Intracellular calcium signals regulate growth of hepatic stellate cells via specific effects on cell cycle progression

Novel Inositol 1,4,5-Trisphosphate Receptor Inhibitor Antagonizes Hepatic Stellate Cell Activation: A Potential Drug to Treat Liver Fibrosis

Liver fibrosis, characterized by excessive extracellular matrix (ECM) deposition, can progress to cirrhosis and increases the risk of liver cancer. Hepatic stellate cells (HSCs) play a pivotal role in fibrosis progression, transitioning from a quiescent to activated state upon liver injury, wherein they proliferate, migrate, and produce ECM. Calcium signaling, involving the inositol 1,4,5-trisphosphate receptor (IP3R), regulates HSC activation. This study investigated the efficacy of a novel IP3R inhibitor, desmethylxestospongin B (dmXeB), in preventing HSC activation. Freshly isolated rat HSCs were activated in vitro in the presence of varying dmXeB concentrations. The dmXeB effectively inhibited HSC proliferation, migration, and expression of fibrosis markers without toxicity to the primary rat hepatocytes or human liver organoids. Furthermore, dmXeB preserved the quiescent phenotype of HSCs marked by retained vitamin A storage. Mechanistically, dmXeB suppressed mitochondrial respiration in activated HSCs while enhancing glycolytic activity. Notably, methyl pyruvate, dimethyl α-ketoglutarate, and nucleoside supplementation all individually restored HSC proliferation despite dmXeB treatment. Overall, dmXeB demonstrates promising anti-fibrotic effects by inhibiting HSC activation via IP3R antagonism without adverse effects on other liver cells. These findings highlight dmXeB as a potential therapeutic agent for liver fibrosis treatment, offering a targeted approach to mitigate liver fibrosis progression and its associated complications.

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.

TRPC6, a therapeutic target for pulmonary hypertension

Idiopathic pulmonary arterial hypertension (PAH) is a fatal and progressive disease. Sustained vasoconstriction due to pulmonary arterial smooth muscle cell (PASMC) contraction and concentric arterial remodeling due partially to PASMC proliferation are the major causes for increased pulmonary vascular resistance and increased pulmonary arterial pressure in patients with precapillary pulmonary hypertension (PH) including PAH and PH due to respiratory diseases or hypoxemia. We and others observed upregulation of TRPC6 channels in PASMCs from patients with PAH. A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) in PASMC triggers PASMC contraction and vasoconstriction, while Ca2+-dependent activation of PI3K/AKT/mTOR pathway is a pivotal signaling cascade for cell proliferation and gene expression. Despite evidence supporting a pathological role of TRPC6, no selective and orally bioavailable TRPC6 antagonist has yet been developed and tested for treatment of PAH or PH. In this study, we sought to investigate whether block of receptor-operated Ca2+ channels using a nonselective blocker of cation channels, 2-aminoethyl diphenylborinate (2-APB, administered intraperitoneally) and a selective blocker of TRPC6, BI-749327 (administered orally) can reverse established PH in mice. The results from the study show that intrapulmonary application of 2-APB (40 µM) or BI-749327 (3-10 µM) significantly and reversibly inhibited acute alveolar hypoxia-induced pulmonary vasoconstriction. Intraperitoneal injection of 2-APB (1 mg/kg per day) significantly attenuated the development of PH and partially reversed established PH in mice. Oral gavage of BI-749327 (30 mg/kg, every day, for 2 wk) reversed established PH by ∼50% via regression of pulmonary vascular remodeling. Furthermore, 2-APB and BI-749327 both significantly inhibited PDGF- and serum-mediated phosphorylation of AKT and mTOR in PASMC. In summary, the receptor-operated and mechanosensitive TRPC6 channel is a good target for developing novel treatment for PAH/PH. BI-749327, a selective TRPC6 blocker, is potentially a novel and effective drug for treating PAH and PH due to respiratory diseases or hypoxemia.

Extracellular adenosine: a critical signal in liver fibrosis

Extracellular adenosine nucleoside is a potent, endogenous mediator that signals through specific G protein-coupled receptors, and exerts pleiotropic effects on liver physiology, in health and disease. Particularly, adenosinergic or adenosine-mediated signaling pathways impact the progression of hepatic fibrosis, a common feature of chronic liver diseases, through regulation of matrix deposition by liver myofibroblasts. This review examines the current lines of evidence on adenosinergic regulation of liver fibrosis and myofibroblasts, identifies unanswered research questions, and proposes important future areas of investigation.

Knockdown of histidine-rich calcium-binding protein (HRC) suppresses liver fibrosis by inhibiting the activation of hepatic stellate cells

The histidine-rich calcium-binding protein (HRC) is a regulator of Ca²⁺ homeostasis and it plays a significant role in hepatocellular carcinoma (HCC) progression. However, the relationship between HRC and liver fibrogenesis is still unknown. Our data demonstrates that HRC was upregulated in fibrotic liver and activated hepatic stellate cells (HSCs). TGF-β treatment increased α-SMA and HRC expression dose-dependently in HSCs. Repression of HRC reduced α-SMA, CTGF and collagen expression, and inhibited HSC proliferation and migration. In addition, we found that the anti-fibrosis effect of HRC knockdown was associated with endoplasmic reticulum (ER) stress. Silencing of HRC decreased the expression of ER stress and autophagy markers. Moreover, ER stress agonist thapsigargin (TG) enhanced, whereas ER stress antagonist 4-phenylbutyric acid (4-PBA) alleviated HSCs activation and autophagy. In conclusion, these data indicate that depletion of HRC inhibited HSC activation through the ER stress pathway, and HRC may be a potential regulator of liver fibrosis.

The Role of Embryonic Stem Cell-expressed RAS (ERAS) in the Maintenance of Quiescent Hepatic Stellate Cells

Hepatic stellate cells (HSCs) were recently identified as liver-resident mesenchymal stem cells. HSCs are activated after liver injury and involved in pivotal processes, such as liver development, immunoregulation, regeneration, and also fibrogenesis. To date, several studies have reported candidate pathways that regulate the plasticity of HSCs during physiological and pathophysiological processes. Here we analyzed the expression changes and activity of the RAS family GTPases and thereby investigated the signaling networks of quiescent HSCs versus activated HSCs. For the first time, we report that embryonic stem cell-expressed RAS (ERAS) is specifically expressed in quiescent HSCs and down-regulated during HSC activation via promoter DNA methylation. Notably, in quiescent HSCs, the high level of ERAS protein correlates with the activation of AKT, STAT3, mTORC2, and HIPPO signaling pathways and inactivation of FOXO1 and YAP. Our data strongly indicate that in quiescent HSCs, ERAS targets AKT via two distinct pathways driven by PI3Kα/δ and mTORC2, whereas in activated HSCs, RAS signaling shifts to RAF-MEK-ERK. Thus, in contrast to the reported role of ERAS in tumor cells associated with cell proliferation, our findings indicate that ERAS is important to maintain quiescence in HSCs.

ATP promotes cell survival via regulation of cytosolic [Ca2+] and Bcl-2/Bax ratio in lung cancer cells

Adenosine triphosphate (ATP) is a ubiquitous extracellular messenger elevated in the tumor microenvironment. ATP regulates cell functions by acting on purinergic receptors (P2X and P2Y) and activating a series of intracellular signaling pathways. We examined ATP-induced Ca(2+) signaling and its effects on antiapoptotic (Bcl-2) and proapoptotic (Bax) proteins in normal human airway epithelial cells and lung cancer cells. Lung cancer cells exhibited two phases (transient and plateau phases) of increase in cytosolic [Ca(2+)] ([Ca(2+)]cyt) caused by ATP, while only the transient phase was observed in normal cells. Removal of extracellular Ca(2+) eliminated the plateau phase increase of [Ca(2+)]cyt in lung cancer cells, indicating that the plateau phase of [Ca(2+)]cyt increase is due to Ca(2+) influx. The distribution of P2X (P2X1-7) and P2Y (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11) receptors was different between lung cancer cells and normal cells. Proapoptotic P2X7 was nearly undetectable in lung cancer cells, which may explain why lung cancer cells showed decreased cytotoxicity when treated with high concentration of ATP. The Bcl-2/Bax ratio was increased in lung cancer cells following treatment with ATP; however, the antiapoptotic protein Bcl-2 demonstrated more sensitivity to ATP than proapoptotic protein Bax. Decreasing extracellular Ca(2+) or chelating intracellular Ca(2+) with BAPTA-AM significantly inhibited ATP-induced increase in Bcl-2/Bax ratio, indicating that a rise in [Ca(2+)]cyt through Ca(2+) influx is the critical mediator for ATP-mediated increase in Bcl-2/Bax ratio. Therefore, despite high ATP levels in the tumor microenvironment, which would induce cell apoptosis in normal cells, the decreased P2X7 and elevated Bcl-2/Bax ratio in lung cancer cells may enable tumor cells to survive. Increasing the Bcl-2/Bax ratio by exposure to high extracellular ATP may, therefore, be an important selective pressure promoting transformation and cancer progression.

Dephosphorylation of CaMKII at T253 controls the metaphase-anaphase transition

Calcium/calmodulin-stimulated protein kinase II (CaMKII) is a multi-functional serine/threonine protein kinase that controls a range of cellular functions, including proliferation. The biological properties of CaMKII are regulated by multi-site phosphorylation and targeting via interactions with specific proteins. To investigate the role specific CaMKII phosphorylation sites play in controlling cell proliferation and cell cycle progression, we examined phosphorylation of CaMKII at two sites (T253 and T286) at various stages of the cell cycle, and also examined the effects of overexpression of wild-type (WT), T286D phosphomimic, T253D phosphomimic and T253V phosphonull forms of CaMKIIα in MDA-MB-231 breast cancer and SHSY5Y neuroblastoma cells on cellular proliferation and cell cycle progression. We demonstrate herein that whilst there is no change in total CaMKII expression or T286 phosphorylation throughout the cell cycle, a marked dephosphorylation of CaMKII at T253 occurs during the G2 and/or M phases. Additionally, we show by molecular inhibition, as well as pharmacological activation, that protein phosphatase 2A (PP2A) is the phosphatase responsible for this dephosphorylation. Furthermore, we show that inducible overexpression of WT, T286D and T253V forms of CaMKIIα in MDA-MB-231 and SHSY5Y cells increases cellular proliferation, with no alteration in cell cycle profiles. By contrast, overexpression of a T253D phosphomimic form of CaMKIIα significantly decreases proliferation, and cells accumulate in mitosis, specifically in metaphase. Taken together, these results strongly suggest that the dephosphorylation of CaMKII at T253 is involved in controlling the cell cycle, specifically the metaphase-anaphase transition.

Calcium signaling in the liver

Intracellular free Ca(2+) ([Ca(2+)]i) is a highly versatile second messenger that regulates a wide range of functions in every type of cell and tissue. To achieve this versatility, the Ca(2+) signaling system operates in a variety of ways to regulate cellular processes that function over a wide dynamic range. This is particularly well exemplified for Ca(2+) signals in the liver, which modulate diverse and specialized functions such as bile secretion, glucose metabolism, cell proliferation, and apoptosis. These Ca(2+) signals are organized to control distinct cellular processes through tight spatial and temporal coordination of [Ca(2+)]i signals, both within and between cells. This article will review the machinery responsible for the formation of Ca(2+) signals in the liver, the types of subcellular, cellular, and intercellular signals that occur, the physiological role of Ca(2+) signaling in the liver, and the role of Ca(2+) signaling in liver disease.

Posttranslational regulation of tissue inhibitor of metalloproteinase-1 by calcium-dependent vesicular exocytosis

Liver myofibroblasts derived from hepatic stellate cells (HSC) are critical mediators of liver fibrosis. Release of tissue inhibitor of metalloproteinase-1 (TIMP-1) advances liver fibrosis by blocking fibrinolysis. The mechanisms responsible for the posttranslational regulation of TIMP-1 by myofibroblastic HSC are unknown. Here, we demonstrate that TIMP-1 release by HSC is regulated in a posttranslational fashion via calcium-sensitive vesicular exocytosis. To our knowledge, this is the first article to directly examine vesicular trafficking in myofibroblastic HSC, potentially providing a new target to treat and or prevent liver fibrosis.

Cytoplasmic-targeted parvalbumin blocks the proliferation of multipotent mesenchymal stromal cells in prophase

Introduction

Multipotent mesenchymal stromal cells (MSCs) have gained considerable interest because of their potential use in the treatment of a variety of diseases and injuries. Although remarkable advancements have been made in clinical studies, substantial concerns still regard the safety of MSCs. Some evidence suggests that MSCs can spontaneously generate a population of cells with tumorigenic potential. Thus, studying the molecular mechanisms that control the proliferation of MSCs may be a necessary step toward the development of strategies for safe clinical practice. Ca²⁺ is a second messenger that mediates a wide range of cellular responses, including the regulation of cell proliferation, but little is known about its function in MSCs. The aim of this study was to investigate the effects of targeted Ca²⁺ buffering on MSCs proliferation in vitro.

Methods

Here, we used an adenoviral (Ad) vector encoding the Ca²⁺ chelator protein parvalbumin (PV) fused to a nuclear exclusion signal (NES) and the Discosoma red fluorescent protein (DsRed) to investigate the function of cytoplasmic Ca²⁺ signals on MSC proliferation. Confocal microscopy was used to demonstrate that PV-NES-DsRed was expressed in the cytoplasm. Ca²⁺ signaling was monitored by using Fluo-4-AM. Fluorescence-activated cell sorting (FACS) analysis of cells that were stained with propidium iodide was used as a quantitative measure of cell death. The mitotic index was assessed by immunofluorescence, and the expression of cyclins was examined with Western blot.

Results

Our results show that the Ad-PV-NES-DsRed fusion protein decreased serum-induced Ca²⁺ signaling and blocked the proliferation of rat adipose-derived MSCs (AT-MSCs) in prophase. FACS analysis revealed that Ad-PV-NES-DsRed did not induce cell death in AT-MSCs. Furthermore, Western blot analysis demonstrated that Ad-PV-NES-DsRed reduced extracellular signal-regulated kinase (Erk1/2) phosphorylation and cyclin B1 expression. Buffering cytosolic Ca²⁺ did not alter the expression of cyclins A/D1/D2/D3/E and E2.

Conclusions

Our results show that cytoplasmic Ca²⁺ signals are important for AT-MSCs progression beyond prophase because of their effects on Erk phosphorylation and cyclin B1 expression.

Intracellular and extracellular pH and Ca are bound to control mitosis in the early sea urchin embryo via ERK and MPF activities

Studies aiming to predict the impact on marine life of ocean acidification and of altered salinity have shown altered development in various species including sea urchins. We have analyzed how external Na, Ca, pH and bicarbonate control the first mitotic divisions of sea urchin embryos. Intracellular free Ca (Ca_i) and pH (pH_i) and the activities of the MAP kinase ERK and of MPF regulate mitosis in various types of cells including oocytes and early embryos. We found that intracellular acidification of fertilized eggs by Na-acetate induces a huge activation of ERK at time of mitosis. This also stops the cell cycle and leads to cell death, which can be bypassed by treatment with the MEK inhibitor U0126. Similar intracellular acidification induced in external medium containing low sodium or 5-(N-Methyl-N-isobutyl) amiloride, an inhibitor of the Na⁺/H⁺ exchanger, also stops the cell cycle and leads to cell death. In that case, an increase in Ca_i and in the phosphorylation of tyr-cdc2 occurs during mitosis, modifications that depend on external Ca. Our results indicate that the levels of pH_i and Ca_i determine accurate levels of Ptyr-Cdc2 and P-ERK capable of ensuring progression through the first mitotic cycles. These intracellular parameters rely on external Ca, Na and bicarbonate, alterations of which during climate changes could act synergistically to perturb the early marine life.

Kv3.4 potassium channel-mediated electrosignaling controls cell cycle and survival of irradiated leukemia cells

Aberrant ion channel expression in the plasma membrane is characteristic for many tumor entities and has been attributed to neoplastic transformation, tumor progression, metastasis, and therapy resistance. The present study aimed to define the function of these "oncogenic" channels for radioresistance of leukemia cells. Chronic myeloid leukemia cells were irradiated (0-6 Gy X ray), ion channel expression and activity, Ca(2+)- and protein signaling, cell cycle progression, and cell survival were assessed by quantitative reverse transcriptase-polymerase chain reaction, patch-clamp recording, fura-2 Ca(2+)-imaging, immunoblotting, flow cytometry, and clonogenic survival assays, respectively. Ionizing radiation-induced G2/M arrest was preceded by activation of Kv3.4-like voltage-gated potassium channels. Channel activation in turn resulted in enhanced Ca(2+) entry and subsequent activation of Ca(2+)/calmodulin-dependent kinase-II, and inactivation of the phosphatase cdc25B and the cyclin-dependent kinase cdc2. Accordingly, channel inhibition by tetraethylammonium and blood-depressing substance-1 and substance-2 or downregulation by RNA interference led to release from radiation-induced G2/M arrest, increased apoptosis, and decreased clonogenic survival. Together, these findings indicate the functional significance of voltage-gated K(+) channels for the radioresistance of myeloid leukemia cells.

Nucleoplasmic calcium signaling and cell proliferation: calcium signaling in the nucleus

Calcium (Ca²⁺) is an essential signal transduction element involved in the regulation of several cellular activities and it is required at various key stages of the cell cycle. Intracellular Ca²⁺ is crucial for the orderly cell cycle progression and plays a vital role in the regulation of cell proliferation. Recently, it was demonstrated by in vitro and in vivo studies that nucleoplasmic Ca²⁺ regulates cell growth. Even though the mechanism by which nuclear Ca²⁺ regulates cell proliferation is not completely understood, there are reports demonstrating that activation of tyrosine kinase receptors (RTKs) leads to translocation of RTKs to the nucleus to generate localized nuclear Ca²⁺ signaling which are believed to modulate cell proliferation. Moreover, nuclear Ca²⁺ regulates the expression of genes involved in cell growth. This review will describe the nuclear Ca²⁺ signaling machinery and its role in cell proliferation. Additionally, the potential role of nuclear Ca²⁺ as a target in cancer therapy will be discussed.

Store-operated Ca2+ entry is remodelled and controls in vitro angiogenesis in endothelial progenitor cells isolated from tumoral patients

BACKGROUND

Endothelial progenitor cells (EPCs) may be recruited from bone marrow to sustain tumor vascularisation and promote the metastatic switch. Understanding the molecular mechanisms driving EPC proliferation and tubulogenesis could outline novel targets for alternative anti-angiogenic treatments. Store-operated Ca(2+) entry (SOCE), which is activated by a depletion of the intracellular Ca(2+) pool, regulates the growth of human EPCs, where is mediated by the interaction between the endoplasmic reticulum Ca(2+)-sensor, Stim1, and the plasmalemmal Ca(2+) channel, Orai1. As oncogenesis may be associated to the capability of tumor cells to grow independently on Ca(2+) influx, it is important to assess whether SOCE regulates EPC-dependent angiogenesis also in tumor patients.

METHODOLOGY/PRINCIPAL FINDINGS

The present study employed Ca(2+) imaging, recombinant sub-membranal and mitochondrial aequorin, real-time polymerase chain reaction, gene silencing techniques and western blot analysis to investigate the expression and the role of SOCE in EPCs isolated from peripheral blood of patients affected by renal cellular carcinoma (RCC; RCC-EPCs) as compared to control EPCs (N-EPCs). SOCE, activated by either pharmacological (i.e. cyclopiazonic acid) or physiological (i.e. ATP) stimulation, was significantly higher in RCC-EPCs and was selectively sensitive to BTP-2, and to the trivalent cations, La(3+) and Gd(3+). Furthermore, 2-APB enhanced thapsigargin-evoked SOCE at low concentrations, whereas higher doses caused SOCE inhibition. Conversely, the anti-angiogenic drug, carboxyamidotriazole (CAI), blocked both SOCE and the intracellular Ca(2+) release. SOCE was associated to the over-expression of Orai1, Stim1, and transient receptor potential channel 1 (TRPC1) at both mRNA and protein level The intracellular Ca(2+) buffer, BAPTA, BTP-2, and CAI inhibited RCC-EPC proliferation and tubulogenesis. The genetic suppression of Stim1, Orai1, and TRPC1 blocked CPA-evoked SOCE in RCC-EPCs.

CONCLUSIONS

SOCE is remodelled in EPCs from RCC patients and stands out as a novel molecular target to interfere with RCC vascularisation due to its ability to control proliferation and tubulogenesis.

Ca(2+) /calmodulin- dependent protein kinase II mediates transforming growth factor-β-induced hepatic stellate cells proliferation but not in collagen α1(I) production

AIM

  Hepatic stellate cells (HSC) are the major players in hepatic fibrosis. As a most potent mitogen, transforming growth factor-β (TGF-β) strongly activates HSC and increases intracellular Ca(2+) concentration. Here, we assessed the potential role of Ca(2+) /calmodulin-dependent protein kinase II (CaMKII), a main downstream effector of the Ca(2+) signal in liver fibrogenesis cascade.

METHODS

  A human immortal HSC cell line, LX-2, and primary rat hepatic stellate cells were used in current study. CaMKII blockage and Akt inhibition were performed by KN-93/CaMKIIα siRNA and LY294002, respectively. HSC proliferation was detected by 5-bromodeoxyuridine incorporation assay. Real-time polymerase chain reaction, western blot and enzyme-linked immunosorbent assay were used to measure mRNA, cellular protein and protein in medium, respectively. Procollagen α1(I) expression was detected by immunocytochemistry. The role of CaMKII on TGF-β/Smad-induced collagen α1(I) expression was determined by (CAGA)(12) -MLP luciferase activity assay.

RESULTS

  TGF-β dramatically increased CaMKII mRNA, and total and phosphorylated CaMKII expression. KN-93 and CaMKIIα siRNA suppressed TGF-β-mediated HSC proliferation. CaMKII interruption blocked TGF-β-elicited Akt activation. LY294002 arrested HSC proliferation and collagen α1(I) production but had no effect on CaMKII. Furthermore, CaMKII led to increased p21 and p27 expression. KN-93 and CaMKIIα siRNA inhibited TGF-β-induced and basal collagen α1(I) production but had no effect on the activity of (CAGA)(12) -MLP luciferase in response to TGF-β stimulation.

CONCLUSION

  CaMKII is a pivotal signal in TGF-β-induced fibrogenic cascades by means of stimulating HSC proliferation, and involved in a basal collagen production. Therefore, CaMKII will be a potentially effective target in the development of therapeutic intervention strategies to attenuate hepatic fibrosis.

Kinase activation of ClC-3 accelerates cytoplasmic condensation during mitotic cell rounding

"Mitotic cell rounding" describes the rounding of mammalian cells before dividing into two daughter cells. This shape change requires coordinated cytoskeletal contraction and changes in osmotic pressure. While considerable research has been devoted to understanding mechanisms underlying cytoskeletal contraction, little is known about how osmotic gradients are involved in cell division. Here we describe cytoplasmic condensation preceding cell division, termed "premitotic condensation" (PMC), which involves cells extruding osmotically active Cl(-) via ClC-3, a voltage-gated channel/transporter. This leads to a decrease in cytoplasmic volume during mitotic cell rounding and cell division. Using a combination of time-lapse microscopy and biophysical measurements, we demonstrate that PMC involves the activation of ClC-3 by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) in human glioma cells. Knockdown of endogenous ClC-3 protein expression eliminated CaMKII-dependent Cl(-) currents in dividing cells and impeded PMC. Thus, kinase-dependent changes in Cl(-) conductance contribute to an outward osmotic pressure in dividing cells, which facilitates cytoplasmic condensation preceding cell division.

Phenotypic changes in mouse pancreatic stellate cell Ca2+ signaling events following activation in culture and in a disease model of pancreatitis

The specific characteristics of intracellular Ca 2+ signaling and the downstream consequences of these events were investigated in mouse pancreatic stellate cells (PSC) in culture and in situ using multiphoton microscopy in pancreatic lobules. PSC undergo a phenotypic transformation from a quiescent state to a myofibroblast-like phenotype in culture. This is believed to parallel the induction of an activated state observed in pancreatic disease such as chronic pancreatitis and pancreatic cancer. By day 7 in culture, the complement of cell surface receptors coupled to intracellular Ca 2+ signaling was shown to be markedly altered. Specifically, protease-activated receptors (PAR) 1 and 2, responsive to thrombin and trypsin, respectively, and platelet-derived growth factor (PDGF) receptors were expressed only in activated PSC (aPSC). PAR-1, ATP, and PDGF receptor activation resulted in prominent nuclear Ca 2+ signals. Nuclear Ca 2+ signals and aPSC proliferation were abolished by expression of parvalbumin targeted to the nucleus. In pancreatic lobules, PSC responded to agonists consistent with the presence of only quiescent PSC. aPSC were observed following induction of experimental pancreatitis. In contrast, in a mouse model of pancreatic disease harboring elevated K-Ras activity in acinar cells, aPSC were present under control conditions and their number greatly increased following induction of pancreatitis. These data are consistent with nuclear Ca 2+ signaling generated by agents such as trypsin and thrombin, likely present in the pancreas in disease states, resulting in proliferation of "primed" aPSC to contribute to the severity of pancreatic disease.

Mitochondrial calcium regulates rat liver regeneration through the modulation of apoptosis

Subcellular Ca(2+) signals control a variety of responses in the liver. For example, mitochondrial Ca(2+) (Ca(mit)(2+)) regulates apoptosis, whereas Ca(2+) in the nucleus regulates cell proliferation. Because apoptosis and cell growth can be related, we investigated whether Ca(mit)(2+) also affects liver regeneration. The Ca(2+)-buffering protein parvalbumin, which was targeted to the mitochondrial matrix and fused to green fluorescent protein, was expressed in the SKHep1 liver cell line; the vector was called parvalbumin-mitochondrial targeting sequence-green fluorescent protein (PV-MITO-GFP). This construct properly localized to and effectively buffered Ca(2+) signals in the mitochondrial matrix. Additionally, the expression of PV-MITO-GFP reduced apoptosis induced by both intrinsic and extrinsic pathways. The reduction in cell death correlated with the increased expression of antiapoptotic genes [B cell lymphoma 2 (bcl-2), myeloid cell leukemia 1, and B cell lymphoma extra large] and with the decreased expression of proapoptotic genes [p53, B cell lymphoma 2-associated X protein (bax), apoptotic peptidase activating factor 1, and caspase-6]. PV-MITO-GFP was also expressed in hepatocytes in vivo with an adenoviral delivery system. Ca(mit)(2+) buffering in hepatocytes accelerated liver regeneration after partial hepatectomy, and this effect was associated with the increased expression of bcl-2 and the decreased expression of bax.

CONCLUSION

Together, these results reveal an essential role for Ca(mit)(2+) in hepatocyte proliferation and liver regeneration, which may be mediated by the regulation of apoptosis.

p38 MAPK regulates calcium signal-mediated lipid accumulation through changing VDR expression in primary preadipocytes of mice

In the present study we have examined whether p38 mitogen activated protein kinase (p38 MAPK) signal pathway interacts with calcium signal on lipid accumulation in primary preadipocytes of mice. The primary preadipocytes were treated with p38 MAPK inhibitor SB203580, blockers and excitomotors of calcium channel for 24 h, respectively. Intracellular triglyceride (TG) content was measured by triglyceride kit and lipid accumulation was determined by Oil Red O staining. Meanwhile, the mRNA expressions of peroxisome proliferators-activated receptor gamma (PPARγ) gene, fatty acid synthetase (FAS) gene, lipoprotein lipase (LPL) gene, vitamin D receptor (VDR) gene and extracellular Ca(2+)-sensing receptor (CaSR) gene were analyzed with real-time PCR. The protein content and phosphorylation of VDR and p38 were tested with Western Blotting. The data showed that intracellular TG content and the mRNA expression levels of PPARγ, FAS, LPL in N group and L group as well as FAS, LPL in C group were increased significantly (P < 0.01) compared to the control. On the contrary, intracellular TG content and the mRNA expression levels of PPARγ, FAS in B group as well as intracellular TG content and PPARγ, FAS, LPL in SB group and B+SB group were decreased significantly (P < 0.01). VDR mRNA expression and protein content were decreased in B, C, and SB added groups (P < 0.01). In addition, p38 phosphorylation levels increased in N and L groups (P < 0.01) and decreased in SB added groups (P < 0.01). These findings suggest that p38 MAPK pathway through regulating VDR mRNA expression participates in mediation of calcium signal and affects calcium signal regulating lipid accumulation in mice preadipocytes through changing PPARγ, FAS and LPL mRNA expression. In addition, calcium signal have a feedback effect in phosphorylation of p38.

Pathogenesis of liver fibrosis

Liver fibrosis is a major cause of morbidity and mortality worldwide due to chronic viral hepatitis and, more recently, from fatty liver disease associated with obesity. Hepatic stellate cell activation represents a critical event in fibrosis because these cells become the primary source of extracellular matrix in liver upon injury. Use of cell-culture and animal models has expanded our understanding of the mechanisms underlying stellate cell activation and has shed new light on genetic regulation, the contribution of immune signaling, and the potential reversibility of the disease. As pathways of fibrogenesis are increasingly clarified, the key challenge will be translating new advances into the development of antifibrotic therapies for patients with chronic liver disease.

Needle-based confocal laser endomicroscopy to assess liver histology in vivo

BACKGROUND

Confocal endomicroscopy enables histopathology of the GI lumen to be observed in vivo. Recent prototypes of a confocal miniprobe are thin enough to be introduced through a needle.

OBJECTIVE

To evaluate the ability of needle-based confocal laser endomicroscopy to distinguish between normal and cirrhotic liver tissue in vivo in a rat model.

DESIGN

Feasibility study, nonsurvival animal experiments.

SETTING

Academic research facility.

INTERVENTION

Three normal control and 4 cirrhotic rats were examined under general anesthesia. The liver was exposed by laparotomy and imaged by using 3 different prototypes of confocal miniprobes, with 0, 50, and 100 μm working distances. Images were acquired on the surface of the liver capsule and through a 19-gauge needle inserted into the liver parenchyma. Real-time sequences were recorded after intravenous injection of fluorescein. Biopsy specimens were taken for standard histopathology.

MAIN OUTCOME MEASUREMENTS

Confocal microscopic images of the surface and interior of livers in normal and cirrhotic rats.

RESULTS

Miniprobes with 50 or 100 μm working distances identified cords of hepatocytes radiating toward central venules in normal livers and distorted hepatic architecture in cirrhotic livers when the miniprobes were either placed on the liver capsule or inserted into the parenchyma. The miniprobe with a 0 μm working distance identified a novel reticular pattern on the liver surface that was detected only in cirrhosis. Like the 2 longer-working-distance probes, this probe also identified cords of hepatocytes radiating toward central venules in normal livers and distorted hepatic architecture in cirrhotic livers, but this occurred only when the probe was inserted into the parenchyma.

LIMITATIONS

Data were assessed in an experimental animal setting, confocal imaging was performed invasively during laparotomy, only 1 model of cirrhosis was used, and no noncirrhotic liver diseases were examined.

CONCLUSION

Needle-based confocal laser endomicroscopy provides sufficient detail to distinguish normal from cirrhotic livers in a rat model. This innovative, minimally invasive technique has the potential to provide real-time identification of liver histology during EUS or natural-orifice transluminal endoscopic surgery procedures.

Cytosolic calcium regulates liver regeneration in the rat

Liver regeneration is regulated by growth factors, cytokines, and other endocrine and metabolic factors. Calcium is important for cell division, but its role in liver regeneration is not known. The purpose of this study was to understand the effects of cytosolic calcium signals in liver growth after partial hepatectomy (PH). The gene encoding the calcium-binding protein parvalbumin (PV) targeted to the cytosol using a nuclear export sequence (NES), and using a discosoma red fluorescent protein (DsR) marker, was transfected into rat livers by injecting it, in recombinant adenovirus (Ad), into the portal vein. We performed two-thirds PH 4 days after Ad-PV-NES-DsR or Ad-DsR injection, and liver regeneration was analyzed. Calcium signals were analyzed with fura-2-acetoxymethyl ester in hepatocytes isolated from Ad-infected rats and in Ad-infected Hela cells. Also, isolated hepatocytes were infected with Ad-DsR or Ad-PV-NES-DsR and assayed for bromodeoxyuridine incorporation. Ad-PV-NES-DsR injection resulted in PV expression in the hepatocyte cytosol. Agonist-induced cytosolic calcium oscillations were attenuated in both PV-NES-expressing Hela cells and hepatocytes, as compared to DsR-expressing cells. Bromodeoxyuridine incorporation (S phase), phosphorylated histone 3 immunostaining (mitosis), and liver mass restoration after PH were all significantly delayed in PV-NES rats. Reduced cyclin expression and retinoblastoma protein phosphorylation confirmed this observation. PV-NES rats exhibited reduced c-fos induction and delayed extracellular signal-regulated kinase 1/2 phosphorylation after PH. Finally, primary PV-NES-expressing hepatocytes exhibited less proliferation and agonist-induced cyclic adenosine monophosphate responsive element binding and extracellular signal-regulated kinase 1/2 phosphorylation, as compared with control cells.

CONCLUSION

Cytosolic calcium signals promote liver regeneration by enhancing progression of hepatocytes through the cell cycle.

Role of membrane potential in the regulation of cell proliferation and differentiation

Biophysical signaling, an integral regulator of long-term cell behavior in both excitable and non-excitable cell types, offers enormous potential for modulation of important cell functions. Of particular interest to current regenerative medicine efforts, we review several examples that support the functional role of transmembrane potential (V(mem)) in the regulation of proliferation and differentiation. Interestingly, distinct V(mem) controls are found in many cancer cell and precursor cell systems, which are known for their proliferative and differentiation capacities, respectively. Collectively, the data demonstrate that bioelectric properties can serve as markers for cell characterization and can control cell mitotic activity, cell cycle progression, and differentiation. The ability to control cell functions by modulating bioelectric properties such as V(mem) would be an invaluable tool for directing stem cell behavior toward therapeutic goals. Biophysical properties of stem cells have only recently begun to be studied and are thus in need of further characterization. Understanding the molecular and mechanistic basis of biophysical regulation will point the way toward novel ways to rationally direct cell functions, allowing us to capitalize upon the potential of biophysical signaling for regenerative medicine and tissue engineering.