Calcium signaling in the liver

Purinergic signaling in liver disease: calcium signaling and induction of inflammation

Purinergic signaling regulates many metabolic functions and is implicated in liver physiology and pathophysiology. Liver functionality is modulated by ionotropic P2X and metabotropic P2Y receptors, specifically P2Y1, P2Y2, and P2Y6 subtypes, which physiologically exert their influence through calcium signaling, a key second messenger controlling glucose and fat metabolism in hepatocytes. Purinergic receptors, acting through calcium signaling, play an important role in a range of liver diseases. Ionotropic P2X receptors, such as the P2X7 subtype, and certain metabotropic P2Y receptors can induce aberrant intracellular calcium transients that impact normal hepatocyte function and initiate the activation of other liver cell types, including Kupffer and stellate cells. These P2Y- and P2X-dependent intracellular calcium increases are particularly relevant in hepatic disease states, where stellate and Kupffer cells respond with innate immune reactions to challenges, such as excess fat accumulation, chronic alcohol abuse, or infections, and can eventually lead to liver fibrosis. This review explores the consequences of excessive extracellular ATP accumulation, triggering calcium influx through P2X4 and P2X7 receptors, inflammasome activation, and programmed cell death. In addition, P2Y2 receptors contribute to hepatic steatosis and insulin resistance, while inhibiting the expression of P2Y6 receptors can alleviate alcoholic liver steatosis. Adenosine receptors may also contribute to fibrosis through extracellular matrix production by fibroblasts. Thus, pharmacological modulation of P1 and P2 receptors and downstream calcium signaling may open novel therapeutic avenues.

Tankyrase1/2 inhibitor XAV-939 reverts EMT and suggests that PARylation partially regulates aerobic activities in human hepatocytes and HepG2 cells

The maintenance of a highly functional metabolic epithelium in vitro is challenging. Metabolic impairments in primary human hepatocytes (PHHs) over time is primarily due to epithelial-to-mesenchymal transitioning (EMT). The immature hepatoma cell line HepG2 was used as an in vitro model to explore strategies for enhancing the hepatic phenotype. The phenotypic characterization includes measuring the urea cycle, lipid storage, tricarboxylic acid-related metabolites, reactive oxygen species, endoplasmic reticulum calcium efflux, mitochondrial membrane potentials, oxygen consumptions rate, and CYP450 biotransformation capacity. Expression studies were performed with transcriptomics, co-immunoprecipitation and proteomics. CRISPR/Cas9 was also employed to genetically engineer HepG2 cells. After confirming that PHHs develop an EMT phenotype, expression of tankyrase1/2 was found to increase over time. EMT was reverted when blocking tankyrases1/2-dependent poly-ADP-ribosylation (PARylation) activity, by biochemical and genetic perturbation. Wnt/β-catenin inhibitor XAV-939 blocks tankyrase1/2 and treatment elevated several oxygen-consuming reactions (electron-transport chain, OXHPOS, CYP450 mono-oxidase activity, phase I/II xenobiotic biotransformation, and prandial turnover), suggesting that cell metabolism was enhanced. Glutathione-dependent redox homeostasis was also significantly improved in the XAV-939 condition. Oxygen consumption rate and proteomics experiments in tankyrase1/2 double knockout HepG2 cells then uncovered PARylation as master regulator of aerobic-dependent cell respiration. Furthermore, novel tankyrase1/2-dependent PARylation targets, including mitochondrial DLST, and OGDH, were revealed. This work exposed a new mechanistic framework by linking PARylation to respiration and metabolism, thereby broadening the current understanding that underlies these vital processes. XAV-939 poses an immediate and straightforward strategy to improve aerobic activities, and metabolism, in (immature) cell cultures.

Unravelling the complexity of the mitochondrial Ca2+ uniporter: regulation, tissue specificity, and physiological implications

Calcium (Ca2+) signalling acts a pleiotropic message within the cell that is decoded by the mitochondria through a sophisticated ion channel known as the Mitochondrial Ca2+ Uniporter (MCU) complex. Under physiological conditions, mitochondrial Ca2+ signalling is crucial for coordinating cell activation with energy production. Conversely, in pathological scenarios, it can determine the fine balance between cell survival and death. Over the last decade, significant progress has been made in understanding the molecular bases of mitochondrial Ca2+ signalling. This began with the elucidation of the MCU channel components and extended to the elucidation of the mechanisms that regulate its activity. Additionally, increasing evidence suggests molecular mechanisms allowing tissue-specific modulation of the MCU complex, tailoring channel activity to the specific needs of different tissues or cell types. This review aims to explore the latest evidence elucidating the regulation of the MCU complex, the molecular factors controlling the tissue-specific properties of the channel, and the physiological and pathological implications of mitochondrial Ca2+ signalling in different tissues.

A deep learning-based approach for efficient detection and classification of local Ca²⁺ release events in Full-Frame confocal imaging

The release of Ca2+ ions from intracellular stores plays a crucial role in many cellular processes, acting as a secondary messenger in various cell types, including cardiomyocytes, smooth muscle cells, hepatocytes, and many others. Detecting and classifying associated local Ca2+ release events is particularly important, as these events provide insight into the mechanisms, interplay, and interdependencies of local Ca2+release events underlying global intracellular Ca2+signaling. However, time-consuming and labor-intensive procedures often complicate analysis, especially with low signal-to-noise ratio imaging data. Here, we present an innovative deep learning-based approach for automatically detecting and classifying local Ca2+ release events. This approach is exemplified with rapid full-frame confocal imaging data recorded in isolated cardiomyocytes. To demonstrate the robustness and accuracy of our method, we first use conventional evaluation methods by comparing the intersection between manual annotations and the segmentation of Ca2+ release events provided by the deep learning method, as well as the annotated and recognized instances of individual events. In addition to these methods, we compare the performance of the proposed model with the annotation of six experts in the field. Our model can recognize more than 75 % of the annotated Ca2+ release events and correctly classify more than 75 %. A key result was that there were no significant differences between the annotations produced by human experts and the result of the proposed deep learning model. We conclude that the proposed approach is a robust and time-saving alternative to conventional full-frame confocal imaging analysis of local intracellular Ca2+ events.

Dietary Amino Acids Promote Glucagon-like Hormone Release to Generate Novel Calcium Waves in Adipose Tissues

Nutrient sensing and the subsequent metabolic responses are fundamental functions of animals, closely linked to diseases such as type 2 diabetes and various obesity-related morbidities. Among different metabolic regulatory signals, cytosolic Ca2+ plays pivotal roles in metabolic regulation, including glycolysis, gluconeogenesis, and lipolysis. Recently, intercellular calcium waves (ICWs), the propagation of Ca2+ signaling through tissues, have been found in different systems to coordinate multicellular responses. Nevertheless, our understanding of how ICWs are modulated and operate within living organisms remains limited. In this study, we explore the real-time dynamics, both in organ culture and free-behaving animals, of ICWs in Drosophila larval and adult adipose tissues. We identified Adipokinetic hormone (AKH), the fly functional homolog of mammalian glucagon, as the key factor driving Ca2+ activities in adipose tissue. Interestingly, we found that AKH, which is released in a pulsatile manner into the circulating hemolymph from the AKH-producing neurosecretory cells (APCs) in the brain, stimulates ICWs in the larval fat by a previously unrecognized gap-junction-independent mechanism to promote lipolysis. In the adult fat body, however, gap-junction-dependent random ICWs are triggered by a presumably uniformly diffused AKH. This highlights the stage-specific interplay of hormone secretion, extracellular diffusion, and intercellular communication in the regulation of Ca2+ dynamics. Additionally, we discovered that specific dietary amino acids activate the APCs, leading to increased intracellular Ca2+ and subsequent AKH secretion. Altogether, our findings identify that dietary amino acids regulate the release of AKH peptides from the APCs, which subsequently stimulates novel gap-junction-independent ICWs in adipose tissues, thereby enhancing lipid metabolism.

Mitochondrial Calcium Waves by Electrical Stimulation in Cultured Hippocampal Neurons

Mitochondria are critical to cellular Ca2+ homeostasis via the sequestering of cytosolic Ca2+ in the mitochondrial matrix. Mitochondrial Ca2+ buffering regulates neuronal activity and neuronal death by shaping cytosolic and presynaptic Ca2+ or controlling energy metabolism. Dysfunction in mitochondrial Ca2+ buffering has been implicated in psychological and neurological disorders. Ca2+ wave propagation refers to the spreading of Ca2+ for buffering and maintaining the associated rise in Ca2+ concentration. We investigated mitochondrial Ca2+ waves in hippocampal neurons using genetically encoded Ca2+ indicators. Neurons transfected with mito-GCaMP5G, mito-RCaMP1h, and CEPIA3mt exhibited evidence of mitochondrial Ca2+ waves with electrical stimulation. These waves were observed with 200 action potentials at 40 Hz or 20 Hz but not with lower frequencies or fewer action potentials. The application of inhibitors of mitochondrial calcium uniporter and oxidative phosphorylation suppressed mitochondrial Ca2+ waves. However, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and N-methyl-d-aspartate receptor blockade had no effect on mitochondrial Ca2+ wave were propagation. The Ca2+ waves were not observed in endoplasmic reticula, presynaptic terminals, or cytosol in association with electrical stimulation of 200 action potentials at 40 Hz. These results offer novel insights into the mechanisms underlying mitochondrial Ca2+ buffering and the molecular basis of mitochondrial Ca2+ waves in neurons in response to electrical stimulation.

Numerical Analysis of Compound Biochemical Calcium Oscillations Process in Hepatocyte Cells

The hepatocyte cells regulate the wide range of liver function by moderating cellular activities such as lipid, protein metabolism, carbohydrate, and interact with other cells for proliferation and maintenance. In hepatocyte cells, the concentration of calcium uptake is quite extensive from various agonists such as activeG α ${G_\alpha}$ subunit, active phospholipase C, free calcium in the cytosol, and endoplasmic reticulum. The overproduction and degradation of calcium signals can cause homeostasis, liver inflammation, and liver diseases. The spatiotemporal behavior of calcium oscillation reveals the physiological role of these cellular entities in understanding the process of production and degradation. No computational attempt has been registered to date on the compound calcium regulation of these cellular entities including the memory of cells. Hence, the authors proposed a fractional order compartmental model that systematically simulates the exchange of calcium intake in cellular entities. The nonlinear equations of the rate of changes in the activeG α ${G_\alpha}$ subunit, active phospholipase C, free calcium in the cytosol, and endoplasmic reticulum are coupled to form a nonlinear fractional order initial value problem. The existence and uniqueness, stability analysis of the model is performed that validate the theoretical results and explore the dynamic behaviour of calcium oscillation in each compartment.

Sensing of dietary amino acids and regulation of calcium dynamics in adipose tissues through Adipokinetic hormone in Drosophila

Nutrient sensing and the subsequent metabolic responses are fundamental functions of animals, closely linked to diseases such as type 2 diabetes and various obesity-related diseases. Drosophila melanogaster has emerged as an excellent model for investigating metabolism and its associated disorders. In this study, we used live-cell imaging to demonstrate that the fly functional homolog of mammalian glucagon, Adipokinetic hormone (AKH), secreted from AKH hormone-producing cells (APCs) in the corpora cardiaca, stimulates intracellular Ca 2+ waves in the larval fat body/adipose tissue to promote lipid metabolism. Further, we show that specific dietary amino acids activate the APCs, leading to increased intracellular Ca 2+ and subsequent AKH secretion. Finally, a comparison of Ca 2+ dynamics in larval and adult fat bodies revealed different mechanisms of regulation, highlighting the interplay of pulses of AKH secretion, extracellular diffusion of the hormone, and intercellular communication through gap junctions. Our study underscores the suitability of Drosophila as a powerful model for exploring real-time nutrient sensing and inter-organ communication dynamics.

Effects of Extracellular Calcium Concentration on Hepatic Ischemia-Reperfusion Injury in a Rat Model

OBJECTIVES

Hypocalcemia is frequently identified during liver transplant. However, supplementation of extracellular calcium could induce increased intracellular calcium concentration, as a potential factor for injury to the liver graft. We evaluated the effects of regulating extracellular calcium concentrations on hepatic ischemia-reperfusion injury.

MATERIALS AND METHODS

We randomly divided 24 Sprague-Dawley rats into 3 groups: group C received normal saline (n = 8), group L received citrate to induce hypocalcemia (n = 8), and group L-Co received citrate followed by calcium gluconate to ameliorate hypocalcemia (n = 8). Liver enzyme levels and extracellular calcium were measured before surgery, 1 hour after ischemia, and 2 hours after reperfusion. The primary outcome was liver enzyme levels measured 2 hours after reperfusion. In addition, we evaluated intracellular calcium levels, lactate dehydrogenase activity, and histopathological results in liver tissue.

RESULTS

Three groups demonstrated significant differences in extracellular calcium concentrations, but intracellular calcium concentrations in liver tissue were not significantly different. Group L showed significantly lower mean arterial pressure than other groups at 1 hour after ischemia (93.6 ± 20.8 vs 69.4 ± 14.2 vs 86.6 ± 10.4 mmHg; P = .02, for group C vs L vs L-Co, respectively). At 2 hours after reperfusion, group L showed significantly higher liver enzymes than other groups (aspartate aminotransferase 443.0 ± 353.2 vs 952.3 ± 94.8 vs 502.4 ± 327.3 U/L, P = .01; and alanine aminotransferase 407.9 ± 406.5 vs 860.6 ± 210.9 vs 333.9 ± 304.2 U/L, P = .02; for group C vs L vs L-Co, respectively). However, no significant difference was shown in lactate dehydrogenase and histological liver injury grade.

CONCLUSIONS

Administering calcium to rats with hypocalcemia did not increase intracellular calcium accumulation but instead resulted in less hepatic injury compared with rats with low extracellular calcium concentrations in this rat model study.

Numerical simulation of calcium dynamics dependent ATP degradation, IP3 and NADH production due to obesity in a hepatocyte cell

Calcium (Ca[Formula: see text]) signals have a crucial role in regulating various processes of almost every cell to maintain its structure and function. Calcium dynamics has been studied in various cells including hepatocytes by many researchers, but the mechanisms of calcium signals involved in regulation and dysregulation of various processes like ATP degradation rate, IP[Formula: see text] and NADH production rate respectively in normal and obese cells are still poorly understood. In this paper, a reaction diffusion equation of calcium is employed to propose a model of calcium dynamics by coupling ATP degradation rate, IP[Formula: see text] and NADH production rate in hepatocyte cells under normal and obese conditions. The processes like source influx, buffer, endoplasmic reticulum (ER), mitochondrial calcium uniporters (MCU) and Na[Formula: see text]/Ca[Formula: see text] exchanger (NCX) have been incorporated in the model. Linear finite element method is used along spatial dimension, and Crank-Nicolson method is used along temporal dimension for numerical simulation. The results have been obtained for the normal hepatocyte cells and for cells due to obesity. The comparative study of these results reveal significant difference caused due to obesity in Ca[Formula: see text] dynamics as well as in ATP degradation rate, IP[Formula: see text] and NADH production rate.

Selenium deficiency caused hepatitis in chickens via the miR-138-5p/SelM/ROS/Ca2+ overload pathway induced by hepatocyte necroptosis

Selenoprotein M (SelM), a key thioredoxin like enzyme in the endoplasmic reticulum (ER), is closely related to hepatocyte degeneration. However, the role of miR-138-5p/SelM and necroptosis in chicken SelM-deficient hepatitis and the specific biological mechanism of liver inflammation caused by SelM deficiency have not been elucidated. We established an in vivo chicken liver Se deficiency model by feeding a low-Se diet. The miR-138-5p knockdown and overexpression models and SelM knockdown models were established in LMH cells for an in vitro study. Transmission electron microscopy, H&E staining, Fluo4-AM/ER staining, and flow cytometry were used to detect the morphological changes in chicken liver tissue and the expression changes of necroptosis and inflammation in chicken liver cells. We observed that Se deficiency resulted in liver inflammation, up-regulation of miR-138-5p expression and down-regulation of SelM expression in chickens. Oxidative stress, Ca2+ overload, energy metabolism disorder and necroptosis occurred in chicken liver tissue. Importantly, ROS and the Ca2+ inhibitor could effectively alleviate the energy metabolism disorder, necroptosis and inflammatory cytokine secretion caused by miR-138-5p overexpression and SelM knockdown in LMH cells. In conclusion, selenium deficiency causes hepatitis by upregulating miR-138-5p targeting SelM. Our research findings enrich our knowledge about the biological functions of SelM and provide a theoretical basis for the lack of SelM leading to liver inflammation in chickens.

Arachidonic acid metabolism in health and disease

Arachidonic acid (AA), an n-6 essential fatty acid, is a major component of mammalian cells and can be released by phospholipase A2. Accumulating evidence indicates that AA plays essential biochemical roles, as it is the direct precursor of bioactive lipid metabolites of eicosanoids such as prostaglandins, leukotrienes, and epoxyeicosatrienoic acid obtained from three distinct enzymatic metabolic pathways: the cyclooxygenase pathway, lipoxygenase pathway, and cytochrome P450 pathway. AA metabolism is involved not only in cell differentiation, tissue development, and organ function but also in the progression of diseases, such as hepatic fibrosis, neurodegeneration, obesity, diabetes, and cancers. These eicosanoids are generally considered proinflammatory molecules, as they can trigger oxidative stress and stimulate the immune response. Therefore, interventions in AA metabolic pathways are effective ways to manage inflammatory-related diseases in the clinic. Currently, inhibitors targeting enzymes related to AA metabolic pathways are an important area of drug discovery. Moreover, many advances have also been made in clinical studies of AA metabolic inhibitors in combination with chemotherapy and immunotherapy. Herein, we review the discovery of AA and focus on AA metabolism in relation to health and diseases. Furthermore, inhibitors targeting AA metabolism are summarized, and potential clinical applications are discussed.

Calcium signalling in hepatic metabolism: Health and diseases

The flexibility between the wide array of hepatic functions relies on calcium (Ca2+) signalling. Indeed, Ca2+ is implicated in the control of many intracellular functions as well as intercellular communication. Thus, hepatocytes adapt their Ca2+ signalling depending on their nutritional and hormonal environment, leading to opposite cellular functions, such as glucose storage or synthesis. Interestingly, hepatic metabolic diseases, such as obesity, type 2 diabetes and non-alcoholic fatty liver diseases, are associated with impaired Ca2+ signalling. Here, we present the hepatocytes' toolkit for Ca2+ signalling, complete with regulation systems and signalling pathways activated by nutrients and hormones. We further discuss the current knowledge on the molecular mechanisms leading to alterations of Ca2+ signalling in hepatic metabolic diseases, and review the literature on the clinical impact of Ca2+-targeting therapeutics.

Lack of Stim2 Affects Vision-Dependent Behavior and Sensitivity to Hypoxia

Stromal interaction molecules (STIMs) are endoplasmic reticulum-resident proteins that regulate Ca2+ homeostasis and signaling by store-operated calcium entry (SOCE). The different properties and functions of STIM1 and STIM2 have been described mostly based on work in vitro. STIM2 knockout mice do not survive until adulthood. Therefore, we generated and characterized stim2a and stim2b double-knockout zebrafish. The (stim2a;stim2b)-/- zebrafish did not have any apparent morphological phenotype. However, RNA sequencing revealed 1424 differentially expressed genes. One of the most upregulated genes was annexin A3a, which is a marker of activated microglia. This corresponded well to an increase in Neutral Red staining in the in vivo imaging of the (stim2a;stim2b)-/- zebrafish brain. The lack of Stim2 decreased zebrafish survival under low oxygen conditions. Behavioral tests, such as the visual-motor response test and dark-light preference test, indicated that (stim2a;stim2b)-/- larvae might have problems with vision. This was consistent with the downregulation of many genes that are related to light perception. The periodic acid-Schiff staining of retina sections from adult zebrafish revealed alterations of the stratum pigmentosum, suggesting the involvement of a Stim2-dependent process in visual perception. Altogether, these data reveal new functions for Stim2 in the nervous system.

A modular analysis of bile canalicular function and its implications for cholestasis

Hepatocytes produce bile components and secrete them into a lumen, known as a bile canaliculus, that is formed by the apical membranes of adjoining hepatocytes. Bile canaliculi merge to form tubular structures that subsequently connect to the canal of Hering and larger intra- and extrahepatic bile ducts formed by cholangiocytes, which modify bile and enable flow through the small intestine. The major functional requirements for bile canaliculi are the maintenance of canalicular shape to preserve the blood-bile barrier and regulation of bile flow. These functional requirements are mediated by functional modules, primarily transporters, the cytoskeleton, cell-cell junctions, and mechanosensing proteins. I propose here that bile canaliculi behave as robust machines whereby the functional modules act in a coordinated manner to perform the multistep task of maintaining canalicular shape and bile flow. Cholestasis, the general term for aberrant bile flow, stems from drug/toxin-induced or genetic dysregulation of one or more of the protein components in the functional modules. Here, I discuss the interactions between components of the various functional modules in bile canaliculi and describe how these functional modules regulate canalicular morphology and function. I use this framework to provide a perspective on recent studies of bile canalicular dynamics.

Combined use of biomarkers to assess the impact of untreated wastewater from the Danube River, Serbia

In this study a battery of bioassays, both in vivo (metals and metalloids concentrations, erythrocyte morphometry, comet assay, micronucleus assay, and histopathological analyses) on vimba bream Vimba vimba (L., 1758) and white bream Blicca bjoerkna (L., 1758), and in vitro (treatment of HepG2 cells with native water samples) was applied to assess the harmful potential of untreated wastewater. Faecal indicator bacteria were quantified to assess the microbiological water quality. Vimba bream had significantly higher Fe concentrations in both liver and muscle, while white bream had higher Ca and Cu concentrations in liver. Vimba bream had a significantly higher level of DNA damage in both liver and blood cells, in comparison to white bream. Low levels of micronucleus and nuclear abnormalities were observed in both species. Erythrocytes morphometry did not show significant interspecific differences. Histopathological analyses revealed a similar response of the studied species, with a significantly higher presence of ceroid pigments in the liver of vimba bream. Treatment of HepG2 cells revealed the high genotoxic potential of water downstream of the discharge point. The results of this study clearly demonstrate the importance of effect-based monitoring, in order to enforce more efficient management of natural resources and implementation of wastewater treatment systems.

Vanillic acid mitigates hyperinsulinemia induced ER stress mediated altered calcium homeostasis, MAMs distortion and surplus lipogenesis in HepG2 cells

Hyperinsulinemia (HI) induced insulin resistance (IR) and associated pathologies are the burning and unsolvable issues in diabetes treatment. The cellular, molecular and biochemical events associated with HI are not yet elucidated. Similarly, no focused research on designing therapeutic strategies with natural products for attenuation of HI are seen in literature. Keeping this in mind we planned the present study to evaluate the alterations occurring at ER/Ca²⁺ homeostasis/mitochondria associated endoplasmic reticulum membranes (MAMs) in HepG2 cells during HI and to evaluate the possible beneficial effect of vanillic acid (VA) to mitigate the complications. An in vitro model of HI was established by treating HepG2 cells with human insulin (1 μM) for 24 h. Then, ER stress, Ca²⁺ homeostasis, MAMs, IR and hepatic lipogenesis were studied at protein level. Various proteins critical to ER, Ca²⁺ homeostasis and MAMs such as p-IRE-1α, ATF6, p-PERK, p-eIF2α, CHOP, XBP1, p-CAMKII, InsP3R, SERCA, JNK, GRP78, VDAC, Cyp D, GRP75, MFN2, PTEN and mTORC were studied and found altered significantly causing ER stress, defect in Ca²⁺ movements and distortion of MAMs. The decreased expression of IRS2 and an unaltered expression of IRS1 confirmed the development of selective insulin resistance in hepatocytes during HI and this was the crucial factor for the progression of the hepatic lipid accumulation. We found simultaneous treatment of VA is beneficial up to a certain extent to protect HepG2 cells from the adverse effect of HI via its antioxidant, antilipogenic, mitochondrial and ER protection properties.

In vivo imaging of calcium dynamics in zebrafish hepatocytes

BACKGROUND AND AIMS

Hepatocytes were the first cell type for which oscillations of cytoplasmic calcium levels in response to hormones were described. Since then, investigation of calcium dynamics in liver explants and culture has greatly increased our understanding of calcium signaling. A bottleneck, however, exists in observing calcium dynamics in a noninvasive manner because of the optical inaccessibility of the mammalian liver. Here, we aimed to take advantage of the transparency of the zebrafish larvae to image hepatocyte calcium dynamics in vivo at cellular resolution.

APPROACH AND RESULTS

We developed a transgenic model expressing a calcium sensor, GCaMP6s, specifically in zebrafish hepatocytes. Using this, we provide a quantitative assessment of intracellular calcium dynamics during multiple contexts, including growth, feeding, ethanol-induced stress, and cell ablation. Specifically, we show that synchronized calcium oscillations are present in vivo , which are lost upon starvation. Starvation induces lipid accumulation in the liver. Feeding recommences calcium waves in the liver, but in a spatially restricted manner, as well as resolves starvation-induced hepatic steatosis. By using a genetically encoded scavenger for calcium, we show that dampening of calcium signaling accelerates the accumulation of starvation-related lipid droplets in the liver. Furthermore, ethanol treatment, as well as cell ablation, induces calcium flux, but with different dynamics. The former causes asynchronous calcium oscillations, whereas the latter leads to a single calcium spike.

CONCLUSIONS

We demonstrate the presence of oscillations, waves, and spikes in vivo . Calcium waves are present in response to nutrition and negatively regulate starvation-induced accumulation of lipid droplets.

Genetic polymorphisms of Ca2+ transport proteins and molecular chaperones in mitochondria-associated endoplasmic reticulum membrane and non-alcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is recognized to be closely associated with endoplasmic reticulum stress and mitochondrial dysfunction, while previous studies have emphasized the important role of calcium homeostasis from the mitochondria-associated endoplasmic reticulum membrane (MAM) in the endoplasmic reticulum and mitochondria. This article will assess the association between genetic polymorphisms of Ca2+ transport proteins and molecular chaperones in MAM and NAFLD risk.

Methods

A case-control study was conducted in a community of Nanjing, China during April to December 2020. 2701 subjects were enrolled and genotyped for 6 genetic variants in HSPA5 and ITPR2 genes. Logistic regression analysis was used to assess impact of these variants on NAFLD risk.

Results

After adjusting for age, gender, total cholesterol and glucose, we identified that HSPA5 rs12009 variant genotypes (recessive model: OR= 0.801, 95% CI= 0.652-0.986, P= 0.036), rs430397 variant genotypes (recessive model: OR= 0.546, 95% CI= 0.314-0.950, P= 0.032), and ITPR2 rs11048570 variant genotypes (recessive model: OR= 0.673, 95% CI= 0.453-0.999, P= 0.049) were associated with a reduced risk of NAFLD. Multivariate stepwise regression analysis indicated that gender, glucose, body mass index, triglycerides and favorable alleles were independent influencers of NAFLD (all P< 0.05). The area under the receiver operating characteristic curve was 0.764 (95% CI= 0.745-0.783, P< 0.001).

Conclusion

The variant genotypes of Ca2+ transport-associated genes HSPA5 (rs12009 and rs430397) and ITPR2 (rs11048570) might contribute to the reduction of the NAFLD risk in Chinese Han population, which can provide new insight into NAFLD pathogenesis.

Involvement of oxidative species in cyclosporine-mediated cholestasis

Cyclosporine is an established medication for the prevention of transplant rejection. However, adverse consequences such as nephrotoxicity, hepatotoxicity, and cholestasis have been associated with prolonged usage. In cyclosporine-induced obstructive and chronic cholestasis, for example, the overproduction of oxidative stress is significantly increased. Additionally, cyclosporine exerts adverse effects on liver function and redox balance responses in treated rats, as evidenced by its increasing levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), and bilirubin while also decreasing the levels of glutathione and NADPH. Cyclosporine binds to cyclophilin to produce its therapeutic effects, and the resulting complex inhibits calcineurin, causing calcium to accumulate in the mitochondria. Accumulating calcium with concomitant mitochondrial abnormalities induces oxidative stress, perturbation in ATP balance, and failure of calcium pumps. Also, cyclosporine-induced phagocyte oxidative stress generation via the interaction of phagocytes with Toll-like receptor-4 has been studied. The adverse effect of cyclosporine may be amplified by the release of mitochondrial DNA, mediated by oxidative stress-induced mitochondrial damage. Given the uncertainty surrounding the mechanism of cyclosporine-induced oxidative stress in cholestasis, we aim to illuminate the involvement of oxidative stress in cyclosporine-mediated cholestasis and also explore possible strategic interventions that may be applied in the future.

Cellular and molecular mechanisms of NiONPs toxicity on eel hepatocytes HEPA-E1: An illustration of the impact of Ni release from mining activity in New Caledonia

Anthropic activities such as open pit mining, amplify the natural erosion of metals contained in the soils, particularly in New Caledonia, leading to atmospheric emission of nickel oxide nanoparticles (NiONPs). These particles are produced during extraction end up in aquatic ecosystems through deposition or leaching in the rivers. Despite alarming freshwater Ni concentrations, only few studies have focused on the cellular and molecular mechanisms of NiONPs toxicity on aquatic organisms and particularly on eels. Those fish are known to be sensitive to metal contamination, especially their liver, which is a key organ for lipid metabolism, detoxification and reproduction. The objective of this study was to assess in vitro the cytotoxic effects of NiONPs on Anguilla japonica hepatocytes, HEPA-E1. HEPA-E1 were exposed to NiONPs (0.5-5 μg/cm²) for 4 or 24 h. Several endpoints were studied: (i) viability, (ii) ROS production, SOD activity and selected anti-oxidant genes expression, (iii) inflammation, (iv) calcium signalling, (v) mitochondrial function and (vi) apoptosis. The results evidenced that NiONPs induce a decrease of cell viability and an increase in oxidative stress with a significant superoxide anion production. An increase of mitochondrial calcium concentration and a decrease of mitochondrial membrane potential were observed, leading to apoptosis. These results underline the potential toxic impact of NiONPs on eels living in mining areas. Therefore, eel exposure to NiONPs can affect their migration and reproduction in New Caledonia.

Cross Talk Between Insulin and Glucagon Receptor Signaling in the Hepatocyte

While the consumption of external energy (i.e., feeding) is essential to life, this action induces a temporary disturbance of homeostasis in an animal. A primary example of this effect is found in the regulation of glycemia. In the fasted state, stored energy is released to maintain physiological glycemic levels. Liver glycogen is liberated to glucose, glycerol and (glucogenic) amino acids are used to build new glucose molecules (i.e., gluconeogenesis), and fatty acids are oxidized to fuel long-term energetic demands. This regulation is driven primarily by the counterregulatory hormones epinephrine, growth hormone, cortisol, and glucagon. Conversely, feeding induces a rapid influx of diverse nutrients, including glucose, that disrupt homeostasis. Consistently, a host of hormonal and neural systems under the coordination of insulin are engaged in the transition from fasting to prandial states to reduce this disruption. The ultimate action of these systems is to appropriately store the newly acquired energy and to return to the homeostatic norm. Thus, at first glance it is tempting to assume that glucagon is solely antagonistic regarding the anabolic effects of insulin. We have been intrigued by the role of glucagon in the prandial transition and have attempted to delineate its role as beneficial or inhibitory to glycemic control. The following review highlights this long-known yet poorly understood hormone.

Cellular and transcriptional heterogeneity in the intrahepatic biliary epithelium

Epithelial tissues comprise heterogeneous cellular subpopulations, which often compartmentalize specialized functions like absorption and secretion to distinct cell types. In the liver, hepatocytes and biliary epithelial cells (BECs; also called cholangiocytes) are the two major epithelial lineages and play distinct roles in (1) metabolism, protein synthesis, detoxification, and (2) bile transport and modification, respectively. Recent technological advances, including single cell transcriptomic assays, have shed new light on well-established heterogeneity among hepatocytes, endothelial cells, and immune cells in the liver. However, a "ground truth" understanding of molecular heterogeneity in BECs has remained elusive, and the field currently lacks a set of consensus biomarkers for identifying BEC subpopulations. Here, we review long-standing definitions of BEC heterogeneity as well as emerging studies that aim to characterize BEC subpopulations using next generation single cell assays. Understanding cellular heterogeneity in the intrahepatic bile ducts holds promise for expanding our foundational mechanistic knowledge of BECs during homeostasis and disease.

Calcium influx and spermatogenesis in the testis and liver enzyme activities in the zebrafish are rapidly modulated by the calcium content of the water

This study investigated the effects of varying environmental Ca²⁺ concentrations on the influx of Ca²⁺ to the testis, testicular morphology, and liver enzymes in the zebrafish. Adult zebrafish (Danio rerio) were held in water containing low (0.02 mM), control (0. 7 mM) or high (2 mM) Ca²⁺ concentrations for 12 h. Testes were then incubated in vitro with 0.1 μCi/mL ⁴⁵Ca²⁺ to measure Ca²⁺ influx at 30 and 60 min and qualitative and quantitative testicular histological analyses were conducted. In addition, activity of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transpeptidase (GGT), enzymes that indicate tissue damage, were evaluated in the liver. The testes from zebrafish exposed in vivo to low (0.02 mM) and high (2 mM) Ca²⁺ content water had a higher Ca²⁺ influx than the control group after 30 min of incubation, and at 60 min (high Ca²⁺ group only). There were morphological changes in the testes from the low and high Ca²⁺ groups including spermatozoa distributed in dense agglomerates and apoptotic cells. Furthermore, zebrafish exposed to high Ca²⁺ containing water had an increased density of haploid cells (spermatids and spermatozoa). In addition, both low and high Ca²⁺ water affected liver function by increasing ALT and GGT activities. Collectively, these studies show that alterations in calcium homeostasis in the testis, stimulation of the spermatogenic wave and hepatic injury were rapid responses to changes in the concentration of Ca²⁺ in the water.

Liver fat metabolism of broilers regulated by Bacillus amyloliquefaciens TL via stimulating IGF-1 secretion and regulating the IGF signaling pathway

Bacillus amyloliquefaciens TL (B.A-TL) is well-known for its capability of promoting protein synthesis and lipid metabolism, in particular, the abdominal fat deposition in broilers. However, the underlying molecular mechanism remains unclear. In our study, the regulations of lipid metabolism of broilers by B.A-TL were explored both in vivo and in vitro. The metabolites of B.A-TL were used to simulate in vitro the effect of B.A-TL on liver metabolism based on the chicken hepatocellular carcinoma cell line (i.e., LMH cells). The effects of B.A-TL on lipid metabolism by regulating insulin/IGF signaling pathways were investigated by applying the signal pathway inhibitors in vitro. The results showed that the B.A-TL metabolites enhanced hepatic lipid synthesis and stimulated the secretion of IGF-1. The liver transcriptome analysis revealed the significantly upregulated expressions of four genes (SI, AMY2A, PCK1, and FASN) in the B.A-TL treatment group, mainly involved in carbohydrate digestion and absorption as well as biomacromolecule metabolism, with a particularly prominent effect on fatty acid synthase (FASN). Results of cellular assays showed that B.A-TL metabolites were involved in the insulin/IGF signaling pathway, regulating the expressions of lipid metabolism genes (e.g., FASN, ACCα, LPIN, and ACOX) and the FASN protein, ultimately regulating the lipid metabolism via the IGF/PI3K/FASN pathway in broilers.

Identification of proteome markers for drug-induced liver injury in zebrafish embryos

The zebrafish embryo (ZFE) is a promising alternative non-rodent model in toxicology, and initial studies suggested its applicability in detecting hepatic responses related to drug-induced liver injury (DILI). Here, we hypothesize that detailed analysis of underlying mechanisms of hepatotoxicity in ZFE contributes to the improved identification of hepatotoxic properties of compounds and to the reduction of rodents used for hepatotoxicity assessment. ZFEs were exposed to nine reference hepatotoxicants, targeted at induction of steatosis, cholestasis, and necrosis, and effects compared with negative controls. Protein profiles of the individual compounds were generated using LC-MS/MS. We identified differentially expressed proteins and pathways, but as these showed considerable overlap, phenotype-specific responses could not be distinguished. This led us to identify a set of common hepatotoxicity marker proteins. At the pathway level, these were mainly associated with cellular adaptive stress-responses, whereas single proteins could be linked to common hepatotoxicity-associated processes. Applying several stringency criteria to our proteomics data as well as information from other data sources resulted in a set of potential robust protein markers, notably Igf2bp1, Cox5ba, Ahnak, Itih3b.2, Psma6b, Srsf3a, Ces2b, Ces2a, Tdo2b, and Anxa1c, for the detection of adverse responses.

Inositol 1,4,5-trisphosphate receptor type 3 is involved in resistance to apoptosis and maintenance of human hepatocellular carcinoma

The expression of the inositol 1,4,5-trisphosphate receptor type 3 (ITRP3) in hepatocytes is a common event in the pathogenesis of hepatocellular carcinoma (HCC), regardless of the type of underlying liver disease. However, it is not known whether ITPR3 expression in hepatocytes is involved in tumor maintenance. The aim of the present study was to determine whether there is an association between ITPR3 expression and clinical and morphological parameters using HCC samples obtained from liver explants from patients (n=53) with different etiologies of underlying chronic liver disease (CLD). ITPR3 expression, mitosis and apoptosis were analyzed in human liver samples by immunohistochemistry. Clinical and event-free survival data were combined to assess the relationship between ITPR3 and liver cancer growth in patients. RNA sequencing analysis was performed to identify apoptotic genes altered by ITPR3 expression in a liver tumor cell line. ITPR3 was highly expressed in HCC tumor cells relative to adjacent CLD tissue and healthy livers. There was an inverse correlation between ITPR3 expression and mitotic and apoptotic indices in HCC, suggesting that ITPR3 contributed to the maintenance of HCC by promoting resistance to apoptosis. This was confirmed by the upregulation of CTSB, CHOP and GADD45, genes involved in the apoptotic pathway in HCC. The expression of ITPR3 in the liver may be a promising prognostic marker of HCC.

Emerging Roles of Calcium Signaling in the Development of Non-Alcoholic Fatty Liver Disease

The liver plays a central role in energy metabolism. Dysregulated hepatic lipid metabolism is a major cause of non-alcoholic fatty liver disease (NAFLD), a chronic liver disorder closely linked to obesity and insulin resistance. NAFLD is rapidly emerging as a global health problem with currently no approved therapy. While early stages of NAFLD are often considered benign, the disease can progress to an advanced stage that involves chronic inflammation, with increased risk for developing end-stage disease including fibrosis and liver cancer. Hence, there is an urgent need to identify potential pharmacological targets. Ca²⁺ is an essential signaling molecule involved in a myriad of cellular processes. Intracellular Ca²⁺ is intricately compartmentalized, and the Ca²⁺ flow is tightly controlled by a network of Ca²⁺ transport and buffering proteins. Impaired Ca²⁺ signaling is strongly associated with endoplasmic reticulum stress, mitochondrial dysfunction and autophagic defects, all of which are etiological factors of NAFLD. In this review, we describe the recent advances that underscore the critical role of dysregulated Ca²⁺ homeostasis in lipid metabolic abnormalities and discuss the feasibility of targeting Ca²⁺ signaling as a potential therapeutic approach.

A Spatial Model of Hepatic Calcium Signaling and Glucose Metabolism Under Autonomic Control Reveals Functional Consequences of Varying Liver Innervation Patterns Across Species

Rapid breakdown of hepatic glycogen stores into glucose plays an important role during intense physical exercise to maintain systemic euglycemia. Hepatic glycogenolysis is governed by several different liver-intrinsic and systemic factors such as hepatic zonation, circulating catecholamines, hepatocellular calcium signaling, hepatic neuroanatomy, and the central nervous system (CNS). Of the factors regulating hepatic glycogenolysis, the extent of lobular innervation varies significantly between humans and rodents. While rodents display very few autonomic nerve terminals in the liver, nearly every hepatic layer in the human liver receives neural input. In the present study, we developed a multi-scale, multi-organ model of hepatic metabolism incorporating liver zonation, lobular scale calcium signaling, hepatic innervation, and direct and peripheral organ-mediated communication between the liver and the CNS. We evaluated the effect of each of these governing factors on the total hepatic glucose output and zonal glycogenolytic patterns within liver lobules during simulated physical exercise. Our simulations revealed that direct neuronal stimulation of the liver and an increase in circulating catecholamines increases hepatic glucose output mediated by mobilization of intracellular calcium stores and lobular scale calcium waves. Comparing simulated glycogenolysis between human-like and rodent-like hepatic innervation patterns (extensive vs. minimal) suggested that propagation of calcium transients across liver lobules acts as a compensatory mechanism to improve hepatic glucose output in sparsely innervated livers. Interestingly, our simulations suggested that catecholamine-driven glycogenolysis is reduced under portal hypertension. However, increased innervation coupled with strong intercellular communication can improve the total hepatic glucose output under portal hypertension. In summary, our modeling and simulation study reveals a complex interplay of intercellular and multi-organ interactions that can lead to differing calcium dynamics and spatial distributions of glycogenolysis at the lobular scale in the liver.

Molecular targets regulating endoplasmic reticulum-mitochondria crosstalk for NAFLD treatment

Non-alcoholic fatty liver disease (NAFLD) as the most common chronic liver disease poses a significant impact on public healthcare and economic risk worldwide. As a multifactorial disease, NAFLD is usually associated with many comorbidities such as obesity, insulin resistance, hypertension, hyperlipidemia, diabetes, and cardiovascular disease. Without effectively preventive intervention, the advanced stage of NAFLD, non-alcoholic steatohepatitis (NASH), can progress to cirrhosis and hepatocellular carcinoma (HCC). However, there is no approved therapeutic treatment. Excessive fat accumulation in the liver is the hallmark of NAFLD, which can lead to mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Dysfunction of two organelles also induces the upregulation of reactive oxygen species (ROS), activation of the unfolded protein response (UPR), and disruption of calcium transport, which promote NAFLD progression. Herein, this review summarized the current understanding of the roles of mitochondrial dysfunction and ER stress in the pathogenesis of NAFLD. Specifically, this review focused on the key molecules associated with the ER-mitochondria communication and different treatment options by targeting ER stress and mitochondrial dysfunction to treat NAFLD or NASH. Clinical trials to evaluate the therapeutic efficacy of representative agents, such as natural products, metabolites, and modulators of stress, have been reviewed and analyzed. Overall, recent findings suggest that targeting ER stress and mitochondrial dysfunction holds a promise for NAFLD treatment.

Cypermethrin induces Sertoli cell apoptosis through mitochondrial pathway associated with calcium

Cypermethrin, one kind of pyrethroid pesticides, has been shown to act as endocrine-disrupting chemicals (EDCs). The purpose of this study was to explore the roles of Sertoli cell apoptosis through mitochondrial pathway associated with calcium (Ca²⁺) in cypermethrin-induced male reproductive toxicology. The mouse Sertoli cells TM4 were cultured with 0 μM, 10 μM, 20 μM, 40 μM and 80 μM of cypermethrin. We used flow cytometry, Fluo-4 AM, western blot and JC-1 Assay Kit to examine apoptosis, intracellular Ca²⁺, expressions of mitochondrial apoptotic pathway-related proteins and mitochondrial membrane potential. We found cypermethrin increased apoptosis rate of TM4 cells significantly and with a significant increase in intracellular Ca²⁺ concentration. Cypermethrin significantly decreased the protein expressions of cytosolic B-cell lymphoma-2 (Bcl-2) and mitochondrial cytochrome c (Cyt-c). The protein expressions of cytosolic Bcl-2-associated x (Bax), Cyt-c, cleaved caspase-3, calmodulin (CaM), Ca²⁺/CaM-dependent protein kinases II (CaMKII) and phosphorylated CaMKII were increased significantly in cypermethrin-exposed TM4 cells. Cypermethrin decreased mitochondrial membrane potential significantly. Then, Bcl-2 family and Ca²⁺/CaM/CaMKII pathway participate in cypermethrin-induced homeostasis. Ca²⁺ overload activates mitochondrial pathway by increasing permeability of mitochondrial membrane and decreasing mitochondrial membrane potential. We suggest cypermethrin induces Sertoli cell apoptosis involving mitochondrial pathway associated with Ca²⁺ regulated by Bcl-2 family and Ca²⁺/CaM/CaMKII pathway. The study provides a new insight into mechanisms involved in cypermethrin-induced male reproductive toxicology.

Polystyrene microplastics trigger hepatocyte apoptosis and abnormal glycolytic flux via ROS-driven calcium overload

Human health could be affected by the spread of microplastics in the food chain. Our previous research has indicated that microplastics accumulated in the liver and subsequently induce oxidative damage. However, the molecular events linking oxidative stress to calcium ion (Ca²⁺) signaling during microplastics stress remains elusive. The present research demonstrated that up-regulation of Orai 1 and stromal interaction molecule 1 (Stim1) expression participated in the microplastics-triggered Ca²⁺ overload, accompanied with the down-regulation of arcoplasmic reticulum Ca²⁺ ATPase (SERCA). However, when the protein expression of Stim1/SERCA is restored, microplastics-induced Ca²⁺ overload is ameliorated. Further analysis revealed that inhibiting the microplastics-induced Ca²⁺ overload was integral to prevent hepatocyte apoptosis and S phase arrest in the L02 hepatocyte. Simultaneously, we observed that inhibiting microplastics-evoked reactive oxygen species (ROS) could alleviate Ca²⁺ overload via reversing expression of store-operated Ca²⁺ channels (SOCs). These changes were accompanied by restoration of glycolytic flux, likely due to the regulation of AMP-activated protein kinase (AMPK)-PGC-1α signaling. Our findings highlight the role of SOCs at microplastics-evoked ROS in Ca²⁺ overload, and its a crucial step in triggering hepatocyte death. Collectively, this study reveals a regulatory paradigm that links ROS with AMPK and Ca²⁺ signaling in microplastics-triggered hepatotoxicity.

Transcriptional and epigenetic landscape of Ca2+-signaling genes in hepatocellular carcinoma

Calcium (Ca2+) signaling has a major role in regulating a wide range of cellular mechanisms, including gene expression, proliferation, metabolism, cell death, muscle contraction, among others. Recent evidence suggests that ~ 1600 genes are related to the Ca2+ signaling. Some of these genes' expression is altered in several pathological conditions, including different cancer types, and epigenetic mechanisms are involved. However, their expression and regulation in hepatocellular carcinoma (HCC) and the liver are barely known. Here, we aimed to explore the expression of genes involved in the Ca2+-signaling in HCC, liver regeneration, and hepatocyte differentiation, and whether their expression is regulated by epigenetic mechanisms such as DNA methylation and histone posttranslational modifications (HPM). Results show that several Ca2+-signaling genes' expression is altered in HCC samples; among these, a subset of twenty-two correlate with patients' survival. DNA methylation correlates with eight of these genes' expression, and Guadecitabine, a hypomethylating agent, regulates the expression of seven down-regulated and three up-regulated genes in HepG2 cells. The down-regulated genes displayed a marked decrease of euchromatin histone marks, whereas up-regulated genes displayed gain in these marks. Additionally, the expression of these genes is modulated during liver regeneration and showed similar profiles between in vitro differentiated hepatocytes and liver-derived hepatocytes. In conclusion, some components of the Ca2+-signaling are altered in HCC and displayed a correlation with patients' survival. DNA methylation and HMP are an attractive target for future investigations to regulate their expression. Ca2+-signaling could be an important regulator of cell proliferation and differentiation in the liver.

Impaired Ca2+ signaling due to hepatic steatosis mediates hepatic insulin resistance in Alström syndrome mice that is reversed by GLP-1 analog treatment

Ca²⁺ signaling plays a critical role in the regulation of hepatic metabolism by hormones including insulin. Changes in cytoplasmic Ca²⁺ regulate synthesis and posttranslational modification of key signaling proteins in the insulin pathways. Emerging evidence suggests that hepatocyte intracellular Ca²⁺ signaling is altered in lipid-loaded liver cells isolated from obese rodent models. The mechanisms of altered Ca²⁺-insulin and insulin-Ca²⁺ signaling pathways in obesity remain poorly understood. Here, we show that the kinetics of insulin-initiated intracellular (initial) Ca²⁺ release from endoplasmic reticulum is significantly impaired in steatotic hepatocytes from obese Alström syndrome mice. Furthermore, exenatide, a glucagon-like peptide-1 (GLP-1) analog, reversed lipid-induced inhibition of intracellular Ca²⁺ release kinetics in steatotic hepatocytes, without affecting the total content of intracellular Ca²⁺ released. Exenatide reversed the lipid-induced inhibition of intracellular Ca²⁺ release, at least partially, via lipid reduction in hepatocytes, which then restored hormone-regulated cytoplasmic Ca²⁺ signaling and insulin sensitivity. This data provides additional evidence for the important role of Ca²⁺ signaling pathways in obesity-associated impaired hepatic lipid homeostasis and insulin signaling. It also highlights a potential advantage of GLP-1 analogs when used to treat type 2 diabetes associated with hepatic steatosis.

Cortisol modulates calcium release-activated calcium channel gating in fish hepatocytes

Glucocorticoids (GCs) are rapidly released in response to stress and play an important role in the physiological adjustments to re-establish homeostasis. The mode of action of GCs for stress coping is mediated largely by the steroid binding to the glucocorticoid receptor (GR), a ligand-bound transcription factor, and modulating the expression of target genes. However, GCs also exert rapid actions that are independent of transcriptional regulation by modulating second messenger signaling. However, a membrane-specific protein that transduces rapid GCs signal is yet to be characterized. Here, using freshly isolated hepatocytes from rainbow trout (Oncorhynchus mykiss) and fura2 fluorescence microscopy, we report that stressed levels of cortisol rapidly stimulate the rise in cytosolic free calcium ([Ca²⁺]i). Pharmacological manipulations using specific extra- and intra-cellular calcium chelators, plasma membrane and endoplasmic reticulum channel blockers and receptors, indicated extracellular Ca²⁺ entry is required for the cortisol-mediated rise in ([Ca²⁺]i). Particularly, the calcium release-activated calcium (CRAC) channel gating appears to be a key target for the rapid action of cortisol in the ([Ca²⁺]i) rise in trout hepatocytes. To test this further, we carried out in silico molecular docking studies using the Drosophila CRAC channel modulator 1 (ORAI1) protein, the pore forming subunit of CRAC channel that is highly conserved. The result predicts a putative binding site on CRAC for cortisol to modulate channel gating, suggesting a direct, as well as an indirect regulation (by other membrane receptors) of CRAC channel gating by cortisol. Altogether, CRAC channel may be a novel cortisol-gated Ca²⁺ channel transducing rapid nongenomic signalling in hepatocytes during acute stress.

Calcium-dependent insulin resistance in hepatocytes: mathematical model

Hepatocyte insulin resistance is one of the early factors of developing type II diabetes. If insulin resistance is treated early, type II diabetes could be prevented. In recent years, scientists have been conducting extensive research on the underlying issues on a cellular and molecular level. It was found that the modulation of IP₃-receptors, the mitochondrial ability to form the mitochondria-associated membranes (MAMs) and the endoplasmic reticulum stress during Ca²⁺ signaling play a key role in hepatocyte being able to maintain euglycemia and provide metabolic flexibility. However, researchers cannot agree on what factor is the key one in resulting in insulin resistance. In this work, we propose a mathematical model of Ca²⁺ signaling. We included in the model all the major contributors of a proper Ca²⁺ signaling during both the fasting and the postprandial state. Our modeling results are in good agreement with available experimental data. The analysis of modeling results suggests that MAMs dysfunction alone cannot result in abnormal Ca²⁺ signaling and the wrong modulation of IP₃-receptors is a more definite reason. However, both the MAMs dysfunction and the IP₃ signaling dysregulation combined can lead to a robust Ca²⁺ signal and improper glucose release. In addition, our model results suggest a strong dependence of Ca²⁺ oscillations pattern on morphological characteristics of the ER and the mitochondria.

Mitochondrial metabolism and calcium homeostasis in the development of NAFLD leading to hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) is a metabolic syndrome characterized by excessive accumulation of hepatic lipid droplets. The disease progresses with steatosis as the premise for hepatocytic damage and tissue scarring, often culminating in hepatocellular carcinoma (HCC). Perturbations in mitochondrial metabolism and energetics were found to be associated with, and often instrumental in various stages of this progression. Functional impairment of the mitochondria affects all aspects of cellular functioning and a particularly important one is calcium signalling. Changes in mitochondrial calcium specifically in hepatocytes of a fatty liver, is reflected by alterations in calcium signalling as well as calcium transporter activities. This deranged Ca²⁺ homeostasis aids in even more uptake of lipids into the mitochondria and a shift in equilibrium, both metabolically as well as in terms of energy production, leading to completely altered cellular states. These alterations have been reviewed as a perspective to understand the disease progression through NAFLD leading to HCC.

Ethanol Disrupts Hormone-Induced Calcium Signaling in Liver

Receptor-coupled phospholipase C (PLC) is an important target for the actions of ethanol. In the ex vivo perfused rat liver, concentrations of ethanol >100 mM were required to induce a rise in cytosolic calcium (Ca²⁺) suggesting that these responses may only occur after binge ethanol consumption. Conversely, pharmacologically achievable concentrations of ethanol (≤30 mM) decreased the frequency and magnitude of hormone-stimulated cytosolic and nuclear Ca²⁺ oscillations and the parallel translocation of protein kinase C-β to the membrane. Ethanol also inhibited gap junction communication resulting in the loss of coordinated and spatially organized intercellular Ca²⁺ waves in hepatic lobules. Increasing the hormone concentration overcame the effects of ethanol on the frequency of Ca²⁺ oscillations and amplitude of the individual Ca²⁺ transients; however, the Ca²⁺ responses in the intact liver remained disorganized at the intercellular level, suggesting that gap junctions were still inhibited. Pretreating hepatocytes with an alcohol dehydrogenase inhibitor suppressed the effects of ethanol on hormone-induced Ca²⁺ increases, whereas inhibiting aldehyde dehydrogenase potentiated the inhibitory actions of ethanol, suggesting that acetaldehyde is the underlying mediator. Acute ethanol intoxication inhibited the rate of rise and the magnitude of hormone-stimulated production of inositol 1,4,5-trisphosphate (IP₃), but had no effect on the size of Ca²⁺ spikes induced by photolysis of caged IP₃. These findings suggest that ethanol inhibits PLC activity, but does not affect IP₃ receptor function. We propose that by suppressing hormone-stimulated PLC activity, ethanol interferes with the dynamic modulation of [IP₃] that is required to generate large, amplitude Ca²⁺ oscillations.

Role of mitochondria in liver metabolic health and diseases

The liver is a major organ that coordinates the metabolic flexibility of the whole body, which is characterized by the ability to adapt dynamically in response to fluctuations in energy needs and supplies. In this context, hepatocyte mitochondria are key partners in fine-tuning metabolic flexibility. Here we review the metabolic and signalling pathways carried by mitochondria in the liver, the major pathways that regulate mitochondrial function and how they function in health and metabolic disorders associated to obesity, i.e. insulin resistance, non-alcoholic steatosis and steatohepatitis and hepatocellular carcinoma. Finally, strategies targeting mitochondria to counteract liver disorders are discussed.

The Two-Way Relationship Between Calcium and Metabolism in Cancer

Calcium ion (Ca²⁺) signaling is critical to many physiological processes, and its kinetics and subcellular localization are tightly regulated in all cell types. All Ca²⁺ flux perturbations impact cell function and may contribute to various diseases, including cancer. Several modulators of Ca²⁺ signaling are attractive pharmacological targets due to their accessibility at the plasma membrane. Despite this, the number of specific inhibitors is still limited, and to date there are no anticancer drugs in the clinic that target Ca²⁺ signaling. Ca²⁺ dynamics are impacted, in part, by modifications of cellular metabolic pathways. Conversely, it is well established that Ca²⁺ regulates cellular bioenergetics by allosterically activating key metabolic enzymes and metabolite shuttles or indirectly by modulating signaling cascades. A coordinated interplay between Ca²⁺ and metabolism is essential in maintaining cellular homeostasis. In this review, we provide a snapshot of the reciprocal interaction between Ca²⁺ and metabolism and discuss the potential consequences of this interplay in cancer cells. We highlight the contribution of Ca²⁺ to the metabolic reprogramming observed in cancer. We also describe how the metabolic adaptation of cancer cells influences this crosstalk to regulate protumorigenic signaling pathways. We suggest that the dual targeting of these processes might provide unprecedented opportunities for anticancer strategies. Interestingly, promising evidence for the synergistic effects of antimetabolites and Ca²⁺-modulating agents is emerging.

PDE2A Is Indispensable for Mouse Liver Development and Hematopoiesis

Phosphodiesterase 2A (PDE2A) is a cAMP-cGMP hydrolyzing enzyme essential for mouse development and the PDE2A knockout model (PDE2A^−/−) is embryonic lethal. Notably, livers of PDE2A^−/− embryos at embryonic day 14.5 (E14.5) have extremely reduced size. Morphological, cellular and molecular analyses revealed loss of integrity in the PDE2A^−/− liver niche that compromises the hematopoietic function and maturation. Hematopoietic cells isolated from PDE2A^−/− livers are instead able to differentiate in in vitro assays, suggesting the absence of blood cell-autonomous defects. Apoptosis was revealed in hepatoblasts and at the endothelial and stromal compartments in livers of PDE2A^−/− embryos. The increase of the intracellular cAMP level and of the inducible cAMP early repressor (ICER) in liver of PDE2A^−/− embryos might explain the impairment of liver development by downregulating the expression of the anti-apoptotic gene Bcl2. In summary, we propose PDE2A as an essential gene for integrity maintenance of liver niche and the accomplishment of hematopoiesis.

Type 3 Inositol 1,4,5-Trisphosphate Receptor Is Increased and Enhances Malignant Properties in Cholangiocarcinoma

Cholangiocarcinoma (CCA) is the second most common malignancy arising in the liver. It carries a poor prognosis, in part because its pathogenesis is not well understood. The type 3 inositol 1,4,5-trisphosphate receptor (ITPR3) is the principal intracellular calcium ion (Ca2+ ) release channel in cholangiocytes, and its increased expression has been related to the pathogenesis of malignancies in other types of tissues, so we investigated its role in CCA. ITPR3 expression was increased in both hilar and intrahepatic CCA samples as well as in CCA cell lines. Deletion of ITPR3 from CCA cells impaired proliferation and cell migration. A bioinformatic analysis suggested that overexpression of ITPR3 in CCA would have a mitochondrial phenotype, so this was also examined. ITPR3 normally is concentrated in a subapical region of endoplasmic reticulum (ER) in cholangiocytes, but both immunogold electron microscopy and super-resolution microscopy showed that ITPR3 in CCA cells was also in regions of ER in close association with mitochondria. Deletion of ITPR3 from these cells impaired mitochondrial Ca2+ signaling and led to cell death. Conclusion: ITPR3 expression in cholangiocytes becomes enhanced in CCA. This contributes to malignant features, including cell proliferation and migration and enhanced mitochondrial Ca2+ signaling.

The expression pattern of calcium signaling-related genes during smoltification of Salmo salar in productive conditions

Variations in the mRNA expression of hepatic and muscle genes that are related to calcium signaling were analyzed by real-time qPCR in farmed Atlantic salmon (Salmo salar L. 1758) to determine changes in expression between parr and smolt stages. These organs were selected due to their close relationship with calcium signaling and metabolism (e.g., glycolysis, oxidative phosphorylation, muscle contraction). Differential expression between smolt and parr specimens and between organs was observed. Compared to parr specimens, smolts exhibited upregulated expression of the calcitonin receptor precursor, calcitonin receptor, calcitonin isoform, parathyroid hormone, and calmodulin in the liver. This pattern was inverse in muscle, with the exception of calmodulin, which was significantly upregulated in smolts compared to parr. Additionally, plasma calcium was decreased in the smolt condition. This study is the first to characterize the expression pattern of calcium signaling-related genes in the liver and muscle of parr and smolt S. salar. However, further functional studies are required to obtain a wider understanding about the physiological changes that accompany the productive conditions during smoltification.

Calcium Signaling As a Therapeutic Target for Liver Steatosis

Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from various pathophysiological conditions. While lipid metabolism in the liver is normally balanced such that there is no excessive lipid accumulation, when this homeostasis is disrupted lipid droplets (LDs) accumulate in hepatocytes resulting in cellular toxicity. The mechanisms underlying this accumulation and the subsequent hepatocellular damage are multifactorial and poorly understood, with the result that there are no currently approved treatments for NAFLD. Impaired calcium signaling has recently been identified as a cause of increased endoplasmic reticulum (ER) stress contributing to hepatic lipid accumulation. This review highlights new findings on the role of impaired Ca²⁺ signaling in the development of steatosis and discusses potential new approaches to NAFLD treatment based on these new insights.

Calcium Signaling in Cholangiocytes: Methods, Mechanisms, and Effects

Calcium (Ca²⁺) is a versatile second messenger that regulates a number of cellular processes in virtually every type of cell. The inositol 1,4,5-trisphosphate receptor (ITPR) is the only intracellular Ca²⁺ release channel in cholangiocytes, and is therefore responsible for Ca²⁺-mediated processes in these cells. This review will discuss the machinery responsible for Ca²⁺ signals in these cells, as well as experimental models used to investigate cholangiocyte Ca²⁺ signaling. We will also discuss the role of Ca²⁺ in the normal and abnormal regulation of secretion and apoptosis in cholangiocytes, two of the best characterized processes mediated by Ca²⁺ in this cell type.

Causality Analysis and Cell Network Modeling of Spatial Calcium Signaling Patterns in Liver Lobules

Dynamics as well as localization of Ca²⁺ transients plays a vital role in liver function under homeostatic conditions, repair, and disease. In response to circulating hormonal stimuli, hepatocytes exhibit intracellular Ca²⁺ responses that propagate through liver lobules in a wave-like fashion. Although intracellular processes that control cell autonomous Ca²⁺ spiking behavior have been studied extensively, the intra- and inter-cellular signaling factors that regulate lobular scale spatial patterns and wave-like propagation of Ca²⁺ remain to be determined. To address this need, we acquired images of cytosolic Ca²⁺ transients in 1300 hepatocytes situated across several mouse liver lobules over a period of 1600 s. We analyzed this time series data using correlation network analysis, causal network analysis, and computational modeling, to characterize the spatial distribution of heterogeneity in intracellular Ca²⁺ signaling components as well as intercellular interactions that control lobular scale Ca²⁺ waves. Our causal network analysis revealed that hepatocytes are causally linked to multiple other co-localized hepatocytes, but these influences are not necessarily aligned uni-directionally along the sinusoids. Our computational model-based analysis showed that spatial gradients of intracellular Ca²⁺ signaling components as well as intercellular molecular exchange are required for lobular scale propagation of Ca²⁺ waves. Additionally, our analysis suggested that causal influences of hepatocytes on Ca²⁺ responses of multiple neighbors lead to robustness of Ca²⁺ wave propagation through liver lobules.

Grain Amaranth Is Associated with Improved Hepatic and Renal Calcium Metabolism in Type 2 Diabetes Mellitus of Male Wistar Rats

Background

Dysregulation of calcium signaling is a hallmark of diabetes mellitus (DM) and grain amaranth (AG) has antidiabetic properties. Information on the mechanism of action of AG on blood, renal, and hepatic tissues is sparse, although it continues to be an important alternative medicinal plant in several developing countries. The objective of the study was to determine key changes in calcium levels and s100a1 protein levels and antioxidant and histopathologic changes in blood, renal, and hepatic tissues of male diabetic Wistar rats.

Materials and Methods

This was an experimental study in which 30 male Wistar rats were kept for 5 weeks (6 groups, N =5). Groups 1-IV had T2DM induced using Nicotinamide and Streptozotocin: Group I, Mixtard®; group II, positive control; group III, 25% AG; group IV, 50% AG. Furthermore, group V consisted of normal rats given 50% GA and group VI was negative control. Blood, renal, and hepatic tissues were collected and analyzed for calcium, s100a1 protein levels, and antioxidant and histopathological changes.

Results and Discussion

In blood, renal, and hepatic tissue, calcium and s100a1 levels were low during T2DM and these increased following AG supplementation. This was important for improved metabolic processes, thus leading to the low malondialdehyde (MDA) and glutathione peroxidase (GPx) activity in the tissues. Efficient antioxidant status was important for improved calcium signaling mechanisms, thus leading to improved tissue function and protection demonstrating the importance of AG as an alternative medicinal source through the calcium signaling pathway.

Conclusion

Grain amaranth exerts its antidiabetic properties through improved calcium homeostasis in blood, kidney, and liver.

Regulation of bile secretion by calcium signaling in health and disease

Calcium (Ca²⁺) signaling controls secretion in many types of cells and tissues. In the liver, Ca²⁺ regulates secretion in both hepatocytes, which are responsible for primary formation of bile, and cholangiocytes, which line the biliary tree and further condition the bile before it is secreted. Cholestatic liver diseases, which are characterized by impaired bile secretion, may result from impaired Ca²⁺ signaling mechanisms in either hepatocytes or cholangiocytes. This review will discuss the Ca²⁺ signaling machinery and mechanisms responsible for regulation of secretion in both hepatocytes and cholangiocytes, and the pathophysiological changes in Ca²⁺ signaling that can occur in each of these cell types to result in cholestasis.