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

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.

Potential targets for the treatment of MI: GRP75-mediated Ca2+ transfer in MAM

After myocardial infarction (MI), there is a notable disruption in cellular calcium ion homeostasis and mitochondrial function, which is believed to be intricately linked to endoplasmic reticulum (ER) stress. This research endeavors to elucidate the involvement of glucose regulated protein 75 (GRP75) in post-MI calcium ion homeostasis and mitochondrial function. In MI rats, symptoms of myocardial injury were accompanied by an increase in the activation of ER stress. Moreover, in oxygen-glucose deprivation (OGD)-induced cardiomyocytes, it was confirmed that inhibiting ER stress exacerbated intracellular Ca2+ disruption and cell apoptosis. Concurrently, the co-localization of GRP75 with IP3R and VDAC1 increased under ER stress in cardiomyocytes. In OGD-induced cardiomyocytes, knockdown of GRP75 not only reduced the Ca2+ levels in both the ER and mitochondria and improved the ultrastructure of cardiomyocytes, but it also increased the number of contact points between the ER and mitochondria, reducing mitochondria associated endoplasmic reticulum membrane (MAM) formation, and decreased cell apoptosis. Significantly, knockdown of GRP75 did not affect the protein expression of PERK and hypoxia-inducible factor 1α (HIF-1α). Transcriptome analysis of cardiomyocytes revealed that knockdown of GRP75 mainly influenced the molecular functions of sialyltransferase and IP3R, as well as the biosynthesis of glycosphingolipids and lactate metabolism. The complex interaction between the ER and mitochondria, driven by the GRP75 and its associated IP3R1-GRP75-VDAC1 complex, is crucial for calcium homeostasis and cardiomyocyte's adaptive response to ER stress. Modulating GRP75 could offer a strategy to regulate calcium dynamics, diminish glycolysis, and thereby mitigate cardiomyocyte apoptosis.

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.

Cypermethrin induces Sertoli cell apoptosis through endoplasmic reticulum-mitochondrial coupling involving IP3R1-GRP75-VDAC1

A widely used type II pyrethroid pesticide cypermethrin (CYP) is one of endocrine disrupting chemicals (EDCs) with anti-androgenic activity to induce male reproductive toxicology. However, the mechanisms have not been fully elucidated. This study was to explore the effects of CYP on apoptosis of mouse Sertoli cells (TM4) and the roles of endoplasmic reticulum (ER)-mitochondria coupling involving 1,4,5-trisphosphate receptor type1-glucose-regulated protein 75-voltage-dependent anion channel 1 (IP3R1-GRP75-VDAC1). TM4 were cultured with different concentrations of CYP. Flow cytometry, calcium (Ca2+) fluorescent probe, transmission electron microscopy and confocal microscopy, and western blot were to examine apoptosis of TM4, mitochondrial Ca2+, ER-mitochondria coupling, and expressions of related proteins. CYP was found to increase apoptotic rates of TM4 significantly. CYP was shown to significantly increase expressions of cleaved caspase-3, cleaved poly ADP-ribose polymerase (PARP). Concentration of mitochondrial Ca2+ was increased by CYP treatment significantly. CYP significantly enhanced ER-mitochondria coupling. CYP was shown to increase expressions of IP3R, Grp75 and VDAC1 significantly. We suggest that CYP induces apoptosis in TM4 cells by facilitating mitochondrial Ca2+ overload regulated by ER-mitochondria coupling involving IP3R1-GRP75-VDAC1. This study identifies a novel mechanism of CYP-induced apoptosis in Sertoli cells.

The role of endoplasmic reticulum-mitochondria-associated membranes in diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease worldwide. The pathomechanisms of DKD are multifactorial, yet haemodynamic and metabolic changes in the early stages of the disease appear to predispose towards irreversible functional loss and histopathological changes. Recent studies highlight the importance of endoplasmic reticulum-mitochondria-associated membranes (ER-MAMs), structures conveying important cellular homeostatic and metabolic effects, in the pathology of DKD. Disruption of ER-MAM integrity in diabetic kidneys is associated with DKD progression, but the regulation of ER-MAMs and their pathogenic contribution remain largely unknown. Exploring the cell-specific components and dynamic changes of ER-MAMs in diabetic kidneys may lead to the identification of new approaches to detect and stratify diabetic patients with DKD. In addition, these insights may lead to novel therapeutic approaches to target and/or reverse disease progression. In this review, we discuss the association of ER-MAMs with key pathomechanisms driving DKD such as insulin resistance, dyslipidaemia, ER stress, and inflammasome activation and the importance of further exploration of ER-MAMs as diagnostic and therapeutic targets in DKD.

Pinacidil ameliorates cardiac microvascular ischemia-reperfusion injury by inhibiting chaperone-mediated autophagy of calreticulin

Calcium overload is the key trigger in cardiac microvascular ischemia-reperfusion (I/R) injury, and calreticulin (CRT) is a calcium buffering protein located in the endoplasmic reticulum (ER). Additionally, the role of pinacidil, an antihypertensive drug, in protecting cardiac microcirculation against I/R injury has not been investigated. Hence, this study aimed to explore the benefits of pinacidil on cardiac microvascular I/R injury with a focus on endothelial calcium homeostasis and CRT signaling. Cardiac vascular perfusion and no-reflow area were assessed using FITC-lectin perfusion assay and Thioflavin-S staining. Endothelial calcium homeostasis, CRT-IP3Rs-MCU signaling expression, and apoptosis were assessed by real-time calcium signal reporter GCaMP8, western blotting, and fluorescence staining. Drug affinity-responsive target stability (DARTS) assay was adopted to detect proteins that directly bind to pinacidil. The present study found pinacidil treatment improved capillary density and perfusion, reduced no-reflow and infraction areas, and improved cardiac function and hemodynamics after I/R injury. These benefits were attributed to the ability of pinacidil to alleviate calcium overload and mitochondria-dependent apoptosis in cardiac microvascular endothelial cells (CMECs). Moreover, the DARTS assay showed that pinacidil directly binds to HSP90, through which it inhibits chaperone-mediated autophagy (CMA) degradation of CRT. CRT overexpression inhibited IP3Rs and MCU expression, reduced mitochondrial calcium inflow and mitochondrial injury, and suppressed endothelial apoptosis. Importantly, endothelial-specific overexpression of CRT shared similar benefits with pinacidil on cardiovascular protection against I/R injury. In conclusion, our data indicate that pinacidil attenuated microvascular I/R injury potentially through improving CRT degradation and endothelial calcium overload.

The role of endoplasmic reticulum stress, mitochondrial dysfunction and their crosstalk in intervertebral disc degeneration

Low back pain (LBP) is a pervasive global health issue. Roughly 40% of LBP cases are attributed to intervertebral disc degeneration (IVDD). While the underlying mechanisms of IVDD remain incompletely understood, it has been confirmed that apoptosis and extracellular matrix (ECM) degradation caused by many factors such as inflammation, oxidative stress, calcium (Ca2+) homeostasis imbalance leads to IVDD. Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are involved in these processes. The initiation of ER stress precipitates cell apoptosis, and is also related to inflammation, levels of oxidative stress, and Ca2+ homeostasis. Additionally, mitochondrial dynamics, antioxidative systems, disruption of Ca2+ homeostasis are closely associated with Reactive Oxygen Species (ROS) and inflammation, promoting cell apoptosis. However, numerous crosstalk exists between the ER and mitochondria, where they interact through inflammatory cytokines, signaling pathways, ROS, or key molecules such as CHOP, forming positive and negative feedback loops. Furthermore, the contact sites between the ER and mitochondria, known as mitochondria-associated membranes (MAM), facilitate direct signal transduction such as Ca2+ transfer. However, the current attention towards this issue is insufficient. Therefore, this review summarizes the impacts of ER stress and mitochondrial dysfunction on IVDD, along with the possibly potential crosstalk between them, aiming to unveil novel avenues for IVDD intervention.

MicroRNA-129-1-3p protects chicken granulosa cells from cadmium-induced apoptosis by down-regulating the MCU-mediated Ca2+ signaling pathway

Cadmium (Cd) is known as a female reproductive toxicant. Our previous study has shown that Cd can influence the proliferation and cell cycle of granulosa cells and induce apoptosis. MicroRNAs (miRNAs) play an important role in the regulation of Cd-induced granulosa cell damage in chickens. However, the mechanism remains unclear. In this study, we investigated the mechanisms by which microRNA-129-1-3p (miR-129-1-3p) regulates Cd-induced cytotoxicity in chicken granulosa cells. As anticipated, exposure to Cd resulted in the induction of oxidative stress in granulosa cells, accompanied by the downregulation of antioxidant molecules and/or enzymes of Nrf2, Mn-SOD, Cu-Zn SOD and CAT, and the upregulation of Keap1, GST, GSH-Px, GCLM, MDA, hydrogen peroxide and mitochondrial reactive oxygen species (mtROS). Further studies found that Cd exposure causes mitochondrial calcium ions (Ca2+) overload, provoking mitochondrial damage and apoptosis by upregulating IP3R, GRP75, VDAC1, MCU, CALM1, MFF, caspase 3, and caspase 9 gene and/or protein expressions and mitochondrial Ca2+ levels, while downregulating NCX1, NCLX and MFN2 gene and/or protein expressions and mitochondrial membrane potential (MMP). The Ca2+ chelator BAPTA-AM or the MCU inhibitor MCU-i4 significantly rescued Cd-induced mitochondrial dysfunction, thereby attenuating apoptosis. Additionally, a luciferase reported assay and western blot analysis confirmed that miR-129-1-3p directly target MCU. MiR-129-1-3p overexpression almost completely inhibited protein expression of MCU, increased the gene and protein expressions of NCLX and MFN2 downregulated by Cd, and attenuated mitochondrial Ca2+ overload, MMP depression and mitochondria damage induced by Cd. Moreover, the overexpression of miR-129-1-3p led to a reduction in mtROS and cell apoptosis levels, and a suppression of the gene and protein expressions of caspase 3 and caspase 9. As above, these results provided the evidence that IP3R-MCU signaling pathway activated by Cd plays a significant role in inducing mitochondrial Ca2+ overload, mitochondrial damage, and apoptosis. MiR-129-1-3p exerts a protective effect against Cd-induced granulosa cell apoptosis through the direct inhibition of MCU expression in the ovary of laying hens.

IP3R-1 aggravates endotoxin-induced acute lung injury in mice by regulating MAM formation and mitochondrial function

Acute lung injury (ALI) caused by endotoxin represents one of the common clinical emergencies. Mitochondria-associated endoplasmic reticulum membranes (MAM) serve as a critical link between mitochondria and endoplasmic reticulum (ER), which has an essential effect on maintaining intracellular homeostasis. As an important component of MAM, type-1 inositol-1,4,5-trisphosphate receptor (IP3R-1) mediates the ER-to-mitochondrial transport of Ca2+. This study explored the role of IP3R-1 and MAM in ALI. Besides the levels of inflammasome-associated components interleukin (IL)-6, tumor necrosis factor (TNF)-α, and malonyldialdehyde (MDA) were increased in both bronchoalveolar lavage fluid (BALF) and serum, increased cross-sectional area of mitochondria, elevated MAM formation, and decreased respiratory control ratio (RCR) were observed within lung tissues collected in lipopolysaccharide (LPS)-treated mice, accompanied by upregulation of IP3R-1 in total lung lysates and MAM. Ca2+ uptake level in the mitochondria, production of reactive oxygen species (ROS) in the mitochondria, and the formation of MAM were elevated within LPS-treated MLE-12 cells, and all those changes in response to LPS were partly inhibited by knocking down of IP3R-1 expression in MLE-12 cells. Collectively, IP3R-1 has a critical effect on MAM formation and mitochondrial dysfunction, which could be innovative therapeutic targets for ALI caused by endotoxin.

Inhibition of calcium imbalance protects hepatocytes from vanadium exposure-induced inflammation by mediating mitochondrial-associated endoplasmic reticulum membranes in ducks

Vanadium (V) is an essential mineral element in animals, but excessive V can lead to many diseases, affecting the health of humans and animals. However, the molecular crosstalk between mitochondria-associated endoplasmic reticulum membranes (MAMs) and inflammation under V exposure is still at the exploratory stage. This study was conducted to determine the molecular crosstalk between MAMs and inflammation under V exposure in ducks. In this study, duck hepatocytes were treated with NaVO3 (0 μM, 100 μM, and 200 μM) and 2-aminoethyl diphenyl borate (2-APB) (IP3R inhibitor) alone or in combination for 24 h. The data showed that V exposure-induced cell vacuolization, enlarged intercellular space, and decreased density and viability. Meanwhile, hydrogen peroxide (H2O2), malonaldehyde (MDA), catalase (CAT), superoxide dismutase (SOD), and reactive oxygen species (ROS) levels were upregulated under V treatment. In addition, excessive V could lead to a marked reduction in the MAMs structure, destruction of the membrane structure and overload of intracellular Ca2+ and mitochondrial Ca2+. Moreover, V treatment resulted in notable upregulation of the levels of MAMs-relevant factors (IP3R, Mfn2, Grp75, MCU, VDAC1) but downregulated the levels of IL-18, IL-1β, and lactate dehydrogenase (LDH) in the cell supernatant. Additionally, it also significantly elevated the levels of inflammation-relevant factors (NLRP3, ASC, caspase-1, MAVS, IL-18, IL-1β, and TXNIP). However, the inhibition of IP3R expression attenuated the V-induced variations in the above indicators. Collectively, our results revealed that the maintenance of calcium homeostasis could protect duck hepatocytes from V-induced inflammation injury via MAMs.

Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone mediates Ca+2 dysregulation, mitochondrial dysfunction, and apoptosis in human peripheral blood lymphocytes

N-(3-oxododecanoyl)-l-homoserine lactone is a Pseudomonas aeruginosa secreted quorum-sensing molecule that mediates the secretion of virulence factors, biofilm formation and plays a pivotal role in proliferation and persistence in the host. Apart from regulating quorum-sensing, the autoinducer signal molecule N-(3-oxododecanoyl)-l-homoserine lactone (3O-C12-HSL or C12) of a LasI-LasR circuit exhibits immunomodulatory effects and induces apoptosis in various host cells. However, the precise pathophysiological impact of C12 on human peripheral blood lymphocytes and its involvement in mitochondrial dysfunction remained largely elusive. In this study, the results suggest that C12 (100 μM) induces upregulation of cytosolic and mitochondrial Ca+2 levels and triggers mitochondrial dysfunction through the generation of mitochondrial ROS (mROS), disruption of mitochondrial transmembrane potential (ΔΨm), and opening of the mitochondrial permeability transition pore (mPTP). Additionally, it was observed that C12 induces phosphatidylserine (PS) exposure and promotes apoptosis in human peripheral blood lymphocytes. However, apoptosis plays a critical role in the homeostasis and development of lymphocytes, whereas enhanced apoptosis can cause immunodeficiency through cell loss. These findings suggest that C12 exerts a detrimental effect on lymphocytes by mediating mitochondrial dysfunction and enhancing apoptosis, which might further impair the effective mounting of immune responses during Pseudomonas aeruginosa-associated infections.

Mitochondria, a Key Target in Amyotrophic Lateral Sclerosis Pathogenesis

Mitochondrial dysfunction occurs in numerous neurodegenerative diseases, particularly amyotrophic lateral sclerosis (ALS), where it contributes to motor neuron (MN) death. Of all the factors involved in ALS, mitochondria have been considered as a major player, as secondary mitochondrial dysfunction has been found in various models and patients. Abnormal mitochondrial morphology, defects in mitochondrial dynamics, altered activities of respiratory chain enzymes and increased production of reactive oxygen species have been described. Moreover, the identification of CHCHD10 variants in ALS patients was the first genetic evidence that a mitochondrial defect may be a primary cause of MN damage and directly links mitochondrial dysfunction to the pathogenesis of ALS. In this review, we focus on the role of mitochondria in ALS and highlight the pathogenic variants of ALS genes associated with impaired mitochondrial functions. The multiple pathways demonstrated in ALS pathogenesis suggest that all converge to a common endpoint leading to MN loss. This may explain the disappointing results obtained with treatments targeting a single pathological process. Fighting against mitochondrial dysfunction appears to be a promising avenue for developing combined therapies in the future.

The intersection between cysteine proteases, Ca2+ signalling and cancer cell apoptosis

Apoptosis is a highly complex and regulated cell death pathway that safeguards the physiological balance between life and death. Over the past decade, the role of Ca2+ signalling in apoptosis and the mechanisms involved have become clearer. The initiation and execution of apoptosis is coordinated by three distinct groups of cysteines proteases: the caspase, calpain and cathepsin families. Beyond its physiological importance, the ability to evade apoptosis is a prominent hallmark of cancer cells. In this review, we will explore the involvement of Ca2+ in the regulation of caspase, calpain and cathepsin activity, and how the actions of these cysteine proteases alter intracellular Ca2+ handling during apoptosis. We will also explore how apoptosis resistance can be achieved in cancer cells through deregulation of cysteine proteases and remodelling of the Ca2+ signalling toolkit.

MicroRNA-129-1-3p attenuates autophagy-dependent cell death by targeting MCU in granulosa cells of laying hens under H2O2-induced oxidative stress

The present study aimed to investigate the mechanism of microRNA-129-1-3p (miR-129-1-3p) in regulating hydrogen peroxide (H2O2)-induced autophagic death of chicken granulosa cell by targeting mitochondrial calcium uniporter (MCU). The results indicated that the exposure of hens' ovaries to H2O2 resulted in a significant elevation in reactive oxygen species (ROS) levels, as well as the apoptosis of granulosa cells and follicular atresia. This was accompanied by an upregulation of glucose-regulated protein 75 (GRP75), voltage-dependent anion-selective channel 1 (VDAC1), MCU, mitochondria fission factor (MFF), microtubule-associated protein 1 light chain 3 (LC3) I, and LC3II expression, and a downregulation of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) and mitofusin-2 (MFN2) expression. In hens' granulosa cells, a luciferase reporter assay confirmed that miR-129-1-3p directly regulates MCU. The induction of oxidative stress through H2O2 resulted in the activation of the permeability transition pore, an overload of calcium, depolarization of the mitochondrial membrane potential, dysfunction of mitochondria-associated endoplasmic reticulum membranes (MAMs), and ultimately, autophagic cell death. The overexpression of miR-129-1-3p effectively mitigated these H2O2-induced changes. Furthermore, miR-129-1-3p overexpression in granulosa cells prevented the alterations induced by H2O2 in the expression of key proteins that play crucial roles in maintaining the integrity of MAMs and regulating autophagy, such as GRP75, VDAC1, MFN2, PTEN-induced kinase 1 (Pink1), and parkin RBR E3 ubiquitin-protein ligase (Parkin). Together, these in vitro- and in vivo-based experiments suggest that miR-129-1-3p protects granulosa cells from oxidative stress-induced autophagic cell death by downregulating the MCU-mediated mitochondrial autophagy. miR-129-1-3p/MCU calcium signaling pathway may act as a new target to alleviate follicular atresia caused by oxidative stress in laying hens.

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.

Mitochondrial Calcium Overload Plays a Causal Role in Oxidative Stress in the Failing Heart

Heart failure is a serious global health challenge, affecting more than 6.2 million people in the United States and is projected to reach over 8 million by 2030. Independent of etiology, failing hearts share common features, including defective calcium (Ca2+) handling, mitochondrial Ca2+ overload, and oxidative stress. In cardiomyocytes, Ca2+ not only regulates excitation-contraction coupling, but also mitochondrial metabolism and oxidative stress signaling, thereby controlling the function and actual destiny of the cell. Understanding the mechanisms of mitochondrial Ca2+ uptake and the molecular pathways involved in the regulation of increased mitochondrial Ca2+ influx is an ongoing challenge in order to identify novel therapeutic targets to alleviate the burden of heart failure. In this review, we discuss the mechanisms underlying altered mitochondrial Ca2+ handling in heart failure and the potential therapeutic strategies.

Suberoylanilide hydroxamic acid upregulates reticulophagy receptor expression and promotes cell death in hepatocellular carcinoma cells

BACKGROUND

Hepatocellular carcinoma (HCC) is a common clinical condition with a poor prognosis and few effective treatment options. Potent anticancer agents for treating HCC must be identified. Epigenetics plays an essential role in HCC tumorigenesis. Suberoylanilide hydroxamic acid (SAHA), the most common histone deacetylase inhibitor agent, triggers many forms of cell death in HCC. However, the underlying mechanism of action remains unclear. Family with sequence similarity 134 member B (FAM134B)-induced reticulophagy, a selective autophagic pathway, participates in the decision of cell fate and exhibits anticancer activity. This study focused on the relationship between FAM134B-induced reticulophagy and SAHA-mediated cell death.

AIM

To elucidate potential roles and underlying molecular mechanisms of reticulophagy in SAHA-induced HCC cell death.

METHODS

The viability, apoptosis, cell cycle, migration, and invasion of SAHA-treated Huh7 and MHCC97L cells were measured. Proteins related to the reticulophagy pathway, mitochondria-endoplasmic reticulum (ER) contact sites, intrinsic mitochondrial apoptosis, and histone acetylation were quantified using western blotting. ER and lysosome colocalization, and mitochondrial Ca2+ levels were characterized via confocal microscopy. The level of cell death was evaluated through Hoechst 33342 staining and propidium iodide colocalization. Chromatin immunoprecipitation was used to verify histone H4 lysine-16 acetylation in the FAM134B promoter region.

RESULTS

After SAHA treatment, the proliferation of Huh7 and MHCC97L cells was significantly inhibited, and the migration and invasion abilities were greatly blocked in vitro. This promoted apoptosis and caused G1 phase cells to increase in a concentration-dependent manner. Following treatment with SAHA, ER-phagy was activated, thereby triggering autophagy-mediated cell death of HCC cells in vitro. Western blotting and chromatin immunoprecipitation assays confirmed that SAHA regulated FAM134B expression by enhancing the histone H4 lysine-16 acetylation in the FAM134B promoter region. Further, SAHA disturbed the Ca2+ homeostasis and upregulated the level of autocrine motility factor receptor and proteins related to mitochondria-endoplasmic reticulum contact sites in HCC cells. Additionally, SAHA decreased the mitochondrial membrane potential levels, thereby accelerating the activation of the reticulophagy-mediated mitochondrial apoptosis pathway and promoting HCC cell death in vitro.

CONCLUSION

SAHA stimulates FAM134B-mediated ER-phagy to synergistically enhance the mitochondrial apoptotic pathway, thereby enhancing HCC cell death.

The BCL-2 family protein BCL-RAMBO interacts and cooperates with GRP75 to promote its apoptosis signaling pathway

The BCL-2 family protein BCL-RAMBO, also known as BCL2-like 13, anchors at the outer mitochondrial membrane and regulates apoptosis, mitochondrial fragmentation, and mitophagy. However, the mechanisms underlying the proapoptotic role of BCL-RAMBO remain unclear. In the present study, we demonstrated that BCL-RAMBO interacted with glucose-regulated protein 75 (GRP75), also known as heat shock protein family A member 9, and mortalin using co-immunoprecipitation and glutathione S-transferase-based pull-down assays. BCL-RAMBO interacted with GRP75 via its No BCL-2 homology domain. The interaction between BCL-RAMBO and GRP75 was confirmed by genetic interactions in Drosophila because a rough eye phenotype caused by the ectopic expression of BCL-RAMBO was partially suppressed by mutations in Hsc70-5, a mammalian GRP75 ortholog. In human embryonic kidney 293T cells, the co-expression of BCL-RAMBO and GRP75 facilitated an elevation in executioner caspase activity and poly (ADP-ribose) polymerase 1 (PARP-1) cleavage. In contrast, the knockdown of GRP75 suppressed elevated executioner caspase activity and PARP-1 cleavage in BCL-RAMBO-transfected cells. The mitochondrial release of cytochrome c induced by BCL-RAMBO was also attenuated by the knockdown of GRP75. These results indicate that GRP75 interacts with BCL-RAMBO and plays a crucial role in the BCL-RAMBO-dependent apoptosis signaling pathway.

β-carotene targets IP3R/GRP75/VDAC1-MCU axis to renovate LPS-induced mitochondrial oxidative damage by regulating STIM1

Endoplasmic reticulum (ER) and mitochondria are the main sites for the storage and regulation of Ca2+ homeostasis. An imbalance of Ca2+ homeostasis can cause ER stress and mitochondrial dysfunction, thereby inducing apoptosis. The store-operated calcium entry (SOCE) is the main channel for extracellular calcium influx. Mitochondria-associated endoplasmic reticulum (MAM) is an important agent for Ca2+ transfer from the ER to the mitochondria. Therefore, regulation of SOCE and MAMs has potential therapeutic value for disease prevention and treatment. In this study, bovine mammary epithelial cells (BMECs) and mice were used as models to explore the mechanisms of β-carotene to relieve ER stress and mitochondrial dysfunction. BAPTA-AM, EGTA (Ca2+ inhibitor), and BTP2 (SOCE channel inhibitor) alleviated ER stress and mitochondrial oxidative damage induced by increased intracellular Ca2+ levels after lipopolysaccharide (LPS) stimulation. Furthermore, inhibition of ER stress by 4-PBA (ER stress inhibitor), 2-APB (IP3R inhibitor), and ruthenium red (mitochondrial calcium uniporter (MCU) inhibitor) restored mitochondrial function by reducing mitochondrial ROS. Our data also confirm that β-carotene targeted STIM1 and IP3R channels to repair LPS-induced ER stress and mitochondrial disorders. Consistent with the in vitro study, in vito experiments in mice further showed that β-carotene attenuated LPS-induced ER stress and mitochondrial oxidative damage by inhibiting the expression of STIM1 and ORAI1, and reducing the level of Ca2+ in mouse mammary glands. Therefore, ER stress-mitochondrial oxidative damage mediated by the STIM1-ER-IP3R/GRP75/VDAC1-MCU axis plays an vital role in the development of mastitis. Our results provided novel ideas and therapeutic targets for the prevention and treatment of mastitis.

Mitochondria-associated endoplasmic reticulum membranes participate mitochondrial dysfunction and endoplasmic reticulum stress caused by copper in duck kidney

Copper (Cu) can be harmful to host physiology at high levels, although it is still unclear exactly how it causes nephrotoxicity. Mitochondrial dysfunction and endoplasmic reticulum (ER) stress are associated with heavy metal intoxication. Meanwhile, mitochondria and ER are connected via mitochondria-associated ER membranes (MAM). In order to reveal the crosstalk between them, a total of 144 1-day-old Peking ducks were randomly divided into four groups: control (basal diet), 100 mg/kg Cu, 200 mg/kg Cu, and 400 mg/kg Cu groups. Results found that excessive Cu disrupted MAM integrity, reduced the co-localization of IP3R and VDAC1, and significantly changed the MAM-related factors levels (Grp75, Mfn2, IP3R, MCU, PACS2, and VDAC1), leading to MAM dysfunction. We further found that Cu exposure induced mitochondrial dysfunction via decreasing the ATP level and the expression levels of COX4, TOM20, SIRT1, and OPA1 and up-regulating Parkin expression level. Meanwhile, Cu exposure dramatically increased the expression levels of Grp78, CRT, and ATF4, resulting in ER stress. Overall, these findings demonstrated MAM plays the critical role in Cu-induced kidney mitochondrial dysfunction and ER stress, which deepened our understanding of Cu-induced nephrotoxicity.

Mitochondria-associated endoplasmic reticulum membranes (MAMs) and their role in glaucomatous retinal ganglion cell degeneration-a mini review

Glaucoma is a leading cause of blindness worldwide, commonly associated with elevated intraocular pressure (IOP), leading to degeneration of the optic nerve and death of retinal ganglion cells, the output neurons in the eye. In recent years, many studies have implicated mitochondrial dysfunction as a crucial player in glaucomatous neurodegeneration. Mitochondrial function has been an increasingly researched topic in glaucoma, given its vital role in bioenergetics and propagation of action potentials. One of the most metabolically active tissues in the body characterized by high oxygen consumption is the retina, particularly the retinal ganglion cells (RGCs). RGCs, which have long axons that extend from the eyes to the brain, rely heavily on the energy generated by oxidative phosphorylation for signal transduction, rendering them more vulnerable to oxidative damage. In various glaucoma models, mitochondrial dysfunction and stress from protein aggregates in the endoplasmic reticulum (ER) have been observed in the RGCs. However, it has been shown that the two organelles are connected through a network called mitochondria-associated ER membranes (MAMs); hence this crosstalk in a pathophysiological condition such as glaucoma should be evaluated. Here, we review the current literature suggestive of mitochondrial and ER stress related to glaucoma, indicating potential cross-signaling and the potential roles of MAMs.

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.

The ER-mitochondria interface, where Ca2+ and cell death meet

Endoplasmic reticulum (ER)-mitochondria contact sites are crucial to allow Ca²⁺ flux between them and a plethora of proteins participate in tethering both organelles together. Inositol 1,4,5-trisphosphate receptors (IP₃Rs) play a pivotal role at such contact sites, participating in both ER-mitochondria tethering and as Ca²⁺-transport system that delivers Ca²⁺ from the ER towards mitochondria. At the ER-mitochondria contact sites, the IP₃Rs function as a multi-protein complex linked to the voltage-dependent anion channel 1 (VDAC1) in the outer mitochondrial membrane, via the chaperone glucose-regulated protein 75 (GRP75). This IP₃R-GRP75-VDAC1 complex supports the efficient transfer of Ca²⁺ from the ER into the mitochondrial intermembrane space, from which the Ca²⁺ ions can reach the mitochondrial matrix through the mitochondrial calcium uniporter. Under physiological conditions, basal Ca²⁺ oscillations deliver Ca²⁺ to the mitochondrial matrix, thereby stimulating mitochondrial oxidative metabolism. However, when mitochondrial Ca²⁺ overload occurs, the increase in [Ca²⁺] will induce the opening of the mitochondrial permeability transition pore, thereby provoking cell death. The IP₃R-GRP75-VDAC1 complex forms a hub for several other proteins that stabilize the complex and/or regulate the complex's ability to channel Ca²⁺ into the mitochondria. These proteins and their mechanisms of action are discussed in the present review with special attention for their role in pathological conditions and potential implication for therapeutic strategies.

Targeting Mitochondrial Oxidative Stress as a Strategy to Treat Aging and Age-Related Diseases

Mitochondria are one of the organelles undergoing rapid alteration during the senescence process. Senescent cells show an increase in mitochondrial size, which is attributed to the accumulation of defective mitochondria, which causes mitochondrial oxidative stress. Defective mitochondria are also targets of mitochondrial oxidative stress, and the vicious cycle between defective mitochondria and mitochondrial oxidative stress contributes to the onset and development of aging and age-related diseases. Based on the findings, strategies to reduce mitochondrial oxidative stress have been suggested for the effective treatment of aging and age-related diseases. In this article, we discuss mitochondrial alterations and the consequent increase in mitochondrial oxidative stress. Then, the causal role of mitochondrial oxidative stress on aging is investigated by examining how aging and age-related diseases are exacerbated by induced stress. Furthermore, we assess the importance of targeting mitochondrial oxidative stress for the regulation of aging and suggest different therapeutic strategies to reduce mitochondrial oxidative stress. Therefore, this review will not only shed light on a new perspective on the role of mitochondrial oxidative stress in aging but also provide effective therapeutic strategies for the treatment of aging and age-related diseases through the regulation of mitochondrial oxidative stress.

Inhibition of Mitochondrial Fission Alleviates Zearalenone-Induced Mitochondria-Associated Endoplasmic Reticulum Membrane Dysfunction in Piglet Sertoli Cells

This study aimed to investigate the effects of zearalenone (ZEA) on piglet Sertoli cell (SC)-mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) based on mitochondrial fission, and to explore the molecular mechanism of ZEA-induced cell damage. After the SCs were exposed to the ZEA, the cell viability decreased, the Ca2+ levels increased, and the MAM showed structural damage. Moreover, glucose-regulated protein 75 (Grp75) and mitochondrial Rho-GTPase 1 (Miro1) were upregulated at the mRNA and protein levels. However, phosphofurin acidic cluster protein 2 (PACS2), mitofusin2 (Mfn2), voltage-dependent anion channel 1 (VDAC1), and inositol 1,4,5-trisphosphate receptor (IP3R) were downregulated at the mRNA and protein levels. A pretreatment with mitochondrial division inhibitor 1 (Mdivi-1) decreased the ZEA-induced cytotoxicity toward the SCs. In the ZEA + Mdivi-1 group, the cell viability increased, the Ca2+ levels decreased, the MAM damage was repaired, and the expression levels of Grp75 and Miro1 decreased, while those of PACS2, Mfn2, VDAC1, and IP3R increased compared with those in the ZEA-only group. Thus, ZEA causes MAM dysfunction in piglet SCs through mitochondrial fission, and mitochondria can regulate the ER via MAM.

Myostatin silencing inhibits podocyte apoptosis in membranous nephropathy through Smad3/PKA/NOX4 signaling pathway

This article focuses on deciphering the effect of myostatin (MSTN) on podocyte apoptosis in membranous nephropathy (MN) and fathoming out its underlying mechanism. Rats received the intravenous injection of cationized-bovine serum albumin to induce MN in vivo, while angiotensin II (Ang II) was exposed to AB8/13 cells to induce MN model in vitro. The mRNA expression of MSTN was detected by qRT-PCR. The effects of MSTN silencing on MN model rats and cells were assessed by cell counting kit-8 assay, flow cytometry, hematoxylin and eosin staining, and TUNEL assay. The expressions of proteins related to apoptosis and Smad3/protein kinase A (PKA)/NADPH oxidase 4 (NOX4) signaling pathway were examined by western blot. As a result, MSTN was highly expressed in MN cell and rat models. Besides, knockdown of MSTN elevated the MN cell viability and dwindled apoptosis rate, as well as attenuated kidney injury in MN rats. Meanwhile, MSTN silencing lessened the expressions of phosphorylated (p)-Smad3 and Nox4, while boosting the p-PKA expression in MN rats and cells. Additionally, Smad3 overexpression reversed the above effects of MSTN silencing on Ang II-induced podocytes. In conclusion, MSTN knockdown restrains the podocyte apoptosis through regulating Smad3/PKA/NOX4 signaling pathway.

Inhibition of ferroptosis through regulating neuronal calcium homeostasis: An emerging therapeutic target for Alzheimer's disease

Alzheimer's disease (AD), a chronic and progressive neurodegenerative disease, generates a serious threat to the health of the elderly. The AD brain is microscopically characterized by amyloid plaques and neurofibrillary tangles. There are still no effective therapeutic drugs to restrain the progression of AD though much attention has been paid to exploit AD treatments. Ferroptosis, a type of programmed cell death, has been reported to promote the pathological occurrence and development of AD, and inhibition of neuronal ferroptosis can effectively improve the cognitive impairment of AD. Studies have shown that calcium (Ca²⁺) dyshomeostasis is closely related to the pathology of AD, and can drive the occurrence of ferroptosis through several pathways, such as interacting with iron, and regulating the crosstalk between endoplasmic reticulum (ER) and mitochondria. This paper mainly reviews the roles of ferroptosis and Ca²⁺ in the pathology of AD, and highlights that restraining ferroptosis through maintaining the homeostasis of Ca²⁺ may be an innovative target for the treatment of AD.

Mitochondria-associated endoplasmic reticulum membranes (MAMs): Possible therapeutic targets in heart failure

Mitochondria-associated endoplasmic reticulum membranes (MAMs) are formed by physical connections of the endoplasmic reticulum and mitochondria. Over the past decades, great breakthroughs have been made in the study of ER-mitochondria communications. It has been identified that MAM compartments are pivotal in regulating neurological function. Accumulating studies indicated that MAMs participate in the development of cardiovascular diseases. However, the specific role of MAMs in heart failure remains to be fully understood. In this article, we first summarize the structural and functional properties of MAM and MAM-associated proteins. We then focus on the roles of MAMs in myocardial infarction, cardiomyopathy and heart failure, and discuss the involvement of MAMs in disease progression and treatment. Elucidating these issues may provide important insights into therapeutic intervention of heart failure.

Mortalin: Protein partners, biological impacts, pathological roles, and therapeutic opportunities

Mortalin (GRP75, HSPA9A), a heat shock protein (HSP), regulates a wide range of cellular processes, including cell survival, growth, and metabolism. The regulatory functions of mortalin are mediated through a diverse set of protein partners associated with different cellular compartments, which allows mortalin to perform critical functions under physiological conditions, including mitochondrial protein quality control. However, alteration of mortalin's activities, its abnormal subcellular compartmentalization, and its protein partners turn mortalin into a disease-driving protein in different pathological conditions, including cancers. Here, mortalin's contributions to tumorigenic pathways are explained. Pathology information based on mortalin's RNA expression extracted from The Cancer Genome Atlas (TCGA) transcriptomic database indicates that mortalin has an independent prognostic value in common tumors, including lung, breast, and colorectal cancer (CRC). Subsequently, the binding partners of mortalin reported in different cellular models, from yeast to mammalian cells, and its regulation by post-translational modifications are discussed. Finally, we focus on colorectal cancer and discuss how mortalin and its tumorigenic downstream protein targets are regulated by a ubiquitin-like protein through the 26S proteasomal degradation machinery. A broader understanding of the function of mortalin and its positive and negative regulation in the formation and progression of human diseases, particularly cancer, is essential for developing new strategies to treat a diverse set of human diseases critically associated with dysregulated mortalin.

Nicorandil protects podocytes via modulation of antioxidative capacity in acute puromycin aminonucleoside-induced nephrosis in rats

Nephrotic syndrome, characterized by proteinuria and hypoalbuminemia, results from the dysregulation of glomerular podocytes and is a significant cause of end-stage kidney disease. Patients with idiopathic nephrotic syndrome are generally treated with immunosuppressive agents; however, these agents produce various adverse effects. Previously, we reported the renoprotective effects of a stimulator of the mitochondrial ATP-dependent K⁺ channel (MitK_ATP), nicorandil, in a remnant kidney model. Nonetheless, the cellular targets of these effects remain unknown. Here, we examined the effect of nicorandil on puromycin aminonucleoside-induced nephrosis (PAN) rats, a well-established model of podocyte injury and human nephrotic syndrome. PAN was induced using a single intraperitoneal injection. Nicorandil was administered orally at 30 mg/kg/day. We found that proteinuria and hypoalbuminemia in PAN rats were significantly ameliorated following nicorandil treatment. Immunostaining and ultrastructural analysis under electron microscopy demonstrated that podocyte injury in PAN rats showed a significant partial attenuation following nicorandil treatment. Nicorandil ameliorated the increase in the oxidative stress markers nitrotyrosine and 8-hydroxy-2-deoxyguanosine in glomeruli. Conversely, nicorandil prevented the decrease in levels of the antioxidant enzyme manganese superoxide dismutase in PAN rats. We found that mitochondrial Ca²⁺ uniporter levels in glomeruli were higher in PAN rats than in control rats, and this increase was significantly attenuated by nicorandil. We conclude that stimulation of MitK_ATP by nicorandil reduces proteinuria by attenuating podocyte injury in PAN nephrosis, which restores mitochondrial antioxidative capacity, possibly through mitochondrial Ca²⁺ uniporter modulation. These data indicate that MitK_ATP may represent a novel target for podocyte injury and nephrotic syndrome.NEW & NOTEWORTHY Our findings suggest that the mitochondrial Ca²⁺ uniporter may be an upstream regulator of manganese superoxide dismutase and indicate a biochemical basis for the interaction between the ATP-sensitive K⁺ channel and Ca²⁺ signaling. We believe that our study makes a significant contribution to the literature because our results indicate that the ATP-sensitive K⁺ channel may be a potential therapeutic target for podocyte injury and nephrotic syndrome.

Disodium Fumarate Alleviates Endoplasmic Reticulum Stress, Mitochondrial Damage, and Oxidative Stress Induced by the High-Concentrate Diet in the Mammary Gland Tissue of Hu Sheep

The long-term feeding of the high-concentrate diet (HC) reduced rumen pH and induced subacute rumen acidosis (SARA), leading to mammary gland tissue damage among ruminants. Disodium fumarate enhanced rumen bufferation and alleviated a decrease in rumen pH induced by the HC diet. Therefore, the purpose of this study was to investigate whether disodium fumarate could alleviate endoplasmic reticulum (ER) stress, mitochondrial damage, and oxidative stress induced by the high-concentrate diet in the mammary gland tissue of Hu sheep. In this study, 18 Hu sheep in mid-lactation were randomly divided into three groups: one fed with a low-concentrate diet (LC) diet, one fed with a HC diet, and one fed with a HC diet with disodium fumarate (AHC). Each sheep was given an additional 10 g of disodium fumarate/day. The experiment lasted for eight weeks. After the experiment, rumen fluid, blood, and mammary gland tissue were collected. The results show that, compared with the LC diet, the HC diet could reduce rumen pH, and the pH below 5.6 was more than 3 h, and the LPS content of blood and rumen fluid in HC the diet was significantly higher than in the LC diet. This indicates that the HC diet induced SARA in Hu sheep. However, the supplementation of disodium fumarate in the HC diet increased the rumen pH and decreased the content of LPS in blood and rumen fluid. Compared with the LC diet, the HC diet increased Ca²⁺ content in mammary gland tissue. However, the AHC diet decreased Ca²⁺ content. The HC diet induced ER stress in mammary gland tissue by increasing the mRNA and protein expressions of GRP78, CHOP, PERK, ATF6, and IRE1α. The HC diet also activated the IP3R-VDAC1-MCU channel and lead to mitochondrial damage by inhibiting mitochondrial fusion and promoting mitochondrial division, while disodium fumarate could alleviate these changes. In addition, disodium fumarate alleviated oxidative stress induced by the HC diet by activating Nrf2 signaling and reducing ROS production in mammary gland tissue. In conclusion, the supplementation of disodium fumarate at a daily dose of 10 g/sheep enhanced rumen bufferation by maintaining the ruminal pH above 6 and reduced LPS concentration in ruminal fluid and blood. This reaction avoided the negative effect observed by non-supplemented sheep that were fed with a high-concentrate diet involving endoplasmic reticulum stress, oxidative stress, and mitochondrial damage in the mammary gland tissue of Hu sheep.

IP3R at ER-Mitochondrial Contact Sites: Beyond the IP3R-GRP75-VDAC1 Ca2+ Funnel

Membrane contact sites (MCS) circumvent the topological constraints of functional coupling between different membrane-bound organelles by providing a means of communication and exchange of materials. One of the most characterised contact sites in the cell is that between the endoplasmic reticulum and the mitochondrial (ERMCS) whose function is to couple cellular Ca2+ homeostasis and mitochondrial function. Inositol 1,4,5-trisphosphate receptors (IP3Rs) on the ER, glucose-regulated protein 75 (GRP 75) and voltage-dependent anion channel 1 (VDAC1) on the outer mitochondrial membrane are the canonical component of the Ca2+ transfer unit at ERMCS. These are often reported to form a Ca2+ funnel that fuels the mitochondrial low-affinity Ca2+ uptake system. We assess the available evidence on the IP3R subtype selectivity at the ERMCS and consider if IP3Rs have other roles at the ERMCS beyond providing Ca2+. Growing evidence suggests that all three IP3R subtypes can localise and regulate Ca2+ signalling at ERMCS. Furthermore, IP3Rs may be structurally important for assembly of the ERMCS in addition to their role in providing Ca2+ at these sites. Evidence that various binding partners regulate the assembly and Ca2+ transfer at ERMCS populated by IP3R-GRP75-VDAC1, suggesting that cells have evolved mechanisms that stabilise these junctions forming a Ca2+ microdomain that is required to fuel mitochondrial Ca2+ uptake.

Down the membrane hole: Ion channels in protozoan parasites

Parasitic diseases caused by protozoans are highly prevalent around the world, disproportionally affecting developing countries, where coinfection with other microorganisms is common. Control and treatment of parasitic infections are constrained by the lack of specific and effective drugs, plus the rapid emergence of resistance. Ion channels are main drug targets for numerous diseases, but their potential against protozoan parasites is still untapped. Ion channels are membrane proteins expressed in all types of cells, allowing for the flow of ions between compartments, and regulating cellular functions such as membrane potential, excitability, volume, signaling, and death. Channels and transporters reside at the interface between parasites and their hosts, controlling nutrient uptake, viability, replication, and infectivity. To understand how ion channels control protozoan parasites fate and to evaluate their suitability for therapeutics, we must deepen our knowledge of their structure, function, and modulation. However, methodological approaches commonly used in mammalian cells have proven difficult to apply in protozoans. This review focuses on ion channels described in protozoan parasites of clinical relevance, mainly apicomplexans and trypanosomatids, highlighting proteins for which molecular and functional evidence has been correlated with their physiological functions.

The evolution of organellar calcium mapping technologies

Intracellular Ca2+ fluxes are dynamically controlled by the co-involvement of multiple organellar pools of stored Ca2+. Endolysosomes are emerging as physiologically critical, yet underexplored, sources and sinks of intracellular Ca2+. Delineating the role of organelles in Ca2+ signaling has relied on chemical fluorescent probes and electrophysiological strategies. However, the acidic endolysosomal environment presents unique issues, which preclude the use of traditional chemical reporter strategies to map lumenal Ca2+. Here, we broadly address the current state of knowledge about organellar Ca2+ pools. We then outline the application of traditional probes, and their sensing paradigms. We then discuss how a new generation of probes overcomes the limitations of traditional Ca2+probes, emphasizing their ability to offer critical insights into endolysosomal Ca2+, and its feedback with other organellar pools.

Role of mitochondria-associated endoplasmic reticulum membranes in insulin sensitivity, energy metabolism, and contraction of skeletal muscle

Skeletal muscle has a critical role in the regulation of the energy balance of the organism, particularly as the principal tissue responsible for insulin-stimulated glucose disposal and as the major site of peripheral insulin resistance (IR), which has been related to accumulation of lipid intermediates, reduced oxidative capacity of mitochondria and endoplasmic reticulum (ER) stress. These organelles form contact sites, known as mitochondria-associated ER membranes (MAMs). This interconnection seems to be involved in various cellular processes, including Ca²⁺ transport and energy metabolism; therefore, MAMs could play an important role in maintaining cellular homeostasis. Evidence suggests that alterations in MAMs may contribute to IR. However, the evidence does not refer to a specific subcellular location, which is of interest due to the fact that skeletal muscle is constituted by oxidative and glycolytic fibers as well as different mitochondrial populations that appear to respond differently to stimuli and pathological conditions. In this review, we show the available evidence of possible differential responses in the formation of MAMs in skeletal muscle as well as its role in insulin signaling and the beneficial effect it could have in the regulation of energetic metabolism and muscular contraction.

MFN2 mediates ER-mitochondrial coupling during ER stress through specialized stable contact sites

Endoplasmic reticulum (ER) functions critically depend on a suitable ATP supply to fuel ER chaperons and protein trafficking. A disruption of the ability of the ER to traffic and fold proteins leads to ER stress and the unfolded protein response (UPR). Using structured illumination super-resolution microscopy, we revealed increased stability and lifetime of mitochondrial associated ER membranes (MAM) during ER stress. The consequent increase of basal mitochondrial Ca2+ leads to increased TCA cycle activity and enhanced mitochondrial membrane potential, OXPHOS, and ATP generation during ER stress. Subsequently, OXPHOS derived ATP trafficking towards the ER was increased. We found that the increased lifetime and stability of MAMs during ER stress depended on the mitochondrial fusion protein Mitofusin2 (MFN2). Knockdown of MFN2 blunted mitochondrial Ca2+ effect during ER stress, switched mitochondrial F1FO-ATPase activity into reverse mode, and strongly reduced the ATP supply for the ER during ER stress. These findings suggest a critical role of MFN2-dependent MAM stability and lifetime during ER stress to compensate UPR by strengthening ER ATP supply by the mitochondria.

Impact of Calcium Influx on Endoplasmic Reticulum in Excitotoxic Neurons: Role of Chemical Chaperone 4-PBA

Excessive activation of α-amino-3-hydroxy-5-methyl-4-isoxazole propoinic acid (AMPA) receptors instigates excitotoxicity via enhanced calcium influx in the neurons thus inciting deleterious consequences. Additionally, Endoplasmic Reticulum (ER) is pivotal in maintaining the intracellular calcium balance. Considering this, studying the aftermath of enhanced calcium uptake by neurons and its effect on ER environment can assist in delineating the pathophysiological events incurred by excitotoxicty. The current study was premeditated to decipher the role of ER pertaining to calcium homeostasis in AMPA-induced excitotoxicity. The findings showed, increased intracellular calcium levels (measured by flowcytometry and spectroflourimeter using Fura 2AM) in AMPA excitotoxic animals (male Sprague dawely rats) (intra-hippocampal injection of 10 mM AMPA). Further, ER resident proteins like calnexin, PDI and ERp72 were found to be upregulated, which further modulated the functioning of ER membrane calcium channels viz. IP3R, RyR, and SERCA pump. Altered calcium homeostasis further led to ER stress and deranged the protein folding capacity of ER post AMPA toxicity, which was ascertained by unfolded protein response (UPR) pathway markers such as IRE1α, eIF2α, and ATF6α. Chemical chaperone, 4-phenybutric acid (4-PBA), ameliorated the protein folding capacity and subsequent UPR markers. In addition, modulation of calcium channels and calcium regulating machinery of ER post 4-PBA administration restored the calcium homeostasis. Therefore the study reinforces the significance of ER stress, a debilitating outcome of impaired calcium homeostasis, under AMPA-induced excitotoxicity. Also, employing chaperone-based therapeutic approach to curb ER stress can restore the calcium imbalance in the neuropathological diseases.

The aging of ER-mitochondria communication: A journey from undifferentiated to aged cells

The complex physiology of eukaryotic cells requires that a variety of subcellular organelles perform unique tasks, even though they form highly dynamic communication networks. In the case of the endoplasmic reticulum (ER) and mitochondria, their functional coupling relies on the physical interaction between their membranes, mediated by domains known as mitochondria-ER contacts (MERCs). MERCs act as shuttles for calcium and lipid transfer between organelles, and for the nucleation of other subcellular processes. Of note, mounting evidence shows that they are heterogeneous structures, which display divergent behaviors depending on the cell type. Furthermore, MERCs are plastic structures that remodel according to intra- and extracellular cues, thereby adjusting the function of both organelles to the cellular needs. In consonance with this notion, the malfunction of MERCs reportedly contributes to the development of several age-related disorders. Here, we integrate current literature to describe how MERCs change, starting from undifferentiated cells, and their transit through specialization, malignant transformation (i.e., dedifferentiation), and aging/senescence. Along this journey, we will review the function of MERCs and their relevance for pivotal cell types, such as stem and cancer cells, cardiac, skeletal, and smooth myocytes, neurons, leukocytes, and hepatocytes, which intervene in the progression of chronic diseases related to age.

Mitochondrial dysfunction in cell senescence and aging

Mitochondrial dysfunction and cell senescence are hallmarks of aging and are closely interconnected. Mitochondrial dysfunction, operationally defined as a decreased respiratory capacity per mitochondrion together with a decreased mitochondrial membrane potential, typically accompanied by increased production of oxygen free radicals, is a cause and a consequence of cellular senescence and figures prominently in multiple feedback loops that induce and maintain the senescent phenotype. Here, we summarize pathways that cause mitochondrial dysfunction in senescence and aging and discuss the major consequences of mitochondrial dysfunction and how these consequences contribute to senescence and aging. We also highlight the potential of senescence-associated mitochondrial dysfunction as an antiaging and antisenescence intervention target, proposing the combination of multiple interventions converging onto mitochondrial dysfunction as novel, potent senolytics.

The pathological role of damaged organelles in renal tubular epithelial cells in the progression of acute kidney injury

Acute kidney injury (AKI) is a common clinical condition associated with high morbidity and mortality. The pathogenesis of AKI has not been fully elucidated, with a lack of effective treatment. Renal tubular epithelial cells (TECs) play an important role in AKI, and their damage and repair largely determine the progression and prognosis of AKI. In recent decades, it has been found that the mitochondria, endoplasmic reticulum (ER), lysosomes, and other organelles in TECs are damaged to varying degrees in AKI, and that they can influence each other through various signaling mechanisms that affect the recovery of TECs. However, the association between these multifaceted signaling platforms, particularly between mitochondria and lysosomes during AKI remains unclear. This review summarizes the specific pathophysiological mechanisms of the main TECs organelles in the context of AKI, particularly the potential interactions among them, in order to provide insights into possible novel treatment strategies.

Mitochondria-associated membranes: A hub for neurodegenerative diseases

In eukaryotic cells, organelles could coordinate complex mechanisms of signaling transduction metabolism and gene expression through their functional interactions. The functional domain between ER and mitochondria, called mitochondria-associated membranes (MAM), is closely associated with various physiological functions including intracellular lipid transport, Ca²⁺ transfer, mitochondria function maintenance, and autophagosome formation. In addition, more evidence suggests that MAM modulate cellular functions in health and disease. Studies have also demonstrated the association of MAM with numerous diseases, including neurodegenerative diseases, cancer, viral infection, obesity, and diabetes. In fact, recent evidence revealed a close relationship of MAM with Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), and other neurodegenerative diseases. In this view, elucidating the role of MAM in neurodegenerative diseases is particularly important. This review will focus the main tethering protein complexes of MAM and functions of MAM. Besides, the role of MAM in the regulation of neurodegenerative diseases and the potential molecular mechanisms is introduced to provide a new understanding of the pathogenesis of these diseases.

MORTALIN-Ca2+ axis drives innate rituximab resistance in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin's lymphoma, with the combination of rituximab and chemotherapy being the standard treatment for it. Although rituximab monotherapy has a remarkable response rate, drug resistance with unclear mechanisms and lack of effective second-line therapy limit the survival benefits of patients with lymphoma. Here, we report that MORTALIN is highly expressed and correlates with resistance to rituximab-based therapy and poor survival in patients with DLBCL. Mechanistically, gain- and loss-of-function experiments revealed that the voltage-dependent anion channel 1-binding protein, MORTALIN, regulated Ca²⁺ release from the endoplasmic reticulum through mitochondria-associated membrane, facilitating AP1-mediated cell proliferation and YY-1-mediated downregulation of FAS in DLBCL cells. These dual mechanisms contribute to rituximab resistance. In mouse models, genetic depletion of MORTALIN markedly increased the antitumor activity of rituximab. We shed mechanistic light on MORTALIN-Ca²⁺-CaMKII-AP1-mediated proliferation and MORTALIN-Ca²⁺-CaMKII-inhibited death receptor in DLBCL, leading to rituximab resistance, and propose MORTALIN as a novel target for the treatment of DLBCL.

Targeting calcium-mediated inter-organellar crosstalk in cardiac diseases

INTRODUCTION

Abnormal calcium signaling between organelles such as the sarcoplasmic reticulum (SR), mitochondria and lysosomes is a key feature of heart diseases. Calcium serves as a secondary messenger mediating inter-organellar crosstalk, essential for maintaining the cardiomyocyte function.

AREAS COVERED

This article examines the available literature related to calcium channels and transporters involved in inter-organellar calcium signaling. The SR calcium-release channels ryanodine receptor type-2 (RyR2) and inositol 1,4,5-trisphosphate receptor (IP₃R), and calcium-transporter SR/ER-ATPase 2a (SERCA2a) are illuminated. The roles of mitochondrial voltage-dependent anion channels (VDAC), the mitochondria Ca²⁺ uniporter complex (MCUC), and the lysosomal H⁺/Ca²⁺ exchanger, two pore channels (TPC), and transient receptor potential mucolipin (TRPML) are discussed. Furthermore, recent studies showing calcium-mediated crosstalk between the SR, mitochondria, and lysosomes as well as how this crosstalk is dysregulated in cardiac diseases are placed under the spotlight.

EXPERT OPINION

Enhanced SR calcium release via RyR2 and reduced SR reuptake via SERCA2a, increased VDAC and MCUC-mediated calcium uptake into mitochondria, and enhanced lysosomal calcium-release via lysosomal TPC and TRPML may all contribute to aberrant calcium homeostasis causing heart disease. While mechanisms of this crosstalk need to be studied further, interventions targeting these calcium channels or combinations thereof might represent a promising therapeutic strategy.

Endoplasmic reticulum-mitochondria coupling attenuates vanadium-induced apoptosis via IP3R in duck renal tubular epithelial cells

Vanadium (V) is necessary for the health and growth of animals, but excessive V has harmful effects on the ecosystem health. Endoplasmic reticulum (ER)-mitochondria coupling as a membrane structure connects the mitochondrial outer membrane with the ER. The mitochondria-associated ER membrane (MAM) is a region of the ER-mitochondria coupling and is essential for normal cell function. Currently, the crosstalk between ER-mitochondrial coupling and apoptosis in the toxic mechanism of V on duck kidney is still unclear. In this study, duck renal tubular epithelial cells were incubated with different concentrations of sodium metavanadate (NaVO₃) and/or inositol triphosphate receptor (IP₃R) inhibitor 2-aminoethyl diphenyl borate (2-APB) for 24 h. The results showed that V could significantly increase lactate dehydrogenase (LDH) release, the mitochondrial calcium level and the numbers of the fluorescent signal points of IP₃R; shortened the length ER-mitochondria coupling and reduced its formation; markedly upregulate the mRNA levels of MAM-related genes and protein levels, causing MAM dysfunction. Additionally, V treatment appeared to upregulate pro-apoptotic genes and downregulate anti-apoptotic genes, followed by cell apoptosis. The V-induced changes were alleviated by treatment with IP₃R inhibitor. In summary, V could induce the dysfunction of ER-mitochondrial coupling and apoptosis, and inhibition of ER-mitochondrial coupling could attenuate V-induced apoptosis in duck renal tubular epithelial cells.

IP3R1/GRP75/VDAC1 complex mediates endoplasmic reticulum stress-mitochondrial oxidative stress in diabetic atrial remodeling

Rationale

Endoplasmic reticulum (ER) stress and mitochondrial dysfunction are important mechanisms of atrial remodeling, predisposing to the development of atrial fibrillation (AF) in type 2 diabetes mellitus (T2DM). However, the molecular mechanisms underlying these processes especially their interactions have not been fully elucidated.

Objective

To explore the potential role of ER stress–mitochondrial oxidative stress in atrial remodeling and AF induction in diabetes.

Methods and results

Mouse atrial cardiomyocytes (HL-1 cells) and rats with T2DM were used as study models. Significant ER stress was observed in the diabetic rat atria. After treatment with tunicamycin (TM), an ER stress agonist, mass spectrometry (MS) identified several known ER stress and calmodulin proteins, including heat shock protein family A (HSP70) member [HSPA] 5 [GRP78]) and HSPA9 (GRP75, glucose-regulated protein 75). In situ proximity ligation assay indicated that TM led to increased protein expression of the IP3R1–GRP75–VDAC1 (inositol 1,4,5-trisphosphate receptor 1–glucose-regulated protein 75–voltage-dependent anion channel 1) complex in HL-1 cells. Small interfering RNA silencing of GRP75 in HL-1 cells and GRP75 conditional knockout in a mouse model led to impaired calcium transport from the ER to the mitochondria and alleviated mitochondrial oxidative stress and calcium overload. Moreover, GRP75 deficiency attenuated atrial remodeling and AF progression in Myh6-Cre⁺/Hspa9^flox/flox + TM mice.

Conclusions

The IP3R1–GRP75–VDAC1 complex mediates ER stress–mitochondrial oxidative stress and plays an important role in diabetic atrial remodeling.

•

Endoplasmic reticulum stress associated with atrial fibrillation.

•

GRP75 contributes to the ER-mitochondria crosstalk.

•

Inhibition of GRP75 attenuated diabetic atrial remodeling.

Mitochondrial Ca2+ Homeostasis: Emerging Roles and Clinical Significance in Cardiac Remodeling

Mitochondria are the sites of oxidative metabolism in eukaryotes where the metabolites of sugars, fats, and amino acids are oxidized to harvest energy. Notably, mitochondria store Ca²⁺ and work in synergy with organelles such as the endoplasmic reticulum and extracellular matrix to control the dynamic balance of Ca²⁺ concentration in cells. Mitochondria are the vital organelles in heart tissue. Mitochondrial Ca²⁺ homeostasis is particularly important for maintaining the physiological and pathological mechanisms of the heart. Mitochondrial Ca²⁺ homeostasis plays a key role in the regulation of cardiac energy metabolism, mechanisms of death, oxygen free radical production, and autophagy. The imbalance of mitochondrial Ca²⁺ balance is closely associated with cardiac remodeling. The mitochondrial Ca²⁺ uniporter (mtCU) protein complex is responsible for the uptake and release of mitochondrial Ca²⁺ and regulation of Ca²⁺ homeostasis in mitochondria and consequently, in cells. This review summarizes the mechanisms of mitochondrial Ca²⁺ homeostasis in physiological and pathological cardiac remodeling and the regulatory effects of the mitochondrial calcium regulatory complex on cardiac energy metabolism, cell death, and autophagy, and also provides the theoretical basis for mitochondrial Ca²⁺ as a novel target for the treatment of cardiovascular diseases.

ENSMUST00000147869 regulates proliferation and fibrosis of mesangial cells in diabetic nephropathy by interacting with Hspa9

AIMS

Our previous study showed that ENSMUST00000147869 was abnormally low expressed in the early stage of diabetic nephropathy (DN). ENSMUST00000147869 could inhibit the fibrosis and proliferation of mouse mesangial cells (MMCs), but the mechanism is still unclear. This study aims to explore the specific mechanism underline ENSMUST00000147869 regulates the proliferation and fibrosis of MMCs in DN.

METHODS

Nucleocytoplasmic fractionation was applied to define the location of ENSMUST00000147869 in MMCs. RNA-protein pulldown, RNA immunoprecipitation and mass spectrometry were used to identify upregulated Hspa9 directly interacting with ENSMUST00000147869. SiRNA and lentivirus packaging were used to clarify the role of Hspa9 downregulated by ENSMUST00000147869 in promoting proliferation and fibrosis in MMCs. CHX and MG132 were used to clarify the regulatory role of ENSMUST00000147869 to Hspa9. Immunoprecipitation confirmed the binding of Hspa9 and HMGB1.

RESULTS

HSPA9 was a direct binding protein of ENSMUST00000147869, and ENSMUST00000147869 could inhibit proliferation and fibrosis of MMCs by down-regulating HSPA9 through ubiquitination process. HMGB1 was the downstream binding protein of Hspa9, and ENSMUST00000147869 could inhibit the interaction between Hspa9 and HMGB1.

CONCLUSION

Our data showed that ENSMUST00000147869 regulates Hspa9 through the ubiquitin proteasome pathway, and inhibits the binding of Hspa9 and HMGB1. ENSMUST00000147869/Hspa9/HMGB1 axis may act as a diagnostic molecular marker and an effective therapeutic target for DN. This article is protected by copyright. All rights reserved.

GRP75 mediates endoplasmic reticulum-mitochondria coupling during palmitate-induced pancreatic β-cell apoptosis

The endoplasmic reticulum (ER) and mitochondria are structurally connected with each other at specific sites termed mitochondria-associated membranes (MAMs). These physical links are composed of several tethering proteins and are important during varied cellular processes, such as calcium homeostasis, lipid metabolism and transport, membrane biogenesis, and organelle remodeling. However, the attributes of specific tethering proteins in these cellular functions remain debatable. Here, we present data to show that one such tether protein, glucose regulated protein 75 (GRP75), is essential in increasing ER-mitochondria contact during palmitate-induced apoptosis in pancreatic insulinoma cells. We demonstrate that palmitate increased GRP75 levels in mouse and rat pancreatic insulinoma cells as well as in mouse primary islet cells. This was associated with increased mitochondrial Ca2+ transfer, impaired mitochondrial membrane potential, increased ROS production, and enhanced physical coupling between the ER and mitochondria. Interestingly, GRP75 inhibition prevented these palmitate-induced cellular aberrations. Additionally, GRP75 overexpression alone was sufficient to impair mitochondrial membrane potential, increase mitochondrial Ca2+ levels and ROS generation, augment ER-mitochondria contact, and induce apoptosis in these cells. In vivo injection of palmitate induced hyperglycemia and hypertriglyceridemia, as well as impaired glucose and insulin tolerance in mice. These animals also exhibited elevated GRP75 levels accompanied by enhanced apoptosis within the pancreatic islets. Our findings suggest that GRP75 is critical in mediating palmitate-induced ER-mitochondrial interaction leading to apoptosis in pancreatic islet cells.

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.