P53 mediates the apoptotic response to GTP depletion after renal ischemia-reperfusion: protective role of a p53 inhibitor

Aquaporin 1 is renoprotective in septic acute kidney injury by attenuating inflammation, apoptosis and fibrosis through inhibition of P53 expression

Sepsis associated Acute kidney injury (AKI) is a common clinical syndrome characterized by suddenly decreased in renal function and urinary volume. This study was designed to investigate the role of Aquaporin 1 (AQP1) and P53 in the development of sepsis-induced AKI and their potential regulatory mechanisms. Firstly, transcriptome sequencing analysis of mice kidney showed AQP1 expression was reduced and P53 expression was elevated in Cecal ligation and puncture (CLP)-induced AKI compared with controls. Bioinformatics confirmed that AQP1 expression was remarkably decreased and P53 expression was obviously elevated in renal tissues or peripheral blood of septic AKI patients. Moreover, we found in vivo experiments that AQP1 mRNA levels were dramatically decreased and P53 mRNA significantly increased following the increased expression of inflammation, apoptosis, fibrosis, NGAL and KIM-1 at various periods in septic AKI. Meanwhile, AQP1 and P53 protein levels increased significantly first and then decreased gradually in kidney tissue and serum of rats in different stages of septic AKI. Most importantly, in vivo and vitro experiments demonstrated that silencing of AQP1 greatly exacerbates renal or cellular injury by up-regulating P53 expression promoting inflammatory response, apoptosis and fibrosis. Overexpression of AQP1 prevented the elevation of inflammation, apoptosis and fibrosis by down-regulating P53 expression in Lipopolysaccharide (LPS)-induced AKI or HK-2 cells. Therefore, our results suggested that AQP1 plays a protective role in modulating AKI and can attenuate inflammatory response, apoptosis and fibrosis via downregulating P53 in septic AKI or LPS-induced HK-2cells. The pharmacological targeting of AQP1 mediated P53 expression might be identified as potential targets for the early treatment of septic AKI.

Efficacy and safety of Yiqi Peiyuan granules for improving the short-term prognosis of patients with acute kidney injury: A multicenter, double-blind, placebo-controlled, randomized trial

BACKGROUND

Yiqi Peiyuan (YQPY) prescription, a composite prescription of traditional Chinese medicine, has been used to prevent or delay the continued deterioration of renal function after acute kidney injury (AKI) in some institutions and has shown considerable efficacy.

OBJECTIVE

This is the first randomized controlled trial to assess efficacy and safety of YQPY for improving short-term prognosis in adult patients with AKI.

DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONS

This is a prospective, double-blind, multicenter, randomized, and placebo-controlled clinical trial. A total of 144 enrolled participants were randomly allocated to two groups according to a randomization schedule. Participants, caregivers and investigators assessing the outcomes were blinded to group assignment. Patients in the YQPY group received 36 g YQPY granules twice a day for 28 days. Patients in the placebo group received a placebo in the same dose as the YQPY granules.

MAIN OUTCOME MEASURES

The primary outcome was the change in the estimated glomerular filtration rate (eGFR) between baseline and after 4 and 24 weeks of treatment. The secondary outcomes were the change of serum creatinine (Scr) level between baseline and after treatment, and the incidence of endpoint events, defined as eGFR increasing by more than 25% above baseline, eGFR >75 mL/min per 1.73 m2 or the composite endpoint, which was defined as the sum of patients meeting either of the above criteria.

RESULTS

Data from a total of 114 patients (59 in the YQPY group and 55 in the control group) were analyzed. The mean changes in eGFR and Scr in weeks 4 and 24 had no difference between the two groups. In further subgroup analysis (22 in the YQPY group and 31 in the control group), the mean change in eGFR after treatment for 4 weeks was 27.39 mL/min per 1.73 m2 in the YQPY group and 5.78 mL/min per 1.73 m2 in the placebo group, and the mean difference between groups was 21.61 mL/min per 1.73 m2 (P < 0.001). Thirteen (59.1%) patients in the YQPY group and 5 (16.1%) in the placebo group reached the composite endpoints (P = 0.002). During the intervention, 2 and 4 severe adverse events were reported in the YQPY and placebo groups, respectively.

CONCLUSION

The YQPY granules can effectively improve the renal function of patients 4 weeks after the onset of AKI, indicating that it has good efficacy for improving short-term renal outcomes in patients with AKI. The YQPY granules may be a promising therapy for adults with AKI.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2100051723. Please cite this article as: Wu JJ, Zhang TY, Qi YH, Zhu MY, Fang Y, Qi CJ, Cao LO, Lu JF, Lu BH, Tang LM, Shen JX, Mou S. Efficacy and safety of Yiqi Peiyuan granules for improving the short-term prognosis of patients with acute kidney injury: a multicenter, double-blind, placebo-controlled, randomized trial. J Integr Med. 2024; 22(3): 279-285.

Cellular senescence in acute kidney injury: Target and opportunity

Acute kidney injury (AKI) is a common clinical disease with a high incidence and mortality rate. It typically arises from hemodynamic alterations, sepsis, contrast agents, and toxic drugs, instigating a series of events that culminate in tissue and renal damage. This sequence of processes often leads to acute renal impairment, prompting the initiation of a repair response. Cellular senescence is an irreversible arrest of the cell cycle. Studies have shown that renal cellular senescence is closely associated with AKI through several mechanisms, including the promotion of oxidative stress and inflammatory response, telomere shortening, and the down-regulation of klotho expression. Exploring the role of cellular senescence in AKI provides innovative therapeutic ideas for both the prevention and treatment of AKI. Furthermore, it has been observed that targeted removal of senescent cells in vivo can efficiently postpone senescence, resulting in an enhanced prognosis for diseases associated with senescence. This article explores the effects of common anti-senescence drugs senolytics and senostatic and lifestyle interventions on renal diseases, and mentions the rapid development of mesenchymal stem cells (MSCs). These studies have taken senescence-related research to a new level. Overall, this article comprehensively summarizes the studies on cellular senescence in AKI, aiming is to elucidate the relationship between cellular senescence and AKI, and explore treatment strategies to improve the prognosis of AKI.

Mechanisms of norcantharidin against renal tubulointerstitial fibrosis

Renal tubulointerstitial fibrosis (RTIF) is a common feature and inevitable consequence of all progressive chronic kidney diseases, leading to end-stage renal failure regardless of the initial cause. Although research over the past few decades has greatly improved our understanding of the pathophysiology of RTIF, until now there has been no specific treatment available that can halt the progression of RTIF. Norcantharidin (NCTD) is a demethylated analogue of cantharidin, a natural compound isolated from 1500 species of medicinal insect, the blister beetle (Mylabris phalerata Pallas), traditionally used for medicinal purposes. Many studies have found that NCTD can attenuate RTIF and has the potential to be an anti-RTIF drug. This article reviews the recent progress of NCTD in the treatment of RTIF, with emphasis on the pharmacological mechanism of NCTD against RTIF.

IL-22 is secreted by proximal tubule cells and regulates DNA damage response and cell death in acute kidney injury

Acute kidney injury (AKI) affects over 13 million people worldwide annually and is associated with a 4-fold increase in mortality. Our lab and others have shown that DNA damage response (DDR) governs the outcome of AKI in a bimodal manner. Activation of DDR sensor kinases protects against AKI, while hyperactivation of DDR effector proteins, such as p53, induces cell death and worsens AKI. The factors that trigger DDR to switch from pro-repair to pro-cell death remain to be resolved. Here we investigated the role of interleukin 22 (IL-22), an IL-10 family member whose receptor (IL-22RA1) is expressed on proximal tubule cells (PTCs), in DDR activation and AKI. Using cisplatin and aristolochic acid (AA) induced nephropathy as models of DNA damage, we identified PTCs as a novel source of urinary IL-22. Functionally, IL-22 binding IL-22RA1 on PTCs amplified the DDR. Treating primary PTCs with IL-22 alone induced rapid activation of the DDR. The combination of IL-22 and either cisplatin- or AA-induced cell death in primary PTCs, while the same dose of cisplatin or AA alone did not. Global deletion of IL-22 protected against cisplatin- or AA-induced AKI, reduced expression of DDR components, and inhibited PTC cell death. To confirm PTC IL-22 signaling contributed to AKI, we knocked out IL-22RA1 specifically in kidney tubule cells. IL-22RA1ΔTub mice displayed reduced DDR activation, cell death, and kidney injury compared to controls. Thus, targeting IL-22 represents a novel therapeutic approach to prevent the negative consequences of the DDR activation while not interfering with repair of damaged DNA.

YAP nuclear translocation induced by HIF-1α prevents DNA damage under hypoxic conditions

Maladaptive repair of acute kidney injury (AKI) is associated with a high risk of developing chronic kidney disease deemed irremediable even in present days. When AKI arises from ischemia-reperfusion injury, hypoxia usually plays a major role. Although both hypoxia-inducible factor-1α (HIF-1α) and yes-associated protein (YAP) have been proven to promote renal cell survival under hypoxia, there is a lack of research that studies the crosstalk of the two and its effect on kidney repair. In studying the crosstalk, CoCl2 was used to create a mimetic hypoxic environment. Immunoprecipitation and proximity ligation assays were performed to verify protein interactions. The results show that HIF-1α interacts with YAP and promotes nuclear translocation of YAP at a high cell density under hypoxic conditions, suggesting HIF-1α serves as a direct carrier that enables YAP nuclear translocation. This is the first study to identify HIF-1α as a crucial pathway for YAP nuclear translocation under hypoxic conditions. Once translocated into a nucleus, YAP protects cells from DNA damage and apoptosis under hypoxic conditions. Since it is unlikely for YAP to translocate into a nucleus without HIF-1α, any treatment that fosters the crosstalk between the two holds the potential to improve cell recovery from hypoxic insults.

Proximal Tubular Lats2 Ablation Exacerbates Ischemia/Reperfusion Injury (IRI)-Induced Renal Maladaptive Repair through the Upregulation of P53

The Hippo pathway mediates renal maladaptive repair after acute kidney injury (AKI), which has been considered a driving force in the progression to chronic kidney disease (CKD). LATS2, a core kinase of the Hippo pathway, exerts non-Hippo-dependent functions in the regulation of the cell cycle and cell fate, providing new insights into AKI and further repair. However, its role remains unknown. Here, we utilized a proximal tubular Lats2 conditional knockout mouse strain (Lats2-CKO) to evaluate the effect of LATS2 deficiency on ischemia/reperfusion-induced AKI-to-CKD transition. Lats2-CKO mice presented with more severe tubular maladaptive repair, inflammatory infiltration, interstitial fibrosis, and apoptosis following AKI. Importantly, we discovered that Lats2 ablation caused the activation of p53, with increased levels of cellular apoptotic molecules (p21, Bax, and cleaved caspase-3), and decreased levels of anti-apoptotic molecules (Bcl-2 and Bcl-xL). Pifithirin-α (p53 inhibitor) effectively attenuated renal fibrosis, inflammation, and apoptosis in Lats2-CKO mice after AKI. Consistently, in vitro Lats2 overexpression decreased p53, p21, Bax and cleaved caspase 3 expression after hypoxia/reoxygenation (H/R) treatment. Of note, the phosphorylation of MDM2, which promotes the ubiquitination degradation of p53, at site Ser186 was decreased in Lats2-CKO kidneys, but increased by Lats2 overexpression in vitro. Therefore, LATS2 deficiency aggravated ischemia/reperfusion injury (IRI)-induced maladaptive repair via regulating the tubular MDM2-p53 axis in AKI-to-CKD transition.

Early Growth Response 1 Contributes to Renal IR Injury by Inducing Proximal Tubular Cell Apoptosis

Renal ischemia-reperfusion (IR) causes acute kidney injury due to oxidative stress, tubular inflammation, and apoptosis. Early growth response 1 (Egr-1) is a transcription factor belonging to the immediate early gene family and is known to regulate cell proliferation, differentiation, and survival. Egr-1 expression is induced during renal IR; however, its pathogenic role and underlying mechanisms remain elusive. Here, we investigated the function of Egr-1 during renal IR using C57BL/6 mice and cultured renal proximal tubular HK-2 cells. Egr-1 expression increased immediately, 1-4 h after IR, whereas plasma creatinine and oxidative stress increased progressively over 24 h after IR. Egr-1 overexpression showed greater increases in plasma creatinine, renal tubular injury, and apoptosis than in the control after IR. Egr-1 overexpression also showed significant neutrophil infiltration and increased pro-inflammatory cytokines (TNF-α, MIP-2, and IL-6) after IR. Consistently, proximal tubular HK-2 cells showed immediate induction of Egr-1 at 1 h after hypoxia and reoxygenation, where its downstream target, p53, was also increased. Interestingly, Egr-1 overexpression enhanced p53 levels and tubular apoptosis, while the knockdown of Egr-1 reduced p53 levels and tubular apoptosis after H2O2 treatment. Egr-1 was recruited to the p53 promoter, which activates p53 transcription, and Egr-1 induction occurred through Erk/JNK signaling kinases, as the specific inhibitors blocked its expression. Taken together, these results show that Egr-1 is upregulated in proximal tubular cells and contributes to renal IR injury by inducing tubular apoptosis, mediated by p53 transcriptional activation. Thus, Egr-1 could be a potential therapeutic target for renal IR injury.

Renal, but not platelet or skin, extracellular vesicles decrease oxidative stress, enhance nascent peptide synthesis, and protect from ischemic renal injury

Acute kidney injury (AKI) is deadly and expensive, and specific, effective therapy remains a large unmet need. We have demonstrated the beneficial effects of transplanted adult tubular cells and extracellular vesicles (EVs; exosomes) derived from those renal cells on experimental ischemic AKI, even when administered after renal failure is established. To further examine the mechanisms of benefit with renal EVs, we tested the hypothesis that EVs from other epithelia or platelets (a rich source of EVs) might be protective, using a well-characterized ischemia-reperfusion model. When given after renal failure was present, renal EVs, but not those from skin or platelets, markedly improved renal function and histology. The differential effects allowed us to examine the mechanisms of benefit with renal EVs. We found significant decreases in oxidative stress postischemia in the renal EV-treated group with preservation of renal superoxide dismutase and catalase as well as increases in anti-inflammatory interleukin-10. In addition, we propose a novel mechanism of benefit: renal EVs enhanced nascent peptide synthesis following hypoxia in cells and in postischemic kidneys. Although EVs have been used therapeutically, these results serve as "proof of principle" to examine the mechanisms of injury and protection.NEW & NOTEWORTHY Acute kidney injury is common and deadly, yet the only approved treatment is dialysis. Thus, a better understanding of injury mechanisms and potential therapies is needed. We found that organ-specific, but not extrarenal, extracellular vesicles improved renal function and structure postischemia when given after renal failure occurred. Oxidative stress was decreased and anti-inflammatory interleukin-10 increased with renal, but not skin or platelet, exosomes. We also propose enhanced nascent peptide synthesis as a novel protective mechanism.

Endotoxin induced acute kidney injury modulates expression of AQP1, P53 and P21 in rat kidney, heart, lung and small intestine

This study was designed to explore whether aquaporin 1(AQP1), P53 and P21 can be used as diagnostic biomarkers of lipopolysaccharide (LPS)-induced acute kidney injury (AKI) and potential indicators of sepsis-induced multiple organ injury. Bioinformatics results demonstrated that AQP1, P53, P21 was dramatically elevated 6h after Cecal ligation and puncture (CLP)-AKI in rat renal tissue. The expression of AQP1, P53, P21, NGAL and KIM-1 in kidney were increased significantly at first and then decreased gradually in LPS-induced AKI rats. Histopathological sections showed swelling of tubular epithelial cells and destruction of basic structures as well as infiltration of numerous inflammatory cells in LPS-induced AKI. Moreover, the expressions of AQP1, P53 and P21 in heart were significantly increased in LPS treatment rats, while the AQP1 expressions in lung and small intestine were significantly decreased. The level of NGAL mRNA in heart, lung and small intestine was firstly increased and then decreased during LPS treatment rats, but the expression of KIM-1 mRNA was not affected. Therefore, our results suggest that AQP1, P53 and P21 is remarkably upregulated in LPS-induced AKI, which may be considered as a potential novel diagnostic biomarker of Septic AKI. NGAL may serve as a biomarker of sepsis-induced multiple organ damage during the process of LPS-induced AKI.

IL-22 promotes acute kidney injury through activation of the DNA damage response and cell death in proximal tubule cells

Acute kidney injury (AKI) affects over 13 million people world-wide annually and is associated with a fourfold increase in mortality. Our lab and others have shown that DNA damage response (DDR) governs the outcome of AKI in a bimodal manner. Activation of DDR sensor kinases protects against AKI, while hyperactivation of DDR effector proteins, such as p53, induces to cell death and worsens AKI. The factors that trigger the switch from pro-reparative to pro-cell death DDR remain to be resolved. Here we investigate the role of interleukin 22 (IL-22), an IL-10 family member whose receptor (IL-22RA1) is expressed on proximal tubule cells (PTCs), in DDR activation and AKI. Using cisplatin and aristolochic acid (AA) induced nephropathy as models of DNA damage, we identify PTCs as a novel source of urinary IL-22, making PTCs the only epithelial cells known to secret IL-22, to our knowledge. Functionally, IL-22 binding its receptor (IL-22RA1) on PTCs amplifies the DDR. Treating primary PTCs with IL-22 alone induces rapid activation of the DDR in vitro. The combination of IL-22 + cisplatin or AA treatment on primary PTCs induces cell death, while the same dose of cisplatin or AA alone does not. Global deletion of IL-22 protects against cisplatin or AA induced AKI. IL-22 deletion reduces expression of components of the DDR and inhibits PTC cell death. To confirm PTC IL-22 signaling contributes to AKI, we knocked out IL-22RA1 in renal epithelial cells by crossing IL-22RA1floxed mice with Six2-Cre mice. IL-22RA1 KO reduced DDR activation, cell death, and kidney injury. These data demonstrate that IL-22 promotes DDR activation in PTCs, switching pro-recovery DDR responses to a pro-cell death response and worsening AKI. Targeting IL-22 represents a novel therapeutic approach to prevent the negative consequences of the DDR activation while not interfering with the processes necessary for repair of damaged DNA.

Impaired microvascular circulation in distant organs following renal ischemia

Mortality in acute kidney injury (AKI) patients remains very high, although very important advances in understanding the pathophysiology and in diagnosis and supportive care have been made. Most commonly, adverse outcomes are related to extra-renal organ dysfunction and failure. We and others have documented inflammation in remote organs as well as microvascular dysfunction in the kidney after renal ischemia. We hypothesized that abnormal microvascular flow in AKI extends to distant organs. To test this hypothesis, we employed intravital multiphoton fluorescence imaging in a well-characterized rat model of renal ischemia/reperfusion. Marked abnormalities in microvascular flow were seen in every organ evaluated, with decreases up to 46% observed 48 hours postischemia (as compared to sham surgery, p = 0.002). Decreased microvascular plasma flow was found in areas of erythrocyte aggregation and leukocyte adherence to endothelia. Intravital microscopy allowed the characterization of the erythrocyte formations as rouleaux that flowed as one-dimensional aggregates. Observed microvascular abnormalities were associated with significantly elevated fibrinogen levels. Plasma flow within capillaries as well as microthrombi, but not adherent leukocytes, were significantly improved by treatment with the platelet aggregation inhibitor dipyridamole. These microvascular defects may, in part, explain known distant organ dysfunction associated with renal ischemia. The results of these studies are relevant to human acute kidney injury.

p53 and Myofibroblast Apoptosis in Organ Fibrosis

Organ fibrosis represents a dysregulated, maladaptive wound repair response that results in progressive disruption of normal tissue architecture leading to detrimental deterioration in physiological function, and significant morbidity/mortality. Fibrosis is thought to contribute to nearly 50% of all deaths in the Western world with current treatment modalities effective in slowing disease progression but not effective in restoring organ function or reversing fibrotic changes. When physiological wound repair is complete, myofibroblasts are programmed to undergo cell death and self-clearance, however, in fibrosis there is a characteristic absence of myofibroblast apoptosis. It has been shown that in fibrosis, myofibroblasts adopt an apoptotic-resistant, highly proliferative phenotype leading to persistent myofibroblast activation and perpetuation of the fibrotic disease process. Recently, this pathological adaptation has been linked to dysregulated expression of tumour suppressor gene p53. In this review, we discuss p53 dysregulation and apoptotic failure in myofibroblasts and demonstrate its consistent link to fibrotic disease development in all types of organ fibrosis. An enhanced understanding of the role of p53 dysregulation and myofibroblast apoptosis may aid in future novel therapeutic and/or diagnostic strategies in organ fibrosis.

Fanconi syndrome in an elderly patient with membranous nephropathy during treatment with the immunosuppressant mizoribine

We report on an 80-year-old man diagnosed with Fanconi syndrome induced by mizoribine after 4 weeks of administration to treat membranous nephropathy. Mizoribine is an oral immunosuppressant that inhibits inosine monophosphate dehydrogenase and is widely used in Japan for the treatment of autoimmune diseases and nephrotic syndrome, as well as after renal transplantation. Acquired Fanconi syndrome is often caused by drugs (antibacterial, antiviral, anticancer, and anticonvulsant drugs) and is sometimes caused by autoimmune diseases, monoclonal light chain-associated diseases, or heavy metal poisoning. In our patient, hypokalemia, hypophosphatemia, glucosuria, hypouricemia, and severe proteinuria resolved gradually after discontinuation of mizoribine administration, despite oral administration of prednisolone followed by a single intravenous injection of rituximab. The patient was ultimately diagnosed with Fanconi syndrome induced by mizoribine based on his clinical course and his typical laboratory data with the absence of proximal tubular acidosis. To our knowledge, this is the first report of Fanconi syndrome possibly induced by mizoribine. Although the precise mechanism by which mizoribine induces proximal tubular dysfunction is unknown, we suggest that nephrologists should be aware of the onset of Fanconi syndrome, a rare complication during mizoribine treatment.

Analysis of the potential ferroptosis mechanism and multitemporal expression change of central ferroptosis-related genes in cardiac ischemia–reperfusion injury

Acute myocardial infraction is the most severe type of coronary artery disease and remains a substantial burden to the health care system globally. Although myocardial reperfusion is critical for ischemic cardiac tissue survival, the reperfusion itself could cause paradoxical injury. This paradoxical phenomenon is known as ischemia–reperfusion injury (IRI), and the exact molecular mechanism of IRI is still far from being elucidated and is a topic of controversy. Meanwhile, ferroptosis is a nonapoptotic form of cell death that has been reported to be associated with various cardiovascular diseases. Thus, we explored the potential ferroptosis mechanism and target in cardiac IRI via bioinformatics analysis and experiment. GSE4105 data were obtained from the GEO database and consist of a rat IRI model and control. After identifying differentially expressed ferroptosis-related genes (DEFRGs) and hub genes of cardiac IRI, we performed enrichment analysis, coexpression analysis, drug–gene interaction prediction, and mRNA–miRNA regulatory network construction. Moreover, we validated and explored the multitemporal expression of hub genes in a hypoxia/reoxygenation (H/R)-induced H9C2 cell injury model under different conditions via RT-qPCR. A total of 43 DEFRGs and 7 hub genes (tumor protein p53 [Tp53], tumor necrosis factor [Tnf], hypoxia-inducible factor 1 subunit alpha [Hif1a], interleukin 6 [Il6], heme oxygenase 1 [Hmox1], X-box binding protein 1 [Xbp1], and caspase 8 [Casp8]) were screened based on bioinformatics analysis. The functional annotation of these genes revealed apoptosis, and the related signaling pathways could have association with the pathogenesis of ferroptosis in cardiac IRI. In addition, the expression of the seven hub genes in IRI models were found higher than that of control under different H/R conditions and time points. In conclusion, the analysis of 43 DEFRGs and 7 hub genes could reveal the potential biological pathway and mechanism of ferroptosis in cardiac IRI. In addition, the multitemporal expression change of hub genes in H9C2 cells under different H/R conditions could provide clues for further ferroptosis mechanism exploring, and the seven hub genes could be potential biomarkers or therapeutic targets in cardiac IRI.

Inhibition of PLK3 Attenuates Tubular Epithelial Cell Apoptosis after Renal Ischemia–Reperfusion Injury by Blocking the ATM/P53-Mediated DNA Damage Response

Objective

Renal ischemia–reperfusion (I/R) injury is a major cause of acute kidney injury (AKI) in transplanted kidneys. This study was aimed at exploring the role of PLK3 (polo-like kinase 3) in renal I/R injury, focusing on its relationship with oxidative stress-induced DNA damage and renal tubular epithelial cell (TEC) apoptosis.

Methods

TRAP-seq data from the development dataset GSE52004 and the validation dataset GSE121191 were analyzed using GEO2R. PLK3 overexpression plasmids and targeted silencing siRNAs were used in a model of hypoxia/reoxygenation (H/R) injury, and rAAV-9-PLK3-KD were administered to C57BL/6J mice exposed to I/R injury. The ATM-specific inhibitor KU-60019 was used to block the DNA damage response (DDR). Western blotting was performed to measure DDR- and apoptosis-associated protein expression. Cell viability was measured by CCK-8 reagent, and apoptosis was examined by flow cytometry and TUNEL assay. Furthermore, the fluorescent probes H₂DCFH-DA and DHE were used to measure ROS production in vitro. The MDA level and SOD activity were measured to assess oxidative stress in vivo. KIM-1 staining and Scr and BUN were used to evaluate kidney injury.

Results

The mRNA and protein levels of PLK3 were markedly increased in the H/R injury and I/R injury models. GO terms showed that PLK3 was mainly involved in oxidative stress and DNA damage after renal I/R injury. Overexpression of PLK3 decreased cell viability and increased apoptosis. In contrast, targeted silencing of PLK3 expression decreased the Bax/Bcl-2 ratio by decreasing P53 phosphorylation, thereby reducing TEC apoptosis. Furthermore, KU-60019 reduced PLK3 activation and DDR-induced apoptosis, while overexpression of PLK3 reversed the mitigating effect of KU-60019 on TEC apoptosis. Similarly, rAAV-9-PLK3 KD mice exhibited a lower rate of TEC apoptosis and milder renal damage after I/R injury.

Conclusion

We demonstrate for the first time that PLK3 is involved in oxidative stress-induced DNA damage and TEC apoptosis in renal I/R injury. Inhibition of PLK3 attenuates TEC apoptosis after I/R injury by blocking the ATM/P53-mediated DDR. Therefore, PLK3 may serve as a potential therapeutic target for ischemic AKI.

Modified chitosan for effective renal delivery of siRNA to treat acute kidney injury

Acute kidney injury (AKI) is characterized by a sudden decrease in renal function and impacts growing number of people worldwide. RNA interference (RNAi) showed potential to treat diseases with no or limited conventional therapies, including AKI. Suitable carriers are needed to protect and selectively deliver RNAi to target cells to fully explore this therapeutic modality. Here, we report on the synthesis of chitosan modified with α-cyclam-p-toluic acid (C-CS) as a novel siRNA carrier for targeted delivery to injured kidneys. We demonstrate that conjugation of the α-cyclam-p-toluic acid to chitosan imparts the C-CS polymer with targeting and antagonistic properties to cells overexpressing chemokine receptor CXCR4. In contrast, the parent α-cyclam-p-toluic acid showed no such properties. Self-assembled C-CS/siRNA nanoparticles rapidly accumulate in the injured kidneys and show long retention in renal tubules. Apoptosis and metabolic and inflammatory pathways induced by p53 are important pathological mechanisms in the development of AKI. Nanoparticles with siRNA against p53 (sip53) were formulated and intravenously injected for attenuation of IRI-AKI. Due to the favorable accumulation in injured kidneys, the treatment with C-CS/sip53 decreased renal injury, extent of renal apoptosis, macrophage and neutrophil infiltration, and improved renal function. Overall, our study suggests that C-CS/siRNA nanoparticles have the potential to effectively accumulate and deliver therapeutic siRNAs to injured kidneys through CXCR4 binding, providing a novel way for AKI therapy.

Preferential siRNA delivery to injured kidneys for combination treatment of acute kidney injury

Acute kidney injury (AKI) is characterized by a sudden loss of renal function and is associated with high morbidity and mortality. Tumor suppressor p53 and chemokine receptor CXCR4 were both implicated in the AKI pathology. Here, we report on the development and evaluation of polymeric CXCR4 antagonist (PCX) siRNA carrier for selective delivery to injured kidneys in AKI. Our results show that PCX/siRNA nanoparticles (polyplexes) provide protection against cisplatin injury to tubule cells in vitro when both CXCR4 and p53 are inhibited. The polyplexes selectively accumulate and are retained in the injured kidneys in cisplatin and bilateral ischemia reperfusion injury models of AKI. Treating AKI with the combined CXCR4 inhibition and p53 gene silencing with the PCX/sip53 polyplexes improves kidney function and decreases renal damage. Overall, our results suggest that the PCX/sip53 polyplexes have a significant potential to enhance renal accumulation in AKI and deliver therapeutic siRNA.

Proximal Tubule p53 in Cold Storage/Transplantation-Associated Kidney Injury and Renal Graft Dysfunction

Kidney injury associated with cold storage/transplantation is a primary factor for delayed graft function and poor outcome of renal transplants. p53 contributes to both ischemic and nephrotoxic kidney injury, but its involvement in kidney cold storage/transplantation is unclear. Here, we report that p53 in kidney proximal tubules plays a critical role in cold storage/transplantation kidney injury and inhibition of p53 can effectively improve the histology and function of transplanted kidneys. In a mouse kidney cold storage/transplantation model, we detected p53 accumulation in proximal tubules in a cold storage time-dependent manner, which correlated with tubular injury and cell death. Pifithrin-α, a pharmacologic p53 inhibitor, could reduce acute tubular injury, apoptosis and inflammation at 24 h after cold storage/transplantation. Similar effects were shown by the ablation of p53 from proximal tubule cells. Notably, pifithrin-α also ameliorated kidney injury and improved the function of transplanted kidneys in 6 days when it became the sole life-supporting kidney in recipient mice. in vitro, cold storage followed by rewarming induced cell death in cultured proximal tubule cells, which was accompanied by p53 activation and suppressed by pifithrin-α and dominant-negative p53. Together, these results support a pathogenic role of p53 in cold storage/transplantation kidney injury and demonstrate the therapeutic potential of p53 inhibitors.

Pioglitazone Ameliorates Renal Ischemia-Reperfusion Injury via Inhibition of NF-κB Activation and Inflammation in Rats

Renal ischemia-reperfusion injury (IRI) is considered as a major cause of acute kidney injury. In this study, we investigated the role of the NF-κB signaling pathway and inflammation in the amelioration of renal IRI using pioglitazone. Sprague–Dawley (SD) rats were subjected to bilateral renal artery clamping for 45 min followed by perfusion restoration for establishing a simulated renal IRI model. At 24 h post-operatively, we assessed the serum levels of creatinine and urea nitrogen, expression levels of peroxisome proliferator-activated receptor gamma (PPAR-γ) and NF-κB-related (p-IKK-β and IκB-α) proteins, and mRNA expression levels of the inflammatory cytokines, including TNF-α and MCP-1, in the renal tissue of various study groups. The histopathological evaluation of renal tissue was also conducted. In rat renal tissue, pioglitazone treatment decreased the serum levels of post-renal IRI creatinine and urea nitrogen, as well as necrosis. Furthermore, it elevated the expression of PPAR-γ protein and decreased the expression of NF-κB-related proteins. Pioglitazone also decreased the mRNA expression of TNF-α and MCP-1 in the renal tissue. Thus, pioglitazone ameliorates renal IRI by inhibiting the NF-κB signaling pathway and inflammatory response in rats.

RvD1 Attenuated Susceptibility to Ischemic AKI in Diabetes by Downregulating Nuclear Factor-κ B Signal and Inhibiting Apoptosis

Background

Acute kidney injury (AKI), when occurring in diabetic kidney disease (DKD), is known to be more severe and difficult to recover from. Inflammation and apoptosis may contribute to the heightened sensitivity of, and non-recovery from, AKI in patients with DKD. Resolvin D1 (RvD1) is a potent lipid mediator which can inhibit the inflammatory response and apoptosis in many diseases. However, it has been reported that the RvD1 levels were decreased in diabetes, which may explain why DKD is more susceptible to AKI.

Methods

For animal experiments, diabetic nephropathy (DN) mice were induced by streptozotocin (STZ) injection intraperitoneally. Renal ischemia–reperfusion was used to induce AKI. Blood urea nitrogen (BUN) and serum creatinine were determined using commercial kits to indicate renal function. Renal apoptosis was examined by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. Real-time polymerase chain reaction (PCR) was used to detect the marker of inflammatory response. Western blot was used to detect the expression of nuclear factor-κB (NF-κB)-related proteins. For clinical study, 12 cases diagnosed with DKD were enrolled in this study, and an equal number of non-diabetic renal disease patients (NDKD) were recruited as a control group. The serum RvD1 in DKD or NDKD patients were detected through an ELISA kit.

Results

In clinical study, we found that the serum RvD1 levels were decreased in DKD patients compared to those in NDKD patients. Decreased serum RvD1 levels were responsible for the susceptibility to ischemic AKI in DKD patients. In animal experiments, both the serum RvD1 and renal ALX levels were downregulated. RvD1 treatment could ameliorate renal function and histological damage after ischemic injury in DN mice. RvD1 treatment also could inhibit the inflammatory response. Di-tert-butyl dicarbonate (BOC-2) treatment could deteriorate renal function and histological damage after ischemic injury in non-diabetic mice. RvD1 could inhibit the NF-κB activation and suppress inflammatory response mainly by inhibiting NF-κB signaling.

Conclusion

RvD1 attenuated susceptibility to ischemic AKI in diabetes by downregulating NF-κB signaling and inhibiting apoptosis. Downregulated serum RvD1 levels could be the crucial factor for susceptibility to ischemic AKI in diabetes.

The Genomic Response to TGF-β1 Dictates Failed Repair and Progression of Fibrotic Disease in the Obstructed Kidney

Tubulointerstitial fibrosis is a common and diagnostic hallmark of a spectrum of chronic renal disorders. While the etiology varies as to the causative nature of the underlying pathology, persistent TGF-β1 signaling drives the relentless progression of renal fibrotic disease. TGF-β1 orchestrates the multifaceted program of kidney fibrogenesis involving proximal tubular dysfunction, failed epithelial recovery or re-differentiation, capillary collapse and subsequent interstitial fibrosis eventually leading to chronic and ultimately end-stage disease. An increasing complement of non-canonical elements function as co-factors in TGF-β1 signaling. p53 is a particularly prominent transcriptional co-regulator of several TGF-β1 fibrotic-response genes by complexing with TGF-β1 receptor-activated SMADs. This cooperative p53/TGF-β1 genomic cluster includes genes involved in cellular proliferative control, survival, apoptosis, senescence, and ECM remodeling. While the molecular basis for this co-dependency remains to be determined, a subset of TGF-β1-regulated genes possess both p53- and SMAD-binding motifs. Increases in p53 expression and phosphorylation, moreover, are evident in various forms of renal injury as well as kidney allograft rejection. Targeted reduction of p53 levels by pharmacologic and genetic approaches attenuates expression of the involved genes and mitigates the fibrotic response confirming a key role for p53 in renal disorders. This review focuses on mechanisms underlying TGF-β1-induced renal fibrosis largely in the context of ureteral obstruction, which mimics the pathophysiology of pediatric unilateral ureteropelvic junction obstruction, and the role of p53 as a transcriptional regulator within the TGF-β1 repertoire of fibrosis-promoting genes.

Epithelial proliferation and cell cycle dysregulation in kidney injury and disease

Various cellular insults and injury to renal epithelial cells stimulate repair mechanisms to adapt and restore the organ homeostasis. Renal tubular epithelial cells are endowed with regenerative capacity, which allows for a restoration of nephron function after acute kidney injury. However, recent evidence indicates that the repair is often incomplete, leading to maladaptive responses that promote the progression to chronic kidney disease. The dysregulated cell cycle and proliferation is also a key feature of renal tubular epithelial cells in polycystic kidney disease and HIV-associated nephropathy. Therefore, in this review, we provide an overview of cell cycle regulation and the consequences of dysregulated cell proliferation in acute kidney injury, polycystic kidney disease, and HIV-associated nephropathy. An increased understanding of these processes may help define better targets for kidney repair and combat chronic kidney disease progression.

Toll-like receptor 4: An attractive therapeutic target for acute kidney injury

Acute kidney injury (AKI) is a progressive renal complication which significantly affects the patient's life with huge economic burden. Untreated acute kidney injury eventually progresses to a chronic form and end-stage renal disease. Although significant breakthroughs have been made in recent years, there are still no effective pharmacological therapies for the treatment of acute kidney injury. Toll-like receptor 4 (TLR4) is a well-characterized pattern recognition receptor, and increasing evidence has shown that TLR4 mediated inflammatory response plays a pivotal role in the pathogenesis of acute kidney injury. The expression of TLR4 has been seen in resident renal cells, including podocytes, mesangial cells, tubular epithelial cells and endothelial cells. Activation of TLR4 signaling regulates the transcription of numerous pro-inflammatory cytokines and chemokines, resulting in renal inflammation. Therefore, targeting TLR4 and its downstream effectors could serve as an effective therapeutic intervention to prevent renal inflammation and subsequent kidney damage. For the first time, this review summarizes the literature on acute kidney injury from the perspective of TLR4 from year 2010 to 2020. In the current review, the role of TLR4 signaling pathway in AKI with preclinical evidence is discussed. Furthermore, we have highlighted several compounds of natural and synthetic origin, which have the potential to avert the renal TLR4 signaling in preclinical AKI models and have shown protection against AKI. This scientific review provides new ideas for targeting TLR4 in the treatment of AKI and provides strategies for the drug development against AKI.

New drugs for acute kidney injury

PURPOSE OF REVIEW

To describe recent advances in the development of therapeutic agents for acute kidney injury (AKI).

RECENT FINDINGS

Traditional care for AKI is mostly supportive. At present, no specific therapy has been developed to prevent or treat AKI. However, based on a better understanding of the pathophysiology of AKI, various potential compounds have been recently identified and tested. A variety of pathways has been targeted, including oxidative and mitochondrial stress, cellular metabolism and repair, inflammation, apoptosis and hemodynamics. Many of these potential agents are currently ongoing early-phase clinical trials, and the purpose of this review is to provide a summary of those with the most potential.

SUMMARY

Despite the lack of therapies specifically approved for AKI, many interesting potential agents are entering clinical trials, with the potential to transform the care of patients with AKI.

Snai1-induced partial epithelial-mesenchymal transition orchestrates p53-p21-mediated G2/M arrest in the progression of renal fibrosis via NF-κB-mediated inflammation

Renal fibrosis is the common feature of all progressive kidney diseases and exerts great burden on public health worldwide. The maladaptive repair mechanism of tubular epithelial cells, an important mediator of renal fibrogenesis, manifests with partial epithelial-mesenchymal transition (EMT) and cell cycle arrest. The aim of this study is to investigate the possible correlation between partial EMT and cell cycle arrest, and elucidate the underlying mechanism. We examined human kidney allograft samples with interstitial fibrosis and three mice renal fibrosis models, unilateral ureter obstruction (UUO), ischemia-reperfusion injury, and Adriamycin nephropathy. The partial EMT process and p53-p21 axis were elevated in both human allograft with interstitial fibrosis, as well as three mice renal fibrosis models, and showed a time-dependent increase as fibrosis progressed in the UUO model. Snai1 controlled the partial EMT process, and led to parallel changes in renal fibrosis, G2/M arrest, and inflammation. p53-p21 axis arrested cell cycle at G2/M, and prompted partial EMT and fibrosis together with inflammation. NF-κB inhibitor Bay11-7082 disrupted the reciprocal loop between Snai1-induced partial EMT and p53-p21-mediated G2/M arrest. We demonstrated the reciprocal loop between partial EMT and G2/M arrest of TECs during renal fibrogenesis and revealed NF-κB-mediated inflammatory response as the underlying mechanism. This study suggests that targeting NF-κB might be a plausible therapeutic strategy to disrupt the reciprocal loop between partial EMT and G2/M arrest, therefore alleviating renal fibrosis.

Exploring the multiple roles of guardian of the genome: P53

Background

Cells have evolved balanced mechanisms to protect themselves by initiating a specific response to a variety of stress. TheTP53gene, encoding P53 protein, is one of the many widely studied genes in human cells owing to its multifaceted functions and complex dynamics. The tumour-suppressing activity of P53 plays a principal role in the cellular response to stress. The majority of the human cancer cells exhibit the inactivation of the P53 pathway. In this review, we discuss the recent advancements in P53 research with particular focus on the role of P53 in DNA damage responses, apoptosis, autophagy, and cellular metabolism. We also discussed important P53-reactivation strategies that can play a crucial role in cancer therapy and the role of P53 in various diseases.

Main body

We used electronic databases like PubMed and Google Scholar for literature search. In response to a variety of cellular stress such as genotoxic stress, ischemic stress, oncogenic expression, P53 acts as a sensor, and suppresses tumour development by promoting cell death or permanent inhibition of cell proliferation. It controls several genes that play a role in the arrest of the cell cycle, cellular senescence, DNA repair system, and apoptosis. P53 plays a crucial role in supporting DNA repair by arresting the cell cycle to purchase time for the repair system to restore genome stability. Apoptosis is essential for maintaining tissue homeostasis and tumour suppression. P53 can induce apoptosis in a genetically unstable cell by interacting with many pro-apoptotic and anti-apoptotic factors.

Furthermore, P53 can activate autophagy, which also plays a role in tumour suppression. P53 also regulates many metabolic pathways of glucose, lipid, and amino acid metabolism. Thus under mild metabolic stress, P53 contributes to the cell’s ability to adapt to and survive the stress.

Conclusion

These multiple levels of regulation enable P53 to perform diversified roles in many cell responses. Understanding the complete function of P53 is still a work in progress because of the inherent complexity involved in between P53 and its target proteins. Further research is required to unravel the mystery of this Guardian of the genome “TP53”.

Critical hubs of renal ischemia-reperfusion injury: endoplasmic reticulum-mitochondria tethering complexes

Mitochondrial injury and endoplasmic reticulum (ER) stress are considered to be the key mechanisms of renal ischemia-reperfusion (I/R) injury. Mitochondria are membrane-bound organelles that form close physical contact with a specific domain of the ER, known as mitochondrial-associated membranes. The close physical contact between them is mainly restrained by ER-mitochondria tethering complexes, which can play an important role in mitochondrial damage, ER stress, lipid homeostasis, and cell death. Several ER-mitochondria tethering complex components are involved in the process of renal I/R injury. A better understanding of the physical and functional interaction between ER and mitochondria is helpful to further clarify the mechanism of renal I/R injury and provide potential therapeutic targets. In this review, we aim to describe the structure of the tethering complex and elucidate its pivotal role in renal I/R injury by summarizing its role in many important mechanisms, such as mitophagy, mitochondrial fission, mitochondrial fusion, apoptosis and necrosis, ER stress, mitochondrial substance transport, and lipid metabolism.

WWP2 ameliorates acute kidney injury by mediating p53 ubiquitylation and degradation

E3 ubiquitin ligase gene, WWP2, is associated with acute kidney injury (AKI). This research was conducted to explore the role of WWP2 in AKI. AKI cell model was produced in human renal proximal tubular epithelial cell line (HK-2) by ischemia-reperfusion (IR) injury. CCK8 and flow cytometry assay were performed to explore the influence of WWP2 overexpression on cell proliferation and apoptosis of IR-induced HK-2 cells. Quantitative real-time PCR and immunoblotting (IB) were performed to assess the gene and protein expression. Then, the influence of WWP2 on p53 ubiquitylation and degradation was estimated by immunoprecipitation assay. Our data indicated that WWP2 was down-regulated and p53 was up-regulated in IR-induced HK-2 cells. WWP2 overexpression promoted proliferation and inhibited apoptosis of IR-induced HK-2 cells. And WWP2 interacted with p53 and regulated p53 ubiquitylation and degradation. Furthermore, the influence of WWP2 on cell proliferation and apoptosis was rescued by MG132 (proteasome inhibitor) treatment. In conclusion, our work described for the first time the role of WWP2 in AKI, showing that WWP2 ameliorated AKI by mediating p53 ubiquitylation and degradation. Moreover, the study offers some important insights into the occurrence of AKI and WWP2 may be a novel target of AKI treatment. SIGNIFICANCE OF THE STUDY: Our data elaborates that WWP2 has protective effect against AKI by mediating p53 ubiquitylation and degradation. Thus, WWP2 might be a therapeutic target for AKI.

Ischemia and Reperfusion Injury in Kidney Transplantation: Relevant Mechanisms in Injury and Repair

Ischemia and reperfusion injury (IRI) is a complex pathophysiological phenomenon, inevitable in kidney transplantation and one of the most important mechanisms for non- or delayed function immediately after transplantation. Long term, it is associated with acute rejection and chronic graft dysfunction due to interstitial fibrosis and tubular atrophy. Recently, more insight has been gained in the underlying molecular pathways and signalling cascades involved, which opens the door to new therapeutic opportunities aiming to reduce IRI and improve graft survival. This review systemically discusses the specific molecular pathways involved in the pathophysiology of IRI and highlights new therapeutic strategies targeting these pathways.

p53-cyclophilin D mediates renal tubular cell apoptosis in ischemia-reperfusion-induced acute kidney injury

Ischemia-reperfusion (I/R)-induced acute kidney injury (I/R-AKI) favors mitochondrial permeability transition pore (mPTP) opening and subsequent cell death. Cyclophilin D (CypD) is an essential component of the mPTP, and recent findings have implicated the p53-CypD complex in cell death. To evaluate the role of p53-CypD after I/R-AKI, we tested the hypothesis that the p53-CypD complex mediates renal tubular cell apoptosis in I/R-AKI via mPTP opening. Expression of p53 and cleaved caspase-3 was significantly increased in rats subjected to I/R-AKI compared with normal controls and sham-operated controls. The underlying mechanisms were determined using an in vitro model of ATP depletion. Inhibition of mPTP opening using the CypD inhibitor cyclosporin A or siRNA for p53 in ATP-depleted HK-2 cells prevented mitochondrial membrane depolarization and reduced apoptosis. Furthermore, p53 bound to CypD in ATP-depleted HK-2 cells. These results suggest that the p53-CypD complex mediates renal tubular cell apoptosis in I/R-AKI via mPTP opening.

c-Myc promotes tubular cell apoptosis in ischemia-reperfusion-induced renal injury by negatively regulating c-FLIP and enhancing FasL/Fas-mediated apoptosis pathway

c-Myc plays an important role in cell proliferation, differentiation, and cell apoptosis. FasL/Fas pathway is a key regulator of cell apoptosis. This study was aimed to investigate the effects of c-Myc on the FasL/Fas pathway in ischemia-reperfusion (I/R)-induced renal injury. Rats were objected to bilateral renal ischemia for 60 min and reperfused for 24 or 48 h. NRK-52E cells were treated with hypoxia-reoxygenation (H/R) or FasL. Immunohistochemistry was used to identify the distribution of c-Myc. Cell apoptosis was assessed by TUNEL staining. Ad-c-Myc and recombinant pcDAN 3.0 were used to overexpress c-Myc and c-FLIP, respectively. ChIP assay and luciferase assay were used to detect the binding of c-Myc to c-FLIP promoter. In I/R rats, c-Myc was increased significantly and mainly located in renal tubular epithelial cells; meanwhile, c-FLIP was decreased, cleaved caspase-8, cleaved caspase-3 and TUNEL-positive staining cells were increased. Treatment of I/R rats with c-Myc inhibitor 10058-F4 significantly attenuated the decrease in c-FLIP, the increase in cleaved caspase-8, cleaved caspase-3, TUNEL-positive cells, Scr and BUN in I/R rats. In NRK-52E cells, hypoxia and reoxygen induced the increase in c-Myc and decrease in c-FLIP. ChIP and luciferase assay results indicated that c-Myc binds to the promoter region of c-FLIP gene. Overexpression of c-Myc markedly decreased c-FLIP. Overexpression of c-FLIP inhibited the increase in cleaved caspase-8 and caspase-3 induced by FasL. Data indicated that c-Myc is increased in kidneys of I/R rats and negatively regulates the expression of c-FLIP, then enhanced FasL-induced cell apoptosis in I/R stress.

Drugs in Development for Acute Kidney Injury

The care of patients with acute kidney injury (AKI) has been limited due to the lack of effective therapeutics that can either prevent AKI during high-risk situations or treat AKI once established. A revolution in the scientific understanding of the pathogenesis of AKI has led to the identification of potential therapeutic targets. These targets include pathways involved in inflammation, cellular repair and fibrosis, cellular metabolism and mitochondrial function, oxidative stress, apoptosis, and hemodynamics and oxygen delivery. Many compounds are entering early-phase clinical trials. In addition, efforts to better describe sub-categories of AKI (through endo-phenotyping) hold promise to target therapies more effectively based upon pathways that are operative in the pathogenesis. These advances bring optimism that the care of patients with AKI will be transformed with the hope of better outcomes.

Acute kidney injury induces dramatic p21 upregulation via a novel, glucocorticoid-activated, pathway

The cyclin kinase inhibitor p21 is acutely upregulated during acute kidney injury (AKI) and exerts cytoprotective effects. A proposed mechanism is oxidant stress-induced activation of p53, the dominant p21 transcription factor. Glycerol-induced rhabdomyolysis induces profound renal oxidant stress. Hence, we studied this AKI model to determine whether p53 activation corresponds with p21 gene induction and/or whether alternative mechanism(s) might be involved. CD-1 mice were subjected to glycerol-induced AKI. After 4 or 18 h, plasma, urinary, and renal cortical p21 protein and mRNA levels were assessed. Renal p53 activation was gauged by measurement of both total and activated (Ser15-phosphorylated) p53 and p53 mRNA levels. Glycerol evoked acute, progressive increases in renal cortical p21 mRNA and protein levels. Corresponding plasma (~25-fold) and urinary (~75-fold) p21 elevations were also observed. Renal cortical ratio of total to phosphorylated (Ser15) p53 rose three- to fourfold. However, the p53 inhibitor pifithrin-α failed to block glycerol-induced p21 gene induction, suggesting that an alternative p21 activator might also be at play. To this end, it was established that glycerol-induced AKI 1) dramatically increased plasma (~5-fold) and urinary (~75-fold) cortisol levels, 2) the glucocorticoid receptor antagonist mifepristone blocked glycerol-induced p21 mRNA and protein accumulation, and 3) dexamethasone or cortisol injections markedly increased p21 protein and mRNA in both normal and glycerol-treated mice, although no discernible p53 protein or mRNA increases were observed. We conclude that AKI-induced "systemic stress" markedly increases plasma and urinary cortisol, which can then activate renal p21 gene expression, at least in part, via a glucocorticoid receptor-dependent signaling pathway. Discernible renal cortical p53 increases are not required for this dexamethasone-mediated p21 response.

Effect of long non-coding RNA growth arrest-specific 5 on apoptosis in renal ischaemia/reperfusion injury

AIM

Long non-coding RNA (lncRNAs) have been shown to play a critical role in a variety of pathophysiological processes, such as cell proliferation, apoptosis and migration. However, there were few studies addressing the function of lncRNAs in renal ischaemia/reperfusion (I/R) injury. Apoptosis is an important pathogenesis during I/R injury. Here, we identified the effect of hypoxia-responsive lncRNA growth arrest-specific 5 (GAS5) on apoptosis in renal I/R injury.

METHODS

Ischaemia/reperfusion injury in mice or hypoxia/re-oxygenation (H/R) in human proximal renal tubular epithelial cells (HK-2) was practiced to induce apoptosis. The kidneys and blood were collected at 24 h after reperfusion. The GAS5 messenger RNA (mRNA) expression and apoptosis-related gene mRNA and protein levels, including p53, cellular inhibitor of apoptosis protein 2 (cIAP2) and thrombospondin-1 (TSP-1), were analysed. GAS5 small-interfering RNA was transfected with H/R induced cells. Over-expression of GAS5 was performed by plasmid transfection.

RESULTS

Apoptotic cells significantly increased in I/R-injured kidneys. GAS5 could be up-regulated in kidneys at 24 h after reperfusion and 3 h after re-oxygenation, combined with increased expression of its downstream apoptosis-related proteins p53 and cIAP2. GAS5 small-interfering RNA treatment down-regulated the mRNA and protein levels of p53 and TSP-1, and attenuated apoptosis induced by H/R in HK-2 cells. Conversely, over-expression of GAS5 up-regulated the mRNA and protein levels of p53 and TSP-1, and promoted apoptosis in HK-2 cells.

CONCLUSION

Long non-coding RNA GAS5 induced by I/R injury could promote apoptosis in kidney. TSP-1 might be one of the downstream effectors of GAS5, which will be explored in the future.

Time-dependent p53 inhibition determines senescence attenuation and long-term outcome after renal ischemia-reperfusion

Inhibition of p53 has been shown to be an efficient strategy for ameliorating kidney ischemia-reperfusion (I/R) injury in experimental models. The therapeutic value of p53 siRNA-based inhibition for I/R in renal transplantation is currently being evaluated in clinical studies. While the major rationale for these studies is the suppression of proapoptotic properties, there are more equally important injury response pathways regulated by p53. A p53-dependent pathway shown to be crucial for renal long-term outcome is cellular senescence. In this study, we tested the hypothesis that p53 siRNA reduces I/R-induced senescence and thereby improves kidney outcome. By comparing the impact of different treatment durations in a mouse model of renal I/R, we found that repetitive administration of p53 siRNA during the first 14 days after I/R reduced the senescence load and ameliorated the postischemic phenotype. Prolonged application of p53 siRNA over a 26-day period after I/R, however, did not provide any additional benefit for senescence reduction but reversed some of the renoprotective effects of the early treatment. These data suggest a time-dependent role of p53 activity supporting the current therapeutic concept of a short-term inhibition, while advocating against a prolonged treatment after I/R.

Origin and Consequences of Necroinflammation

When cells undergo necrotic cell death in either physiological or pathophysiological settings in vivo, they release highly immunogenic intracellular molecules and organelles into the interstitium and thereby represent the strongest known trigger of the immune system. With our increasing understanding of necrosis as a regulated and genetically determined process (RN, regulated necrosis), necrosis and necroinflammation can be pharmacologically prevented. This review discusses our current knowledge about signaling pathways of necrotic cell death as the origin of necroinflammation. Multiple pathways of RN such as necroptosis, ferroptosis, and pyroptosis have been evolutionary conserved most likely because of their differences in immunogenicity. As the consequence of necrosis, however, all necrotic cells release damage associated molecular patterns (DAMPs) that have been extensively investigated over the last two decades. Analysis of necroinflammation allows characterizing specific signatures for each particular pathway of cell death. While all RN-pathways share the release of DAMPs in general, most of them actively regulate the immune system by the additional expression and/or maturation of either pro- or anti-inflammatory cytokines/chemokines. In addition, DAMPs have been demonstrated to modulate the process of regeneration. For the purpose of better understanding of necroinflammation, we introduce a novel classification of DAMPs in this review to help detect the relative contribution of each RN-pathway to certain physiological and pathophysiological conditions.

P53 in kidney injury and repair: Mechanism and therapeutic potentials

Acute kidney injury (AKI) is a major kidney disease with poor clinical outcome. Besides its acute consequence of high mortality, AKI may also contribute significantly to the occurrence and progression of chronic kidney diseases (CKD). Accumulating evidence has demonstrated that maladaptive and incomplete kidney repair after AKI leads to the development of renal fibrosis and, ultimately, CKD. p53, a well-known tumor suppressor, plays a critical role in AKI and subsequent kidney repair through the regulation of various cell biologic processes, including apoptosis, cell cycle arrest, and autophagy. Despite the notable progress in deciphering the involvement of p53 in kidney injury and repair, the underlying mechanisms of p53 in these pathological processes remain largely unknown. Further investigation in this area is essential for the application of p53 as therapeutic target to prevent and treat AKI or impede its progression to CKD. In this review, we summarize the recent advances in understanding p53 regulation of AKI and kidney repair, pinpoint the potential of p53 as a therapeutic target, and present future research interests and directions.

Down-regulation of GRP78 alleviates lipopolysaccharide-induced acute kidney injury

PURPOSE

Acute kidney injury (AKI) is accompanied with life-threatening sepsis. It is necessary to develop effective therapy agent or strategy for treating AKI. LPS is a primary pathogenic factor that induces sepsis. Glucose-regulated protein 78 (GRP78) is closely related to cell injuries. The objective of this study was to examine the role of GRP78 in LPS-induced AKI.

METHODS

Cell counting kit-8 (CCK-8) assay and flow cytometry (FCM) were respectively performed to assess the cell viability and apoptosis. Available commercial kits were used to detect the reactive oxygen species (ROS) contents and the activity of oxidative indicators. The expressions of the relevant factors were determined by real-time PCR (RT-PCR) and Western blot.

RESULTS

The results showed that the expression of GRP78 was apparently increased by LPS treatment, and that the down-regulation of GRP78 by small RNA interference improved the proliferation ability of renal cells in comparison to LPS group. The LPS-induced immune response and oxidative stress was alleviated by the depletion of GRP78. Moreover, the LPS-induced apoptosis was reduced in the GRP78 group by regulating the expression of mitochondrial apoptosis (Bcl-2, Bax) and endoplasmic reticulum (ER) stress (CHOP, caspase-12)-associated proteins. In addition, the protective role of GRP78 reduction was partly related to the balance of NF-κB/IκB.

CONCLUSIONS

Down-regulation of GRP78 attenuated LPS-induced AKI through inhibiting immune response/oxidative stress-associated apoptosis.

RIP3-deficience attenuates potassium oxonate-induced hyperuricemia and kidney injury

Recent preclinical and clinical evidence suggests that hyperuricemia (HU) is an independent risk factor for metabolic syndrome, hypertension, cardiovascular disease and chronic kidney disease. Receptor-interacting protein 3 (RIP3) is an important contributor in inducing programmed necrosis, representing a newly identified mechanism of cell death combining features of both apoptosis and necrosis. In our study, RIP3 was strongly expressed in mice with hyperuricemia. RIP3 deficiency attenuated hyperuricemia in mice, evidenced by reduced serum uric acid and creatinine and enhanced urinary uric acid and creatinine, as well as the improved histological alterations in renal sections. Additionally, RIP3-deletion reduced malondialdehyde (MDA), H₂O₂ and O₂^-, whereas enhanced superoxide dismutase (SOD), GSH and GSH-Px levels in potassium oxonate-induced mice. Potassium oxonate-treated mice showed significantly high mRNA levels of ATP-binding cassette, subfamily G, membrane 2 (ABCG2), organic anion transporter 1 (OAT1), OAT3, organic cation transporter 1 (OCT1) and organic cation/carnitine transporter 1 (OCTN1) in renal tissue samples, which were reversed by RIP3-deficiency. Meanwhile, down-regulation of circulating and kidney pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) were observed in RIP3-knockout mice with hyperuricemia, associated with inactivation of toll-like receptor 4 (TLR4), inhibitor of NF-κB alpha (IκBα) and nuclear factor kappa B (NF-κB). NLR family, pyrin domain-containing 3 (NLRP3) inflammasome was also suppressed by RIP3 knockout in potassium oxonate-treated mice. Importantly, RIP3-knockout mice exhibited the decrease of FAS-associated protein with a death domain (FADD), cleaved Caspase-8/-3 and Poly (ADP-ribose) polymerase (PARP) in renal samples, along with TUNEL reduction in mice with hyperuricemia. Similar results were observed in uric acid-incubated cells with RIP3 knockdown. Thus, we suggested that RIP3 played an important role in mice with hyperuricemia, which might be a novel signal pathway targeting for therapeutic strategies in future.

Macrophage heme oxygenase-1-SIRT1-p53 axis regulates sterile inflammation in liver ischemia-reperfusion injury

BACKGROUND & AIMS

Hepatic ischemia-reperfusion injury (IRI), characterized by exogenous antigen-independent local inflammation and hepatocellular death, represents a risk factor for acute and chronic rejection in liver transplantation. We aimed to investigate the molecular communication involved in the mechanism of liver IRI.

METHODS

We analyzed human liver transplants, primary murine macrophage cell cultures and IR-stressed livers in myeloid-specific heme oxygenase-1 (HO-1) gene mutant mice, for anti-inflammatory and cytoprotective functions of macrophage-specific HO-1/SIRT1 (sirtuin 1)/p53 (tumor suppressor protein) signaling.

RESULTS

Decreased HO-1 expression in human post-reperfusion liver transplant biopsies correlated with a deterioration in hepatocellular function (serum ALT; p<0.05) and inferior patient survival (p<0.05). In the low HO-1 liver transplant biopsy group, SIRT1/Arf (alternative reading frame)/p53/MDM2 (murine double minute 2) expression levels decreased (p<0.05) while cleaved caspase 3 and frequency of TUNEL+cells simultaneously increased (p<0.05). Immunofluorescence showed macrophages were the principal source of HO-1 in human and mouse IR-stressed livers. In vitro macrophage cultures revealed that HO-1 induction positively regulated SIRT1 signaling, whereas SIRT1-induced Arf inhibited ubiquitinating activity of MDM2 against p53, which in turn attenuated macrophage activation. In a murine model of hepatic warm IRI, myeloid-specific HO-1 deletion lacked SIRT1/p53, exacerbated liver inflammation and IR-hepatocellular death, whereas adjunctive SIRT1 activation restored p53 signaling and rescued livers from IR-damage.

CONCLUSION

This bench-to-bedside study identifies a new class of macrophages activated via the HO-1-SIRT1-p53 signaling axis in the mechanism of hepatic sterile inflammation. This mechanism could be a target for novel therapeutic strategies in liver transplant recipients.

LAY SUMMARY

Post-transplant low macrophage HO-1 expression in human liver transplants correlates with reduced hepatocellular function and survival. HO-1 regulates macrophage activation via the SIRT1-p53 signaling network and regulates hepatocellular death in liver ischemia-reperfusion injury. Thus targeting this pathway in liver transplant recipients could be of therapeutic benefit.

TGF-β1/p53 signaling in renal fibrogenesis

Fibrotic disorders of the renal, pulmonary, cardiac, and hepatic systems are associated with significant morbidity and mortality. Effective therapies to prevent or curtail the advancement to organ failure, however, remain a major clinical challenge. Chronic kidney disease, in particular, constitutes an increasing medical burden affecting >15% of the US population. Regardless of etiology (diabetes, hypertension, ischemia, acute injury, urologic obstruction), persistently elevated TGF-β1 levels are causatively linked to the activation of profibrotic signaling networks and disease progression. TGF-β1 is the principal driver of renal fibrogenesis, a dynamic pathophysiologic process that involves tubular cell injury/apoptosis, infiltration of inflammatory cells, interstitial fibroblast activation and excess extracellular matrix synthesis/deposition leading to impaired kidney function and, eventually, to chronic and end-stage disease. TGF-β1 activates the ALK5 type I receptor (which phosphorylates SMAD2/3) as well as non-canonical (e.g., src kinase, EGFR, JAK/STAT, p53) pathways that collectively drive the fibrotic genomic program. Such multiplexed signal integration has pathophysiological consequences. Indeed, TGF-β1 stimulates the activation and assembly of p53-SMAD3 complexes required for transcription of the renal fibrotic genes plasminogen activator inhibitor-1, connective tissue growth factor and TGF-β1. Tubular-specific ablation of p53 in mice or pifithrin-α-mediated inactivation of p53 prevents epithelial G₂/M arrest, reduces the secretion of fibrotic effectors and attenuates the transition from acute to chronic renal injury, further supporting the involvement of p53 in disease progression. This review focuses on the pathophysiology of TGF-β1-initiated renal fibrogenesis and the role of p53 as a regulator of profibrotic gene expression.

AKI on CKD: heightened injury, suppressed repair, and the underlying mechanisms

Acute kidney injury (AKI) and chronic kidney disease (CKD) are interconnected. Although AKI-to-CKD transition has been intensively studied, the information of AKI on CKD is very limited. Nonetheless, AKI, when occurring in patients with CKD, is known to be more severe and difficult to recover. CKD is associated with significant changes in cell signaling in kidney tissues, including the activation of transforming growth factor-β, p53, hypoxia-inducible factor, and major developmental pathways. At the cellular level, CKD is characterized by mitochondrial dysfunction, oxidative stress, and aberrant autophagy. At the tissue level, CKD is characterized by chronic inflammation and vascular dysfunction. These pathologic changes may contribute to the heightened sensitivity of, and nonrecovery from, AKI in patients with CKD.

Safety and Tolerability Study of an Intravenously Administered Small Interfering Ribonucleic Acid (siRNA) Post On-Pump Cardiothoracic Surgery in Patients at Risk of Acute Kidney Injury

Introduction

Patients undergoing on-pump cardiac surgery are at an increased risk of acute kidney injury. QPI-1002, a small interfering ribonucleic acid, is under clinical development for the prevention of acute kidney injury. The safety, tolerability, and pharmacokinetics of QPI-1002 was evaluated in this first-in-man, Phase 1 study of a small, interfering ribonucleic acid in patients at risk of acute kidney injury after on-pump cardiac surgery.

Methods

In this phase 1 randomized, placebo-controlled dose-escalation study, a single i.v. dose of QPI-1002 was administered in subjects undergoing on-pump cardiac surgery. Subjects received placebo (n = 4), or QPI-1002 in increasing doses of 0.5 mg/kg (n = 3), 1.5 mg/kg (n = 3), 5 mg/kg (n = 3), and 10 mg/kg (n = 3).

Results

A total of 16 subjects were enrolled in the study. The average maximum concentration and area under the curve from the time of dosing to the last measurable concentration of QPI-1002 were generally dose proportional, indicating that exposure increased with increasing dose. The average mean residence time (mean residence time to the last measurable concentration) was 10 to 13 minutes in all 4 drug-dosing cohorts. Adverse events occurred at a similar rate in all study groups. Of the total 109 reported adverse events, the events were distributed as 26 in the placebo group and 21, 19, 24, and 19 in the QPI-1002 0.5, 1.5, 5.0, and 10.0 mg/kg groups, respectively. Eight of the 16 subjects experienced at least 1 serious adverse event: 4 (100%) in the placebo group and 4 (33.3%) in the combined QPI-1002 cohorts.

Discussion

QPI-1002 was rapidly eliminated from plasma. QPI-1002 was safe and well tolerated across all dose groups. Overall, no dose-limiting toxicities or safety signals were observed in the study. Further development of QPI-1002 for prophylaxis of acute kidney injury is warranted.

MAOA-a novel decision maker of apoptosis and autophagy in hormone refractory neuroendocrine prostate cancer cells

Autophagy and apoptosis are two well-controlled mechanisms regulating cell fate. An understanding of decision-making between these two pathways is in its infancy. Monoamine oxidase A (MAOA) is a mitochondrial enzyme that is well-known in psychiatric research. Emerging reports showed that overexpression MAOA is associated with prostate cancer (PCa). Here, we show that MAOA is involved in mediating neuroendocrine differentiation of PCa cells, a feature associated with hormone-refractory PCa (HRPC), a lethal type of disease. Following recent reports showing that NED of PCa requires down-regulation of repressor element-1 silencing transcription factor (REST) and activation of autophagy; we observe that MAOA is a novel direct target gene of REST. Reactive oxygen species (ROS) produced by overexpressed MAOA plays an essential role in inhibiting apoptosis and activating autophagy in NED PCa cells. MAOA inhibitors significantly reduced NED and autophagy activation of PCa cells. Our results here show MAOA as a new decision-maker for activating autophagy and MAOA inhibitors may be useful as a potential therapy for neuroendocrine tumors.

TRIP13-deficient tubular epithelial cells are susceptible to apoptosis following acute kidney injury

Damage to renal tubular epithelial cells by genetic, environmental, or biological insults can initiate complex signaling mechanisms that promote kidney repair and functional recovery. In this study, we demonstrated that thyroid receptor interacting protein 13 (TRIP13) is a critical modulator of tubular epithelial cell repair following ischemia‐reperfusion injury (IRI), a common type of renal stressor. In Trip13^Gt/Gthypomorph mice treated with unilateral renal IRI, persistent tubular epithelial cell damage was determined in the IRI-treated kidney throughout the 168 hours of experimental period compared to the contralateral kidneys. The damaged epithelial cells were associated with increased levels of DNA damage (ɣH2AX) and apoptotic markers (p53, cleaved caspase-7, and TUNEL-positive cells). Correspondingly, TRIP13 was found to directly interact with Tetratricopeptide Repeat Domain 5 (TTC5), a p53 co‐factor, and genetic knockdown of TRIP13 in murine inner medullary collecting duct cells in the presence of hydrogen peroxide showed increased activity of p53 at Serine 15. In all, these studies suggest that insufficient TRIP13 increased the susceptibility of damaged tubular epithelial cells to progress towards apoptotic cell death.

Rhizoma smilacis glabrae protects rats with gentamicin-induced kidney injury from oxidative stress-induced apoptosis by inhibiting caspase-3 activation

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma smilacis glabrae (RSG), which is mild-natured and tastes sweet or bland, has pharmacological action of eliminating dampness, detoxifying, and ensuring that joints were healthy and supple in traditional Chinese medicine.

AIM OF THE STUDY

To discuss the protective effect of RSG on gentamicin (GM)-induced kidney injury in rats and its regulatory mechanisms of oxidative stress-induced apoptosis by inhibiting caspase-3 activation.

MATERIALS AND METHODS

A total of 40 Sprague-Dawley (SD) rats were randomly divided into 5 groups: control group, model group, and RSG low, middle, and high dose groups (0.75，1.5，3gkg^-1). Six hours after intramuscular GM injections, rats in the model group were given distilled water by intragastric administration, and rats in the 3 RSG intervention groups were given different dosages of RSG water-extracts. Twenty-four hours after the last administration, blood and kidney samples were collected to test for biochemical indexes of kidney injury, oxidative stress, histopathological defects, apoptosis rate, and caspase-3 protein expression to assess the protective effect of RSG water-extracts against GM-induced kidney injury.

RESULTS

Compared with the model group, serum TP and ALB levels were significantly higher (P<0.05), and BUN, CRE, and UA levels were significantly lower (P<0.05) in the 3 RSG intervention groups. In kidney tissues, SOD, CAT, and GSH levels increased significantly (P<0.05), while MDA level decreased significantly (P<0.05). Total apoptosis rate dropped markedly (P<0.01), and the protein expressions of caspase-3 increased, while expressions of activated caspase-3 decreased. Histopathological analysis showed shrinkage of kidney cells reduced with appearance of complete kidney structure and decrease in activated caspase-3 expressions in impaired renal tubules decreased. Among the 3 RSG intervention groups, the middle dose group (1.5gkg^-1) showed the best protective effect.

CONCLUSIONS

RSG water-extracts had protective effects against GM-induced kidney injury in rats, and its mechanism of action was related to oxidative stress-induced apoptosis by inhibiting caspase-3 activation.

Hydrodynamic Isotonic Fluid Delivery Ameliorates Moderate-to-Severe Ischemia-Reperfusion Injury in Rat Kidneys

Highly aerobic organs like the kidney are innately susceptible to ischemia-reperfusion (I/R) injury, which can originate from sources including myocardial infarction, renal trauma, and transplant. Therapy is mainly supportive and depends on the cause(s) of damage. In the absence of hypervolemia, intravenous fluid delivery is frequently the first course of treatment but does not reverse established AKI. Evidence suggests that disrupting leukocyte adhesion may prevent the impairment of renal microvascular perfusion and the heightened inflammatory response that exacerbate ischemic renal injury. We investigated the therapeutic potential of hydrodynamic isotonic fluid delivery (HIFD) to the left renal vein 24 hours after inducing moderate-to-severe unilateral IRI in rats. HIFD significantly increased hydrostatic pressure within the renal vein. When conducted after established AKI, 24 hours after I/R injury, HIFD produced substantial and statistically significant decreases in serum creatinine levels compared with levels in animals given an equivalent volume of saline via peripheral infusion (P<0.05). Intravital confocal microscopy performed immediately after HIFD showed improved microvascular perfusion. Notably, HIFD also resulted in immediate enhancement of parenchymal labeling with the fluorescent dye Hoechst 33342. HIFD also associated with a significant reduction in the accumulation of renal leukocytes, including proinflammatory T cells. Additionally, HIFD significantly reduced peritubular capillary erythrocyte congestion and improved histologic scores of tubular injury 4 days after IRI. Taken together, these results indicate that HIFD performed after establishment of AKI rapidly restores microvascular perfusion and small molecule accessibility, with improvement in overall renal function.