Stress Signal Network between Hypoxia and ER Stress in Chronic Kidney Disease

Natural products derived from traditional Chinese medicines targeting ER stress for the treatment of kidney diseases

Various factors, both internal and external, can disrupt endoplasmic reticulum (ER) homeostasis and increase the burden of protein folding, resulting in ER stress. While short periods of ER stress can help cells return to normal function, excessive or prolonged ER stress triggers a complex signaling network that negatively affects cells. Numerous studies have demonstrated the significant role of ER stress in various kidney diseases, such as immune-related kidney injury, diabetic kidney diseases, renal ischemia reperfusion injury, and renal fibrosis. To date, there is a severe shortage of medications for the treatment of acute and chronic kidney diseases of all causes. Natural products derived from various traditional Chinese medicines (TCM), which are a major source of new drugs, have garnered considerable attention. Recent research has revealed that many natural products have renoprotective effects by targeting ER stress-mediated events, such as apoptosis, oxidative stress, inflammation, autophagy, and epithelial-mesenchymal transition. This article provides a comprehensive review of the current research progress on natural products targeting ER stress for the treatment of kidney diseases.

Spotlight on endoplasmic reticulum stress in acute kidney injury: A bibliometric analysis and visualization from 1997 to 2024

BACKGROUND

Endoplasmic reticulum (ER) stress, a protective stress response of body and play important role in maintain ER stability. Acute kidney injury (AKI) is a severe syndrome, and the molecular mechanisms of AKI has not been fully elucidated. With an increasing understanding of ER stress, ER stress has been investigated and considered a potential and novel therapeutic target in AKI. This study aims to employ a bibliometric approach to analyze research trends and focal points in ER stress associated with AKI over 3 decades.

METHODS

Data were retrieved from the Web of Science Core Collection on April 15, 2024. CiteSpace and VOSviewer bibliometric software were mainly used to measure bibliometrics and analyze knowledge graphs to predict the latest research trends in the field.

RESULTS

There were 452 "ER stress in AKI" articles in the Web of Science Core Collection. According to the report, China and the United States were the leading research drivers in this field. Central South University was the most active academic institution, contributing the most documents. In this field, Dong Zheng was the most prolific author. The American Journal of Physiology-Renal Physiology was the journal with the most records among all journals. The keywords "NLRP3 inflammasome," "redox signaling," and novel forms of cell death such as "ferroptosis" may represent current research trends and directions.

CONCLUSION

The bibliometric analysis comprehensively examines the trends and hotspots on "ER stress and AKI." Studies on AKI related to stress in the ER are still in their infancy. Research should focus on understanding the relationship between ER stress and inflammasome, redox signal pathways and new forms of cell death such as ferroptosis.

Activation of PERK/eIF2α/ATF4/CHOP branch of endoplasmic reticulum stress response and cooperation between HIF-1α and ATF4 promotes Daprodustat-induced vascular calcification

Introduction: Vascular calcification is accelerated in patients with chronic kidney disease (CKD) and increases the risk of cardiovascular events. CKD is frequently associated with anemia. Daprodustat (DPD) is a prolyl hydroxylase inhibitor for the treatment of CKD-associated anemia that enhances erythropoiesis through the activation of the hypoxia-inducible factor 1 (HIF-1) pathway. Studies showed that DPD promotes osteogenic differentiation of human aortic smooth muscle cells (HAoSMCs) and increases aorta calcification in mice with CKD. HIF-1 activation has been linked with endoplasmic reticulum (ER) stress; therefore, here we investigated the potential contribution of ER stress, particularly activating transcription factor 4 (ATF4), to the pro-calcification effect of DPD. Methods: Here, we used an adenine-induced CKD mouse model and HAoSMCs as an in vitro vascular calcification model to study the effect of DPD. Results: DPD treatment (15 mg/kg/day) corrects anemia but increases the expression of hypoxia (Glut1, VEGFA), ER stress (ATF4, CHOP, and GRP78), and osteo-/chondrogenic (Runx2, Sox9, BMP2, and Msx2) markers and accelerates aorta and kidney calcification in CKD mice. DPD activates the PERK/eIF2α/ATF4/CHOP pathway and promotes high phosphate-induced osteo-/chondrogenic differentiation of HAoSMCs. Inhibition of ER stress with 4-PBA or silencing of ATF4 attenuates HAoSMC calcification. DPD-induced ATF4 expression is abolished in the absence of HIF-1α; however, knockdown of ATF4 does not affect HIF-1α expression. Conclusion: We concluded that DPD induces ER stress in vitro and in vivo, in which ATF4 serves as a downstream effector of HIF-1 activation. Targeting ATF4 could be a potential therapeutic approach to attenuate the pro-calcific effect of DPD.

Protein-rich foods, sea foods, and gut microbiota amplify immune responses in chronic diseases and cancers - Targeting PERK as a novel therapeutic strategy for chronic inflammatory diseases, neurodegenerative disorders, and cancer

The endoplasmic reticulum (ER) is a cellular organelle that is physiologically responsible for protein folding, calcium homeostasis, and lipid biosynthesis. Pathological stimuli such as oxidative stress, ischemia, disruptions in calcium homeostasis, and increased production of normal and/or folding-defective proteins all contribute to the accumulation of misfolded proteins in the ER, causing ER stress. The adaptive response to ER stress is the activation of unfolded protein response (UPR), which affect a wide variety of cellular functions to maintain ER homeostasis or lead to apoptosis. Three different ER transmembrane sensors, including PKR-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme-1 (IRE1), are responsible for initiating UPR. The UPR involves a variety of signal transduction pathways that reduce unfolded protein accumulation by boosting ER-resident chaperones, limiting protein translation, and accelerating unfolded protein degradation. ER is now acknowledged as a critical organelle in sensing dangers and determining cell life and death. On the other hand, UPR plays a critical role in the development and progression of several diseases such as cardiovascular diseases (CVD), metabolic disorders, chronic kidney diseases, neurological disorders, and cancer. Here, we critically analyze the most current knowledge of the master regulatory roles of ER stress particularly the PERK pathway as a conditional danger receptor, an organelle crosstalk regulator, and a regulator of protein translation. We highlighted that PERK is not only ER stress regulator by sensing UPR and ER stress but also a frontier sensor and direct senses for gut microbiota-generated metabolites. Our work also further highlighted the function of PERK as a central hub that leads to metabolic reprogramming and epigenetic modification which further enhanced inflammatory response and promoted trained immunity. Moreover, we highlighted the contribution of ER stress and PERK in the pathogenesis of several diseases such as cancer, CVD, kidney diseases, and neurodegenerative disorders. Finally, we discuss the therapeutic target of ER stress and PERK for cancer treatment and the potential novel therapeutic targets for CVD, metabolic disorders, and neurodegenerative disorders. Inhibition of ER stress, by the development of small molecules that target the PERK and UPR, represents a promising therapeutic strategy.

Acute kidney injury: exploring endoplasmic reticulum stress-mediated cell death

Acute kidney injury (AKI) is a global health problem, given its substantial morbidity and mortality rates. A better understanding of the mechanisms and factors contributing to AKI has the potential to guide interventions aimed at mitigating the risk of AKI and its subsequent unfavorable outcomes. Endoplasmic reticulum stress (ERS) is an intrinsic protective mechanism against external stressors. ERS occurs when the endoplasmic reticulum (ER) cannot deal with accumulated misfolded proteins completely. Excess ERS can eventually cause pathological reactions, triggering various programmed cell death (autophagy, ferroptosis, apoptosis, pyroptosis). This article provides an overview of the latest research progress in deciphering the interaction between ERS and different programmed cell death. Additionally, the report consolidates insights into the roles of ERS in AKI and highlights the potential avenues for targeting ERS as a treatment direction toward for AKI.

Physical Exercise Decreases Endoplasmic Reticulum Stress in Central and Peripheral Tissues of Rodents: A Systematic Review

Endoplasmic reticulum stress (ER stress) affects many tissues and contributes to the development and severity of chronic diseases. In contrast, regular physical exercise (PE) has been considered a powerful tool to prevent and control several chronic diseases. The present systematic review aimed to evaluate the impact of different PE protocols on ER stress markers in central and peripheral tissues in rodents. The eligibility criteria were based on PICOS (population: rodents; intervention: physical exercise/physical training; control: animals that did not undergo training; outcomes: endoplasmic reticulum stress; studies: experimental). The PubMed/Medline, Science Direct, Scopus, and Scielo databases were analyzed systematically. Quality assessment was performed using SYRCLE's risk of bias tool for animal studies. The results were qualitatively synthesized. Initially, we obtained a total of 2.490 articles. After excluding duplicates, 30 studies were considered eligible. Sixteen studies were excluded for not meeting the eligibility criteria. Therefore, 14 articles were included. The PE protocol showed decreased levels/expression of markers of ER stress in the central and peripheral tissues of rodents. PE can decrease ER stress by reducing cellular stress in the cardiac, brain, and skeletal muscle tissues in rodents. However, robust PE protocols must be considered, including frequency, duration, and intensity, to optimize the PE benefits of counteracting ER stress and its associated conditions.

Five-Aminolevulinic Acid (5-ALA) Induces Heme Oxygenase-1 and Ameliorates Palmitic Acid-Induced Endoplasmic Reticulum Stress in Renal Tubules

Steatosis, or ectopic lipid deposition, is the fundamental pathophysiology of non-alcoholic steatohepatitis and chronic kidney disease. Steatosis in the renal tubule causes endoplasmic reticulum (ER) stress, leading to kidney injury. Thus, ER stress could be a therapeutic target in steatonephropathy. Five-aminolevulinic acid (5-ALA) is a natural product that induces heme oxygenase (HO)-1, which acts as an antioxidant. This study aimed to investigate the therapeutic potential of 5-ALA in lipotoxicity-induced ER stress in human primary renal proximal tubule epithelial cells. Cells were stimulated with palmitic acid (PA) to induce ER stress. Cellular apoptotic signals and expression of genes involved in the ER stress cascade and heme biosynthesis pathway were analyzed. The expression of glucose-regulated protein 78 (GRP78), a master regulator of ER stress, increased significantly, followed by increased cellular apoptosis. Administration of 5-ALA induced a remarkable increase in HO-1 expression, thus ameliorating PA-induced GRP78 expression and apoptotic signals. BTB and CNC homology 1 (BACH1), a transcriptional repressor of HO-1, was significantly downregulated by 5-ALA treatment. HO-1 induction attenuates PA-induced renal tubular injury by suppressing ER stress. This study demonstrates the therapeutic potential of 5-ALA against lipotoxicity through redox pathway.

Renal fibrosis in type 2 cardiorenal syndrome: An update on mechanisms and therapeutic opportunities

Cardiorenal syndrome (CRS) is a state of coexisting heart failure and renal insufficiency in which acute or chronic dysfunction of the heart or kidney lead to acute or chronic dysfunction of the other organ.It was found that renal fibrosis is an important pathological process in the progression of type 2 CRS to end-stage renal disease, and progressive renal impairment accelerates the deterioration of cardiac function and significantly increases the hospitalization and mortality rates of patients. Previous studies have found that Hemodynamic Aiteration, RAAS Overactivation, SNS Dysfunction, Endothelial Dysfunction and Imbalance of natriuretic peptide system contribute to the development of renal disease in the decompensated phase of heart failure, but the exact mechanisms is not clear. Therefore, in this review, we focus on the molecular pathways involved in the development of renal fibrosis due to heart failure and identify the canonical and non-canonical TGF-β signaling pathways and hypoxia-sensing pathways, oxidative stress, endoplasmic reticulum stress, pro-inflammatory cytokines and chemokines as important triggers and regulators of fibrosis development, and summarize the therapeutic approaches for the above signaling pathways, including SB-525334 Sfrp1, DKK1, IMC, rosarostat, 4-PBA, etc. In addition, some potential natural drugs for this disease are also summarized, including SQD4S2, Wogonin, Astragaloside, etc.

4-PBA inhibits hypoxia-induced lipolysis in rat adipose tissue and lipid accumulation in the liver through regulating ER stress

High-altitude hypoxia may disturb the metabolic modulation and function of both adipose tissue and liver. The endoplasmic reticulum (ER) is a crucial organelle in lipid metabolism and ER stress is closely correlated with lipid metabolism dysfunction. The aim of this study is to elucidate whether the inhibition of ER stress could alleviate hypoxia-induced white adipose tissue (WAT) lipolysis and liver lipid accumulation-mediated hepatic injury. A rat model of high-altitude hypoxia (5500 m) was established using hypobaric chamber. The response of ER stress and lipolysis-related pathways were analyzed in WAT under hypoxia exposure with or without 4-phenylbutyric acid (PBA) treatment. Liver lipid accumulation, liver injury, and apoptosis were evaluated. Hypoxia evoked significant ER stress in WAT, evidenced by increased GRP78, CHOP, and phosphorylation of IRE1α, PERK. Moreover, Lipolysis in perirenal WAT significantly increased under hypoxia, accompanied with increased phosphorylation of hormone-sensitive lipase (HSL) and perilipin. Treatment with 4-PBA, inhibitor of ER stress, effectively attenuated hypoxia-induced lipolysis via cAMP-PKA-HSL/perilipin pathway. In addition, 4-PBA treatment significantly inhibited the increase in fatty acid transporters (CD36, FABP1, FABP4) and ameliorated liver FFA accumulation. 4-PBA treatment significantly attenuated liver injury and apoptosis, which is likely resulting from decreased liver lipid accumulation. Our results highlight the importance of ER stress in hypoxia-induced WAT lipolysis and liver lipid accumulation.

Ochratoxin A induces endoplasmic reticulum stress and fibrosis in the kidney via the HIF-1α/miR-155-5p link

Ochratoxin A (OTA) is a ubiquitous fungal toxin found in agricultural products and foods that is toxic to both humans and animals. OTA mainly affects kidney, but the mechanisms underlying OTA-induced nephrotoxicity remain not fully understood. MicroRNA (miRNA) is involved in key cellular processes. The toxic mechanism and regulatory effects of miRNAs on OTA toxicity in kidney, and particularly the role of HIFα-1/miR-155-5p on OTA-caused ER stress and fibrosis, were investigated in this study. OTA induced hypoxia-like conditions such as ER stress and fibrosis in HK-2 cells and renal tissues via modulating HIF-1α, which was followed by regulation of ER stress-related proteins (GRP78 and ATF-4), as well as fibrosis-related markers (fibronectin, α-SMA, and E-cadherin). Notably, a total of 62 miRNAs showed significant differential expression in kidney of OTA-treated mice. Under OTA exposure, HIF-1α enhanced miR-155-5p expression, causing ER stress and fibrosis in HK-2 cells. HIF-1α knockdown decreased OTA-induced miR-155-5p expression as well as ER stress and fibrotic responses, whereas miR-155-5p overexpression restored this. Our data suggest that OTA enhances ER stress and fibrosis in the kidney through upregulating the HIF-1α/miR-155-5p link.

Modulation of miR-205/ EGLN2 by rosuvastatin mitigates colistin-induced nephrotoxicity in rats: Involvement of ATF4/ CHOP and Nrf2 pathways

Although the beneficial role of microRNA has been investigated thoroughly, the reno-protective role of microRNA-205 (miR-205) against colistin-induced nephrotoxicity has not yet been tackled. Hence, our study sought to study the possible modulatory effect of rosuvastatin on miR-205 and its downstream target, Egl-9 family hypoxia-inducible factor 2 (EGLN2) to combat oxidative and endoplasmic reticulum (ER) stresses as pivotal contributors to colistin-associated renal injury. Rats were randomly divided into four groups; normal, colistin (300 000 IU/Kg/day; i.p), colistin pretreated with rosuvastatin (10 mg/kg; p.o) and colistin pretreated with rosuvastatin (20 mg/kg; p.o) for 6 successive days. Pretreatment with rosuvastatin attenuated renal injury induced by colistin and enhanced kidney function with a marked reduction in renal injury markers, neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1. Besides, rosuvastatin upregulated renal miR-205 expression and suppressed gene expression of EGLN2. In addition, it downregulated ER stress-related genes (activation transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP)) along with caspases 12 and 3. It also induced the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) as detected by immunohistochemical examination besides increased renal antioxidants, reduced glutathione, and superoxide dismutase. In conclusion, rosuvastatin triggered a series of protective mechanisms against colistin-induced nephrotoxicity through modulating miR-205 and EGLN2 expression. Rosuvastatin suppressed ATF4/ CHOP trajectory and activated the Nrf2 pathway to substantiate its antioxidant and anti-apoptotic capacities.

Transcriptome analysis endoplasmic reticulum-stress response in Litopenaeus vannamei hemocytes

Numerous studies have proved that endoplasmic reticulum (ER)-stress is an important cause of aquatic animal diseases. Therefore, for effectively preventing and controlling aquatic animal diseases, a systematic and in-depth understanding of the environmental stress response in aquatic animals is necessary. In present study, the influence of ER-stress in Litopenaeus vannamei was investigated using Illumina HiSeq based RNA-Seq. Comparing to the cDNA library of hemocytes treated with DMSO in L. vannamei, 286 unigenes were significantly upregulated and 473 unigenes were significantly down-regulated in the Thapsigargin treated group. KEGG analysis indicated that the differentially expressed genes (DEGs) are mainly related to ER-stress, immune as well as metabolism. Besides the classical ER-stress response pathways, the regulation of cell cycle and DNA replication are also important measures of ER-stress response. It has been suggested that the influence of ER-stress on immune genes might be an important factor in environmental stress inducing shrimp disease. Our investigation exhibited that immune-related DEG Prophenoloxidase activating enzyme 2 (LvPPAE2) roled in anti-pathogen immunity of shrimp. This study provides a solid foundation for uncovering the environmental adaptation response and especially its relationship with L. vannamei immune system.

Involvement of Inflammasome Components in Kidney Disease

Inflammasomes are multiprotein complexes with an important role in the innate immune response. Canonical activation of inflammasomes results in caspase-1 activation and maturation of cytokines interleukin-1β and -18. These cytokines can elicit their effects through receptor activation, both locally within a certain tissue and systemically. Animal models of kidney diseases have shown inflammasome involvement in inflammation, pyroptosis and fibrosis. In particular, the inflammasome component nucleotide-binding domain-like receptor family pyrin domain containing 3 (NLRP3) and related canonical mechanisms have been investigated. However, it has become increasingly clear that other inflammasome components are also of importance in kidney disease. Moreover, it is becoming obvious that the range of molecular interaction partners of inflammasome components in kidney diseases is wide. This review provides insights into these current areas of research, with special emphasis on the interaction of inflammasome components and redox signalling, endoplasmic reticulum stress, and mitochondrial function. We present our findings separately for acute kidney injury and chronic kidney disease. As we strictly divided the results into preclinical and clinical data, this review enables comparison of results from those complementary research specialities. However, it also reveals that knowledge gaps exist, especially in clinical acute kidney injury inflammasome research. Furthermore, patient comorbidities and treatments seem important drivers of inflammasome component alterations in human kidney disease.

Quantitative super-resolution microscopy reveals promoting mitochondrial interconnectivity protects against AKI

Background

The root of many kidney diseases in humans can be traced to alterations or damage to subcellular organelles. Mitochondrial fragmentation, endoplasmic reticulum (ER) stress, and lysosomal inhibition, among others, ultimately contribute to kidney injury and are the target of therapeutics in development. Although recent technological advancements allow for the understanding of disease states at the cellular level, investigating changes in subcellular organelles from kidney tissue remains challenging.

Methods

Using structured illumination microscopy, we imaged mitochondria and other organelles from paraffin sections of mouse tissue and human kidney biopsy specimens. The resulting images were 3D rendered to quantify mitochondrial size, content, and morphology. Results were compared with those from transmission electron microscopy and segmentation.

Results

Super-resolution imaging reveals kidney tubular epithelial cell mitochondria in rodent and human kidney tissue form large, interconnected networks under basal conditions, which are fragmented with injury. This approach can be expanded to other organelles and cellular structures including autophagosomes, ER, brush border, and cell morphology. We find that, during unilateral ischemia, mitochondrial fragmentation occurs in most tubule cells, and they remain fragmented for >96 hours. Promoting mitochondrial fusion with the fusion promotor M1 preserves mitochondrial morphology and interconnectivity and protects against cisplatin-induced kidney injury.

Conclusions

We provide, for the first time, a nonbiased, semiautomated approach for quantification of the 3D morphology of mitochondria in kidney tissue. Maintaining mitochondrial interconnectivity and morphology protects against kidney injury. Super-resolution imaging has the potential to both drive discovery of novel pathobiologic mechanisms in kidney tissue and broaden the diagnoses that can be made on human biopsy specimens.

Prospective Pharmacological Potential of Resveratrol in Delaying Kidney Aging

Aging is an unavoidable part of life. The more aged we become, the more susceptible we become to various complications and damages to the vital organs, including the kidneys. The existing drugs for kidney diseases are mostly of synthetic origins; thus, natural compounds with minimal side-effects have attracted growing interest from the scientific community and pharmaceutical companies. A literature search was carried out to collect published research information on the effects of resveratrol on kidney aging. Recently, resveratrol has emerged as a potential anti-aging agent. This versatile polyphenol exerts its anti-aging effects by intervening in various pathologies and multi-signaling systems, including sirtuin type 1, AMP-activated protein kinase, and nuclear factor-κB. Researchers are trying to figure out the detailed mechanisms and possible resveratrol-mediated interventions in divergent pathways at the molecular level. This review highlights (i) the causative factors implicated in kidney aging and the therapeutic aspects of resveratrol, and (ii) the effectiveness of resveratrol in delaying the aging process of the kidney while minimizing all possible side effects.

A Review of Traditional Chinese Medicine in Treating Renal Interstitial Fibrosis via Endoplasmic Reticulum Stress-Mediated Apoptosis

Renal interstitial fibrosis (RIF) is the main pathological manifestation of end-stage renal disease. Recent studies have shown that endoplasmic reticulum (ER) stress is involved in the pathogenesis and development of RIF. Traditional Chinese medicine (TCM), as an effective treatment for kidney diseases, can improve kidney damage by affecting the apoptotic signaling pathway mediated by ER stress. This article reviews the apoptotic pathways mediated by ER stress, including the three major signaling pathways of unfolded protein response, the main functions of the transcription factor C/EBP homologous protein. We also present current research on TCM treatment of RIF, focusing on medicines that regulate ER stress. A new understanding of using TCM to treat kidney disease by regulating ER stress will promote clinical application of Chinese medicine and discovery of new drugs for the treatment of RIF.

Use of Anti-Diabetic Agents in Non-Diabetic Kidney Disease: From Bench to Bedside

New drugs were recently developed to treat hyperglycemia in patients with type 2 diabetes mellitus (T2D). However, metformin remains the first-line anti-diabetic agent because of its cost-effectiveness. It has pleiotropic action that produces cardiovascular benefits, and it can be useful in diabetic nephropathy, although metformin-associated lactic acidosis is a hindrance to its use in patients with kidney failure. New anti-diabetic agents, including glucagon-like peptide-1 receptor (GLP-1R) agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-glucose transporter-2 (SGLT-2) inhibitors, also produce cardiovascular or renal benefits in T2D patients. Their glucose-independent beneficial actions can lead to cardiorenal protection via hemodynamic stabilization and inflammatory modulation. Systemic hypertension is relieved by natriuresis and improved vascular dysfunction. Enhanced tubuloglomerular feedback can be restored by SGLT-2 inhibition, reducing glomerular hypertension. Patients with non-diabetic kidney disease might also benefit from those drugs because hypertension, proteinuria, oxidative stress, and inflammation are common factors in the progression of kidney disease, irrespective of the presence of diabetes. In various animal models of non-diabetic kidney disease, metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors were favorable to kidney morphology and function. They strikingly attenuated biomarkers of oxidative stress and inflammatory responses in diseased kidneys. However, whether those animal results translate to patients with non-diabetic kidney disease has yet to be evaluated. Considering the paucity of new agents to treat kidney disease and the minimal adverse effects of metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors, these anti-diabetic agents could be used in patients with non-diabetic kidney disease. This paper provides a rationale for clinical trials that apply metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors to non-diabetic kidney disease.

Therapeutic Effect of Endothelin-Converting Enzyme Inhibitor on Chronic Kidney Disease through the Inhibition of Endoplasmic Reticulum Stress and the NLRP3 Inflammasome

Chronic inflammation and oxidative stress significantly contribute to the development and progression of chronic kidney disease (CKD). The NOD-like receptor family pyrin containing domain-3 (NLRP3) inflammasome plays a key role in the inflammatory response. The renal endothelin (ET) system is activated in all cases of CKD. Furthermore, ET-1 promotes renal cellular injury, inflammation, fibrosis and proteinuria. Endothelin-converting enzymes (ECEs) facilitate the final processing step of ET synthesis. However, the roles of ECEs in CKD are not clear. In this study, we investigated the effects of ETs and ECEs on kidney cells. We found that ET-1 and ET-2 expression was significantly upregulated in the renal tissues of CKD patients. ET-1 and ET-2 showed no cytotoxicity on human kidney tubular epithelial cells. However, ET-1 and ET-2 caused endoplasmic reticulum (ER) stress and NLRP3 inflammasome activation in tubular epithelial cells. The ECE inhibitor phosphoramidon induced autophagy. Furthermore, phosphoramidon inhibited ER stress and the NLRP3 inflammasome in tubular epithelial cells. In an adenine diet-induced CKD mouse model, phosphoramidon attenuated the progression of CKD by regulating autophagy, the NLRP3 inflammasome and ER stress. In summary, these findings showed a new strategy to delay CKD progression by inhibiting ECEs through autophagy activation and restraining ER stress and the NLRP3 inflammasome.

Regulated cell death in cisplatin-induced AKI: relevance of myo-inositol metabolism

Regulated cell death (RCD), distinct from accidental cell death, refers to a process of well-controlled programmed cell death with well-defined pathological mechanisms. In the past few decades, various terms for RCDs were coined, and some of them have been implicated in the pathogenesis of various types of acute kidney injury (AKI). Cisplatin is widely used as a chemotherapeutic drug for a broad spectrum of cancers, but its usage was hampered because of being highly nephrotoxic. Cisplatin-induced AKI is commonly seen clinically, and it also serves as a well-established prototypic model for laboratory investigations relevant to acute nephropathy affecting especially the tubular compartment. Literature reports over a period of three decades have indicated that there are multiple types of RCDs, including apoptosis, necroptosis, pyroptosis, ferroptosis, and mitochondrial permeability transition-mediated necrosis, and some of them are pertinent to the pathogenesis of cisplatin-induced AKI. Interestingly, myo-inositol metabolism, a vital biological process that is largely restricted to the kidney, seems to be relevant to the pathogenesis of certain forms of RCDs. A comprehensive understanding of RCDs in cisplatin-induced AKI and their relevance to myo-inositol homeostasis may yield novel therapeutic targets for the amelioration of cisplatin-related nephropathy.

Melatonin Attenuates ox-LDL-Induced Endothelial Dysfunction by Reducing ER Stress and Inhibiting JNK/Mff Signaling

Endothelial dysfunction, which is characterized by damage to the endoplasmic reticulum (ER) and mitochondria, is involved in a variety of cardiovascular disorders. Here, we explored whether mitochondrial damage and ER stress are associated with endothelial dysfunction. We also examined whether and how melatonin protects against oxidized low-density lipoprotein- (ox-LDL-) induced damage in endothelial cells. We found that CHOP, GRP78, and PERK expressions, which are indicative of ER stress, increased significantly in response to ox-LDL treatment. ox-LDL also induced mitochondrial dysfunction as evidenced by decreased mitochondrial membrane potential, increased mitochondrial ROS levels, and downregulation of mitochondrial protective factors. In addition, ox-LDL inhibited antioxidative processes, as evidenced by decreased antioxidative enzyme activity and reduced Nrf2/HO-1 expression. Melatonin clearly reduced ER stress and promoted mitochondrial function and antioxidative processes in the presence of ox-LDL. Molecular investigation revealed that ox-LDL activated the JNK/Mff signaling pathway, and melatonin blocked this effect. These results demonstrate that ox-LDL induces ER stress and mitochondrial dysfunction and activates the JNK/Mff signaling pathway, thereby contributing to endothelial dysfunction. Moreover, melatonin inhibited JNK/Mff signaling and sustained ER homeostasis and mitochondrial function, thereby protecting endothelial cells against ox-LDL-induced damage.

Inhibition of ER stress attenuates kidney injury and apoptosis induced by 3-MCPD via regulating mitochondrial fission/fusion and Ca2+ homeostasis

3-Chloro-1, 2-propanediol (3-MCPD) is a food-borne toxic substance well-known for more than 40 years that is mainly associated with nephrotoxicity. A better understanding of 3-MCPD nephrotoxicity is required to devise efficacious strategies to counteract its toxicity. In the present work, the role of endoplasmic reticulum (ER) stress along with its underlying regulatory mechanism in 3-MCPD-mediated renal cytotoxicity was investigated in vivo and in vitro. Our data indicated that 3-MCPD-stimulated ER stress response evidenced by sustained activation of PERK-ATF4-p-CHOP and IRE1 branches in Sprague Dawley (SD) rats and human embryonic kidney (HEK293) cells. Moreover, ER stress-associated specific apoptotic initiator, caspase 12, was over-expressed. Blocking ER stress with its antagonist, 4-phenylbutyric acid (4-PBA), improved the morphology and function of kidney effectively. 4-PBA also increased cell viability, relieved mitochondrial vacuolation, and inhibited cell apoptosis through regulating caspase-dependent intrinsic apoptosis pathways. Furthermore, the enhanced expressions of two mitochondrial fission proteins, DRP1/p-DRP1 and FIS1, and the relocation of DRP1 on mitochondria subjected to 3-MPCD were reversed by 4-PBA, while the expression of the fusion protein, MFN2, was restored. Moreover, cellular Ca²⁺ overload, the over-expression of CaMKK2, and the loss of mitochondria-associated membranes (MAM) were also relieved after 4-PBA co-treatment. Collectively, our data emphasized that ER stress plays critical role in 3-MCPD-mediated mitochondrial dysfunction and subsequent apoptosis as well as blockage of ER stress ameliorated kidney injury through improving mitochondrial fission/fusion and Ca²⁺ homeostasis. These findings provide a novel insight into the regulatory role of ER stress in 3-MCPD-associated nephropathy and a potential therapeutic strategy. Graphical Headlights 1. 4-PBA inhibits ER stress mainly through regulating PERK-ATF4-CHOP and IRE1-XBP1s branches. 2. Inhibition of ER stress by 4-PBA mitigates ER associated and mitochondrial apoptosis 3. Inhibition of ER stress by 4-PBA helps maintaining calcium homeostasis and mitochondrial dynamic.

Hypoxia and Hypoxia-Inducible Factor-1α Regulate Endoplasmic Reticulum Stress in Nucleus Pulposus Cells: Implications of Endoplasmic Reticulum Stress for Extracellular Matrix Secretion

Endoplasmic reticulum (ER) stress is shown to promote nucleus pulposus (NP) cell apoptosis and intervertebral disc degeneration. However, little is known about ER stress regulation by the hypoxic disc microenvironment and its contribution to extracellular matrix homeostasis. NP cells were cultured under hypoxia (1% partial pressure of oxygen) to assess ER stress status, and gain-of-function and loss-of-function approaches were used to assess the role of hypoxia-inducible factor (HIF)-1α in this pathway. In addition, the contribution of ER stress induction on the NP cell secretome was assessed by a nontargeted quantitative proteomic analysis by sequential windowed data independent acquisition of the total high-resolution mass spectra-mass spectrometry. NP cells exhibited a lower ER stress burden under hypoxia. Knockdown of HIF-1α increased C/EBP homologous protein, protein kinase RNA-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6) levels, whereas HIF-1α stabilization decreased the expression of ER stress markers Ddit3, Hsp5a, Atf6, and Eif2a. Interestingly, ER stress inducers tunicamycin and thapsigargin induced HIF-1α activity under hypoxia while promoting the unfolded protein response. NP cell secretome analysis demonstrated an impact of ER stress induction on extracellular matrix secretion, with decreases in collagens and cell adhesion-related proteins. Moreover, analysis of transcriptomic data of NP tissues from aged mice and degenerated human discs showed higher levels of unfolded protein response markers and decreased levels of matrix components. Our study shows, for the first time, that hypoxia and HIF-1α attenuate ER stress responses in NP cells, and ER stress promotes inefficient extracellular matrix secretion under hypoxia.

Blood-Spinal Cord Barrier in Spinal Cord Injury: A Review

The blood-spinal cord barrier (BSCB), a physical barrier between the blood and spinal cord parenchyma, prevents the toxins, blood cells, and pathogens from entering the spinal cord and maintains a tightly controlled chemical balance in the spinal environment, which is necessary for proper neural function. A BSCB disruption, however, plays an important role in primary and secondary injury processes related to spinal cord injury (SCI). After SCI, the structure of the BSCB is broken down, which leads directly to leakage of blood components. At the same time, the permeability of the BSCB is also increased. Repairing the disruption of the BSCB could alleviate the SCI pathology. We review the morphology and pathology of the BSCB and progression of therapeutic methods targeting BSCB in SCI.

Neuroprotective Role of Akt in Hypoxia Adaptation in Andeans

Chronic mountain sickness (CMS) is a disease that potentially threatens a large segment of high-altitude populations during extended living at altitudes above 2,500 m. Patients with CMS suffer from severe hypoxemia, excessive erythrocytosis and neurologic deficits. The cellular mechanisms underlying CMS neuropathology remain unknown. We previously showed that iPSC-derived CMS neurons have altered mitochondrial dynamics and increased susceptibility to hypoxia-induced cell death. Genome analysis from the same population identified many ER stress-related genes that play an important role in hypoxia adaptation or lack thereof. In the current study, we showed that iPSC-derived CMS neurons have increased expression of ER stress markers Grp78 and XBP1s under normoxia and hyperphosphorylation of PERK under hypoxia, alleviating ER stress does not rescue the hypoxia-induced CMS neuronal cell death. Akt is a cytosolic regulator of ER stress with PERK as a direct target of Akt. CMS neurons exhibited lack of Akt activation and lack of increased Parkin expression as compared to non-CMS neurons under hypoxia. By enhancing Akt activation and Parkin overexpression, hypoxia-induced CMS neuronal cell death was reduced. Taken together, we propose that increased Akt activation protects non-CMS from hypoxia-induced cell death. In contrast, impaired adaptive mechanisms including failure to activate Akt and increase Parkin expression render CMS neurons more susceptible to hypoxia-induced cell death.

Withaferin A protects against endoplasmic reticulum stress-associated apoptosis, inflammation, and fibrosis in the kidney of a mouse model of unilateral ureteral obstruction

BACKGROUND

Withaferin A is a functional ingredient of a traditional medicinal plant, Withania somnifera, which has been broadly used in India for protecting against chronic diseases. This bioactive steroidal lactone possesses multiple functions such as anti-oxidation, anti-inflammation, and immunomodulation. Chronic kidney disease (CKD) is one of the major health problems worldwide with the high complication, morbidity, and mortality rates. The detailed effects and underlying mechanisms of withaferin A on CKD progression still remain to be clarified.

PURPOSE

We aimed to investigate whether withaferin A treatment ameliorates the development of renal fibrosis and its related mechanisms in a CKD mouse model.

METHODS

A mouse model of unilateral ureteral obstruction (UUO) was used to mimic the progression of CKD. Male adult C57BL/6J mice were orally administered with 3 mg/kg/day withaferin A for 14 consecutive days after UUO surgery. Candesartan (5 mg/kg/day) was used as a positive control.

RESULTS

Both Withaferin A and candesartan treatments significantly ameliorated the histopathological changes and collagen deposition in the UUO kidneys. Withaferin A could significantly reverse the increases in the protein levels of pro-fibrotic factors (fibronectin, transforming growth factor-β, and α-smooth muscle actin), inflammatory signaling molecules (phosphorylated nuclear factor-κB-p65, interleukin-1β, and cyclooxygenase-2), and cleaved caspase-3, apoptosis, and infiltration of neutrophils in the UUO kidneys. The protein levels of endoplasmic reticulum (ER) stress-associated molecules (GRP78, GRP94, ATF4, CHOP, phosphorylated eIF2α, and cleaved caspase 12) were increased in the kidneys of UUO mice, which could be significantly reversed by withaferin A treatment.

CONCLUSION

Withaferin A protects against the CKD progression that is, at least in part, associated with the moderation of ER stress-related apoptosis, inflammation, and fibrosis in the kidneys of CKD. Withaferin A may serve as a potential therapeutic agent for the development of CKD.

Tangeretin Ameliorates Glucose-Induced Podocyte Injury through Blocking Epithelial to Mesenchymal Transition Caused by Oxidative Stress and Hypoxia

Podocyte injury inevitably results in leakage of proteins from the glomerular filter and is vital in the pathogenesis of diabetic nephropathy (DN). The underlying mechanisms of podocyte injury facilitate finding of new therapeutic targets for DN treatment and prevention. Tangeretin is an O-polymethoxylated flavone present in citrus peels with anti-inflammatory and antioxidant properties. This study investigated the renoprotective effects of tangeretin on epithelial-to-mesenchymal transition-mediated podocyte injury and fibrosis through oxidative stress and hypoxia caused by hyperglycemia. Mouse podocytes were incubated in media containing 33 mM glucose in the absence and presence of 1–20 μM tangeretin for up to 6 days. The in vivo animal model employed db/db mice orally administrated with 10 mg/kg tangeretin for 8 weeks. Non-toxic tangeretin inhibited glucose-induced expression of the mesenchymal markers of N-cadherin and α-smooth muscle actin in podocytes. However, the reduced induction of the epithelial markers of E-cadherin and P-cadherin was restored by tangeretin in diabetic podocytes. Further, tangeretin enhanced the expression of the podocyte slit diaphragm proteins of nephrin and podocin down-regulated by glucose stimulation. The transmission electron microscopic images revealed that foot process effacement and loss of podocytes occurred in diabetic mouse glomeruli. However, oral administration of 10 mg/kg tangeretin reduced urine albumin excretion and improved foot process effacement of diabetic podocytes through inhibiting loss of slit junction and adherenes junction proteins. Glucose enhanced ROS production and HIF-1α induction in podocytes, leading to induction of oxidative stress and hypoxia. Similarly, in diabetic glomeruli reactive oxygen species (ROS) production and HIF-1α induction were observed. Furthermore, hypoxia-evoking cobalt chloride induced epithelial-to-mesenchymal transition (EMT) process and loss of slit diaphragm proteins and junction proteins in podocytes, which was inhibited by treating submicromolar tangeretin. Collectively, these results demonstrate that tangeretin inhibited podocyte injury and fibrosis through blocking podocyte EMT caused by glucose-induced oxidative stress and hypoxia.

Nicotine Causes Nephrotoxicity through the Induction of NLRP6 Inflammasome and Alpha7 Nicotinic Acetylcholine Receptor

Current cigarette smoking is associated with chronic kidney disease (CKD) or death from end-stage renal disease (ESRD). Mainstream cigarette smoke includes over 4000 compounds. Among the compounds present in tobacco smoke, nicotine is one of a large number of biologically stable and active compounds present in tobacco. However, the mechanisms by which nicotine exacerbates kidney disease progression have not been identified. It is known that the inflammasomes constitute an important innate immune pathway and contribute to the pathophysiology of diverse kidney diseases. The relationship between inflammasomes and nicotine-induced kidney damage still remains unclear. In the present study, we studied the mechanisms of nicotine-induced nephrotoxicity. We found that nicotine decreased cell viability and induced reactive oxygen species (ROS) generation in human kidney cells. Furthermore, nicotine significantly increased the expression of the alpha7 nicotinic acetylcholine receptor (α7nAChR). Nicotine activated the NLRP6 inflammasome and induced endoplasmic reticulum (ER) stress. Nicotine caused mild apoptosis and necrosis but triggered significant autophagy in human kidney cells. In addition, nicotine induced the NLRP6 inflammasome and autophagy via α7nAChR. In an animal model, the histological analysis in kidney showed evident changes and injury. The results indicated that α7nAChR, IRE1α, LC3 and NLRP6 expression in kidney sections was markedly increased in the nicotine groups. These findings suggest that nicotine causes kidney damage by modulating α7nAChR, NLRP6 inflammasome, ER stress and autophagy.

C57BL/6 mice require a higher dose of cisplatin to induce renal fibrosis and CCL2 correlates with cisplatin-induced kidney injury

C57BL/6 mice are one of the most commonly used mouse strains in research, especially in kidney injury studies. However, C57BL/6 mice are resistant to chronic kidney disease-associated pathologies, particularly the development of glomerulosclerosis and interstitial fibrosis. Our laboratory and others developed a more clinically relevant dosing regimen of cisplatin (7 mg/kg cisplatin once a week for 4 wk and mice euthanized at day 24) that leads to the development of progressive kidney fibrosis in FVB/n mice. However, we found that treating C57BL/6 mice with this same dosing regimen does not result in kidney fibrosis. In this study, we demonstrated that increasing the dose of cisplatin to 9 mg/kg once a week for 4 wk is sufficient to consistently induce fibrosis in C57BL/6 mice while maintaining animal survival. In addition, we present that cohorts of C57BL/6 mice purchased from Jackson 1 yr apart and mice bred in-house display variability in renal outcomes following repeated low-dose cisplatin treatment. Indepth analyses of this intra-animal variability revealed C-C motif chemokine ligand 2 as a marker of cisplatin-induced kidney injury through correlation studies. In addition, significant immune cell infiltration was observed in the kidney after four doses of 9 mg/kg cisplatin, contrary to what has been previously reported. These results indicate that multiple strains of mice can be used with our repeated low-dose cisplatin model with dose optimization. Results also indicate that littermate control mice should be used with this model to account for population variability.

Modulation of endoplasmic reticulum stress response in gut-origin encephalopathy: Impact of vascular endothelial growth factor receptor-2 manipulation

BACKGROUND

Septic encephalopathy, the most frequent complication of sepsis, is orchestrated by a complex interplay of signals that leads to high mortality rates among intensive care unit patients. However, the role of the vascular endothelial growth factor receptor-2 (VEGFR2) in endoplasmic reticulum stress response (ERSR), during septic encephalopathy, is still elusive.

AIM

This study was aimed to examine the effect of an in-house designed/synthesized VEGFR2 antagonist, named WAG4S, on septic encephalopathy using cecal ligation and perforation (CLP).

MAIN METHODS

Rats were intraperitoneally injected with WAG-4S (1 mg/kg/d) for 7 days post-CLP.

KEY FINDINGS

In septic animals, VEGFR2 antagonism declined the expression of cortical p-VEGFR2 and p-mammalian target of rapamycin complex-1 (p-mTORC1). It also worsened the behavioral and histopathological alterations beyond CLP. However, and contrary to CLP, WAG-4S decreased the p-protein kinase R-like ER kinase (p-PERK) and eukaryotic initiation factor-2α (p-eIF2α) expression. Moreover, VEGFR2 blockade upregulated the mRNA expression of activating transcription factor-4 (ATF4), binding immunoglobulin protein/glucose-regulated protein-78 (Bip/GRP78), growth arrest and DNA damage-34 (GADD34) and spliced X-box binding protein-1 (XBP1s) above CLP. Similarly, it boosted inositol requiring enzyme-1α (IRE1α) activation and redox imbalance. In the same context, WAG-4S augmented the protein levels of CLP-induced ERSR apoptotic markers, namely C/EBP homologous protein (CHOP/GADD153), c-jun N-terminal kinase (JNK) and caspase-3.

SIGNIFICANCE

In conclusion, the PERK/eIF2α axis inhibition, during septic encephalopathy, is VEGFR2-independent, whereas the activated IRE1α/XBP1s/CHOP/JNK/caspase-3 cue promotes the ERSR execution module through VEGFR2 inhibition. This has turned VEGFR2 into a potential therapeutic target for ameliorating such an ailment.

Inhibition of oxygen-sensing prolyl hydroxylases increases lipid accumulation in human primary tubular epithelial cells without inducing ER stress

The role of the hypoxia-inducible transcription factor (HIF) pathway in renal lipid metabolism is largely unknown. As HIF stabilizing prolyl hydroxylase (PHD) inhibitors are currently investigated in clinical trials for the treatment of renal anemia, we studied the effects of genetic deletion and pharmacological inhibition of PHDs on renal lipid metabolism in transgenic mice and human primary tubular epithelial cells (hPTEC). Tubular cell-specific deletion of HIF prolyl hydroxylase 2 (Phd2) increased the size of Oil Red-stained lipid droplets in mice. In hPTEC, the PHD inhibitors (PHDi) DMOG and ICA augmented lipid accumulation, which was visualized by Oil Red staining and assessed by microscopy and an infrared imaging system. PHDi-induced lipid accumulation required the exogenous availability of fatty acids and was observed in both proximal and distal hPTEC. PHDi treatment was not associated with structural features of cytotoxicity in contrast to treatment with the immunosuppressant cyclosporine A (CsA). PHDi and CsA differentially upregulated the expression of the lipid droplet-associated genes PLIN2, PLIN4 and HILPDA. Both PHDi and CsA activated AMP-activated protein kinase (AMPK) indicating the initiation of a metabolic stress response. However, only CsA triggered endoplasmic reticulum (ER) stress as determined by the increased mRNA expression of multiple ER stress markers but CsA-induced ER stress was not linked to lipid accumulation. Our data raise the possibility that PHD inhibition may protect tubular cells from toxic free fatty acids by trapping them as triacylglycerides in lipid droplets. This mechanism might contribute to the renoprotective effects of PHDi in experimental kidney diseases.

Autophagy in Kidney Disease

Autophagy is a cellular homeostatic program for the turnover of cellular organelles and proteins, in which double-membraned vesicles (autophagosomes) sequester cytoplasmic cargos, which are subsequently delivered to the lysosome for degradation. Emerging evidence implicates autophagy as an important modulator of human disease. Macroautophagy and selective autophagy (e.g., mitophagy, aggrephagy) can influence cellular processes, including cell death, inflammation, and immune responses, and thereby exert both adaptive and maladaptive roles in disease pathogenesis. Autophagy has been implicated in acute kidney injury, which can arise in response to nephrotoxins, sepsis, and ischemia/reperfusion, and in chronic kidney diseases. The latter includes comorbidities of diabetes and recent evidence for chronic obstructive pulmonary disease-associated kidney injury. Roles of autophagy in polycystic kidney disease and kidney cancer have also been described. Targeting the autophagy pathway may have therapeutic benefit in the treatment of kidney disorders.

Role of Podocyte Injury in Glomerulosclerosis

Finding new therapeutic targets of glomerulosclerosis treatment is an ongoing quest. Due to a living environment of various stresses and pathological stimuli, podocytes are prone to injuries; moreover, as a cell without proliferative potential, loss of podocytes is vital in the pathogenesis of glomerulosclerosis. Thus, sufficient understanding of factors and underlying mechanisms of podocyte injury facilitates the advancement of treating and prevention of glomerulosclerosis. The clinical symptom of podocyte injury is proteinuria, sometimes with loss of kidney functions progressing to glomerulosclerosis. Injury-induced changes in podocyte physiology and function are actually not a simple passive process, but a complex interaction of proteins that comprise the anatomical structure of podocytes at molecular levels. This chapter lists several aspects of podocyte injuries along with potential mechanisms, including glucose and lipid metabolism disorder, hypertension, RAS activation, micro-inflammation, immune disorder, and other factors. These aspects are not technically separated items, but intertwined with each other in the pathogenesis of podocyte injuries.

Impact of Bevacizumab on Liver Damage After Massive Hepatectomy in Rats

BACKGROUND

The aim of this study was to evaluate the impact of pretreatment with bevacizumab on liver damage in a rat model of massive hepatectomy (Hx) model, as a surrogate model of massive Hx for liver metastasis from colorectal cancer.

MATERIALS AND METHODS

Male Wister rats (n=24) were separated into the following two groups: 90% Hx and 90% Hx plus bevacizumab group. Bevacizumab (5 mg/kg) was injected intraperitoneally 7 days before Hx. Samples of blood and remnant liver tissue were obtained 24 hours after hepatectomy and the following parameters were evaluated: Biochemical analysis; liver regeneration rate; survival rate; and real-time polymerase chain reaction for interleukin-1 beta (Il1b), tumor necrosis factor alpha (Tnfa), matrix metalloproteinase (Mmp) 2 and Mmp9 mRNA. In addition, samples of whole liver tissue were obtained immediately before Hx and real-time polymerase chain reaction was performed for X-box binding protein 1 (Xbp1), activating transcription factor 6 (Atf6), C/EBP homologous protein (Chop), glucose-regulated protein 78 (Grp78) and heat-shock protein 70 (Hsp70), as markers of endoplasmic reticulum stress response.

RESULTS

The levels of transaminases 24 hours after Hx were significantly reduced in the group pretreated with bevacizumab compared to that not pretreated (p<0.05). The liver regeneration rate at 24 hours after Hx was significantly increased in the group pretreated with bevacizumab compared with the group which underwent Hx alone (p<0.05). The survival rate for the group pretreated with bevacizumab tended to be higher than that of the Hx-only group, 72 hours after Hx (p=0.09). The expressions of Il1b, Mmp2 and Mmp9 mRNA 24 hours after Hx in the group pretreated with bevacizumab tended to be lower than that of rats which underwent Hx alone (p=0.11, 0.09 and 0.15, respectively). The expression of Xbp1, Chop, Grp78 and Hsp70 mRNA immediately before Hx in the group pretreated with bevacizumab were significantly higher than the 90% Hx group (p<0.05).

CONCLUSION

Bevacizumab pretreatment had protective effects on liver injury after massive hepatectomy in rats, apparently via the induction of the endoplasmic reticulum stress response, i.e. the so-called unfolded protein response.

Thrombospondin 1 and Its Diverse Roles as a Regulator of Extracellular Matrix in Fibrotic Disease

Thrombospondin 1 (TSP1) is a matricellular extracellular matrix protein that has diverse roles in regulating cellular processes important for the pathogenesis of fibrotic diseases. We will present evidence for the importance of TSP1 control of latent transforming growth factor beta activation in renal fibrosis with an emphasis on diabetic nephropathy. Other functions of TSP1 that affect renal fibrosis, including regulation of inflammation and capillary density, will be addressed. Emerging roles for TSP1 N-terminal domain regulation of collagen matrix assembly, direct effects of TSP1-collagen binding, and intracellular functions of TSP1 in mediating endoplasmic reticulum stress responses in extracellular matrix remodeling and fibrosis, which could potentially affect renal fibrogenesis, will also be discussed. Finally, we will address possible strategies for targeting TSP1 functions to treat fibrotic renal disease.

Lipotoxicity in Kidney, Heart, and Skeletal Muscle Dysfunction

Dyslipidemia is a common nutritional and metabolic disorder in patients with chronic kidney disease. Accumulating evidence supports the hypothesis that prolonged metabolic imbalance of lipids leads to ectopic fat distribution in the peripheral organs (lipotoxicity), including the kidney, heart, and skeletal muscle, which accelerates peripheral inflammation and afflictions. Thus, lipotoxicity may partly explain progression of renal dysfunction and even extrarenal complications, including renal anemia, heart failure, and sarcopenia. Additionally, endoplasmic reticulum stress activated by the unfolded protein response pathway plays a pivotal role in lipotoxicity by modulating the expression of key enzymes in lipid synthesis and oxidation. Here, we review the molecular mechanisms underlying lipid deposition and resultant tissue damage in the kidney, heart, and skeletal muscle, with the goal of illuminating the nutritional aspects of these pathologies.

The role of extracellular vesicles in renal fibrosis

As a particularly important mediator of intercellular communication, extracellular vesicles (EVs) have been proved to be extensively involved in various system diseases over the past two decades, including in renal diseases. As is well-known, renal fibrosis is the common pathological process of any ongoing renal disease or adaptive repair of kidney injury based on current knowledge. Although much work has been performed focusing on EVs in various renal diseases, the role of EVs in renal fibrosis has not been described in detail and summarized. In this review, we provide a brief overview of the definition, classification and biological process of EVs. Then, the potential mechanisms of EVs in renal fibrosis are illustrated. Lastly, recent advances in EVs and the implications of EVs for diagnosis and therapy in renal fibrosis disease are introduced. We look forward to a more comprehensive understanding of EVs in renal fibrosis, which could be a boon to patients with renal fibrosis disease.

Sodium 4-phenylbutyrate treatment protects against renal injury in NZBWF1 mice

Systemic lupus erythematosus (SLE) is an autoimmune disease predominantly affecting women and often leading to lupus nephritis and kidney damage. Endoplasmic reticulum (ER) stress has been implicated in several forms of kidney disease, but whether ER stress contributes to renal injury in SLE is unknown. To investigate this, a small molecule chaperone, sodium 4-phenylbutyrate (4-PBA), was administered to the New Zealand Black x New Zealand White F₁ hybrid (NZBWF1) mouse model of SLE. In a prevention study, treatment with 4-PBA from 20 weeks of age (prior to the development of renal injury) delayed the onset of albuminuria and significantly reduced additional indices of renal injury compared with vehicle-treated NZBWF1 mice at 36 weeks of age, including collagen deposition, tubular casts, renal cell apoptosis, and blood urea nitrogen (BUN) concentration. To test whether ER stress contributes to the progression of renal injury once albuminuria has developed, mice were monitored for the onset of albuminuria (3+ or ≥300 mg/dl by dipstick measurement of 24-h urine sample) and once established, were either killed (onset group), or underwent 4-PBA or vehicle treatment for 4 weeks. Treatment with 4-PBA blocked the worsening of glomerular injury, reduced the number of dilated or cast-filled tubules, and reduced the number of apoptotic cells compared with vehicle-treated mice. BUN and left ventricle to bodyweight ratio (LV:BW) were also reduced by 4-PBA treatment. Renal expression of the endogenous chaperones, protein disulphide isomerase (PDI), and 78 kDa glucose-regulated protein (GRP78, also known as binding Ig protein (BiP)), were increased in 4-PBA-treated mice. Together, these results suggest a therapeutic potential for agents like 4-PBA in combating renal injury in SLE.

Ulinastatin inhibits apoptosis induced by serum deprivation in mesenchymal stem cells

Mesenchymal stem cells (MSCs) have exhibited great potential in the therapy of cardiovascular disease. However, the application of MSCs is hampered by apoptosis, which reduces the number of cells in the host cardiac microenvironment. Ulinastatin (UTI), a broad‑spectrum protease inhibitor that can be purified from human urine, has attracted attention for its protective effects through its immunomodulatory and anti‑inflammatory properties. The present study aimed to evaluate the effects of UTI on serum deprivation‑induced apoptosis of MSCs and investigate its molecular mechanisms. Cell viability was determined by the MTT assay. Apoptosis was assessed by flow cytometric analysis with Annexin V/propidium iodide staining. The protein levels of cleaved caspase‑3, B‑cell lymphoma‑2 (Bcl‑2) family proteins, total‑Akt and phospho‑Akt were evaluated by western blot. The results of the present study demonstrated that UTI exhibited a protective effect in serum deprived MSCs, as indicated by increased cell viability, and a reduction in the rate of apoptosis and caspase‑3 activation. In addition, treatment with UTI significantly decreased the expression levels of Bcl‑2, Bcl‑extra large and Bcl‑associated X protein. Furthermore, activation of the Akt signaling pathway was involved in the UTI‑induced anti‑apoptotic effects. The present findings indicated that UTI is able to promote the survival of MSCs under serum deprivation conditions. The present study may be helpful in improving the therapeutic efficacy of MSC transplantation used to cure chronic ischemic heart disease.

Activation of PERK-eIF2α-ATF4-CHOP axis triggered by excessive ER stress contributes to lead-induced nephrotoxicity

Lead (Pb) is a known nephrotoxicant that causes damage to proximal tubular cells. PERK pathway plays an important role in the pathogenesis of renal diseases, but its role in Pb-induced nephrotoxicity remains largely unknown. In this study, data showed that Pb could induce ER stress as shown by increased phosphorylation of PERK with subsequent activation of the eIF2α-ATF4-CHOP axis in primary rat proximal tubular (rPT) cells, indicating the activation of PERK-eIF2α-ATF4-CHOP pathway due to excessive ER stress. Pb-activated PERK pathway can be effectively inhibited by 4-phenylbutyric acid and PERK gene silencing, respectively; whereas continuously up-regulated by tunicamycin (TM) treatment. Moreover, Pb-induced apoptosis and inhibition of autophagic flux in rPT cells were significantly augmented and aggravated by co-treatment with TM, respectively. Pharmacological or genetic inhibition of the PERK pathway results in alleviation of apoptosis and restoration of autophagy inhibition in Pb-exposed rPT cells. Mechanistically, activation of PERK-eIF2α-ATF4-CHOP axis triggered by excessive ER stress in rPT cells leads to Pb-induced apoptosis and blockage of autophagic flux, resulting in nephrotoxicity.

Cyclosporine A binding to COX-2 reveals a novel signaling pathway that activates the IRE1α unfolded protein response sensor

Cyclosporine, a widely used immunosuppressant in organ transplantation and in treatment of various autoimmune diseases, activates the unfolded protein response (UPR), an ER stress coping response. In this study we discovered a new and unanticipated cyclosporine-dependent signaling pathway, with cyclosporine triggering direct activation of the UPR. COX-2 binds to and activates IRE1α, leading to IRE1α splicing of XBP1 mRNA. Molecular interaction and modeling analyses identified a novel interaction site for cyclosporine with COX-2 which caused enhancement of COX-2 enzymatic activity required for activation of the IRE1α branch of the UPR. Cyclosporine-dependent activation of COX-2 and IRE1α in mice indicated that cyclosporine-COX-2-IRE1α signaling pathway was functional in vivo. These findings identify COX-2 as a new IRE1α binding partner and regulator of the IRE1α branch of the UPR pathway, and establishes the mechanism underlying cytotoxicity associated with chronic cyclosporine exposure.

Taurine alleviates endoplasmic reticulum stress in the chondrocytes from patients with osteoarthritis

Osteoarthritis (OA), characterized by pain and stiffness, swelling, deformity and dysfunction of joints, affects large numbers of population. The purpose of this study was to discover the effects of taurine in human OA chondrocytes and explore the underlying mechanisms. 46 patients with different grades of OA were recruited. Of these patients, 24 underwent total knee replacement and cartilages were harvested. The mRNA expressions of type II collagen (Collagen II) and endoplasmic reticulum (ER) stress markers (GRP78, GADD153 and Caspase-12) in cartilages were quantified by qRT-PCR. Cell viability and apoptosis of patient-derived chondrocytes were assessed by the CCK-8 assay and flow cytometry assay, respectively. Meanwhile, protein levels of Collagen II and ER stress markers both in cartilages and chondrocytes were evaluated by Western blot. The mRNA and protein levels of Collagen II decreased as OA progressed, while the expressions of ER stress markers increased dramatically. H₂O₂ induced ER stress in chondrocytes, as shown by the significant increase in the expression of ER stress markers, inhibited chondrocyte viability and Collagen II synthesis, promoted apoptosis. However, taurine treatment inhibited these above phenomena. These results indicated that taurine exhibited anti-OA effect by alleviating H₂O₂ induced ER stress and subsequently inhibiting chondrocyte apoptosis.

Nickel and cobalt affect galactosylation of recombinant IgG expressed in CHO cells

Glycosylation is an important product quality attribute of antibody biopharmaceuticals. It involves enzymatic addition of oligosaccharides on proteins by sequential action of glycosyltransferases and glycosidases in the endoplasmic reticulum and golgi. Some of these enzymes like galactosyltransferase and N-acetylglucosaminyltransferase-I require trace metal cofactors. Variations in trace metal availability during production can thus affect glycosylation of recombinant glycoproteins such as monoclonal antibodies. Variability in trace metal concentrations can be introduced at multiple stages during production such as due to impurities in raw materials for culture medium and leachables from bioreactors. Knowledge of the effect of various trace metals on glycosylation can help in root-cause analysis of unintended variability in glycosylation. In this study, we investigated the effect of nickel and cobalt on glycosylation of recombinant IgG expressed in Chinese hamster ovary cells. Nickel concentrations below 500 µM did not affect glycosylation, but above 500 µM it significantly decreases galactosylation of IgG. Cobalt at 50 µM concentration causes slight increase in G1F glycans (mono galactosylated) as previously reported. However, higher concentrations result in a small increase in G0F (non galactosylated) glycans. This effect of nickel and cobalt on galactosylation of recombinant IgG can be reversed by supplementation of uridine and galactose which are precursors to UDP-Galactose, a substrate for the enzymatic galactosylation reaction.

MiR-4756 promotes albumin-induced renal tubular epithelial cell epithelial-to-mesenchymal transition and endoplasmic reticulum stress via targeting Sestrin2

Accumulating evidence indicates that proteinuria promotes the progression of diabetic kidney disease (DKD) and induces renal epithelial tubular cell epithelial-to-mesenchymal transition (EMT) and endoplasmic reticulum (ER) stress, but the mechanism remains unclear. In our previous research, we found that miR-4756 levels were increased in the urinary extracellular vesicles of type 2 diabetes mellitus patients with macroalbuminuria. In a preliminary study, we found that miR-4756 may be derived from renal tubular epithelial cells, but its role has not been elucidated. Albumin stimulation significantly increased miR-4756 levels in HK-2 cells. In addition, an miR-4756 mimic accelerated albumin-stimulated HK-2 cell EMT and ER stress, and an miR-4756 inhibitor suppressed these events. We then found that miR-4756 targeted the 3'-untranslated region (UTR) of Sestrin2 and directly suppressed Sestrin2 expression. Furthermore, the induction of EMT and ER stress by the overexpression of miR-4756 was abolished by Sestrin2 overexpression. Moreover, the overexpression of miR-4756 increased ERK1/2 activation and decreased 5' monophosphate-activated protein kinase activation. Thus, our study provides evidence that miR-4756 accelerates the process of DKD through Sestrin2, suggesting that targeting miR-4756 may be a novel strategy for DKD treatment.

CAAT/enhancer binding protein-homologous protein deficiency attenuates liver ischemia/reperfusion injury in mice

Ischemia/reperfusion injury (IRI) is one of the main causes of liver dysfunction after liver surgery. Involvement of endoplasmic reticulum (ER) stress in various diseases has been demonstrated, and CAAT/enhancer binding protein-homologous protein (CHOP) is a transcriptional regulator that is induced by ER stress. It is also a key regulator of ER stress-mediated apoptosis. The aim of this study was to investigate the role of CHOP in liver IRI. Wild type (WT) and CAAT/enhancer binding protein-homologous protein knockout (CHOP-/-) mice were subjected to 70% liver warm ischemia/reperfusion for 60 minutes. At different times after reperfusion, liver tissues and blood samples were collected for evaluation. Induction of ER stress including CHOP expression was ascertained. Liver damage was evaluated based on serum liver enzymes, liver histology, and neutrophil infiltration. Hepatocyte death including apoptosis was assessed. Liver warm IRI induced ER stress in both WT and CHOP-/- mice. In addition, CHOP expression was up-regulated in WT mice. At 6 hours after reperfusion, liver damage was attenuated in CHOP-/- mice. On the basis of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining, apoptotic and necrotic cells were significantly reduced in CHOP-/- mice. CHOP deficiency also reduced the cleavage of caspase 3 and expression of the proapoptotic protein B cell lymphoma 2-associated X protein. Liver IRI induces CHOP expression, and CHOP deficiency attenuates liver IRI by inhibiting apoptosis. Elucidation of the function of CHOP in liver IRI may contribute to further investigation for a therapy against liver IRI associated with the ER stress pathway. Liver Transplantation 24 645-654 2018 AASLD.

Endoplasmic reticulum stress in the pathogenesis of fibrotic disease

Eukaryotic cells contain an elegant protein quality control system that is crucial in maintaining cellular homeostasis; however, dysfunction of this system results in endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). Severe or prolonged ER stress is associated with the development of degenerative and fibrotic disorders in multiple organs, as evidenced by the identification of disease-causing mutations in epithelial-restricted genes that lead to protein misfolding or mistrafficking in familial fibrotic diseases. Emerging evidence implicates ER stress and UPR signaling in a variety of profibrotic mechanisms in individual cell types. In epithelial cells, ER stress can induce apoptosis, inflammatory signaling, and epithelial-mesenchymal transition. In other cell types, ER stress is linked to myofibroblast activation, macrophage polarization, and T cell differentiation. ER stress-targeted therapies have begun to emerge using approaches that range from global enhancement of chaperone function to selective targeting of activated ER stress sensors and other downstream mediators. As the complex regulatory mechanisms of this system are further clarified, there are opportunities to develop new disease-modifying therapeutic strategies in a wide range of chronic fibrotic diseases.

Crosstalk Between the Unfolded Protein Response, MicroRNAs, and Insulin Signaling Pathways: In Search of Biomarkers for the Diagnosis and Treatment of Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a metabolic disorder that is characterized by functional defects in glucose metabolism and insulin secretion. Its complex etiology and multifaceted nature have made it difficult to design effective therapies for early diagnosis and treatment. Several lines of evidence indicate that aberrant activation of the unfolded protein response (UPR) in response to endoplasmic reticulum (ER) stress impairs the β cell's ability to respond to glucose and promotes apoptosis. Elucidating the molecular mechanisms that govern β cell dysfunction and cell death can help investigators design therapies to halt or prevent the development of T2DM. Early diagnosis of T2DM, however, warrants additionally the identification of potential biomarkers. MicroRNAs (miRNAs) are key regulators of transcriptional processes that modulate various features of insulin signaling, such as insulin sensitivity, glucose tolerance, and insulin secretion. A deeper understanding of how changes in patterns of expression of miRNAs correlate with altered glucose metabolism can enable investigators to develop methods for the early diagnosis and treatment of T2DM. The first part of this review examines how altered expression of specific UPR pathway proteins disrupts ER function and causes β cell dysfunction, while the second part discusses the potential role of miRNAs in the diagnostic and treatment of T2DM.

Rediscovering Beta-2 Microglobulin As a Biomarker across the Spectrum of Kidney Diseases

There is currently an unmet need for better biomarkers across the spectrum of renal diseases. In this paper, we revisit the role of beta-2 microglobulin (β₂M) as a biomarker in patients with chronic kidney disease and end-stage renal disease. Prior to reviewing the numerous clinical studies in the area, we describe the basic biology of β₂M, focusing in particular on its role in maintaining the serum albumin levels and reclaiming the albumin in tubular fluid through the actions of the neonatal Fc receptor. Disorders of abnormal β₂M function arise as a result of altered binding of β₂M to its protein cofactors and the clinical manifestations are exemplified by rare human genetic conditions and mice knockouts. We highlight the utility of β₂M as a predictor of renal function and clinical outcomes in recent large database studies against predictions made by recently developed whole body population kinetic models. Furthermore, we discuss recent animal data suggesting that contrary to textbook dogma urinary β₂M may be a marker for glomerular rather than tubular pathology. We review the existing literature about β₂M as a biomarker in patients receiving renal replacement therapy, with particular emphasis on large outcome trials. We note emerging proteomic data suggesting that β₂M is a promising marker of chronic allograft nephropathy. Finally, we present data about the role of β₂M as a biomarker in a number of non-renal diseases. The goal of this comprehensive review is to direct attention to the multifaceted role of β₂M as a biomarker, and its exciting biology in order to propose the next steps required to bring this recently rediscovered biomarker into the twenty-first century.

Recent Insights into the Role of Unfolded Protein Response in ER Stress in Health and Disease

Unfolded stress response (UPR) is a conserved cellular pathway involved in protein quality control to maintain homeostasis under different conditions and disease states characterized by cell stress. Although three general schemes of and genes induced by UPR are rather well-established, open questions remain including the precise role of UPR in human diseases and the interactions between different sensor systems during cell stress signaling. Particularly, the issue how the normally adaptive and pro-survival UPR pathway turns into a deleterious process causing sustained endoplasmic reticulum (ER) stress and cell death requires more studies. UPR is also named a friend with multiple personalities that we need to understand better to fully recognize its role in normal physiology and in disease pathology. UPR interacts with other organelles including mitochondria, and with cell stress signals and degradation pathways such as autophagy and the ubiquitin proteasome system. Here we review current concepts and mechanisms of UPR as studied in different cells and model systems and highlight the relevance of UPR and related stress signals in various human diseases.