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To examine the roles of mitochondrial calcium Ca2+ ([Ca2+]mt) and cytosolic Ca2+ ([Ca2+]cyt) in the regulation of hepatic mitochondrial fat oxidation, we studied a liver-specific mitochondrial calcium uniporter knockout (MCU KO) mouse model with reduced [Ca2+]mt and increased [Ca2+]cyt content. Despite decreased [Ca2+]mt, deletion of hepatic MCU increased rates of isocitrate dehydrogenase flux, α-ketoglutarate dehydrogenase flux, and succinate dehydrogenase flux in vivo. Rates of [14C16]palmitate oxidation and intrahepatic lipolysis were increased in MCU KO liver slices, which led to decreased hepatic triacylglycerol content. These effects were recapitulated with activation of CAMKII and abrogated with CAMKII knockdown, demonstrating that [Ca2+]cyt activation of CAMKII may be the primary mechanism by which MCU deletion promotes increased hepatic mitochondrial oxidation. Together, these data demonstrate that hepatic mitochondrial oxidation can be dissociated from [Ca2+]mt and reveal a key role for [Ca2+]cyt in the regulation of hepatic fat mitochondrial oxidation, intrahepatic lipolysis, gluconeogenesis, and lipid accumulation.
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Neutrophil infiltration occurs in a variety of liver diseases, but it is unclear how neutrophils and hepatocytes interact. Neutrophils generally use granule proteases to digest phagocytosed bacteria and foreign substances or neutralize them in neutrophil extracellular traps. In certain pathological states, granule proteases play a destructive role against the host as well. More recently, nondestructive actions of neutrophil granule proteins have been reported, such as modulation of tissue remodeling and metabolism. Here, we report a completely different mechanism by which neutrophils act nondestructively, by inserting granules directly into hepatocytes. Specifically, elastase-containing granules were transferred to hepatocytes where elastase selectively degraded intracellular calcium channels to reduce cell proliferation without cytotoxicity. In response, hepatocytes increased expression of Serpin E2 and A3, which inhibited elastase activity. Elastase insertion was seen in patient specimens of alcohol-associated hepatitis, and the relationship between elastase-mediated ITPR2 degradation and reduced cell proliferation was confirmed in mouse models. Moreover, neutrophils from patients with alcohol-associated hepatitis were more prone to degranulation and more potent in reducing calcium channel expression than neutrophils from healthy individuals. This nondestructive and reversible action on hepatocytes defines a previously unrecognized role for neutrophils in the transient regulation of epithelial calcium signaling mechanisms.
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Sinalização do Cálcio , Hepatite Alcoólica , Hepatócitos , Neutrófilos , Elastase Pancreática , Humanos , Neutrófilos/metabolismo , Neutrófilos/patologia , Animais , Camundongos , Hepatócitos/metabolismo , Hepatócitos/patologia , Hepatite Alcoólica/metabolismo , Hepatite Alcoólica/patologia , Hepatite Alcoólica/genética , Elastase Pancreática/metabolismo , Masculino , Proliferação de Células , Canais de Cálcio/metabolismo , Canais de Cálcio/genética , FemininoRESUMO
The simulation of metals, oxides, and hydroxides can accelerate the design of therapeutics, alloys, catalysts, cement-based materials, ceramics, bioinspired composites, and glasses. Here we introduce the INTERFACE force field (IFF) and surface models for α-Al2O3, α-Cr2O3, α-Fe2O3, NiO, CaO, MgO, ß-Ca(OH)2, ß-Mg(OH)2, and ß-Ni(OH)2. The force field parameters are nonbonded, including atomic charges for Coulomb interactions, Lennard-Jones (LJ) potentials for van der Waals interactions with 12-6 and 9-6 options, and harmonic bond stretching for hydroxide ions. The models outperform DFT calculations and earlier atomistic models (Pedone, ReaxFF, UFF, CLAYFF) up to 2 orders of magnitude in reliability, compatibility, and interpretability due to a quantitative representation of chemical bonding consistent with other compounds across the periodic table and curated experimental data for validation. The IFF models exhibit average deviations of 0.2% in lattice parameters, <10% in surface energies (to the extent known), and 6% in bulk moduli relative to experiments. The parameters and models can be used with existing parameters for solvents, inorganic compounds, organic compounds, biomolecules, and polymers in IFF, CHARMM, CVFF, AMBER, OPLS-AA, PCFF, and COMPASS, to simulate bulk oxides, hydroxides, electrolyte interfaces, and multiphase, biological, and organic hybrid materials at length scales from atoms to micrometers. The nonbonded character of the models also enables the analysis of mixed oxides, glasses, and certain chemical reactions, and well-performing nonbonded models for silica phases, SiO2, are introduced. Automated model building is available in the CHARMM-GUI Nanomaterial Modeler. We illustrate applications of the models to predict the structure of mixed oxides, and energy barriers of ion migration, as well as binding energies of water and organic molecules in outstanding agreement with experimental data and calculations at the CCSD(T) level. Examples of model building for hydrated, pH-sensitive oxide surfaces to simulate solid-electrolyte interfaces are discussed.
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Mitochondria-associated membranes (MAMs) are signaling domains formed at points of contact between the endoplasmic reticulum and mitochondria that are essential for mitochondrial Ca2+ signaling, energy metabolism and cell survival. Thoudam et al. now show that MAMs are dynamically regulated by pyruvate dehydrogenase kinase 4 in alcohol-associate liver disease, adding one more piece to the ever more complex puzzle of ER-mitochondria interactions in health and disease.
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Sinalização do Cálcio , Membranas Mitocondriais , Membranas Mitocondriais/metabolismo , Mitocôndrias/metabolismo , Estresse do Retículo Endoplasmático , Retículo Endoplasmático/metabolismoRESUMO
BACKGROUND AND AIMS: TGF-ß induces multiple structural and functional changes in quiescent HSCs, including an increase in proliferation, mitochondrial mass, and matrix deposition. HSC transdifferentiation requires significant bioenergetic capacity, and it is not known how TGF-ß-mediated transcriptional upregulation is coordinated with the bioenergetic capacity of HSCs. APPROACH AND RESULTS: Mitochondria are key bioenergetic organelles, and here, we report that TGF-ß induces release of mitochondrial DNA (mtDNA) from healthy HSCs through voltage-dependent anion channels (VDACs), with the formation of an mtDNA-CAP on the external mitochondrial membrane. This stimulates organization of cytosolic cyclic GMP-AMP synthase (cGAS) onto the mtDNA-CAP and subsequent activation of the cGAS-STING-IRF3 pathway. TGF-ß is unable to induce conversion of HSCs from a quiescent to a transdifferentiated phenotype in the absence of mtDNA, VDAC, or stimulator of interferon genes (STING). Transdifferentiation by TGF-ß is blocked by a STING inhibitor, which also reduces liver fibrosis prophylactically and therapeutically. CONCLUSIONS: We have identified a pathway that requires the presence of functional mitochondria for TGF-ß to mediate HSC transcriptional regulation and transdifferentiation and therefore provides a key link between bioenergetic capacity of HSCs and signals for transcriptional upregulation of genes of anabolic pathways.
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DNA Mitocondrial , Células Estreladas do Fígado , Proteínas de Membrana , Fator de Crescimento Transformador beta , Humanos , Diferenciação Celular/genética , Diferenciação Celular/fisiologia , DNA Mitocondrial/genética , DNA Mitocondrial/metabolismo , Células Estreladas do Fígado/metabolismo , Proteínas de Membrana/metabolismo , Mitocôndrias/metabolismo , Nucleotidiltransferases/metabolismo , Transdução de Sinais , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta/metabolismoRESUMO
Fluid and bicarbonate secretion is a principal function of cholangiocytes, and impaired secretion results in cholestasis. Cholangiocyte secretion depends on peri-apical expression of the type 3 inositol trisphosphate receptor (ITPR3), and loss of this intracellular Ca2+ release channel is a final common event in most cholangiopathies. Here we investigated the mechanism by which ITPR3 localizes to the apical region to regulate secretion. Isolated bile duct units, primary mouse cholangiocytes, and polarized Madin-Darby canine kidney (MDCK) cells were examined using a combination of biochemical and fluorescence microscopy techniques to investigate the mechanism of ITPR3 targeting to the apical region. Apical localization of ITPR3 depended on the presence of intact lipid rafts as well as interactions with both caveolin 1 (CAV1) and myosin heavy chain 9 (MYH9). Chemical disruption of lipid rafts or knockdown of CAV1 or MYH9 redistributed ITPR3 away from the apical region. MYH9 interacted with the five c-terminal amino acids of the ITPR3 peptide. Disruption of lipid rafts impaired Ca2+ signaling, and absence of CAV1 impaired both Ca2+ signaling and fluid secretion. Conclusion: A cooperative mechanism involving MYH9, CAV1, and apical lipid rafts localize ITPR3 to the apical region to regulate Ca2+ signaling and secretion in cholangiocytes.
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Sinalização do Cálcio , Caveolina 1 , Aminoácidos/metabolismo , Animais , Bicarbonatos/metabolismo , Sinalização do Cálcio/fisiologia , Caveolina 1/genética , Cães , Inositol , Receptores de Inositol 1,4,5-Trifosfato/genética , Camundongos , Cadeias Pesadas de Miosina/genéticaRESUMO
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.
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BACKGROUND & AIMS: Annexin A11 was identified as autoantigen in IgG4-related cholangitis (IRC), a B-cell driven disease. Annexin A11 modulates calcium-dependent exocytosis, a crucial mechanism for insertion of proteins into their target membranes. Human cholangiocytes form an apical 'biliary bicarbonate umbrella' regarded as defense against harmful hydrophobic bile acid influx. The bicarbonate secretory machinery comprises the chloride/bicarbonate exchanger AE2 and the chloride channel ANO1. We aimed to investigate the expression and function of annexin A11 in human cholangiocytes and a potential role of IgG1/IgG4-mediated autoreactivity against annexin A11 in the pathogenesis of IRC. METHODS: Expression of annexin A11 in human liver was studied by immunohistochemistry and immunofluorescence. In human control and ANXA11 knockdown H69 cholangiocytes, intracellular pH, AE2 and ANO1 surface expression, and bile acid influx were examined using ratio microspectrofluorometry, cell surface biotinylation, and 22,23-3H-glycochenodeoxycholic acid permeation, respectively. The localization of annexin A11-mEmerald and ANO1-mCherry was investigated by live-cell microscopy in H69 cholangiocytes after incubation with IRC patient serum containing anti-annexin A11 IgG1/IgG4-autoantibodies or disease control serum. RESULTS: Annexin A11 was strongly expressed in human cholangiocytes, but not hepatocytes. Knockdown of ANXA11 led to reduced plasma membrane expression of ANO1, but not AE2, alkalization of intracellular pH and uncontrolled bile acid influx. High intracellular calcium conditions led to annexin A11 membrane shift and colocalization with ANO1. Incubation with IRC patient serum inhibited annexin A11 membrane shift and reduced ANO1 surface expression. CONCLUSION: Cholangiocellular annexin A11 mediates apical membrane abundance of the chloride channel ANO1, thereby supporting biliary bicarbonate secretion. Insertion is inhibited by IRC patient serum containing anti-annexin A11 IgG1/IgG4-autoantibodies. Anti-annexin A11 autoantibodies may contribute to the pathogenesis of IRC by weakening the 'biliary bicarbonate umbrella'. LAY SUMMARY: We previously identified annexin A11 as a specific autoantigen in immunoglobulin G4-related cholangitis (IRC), a B-cell driven disease affecting the bile ducts. Human cholangiocytes are protected against harmful hydrophobic bile acid influx by a defense mechanism referred to as the 'biliary bicarbonate umbrella'. We found that annexin A11 is required for the formation of a robust bicarbonate umbrella. Binding of patient-derived annexin A11 autoantibodies inhibits annexin A11 function, possibly contributing to bile duct damage by weakening the biliary bicarbonate umbrella in patients with IRC.
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Colangite/etiologia , Doença Relacionada a Imunoglobulina G4/complicações , Fatores de Proteção , Idoso , Anexinas/farmacologia , Anexinas/uso terapêutico , Autoantígenos/farmacologia , Autoantígenos/uso terapêutico , Biópsia/métodos , Biópsia/estatística & dados numéricos , Colangite/fisiopatologia , Feminino , Humanos , Doença Relacionada a Imunoglobulina G4/fisiopatologia , Fígado/patologia , Masculino , Pessoa de Meia-IdadeRESUMO
Liver test abnormalities are frequently observed in patients with coronavirus disease 2019 (COVID-19) and are associated with worse prognosis. However, information is limited about pathological changes in the liver in this infection, so the mechanism of liver injury is unclear. Here we describe liver histopathology and clinical correlates of 27 patients who died of COVID-19 in Manaus, Brazil. There was a high prevalence of liver injury (elevated alanine aminotransferase and aspartate aminotransferase in 44% and 48% of patients, respectively) in these patients. Histological analysis showed sinusoidal congestion and ischemic necrosis in more than 85% of the cases, but these appeared to be secondary to systemic rather than intrahepatic thrombotic events, as only 14% and 22% of samples were positive for CD61 (marker of platelet activation) and C4d (activated complement factor), respectively. Furthermore, the extent of these vascular findings did not correlate with the extent of transaminase elevations. Steatosis was present in 63% of patients, and portal inflammation was present in 52%. In most cases, hepatocytes expressed angiotensin-converting enzyme 2 (ACE2), which is responsible for binding and entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), even though this ectoenzyme was minimally expressed on hepatocytes in normal controls. However, SARS-CoV-2 staining was not observed. Most hepatocytes also expressed inositol 1,4,5-triphosphate receptor 3 (ITPR3), a calcium channel that becomes expressed in acute liver injury. Conclusion: The hepatocellular injury that commonly occurs in patients with severe COVID-19 is not due to the vascular events that contribute to pulmonary or cardiac damage. However, new expression of ACE2 and ITPR3 with concomitant inflammation and steatosis suggests that liver injury may result from inflammation, metabolic abnormalities, and perhaps direct viral injury.
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COVID-19/complicações , Hepatopatias/patologia , Hepatopatias/virologia , Fígado/patologia , Fígado/virologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Brasil , COVID-19/mortalidade , COVID-19/patologia , COVID-19/fisiopatologia , Feminino , Humanos , Fígado/fisiopatologia , Hepatopatias/diagnóstico , Hepatopatias/fisiopatologia , Testes de Função Hepática , Masculino , Pessoa de Meia-IdadeRESUMO
Liver fibrosis is a common characteristic of chronic liver diseases. The activation of hepatic stellate cells (HSCs) plays a key role in fibrogenesis in response to liver injury, yet the mechanism by which damaged hepatocytes modulate the activation of HSCs is poorly understood. Our previous studies have established that liver-specific deletion of O-GlcNAc transferase (OGT)leads to hepatocyte necroptosis and spontaneous fibrosis. Here, we report that OGT-deficient hepatocytes secrete trefoil factor 2 (TFF2) that activates HSCs and contributes to the fibrogenic process. The expression and secretion of TFF2 are induced in OGT-deficient hepatocytes but not in WT hepatocytes. TFF2 activates the platelet-derived growth factor receptor beta signaling pathway that promotes the proliferation and migration of primary HSCs. TFF2 protein expression is elevated in mice with carbon tetrachloride-induced liver injury. These findings identify TFF2 as a novel factor that mediates intercellular signaling between hepatocytes and HSCs and suggest a role of the hepatic OGT-TFF2 axis in the process of fibrogenesis.
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Células Estreladas do Fígado/metabolismo , Hepatócitos/metabolismo , Cirrose Hepática/metabolismo , Fator Trefoil-2/metabolismo , Animais , Tetracloreto de Carbono/toxicidade , Linhagem Celular , Células Cultivadas , Exocitose , Células Estreladas do Fígado/patologia , Hepatócitos/patologia , Humanos , Cirrose Hepática/etiologia , Camundongos , N-Acetilglucosaminiltransferases/deficiência , N-Acetilglucosaminiltransferases/genética , N-Acetilglucosaminiltransferases/metabolismo , Necroptose , Transdução de Sinais , Fator Trefoil-2/genéticaRESUMO
BACKGROUND & OBJECTIVES: Alcoholic hepatitis (AH) is a common but life-threatening disease with limited treatment options. It is thought to result from hepatocellular damage, but the presence of cholestasis worsens prognosis, so we examined whether bile ducts participate in the pathogenesis of this disease. DESIGN: Cholangiocytes derived from human bile ducts were co-cultured with neutrophils from patients with AH or controls. Loss of type 3 inositol 1,4,5-trisphosphate receptor (ITPR3), an apical intracellular calcium channel necessary for cholangiocyte secretion, was used to reflect cholestatic changes. Neutrophils in contact with bile ducts were quantified in liver biopsies from patients with AH and controls and correlated with clinical and pathological findings. RESULTS: Liver biopsies from patients with AH revealed neutrophils in contact with bile ducts, which correlated with biochemical and histological parameters of cholestasis. Cholangiocytes co-cultured with neutrophils lost ITPR3, and neutrophils from patients with AH were more potent than control neutrophils. Biochemical and histological findings were recapitulated in an AH animal model. Loss of ITPR3 was attenuated by neutrophils in which surface membrane proteins were removed. RNA-seq analysis implicated integrin ß1 (ITGB1) in neutrophil-cholangiocyte interactions and interference with ITGB1 on cholangiocytes blocked the ability of neutrophils to reduce cholangiocyte ITPR3 expression. Cell adhesion molecules on neutrophils interacted with ITGB1 to trigger RAC1-induced JNK activation, causing a c-Jun-mediated decrease in ITPR3 in cholangiocytes. CONCLUSIONS: Neutrophils bind to ITGB1 on cholangiocytes to contribute to cholestasis in AH. This previously unrecognised role for cholangiocytes in this disease alters our understanding of its pathogenesis and identifies new therapeutic targets.
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Ductos Biliares/citologia , Colestase/complicações , Hepatite Alcoólica/etiologia , Neutrófilos/fisiologia , Adulto , Animais , Ductos Biliares/patologia , Colestase/patologia , Técnicas de Cocultura , Modelos Animais de Doenças , Feminino , Hepatite Alcoólica/patologia , Humanos , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Fígado/patologia , Masculino , Camundongos Endogâmicos C57BL , Pessoa de Meia-IdadeRESUMO
Hepatic ischemia-reperfusion injury is seen in a variety of clinical conditions, including hepatic thrombosis, systemic hypotension, and liver transplantation. Calcium (Ca2+) signaling mediates several pathophysiological processes in the liver, but it is not known whether and how intracellular Ca2+ channels are involved in the hepatocellular events secondary to ischemia-reperfusion. Using an animal model of hepatic ischemia-reperfusion injury, we observed a progressive increase in expression of the type 3 isoform of the inositol trisphosphate receptor (ITPR3), an intracellular Ca2+ channel that is not normally expressed in healthy hepatocytes. ITPR3 expression was upregulated, at least in part, by a combination of demethylation of the ITPR3 promoter region and the increased transcriptional activity of the nuclear factor of activated T-cells (NFAT). Additionally, expression of pro-inflammatory interleukins and necrotic surface area were less pronounced in livers of control animals compared to liver-specific ITPR3 KO mice subjected to hepatic damage. Corroborating these findings, ITPR3 expression and activation of NFAT were observed in hepatocytes of liver biopsies from patients who underwent liver ischemia caused by thrombosis after organ transplant. Together, these results are consistent with the idea that ITPR3 expression in hepatocytes plays a protective role during hepatic injury induced by ischemia-reperfusion.
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Hepatócitos/metabolismo , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Fígado/metabolismo , Fígado/patologia , Substâncias Protetoras/metabolismo , Traumatismo por Reperfusão/metabolismo , Animais , Sinalização do Cálcio , Desmetilação do DNA , Modelos Animais de Doenças , Humanos , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Fatores de Transcrição NFATC/metabolismo , Regiões Promotoras Genéticas/genéticaRESUMO
BACKGROUND AND AIMS: The coronavirus-19 disease (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 virus, is associated with significant morbidity and mortality attributable to pneumonia, acute respiratory distress syndrome, and multiorgan failure. Liver injury has been reported as a nonpulmonary manifestation of COVID-19, but characterization of liver test abnormalities and their association with clinical outcomes is incomplete. APPROACH AND RESULTS: We conducted a retrospective cohort study of 1,827 patients with confirmed COVID-19 who were hospitalized within the Yale-New Haven Health System between March 14, 2020 and April 23, 2020. Clinical characteristics, liver tests (aspartate aminotransferase [AST], alanine aminotransferase [ALT], alkaline phosphatase [ALP], total bilirubin [TBIL], and albumin) at three time points (preinfection baseline, admission, and peak hospitalization), and hospitalization outcomes (severe COVID-19, intensive care unit [ICU] admission, mechanical ventilation, and death) were analyzed. Abnormal liver tests were commonly observed in hospitalized patients with COVID-19, both at admission (AST 66.9%, ALT 41.6%, ALP 13.5%, and TBIL 4.3%) and peak hospitalization (AST 83.4%, ALT 61.6%, ALP 22.7%, and TBIL 16.1%). Most patients with abnormal liver tests at admission had minimal elevations 1-2× the upper limit of normal (ULN; AST 63.7%, ALT 63.5%, ALP 80.0%, and TBIL 75.7%). A significant proportion of these patients had abnormal liver tests prehospitalization (AST 25.9%, ALT 38.0%, ALP 56.8%, and TBIL 44.4%). Multivariate analysis revealed an association between abnormal liver tests and severe COVID-19, including ICU admission, mechanical ventilation, and death; associations with age, male sex, body mass index, and diabetes mellitus were also observed. Medications used in COVID-19 treatment (lopinavir/ritonavir, hydroxychloroquine, remdesivir, and tocilizumab) were associated with peak hospitalization liver transaminase elevations >5× ULN. CONCLUSIONS: Abnormal liver tests occur in most hospitalized patients with COVID-19 and may be associated with poorer clinical outcomes.
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COVID-19/fisiopatologia , Fígado/fisiopatologia , SARS-CoV-2 , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Criança , Pré-Escolar , Feminino , Hospitalização , Humanos , Lactente , Testes de Função Hepática , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Adulto JovemRESUMO
Yellow fever (YF) is a viral hemorrhagic fever that typically involves the liver. Brazil recently experienced its largest recorded YF outbreak, and the disease was fatal in more than a third of affected individuals, mostly because of acute liver failure. Affected individuals are generally treated only supportively, but during the recent Brazilian outbreak, selected patients were treated with liver transplant. We took advantage of this clinical experience to better characterize the clinical and pathological features of YF-induced liver failure and to examine the mechanism of hepatocellular injury in YF, to identify targets that would be amenable to therapeutic intervention in preventing progression to liver failure and death. Patients with YF liver failure rapidly developed massive transaminase elevations, with jaundice, coagulopathy, thrombocytopenia, and usually hepatic encephalopathy, along with pathological findings that included microvesicular steatosis and lytic necrosis. Hepatocytes began to express the type 3 isoform of the inositol trisphosphate receptor (ITPR3), an intracellular calcium (Ca2+) channel that is not normally expressed in hepatocytes. Experiments in an animal model, isolated hepatocytes, and liver-derived cell lines showed that this new expression of ITPR3 was associated with increased nuclear Ca2+ signaling and hepatocyte proliferation, and reduced steatosis and cell death induced by the YF virus. Conclusion: Yellow fever often induces liver failure characterized by massive hepatocellular damage plus steatosis. New expression of ITPR3 also occurs in YF-infected hepatocytes, which may represent an endogenous protective mechanism that could suggest approaches to treat affected individuals before they progress to liver failure, thereby decreasing the mortality of this disease in a way that does not rely on the costly and limited resource of liver transplantation.
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Alterations in calcium signaling in pancreatic acinar cells can result in pancreatitis. Although pressure changes in the pancreas can elevate cytosolic calcium (Ca2+) levels, it is not known how transient pressure-activated elevations in calcium can cause prolonged calcium changes and consequent pancreatitis. In this issue of the JCI, Swain et al. describe roles for the mechanically activated plasma membrane calcium channels Piezo1 and transient receptor potential vanilloid subfamily 4 (TRPV4) in acinar cells. The authors used genetic deletion models and cell culture systems to investigate calcium signaling. Notably, activation of the Piezo1-dependent TRPV4 pathway was independent of the cholecystokinin (CCK) stimulation pathway. These results elegantly resolve an apparent discrepancy in calcium signaling and the pathogenesis of pancreatitis in pancreatic acinar cells.
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Pâncreas Exócrino , Pancreatite , Canais de Potencial de Receptor Transitório , Células Acinares/metabolismo , Cálcio/metabolismo , Colecistocinina/genética , Colecistocinina/metabolismo , Humanos , Canais Iônicos , Pâncreas/metabolismo , Pâncreas Exócrino/metabolismo , Pancreatite/genética , Canais de Cátion TRPV/genéticaRESUMO
Although it is well-established that reductions in the ratio of insulin to glucagon in the portal vein have a major role in the dysregulation of hepatic glucose metabolism in type-2 diabetes1-3, the mechanisms by which glucagon affects hepatic glucose production and mitochondrial oxidation are poorly understood. Here we show that glucagon stimulates hepatic gluconeogenesis by increasing the activity of hepatic adipose triglyceride lipase, intrahepatic lipolysis, hepatic acetyl-CoA content and pyruvate carboxylase flux, while also increasing mitochondrial fat oxidation-all of which are mediated by stimulation of the inositol triphosphate receptor 1 (INSP3R1). In rats and mice, chronic physiological increases in plasma glucagon concentrations increased mitochondrial oxidation of fat in the liver and reversed diet-induced hepatic steatosis and insulin resistance. However, these effects of chronic glucagon treatment-reversing hepatic steatosis and glucose intolerance-were abrogated in Insp3r1 (also known as Itpr1)-knockout mice. These results provide insights into glucagon biology and suggest that INSP3R1 may represent a target for therapies that aim to reverse nonalcoholic fatty liver disease and type-2 diabetes.
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Glucagon/farmacologia , Gluconeogênese/efeitos dos fármacos , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Fígado/efeitos dos fármacos , Acetilcoenzima A/metabolismo , Tecido Adiposo/efeitos dos fármacos , Animais , Diabetes Mellitus Tipo 2/fisiopatologia , Ativação Enzimática/efeitos dos fármacos , Glucagon/sangue , Receptores de Inositol 1,4,5-Trifosfato/genética , Lipase/metabolismo , Lipólise/efeitos dos fármacos , Lipólise/genética , Camundongos Knockout , Mitocôndrias/efeitos dos fármacos , Hepatopatia Gordurosa não Alcoólica/fisiopatologia , Oxirredução/efeitos dos fármacosRESUMO
Inositol 1,4,5 trisphosphate receptors (ITPRs) are a family of endoplasmic reticulum Ca2+ channels essential for the control of intracellular Ca2+ levels in virtually every mammalian cell type. The three isoforms (ITPR1, ITPR2 and ITPR3) are highly homologous in amino acid sequence, but they differ considerably in terms of biophysical properties, subcellular localization, and tissue distribution. Such differences underscore the variety of cellular responses triggered by each isoform and suggest that the expression/activity of specific isoforms might be linked to particular pathophysiological states. Indeed, recent findings demonstrate that changes in expression of ITPR isoforms are associated with a number of human diseases ranging from fatty liver disease to cancer. ITPR3 is emerging as the isoform that is particularly important in the pathogenesis of various human diseases. Here we review the physiological and pathophysiological roles of ITPR3 in various tissues and the mechanisms by which the expression of this isoform is modulated in health and disease.
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Canais de Cálcio/metabolismo , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Animais , Fenômenos Biofísicos , Doença , Retículo Endoplasmático/metabolismo , Humanos , Mitocôndrias/metabolismo , Modelos BiológicosRESUMO
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.
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Neoplasias dos Ductos Biliares/etiologia , Neoplasias dos Ductos Biliares/patologia , Colangiocarcinoma/etiologia , Colangiocarcinoma/patologia , Receptores de Inositol 1,4,5-Trifosfato/fisiologia , Células Cultivadas , HumanosRESUMO
Worldwide, over a billion people suffer from chronic liver diseases, which often lead to fibrosis and then cirrhosis. Treatments for fibrosis remain experimental, in part because no unifying mechanism has been identified that initiates liver fibrosis. Necroptosis has been implicated in multiple liver diseases. Here, we report that O-linked ß-N-acetylglucosamine (O-GlcNAc) modification protects against hepatocyte necroptosis and initiation of liver fibrosis. Decreased O-GlcNAc levels were seen in patients with alcoholic liver cirrhosis and in mice with ethanol-induced liver injury. Liver-specific O-GlcNAc transferase-KO (OGT-LKO) mice exhibited hepatomegaly and ballooning degeneration at an early age and progressed to liver fibrosis and portal inflammation by 10 weeks of age. OGT-deficient hepatocytes underwent excessive necroptosis and exhibited elevated protein expression levels of receptor-interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like (MLKL), which are key mediators of necroptosis. Furthermore, glycosylation of RIPK3 by OGT is associated with reduced RIPK3 protein stability. Taken together, these findings identify OGT as a key suppressor of hepatocyte necroptosis, and OGT-LKO mice may serve as an effective spontaneous genetic model of liver fibrosis.