Proteostasis as a therapeutic target in glomerular injury associated with mutant α-actinin-4

Mutations in α-actinin-4 (actinin-4) result in hereditary focal segmental glomerulosclerosis (FSGS) in humans. Actinin-4 mutants induce podocyte injury because of dysregulation of the cytoskeleton and proteotoxicity. Injury may be associated with endoplasmic reticulum (ER) stress and polyubiquitination of proteins. We assessed if the chemical chaperone 4-phenylbutyrate (4-PBA) can ameliorate the proteotoxicity of an actinin-4 mutant. Actinin-4 K255E, which causes FSGS in humans (K256E in the mouse), showed enhanced ubiquitination, accelerated degradation, aggregate formation, and enhanced association with filamentous (F)-actin in glomerular epithelial cells (GECs). The mutant disrupted ER function and stimulated autophagy. 4-PBA reduced actinin-4 K256E aggregation and its tight association with F-actin. Transgenic mice that express actinin-4 K256E in podocytes develop podocyte injury, proteinuria, and FSGS in association with glomerular ER stress. Treatment of these mice with 4-PBA in the drinking water over a 10-wk period significantly reduced albuminuria and ER stress. Another drug, celastrol, which enhanced expression of ER and cytosolic chaperones in GECs, tended to reduce actinin-4 aggregation but did not decrease the tight association of actinin-4 K256E with F-actin and did not reduce albuminuria in actinin-4 K256E transgenic mice. Thus, chemical chaperones, such as 4-PBA, may represent a novel therapeutic approach to certain hereditary glomerular diseases.

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Downregulation of ephrin-B1 is a critical event of podocyte injury

10.36811/cjn.2021.110004 ◽

2021 ◽

pp. 1-6

Author(s):

Yoshiyasu Fukusumi ◽

Veniamin Ivanov ◽

Ying Zhang ◽

Hidenori Yasuda ◽

Hiroshi Kawachi

Keyword(s):

Slit Diaphragm ◽

Cell Junction ◽

Critical Event ◽

Glomerular Diseases ◽

Podocyte Injury ◽

Related Molecule ◽

Glomerular Epithelial Cells ◽

Essential Components ◽

Cellular Domain ◽

A Cell

Proteinuria in several glomerular diseases results from dysfunction of the slit diaphragm, a cell-cell junction of glomerular epithelial cells (podocytes). Ephrin-B1 and its related molecule NHERF 2 are novel essential components of the slit diaphragm. Ephrin-B1 interacts with nephrin via the extra-cellular domain and interacts with NHERF2 via the cytoplasmic site. In the proteinuric state induced by the stimulation to nephrin, nephrin and ephrin-B1 are phosphorylated, and NHERF2 is de- phosphorylated and consequent disruption of the linkage and downregulation of nephrin, ephrin-B1 and NHERF2 are a critical pathogenic event of podocyte injury. Keywords: Podocyte; Slit Diaphragm; Ephrin-B1; Nephrin; NHERF2

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SIRT1 Alleviates Aldosterone-Induced Podocyte Injury by Suppressing Mitochondrial Dysfunction and NLRP3 Inflammasome Activation

Kidney Diseases ◽

10.1159/000513884 ◽

2021 ◽

pp. 1-13

Author(s):

Mingzhu Jiang ◽

Min Zhao ◽

Mi Bai ◽

Juan Lei ◽

Yanggang Yuan ◽

...

Keyword(s):

Mitochondrial Dysfunction ◽

Knockout Mice ◽

Nlrp3 Inflammasome ◽

Inflammasome Activation ◽

Glomerular Injury ◽

Glomerular Diseases ◽

Podocyte Injury ◽

Pyrin Domain ◽

Nlrp3 Inflammasome Activation

Background: Podocyte injury contributes to progressive glomerulosclerosis. Previously, we demonstrated the important role of the NLR family pyrin domain containing 3 (NLRP3) inflammasome in mediating the podocyte injury induced by aldosterone. Silent mating type information regulation 2 homolog 1 (SIRT1) is an NAD+-dependent deacetylase that is associated with the regulation of cellular inflammation. However, whether the activation of the NLRP3 inflammasome in podocytes is regulated by SIRT1, and the mechanism involved, remains unknown. Methods: In this study, we detected SIRT1 expression in patients with podocyte disease and performed an aldosterone infusion model in podocyte-specific Sirt1 knockout mice. In cultured podocytes, we used plasmids to overexpress SIRT1 and treated the podocyte with aldosterone. Results: SIRT1 was significantly decreased in the glomeruli of patients with podocyte disease. Sirt1-deficient mice showed significant urinary albumin excretion after aldosterone infusion, and the severity of the glomerular injury was significantly greater in podocyte-specific Sirt1 knockout mice than in the wild-type mice. Moreover, podocyte conditional Sirt1 knockout aggravated NLRP3 inflammasome activation and mitochondrial dysfunction (MtD). In vitro, overexpression of SIRT1 inhibited NLRP3 activation, protected against MtD and podocyte injury. Conclusion: Taken together, these findings revealed a novel regulatory mechanism of the NLRP3 inflammasome by SIRT1 by promoting mitochondrial function, which provides some potential targets for the treatment of glomerular diseases.

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Genetic ablation of SLK exacerbates glomerular injury in adriamycin nephrosis in mice

AJP Renal Physiology ◽

10.1152/ajprenal.00028.2020 ◽

2020 ◽

Vol 318 (6) ◽

pp. F1377-F1390 ◽

Cited By ~ 1

Author(s):

Boyan Woychyshyn ◽

Joan Papillon ◽

Julie Guillemette ◽

José R. Navarro-Betancourt ◽

Andrey V. Cybulsky

Keyword(s):

Apical Membrane ◽

Glomerular Injury ◽

Podocyte Injury ◽

Genetic Ablation ◽

Apical Domain ◽

Glomerular Epithelial Cells ◽

The Matrix ◽

Muscle Homeostasis ◽

Specific Deletion

Ste20-like kinase SLK is critical for embryonic development and may play an important role in wound healing, muscle homeostasis, cell migration, and tumor growth. Mice with podocyte-specific deletion of SLK show albuminuria and damage to podocytes as they age. The present study addressed the role of SLK in glomerular injury. We induced adriamycin nephrosis in 3- to 4-mo-old control and podocyte SLK knockout (KO) mice. Compared with control, SLK deletion exacerbated albuminuria and loss of podocytes, synaptopodin, and podocalyxin. Glomeruli of adriamycin-treated SLK KO mice showed diffuse increases in the matrix and sclerosis as well as collapse of the actin cytoskeleton. SLK can phosphorylate ezrin. The complex of phospho-ezrin, Na+/H+ exchanger regulatory factor 2, and podocalyxin in the apical domain of the podocyte is a key determinant of normal podocyte architecture. Deletion of SLK reduced glomerular ezrin and ezrin phosphorylation in adriamycin nephrosis. Also, deletion of SLK reduced the colocalization of ezrin and podocalyxin in the glomerulus. Cultured glomerular epithelial cells with KO of SLK showed reduced ezrin phosphorylation and podocalyxin expression as well as reduced F-actin. Thus, SLK deletion leads to podocyte injury as mice age and exacerbates injury in adriamycin nephrosis. The mechanism may at least in part involve ezrin phosphorylation as well as disruption of the cytoskeleton and podocyte apical membrane structure.

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Podocytes exhibit a specialized protein quality control employing derlin-2 in kidney disease

AJP Renal Physiology ◽

10.1152/ajprenal.00691.2016 ◽

2018 ◽

Vol 314 (3) ◽

pp. F471-F482 ◽

Cited By ~ 4

Author(s):

Guohui Ren ◽

Nicholas J. Tardi ◽

Fumihiko Matsuda ◽

Kwi Hye Koh ◽

Phillip Ruiz ◽

...

Keyword(s):

Quality Control ◽

Cell Death ◽

Kidney Disease ◽

Er Stress ◽

Protein Quality ◽

Protein Quality Control ◽

Cellular Injury ◽

Glomerular Injury ◽

Glomerular Diseases ◽

Filtration Barrier

Podocytes are terminally differentiated cells of the kidney filtration barrier with a limited proliferative capacity and are the primary glomerular target for various sources of cellular stress. Accordingly, it is particularly important for podocytes to cope with stress efficiently to circumvent cell death and avoid compromising renal function. Improperly folded proteins within the endoplasmic reticulum (ER) are associated with increased cellular injury and cell death. To relieve ER stress, protein quality control mechanisms like ER-associated degradation (ERAD) are initiated. Derlin-2 is an important dislocation channel component in the ERAD pathway, having an indispensable role in clearing misfolded glycoproteins from the ER lumen. With studies linking ER stress to kidney disease, we investigated the role of derlin-2 in the susceptibility of podocytes to injury due to protein misfolding. We show that podocytes employ derlin-2 to mediate the ER quality control system to maintain cellular homeostasis in both mouse and human glomeruli. Patients with focal segmental glomerulosclerosis (FSGS) or diabetic nephropathy (DN) upregulate derlin-2 expression in response to glomerular injury, as do corresponding mouse models. In derlin-2-deficient podocytes, compensatory responses were lost under adriamycin (ADR)-induced ER dysfunction, and severe cellular injury ensued via a caspase-12-dependent pathway. Moreover, derlin-2 overexpression in vitro attenuated ADR-induced podocyte injury. Thus derlin-2 is part of a protein quality control mechanism that can rescue glomerular injury attributable to impaired protein folding pathways in the ER. Induction of derlin-2 expression in vivo may have applications in prevention and treatment of glomerular diseases.

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Plasminogenuria is associated with podocyte injury, edema, and kidney dysfunction in incident glomerular disease

10.1101/19006809 ◽

2019 ◽

Author(s):

Marc A. Egerman ◽

Jenny S. Wong ◽

Tian Runxia ◽

Gohar Mosoyan ◽

Kinsuk Chauhan ◽

...

Keyword(s):

Oxidative Stress ◽

Kidney Disease ◽

Glomerular Disease ◽

Causative Role ◽

Glomerular Injury ◽

Puromycin Aminonucleoside ◽

Glomerular Diseases ◽

Podocyte Injury ◽

Cardiovascular Morbidity And Mortality

ABSTRACTUrinary plasminogen/plasmin, or plasmin(ogen)uria, has been demonstrated in proteinuric patients and exposure of cultured podocytes to plasminogen results in injury via oxidative stress pathways. A causative role for plasmin(ogen) as a “second hit” in kidney disease progression has yet to be demonstrated in vivo, and the association between plasmin(ogen)uria and kidney function in glomerular diseases remains unclear. We performed comparative studies in a puromycin aminonucleoside (PAN) nephropathy rat model treated with amiloride, an inhibitor of plasminogen activation, and measured changes in plasmin(ogen)uria and urinary endothelin-1 (ET1). In a glomerular disease biorepository cohort (n=128), we measured time-of-biopsy albuminuria, proteinuria, and plasmin(ogen)uria for correlations with renal outcomes. Increased glomerular plasmin(ogen) was found in PAN rats and FSGS patients. PAN nephropathy was associated with increases in plasmin(ogen)uria, proteinuria, and urinary ET1. Amiloride was protective against PAN-induced glomerular injury, reducing urinary ET1 and oxidative stress. In patients, we found associations between plasmin(ogen)uria and edema status as well as eGFR. Our study demonstrates a role for plasmin(ogen)-induced podocyte injury in the PAN nephropathy model, with amiloride having podocyte-protective properties. In one of largest glomerular disease cohorts to study plasminogen, we validated previous findings while suggesting a potentially novel relationship between plasmin(ogen)uria and eGFR. Together, these findings suggest a role for plasmin(ogen) in mediating glomerular injury and as a viable targetable biomarker for podocyte-sparing treatments.TRANSLATIONAL STATEMENTProteinuria is associated with CKD progression, and increased cardiovascular morbidity and mortality. The underlying mechanisms of podocyte injury, the hallmark of proteinuric kidney disease, are poorly understood with limited, non-specific therapeutic options. This study adds to the evidence that plasmin(ogen) in the urine of proteinuric patients is associated with podocyte injury, edema, and impaired renal function. Previously published results from us and others, taken together with our current rodent model and human data, suggest that urinary plasmin(ogen) is a potential targetable biomarker. Efforts to decrease plasmin(ogen)-mediated podocyte injury could be part of a novel therapeutic strategy for glomerular disease.

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Molecular and Cellular Effects of Chemical Chaperone—TUDCA on ER-Stressed NHAC-kn Human Articular Chondrocytes Cultured in Normoxic and Hypoxic Conditions

Molecules ◽

10.3390/molecules26040878 ◽

2021 ◽

Vol 26 (4) ◽

pp. 878

Author(s):

Magdalena Kusaczuk ◽

Monika Naumowicz ◽

Rafał Krętowski ◽

Bartosz Cukierman ◽

Marzanna Cechowska-Pasko

Keyword(s):

Er Stress ◽

Articular Chondrocytes ◽

Potential Candidate ◽

Chemical Chaperone ◽

Cellular Effects ◽

Chop Expression ◽

Hypoxic Conditions ◽

Stressed Cells ◽

Apoptotic Activity ◽

Potential Therapeutics

Osteoarthritis (OA) is considered one of the most common arthritic diseases characterized by progressive degradation and abnormal remodeling of articular cartilage. Potential therapeutics for OA aim at restoring proper chondrocyte functioning and inhibiting apoptosis. Previous studies have demonstrated that tauroursodeoxycholic acid (TUDCA) showed anti-inflammatory and anti-apoptotic activity in many models of various diseases, acting mainly via alleviation of endoplasmic reticulum (ER) stress. However, little is known about cytoprotective effects of TUDCA on chondrocyte cells. The present study was designed to evaluate potential effects of TUDCA on interleukin-1β (IL-1β) and tunicamycin (TNC)-stimulated NHAC-kn chondrocytes cultured in normoxic and hypoxic conditions. Our results showed that TUDCA alleviated ER stress in TNC-treated chondrocytes, as demonstrated by reduced CHOP expression; however, it was not effective enough to prevent apoptosis of NHAC-kn cells in either normoxia nor hypoxia. However, co-treatment with TUDCA alleviated inflammatory response induced by IL-1β, as shown by down regulation of Il-1β, Il-6, Il-8 and Cox2, and increased the expression of antioxidant enzyme Sod2. Additionally, TUDCA enhanced Col IIα expression in IL-1β- and TNC-stimulated cells, but only in normoxic conditions. Altogether, these results suggest that although TUDCA may display chondoprotective potential in ER-stressed cells, further analyses are still necessary to fully confirm its possible recommendation as potential candidate in OA therapy.

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Activation of endoplasmic reticulum stress response during the development of ischemic heart disease

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.01378.2005 ◽

2006 ◽

Vol 291 (3) ◽

pp. H1411-H1420 ◽

Cited By ~ 157

Author(s):

Asim Azfer ◽

Jianli Niu ◽

Linda M. Rogers ◽

Frances M. Adamski ◽

Pappachan E. Kolattukudy

Keyword(s):

Endoplasmic Reticulum ◽

Heart Disease ◽

Stress Response ◽

Transgenic Mice ◽

Ischemic Heart Disease ◽

Er Stress ◽

Stress Proteins ◽

Gene Array ◽

Ischemic Heart ◽

Endoplasmic Reticulum Stress Response

Endoplasmic reticulum (ER) stress has been found to be associated with neurodegenerative diseases and diabetes mellitus. Whether ER stress is involved in the development of heart disease is not known. Cardiac-specific expression of monocyte chemoattractant protein-1 (MCP-1) in mice causes the development of ischemic heart disease. Here we report that microarray analysis of gene expression changes in the heart of these transgenic mice revealed that a cluster of ER stress-related genes was transcriptionally activated in the heart during the development of ischemic heart disease. The gene array results were verified by quantitative real-time PCR that showed highly elevated transcript levels of genes involved in unfolded protein response such as ER and cytoplasmic chaperones, oxidoreductases, protein disulfide isomerase (PDI) family, and ER-associated degradation system such as ubiquitin. Immunoblot analysis confirmed the expression of chaperones, PDI, and ubiquitin. Immunohistochemical analyses showed that ER stress proteins were associated mainly with the degenerating cardiomyocytes. A novel ubiquitin fold modifier (Ufm1) that has not been previously associated with ER stress and not found to be induced under any condition was also found to be upregulated in the hearts of MCP mice (transgenic mice that express MCP-1 specifically in the heart). The present results strongly suggest that activation of ER stress response is involved in the development of ischemic heart disease in this murine model.

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Podocyte injury: the role of proteinuria, urinary plasminogen, and oxidative stress

AJP Renal Physiology ◽

10.1152/ajprenal.00162.2016 ◽

2016 ◽

Vol 311 (6) ◽

pp. F1308-F1317 ◽

Cited By ~ 28

Author(s):

Leopoldo Raij ◽

Runxia Tian ◽

Jenny S. Wong ◽

John C. He ◽

Kirk N. Campbell

Keyword(s):

Oxidative Stress ◽

Glomerular Filtration ◽

Biologically Active ◽

Current Evidence ◽

Glomerular Sclerosis ◽

Glomerular Diseases ◽

Podocyte Injury ◽

Filtration Barrier ◽

Focal Segmental Glomerular Sclerosis

Podocytes are the key target for injury in proteinuric glomerular diseases that result in podocyte loss, progressive focal segmental glomerular sclerosis (FSGS), and renal failure. Current evidence suggests that the initiation of podocyte injury and associated proteinuria can be separated from factors that drive and maintain these pathogenic processes leading to FSGS. In nephrotic urine aberrant glomerular filtration of plasminogen (Plg) is activated to the biologically active serine protease plasmin by urokinase-type plasminogen activator (uPA). In vivo inhibition of uPA mitigates Plg activation and development of FSGS in several proteinuric models of renal disease including 5/6 nephrectomy. Here, we show that Plg is markedly increased in the urine in two murine models of proteinuric kidney disease associated with podocyte injury: Tg26 HIV-associated nephropathy and the Cd2ap −/− model of FSGS. We show that human podocytes express uPA and three Plg receptors: uPAR, tPA, and Plg-RKT. We demonstrate that Plg treatment of podocytes specifically upregulates NADPH oxidase isoforms NOX2/NOX4 and increases production of mitochondrial-dependent superoxide anion (O2−) that promotes endothelin-1 synthesis. Plg via O2− also promotes expression of the B scavenger receptor CD36 and subsequent increased intracellular cholesterol uptake resulting in podocyte apoptosis. Taken together, our findings suggest that following disruption of the glomerular filtration barrier at the onset of proteinuric disease, podocytes are exposed to Plg resulting in further injury mediated by oxidative stress. We suggest that chronic exposure to Plg could serve as a “second hit” in glomerular disease and that Plg is potentially an attractive target for therapeutic intervention.

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Maternal high-fat diet induces metabolic stress response disorders in offspring hypothalamus

Journal of Molecular Endocrinology ◽

10.1530/jme-17-0056 ◽

2017 ◽

Vol 59 (1) ◽

pp. 81-92 ◽

Cited By ~ 7

Author(s):

Long The Nguyen ◽

Sonia Saad ◽

Yi Tan ◽

Carol Pollock ◽

Hui Chen

Keyword(s):

Endoplasmic Reticulum ◽

Body Weight ◽

Er Stress ◽

High Fat Diet ◽

Maternal Obesity ◽

Mrna Level ◽

Metabolic Stress ◽

High Fat ◽

Chemical Chaperone ◽

Protein Levels

Maternal obesity has been shown to increase the risk of obesity and related disorders in the offspring, which has been partially attributed to changes of appetite regulators in the offspring hypothalamus. On the other hand, endoplasmic reticulum (ER) stress and autophagy have been implicated in hypothalamic neuropeptide dysregulation, thus may also play important roles in such transgenerational effect. In this study, we show that offspring born to high-fat diet-fed dams showed significantly increased body weight and glucose intolerance, adiposity and plasma triglyceride level at weaning. Hypothalamic mRNA level of the orexigenic neuropeptide Y (NPY) was increased, while the levels of the anorexigenic pro-opiomelanocortin (POMC), NPY1 receptor (NPY1R) and melanocortin-4 receptor (MC4R) were significantly downregulated. In association, the expression of unfolded protein response (UPR) markers including glucose-regulated protein (GRP)94 and endoplasmic reticulum DNA J domain-containing protein (Erdj)4 was reduced. By contrast, protein levels of autophagy-related genes Atg5 and Atg7, as well as mitophagy marker Parkin, were slightly increased. The administration of 4-phenyl butyrate (PBA), a chemical chaperone of protein folding and UPR activator, in the offspring from postnatal day 4 significantly reduced their body weight, fat deposition, which were in association with increased activating transcription factor (ATF)4, immunoglobulin-binding protein (BiP) and Erdj4 mRNA as well as reduced Parkin, PTEN-induced putative kinase (PINK)1 and dynamin-related protein (Drp)1 protein expression levels. These results suggest that hypothalamic ER stress and mitophagy are among the regulatory factors of offspring metabolic changes due to maternal obesity.

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Attenuation of endoplasmic reticulum stress by caffeine ameliorates hyperoxia-induced lung injury

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.00405.2016 ◽

2017 ◽

Vol 312 (5) ◽

pp. L586-L598 ◽

Cited By ~ 38

Author(s):

Ru-Jeng Teng ◽

Xigang Jing ◽

Teresa Michalkiewicz ◽

Adeleye J. Afolayan ◽

Tzong-Jin Wu ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Lung Injury ◽

Er Stress ◽

Saline Control ◽

Sprague Dawley ◽

Chemical Chaperone ◽

Stress Markers ◽

Rat Pups ◽

Caffeine Treatment ◽

Downstream Effectors

Rodent pups exposed to hyperoxia develop lung changes similar to bronchopulmonary dysplasia (BPD) in extremely premature infants. Oxidative stress from hyperoxia can injure developing lungs through endoplasmic reticulum (ER) stress. Early caffeine treatment decreases the rate of BPD, but the mechanisms remain unclear. We hypothesized that caffeine attenuates hyperoxia-induced lung injury through its chemical chaperone property. Sprague-Dawley rat pups were raised either in 90 (hyperoxia) or 21% (normoxia) oxygen from postnatal day 1 (P1) to postnatal day 10 (P10) and then recovered in 21% oxygen until P21. Caffeine (20 mg/kg) or normal saline (control) was administered intraperitoneally daily starting from P2. Lungs were inflation-fixed for histology or snap-frozen for immunoblots. Blood caffeine levels were measured in treated pups at euthanasia and were found to be 18.4 ± 4.9 μg/ml. Hyperoxia impaired alveolar formation and increased ER stress markers and downstream effectors; caffeine treatment attenuated these changes at P10. Caffeine also attenuated the hyperoxia-induced activation of cyclooxygenase-2 and markers of apoptosis. In conclusion, hyperoxia-induced alveolar growth impairment is mediated, in part, by ER stress. Early caffeine treatment protects developing lungs from hyperoxia-induced injury by attenuating ER stress.

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