A two-stage bilateral ischemia-reperfusion injury-induced AKI to CKD transition model in mice

Robust Rat and Mouse Models of Bilateral Renal Ischemia Reperfusion Injury

BACKGROUND/AIM

Acute and chronic kidney diseases are a major contributor to morbidity and mortality worldwide, with no specific treatments currently available for these. To enable understanding the pathophysiology of and testing novel treatments for acute and chronic kidney disease, a suitable in vivo model of kidney disease is essential. In this article, we describe two reliable rodent models (rats and mice) of efficacious kidney injury displaying acute to chronic kidney injury progression, which is also reversible through novel therapeutic strategies such as ischemic preconditioning (IPC).

MATERIALS AND METHODS

We utilized adult male Lewis rats and adult male wildtype (C57BL/6) mice, performed a midline laparotomy, and induced warm ischemia to both kidneys by bilateral clamping of both renal vascular pedicles for a set time, to mimic the hypoxic etiology of disease commonly found in kidney injury.

RESULTS

Bilateral ischemia reperfusion injury caused marked structural and functional kidney injury as exemplified by histology damage scores, serum creatinine levels, and kidney injury biomarker levels in both rodents. Furthermore, this effect displayed a dose-dependent response in the mouse model.

CONCLUSION

These rodent models of bilateral kidney IRI are reliable, reproducible, and enable detailed mechanistic study of the underlying pathophysiology of both acute and chronic kidney disease. They have been carefully optimised for single operator use with a strong track record of training both surgically trained and surgically naïve operators.

Pyruvate kinase M2 regulates kidney fibrosis through pericyte glycolysis during the progression from acute kidney injury to chronic kidney disease

We aimed to investigate the role of renal pericyte pyruvate kinase M2 (PKM2) in the progression of acute kidney injury (AKI) to chronic kidney disease (CKD). The role of PKM2 in renal pericyte-myofibroblast transdifferentiation was investigated in an AKI-CKD mouse model. Platelet growth factor receptor beta (PDGFRβ)-iCreERT2; tdTomato mice were used for renal pericyte tracing. Western blotting and immunofluorescence staining were used to examine protein expression. An 5-ethynyl-2'-deoxyuridine assay was used to measure renal pericyte proliferation. A scratch cell migration assay was used to analyse cell migration. Seahorse experiments were used to examine glycolytic rates. Enzyme-linked immunoassay was used to measure pyruvate kinase enzymatic activity and lactate concentrations. The PKM2 nuclear translocation inhibitors Shikonin and TEPP-46 were used to alter pericyte transdifferentiation. In AKI-CKD, renal pericytes proliferated and transdifferentiated into myofibroblasts and PKM2 is highly expressed in renal pericytes. Shikonin and TEPP-46 inhibited pericyte proliferation, migration, and pericyte-myofibroblast transdifferentiation by reducing nuclear PKM2 entry. In the nucleus, PKM2 promoted downstream lactate dehydrogenase A (LDHA) and glucose transporter 1 (GLUT1) transcription, which are critical for glycolysis. Therefore, PKM2 regulates pericyte glycolytic and lactate production, which regulates renal pericyte-myofibroblast transdifferentiation. PKM2-regulated renal pericyte-myofibroblast transdifferentiation by regulating downstream LDHA and GLUT1 transcription and lactate production. Reducing nuclear PKM2 import can reduce renal pericytes-myofibroblasts transdifferentiation, providing new ideas for AKI-CKD treatment.

Macula Densa Nitric Oxide Synthase 1 Controls Renin Release and Renin-Dependent Blood Pressure Changes

BACKGROUND

The function of macula densa nitric oxide synthase 1 (NOS1) in the regulation of renin release is controversial. This study was conducted to further elucidate the role of macula densa NOS1 in renin release and blood pressure regulation in response to salt challenges and hemorrhagic shock.

METHODS

To investigate the specific role of NOS1 in the macula densa within the kidney in response to varying sodium concentrations in the diet, tissue macula densa-specific NOS1 knockout (MD-NOS1KO) and wild type (WT) mice were subjected to sequential low (0.1% NaCl) and high (1.4% NaCl) sodium diets. Separate groups of mice, consisting of both MD-NOS1KO subgroup and WT subgroup, were induced hemorrhagic shock by retro-orbital bleeding of 12 mL blood/kg body weight. Mean arterial pressure (MAP) was measured by a radio-telemetry system. Plasma renin concentration (PRC) was measured with the radioimmunoassay for both sodium diet and hemorrhagic shock experiments.

RESULTS

PRCs were 371 ± 95 and 411 ± 68 ng/mL/hr in WT and MD-NOS1KO mice fed a normal sodium diet, respectively. Low salt intake stimulated an increase in the renin release by about 260% in WT mice (PRC = 1364 ± 217 ng/mL/hr, p < 0.0001) compared to the PRC under normal salt diet. However, the stimulation was significantly blunted in MD-NOS1KO mice (PRC = 678 ± 104 ng/mL/hr, p < 0.001). High salt intake suppressed the PRC to about 61% of the PRC level under a normal salt diet (p < 0.0001). Deletion of macula densa NOS1 further inhibited renin release to 33% of the levels of a normal salt diet. Hemorrhagic shock induced about a 3-fold increase in PRC in WT mice, but only about a 54% increase in the MD-NOS1KO mice (p < 0.0001). The MAP values were substantially greater in WT mice than in MD-NOS1KO mice within the first 6 hours following hemorrhagic shock (p < 0.001). Thus, WT mice showed a much quicker recovery in MAP than MD-NOS1KO mice.

CONCLUSIONS

Our study demonstrated that macula densa NOS1 plays an important role in mediating renin release. This mechanism is essential in maintaining blood pressure under hypovolemic situations such as hemorrhagic shock.

Sestrin2 Mediates Metformin Rescued the Age-Related Cardiac Dysfunctions of Cardiorenal Syndrome Type 3

Acute kidney injury (AKI) leads to acute cardiac injury and dysfunction in cardiorenal syndrome Type 3 (CRS3) through oxidative stress (OS). The stress-inducible Sestrin2 (Sesn2) protein reduces reactive oxygen species (ROS) accumulation and activates AMP-dependent protein kinase (AMPK) to regulate cellular metabolism and energetics during OS. Sesn2 levels and its protective effects decline in the aged heart. Antidiabetic drug metformin upregulates Sesn2 levels in response to ischemia-reperfusion (IR) stress. However, the role of metformin in CRS3 remains unknown. This study seeks to explore how the age-related decrease in cardiac Sesn2 levels contributes to cardiac intolerance to AKI-induced insults, and how metformin ameliorates CRS3 through Sesn2. Young (3-5 months) and aged (21-23 months) C57BL/6J wild-type mice along with cardiomyocyte-specific knockout (cSesn2-/-) and their wild type of littermate (Sesn2f/f) C57BL/6J mice were subjected to AKI for 15 min followed by 24 h of reperfusion. Cardiac and mitochondrial functions were evaluated through echocardiograms and seahorse mitochondria respirational analysis. Renal and cardiac tissue was collected for histological analysis and immunoblotting. The results indicate that metformin could significantly rescue AKI-induced cardiac dysfunction and injury via Sesn2 through an improvement in systolic and diastolic function, fibrotic and cellular damage, and mitochondrial function in young, Sesn2f/f, and especially aged mice. Metformin significantly increased Sesn2 expression under AKI stress in the aged left-ventricular tissue. Thus, this study suggests that Sesn2 mediates the cardioprotective effects of metformin during post-AKI.

Effects of contralateral nephrectomy timing and ischemic conditions on kidney fibrosis after unilateral kidney ischemia-reperfusion injury

Acute kidney injury (AKI) is an important cause of chronic kidney disease (CKD), but the underlying mechanisms are unclear. Animal models are tools for studying the AKI-CKD progression. Kidney ischemia-reperfusion injury (IRI) models, especially the unilateral IRI (uIRI) model with delayed contralateral kidney resection, are commonly used to induce fibrotic progression to CKD after AKI. However, in previous studies, we found that details of the operation had a significant impact on the long-term outcomes of the kidney in this uIRI model. In this study, we investigated the effects of resection timing of the contralateral intact kidney, core body temperatures during ischemia, and time length of kidney ischemia on kidney function, histological injury and kidney fibrosis after AKI, using a mouse uIRI model with delayed contralateral nephrectomy. The results showed that all these parameters significantly affected the AKI-CKD transition. The post-AKI fibrosis worsened and the survival rate declined with a longer interval between contralateral nephrectomy and uIRI, higher ischemic body temperature, or longer ischemic duration when the other two variables were fixed. In conclusion, in the uIRI model with delayed contralateral nephrectomy, kidney fibrosis after AKI is influenced by many factors. Strictly controlling the experimental conditions is very important for the stability and consistency of the model.

No safe renal warm ischemia time-The molecular network characteristics and pathological features of mild to severe ischemia reperfusion kidney injury

Ischemic acute kidney injury (AKI) has always been a hot and difficult research topic in the field of renal diseases. This study aims to illustrate the safe warm ischemia time of kidney and the molecular network characteristics and pathological features of mild to severe ischemia reperfusion kidney injury. We established varying degrees of renal injury due to different ischemia time (0 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, and 30 min) on unilateral (left kidney) ischemia-reperfusion injury and contralateral (right kidney) resection (uIRIx) mouse model. Mice were sacrificed 24 h after uIRIx, blood samples were harvested to detect serum creatinine (Scr), and kidney tissue samples were harvested to perform Periodic Acid-Schiff (PAS) staining and RNA-Seq. Differentially expressed genes (DEGs) were identificated, time-dependent gene expression patterns and functional enrichment analysis were further performed. Finally, qPCR was performed to validated RNA-Seq results. Our results indicated that there was no absolute safe renal warm ischemia time, and every minute of ischemia increases kidney damage. Warm ischemia 26min or above in mice makes severe kidney injury, renal pathology and SCr were both significantly changed. Warm ischemia between 18 and 26 min makes mild kidney injury, with changes in pathology and renal molecular expression, while SCr did not change. No obvious pathological changes but significant differences in molecular expression were found less than 16min warm ischemia. There are two key time intervals in the process of renal ischemia injury, 0 min-16 min (short-term) and 26 min-28 min (long-term). Gene expression of immune-related pathways were most significantly down-regulated in short-term ischemia, while metabolism-related pathways were the mainly enriched pathway in long-term ischemia. Taken together, this study provides novel insights into safe renal artery occlusion time in partial nephrectomy, and is of great value for elucidating molecular network characteristics and pathological features of mild to severe ischemia reperfusion kidney injury, and key genes related to metabolism and immune found in this study also provide potential diagnostic and therapeutic biomarkers for AKI.

Renoprotective Effects of Luteolin: Therapeutic Potential for COVID-19-Associated Acute Kidney Injuries

Acute kidney injury (AKI) has been increasingly reported in critically-ill COVID-19 patients. Moreover, there was significant positive correlation between COVID-19 deaths and renal disorders in hospitalized COVID-19 patients with underlying comorbidities who required renal replacement therapy. It has suggested that death in COVID-19 patients with AKI is 3-fold higher than in COVID-19 patients without AKI. The pathophysiology of COVID-19-associated AKI could be attributed to unspecific mechanisms, as well as COVID-19-specific mechanisms such as direct cellular injury, an imbalanced renin-angiotensin-aldosterone system, pro-inflammatory cytokines elicited by the viral infection and thrombotic events. To date, there is no specific treatment for COVID-19 and its associated AKI. Luteolin is a natural compound with multiple pharmacological activities, including anticoronavirus, as well as renoprotective activities against kidney injury induced by sepsis, renal ischemia and diverse nephrotoxic agents. Therefore, in this review, we mechanistically discuss the anti-SARS-CoV-2 and renoprotective activities of luteolin, which highlight its therapeutic potential in COVID-19-AKI patients.

Non-HLA Antibodies in Kidney Transplantation: Immunity and Genetic Insights

The polymorphic human leukocyte antigen (HLA) system has been considered the main target for alloimmunity, but the non-HLA antibodies and autoimmunity have gained importance in kidney transplantation (KT). Apart from the endothelial injury, secondary self-antigen exposure and the presence of polymorphic alloantigens, respectively, auto- and allo- non-HLA antibodies shared common steps in their development, such as: antigen recognition via indirect pathway by recipient antigen presenting cells, autoreactive T cell activation, autoreactive B cell activation, T helper 17 cell differentiation, loss of self-tolerance and epitope spreading phenomena. Both alloimmunity and autoimmunity play a synergic role in the formation of non-HLA antibodies, and the emergence of transcriptomics and genome-wide evaluation techniques has led to important progress in understanding the mechanistic features. Among them, non-HLA mismatches between donors and recipients provide valuable information regarding the role of genetics in non-HLA antibody immunity and development.

Transition of acute kidney injury to chronic kidney disease: role of metabolic reprogramming

Acute kidney injury (AKI) is a global public health concern associated with high morbidity and mortality. Although advances in medical management have improved the in-hospital mortality of severe AKI patients, the renal prognosis for AKI patients in the later period is not encouraging. Recent epidemiological investigations have indicated that AKI significantly increases the risk for the development of chronic kidney disease (CKD) and end-stage renal disease (ESRD) in the future, further contributing to the economic burden on health care systems. The transition of AKI to CKD is complex and often involves multiple mechanisms. Recent studies have suggested that renal tubular epithelial cells (TECs) are more prone to metabolic reprogramming during AKI, in which the metabolic process in the TECs shifts from fatty acid β-oxidation (FAO) to glycolysis due to hypoxia, mitochondrial dysfunction, and disordered nutrient-sensing pathways. This change is a double-edged role. On the one hand, enhanced glycolysis acts as a compensation pathway for ATP production; on the other hand, long-term shut down of FAO and enhanced glycolysis lead to inflammation, lipid accumulation, and fibrosis, contributing to the transition of AKI to CKD. This review discusses developments and therapies focused on the metabolic reprogramming of TECs during AKI, and the emerging questions in this evolving field.

Reducing ischemic kidney injury through application of a synchronization modulation electric field to maintain Na+/K+-ATPase functions

Renal ischemia-reperfusion injury is an important contributor to the development of delayed graft function after transplantation, which is associated with higher rejection rates and poorer long-term outcomes. One of the earliest impairments during ischemia is Na⁺/K⁺-ATPase (Na/K pump) dysfunction due to insufficient ATP supply, resulting in subsequent cellular damage. Therefore, strategies that preserve ATP or maintain Na/K pump function may limit the extent of renal injury during ischemia-reperfusion. Here, we applied a synchronization modulation electric field to activate Na/K pumps, thereby maintaining cellular functions under ATP-insufficient conditions. We tested the effectiveness of this technique in two models of ischemic renal injury: an in situ renal ischemia-reperfusion injury model (predominantly warm ischemia) and a kidney transplantation model (predominantly cold ischemia). Application of the synchronization modulation electric field to a renal ischemia-reperfusion injury mouse model preserved Na/K pump activity, thereby reducing kidney injury, as reflected by 40% lower plasma creatinine (1.17 ± 0.03 mg/dl) in the electric field-treated group as compared to the untreated control group (1.89 ± 0.06 mg/dl). In a mouse kidney transplantation model, renal graft function was improved by more than 50% with the application of the synchronization modulation electric field according to glomerular filtration rate measurements (85.40 ± 12.18 μl/min in the untreated group versus 142.80 ± 11.65 μl/min in the electric field-treated group). This technique for preserving Na/K pump function may have therapeutic potential not only for ischemic kidney injury but also for other diseases associated with Na/K pump dysfunction due to inadequate ATP supply.

Repair phase modeling of ischemic acute kidney injury: recovery vs. transition to chronic kidney disease

The repair mechanism after ischemic acute kidney injury (AKI) involves complex immunologic processes, which determine long-term renal outcomes. Through investigating two murine ischemia-reperfusion injury (IRI) models: bilateral IRI (BIRI) and unilateral IRI (UIRI), we aimed to determine an appropriate murine model that could simulate the recovery phase of ischemic AKI. Changes in renal function, phenotypes of kidney mononuclear cells, renal fibrosis, and intrarenal cytokine/chemokine expression were serially analyzed up to 12 weeks after IRI. Plasma creatinine and BUN concentrations increased and remained elevated in the BIRI group until 7 days but decreased to comparable levels with the sham control group at 2 weeks after surgery and thereafter, whereas plasma creatinine and BUN concentrations remained unchanged in the UIRI group. Intrarenal total leukocytes, and effector memory and activated phenotypes of CD4 and CD8 T cells markedly increased in the postischemic kidneys in both IRI groups. Expression of proinflammatory cytokines/chemokines and TGF-β1 was enhanced in the postischemic kidneys of both IRI groups with a higher degree in the UIRI group. Importantly, intrarenal immunologic changes of the BIRI group persisted until 6 weeks despite full functional recovery. The postischemic kidneys of the UIRI group showed earlier and more pronounced proinflammatory conditions as well as more severe atrophic and fibrotic changes compared to the BIRI group. These findings support the utility of longer follow-ups of BIRI and UIRI models for investigating the adaptive repair process, which facilitates recovery of ischemic AKI and maladaptive repair process may result in AKI to CKD transition, respectively.

Early elimination of uremic toxin ameliorates AKI-to-CKD transition

Acute kidney injury (AKI)-related fibrosis is emerging as a major driver of chronic kidney disease (CKD) development. Aberrant kidney recovery after AKI is multifactorial and still poorly understood. The accumulation of indoxyl sulfate (IS), a protein-bound uremic toxin, has been identified as a detrimental factor of renal fibrosis. However, the mechanisms underlying IS-related aberrant kidney recovery after AKI is still unknown. The present study aims to elucidate the effects of IS on tubular damage and its involvement in the pathogenesis of AKI-to-CKD transition. Our results showed that serum IS started to accumulate associated with the downregulation of tubular organic anion transporter but not observed in the small-molecule uremic toxins of the unilateral ischemia-reperfusion injury (UIRI) without a contralateral nephrectomy model. Serum IS is positively correlated with renal fibrosis and binding immunoglobulin protein (BiP) and CAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) expression induction in the UIRI with a contralateral nephrectomy model (UIRI+Nx). To evaluate the effects of IS in the AKI-to-CKD transition, we administered indole, a precursor of IS, at the early stage of UIRI. Our results demonstrated IS potentiates renal fibrosis, senescence-associated secretory phenotype (SASP), and activation of endoplasmic reticulum (ER) stress, which is attenuated by synergistic AST-120 administration. Furthermore, we clearly demonstrated that IS exposure potentiated hypoxia-reperfusion (H/R) induced G2/M cell cycle arrest, epithelial-mesenchymal transition (EMT) and aggravated ER stress induction in vitro. Finally, the ER chemical chaperon, 4-phenylbutyric acid (4-PBA), successfully reversed the above-mentioned AKI-to-CKD transition. Taken together, early IS elimination in the early stage of AKI is likely to be a useful strategy in the prevention and/or treatment of the AKI-to-CKD transition.

Knockout of Macula Densa Neuronal Nitric Oxide Synthase Increases Blood Pressure in db/db Mice

[Figure: see text].

A new mechanism for the sex differences in angiotensin II-induced hypertension: the role of macula densa NOS1β-mediated tubuloglomerular feedback

Females are protected against the development of angiotensin II (ANG II)-induced hypertension compared with males, but the mechanisms have not been completely elucidated. In the present study, we hypothesized that the effect of ANG II on the macula densa nitric oxide (NO) synthase 1β (NOS1β)-mediated tubuloglomerular feedback (TGF) mechanism is different between males and females, thereby contributing to the sexual dimorphism of ANG II-induced hypertension. We used microperfusion, micropuncture, clearance of FITC-inulin, and radio telemetry to examine the sex differences in the changes of macula densa NOS1β expression and activity, TGF response, natriuresis, and blood pressure (BP) after a 2-wk ANG II infusion in wild-type and macula densa-specific NOS1 knockout mice. In wild-type mice, ANG II induced higher expression of macula densa NOS1β, greater NO generation by the macula densa, and a lower TGF response in vitro and in vivo in females than in males; the increases of glomerular filtration rate, urine flow rate, and Na⁺ excretion in response to an acute volume expansion were significantly greater and the BP responses to ANG II were significantly less in females than in males. In contrast, these sex differences in the effects of ANG II on TGF, natriuretic response, and BP were largely diminished in knockout mice. In addition, tissue culture of human kidney biopsies (renal cortex) with ANG II resulted in a greater increase in NOS1β expression in females than in males. In conclusion, macula densa NOS1β-mediated TGF is a novel and important mechanism for the sex differences in ANG II-induced hypertension.