ERK1/2 MAPK promotes autophagy to suppress ER stress-mediated apoptosis induced by cadmium in rat proximal tubular cells

Organelles play important roles in maintaining cellular homeostasis. Organelle stress responses, especially in mitochondria, endoplasmic reticula (ER), and primary cilia, are deeply involved in kidney disease pathophysiology. Mitochondria are the center of energy production in most eukaryotic cells. Renal proximal tubular cells are highly energy demanding and abundant in mitochondria. Mitochondrial dysfunctions in association with energy metabolism alterations produce reactive oxygen species and promote inflammation in proximal tubular cells, resulting in progression of kidney disease. The ER play critical roles in controlling protein quality. Unfolded protein response (UPR) pathways are the adaptive response to ER stress for maintaining protein homeostasis. UPR pathway dysregulation under pathogenic ER stress often occurs in glomerular and tubulointerstitial cells and promotes progression of kidney disease. The primary cilia sense extracellular signals and maintain calcium homeostasis in cells. Dysfunction of the primary cilia in autosomal dominant polycystic kidney disease reduces the calcium concentration in proximal tubular cells, leading to increased cell proliferation and retention of cyst fluid. In recent years, the direct interaction at membrane contact sites has received increased attention in association with the development of imaging technologies. The part of the ER that is directly connected to mitochondria is termed the mitochondria-associated ER membrane (MAM), which regulates calcium homeostasis and phospholipid metabolism in cells. Disruption of MAM integrity collapses cellular homeostasis and leads to diseases such as diabetes and Alzheimer disease. This review summarizes recent research on organelle stress and crosstalk, and their involvement in kidney disease pathophysiology. In addition, potential treatment options that target organelle stress responses are discussed.

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Advanced Oxidation Protein Products Induce Hypertrophy and Epithelial-To-Mesenchymal Transition in Human Proximal Tubular Cells through Induction of Endoplasmic Reticulum Stress

Cellular Physiology and Biochemistry ◽

10.1159/000369740 ◽

2015 ◽

Vol 35 (2) ◽

pp. 816-828 ◽

Cited By ~ 17

Author(s):

Xun Tang ◽

Guang Rong ◽

Yang Bu ◽

Shaojie Zhang ◽

Min Zhang ◽

...

Keyword(s):

Protein Expression ◽

Er Stress ◽

Total Protein ◽

Epithelial To Mesenchymal Transition ◽

Proximal Tubular Cells ◽

Advanced Oxidation Protein Products ◽

Mesenchymal Transition ◽

Tubular Cells ◽

Cell Hypertrophy ◽

Proximal Tubular

Background: In chronic kidney disease (CKD), the accumulation of advanced oxidation protein products (AOPPs) is prevalent. Hypertrophy and epithelial-to-mesenchymal transition (EMT) of tubular cells are associated with the pathogenesis of CKD. However, whether AOPPs induce tubular-cell hypertrophy and EMT is unclear. In this study, we investigated the effect of AOPPs on human proximal tubular cells (HK-2 cells) and the mechanisms underlying tubular-cell hypertrophy and EMT in vitro. Methods: The mRNA and protein expression of CCAAT/enhancer-binding protein-homologous protein (CHOP), glucose-regulated protein (GRP) 78, p27, α-smooth muscle actin (α-SMA) and E-cadherin were evaluated by quantitative real-time PCR and western blot, respectively. Cell cycle was detected by flow cytometry. Bicinchoninic acid method was performed to measure total protein content. Results: AOPP treatment upregulated total protein expression, caused an increase in the percentage of G1-phase cells, and induced the overexpression of p27 and α-SMA, lowered the expression of E-cadherin. Furthermore, AOPP treatment induced the overexpression of GRP78 and CHOP. Moreover, the aforementioned effects were reversed following the treatment of cells with an NADPH oxidase inhibitor, a reactive oxygen species (ROS) scavenger, or salubrinal, which is an inhibitor of ER stress, whereas these effects were produced after exposure to thapsigargin, an inducer of ER stress. Conclusion: Our results suggest that AOPPs induced HK-2-cell hypertrophy and EMT by inducing ER stress, which was likely mediated by ROS. These findings could facilitate the development of novel therapeutic strategies for suppressing the progression of CKD.

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Abrogation of store-operated Ca2+ entry protects against crystal-induced ER stress in human proximal tubular cells

Cell Death Discovery ◽

10.1038/s41420-019-0203-5 ◽

2019 ◽

Vol 5 (1) ◽

Cited By ~ 5

Author(s):

Farai C. Gombedza ◽

Samuel Shin ◽

Yianni L. Kanaras ◽

Bidhan C. Bandyopadhyay

Keyword(s):

Er Stress ◽

Proximal Tubular Cells ◽

Tubular Cells ◽

Proximal Tubular

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Potential Protection Effect of ER Homeostasis of N6-(2-Hydroxyethyl)adenosine Isolated from Cordyceps cicadae in Nonsteroidal Anti-Inflammatory Drug-Stimulated Human Proximal Tubular Cells

International Journal of Molecular Sciences ◽

10.3390/ijms22041577 ◽

2021 ◽

Vol 22 (4) ◽

pp. 1577

Author(s):

Charng-Cherng Chyau ◽

Huei-Lin Wu ◽

Chiung-Chi Peng ◽

Shiau-Huei Huang ◽

Chin-Chu Chen ◽

...

Keyword(s):

Gene Expression ◽

Er Stress ◽

Cell Damage ◽

Proximal Tubular Cells ◽

Tubular Cells ◽

Protein Levels ◽

Cordyceps Cicadae ◽

Proximal Tubular ◽

Anti Inflammatory ◽

Er Homeostasis

Nonsteroidal anti-inflammatory drugs (NSAIDs) belong to a class of universally and commonly used anti-inflammatory analgesics worldwide. A diversity of drawbacks of NSAIDs have been reported including cellular oxidative stress, which in turn triggers the accumulation of unfolded proteins, enhancing endoplasmic reticulum stress, and finally resulting in renal cell damage. Cordyceps cicadae (CC) has been used as a traditional medicine for improving renal function via its anti-inflammatory effects. N6-(2-hydroxyethyl)adenosine (HEA), a physiologically active compound, has been reported from CC mycelia (CCM) with anti-inflammatory effects. We hypothesize that HEA could protect human proximal tubular cells (HK–2) from NSAID-mediated effects on differential gene expression at the mRNA and protein levels. To verify this, we first isolated HEA from CCM using Sephadex® LH–20 column chromatography. The MTT assay revealed HEA to be nontoxic up to 100 µM toward HK–2 cells. The HK–2 cells were pretreated with HEA (10–20 µM) and then insulted with the NSAIDs diclofenac (DCF, 200 µM) and meloxicam (MXC, 400 µM) for 24 h. HEA (20 µM) effectively prevented ER stress by attenuating ROS production (p < 0.001) and gene expression of ATF–6, PERK, IRE1α, CDCFHOP, IL1β, and NFκB within 24 h. Moreover, HEA reversed the increase of GRP78 and CHOP protein expression levels induced by DCF and MXC, and restored the ER homeostasis. These results demonstrated that HEA treatments effectively protect against DCF- and MXC-induced ER stress damage in human proximal tubular cells through regulation of the GRP78/ATF6/PERK/IRE1α/CHOP pathway.

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Correction: Abrogation of store-operated Ca2+ entry protects against crystal-induced ER stress in human proximal tubular cells

Cell Death Discovery ◽

10.1038/s41420-021-00445-9 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Farai C. Gombedza ◽

Samuel Shin ◽

Yianni L. Kanaras ◽

Bidhan C. Bandyopadhyay

Keyword(s):

Er Stress ◽

Proximal Tubular Cells ◽

Tubular Cells ◽

Proximal Tubular

A Correction to this paper has been published: https://doi.org/10.1038/s41420-021-00445-9

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Indoxyl sulfate inhibits proliferation of human proximal tubular cells via endoplasmic reticulum stress

AJP Renal Physiology ◽

10.1152/ajprenal.00659.2009 ◽

2010 ◽

Vol 299 (3) ◽

pp. F568-F576 ◽

Cited By ~ 50

Author(s):

Takahisa Kawakami ◽

Reiko Inagi ◽

Takehiko Wada ◽

Tetsuhiro Tanaka ◽

Toshiro Fujita ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Er Stress ◽

Kinase Inhibitor ◽

Indoxyl Sulfate ◽

Uremic Toxin ◽

Proximal Tubular Cells ◽

Trypan Blue Exclusion ◽

Tubular Cells ◽

Activating Transcription Factor 4 ◽

Proximal Tubular

Uremic toxins can deteriorate renal function, but little is known about its mechanism. Because tubular injury is central to progression of chronic kidney disease (CKD), we investigated the effects of a representative uremic toxin indoxyl sulfate (IS) on tubular cells. IS induced endoplasmic reticulum (ER) stress in cultured human proximal tubular cells, demonstrated by the increase in C/EBP homologous protein (CHOP) in the immunoblots. Moreover, administration of an oral adsorbent AST-120 reduced serum IS concentration and decreased tubular expression of CHOP in immunohistochemistry in 5/6-nephretomized, CKD model, rats. Furthermore, we disclosed that IS inhibited proliferation of tubular cells in 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium and 5-bromo-2′-deoxyuridine assay, whereas the results of trypan blue exclusion and lactate dehydrogenase assay showed that IS did not promote cell death. This inhibition was mitigated by small interfering (si) RNA against CHOP. Furthermore, IS increased the cyclin-dependent kinase inhibitor p21WAF1/CIP1(p21). Surprisingly, this was mediated by the inflammatory cytokine interleukin (IL)-6, the expression of which was decreased by siRNA against activating transcription factor 4, another ER stress marker; however, the induction of IL-6 and p21 by IS was not suppressed by siRNA targeted to CHOP, suggesting that they were downstream of ER stress, but independent of CHOP. Moreover, we found that their upregulation was dependent on ERK, using the ERK pathway inhibitor U-0126. Collectively, we demonstrated that IS induced ER stress in tubular cells and inhibited cell proliferation via two pathways downstream of ER stress, namely CHOP and ERK-IL-6-p21. These are possible targets for suppressing progression of CKD.

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TDAG51 mediates epithelial-to-mesenchymal transition in human proximal tubular epithelium

AJP Renal Physiology ◽

10.1152/ajprenal.00481.2011 ◽

2012 ◽

Vol 303 (3) ◽

pp. F467-F481 ◽

Cited By ~ 28

Author(s):

Rachel E. Carlisle ◽

Alana Heffernan ◽

Elise Brimble ◽

Limin Liu ◽

Danielle Jerome ◽

...

Keyword(s):

Er Stress ◽

Epithelial To Mesenchymal Transition ◽

Nuclear Translocation ◽

Tubular Epithelium ◽

Proximal Tubular Cells ◽

Mesenchymal Transition ◽

Tubular Cells ◽

Proximal Tubular ◽

Proximal Tubular Epithelium ◽

Tgf Β1

Epithelial-to-mesenchymal transition (EMT) contributes to renal fibrosis in chronic kidney disease. Endoplasmic reticulum (ER) stress, a feature of many forms of kidney disease, results from the accumulation of misfolded proteins in the ER and leads to the unfolded protein response (UPR). We hypothesized that ER stress mediates EMT in human renal proximal tubules. ER stress is induced by a variety of stressors differing in their mechanism of action, including tunicamycin, thapsigargin, and the calcineurin inhibitor cyclosporine A. These ER stressors increased the UPR markers GRP78, GRP94, and phospho-eIF2α in human proximal tubular cells. Thapsigargin and cyclosporine A also increased cytosolic Ca2+ concentration and T cell death-associated gene 51 (TDAG51) expression, whereas tunicamycin did not. Thapsigargin was also shown to increase levels of active transforming growth factor (TGF)-β1 in the media of cultured human proximal tubular cells. Thapsigargin induced cytoskeletal rearrangement, β-catenin nuclear translocation, and α-smooth muscle actin and vinculin expression in proximal tubular cells, indicating an EMT response. Subconfluent primary human proximal tubular cells were induced to undergo EMT by TGF-β1 treatment. In contrast, tunicamycin treatment did not produce an EMT response. Plasmid-mediated overexpression of TDAG51 resulted in cell shape change and β-catenin nuclear translocation. These results allowed us to develop a two-hit model of ER stress-induced EMT, where Ca2+ dysregulation-mediated TDAG51 upregulation primes the cell for mesenchymal transformation via Wnt signaling and then TGF-β1 activation leads to a complete EMT response. Thus the release of Ca2+ from ER stores mediates EMT in human proximal tubular epithelium via the induction of TDAG51.

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Reciprocal regulation between ER stress and autophagy in renal tubular fibrosis and apoptosis

Cell Death and Disease ◽

10.1038/s41419-021-04274-7 ◽

2021 ◽

Vol 12 (11) ◽

Author(s):

Shaoqun Shu ◽

Hui Wang ◽

Jiefu Zhu ◽

Zhiwen Liu ◽

Danyi Yang ◽

...

Keyword(s):

Er Stress ◽

Kidney Injury ◽

Proximal Tubular Cells ◽

Reciprocal Regulation ◽

Tubular Cells ◽

Chronic Kidney Injury ◽

Proximal Tubular ◽

Kidney Proximal Tubular Cells ◽

Tgf Β1

AbstractBoth endoplasmic reticulum (ER) stress and autophagy have been implicated in chronic kidney injury and renal fibrosis. However, the relationship and regulatory mechanisms between ER stress and autophagy under this condition remain largely unknown. In this study, we first established a mouse model of ER stress-induced chronic kidney injury by 2 weekly injections of a low dose of tunicamycin (TM), a classical ER stress inducer. This model showed the induction of ER stress, autophagy, fibrosis and apoptosis in kidney tissues. In vitro, TM also induced ER stress, autophagy, fibrosis and apoptosis in HK-2 human kidney proximal tubular cells and BUMPT-306 mouse kidney proximal tubular cells. In these cells, autophagy inhibitor suppressed TM-induced fibrotic changes and apoptosis, suggesting an involvement of autophagy in ER stress-associated chronic kidney injury. PERK inhibitor ameliorated autophagy, fibrotic protein expression and apoptosis in TM-treated cells, indicating a role of the PERK/eIF2α pathway in autophagy activation during ER stress. Similar results were shown in TGF-β1-treated HK-2 cells. Interestingly, in both TM- or TGF-β1-treated kidney proximal tubular cells, inhibition of autophagy exaggerated ER stress, suggesting that autophagy induced by ER stress provides a negative feedback mechanism to reduce the stress. Together, these results unveil a reciprocal regulation between ER stress and autophagy in chronic kidney injury and fibrosis.

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