Inositol 1,4,5-trisphosphate receptor in the liver:Expression and function

The liver is a complex organ that performs several functions to maintain homeostasis.These functions are modulated by calcium,a second messenger that regulates several intracellular events.In hepatocytes and cholangiocytes,which are the epithelial cell types in the liver,inositol 1,4,5-trisphosphate(InsP3)receptors(ITPR)are the only intracellular calcium release channels.Three isoforms of the ITPR have been described,named type 1,type 2 and type 3.These ITPR isoforms are differentially expressed in liver cells where they regulate distinct physiological functions.Changes in the expression level of these receptors correlate with several liver diseases and hepatic dysfunctions.In this review,we highlight how the expression level,modulation,and localization of ITPR isoforms in hepatocytes and cholangiocytes play a role in hepatic homeostasis and liver pathology.

High expression of type I inositol 1,4,5-trisphosphate receptor in the kidney of rats with hepatorenal syndrome

AIM To detect the expression of typeⅠ inositol 1,4,5-trisphosphate receptor(IP3 RI) in the kidney of rats with hepatorenal syndrome(HRS).METHODS One hundred and twenty-five Sprague-Dawley rats were randomly divided into four groups to receive an intravenous injection of D-galactosamine(D-Gal N) plus lipopolysaccharide(LPS; group G/L, n = 50), D-Gal N alone(group G, n = 25), LPS alone(group L, n = 25), and normal saline(group NS, n = 25), respectively.At 3, 6, 9, 12, and 24 h after injection, blood, liver, and kidney samples were collected. Hematoxylineosin staining of liver tissue was performed to assess hepatocyte necrosis. Electron microscopy was used to observe ultrastructural changes in the kidney. Western blot analysis and real-time PCR were performed to detect the expression of IP3 RI protein and m RNA in the kidney, respectively.RESULTS Hepatocyte necrosis was aggravated gradually, which was most significant at 12 h after treatment with D-galactosamine/lipopolysaccharide, and was characterized by massive hepatocyte necrosis. At the same time, serum levels of biochemical indicators including liver and kidney function indexes were all significantly changed. The structure of the renal glomerulus and tubules was normal at all time points. Western blot analysis indicated that IP3 RI protein expression began to rise at 3 h(P < 0.05) and peaked at 12 h(P < 0.01). Real-time PCR demonstrated that IP3 RI m RNA expression began to rise at 3 h(P < 0.05) and peaked at 9 h(P < 0.01).CONCLUSION IP3 RI protein expression is increased in the kidney of HRS rats, and may be regulated at the transcriptional level.

Altered expression of stromal interaction molecule(STIM)-calcium release-activated calcium channel protein(ORAI) and inositol1,4,5-trisphosphate receptors(IP_3Rs)in cancer:will they become a new battlefield for oncotherapy?

The stromal interaction molecule(STIM)-calcium release-activated calcium channel protein(ORAI) and inositol1,4,5-trisphosphate receptors(IP_3Rs) play pivotal roles in the modulation of Ca^(2+)-regulated pathways from gene transcription to cell apoptosis by driving calcium-dependent signaling processes.Increasing evidence has implicated the dysregulation of STIM-ORAI and IP_3Rs in tumorigenesis and tumor progression.By controlling the activities,structure,and/or expression levels of these Ca^(2+)-transporting proteins,malignant cancer cells can hijack them to drive essential biological functions for tumor development.However,the molecular mechanisms underlying the participation of STIM-ORAI and IP_3Rs in the biological behavior of cancer remain elusive.In this review,we summarize recent advances regarding STIM-ORAI and IP_3Rs and discuss how they promote cell proliferation,apoptosis evasion,and cell migration through temporal and spatial rearrangements in certain types of malignant cells.An understanding of the essential roles of STIM-ORAI and IP_3Rs may provide new pharmacologic targets that achieve a better therapeutic effect by inhibiting their actions in key intracellular signaling pathways.

Temperature-dependence and conformational basis of inositol 1,4,5-trisphosphate receptor regulated by Ca^(2+)

The inositol 1,4,5-trisphosphate (lnsP3) receptor was purified from bovine cerebellum and reconstituted in liposomes composed of phosphatidylcholine (PC) and phosphatidylethanola-mine (PE) (1:1) successfully. No effect of Ca2+ concentration on [3H]-lnsP3 binding to unreconsti-tuted lnsP3 receptor could be observed either at 4℃ or at 25℃, whereas the effect of [Ca2+] on reconstituted lnsP3 receptor depended on the temperature. The Ca2+ concentration outside the proteolipsome ([Ca2+]o) had no detectable effect on lnsP3 binding to lnsP3 receptor at 4℃. In contrast, with increase of [Ca2+]o from 0 to 100 nmol/L at 25℃, the lnsP3 binding activity increased gradually. Then the lnsP3 binding activity was decreased drastically at higher [Ca2+]0 and inhibited entirely at 50 nmol/L [Ca2+]. Conformational studies on intrinsic fluorescence of the reconstituted lnsP3 receptor and its quenching by Kl and HB indicated that the global conformation of reconstituted lnsP3 receptor could not be affected by [Ca2+]o at 4℃. While at 25℃, the effects of 10μmol/L [Ca2+]0 on global, membrane and cytoplasmic conformation of the reconstituted lnsP3 receptor were different significantly from that of 100 nmol/L [Ca2+]0.

New insights into the pathogenesis of primary biliary cholangitis asymptomatic stage

Primary biliary cholangitis(PBC)is a chronic cholestatic progressive liver disease and one of the most important progressive cholangiopathies in adults.Damage to cholangiocytes triggers the development of intrahepatic cholestasis,which progresses to cirrhosis in the terminal stage of the disease.Accumulating data indicate that damage to biliary epithelial cells[(BECs),cholangiocytes]is most likely associated with the intracellular accumulation of bile acids,which have potent detergent properties and damaging effects on cell membranes.The mechanisms underlying uncontrolled bile acid intake into BECs in PBC are associated with pH change in the bile duct lumen,which is controlled by the bicarbonate(HCO3-)buffer system“biliary HCO3-umbrella”.The impaired production and entry of HCO3-from BECs into the bile duct lumen is due to epigenetic changes in expression of the X-linked microRNA 506.Based on the growing body of knowledge on the molecular mechanisms of cholangiocyte damage in patients with PBC,we propose a hypothesis explaining the pathogenesis of the first morphologic(ductulopenia),immunologic(antimitochondrial autoantibodies)and clinical(weakness,malaise,rapid fatigue)signs of the disease in the asymptomatic stage.This review focuses on the consideration of these mechanisms.

Emodin and baicalein inhibit sodium taurocholate-induced vacuole formation in pancreatic acinar cells

AIM To investigate the effects of combined use of emodin and baicalein(CEB) at the cellular and organism levelsin severe acute pancreatitis(SAP) and explore the underlying mechanism.METHODS SAP was induced by retrograde infusion of 5% sodium taurocholate into the pancreatic duct in 48 male SD rats. Pancreatic histopathology score, serum amylase activity, and levels of tumour necrosis factor alpha(TNf-α), interleukin 6(IL-6), and IL-10 were determined to assess the effects of CEB at 12 h after the surgery. The rat pancreatic acinar cells were isolated from healthy male SD rats using collagenase. The cell viability, cell ultrastructure, intracellular free Ca2+ concentration, and inositol(1,4,5)-trisphosphate receptor(IP3 R) expression were investigated to assess the mechanism of CEB.RESULTS Pancreatic histopathology score(2.07 ± 1.20 vs 6.84 ± 1.13, P < 0.05) and serum amylase activity(2866.2 ± 617.7 vs 5241.3 ± 1410.0, P < 0.05) were significantly decreased in the CEB(three doses) treatment group compared with the SAP group(2.07 ± 1.20 vs 6.84 ± 1.13, P < 0.05). CEB dose-dependently reduced the levels of the pro-inflammatory cytokines IL-6(466.82 ± 48.55 vs 603.50 ± 75.53, P < 0.05) and TNF-α(108.04 ± 16.10 vs 215.56 ± 74.67, P < 0.05) and increased the level of the anti-inflammatory cytokine IL-10(200.96 ± 50.76 vs 54.18 ± 6.07, P < 0.05) compared with those in the SAP group. CEB increased cell viability, inhibited cytosolic Ca2+ concentration, and significantly ameliorated intracellular vacuoles and IP3 m RNA expression compared with those in the SAP group(P < 0.05). There was a trend towards decreased IP3 R protein in the CEB treatment group; however, it did not reach statistical significance(P > 0.05).CONCLUSION These results at the cellular and organism levels reflect a preliminary mechanism of CEB in SAP and indicate that CEB is a suitable approach for SAP treatment.

The Involvement of Ca^2＋ Signal Pathways in Distal Colonic Myocytes in a Rat Model of Dextran Sulfate Sodium-induced Colitis

Background： Disrupted Ca2＋ homeostasis contributes to the development of colonic dysmotility in ulcerative colitis （UC）, but the underlying mechanisms are unknown. This study aimed to examine the alteration of colonic smooth muscle （SM） Ca2＋ signaling and Ca2＋ handling proteins in a rat model of dextran sulfate sodium （DSS）-induced UC. Methods： Male Sprague-Dawley rats were randomly divided into control （n = 18） and DSS （n = 17） groups. Acute colitis was induced by 5% DSS in the drinking water for 7 days. Contractility of colonic SM strips （controls, n = 8 and DSS, n = 7） was measured in an organ bath. Cytosolic resting Ca2＋ levels （n = 3 in each group） and Ca2＋ transients （n = 3 in each group） were measured in single colonic SM cells. Ca2＋ handling protein expression was determined by Western blotting （n = 4 in each group）. Differences between control and DSS groups were analyzed by a two-sample independent t-test. Results： Average tension and amplitude of spontaneous contractions of colonic muscle strips were significantly enhanced in DSS-treated rats compared with controls （1.25 ± 0.08 g vs. 0.96 - 0.05 g, P = 0.007; and 2.67 - 0.62 g vs. 0.52 ±0.10 g, P= 0.013）. Average tensions of carbachol-evoked contractions were much weaker in the DSS group （1.08 ±0.10 g vs. 1.80 ±0.19 g, P = 0.006）. Spontaneous Ca2＋ transients were observed in more SM cells from DSS-treated rats （15/30 cells） than from controls （5/36 cells）. Peak caffeine-induced intracellular Ca2＋ release was lower in SM cells of DSS-treated rats than controls （0.413 ±0.046 vs. 0.548 ±0.041, P = 0.033）. Finally, several Ca2＋ handling proteins in colonic SM were altered by DSS treatment, including sarcoplasmic reticulum calcium-transporting ATPase 2a downregulation and phospholamban and inositol 1,4,5-trisphosphate receptor 1 upregulation. Conclusions： Impaired intracellular Ca2＋ signaling of colonic SM, caused by alteration of Ca2＋ handing proteins, contribute to colonic dysmotility in DSS-induced UC.