Activation of GSK3β/β-TrCP axis via PHLPP1 exacerbates Nrf2 degradation leading to impairment in cell survival pathway during diabetic nephropathy

Involvement of Sirt1-FoxO3a-Bnip3 axis and autophagy mediated mitochondrial turnover in according protection to hyperglycemic NRK-52E cells by Berberine

Aberrant accumulation of dysfunctional mitochondria in renal cells during hyperglycemia signifies perturbed autophagy and mitochondrial turnover. This study aims to focus on the underlying mechanism involved in autophagy and mitophagy inducing efficacy of Berberine (isoquinoline alkaloid) in hyperglycemic NRK-52E cells. Berberine mediated protection to hyperglycemic cells prevented alteration in mitochondrial structure and function. Treatment with SRT-1720 (Sirt1 activator) enhanced autophagy, decreased apoptosis, upregulated expression of downstream moieties (FoxO3a and Bnip3) and ameliorated mitochondria related anomalies while nicotinamide (Sirt1 inhibitor) treatment exhibited reversal of the same. GFP reporter assay ascertained enhanced transcriptional activity of FoxO in Berberine-treated hyperglycemic cells, which was found to be correlated to increased expression of downstream protein Bnip3. Knocking down FoxO3a disrupted autophagy and stimulated apoptosis. N-acetyl-L-cysteine pre-treatment confirmed that generation of ROS intervened high glucose induced toxicity in NRK-52E cells. Berberine co-treatment resulted in differential expressions of key proteins involved in autophagy and mitophagy like LC3B, ATGs, Beclin1, Sirt1, Bnip3, FoxO3a and Parkin. Further, enhanced mitophagy in Berberine-treated cells was confirmed by transmission electron microscopy. Thus, our findings give evidence that the protection accorded by Berberine against hyperglycemia in renal proximal tubular cells (NRK-52E) involves instigation of Sirt1-FoxO3a-Bnip3 axis and autophagy mediated mitophagy induction.

Targeting the AMPK/Nrf2 Pathway: A Novel Therapeutic Approach for Acute Lung Injury

ALI(acute lung injury) is a severe respiratory dysfunction caused by various intrapulmonary and extrapulmonary factors. It is primarily characterized by oxidative stress and affects the integrity of the pulmonary barrier. In severe cases, ALI can progress to ARDS(acute respiratory distress syndrome), a condition that poses a serious threat to the lives of affected patients. To date, the etiological mechanisms underlying ALI remain elusive, and available therapeutic options are quite limited. AMPK(AMP-activated protein kinase), an essential serine/threonine protein kinase, performs a pivotal function in the regulation of cellular energy levels and cellular regulatory mechanisms, including the detection of redox signals and mitigating oxidative stress. Meanwhile, Nrf2(nuclear factor erythroid 2-related factor 2), a critical transcription factor, alleviates inflammation and oxidative responses by interacting with multiple signaling pathways and contributing to the modulation of oxidative enzymes associated with inflammation and programmed cell death. Indeed, AMPK induces the dissociation of Nrf2 from Keap1(kelch-like ECH-associated protein-1) and facilitates its translocation into the nucleus to trigger the transcription of downstream antioxidant genes, ultimately suppressing the expression of inflammatory cells in the lungs. Given their roles, AMPK and Nrf2 hold promise as novel treatment targets for ALI. This study aimed to summarise the current status of research on the AMPK/Nrf2 signaling pathway in ALI, encompassing recently reported natural compounds and drugs that can activate the AMPK/Nrf2 signaling pathway to alleviate lung injury, and provide a theoretical reference for early intervention in lung injury and future research on lung protection.

The role of Interleukin-22 in severe acute pancreatitis

Severe acute pancreatitis (SAP) begins with premature activation of enzymes, promoted by the immune system, triggering a potential systemic inflammatory response that leads to organ failure with increased mortality and a bleak prognosis. Interleukin-22 (IL-22) is a cytokine that may have a significant role in SAP. IL-22, a member of the IL-10 cytokine family, has garnered growing interest owing to its potential tissue-protective properties. Recently, emerging research has revealed its specific effects on pancreatic diseases, particularly SAP. This paper provides a review of the latest knowledge on the role of IL-22 and its viability as a therapeutic target in SAP.

The ubiquitin codes in cellular stress responses

Ubiquitination/ubiquitylation, one of the most fundamental post-translational modifications, regulates almost every critical cellular process in eukaryotes. Emerging evidence has shown that essential components of numerous biological processes undergo ubiquitination in mammalian cells upon exposure to diverse stresses, from exogenous factors to cellular reactions, causing a dazzling variety of functional consequences. Various forms of ubiquitin signals generated by ubiquitylation events in specific milieus, known as ubiquitin codes, constitute an intrinsic part of myriad cellular stress responses. These ubiquitination events, leading to proteolytic turnover of the substrates or just switch in functionality, initiate, regulate, or supervise multiple cellular stress-associated responses, supporting adaptation, homeostasis recovery, and survival of the stressed cells. In this review, we attempted to summarize the crucial roles of ubiquitination in response to different environmental and intracellular stresses, while discussing how stresses modulate the ubiquitin system. This review also updates the most recent advances in understanding ubiquitination machinery as well as different stress responses and discusses some important questions that may warrant future investigation.

GSK3β: A ray of hope for the treatment of diabetic kidney disease

Diabetic kidney disease (DKD), a major microvascular complication of diabetes, is characterized by its complex pathogenesis, high risk of chronic renal failure, and lack of effective diagnosis and treatment methods. GSK3β (glycogen synthase kinase 3β), a highly conserved threonine/serine kinase, was found to activate glycogen synthase. As a key molecule of the glucose metabolism pathway, GSK3β participates in a variety of cellular activities and plays a pivotal role in multiple diseases. However, these effects are not only mediated by affecting glucose metabolism. This review elaborates on the role of GSK3β in DKD and its damage mechanism in different intrinsic renal cells. GSK3β is also a biomarker indicating the progression of DKD. Finally, the protective effects of GSK3β inhibitors on DKD are also discussed.

Nrf2: A promising therapeutic target in bone-related diseases

Nuclear factor erythroid-2-related factor 2 (Nrf2) plays an important role in maintaining cellular homeostasis, as it suppresses cell damage caused by external stimuli by regulating the transcription of intracellular defense-related genes. Accumulating evidence has highlighted the crucial role of reduction-oxidation (REDOX) imbalance in the development of bone-related diseases. Nrf2, a transcription factor linked to nuclear factor-erythrocyte 2, plays a pivotal role in the regulation of oxidative stress and induction of antioxidant defenses. Therefore, further investigation of the mechanism and function of Nrf2 in bone-related diseases is essential. Considerable evidence suggests that increased nuclear transcription of Nrf2 in response to external stimuli promotes the expression of intracellular antioxidant-related genes, which in turn leads to the inhibition of bone remodeling imbalance, improved fracture recovery, reduced occurrence of osteoarthritis, and greater tumor resistance. Certain natural extracts can selectively target Nrf2, potentially offering therapeutic benefits for osteogenic arthropathy. In this article, the biological characteristics of Nrf2 are reviewed, the intricate interplay between Nrf2-regulated REDOX imbalance and bone-related diseases is explored, and the potential preventive and protective effects of natural products targeting Nrf2 in these diseases are elucidated. A comprehensive understanding of the role of Nrf2 in the development of bone-related diseases provides valuable insights into clinical interventions and can facilitate the discovery of novel Nrf2-targeting drugs.

Reactive Oxygen Species and Strategies for Antioxidant Intervention in Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a life-threatening pulmonary condition characterized by the sudden onset of respiratory failure, pulmonary edema, dysfunction of endothelial and epithelial barriers, and the activation of inflammatory cascades. Despite the increasing number of deaths attributed to ARDS, a comprehensive therapeutic approach for managing patients with ARDS remains elusive. To elucidate the pathological mechanisms underlying ARDS, numerous studies have employed various preclinical models, often utilizing lipopolysaccharide as the ARDS inducer. Accumulating evidence emphasizes the pivotal role of reactive oxygen species (ROS) in the pathophysiology of ARDS. Both preclinical and clinical investigations have asserted the potential of antioxidants in ameliorating ARDS. This review focuses on various sources of ROS, including NADPH oxidase, uncoupled endothelial nitric oxide synthase, cytochrome P450, and xanthine oxidase, and provides a comprehensive overview of their roles in ARDS. Additionally, we discuss the potential of using antioxidants as a strategy for treating ARDS.

Insight into Nrf2: a bibliometric and visual analysis from 2000 to 2022

Background: Nrf2 plays a pivotal role in governing the antioxidant defense system, triggering the transcription of diverse genes involved in cellular protection. Its role in mitigating oxidative damage and modulating inflammatory processes has made Nrf2 an attractive target for therapeutic interventions. Despite the growing interest in Nrf2 research, a bibliometric analysis is relatively rare. This study aimed to clarify Nrf2's role in multiple diseases, identify emerging trends and hotspots using bibliometric analysis, and provide valuable insights and potential directions for future therapeutic interventions. Methods: The Science Citation Index of Web of Science Core library from 2000 to 2022 was searched on 22 October 2022. Use Microsoft Excel, CiteSpace, Bibliometrix, and VOS viewers for data collection and visualization of research focus and trends. Results: A vast collection of 22,040 research studies on Nrf2 published between 2000 and 2022 were identified. Nrf2 research has seen significant growth globally from 2000 to 2022. China leaded in publication numbers (9,623, 43.66%), while the United States dominated in citation frequency with 261,776 citations. China Medical University was the most productive institutions (459, 2.08%). Masayuki Yamamoto topped in publications (307), while Itoh K. ranked first in citations with 3669. Free Radical Biology and Medicine was the journal with the most studies and citations on Nrf2 (613, 29,687 citations). The analysis of keyword clustering enhanced the categorization of topics and can be summarized as oxidative stress, cancer, disorders in glycolipid metabolism, inflammation, and neurological conditions. Conclusion: China and the United States are the pioneers in Nrf2 research. Recently, there has been a comprehensive exploration of Nrf2 involving both experimental and clinical aspects, as well as mechanisms and therapeutic applications. Investigating novel molecular mechanisms, including NF-κB, Ho1, and Keap1, and developing enhanced, targeted Nrf2 activators or inhibitors to uncover the interplay among cancer, glycolipid metabolic disorder, inflammation, and neurological disorders will be upcoming trends and hotspots.

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.

Active Nrf2 signaling flexibly regulates HO-1 and NQO-1 in hypoxic Gansu Zokor (Eospalax cansus)

Gansu zokor (Eospalax cansus) is a typical subterranean rodent species with resistance to ambient hypoxia. The nuclear factor erythroid 2-related factor 2 (Nrf2) signaling plays a key role in regulating redox homeostasis. However, little is known about the regulation of Nrf2 signaling in Gansu zokor. We exposed Gansu zokors and SD rats to chronic hypoxia (44 h at 10.5% O₂) or acute hypoxia (6 h at 6.5% O₂) andmeasured the activities of heme oxygenase-1 (HO-1) and NAD(P)H quinone oxidoreductase-1 (NQO-1)，gene expression of HO-1, NQO-1, Nrf2, Kelch-like ECH-associated protein-1 (KEAP1), and β-transducin repeat-containing protein (β-TRCP) in the brain and liver. We found that Gansu zokor increased the NQO-1 protein content and activity, HO-1 protein content in the brain, and increased HO-1 activity and mRNA level, NQO-1 activity and protein content in the liver by up regulating Nrf2 gene expression under chronic hypoxia. Although acute hypoxia enhanced the expression of Nrf2 gene, only the level of HO-1 mRNA in the liver increased. Besides, the HO-1 and NQO-1 genes in the brain, HO-1 genes and NQO-1 mRNA in the Gansu zokor liver were significantly higher than those in SD rats under normoxia. Negative regulators of Nrf2 signaling were tissue specific: KEAP1 protein decreased in the brain, and β-TRCP decreased in the liver. The Nrf2 signaling and expression of downstream antioxidant enzymes were different under different oxygen concentrations, reflecting the flexible characteristics of Gansu zokor to deal with the hypoxic environment.

Empagliflozin attenuates the renal tubular ferroptosis in diabetic kidney disease through AMPK/NRF2 pathway

Renal tubular damage plays a key role in the pathogenesis of diabetic kidney disease (DKD), and one of the main pathological process associated with DKD in diabetic mice is the ferroptosis, a novel form of cell death caused by iron-dependent lipid peroxidation. Several researches suggested that empagliflozin may treat renal injury, but its effects on diabetic-related ferroptosis and underlying mechanisms were not fully elucidated. In this study, the influence of empagliflozin on renal injury was evaluated in vivo and in vitro in a mouse model and in high-glucose (HG) or Erastin-stimulated renal HK-2 cell line, respectively. Ferroptosis-related markers were assessed, including GSH, labile iron levels, and ferroptosis regulators by Western blot, qRT-PCR, immunohistochemistry, and immunofluorescence. The level of malondialdehyde (MDA) and the fluorescence intensity of BODIPY probe indicated the level of lipid peroxidation. It was demonstrated that solute carrier family 7, member 11 (SLC7A11) and glutathione peroxidase 4 (GPX4) were less expressed in renal biopsy samples from patients affected by DKD than in those from non-diabetic renal disease patients (NDRD), proving the ferroptosis of tubular epithelial cells in case of DKD. Furthermore, empagliflozin markedly decreased the ferroptosis impairment in DKD mice, as well as in HG model of HK-2 cells. Our investigations showed the ability of empagliflozin to suppress ferroptosis was partially countered by AMP-activated protein kinase (AMPK) inhibitor, which led to a reduction of the nuclear translocation of the antioxidant transcription factor NFE2-related factor 2 (NRF2) and downregulation of target genes such as GPX4, ferritin heavy chain 1 (FTH1), and SLC7A11, while AMPK agonists were responsible for the enhancement of the protective effects of empagliflozin. Taken together, our findings showed that empagliflozin may prevent the development of ferroptosis by promoting the AMPK-mediated NRF2 activation pathway, providing important insights for possible novel treatment approaches for DKD.

CircRNA_45478 promotes ischemic AKI by targeting the miR-190a-5p/PHLPP1 axis

A few studies suggested that circular RNAs were involved in the development of ischemic acute kidney injury (AKI). However, the function and regulation mechanism of circRNA_45478 in ischemic AKI remains unknown. In the present study, ischemic injury induced the expressions of circRNA_45478 in mouse proximal tubule-derived cell lines (BUMPT cells) and kidneys of C57BL/6 mice. Functionally, circRNA_45478 mediated I/R-induced apoptosis in BUMPT cells. Mechanistically, circRNA_45478 upregulated the expression of Pleckstrin homology (PH) domain leucine-rich repeat protein phosphatase 1 (PHLPP1) via sponging of microRNA (miR)-190a-5p. Finally, inhibition of circRNA_45478 significantly alleviated the progression of ischemic AKI through regulation of the miR-190a-5p/PHLPP1 pathway. Taken together, our data showed that circRNA_45478/miR-190a-5p/PHLPP1 axis mediated the progression of ischemic AKI.

The protective effect of natural medicines against excessive inflammation and oxidative stress in acute lung injury by regulating the Nrf2 signaling pathway

Acute lung injury (ALI) is a common critical disease of the respiratory system that progresses into acute respiratory distress syndrome (ARDS), with high mortality, mainly related to pulmonary oxidative stress imbalance and severe inflammation. However, there are no clear and effective treatment strategies at present. Nuclear factor erythroid 2-related factor 2(Nrf2) is a transcription factor that interacts with multiple signaling pathways and regulates the activity of multiple oxidases (NOX, NOS, XO, CYP) related to inflammation and apoptosis, and exhibits antioxidant and anti-inflammatory roles in ALI. Recently, several studies have reported that the active ingredients of natural medicines show protective effects on ALI via the Nrf2 signaling pathway. In addition, they are cheap, naturally available, and possess minimal toxicity, thereby having good clinical research and application value. Herein, we summarized various studies on the protective effects of natural pharmaceutical components such as polyphenols, flavonoids, terpenoids, alkaloids, and polysaccharides on ALI through the Nrf2 signaling pathway and demonstrated existing gaps as well as future perspectives.

PHLPPs: Emerging players in metabolic disorders

That reversible protein phosphorylation by kinases and phosphatases occurs in metabolic disorders is well known. Various studies have revealed that a multi-faceted and tightly regulated phosphatase, pleckstrin homology domain leucine-rich repeat protein phosphatase (PHLPP)-1/2 displays robust effects in cardioprotection, ischaemia/reperfusion (I/R), and vascular remodelling. PHLPP1 promotes foamy macrophage development through ChREBP/AMPK-dependent pathways. Adipocyte-specific loss of PHLPP2 reduces adiposity, improves glucose tolerance,and attenuates fatty liver via the PHLPP2-HSL-PPARα axis. Discoveries of PHLPP1-mediated insulin resistance and pancreatic β cell death via the PHLPP1/2-Mst1-mTORC1 triangular loop have shed light on its significance in diabetology. PHLPP1 downregulation attenuates diabetic cardiomyopathy (DCM) by restoring PI3K-Akt-mTOR signalling. In this review, we summarise the functional role of, and cellular signalling mediated by, PHLPPs in metabolic tissues and discuss their potential as therapeutic targets.

The Putative Role of Astaxanthin in Neuroinflammation Modulation: Mechanisms and Therapeutic Potential

Neuroinflammation is a protective mechanism against insults from exogenous pathogens and endogenous cellular debris and is essential for reestablishing homeostasis in the brain. However, excessive prolonged neuroinflammation inevitably leads to lesions and disease. The use of natural compounds targeting pathways involved in neuroinflammation remains a promising strategy for treating different neurological and neurodegenerative diseases. Astaxanthin, a natural xanthophyll carotenoid, is a well known antioxidant. Mounting evidence has revealed that astaxanthin is neuroprotective and has therapeutic potential by inhibiting neuroinflammation, however, its functional roles and underlying mechanisms in modulating neuroinflammation have not been systematically summarized. Hence, this review summarizes recent progress in this field and provides an update on the medical value of astaxanthin. Astaxanthin modulates neuroinflammation by alleviating oxidative stress, reducing the production of neuroinflammatory factors, inhibiting peripheral inflammation and maintaining the integrity of the blood-brain barrier. Mechanistically, astaxanthin scavenges radicals, triggers the Nrf2-induced activation of the antioxidant system, and suppresses the activation of the NF-κB and mitogen-activated protein kinase pathways. With its good biosafety and high bioavailability, astaxanthin has strong potential for modulating neuroinflammation, although some outstanding issues still require further investigation.

MicroRNA-299a-5p Protects against Spinal Cord Injury through Activating AMPK Pathway

Objective

Inflammation and oxidative stress are implicated in the pathogenesis of spinal cord injury (SCI). The present study is aimed at investigating the function and molecular basis of microRNA-299a-5p (miR-299a-5p) during SCI in mice.

Methods

Mice were exposed to SCI surgery and then intrathecally injected with the agomir, antagomir, or matched negative controls of miR-299a-5p to overexpress or silence miR-299a-5p. To inhibit AMP-activated protein kinase (AMPK), mice were intraperitoneally injected with compound C (CC). To overexpress pH domain and leucine-rich repeat protein phosphatase 1 (PHLPP1), lentiviral vectors were used.

Results

The miR-299a-5p expression in the spinal cord was dramatically reduced by SCI stimulation. The miR-299a-5p agomir prevents, while the miR-299a-5p antagomir exacerbates inflammation, oxidative stress, and SCI in mice. Mechanistically, we found that miR-299a-5p directly inhibited PHLPP1 and subsequently activated AMPK pathway. The PHLPP1 overexpression of AMPK inhibition with either genetic or pharmacologic methods dramatically abolished the miR-299a-5p agomir-mediated protective effects against SCI.

Conclusion

miR-299a-5p protects against spinal cord injury through activating AMPK pathway.

Targeting NRF2 in Type 2 diabetes mellitus and depression: Efficacy of natural and synthetic compounds

Evidence supports a strong bidirectional association between depression and Type 2 diabetes mellitus (T2DM). The harmful impact of oxidative stress and chronic inflammation on the development of both disorders is widely accepted. Nuclear factor erythroid 2-related factor 2 (NRF2) is a pertinent target in disease management owing to its reputation as the master regulator of antioxidant responses. NRF2 influences the expression of various cytoprotective phase 2 antioxidant genes, which is hampered in both depression and T2DM. Through interaction and crosstalk with several signaling pathways, NRF2 endeavors to contain the widespread oxidative damage and persistent inflammation involved in the pathophysiology of depression and T2DM. NRF2 promotes the neuroprotective and insulin-sensitizing properties of its upstream and downstream targets, thereby interrupting and preventing disease advancement. Standard antidepressant and antidiabetic drugs may be powerful against these disorders, but unfortunately, they come bearing distressing side effects. Therefore, exploiting the therapeutic potential of NRF2 activators presents an exciting opportunity to manage such bidirectional and comorbid conditions.

p-Chloro-diphenyl diselenide modulates Nrf2/Keap1 signaling and counteracts renal oxidative stress in mice exposed to dexamethasone repeated administrations

Dexamethasone is a synthetic glucocorticoid that has been associated with oxidative stress in central and peripheral tissues. p-Chloro-diphenyl diselenide (p-ClPhSe)2 is an antioxidant organoselenium compound. The present study aimed to evaluate whether Nrf2/Keap-1 signaling contributes to the (p-ClPhSe)2 antioxidant effects in the kidney of mice exposed to dexamethasone. Adult Swiss mice received dexamethasone (i.p) at a dose of 2 mg/kg or its vehicle for 21 days. After, mice were treated with (p-ClPhSe)2 (i.g)(1, 5, or 10 mg/kg) for 7 days. Samples of kidneys were collected for biochemical assays. (p-ClPhSe)2 at dose of 1 mg/kg reversed the renal reactive oxygen species (ROS) and carbonyl protein (CP) levels increased by dexamethasone. (p-ClPhSe)2 at doses of 5 and 10 mg/kg was effective against the increase of TBARS (thiobarbituric acid reactive substances), ROS, and CP as well as the decrease of δ-aminolevulinic acid dehydratase (δ-ALA-D) activity and non-protein SH (NPSH) levels induced by dexamethasone. At 5 mg/kg, (p-ClPhSe)2 reduced the renal levels of 4-OH-2-HNE and HO-1 as well as modulated the Nrf2/Keap-1 signaling in mice exposed to dexamethasone. The present findings revealed that (p-ClPhSe)2 antioxidant effects were associated with the modulation of Nrf2/Keap-1 signaling pathway in the kidney of mice exposed to dexamethasone.

Endoplasmic reticulum stress-dependent activation of TRB3-FoxO1 signaling pathway exacerbates hyperglycemic nephrotoxicity: Protection accorded by Naringenin

Endoplasmic reticulum (ER) dysfunction contributes greatly to the pathophysiology of hyperglycemic nephrotoxicity. This study unravels the critical role of Tribbles 3 (TRB3)-Forkhead box O1 (FoxO1) signaling pathway during hyperglycemic renal toxicity. It also uncovers the novel role of Naringenin, a flavanone, in regulating ER stress in proximal tubular cells, NRK 52E, and kidneys of streptozotocin/nicotinamide induced experimental diabetic Wistar rats. Results demonstrate that expression of ER stress marker proteins including phosphorylated protein kinase ER like kinase (p-PERK), phosphorylated eukaryotic Initiation Factor 2α (p-eIF2α), X Box Binding Protein 1 spliced (XBP1s), Activating Transcription Factor 4 (ATF4) and C/EBP Homologous Protein (CHOP) were upregulated in diabetic kidneys indicating the activation of ER stress response due to nephrotoxicity. Treatment with Naringenin reduced the expression of TRB3, an ER stress-inducible pseudokinase, both in vitro and in vivo. Gene silencing of TRB3 enhanced Akt and FoxO1 phosphorylation and alleviated FoxO1 mediated apoptosis during hyperglycemic nephrotoxicity. Notably, TRB3 gene silencing effects were comparable to the response with Naringenin treatment. Prevention of nuclear colocalization of ATF4 and CHOP in Naringenin treated cells was evident. Naringenin also reduced insulin resistance, apoptosis and glycogen accumulation along with enhancement of glucose tolerance in diabetic rats. Prevention of ultrastructural aberrations in the ER of hyperglycemic renal cells by Naringenin confirmed its anti-ER stress effects. These findings affirm that activation of TRB3-FoxO1 signaling is critical in the pathogenesis of hyperglycemia-induced renal toxicity and protective effect of Naringenin via modulation of ER stress may be exploited as a novel approach for its management.

LncRNA ZFAS1 regulates the proliferation, oxidative stress, fibrosis, and inflammation of high glucose-induced human mesangial cells via the miR-588/ROCK1 axis

BACKGROUND

Diabetic nephropathy (DN) is a critical and the most common microvascular complication and its pathogenesis is still faintly understood. Thus, this study was performed to examine the long non-coding RNA ZNFX1 Antisense Gene Protein 1 (lncRNA ZFAS1) biological function and mechanism of regulation in DN.

METHOD

Human glomerular mesangial cells (HGMC) were induced with high glucose (HG, 25 mM) to establish HG-induced cell viability, pro-inflammation observed in DN. After, target miRNA and mRNA were predicted through Lncbase and Targetscan. Subsequently, the expression of ZFAS1, miR-588, and ROCK1 in DN clinical samples and cell-model was examined through qRT-PCR and western blot analysis. We upheld the targeted interaction between miR-588 and ZFAS1 or ROCK1 through a dual-luciferase reporter assay. The proliferation of the cell was also examined through CCK-8 assay, while the level of HG-induced oxidative stress was established by measuring reactive oxygen species (ROS) level, and also the activities of antioxidant enzymes in the cell. Lastly, the level of accumulated extracellular matrix (ECM) protein-fibronectin and collagen type IV, and inflammatory cytokines produced by the cell was analyzed through western blot analysis and ELISA.

RESULTS

ZFAS1 was significantly upregulated in the DN blood samples and HG-induced HGMC. Prediction result revealed that the ZFAS1 endogenously targets the miR-588 seed sequence while miR-588 plays a role in post-transcriptional regulation of ROCK1 mRNA. Moreover, we found that miR-588 expression was significantly downregulated in DN blood samples and negatively correlates with ZFAS1 expression. Further results show that silencing ZFAS1 had a protective effect on HG-induced proliferation, oxidative stress, fibrosis, and inflammation in HGMC while miR-588 inhibition and ROCK1 overexpression reversed this effect.

CONCLUSIONS

Altogether, our data suggest that ZFAS1 regulates the proliferation, oxidative stress, fibrosis, and inflammation of high glucose-induced diabetic nephropathy through the miR-588/ROCK1 axis.

Knockdown of transient receptor potential melastatin 2 reduces renal fibrosis and inflammation by blocking transforming growth factor-β1-activated JNK1 activation in diabetic mice

BACKGROUND

Diabetic nephropathy is a major complication of diabetes. We explore the protective effect of TRPM2 knockdown on the progression of diabetic nephropathy.

METHODS

A type 2 diabetes animal model was established in C57BL/6N mice by long-term high-fat diet (HFD) feeding combined with a single injection of 100 mg/kg streptozotocin (STZ). Genetic knockdown of TRPM2 in mouse kidneys was accomplished by the intravenous injection via the tail vein of adeno-associated virus type 2 carrying TRPM2 shRNA.

RESULTS

Mice with HFD/STZ-induced diabetes exhibited kidney dysfunction, as demonstrated by increased blood creatinine and urea nitrogen levels, accompanied by glomerulus derangement, tubule damage and extracellular matrix deposition in the interstitium. The protein expression of TRPM2, transforming growth factor-β1 (TGF-β1), connective tissue growth factor, α-smooth muscles actin, fibronectin, collagen I and collagen III, and the mRNA expression and contents of inflammatory factors, including interleukin-1β, interleukin-6, interferon-α, tumour necrosis factor -α and monocyte chemotactic protein -1, were significantly elevated in the renal tissues of the HFD/STZ-induced diabetes group compared to those of the two control groups. Furthermore, fluorescent staining of TRPM2 was markedly increased in the renal tubular epithelial cells from diabetic mice. Knockdown of TRPM2 significantly attenuated HFD/STZ-induced renal inflammatory responses and fibrosis, which was accompanied by activation of TGF-β1-activated c-Jun N-terminal protein kinase-1 (JNK1) signalling. JNK1 inactivation reversed hyperglycaemia-induced fibrosis and inflammation in HK-2 cells.

CONCLUSION

TRPM2 silencing significantly attenuated fibrosis and inflammation in the kidneys of mice with HFD/STZ-induced diabetes, which was largely achieved via the inhibition of TGF-β1-activated JNK1 activation.

Naringenin alleviates hyperglycemia-induced renal toxicity by regulating activating transcription factor 4-C/EBP homologous protein mediated apoptosis

Endoplasmic reticulum (ER) dysfunction plays a prominent role in the pathophysiology of diabetic nephropathy (DN). This study aimed to investigate the novel role of Naringenin (a flavanone mainly found in citrus fruits) in modulating ER stress in hyperglycemic NRK 52E cells and STZ/nicotinamide induced diabetes in Wistar rats. The results demonstrated that Naringenin supplementation downregulated the expression of ER stress marker proteins, including p-PERK, p-eIF2α, XBP1s, ATF4 and CHOP during hyperglycemic renal toxicity in vitro and in vivo. Naringenin abrogated hyperglycemia-induced ultrastructural changes in ER, evidencing its anti-ER stress effects. Interestingly, treatment of Naringenin prevented nuclear translocation of ATF4 and CHOP in hyperglycemic renal cells and diabetic kidneys. Naringenin prevented apoptosis in hyperglycemic renal cells and diabetic kidney tissues by downregulating expression of apoptotic marker proteins. Further, photomicrographs of TEM confirmed anti-apoptotic potential of Naringenin as it prevented membrane blebbing and formation of apoptotic bodies in hyperglycemic renal cells. Naringenin improved glucose tolerance, restored serum insulin level and reduced serum glucose level in diabetic rats evidencing its anti-hyperglycemic effects. Histopathological examination of kidney tissues also confirmed prevention of damage after 28 days of Naringenin treatment in diabetic rats. Additionally, Naringenin diminished oxidative stress and improved antioxidant defense response during hyperglycemic renal toxicity. Taken together, our study revealed a novel role of Naringenin in ameliorating ER stress during hyperglycemic renal toxicity along with prevention of apoptosis, cellular and tissue damage. The findings suggest that prevention of ER stress can be exploited as a novel approach for the management of hyperglycemic nephrotoxicity.

Salusin‑β participates in high glucose‑induced HK‑2 cell ferroptosis in a Nrf‑2‑dependent manner

Ferroptosis is critically involved in the pathophysiology of diabetic nephropathy (DN). As a bioactive peptide, salusin‑β is abundantly expressed in the kidneys. However, it is unclear whether salusin‑β participates in the pathologies of diabetic kidney damage by regulating ferroptosis. The present study found that high glucose (HG) treatment upregulated the protein expressions of salusin‑β in a dose‑ and time‑dependent manner. Genetic knockdown of salusin‑β retarded, whereas overexpression of salusin‑β aggravated, HG‑triggered iron overload, antioxidant capability reduction, massive reactive oxygen species production and lipid peroxidation in HK‑2 cells. Mechanistically, salusin‑β inactivated nuclear factor erythroid‑derived 2‑like 2 (Nrf‑2) signaling, thus contributing to HG‑induced ferroptosis‑related changes in HK‑2 cells. Notably, the protein expression of salusin‑β was upregulated by ferroptosis activators, such as erastin, RSL3, FIN56 and buthionine sulfoximine. Pretreatment with ferrostatin‑1 (a ferroptosis inhibitor) prevented the upregulated protein expression of salusin‑β in HK‑2 cells exposed to HG. Taken together, these results suggested that a positive feedback loop between salusin‑β and ferroptosis primes renal tubular cells for injury in diabetes.

Ticagrelor and Dapagliflozin Have Additive Effects in Ameliorating Diabetic Nephropathy in Mice with Type-2 Diabetes Mellitus

PURPOSE

Ticagrelor and dapagliflozin can suppress the activation of the NOD-like receptor 3 (NLRP3)-inflammasome and activate AMP-activated protein kinase (AMPK). The anti-inflammatory effects of dapagliflozin has been shown to depend on AMPK activation. Dapagliflozin and ticagrelor have been shown to have additive effects on the progression of diabetic cardiomyopathy in BTBR ob/ob mice with type-2 diabetes. We assessed whether dapagliflozin and ticagrelor have additive effects on the activation of the NLRP3-inflammasome and the progression of diabetic nephropathy in mice with type-2 diabetes.

METHODS

Eight-week-old BTBR received either no-drug, dapagliflozin (1.5 mg/kg/d), ticagrelor (100 mg/kg/d), or their combination for 12 weeks. Blood was assessed weekly for glucose and urine for glucose and albumin. After 12 weeks, blood creatinine, cystatin C, inflammasome activation, and insulin were assessed by ELISA. Renal cortex samples were assessed by hematoxylin and eosin and periodic acid-Schiff staining. RT-PCR and immunoblotting were used to evaluate fibrosis and the activation of Akt, AMPK and the inflammasome.

RESULTS

Both ticagrelor and dapagliflozin reduced serum creatinine and cystatin C levels and urinary albumin. Both drugs attenuated the increase in glomerular area and mesangial matrix index. Both drugs decreased collagen-1 and collagen-3 expression and the activation of the NLRP3-inflammasome. Both drugs increased P-AMPK levels, but only dapagliflozin increased P-Akt levels. Overall, the protective effects of dapagliflozin and ticagrelor were additive.

CONCLUSIONS

Dapagliflozin and ticagrelor attenuated the progression of diabetic nephropathy in BTBR ob/ob mice with additive effects of the combination. This was associated with AMPK activation and reduced activation of the NLRP3 inflammasome, whereas only dapagliflozin increased Akt activation.

PHLPP1/Nrf2-Mdm2 axis induces renal apoptosis via influencing nucleo-cytoplasmic shuttling of FoxO1 during diabetic nephropathy

Impaired PI3K/Akt signaling (insulin resistance) and poor glycemic control (hyperglycemia) are the major risk factors involved in the progression of diabetic nephropathy (DN). This study was designed to identify factors influencing cell survival during DN. We found that high glucose exposure in renal proximal tubular cells (NRK52E) upregulated PHLPP1, an Akt phosphatase (Ser473), causing suppression in Akt and IGF1β phosphorylation leading to inhibition in insulin signaling pathway. Results demonstrate that sustained activation of PHLPP1 promoted nuclear retention of FoxO1 by preventing its ubiquitination via Mdm2, an Akt/ Nrf2-dependent E3 ligase. Thus, enhanced FoxO1 nuclear stability caused aberration in renal gluconeogenesis and activated apoptotic cascade. Conversely, gene silencing of PHLPP1-enhanced Nrf2 expression and attenuated FoxO1 regulated apoptosis compared to hyperglycemic cells. Mechanistic aspects of PHLPP1-Nrf2/FoxO1 signaling were further validated in STZ-nicotinamide-induced type 2 diabetic Wistar rats. Importantly, we observed via immunoblotting and dual immunocytochemical studies that treatment of Morin (2',3,4',5,7-Pentahydroxyflavone) during diabetes significantly augmented FoxO1 nuclear exclusion, resulting in its ubiquitination via Akt-Nrf2/Mdm2 pathway. Furthermore, lowering of PHLPP1 expression by Morin also prevented FoxO1/Mst1-mediated apoptotic signaling in vitro and in vivo. Morin treatment under the experimental conditions, effectively decreased blood glucose levels, ameliorated insulin resistance, alleviated oxidative stress and attenuated renal apoptosis in diabetic rats comparable to metformin thereby exhibiting tremendous potential against renal complications of diabetes. These novel results further acclaim that inhibition of PHLPP1/FoxO1-Mdm2 axis is critical in the pathogenesis of diabetic nephropathy.

Ginsenoside Rh1 Improves Type 2 Diabetic Nephropathy through AMPK/PI3K/Akt-Mediated Inflammation and Apoptosis Signaling Pathway

Although ginseng (Panax ginseng C.A. Meyer) has received extensive attention in the treatment and prevention of type 2 diabetes mellitus (T2DM) in the past few decades, there are few studies on the complications of T2DM. At present, obesity-linked diabetic nephropathy (DN) has become the most prevailing element of the end-stage renal failure in the world. The aim of this work is to evaluate the ameliorative effects of ginsenoside Rh1 (G-Rh1) on DN induced by high fat diet plus streptozotocin (HFD/STZ) through some potential and combined mechanisms of action. The results showed that G-Rh1 treatment at 5 and 10 mg/kg for 8 weeks exerted excellent effects in controlling fasting blood glucose (FBG), improving glucose tolerance, and increasing insulin level. In addition, G-Rh1 effectively prevents the excessive production of advanced glycation end products (AGEs), a diabetic nephropathy marker, in HFD/STZ induced DN mice. Meanwhile, oxidation indicators including SOD, GSH, and MDA were improved by G-Rh1 treatment to varying degrees. It is worth noting that G-Rh1 not only inhibits the secretion of Nox1 and Nox4 in kidney tissues, but also has an inhibitory effect on inflammatory factors and NF-[Formula: see text]B signaling pathway. Importantly, further in-depth research on molecular mechanisms provides vital evidence that the ameliorative effect of G-Rh1 on DN is related to the inhibition of apoptosis and the AMPK/PI3K/Akt signaling pathway. In summary, G-Rh1 may be of great value in improving the treatment of DN although more experimental data is needed.

Alleviative effects of 20(R)-Rg3 on HFD/STZ-induced diabetic nephropathy via MAPK/NF-κB signaling pathways in C57BL/6 mice

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic nephropathy (DN) is a major complication of diabetes. The kidney disease develops in nearly 20%-40% of type 2 diabetes (T2D) patients. Ginseng is the root of Panax ginseng C. A. Meyer and has been used in prevention and treatment of diseases for more than 2000 years as a traditional oriental medicine. The 20(R)-ginsenoside Rg3, an active saponin isolated from ginseng, can prevent and treat many diseases. The object of this research was to explore the alleviative effects of 20(R)-Rg3 on DN in mice.

MATERIALS AND METHODS

The T2D animal model was induced by continuous access to a high fat diet (HFD) combined with a single injection of 100 mg/kg streptozotocin (STZ) in C57BL/6 mice. The mice were treated by oral gavage of the 20(R)-Rg3 (10, 20 mg/kg) for 8 weeks. Functional and histopathological analyses of the kidneys were then performed. Protein expression levels of MAPKs and NF-κB signal pathways in the kidney were evaluated by western blotting. The expressions of HO-1 and NF-κB in the kidney were measured by fluorescent labeling staining. Other assessments including fasting blood glucose (FBG) levels, blood lipids, oxidative indicators, and inflammatory factors were all performed.

RESULTS

Abnormally elevated FBG levels were observed in HFD/STZ mice, contributing significantly to the occurrence of DN. Simultaneously, HFD/STZ mice showed the rise of serum total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C) levels, and the decrease in high density lipoprotein cholesterol (HDL-C). DN was evidenced by the overproduction of malondialdehyde (MDA), decreased levels of superoxide dismutase (SOD) and catalase (CAT) enzymatic activities, high levels of serum blood urea nitrogen (BUN) and creatinine (Cr). Simultaneously, the results of the immunofluorescence assay showed an increased expression level in NF-κB p65 while a decrease in antioxidant enzyme HO-1 was observed. Herein, 20(R)-Rg3 treatment for 8 weeks not only attenuated FBG levels and advanced glycation end products (AGEs) levels but also improved insulin (INS) level, blood lipids, oxidative stress, and renal function by regulating MAPKs and NF-κB signal pathways in DN mice.

CONCLUSION

Taken together, the findings from the present study explicitly confirmed that 20(R)-Rg3 exerted ameliorative effects on DN mice via improving anti-oxidative activity and reducing renal inflammation.

Mitochondrial Dysfunction and Diabetic Nephropathy: Nontraditional Therapeutic Opportunities

Diabetic nephropathy (DN) is a progressive microvascular diabetic complication. Growing evidence shows that persistent mitochondrial dysfunction contributes to the progression of renal diseases, including DN, as it alters mitochondrial homeostasis and, in turn, affects normal kidney function. Pharmacological regulation of mitochondrial networking is a promising therapeutic strategy for preventing and restoring renal function in DN. In this review, we have surveyed recent advances in elucidating the mitochondrial networking and signaling pathways in physiological and pathological contexts. Additionally, we have considered the contributions of nontraditional therapy that ameliorate mitochondrial dysfunction and discussed their molecular mechanism, highlighting the potential value of nontraditional therapies, such as herbal medicine and lifestyle interventions, in therapeutic interventions for DN. The generation of new insights using mitochondrial networking will facilitate further investigations on nontraditional therapies for DN.

Atorvastatin Regulates MALAT1/miR-200c/NRF2 Activity to Protect Against Podocyte Pyroptosis Induced by High Glucose

BACKGROUND

Diabetic nephropathy (DN) is one of the main complications of diabetes mellitus (DM), which leads to the long-term loss of kidney functions. Long noncoding RNAs (LncRNAs) can alleviate DN by interacting with microRNAs (miRNAs). In this work, we aimed to explore the effects of the MALAT1/miR-200c/NRF2 regulatory axis on the pyroptosis and oxidative stress (Oxidative stress, OS) of renal podocytes in high glucose (HG) environment and whether the lipid-lowering drug atorvastatin (AT) can relieve renal OS through this approach.

METHODS

MPC-5, a mouse podocyte cell line, was induced by HG as a cell model. The protein expressions of caspase-1, GSDMD, NLRP3, NRF2, etc. were detected by Western blotting and immunofluorescence, and the mRNA level of caspase-1, GSDMD, NLRP3, NRF2, MALAT1, miR-200c was tested by qRT-PCR. The cell pyroptosis of podocytes treated with AT was verified by CCK-8 or flow cytometry. The levels of Malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) were measured by spectrophotometer, respectively.

RESULTS

The caspase-1 was upregulated in time-dependent manner and got the peak at 48 h and 30 mmol/L respectively in MPC-5 cells treated with HG. Further, the expression of GSDMD, MALAT1 and miR-200c were increased, while the level of NRF2, HO-1, OS-related indicators, were decreased simultaneously. Knockdown the MALAT1 protected MPC-5 cells from pyroptosis and OS induced by HG. However, overexpressing miR-200c in control-group cells increased pyroptosis and upregulated the OS level with HG culture medium. Further, atorvastatin protected MPC-5 cells from cell pyroptosis and downregulated the level of renal OS via attenuating the expression of MALAT1 and miR-200c.

CONCLUSION

Atorvastatin protects podocyte cells via MALAT1/miR-200c/NRF2 signal pathway from pyroptosis and OS induced by HG.

Inhibition of ferroptosis by up-regulating Nrf2 delayed the progression of diabetic nephropathy

Diabetic nephropathy (DN) is now considered the leading cause of end-stage renal disease. In diabetes, the accumulation of reactive oxygen species (ROS) and iron overload are important determinants that promote the occurrence of DN. However, the underlying mechanism of how they cause diabetic kidney damage remains unclear. Ferroptosis, characterized by iron-dependent lipid peroxidation, provided us with a new idea to explore the progression of DN. Iron overload, reduced antioxidant capability, massive ROS and lipid peroxidation were detected in the kidneys of streptozotocin-induced DBA/2J diabetic mice and high-glucose cultured human renal proximal tubular (HK-2) cells, which were the symbolic changes of ferroptosis. Furthermore, the characteristic mitochondrial morphological changes of ferroptosis were observed in high glucose cultured cells. Additional treatment of Ferrostatin-1 (Fer-1) in DN models significantly rescued these changes and alleviated the renal pathological injuries in diabetic mice. Besides, the decreased NFE2-related factor 2 (Nrf2) was observed in DN models. The specific knockdown of Nrf2 increased the sensitivity of cells to ferroptosis in the high glucose condition. In Nrf2 knockdown cells, up-regulating Nrf2 by treating with fenofibrate improved the situation of ferroptosis, which was verified in RSL-3 induced cells. Moreover, the ferroptosis-related changes were inhibited by increasing Nrf2 in fenofibrate treated diabetic mice, which delayed the progression of DN. Collectively, we demonstrated that ferroptosis was involved in the development of DN, and up-regulating Nrf2 by treating with fenofibrate inhibited diabetes-related ferroptosis, delaying the progression of DN. Our research revealed the development mechanism of DN from a new perspective, and provide a new approach delaying the progression of DN.

Isoliquiritigenin prevents hyperglycemia-induced renal injuries by inhibiting inflammation and oxidative stress via SIRT1-dependent mechanism

Diabetic nephropathy (DN) as a global health concern is closely related to inflammation and oxidation. Isoliquiritigenin (ISL), a natural flavonoid compound, has been demonstrated to inhibit inflammation in macrophages. Herein, we investigated the effect of ISL in protecting against the injury in STZ-induced type 1 DN and in high glucose-induced NRK-52E cells. In this study, it was revealed that the administration of ISL not only ameliorated renal fibrosis and apoptosis, but also induced the deterioration of renal function in diabetic mice. Mediated by MAPKs and Nrf-2 signaling pathways, respectively, upstream inflammatory response and oxidative stress were neutralized by ISL in vitro and in vivo. Moreover, as further revealed by the results of molecular docking, sirtuin 1 (SIRT1) binds to ISL directly, and the involvement of SIRT1 in ISL-mediated renoprotective effects was confirmed by studies using in vitro models of SIRT1 overexpression and knockdown. In summary, by reducing inflammation and oxidative stress, ISL has a significant pharmacological effect on the deterioration of DN. The benefits of ISL are associated with the direct binding to SIRT1, the inhibition of MAPK activation, and the induction of Nrf-2 signaling, suggesting the potential of ISL for DN treatment.

Downregulation of PHLPP1 ameliorates high glucose-evoked injury in retinal ganglion cells by attenuating apoptosis and oxidative stress through enhancement of Nrf2 activation

High glucose (HG)-induced oxidative stress contributes significantly to the pathogenesis of diabetic retinopathy. Pleckstrin homology domain and leucine rich repeat protein phosphatase 1 (PHLPP1) has emerged as a key regulator of oxidative stress implicated in various pathological processes. However, whether PHLPP1 participates in the regulation of HG-induced oxidative stress injury of retinal ganglion cells (RGCs) in diabetic retinopathy is undetermined. The purpose of this study was to explore the potential role and molecular mechanism of PHLPP1 in regulating HG-induced injury of RGCs. Our data showed that PHLPP1 expression was markedly elevated in RGCs from diabetic rats and HG-exposed RGCs. Our functional assay elucidated that knockdown of PHLPP1 improved cell viability and decreased cell apoptosis and reactive oxygen species (ROS) production in HG-exposed RGCs. Additionally, upregulation of PHLPP1 lowered cell viability and increased cell apoptosis and ROS production in HG-exposed RGCs. Mechanistically, knockdown of PHLPP1 resulted in an increase in nuclear factor erythroid-2 related factor 2 (Nrf2) nuclear expression and Nrf2/antioxidant response element (ARE)-mediated transcription associated with upregulation of glycogen synthase kinase-3β (GSK-3β) phosphorylation. Moreover, inhibition of GSK-3β significantly reversed the suppressive effect of PHLPP1 overexpression on Nrf2/ARE activation. Notably, the protective effect of PHLPP1 knockdown on HG-induced injury in RGCs was markedly abolished by Nrf2 inhibition. In conclusion, Our findings demonstrate that downregulation of PHLPP1 activates Nrf2/ARE signaling to protect RGCs from HG-induced apoptosis and oxidative stress. This study indicates a potential role of PHLPP1 in regulating HG-induced injury of RGCs during the development and progression of diabetic retinopathy.

Insulin signaling pathway and related molecules: Role in neurodegeneration and Alzheimer's disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases. Its major pathological hallmarks, neurofibrillary tangles (NFT), and amyloid-β plaques can result from dysfunctional insulin signaling. Insulin is an important growth factor that regulates cell growth, energy utilization, mitochondrial function, autophagy, oxidative stress, synaptic plasticity, and cognitive function. Insulin and its downstream signaling molecules are located majorly in the regions of cortex and hippocampus. The major molecules involved in impaired insulin signaling include IRS, PI3K, Akt, and GSK-3β. Activation or inactivation of these major molecules through increased or decreased phosphorylation plays a role in insulin signaling abnormalities or insulin resistance. Insulin resistance, therefore, is considered as a major culprit in generating the hallmarks of AD arising from neuroinflammation and oxidative stress, etc. Moreover, caspases, Nrf2, and NF-κB influence this pathway in an indirect way. Various studies also suggest a strong link between Diabetes Mellitus and AD due to the impairment of insulin signaling pathway. Moreover, studies also depict a strong correlation of other neurodegenerative diseases such as Parkinson's disease and Huntington's disease with insulin resistance. Hence this review will provide an insight into the role of insulin signaling pathway and related molecules as therapeutic targets in AD and other neurodegenerative diseases.

GSK3β is a key regulator of the ROS-dependent necrotic death induced by the quinone DMNQ

Signaling pathways controlling necrosis are still mysterious and debated. We applied a shRNA-based viability screen to identify critical elements of the necrotic response. We took advantage from a small molecule (G5) that makes covalent adducts with free thiols by Michael addition and elicits multiple stresses. In cells resistant to apoptosis, G5 triggers necrosis through the induction of protein unfolding, glutathione depletion, ER stress, proteasomal impairments, and cytoskeletal stress. The kinase GSK3β was isolated among the top hits of the screening. Using the quinone DMNQ, a ROS generator, we demonstrate that GSK3β is involved in the regulation of ROS-dependent necrosis. Our results have been validated using siRNA and by knocking-out GSK3β with the CRISPR/Cas9 technology. In response to DMNQ GSK3β is activated by serine 9 dephosphorylation, concomitantly to Akt inactivation. During the quinone-induced pro-necrotic stress, GSK3β gradually accumulates into the nucleus, before the collapse of the mitochondrial membrane potential. Accumulation of ROS in response to DMNQ is impaired by the absence of GSK3β. We provide evidence that the activities of the obligatory two-electrons reducing flavoenzymes, NQO1 (NAD(P)H quinone dehydrogenase 1) and NQO2 are required to suppress DMNQ-induced necrosis. In the absence of GSK3β the expression of NQO1 and NQO2 is dramatically increased, possibly because of an increased transcriptional activity of NRF2. In summary, GSK3β by blunting the anti-oxidant response and particularly NQO1 and NQO2 expression, favors the appearance of necrosis in response to ROS, as generated by the quinone DMNQ.

Bergenin impedes the generation of extracellular matrix in glomerular mesangial cells and ameliorates diabetic nephropathy in mice by inhibiting oxidative stress via the mTOR/β-TrcP/Nrf2 pathway

Bergenin, a plant polyphenol, has been reported to lower the blood glucose level and ameliorate kidney function in streptozotocin (STZ)-induced diabetic rats. Herein, its protective effect on diabetic nephropathy (DN) was explored in view of extracellular matrix (ECM) generation in glomerular mesangial cells. Glomerular mesangial cells were treated with high glucose, and Q-PCR as well as western blot were used to determine the expression of ECM. To establish the participation and role of mammalian target of rapamycin (mTOR) and nuclear factor erythroid-derived 2-related factor 2 (Nrf2) in ECM generation, a combination of l-leucine (activator of mTOR) and Nrf2 shRNA transfection were performed, respectively. Moreover, a DN model was established in mice using high-glucose/high-fat diet and STZ. Bergenin impeded the generation of TGF-β1 and ECM, decreased the levels of intracellular superoxide anion and hydrogen peroxide, and increased the activity of antioxidant enzymes in the glomerular mesangial cells (HBZY-1 and HRMC cells) treated with high glucose. The inhibition of ECM generation by bergenin was dependent on the down-regulation of oxidative stress as confirmed via a superoxide overexpression system. The activation of Nrf2 was required for bergenin to inhibit the oxidative stress and ECM generation. Moreover, bergenin was found to inhibit the phosphorylation of mTOR, which is located at the upstream of Nrf2. Bergenin did not interfere with the expression of Nrf2 mRNA and Keap1 (the classic degradation control factor of Nrf2), but markedly inhibited the protein expression of the β-TrcP, an effect which could be abolished by l-leucine. In DN model mice, l-leucine diminished the ability of bergenin to reduce the levels of superoxide anion, hydrogen peroxide and ECM, which contributed to the eradication of the ameliorative effect of bergenin on nephropathy. Bergenin can inhibit glucose-induced ECM production in glomerular mesangial cells through the down-regulation of oxidative stress via the mTOR/β-TrcP/Nrf2 pathway, and it might be a candidate drug for the prevention and treatment of DN.

Emerging Roles for NLRC5 in Immune Diseases

Innate immunity activates the corresponding immune response relying on multiple pattern recognition receptors (PRRs) that includes pattern recognition receptors (PRRs), like NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and C-type lectin receptors (CLRs), which could accurately recognize invasive pathogens. In particular, NLRs belong to a large protein family of pattern recognition receptors in the cytoplasm, where they are highly correlated with activation of inflammatory response system followed by rapid clearance of invasive pathogens. Among the NLRs family, NLRC5, also known as NOD4 or NOD27, accounts for a large proportion and involves in immune responses far and wide. Notably, in the above response case of inflammation, the expression of NLRC5 remarkably increased in immune cells and immune-related tissues. However, the evidence for higher expression of NLRC5 in immune disease still remains controversial. It is noted that the growing evidence further accounts for the participation of NLRC5 in the innate immune response and inflammatory diseases. Moreover, NLRC5 has also been confirmed to exert a critical role in the control of regulatory diverse signaling pathways. Together with its broad participation in the occurrence and development of immune diseases, NLRC5 can be consequently treated as a potential therapeutic target. Nevertheless, the paucity of absolute understanding of intrinsic characteristics and underlying mechanisms of NLRC5 still make it hard to develop targeting drugs. Therefore, current summary about NLRC5 information is indispensable. Herein, current knowledge of NLRC5 is summarized, and research advances in terms of NLRC5 in characteristics, biological function, and regulatory mechanisms are reviewed.

Inhibition of PDE4 protects neurons against oxygen-glucose deprivation-induced endoplasmic reticulum stress through activation of the Nrf-2/HO-1 pathway

Inhibition of phosphodiesterase 4 (PDE4) produces neuroprotective effects against cerebral ischemia. However, the involved mechanism remains unclear. Augmentation of endoplasmic reticulum (ER) stress promotes neuronal apoptosis, and excessive oxidative stress is an inducer of ER stress. The present study aimed to determine whether suppression of ER stress is involved in the protective effects of PDE4 inhibition against cerebral ischemia. We found that exposing HT-22 cells to oxygen-glucose deprivation (OGD) significantly activated ER stress, as evidenced by increased expression of the 78-kDa glucose-regulated protein (GRP78), phosphorylated eukaryotic translation-initiation factor 2α (eIF2α), and C/EBP-homologous protein (CHOP). Overexpression of PDE4B increased ER stress, while knocking down PDE4B or treatment with the PDE4 inhibitor, FCPR03, prevented OGD-induced ER stress in HT-22 cells. Furthermore, FCPR03 promoted the translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2) from the cytoplasm to the nucleus. Importantly, the Nrf-2 inhibitor, ML385, blocked the inhibitory role of FCPR03 on OGD-induced ER stress. ML385 also abolished the protective role of FCPR03 in HT-22 cells subjected to OGD. Knocking down heme oxygenase-1 (HO-1), which is a target of Nrf-2, also blocked the protective role of FCPR03, enhanced the level of reactive oxygen species (ROS), and increased ER stress and cell death. We then found that FCPR03 or the antioxidant, N-Acetyl-l-cysteine, reduced oxidative stress in cells exposed to OGD. This effect was accompanied by increased cell viability and decreased ER stress. In primary cultured neurons, we found that FCPR03 reduced OGD-induced production of ROS and phosphorylation of eIF2α. The neuroprotective effect of FCPR03 against OGD in neurons was blocked by ML385. These results demonstrate that inhibition of PDE4 activates Nrf-2/HO-1, attenuates the production of ROS, and thereby attenuates ER stress in neurons exposed to OGD. Additionally, we conclude that FCPR03 may represent a promising therapeutic agent for the treatment of ER stress-related disorders.

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Overexpression of PDE4 increased ER stress under both basal and OGD conditions.

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Inhibition of PDE4 reduced ER stress and neuronal apoptosis in neurons exposed to OGD.

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PDE4 inhibition activated Nrf-2, and increased the level of antioxidant enzyme HO-1.

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Inhibition of Nrf-2 attenuated the role of FCPR03 on ER stress and cell viability.

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HO-1 knockdown abolished the effects of FCPR03 on ER stress and ROS production.

Ultraviolet B irradiation induced Nrf2 degradation occurs via activation of TRPV1 channels in human dermal fibroblasts

Ultraviolet (UV) irradiation causes cellular oxidative stress. Under redox imbalance, Keap1-dependent Nrf2 degradation is minimal. In this study, we examined the role of Ca²⁺ in Nrf2 homeostasis after UVB irradiation using human dermal fibroblasts. UVB irradiation stimulates 12-lipoxygenase and the product 12-hydroxyeicosatetraenoic acid then activates TRPV1 increasing the cell's cytosolic Ca²⁺ concentration. UVB irradiation induced reactive oxygen species generation and apoptosis are inhibited in the absence of Ca²⁺ or in the presence of either a 12-lipoxygenase inhibitor or a TRPV1 inhibitor during and after UVB irradiation. Thus, the Ca²⁺ increase via TRPV1 is a critical factor in UVB irradiation induced oxidative stress. UVB irradiation induces a Ca²⁺ dependent Nrf2 degradation and thus activation of TRPV1 with 12-hydroxyeicosatetraenoic acid also decreasing Nrf2 levels. UVB irradiation induced Nrf2 degradation is inhibited by co-treatment of cells with W-7, cyclosporin A, SB-216763 or MG-132, which are inhibitors of calmodulin, calcineurin, GSK3β and the proteasome, respectively. Furthermore, UVB irradiation in parallel induces GSK3β dephosphorylation in a Ca²⁺ dependent manner. Co-immunoprecipitation showed that UVB irradiation induces an increase in Nrf2 phosphorylation, an increase in the binding of β-TrCP and Nrf2, and an increase in Nrf2 ubiquitination; these effects are all Ca²⁺ dependent. These findings suggest that UVB irradiation induced GSK3β activation in a Ca²⁺ dependent manner, which then stimulates the phosphorylation and ubiquitination of Nrf2 via β-TrCP. Indeed, silencing of β-TrCP was found to inhibit UVB irradiation-induced oxidative stress, Nrf2 degradation and apoptosis, while it had no effect on the Ca²⁺ increase. Taken together, our results suggest that a Ca²⁺ influx via TRPV1 is responsible for UVB irradiation-induced Nrf2 degradation and that modulation of the Ca²⁺-calmodulin-calcineurin-GSK3β-Nrf2-β-TrCP-Cullin-1 pathway may explain Ca²⁺ dependent Nrf2 degradation.

XBP1 inhibits mesangial cell apoptosis in response to oxidative stress via the PTEN/AKT pathway in diabetic nephropathy

Diabetic nephropathy (DN) is a complication of diabetes mellitus (DM) that frequently results in renal disease, and is characterized by a variety of symptoms, including albuminuria. It has been shown that apoptosis of glomerular mesangial cells (MCs) can aggravate albuminuria and contribute to the development of diabetic glomerulosclerosis. Hence, determination of the mechanisms leading to MC apoptosis may help us gain insights into the pathogenesis of DN. As our understanding of the role of high glucose (HG) in MC apoptosis remains elusive, we explored the interplay between X‐box binding protein 1 (XBP1) and MC apoptosis in this study. XBP1 was observed to be downregulated both in vivo and in vitro. Treatment of XBP1‐overexpressing cells with HG resulted in a decrease of reactive oxygen species (ROS) and a suppression of cell apoptosis, concomitant with decreases in cleaved caspase‐3 and Bax. Subsequent analyses demonstrated that XBP1 overexpression inhibited the expression of phosphatase and tensin homolog deleted on chromosome ten (PTEN) and enhanced the activation of AKT in MCs exposed to HG. In addition, XBP1‐induced injuries in MC were reversed by overexpression of PTEN, and XBP1 inhibited apoptosis, which was mediated by the activated PTEN/AKT signaling pathway. Thus, our data indicate that XBP1 can activate the PTEN/AKT signaling pathway, thereby alleviating oxidative stress caused by HG or MC apoptosis. These findings suggest that XBP1 may have potential in the development of treatment methods for DN.

Mechanism of Rapid Nuclear Factor-E2-Related Factor 2 (Nrf2) Activation via Membrane-Associated Estrogen Receptors: Roles of NADPH Oxidase 1, Neutral Sphingomyelinase 2 and Epidermal Growth Factor Receptor (EGFR)

Membrane-associated estrogen receptors (ER)-α36 and G protein-coupled estrogen receptor (GPER) play important roles in the estrogen’s rapid non-genomic actions including stimulation of cell proliferation. Estrogen via these receptors induces rapid activation of transcription factor nuclear factor-E2-related factor 2 (Nrf2), a master regulator of detoxification and antioxidant systems, playing a key role in the metabolic reprogramming to support cell proliferation. This review highlights the possible mechanism underlying rapid Nrf2 activation via membrane-associated estrogen receptors by estrogen and phytoestrogens. Stimulation of ER-α36-GPER signaling complex rapidly induces Src-mediated transactivation of epidermal growth factor receptor (EGFR) leading to a kinase-mediated signaling cascade. We propose a novel hypothesis that ER-α36-GPER signaling initially induces rapid and temporal activation of NADPH oxidase 1 to generate superoxide, which subsequently activates redox-sensitive neutral sphingomyelinase 2 generating the lipid signaling mediator ceramide. Generation of ceramide is required for Ras activation and ceramide-protein kinase C ζ-casein kinase 2 (CK2) signaling. Notably, CK2 enhances chaperone activity of the Cdc37-Hsp90 complex supporting activation of various signaling kinases including Src, Raf and Akt (protein kinase B). Activation of Nrf2 may be induced by cooperation of two signaling pathways, (i) Nrf2 stabilization by direct phosphorylation by CK2 and (ii) EGFR-Ras-PI 3 kinase (PI3K)-Akt axis which inhibits glycogen synthase kinase 3β leading to enhanced nuclear transport and stability of Nrf2.

Critical Role of Nrf2 in Experimental Ischemic Stroke

Ischemic stroke is one of the leading causes of death and long-term disability worldwide; however, effective clinical approaches are still limited. The transcriptional factor Nrf2 is a master regulator in cellular and organismal defense against endogenous and exogenous stressors by coordinating basal and stress-inducible activation of multiple cytoprotective genes. The Nrf2 network not only tightly controls redox homeostasis but also regulates multiple intermediary metabolic processes. Therefore, targeting Nrf2 has emerged as an attractive therapeutic strategy for the prevention and treatment of CNS diseases including stroke. Here, the current understanding of the Nrf2 regulatory network is critically examined to present evidence for the contribution of Nrf2 pathway in rodent ischemic stroke models. This review outlines the literature for Nrf2 studies in preclinical stroke and focuses on the in vivo evidence for the role of Nrf2 in primary and secondary brain injuries. The dynamic change and functional importance of Nrf2 signaling, as well as Nrf2 targeted intervention, are revealed in permanent, transient, and global cerebral ischemia models. In addition, key considerations, pitfalls, and future potentials for Nrf2 studies in preclinical stroke investigation are discussed.

Targeting the cell signaling pathway Keap1-Nrf2 as a therapeutic strategy for adenocarcinomas of the lung

INTRODUCTION

Kelch-like ECH associated protein 1/Nuclear factor erythroid 2-like factor 2 (Keap1-Nrf2) signaling plays a pivotal role in response to oxidative stress in lung cancer. Mutations in KEAP1/NFE2L2 genes always cause persistent Nrf2 activation in lung cancer cells that confer therapeutic resistance and aggressive tumorigenic activity, dictating either poor prognosis or short duration of response to chemotherapy in clinical observations. Areas covered: We provide a review of the mechanisms underlying the regulation of Keap1-Nrf2 at different stages, including genetic mutations, epigenetic modifications, translational/post-translational alterations, and protein-protein interactions. Based on the current knowledge, we discuss the possibilities of intervening Keap1-Nrf2 in lung adenocarcinoma as a therapeutic target. Expert opinion: It is prevalently conceived that Keap1-Nrf2 signaling plays different roles at diverse stages of cancer. Although various Nrf2 or Keap1 inhibitors have been reported during the last decades, none of these inhibitors are currently under clinical studies or in clinical applications, suggesting that sole inhibition of Nrf2 might not be sufficient to suppress tumor growth. On the basis of current studies, we suggest that the rational combination of Nrf2 suppression with chemical agents which cause enhanced oxidative imbalance or abnormal metabolism would be promising in the treatment of lung adenocarcinoma.