Survivin mediates renal proximal tubule recovery from AKI

EHHADH deficiency regulates pexophagy and accelerates tubulointerstitial injury in diabetic kidney disease

Peroxisomal L-bifunctional enzyme (EHHADH) plays a role in the classic peroxisomal fatty acid β-oxidation pathway; however, the relationship between EHHADH expression and diabetic kidney disease has not been well understood. Here, we found that endogenous EHHADH levels were strongly correlated with the progression and severity of diabetic nephropathy in T2D patients. EHHADH knockout mice exhibited worsened renal tubular injury in diabetic mice. Furthermore, EHHADH is a modulator of pexophagy. In renal tubular epithelial cells (RTECs) in vitro, the knockdown of EHHADH induced a dramatic loss of peroxisomes. The loss of peroxisomes in EHHADH-deficient RTECs was restored by either an autophagic inhibitor 3-methyladenine or bafilomycin A1 both in vitro and in vivo. NBR1 was required for pexophagy in EHHADH-knockdown cells, where the level of reactive oxygen species (ROS) was increased, while inhibition of ROS blocked pexophagy. In summary, our findings revealed EHHADH deficiency accelerated renal injury in DKD as a modulator of pexophagy.

Acute and Chronic Kidney Disease Worsen Outcomes in Experimental Sepsis

Key Points

Acute kidney disease (AKD) and CKD are common conditions associated with high rates of incident infection, and poor outcomes once infection have been established. We successfully modeled AKD and CKD in rodents and then administered a cecal slurry solution to create peritonitis and tracked sepsis severity, end organ injury, and inflammatory changes. Our results indicate that AKD mice are more susceptible to infection than CKD mice, developing an aggravated inflammatory response and suggests that this condition predisposes to disparate infection risk.

Background

Infection is a leading cause of morbidity in individuals with acute kidney disease (AKD) and CKD. However, there is significant difficulty in modeling infection into an animal host with preexisting kidney disease. We report a novel method of peritoneal infection induced via cecal slurry (CS) inoculation deployed into mice with experimental aristolochic acid–induced AKD and CKD.

Methods

AKD, CKD, and paired control mice were injected with sham, low, or higher doses of donor–recipient matched CS solution. Animal survival, sepsis severity, and change in GFR were tracked longitudinally throughout the study. Histology for kidney injury, flow cytometry, plasma cytokines, and evidence of indirect organ injury from sepsis were also assessed.

Results

Infected AKD mice experienced significantly heightened sepsis severity, with 100% mortality by 24 hours after high CS doses versus no mortality in control mice. In addition, AKD mice receiving lower CS doses developed dramatically increased proinflammatory cytokines and persistent cytopenias. Infected CKD mice also had worse outcomes than paired CKD controls, although less severe than in AKD mice. Interestingly, animals with AKD had worse outcomes than mice with CKD after any CS dose or time point after inoculation, despite higher baseline kidney function and less uremic sequela.

Conclusions

These data confirm that acute bacterial infection can be modeled in animals with established kidney disease and suggest that the clinical state of kidney disease (AKD versus CKD) may influence host susceptibility to infection more than the degree of kidney failure alone.

Parental obesity predisposes offspring to kidney dysfunction and increased susceptibility to ischemia-reperfusion injury in a sex-dependent manner

Although obesity is recognized as a risk factor for cardiorenal and metabolic diseases, the impact of parental obesity on the susceptibility of their offspring to renal injury at adulthood is unknown. We examined the impact of parental obesity on offspring kidney function, morphology, and markers of kidney damage after acute kidney injury (AKI). Offspring from normal (N) diet-fed C57BL/6J parents were fed either N (NN) or a high-fat (H) diet (NH) from weaning until adulthood. Offspring from obese H diet-fed parents were fed N (HN) or H diet (HH) after weaning. All offspring groups were submitted to bilateral AKI by clamping the left and right renal pedicles for 30 min. Compared with male NH and NN offspring from lean parents, male HH and HN offspring from obese parents exhibited higher kidney injury markers such as urinary, renal osteopontin, plasma creatinine, urinary albumin excretion, and neutrophil gelatinase-associated lipocalin (NGAL) levels, and worse histological injury score at 22 wk of age. Only albumin excretion and NGAL were elevated in female HH offspring from obese parents compared with lean and obese offspring from lean parents. We also found an increased mortality rate and worse kidney injury scores after AKI in male offspring from obese parents, regardless of the diet consumed after weaning. Female offspring were protected from major kidney injury after AKI. These results indicate that parental obesity leads to increased kidney injury in their offspring after ischemia-reperfusion in a sex-dependent manner, even when their offspring remain lean.NEW & NOTEWORTHY Offspring from obese parents are more susceptible to kidney injury and worse outcomes following an acute ischemia-reperfusion insult. Male, but not female, offspring from obese parents exhibit increased blood pressure early in life. Female offspring are partially protected against major kidney injury induced by ischemia-reperfusion.

Mice with renal-specific alterations of stem cell-associated signaling develop symptoms of chronic kidney disease but surprisingly no tumors

Previously, we found that Wnt and Notch signaling govern stem cells of clear cell kidney cancer (ccRCC) in patients. To mimic stem cell responses in the normal kidney in vitro in a marker-unbiased fashion, we have established tubular organoids (tubuloids) from total single adult mouse kidney epithelial cells in Matrigel and serum-free conditions. Deep proteomic and phosphoproteomic analyses revealed that tubuloids resembled renewal of adult kidney tubular epithelia, since tubuloid cells displayed activity of Wnt and Notch signaling, long-term proliferation and expression of markers of proximal and distal nephron lineages. In our wish to model stem cell-derived human ccRCC, we have generated two types of genetic double kidney mutants in mice: Wnt-β-catenin-GOF together with Notch-GOF and Wnt-β-catenin-GOF together with a most common alteration in ccRCC, Vhl-LOF. An inducible Pax8-rtTA-LC1-Cre was used to drive recombination specifically in adult kidney epithelial cells. We confirmed mutagenesis of β-catenin, Notch and Vhl alleles on DNA, protein and mRNA target gene levels. Surprisingly, we observed symptoms of chronic kidney disease (CKD) in mutant mice, but no increased proliferation and tumorigenesis. Thus, the responses of kidney stem cells in the tubuloid and genetic systems produced different phenotypes, i.e. enhanced renewal versus CKD.

Protective Effect of Platelet-Rich Plasma on Cisplatin-Induced Nephrotoxicity in Adult Male Albino Rats: Histological and Immunohistochemical Study

Cisplatin is a potent antineoplastic drug that is used for treatment of many solid tumors. It has a wide range of adverse effects. Nephrotoxicity is the most common one of them. Platelet-rich plasma (PRP) is an autologous human plasma that activates the tissue regeneration through cell proliferation and differentiation. Study the role of PRP in amelioration of cisplatin-induced nephrotoxicity on the kidney of adult male albino rats by biochemical, morphometric, histological, and immunohistochemical studies. Thirty-five adult male albino rats were used. Thirty rats were included as experimental group and five were used to obtain the PRP. The experimental group was classified into as follows: control group which received 1mL of sterile saline by intraperitoneal injection (IP), cisplatin-treated group which received cisplatin 7.5 mg/kg IP in a single dose and cisplatin and PRP-treated group rats received cisplatin 7.5 mg/kg single IP dose followed by 1ml of PRP IP after 24 h of cisplatin injection. There was a significant increase in urea and creatinine levels in cisplatin-treated group in comparison to the control and the PRP groups. The kidneys of cisplatin-treated group showed distorted renal structure, where specimens of PRP-treated group revealed restoration of the classical appearance of the renal tissue similar to the control group. PRP has protective effects on renal structure and functions and it helps to ameliorate the histological changes induced by cisplatin.

Cisplatin Nephrotoxicity Is Critically Mediated by the Availability of BECLIN1

Cisplatin nephrotoxicity is a critical limitation of solid cancer treatment. Until now, the complex interplay of various pathophysiological mechanisms leading to proximal tubular cell apoptosis after cisplatin exposure has not been fully understood. In our study, we assessed the role of the autophagy-related protein BECLIN1 (ATG6) in cisplatin-induced acute renal injury (AKI)-a candidate protein involved in autophagy and with putative impact on apoptosis by harboring a B-cell lymphoma 2 (BCL2) interaction site of unknown significance. By using mice with heterozygous deletion of Becn1, we demonstrate that reduced intracellular content of BECLIN1 does not impact renal function or autophagy within 12 months. However, these mice were significantly sensitized towards cisplatin-induced AKI, and by using Becn1+/-;Sglt2-Cre;Tomato/EGFP mice with subsequent primary cell analysis, we confirmed that nephrotoxicity depends on proximal tubular BECLIN1 content. Mechanistically, BECLIN1 did not impact autophagy or primarily the apoptotic pathway. In fact, a lack of BECLIN1 sensitized mice towards cisplatin-induced ER stress. Accordingly, the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) blunted cisplatin-induced cell death in Becn1 heterozygosity. In conclusion, our data first highlight a novel role of BECLIN1 in protecting against cellular ER stress independent from autophagy. These novel findings open new therapeutic avenues to intervene in this important intracellular stress response pathway with a promising impact on future AKI management.

Protein and peptide-based renal targeted drug delivery systems

Renal diseases have become an increasingly concerned public health problem in the world. Kidney-targeted drug delivery has profound transformative potential on increasing renal efficacy and reducing extra-renal toxicity. Protein and peptide-based kidney targeted drug delivery systems have garnered more and more attention due to its controllable synthesis, high biocompatibility and low immunogenicity. At the same time, the targeting methods based on protein/peptide are also abundant, including passive renal targeting based on macromolecular protein and active targeting mediated by renal targeting peptide. Here, we review the application and the drug loading strategy of different proteins or peptides in targeted drug delivery, including the ferritin family, albumin, low molecular weight protein (LMWP), different peptide sequence and antibodies. In addition, we summarized the factors influencing passive and active targeting in drug delivery system, the main receptors related to active targeting in different kidney diseases, and a variety of nano forms of proteins based on the controllable synthesis of proteins.

Pax protein depletion in proximal tubules triggers conserved mechanisms of resistance to acute ischemic kidney injury preventing transition to chronic kidney disease

Acute kidney injury (AKI) is a common condition that lacks effective treatments. In part, this shortcoming is due to an incomplete understanding of the genetic mechanisms that control pathogenesis and recovery. Identifying the molecular and genetic regulators unique to nephron segments that dictate vulnerability to injury and regenerative potential could lead to new therapeutic targets to treat ischemic kidney injury. Pax2 and Pax8 are homologous transcription factors with overlapping functions that are critical for kidney development and are re-activated in AKI. Here, we examined the role of Pax2 and Pax8 in recovery from ischemic AKI and found them upregulated after severe AKI and correlated with chronic injury. Surprisingly, proximal-tubule-selective deletion of Pax2 and Pax8 resulted in a less severe chronic injury phenotype. This effect was mediated by protection against the acute insult, similar to pre-conditioning. Prior to injury, Pax2 and Pax8 mutant mice develop a unique subpopulation of proximal tubule cells in the S3 segment that displayed features usually seen only in acute or chronic injury. The expression signature of these cells was strongly enriched with genes associated with other mechanisms of protection against ischemic AKI including caloric restriction, hypoxic pre-conditioning, and female sex. Thus, our results identified a novel role for Pax2 and Pax8 in mature proximal tubules that regulates critical genes and pathways involved in both the injury response and protection from ischemic AKI.

Renal-specific loss of ferroportin disrupts iron homeostasis and attenuates recovery from acute kidney injury

Chronic kidney disease is increasing at an alarming rate and correlates with the increase in diabetes, obesity, and hypertension that disproportionately impact socioeconomically disadvantaged communities. Iron plays essential roles in many biological processes including oxygen transport, mitochondrial function, cell proliferation, and regeneration. However, excess iron induces the generation and propagation of reactive oxygen species, which lead to oxidative stress, cellular damage, and ferroptosis. Iron homeostasis is regulated in part by the kidney through iron resorption from the glomerular filtrate and exports into the plasma by ferroportin (FPN). Yet, the impact of iron overload in the kidney has not been addressed. To test more directly whether excess iron accumulation is toxic to kidneys, we generated a kidney proximal tubule-specific knockout of FPN. Despite significant intracellular iron accumulation in FPN mutant tubules, basal kidney function was not measurably different from wild type kidneys. However, upon induction of acute kidney injury (AKI), FPN mutant kidneys exhibited significantly more damage and failed recovery, evidence for ferroptosis, and increased fibrosis. Thus, disruption of iron export in proximal tubules, leading to iron overload, can significantly impair recovery from AKI and can contribute to progressive renal damage indicative of chronic kidney disease. Understanding the mechanisms that regulate iron homeostasis in the kidney may provide new therapeutic strategies for progressive kidney disease and other ferroptosis-associated disorders.NEW & NOTEWORTHY Physiological iron homeostasis depends in part on renal resorption and export into the plasma. We show that specific deletion of iron exporters in the proximal tubules sensitizes cells to injury and inhibits recovery. This can promote a chronic kidney disease phenotype. Our paper demonstrates the need for iron balance in the proximal tubules to maintain and promote healthy recovery after acute kidney injury.

2, 2-dimethylthiazolidine hydrochloride protects against experimental contrast-induced acute kidney injury via inhibition of tubular ferroptosis

Contrast-induced acute kidney injury (CI-AKI) has become the third leading cause of AKI acquired in hospital, lacking of effective interventions. In the study, we identified the renal beneficial role of 2, 2-dimethylthiazolidine hydrochloride (DMTD), a safer compound which is readily hydrolyzed to cysteamine, in the rodent model of CI-AKI. Our data showed that administration of DMTD attenuated the impaired renal function and tubular injury induced by the contrast agent. Levels of MDA, 4-hydroxynonenal, ferrous iron and morphological signs showed that contrast agent induced ferroptosis, which could be inhibited in the DMTD group. In vitro, DMTD suppressed ferroptosis induced by ioversol in the cultured tubular cells. Treatment of DMTD upregulated glutathione (GSH) and glutathione peroxidase 4 (GPX4). Moreover, we found that DMTD promoted the ubiquitin-mediated proteasomal degradation of Keap1, and thus increased the activity of nuclear factor erythroid 2-related factor 2 (Nrf2). Mechanistically, increase of the ubiquitylation degradation of Keap1 mediates the upregulated effect of DMTD on Nrf2. Consequently, activated Nrf2/Slc7a11 results in the increase of GSH and GPX4, and therefore leads to the inhibition of ferroptosis. Herein, we imply DMTD as a potential therapeutic agent for the treatment of CI-AKI.

Module 4-Deficient CCN2/Connective Tissue Growth Factor Attenuates the Progression of Renal Fibrosis via Suppression of Focal Adhesion Kinase Phosphorylation in Tubular Epithelial Cells

CCN2/connective tissue growth factor (CTGF) potentially serves as a therapeutic target for chronic kidney disease. Here we investigated CCN2 module-4, encoded by Ccn2 exon 5, through the generation of Ccn2 exon 5 knockout mice (Ex5-/- mice). To investigate renal fibrosis pathogenesis, Ex5-/- mice were employed to model unilateral ureteral obstruction (UUO), unilateral ischemic-reperfusion injury (UIRI), and 5/6 nephrectomy. Interstitial fibrosis was significantly attenuated in the Ex5-/- mice in the three models. Furthermore, phosphorylated focal adhesion kinase (FAK) levels in tubular epithelial cells were significantly lower in the kidneys of the UUO- and UIRI-Ex5-/- mice than those of the Ex5+/+ mice. Moreover, CCN2 module 4-mediated renal tubule FAK and promoted fibrosis. These findings indicate that CCN2 module-4-FAK pathway components will serve as therapeutic targets for effectively attenuating renal fibrosis.

Pax Protein Depletion in Proximal Tubules Triggers Conserved Mechanisms of Resistance to Acute Ischemic Kidney Injury and Prevents Transition to Chronic Kidney Disease

Acute kidney injury (AKI) is a common condition that lacks effective treatments. In part this shortcoming is due to an incomplete understanding of the genetic mechanisms that control pathogenesis and recovery. Pax2 and Pax8 are homologous transcription factors with overlapping functions that are critical for kidney development and are re-activated in AKI. In this report, we examined the role of Pax2 and Pax8 in recovery from ischemic AKI. We found that Pax2 and Pax8 are upregulated after severe AKI and correlate with chronic injury. Surprisingly, we then discovered that proximal-tubule-selective deletion of Pax2 and Pax8 resulted in a less severe chronic injury phenotype. This effect was mediated by protection against the acute insult, similar to preconditioning. Prior to injury, Pax2 and Pax8 mutant mice develop a unique subpopulation of S3 proximal tubule cells that display features usually seen only in acute or chronic injury. The expression signature of these cells was strongly enriched with genes associated with other mechanisms of protection against ischemic AKI including caloric restriction, hypoxic preconditioning, and female sex. Taken together, our results identify a novel role for Pax2 and Pax8 in mature proximal tubules that regulates critical genes and pathways involved in both injury response and protection from ischemic AKI.

TRANSLATIONAL STATEMENT

Identifying the molecular and genetic regulators unique to the nephron that dictate vulnerability to injury and regenerative potential could lead to new therapeutic targets to treat ischemic kidney injury. Pax2 and Pax8 are two homologous nephron-specific transcription factors that are critical for kidney development and physiology. Here we report that proximal-tubule-selective depletion of Pax2 and Pax8 protects against both acute and chronic injury and induces an expression profile in the S3 proximal tubule with common features shared among diverse conditions that protect against ischemia. These findings highlight a new role for Pax proteins as potential therapeutic targets to treat AKI.

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

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

P53 and VEGF are promising biomarkers for sorafenib efficacy in an experimental model of NASH-related HCC

The efficacy of systemic therapy for hepatocellular carcinoma (HCC) related to non-alcoholic steatohepatitis (NASH) is poorly understood. In this study we evaluated the effects of sorafenib based on the expression of molecular markers related to major hepatocarcinogenesis pathways and angiogenesis in a NASH-related HCC model. Forty male rats were submitted to NASH-HCC induction through the combination of a high-fat and choline deficient diet and diethylnitrosamine (100 mg/L) administration in the drinking water for 13 and 16 weeks. After the induction period, the rats received daily gavage administration of saline solution (control) or Sorafenib (5 mg/kg/day) for 3 weeks. Thereafter, the animals were euthanized and samples from liver nodules were collected for histopathological analysis and immunohistochemical assessment of HEP-PAR-1, glutamine-synthetase, VEGF, survivin, β-catenin and p53. A semi-quantitative score was used for VEGF, survivin and β-catenin analysis. For p53, the percentage of positive cells was determined. Results were processed by Wilcoxon's test or Student's t-test. Both protocols efficiently induced HCC, most of them being moderately to poorly differentiated. Sorafenib-treated animals showed a decreased expression of VEGF and p53 in HCCs generated at 13 weeks when compared to control animals (p = 0.03; p = 0.04, respectively). No significant difference in β-catenin and survivin were observed. There was a significant decrease in VEGF and p53 expression when comparing the two control groups (13 vs. 16 weeks, p < 0.01). p53 and VEGF are promising biomarkers for assessment of efficacy of Sorafenib, whereas survivin and β-catenin were not found useful. Decreased immunohistochemical expression of p53 and VEGF in the 16 week control group may indicate a different metabolic status of HCC.

The Apoptosis Inhibitor Protein Survivin Is a Critical Cytoprotective Resistor against Silica-Based Nanotoxicity

Exposure to nanoparticles is inevitable as they become widely used in industry, cosmetics, and foods. However, knowledge of their (patho)physiological effects on biological entry routes of the human body and their underlying molecular mechanisms is still fragmented. Here, we examined the molecular effects of amorphous silica nanoparticles (aSiNPs) on cell lines mimicking the alveolar-capillary barrier of the lung. After state-of-the-art characterization of the used aSiNPs and the cell model, we performed cell viability-based assays and a protein analysis to determine the aSiNP-induced cell toxicity and underlying signaling mechanisms. We revealed that aSiNPs induce apoptosis in a dose-, time-, and size-dependent manner. aSiNP-induced toxicity involves the inhibition of pro-survival pathways, such as PI3K/AKT and ERK signaling, correlating with reduced expression of the anti-apoptotic protein Survivin on the protein and transcriptional levels. Furthermore, induced Survivin overexpression mediated resistance against aSiNP-toxicity. Thus, we present the first experimental evidence suggesting Survivin as a critical cytoprotective resistor against silica-based nanotoxicity, which may also play a role in responses to other NPs. Although Survivin's relevance as a biomarker for nanotoxicity needs to be demonstrated in vivo, our data give general impetus to investigate the pharmacological modulation of Survivin`s functions to attenuate the harmful effects of acute or chronic inhalative NP exposure.

NRF2 Deficiency Attenuates Diabetic Kidney Disease in Db/Db Mice via Down-Regulation of Angiotensinogen, SGLT2, CD36, and FABP4 Expression and Lipid Accumulation in Renal Proximal Tubular Cells

The role(s) of nuclear factor erythroid 2-related factor 2 (NRF2) in diabetic kidney disease (DKD) is/are controversial. We hypothesized that Nrf2 deficiency in type 2 diabetes (T2D) db/db mice (db/dbNrf2 knockout (KO)) attenuates DKD progression through the down-regulation of angiotensinogen (AGT), sodium-glucose cotransporter-2 (SGLT2), scavenger receptor CD36, and fatty -acid-binding protein 4 (FABP4), and lipid accumulation in renal proximal tubular cells (RPTCs). Db/dbNrf2 KO mice were studied at 16 weeks of age. Human RPTCs (HK2) with NRF2 KO via CRISPR-Cas9 genome editing and kidneys from patients with or without T2D were examined. Compared with db/db mice, db/dbNrf2 KO mice had lower systolic blood pressure, fasting blood glucose, kidney hypertrophy, glomerular filtration rate, urinary albumin/creatinine ratio, tubular lipid droplet accumulation, and decreased expression of AGT, SGLT2, CD36, and FABP4 in RPTCs. Male and female mice had similar results. NRF2 KO attenuated the stimulatory effect of the Nrf2 activator, oltipraz, on AGT, SGLT2, and CD36 expression and high-glucose/free fatty acid (FFA)-stimulated lipid accumulation in HK2. Kidneys from T2D patients exhibited markedly higher levels of CD36 and FABP4 in RPTCs than kidneys from non-diabetic patients. These data suggest that NRF2 exacerbates DKD through the stimulation of AGT, SGLT2, CD36, and FABP4 expression and lipid accumulation in RPTCs of T2D.

TP53RK Drives the Progression of Chronic Kidney Disease by Phosphorylating Birc5

Renal fibrosis is a common characteristic of various chronic kidney diseases (CKDs) driving the loss of renal function. During this pathological process, persistent injury to renal tubular epithelial cells and activation of fibroblasts chiefly determine the extent of renal fibrosis. In this study, the role of tumor protein 53 regulating kinase (TP53RK) in the pathogenesis of renal fibrosis and its underlying mechanisms is investigated. TP53RK is upregulated in fibrotic human and animal kidneys with a positive correlation to kidney dysfunction and fibrotic markers. Interestingly, specific deletion of TP53RK either in renal tubule or in fibroblasts in mice can mitigate renal fibrosis in CKD models. Mechanistic investigations reveal that TP53RK phosphorylates baculoviral IAP repeat containing 5 (Birc5) and facilitates its nuclear translocation; enhanced Birc5 displays a profibrotic effect possibly via activating PI3K/Akt and MAPK pathways. Moreover, pharmacologically inhibiting TP53RK and Birc5 using fusidic acid (an FDA-approved antibiotic) and YM-155(currently in clinical phase 2 trials) respectively both ameliorate kidney fibrosis. These findings demonstrate that activated TP53RK/Birc5 signaling in renal tubular cells and fibroblasts alters cellular phenotypes and drives CKD progression. A genetic or pharmacological blockade of this axis serves as a potential strategy for treating CKDs.

Acute kidney injury in diabetes mellitus: Epidemiology, diagnostic, and therapeutic concepts

Acute kidney injury (AKI) and diabetes mellitus (DM) are public health problems that cause a high socioeconomic burden worldwide. In recent years, the landscape of AKI etiology has shifted: Emerging evidence has demonstrated that DM is an independent risk factor for the onset of AKI, while an alternative perspective considers AKI as a bona fide complication of DM. Therefore, it is necessary to systematically characterize the features of AKI in DM. In this review, we summarized the epidemiology of AKI in DM. While focusing on circulation- and tissue-specific microenvironment changes after DM, we described the active cellular and molecular mechanisms of increased kidney susceptibility to AKI under DM stress. We also reviewed the current diagnostic and therapeutic strategies for AKI in DM recommended in the clinic. Updated recognition of the epidemiology, pathophysiology, diagnosis, and medications of AKI in DM is believed to reveal a path to mitigate the frequency of AKI and DM comorbidity that will ultimately improve the quality of life in DM patients.

Longitudinal associations of serum survivin with the severity and prognosis of community-acquired pneumonia patients

BACKGROUND

Survivin is a member of apoptosis inhibitor proteins that evokes cellular proliferation and inhibits apoptosis. However, the role of survivin in community-acquired pneumonia (CAP) patients remains to be firmly established. The aim of this cohort study was to evaluate the correlations of serum survivin with the severity and prognosis of CAP patients.

METHODS

This research included 470 eligible CAP patients. Serum fasting samples were drawn from patients, and serum survivin was measured by enzyme-linked immunosorbent assay (ELISA). Meanwhile, demographic characteristics and clinical information were collected. The prognosis of CAP patients was tracked.

RESULTS

Serum survivin gradually decreased with elevated CAP severity scores. Additionally, the correlative analysis suggested that serum survivin was associated with many clinical characteristics. Furthermore, mixed linear and logistic regression models indicated that serum survivin was negatively associated with severity. After adjusting for confounding factors, logistic regression analyses found that lower serum survivin on admission elevated the risks of mechanical ventilation, vasoactive agent usage, longer hospital stays, ICU admission, and even death during hospitalization. Serum survivin in combination with CAP severity scores elevated the predictive capacities for severity and death in CAP patients compared with a single indicator.

CONCLUSION

On admission, there are inverse dose-response associations of serum survivin with severity and poor prognosis in CAP patients, demonstrating that serum survivin may be involved in the pathophysiology process of CAP. Serum survivin may serve as a potential biomarker for disease evaluation and prognosis in CAP patients.

T cell depletion increases humoral response by favoring T follicular helper cells expansion

Antibody-mediated rejection is a major cause of long-term graft loss in kidney transplant patients. T follicular helper (Tfh) cells are crucial for assisting B cell differentiation and are required for an efficient antibody response. Anti-thymocyte globulin (ATG) is a widely used lymphocyte-depleting induction therapy. However, less is known about how ATG affects Tfh cell development and donor-specific antibody (DSA) formation. We observed an increase in circulating Tfh cells at 6 months after kidney transplant in patients who received ATG. Using an NP-OVA immunization model, we found that ATG-treated mice had a higher percentage of Tfh cells, germinal center B cells, and higher titers of antigen-specific antibodies compared to controls. ATG-treated animals had lower levels of IL-2, a known Bcl-6 repressor, but higher levels of IL-21, pSTAT3 and Bcl-6, favoring Tfh differentiation. In a mouse kidney transplant model, ATG-treated recipients showed an increase in Tfh cells, DSA and C4d staining in the allograft. Although ATG was effective in depleting T cells, it favored the expansion of Tfh cells following depletion. Concomitant use of IL-2, tacrolimus, or rapamycin with ATG was essential to control Tfh cell expansion. In summary, ATG depletion favors Tfh expansion, enhancing antibody-mediated response.

Nanoformulation of a carbon monoxide releasing molecule protects against cyclosporin A-induced nephrotoxicity and renal fibrosis via the suppression of the NLRP3 inflammasome mediated TGF-β/Smad pathway

Cyclosporin A (CsA) induced nephrotoxicity i.e., renal fibrosis is a critical clinical problem in renal transplant patients, in which chronic inflammatory response is the major cause. Previously, we developed a nano-drug delivery system for carbon monoxide (CO), a multi-functional gaseous molecule with a potent anti-inflammatory effect, i.e., SMA/CORM2, which showed therapeutic potential in several inflammatory disease models. Accordingly, in this study, we explored the potential and usefulness of SMA/CORM2 on CsA induced renal fibrosis. When mice were exposed to CsA for 4 weeks, severe injuries in the kidney as revealed by decreased kidney function and histological examination, and activation of NLRP3 inflammasome, as well as renal fibrosis along with the upregulation of transforming growth factor β (TGFβ)/Smad signaling molecule were observed, whereas SMA/CORM2 (1 mg/kg) treatment remarkably ameliorated the inflammatory injury and fibrosis in the kidney. CO is the major effector molecule of SMA/CORM2 which significantly suppressed the activation of NLRP3 inflammasome, and induced the downregulation of TGFβ/Smad signaling. Inhibition of NLRP3 inflammasome by its inhibitor MCC950 also similarly decreased TGFβ/Smad expression and subsequently improved kidney injury and renal fibrosis, suggesting SMA/CORM2 induced suppression of TGFβ/Smad signaling and renal signaling via an NLRP3 inflammasome-dependent pathway. Compared to native CORM2, SMA/CORM2 exhibited better therapeutic/preventive effects owing to its superior water-solubility and bioavailability. These findings strongly indicated the applicability of SMA/CORM2 as an enhanced permeability and retention (EPR) effect-based nanomedicine for CsA induced renal fibrosis as well as other inflammatory diseases. STATEMENT OF SIGNIFICANCE: Carbon monoxide (CO) is an important gaseous signaling molecule that plays a crucial role in the maintenance of homeostasis. Because of its versatile functions, it exhibits the potential as the target molecule for many diseases, including inflammatory diseases and cancer. The development of stable and disease-targeted delivery systems of CO is thus of interest and importance. Previously we developed a nano micellar CO donor SMA/CORM2 which shows superior bioavailability and therapeutic potential in many inflammatory disease models. We reported here, SMA/CORM2, through controlled release of CO, greatly ameliorated CsA-induced renal fibrosis via suppressing the NLRP3 inflammasome mediated TGF-β/Smad pathway. These findings suggest a new anti-inflammatory mechanism of CO, which also provides a new approach for controlling CsA-induced nephrotoxicity.

Inflammation-sensing catalase-mimicking nanozymes alleviate acute kidney injury via reversing local oxidative stress

Background

The reactive oxygen species (ROS) and inflammation, a critical contributor to tissue damage, is well-known to be associated with various disease. The kidney is susceptible to hypoxia and vulnerable to ROS. Thus, the vicious cycle between oxidative stress and renal hypoxia critically contributes to the progression of chronic kidney disease and finally, end-stage renal disease. Thus, delivering therapeutic agents to the ROS-rich inflammation site and releasing the therapeutic agents is a feasible solution.

Results

We developed a longer-circulating, inflammation-sensing, ROS-scavenging versatile nanoplatform by stably loading catalase-mimicking 1-dodecanethiol stabilized Mn₃O₄ (dMn₃O₄) nanoparticles inside ROS-sensitive nanomicelles (PTC), resulting in an ROS-sensitive nanozyme (PTC-M). Hydrophobic dMn₃O₄ nanoparticles were loaded inside PTC micelles to prevent premature release during circulation and act as a therapeutic agent by ROS-responsive release of loaded dMn₃O₄ once it reached the inflammation site.

Conclusions

The findings of our study demonstrated the successful attenuation of inflammation and apoptosis in the IRI mice kidneys, suggesting that PTC-M nanozyme could possess promising potential in AKI therapy. This study paves the way for high-performance ROS depletion in treating various inflammation-related diseases.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01410-z.

Dietary intake of n-3 polyunsaturated fatty acids alters the lipid mediator profile of the kidney but does not attenuate renal insufficiency

The efficacy of n-3 polyunsaturated fatty acids (PUFAs) in improving outcomes in a renal ischemia-reperfusion injury (IRI) model has previously been reported. However, the underlying mechanisms remain poorly understood and few reports demonstrate how dietary n-3 PUFAs influence the composition of membrane phospholipids in the kidney. Additionally, it has not been elucidated whether perilla oil (PO), which is mainly composed of the n-3 alpha-linolenic acid, mitigates renal IRI. In this study, we investigated the effect of dietary n-3 PUFAs (PO), compared with an n-6 PUFA-rich soybean oil (SO) diet, on IRI-induced renal insufficiency in a rat model. Levels of membrane phospholipids containing n-3 PUFAs were higher in the kidney of PO-rich diet-fed rats than the SO-rich diet-fed rats. Levels of blood urea nitrogen and serum creatinine were significantly higher in the ischemia-reperfusion group than the sham group under both dietary conditions. However, no significant differences were observed in blood urea nitrogen, serum creatinine, or histological damage between PO-rich diet-fed rats and SO-rich diet-fed rats. In the kidney of PO-rich diet-fed rats, levels of arachidonic acid and arachidonic acid-derived pro-inflammatory lipid mediators were lower than SO-rich diet-fed rats. Eicosapentaenoic acid and eicosapentaenoic acid-derived lipid mediators were significantly higher in the kidney of PO-rich than SO-rich diet-fed rats. These results suggest that dietary n-3 PUFAs alter the fatty acid composition of membrane phospholipids and lipid mediators in the kidney; however, this does not attenuate renal insufficiency or histological damage in a renal IRI model.

Renal subcapsular delivery of PGE2 promotes kidney repair by activating endogenous Sox9+ stem cells

Prostaglandin E₂ (PGE₂) has recently been recognized to play a role in immune regulation and tissue regeneration. However, the short half-life of PGE₂ limits its clinical application. Improving the delivery of PGE₂ specifically to the target organ with a prolonged release method is highly desirable. Taking advantage of the adequate space and proximity of the renal parenchyma, renal subcapsular delivery allows minimally invasive and effective delivery to the entire kidney. Here, we report that by covalently cross-linking it to a collagen matrix, PGE₂ exhibits an adequate long-term presence in the kidney with extensive intraparenchymal penetration through renal subcapsular delivery and significantly improves kidney function. Sox9 cell lineage tracing with intravital microscopy revealed that PGE₂ could activate the endogenous renal progenitor Sox9⁺ cells through the Yap signaling pathway. Our results highlight the prospects of utilizing renal subcapsular-based drug delivery and facilitate new applications of PGE₂-releasing matrices for regenerative therapy.

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PGE₂ exhibits an adequate long-term release by being covalently cross-linked to collagen

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The renal subcapsular space serves as a reservoir for the delivery of PGE₂

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Sox9⁺ renal progenitor cells can be lineage traced intravitally by microscopy

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PGE₂ activates the endogenous renal progenitor Sox9⁺ cells through the YAP pathway

Single-cell RNA sequencing reveals differential cell cycle activity in key cell populations during nephrogenesis

The kidney is a complex organ composed of more than 30 terminally differentiated cell types that all are required to perform its numerous homeostatic functions. Defects in kidney development are a significant cause of chronic kidney disease in children, which can lead to kidney failure that can only be treated by transplant or dialysis. A better understanding of molecular mechanisms that drive kidney development is important for designing strategies to enhance renal repair and regeneration. In this study, we profiled gene expression in the developing mouse kidney at embryonic day 14.5 at single-cell resolution. Consistent with previous studies, clusters with distinct transcriptional signatures clearly identify major compartments and cell types of the developing kidney. Cell cycle activity distinguishes between the "primed" and "self-renewing" sub-populations of nephron progenitors, with increased expression of the cell cycle-related genes Birc5, Cdca3, Smc2 and Smc4 in "primed" nephron progenitors. In addition, augmented expression of cell cycle related genes Birc5, Cks2, Ccnb1, Ccnd1 and Tuba1a/b was detected in immature distal tubules, suggesting cell cycle regulation may be required for early events of nephron patterning and tubular fusion between the distal nephron and collecting duct epithelia.

Tubular Cell Cycle Response upon AKI: Revising Old and New Paradigms to Identify Novel Targets for CKD Prevention

Acute kidney injury (AKI) is characterized by a rapid deterioration of kidney function, representing a global healthcare concern. In addition, AKI survivors frequently develop chronic kidney disease (CKD), contributing to a substantial proportion of disease burden globally. Yet, over the past 30 years, the burden of CKD has not declined to the same extent as many other important non-communicable diseases, implying a substantial deficit in the understanding of the disease progression. The assumption that the kidney response to AKI is based on a high proliferative potential of proximal tubular cells (PTC) caused a critical confounding factor, which has led to a limited development of strategies to prevent AKI and halt progression toward CKD. In this review, we discuss the latest findings on multiple mechanisms of response related to cell cycle behavior of PTC upon AKI, with a specific focus on their biological relevance. Collectively, we aim to (1) provide a new perspective on interpreting cell cycle progression of PTC in response to damage and (2) discuss how this knowledge can be used to choose the right therapeutic window of treatment for preserving kidney function while avoiding CKD progression.

Discovery of Novel Proteomic Biomarkers for the Prediction of Kidney Recovery from Dialysis-Dependent AKI Patients

BACKGROUND

AKI requiring dialysis (AKI-D) is associated with prolonged hospitalization, mortality, and progressive CKD among survivors. Previous studies have examined only select urine or serum biomarkers for predicting kidney recovery from AKI.

METHODS

Serum samples collected on day 8 of randomized RRT from 72 patients enrolled in the Veteran's Affairs/National Institutes of Health Acute Renal Failure Trial Network study were analyzed by the SOMAscan proteomic platform to profile 1305 proteins in each sample. Of these patients, 38 recovered kidney function and dialysis was discontinued, whereas another 34 patients remained on dialysis by day 28.

RESULTS

Differential serum levels of 119 proteins, with 53 higher and 66 lower, were detected in samples from patients who discontinued dialysis, compared with patients who remained on dialysis by day 28. Patients were classified into tertiles on the basis of SOMAscan protein measurements for the 25 proteins most differentially expressed. The association of serum levels of each protein with kidney recovery was further evaluated using logistic regression analysis. Higher serum levels of CXCL11, CXCL2/CXCL3, CD86, Wnt-7a, BTK, c-Myc, TIMP-3, CCL5, ghrelin, PDGF-C, survivin, CA2, IL-9, EGF, and neuregulin-1, and lower levels of soluble CXCL16, IL1RL1, stanniocalcin-1, IL-6, and FGF23 when classified in tertiles were significantly associated with better kidney recovery. This significant association persisted for each of these proteins after adjusting for potential confounding risk factors including age, sex, cardiovascular SOFA score, congestive heart failure, diabetes, modality of intensive dialysis treatment, cause of AKI, baseline serum creatinine, day 8 urine volume, and estimated 60-day mortality risk.

CONCLUSIONS

These results suggest concerted changes between survival-related proteins and immune-regulatory chemokines in regulating angiogenesis, endothelial and epithelial remodeling, and kidney cell regeneration, illustrating potential mechanisms of kidney recovery. Thus, this study identifies potential novel predictive biomarkers of kidney recovery in patients with AKI-D.

FGF21 prevents low-protein diet-induced renal inflammation in aged mice

Low-protein (LP) diets extend lifespan through a comprehensive improvement in metabolic health across multiple tissues and organs. Many of these metabolic responses to protein restriction are secondary to transcriptional activation and release of FGF21 from the liver. However, the effects of an LP diet on the kidney in the context of aging has not been examined. Therefore, the goal of the current study was to investigate the impact of chronic consumption of an LP diet on the kidney in aging mice lacking FGF21. Wild-type (WT; C57BL/6J) and FGF21 knockout (KO) mice were fed a normal protein diet (20% casein) or an LP (5% casein) diet ad libitum from 3 to 22 mo of age. The LP diet led to a decrease in kidney weight and urinary albumin-to-creatinine ratio in both WT and FGF21 KO mice. Although the LP diet produced only mild fibrosis and infiltration of leukocytes in WT kidneys, the effects were significantly exacerbated by the absence of FGF21. Accordingly, transcriptomic analysis showed that inflammation-related pathways were significantly enriched and upregulated in response to LP diet in FGF21 KO mice but not WT mice. Collectively, these data demonstrate that the LP diet negatively affected the kidney during aging, but in the absence of FGF21, the LP diet-induced renal damage and inflammation were significantly worse, indicating a protective role of FGF21 in the kidney.NEW & NOTEWORTHY Long-term protein restriction is not advantageous for an otherwise healthy, aging kidney, as it facilitates the development of renal tubular injury and inflammatory cell infiltration. We provide evidence using FGF21 knockout animals that FGF21 is essential to counteract the renal injury and inflammation during aging on a low-protein diet.

Antioxidant Properties of Alpha-Lipoic (Thioctic) Acid Treatment on Renal and Heart Parenchyma in a Rat Model of Hypertension

Renal and cardiac impairments are frequent events in the presence of hypertension. Organ damage is mainly linked to oxidative stress due to high blood pressure and may be reduced by antioxidant supplementation. Alpha-lipoic acid (ALA) is one of most effective antioxidants. It is widely used as a nutritional supplement in a racemic mixture (+/–), even though the (+)-enantiomer is biologically active. This study was designed to investigate the effect of treatment with (+/–)-ALA and its enantiomers on renal and heart parenchyma in spontaneously hypertensive rats (SHR), using immunochemical and immunohistochemical techniques. The results confirmed that the oxidative mechanisms of organ alterations, due to hypertension, and characterized by glomerular and tubular lesions, left ventricular hypertrophy, and fibrosis but not by apoptosis were accompanied by proteins’ and nucleic acids’ oxidation. We found greater effectiveness of (+)-ALA compared to (+/−)-ALA in reducing oxidative stress, cardiac and renal damages in SHR. To conclude, these data propose (+)-ALA as one of the more appropriate antioxidant molecules to prevent renal and cardiac alterations associated with hypertension.

Dl-3-n-butylphthalide pretreatment attenuates renal ischemia/reperfusion injury

BACKGROUND

Renal ischemia reperfusion injury (IRI) has become a growing concern in clinical practice with high morbidity and mortality rates. There is currently no effective prophylactic regimen available to prevent its occurrence and to improve its clinical prognosis. Dl-3-n-butylphthalide (NBP) has been used for stroke treatment in China for years. Little is known about its role in preventing kidney injury.

METHODS

The kidneys of male C57BL/6J mice were subjected to 33 min of ischemia followed by 24 h of reperfusion. NBP was administered by gavage prior to surgery. The reno-protective effect of NBP was evaluated by serum creatinine, kidney injury markers and renal pathological changes. Furthermore, the inflammation, oxidative stress, and apoptosis markers in kidney tissue were examined. In vitro, HK2 cells were treated prophylactically with NBP and then exposed to hypoxia/reoxygenation (H/R). Cell viability and apoptosis related protein were quantified to verify the protective effect of NBP. Pro-inflammation genes expression as well as ROS generation were further investigated also.

RESULTS

NBP pretreatment significantly improved renal dysfunction and alleviated pathological injury, renal inflammation response, oxidative stress and cell apoptosis. Consistently, NBP attenuated H/R induced increases in ROS, pro-inflammatory genes expression, apoptosis and cleaved caspase-3 levels in HK2 cells.

CONCLUSION

Our promising results validated for the first time that NBP could ameliorate renal IRI via attenuating inflammation, oxidative stress, and apoptosis, which indicated that NBP might be a good candidate against AKI.

PMMA-Based Continuous Hemofiltration Modulated Complement Activation and Renal Dysfunction in LPS-Induced Acute Kidney Injury

Sepsis-induced acute kidney injury (AKI) is a frequent complication in critically ill patients, refractory to conventional treatments. Aberrant activation of innate immune system may affect organ damage with poor prognosis for septic patients. Here, we investigated the efficacy of polymethyl methacrylate membrane (PMMA)-based continuous hemofiltration (CVVH) in modulating systemic and tissue immune activation in a swine model of LPS-induced AKI. After 3 h from LPS infusion, animals underwent to PMMA-CVVH or polysulfone (PS)-CVVH. Renal deposition of terminal complement mediator C5b-9 and of Pentraxin-3 (PTX3) deposits were evaluated on biopsies whereas systemic Complement activation was assessed by ELISA assay. Gene expression profile was performed from isolated peripheral blood mononuclear cells (PBMC) by microarrays and the results validated by Real-time PCR. Endotoxemic pigs presented oliguric AKI with increased tubulo-interstitial infiltrate, extensive collagen deposition, and glomerular thrombi; local PTX-3 and C5b-9 renal deposits and increased serum activation of classical and alternative Complement pathways were found in endotoxemic animals. PMMA-CVVH treatment significantly reduced tissue and systemic Complement activation limiting renal damage and fibrosis. By microarray analysis, we identified 711 and 913 differentially expressed genes with a fold change >2 and a false discovery rate <0.05 in endotoxemic pigs and PMMA-CVVH treated-animals, respectively. The most modulated genes were Granzyme B, Complement Factor B, Complement Component 4 Binding Protein Alpha, IL-12, and SERPINB-1 that were closely related to sepsis-induced immunological process. Our data suggest that PMMA-based CVVH can efficiently modulate immunological dysfunction in LPS-induced AKI.

Blockade of tumor necrosis factor superfamily members CD30 and OX40 abrogates disease activity in murine immune-mediated glomerulonephritis

Co-stimulation is a prerequisite for pathogenic activity in T cell-mediated diseases and has been demonstrated to achieve tolerance in organ-specific autoimmunity as a therapeutic target. Here, we evaluated the involvement of the tumor necrosis factor family members CD30 and OX40 in immune-complex mediated kidney disease. In vitro stimulation and proliferation studies were performed with CD4⁺ cells from wild type and CD30/OX40 double knock-out (CD30OX40^-/-) mice. In vivo studies were performed by induction of nephrotoxic serum nephritis in wild type, CD30OX40^{- /-} , CD30^-/-, OX40^-/-, reconstituted Rag1^-/- and C57Bl/6J mice treated with αCD30L αOX40L antibodies. CD30, OX40 and their ligands were upregulated on various leukocytes in nephrotoxic serum nephritis. CD30OX40^-/- mice, but not CD30^-/- or OX40^-/- mice were protected from nephrotoxic serum nephritis. Similar protection was found in Rag1^-/- mice injected with CD4⁺ T cells from CD30OX40^-/- mice compared to Rag1^-/- mice injected with CD4⁺ T cells from wild type mice. Furthermore, CD4⁺ T cells deficient in CD30OX40^-/- displayed decreased expression of CCR6 in vivo. CD30OX40^-/- cells were fully capable of differentiating into disease mediating T helper cell subsets, but showed significantly decreased levels of proliferation in vivo and in vitro compared to wild type cells. Blocking antibodies against CD30L and OX40L ameliorated nephrotoxic serum nephritis without affecting pan-effector or memory T cell populations. Thus, our results indicate disease promotion via CD30 and OX40 signaling due to facilitation of exaggerated T cell proliferation and migration of T helper 17 cells in nephrotoxic serum nephritis. Hence, co-stimulation blockade targeting the CD30 and OX40 signaling pathways may provide a novel therapeutic strategy in autoimmune kidney disease.

Knockout of Trpa1 Exacerbates Renal Ischemia-Reperfusion Injury With Classical Activation of Macrophages

BACKGROUND

Classically activated macrophages contribute to the development of renal ischemia-reperfusion injury (IRI). This study aimed to investigate the role of transient receptor potential ankyrin 1 (Trpa1), a regulator of macrophage activation, in IRI-induced acute kidney injury (AKI) by using the Trpa1 gene knockout (Trpa1-/-) mouse model.

METHODS

Male 8-week-old Trpa1-/- mice and wild-type (WT) littermates were subjected to renal ischemia for 35 minutes by clamping bilateral renal pedicles under isoflurane anesthesia, and blood and tissue samples were collected 24 hours after reperfusion and analyzed with histological and molecular measurements.

RESULTS

Following IRI, Trpa1-/- mice developed more deteriorated biochemical and morphological signs of AKI when comparing with WT mice. More classically activated M1 macrophages were found in the kidneys of Trpa1-/- mice comparing with WT mice after IRI, while the counts of alternatively activated M2 macrophages in the kidney were similar between the 2 strains after IRI. Furthermore, significantly higher expression levels of proinflammatory markers including interleukin-1 beta and tumor necrosis factor alpha were detected in the kidney of Trpa1-/- mice compared with WT mice after IRI. The levels of TRPA1 protein in the kidney of WT mice were also decreased after IRI.

CONCLUSIONS

Our results show that ablation of Trpa1 exacerbates infiltration of classically activated macrophages, renal inflammation, and renal injury in mice after IRI. These findings suggest that activation of TRPA1 may protect against IRI-induced AKI via regulation of macrophage-mediated inflammatory pathway.

Nuclear exclusion of YAP exacerbates podocyte apoptosis and disease progression in Adriamycin-induced focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a chronic glomerular disease with poor clinical outcomes. Podocyte loss via apoptosis is one important mechanism underlying the pathogenesis of FSGS. Recently, Yes-associated-protein (YAP), a key downstream protein in the Hippo pathway, was identified as an activator for multiple gene transcriptional factors in the nucleus to control cell proliferation and apoptosis. To investigate the potential role of YAP in the progression of FSGS, we examined kidney samples from patients with minimal change disease or FSGS and found that increases in podocyte apoptosis is positively correlated with the cytoplasmic distribution of YAP in human FSGS. Utilizing an established mT/mG transgenic mouse model and primary cultured podocytes, we found that YAP was distributed uniformly in nucleus and cytoplasm in the podocytes of control animals. Adriamycin treatment induced gradual nuclear exclusion of YAP with enhanced phospho-YAP/YAP ratio, accompanied by the induction of podocyte apoptosis both in vivo and in vitro. Moreover, we used verteporfin to treat an Adriamycin-induced FSGS mouse model, and found YAP inhibition by verteporfin induced nuclear exclusion of YAP, thus increasing podocyte apoptosis and accelerating disease progression. Therefore, our findings suggest that YAP nuclear distribution and activation in podocytes is an important endogenous anti-apoptotic mechanism during the progression of FSGS.

Protective effect of taraxasterol on ischemia/reperfusion-induced acute kidney injury via inhibition of oxidative stress, inflammation, and apoptosis

Ischemia/reperfusion injury (IRI), the most common cause of acute kidney injury (AKI), is correlated with oxidative stress and subsequent inflammation. Taraxasterol, a natural product, has been shown to exert anti-oxidative and anti-inflammatory effects. However, the role of taraxasterol in renal IRI remains unknown. In this study, mice were subjected to 30 min of bilateral renal ischemia-reperfusion to induce AKI. Cellular hypoxia/reoxygenation (H/R) was used to mimic IRI in vitro. Western blotting, immunochemistry, immunofluorescence, TUNEL staining, ELISA, and flow cytometry were performed to evaluate kidney damage, oxidative stress, inflammation, and apoptosis in vivo and in vitro. Treatment with taraxasterol attenuated the following in a dose-dependent manner: tubular damage; infiltration of F4/80-positive macrophages; renal interstitial fibrosis; myeloperoxidase (MPO) activity; and expression of the inflammatory cytokines tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and monocyte chemoattractant protein-1 (MCP-1). Moreover, taraxasterol treatment remarkably ameliorated apoptosis in the kidney by decreasing Bax expression and conserving Bcl2. Notably, MitoSOX assay revealed that treatment with taraxasterol suppressed the production of mitochondrial reactive oxygen species. Furthermore, taraxasterol suppressed phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) of the mitogen-activated protein kinase (MAPK) signaling pathways in vivo and in vitro. In conclusion, these findings indicate that taraxasterol has a protective effect on IRI-induced AKI via inhibition of oxidative stress, inflammation, and apoptosis.

Protective Effects of Simvastatin on Endotoxin-Induced Acute Kidney Injury through Activation of Tubular Epithelial Cells' Survival and Hindering Cytochrome C-Mediated Apoptosis

Increasing evidence suggests that apoptosis of tubular cells and renal inflammation mainly determine the outcome of sepsis-associated acute kidney injury (AKI). The study aim was to investigate the molecular mechanism involved in the renoprotective effects of simvastatin in endotoxin (lipopolysaccharide, LSP)-induced AKI. A sepsis model was established by intraperitoneal injection of a single non-lethal LPS dose after short-term simvastatin pretreatment. The severity of the inflammatory injury was expressed as renal damage scores (RDS). Apoptosis of tubular cells was detected by Terminal deoxynucleotidyl transferase-mediated dUTP Nick End Labeling (TUNEL assay) (apoptotic DNA fragmentation, expressed as an apoptotic index, AI) and immunohistochemical staining for cleaved caspase-3, cytochrome C, and anti-apoptotic Bcl-xL and survivin. We found that endotoxin induced severe renal inflammatory injury (RDS = 3.58 ± 0.50), whereas simvastatin dose-dependently prevented structural changes induced by LPS. Furthermore, simvastatin 40 mg/kg most profoundly attenuated tubular apoptosis, determined as a decrease of cytochrome C, caspase-3 expression, and AIs (p  <  0.01 vs. LPS). Conversely, simvastatin induced a significant increase of Bcl-XL and survivin, both in the strong inverse correlations with cleaved caspase-3 and cytochrome C. Our study indicates that simvastatin has cytoprotective effects against LPS-induced tubular apoptosis, seemingly mediated by upregulation of cell-survival molecules, such as Bcl-XL and survivin, and inhibition of the mitochondrial cytochrome C and downstream caspase-3 activation.

Specific expression of survivin, SOX9, and CD44 in renal tubules in adaptive and maladaptive repair processes after acute kidney injury in rats

Acute kidney injury (AKI) is thought to be a reversible condition; however, growing evidence has suggested that AKI may be associated with subsequent development of chronic kidney disease. Although renal tubules have intrinsic regeneration capacity, disruption of the regeneration mechanisms leads to irreversible interstitial fibrosis. In this study, we investigated immunohistochemical markers of renal tubules in adaptive and maladaptive repair processes to predict AKI reversibility. Histopathological analysis demonstrated that regenerative tubules and dilated tubules were observed in the kidneys of AKI model rats after ischemia/reperfusion (I/R). Regenerative tubules gradually redifferentiated after I/R, whereas dilated tubules exhibited no tendency for redifferentiation. In fibrotic areas of the kidney in renal fibrosis model rats subjected to I/R, renal tubules were dilated or atrophied. There results suggested that the histopathological features of renal tubules in the maladaptive repair were dilation or atrophy. From microarray data of regenerative tubules, survivin, SOX9, and CD44 were extracted as candidate markers. Immunohistochemical analysis demonstrated that survivin and SOX9 were expressed in regenerative tubules, whereas SOX9 was also detected in renal tubules in fibrotic areas. These findings indicated that survivin and SOX9 contributed to renal tubular regeneration, whereas sustained SOX9 expression may be associated to fibrosis. CD44 was expressed in dilated tubules in the kidneys of AKI model rats and in the tubules of fibrotic areas of renal fibrosis model rats, suggesting that CD44 was expressed in renal tubules in maladaptive repair. Thus, these factors could be useful markers for detecting disruption of the regenerative mechanisms of renal tubules.

Analysis of Differentially Expressed Long Noncoding RNA in Renal Ischemia-Reperfusion Injury

BACKGROUND

Renal ischemia-reperfusion (IR) injury is one of the major causes of acute renal failure which seriously endangers the health and life of patients. Currently, there is still lack of comprehensive knowledge of the molecular mechanism of renal IR injury, and the regulatory role of long noncoding RNA (lncRNA) in renal IR damage remains poorly understood.

AIM

The aim of this study was to analyze the expression spectrum of lncRNA in renal IR damage in mice and to explore specific lncRNA that may be involved in regulating the development of human renal IR injury.

METHODS

RNA-Seq was used to investigate the lncRNA profile of renal IR injury in a mouse model, and conservation analysis was performed on mouse lncRNAs with differential expression (fragments per kilobase of transcript per million mapped reads ≥2) by BLASTN. The potential functions and associated pathways of the differentially expressed lncRNA were explored by bioinformatics analysis. The cell hypoxia model was used to detect the expression of the candidate lncRNA.

RESULTS

Of the 45,923 lncRNA transcripts detected in the samples, and 5,868 lncRNAs were found to be significantly differentially expressed (p < 0.05 and fold change ≥ 2) in 24-h IR kidney tissue compared to the expression in the control group. It was found that 56 differently expressed mouse lncRNA transcripts have human homology by analyzing the conserved sequences. We also found that lncRNA-NONHSAT183385.1 expression significantly increased in HK2 cells after 24 h of hypoxia and increased further 6 h after reoxygenation, and after 24 h of reoxygenation it was dramatically downregulated, indicating that NONHSAT183385.1 may be involved in the pathophysiological process of renal tubular epithelial cells in response to ischemia in human renal IR.

CONCLUSION

Our study revealed differentially expressed lncRNAs in renal IR damage in mice and identified a set of conserved lncRNAs, which would help to explore lncRNAs that may play important regulatory roles in human renal IR injury.

STAT signaling in polycystic kidney disease

The most common form of polycystic kidney disease (PKD) in humans is caused by mutations in the PKD1 gene coding for polycystin1 (PC1). Among the many identified or proposed functions of PC1 is its ability to regulate the activity of transcription factors of the STAT family. Most STAT proteins that have been investigated were found to be aberrantly activated in kidneys in PKD, and some have been shown to be drivers of disease progression. In this review, we focus on the role of signal transducer and activator of transcription (STAT) signaling pathways in various renal cell types in healthy kidneys as compared to polycystic kidneys, on the mechanisms of STAT regulation by PC1 and other factors, and on the possibility to target STAT signaling for PKD therapy.

Does survivin overexpression enhance the efficiency of fibroblast cell-based wound therapy?

Cell-based wound therapy is faced with some limiting factors that decrease the therapeutic efficacy of transplanted cells. In this study, we aimed to genetically modify fibroblast cells with anti-apoptotic Survivin gene (Birc5) before cell transplantation. In vitro, pIRES2-eGFP-Survivin plasmid was transfected into the fibroblast cells and the growth curve was evaluated for transfected and normal cells performing MTT assay. In vivo, two 6-diameter cutaneous wounds were created at mice dorsal skin. Fibrin clot was used as a delivery vehicle to transfer cells into the wound bed. The effects of four treatment groups including (a) Cell-SVV-Clot (b) Cell-GFP-Clot, (c) Normal cell-Clot and, (d) Clot alone were evaluated. After 1,2,3,7 and 14 days post-transplantation, the wounds were photographed for evaluating the wound closure rate and wound samples were obtained. Angiogenesis and formation of granulated tissue were assessed via H&E staining for wound samples. The expression levels of Survivin, VEGF, and bFGF genes were also determined using qRT-PCR. The MTT assay showed similar proliferation potential of transfected cells with normal cells verifying that Survivin had no detrimental effect. Compared to the Normal cell-Clot group, the Survivin overexpression was seen for 3 days in the Cell-SVV-Clot group verifying the cell survival during the early stage of wound healing. The Survivin further upregulated VEGF and bFGF expressions resulting in more angiogenesis and formation of granulated tissue by day 3 and 14. The treated wounds with Cell-SVV-Clot were regenerated with a higher wound closure rate by day 7 compared to Normal cell-Clot and Clot groups. Survivin enhanced wound healing through induction of VEGF and bFGF at particular times post-wounding that led to a more structured-epidermis with higher angiogenesis and granulation tissue formation rate.

Downregulation of serum survivin correlates with increased inflammation, enhanced disease severity and worse prognosis in sepsis patients

This study aimed to determine the role of survivin in sepsis patients.Serum samples of 288 sepsis patients and 290 healthy individuals (as healthy controls) were collected 24 hours within enrollment. Serum survivin and inflammatory cytokines were detected by enzyme-linked immunosorbent assay, and biochemical indexes were recorded. In sepsis patients, acute pathologic and chronic health evaluation II score and sequential organ failure assessment score were evaluated, and 28-day mortality was recorded.Survivin was greatly decreased in sepsis patients compared to healthy controls (P < .001) and it predicted decreased sepsis risk (area under curve (AUC): 0.921, 95% confidence interval (CI): 0.900-0.942). For clinical characteristics of sepsis patients, survivin was negatively correlated with acute pathologic and chronic health evaluation II score (P < .001), score and sequential organ failure assessment score (P < .001), serum creatinine (P < .001), white blood cell (P = .037), C-reactive protein (P < .001), tumor necrosis factor-α (P < .001), interleukin (IL)-1β (P < .001), IL-6 (P < .001), and IL-8 (P < .001), while positively correlated with albumin (P < .001). For prognosis of sepsis patients, survivin was decreased in deaths compared to survivors (P < .001), and it predicted decreased death risk (AUC: 0.625, 95% CI: 0.558-0.692). Meanwhile, accumulating mortality was decreased in survivin high patients compared to survivin low patients (P = .006). However, multivariate logistic regression revealed survivin was not an independent predictive factor for 28-day mortality, indicating it might interact with other independent factors to affect prognosis of sepsis patients.Survivin was decreased in sepsis patients and predicted decreased sepsis risk. Meanwhile, survivin was correlated with declined inflammation, reduced disease severity, and favorable prognosis in sepsis patients.

Enhancer and super-enhancer dynamics in repair after ischemic acute kidney injury

The endogenous repair process can result in recovery after acute kidney injury (AKI) with adaptive proliferation of tubular epithelial cells, but repair can also lead to fibrosis and progressive kidney disease. There is currently limited knowledge about transcriptional regulators regulating these repair programs. Herein we establish the enhancer and super-enhancer landscape after AKI by ChIP-seq in uninjured and repairing kidneys on day two after ischemia reperfusion injury (IRI). We identify key transcription factors including HNF4A, GR, STAT3 and STAT5, which show specific binding at enhancer and super-enhancer sites, revealing enhancer dynamics and transcriptional changes during kidney repair. Loss of bromodomain-containing protein 4 function before IRI leads to impaired recovery after AKI and increased mortality. Our comprehensive analysis of epigenetic changes after kidney injury in vivo has the potential to identify targets for therapeutic intervention. Importantly, our data also call attention to potential caveats involved in use of BET inhibitors in patients at risk for AKI.

Metformin effectively treats Tsc1 deletion-caused kidney pathology by upregulating AMPK phosphorylation

Tuberous sclerosis complex (TSC) is characterized by hamartomatous lesions in multiple organs, with most patients developing polycystic kidney disease and leading to a decline of renal function. TSC is caused by loss-of-function mutations in either Tsc1 or Tsc2 gene, but currently, there is no effective treatment for aberrant kidney growth in TSC patients. By generating a renal proximal tubule-specific Tsc1 gene-knockout (Tsc1 ptKO) mouse model, we observed that Tsc1 ptKO mice developed aberrantly enlarged kidneys primarily due to hypertrophy and proliferation of proximal tubule cells, along with some cystogenesis, interstitial inflammation, and fibrosis. Mechanistic studies revealed inhibition of AMP-activated protein kinase (AMPK) phosphorylation at Thr-172 and activation of Akt phosphorylation at Ser-473 and Thr-308. We therefore treated Tsc1 ptKO mice with the AMPK activator, metformin, by daily intraperitoneal injection. Our results indicated that metformin increased the AMPK phosphorylation, but decreased the Akt phosphorylation. These signaling modulations resulted in inhibition of proliferation and induction of apoptosis in the renal proximal tubule cells of Tsc1 ptKO mice. Importantly, metformin treatment effectively prevented aberrant kidney enlargement and cyst growth, inhibited inflammatory response, attenuated interstitial fibrosis, and protected renal function. The effects of metformin were further confirmed by in vitro experiments. In conclusion, this study indicates a potential therapeutic effect of metformin on Tsc1 deletion-induced kidney pathology, although currently metformin is primarily prescribed to treat patients with type 2 diabetes.

Sitagliptin ameliorates renal tubular injury in diabetic kidney disease via STAT3-dependent mitochondrial homeostasis through SDF-1α/CXCR4 pathway

Mitochondrial abnormalities play critical roles in diabetic tubular injury progression. Dipeptidyl peptidase-4 (DPP4) inhibitors are widely used antihyperglycemic agents that exert renal protective and positive effects against mitochondrial dysfunction in diabetic kidney disease (DKD). However, their underlying mechanism remains unclear. In this study, DPP4 upregulation, mitochondrial fragmentation, and altered mitochondrial dynamics-associated protein expression were observed in the tubules of DBA2/J (D2) diabetic mice with unilateral nephrectomy and in albumin-stimulated tubular cells. The inhibition of DPP4 by sitagliptin (Sita) ameliorated these mitochondrial perturbations both in vivo and in vitro, whereas DPP4 overexpression aggravated mitochondrial fusion-fission disorder and tubular cell injury in albumin-treated HK-2 cells. Downstream of DPP4, the SDF-1α/CXCR4 pathway was significantly suppressed in diabetic tubules. After Sita treatment, this signaling pathway was restored, and the mitochondrial dynamics was improved. Furthermore, a direct interaction between STAT3 and OPA1 was found in the mitochondria of tubular cells, and this effect was weakened by overloading albumin and by CXCR4 siRNA treatment, suggesting a possible link between DPP4-mediated SDF-1α/CXCR4/STAT3 signaling and mitochondrial dysfunction in diabetic tubular cells. The results suggest that a novel mechanism links the DPP4 enzyme to impaired mitochondrial dynamics homeostasis during tubular injury in DKD and highlight that the SDF-1α/CXCR4/STAT3 signaling pathway could become a potential target for managing DKD.

Notch Signaling in Kidney Development, Maintenance, and Disease

Kidney development involves formation of nephrons intricately aligned with the vasculature and connected to a branched network of collecting ducts. Notch signaling plays multiple roles during kidney development involving the formation of nephrons composed of diverse epithelial cell types arranged into tubular segments, all the while maintaining a nephron progenitor niche. Here, we review the roles of Notch signaling identified from rodent kidney development and injury studies, while discussing human kidney diseases associated with aberrant Notch signaling. We also review Notch signaling requirement in maintenance of mature kidney epithelial cell states and speculate that Notch activity regulation mediates certain renal physiologic adaptations.

Heme oxygenase-2 protects against ischemic acute kidney injury: influence of age and sex

Heme oxygenase (HO) activity is exhibited by inducible (HO-1) and constitutive (HO-2) proteins. HO-1 protects against ischemic and nephrotoxic acute kidney injury (AKI). We have previously demonstrated that HO-2 protects against heme protein-induced AKI. The present study examined whether HO-2 is protective in ischemic AKI. Renal ischemia was imposed on young and aged HO-2+/+ and HO-2-/- mice. On days 1 and 2 after renal ischemia, there were no significant differences in renal function between young male HO-2+/+ and HO-2-/- mice, between young female HO-2+/+ and HO-2-/- mice, or between aged female HO-2+/+ and HO-2-/- mice. However, in aged male mice, HO-2 deficiency worsened renal function on days 1 and 2 after ischemic AKI, and, on day 2 after ischemia, such deficiency augmented upregulation of injury-related genes and worsened histological injury. Renal HO activity was markedly decreased in unstressed aged male HO-2-/- mice and remained so after ischemia, despite exaggerated HO-1 induction in HO-2-/- mice after ischemia. Such exacerbation of deficiency of HO-2 protein and HO activity may reflect phosphorylated STAT3, as activation of this proinflammatory transcription factor was accentuated early after ischemia in aged male HO-2-/- mice. This exacerbation may not reflect impaired induction of nephroprotectant genes, since the induction of HO-1, sirtuin 1, and β-catenin was accentuated in aged male HO-2-/- mice after ischemia. We conclude that aged male mice are hypersensitive to ischemic AKI and that HO-2 mitigates such sensitivity. We speculate that this protective effect of HO-2 may be mediated, at least in part, by suppression of phosphorylated STAT3-dependent signaling.

Early activation of fibroblasts is required for kidney repair and regeneration after injury

Acute kidney injury (AKI) is a devastating condition with high morbidity and mortality. AKI is characterized by tubular injury, inflammation, and vascular impairment. However, the role of interstitial fibroblasts in the pathogenesis of AKI is largely unknown. Here, we show that fibroblasts were activated, as defined by vimentin expression, at 1 h after AKI triggered by ischemia-reperfusion injury (IRI). They rapidly entered the cell cycle with Ki-67-positive staining, which started at 1 h and peaked at 12 h after IRI, whereas tubular cell proliferation peaked at 3 d. The trigger for such an early activation of fibroblasts was identified as sonic hedgehog (Shh), which was rapidly induced in renal tubules and could target interstitial fibroblasts. Tubule-specific knockout of Shh in mice inhibited fibroblast activation and aggravated kidney injury and functional decline after IRI. Likewise, pharmacologic inhibition of Shh signaling with cyclopamine also hindered fibroblast activation and exacerbated kidney damage. These studies uncover that tubule-derived Shh triggers the early activation of fibroblasts, which is required for kidney repair and regeneration. Our findings for the first time illustrate a previously unrecognized importance of interstitial fibroblasts in conferring renal protection in AKI.-Zhou, D., Fu, H., Liu, S., Zhang, L., Xiao, L., Bastacky, S. I., Liu, Y. Early activation of fibroblasts is required for kidney repair and regeneration after injury.

Identification of dicarbonyl and L-xylulose reductase as a therapeutic target in human chronic kidney disease

An imbalance of nephroprotective factors and renal damaging molecules contributes to development and progression of chronic kidney disease (CKD). We investigated associations of renoprotective factor gene expression patterns with CKD severity and outcome. Gene expression profiles of 197 previously reported renoprotective factors were analyzed in a discovery cohort in renal biopsies of 63 CKD patients. Downregulation of dicarbonyl and L-xylulose reductase (DCXR) showed the strongest association with disease progression. This significant association was validated in an independent set of 225 patients with nephrotic syndrome from the multicenter NEPTUNE cohort. Reduced expression of DCXR was significantly associated with degree of histological damage as well as with lower estimated glomerular filtration rate and increased urinary protein levels. DCXR downregulation in CKD was confirmed in 3 publicly available transcriptomics data sets in the context of CKD. Expression of DCXR showed positive correlations to enzymes that are involved in dicarbonyl stress detoxification based on transcriptomics profiles. The sodium glucose cotransporter-2 (SGLT2) inhibitors canagliflozin and empagliflozin showed a beneficial effect on renal proximal tubular cells under diabetic stimuli-enhanced DCXR gene expression. In summary, lower expression of the renoprotective factor DCXR in renal tissue is associated with more severe disease and worse outcome in human CKD.

Blocking interleukin-6 trans-signaling protects against renal fibrosis by suppressing STAT3 activation

Rationale: Renal fibrosis is the terminal manifestation of chronic and irreversible renal disease. Effective therapies other than dialysis are extremely limited. In this study, we investigated the potential effects of targeting elevated interleukin-6 (IL-6) levels in the treatment of renal fibrosis.

Methods: Fc-gp130 was used to specifically block IL-6 trans-signaling. Unilateral ureteral occlusion (UUO) and ischemia reperfusion (IR) mouse models were constructed to investigate the therapeutic effect of Fc-gp130 on renal fibrosis. The role of IL-6 trans-signaling and phosphorylation of signal transducer and activator of transcription (STAT) 3 in regulating fibroblast accumulation and extracellular matrix protein deposition were evaluated in cell experiments and mouse models.

Results: The kidneys of mice with UUO were found to have elevated soluble IL-6 receptor (sIL-6R) levels in the progression of fibrosis. Fc-gp130 attenuated renal fibrosis in mice, as evidenced by reductions in tubular atrophy and the production of extracellular matrix protein. Blockade of IL-6 trans-signaling with Fc-gp130 also reduced inflammation levels, immune cell infiltration, and profibrotic cytokines expression in renal tissue, with decreased STAT3 phosphorylation and reduced fibroblast accumulation in the renal tissue. In vitro, Fc-gp130 also reduced the phosphorylation of STAT3 induced by transforming growth factor (TGF)-β1 in fibroblasts. Furthermore, the therapeutic effect of Fc-gp130 was confirmed in a model of acute kidney injury-chronic kidney disease.

Conclusion: Overall, IL-6 trans-signaling may contribute to crucial events in the development of renal fibrosis, and the targeting of IL-6 trans-signaling by Fc-gp130 may provide a novel therapeutic strategy for the treatment of renal fibrosis.