JNK1/2 regulates ER-mitochondrial Ca2+ cross-talk during IL-1β-mediated cell death in RINm5F and human primary β-cells

TRPV4 mediates IL-1-induced Ca2+ signaling, ERK activation and MMP expression

Ca2+ permeation through TRPV4 in fibroblasts is associated with pathological matrix degradation. In human gingival fibroblasts, IL-1β binding to its signaling receptor (IL-1R1) induces activation of extracellular regulated kinase (ERK) and MMP1 expression, processes that require Ca2+ flux across the plasma membrane. It is not known how IL-1R1, which does not conduct Ca2+, generates Ca2+ signals in response to IL-1. We examined whether TRPV4 mediates the Ca2+ fluxes required for ERK signaling in IL-1 stimulated gingival fibroblasts. TRPV4 was immunostained in fibroblasts of human gingival connective tissue and in focal adhesions of cultured mouse gingival fibroblasts. Human gingival fibroblasts treated with IL-1β showed no change of TRPV4 expression but there was increased MMP1 expression. In mouse, gingival fibroblasts expressing TRPV4, IL-1 strongly increased [Ca2+]i. Pre-incubation of cells with IL-1 Receptor Antagonist blocked Ca2+ entry induced by IL-1 or the TRPV4 agonist GSK101. Knockout of TRPV4 or expression of a non-Ca2+-conducting TRPV4 pore-mutant or pre-incubation with the TRPV4 inhibitor RN1734, blocked IL-1-induced Ca2+ transients and expression of the mouse interstitial collagenase, MMP13. Treatment of mouse gingival fibroblasts with GSK101 phenocopied Ca2+ and ERK responses induced by IL-1; these responses were absent in TRPV4-null cells or cells expressing a non-conducting TRPV4 pore-mutant. Immunostained IL-1R1 localized with TRPV4 in adhesions within cell extensions. While TRPV4 immunoprecipitates analyzed by mass spectrometry showed no association with IL-1R1, TRPV4 associated with Src-related proteins and Src co-immunoprecipitated with TRPV4. Src inhibition reduced IL-1-induced Ca2+ responses. The functional linkage of TRPV4 with IL-1R1 expands its repertoire of innate immune signaling processes by mediating IL-1-driven Ca2+ responses that drive matrix remodeling in fibroblasts. Thus, inhibiting TRPV4 activity may provide a new pharmacological approach for blunting matrix degradation in inflammatory diseases.

PLC-CN-NFAT1 signaling-mediated Aβ and IL-1β crosstalk synergistically promotes hippocampal neuronal damage

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Neuronal calcium overload plays an important role in Aβ deposition and neuroinflammation, which are strongly associated with AD. However, the specific mechanisms by which calcium overload contributes to neuroinflammation and AD and the relationship between them have not been elucidated. Phospholipase C (PLC) is involved in regulation of calcium homeostasis, and CN-NFAT1 signaling is dependent on intracellular Ca2+ ([Ca2+]i) to regulate transcription of genes. Therefore, we hypothesized that the PLC-CN-NFAT1 signaling might mediate the interaction between Aβ and inflammation to promote neuronal injury in AD. In this experiment, the results showed that the levels of Aβ, IL-1β and [Ca2+]i in the hippocampal primary neurons of APP/PS1 mice (APP neurons) were significantly increased. IL-1β exposure also significantly increased Aβ and [Ca2+]i in HT22 cells, suggesting a close association between Aβ and IL-1β in the development of AD. Furthermore, PLC activation induced significant calcium homeostasis imbalance, cell apoptosis, Aβ and ROS production, and significantly increased expressions of CN and NFAT1, while PLC inhibitor significantly reversed these changes in APP neurons and IL-1β-induced HT22 cells. Further results indicated that PLC activation significantly increased the expressions of NOX2, APP, BACE1, and NCSTN, which were inhibited by PLC inhibitor in APP neurons and IL-1β-induced HT22 cells. All indications point to a synergistic interaction between Aβ and IL-1β by activating the PLC-CN-NFAT1 signal, ultimately causing a vicious cycle, resulting in neuronal damage in AD. The study may provide a new idea and target for treatment of AD.

Melatonin enhanced the cardioprotective effects of HTK solution on Langendorff-perfused mouse hearts subjected to ischemia/reperfusion

Objectives

Cardiac arrest is a crucial procedure in various cardiac surgeries, during which the heart is subjected to an ischemic state. The occurrence of ischemia/reperfusion (I/R) injury is inevitable due to aortic blockage and opening. The Histidine-tryptophan-ketoglutarate (HTK) solution is commonly used as an organ protection liquid to mitigate cardiac injury during cardiac surgery. Despite its widespread use, there is significant potential for improving its protective efficacy.

Materials and Methods

The cardioprotective effect of HTK solution with and without melatonin was evaluated using the isolated Langendorff-perfused mouse heart model. The isolated C57bL/6 mouse hearts were randomly divided into four groups: control, I/R, HTK solution treatment before reperfusion (HTK+I/R), and HTK solution combined with melatonin before reperfusion (HTK+M+I/R). Cardiac function and myocardial injury markers were then measured. AMP-activated protein kinase α2 (AMPKα2) KO mice were used to investigate the underlying mechanism.

Results

In our study, we found that melatonin significantly improved the protective effects of HTK solution in an isolated Langendorff-perfused mouse model, mechanistically by reducing mitochondrial damage, improving energy metabolism, inhibiting cardiomyocyte apoptosis, and reducing myocardial infarction size. We also observed that the HTK solution alone was ineffective in inhibiting ER stress, but when melatonin was added, there was a significant reduction in ER stress. Furthermore, melatonin was found to alleviate carbonyl stress during cardiac I/R. Interestingly, our results showed that the cardioprotective properties of melatonin were dependent on AMPKα2.

Conclusion

The findings presented in this study offer a valuable empirical foundation for the development of perioperative cardioprotective strategies.

Control of human pancreatic beta cell kinome by glucagon-like peptide-1 receptor biased agonism

AIM

To determine the kinase activity profiles of human pancreatic beta cells downstream of glucagon-like peptide-1 receptor (GLP-1R) balanced versus biased agonist stimulations.

MATERIALS AND METHODS

This study analysed the kinomic profiles of human EndoC-βh1 cells following vehicle and GLP-1R stimulation with the pharmacological agonist exendin-4, as well as exendin-4-based biased derivatives exendin-phe1 and exendin-asp3 for acute (10-minute) versus sustained (120-minute) responses, using PamChip protein tyrosine kinase and serine/threonine kinase assays. The raw data were filtered and normalized using BioNavigator. The kinase analyses were conducted with R, mainly including kinase-substrate mapping and Kyoto Encyclopedia of Genes and Genomes pathway analysis.

RESULTS

The present analysis reveals that kinomic responses are distinct for acute versus sustained GLP-1R agonist exposure, with individual responses associated with agonists presenting specific bias profiles. According to pathway analysis, several kinases, including JNKs, PKCs, INSR and LKB1, are important GLP-1R signalling mediators, constituting potential targets for further research on biased GLP-1R downstream signalling.

CONCLUSION

The results from this study suggest that differentially biased exendin-phe1 and exendin-asp3 can modulate distinct kinase interaction networks. Further understanding of these mechanisms will have important implications for the selection of appropriate anti-type 2 diabetes therapies with optimized downstream kinomic profiles.

Systemic inflammation after stroke: implications for post-stroke comorbidities

Immunological mechanisms have come into the focus of current translational stroke research, and the modulation of neuroinflammatory pathways has been identified as a promising therapeutic approach to protect the ischemic brain. However, stroke not only induces a local neuroinflammatory response but also has a profound impact on systemic immunity. In this review, we will summarize the consequences of ischemic stroke on systemic immunity at all stages of the disease, from onset to long‐term outcome, and discuss underlying mechanisms of systemic brain‐immune communication. Furthermore, since stroke commonly occurs in patients with multiple comorbidities, we will also overview the current understanding of the potential role of systemic immunity in common stroke‐related comorbidities, such as cardiac dysfunction, atherosclerosis, diabetes, and infections. Finally, we will highlight how targeting systemic immunity after stroke could improve long‐term outcomes and alleviate comorbidities of stroke patients.

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.

Mechanism of Endoplasmic Reticulum Stress in Cerebral Ischemia

Endoplasmic reticulum (ER) is the main organelle for protein synthesis, trafficking and maintaining intracellular Ca²⁺ homeostasis. The stress response of ER results from the disruption of ER homeostasis in neurological disorders. Among these disorders, cerebral ischemia is a prevalent reason of death and disability in the world. ER stress stemed from ischemic injury initiates unfolded protein response (UPR) regarded as a protection mechanism. Important, disruption of Ca²⁺ homeostasis resulted from cytosolic Ca²⁺ overload and depletion of Ca²⁺ in the lumen of the ER could be a trigger of ER stress and the misfolded protein synthesis. Brain cells including neurons, glial cells and endothelial cells are involved in the complex pathophysiology of ischemic stroke. This is generally important for protein underfolding, but even more for cytosolic Ca²⁺ overload. Mild ER stress promotes cells to break away from danger signals and enter the adaptive procedure with the activation of pro-survival mechanism to rescue ischemic injury, while chronic ER stress generally serves as a detrimental role on nerve cells via triggering diverse pro-apoptotic mechanism. What’s more, the determination of some proteins in UPR during cerebral ischemia to cell fate may have two diametrically opposed results which involves in a specialized set of inflammatory and apoptotic signaling pathways. A reasonable understanding and exploration of the underlying molecular mechanism related to ER stress and cerebral ischemia is a prerequisite for a major breakthrough in stroke treatment in the future. This review focuses on recent findings of the ER stress as well as the progress research of mechanism in ischemic stroke prognosis provide a new treatment idea for recovery of cerebral ischemia.

Iron overload induces apoptosis of osteoblast cells via eliciting ER stress-mediated mitochondrial dysfunction and p-eIF2α/ATF4/CHOP pathway in vitro

Iron is an essential element for crucial biological function; whereas excess iron sedimentation impairs the main functions of tissues or organs. Cumulative researches have shown that the disturbances in iron metabolism, especially iron overload is closely concatenating with bone loss. Nevertheless, the specific process of iron overload-induced apoptosis in osteoblasts has not been thoroughly studied. In this study, our purpose is to elucidate the mechanism of osteoblast apoptosis induced by iron overload via the MC3T3-E1 cell line. Ferric ammonium citrate (FAC) was utilized to simulate iron overload conditions in vitro. These results showed that treatment with FAC dose-dependently induced the apoptosis of MC3T3-E1 cells at 48 h, dysfunction of iron metabolism, and increased intracellular reactive oxygen species (ROS) levels. Following, FAC does-dependently caused the calcium dyshomeostasis, decreased the calcium concentration in endoplasmic reticulum (ER), but increased the crosstalk between ER and mitochondria, and calcium concentration in the mitochondria. Moreover, FAC dose-dependently decreased mitochondrial membrane potential (MMP) and enhanced the expression of apoptosis related proteins (Bax, Cyto-C and C-caspase3). We furthermore revealed that FAC treatment activated the ER-mediated cell apoptosis via p-eIF2α/ATF4/CHOP pathway in MC3T3-E1 osteoblasts cells. In addition, pretreatment with the N-acetylcysteine (NAC) or Tauroursodeoxycholate Sodium (TUDC) attenuated cell apoptosis, ROS levels, mitochondria fragmentation and ER stress-related protein expression, and recovered the protein expression related to iron metabolism. In conclusion, our finding suggested that iron overload induced apoptosis via eliciting ER stress, which resulted in mitochondrial dysfunction and activated p-eIF2α/ATF4/CHOP pathway.

Death sentence: The tale of a fallen endoplasmic reticulum

Endoplasmic Reticulum (ER) stress signaling is an adaptive mechanism triggered when protein folding demand overcomes the folding capacity of this compartment, thereby leading to the accumulation of improperly folded proteins. This stress signaling pathway is named the Unfolded Protein Response (UPR) and aims at restoring ER homeostasis. However, if this fails, mechanisms orienting cells towards death processes are initiated. Herein, we summarize the most recent findings connecting ER stress and the UPR with identified death mechanisms including apoptosis, necrosis, pyroptosis, ferroptosis, and autophagy. We highlight new avenues that could be investigated and controlled through actionable mechanisms in physiology and pathology.

EGCG Upregulates UCP3 Levels to Protect MIN6 Pancreatic Islet Cells from Interleukin-1β-Induced Apoptosis

Objective

The protective effects of epigallocatechin gallate (EGCG) on interleukin-1β (IL-1β)-induced apoptosis were investigated in murine MIN₆ pancreatic β-cells. The role of uncoupling protein-3 (UCP₃) signaling in this process was also explored.

Methods

After treatment with IL-1β and EGCG, cells were collected and analyzed. Cell viability was measured using the CCK₈ assay and the function of β-cells was evaluated by analyzing insulin secretion. Detection of mitochondrial function in cells was performed by measuring mitochondrial membrane potential, the concentration of ATP and activity of ROS. Apoptosis was analyzed by Hochest33258 staining and flow cytometry. Expression levels of UCP₃ were interrogated using immunohistochemistry, RT-PCR and Western blotting.

Results

Compared with the control group, IL-1β treatment (20nM) for 24 h significantly decreased cell viability and insulin secretion, damaged mitochondrial function and increased ROS activity. Results also showed increased apoptosis and a decrease in UCP₃ expression levels (p<0.01). However, treatment with low (1mM) or high (5mM) concentrations of EGCG significantly decreased IL-1β-induced apoptosis (p<0.01), restored mitochondrial function and subsequently increased UCP₃ levels in IL-1β-induced β-cells (p<0.01).

Conclusion

These results suggest that EGCG protects against IL-1β-induced mitochondrial injury and apoptosis in β-cells through the up-regulation of UCP₃.

Impact of Conventional and Atypical MAPKs on the Development of Metabolic Diseases

The family of mitogen-activated protein kinases (MAPKs) consists of fourteen members and has been implicated in regulation of virtually all cellular processes. MAPKs are divided into two groups, conventional and atypical MAPKs. Conventional MAPKs are further classified into four sub-families: extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK1, 2 and 3), p38 (α, β, γ, δ), and extracellular signal-regulated kinase 5 (ERK5). Four kinases, extracellular signal-regulated kinase 3, 4, and 7 (ERK3, 4 and 7) as well as Nemo-like kinase (NLK) build a group of atypical MAPKs, which are activated by different upstream mechanisms than conventional MAPKs. Early studies identified JNK1/2 and ERK1/2 as well as p38α as a central mediators of inflammation-evoked insulin resistance. These kinases have been also implicated in the development of obesity and diabetes. Recently, other members of conventional MAPKs emerged as important mediators of liver, skeletal muscle, adipose tissue, and pancreatic β-cell metabolism. Moreover, latest studies indicate that atypical members of MAPK family play a central role in the regulation of adipose tissue function. In this review, we summarize early studies on conventional MAPKs as well as recent findings implicating previously ignored members of the MAPK family. Finally, we discuss the therapeutic potential of drugs targeting specific members of the MAPK family.

A Putative Prohibitin-Calcium Nexus in β-Cell Mitochondria and Diabetes

The role of mitochondria in apoptosis is well known; however, the mechanisms linking mitochondria to the proapoptotic effects of proinflammatory cytokines, hyperglycemia, and glucolipotoxicity are not completely understood. Complex Ca²⁺ signaling has emerged as a critical contributor to these proapoptotic effects and has gained significant attention in regulating the signaling processes of mitochondria. In pancreatic β-cells, Ca²⁺ plays an active role in β-cell function and survival. Prohibitin (PHB), a mitochondrial chaperone, is actively involved in maintaining the architecture of mitochondria. However, its possible interaction with Ca²⁺-activated signaling pathways has not been explored. The present review aims to examine potential crosstalk between Ca²⁺ signaling and PHB function in pancreatic β-cells. Moreover, this review will focus on the effects of cytokines and glucolipotoxicity on Ca²⁺ signaling and its possible interaction with PHB. Improved understanding of this important mitochondrial protein may aid in the design of more targeted drugs to identify specific pathways involved with stress-induced dysfunction in the β-cell.

Cadmium exposure induces pancreatic β-cell death via a Ca2+-triggered JNK/CHOP-related apoptotic signaling pathway

Cadmium (Cd) is known to be ranked the 7^th hazardous substance in the Substance Priority List by Agency for Toxic Substances and Disease Registry. The experimental and epidemiological data have suggested that Cd is linked to the development of diabetes mellitus (DM). The molecular mechanism of Cd on the pancreatic β-cell cytotoxicity still remains unclear. Evidence has pointed toward that Ca²⁺ is an important regulator of toxic insult-induced β-cell cytotoxicity. The role of Ca²⁺ in the Cd-induced β-cell cytotoxicity is still unknown. In this study, we found that Cd exposure significantly inhibited insulin secretion and cell viability in the pancreatic β-cell-derived RIN-m5F cells. Cd exposure induced apoptotic events, including the increased populations of apoptotic cells and sub-G1 hypodiploid cells, and caspase-3/-7/-9 and poly (ADP-ribose) polymerase (PARP) activation, which largely depended on the activation of c-Jun N-terminal kinase (JNK) and C/EBP homologous protein (CHOP). Transfection with siRNAs for JNK and CHOP or pretreatment with specific pharmacological inhibitor of JNK (SP600125) in β-cells effectively prevented the Cd-induced insulin secretion dysfunction and apoptosis. JNK-specific siRNA dramatically suppressed Cd-induced JNK phosphorylation and CHOP protein expression, but JNK phosphorylation could not be inhibited by CHOP-specific siRNA. Furthermore, Cd exposure significantly increased the intracellular calcium ([Ca²⁺]_i) levels. Buffering the Ca²⁺ response with BAPTA/AM effectively abrogated the Cd-induced [Ca²⁺]_i elevation, insulin secretion dysfunction, apoptosis, and protein expression of JNK phosphorylation and CHOP activation. Taken together, these findings demonstrated that Cd exposure exerts β-cell death via a [Ca²⁺]_i-dependent JNK activation-activated downstream CHOP-related apoptotic signaling pathway.

PARP inhibition protects mitochondria and reduces ROS production via PARP-1-ATF4-MKP-1-MAPK retrograde pathway

Oxidative stress induces DNA breaks and PARP-1 activation which initiates mitochondrial reactive oxygen species (ROS) production and cell death through pathways not yet identified. Here, we show the mechanism by which PARP-1 influences these processes via PARylation of activating transcription factor-4 (ATF4) responsible for MAP kinase phosphatase-1 (MKP-1) expression and thereby regulates MAP kinases. PARP inhibitor, or silencing, of PARP induced MKP-1 expression by ATF4-dependent way, and inactivated JNK and p38 MAP kinases. Additionally, it induced ATF4 expression and binding to cAMP-response element (CRE) leading to MKP-1 expression and the inactivation of MAP kinases. In contrast, PARP-1 activation induced the PARylation of ATF4 and reduced its binding to CRE sequence in vitro. CHIP-qPCR analysis showed that PARP inhibitor increased the ATF4 occupancy at the initiation site of MKP-1. In oxidative stress, PARP inhibition reduced ROS-induced cell death, suppressed mitochondrial ROS production and protected mitochondrial membrane potential on an ATF4 and MKP-1 dependent way. Basically identical results were obtained in WRL-68, A-549 and T24/83 human cell lines indicating that the aforementioned mechanism can be universal. Here, we provide the first description of PARP-1-ATF4-MKP-1-JNK/p38 MAPK retrograde pathway, which is responsible for the regulation of mitochondrial integrity, ROS production and cell death in oxidative stress, and may represent a new mechanism of PARP in cancer therapy since cancer stem cells development is JNK-dependent.

Hydrogen sulfide protects against endoplasmic reticulum stress and mitochondrial injury in nucleus pulposus cells and ameliorates intervertebral disc degeneration

It has been suggested that excessive apoptosis in intervertebral disc cells induced by inflammatory cytokines, such as interleukin (IL)-1β, is related to the process of intervertebral disc degeneration (IVDD). Hydrogen sulfide (H₂S), a gaseous signaling molecule, has drawn attention for its anti-apoptosis role in various pathophysiological processes in degenerative diseases. To date, there has been no investigation of the correlation of H₂S production and IVDD or of the effects of H₂S on IL-1β-induced apoptosis in nucleus pulposus (NP) cells. Here, we found that the expression levels of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), two key enzymes in the generation of H₂S, were significantly decreased in human degenerate NP tissues as well as in IL-1β-treated NP cells. NaHS (H₂S donor) administration showed a protective effect by inhibiting the endoplasmic reticulum (ER) stress response and mitochondrial dysfunction induced by IL-1β stimulation in vitro, the effect was related to activation of the PI3K/Akt and ERK1/2 signaling pathways. Suppression of these pathways by specific inhibitors, LY294002 and PD98059, partially reduced the protective effect of NaHS. Moreover, in the percutaneous needle puncture disc degeneration rat tail model, disc degeneration was partially reversed by NaHS administration. Taken together, our results suggest that H₂S plays a protective role in IVDD and the underlying mechanism involves PI3K/Akt and ERK1/2 signaling pathways-mediated suppression of ER stress and mitochondrial dysfunction in IL-1β-induced NP cells.

Cadmium-induced apoptosis of Siberian tiger fibroblasts via disrupted intracellular homeostasis

Background

Heavy metals can cause great harm to Siberian tigers in the natural environment. Cadmium (Cd²⁺) is an environmental contaminant that affects multiple cellular processes, including cell proliferation, differentiation, and survival. It has been shown to induce apoptosis in a variety of cell types and tissues.

Results

We investigated the apoptotic effects of Cd²⁺ on Siberian tiger fibroblasts in vitro. Our research revealed the typical signs of apoptosis after Cd²⁺ exposure. Apoptosis was dose- (0–4.8 μM) and duration-dependent (12–48 h), and proliferation was strongly inhibited. Cd²⁺ increased the activity of caspase-3, -8, and -9 and disrupted calcium homeostasis by causing oxidative stress and mitochondrial dysfunction. It also increased K⁺ efflux and altered the mRNA levels of Bax, Bcl-2, caspase-3, caspase-8, Fas, and p53.

Conclusions

Our results suggest that Cd²⁺ triggers the apoptosis of Siberian tiger fibroblasts by disturbing intracellular homeostasis. These results will aid in our understanding of the effects of Cd²⁺ on Siberian tigers and in developing interventions to treat and prevent cadmium poisoning.

Obligatory Role of Early Ca(2+) Responses in H2O2-Induced β-Cell Apoptosis

Our previous study using apoptosis analysis suggested that Ca(2+) release through inositol 1,4,5-trisphosphate (IP3) receptors and the subsequent Ca(2+) influx through store-operated channels (SOCs) constitute a triggering signal for H2O2-induced β-cell apoptosis. In the present study, we further examined the obligatory role of early Ca(2+) responses in β-cell apoptosis induction. H2O2 induced elevation of the cytosolic Ca(2+) concentration ([Ca(2+)]c) consisting of two phases: an initial transient [Ca(2+)]c elevation within 30 min and a slowly developing one thereafter. The first phase was almost abolished by 2-aminoethoxydiphenylborate (2-APB), which blocks IP3 receptors and cation channels including SOCs, while the second phase was only partially inhibited by 2-APB. The inhibition by 2-APB of the second phase was not observed when 2-APB was added 30 min after the treatment with H2O2. 2-APB also largely inhibited elevation of the mitochondrial Ca(2+) concentration ([Ca(2+)]m) induced by H2O2 when 2-APB was applied simultaneously with H2O2, but not when applied 30 min after H2O2 application. In addition, 2-APB inhibited the release of mitochondrial cytochrome c to the cytosol induced by H2O2 when 2-APB was applied simultaneously with H2O2 but not 30 min post-treatment. H2O2-induced [Ca(2+)]m elevation and cell death were not inhibited by Ru360, an inhibitor of the mitochondrial calcium uniporter (MCU). These results suggest that the H2O2-induced initial [Ca(2+)]c elevation, occurring within 30 min and mediated by Ca(2+) release through IP3 receptors and subsequent Ca(2+) influx through SOCs, leads to [Ca(2+)]m elevation, possibly through a mechanism independent of MCU, thereby inducing cytochrome c release and consequent apoptosis.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Decoding the oxidative stress hypothesis in diabetic embryopathy through proapoptotic kinase signaling

Maternal diabetes-induced birth defects occur in 6-10% of babies born to mothers with pregestational diabetes, representing a significant maternal-fetal health problem. Currently, these congenital malformations represent a significant maternal-fetal medicine issue, but are likely to create an even greater public health threat as 3 million women of reproductive age (19-44 years) have diabetes in the United States alone, and this number is expected to double by 2030. Neural tube defects (NTDs) and congenital heart defects are the most common types of birth defects associated with maternal diabetes. Animal studies have revealed that embryos under hyperglycemic conditions exhibit high levels of oxidative stress resulting from enhanced production of reactive oxygen species and impaired antioxidant capability. Oxidative stress activates a set of proapoptotic kinase signaling intermediates leading to abnormal cell death in the embryonic neural tube, which causes NTD formation. Work in animal models also has revealed that maternal diabetes triggers a series of signaling intermediates: protein kinase C (PKC) isoforms, PKCα, βII and δ; apoptosis signal-regulating kinase 1; c-Jun-N-terminal kinase (JNK)1/2; caspase; and apoptosis. Specifically, maternal diabetes in rodent models activates the proapoptotic unfolded protein response and endoplasmic reticulum (ER) stress. A reciprocal causation between JNK1/2 activation and ER stress exists in diabetic embryopathy. Molecular studies further demonstrate that deletion of the genes for Prkc, Ask1, Jnk1, or Jnk2 abolishes maternal diabetes-induced neural progenitor apoptosis and ameliorates NTD formation. Similar preventive effects are also observed when apoptosis signal-regulating kinase 1, JNK1/2, or ER stress is inhibited. Cell membrane stabilizers and antioxidant supplements are also effective in prevention of diabetes-induced birth defects. Mechanistic studies have revealed important insights into our understanding the cause of diabetic embryopathy and have provided a basis for future interventions against birth defects or other pregnancy complications associated with maternal diabetes. The knowledge of a molecular pathway map identified in animal studies has created unique opportunities to identify molecular targets for therapeutic intervention.

Mitochondrial metabolism directs stemness and differentiation in P19 embryonal carcinoma stem cells

The relationship between mitochondrial metabolism and cell viability and differentiation in stem cells (SCs) remains poorly understood. In the present study, we compared mitochondrial physiology and metabolism between P19SCs before/after differentiation and present a unique fingerprint of the association between mitochondrial activity, cell differentiation and stemness. In comparison with their differentiated counterparts, pluripotency of P19SCs was correlated with a strong glycolytic profile and decreased mitochondrial biogenesis and complexity: round, low-polarized and inactive mitochondria with a closed permeability transition pore. This decreased mitochondrial capacity increased their resistance against dichloroacetate. Thus, stimulation of mitochondrial function by growing P19SCs in glutamine/pyruvate-containing medium reduced their glycolytic phenotype, induced loss of pluripotent potential, compromised differentiation and became P19SCs sensitive to dichloroacetate. Because of the central role of this type of SCs in teratocarcinoma development, our findings highlight the importance of mitochondrial metabolism in stemness, proliferation, differentiation and chemoresistance. In addition, the present work suggests the regulation of mitochondrial metabolism as a tool for inducing cell differentiation in stem line therapies.