GSK3beta promotes apoptosis after renal ischemic injury

Role of cAMP/pCREB and GSK-3β/NF-κB p65 signaling pathways in the renoprotective effect of mirabegron against renal ischemia-reperfusion injury in rats

Acute kidney injury and other renal disorders are thought to be primarily caused by renal ischemia-reperfusion (RIR). Cyclic adenosine monophosphate (cAMP) has plenty of physiological pleiotropic effects and preserves tissue integrity and functions. This research aimed to examine the potential protective effects of the β3-adrenergic receptors agonist mirabegron in a rat model of RIR and its underlying mechanisms. Male rats enrolled in this work were given an oral dose of 30 mg/kg mirabegron for two days before surgical induction of RIR. Renal levels of kidney injury molecule-1 (KIM-1), monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), Interleukin-10 (IL-10), cAMP, cAMP-responsive element binding protein (pCREB), and glycogen synthase kinase-3 beta (GSK-3β) were assessed along with blood urea nitrogen and serum creatinine. Additionally, caspase-3 and nuclear factor-kappa B (NF-κB) p65 were explored by immunohistochemical analysis. Renal specimens were inspected for histopathological changes. RIR led to renal tissue damage with elevated blood urea nitrogen and serum creatinine levels. The renal KIM-1, MCP-1, TNF-α, and GSK-3β were significantly increased, while IL-10, cAMP, and pCREB levels were reduced. Moreover, upregulation of caspase-3 and NF-κB p65 protein expression was seen in RIR rats. Mirabegron significantly reduced kidney dysfunction, histological abnormalities, inflammation, and apoptosis in the rat renal tissues. Mechanistically, mirabegron mediated these effects via modulation of cAMP/pCREB and GSK-3β/NF-κB p65 signaling pathways. Mirabegron administration could protect renal tissue and maintain renal function against RIR.

Proximal tubular FHL2, a novel downstream target of hypoxia inducible factor 1, is a protector against ischemic acute kidney injury

Four-and-a-half LIM domains protein 2 (FHL2) is an adaptor protein that may interact with hypoxia inducible factor 1α (HIF-1α) or β-catenin, two pivotal protective signaling in acute kidney injury (AKI). However, little is known about the regulation and function of FHL2 during AKI. We found that FHL2 was induced in renal tubular cells in patients with acute tubular necrosis and mice model of ischemia-reperfusion injury (IRI). In cultured renal proximal tubular cells (PTCs), hypoxia induced FHL2 expression and promoted the binding of HIF-1 to FHL2 promoter. Compared with control littermates, mice with PTC-specific deletion of FHL2 gene displayed worse renal function, more severe morphologic lesion, more tubular cell death and less cell proliferation, accompanying by downregulation of AQP1 and Na, K-ATPase after IRI. Consistently, loss of FHL2 in PTCs restricted activation of HIF-1 and β-catenin signaling simultaneously, leading to attenuation of glycolysis, upregulation of apoptosis-related proteins and downregulation of proliferation-related proteins during IRI. In vitro, knockdown of FHL2 suppressed hypoxia-induced activation of HIF-1α and β-catenin signaling pathways. Overexpression of FHL2 induced physical interactions between FHL2 and HIF-1α, β-catenin, GSK-3β or p300, and the combination of these interactions favored the stabilization and nuclear translocation of HIF-1α and β-catenin, enhancing their mediated gene transcription. Collectively, these findings identify FHL2 as a direct downstream target gene of HIF-1 signaling and demonstrate that FHL2 could play a critical role in protecting against ischemic AKI by promoting the activation of HIF-1 and β-catenin signaling through the interactions with its multiple protein partners.

Empagliflozin and pirfenidone confer renoprotection through suppression of glycogen synthase kinase-3β and promotion of tubular regeneration in rats with induced metabolic syndrome

Metabolic syndrome (MetS) is largely coupled with chronic kidney disease (CKD). Glycogen synthase kinase-3β (GSK-3β) pathway drives tubular injury in animal models of acute kidney injury; but its contribution in CKD is still elusive. This study investigated the effect empagliflozin and/or pirfenidone against MetS-induced kidney dysfunction, and to clarify additional underpinning mechanisms particularly the GSK-3β signaling pathway. Adult male rats received 10%w/v fructose in drinking water for 20 weeks to develop MetS, then treated with either drug vehicle, empagliflozin (30 mg/kg/day) and/or pirfenidone (100 mg/kg/day) via oral gavage for subsequent 4 weeks, concurrently with the high dietary fructose. Age-matched rats receiving normal drinking water were used as controls. After 24 weeks, blood and kidneys were harvested for subsequent analyses. Rats with MetS showed signs of kidney dysfunction, structural changes and interstitial fibrosis. Activation of GSK-3β, decreased cyclinD1 expression and enhanced apoptotic signaling were found in kidneys of MetS rats. There was abundant alpha-smooth muscle actin (α-SMA) expression along with up-regulation of TGF-β1/Smad3 in kidneys of MetS rats. These derangements were almost alleviated by empagliflozin or pirfenidone, with evidence that the combined therapy was more effective than either individual drug. This study emphasizes a novel mechanism underpinning the beneficial effects of empagliflozin and pirfenidone on kidney dysfunction associated with MetS through targeting GSK-3β signaling which can mediate the regenerative capacity, anti-apoptotic effects and anti-fibrotic properties of such drugs. These findings recommend the possibility of using empagliflozin and pirfenidone as promising therapies for management of CKD in patients with MetS.

CK1α deficiency impairs mouse uterine adenogenesis by inducing epithelial cell apoptosis through GSK3β pathway and inhibiting Foxa2 expression through p53 pathway†

Uterine glands and their secretions are crucial for conceptus survival and implantation in rodents and humans. In mice, the development of uterine gland known as adenogenesis occurs after birth, whereas the adenogenesis in humans initiates from fetal life and completed at puberty. Uterine adenogenesis involves dynamic epithelial cell proliferation, differentiation, and apoptosis. However, it is largely unexplored about the mechanisms governing adenogenesis. CK1α plays important roles in regulating cell division, differentiation, and death, but it is unknown whether CK1α affects adenogenesis. In the current study, uterus-specific CK1α knockout female mice (Csnk1a1d/d) were infertile resulted from lack of uterine glands. Subsequent analysis revealed that CK1α deletion induced massive apoptosis in uterine epithelium by activating GSK3β, which was confirmed by injections of GSK3β inhibitor SB216763 to Csnk1a1d/d females, and the co-treatment of SB216763 and CK1 inhibitor d4476 on cultured epithelial cells. Another important finding was that our results revealed CK1α deficiency activated p53, which then blocked the expression of Foxa2, an important factor for glandular epithelium development and function. This was confirmed by that Foxa2 expression level was elevated in p53 inhibitor pifithrin-α injected Csnk1a1d/d mouse uterus and in vitro dual-luciferase reporter assay between p53 and Foxa2. Collectively, these studies reveal that CK1α is a novel factor regulating uterine adenogenesis by inhibiting epithelial cell apoptosis through GSK3β pathway and regulating Foxa2 expression through p53 pathway. Uncovering the mechanisms of uterine adenogenesis is expected to improve pregnancy success in humans and other mammals.

Lactoferrin ameliorates carfilzomib-induced renal and pulmonary deficits: Insights to the inflammasome NLRP3/NF-κB and PI3K/Akt/GSK-3β/MAPK axes

AIMS

Carfilzomib, an irreversible proteasome inhibitor, has been increasingly used to treat multiple myeloma worldwide. However, case studies showed its treatment has been associated with cardiac, renal, and pulmonary deleterious effects. Lactoferrin is an iron-binding glycoprotein present in milk. It is a multifunctional protein with antimicrobial activity, antitumor, antioxidant, and anti-inflammatory effects. Thus, this study aimed to assess the protective effects of lactoferrin against carfilzomib-induced nephrotoxicity and pulmonary toxicity, in addition to identifying the possible underlying molecular mechanisms.

MAIN METHODS

Mice were treated with lactoferrin (300 mg/kg/day) concomitantly with carfilzomib (4 mg/kg, i.p.) twice weekly for three weeks. Kidney and lung indices, serum creatinine, blood urea nitrogen (BUN), uric acid, kidney injury molecule-1 (KIM-1), lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and histological examination were assessed. In addition, biochemical analyses of the inflammasome NLRP3/NF-κB and PI3K/Akt/GSK-3β/MAPK axes were conducted.

KEY FINDINGS

Treatment with lactoferrin decreased serum levels of creatinine, BUN, uric acid, KIM-1, ALP, AST, and LDH and reversed carfilzomib-induced histological changes in both kidney and lung. The inflammatory markers NLRP3, p65 NF-kB, caspases1, interleukin-1β, and interleukin-18, as well as the MAPK signaling pathway, were significantly reduced in renal and pulmonary tissues of mice following lactoferrin administration. Moreover, lactoferrin significantly counteracted carfilzomib-induced reduced expression of pAkt and pGSK-3β in both renal and pulmonary tissues.

SIGNIFICANCE

The current study suggests lactoferrin might be a promising candidate for ameliorating carfilzomib-induced nephrotoxicity and pulmonary toxicity.

Novel insights into the augmented effect of curcumin and liraglutide in ameliorating cisplatin-induced nephrotoxicity in rats: Effects on oxidative stress, inflammation, apoptosis and pyroptosis via GSK-3β

Cisplatin dose-dependent nephrotoxicity is a major issue limiting its proper use in cancer treatment. Inflammation, redox imbalance, and dysregulated cell death are the most plausible underlying pathomechanics. Curcumin and the glucagon-like peptide-1 receptor agonist, liraglutide, have been investigated in various experimental models for their antioxidant, anti-inflammatory, and cell death modulatory effects. Hence, this work was designed to investigate curcumin and liraglutide nephroprotective effects and how they behave together against cisplatin-induced acute kidney injury (AKI) in an experimental Wistar rat model. The study comprised 61 rats divided randomly into 6 unequal groups: control I and II, cisplatin-induced nephrotoxicity, curcumin-treated, liraglutide-treated, and co-treated groups. Renal index, serum nephrotoxicity markers (Cr, BUN, NGAL), renal glycogen synthase kinase-3 β (GSK-3β), oxidant/antioxidant parameters (MDA, MPO, GSH, NQO1, HO-1), and inflammatory biomolecules (TNF-α, IL-1β) were assayed. Moreover, renal cleaved-caspase3 and the pyroptotic biomolecules (nod-like receptor family pyrin domain containing 3, gasdermin D N-terminal fragment) were immunoassayed. Furthermore, relative renal expression of both nuclear factor erythroid 2-related factor 2 (Nr-F2) and caspase1 was evaluated by qRT-PCR. Histopathological examination of renal tissue was carried out along with detection of Bcl-2 and Bax immunoreactivity. Cisplatin induced acute renal damage, augmented inflammation, dysregulated redox balance and induced apoptosis and pyroptosis. On the other hand, curcumin and liraglutide corrected the dysregulated mechanisms and normalized results to a great extent. Mutual use of curcumin and liraglutide exerted the greatest effect in the co-treatment group. Nr-F2/HO-1 axis and GSK-3β play a master role in their nephroprotective effect. In conclusion, curcumin and liraglutide have an ameliorative effect against cisplatin-induced nephrotoxicity and can be used alone or better in combination owing to their augmented effect launching promising avenues for cancer patients under cisplatin treatment, retarding AKI and enabling them to gain the best protocol effectiveness.

Insights into the role of PHLPP2/Akt/GSK3β/Fyn kinase/Nrf2 trajectory in the reno-protective effect of rosuvastatin against colistin-induced acute kidney injury in rats

OBJECTIVES

Oxidative stress-mediated colistin's nephrotoxicity is associated with the diminished activity of nuclear factor erythroid 2-related factor 2 (Nrf2) that is primarily correlated with cellular PH domain and leucine-rich repeat protein phosphatase (PHLPP2) levels. This study investigated the possible modulation of PHLPP2/protein kinase B (Akt) trajectory as a critical regulator of Nrf2 stability by rosuvastatin (RST) to guard against colistin-induced oxidative renal damage in rats.

METHODS

Colistin (300,000 IU/kg/day; i.p.) was injected for 6 consecutive days, and rats were treated simultaneously with RST orally at 10 or 20 mg/kg.

KEY FINDINGS

RST enhanced renal nuclear Nrf2 translocation as revealed by immunohistochemical staining to boost the renal antioxidants, superoxide dismutase (SOD) and reduced glutathione (GSH) along with a marked reduction in caspase-3. Accordingly, rats treated with RST showed significant restoration of normal renal function and histological features. On the molecular level, RST effectively decreased the mRNA expression of PHLPP2 to promote Akt phosphorylation. Consequently, it deactivated GSK-3β and reduced the gene expression of Fyn kinase in renal tissues.

CONCLUSIONS

RST could attenuate colistin-induced oxidative acute kidney injury via its suppressive effect on PHLPP2 to endorse Nrf2 activity through modulating Akt/GSK3 β/Fyn kinase trajectory.

Dulaglutide mitigates high dietary fructose-induced renal fibrosis in rats through suppressing epithelial-mesenchymal transition mediated by GSK-3β/TGF-β1/Smad3 signaling pathways

AIMS

High dietary fructose consumption has been linked to the development of renal fibrosis. Dulaglutide is a long acting glucagon like peptide-1 (GLP-1) analog, showing some renoprotective properties; however its action on renal fibrosis remains uncertain. We investigated the effect of dulaglutide on fructose-induced renal fibrosis in comparison to pirfenidone, as well-established anti-fibrotic drug, and the contribution of epithelial-mesenchymal transition (EMT) process and its upstream signaling.

MAIN METHODS

Six week-old male Wistar albino rats received 10%w/v fructose solution in drinking water for 24 weeks and co-treated with either pirfenidone (100 mg/kg/day, orally) or dulaglutide (0.2 mg/kg/week, s.c) for the last four weeks. Lipid profile, glucose homeostasis, kidney functions were assessed. Kidneys were harvested for biochemical and histological analyses.

KEY FINDINGS

High dietary fructose consumption for 24 weeks induced insulin resistance, dyslipidemia and renal dysfunction that were ameliorated by dulaglutide and pirfenidone to lesser extent. Histological examination revealed histological lesions and interstitial fibrosis in renal sections of high fructose-fed rats, which were reversed by dulaglutide or pirfenidone treatment. Both drugs modulated the EMT-related proteins by increasing the epithelial marker, E-cadherin, while suppressing the mesenchymal markers, vimentin and alpha-smooth muscle actin (α-SMA) in renal tissue. Moreover, both drugs attenuated fructose-induced upregulation of GSK-3β/TGF-β1/Smad3 signaling.

SIGNIFICANCE

These findings suggest that dulaglutide can emerge as a promising therapeutic agent for fructose-induced renal fibrosis. These results add mechanistic insights into the anti-fibrotic action of dulaglutide through suppressing EMT and the upstream GSK-3β/TGF-β1/Smad3 signaling.

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

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

ISG15 deficiency features a complex cellular phenotype that responds to treatment with itaconate and derivatives

Background

Congenital ISG15 deficiency is a rare autoinflammatory disorder that is driven by chronically elevated systemic interferon levels and predominantly affects central nervous system and skin.

Methods and results

We have developed induced pluripotent stem cell‐derived macrophages and endothelial cells as a model to study the cellular phenotype of ISG15 deficiency and identify novel treatments. ISG15^–/– macrophages exhibited the expected hyperinflammatory responses, but normal phagocytic function. In addition, they displayed a multifaceted pathological phenotype featuring increased apoptosis/pyroptosis, oxidative stress, glycolysis, and acylcarnitine levels, but decreased glutamine uptake, BCAT1 expression, branched chain amino acid catabolism, oxidative phosphorylation, β‐oxidation, and NAD(P)H‐dependent oxidoreductase activity. Furthermore, expression of genes involved in mitochondrial biogenesis and respiratory chain complexes II–V was diminished in ISG15^–/– cells. Defective mitochondrial respiration was restored by transduction with wild‐type ISG15, but only partially by a conjugation‐deficient variant, suggesting that some ISG15 functions in mitochondrial respiration require ISGylation to cellular targets. Treatment with itaconate, dimethyl‐itaconate, 4‐octyl‐itaconate, and the JAK1/2 inhibitor ruxolitinib ameliorated increased inflammation, propensity for cell death, and oxidative stress. Furthermore, the treatments greatly improved mitochondria‐related gene expression, BCAT1 levels, redox balance, and intracellular and extracellular ATP levels. However, efficacy differed among the compounds according to read‐out and cell type, suggesting that their effects on cellular targets are not identical. Indeed, only itaconates increased expression of anti‐oxidant genes NFE2L2, HMOX1, and GPX7, and dimethyl‐itaconate improved redox balance the most. Even though itaconate treatments normalized the elevated expression of interferon‐stimulated genes, ISG15^–/– macrophages maintained their reduced susceptibility to influenza virus infection.

Conclusions

These findings expand the cellular phenotype of human ISG15 deficiency and reveal the importance of ISG15 for regulating oxidative stress, branched chain amino acid metabolism, and mitochondrial function in humans. The results validate ruxolitinib as treatment for ISG15 deficiency and suggest itaconate‐based medications as additional therapeutics for this rare disorder.

Doxorubicin-induced hepatic toxicity in rats: Mechanistic protective role of Omega-3 fatty acids through Nrf2/HO-1 activation and PI3K/Akt/GSK-3β axis modulation

Doxorubicin (DOX), a common antibiotic used to treat a variety of tumors, has several substantial adverse effects that limit its clinical use. As a result, finding effective protective agents to combat DOX-induced organ damage is a necessity. The current study was set to delineate the hepatoprotective role of omega‐3 fatty acids (ω-3FA) against DOX-mediated acute liver damage in rats and the underlined mechanism of GSK-3β inhibition. Five groups of rats were orally received either saline (groups 1 & 2) or ω-3FA (25, 50 and 100 mg/kg/day; groups 3, 4 & 5, respectively) for 28 consecutive days. Single DOX intraperitoneal injection (20 mg/kg) was used to induce hepatic toxicity in all groups except group 1 (negative control). Blood samples and liver tissues were collected 48-hr after injection. Our results revealed that pre-administration of ω-3FA (25, 50 and 100 mg/kg) to DOX-induced hepatic injured rats showed a significant reduction in serum hepatic injury biomarkers (ALT, AST, total and direct bilirubin) as well as hepatic contents of MDA, GSH, Nrf2 and HO-1. Additionally, hepatic PI3K, pAkt and GSK-3β have been restored significantly in a dose-dependent manner. Furthermore, all the hepatic histopathological features have been retained upon ω-3FA treatment together with the immunostaining intensity of tumor necrosis factor-α and caspase-3. These results suggest that ω-3FA have shown a marked activation of the Nrf2/HO-1 signaling pathway and modulation of the PI3K/pAkt/GSK-3β axis against DOX-induced hepatotoxicity.

NAD+ ameliorates endotoxin-induced acute kidney injury in a sirtuin1-dependent manner via GSK-3β/Nrf2 signalling pathway

Acute kidney injury (AKI) is a substantial worldwide public health concern with no specific and effective therapies in clinic. NAD⁺ is a pivotal determinant of cellular energy metabolism involved in the progression of AKI; however, its mechanism in kidney injury remains poorly understood. Sirtuin 1 (SIRT1) is an NAD⁺‐dependent deacetylase associated with renal protection and acute stress resistance. In this study, we have investigated the role of NAD⁺ in AKI and the potential mechanism(s) involved in its renoprotective effect. NAD⁺ was notably decreased and negatively correlated with kidney dysfunction in AKI, restoring NAD⁺ with NMN significantly ameliorates LPS‐induced oxidative stress and apoptosis and attenuates renal damage. We also found that the protection of NAD⁺ is associated with SIRT1 expressions and performs in a SIRT1‐dependent manner. Inhibition of SIRT1 blunted the protective effect of NAD⁺ and up‐regulated the activity of glycogen synthase kinase‐3β (GSK‐3β) that was concomitant with mitigated Nrf2 nuclear accumulation, thereby exacerbates AKI. These findings suggest that NAD⁺/SIRT1/GSK‐3β/Nrf2 axis is an important mechanism that can protect against AKI which might be a potential therapeutic target for the treatment of AKI.

Mechanisms of nucleophosmin (NPM)-mediated regulated cell death elucidated by Hsp70 during renal ischemia

Nucleophosmin (NPM), a nucleolar-based protein chaperone, promotes Bax-mediated mitochondrial injury and regulates cell death during acute kidney injury. However, the steps that transform NPM from an essential to a toxic protein during stress are unknown. To localize NPM-mediated events causing regulated cell death during ischemia, wild type (WT) and Hsp70 mutant proteins with characterized intracellular trafficking defects that restrict movement to either the nucleolar region (M45) or cytosol (985A) were expressed in primary murine proximal tubule epithelial cells (PTEC) harvested from Hsp70 null mice. After ischemia in vitro, PTEC survival was significantly improved and apoptosis reduced in rank order by selectively overexpressing WT > M45 > 985A Hsp70 proteins. Only Hsp70 with nuclear access (WT and M45) inhibited T95 NPM phosphorylation responsible for NPM translocation and also reduced cytosolic NPM accumulation. In contrast, WT or 985A > M45 significantly improved survival in Hsp70 null PTEC that expressed a cytosol-restricted NPM mutant, more effectively bound NPM, and also reduced NPM-Bax complex formation required for mitochondrial injury and cell death. Hsp70 knockout prevented the cytoprotective effect of suppressing NPM in ischemic PTEC and also increased cytosolic NPM accumulation after acute renal ischemia in vivo, emphasizing the inhibitory effect of Hsp70 on NPM-mediated toxicity. Distinct cytoprotective mechanisms by wild type and mutant Hsp70 proteins identify dual nuclear and cytosolic events that mediate NPM toxicity during stress-induced apoptosis and are rational targets for therapeutic AKI interventions. Antagonizing these early events in regulated cell death promotes renal cell survival during experimental AKI.

IL-1 receptor signaling in podocytes limits susceptibility to glomerular damage

Interleukin (IL)-1 receptor type 1 (IL-1R1) activation triggers a proinflammatory signaling cascade that can exacerbate kidney injury. However, the functions of podocyte IL-1R1 in glomerular disease remain unclear. To study the role of IL-1R1 signaling in podocytes, we selectively ablated podocyte IL-1R1 in mice (PKO mice). We then subjected PKO mice and wild-type controls to two glomerular injury models: nephrotoxic serum (NTS)- and adriamycin-induced nephropathy. Surprisingly, we found that IL-1R1 activation in podocytes limited albuminuria and podocyte injury during NTS- and adriamycin-induced nephropathy. Moreover, deletion of IL-1R1 in podocytes drove podocyte apoptosis and glomerular injury through diminishing Akt activation. Activation of Akt signaling abrogated the differences in albuminuria and podocyte injury between wild-type and PKO mice during NTS. Thus, IL-1R1 signaling in podocytes limits susceptibility to glomerular injury via an Akt-dependent signaling pathway. These data identify an unexpected protective role for IL-1R1 signaling in podocytes in the pathogenesis of glomerular disease.NEW & NOTEWORTHY The present study establishes that activation of the receptor for interleukin-1 limits susceptibility to damage to the kidney glomerulus in preclinical mouse models by stimulating Akt signaling cascades inside the podocyte.

Diabetes modulation of the myocardial infarction- acute kidney injury axis

Since there is crosstalk in functions of the heart and kidney, acute or chronic injury in one of the two organs provokes adaptive and/or maladaptive responses in both organs, leading to cardiorenal syndrome (CRS). Acute kidney injury (AKI) induced by acute heart failure is referred to as type 1 CRS, and a frequent cause of this type of CRS is acute myocardial infarction (AMI). Diabetes mellitus increases the risk of AMI and also the risk of AKI of various causes. However, there have been only a few studies in which animal models of diabetes were used to examine how diabetes modulates AMI-induced AKI. In this review, we summarize findings regarding the mechanisms of type 1 CRS and the impact of diabetes on both AMI and renal susceptibility to AKI and we discuss mechanisms by which diabetes modulates AMI-induced AKI. Hemodynamic alterations induced by AMI could be augmented by diabetes via its detrimental effect on infarct size and contractile function of the non-infarcted region in the heart. Diabetes increases susceptibility of renal cells to hypoxia and oxidative stress by modulation of signaling pathways that regulate cell survival and autophagy. Recent studies have shown that diabetes mellitus even at early stage of cardiomyopathy/nephropathy predisposes the kidney to AMI-induced AKI, in which activation of toll-like receptors and reactive oxygen species derived from NADPH oxidases are involved. Further analysis of crosstalk between diabetic cardiomyopathy and diabetic kidney disease is necessary for obtaining a more comprehensive understanding of modulation of the AMI-AKI axis by diabetes.

HDAC inhibition prevents hypobaric hypoxia-induced spatial memory impairment through PΙ3K/GSK3β/CREB pathway

Hypobaric hypoxia at higher altitudes usually impairs cognitive function. Previous studies suggested that epigenetic modifications are the culprits for this condition. Here, we set out to determine how hypobaric hypoxia mediates epigenetic modifications and how this condition worsens neurodegeneration and memory loss in rats. In the current study, different duration of hypobaric hypoxia exposure showed a discrete pattern of histone acetyltransferases and histone deacetylases (HDACs) gene expression in the hippocampus when compared with control rat brains. The level of acetylation sites in histone H2A, H3 and H4 was significantly decreased under hypobaric hypoxia exposure compared to the control rat's hippocampus. Additionally, inhibiting the HDAC family with sodium butyrate administration (1.2 g/kg body weight) attenuated neurodegeneration and memory loss in hypobaric hypoxia-exposed rats. Moreover, histone acetylation increased at the promoter regions of brain-derived neurotrophic factor (BDNF); thereby its protein expression was enhanced significantly in hypobaric hypoxia exposed rats treated with HDAC inhibitor compared with hypoxic rats. Thus, BDNF expression upregulated cAMP-response element binding protein (CREB) phosphorylation by stimulation of PI3K/GSK3β/CREB axis, which counteracts hypobaric hypoxia-induced spatial memory impairment. In conclusion, these results suggested that sodium butyrate is a novel therapeutic agent for the treatment of spatial memory loss associated with hypobaric hypoxia, and also further studies are warranted to explore specific HDAC inhibitors in this condition.

Pharmacologically Inhibiting Glycogen Synthase Kinase-3β Ameliorates Renal Inflammation and Nephrotoxicity in an Animal Model of Cisplatin-Induced Acute Kidney Injury

The adverse effect of cisplatin administration causes acute kidney injury (AKI) following renal inflammation and nephrotoxicity, characterized by proximal tubular cell apoptosis and necrosis. Pro-apoptotic and pro-inflammatory roles of glycogen synthase kinase (GSK)-3β have been reported. This study investigated the therapeutic blockade of GSK-3β in cisplatin-induced AKI. A renal cisplatin nephrotoxicity model showed activation of GSK-3β in vivo, particularly in proximal tubular epithelial cells. Pharmacologically inhibiting GSK-3β abolished cisplatin nephrotoxicity, including proximal tubular injury, cell cytotoxicity, and biochemical dysfunction. Additionally, GSK-3β inhibitor treatment ameliorated renal inflammation by reducing immune cell infiltration, cell adhesion molecule expression, and pro-inflammatory cytokine/chemokine production. Cisplatin treatment caused GSK-3β activation in vitro in the human renal proximal tubular epithelial cell line HK-2, whereas either pharmacological administration of GSK-3β inhibitors or genetic transduction of GSK-3β short-hairpin RNA impeded cisplatin-induced cytotoxicity. These results indicate that cisplatin activates GSK-3β followed by GSK-3β-mediated renal inflammation and nephrotoxicity, contributing to AKI.

Wnt/β-Catenin in Acute Kidney Injury and Progression to Chronic Kidney Disease

Acute kidney injury (AKI) portends a poor clinical prognosis and increases the risk for the development of chronic kidney disease (CKD). Currently, there are no therapies to treat AKI or prevent its progression to CKD. Wnt/β-catenin is a critical regulator of kidney development that is up-regulated after injury. Most of the literature support a beneficial role for Wnt/β-catenin in AKI, but suggest that this pathway promotes the progression of tubulointerstitial fibrosis, the hallmark of CKD progression. We review the role of Wnt/β-catenin in renal injury with a focus on its potential as a therapeutic target in AKI and in AKI to CKD transition.

Permissive effect of GSK3β on profibrogenic plasticity of renal tubular cells in progressive chronic kidney disease

Renal tubular epithelial cells (TECs) play a key role in renal fibrogenesis. After persistent injuries that are beyond self-healing capacity, TECs will dedifferentiate, undergo growth arrest, convert to profibrogenic phenotypes, and resort to maladaptive plasticity that ultimately results in renal fibrosis. Evidence suggests that glycogen synthase kinase (GSK) 3β is centrally implicated in kidney injury. However, its role in renal fibrogenesis is obscure. Analysis of publicly available kidney transcriptome database demonstrated that patients with progressive chronic kidney disease (CKD) exhibited GSK3β overexpression in renal tubulointerstitium, in which the predefined hallmark gene sets implicated in fibrogenesis were remarkably enriched. In vitro, TGF-β1 treatment augmented GSK3β expression in TECs, concomitant with dedifferentiation, cell cycle arrest at G2/M phase, excessive accumulation of extracellular matrix, and overproduction of profibrotic cytokines like PAI-1 and CTGF. All these profibrogenic phenotypes were largely abrogated by GSK3β inhibitors or by ectopic expression of a dominant-negative mutant of GSK3β but reinforced in cells expressing the constitutively active mutant of GSK3β. Mechanistically, GSK3β suppressed, whereas inhibiting GSK3β facilitated, the activity of cAMP response element-binding protein (CREB), which competes for CREB-binding protein, a transcriptional coactivator essential for TGF-β1/Smad signaling pathway to drive TECs profibrogenic plasticity. In vivo, in mice with folic acid-induced progressive CKD, targeting of GSK3β in renal tubules via genetic ablation or by microdose lithium mitigated the profibrogenic plasticity of TEC, concomitant with attenuated interstitial fibrosis and tubular atrophy. Collectively, GSK3β is likely a pragmatic therapeutic target for averting profibrogenic plasticity of TECs and improving renal fibrosis.

T95 nucleophosmin phosphorylation as a novel mediator and marker of regulated cell death in acute kidney injury

The function of site-specific phosphorylation of nucleophosmin (NPM), an essential Bax chaperone, in stress-induced cell death is unknown. We hypothesized that NPM threonine 95 (T95) phosphorylation both signals and promotes cell death. In resting cells, NPM exclusively resides in the nucleus and T95 is nonphosphorylated. In contrast, phosphorylated T95 NPM (pNPM T95) accumulates in the cytosol after metabolic stress, in multiple human cancer cell lines following γ-radiation, and in postischemic human kidney tissue. Based on the T95 phosphorylation consensus sequence, we hypothesized that glycogen synthase kinase-3β (GSK-3β) regulates cytosolic NPM translocation by phosphorylating T95 NPM. In a cell-free system, GSK-3β phosphorylated a synthetic NPM peptide containing T95. In vitro, bidirectional manipulation of GSK-3β activity substantially altered T95 phosphorylation, cytosolic NPM translocation, and cell survival during stress, mechanistically linking these lethal events. Furthermore, GSK-3β inhibition in vivo decreased cytosolic pNPM T95 accumulation in kidney tissue after experimental ischemia. In patients with acute kidney injury, both cytosolic NPM accumulation in proximal tubule cells and NPM-rich intratubular casts were detected in frozen renal biopsy tissue. These observations show, for the first time, that GSK-3β promotes cell death partly by phosphorylating NPM at T95, to promote cytosolic NPM accumulation. T95 NPM is also a rational therapeutic target to ameliorate ischemic renal cell injury and may be a universal injury marker in mammalian cells.

Glycogen synthase kinase-3β inhibits tubular regeneration in acute kidney injury by a FoxM1-dependent mechanism

Acute kidney injury (AKI) is characterized by injury to the tubular epithelium that leads to the sudden loss of renal function. Proper tubular regeneration is essential to prevent progression to chronic kidney disease. In this study, we examined the role of FoxM1, a forkhead box family member transcription factor in tubular repair after AKI. Renal FoxM1 expression increased after renal ischemia/reperfusion (I/R)-induced AKI in mouse kidneys. Treatment with thiostrepton, a FoxM1 inhibitor, reduced FoxM1 regulated pro-proliferative factors and cell proliferation in vitro, and tubular regeneration in mouse kidneys after AKI. Glycogen synthase kinase-3 (GSK3) was found to be an upstream regulator of FoxM1 because GSK3 inhibition or renal tubular GSK3β gene deletion significantly increased FoxM1 expression, and improved tubular repair and renal function. GSK3 inactivation increased β-catenin, Cyclin D1, and c-Myc, and reduced cell cycle inhibitors p21 and p27. Importantly, thiostrepton treatment abolished the improved tubular repair in GSK3β knockout mice following AKI. These results demonstrate that FoxM1 is important for renal tubular regeneration following AKI and that GSK3β suppresses tubular repair by inhibiting FoxM1.

Glycogen Synthase Kinase-3 Signaling in Acute Kidney Injury

Acute kidney injury (AKI) is a common clinical syndrome that involves renal tubular epithelial cell death and leads to acute decline in renal function. Improper tubular regeneration following AKI often leads to CKD. We discuss the role of a serine/threonine protein kinase called glycogen synthase kinase-3 (GSK3) in renal tubular injury and renal fibrosis. We also highlight the importance of GSK3 as a potential drug target in AKI patients and molecular mechanisms promoting tissue regeneration.

Interleukin-27 Ameliorates Renal Ischemia-Reperfusion Injury through Signal Transducers and Activators of Transcription 3 Signaling Pathway

BACKGROUND

Acute kidney injury (AKI) is a clinical syndrome characterized by significant morbidity and a high death rate. Interleukin (IL)-27 is a newly described member of the IL-6/IL-12 heterodimeric cytokine family and displays anti-inflammatory and antiapoptotic properties.

OBJECTIVES

To determine the effect and mechanism of IL-27 in AKI.

METHOD

We used a mouse model of renal ischemia/reperfusion (I/R) injury to investigate whether IL-27 has a therapeutic potential for the treatment of AKI. For the IL-27 administration group, IL-27 protein was injected 1 h before ischemia. Human proximal tubular epithelial cells were exposed to ischemia for 2 h and followed by 2 h of reperfusion (I2h+R2h treatment) used as an in vitro model to investigate the effect of IL-27.

RESULTS

Two IL-27 subunits, Epstein-Barr virus gene 3 and p28, were upregulated in kidneys 24 h after I/R. Renal expression of IL-27 receptor subunits (gp130 and WSX-1) was also increased. Treatment with IL-27 reduced structural/functional damages, ameliorated renal inflammation, inhibited the cleaved caspase-3 expression, upregulated antiapoptotic protein Bcl-2 and downregulated proapoptotic protein Bax in the kidneys of mice subjected to I/R. Meanwhile, the level of IL-27 receptor on renal tubular epithelial cells was increased after I2h+R2h treatment, and IL-27 administration suppressed I2h+R2h-induced epithelial cell apoptosis. Furthermore, IL-27 treatment led to activation of signal transducer and activator of transcription 3 (STAT3) both in vivo and in vitro, and IL-27-mediated protection against I2h+R2h injury was abolished by STAT3 inhibition.

CONCLUSIONS

IL-27 protects against renal I/R injury by activating STAT3, suggesting that IL-27 may represent a novel strategy for the treatment of AKI.

Nucleophosmin Phosphorylation as a Diagnostic and Therapeutic Target for Ischemic AKI

Background Ischemic AKI lacks a urinary marker for early diagnosis and an effective therapy. Differential nucleophosmin (NPM) phosphorylation is a potential early marker of ischemic renal cell injury and a therapeutic target.Methods Differential NPM phosphorylation was assessed by mass spectrometry in NPM harvested from murine and human primary renal epithelial cells, fresh kidney tissue, and urine before and after ischemic injury. The biologic behavior and toxicity of NPM was assessed using phospho-NPM mutant proteins that either mimic stress-induced or normal NPM phosphorylation. Peptides designed to interfere with NPM function were used to explore NPM as a therapeutic target.Results Within hours of stress, virtually identical phosphorylation changes were detected at distinct serine/threonine sites in NPM harvested from primary renal cells, tissue, and urine. A phosphomimic NPM protein that replicated phosphorylation under stress localized to the cytosol, formed monomers that interacted with Bax, a cell death protein, coaccumulated with Bax in isolated mitochondria, and significantly increased cell death after stress; wild-type NPM or a phosphomimic NPM with a normal phosphorylation configuration did not. Three renal targeted peptides designed to interfere with NPM at distinct functional sites significantly protected against cell death, and a single dose of one peptide administered several hours after ischemia that would be lethal in untreated mice significantly reduced AKI severity and improved survival.Conclusions These findings establish phosphorylated NPM as a potential early marker of ischemic AKI that links early diagnosis with effective therapeutic interventions.

A synthetic epoxyeicosatrienoic acid analogue prevents the initiation of ischemic acute kidney injury

AIM

Imbalances in cytochrome P450 (CYP)-dependent eicosanoid formation may play a central role in ischemic acute kidney injury (AKI). We reported previously that inhibition of 20-hydroxyeicosatetraenoic acid (20-HETE) action ameliorated ischemia/reperfusion (I/R)-induced AKI in rats. Now we tested the hypothesis that enhancement of epoxyeicosatrienoic acid (EET) actions may counteract the detrimental effects of 20-HETE and prevent the initiation of AKI.

METHODS

Male Lewis rats underwent right nephrectomy and ischemia was induced by 45 min clamping of the left renal pedicle followed by up to 48 h of reperfusion. Circulating CYP-eicosanoid profiles were compared in patients who underwent cardiac surgery with (n = 21) and without (n = 38) developing postoperative AKI.

RESULTS

Ischemia induced an about eightfold increase of renal 20-HETE levels, whereas free EETs were not accumulated. To compensate for this imbalance, a synthetic 14,15-EET analogue was administered by intrarenal infusion before ischemia. The EET analogue improved renal reoxygenation as monitored by in vivo parametric MRI during the initial 2 h reperfusion phase. The EET analogue improved PI3K- as well as mTORC2-dependent rephosphorylation of Akt, induced inactivation of GSK-3β, reduced the development of tubular apoptosis and attenuated inflammatory cell infiltration. The EET analogue also significantly alleviated the I/R-induced drop in creatinine clearance. Patients developing postoperative AKI featured increased preoperative 20-HETE and 8,9-EET levels.

CONCLUSIONS

Pharmacological interventions targeting the CYP-eicosanoid pathway could offer promising new options for AKI prevention. Individual differences in CYP-eicosanoid formation may contribute to the risk of developing AKI in clinical settings.

Fenbendazole induces apoptosis of porcine uterine luminal epithelial and trophoblast cells during early pregnancy

Fenbendazole, is an effective benzimidazole anthelmintic that prevents parasite infection in both human and veterinary health care. Although the well-known and effect of benzimidazole was recently shown to have a broad spectrum of biological abilities, such as anticancer and anti-inflammation activities, the mechanism of benzimidazole's antiproliferative effect via cell signaling pathways and its role in preimplantation has not been studied. Therefore, the purpose of this study was to determine the effects of fenbendazole on porcine trophectoderm and luminal epithelial cells. First, we investigated cell viability in response to a low dose of fenbendazole, which highly inhibited cell proliferation. In addition, we investigated apoptotic molecules in the mitochondria, imbalanced intracellular calcium homeostasis, and the expression of some genes involved in apoptosis to explain the decrease in proliferation. Finally, we examined the intracellular mechanisms of fenbendazole by measuring the extracellular signal-regulated kinase, PI3K/AKT, and c-Jun N-terminal kinase signaling proteins by western blot analysis. Our findings suggest that fenbendazole functions as an effective anti-proliferative molecule that induces critical apoptosis in the porcine trophectoderm and uterine luminal epithelial cells by disrupting the mitochondria membrane potential during early pregnancy.

Cell Death in the Kidney

Apoptotic cell death is usually a response to the cell's microenvironment. In the kidney, apoptosis contributes to parenchymal cell loss in the course of acute and chronic renal injury, but does not trigger an inflammatory response. What distinguishes necrosis from apoptosis is the rupture of the plasma membrane, so necrotic cell death is accompanied by the release of unprocessed intracellular content, including cellular organelles, which are highly immunogenic proteins. The relative contribution of apoptosis and necrosis to injury varies, depending on the severity of the insult. Regulated cell death may result from immunologically silent apoptosis or from immunogenic necrosis. Recent advances have enhanced the most revolutionary concept of regulated necrosis. Several modalities of regulated necrosis have been described, such as necroptosis, ferroptosis, pyroptosis, and mitochondrial permeability transition-dependent regulated necrosis. We review the different modalities of apoptosis, necrosis, and regulated necrosis in kidney injury, focusing particularly on evidence implicating cell death in ectopic renal calcification. We also review the evidence for the role of cell death in kidney injury, which may pave the way for new therapeutic opportunities.

GSK3β-mediated Keap1-independent regulation of Nrf2 antioxidant response: A molecular rheostat of acute kidney injury to chronic kidney disease transition

Transition of acute kidney injury (AKI) to chronic kidney disease (CKD) represents an important cause of kidney failure. However, how AKI is transformed into CKD remains elusive. Following folic acid injury, mice developed AKI with ensuing CKD transition, featured by variable degrees of interstitial fibrosis and tubular cell atrophy and growth arrest. This lingering injury of renal tubules was associated with sustained oxidative stress that was concomitant with an impaired Nrf2 antioxidant defense, marked by mitigated Nrf2 nuclear accumulation and blunted induction of its target antioxidant enzymes, like heme oxygenase (HO)-1. Activation of the canonical Keap1/Nrf2 signaling, nevertheless, seems intact during CKD transition because Nrf2 in injured tubules remained activated and elevated in cytoplasm. Moreover, oxidative thiol modification and activation of Keap1, the cytoplasmic repressor of Nrf2, was barely associated with CKD transition. In contrast, glycogen synthase kinase (GSK)3β, a key modulator of the Keap1-independent Nrf2 regulation, was persistently overexpressed and hyperactive in injured tubules. Likewise, in patients who developed CKD following AKI due to diverse etiologies, like volume depletion and exposure to radiocontrast agents or aristolochic acid, sustained GSK3β overexpression was evident in renal tubules and coincided with oxidative damages, impaired Nrf2 nuclear accumulation and mitigated induction of antioxidant gene expression. Mechanistically, the Nrf2 response against oxidative insult was sabotaged in renal tubular cells expressing a constitutively active mutant of GSK3β, but reinforced by ectopic expression of dominant negative GSK3β in a Keap1-independent manner. In vivo in folic acid-injured mice, targeting GSK3β in renal tubules via conditional knockout or by weekly microdose lithium treatment reinstated Nrf2 antioxidant response in the kidney and hindered AKI to CKD transition. Ergo, our findings suggest that GSK3β-mediated Keap1-independent regulation of Nrf2 may serve as an actionable therapeutic target for modifying the long-term sequelae of AKI.

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AKI to CKD transition involves sustained GSK3β overactivation and impaired Nrf2 response in injured renal tubules.

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Microdose lithium rectifies GSK3β overactivity in the kidney, reinstates Nrf2 response and hinders AKI to CKD transition.

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GSK3β-mediated Keap1-independent regulation of Nrf2 is a novel therapeutic target for modifying long-term sequelae of AKI.

Dexmedetomidine ameliorates lipopolysaccharide-induced acute kidney injury in rats by inhibiting inflammation and oxidative stress via the GSK-3β/Nrf2 signaling pathway

Acute kidney injury (AKI) is a frequent and serious complication of sepsis; however, there are currently no effective therapies. Inflammation and oxidative stress are the major mechanisms implicated in lipopolysaccharide (LPS)-induced AKI. Dexmedetomidine (DEX) has been reported to have remarkable anti-inflammatory and antioxidant effects. Here, we examined the renoprotective effects of DEX and potential underlying mechanisms in rats with LPS-induced AKI. We analyzed renal function and structure; serum inflammatory cytokine; renal oxidant and antioxidant levels; and renal expression of glycogen synthase kinase-3β (GSK-3β)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway-related proteins in rats 4 hr after administration of LPS. Pretreatment with DEX improved renal function and significantly reduced the levels of inflammatory cytokines and oxidative stress markers. Treatment with DEX and the GSK-3β inhibitor SB216367 promoted phosphorylation of GSK-3β, induced Nrf2 nuclear translocation, and increased transcription of the Nrf2 target genes heme oxygenase-1 and NAD(P)H quinone oxidoreductase-1, primarily in renal tubules. Alpha-2-adrenergic receptor (α2-AR) antagonist atipamezole and imidazoline I ₂ receptor (I ₂ R) antagonist idazoxan reversed the effects of DEX. These results suggest that the renoprotective effects of DEX are mediated via α2-AR and I ₂ R-dependent pathways that reduce inflammation and oxidative stress through GSK-3β/Nrf2 signaling.

Urinary procollagen III aminoterminal propeptide and β-catenin - New diagnostic biomarkers in solitary functioning kidney?

PURPOSE

We aimed at evaluating urinary levels of procollagen III aminoterminal propeptide (PIIINP) and β-catenin and the relationship between these markers and clinical and laboratory variables in children with a solitary functioning kidney (SFK).

PATIENTS AND METHODS

The study group consisted of 98 (M/F: 62/36) children with an SFK with a median age of 8 years. An age-matched control group contained 54 healthy peers. Urinary levels of procollagen III aminoterminal propeptide and β-catenin were measured using a commercially available immunoassay kit.

RESULTS

The urinary values of PIIINP (UPIIINP) were significantly increased in patients with SFK versus controls (p < 0.01). Our analysis revealed no significant differences in urinary β-catenin levels between the SFK patients and control subjects (p > 0.05). Only urinary PIIINP levels were correlated to renal function tests, such as serum creatinine, urea, uric acid, and estimated glomerular filtration rate (p<0.05).

CONCLUSIONS

An increased urinary level of PIIINP may indicate early kidney impairment in children with SFK. Urinary β-catenin does not seem to play any important role as a marker of renal function in children with SFK. Further long-term studies are required in order to evaluate the clinical usefulness of these markers and their predictive value of chronic kidney disease (CKD) progression.

Glucocorticoid induces osteonecrosis of the femoral head in rats through GSK3β-mediated osteoblast apoptosis

OBJECTIVE

One of the important causes of glucocorticoids (GCs)-induced osteonecrosis of the femoral head (ONFH) is osteoblast apoptosis. Glycogen synthase kinase 3β (GSK3β) has been reported to be related to dexamethasone (Dex)-induced osteoblast apoptosis. This study aimed to determine whether GSK3β plays role in GC-induced ONFH and investigate the underlying mechanism.

METHODS

18 male Sprague-Dawley rats were divided into 3 groups. Rats from ONFH group underwent lipopolysaccharide and methylprednisolone injection. Lithium chloride (LiCl, a GSK3β inhibitor) group were fed with LiCl solution. The control group were untreated. Osteonecrosis, apoptosis and bone loss were evaluated by HE staining, TUNEL staining and micro-CT respectively. Protein expressions were examined by western blotting. In addition, primary osteoblast cells were transfected by GSK3β-siRNA and related signaling pathway and proteins were examined.

RESULTS

ONFH group showed a relative high percentage of empty lacunae and apoptotic cells, whilst LiCl treatment markedly decreased the percentage. LiCl treatment decreased GC-induced bone loss. Immunoblot analysis for GSK3β showed decreased level of Ser9-phosphorylated GSK3β in ONFH group compared with control group. Knockdown of GSK3β by siRNA in primary osteoblast cells attenuated DEX-induced apoptosis and loss of mitochondrial transmembrane potential (Δψm). GSK3β knockdown also reversed the release of cytochrome C (Cyt C) from mitochondria to the cytosol. GSK3β decreased apoptosis-related protein expression both in vitro and in vivo.

CONCLUSION

Our findings suggest that GC induces ONFH in rats through GSK3β-mediated osteoblast apoptosis, with involvement of mitochondrial apoptotic pathway.

UCP2-dependent improvement of mitochondrial dynamics protects against acute kidney injury

Acute kidney injury (AKI) is a public health concern, with high morbidity and mortality rates in hospitalized patients and because survivors have an increased risk of progression to chronic kidney disease. Mitochondrial damage is the critical driver of AKI-associated dysfunction and loss of tubular epithelial cells; however, the pathways that mediate these events are poorly defined. Here, in murine ischemia/reperfusion (I/R)-induced AKI, we determined that mitochondrial damage is associated with the level of renal uncoupling protein 2 (UCP2). In hypoxia-damaged proximal tubular cells, a disruption of mitochondrial dynamics demonstrated by mitochondrial fragmentation and disturbance between fusion and fission was clearly indicated. Ucp2-deficient mice (knockout mice) with I/R injury experienced more severe AKI and mitochondrial fragmentation than wild-type mice. Moreover, genetic or pharmacological treatment increased UCP2 expression, improved renal function, reduced tubular injury and limited mitochondrial fission. In cultured proximal tubular epithelial cells, hypoxia-induced mitochondrial fission was exacerbated in cells with UCP2 deletion, whereas an increase in UCP2 ameliorated the hypoxia-induced disturbance of the balance between mitochondrial fusion and fission. Furthermore, results following modulation of UCP2 suggested it has a role in preserving mitochondrial integrity by preventing loss of membrane potential and reducing subsequent mitophagy. Taken together, our results indicate that UCP2 is protective against AKI and suggest that enhancing UCP2 to improve mitochondrial dynamics has potential as a strategy for improving outcomes of renal injury. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Tempol Protects Against Acute Renal Injury by Regulating PI3K/Akt/mTOR and GSK3β Signaling Cascades and Afferent Arteriolar Activity

BACKGROUND/AIMS

Free radical scavenger tempol is a protective antioxidant against ischemic injury. Tubular epithelial apoptosis is one of the main changes in the renal ischemia/reperfusion (I/R) injury. Meanwhile some proteins related with apoptosis and inflammation are also involved in renal I/R injury. We tested the hypothesis that tempol protects against renal I/R injury by activating protein kinase B/mammalian target of rapamycin (PKB, Akt/mTOR) and glycogen synthase kinase 3β (GSK3β) pathways as well as the coordinating apoptosis and inflammation related proteins.

METHODS

The right renal pedicle of C57Bl/6 mouse was clamped for 30 minutes and the left kidney was removed in the study. The renal injury was assessed with serum parameters by an automatic chemistry analyzer. Renal expressions of Akt/mTOR and GSK3β pathways were measured by western blot in I/R mice treated with saline or tempol (50mg/kg) and compared with sham-operated mice.

RESULTS

The levels of blood urea nitrogen (BUN), creatinine and superoxide anion (O2.-) increased, and superoxide dismutase (SOD) and catalase (CAT) decreased significantly after renal I/R injury. However, tempol treatment prevented the changes. Besides, I/R injury reduced renal expression of p-Akt, p-GSK3β, p-mTOR, Bcl2 and increased NF-κB, p-JNK and p53 in kidney, tempol significantly normalized these changes. In addition, renal I/R injury reduced the response of afferent arteriole to Angiotensin II (Ang II), while tempol treatment improved the activity of afferent arteriole.

CONCLUSION

Tempol attenuates renal I/R injury. The protective mechanisms seem to relate with activation of PI3K/Akt/mTOR and GSK3β pathways, inhibition of cellular damage markers and inflammation factors, as well as improvement of afferent arteriolar activity.

Renal Tubule Repair: Is Wnt/β-Catenin a Friend or Foe?

Wnt/β-catenin signaling is extremely important for proper kidney development. This pathway is also upregulated in injured renal tubular epithelia, both in acute kidney injury and chronic kidney disease. The renal tubular epithelium is an important target of kidney injury, and its response (repair versus persistent injury) is critical for determining whether tubulointerstitial fibrosis, the hallmark of chronic kidney disease, develops. This review discusses how Wnt/β-catenin signaling in the injured tubular epithelia promotes either repair or fibrosis after kidney injury. There is data suggesting that epithelial Wnt/β-catenin signaling is beneficial in acute kidney injury and important in tubular progenitors responsible for epithelial repair. The role of Wnt/β-catenin signaling in chronically injured epithelia is less clear. There is convincing data that Wnt/β-catenin signaling in interstitial fibroblasts and pericytes contributes to the extracellular matrix accumulation that defines fibrosis. However, some recent studies question whether Wnt/β-catenin signaling in chronically injured epithelia actually promotes fibrosis or repair.

Epoxide metabolites of arachidonate and docosahexaenoate function conversely in acute kidney injury involved in GSK3β signaling

Acute kidney injury (AKI) causes severe morbidity and mortality for which new therapeutic strategies are needed. Docosahexaenoic acid (DHA), arachidonic acid (ARA), and their metabolites have various effects in kidney injury, but their molecular mechanisms are largely unknown. Here, we report that 14 (15)-epoxyeicosatrienoic acid [14 (15)-EET] and 19 (20)-epoxydocosapentaenoic acid [19 (20)-EDP], the major epoxide metabolites of ARA and DHA, respectively, have contradictory effects on kidney injury in a murine model of ischemia/reperfusion (I/R)-caused AKI. Specifically, 14 (15)-EET mitigated while 19 (20)-EDP exacerbated I/R kidney injury. Manipulation of the endogenous 19 (20)-EDP or 14 (15)-EET by alteration of their degradation or biosynthesis with selective inhibitors resulted in anticipated effects. These observations are supported by renal histological analysis, plasma levels of creatinine and urea nitrogen, and renal NGAL. The 14 (15)-EET significantly reversed the I/R-caused reduction in glycogen synthase kinase 3β (GSK3β) phosphorylation in murine kidney, dose-dependently inhibited the hypoxia/reoxygenation (H/R)-caused apoptosis of murine renal tubular epithelial cells (mRTECs), and reversed the H/R-caused reduction in GSK3β phosphorylation in mRTECs. In contrast, 19 (20)-EDP dose-dependently promoted H/R-caused apoptosis and worsened the reduction in GSK3β phosphorylation in mRTECs. In addition, 19 (20)-EDP was more metabolically stable than 14 (15)-EET in vivo and in vitro. Overall, these epoxide metabolites of ARA and DHA function conversely in I/R-AKI, possibly through their largely different metabolic stability and their opposite effects in modulation of H/R-caused RTEC apoptosis and GSK3β phosphorylation. This study provides AKI patients with promising therapeutic strategies and clinical cautions.

Inhibition of GSK-3β increases trabecular bone volume but not cortical bone volume in adenine-induced uremic mice with severe hyperparathyroidism

Patients with chronic kidney disease (CKD) are at increased risk for bone fractures compared with the general population. Repression of the Wnt/β‐catenin signaling pathway is associated with bone abnormalities. Inhibition of glycogen synthase kinase (GSK)‐3β, a critical component of the Wnt/β‐catenin signaling pathway, increases bone volume through accumulation of β‐catenin. It remains unknown whether inhibition of GSK‐3β increases bone volume in CKD. The present in vivo study examined the effects of GSK‐3β inhibition on bone volume in CKD mice. Wild‐type mice were divided into three groups. One group was fed a control diet (CNT) and the other two groups were fed a diet containing 0.2% adenine and given water with or without lithium chloride (LiCl), a GSK‐3 inhibitor (CKD, CKD+LiCl, respectively). GSK‐3β heterozygous knockout mice were fed a diet containing 0.2% adenine (CKD‐GSK‐3β^+/−). After 6 weeks, trabecular and cortical bone volumes of the femur were analyzed using microcomputed tomography. CKD mice developed azotemia, hyperphosphatemia, and hyperparathyroidism, followed by a decrease in cortical bone volume without any change in trabecular bone volume. Serum levels of urea nitrogen, phosphate, and parathyroid hormone were comparable among the three groups of CKD mice. Trabecular bone volume increased in CKD‐GSK‐3β^+/− and CKD+LiCl mice compared with CNT and CKD mice. However, there were no significant differences in cortical bone volume among the three groups of CKD mice. The results suggest that inhibition of GSK‐3β increases trabecular bone volume but not cortical bone volume in adenine‐induced uremic mice with uncontrolled hyperparathyroidism.

Effects of chronic alcohol exposure on ischemia-reperfusion-induced acute kidney injury in mice: the role of β-arrestin 2 and glycogen synthase kinase 3

Little is known about the effects of chronic alcohol intake on the outcome of acute kidney injury (AKI). Hence, we examined the effects of chronic alcohol intake on the development of renal fibrosis following AKI in an animal model of bilateral renal ischemia–reperfusion (IR) injury. We first found that chronic alcohol exposure exacerbated bilateral IR-induced renal fibrosis and renal function impairment. This phenomenon was associated with increased bilateral IR-induced extracellular matrix deposition and an increased myofibroblast population as well as increased bilateral IR-induced expression of fibrosis-related genes in the kidneys. To explore the mechanisms underlying this phenomenon, we showed that chronic alcohol exposure enhanced β-arrestin 2 (Arrb2) expression and Akt and glycogen synthase kinase-3 (GSK3)β activation in the kidneys. Importantly, pharmacological GSK3 inhibition alleviated bilateral IR-induced renal fibrosis and renal function impairment. Furthermore, we demonstrated that Arrb2^−/− mice exhibited resistance to IR-induced renal fibrosis and renal function impairment following chronic alcohol exposure, and these effects were associated with attenuated GSK3β activation in the kidneys. Taken together, our results suggest that chronic alcohol exposure may potentiate AKI via β-arrestin 2/Akt/GSK3β-mediated signaling in the kidney.

UCP2 attenuates apoptosis of tubular epithelial cells in renal ischemia-reperfusion injury

Uncoupling protein-2 (UCP2) plays critical roles in energy metabolism and cell survival. Previous investigations showed that UCP2 regulated the production of extracellular matrix and renal fibrosis. However, little is known about UCP2 in acute kidney injury (AKI). Here, we used Ucp2 knockout mice to investigate the role of UCP2 in an AKI model generated by renal ischemia-reperfusion (I/R) injury. The Ucp2 global knockout mice were born and grew normally without kidney histological abnormality or renal dysfunction. Compared with littermates, deletion of Ucp2 exacerbated I/R-induced AKI whereas increase of UCP2 by conjugated linoleic acid (CLA) attenuated I/R injury. Tubular cell apoptosis and autophagy were induced by I/R. After injury, more tubular cell apoptosis and less autophagy were identified in the kidneys of knockout mice compared with their littermates, and less apoptosis and more autophagy were observed in mice fed with CLA. In vitro rotenone, an inhibitor of electron transport chain complex I, was applied to induce energy depletion in cultured tubular epithelial cells. As expected, rotenone-recovery (R/R) treatment induced tubular cell apoptosis and autophagy. UCP2 plasmid transfection reduced cell apoptosis and facilitated autophagy after R/R treatment, whereas UCP2 small interfering RNA (siRNA) transfection sensitized cell apoptosis but reduced autophagy induced by R/R treatment. Interference of autophagy by treatment with autophagy inhibitor 3-methyladenine or autophagy initiation protein Beclin-1 siRNA transfection resulted in tubular cell apoptosis. Thus UCP2 attenuates I/R-induced AKI, probably by reducing cell apoptosis through protection of autophagy.

AKT/GSK3β signaling pathway is critically involved in human pluripotent stem cell survival

Human embryonic and induced pluripotent stem cells are self-renewing pluripotent stem cells (PSC) that can differentiate into a wide range of specialized cells. Basic fibroblast growth factor is essential for PSC survival, stemness and self-renewal. PI3K/AKT pathway regulates cell viability and apoptosis in many cell types. Although it has been demonstrated that PI3K/AKT activation by bFGF is relevant for PSC stemness maintenance its role on PSC survival remains elusive. In this study we explored the molecular mechanisms involved in the regulation of PSC survival by AKT. We found that inhibition of AKT with three non-structurally related inhibitors (GSK690693, AKT inhibitor VIII and AKT inhibitor IV) decreased cell viability and induced apoptosis. We observed a rapid increase in phosphatidylserine translocation and in the extent of DNA fragmentation after inhibitors addition. Moreover, abrogation of AKT activity led to Caspase-9, Caspase-3, and PARP cleavage. Importantly, we demonstrated by pharmacological inhibition and siRNA knockdown that GSK3β signaling is responsible, at least in part, of the apoptosis triggered by AKT inhibition. Moreover, GSK3β inhibition decreases basal apoptosis rate and promotes PSC proliferation. In conclusion, we demonstrated that AKT activation prevents apoptosis, partly through inhibition of GSK3β, and thus results relevant for PSC survival.

Proteinuria causes dysfunctional autophagy in the proximal tubule

Proteinuria is a major risk factor for chronic kidney disease progression. Furthermore, exposure of proximal tubular epithelial cells to excess albumin promotes tubular atrophy and fibrosis, key predictors of progressive organ dysfunction. However, the link between proteinuria and tubular damage is unclear. We propose that pathological albumin exposure impairs proximal tubular autophagy, an essential process for recycling damaged organelles and toxic intracellular macromolecules. In both mouse primary proximal tubule and immortalized human kidney cells, albumin exposure decreased the number of autophagosomes, visualized by the autophagosome-specific fluorescent markers monodansylcadaverine and GFP-LC3, respectively. Similarly, renal cortical tissue harvested from proteinuric mice contained reduced numbers of autophagosomes on electron micrographs, and immunoblots showed reduced steady-state LC3-II content. Albumin exposure decreased autophagic flux in vitro in a concentration-dependent manner as assessed by LC3-II accumulation rate in the presence of bafilomycin, an H⁺-ATPase inhibitor that prevents lysosomal LC3-II degradation. In addition, albumin treatment significantly increased the half-life of radiolabeled long-lived proteins, indicating that the primary mechanism of degradation, autophagy, is dysfunctional. In vitro, mammalian target of rapamycin (mTOR) activation, a potent autophagy inhibitor, suppressed autophagy as a result of intracellular amino acid accumulation from lysosomal albumin degradation. mTOR activation was demonstrated by the increased phosphorylation of its downstream target, S6K, with free amino acid or albumin exposure. We propose that excess albumin uptake and degradation inhibit proximal tubule autophagy via an mTOR-mediated mechanism and contribute to progressive tubular injury.

Foscarnet, an inhibitor of the sodium-phosphate cotransporter NaPi-IIa, inhibits phosphorylation of glycogen synthase kinase-3β by lithium in the rat kidney cortex

Lithium, which is used in the treatment of and prophylaxis for bipolar disease, inhibits glycogen synthase kinase-3β (GSK3β) by producing its phosphorylated form (p-GSK3β). GSK3β plays a role in apoptosis and some kinds of acute kidney injuries, and the formation of p-GSK3β is considered to contribute to protection against acute kidney injury. We previously reported that the sodium-phosphate cotransporter NaPi-IIa (SLC34A1) mediated the reabsorption of lithium in the rat kidney. In the present study, the phosphorylation status of GSK3β in the kidney cortex of rats administered lithium chloride and foscarnet, a typical inhibitor of NaPi-IIa, was examined using Western blotting. Under a 2-h infusion of lithium chloride, the plasma concentration of lithium was 1.06 mEq/l, and its renal clearance was calculated as 1.18 ml/min/kg, which was 29.6% of creatinine clearance. The abundance of p-GSK3β in the kidney cortex was augmented by the administration of lithium. The simultaneous infusion of foscarnet increased the renal clearance of lithium and its ratio to creatinine clearance as well as the urinary excretion of phosphate. Foscarnet also inhibited the lithium-induced phosphorylation of GSK3β. These results suggest that the reabsorption of lithium by NaPi-IIa triggers the phosphorylation of GSK3β in the rat kidney cortex.

A cAMP and CREB-mediated feed-forward mechanism regulates GSK3β in polycystic kidney disease

Glycogen synthase kinase 3β (GSK3β), a serine/threonine protein kinase, is commonly known to be regulated at the level of its activity. However, in some diseases including polycystic kidney disease (PKD), GSK3β expression is increased and plays a pathophysiological role. The current studies aimed to determine the mechanism for the increased GSK3β expression in PKD and its significance to disease progression. In mouse models of PKD, increases in renal GSK3β corresponded with increases in renal cAMP levels and disease progression. In vivo and in vitro studies revealed that GSK3β is a cAMP-responsive gene, and elevated cAMP levels, as seen in PKD, can increase GSK3β expression. In normal mice, vasopressin signaling induced by water deprivation increased GSK3β expression, which decreased following rehydration. Examination of the GSK3β promoter revealed five potential binding sites for the transcription factor, cAMP response element binding protein (CREB). CREB was found to bind to GSK3β promoter and essential for cAMP-mediated regulation of GSK3β. Importantly, this regulation was demonstrated to be part of a feed-forward loop in which cAMP through CREB regulates GSK3β expression, and GSK3β in turn positively regulates cAMP generation. GSK3β or CREB inhibition reduced transepithelial fluid secretion and cyst expansion in vitro Thus, disruption at any point of this destructive cycle may be therapeutically useful to reduce cyst expansion and preserve renal function in PKD.

Glycogen synthase kinase 3β dictates podocyte motility and focal adhesion turnover by modulating paxillin activity: implications for the protective effect of low-dose lithium in podocytopathy

Aberrant focal adhesion turnover is centrally involved in podocyte actin cytoskeleton disorganization and foot process effacement. The structural and dynamic integrity of focal adhesions is orchestrated by multiple cell signaling molecules, including glycogen synthase kinase 3β (GSK3β), a multitasking kinase lately identified as a mediator of kidney injury. However, the role of GSK3β in podocytopathy remains obscure. In doxorubicin (Adriamycin)-injured podocytes, lithium, a GSK3β inhibitor and neuroprotective mood stabilizer, obliterated the accelerated focal adhesion turnover, rectified podocyte hypermotility, and restored actin cytoskeleton integrity. Mechanistically, lithium counteracted the doxorubicin-elicited GSK3β overactivity and the hyperphosphorylation and overactivation of paxillin, a focal adhesion-associated adaptor protein. Moreover, forced expression of a dominant negative kinase dead mutant of GSK3β highly mimicked, whereas ectopic expression of a constitutively active GSK3β mutant abolished, the effect of lithium in doxorubicin-injured podocytes, suggesting that the effect of lithium is mediated, at least in part, through inhibition of GSK3β. Furthermore, paxillin interacted with GSK3β and served as its substrate. In mice with doxorubicin nephropathy, a single low dose of lithium ameliorated proteinuria and glomerulosclerosis. Consistently, lithium therapy abrogated GSK3β overactivity, blunted paxillin hyperphosphorylation, and reinstated actin cytoskeleton integrity in glomeruli associated with an early attenuation of podocyte foot process effacement. Thus, GSK3β-modulated focal adhesion dynamics might serve as a novel therapeutic target for podocytopathy.

Renoprotective approaches and strategies in acute kidney injury

Acute kidney injury (AKI) is a major renal disease associated with high mortality rate and increasing prevalence. Decades of research have suggested numerous chemical and biological agents with beneficial effects in AKI. In addition, cell therapy and molecular targeting have been explored for reducing kidney tissue damage and promoting kidney repair or recovery from AKI. Mechanistically, these approaches may mitigate oxidative stress, inflammation, cell death, and mitochondrial and other organellar damage, or activate cytoprotective mechanisms such as autophagy and pro-survival factors. However, none of these findings has been successfully translated into clinical treatment of AKI. In this review, we analyze these findings and propose experimental strategies for the identification of renoprotective agents or methods with clinical potential. Moreover, we propose the consideration of combination therapy by targeting multiple targets in AKI.

Muc1 enhances the β-catenin protective pathway during ischemia-reperfusion injury

The hypoxia-inducible factor (HIF)-1 and β-catenin protective pathways represent the two most significant cellular responses that are activated in response to acute kidney injury. We previously reported that murine mucin (Muc)1 protects kidney function and morphology in a mouse model of ischemia-reperfusion injury (IRI) by stabilizing HIF-1α, enhancing HIF-1 downstream signaling, and thereby preventing metabolic stress (Pastor-Soler et al. Muc1 is protective during kidney ischemia-reperfusion injury. Am J Physiol Renal Physiol 308: F1452-F1462, 2015). We asked if Muc1 regulates the β-catenin protective pathway during IRI as 1) β-catenin nuclear targeting is MUC1 dependent in cultured human cells, 2) β-catenin is found in coimmunoprecipitates with human MUC1 in extracts of both cultured cells and tissues, and 3) MUC1 prevents β-catenin phosphorylation by glycogen synthase kinase (GSK)3β and thereby β-catenin degradation. Using the same mouse model of IRI, we found that levels of active GSK3β were significantly lower in kidneys of control mice compared with Muc1 knockout (KO) mice. Consequently, β-catenin was significantly upregulated at 24 and 72 h of recovery and appeared in the nuclear fraction at 72 h in control mouse kidneys. Both β-catenin induction and nuclear targeting were absent in Muc1 KO mice. We also found downstream induction of β-catenin prosurvival factors (activated Akt, survivin, transcription factor T cell factor 4 (TCF4), and its downstream target cyclin D1) and repression of proapoptotic factors (p53, active Bax, and cleaved caspase-3) in control mouse kidneys that were absent or aberrant in kidneys of Muc1 KO mice. Altogether, the data clearly indicate that Muc1 protection during acute kidney injury proceeds by enhancing both the HIF-1 and β-catenin protective pathways.

Lithium in the Kidney: Friend and Foe?

Trace amounts of lithium are essential for our physical and mental health, and administration of lithium has improved the quality of life of millions of patients with bipolar disorder for >60 years. However, in a substantial number of patients with bipolar disorder, long-term lithium therapy comes at the cost of severe renal side effects, including nephrogenic diabetes insipidus and rarely, ESRD. Although the mechanisms underlying the lithium-induced renal pathologies are becoming clearer, several recent animal studies revealed that short-term administration of lower amounts of lithium prevents different forms of experimental AKI. In this review, we discuss the knowledge of the pathologic and therapeutic effects of lithium in the kidney. Furthermore, we discuss the underlying mechanisms of these seemingly paradoxical effects of lithium, in which fine-tuned regulation of glycogen synthase kinase type 3, a prime target for lithium, seems to be key. The new discoveries regarding the protective effect of lithium against AKI in rodents call for follow-up studies in humans and suggest that long-term therapy with low lithium concentrations could be beneficial in CKD.