Calcium Uptake via Mitochondrial Uniporter Contributes to Palmitic Acid-Induced Apoptosis in Mouse Podocytes

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.

Calcium signalling and transport in the kidney

The kidney plays a pivotal role in regulating calcium levels within the body. Approximately 98% of the filtered calcium is reabsorbed in the nephron, and this process is tightly controlled to maintain calcium homeostasis, which is required to facilitate optimal bone mineralization, preserve serum calcium levels within a narrow range, and support intracellular signalling mechanisms. The maintenance of these functions is attributed to a delicate balance achieved by various calcium channels, transporters, and calcium-binding proteins in renal cells. Perturbation of this balance due to deficiency or dysfunction of calcium channels and calcium-binding proteins can lead to severe complications. For example, polycystic kidney disease is linked to aberrant calcium transport and signalling. Furthermore, dysregulation of calcium levels can promote the formation of kidney stones. This Review provides an updated description of the key aspects of calcium handling in the kidney, focusing on the function of various calcium channels and the physiological stimuli that control these channels or are communicated through them. A discussion of the role of calcium as an intracellular second messenger and the pathophysiology of renal calcium dysregulation, as well as a summary of gaps in knowledge and future prospects, are also included.

Deoxynivalenol induced intestinal barrier injury, mitochondrial dysfunction and calcium overload by inositol 1,4,5-triphosphate receptors (IP3Rs)-mitochondrial calcium uniporter (MCU) calcium axis

Deoxynivalenol (DON) contamination is widespread in crops and could easily cause intestinal injury, which brings hazards to animals. Mitochondria are considered as an important target of DON, nevertheless, the mechanism is still unclear. Mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) have gained arousing interest and are recognized as critical signaling hubs that control calcium signaling transduction between ER and mitochondria. This study aims to investigate the effects of DON on intestinal barrier, mitochondria, MAMs and inositol 1,4,5-triphosphate receptors (IP3Rs)-mitochondrial calcium uniporter (MCU) calcium axis in piglets and porcine intestinal epithelial cells (IPEC-J2). Furthermore, inhibition of IP3Rs or MCU was used to explore whether IP3Rs-MCU axis of MAMs was involved in the mitochondria dysfunction and intestinal epithelium barrier injury induced by DON in IPEC-J2. The data showed that DON induced intestinal barrier injury, mitochondrial dysfunction and ERS in piglets' jejunum and IPEC-J2. Moreover, DON increased MAMs by upregulating the protein level of Mitofusin 2 (Mfn2), increasing the percentage of mitochondria with MAMs/total mitochondria and the ratio of MAMs length/mitochondrial perimeter and shortening the distance between mitochondria and ER of MAMs. Importantly, DON influenced IP3Rs-glucose-regulated protein 75 (GRP75)-voltage-dependent anion channel 1 (VDAC1)-MCU calcium axis by increasing the protein levels of GRP75 and MCU and the interaction of VDAC1-GRP75-IP3Rs complex, which in turn induced mitochondrial calcium overload. Furthermore, inhibition of IP3Rs or MCU alleviated DON-induced intestinal epithelium barrier injury, mitochondrial dysfunction and mitochondrial calcium overload of IPEC-J2. The current investigation proposed that DON induced intestinal injury, mitochondrial dysfunction and calcium overload via IP3Rs-GRP75-VDAC1-MCU calcium axis.

Biofactors regulating mitochondrial function and dynamics in podocytes and podocytopathies

Podocytes are terminally differentiated kidney cells acting as the main gatekeepers of the glomerular filtration barrier; hence, inhibiting proteinuria. Podocytopathies are classified as kidney diseases caused by podocyte damage. Different genetic and environmental risk factors can cause podocyte damage and death. Recent evidence shows that mitochondrial dysfunction also contributes to podocyte damage. Understanding alterations in mitochondrial metabolism and function in podocytopathies and whether altered mitochondrial homeostasis/dynamics is a cause or effect of podocyte damage are issues that need in-depth studies. This review highlights the roles of mitochondria and their bioenergetics in podocytes. Then, factors/signalings that regulate mitochondria in podocytes are discussed. After that, the role of mitochondrial dysfunction is reviewed in podocyte injury and the development of different podocytopathies. Finally, the mitochondrial therapeutic targets are considered.

Implications of MCU complex in metabolic diseases

Metabolic diseases are considered the primary culprit for physical and mental health of individuals. Although the diagnosis of these diseases is relatively easy, more effective and convenient potent drugs are still being explored. Ca2+ across the inner mitochondrial membrane is a vital intracellular messenger that regulates energy metabolism and cellular Ca2+ homeostasis and is involved in cell death. Mitochondria rely on a selective mitochondrial Ca2+ unidirectional transport complex (MCU complex) in their inner membrane for Ca2+ uptake. We found that the channel contains several subunits and undergoes dramatic transformations in various pathological processes, especially in metabolic diseases. In this way, we believe that the MCU complex becomes a target with significant potential for these diseases. However, there is no review linking the two factors, thus hindering the possibility of new drug production. Here, we highlight the connection between MCU complex-related Ca2+ transport and the pathophysiology of metabolic diseases, adding understanding and insight at the molecular level to provide new insights for targeting MCU to reverse metabolism-related diseases.

Store-operated Ca2+ entry inhibition ameliorates high glucose and ANG II-induced podocyte apoptosis and mitochondrial damage

Hyperglycemia and increased activity of the renal angiotensin II (ANG II) system are two primary pathogenic stimuli for the onset and progression of podocyte injury in diabetic nephropathy. However, the underlying mechanisms are not fully understood. Store-operated Ca2+ entry (SOCE) is an important mechanism that helps maintain cell Ca2+ homeostasis in both excitable and nonexcitable cells. Our previous study demonstrated that high glucose (HG) enhanced podocyte SOCE (1). It is also known that ANG II activates SOCE by releasing endoplasmic reticulum Ca2+. However, the role of SOCE in stress-induced podocyte apoptosis and mitochondrial dysfunction remains unclear. The present study was aimed to determine whether enhanced SOCE mediated HG- and ANG II-induced podocyte apoptosis and mitochondrial damage. In kidneys of mice with diabetic nephropathy, the number of podocytes was significantly reduced. In cultured human podocytes, both HG and ANG II treatment induced podocyte apoptosis, which was significantly blunted by an SOCE inhibitor, BTP2. Seahorse analysis showed that podocyte oxidative phosphorylation in response to HG and ANG II was impaired. This impairment was significantly alleviated by BTP2. The SOCE inhibitor, but not a transient receptor potential cation channel subfamily C member 6 inhibitor, significantly blunted the damage of podocyte mitochondrial respiration induced by ANG II treatment. Furthermore, BTP2 reversed impaired mitochondrial membrane potential and ATP production and enhanced mitochondrial superoxide generation induced by HG treatment. Finally, BTP2 prevented the overwhelming Ca2+ uptake in HG-treated podocytes. Taken together, our results suggest that enhanced SOCE mediated HG- and ANG II-induced podocyte apoptosis and mitochondrial injury.NEW & NOTEWORTHY This study tested the hypothesis that overwhelming store-operated Ca2+ entry is a novel mechanism contributing to high glucose- and angiotensin II-induced podocyte apoptosis and mitochondrial injury.

Protease-activated receptors in kidney diseases: A comprehensive review of pathological roles, therapeutic outcomes and challenges

Studies have demonstrated that protease-activated receptors (PARs) with four subtypes (PAR1-4) are mainly expressed in the renal epithelial, endothelial, and podocyte cells. Some endogenous and urinary proteases, namely thrombin, trypsin, urokinase, and kallikrein released during diseased conditions, are responsible for activating different subtypes of PARs. Each PAR receptor subtype is involved in kidney disease of distinct aetiology. PAR1 and PAR2 have shown differential therapeutic outcomes in rodent models of type-1 and type-2 diabetic kidney diseases due to the distinct etiological basis of each disease type, however such findings need to be confirmed in other diabetic renal injury models. PAR1 and PAR2 blockers have been observed to abolish drug-induced nephrotoxicity in rodents by suppressing tubular inflammation and fibrosis and preventing mitochondrial dysfunction. Notably, PAR2 inhibition improved autophagy and prevented fibrosis, inflammation, and remodeling in the urethral obstruction model. Only the PAR1/4 subtypes have emerged as a therapeutic target for treating experimentally induced nephrotic syndrome, where their respective antibodies attenuated the podocyte apoptosis induced upon thrombin activation. Strikingly PAR2 and PAR4 subtypes involvement has been tested in sepsis-induced acute kidney injury (AKI) and renal ischemia-reperfusion injury models. Thus, more studies are required to delineate the role of other subtypes in the sepsis-AKI model. Evidence suggests that PARs regulate oxidative, inflammatory stress, immune cell activation, fibrosis, autophagic flux, and apoptosis during kidney diseases.

Acacetin antagonized lipotoxicity in pancreatic β-cells via ameliorating oxidative stress and endoplasmic reticulum stress

PURPOSE

During the pathogenesis and progression of diabetes, lipotoxicity is a major threat to the function and survival of pancreatic β-cells. To battle against the lipotoxicity induced cellular damages, the present study investigated the beneficial effects of acacetin, a natural antioxidant, on free fatty acid (FFA) stressed RINm5F cells and the potential mechanism involved.

MATERIALS AND METHODS

RINm5F cells with or without 1 h pretreatment of acacetin were treated with 0.35 mM sodium palmitate for 24 h. Cell viability, intracellular reactive oxygen species (ROS) level, antioxidant capacity, cellular apoptosis, and endoplasmic reticulum (ER) stress biomarker expression were investigated.

RESULTS

Our experiments demonstrated that acacetin treatment significantly scavenged the intracellular ROS, upregulated the endogenous antioxidant enzymes, and diminished the sub-G₁ DNA fraction in the cells exposed to FFA, suggesting its efficacy against oxidative stress. Meanwhile, acacetin treatment significantly mitigated the overload of intracellular Ca²⁺ and reduced the pro-apoptotic protein expression in the FFA stimulated cells, and thereby attenuated the ER stress-mediated cell apoptosis. Furthermore, siRNA interference results confirmed that the suppressing of C/EBP-homologous protein (CHOP) was critical to improve FFA-induced reduction in cell viability and ameliorated the ER stress caused by FFA stimulation.

CONCLUSIONS

Acacetin may antagonize lipotoxicity in pancreatic cells by attenuating the oxidative stress and ER stress.

Calcium Signaling Mediates Cell Death and Crosstalk with Autophagy in Kidney Disease

The kidney is an important organ for the maintenance of Ca²⁺ homeostasis in the body. However, disruption of Ca²⁺ homeostasis will cause a series of kidney diseases, such as acute kidney injury (AKI), chronic kidney disease (CKD), renal ischemia/reperfusion (I/R) injury, autosomal dominant polycystic kidney disease (ADPKD), podocytopathy, and diabetic nephropathy. During the progression of kidney disease, Ca²⁺ signaling plays key roles in various cell activities such as necrosis, apoptosis, eryptosis and autophagy. Importantly, there are complex Ca²⁺ flux networks between the endoplasmic reticulum (ER), mitochondria and lysosomes which regulate intracellular Ca²⁺ signaling in renal cells and contribute to kidney disease. In addition, Ca²⁺ signaling also links the crosstalk between various cell deaths and autophagy under the stress of heavy metals or high glucose. In this regard, we present a review of Ca²⁺ signaling in cell death and crosstalk with autophagy and its potential as a therapeutic target for the development of new and efficient drugs against kidney diseases.

Intracellular Calcium Homeostasis and Kidney Disease

Kidney disease is a serious health problem that burdens our healthcare system. It is crucial to find the accurate pathogenesis of various types of kidney disease to provide guidance for precise therapies for patients suffering from these diseases. However, the exact molecular mechanisms underlying these diseases have not been fully understood. Disturbance of calcium homeostasis in renal cells plays a fundamental role in the development of various types of kidney disease, such as primary glomerular disease, diabetic nephropathy, acute kidney injury and polycystic kidney disease, through promoting cell proliferation, stimulating extracellular matrix accumulation, aggravating podocyte injury, disrupting cellular energetics as well as dysregulating cell survival and death dynamics. As a result, preventing the disturbance of calcium homeostasis in specific renal cells (such as tubular cells, podocytes and mesangial cells) is becoming one of the most promising therapeutic strategies in the treatment of kidney disease. The endoplasmic reticulum and mitochondria are two vital organelles in this process. Calcium ions cycle between the endoplasmic reticulum and mitochondria at the conjugation of these two organelles known as the mitochondria-associated endoplasmic reticulum membrane, maintaining calcium homeostasis. The pharmacologic modulation of cellular calcium homeostasis can be viewed as a novel therapeutic method for renal diseases. Here, we will introduce calcium homeostasis under physiological conditions and the disturbance of calcium homeostasis in kidney diseases. We will focus on the calcium homeostasis regulation in renal cells (including tubular cells, podocytes and mesangial cells), especially in the mitochondria- associated endoplasmic reticulum membranes of these renal cells.

Homoarginine ameliorates diabetic nephropathy independent of nitric oxide synthase-3

Recently we showed that homoarginine supplementation confers kidney protection in diabetic mouse models. In this study we tested whether the protective effect of homoarginine is nitric oxide synthase-3 (NOS3)-independent in diabetic nephropathy (DN). Experiments were conducted in NOS3 deficient (NOS3-/- ) mice and their wild type littermate using multiple low doses of vehicle or streptozotocin and treated with homoarginine via drinking water for 24 weeks. Homoarginine supplementation for 24 weeks in diabetic NOS3-/- mice significantly attenuated albuminuria, increased blood urea nitrogen, histopathological changes and kidney fibrosis, kidney fibrotic markers, and kidney macrophage recruitment compared with vehicle-treated diabetic NOS3-/- mice. Furthermore, homoarginine supplementation restored kidney mitochondrial function following diabetes. Importantly, there were no significant changes in kidney NOS1 or NOS2 mRNA expression between all groups. In addition, homoarginine supplementation improved cardiac function and reduced cardiac fibrosis following diabetes. These data demonstrate that the protective effect of homoarginine is independent of NOS3, which will ultimately change our understanding of the mechanism(s) by which homoarginine induce renal and cardiac protection in DN. Homoarginine protective effect in DN could be mediated via improving mitochondrial function.

Astragaloside IV inhibits palmitic acid-induced apoptosis through regulation of calcium homeostasis in mice podocytes

Loss of podocytes is a hallmark of diabetic nephropathy, and a growing body of evidence indicates that podocytes are susceptible to palmitic acid (PA). We have previously shown that AS-IV inhibited PA-induced podocyte apoptosis by activating sarcoendoplasmic reticulum Ca²⁺ ATPase (SERCA), which indicate calcium regulation may involve in the process. Immunofluorescence staining, Western blot and flow cytometry were used to measure the protective efficacy of AS-IV to ameliorate PA-induced ER stress and podocyte apoptosis. Meanwhile, AS-IV inhibited cytochrome c release, decreased mitochondrial membrane potential, accompany with the depletion of endoplasmic reticulum Ca²⁺ and elevation of cytosolic and mitochondrial Ca²⁺. Sequestration of cytosolic calcium with BAPTA-AM limited the response of podocyte apoptosis, while during the process the effect of AS-IV was also restrained. In contrast, elevation of cytosolic calcium with calcium ionophore ionomycin was depressed by AS-IV addition. Furthermore, inhibiting TRPC6 expression with SKF96365 or TRPC6 siRNA counteracted the beneficial effect of AS-IV. Our study provides further evidence to conclude the inhibitory effect of AS-IV to podocyte apoptosis is Ca²⁺-dependent. And the efficacy correlates with inhibiting TRPC6-mediated Ca²⁺ influx, and then cellular Ca²⁺ disturbance was coordinated.

Altered VDAC-HK association and apoptosis in mouse peripheral blood lymphocytes exposed to diabetic condition: an in vitro and in vivo study

Increased apoptotic lymphocytes have been correlated to a high incidence of infection in poorly controlled diabetes. This study aimed to determine whether altered voltage-dependent anion channel (VDAC)-hexokinase (HK) association contributes to the increase in apoptosis. Mouse peripheral blood lymphocytes (PBL) exposed to high glucose (Glc)/palmitic acid (PA) were used as the in vitro model, which was compared with PBL isolated from alloxan-induced diabetic mice (in vivo model). Our results showed a significant increase in apoptosis as indicated by the apoptotic index, caspase-3 activity, mitochondrial membrane potential and ultrastructural study. HK and glucose-6-phosphate dehydrogenase (G6PDH) activities were markedly reduced with a profound increase in glucose-6-phosphate level. Co-immunoprecipitation confirms HK interaction with VDAC, an outer mitochondrial membrane protein. Inhibited glycolytic enzyme, i.e. HK and reduced HK-VDAC interaction in our study could contribute to increased apoptosis in lymphocytes exposed to high Glc/PA. Targeting HK-VDAC interaction may therefore provide therapeutic potential for the treatment of diabetes-associated infection.

Vigilin interacts with ER-β to protect against palmitic acid-induced granulosa cells apoptosis via inhibiting calcineurin-mediated Drp1 signaling pathway

BACKGROUND

Hypercholesterolemia is one of the causes of female infertility, and as a common fatty acid in follicular fluid, palmitic acid (PA) level plays a vital role in granule cell which is closely related to the developmental potential of follicle.

METHODS

The ovarian granulosa cell-like human granulosa (KGN) cell line and the immortalized normal ovarian surface epithelial cell line (IOSE80) were used to verify the effect of PA on cell viability and apoptosis by MTT and flow cytometry assay, respectively. Then mitochondria damage was confirmed by mitochondrial membrane potential, mitochondrial ROS detection assay and western blot in KGN cells. Thorough luciferase reporter assay and RIP-qPCR, the relationship between vigilin and ER-β was investigated.

RESULTS

In our study, PA induced mitochondrial damage-mediated cell apoptosis of KGN cells was dose-dependently, while PA shown no effects on in IOSE80 cells. Then the role of calcineurin (CnA)-mediated Drp1 signaling pathway on KGN cells was confirmed by treating with Mdivi-1 or FK506T. In addition, the changed level of vigilin and ER-β was observed in cell apoptosis of KGN cells induced by PA. By transfecting vigilin vector or ER-β vector into KGN cells, respectively, vigilin and ER-β were demonstrated to regulate the apoptosis of KGN cells. And vigilin was a binding protein of ER-β mRNA.

CONCLUSION

Vigilin could interact with ER-β mRNA to promote ER-β expression. And Vigilin/ ER-β relieve the mitochondrial damage and cell apoptosis induced by PA through regulating CnA-mediated Drp1 signaling pathway, which revealed the mechanism and strategy of hypercholesterolemia in female infertility.

The Vicious Cycle of Renal Lipotoxicity and Mitochondrial Dysfunction

The kidney is one of the most energy-demanding organs that require abundant and healthy mitochondria to maintain proper function. Increasing evidence suggests a strong association between mitochondrial dysfunction and chronic kidney diseases (CKDs). Lipids are not only important sources of energy but also essential components of mitochondrial membrane structures. Dysregulation of mitochondrial oxidative metabolism and increased reactive oxygen species (ROS) production lead to compromised mitochondrial lipid utilization, resulting in lipid accumulation and renal lipotoxicity. However, lipotoxicity can be either the cause or the consequence of mitochondrial dysfunction. Imbalanced lipid metabolism, in turn, can hamper mitochondrial dynamics, contributing to the alteration of mitochondrial lipids and reduction in mitochondrial function. In this review, we summarize the interplay between renal lipotoxicity and mitochondrial dysfunction, with a focus on glomerular diseases.

Pulsatilla chinensis saponins cause liver injury through interfering ceramide/sphingomyelin balance that promotes lipid metabolism dysregulation and apoptosis

BACKGROUND

P. chinensis saponins (PRS) are pentacyclic triterpenoid bioactive constituents from Pulsatilla chinensis (Bunge) Regel. In our previous study, PRS caused chronic liver injury (CLI) with the significant changes of lipid metabolites including sphingomyelin (SM) in serum after long-term administration. The SM in the hepatocytes membrane plays an indispensable role in maintaining cell membrane stability and regulating the extracellular and intracellular signal transduction. However, it is still unknown the pathway related to SM and the mechanism of CLI on hepatocyte.

PURPOSE

The purpose of this study was to explore the hepatotoxicity mechanism of PRS in vivo and in vitro, to reveal the action of mechanism of SM and the pathway related to liver injury.

METHODS

SD rats were orally administered with PRS for 240 days and liver injury was evaluated by histological examinations. Metabolomics analysis was used to explore the liver metabolic pathway affected by PRS, and the expressions of related proteins were evaluated by western blots. To discover and elucidate the underlying mechanisms of metabolites changes induced by PRS at the cellular level, cellular morphology, MTT assays, western blots and cell membrane potential measurements were carried out using LO2 cells. Furthermore, the roles of SM and cholesterol (Chol) in hepatocyte injury were investigated individually in overload Chol and SM groups. Sphingolipid metabolic pathway related with ceramide/sphingomyelin (Cer/SM) balance was explored using cellular lipidomics and RT-PCR.

RESULTS

PRS gradually damaged the rat's liver in a time-dependent manner. The analysis of liver metabolism profiles showed that lipids metabolites were changed, including sphingolipid, bile acid, linoleic acid and fatty acid. We found that PRS induced apoptosis by interfering with bile acid-mediated sphingolipid metabolic pathway and Cer/SM balance in CLI. In in vitro experiments, PRS led to the increase of LDH leakage, depolarized cell membrane potential and caused cell membrane toxicity. Furthermore, PRS inducedG0/G1 phase cell cycle arrest in LO2 cells, simultaneously activated cellular extrinsic and intrinsic apoptosis pathways. PRS acted on SM and interfered with Cer/SM balance, which promote lipid metabolism dysregulation and apoptosis.

CONCLUSION

PRS acted on SM to interfere Cer/SM balance on LO2 cell. Both in vivo and in vitro, PRS induced Cer/SM imbalance which promoted lipid metabolism disorder and apoptosis. Apoptosis and lipids changes gradually damaged the rats liver, and ultimately developed into CLI.

Neurotoxic effects of aflatoxin B1 on human astrocytes in vitro and on glial cell development in zebrafish in vivo

Aflatoxin B1 is one of the well-known mycotoxins and mainly found in contaminated animal feed and various agricultural products inducing acute and chronic toxicology, tumor, and abnormal neural development. However, the effects of aflatoxin B1 on the human brain, especially on astrocytes, have not been studied in depth. In the present study, we studied the neurotoxic effects of aflatoxin B1, in vitro and in vivo. Aflatoxin B1 decreased the proliferation and stopped cell cycle progression at the sub G0/G1 stage with an increase in BAX, BAK, and cytochrome c proteins in human astrocytes. In addition, it increased the mitochondrial depolarization, oxidative stress, and calcium influx in both the cytosol and mitochondria. Surprisingly, inhibition of calcium overload in the cytosol and mitochondria, using calcium chelators and an inhibitor, partially rescued the proliferation of aflatoxin B1-treated astrocytes. Based on the toxicity assays using zebrafish models, aflatoxin B1 decreased the embryo survival rate with physiological changes and an increase in the caspase and tp53 genes. It also decreased the expression of gfap, mbp, and olig2 in the transgenic zebrafish embryo's brain and axon. Our results revealed the specific mechanism of the neurotoxic effects of aflatoxin B1 on human astrocytes and zebrafish glial cells.

Cancer-Related Increases and Decreases in Calcium Signaling at the Endoplasmic Reticulum-Mitochondria Interface (MAMs)

Endoplasmic reticulum (ER)-mitochondria regions are specialized subdomains called also mitochondria-associated membranes (MAMs). MAMs allow regulation of lipid synthesis and represent hubs for ion and metabolite signaling. As these two organelles can module both the amplitude and the spatiotemporal patterns of calcium (Ca²⁺) signals, this particular interaction controls several Ca²⁺-dependent pathways well known for their contribution to tumorigenesis, such as metabolism, survival, sensitivity to cell death, and metastasis. Mitochondria-mediated apoptosis arises from mitochondrial Ca²⁺ overload, permeabilization of the mitochondrial outer membrane, and the release of mitochondrial apoptotic factors into the cytosol. Decreases in Ca²⁺ signaling at the ER-mitochondria interface are being studied in depth as failure of apoptotic-dependent cell death is one of the predominant characteristics of cancer cells. However, some recent papers that linked MAMs Ca²⁺ crosstalk-related upregulation to tumor onset and progression have aroused the interest of the scientific community.In this review, we will describe how different MAMs-localized proteins modulate the effectiveness of Ca²⁺-dependent apoptotic stimuli by causing both increases and decreases in the ER-mitochondria interplay and, specifically, by modulating Ca²⁺ signaling.

Long noncoding RNA MEG3 suppresses podocyte injury in diabetic nephropathy by inactivating Wnt/β-catenin signaling

Background

Diabetic nephropathy (DN) is one of the principal complications of diabetes and podocyte injury plays an important role in the DN pathogenesis. Wnt/β-catenin signaling overactivation confers podocyte injury and promotes multiple types of renal disease. However, the underlying mechanism of Wnt/β-catenin signaling activation in DN progression has not been fully elucidated. Long noncoding RNA (lncRNA) is a large class of endogenous RNA molecules lacking functional code capacity and which participates in the pathogenesis of human disease, including DN.

Method

A diabetes model was constructed by intraperitoneal injection of Streptozotocin in rats. The MPC5 cells were used to create the in vitro model. Western blot and Quantitative reverse-transcriptase-PCR were used to examine the expression of protein and mRNA. The migrated capacity was analyzed by Transwell migration assay. The cell viability was detected by CCK8.

Results

In the present study, we revealed the association of lncRNA Maternally Expressed Gene 3 (MEG3) with aberrant activation of Wnt/β-catenin signaling and the role of MEG3/Wnt axis in podocyte injury. We found that high glucose (HG) treatment suppressed MEG3 expression in cultured podocytes, activated Wnt/β-catenin signaling and caused podocyte injury as indicated by the downregulation of podocyte-specific markers (podocin and synaptopodin) and the upregulation of snail1 and α-smooth muscle actin. Overexpression of MEG3 attenuated HG-induced podocyte injury by reducing Wnt/β-catenin activity, repressing cell migration, reactive oxygen species production and increasing the viability of podocytes. Furthermore, we provided evidences that restoration of Wnt/β-catenin signaling by specific agonist impeded the protective effect of MEG3 on podocyte injury. Current results demonstrated that MEG3/Wnt axis plays an important role in fostering podocyte injury and may serve as a potential therapeutic target for the treatment of DN.

Conclusion

lncRNA MEG3 ameliorates podocyte injury in DN via inactivating Wnt/β-catenin signaling.

Mitochondrial calcium uniporter complex modulation in cancerogenesis

Aberrations in mitochondrial Ca²⁺ homeostasis have been associated with different pathological conditions, including neurological defects, cardiovascular diseases, and, in the last years, cancer. With the recent molecular identification of the mitochondrial calcium uniporter (MCU) complex, the channel that allows Ca²⁺ accumulation into the mitochondrial matrix, alterations in the expression levels or functioning in one or more MCU complex members have been linked to different cancers and cancer-related phenotypes. In this review, we will analyze the role of the uniporter and mitochondrial Ca²⁺ derangements in modulating cancer cell sensitivity to death, invasiveness, and migratory capacity, as well as cancer progression in vivo. We will also discuss some critical points and contradictory results to highlight the consequence of MCU complex modulation in tumor development.

IP3R-Grp75-VDAC1-MCU calcium regulation axis antagonists protect podocytes from apoptosis and decrease proteinuria in an Adriamycin nephropathy rat model

BACKGROUND

The mechanism of podocyte apoptosis is not fully understood. In addition, the role of the inositol 1,4,5-triphosphate receptor (IP₃R)/glucose-regulated protein 75 (Grp75)/voltage-dependent anion channel 1 (VDAC1)/mitochondrial calcium uniporter (MCU) calcium regulation axis, which is located at sites of endoplasmic reticulum (ER) mitochondria coupling, in the mechanism of podocyte apoptosis is unclear. This study aimed to understand the roles of this axis in podocyte apoptosis and explore potential targets for podocyte protection.

METHODS

The expression of IP₃R, Grp75, VDAC1, and MCU and mitochondrial Ca²⁺ were analyzed during Adriamycin- or angiotensin II-induced apoptosis in cultured mouse podocytes. The interaction between IP₃R, Grp75, and VDAC1 was investigated using co-immunoprecipitation experiments. The effects of IP₃R, Grp75, and MCU agonists and antagonists on mitochondrial Ca²⁺ and apoptosis were investigated in cultured podocytes. The podocyte-protective effects of an MCU inhibitor were further investigated in rats with Adriamycin-induced nephropathy.

RESULTS

Increased expression of IP₃R, Grp75, VDAC1 and MCU, enhanced interaction among the IP₃R-Grp75-VDAC1 complex, mitochondrial Ca²⁺ overload, and increased active caspase-3 levels were confirmed during Adriamycin- or angiotensin II-induced mouse podocyte apoptosis. Agonists of this axis facilitated mitochondrial Ca²⁺ overload and podocyte apoptosis, whereas specific antagonists against IP₃R, Grp75, or MCU prevented mitochondrial Ca²⁺ overload and podocyte apoptosis. A specific MCU inhibitor prevented Adriamycin-induced proteinuria and podocyte foot process effacement in rats.

CONCLUSIONS

This study identified a novel pathway in which the IP₃R-Grp75-VDAC1-MCU calcium regulation axis mediated podocyte apoptosis by facilitating mitochondrial Ca²⁺ overload. Antagonists that inhibit Ca²⁺ transfer from ER to mitochondria protected mouse podocytes from apoptosis. An MCU inhibitor protected podocytes and decreased proteinuria in rats with Adriamycin-induced nephropathy. Therefore, antagonists to this pathway have promise as novel podocyte-protective drugs.

Palmitic Acid-Induced Podocyte Apoptosis via the Reactive Oxygen Species-Dependent Mitochondrial Pathway

BACKGROUND/AIMS

Chronic kidney disease (CKD) is often accompanied by hyperlipidemia, which accelerates progression of the disease. Podocyte injury can lead to dysfunction of the glomerular filtration barrier, which is associated with proteinuria, a risk marker for the progression of CKD. Our previous studies demonstrated that palmitic acid (PA) can induce podocyte apoptosis; however, the underlying mechanisms are unclear. In the present study, we investigated the specific molecular mechanisms of PA-induced apoptosis in cultured podocytes.

METHODS

We cultured mouse podocytes and treated them with PA. Then, cell viability was measured using the Cell Counting Kit-8 colorimetric assay, lipid uptake was assessed by Oil Red O staining and boron-dipyrromethene staining, apoptosis was measured by flow cytometry, mitochondrial injury was assessed by JC-1 staining and transmission electron microscopy, and mitochondrial production of reactive oxygen species (ROS) was evaluated by fluorescence microscopy using the MitoSOX Red reagent. The effects of PA on the mitochondria-mediated caspase activation pathway were investigated by examining the expression of caspase-8, cleaved caspase-9, cleaved caspase-3, cleaved poly (ADP-ribose) polymerase (PARP), B-cell lymphoma 2 (Bcl-2), Bax, Bid, cytochrome c, and Fas-associated protein with death domain (FADD) using western blotting. The translocation of Bax and cytochrome c were detected by immunofluorescence.

RESULTS

PA treatment significantly increased lipid accumulation and induced podocyte apoptosis. We investigated whether the two primary apoptosis signaling pathways (death receptor-mediated pathway and mitochondria-mediated pathway) were involved in the execution of PA-induced podocyte apoptosis, and found that the levels of FADD, caspase-8, and Bid did not significantly change during this process. Meanwhile, PA treatment induced an increase in Bax protein expression and a decrease in Bcl-2 protein expression, with Bax translocation to the mitochondria. Furthermore, PA treatment induced mitochondrial impairment, and triggered the release of cytochrome c from the mitochondria to cytosol, with a concomitant dose-dependent increase in the levels of cleaved caspase-9, cleaved caspase-3, and PARP. Meanwhile, PA treatment increased mitochondrial production of ROS, and the mitochondria-targeted antioxidant mitoTEMPO significantly ameliorated PA-induced podocyte apoptosis.

CONCLUSION

Our findings indicated that PA induced caspase-dependent podocyte apoptosis through the mitochondrial pathway, and mitochondrial ROS production participated in this process, thus potentially contributing to podocyte injury.

A protease-activated receptor-1 antagonist protects against podocyte injury in a mouse model of nephropathy

The kidney expresses protease-activated receptor-1 (PAR-1). PAR-1 is known as a thrombin receptor, but its role in kidney injury is not well understood. In this study, we examined the contribution of PAR-1 to kidney glomerular injury and the effects of its inhibition on development of nephropathy. Mice were divided into 3 groups: control, doxorubicin + vehicle (15 mg/kg doxorubicin and saline) and doxorubicin + Q94 (doxorubicin at 15 mg/kg and the PAR-1 antagonist Q94 at 5 mg/kg/d) groups. Where indicated, doxorubicin was administered intravenously and PAR-1 antagonist or saline vehicle by subcutaneous osmotic mini-pump. PAR-1 expression was increased in glomeruli of mice treated with doxorubicin. Q94 treatment significantly suppressed the increased albuminuria in these nephropathic mice. Pathological analysis showed that Q94 treatment significantly attenuated periodic acid-Schiff and desmin staining, indicators of podocyte injury, and also decreased glomerular levels of podocin and nephrin. Furthermore, thrombin increased intracellular calcium levels in podocytes. This increase was suppressed by Q94 and Rox4560, a transient receptor potential cation channel (TRPC)3/6 antagonist. In addition, both Q94 and Rox4560 suppressed the doxorubicin-induced increase in activities of caspase-9 and caspase-3 in podocytes. These data suggested that PAR-1 contributes to development of podocyte and glomerular injury and that PAR-1 antagonists have therapeutic potential.

Non-genetic mechanisms of diabetic nephropathy

Diabetic nephropathy (DN) is one of the most common microvascular complications in diabetes mellitus patients and is characterized by thickened glomerular basement membrane, increased extracellular matrix formation, and podocyte loss. These phenomena lead to proteinuria and altered glomerular filtration rate, that is, the rate initially increases but progressively decreases. DN has become the leading cause of end-stage renal disease. Its prevalence shows a rapid growth trend and causes heavy social and economic burden in many countries. However, this disease is multifactorial, and its mechanism is poorly understood due to the complex pathogenesis of DN. In this review, we highlight the new molecular insights about the pathogenesis of DN from the aspects of immune inflammation response, epithelial-mesenchymal transition, apoptosis and mitochondrial damage, epigenetics, and podocyte-endothelial communication. This work offers groundwork for understanding the initiation and progression of DN, as well as provides ideas for developing new prevention and treatment measures.

Polydatin impairs mitochondria fitness and ameliorates podocyte injury by suppressing Drp1 expression

Polydatin (PD), a resveratrol glycoside, has been shown to protect renal function in diabetic nephropathy (DN), but the underlying molecular mechanism remains unclear. This study demonstrates that PD stabilize the mitochondrial morphology and attenuate mitochondrial malfunction in both KKAy mice and in hyperglycemia (HG)‐induced MPC5 cells. We use Western blot analysis to demonstrate that PD reversed podocyte apoptosis induced by HG via suppressing dynamin‐related protein 1 (Drp1). This effect may depend on the ability of PD to inhibit the generation of cellular reactive oxygen species (ROS). In conclusion, we demonstrate that PD may be therapeutically useful in DN, and that, podocyte apoptosis induced by HG can be reversed by PD through suppressing Drp1 expression.