Hepatic fibrogenesis requires sympathetic neurotransmitters

Leveraging adrenergic receptor blockade for enhanced nonalcoholic fatty liver disease treatment via a biomimetic nanoplatform

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive lipid accumulation, steatosis and fibrosis. Sympathetic nerves play a critical role in maintaining hepatic lipid homeostasis and regulating fibrotic progression through adrenergic receptors expressed by hepatocytes and hepatic stellate cells; however, the use of sympathetic nerve-focused strategies for the treatment of NAFLD is still in the infancy. Herein, a biomimetic nanoplatform with ROS-responsive and ROS-scavenging properties was developed for the codelivery of retinoic acid (RA) and the adrenoceptor antagonist labetalol (LA). The nanoplatform exhibited improved accumulation and sufficient drug release in the fibrotic liver, thereby achieving precise codelivery of drugs. Integration of adrenergic blockade effectively interrupted the vicious cycle of sympathetic nerves with hepatic stellate cells (HSCs) and hepatocytes, which not only combined with RA to restore HSCs to a quiescent state but also helped to reduce hepatic lipid accumulation. We demonstrated the excellent ability of the biomimetic nanoplatform to ameliorate liver inflammation, fibrosis and steatosis. Our work highlights the tremendous potential of a sympathetic nerve-focused strategy for the management of NAFLD and provides a promising nanoplatform for the treatment of NAFLD.

Signalling of the neuropeptide calcitonin gene-related peptide (CGRP) through RAMP1 promotes liver fibrosis via TGFβ1/Smad2 and YAP pathways

The liver is innervated by primary sensory nerve fibres releasing the neuropeptide calcitonin gene-related peptide (CGRP). Elevated plasma levels of CGRP have been found in patients with liver fibrosis or cirrhosis. We hypothesised that signalling of CGRP and its receptors might regulate liver fibrosis and propose a novel potential target for the treatment. In this study, hepatic expression of CGRP and its receptor component, the receptor activity-modifying protein 1 (RAMP1), was dramatically increased in diseased livers of patients. In a murine liver fibrosis model, deficiency of RAMP1 resulted in attenuated fibrogenesis characterized by less collagen deposition and decreased activity of hepatic stellate cells (HSC). Mechanistically, activity of the TGFβ1 signalling core component Smad2 was severely impaired in the absence of RAMP1, and Yes-associated protein (YAP) activity was found to be diminished in RAMP1-deficient liver parenchyma. In vitro, stimulation of the HSC line LX-2 cells with CGRP induces TGFβ1 production and downstream signalling as well as HSC activation documented by increased α-SMA expression and collagen synthesis. We further demonstrate in LX-2 cells that CGRP promotes YAP activation and its nuclear translocation subsequent to TGFβ1/Smad2 signals. These data support a promotive effect of CGRP signalling in liver fibrosis via stimulation of TGFβ1/Smad2 and YAP activity.

Neuroimmune modulation in liver pathophysiology

The liver, the largest organ in the human body, plays a multifaceted role in digestion, coagulation, synthesis, metabolism, detoxification, and immune defense. Changes in liver function often coincide with disruptions in both the central and peripheral nervous systems. The intricate interplay between the nervous and immune systems is vital for maintaining tissue balance and combating diseases. Signaling molecules and pathways, including cytokines, inflammatory mediators, neuropeptides, neurotransmitters, chemoreceptors, and neural pathways, facilitate this complex communication. They establish feedback loops among diverse immune cell populations and the central, peripheral, sympathetic, parasympathetic, and enteric nervous systems within the liver. In this concise review, we provide an overview of the structural and compositional aspects of the hepatic neural and immune systems. We further explore the molecular mechanisms and pathways that govern neuroimmune communication, highlighting their significance in liver pathology. Finally, we summarize the current clinical implications of therapeutic approaches targeting neuroimmune interactions and present prospects for future research in this area.

The pathophysiology of MASLD: an immunometabolic perspective

INTRODUCTION

Metabolic-associated liver diseases have emerged pandemically across the globe and are clinically related to metabolic disorders such as obesity and type 2 diabetes. The new nomenclature and definition (i.e. metabolic dysfunction-associated steatotic liver disease - MASLD; metabolic dysfunction-associated steatohepatitis - MASH) reflect the nature of these complex systemic disorders, which are characterized by inflammation, gut dysbiosis and metabolic dysregulation. In this review, we summarize recent advantages in understanding the pathophysiology of MASLD, which we parallel to emerging therapeutic concepts.

AREAS COVERED

We summarize the pathophysiologic concepts of MASLD and its transition to MASH and subsequent advanced sequelae of diseases. Furthermore, we highlight how dietary constituents, microbes and associated metabolites, metabolic perturbations, and immune dysregulation fuel lipotoxicity, hepatic inflammation, liver injury, insulin resistance, and systemic inflammation. Deciphering the intricate pathophysiologic processes that contribute to the development and progression of MASLD is essential to develop targeted therapeutic approaches to combat this escalating burden for health-care systems.

EXPERT OPINION

The rapidly increasing prevalence of metabolic dysfunction-associated steatotic liver disease challenges health-care systems worldwide. Understanding pathophysiologic traits is crucial to improve the prevention and treatment of this disorder and to slow progression into advanced sequelae such as cirrhosis and hepatocellular carcinoma.

Impact of Liver Sympathetic Nervous System on Liver Fibrosis and Regeneration After Bile Duct Ligation in Rats

The sympathetic nervous system (SNS) affects many functions of the body. SNS fibers regulate many aspects of liver function, repair, and regeneration. However, in the model of bile duct ligation (BDL) in rats, the kind of impact caused by the regulation of liver SNS on liver fibrosis and liver regeneration is unclear. The main research objective of this experiment is to examine the effect of SNS on liver fibrosis and liver regeneration. Twenty-four male Sprague-Dawley (SD) rats were assigned randomly to four groups. These groups included the sham surgery group (sham), model group (BDL), 6-hydroxydopamine group (BDL+6-OHDA), and spinal cord injury group (BDL+SCI). In the sham group, only exploratory laparotomy was performed without BDL. In the 6-OHDA group, 6-OHDA was used to remove sympathetic nerves after BDL. In the spinal cord injury group, rats underwent simultaneous BDL and spinal cord injury. After 3 weeks of feeding, four groups of rats were euthanized using high-dose anesthesia without pain. Moreover, liver tissue and blood were taken to detect liver fibrosis and regeneration indicators. After intraperitoneal injection of 6-OHDA into BDL rats, liver fibrosis indicators decreased. The administration of the injection effectively alleviated liver fibrosis and inhibited liver regeneration. However, after SCI surgery in BDL rats, liver fibrosis indicators increased. This resulted in exacerbating liver fibrosis and activating liver regeneration. The SNS plays a role in contributing to the liver injury process in the rat BDL model. Therefore, regulating the SNS may become a novel method for liver injury treatment.

Neuroimmunomodulation of adrenoblockers during liver cirrhosis: modulation of hepatic stellate cell activity

The sympathetic nervous system and the immune system are responsible for producing neurotransmitters and cytokines that interact by binding to receptors; due to this, there is communication between these systems. Liver immune cells and nerve fibres are systematically distributed in the liver, and the partial overlap of both patterns may favour interactions between certain elements. Dendritic cells are attached to fibroblasts, and nerve fibres are connected via the dendritic cell-fibroblast complex. Receptors for most neuroactive substances, such as catecholamines, have been discovered on dendritic cells. The sympathetic nervous system regulates hepatic fibrosis through sympathetic fibres and adrenaline from the adrenal glands through the blood. When there is liver damage, the sympathetic nervous system is activated locally and systemically through proinflammatory cytokines that induce the production of epinephrine and norepinephrine. These neurotransmitters bind to cells through α-adrenergic receptors, triggering a cellular response that secretes inflammatory factors that stimulate and activate hepatic stellate cells. Hepatic stellate cells are key in the fibrotic process. They initiate the overproduction of extracellular matrix components in an active state that progresses from fibrosis to liver cirrhosis. It has also been shown that they can be directly activated by norepinephrine. Alpha and beta adrenoblockers, such as carvedilol, prazosin, and doxazosin, have recently been used to reverse CCl₄-induced liver cirrhosis in rodent and murine models.KEY MESSAGESNeurotransmitters from the sympathetic nervous system activate and increase the proliferation of hepatic stellate cells.Hepatic fibrosis and cirrhosis treatment might depend on neurotransmitter and hepatic nervous system regulation.Strategies to reduce hepatic stellate cell activation and fibrosis are based on experimentation with α-adrenoblockers.

Liver organoid culture methods

Organoids, three-dimensional structures cultured in vitro, can recapitulate the microenvironment, complex architecture, and cellular functions of in vivo organs or tissues. In recent decades, liver organoids have been developed rapidly, and their applications in biomedicine, such as drug screening, disease modeling, and regenerative medicine, have been widely recognized. However, the lack of repeatability and consistency, including the lack of standardized culture conditions, has been a major obstacle to the development and clinical application of liver organoids. It is time-consuming for researchers to identify an appropriate medium component scheme, and the usage of some ingredients remains controversial. In this review, we summarized and compared different methods for liver organoid cultivation that have been published in recent years, focusing on controversial medium components and discussing their advantages and drawbacks. We aimed to provide an effective reference for the development and standardization of liver organoid cultivation.

Axon guidance molecules in liver pathology: Journeys on a damaged passport

BACKGROUND AND AIMS

The liver is an innervated organ that develops a variety of chronic liver disease (CLD). Axon guidance cues (AGCs), of which ephrins, netrins, semaphorins and slits are the main representative, are secreted or membrane-bound proteins that can attract or repel axons through interactions with their growth cones that contain receptors recognizing these messengers. While fundamentally implicated in the physiological development of the nervous system, the expression of AGCs can also be reinduced under acute or chronic conditions, such as CLD, that necessitate redeployment of neural networks.

METHODS

This review considers the ad hoc literature through the neglected canonical neural function of these proteins that is also applicable to the diseased liver (and not solely their observed parenchymal impact).

RESULTS

AGCs impact fibrosis regulation, immune functions, viral/host interactions, angiogenesis, and cell growth, both at the CLD and HCC levels. Special attention has been paid to distinguishing correlative and causal data in such datasets in order to streamline data interpretation. While hepatic mechanistic insights are to date limited, bioinformatic evidence for the identification of AGCs mRNAs positive cells, protein expression, quantitative regulation, and prognostic data have been provided. Liver-pertinent clinical studies based on the US Clinical Trials database are listed. Future research directions derived from AGC targeting are proposed.

CONCLUSION

This review highlights frequent implication of AGCs in CLD, linking traits of liver disorders and the local autonomic nervous system. Such data should contribute to diversifying current parameters of patient stratification and our understanding of CLD.

Magnesium and Liver Metabolism Through the Lifespan

Within the organism, the liver is the main organ responsible for metabolic homeostasis and xenobiotic transformation. To maintain an adequate liver weight-to-bodyweight ratio, this organ has an extraordinary regenerative capacity and is able to respond to an acute insult or partial hepatectomy. Maintenance of hepatic homeostasis is crucial for the proper functioning of the liver, and in this context, adequate nutrition with macro- and micronutrient intake is mandatory. Among all known macro-minerals, magnesium has a key role in energy metabolism and in metabolic and signaling pathways that maintain liver function and physiology throughout its life span. In the present review, the cation is reported as a potential key molecule during embryogenesis, liver regeneration, and aging. The exact role of the cation during liver formation and regeneration is not fully understood due to its unclear role in the activation and inhibition of those processes, and further research in a developmental context is needed. As individuals age, they may develop hypomagnesemia, a condition that aggravates the characteristic alterations. Additionally, risk of developing liver pathologies increases with age, and hypomagnesemia may be a contributing factor. Therefore, magnesium loss must be prevented by adequate intake of magnesium-rich foods such as seeds, nuts, spinach, or rice to prevent age-related hepatic alterations and contribute to the maintenance of hepatic homeostasis. Since magnesium-rich sources include a variety of foods, a varied and balanced diet can meet both macronutrient and micronutrient needs.

Regulatory mucosa-associated invariant T cells controlled by β1 adrenergic receptor signaling contribute to hepatocellular carcinoma progression

BACKGROUND AND AIMS

The innate-like mucosa-associated invariant T (MAIT) cells are enriched in human liver and have been linked to human HCC. However, their contributions to the progression of HCC are controversial due to the heterogeneity of MAIT cells, and new MAIT cell subsets remain to be explored.

APPROACH AND RESULTS

Combining single cell RNA sequencing (scRNA-seq) and flow cytometry analysis, we performed phenotypic and functional studies and found that FOXP3 + CXCR3 + MAIT cells in HCC patients were regulatory MAIT cells (MAITregs) with high immunosuppressive potential. These MAITregs were induced under Treg-inducing condition and predominantly from FOXP3 - CXCR3 + MAIT cells, which displayed mild Treg-related features and represented a pre-MAITreg reservoir. In addition, the induction and function of MAITregs were promoted by β1 adrenergic receptor signaling in pre-MAITregs and MAITregs, respectively. In HCC patients, high proportion of the intratumoral MAITregs inhibited antitumor immune responses and was associated with poor clinical outcomes.

CONCLUSIONS

Together, we reveal an immunosuppressive subset of MAIT cells in HCC patients that contributes to HCC progression, and propose a control through neuroimmune crosstalk.

Liver cell therapies: cellular sources and grafting strategies

The liver has a complex cellular composition and a remarkable regenerative capacity. The primary cell types in the liver are two parenchymal cell populations, hepatocytes and cholangiocytes, that perform most of the functions of the liver and that are helped through interactions with non-parenchymal cell types comprising stellate cells, endothelia and various hemopoietic cell populations. The regulation of the cells in the liver is mediated by an insoluble complex of proteins and carbohydrates, the extracellular matrix, working synergistically with soluble paracrine and systemic signals. In recent years, with the rapid development of genetic sequencing technologies, research on the liver's cellular composition and its regulatory mechanisms during various conditions has been extensively explored. Meanwhile breakthroughs in strategies for cell transplantation are enabling a future in which there can be a rescue of patients with end-stage liver diseases, offering potential solutions to the chronic shortage of livers and alternatives to liver transplantation. This review will focus on the cellular mechanisms of liver homeostasis and how to select ideal sources of cells to be transplanted to achieve liver regeneration and repair. Recent advances are summarized for promoting the treatment of end-stage liver diseases by forms of cell transplantation that now include grafting strategies.

Hepatic Innervations and Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder. Increased sympathetic (noradrenergic) nerve tone has a complex role in the etiopathomechanism of NAFLD, affecting the development/progression of steatosis, inflammation, fibrosis, and liver hemodynamical alterations. Also, lipid sensing by vagal afferent fibers is an important player in the development of hepatic steatosis. Moreover, disorganization and progressive degeneration of liver sympathetic nerves were recently described in human and experimental NAFLD. These structural alterations likely come along with impaired liver sympathetic nerve functionality and lack of adequate hepatic noradrenergic signaling. Here, we first overview the anatomy and physiology of liver nerves. Then, we discuss the nerve impairments in NAFLD and their pathophysiological consequences in hepatic metabolism, inflammation, fibrosis, and hemodynamics. We conclude that further studies considering the spatial-temporal dynamics of structural and functional changes in the hepatic nervous system may lead to more targeted pharmacotherapeutic advances in NAFLD.

β-adrenergic receptor agonist promotes ductular expansion during 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced chronic liver injury

Intrahepatic nerves are involved in the regulation of metabolic reactions and hepatocyte-based regeneration after surgical resection, although their contribution to chronic liver injury remains unknown. Given that intrahepatic nerves are abundant in the periportal tissue, they may be correlated also with cholangiocyte-based regeneration. Here we demonstrate that isoproterenol (ISO), a β-adrenergic receptor agonist, promoted ductular expansion induced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) in vivo. Immunofluorescence analysis shows that nerve fibers positive for tyrosine hydroxylase form synaptophysin-positive nerve endings on epithelial cell adhesion molecule-positive (EpCAM⁺) cholangiocytes as well as on Thy1⁺ periportal mesenchymal cells (PMCs) that surround bile ducts, suggesting that the intrahepatic biliary tissue are targeted by sympathetic nerves. In vitro analyses indicate that ISO directly increases cAMP levels in cholangiocytes and PMCs. Mechanistically, ISO expands the lumen of cholangiocyte organoids, resulting in promotion of cholangiocyte proliferation, whereas it increases expression of fibroblast growth factor 7, a growth factor for cholangiocytes, in PMCs. Taken together, the results indicate that intrahepatic sympathetic nerves regulate remodeling of bile ducts during DDC-injury by the activation of β-adrenergic receptors on cholangiocytes and PMCs.

Drug repurposing in cancer neuroscience: From the viewpoint of the autophagy-mediated innervated niche

Based on the bidirectional interactions between neurology and cancer science, the burgeoning field “cancer neuroscience” has been proposed. An important node in the communications between nerves and cancer is the innervated niche, which has physical contact with the cancer parenchyma or nerve located in the proximity of the tumor. In the innervated niche, autophagy has recently been reported to be a double-edged sword that plays a significant role in maintaining homeostasis. Therefore, regulating the innervated niche by targeting the autophagy pathway may represent a novel therapeutic strategy for cancer treatment. Drug repurposing has received considerable attention for its advantages in cost-effectiveness and safety. The utilization of existing drugs that potentially regulate the innervated niche via the autophagy pathway is therefore a promising pharmacological approach for clinical practice and treatment selection in cancer neuroscience. Herein, we present the cancer neuroscience landscape with an emphasis on the crosstalk between the innervated niche and autophagy, while also summarizing the underlying mechanisms of candidate drugs in modulating the autophagy pathway. This review provides a strong rationale for drug repurposing in cancer treatment from the viewpoint of the autophagy-mediated innervated niche.

Effect of chronic stress on tumorigenesis and development

Chronic stress activates the sympathetic nervous system (SNS) and hypothalamic-pituitary-adrenal (HPA) axis to aggravates tumorigenesis and development. Although the importance of SNS and HPA in maintaining homeostasis has already attracted much attention, there is still a lot remained unknown about the molecular mechanisms by which chronic stress influence the occurrence and development of tumor. While some researches have already concluded the mechanisms underlying the effect of chronic stress on tumor, complicated processes of tumor progression resulted in effects of chronic stress on various stages of tumor remains elusive. In this reviews we concluded recent research progresses of chronic stress and its effects on premalignancy, tumorigenesis and tumor development, we comprehensively summarized the molecular mechanisms in between. And we highlight the available treatments and potential therapies for stressed patients with tumor.

Macrophage polarization is involved in liver fibrosis induced by β 1-adrenoceptor autoantibody

Accumulating evidence suggests that liver injury can be induced by the over-expression of β ₁-adrenergic receptors (β ₁-ARs). High titers of autoantibodies specific to β ₁-adrenergic receptors (β ₁-AA) are detected in the sera of heart failure patients, potentially playing agonist-like roles. However, the role of β ₁-AA in liver function has not been characterized. In this study, we collect the sera of primary biliary cholangitis (PBC) patients, a condition which easily develops into liver fibrosis, and analyze the relationship between PBC and β ₁-AA. A passive immunization model is established to assess the effect of β ₁-AA on the liver. Subsequently, the effect of β ₁-AA on macrophages is investigated in vitro. Results show that PBC patients have a high titer and ratio of β ₁-AA, compared to controls. Liver injury and fibrosis are induced by β ₁-AA. In vitro experiments with ROS probe demonstrate that β ₁-AA induces macrophages to produce ROS and secrete TNFα. These effects can be partially reversed by metoprolol, a blocker for β ₁-AR. Results from the transwell and phagocytosis assays show that β ₁-AA promotes macrophage migration and phagocytosis. FCM tests suggest that β ₁-AA induces the alteration of M1 rather than M2 markers in macrophages. Finally, the Annexin V/PI assay indicates that macrophage culture supernatants stimulated by β ₁-AA cause hepatocyte apoptosis. Overall, these results suggest that β ₁-AA is involved in PBC. The β ₁-AA-induced activation, phagocytosis and phenotypic modification of macrophages may play an important role in the development of hepatic fibrosis and injury.

Cellular crosstalk during liver regeneration: unity in diversity

The liver is unique in its ability to regenerate from a wide range of injuries and diseases. Liver regeneration centers around hepatocyte proliferation and requires the coordinated actions of nonparenchymal cells, including biliary epithelial cells, liver sinusoidal endothelial cells, hepatic stellate cells and kupffer cells. Interactions among various hepatocyte and nonparenchymal cells populations constitute a sophisticated regulatory network that restores liver mass and function. In addition, there are two different ways of liver regeneration, self-replication of liver epithelial cells and transdifferentiation between liver epithelial cells. The interactions among cell populations and regenerative microenvironment in the two modes are distinct. Herein, we first review recent advances in the interactions between hepatocytes and surrounding cells and among nonparenchymal cells in the context of liver epithelial cell self-replication. Next, we discuss the crosstalk of several cell types in the context of liver epithelial transdifferentiation, which is also crucial for liver regeneration.

The liver-gut peripheral neural axis and nonalcoholic fatty liver disease pathologies via hepatic serotonin receptor 2A

Serotonin (5-HT) is one of the key bioamines of nonalcoholic fatty liver disease (NAFLD). Its mechanism of action in autonomic neural signal pathways remains unexplained; hence, we evaluated the involvement of 5-HT and related signaling pathways via autonomic nerves in NAFLD. Diet-induced NAFLD animal models were developed using wild-type and melanocortin 4 receptor (MC4R) knockout (MC4RKO) mice, and the effects of the autonomic neural axis on NAFLD physiology, 5-HT and its receptors (HTRs), and lipid metabolism-related genes were assessed by applying hepatic nerve blockade. Hepatic neural blockade retarded the progression of NAFLD by reducing 5-HT in the small intestine, hepatic HTR2A and hepatic lipogenic gene expression, and treatment with an HTR2A antagonist reproduced these effects. The effects were milder in MC4RKO mice, and brain 5-HT and HTR2C expression did not correlate with peripheral neural blockade. Our study demonstrates that the autonomic liver-gut neural axis is involved in the etiology of diet-induced NAFLD and that 5-HT and HTR2A are key factors, implying that the modulation of the axis and use of HTR2A antagonists are potentially novel therapeutic strategies for NAFLD treatment.

This article has an associated First Person interview with the first author of the paper.

Summary: The hepatic-gut neural axis plays a role in NAFLD progression via serotonin and the serotonin receptor HTR2A in hepatocytes, suggesting that HTR2A antagonists are potential therapeutic agents for NAFLD.

Metabolic associated fatty liver disease is a disease related to sympathetic nervous system activation

Strong evidence from animal and human studies shows that sympathetic nervous system (SNS) activation is a key factor in the development of metabolic associated fatty liver disease (MAFLD). Activation of the sympathetic nervous system plays an important role in the pathogenesis of obesity, metabolic syndrome, diabetes, hypertension, and MAFLD. When genetically susceptible subjects are exposed to a variety of epigenetic changes, their liver damage may develop into MAFLD. Thus, the pathogenesis of MAFLD is complex, involving the complex interaction of insulin resistance, abnormal hormone secretion, obesity, diet, genetic factors, immune activation, gut microbiota, and other factors. In these processes, the role of sympathetic nerves cannot be underestimated. Notably, SNS has been proposed as a therapeutic target for MAFLD by inhibiting sympathetic nerves. It is worthy of further discussion and research.

The Role of Catecholamines in Pathophysiological Liver Processes

Over the last few years, the number of research publications about the role of catecholamines (epinephrine, norepinephrine, and dopamine) in the development of liver diseases such as liver fibrosis, fatty liver diseases, or liver cancers is constantly increasing. However, the mechanisms involved in these effects are not well understood. In this review, we first recapitulate the way the liver is in contact with catecholamines and consider liver implications in their metabolism. A focus on the expression of the adrenergic and dopaminergic receptors by the liver cells is also discussed. Involvement of catecholamines in physiological (glucose metabolism, lipids metabolism, and liver regeneration) and pathophysiological (impact on drug-metabolizing enzymes expression, liver dysfunction during sepsis, fibrosis development, or liver fatty diseases and liver cancers) processes are then discussed. This review highlights the importance of understanding the mechanisms through which catecholamines influence liver functions in order to draw benefit from the adrenergic and dopaminergic antagonists currently marketed. Indeed, as these molecules are well-known drugs, their use as therapies or adjuvant treatments in several liver diseases could be facilitated.

Organ and brain crosstalk: The liver-brain axis in gastrointestinal, liver, and pancreatic diseases

The liver is the largest organ in the human body and is responsible for the metabolism and storage of the three principal nutrients: carbohydrates, fats, and proteins. In addition, the liver contributes to the breakdown and excretion of alcohol, medicinal agents, and toxic substances and the production and secretion of bile. In addition to its role as a metabolic centre, the liver has recently attracted attention for its function in the liver-brain axis, which interacts closely with the central nervous system via the autonomic nervous system, including the vagus nerve. The liver-brain axis influences the control of eating behaviour in the central nervous system through stimuli from the liver. Conversely, neural signals from the central nervous system influence glucose, lipid, and protein metabolism in the liver. The liver also receives a constant influx of nutrients and hormones from the intestinal tract and compounds of bacterial origin via the portal system. As a result, the intestinal tract and liver are involved in various immunological interactions. A good example is the co-occurrence of primary sclerosing cholangitis and ulcerative colitis. These heterogeneous roles of the liver-brain axis are mediated via the vagus nerve in an asymmetrical manner. In this review, we provide an overview of these interactions, mainly with the liver but also with the brain and gut.

Hepatic Nervous System in Development, Regeneration, and Disease

The liver is innervated by autonomic and sensory fibers of the sympathetic and parasympathetic nervous systems that regulate liver function, regeneration, and disease. Although the importance of the hepatic nervous system in maintaining and restoring liver homeostasis is increasingly appreciated, much remains unknown about the specific mechanisms by which hepatic nerves both influence and are influenced by liver diseases. While recent work has begun to illuminate the developmental mechanisms underlying recruitment of nerves to the liver, evolutionary differences contributing to species-specific patterns of hepatic innervation remain elusive. In this review, we summarize current knowledge on the development of the hepatic nervous system and its role in liver regeneration and disease. We also highlight areas in which further investigation would greatly enhance our understanding of the evolution and function of liver innervation.

Role of circadian rhythm and autonomic nervous system in liver function: a hypothetical basis for improving the management of hepatic encephalopathy

Hepatic encephalopathy (HE) is a common, incapacitating complication of cirrhosis that affects many patients with cirrhosis. Although several therapies have proven effective in the treatment and prevention of this condition, several patients continue to suffer from covert disease or episodes of relapse. The circadian rhythm has been demonstrated to be pivotal for many body functions, including those of the liver. Here, we explore the impact of circadian rhythm-dependent signaling on the liver and discuss the evidence of its impact on liver pathology and metabolism. We describe the various pathways through which circadian influences are mediated. Finally, we introduce a novel method for improving patient response to drugs aimed at treating HE by utilizing the circadian rhythm. A digital system that introduces a customization-based technique for improving the response to therapies is presented as a hypothetical approach for improving the effectiveness of current medications used for the treatment of recurrent and persistent hepatic encephalopathy.

Hepatic stellate cell senescence in liver fibrosis: Characteristics, mechanisms and perspectives

Myofibroblasts play an important role in fibrogenesis. Hepatic stellate cells are the main precursors of myofibroblasts. Cellular senescence is the terminal cell fate in which proliferating cells undergo irreversible cell cycle arrest. Senescent hepatic stellate cells were identified in liver fibrosis. Senescent hepatic stellate cells display decreased collagen production and proliferation. Therefore, induction of senescence could be a protective mechanism against progression of liver fibrosis and the concept of therapy-induced senescence has been proposed to treat liver fibrosis. In this review, characteristics of senescent hepatic stellate cells and the essential signaling pathways involved in senescence are reviewed. Furthermore, the potential impact of senescent hepatic stellate cells on other liver cell types are discussed. Senescent cells are cleared by the immune system. The persistence of senescent cells can remodel the microenvironment and interact with inflammatory cells to induce aging-related dysfunction. Therefore, senolytics, a class of compounds that selectively induce death of senescent cells, were introduced as treatment to remove senescent cells and consequently decrease the disadvantageous effects of persisting senescent cells. The effects of senescent hepatic stellate cells in liver fibrosis need further investigation.

Pathophysiologic Role of Neurotransmitters in Digestive Diseases

Neurotransmitters are special molecules that serve as messengers in chemical synapses between neurons, cells, or receptors, including catecholamines, serotonin, dopamine, and other neurotransmitters, which play an important role in both human physiology and pathology. Compelling evidence has indicated that neurotransmitters have an important physiological role in various digestive diseases. They act as ligands in combination with central or peripheral receptors, and transmits signals through chemical synapses, which are involved in regulating the physiological and pathological processes of the digestive tract organs. For instance, neurotransmitters regulate blood circulation and affect intestinal movement, nutrient absorption, the gastrointestinal innate immune system, and the microbiome. In this review, we will focus on the role of neurotransmitters in the pathogenesis of digestive tract diseases to provide novel therapeutic targets for new drug development in digestive diseases.

Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD)-A Condition Associated with Heightened Sympathetic Activation

Metabolic dysfunction-associated fatty liver disease (MAFLD) is the most common liver disease affecting a quarter of the global population and is often associated with adverse health outcomes. The increasing prevalence of MAFLD occurs in parallel to that of metabolic syndrome (MetS), which in fact plays a major role in driving the perturbations of cardiometabolic homeostasis. However, the mechanisms underpinning the pathogenesis of MAFLD are incompletely understood. Compelling evidence from animal and human studies suggest that heightened activation of the sympathetic nervous system is a key contributor to the development of MAFLD. Indeed, common treatment strategies for metabolic diseases such as diet and exercise to induce weight loss have been shown to exert their beneficial effects at least in part through the associated sympathetic inhibition. Furthermore, pharmacological and device-based approaches to reduce sympathetic activation have been demonstrated to improve the metabolic alterations frequently present in patients with obesity, MetSand diabetes. Currently available evidence, while still limited, suggests that sympathetic activation is of specific relevance in the pathogenesis of MAFLD and consequentially may offer an attractive therapeutic target to attenuate the adverse outcomes associated with MAFLD.

Thioacetamide-induced norepinephrine production by hepatocytes is associated with hepatic stellate cell activation and liver fibrosis

BACKGROUND

Collagen production by activated hepatic stellate cells (HSCs) to encapsulate injury is part of the natural wound-healing response in injured liver. However, persistent activation of HSCs can lead to pathological fibrogenesis. Such persistent HSC activation could be mediated by norepinephrine (NE), a reaction product of dopamine beta-hydroxylase (DBH).

OBJECTIVE

To investigate the potential paracrine role of NE in hepatotoxin thioacetamide (TAA)-induced liver fibrosis.

METHODS/RESULTS

In TAA-treated mice, fibrotic liver tissue showed significant increases in the mRNA expression of DBH up to 14-fold and collagen up to 7-fold. Immunohistochemical staining showed increased DBH protein expression in fibrotic liver tissue. Parenchymal hepatocyte cell line HepG2 expressed DBH and secreted NE, and the conditioned medium of HepG2 cells promoted collagenesis in nonparenchymal HSC cell line LX-2. TAA treatment increased DBH expression by 170% in HepG2 cells, as well as increased NE by 120% in the conditioned medium of HepG2 cells. The conditioned medium of TAA-treated HepG2 cells was used to culture LX-2 cells, and was found to increase collagen expression by 80% in LX-2 cells. Collagen expression was reduced by pre-treating HepG2 cells with siRNA targeting DBH or by adding NE antagonists to the conditioned medium. Finally, TAA-induced oxidative stress in HepG2 cells was associated with induction of DBH expression.

CONCLUSION

Collectively, our results suggest a potential role for DBH/NE-mediated crosstalk between hepatocytes and HSCs in fibrogenesis. From a therapeutic standpoint, antagonism of DBH/NE induction in hepatocytes might be a useful strategy to suppress pathological fibrogenesis.

Serum Bile Acid, Vitamin E, and Serotonin Metabolites Are Associated With Future Liver-Related Events in Nonalcoholic Fatty Liver Disease

Identifying patients at higher risk for poor outcomes from nonalcoholic fatty liver disease (NAFLD) remains challenging. Metabolomics, the comprehensive measurement of small molecules in biological samples, has the potential to reveal novel noninvasive biomarkers. The aim of this study was to determine if serum metabolite profiles in patients with NAFLD associate with future liver-related events. We performed a retrospective single-center cohort study of 187 participants with biopsy-proven NAFLD. Metabolomic analysis was performed on serum using ultrahigh performance liquid chromatography/tandem mass spectrometry and gas chromatography/mass spectrometry. We identified liver-related events (variceal bleeding, ascites, spontaneous bacterial peritonitis, hepatic encephalopathy, hepatocellular carcinoma, hepatopulmonary or hepatorenal syndrome) by manual chart review between index biopsy (2007-2013) and April 1, 2018. Generalized linear models and Cox proportional hazards models were used to test the association of metabolites with liver-related events and time to first liver-related event, controlling for covariates and fibrosis stage. Over a mean ± SD follow-up of 6.9 ± 3.2 years, 11 participants experienced 22 liver-related events. Generalized linear models revealed 53 metabolites significantly associated with liver-related events (P < 0.05). In Cox proportional hazards modeling, 69 metabolites were significantly associated with time to future liver-related events (P < 0.05), seven of which met the false discovery rate threshold of 0.10: vitamin E metabolites gamma-carboxyethyl-hydroxychroman (gamma-CEHC) and gamma-CEHC glucuronide; primary bile acid metabolite taurochenodeoxycholate; serotonin metabolite 5-hydroxyindoleacetate; and lipid metabolites (i) 2-hydroxyglutarate, (ii) 3beta,17beta-diol disulfate 1, and (iii) eicosenoyl sphingomyelin. Conclusion: Metabolites of a primary bile acid, vitamin E, and serotonin were associated with future liver-related events. Our results suggest metabolite pathways may be useful for predicting which patients with NAFLD are at higher risk for hepatic decompensation.

Role of the sympathetic nervous system in cardiometabolic control: implications for targeted multiorgan neuromodulation approaches

Sympathetic overdrive plays a key role in the perturbation of cardiometabolic homeostasis. Diet-induced and exercise-induced weight loss remains a key strategy to combat metabolic disorders, but is often difficult to achieve. Current pharmacological approaches result in variable responses in different patient cohorts and long-term efficacy may be limited by medication intolerance and nonadherence. A clinical need exists for complementary therapies to curb the burden of cardiometabolic diseases. One such approach may include interventional sympathetic neuromodulation of organs relevant to cardiometabolic control. The experience from catheter-based renal denervation studies clearly demonstrates the feasibility, safety and efficacy of such an approach. In analogy, denervation of the common hepatic artery is now feasible in humans and may prove to be similarly useful in modulating sympathetic overdrive directed towards the liver, pancreas and duodenum. Such a targeted multiorgan neuromodulation strategy may beneficially influence multiple aspects of the cardiometabolic disease continuum offering a holistic approach.

Hepatic Stellate Cell Regulation of Liver Regeneration and Repair

The hepatic mesenchyme has been studied extensively in the context of liver fibrosis; however, much less is known regarding the role of mesenchymal cells during liver regeneration. As our knowledge of the cellular and molecular mechanisms driving hepatic regeneration deepens, the key role of the mesenchymal compartment during the regenerative response has been increasingly appreciated. Single-cell genomics approaches have recently uncovered both spatial and functional zonation of the hepatic mesenchyme in homeostasis and following liver injury. Here we discuss how the use of preclinical models, from in vivo mouse models to organoid-based systems, are helping to shape our understanding of the role of the mesenchyme during liver regeneration, and how these approaches should facilitate the precise identification of highly targeted, pro-regenerative therapies for patients with liver disease.

Liver regeneration: biological and pathological mechanisms and implications

The liver is the only solid organ that uses regenerative mechanisms to ensure that the liver-to-bodyweight ratio is always at 100% of what is required for body homeostasis. Other solid organs (such as the lungs, kidneys and pancreas) adjust to tissue loss but do not return to 100% of normal. The current state of knowledge of the regenerative pathways that underlie this 'hepatostat' will be presented in this Review. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models that involve partial hepatectomy or chemical injury have revealed extracellular and intracellular signalling pathways that are used to return the liver to equivalent size and weight to those prior to injury. On the other hand, chronic loss of hepatocytes, which can occur in chronic liver disease of any aetiology, often has adverse consequences, including fibrosis, cirrhosis and liver neoplasia. The regenerative activities of hepatocytes and cholangiocytes are typically characterized by phenotypic fidelity. However, when regeneration of one of the two cell types fails, hepatocytes and cholangiocytes function as facultative stem cells and transdifferentiate into each other to restore normal liver structure. Liver recolonization models have demonstrated that hepatocytes have an unlimited regenerative capacity. However, in normal liver, cell turnover is very slow. All zones of the resting liver lobules have been equally implicated in the maintenance of hepatocyte and cholangiocyte populations in normal liver.

Role of G Protein-Coupled Receptors in Hepatic Stellate Cells and Approaches to Anti-Fibrotic Treatment of Non-Alcoholic Fatty Liver Disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) is globally increasing. Gaining control over disease-related events in non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, is currently an unmet medical need. Hepatic fibrosis is a critical prognostic factor in NAFLD/NASH. Therefore, a better understanding of the pathophysiology of hepatic fibrosis and the development of related therapies are of great importance. G protein-coupled receptors (GPCRs) are cell surface receptors that mediate the function of a great variety of extracellular ligands. GPCRs represent major drug targets, as indicated by the fact that about 40% of all drugs currently used in clinical practice mediate their therapeutic effects by acting on GPCRs. Like many other organs, various GPCRs play a role in regulating liver function. It is predicted that more than 50 GPCRs are expressed in the liver. However, our knowledge of how GPCRs regulate liver metabolism and fibrosis in the different cell types of the liver is very limited. In particular, a better understanding of the role of GPCRs in hepatic stellate cells (HSCs), the primary cells that regulate liver fibrosis, may lead to the development of drugs that can improve hepatic fibrosis in NAFLD/NASH. In this review, we describe the functions of multiple GPCRs expressed in HSCs, their roles in liver fibrogenesis, and finally speculate on the development of novel treatments for NAFLD/NASH.

Functions of beta2-adrenergic receptor in human periodontal ligament cells

Adrenergic receptors (ARs) are receptors of noradrenalin and adrenalin, of which there are nine different subtypes. In particular, β2 adrenergic receptor (β2-AR) is known to be related to the restoration and maintenance of homeostasis in bone and cardiac tissues; however, the functional role of signaling through β2-AR in periodontal ligament (PDL) tissue has not been fully examined. In this report, we investigated that β2-AR expression in PDL tissues and their features in PDL cells. β2-AR expressed in rat PDL tissues and human PDL cells (HPDLCs) derived from two different patients (HPDLCs-2G and -3S). Rat PDL tissue with occlusal loading showed high β2-AR expression, while its expression was downregulated in that without loading. In HPDLCs, β2-AR expression was increased exposed to stretch loading. The gene expression of PDL-related molecules was investigated in PDL clone cells (2-23 cells) overexpressing β2-AR. Their gene expression and intracellular cyclic adenosine monophosphate (cAMP) levels were also investigated in HPDLCs treated with a specific β2-AR agonist, fenoterol (FEN). Overexpression of β2-AR significantly promoted the gene expression of PDL-related molecules in 2 to 23 cells. FEN led to an upregulation in the expression of PDL-related molecules and increased intracellular cAMP levels in HPDLCs. In both HPDLCs, inhibition of cAMP signaling by using protein kinase A inhibitor suppressed the FEN-induced gene expression of α-smooth muscle actin. Our findings suggest that the occlusal force is important for β2-AR expression in PDL tissue and β2-AR is involved in fibroblastic differentiation and collagen synthesis of PDL cells. The signaling through β2-AR might be important for restoration and homeostasis of PDL tissue.

Adipose Tissue-Liver Cross Talk in the Control of Whole-Body Metabolism: Implications in Nonalcoholic Fatty Liver Disease

Adipose tissue and the liver play significant roles in the regulation of whole-body energy homeostasis, but they have not evolved to cope with the continuous, chronic, nutrient surplus seen in obesity. In this review, we detail how prolonged metabolic stress leads to adipose tissue dysfunction, inflammation, and adipokine release that results in increased lipid flux to the liver. Overall, the upshot of hepatic fat accumulation alongside an insulin-resistant state is that hepatic lipid enzymatic pathways are modulated and overwhelmed, resulting in the selective buildup of toxic lipid species, which worsens the pro-inflammatory and pro-fibrotic shift observed in nonalcoholic steatohepatitis.

Norepinephrine-stimulated HSCs secrete sFRP1 to promote HCC progression following chronic stress via augmentation of a Wnt16B/β-catenin positive feedback loop

Background

Sustained adrenergic signaling secondary to chronic stress promotes cancer progression; however, the underlying mechanisms for this phenomenon remain unclear. Hepatocellular carcinoma (HCC) frequently develops within fibrotic livers rich in activated hepatic stellate cells (HSCs). Here, we examined whether the stress hormone norepinephrine (NE) could accelerate HCC progression by modulating HSCs activities.

Methods

HCC cells were exposed to conditioned medium (CM) from NE-stimulated HSCs. The changes in cell migration and invasion, epithelial-mesenchymal transition, parameters of cell proliferation, and levels of cancer stem cell markers were analyzed. Moreover, the in vivo tumor progression of HCC cells inoculated with HSCs was studied in nude mice subjected to chronic restraint stress.

Results

CM from NE-treated HSCs significantly promoted cell migration and invasion, epithelial-mesenchymal transition (EMT), and expression of cell proliferation-related genes and cancer stem cell markers in HCC cells. These pro-tumoral effects were markedly reduced by depleting secreted frizzled related protein 1 (sFRP1) in CM. The pro-tumoral functions of sFRP1 were dependent on β-catenin activation, and sFRP1 augmented the binding of Wnt16B to its receptor FZD7, resulting in enhanced β-catenin activity. Additionally, sFRP1 enhanced Wnt16B expression, reinforcing an autocrine feedback loop of Wnt16B/β-catenin signaling. The expression of sFRP1 in HSCs promoted HCC progression in an in vivo model under chronic restraint stress, which was largely attenuated by sFRP1 knockdown.

Conclusions

We identify a new mechanism by which chronic stress promotes HCC progression. In this model, NE activates HSCs to secrete sFRP1, which cooperates with a Wnt16B/β-catenin positive feedback loop. Our findings have therapeutic implications for the treatment of chronic stress-promoted HCC progression.

Pathophysiological-based treatments of complications of cirrhosis

Detailed knowledge and understanding of the pathophysiological mechanisms and changes in hepatic and splanchnic function leading to the development of haemodynamic changes and portal hypertension in patients with cirrhosis are essential since it guides the search for targets to ameliorate liver-related abnormalities. Recent research has focused on the gut-liver axis, changes in intestinal permeability, translocation of bacterial products, and inflammation as important drivers of haemodynamic alterations and thereby targets for treatment. Additionally, treatment strategies should focus on microbiotic modulation, antiangiogenics, anti-inflammatory strategies, and modulation of bile acid metabolism. This paper aims to review contemporary pathophysiological-based treatment principles of the major complications of cirrhosis and portal hypertension and future targets for treatment.

Hepatic Autonomic Nervous System and Neurotrophic Factors Regulate the Pathogenesis and Progression of Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease represents a continuum of excessive hepatic steatosis, inflammation and fibrosis. It is a growing epidemic in the United States of America and worldwide. Progression of non-alcoholic fatty liver disease can lead to morbidity and mortality due to complications such as cirrhosis or hepatocellular carcinoma. Pathogenesis of non-alcoholic fatty liver disease is centered on increased hepatic lipogenesis and decreased hepatic lipolysis in the setting of hepatic and systemic insulin resistance. Adipose tissue and hepatic inflammation can further perpetuate the severity of illness. Currently there are no approved therapies for non-alcoholic fatty liver disease. Most of the drugs being explored for non-alcoholic fatty liver disease focus on classical pathogenic pathways surrounding hepatic lipid accumulation, inflammation or fibrosis. Studies have demonstrated that the autonomic nervous system innervating the liver plays a crucial role in regulation of hepatic lipid homeostasis, inflammation and fibrosis. Additionally, there is growing evidence that neurotrophic factors can modulate all stages of non-alcoholic fatty liver disease. Both the autonomic nervous system and neurotrophic factors are altered in patients and murine models of non-alcoholic fatty liver disease. In this review we focus on the pathophysiological role of the autonomic nervous system and neurotrophic factors that could be potential targets for novel therapeutic approaches to treat non-alcoholic fatty liver disease.

α2-Adrenergic Receptor in Liver Fibrosis: Implications for the Adrenoblocker Mesedin

The noradrenergic system is proposed to play a prominent role in the pathogenesis of liver fibrosis. While α1- and β-adrenergic receptors (ARs) are suggested to be involved in a multitude of profibrogenic actions, little is known about α2-AR-mediated effects and their expression pattern during liver fibrosis and cirrhosis. We explored the expression of α2-AR in two models of experimental liver fibrosis. We further evaluated the capacity of the α2-AR blocker mesedin to deactivate hepatic stellate cells (HSCs) and to increase the permeability of human liver sinusoidal endothelial cells (hLSECs). The mRNA of α2a-, α2b-, and α2c-AR subtypes was uniformly upregulated in carbon tetrachloride-treated mice vs the controls, while in bile duct-ligated mice, only α2b-AR increased in response to liver injury. In murine HSCs, mesedin led to a decrease in α-smooth muscle actin, transforming growth factor-β and α2a-AR expression, which was indicated by RT-qPCR, immunocytochemistry, and Western blot analyses. In a hLSEC line, an increased expression of endothelial nitric oxide synthase was detected along with downregulated transforming growth factor-β. In conclusion, we suggest that the α2-AR blockade alleviates the activation of HSCs and may increase the permeability of liver sinusoids during liver injury.

Dopamine β hydroxylase (DBH) polymorphisms do not contribute towards the clinical course of Wilson's disease in Indian patients

BACKGROUND

Wilson's disease (WD) is a rare copper metabolism disorder with hepatic and neurological symptoms. Dopamine β hydroxylase (DBH) encodes a copper-dependent mono-oxygenase that converts dopamine to norepinephrine, thereby regulating the endogenous dopamine content in the neurons. Polymorphisms of DBH have been reported to be associated with several neurological diseases, such as Parkinson's disease, Alzheimer's disease, schizophrenia and attention-deficit hyperactivity disorder, which have overlapping neurological symptoms with WD. The present study aimed to assess the role of DBH polymorphisms on the clinical course of WD.

METHODS

In total, 141 WD patients from India were included in the present study. Three polymorphisms of DBH (rs1611115 in the promoter, rs1108580 in exon 2 and rs129882 in 3'-UTR) were screened for their association with the clinical attributes (hepatic and neurological features) and age of onset of WD using a polymerase chain reaction-restriction fragment length polymorphsm method and sequencing approach. The distribution of genotype or allele frequencies was tested using 2 × 2 contingency chi-squared and logistic regression analysis (additive, dominant and recessive model).

RESULTS

The genotypic and allelic frequencies of these single nucleotide polymophisms did not vary significantly along with the clinical symptoms (hepatic and neurological) or the age of onset of WD. No significant association was observed when we analyzed our samples with respect to harboring different kinds of ATP7B mutations (nonsense/in-del and missense).

CONCLUSIONS

The data obtained in the present study suggest that the selected DBH variants are unlikely to have any significant contribution towards modifying the clinical symptoms of Indian WD patients.

Human Liver Regeneration: An Etiology Dependent Process

Regeneration of the liver has been an interesting and well-investigated topic for many decades. This etiology and time-dependent mechanism has proven to be extremely challenging to investigate, certainly in human diseases. A reason for this challenge is found in the numerous interactions of different cell components, of which some are even only temporarily present (e.g., inflammatory cells). To orchestrate regeneration of the epithelial cells, their interaction with the non-epithelial components is of utmost importance. Hepatocytes, cholangiocytes, liver progenitor cells, and peribiliary glands have proven to be compartments of regeneration. The ductular reaction is a common denominator in virtually all liver diseases; however, it is predominantly found in late-stage hepatic and biliary diseases. Ductular reaction is an intriguing example of interplay between epithelial and non-epithelial cells and encompasses bipotential liver progenitor cells which are able to compensate for the loss of the exhausted hepatocytes and cholangiocytes in biliary and hepatocytic liver diseases. In this manuscript, we focus on the etiology-specific damage that is observed in different human diseases and how the liver regulates the regenerative response in an acute and chronic setting. Furthermore, we describe the importance of morphological keynotes in different etiologies and how spatial information is of relevance for every basic and translational research of liver regeneration.

Endocrine Diseases and the Liver: An Update

The endocrine system is a complex interconnected system of organs that control corporeal processes and function. Primary endocrine organs are involved in hormonal production and secretion but rely on a bevy of signals from the hypothalamic-pituitary axis and secondary endocrine organs, such as the liver. In turn, proper hepatic function is maintained through hormonal signaling. Thus, the endocrine system and liver are codependent, and diseases affecting either organs can lead to alterations in function within their counterparts. This article explores the hepato-endocrine relationship, including the effects on endocrine diseases on the liver.

Doxazosin and Carvedilol Treatment Improves Hepatic Regeneration in a Hamster Model of Cirrhosis

Regulation of the mechanisms of fibrosis is an important goal in the treatment of liver cirrhosis. One mechanism is the participation of hepatic stellate cells in fibrogenesis when activated by catecholamines. Consequently, α/β adrenoblockers are proposed as an alternative treatment for chronic liver lesions such as fibrosis and/or cirrhosis and for possible liver regeneration. We herein analyzed the effect of doxazosin and carvedilol treatments during the regeneration of tissue in a hamster model of liver cirrhosis. Tissue samples were examined by H&E and PAS to evaluate tissue damage and with Sirius red to assess collagen fiber content. ALT, AST, albumin, and total proteins were examined by spectrophotometry. Determination of the levels of α-SMA and TGF-β in hepatic tissue was examined by Western blot and of the expression of TIMP-2, MMP-13, α-FP, HGF, CK-7, and c-Myc was examined by qPCR. Treatment with doxazosin or carvedilol prompted histological recovery and reduced collagen fibers in the livers of cirrhotic hamsters. The expression of TIMP-2 decreased and that of MMP-13 increases in animals treated with adrenoblockers with respect to the group with cirrhosis. Additionally, the concentration of α-SMA and TGF-β declined with both drugs with respect to placebo p<0.05. On the other hand, each drug treatment led to a distinct scenario for cell proliferation markers. Whereas doxazosin produced no irregularities in α-FP, Ki-67, and c-Myc expression, carvedilol induced an increment in the expression of these markers with respect to the intact. Hence, doxazosin and carvedilol are potential treatments for the regression of hepatic cirrhosis in hamsters in relation to the decrease of collagen in the hepatic parenchyma. However, at regeneration level we observed that doxazosin caused slight morphological changes in hepatocytes, such as its balonization without affecting the hepatic function, and on the other hand, carvedilol elicited a slight irregular expression of cell proliferation markers.

The firing frequency of spontaneous action potentials and their corresponding evoked exocytosis are increased in chromaffin cells of CCl4 -induced cirrhotic rats with respect to control rats

High catecolamine plasma levels because of sympathetic nervous system over-activity contribute to cirrhosis progression. The aim of this study was to investigate whether chromaffin cells of the adrenal gland might potentiate the deleterious effect exerted by this over-activity. Electrophysiological patch-clamp and amperometric experiments with carbon-fibre electrodes were conducted in single chromaffin cells of control and CCl₄ -induced cirrhotic rats. The spontaneous action potential firing frequency was increased in chromaffin cells of cirrhotic rats with respect to control rats. The exocytosis evoked by that firing was also increased. However, exocytosis elicited by ACh did not vary between control and cirrhotic rats. Exocytosis triggered by depolarizing pulses was also unchanged. Amperometric recordings confirmed the lack of increased catecholamine charge released in cirrhosis after ACh or depolarization stimuli. However, the amperometric spikes exhibited faster kinetics of release. The overall Ca²⁺ entry through voltage-dependent Ca²⁺ channels (VDCC), or in particular through Cav1 channels, did not vary between chromaffin cells of control and cirrhotic rats. The inhibition of VDCC by methionine-enkephaline or ATP was not either altered, but it was increased by adrenaline in cells of cirrhotic rats. When a cocktail composed by the three neurotransmitters was tested in order to approach a situation closer to the physiological condition, the inhibition of VDCC was similar between both types of cells. In summary, chromaffin cells of the adrenal gland might contribute to exacerbate the sympathetic nervous system over-activity in cirrhosis because of an increased exocytosis elicited by an enhanced spontaneous electrical activity.

Biliary epithelium: A neuroendocrine compartment in cholestatic liver disease

Hepatic fibrosis is characterized by abnormal accumulation of extracellular matrix (ECM) that can lead to ductopenia, cirrhosis, and even malignant transformation. In this review, we examine cholestatic liver diseases characterized by extensive biliary fibrosis such as primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), polycystic liver disease (PLD), and MDR2-/- and BDL mouse models. Following biliary injury, cholangiocytes, the epithelial cells that line the bile ducts, become reactive and adopt a neuroendocrine phenotype in which they secrete and respond to neurohormones and neuropeptides in an autocrine and paracrine fashion. Emerging evidence indicates that cholangiocytes influence and respond to changes in the ECM and stromal cells in the microenvironment. For example, activated myofibroblasts and hepatic stellate cells are major drivers of collagen deposition and biliary fibrosis. Additionally, the liver is richly innervated with adrenergic, cholinergic, and peptidergic fibers that release neurohormones and peptides to maintain homeostasis and can be deranged in disease states. This review summarizes how cholangiocytes interact with their surrounding environment, with particular focus on how autonomic and sensory regulation affects fibrotic pathophysiology.

Propranolol prevents liver cirrhosis by inhibiting hepatic stellate cell activation mediated by the PDGFR/Akt pathway

Propranolol is known to reduce portal pressure by decreasing blood flow to the splanchnic circulation and the liver. However, it is unknown if propranolol improves fibrogenesis and sinusoidal remodeling in the cirrhotic liver. The aim of this study was to investigate the therapeutic effects of propranolol on carbon tetrachloride (CCl₄)-induced liver fibrosis in a mouse model and the intrinsic mechanisms underlying those effects. In this study, a hepatic cirrhosis mouse model was induced by CCl₄ administration for 6 weeks. Propranolol was simultaneously administered orally in the experimental group. Liver tissue and blood samples were collected for histological and molecular analyses. LX-2 cells induced by platelet-derived growth factor-BB (PDGF-BB) were used to evaluate the anti-fibrogenic effect of propranolol in vitro. The results showed that treatment of mice with CCl₄ induced hepatic fibrosis, as evidenced by inflammatory cell infiltration, collagen deposition and abnormal vascular formation in the liver tissue. All these changes were significantly attenuated by propranolol treatment. Furthermore, we also found that propranolol inhibited PDGF-BB-induced hepatic stellate cell migration, fibrogenesis, and PDGFR/Akt phosphorylation. Taken together, propranolol might prevent CCl₄-induced liver injury and fibrosis at least partially through inhibiting the PDGF-BB-induced PDGFR/Akt pathway. The anti-fibrogenic effect of propranolol may support its status as a first-line treatment in patients with chronic liver disease.

Human hepatic stellate cell isolation and characterization

The hepatic stellate cells (HSCs) localize at the space of Disse in the liver and have multiple functions. They are identified as the major contributor to hepatic fibrosis. Significant understanding of HSCs has been achieved using rodent models and isolated murine HSCs; as well as investigating human liver tissues and human HSCs. There is growing interest and need of translating rodent study findings to human HSCs and human liver diseases. However, species-related differences impose challenges on the translational research. In this review, we focus on the current information on human HSCs isolation methods, human HSCs markers, and established human HSC cell lines.

Adenoviral‑bone morphogenetic protein‑7 and/or doxazosin therapies promote the reversion of fibrosis/cirrhosis in a cirrhotic hamster model

Liver fibrosis occurs in the presence of continuous insults, including toxic or biological agents. Novel treatments must focus on ceasing the progression of cellular damage, promoting the regeneration of the parenchyma and inhibition of the fibrotic process. The present study analyzed the effect of bone morphogenetic protein (BMP)-7 gene therapy with or without co-treatment with doxazosin in a model of liver cirrhosis in hamsters. The serum alanine aminotransferase, aspartate aminotransferase and albumin levels were analyzed spectrophotometrically. Tissue hepatic samples were analyzed by hematoxylin and eosin for parenchymal structure and Sirius red for collagen fiber content. BMP-7 and α-smooth muscle actin (SMA)-positive cells were detected by immunohistochemistry. BMP-7 and collagen type I content in hepatic tissue were analyzed by western blotting, and tissue inhibitor of metalloproteinases (TIMP)-2 and matrix metalloproteinase (MMP)-13 expression levels were detected by reverse transcription-quantitative polymerase chain reaction. The present study detected a significant reduction of collagen type I deposits in the group treated with adenoviral-transduction with BMP-7 and doxazosin. In animals with BMP-7 and doxazosin therapy, α-SMA-positive cells were 31.7 and 29% significantly decreased compared with animals with placebo, respectively. Adenoviral-BMP-7 transduction and/or doxazosin treatments actively induced decrement in type I collagen deposition via increased MMP-13 and reduced TIMP-2 expression. In conclusion, the adenovirus-BMP-7 gene therapy and the doxazosin therapy are potential candidates for the diminution of fibrosis in the liver, although combination of both therapies does not improve the individual anti-fibrotic effect once cirrhosis is established.

The Human Adrenal Gland Proteome Defined by Transcriptomics and Antibody-Based Profiling

The adrenal gland is a composite endocrine organ with vital functions that include the synthesis and release of glucocorticoids and catecholamines. To define the molecular landscape that underlies the specific functions of the adrenal gland, we combined a genome-wide transcriptomics approach using messenger RNA sequencing of human tissues with immunohistochemistry-based protein profiling on tissue microarrays. Approximately two-thirds of all putative protein coding genes were expressed in the adrenal gland, and the analysis identified 253 genes with an elevated pattern of expression in the adrenal gland, with only 37 genes showing a markedly greater expression level (more than fivefold) in the adrenal gland compared with 31 other normal human tissue types analyzed. The analyses allowed for an assessment of the relative expression levels for well-known proteins involved in adrenal gland function but also identified previously poorly characterized proteins in the adrenal cortex, such as the FERM (4.1 protein, ezrin, radixin, moesin) domain containing 5 and the nephroblastoma overexpressed (NOV) protein homolog. We have provided a global analysis of the adrenal gland transcriptome and proteome, with a comprehensive list of genes with elevated expression in the adrenal gland and spatial information with examples of protein expression patterns for corresponding proteins. These genes and proteins constitute important starting points for an improved understanding of the normal function and pathophysiology of the adrenal glands.

Doxazosin Treatment Attenuates Carbon Tetrachloride-Induced Liver Fibrosis in Hamsters through a Decrease in Transforming Growth Factor β Secretion

Background/Aims

The development of therapeutic strategies for the treatment of cirrhosis has become an important focus for basic and clinical researchers. Adrenergic receptor antagonists have been evaluated as antifibrotic drugs in rodent models of carbon tetrachloride (CCl4)-induced cirrhosis. The aim of the present study was to evaluate the effects of carvedilol and doxazosin on fibrosis/cirrhosis in a hamster animal model.

Methods

Cirrhotic-induced hamsters were treated by daily administration of carvedilol and doxazosin for 6 weeks. Hepatic function and histological evaluation were conducted by measuring biochemical markers, including total bilirubin, aspartate aminotransferase, alanine aminotransferase and albumin, and liver tissue slices. Additionally, transforming growth factor β (TGF-β) immunohistochemistry was analyzed.

Results

Biochemical markers revealed that hepatic function was restored after treatment with doxazosin and carvedilol. Histological evaluation showed a decrease in collagen type I deposits and TGF-β-secreting cells.

Conclusions

Taken together, these results suggest that the decrease in collagen type I following treatment with doxazosin or carvedilol is achieved by decreasing the profibrotic activities of TGF-β via the blockage of α1- and β-adrenergic receptor. Consequently, a diminution of fibrotic tissue in the CCl4-induced model of cirrhosis is achieved.