Pre‐treatments enhance the therapeutic effects of mesenchymal stem cells in liver diseases

Liver diseases caused by viral infection, alcohol abuse and metabolic disorders can progress to end‐stage liver failure, liver cirrhosis and liver cancer, which are a growing cause of death worldwide. Although liver transplantation and hepatocyte transplantation are useful strategies to promote liver regeneration, they are limited by scarce sources of organs and hepatocytes. Mesenchymal stem cells (MSCs) restore liver injury after hepatogenic differentiation and exert immunomodulatory, anti‐inflammatory, antifibrotic, antioxidative stress and antiapoptotic effects on liver cells in vivo. After isolation and culture in vitro, MSCs are faced with nutrient and oxygen deprivation, and external growth factors maintain MSC capacities for further applications. In addition, MSCs are placed in a harsh microenvironment, and anoikis and inflammation after transplantation in vivo significantly decrease their regenerative capacity. Pre‐treatment with chemical agents, hypoxia, an inflammatory microenvironment and gene modification can protect MSCs against injury, and pre‐treated MSCs show improved hepatogenic differentiation, homing capacity, survival and paracrine effects in vitro and in vivo in regard to attenuating liver injury. In this review, we mainly focus on pre‐treatments and the underlying mechanisms for improving the therapeutic effects of MSCs in various liver diseases. Thus, we provide evidence for the development of MSC‐based cell therapy to prevent acute or chronic liver injury. Mesenchymal stem cells have potential as a therapeutic to prolong the survival of patients with end‐stage liver diseases in the near future.     

Melatonin and its protective role in attenuating warm or cold hepatic ischaemia/reperfusion injury

Although the liver is the only organ with regenerative capacity, various injury factors induce irreversible liver dysfunction and end‐stage liver disease. Liver resection and liver transplantation (LT) are effective treatments for individuals with liver failure, liver cirrhosis and liver cancers. The remnant or transplanted liver tissues will undergo hepatic ischaemia/reperfusion (IR), which leads to oxidative stress, inflammation, immune injury and liver damage. Moreover, systemic ischaemia induced by trauma, stroke, myocardial ischaemia, haemorrhagic shock and other injury factors also induces liver ischaemia/reperfusion injury (IRI) in individuals. Hepatic IRI can be divided into warm IRI, which is induced by liver surgery and systemic ischaemia, and cold IRI, which is induced by LT. Multiple studies have shown that melatonin (MT) acts as an endogenous free radical scavenger with antioxidant capacity and is also able to attenuate hepatic IRI via its anti‐inflammatory and antiapoptotic capacities. In this review, we discuss the potential mechanisms and current strategies of MT administration in liver surgery for protecting against warm or cold hepatic IRI. We highlight strategies to improve the efficacy and safety of MT for attenuating hepatic IRI in different conditions. After the potential mechanisms underlying the interactions between MT and other important cellular processes during hepatic IR are clarified, more opportunities will be available to use MT to treat liver diseases in the future.     

Application of mesenchymal stem cell exosomes and their drug‐loading systems in acute liver failure

Stem cell exosomes are nanoscale membrane vesicles released from stem cells of various origins that can regulate signal transduction pathways between liver cells, and their functions in intercellular communication have been recognized. Due to their natural substance transport properties and excellent biocompatibility, exosomes can also be used as drug carriers to release a variety of substances, which has great prospects in the treatment of critical and incurable diseases. Different types of stem cell exosomes have been used to study liver diseases. Due to current difficulties in the treatment of acute liver failure (ALF), this review will outline the potential of stem cell exosomes for ALF treatment. Specifically, we reviewed the pathogenesis of acute liver failure and the latest progress in the use of stem cell exosomes in the treatment of ALF, including the role of exosomes in inhibiting the ALF inflammatory response and regulating signal transduction pathways, the advantages of stem cell exosomes and their use as a drug‐loading system, and their pre‐clinical application in the treatment of ALF. Finally, the clinical research status of stem cell therapy for ALF and the current challenges of exosome clinical transformation are summarized.     

Effects of indoleamine 2,3‐dioxygenases in carbon tetrachloride‐induced hepatitis model of rats

Indoleamine 2,3‐dioxygenase (IDO) converts tryptophan to l ‐kynurenine, and it is noted as a relevant molecule in promoting tolerance and suppressing adaptive immunity. In this study, to investigate the effects of IDO in carbon tetrachloride (CCl₄)–induced hepatitis model, the levels of IDO enzymic activities in the mock group, the control group and the 1‐methyl‐d ‐tryptophan (1‐MT)–treated group were confirmed by determination of l ‐kynurenine concentrations. Serum alanine aminotransferase levels in 1‐MT‐treated rats after CCl₄ injection significantly increased compared with those in mock and control groups. In CCl₄‐induced hepatitis models, tumour necrosis factor‐α (TNF‐α) is critical in the development of liver injury. The mRNA expression and secretion levels of TNF‐α in the liver from 1‐MT‐treated rats were more enhanced compared with those in the mock and the control groups. Moreover, the levels of cytokine and chemokine from mock, control group and 1‐MT‐treated rats after treated with CCl₄ were analyzed by ELISA, and the level of interleukin‐6 was found to increase in 1‐MT‐treated rats. It was concluded that the deficiency of IDO exacerbated liver injury in CCl₄‐induced hepatitis and its effect may be connected with TNF‐α and interleukin‐6. Copyright © 2012 John Wiley & Sons, Ltd.     

Polydatin alleviated radiation‐induced lung injury through activation of Sirt3 and inhibition of epithelial–mesenchymal transition

Radiation‐induced lung injury (RILI) is one of the most common and fatal complications of thoracic radiotherapy. It is characterized with two main features including early radiation pneumonitis and fibrosis in later phase. This study was to investigate the potential radioprotective effects of polydatin (PD), which was shown to exert anti‐inflammation and anti‐oxidative capacities in other diseases. In this study, we demonstrated that PD‐mitigated acute inflammation and late fibrosis caused by irradiation. PD treatment inhibited TGF‐β1‐Smad3 signalling pathway and epithelial–mesenchymal transition. Moreover, radiation‐induced imbalance of Th1/Th2 was also alleviated by PD treatment. Besides its free radical scavenging capacity, PD induced a huge increase of Sirt3 in culture cells and lung tissues. The level of Nrf2 and PGC1α in lung tissues was also elevated. In conclusion, our data showed that PD attenuated radiation‐induced lung injury through inhibiting epithelial–mesenchymal transition and increased the expression of Sirt3, suggesting PD as a novel potential radioprotector for RILI.     

Stem/progenitor cells in liver injury repair and regeneration

Morbidity and mortality from cirrhosis is increasing rapidly in the world. Currently, orthotopic liver transplantation is the only definitive therapeutic option. However, its clinical use is limited, because of poor long‐term graft survival, donor organ shortage and high costs associated with the procedure. Stem cell replacement strategies are therefore being investigated as an attractive alternative approach to liver repair and regeneration. In this review we discuss recent preclinical and clinical investigations that explore the therapeutic potential of stem cells in repair of liver injuries. Several types of stem cells. including embryonic stem cells, haematopoietic stem cells and mesenchymal stem cells, can be induced to differentiate into hepatocyte‐like cells by defined culture conditions in vitro. Stem cell transplantation has been shown to significantly improve liver function and increase animal survival in experimentally‐induced liver‐injury models. Moreover, several pilot clinical studies have reported encouraging therapeutic effects in patients treated with stem cells. Although there remain many unresolved issues, the available data support the notion that stem cell technology may lead to the development of effective clinical modalities for human liver diseases.     

Differential function of protective agents at each stage of the hypothermic preservation of hepatocytes

Hypothermic preservation of bioartificial liver (BAL) has long been appreciated in BAL storage and transportation. However, the deterioration of cell activity during hypothermia/rewarming limits its clinical use and the complete prevention of hypothermia-induced hepatocyte injury has not been achieved. In this article, a miniaturized BAL that underwent three preservation stages (i.e. pre-incubation, hypothermia and rewarming) was applied as a hypothermic preservation model to locate the protection of several protective agents against hypothermia-induced cell injury. The agents, including vitamin E, schisandrin B, glycyrrhizic acid, N-acetyl-cysteine, ruthenium red, trehalose, anisodamine, fructose-1, 6-diphosphate, cyclosporin A and matrine (Mat), were found to exert their functions at different preservation stages, which were speculated to associate with the specific protection of each agent as well as the corresponding cell injuries at each stage. Such hypothesis was further strengthened by focusing on Mat, which only suppressed the hypothermia-induced injury through the inhibition of Ca(2+) overload at the rewarming stage, whereas its presence at the hypothermic stage excessively down-regulated the cytosolic free Ca(2+) and then aggravated cell death. The results indicate that the specific cell injury at each preservation stage requires a corresponding protective agent. However, the untimely misuse of the agents may inversely aggravate cell injury.     

Invasion by activated macrophages requires delivery of nascent membrane‐type‐1 matrix metalloproteinase through late endosomes/lysosomes to the cell surface

Macrophage migration into injured or infected tissue is a key aspect in the pathophysiology of many diseases where inflammation is a driving factor. Membrane‐type‐1 matrix metalloproteinase (MT1‐MMP) cleaves extracellular matrix components to facilitate invasion. Here we show that, unlike the constitutive MT1‐MMP surface recycling seen in cancer cells, unactivated macrophages express low levels of MT1‐MMP. Upon lipopolysaccharide (LPS) activation, MT1‐MMP synthesis dramatically increases 10‐fold at the surface by 15 hours. MT1‐MMP is trafficked from the Golgi complex to the surface via late endosomes/lysosomes in a pathway regulated by the late endosome/lysosome R‐SNAREs VAMP7 and VAMP8. These form two separate complexes with the surface Q‐SNARE complex Stx4/SNAP23 to regulate MT1‐MMP delivery to the plasma membrane. Loss of either one of these SNAREs leads to a reduction in surface MT1‐MMP, gelatinase activity and reduced invasion. Thus, inhibiting MT1‐MMP transport through this pathway could reduce macrophage migration and the resulting inflammation.     

Puerarin Protects Human Neuroblastoma SH‐SY5Y Cells against Glutamate‐Induced Oxidative Stress and Mitochondrial Dysfunction

Glutamate, the principal excitatory neurotransmitter, plays a central role in brain metabolism; however, aberrant neurotransmission of glutamate has been linked to neurodegenerative diseases. Therefore, the effective agents that target at glutamate‐induced cell injury will be useful for prevention and treatment of neurodegenerative diseases. In this study, the neuroprotective effect of puerarin, an active isoflavone extracted from the Chinese herb Radix puerariae, against glutamate‐induced cell injury in human neuroblastoma SH‐SY5Y cells was evaluated for the first time. The results showed that the pretreatment of puerarin could attenuate glutamate‐induced cell injury in a dose‐dependent manner. This protective effect was mediated through inhibiting reactive oxygen species generation, attenuating the upregulation of Bax and downregulation of Bcl‐2, preserving mitochondrial membrane potential (MMP), preventing cytochrome c release, and reducing caspase activity. These findings may significantly contribute to a better understanding of the neuroprotective effect of puerarin and provide new insights into its application toward neurodegenerative diseases in the future.     

Salvianic acid A alleviates chronic alcoholic liver disease by inhibiting HMGB1 translocation via down‐regulating BRD4

Alcoholic liver disease (ALD) is the major cause of chronic liver disease and a global health concern. ALD pathogenesis is initiated with liver steatosis, and ALD can progress to steatohepatitis, fibrosis, cirrhosis and even hepatocellular carcinoma. Salvianic acid A (SAA) is a phenolic acid component of Danshen, a Chinese herbal medicine with possible hepatoprotective properties. The purpose of this study was to investigate the effect of SAA on chronic alcoholic liver injury and its molecular mechanism. We found that SAA significantly inhibited alcohol‐induced liver injury and ameliorated ethanol‐induced hepatic inflammation. These protective effects of SAA were likely carried out through its suppression of the BRD4/HMGB1 signalling pathway, because SAA treatment largely diminished alcohol‐induced BRD4 expression and HMGB1 nuclear translocation and release. Importantly, BRD4 knockdown prevented ethanol‐induced HMGB1 release and inflammatory cytokine production in AML‐12 cells. Similarly, alcohol‐induced pro‐inflammatory cytokines were blocked by HMGB1 siRNA. Collectively, our results reveal that activation of the BRD4/HMGB1 pathway is involved in ALD pathogenesis. Therefore, manipulation of the BRD4/HMGB1 pathway through strategies such as SAA treatment holds great therapeutic potential for chronic alcoholic liver disease therapy.     

Imaging liver‐stage malaria parasites

Plasmodium parasites, the causative agents of malaria, first invade and develop within hepatocytes before infecting red blood cells and causing symptomatic disease. Because of the low infection rates in vitro and in vivo, the liver stage of Plasmodium infection is not very amenable to biochemical assays, but the large size of the parasite at this stage in comparison with Plasmodium blood stages makes it accessible to microscopic analysis. A variety of imaging techniques has been used to this aim, ranging from electron microscopy to widefield epifluorescence and laser scanning confocal microscopy. High‐speed live video microscopy of fluorescent parasites in particular has radically changed our view on key events in Plasmodium liver‐stage development. This includes the fate of motile sporozoites inoculated by Anopheles mosquitoes as well as the transport of merozoites within merosomes from the liver tissue into the blood vessel. It is safe to predict that in the near future the application of the latest microscopy techniques in Plasmodium research will bring important insights and allow us spectacular views of parasites during their development in the liver.     

A potential role of GW4064 to inhibit gut bacterial overgrowth by activating FXR in suppression of ethanol-induced liver injury

Hepatic parenchymal and nonparenchymal cells are highly susceptible to ethanol and its metabolites, and excessive alcohol consumption results in damage to the liver. Ethanol induces an increased prevalence for bacterial overgrowth in the small intestine and translocation of endotoxin into the portal blood. Some studies have pointed to a role for activation of Kupffer cells by gut bacteria-derived endotoxin as a primary event in mechanisms of alcoholic liver injury (ALD). GW4064, a potent farnesoid X receptor (FXR) agonist, has been developed as a hepatoprotective agent, and has been used in animal models of a variety of liver diseases. At the same time, previous experimental results showed that BAs and GW4064 inhibit bacterial overgrowth in the small intestine. It is logical to postulate that GW4064 may control or alleviate the ethanol-induced liver injury through inhibiting gut bacterial overgrowth. GW4064 activates FXR, which induces the expression of several genes with potential functions in mucosal defense to prevent intestinal bacteria overgrowth and translocation into the circulation induced by ethanol, and then will alleviate ethanol-induced liver injury. The hypothesis will provide the brand-new direction that we may prevent and treat ALD by using GW4064 through activating FXR to control gut bacteria overgrowth.     

ARRB1 ameliorates liver ischaemia/reperfusion injury via antagonizing TRAF6‐mediated Lysine 6‐linked polyubiquitination of ASK1 in hepatocytes

Hepatic ischaemia/reperfusion (I/R) injury is a major clinical problem during liver surgical procedures, which usually lead to early transplantation failure and higher organ rejection rate, and current effective therapeutic strategies are still limited. Therefore, in‐depth exploring of the molecular mechanisms underlying liver I/R injury is key to the development of new therapeutic methods. β‐arrestins are multifunctional proteins serving as important signalling scaffolds in numerous physiopathological processes, including liver‐specific diseases. However, the role and underlying mechanism of β‐arrestins in hepatic I/R injury remain largely unknown. Here, we showed that only ARRB1, but not ARRB2, was down‐regulated during liver I/R injury. Hepatocyte‐specific overexpression of ARRB1 significantly ameliorated liver damage, as demonstrated by decreases in serum aminotransferases, hepatocellular necrosis and apoptosis, infiltrating inflammatory cells and secretion of pro‐inflammatory cytokines relative to control mice, whereas experiments with ARRB1 knockout mice gotten opposite effects. Mechanistically, ARRB1 directly interacts with ASK1 in hepatocytes and inhibits its TRAF6‐mediated Lysine 6‐linked polyubiquitination, which then prevents the activation of ASK1 and its downstream signalling pathway during hepatic I/R injury. In addition, inhibition of ASK1 remarkably abolished the disruptive effect result from ARRB1 deficiency in liver I/R injury in vivo, indicating that ASK1 was required for ARRB1 function in hepatic I/R injury. In conclusion, we proposed that ARRB1 is a novel protective regulator during liver I/R injury, and modulation of the regulatory axis between ARRB1 and ASK1 could be a novel therapeutic strategy to prevent this pathological process.     

microRNA‐143‐3p attenuated development of hepatic fibrosis in autoimmune hepatitis through regulation of TAK1 phosphorylation

Autoimmune hepatitis (AIH) is a chronic liver disease due to autoimmune system attacks hepatocytes and causes inflammation and fibrosis. Intracellular signalling and miRNA may play an important role in regulation of liver injury. This study aimed to investigate the potential roles of microRNA 143 in a murine AIH model and a hepatocyte injury model. Murine AIH model was induced by hepatic antigen S100, and hepatocyte injury model was induced by LPS. Mice and AML12 cells were separated into six groups with or without the treatment of miRNA‐143. Inflammation and fibrosis as well as gene expression were examined by different cellular and molecular techniques. The model was successfully established with the elevation of ALT and AST as well as inflammatory and fibrotic markers. Infection or transfection of mir‐143 in mice or hepatocytes significantly attenuated the development of alleviation of hepatocyte injury. Moreover, the study demonstrated phosphorylation of TAK1‐mediated miRNA‐143 regulation of hepatic inflammation and fibrosis as well as hepatocyte injury. Our studies demonstrated a significant role of miRNA‐143 in attenuation of liver injury in AIH mice and hepatocytes. miRNA‐143 regulates inflammation and fibrosis through its regulation of TAK1 phosphorylation, which warrants TAK1 as a target for the development of new therapeutic strategy of autoimmune hepatitis.     

Role of cardiac progenitor cell‐derived exosome‐mediated microRNA‐210 in cardiovascular disease

Cardiac progenitor cells are considered to be one of the most promising stem cells for heart regeneration and repair. The cardiac protective effect of CPCs is mainly achieved by reducing tissue damage and/or promoting tissue repair through a paracrine mechanism. Exosome is a factor that plays a major role in the paracrine effect of CPCs. By delivering microRNAs to target cells and regulating their functions, exosomes have shown significant beneficial effects in slowing down cardiac injury and promoting cardiac repair. Among them, miRNA‐210 is an important anoxic‐related miRNA derived from CPCs exosomes, which has great cardiac protective effect of inhibiting myocardial cell apoptosis, promoting angiogenesis and improving cardiac function. In addition, circulating miR‐210 may be a useful biomarker for the prediction or diagnosis of related cardiovascular diseases. In this review, we briefly reviewed the mechanism of miR‐210 derived from CPCs exosomes in cardiac protection in recent years.     

Biomechanics and functionality of hepatocytes in liver cirrhosis

Cirrhosis is a life-threatening condition that is generally attributed to overproduction of collagen fibers in the extracellular matrix that mechanically stiffens the liver. Chronic liver injury due to causes including viral hepatitis, inherited and metabolic liver diseases and external factors such as alcohol abuse can result in the development of cirrhosis. Progression of cirrhosis leads to hepatocellular dysfunction. While extensive studies to understand the complexity underlying liver fibrosis have led to potential application of anti-fibrotic drugs, no such FDA-approved drugs are currently available. Additional studies of hepatic fibrogenesis and cirrhosis primarily have focused on the extracellular matrix, while hepatocyte biomechanics has received limited attention. The role of hepatocyte biomechanics in liver cirrhosis remains elusive, and how the cell stiffness is correlated with biological functions of hepatocytes is also unknown. In this study, we demonstrate that the biomechanical properties of hepatocytes are correlated with their functions (e.g., glucose metabolism), and that hepatic dysfunction can be restored through modulation of the cellular biomechanics. Furthermore, our results indicate the hepatocyte functionality appears to be regulated through a crosstalk between the Rho and Akt signaling. These novel findings may lead to biomechanical intervention of hepatocytes and the development of innovative tissue engineering for clinical treatment to target liver cells rather than exclusively focusing on the extracellular matrix alone in liver cirrhosis.     

Thrombin down‐regulates the TGF‐β‐mediated synthesis of collagen and fibronectin by human proximal tubule epithelial cells through the EPCR‐dependent activation of PAR‐1

Human proximal tubule (HK‐2) cells are commonly used as cellular models to understand the mechanism by which inflammatory mediators cause renal injury. It has been observed that thrombin stimulates the expression of TGF‐β, extracellular matrix (ECM) proteins and proinflammatory cytokines by HK‐2 cells. These in vitro responses correlate well with the pathology of glomerular and tubular diseases observed in acute renal injury. HK‐2 cells express PAR‐1 and the thrombin activation of this receptor has been reported to up‐regulate the TGF‐β‐mediated expression of ECM proteins, suggesting a possible pathogenic role for PAR‐1 signaling by thrombin in acute renal injury. On the other hand, several recent studies have indicated that activated protein C plays a renoprotective role, thus inhibiting the inflammatory responses and attenuating renal injury, presumably by activating the same cell surface receptor. In this study, we show that HK‐2 cells express endothelial protein C receptor (EPCR) and that the occupancy of this receptor by protein C switches the signaling specificity of thrombin so that the activation of PAR‐1 by thrombin inhibits the TNF‐α‐mediated synthesis of IL‐6 and IL‐8 and down‐regulates the TGF‐β‐mediated expression of ECM proteins. These results suggest a possible protective role for EPCR in acute kidney injury. J. Cell. Physiol. 225: 233–239, 2010. © 2010 Wiley‐Liss, Inc.     

Localization and biological activities of melatonin in intact and diseased gastrointestinal tract (GIT).

Melatonin (MT), an indole formed enzymatically from L-trytophan (Trp), was first discovered in the bovine pineal gland in 1958 by Lerner et al. Melatonin is the most versatile and ubiquitous hormonal molecule produced not only in the pineal gland but also in various other tissues of invertebrates and vertebrates, particularly in the gastrointestinal tract (GIT). This review focuses on the localization, production, metabolism and the functions of MT in GIT and the duodenal unit (liver, biliary routes and pancreas), where multi-step biosynthetic pathways of this indole, similar to those in pinealocytes, have been identified. These biosynthetic steps of MT, including two major rate limiting enzymes; arylalkylamine-N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT), transforming L-tryptophan (Trp), originally identified in pinealocytes, have been also detected in entero-endocrine (EE) cells of GIT, where this indole appears to act in endocrine, paracrine and/or luminal pathway directly or through G-protein coupled MT receptors. Studies of the distribution of MT in GIT mucosa showed that this indole is generated in GIT in much larger amounts than it is produced in the pineal gland. Melatonin acts in GIT, partly locally in paracrine fashion and is partly released into portal circulation, to be taken up by the liver. It is then metabolized and excreted with the bile to small bowel and finally returns to liver through entero-hepatic circulation. The production of MT by the pineal gland shows circadian rhythm with high night-time surge, especially at younger age, followed by the fall during the day-light time. As a highly lipophylic substance, MT reaches all body cells within minutes, thus, serving as a convenient circadian timing signal. Following pinealectomy, the light/dark cycle of plasma MT levels disappears, while its day-time blood concentration is maintained mainly due to its release from the GIT. According to our experience, after oral application of Trp, the plasma MT increases in dose-dependent manner both in intact and pinealectomized animals and humans, indicating that GIT but not the pineal gland is a source of this indole. In GIT MT exhibits a wide spectrum of activities such as circadian entrainment, antioxidant and free radicals scavenging activity, Melatonin (MT), an indole formed enzymatically from L-trytophan (Trp), was first discovered in the bovine pineal gland in 1958 by Lerner et al. Melatonin is the most versatile and ubiquitous hormonal molecule produced not only in the pineal gland but also in various other tissues of invertebrates and vertebrates, particularly in the gastrointestinal tract (GIT). This review focuses on the localization, production, metabolism and the functions of MT in GIT and the duodenal unit (liver, biliary routes and pancreas), where multi-step biosynthetic pathways of this indole, similar to those in pinealocytes, have been identified. These biosynthetic steps of MT, including two major rate limiting enzymes; arylalkylamine-N-acetyltransferase (AA-NAT) and hydroxyindole-O-methyltransferase (HIOMT), transforming L-tryptophan (Trp), originally identified in pinealocytes, have been also detected in entero-endocrine (EE) cells of GIT, where this indole appears to act in endocrine, paracrine and/or luminal pathway directly or through G-protein coupled MT receptors. Studies of the distribution of MT in GIT mucosa showed that this indole is generated in GIT in much larger amounts than it is produced in the pineal gland. Melatonin acts in GIT, partly locally in paracrine fashion and is partly released into portal circulation, to be taken up by the liver. It is then metabolized and excreted with the bile to small bowel and finally returns to liver through entero-hepatic circulation. The production of MT by the pineal gland shows circadian rhythm with high night-time surge, especially at younger age, followed by the fall during the day-light time. As a highly lipophylic substance, MT reaches all body cells within minutes, thus, serving as a convenient circadian timing signal. Following pinealectomy, the light/dark cycle of plasma MT levels disappears, while its day-time blood concentration is maintained mainly due to its release from the GIT. According to our experience, after oral application of Trp, the plasma MT increases in dose-dependent manner both in intact and pinealectomized animals and humans, indicating that GIT but not the pineal gland is a source of this indole. In GIT MT exhibits a wide spectrum of activities such as circadian entrainment, antioxidant and free radicals scavenging activity, cytoprotective, anti-inflammatory and healing efficacy of various GIT lesions such as esophagitis, gastritis, peptic ulcer, pancreatitis and colitis. This review concentrates on the generation and pathophysiological implication of MT in GIT and related organs.     

CXCL6‐EGFR‐induced Kupffer cells secrete TGF‐β1 promoting hepatic stellate cell activation via the SMAD2/BRD4/C‐MYC/EZH2 pathway in liver fibrosis

Liver fibrosis is the excessive accumulation of extracellular matrix proteins in response to the inflammatory response that accompanies tissue injury, which at an advanced stage can lead to cirrhosis and even liver failure. This study investigated the role of the CXC chemokine CXCL6 (GCP‐2) in liver fibrosis. The expression of CXCL6 was found to be elevated in the serum and liver tissue of high stage liver fibrosis patients. Furthermore, treatment with CXCL6 (100 ng/mL) stimulated the phosphorylation of EGFR and the expression of TGF‐β in cultured Kupffer cells (KCs). Although treatment with CXCL6 directly did not activate the hepatic stellate cell (HSC) line, HSC‐T6, HSCs cultured with media taken from KCs treated with CXCL6 or TGF‐β showed increased expression of α‐SMA, a marker of HSC activation. CXCL6 was shown to function via the SMAD2/BRD4/C‐MYC/EZH2 pathway by enhancing the SMAD3‐BRD4 interaction and promoting direct binding of BRD4 to the C‐MYC promoter and CMY‐C to the EZH2 promoter, thereby inducing profibrogenic gene expression in HSCs, leading to activation and transdifferentiation into fibrogenic myofibroblasts. These findings were confirmed in a mouse model of CCl₄‐induced chronic liver injury and fibrosis in which the levels of CXCL6 and TGF‐β in serum and the expression of α‐SMA, SMAD3, BRD4, C‐MYC, and EZH2 in liver tissue were increased. Taken together, our results reveal that CXCL6 plays an important role in liver fibrosis through stimulating the release of TGF‐β by KCs and thereby activating HSCs.