, and thrombus. Severe metabolic dysregulation and tissue structure destruction are observed upon restoration of blood flow to the ischemic tissue. The kidney is a highly perfused organ, sensitive to ischemia and reperfusion injury, and the incidence of renal IRI has high morbidity and mortality. Several studies showed that infiltration of inflammatory cells, apoptosis, and angiogenesis are important mechanisms involved in renal IRI. Despite advances in research, effective therapies for renal IRI are lacking. Recently it has been demonstrated the role of KYP2047, a selective inhibitor of prolyl oligopeptidase (POP), in the regulation of inflammation, apoptosis, and angiogenesis. Thus, this research focused on the role of POP in kidney ischemia/reperfusion (KI/R). An in vivo model of KI/R was performed and mice were subjected to KYP2047 treatment (intraperitoneal, 0.5, 1 and 5 mg/kg). Histological analysis, Masson's trichrome and periodic acid shift (PAS) staining, immunohistochemical and Western blots analysis, real-time PCR (RT-PCR) and ELISA were performed on kidney samples. Moreover, serum creatinine and blood urea nitrogen (BUN) were quantified. POP-inhibition by KYP2047 treatment, only at the doses of 1 and 5 mg/kg, significantly reduced renal injury and collagen amount, regulated inflammation through canonical and non-canonical NF-κB pathway, and restored renal function. Moreover, KYP2047 modulated angiogenesis markers, such as TGF-β and VEGF, also slowing down apoptosis. Interestingly, treatment with KYP2047 modulated PP2A activity. Thus, these findings clarified the role of POP inhibition in AKI, also offering novel therapeutic target for renal injury after KI/R.

Vascular Endothelial Cells: Heterogeneity and Targeting Approaches

Forming the inner layer of the vascular system, endothelial cells (ECs) facilitate a multitude of crucial physiological processes throughout the body. Vascular ECs enable the vessel wall passage of nutrients and diffusion of oxygen from the blood into adjacent cellular structures. ECs regulate vascular tone and blood coagulation as well as adhesion and transmigration of circulating cells. The multitude of EC functions is reflected by tremendous cellular diversity. Vascular ECs can form extremely tight barriers, thereby restricting the passage of xenobiotics or immune cell invasion, whereas, in other organ systems, the endothelial layer is fenestrated (e.g., glomeruli in the kidney), or discontinuous (e.g., liver sinusoids) and less dense to allow for rapid molecular exchange. ECs not only differ between organs or vascular systems, they also change along the vascular tree and specialized subpopulations of ECs can be found within the capillaries of a single organ. Molecular tools that enable selective vascular targeting are helpful to experimentally dissect the role of distinct EC populations, to improve molecular imaging and pave the way for novel treatment options for vascular diseases. This review provides an overview of endothelial diversity and highlights the most successful methods for selective targeting of distinct EC subpopulations.

Chronic Kidney Disease: Strategies to Retard Progression

Chronic kidney disease (CKD), defined as the presence of irreversible structural or functional kidney damages, increases the risk of poor outcomes due to its association with multiple complications, including altered mineral metabolism, anemia, metabolic acidosis, and increased cardiovascular events. The mainstay of treatments for CKD lies in the prevention of the development and progression of CKD as well as its complications. Due to the heterogeneous origins and the uncertainty in the pathogenesis of CKD, efficacious therapies for CKD remain challenging. In this review, we focus on the following four themes: first, a summary of the known factors that contribute to CKD development and progression, with an emphasis on avoiding acute kidney injury (AKI); second, an etiology-based treatment strategy for retarding CKD, including the approaches for the common and under-recognized ones; and third, the recommended approaches for ameliorating CKD complications, and the final section discusses the novel agents for counteracting CKD progression.

Kidney toxicity of the BRAF-kinase inhibitor vemurafenib is driven by off-target ferrochelatase inhibition

A multitude of disease and therapy related factors drive the frequent development of kidney disorders in cancer patients. Along with chemotherapy, the newer targeted therapeutics can also cause kidney dysfunction through on and off-target mechanisms. Interestingly, among the small molecule inhibitors approved for the treatment of cancers that harbor BRAF-kinase activating mutations, vemurafenib can trigger tubular damage and acute kidney injury. BRAF is a proto-oncogene involved in cell growth. To investigate the underlying mechanisms, we developed cell culture and mouse models of vemurafenib kidney toxicity. At clinically relevant concentrations vemurafenib induces cell-death in transformed and primary mouse and human kidney tubular epithelial cells. In mice, two weeks of daily vemurafenib treatment causes moderate acute kidney injury with histopathological characteristics of kidney tubular epithelial cells injury. Importantly, kidney tubular epithelial cell-specific BRAF gene deletion did not influence kidney function under normal conditions or alter the severity of vemurafenib-associated kidney impairment. Instead, we found that inhibition of ferrochelatase, an enzyme involved in heme biosynthesis contributes to vemurafenib kidney toxicity. Ferrochelatase overexpression protected kidney tubular epithelial cells and conversely ferrochelatase knockdown increased the sensitivity to vemurafenib-induced kidney toxicity. Thus, our studies suggest that vemurafenib-associated kidney tubular epithelial cell dysfunction and kidney toxicity is BRAF-independent and caused, in part, by off-target ferrochelatase inhibition.

Caspase-3-dependent peritubular capillary dysfunction is pivotal for the transition from acute to chronic kidney disease after acute ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is a major risk factor for chronic renal failure. Caspase-3, an effector responsible for apoptosis execution, is activated within the peritubular capillary (PTC) in the early stage of IRI-induced acute kidney injury (AKI). Recently, we showed that caspase-3-dependent microvascular rarefaction plays a key role in fibrosis development after mild renal IRI. Here, we further characterized the role of caspase-3 in microvascular dysfunction and progressive renal failure in both mild and severe AKI, by performing unilateral renal artery clamping for 30/60 min with contralateral nephrectomy in wild-type (C57BL/6) or caspase-3-/- mice. In both forms of AKI, caspase-3-/- mice showed better long-term outcomes despite worse initial tubular injury. After 3 wk, they showed reduced PTC injury, decreased PTC collagen deposition and α-smooth muscle actin expression, and lower tubular injury scores compared with wild-type animals. Caspase-3-/- mice with severe IRI also showed better preservation of long-term renal function. Intravital imaging and microcomputed tomography revealed preserved PTC permeability and better terminal capillary density in caspase-3-/- mice. Collectively, these results demonstrate the pivotal importance of caspase-3 in regulating long-term renal function after IRI and establish the predominant role of PTC dysfunction as a major contributor to progressive renal dysfunction.NEW & NOTEWORTHY Our findings demonstrate the pivotal importance of caspase-3 in regulating renal microvascular dysfunction, fibrogenesis, and long-term renal impairment after acute kidney injury induced by ischemia-reperfusion injury. Furthermore, this study establishes the predominant role of peritubular capillary integrity as a major contributor to progressive renal dysfunction after ischemia-reperfusion injury.

Pharmacological Interventions for the Prevention and Treatment of Kidney Injury Induced by Radiotherapy: Molecular Mechanisms and Clinical Perspectives

More than half of cancer patients need radiotherapy during the course of their treatment. Despite the beneficial aspects, the destructive effects of radiation beams on normal tissues lead to oxidative stress, inflammation, and cell injury. Kidneys are affected during radiotherapy of abdominal malignancies. Radiation nephropathy eventually leads to the release of factors triggering systemic inflammation. Currently, there is no proven prophylactic or therapeutic intervention for the management of radiation-induced nephropathy. This article reviews the biomarkers involved in the pathophysiology of radiation-induced nephropathy and its underlying molecular mechanisms. The efficacy of compounds with potential radio-protective properties on amelioration of inflammation and oxidative stress is also discussed. By outlining the approaches for preventing and treating this critical side effect, we evaluate the potential treatment of radiation-induced nephropathy. Available preclinical and clinical studies on these compounds are also scrutinized.

Renal Cell-Targeted Drug Delivery Strategy for Acute Kidney Injury and Chronic Kidney Disease: A Mini-Review

Kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD), have become a global public health concern associated with high morbidity, mortality, and healthcare costs. However, at present, very few effective and specific drug therapies are available, owing to the poor therapeutic efficacy and systemic side effects. Kidney-targeted drug delivery, as a potential strategy for solving these problems, has received great attention in the fields of AKI and CKD in recent years. Here, we review the literature on renal targeted, more specifically, renal cell-targeted formulations of AKI and CKD that offered biodistribution data. First, we provide a broad overview of the unique structural characteristics and injured cells of acute and chronic injured kidneys. We then separately summarize literature examples of renal targeted formulations according to the difference of target cells and elaborate on the appropriate formulation design criteria for AKI and CKD. Finally, we propose a hypothetic strategy to improve the renal accumulation of glomerular cell-targeted formulation by escaping the uptake of the reticuloendothelial system and provide some perspectives for future studies.