A deleterious interplay between endoplasmic reticulum stress and its functional linkage to mitochondria in nephrolithiasis

Calcium signaling crosstalk between the endoplasmic reticulum and mitochondria, a new drug development strategies of kidney diseases

Calcium (Ca2+) acts as a second messenger and constitutes a complex and large information exchange system between the endoplasmic reticulum (ER) and mitochondria; this process is involved in various life activities, such as energy metabolism, cell proliferation and apoptosis. Increasing evidence has suggested that alterations in Ca2+ crosstalk between the ER and mitochondria, including alterations in ER and mitochondrial Ca2+ channels and related Ca2+ regulatory proteins, such as sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), inositol 1,4,5-trisphosphate receptor (IP3R), and calnexin (CNX), are closely associated with the development of kidney disease. Therapies targeting intracellular Ca2+ signaling have emerged as an emerging field in the treatment of renal diseases. In this review, we focused on recent advances in Ca2+ signaling, ER and mitochondrial Ca2+ monitoring methods and Ca2+ homeostasis in the development of renal diseases and sought to identify new targets and insights for the treatment of renal diseases by targeting Ca2+ channels or related Ca2+ regulatory proteins.

Central role of Sigma-1 receptor in ochratoxin A-induced ferroptosis

Ochratoxin A (OTA), a secondary fungal metabolite known for its nephrotoxic effects, is prevalent in various feeds and food items. Our recent study suggests that OTA-induced nephrotoxicity is linked to the Sigma-1 receptor (Sig-1R)-mediated mitochondrial pathway apoptosis in human proximal tubule epithelial-originated kidney-2 (HK-2) cells. However, the contribution of Sig-1R to OTA-induced nephrotoxicity involving other forms of regulated cell death, such as ferroptosis, remains unexplored. In this investigation, cell viability, malondialdehyde (MDA) levels, glutathione (GSH) levels, and protein expressions in HK-2 cells treated with OTA and/or Ferrostatin-1/blarcamesine hydrochloride/BD1063 dihydrochloride were assessed. The results indicate that a 24 h-treatment with 1 μM OTA significantly induces ferroptosis by inhibiting Sig-1R, subsequently promoting nuclear receptor coactivator 4 (NCOA4), long-chain fatty acid-CoA ligase 4 (ACSL4), arachidonate 5-lipoxygenase (ALOX5), autophagy protein 5 (ATG5), and ATG7, inhibiting ferritin heavy chain (FTH1), solute carrier family 7 member 11 (SLC7A11/xCT), glutathione peroxidase 4 (GPX4), peroxiredoxin 6 (PRDX6), and ferroptosis suppressor protein 1 (FSP1), reducing GSH levels, and increasing MDA levels (P < 0.05). In conclusion, OTA induces ferroptosis by inhibiting Sig-1R, subsequently promoting ferritinophagy, inhibiting GPX4/FSP1 antioxidant systems, reducing GSH levels, and ultimately increasing lipid peroxidation levels in vitro.

Phenylbutyric acid inhibits hypoxia-induced trophoblast apoptosis and autophagy in preeclampsia via the PERK/ATF-4/CHOP pathway

Preeclampsia (PE) is a common pregnancy complication with a high mortality rate. Abnormally activated endoplasmic reticulum stress (ERS) is believed to be responsible for the destruction of key placental cells-trophoblasts. Phenylbutyric acid (4-PBA), an ERS inhibitor, is involved in regulating the development of ERS-related diseases. At present, how 4-PBA affects trophoblasts and its mechanisms is still unclear. In this study, PE cell models were established by stimulating HTR-8/SVneo cells with hypoxia. To verify the underlying mechanisms of 4-PBA on PE, CCT020312, an activator of PERK, was also used. The results showed that 4-PBA restored hypoxia-induced trophoblast viability, inhibited HIF-1α protein expression, inflammation, and PERK/ATF-4/CHOP pathway. Hoechst 33342 staining and flow cytometry results confirmed that 4-PBA decreased hypoxia-induced apoptosis in trophoblasts. The results of the JC-1 analysis and apoptosis initiation enzyme activity assay also demonstrated that 4-PBA inhibited apoptosis related to the mitochondrial pathway. Furthermore, by detecting autophagy in trophoblasts, an increased number of autophagic vesicles, damaged mitochondria, enhanced dansylcadaverine fluorescence, enhanced levels of autophagy proteins Beclin-1, LC3II, and decreased p62 were seen in hypoxia-stimulated cells. These changes were reversed by 4-PBA. Furthermore, it was observed that CCT020312 reversed the effects of 4-PBA on the viability, apoptosis, and autophagosome number of hypoxia-induced trophoblasts. In summary, 4-PBA reduces autophagy and apoptosis via the PERK/ATF-4/CHOP pathway and mitochondrial pathway, thereby restoring the viability of hypoxic trophoblasts. These findings provide a solid evidence base for the use of 4-PBA in PE treatment and guide a new direction for improving the outcomes of patients with PE.

RTN3 deficiency exacerbates cisplatin-induced acute kidney injury through the disruption of mitochondrial stability

Reticulum 3 (RTN3) is an endoplasmic reticulum (ER) protein that has been reported to act in neurodegenerative diseases and lipid metabolism. However, the role of RTN3 in acute kidney injury (AKI) has not been explored. Here, we employed public datasets, patient data, and animal models to explore the role of RTN3 in AKI. The underlying mechanisms were studied in primary renal tubular epithelial cells and in the HK2 cell line. We found reduced expression of RTN3 in AKI patients, cisplatin-induced mice, and cisplatin-treated HK2 cells. RTN3-null mice exhibit more severe AKI symptoms and kidney fibrosis after cisplatin treatment. Mitochondrial dysfunction was also found in cells with RTN3 knockdown or knockout. A mechanistic study revealed that RTN3 can interact with HSPA9 in kidney cells. RTN3 deficiency may disrupt the RTN3-HSPA9-VDAC2 complex and affect MAMs during ER-mitochondrion contact, which further leads to mitochondrial dysfunction and exacerbates cisplatin-induced AKI. Our study indicated that RTN3 was important in the kidney and that a decrease in RTN3 in the kidney might be a risk factor for the aggravation of AKI.

Mitochondria-derived vesicles and their potential roles in kidney stone disease

Recent evidence has shown significant roles of mitochondria-derived vesicles (MDVs) in mitochondrial quality control (MQC) system. Under mild stress condition, MDVs are formed to carry the malfunctioned mitochondrial components, such as mitochondrial DNA (mtDNA), peptides, proteins and lipids, to be eliminated to restore normal mitochondrial structure and functions. Under severe oxidative stress condition, mitochondrial dynamics (fission/fusion) and mitophagy are predominantly activated to rescue mitochondrial structure and functions. Additionally, MDVs generation can be also triggered as the major MQC machinery to cope with unhealthy mitochondria when mitophagy is unsuccessful for eliminating the damaged mitochondria or mitochondrial fission/fusion fail to recover the mitochondrial structure and functions. This review summarizes the current knowledge on MDVs and discuss their roles in physiologic and pathophysiologic conditions. In addition, the potential clinical relevance of MDVs in therapeutics and diagnostics of kidney stone disease (KSD) are emphasized.

Proteomics and transcriptomics profiling reveals distinct aspects of kidney stone related genes in calculi rats

BACKGROUNDS

Kidney stone also known as urolithiasis or nephrolithiasis, is one of the oldest diseases known to medicine, however, the gene expression changes and related kidney injury remains unclear.

METHODS

A calculi rat model was developed via ethylene glycol- and ammonium chloride-induction. Integrated proteomic and transcriptomic analysis was performed to characterize the distinct gene expression profiles in the kidney of calculi rat. Differential expressed genes (DEGs) were sub-clustered into distinct groups according to the consistency of transcriptome and proteome. Gene Ontology and KEGG pathway enrichment was performed to analyze the functions of each sub-group of DEGs. Immunohistochemistry was performed to validated the expression of identified proteins.

RESULTS

Five thousand eight hundred ninety-seven genes were quantified at both transcriptome and proteome levels, and six distinct gene clusters were identified, of which 14 genes were consistently dysregulated. Functional enrichment analysis showed that the calculi rat kidney was increased expression of injured & apoptotic markers and immune-molecules, and decreased expression of solute carriers & transporters and many metabolic related factors.

CONCLUSIONS

The present proteotranscriptomic study provided a data resource and new insights for better understanding of the pathogenesis of nephrolithiasis, will hopefully facilitate the future development of new strategies for the recurrence prevention and treatment in patients with kidney stone disease.

Sigma-1 Receptor Signaling: In Search of New Therapeutic Alternatives for Cardiovascular and Renal Diseases

Cardiovascular and renal diseases are among the leading causes of death worldwide, and regardless of current efforts, there is a demanding need for therapeutic alternatives to reduce their progression to advanced stages. The stress caused by diseases leads to the activation of protective mechanisms in the cell, including chaperone proteins. The Sigma-1 receptor (Sig-1R) is a ligand-operated chaperone protein that modulates signal transduction during cellular stress processes. Sig-1R interacts with various ligands and proteins to elicit distinct cellular responses, thus, making it a potential target for pharmacological modulation. Furthermore, Sig-1R ligands activate signaling pathways that promote cardioprotection, ameliorate ischemic injury, and drive myofibroblast activation and fibrosis. The role of Sig-1R in diseases has also made it a point of interest in developing clinical trials for pain, neurodegeneration, ischemic stroke, depression in patients with heart failure, and COVID-19. Sig-1R ligands in preclinical models have significantly beneficial effects associated with improved cardiac function, ventricular remodeling, hypertrophy reduction, and, in the kidney, reduced ischemic damage. These basic discoveries could inform clinical trials for heart failure (HF), myocardial hypertrophy, acute kidney injury (AKI), and chronic kidney disease (CKD). Here, we review Sig-1R signaling pathways and the evidence of Sig-1R modulation in preclinical cardiac and renal injury models to support the potential therapeutic use of Sig-1R agonists and antagonists in these diseases.

Protein synthesis inhibition and loss of homeostatic functions in astrocytes from an Alzheimer's disease mouse model: a role for ER-mitochondria interaction

Deregulation of protein synthesis and ER stress/unfolded protein response (ER stress/UPR) have been reported in astrocytes. However, the relationships between protein synthesis deregulation and ER stress/UPR, as well as their role in the altered homeostatic support of Alzheimer's disease (AD) astrocytes remain poorly understood. Previously, we reported that in astrocytic cell lines from 3xTg-AD mice (3Tg-iAstro) protein synthesis was impaired and ER-mitochondria distance was reduced. Here we show that impaired protein synthesis in 3Tg-iAstro is associated with an increase of p-eIF2α and downregulation of GADD34. Although mRNA levels of ER stress/UPR markers were increased two-three-fold, we found neither activation of PERK nor downstream induction of ATF4 protein. Strikingly, the overexpression of a synthetic ER-mitochondrial linker (EML) resulted in a reduced protein synthesis and augmented p-eIF2α without any effect on ER stress/UPR marker genes. In vivo, in hippocampi of 3xTg-AD mice, reduced protein synthesis, increased p-eIF2α and downregulated GADD34 protein were found, while no increase of p-PERK or ATF4 proteins was observed, suggesting that in AD astrocytes, both in vitro and in vivo, phosphorylation of eIF2α and impairment of protein synthesis are PERK-independent. Next, we investigated the ability of 3xTg-AD astrocytes to support metabolism and function of other cells of the central nervous system. Astrocyte-conditioned medium (ACM) from 3Tg-iAstro cells significantly reduced protein synthesis rate in primary hippocampal neurons. When added as a part of pericyte/endothelial cell (EC)/astrocyte 3D co-culture, 3Tg-iAstro, but not WT-iAstro, severely impaired formation and ramification of tubules, the effect, replicated by EML overexpression in WT-iAstro cells. Finally, a chemical chaperone 4-phenylbutyric acid (4-PBA) rescued protein synthesis, p-eIF2α levels in 3Tg-iAstro cells and tubulogenesis in pericyte/EC/3Tg-iAstro co-culture. Collectively, our results suggest that a PERK-independent, p-eIF2α-associated impairment of protein synthesis compromises astrocytic homeostatic functions, and this may be caused by the altered ER-mitochondria interaction.

Norlignans and phenolics from genus Curculigo protect corticosterone-injured neuroblastoma cells SH-SY5Y by inhibiting endoplasmic reticulum stress-mitochondria pathway

ETHNOPHARMACOLOGICAL RELEVANCE

The plants of genus Curculigo are divided into the Section Curculigo and the Section Capitulata, which are mainly distributed in southeastern and southwestern China. Various ancient chinese books record that these plants were used as an important herb for tonifying kidney yang. Traditional Chinese medicine often draws on this property to treat depression syndrome. Thus genus Curculigo has potential for the treatment of neurodegenerative diseases (ND). The study showed that phenolics were the main characteristic components of plants in the Section Curculigo, represented by orcinol glucoside and curculigoside; the norlignans, with Ph-C5-Ph as the basic backbone, were the main characteristic components of the Section Capitulata. However, there is a lack of sufficient scientific evidence as to whether these two types of ingredients have neuroprotective effects.

AIM OF THE STUDY

To determine the neuroprotective effects of phenolics and norlignans in genus Curculigo on human neuroblastoma cells SH-SY5Y. To discuss their structure-activity relationship and screen for compounds with high activity and neuroprotective effects. To reveal that the amelioration of endoplasmic reticulum (ER) stress by two classes of compounds is mediated by the PERK/eIF2α/ATF4 pathway.

MATERIALS AND METHODS

The cytotoxicity of 17 compounds was assayed by MTT. SH-SY5Y cells were damaged by corticosterone (Cort) (200 μM) for 24 h and then co-administered with 17 compounds (0.1-100 μM) and Cort (200 μM) for 24 h. Cell survival was determined by MTT assay. Apoptosis rate, mitochondrial membrane potential (MMP) and intracellular reactive oxygen species (ROS) levels were detected using flow cytometry. Intracellular Ca²⁺ levels were detected using a fluorescent probe. Cellular mitochondrial and ER damage was observed using transmission electron microscopy (TEM). ER stress and apoptotic pathway-related proteins (BiP, CHOP, cleaved caspase-3, cleaved caspase-9, Bax/Bcl-2), and the expression level of PERK/eIF2α/ATF4 pathway was measured via western blot (WB).

RESULTS

The experimental data showed that Cort treatment of SH-SY5Y cells resulted in decreased cell survival and increased apoptosis, mitochondrial depolarization, ROS, and intracellular Ca²⁺ levels. The co-action of 17 compounds and Cort for a period of time significantly increased cell survival. Compounds 3, 7, 12, 13 also reduced apoptosis rate, mitochondrial depolarization, ROS and intracellular Ca²⁺ levels in the subsequent experiments. In addition, TEM observed that Cort caused mitochondrial and ER damage, and the damage was improved after treatment. WB analysis obtained that Cort increased the expression of apoptotic and ER stress-related proteins and activated pathway expression. However, in the presence of compounds 3, 7, 12, 13, the expression of BiP, CHOP, cleaved caspase-3, cleaved caspase-9, and Bax/Bcl-2 was significantly reduced, and the phosphorylation of PERK and eIF2α and the expression of ATF4 were inhibited.

CONCLUSION

This study found that one phenolic (3) and three norlignans (7, 12, 13) from genus Curculigo have significant neuroprotective effects. The results of the structure-activity relationship indicated that the glucosyl polymeric norlignans and the phenolics with benzoic acid as the parent nucleus were more active. The neuroprotective effect of three norlignans is the latest discovery. This finding has important research value in the field of prevention and treatment of neurodegenerative diseases.

Trimethylamine N-oxide promotes hyperoxaluria-induced calcium oxalate deposition and kidney injury by activating autophagy

Calcium oxalate (CaOx) is the most common component of kidney stones. Oxidative stress, inflammation and autophagy-induced cell death are the major causes of CaOx crystal deposition and CaOx crystal deposition can further lead to kidney injury. Trimethylamine N-oxide (TMAO), a gut microbiota-derived metabolite, plays an important role in the pathogenesis of many diseases, such as atherosclerosis, diabetes and chronic kidney disease, but the effect of TMAO on hyperoxaluria-induced CaOx crystal deposition and kidney injury remains unknown. We hypothesize that TMAO aggravates CaOx crystal deposition via promoting CaOx-mediated cell death. C57Bl/6 mice were given high-oxalate diet as a model of hyperoxaluria. TMAO was provided via drinking water. Serum TMAO levels increased 15 days after CaOx treatment (6.30 ± 0.17 μmol/L vs. 34.65 ± 8.95 μmol/L). High-oxalate diet induced inflammation, CaOx deposition and kidney injury, which TMAO aggravated. In accordance, TMAO intensified high-oxalate diet induced oxidative stress, autophagy and apoptosis. Moreover, TMAO enhanced CaOx crystal adhesion to HK-2 cells and reduced cell viability (from 88.9 ± 1.6% to 75.0 ± 2.7%). Protein kinase R-like endoplasmic reticulum kinase (PERK) may mediate these TMAO effects, as TMAO promoted PERK phosphorylation. Consistently, PERK knockdown alleviated TMAO-evoked CaOx-autophagy, apoptosis and oxidative stress in HK-2 cells. In conclusion, TMAO can aggravate hyperoxaluria-induced kidney injury by triggering the PERK/ROS pathway, which enhances autophagy, apoptosis and inflammation, and facilitates CaOx crystal deposition in renal tubular cells.

Inhibition of EZH2 ameliorates hyperoxaluria-induced kidney injury through the JNK/FoxO3a pathway

AIMS

Enhancer of zeste homolog 2 (EZH2), a histone H3 lysine 27 methyltransferase, has been shown to play a role in kidney diseases. However, its role in hyperoxaluria-induced renal tubular epithelial cells (TECs) injury remains unclear.

MATERIALS AND METHODS

A hyperoxaluria rat model was established by providing 0.5% ammonium chloride and drinking water containing 1% ethylene glycol. TECs were exposed to oxalate stress. The 3-DZNeP, a selective EZH2 inhibitor, was administered in vivo and in vitro. Cell viability, ROS production, and apoptosis ratio were evaluated. Crystal deposition was detected by Von Kossa staining and kidney tissue injury was detected by HE staining and TUNEL. EZH2, H3K27me3, cleaved-caspase3, IL-6, and MCP-1 were examined by western blot or immunohistochemistry.

KEY FINDINGS

Inhibition of EZH2 by 3-DZNeP significantly attenuated hyperoxaluria-induced oxidative and inflammatory injury and CaOx crystal deposition in vivo. Similarly, inhibition of EZH2 using 3-DZNeP or shRNA restored cell viability, suppressed LDH release and the production of intracellular ROS in vitro. Furthermore, the MAPK signaling pathway and FoxO3a levels were activated or elevated in TECs exposed to oxalate. EZH2 inhibition using 3-DZNeP blocked these effects. CC90003 (ERK inhibitor) or SB203580 (p38 inhibitor) did not significantly affect the expression of FoxO3a in TECs treated with 3-DZNeP and oxalate; only SP600125 (JNK inhibitor) significantly decreased FoxO3a expression.

SIGNIFICANCE

EZH2 inhibition protects against oxalate-induced TECs injury and reduces CaOx crystal deposition in the kidney may by modulating the JNK/FoxO3a pathway; EZH2 may be a promising therapeutic target in TECs injury.