Cell Death In Hepatic Stellate Cells Research Articles

Cytoplasmic vacuolation with endoplasmic reticulum stress directs sorafenib induced non-apoptotic cell death in hepatic stellate cells

The activated hepatic stellate cells (HSCs) are the major cells that secrete the ECM proteins and drive the pathogenesis of fibrosis in chronic liver disease. Targeting of HSCs by modulating their activation and proliferation has emerged as a promising approach in the development of anti-fibrotic therapy. Sorafenib, a multi-kinase inhibitor has shown anti-fibrotic properties by inhibiting the survival and proliferation of HSCs. In present study we investigated sorafenib induced cytoplasmic vacuolation mediated decreased cell viability of HSCs in dose and time dependent manner. In this circumstance, sorafenib induces ROS and ER stress in HSCs without involvement of autophagic signals. The protein synthesis inhibitor cycloheximide treatment significantly decreased the sorafenib-induced cytoplasmic vacuolation with increasing cell viability. Antioxidant human serum albumin influences the viability of HSCs by reducing sorafenib induced vacuolation and cell death. However, neither caspase inhibitor Z-VAD-FMK nor autophagy inhibitor chloroquine could rescue the HSCs from sorafenib-induced cytoplasmic vacuolation and cell death. Using TEM and ER organelle tracker, we conclude that the cytoplasmic vacuoles are due to ER dilation. Sorafenib treatment induces calreticulin and GPR78, and activates IRE1α-XBP1s axis of UPR pathway, which eventually trigger the non-apoptotic cell death in HSCs. This study provides a notable mechanistic insight into the ER stress directed non-apoptotic cell death with future directions for the development of efficient anti-fibrotic therapeutic strategies.

Soluble egg antigen of Schistosoma japonicum induces pyroptosis in hepatic stellate cells by modulating ROS production

BackgroundInflammation-induced dysfunction of hepatic stellate cells (HSCs) is involved in schistosomiasis-associated liver fibrosis, and soluble egg antigen (SEA) is a crucial pathogen-associated molecular pattern associated with liver injury in schistosomiasis. In addition, numerous studies have shown that caspase-1-mediated pyroptosis participates in the development of multiple inflammation-related diseases. However, whether pyroptotic cell death of HSCs is involved in SEA-mediated liver damage is not well understood.MethodsPrimary cultured HSCs and Schistosoma japonicum-infected mouse liver tissue were analysed for histological changes and caspase-1 activation, and the role of pyroptosis in the mechanisms underlying SEA-induced HSC death was investigated. Accumulation of reactive oxygen species (ROS) in infected livers and SEA-stimulated HSCs was measured by flow cytometry and immunofluorescence.ResultsCaspase-1 activity was elevated in both liver tissues and HSCs of S. japonicum-infected mice. Furthermore, SEA stimulation increased the proportion of pyroptotic HSCs, as shown by lactate dehydrogenase (LDH) release assays and by flow cytometric analysis of propidium iodide (PI) and caspase-1 double staining in cells. In addition, ROS generation was elevated in infected liver tissues and SEA-stimulated HSCs, and ROS inhibition downregulated SEA-induced caspase-1 activation and pyroptosis in HSCs.ConclusionsOur present study demonstrates that pyroptotic cell death in HSCs induced by SEA via ROS-mediated caspase-1 activation may serve as a significant mechanism to initiate the inflammatory response and thereby exacerbate liver injury during S. japonicum infection.

Serum Amyloid A Induces Inflammation, Proliferation and Cell Death in Activated Hepatic Stellate Cells.

Serum amyloid A (SAA) is an evolutionary highly conserved acute phase protein that is predominantly secreted by hepatocytes. However, its role in liver injury and fibrogenesis has not been elucidated so far. In this study, we determined the effects of SAA on hepatic stellate cells (HSCs), the main fibrogenic cell type of the liver. Serum amyloid A potently activated IκB kinase, c-Jun N-terminal kinase (JNK), Erk and Akt and enhanced NF-κB-dependent luciferase activity in primary human and rat HSCs. Serum amyloid A induced the transcription of MCP-1, RANTES and MMP9 in an NF-κB- and JNK-dependent manner. Blockade of NF-κB revealed cytotoxic effects of SAA in primary HSCs with signs of apoptosis such as caspase 3 and PARP cleavage and Annexin V staining. Serum amyloid A induced HSC proliferation, which depended on JNK, Erk and Akt activity. In primary hepatocytes, SAA also activated MAP kinases, but did not induce relevant cell death after NF-κB inhibition. In two models of hepatic fibrogenesis, CCl4 treatment and bile duct ligation, hepatic mRNA levels of SAA1 and SAA3 were strongly increased. In conclusion, SAA may modulate fibrogenic responses in the liver in a positive and negative fashion by inducing inflammation, proliferation and cell death in HSCs.

The novel endocannabinoid noladin ether holds putative anti-fibrotic properties by selectively inducing cell death in hepatic stellate cells

Background: We could previously demonstrate that the endogenous cannabinoid 2-arachidonoyl glycerol (2-AG) is an antifibrotic lipid mediator that blocks proliferation and induces apoptotic cell death in hepatic stellate cells (HSCs), but not in hepatocytes. Recently a novel endocannabinoid termed noladin ether (NE, 2-arachidonyl glyceryl ether) has been identified, which represents a more stable entity against enzymatic hydrolysis than 2-AG. Aims: To test the effects of NE on hepatic cell populations. Methods: Primary hepatocytes and HSCs were isolated from healthy rat or mouse liver by collagenase perfusion. Cell death was analyzed by LDH assay and western blot for caspase 3- and PARP-cleavage. Glutathione (GSH) was depleted by DL-buthionine-(S,R)-sulfoximine (BSO) treatment. Antioxidant resistance was enhanced by Trolox application. ROS formation was detected by DCFDA fluorescence. Membrane cholesterol was depleted by methyl-beta-cyclodextrin (MCD). Results: NE dose-dependently induced cell death in activated primary HSCs after 2–4h, starting from 2µM. In contrast to 2-AG, which induced late apoptosis in HSCs, NE induced hallmarks of necrosis, lack of caspase-3 or PARP cleavage. ROS formation in HSCs was significantly and even more increased by NE than by 2-AG. The antioxidant Trolox significantly decreased NE-induced death, thus indicating an ROS-dependent cell death mechanism. Although the cannabinoid receptors CB1, CB2 and TRPV1 were expressed in HSCs, pharmacological blockade failed to block NE-mediated cell death, indicating a cannabinoid-receptor independent mechanism. Interestingly, membrane cholesterol depletion with MCD completely inhibited NE-induced cell death. Similarly to 2-AG, NE did not induce cell death in hepatocytes. The resistance toward NE in hepatocytes was due to high levels of antioxidants such as GSH, since GSH depletion with BSO significantly increased NE-induced cell death in hepatocytes. Intriguingly, adenoviral overexpression of the putative endocannabinoid degradation enzyme fatty acid amide hydrolase (FAAH) in HSCs did not rescue from NE-induced cell death, underlining the stability of NE against enzymatic hydrolysis. Conclusion: NE effectively caused cell death in activated HSCs, but not in hepatocytes. NE-induced cell death was mediated through membrane cholesterol-rich lipid rafts and pronounced ROS formation, but independently from cannabinoid receptors. The selective induction of cell death in HSCs and its high stability against enzymatic hydrolysis proposes NE as a potential endogenous antifibrogenic mediator.

The endocannabinoid N-arachidonoyl dopamine (NADA) selectively induces oxidative stress-mediated cell death in hepatic stellate cells but not in hepatocytes

The endocannabinoid system is a crucial regulator of hepatic fibrogenesis. We have previously shown that the endocannabinoid anandamide (AEA) is a lipid mediator that blocks proliferation and induces death in hepatic stellate cells (HSCs), the main fibrogenic cell type in the liver, but not in hepatocytes. However, the effects of other endocannabinoids such as N-arachidonoyl dopamine (NADA) have not yet been investigated. The NADA-synthesizing enzyme tyrosine hydroxylase was mainly expressed in sympathetic neurons in portal tracts. Its expression pattern stayed unchanged in normal or fibrotic liver. NADA dose dependently induced cell death in culture-activated primary murine or human HSCs after 2-4 h, starting from 5 μM. Despite caspase 3 cleavage, NADA-mediated cell death showed typical features of necrosis, including ATP depletion. Although the cannabinoid receptors CB1, CB2, or transient receptor potential cation channel subfamily V, member 1 were expressed in HSCs, their pharmacological or genetic blockade failed to inhibit NADA-mediated death, indicating a cannabinoid-receptor-independent mechanism. Interestingly, membrane cholesterol depletion with methyl-β-cyclodextrin inhibited AEA- but not NADA-induced death. NADA significantly induced reactive oxygen species formation in HSCs. The antioxidant glutathione (GSH) significantly decreased NADA-induced cell death. Similar to AEA, primary hepatocytes were highly resistant against NADA-induced death. Resistance to NADA in hepatocytes was due to high levels of GSH, since GSH depletion significantly increased NADA-induced death. Moreover, high expression of the AEA-degrading enzyme fatty acid amide hydrolase (FAAH) in hepatocytes also conferred resistance towards NADA-induced death, since pharmacological or genetic FAAH inhibition significantly augmented hepatocyte death. Thus the selective induction of cell death in HSCs proposes NADA as a novel antifibrogenic mediator.

Fatty Acid Amide Hydrolase Determines Anandamide-induced Cell Death in the Liver

The endocannabinoid anandamide (AEA) induces cell death in many cell types, but determinants of AEA-induced cell death remain unknown. In this study, we investigated the role of the AEA-degrading enzyme fatty acid amide hydrolase (FAAH) in AEA-induced cell death in the liver. Primary hepatocytes expressed high levels of FAAH and were completely resistant to AEA-induced cell death, whereas primary hepatic stellate cells (HSCs) expressed low levels of FAAH and were highly sensitive to AEA-induced cell death. Hepatocytes that were pretreated or with the FAAH inhibitor URB597 isolated from FAAH(-/-) mice displayed increased AEA-induced reactive oxygen species (ROS) formation and were susceptible to AEA-mediated death. Conversely, overexpression of FAAH in HSCs prevented AEA-induced death. Since FAAH inhibition conferred only partial AEA sensitivity in hepatocytes, we analyzed additional factors that might regulate AEA-induced death. Hepatocytes contained significantly higher levels of glutathione (GSH) than HSCs. Glutathione depletion by dl-buthionine-(S,R)-sulfoximine rendered hepatocytes susceptible to AEA-mediated ROS production and cell death, whereas GSH ethyl ester prevented ROS production and cell death in HSCs. FAAH inhibition and GSH depletion had additive effects on AEA-mediated hepatocyte cell death resulting in almost 70% death after 24 h at 50 microm AEA and lowering the threshold for cell death to 500 nm. Following bile duct ligation, FAAH(-/-) mice displayed increased hepatocellular injury, suggesting that FAAH protects hepatocytes from AEA-induced cell death in vivo. In conclusion, FAAH and GSH are determinants of AEA-mediated cell death in the liver.

Endocannabinoid Degradation and Oxidative Defense Mechanisms Determine Anandamide-induced Cell Death in Liver Cell Populations

Background: We have shown that the endogenous cannabinoid anandamide (AEA) induces reactive oxygen species (ROS)-dependent cell death in primary hepatic stellate cells (HSCs), but not in primary hepatocytes. Aim: To determine cellular factors that control AEA-induced cell death in hepatic cell populations. Methods: Fatty acid amide hydrolase (FAAH) expression was analyzed by western blot and real time PCR in primary rat hepatocytes and primary rat HSCs. FAAH activity was determined colorimetrically. Cell death was analyzed by LDH release, propidium iodide uptake and western blot for caspase 3- and PARP cleavage. Glutathione (GSH) levels were measured by the DTNB method. mRNA expression of the endocannabinoid receptors CB1, CB2 and VR1 was determined by real time PCR. ROS production was monitored by DCFDA fluorescence. Results: FAAH mRNA, FAAH protein and FAAH activity were extremely high in primary rat hepatocytes, but virtually absent in primary rat HSCs. Hepatocytes from FAAH -/- mice, or wildtype hepatocytes which had been pretreated with the FAAH inhibitor URB597 were susceptible to AEA-mediated death (45% and 40% at 50 μM after 24h, respectively). Conversely, FAAH overexpression prevented AEA-induced death in HSCs. Anandamide induced an increase in ROS production in hepatocytes which had been pretreated with the FAAH inhibitor URB597 or depleted of GSH by BSO. GSH levels were 10-fold higher in hepatocytes than in HSCs. GSH depletion rendered hepatocytes susceptible to AEA-mediated death while GSH pretreatment prevented cell death in HSCs. The combination of FAAH inhibition and GSH depletion had additive effects on AEA-mediated hepatocyte cell death resulting in almost 70% death after 24h at 50 μM AEA and lowered the threshold for AEA-induced cell death to 500 nM. AEA-induced hepatocyte death after BSO and URB597 pretreatment was purely necrotic and occurred independently of the endocannabinoid receptors CB1, CB2 and VR1 which were virtually absent (CB1, CB2) or expressed at low levels (VR1) in hepatocytes. Conclusion: FAAH and GSH determine endocannabinoid-induced necrosis in hepatocytes and HSCs, independently of expression of cannabinoid receptors. High expression of FAAH and high intracellular GSH levels efficiently prevent AEA-induced cell death in hepatocytes. FAAH-mediated endocannabinoid degradation in hepatocytes leads to a new physiological concept allowing the specific targeting of HSCs in liver fibrosis.

Molecular Pathogenesis of Alcohol‐Induced Hepatic Fibrosis

Alcohol abuse is a main cause of liver fibrosis and cirrhosis in the western world. Although the major mechanisms of fibrogenesis are independent of the origin of liver injury, alcoholic liver fibrosis features distinctive characteristics, including the pronounced inflammatory response of immune cells due to elevated gut-derived endotoxin plasma levels, increased formation of reactive oxygen species (ROS), ethanol-induced pericentral hepatic hypoxia or formation of cell-toxic and pro-fibrogenic ethanol metabolites (e.g., acetaldehyde or lipid oxidation products). These factors are together responsible for increased hepatocellular cell death and activation of hepatic stellate cells (HSCs), the key cell type of liver fibrogenesis. To date, removing the causative agent is the most effective intervention to prevent the manifestation of liver cirrhosis. A novel experimental approach in fibrosis therapy is the selective induction of cell death in HSCs. Substances such as gliotoxin, anandamide or antibody against tissue inhibitor of metalloproteinase (TIMP)-1 can selectively induce cell death in activated HSCs. These new results in basic science are encouraging for the search of new antifibrotic treatment.