Hepatic Nervous System in Development, Regeneration, and Disease

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.

Distribution and developmental timing of zebrafish liver innervation

Hepatic innervation regulates multiple aspects of liver function, repair and regeneration, and liver denervation is associated with higher rates of metabolic disorders in humans. However, the mechanisms regulating the development of the hepatic nervous system, as well as the role of the hepatic nervous system in liver development and maturation, are still largely unknown. Zebrafish are a widely used model of liver development and regeneration, but hepatic innervation in zebrafish has not yet been described in detail. Here, we examine the extent and developmental timing of hepatic innervation in zebrafish. We demonstrate that innervation is restricted to large bile ducts and blood vessels in both juvenile and adult zebrafish livers, as we find no evidence for direct innervation of hepatocytes. Innervation contacting the periphery of the liver is visible as early as 72 h post-fertilization, while intrahepatic innervation is not established until 21 days post-fertilization. Therefore, zebrafish hepatic innervation resembles that of previously examined fish species, making them an excellent model to investigate both the role of the hepatic nervous system during liver maturation and the mechanisms governing the elaboration of the intrahepatic nerve network between fish and mammals.

Construction of Near-Infrared Probes with Remarkable Large Stokes Shift Based on a Novel Purine Platform for the Visualization of mtG4 Upregulation during Mitochondrial Disorder in Somatic Cells and Human Sperms

G-quadruplex structures within the nuclear genome (nG4) is an important regulatory factor, while the function of G4 in the mitochondrial genome (mtG4) still needs to be explored, especially in human sperms. To gain a better understanding of the relationship between mtG4 and mitochondrial function, it is crucial to develop excellent probes that can selectively visualize and track mtG4 in both somatic cells and sperms. Herein, based on our previous research on purine frameworks, we attempted for the first time to extend the conjugated structure from the C-8 site of purine skeleton and discovered that the purine derivative modified by the C-8 aldehyde group is an ideal platform for constructing near-infrared probes with extremely large Stokes shift (>220 nm). Compared with the compound substituted with methylpyridine (PAP), the molecule substituted with methylthiazole orange (PATO) showed better G4 recognition ability, including longer emission (∼720 nm), more significant fluorescent enhancement (∼67-fold), lower background, and excellent photostability. PATO exhibited a sensitive response to mtG4 variation in both somatic cells and human sperms. Most importantly, PATO helped us to discover that mtG4 was significantly increased in cells with mitochondrial respiratory chain damage caused by complex I inhibitors (6-OHDA and rotenone), as well as in human sperms that suffer from oxidative stress. Altogether, our study not only provides a novel ideal molecular platform for constructing high-performance probes but also develops an effective tool for studying the relationship between mtG4 and mitochondrial function in both somatic cells and human sperms.

Metabolic Crosstalk between Liver and Brain: From Diseases to Mechanisms

Multiple organs and tissues coordinate to respond to dietary and environmental challenges. It is interorgan crosstalk that contributes to systemic metabolic homeostasis. The liver and brain, as key metabolic organs, have their unique dialogue to transmit metabolic messages. The interconnected pathogenesis of liver and brain is implicated in numerous metabolic and neurodegenerative disorders. Recent insights have positioned the liver not only as a central metabolic hub but also as an endocrine organ, capable of secreting hepatokines that transmit metabolic signals throughout the body via the bloodstream. Metabolites from the liver or gut microbiota also facilitate a complex dialogue between liver and brain. In parallel to humoral factors, the neural pathways, particularly the hypothalamic nuclei and autonomic nervous system, are pivotal in modulating the bilateral metabolic interplay between the cerebral and hepatic compartments. The term "liver-brain axis" vividly portrays this interaction. At the end of this review, we summarize cutting-edge technical advancements that have enabled the observation and manipulation of these signals, including genetic engineering, molecular tracing, and delivery technologies. These innovations are paving the way for a deeper understanding of the liver-brain axis and its role in metabolic homeostasis.

Electroacupuncture Promotes Liver Regeneration by Activating DMV Acetylcholinergic Neurons-Vagus-Macrophage Axis in 70% Partial Hepatectomy of Mice

Lack of liver regenerative capacity is the primary cause of hepatic failure and even mortality in patients undergoing hepatectomy, with no effective intervention strategies currently available. Therefore, identifying efficacious interventions to enhance liver regeneration is pivotal for optimizing clinical outcomes. Recent studies have demonstrated that vagotomy exerts an inhibitory effect on liver regeneration following partial hepatectomy, thereby substantiating the pivotal role played by the vagus nerve in the process of liver regeneration. In recent years, electroacupuncture (EA) has emerged as a non-invasive technique for stimulating the vagus nerve. However, EA on hepatic regeneration remains uncertain. In this study, a 70% partial hepatectomy (PH) mouse model is utilized to investigate the effects of EA on acute liver regeneration and elucidate its underlying molecular mechanisms. It is observed that EA at ST36 acutely activated cholinergic neurons in the dorsal motor nucleus of the vagus nerve (DMV), resulting in increased release of acetylcholine from hepatic vagal nerve endings and subsequent activation of IL-6 signaling in liver macrophages. Ultimately, these events promoted hepatocyte proliferation and facilitated liver regeneration. These findings provide insights into the fundamental brain-liver axis mechanism through which EA promotes liver regeneration, offering a novel therapeutic approach for post-hepatectomy liver regeneration disorders.

Human liver afferent and efferent nerves revealed by 3-D/Airyscan super-resolution imaging

Neural regulation of hepatic metabolism has long been recognized. However, the detailed afferent and efferent innervation of the human liver has not been systematically characterized. This is largely due to the liver's high lipid and pigment contents, causing false-negative (light scattering and absorption) and false-positive (autofluorescence) results in in-depth fluorescence imaging. Here, to avoid the artifacts in three-dimensional (3-D) liver neurohistology, we embed the bleached human liver in the high-refractive-index polymer for tissue clearing and antifade 3-D/Airyscan super-resolution imaging. Importantly, using the paired substance P (SP, sensory marker) and PGP9.5 (pan-neuronal marker) labeling, we detect the sensory nerves in the portal space, featuring the SP+ varicosities in the PGP9.5+ nerve bundles/fibers, confirming the afferent liver innervation. Also, using the tyrosine hydroxylase (TH, sympathetic marker) labeling, we identify 1) condensed TH+ sympathetic nerves in the portal space, 2) extension of sympathetic nerves from the portal to the intralobular space, in which the TH+ nerve density is 2.6 ± 0.7-fold higher than that of the intralobular space in the human pancreas, and 3) the TH+ nerve fibers and varicosities contacting the ballooning cells, implicating potential sympathetic influence on hepatocytes with macrovesicular fatty change. Finally, using the vesicular acetylcholine transporter (VAChT, parasympathetic marker), PGP9.5, and CK19 (epithelial marker) labeling with panoramic-to-Airyscan super-resolution imaging, we detect and confirm the parasympathetic innervation of the septal bile duct. Overall, our labeling and 3-D/Airyscan imaging approach reveal the hepatic sensory (afferent) and sympathetic and parasympathetic (efferent) innervation, establishing a clinically related setting for high-resolution 3-D liver neurohistology.NEW & NOTEWORTHY We embed the human liver (vs. pancreas, positive control) in the high-refractive-index polymer for tissue clearing and antifade 3-D/Airyscan super-resolution neurohistology. The pancreas-liver comparison reveals: 1) sensory nerves in the hepatoportal space; 2) intralobular sympathetic innervation, including the nerve fibers and varicosities contacting the ballooning hepatocytes; and 3) parasympathetic innervation of the septal bile duct. Our results highlight the sensitivity and resolving power of 3-D/Airyscan super-resolution imaging in human liver neurohistology.

Role of cholinergic innervation in biliary remnants of patients with biliary atresia

Objective

Biliary innervation is considered important in regulating the function of bile ducts, whereas the role of innervation in the hepatobiliary system of patients with biliary atresia (BA) remains unknown. This current study aims to investigate the role of innervation in biliary remnants and analyze the relationship between the innervation and prognosis of BA after surgery.

Methods

Eighty-seven patients with type III BA who underwent the Kasai procedure were consecutively enrolled from January 2017 to September 2020. Innervation and ductules in remnants were examined by pathologists. Liver function, onset of cholangitis, jaundice clearance, and survival with the native liver were recorded. Patients were followed up for 24 months. The relationship between innervation and prognosis was analyzed.

Results

In total, 67 patients had bile drainage postoperatively, and 21 biliary remnants contained neuronal plexuses where there was no neuron but nerve fiber bundles. Acetylcholinesterase staining was positive in all plexuses. In patients with bile drainage, those with plexuses had improved postoperative liver function, significantly better jaundice clearance 3 or 6 months postoperatively (50.0% vs. 19.1%, or 90.0% vs. 63.8%, respectively), fewer episodes of early cholangitis (10.0% vs. 34.0%), and better survival (80.0% vs. 61.7%) compared to those without. In addition, a larger area of plexuses was associated with a larger area of ductules (R2 = 0.786, p = 0.000), less frequent (p = 0.000) and later cholangitis onset (p = 0.012), and better jaundice clearance (p = 0.063).

Conclusions

Increased cholinergic innervation in biliary remnants may help reduce the onset of cholangitis and lead to better and earlier jaundice clearance. Thus, it improves the postoperative prognosis of patients with BA.

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.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.

Effects of Acute Ethanol Intoxication on Spinal Cord Injury Outcomes in Female Mice

Abstract Approximately one in three traumatic spinal cord injuries (SCIs) occurs during or shortly after the consumption of alcohol. A small number of retrospective clinical studies report variable effects of alcohol intoxication on mortality, neurological recovery, and complications after SCI. Some of these studies demonstrate a protective effect of alcohol intoxication on SCI outcomes, whereas others show an increased complication risk. Pre-clinical studies in rat, ferret, and feline SCI models report a detrimental effect of ethanol intoxication on hemorrhage, motor recovery, and biochemical markers of tissue injury. However, no studies to date have investigated the neuropathological consequences of ethanol intoxication at the time of SCI or the reciprocal effect of SCI on ethanol metabolism. Therefore, we combined a pre-clinical mouse model of acute ethanol intoxication and experimental vertebral level T9 contusion SCI to investigate their interactive effects in female mice. We first investigated the effect of SCI on ethanol metabolism and found that T9 SCI does not alter ethanol metabolism. However, we did find that isoflurane anesthesia significantly slowed ethanol metabolism independent of SCI. We also determined how acute ethanol intoxication at the time of SCI alters locomotor recovery and lesion pathology. Using the Basso Mouse Scale (BMS) and CatWalk XT Gait Analysis System, we assessed locomotor recovery for 6 weeks after injury and observed that acute ethanol intoxication at the time of injury did not alter locomotor recovery. We also found no effect of ethanol intoxication on heat hyperalgesia development. There was, however, a detrimental effect of ethanol on tissue sparing after SCI. Therefore, we conclude that acute alcohol intoxication at the time of injury may contribute to the neuropathological consequences of SCI.

The Sympathetic Nervous System Promotes Hepatic Lymphangiogenesis, which Is Protective Against Liver Fibrosis

Liver is the largest lymph-producing organ. In cirrhotic patients, lymph production significantly increases concomitant with lymphangiogenesis. The aim of this study was to determine the mechanism of lymphangiogenesis in liver and its implication in liver fibrosis. Liver biopsies from portal hypertensive patients with portal-sinusoidal vascular disease (n = 22) and liver cirrhosis (n = 5) were evaluated for lymphangiogenesis and compared with controls (n = 9 and n = 6, respectively). For mechanistic studies, rats with partial portal vein ligation (PPVL) and bile duct ligation (BDL) were used. A gene profile data set (GSE77627), including 14 histologically normal liver, 18 idiopathic noncirrhotic portal hypertension, and 22 cirrhotic patients, was analyzed. Lymphangiogenesis was significantly increased in livers from patients with portal-sinusoidal vascular disease, cirrhotic patients, as well as PPVL and BDL rats. Importantly, Schwann cells of sympathetic nerves highly expressed vascular endothelial growth factor-C in PPVL rats. Vascular endothelial growth factor-C neutralizing antibody or sympathetic denervation significantly decreased lymphangiogenesis in livers of PPVL and BDL rats, which resulted in progression of liver fibrosis. Liver specimens from cirrhotic patients showed a positive correlation between sympathetic nerve/Schwann cell-positive areas and lymphatic vessel numbers, which was supported by gene set analysis from patients with noncirrhotic portal hypertension and cirrhotic patients. Sympathetic nerves promote hepatic lymphangiogenesis in noncirrhotic and cirrhotic livers. Increased hepatic lymphangiogenesis can be protective against liver fibrosis.

Changes of biliary cilia, smooth muscle tissue distribution, innervation and extracellular matrices during morphological evolution of hepatic architectures in vertebrates

BACKGROUND

The liver architecture of vertebrates can be classified into two types, the portal triad type (having periportal bile ducts) and the non-portal triad type (having bile ducts independent of the course of portal veins). The former is typically detectable in livers of tetrapods and cartilaginous fish, and its ancestral state is found in the hagfish, an earliest diverged lineage among vertebrates. Teleosts other than osteoglossomorphs have the latter. The aim of the present study is to reveal the changes of the hepatic innervation, biliary cilia and smooth muscle distribution, and extracellular matrices along vertebrate evolution with attention to the two types of liver architectures.

METHODS

The hepatic innervation, biliary cilia and smooth muscle distribution, and collagen deposition were immunohistochemically and histochemically compared among livers of various vertebrates, using anti-acetylated tubulin and anti-α-smooth muscle actin antibodies, and Sirius red staining. These were also ultrastructurally examined.

RESULTS

Although the hagfish liver had periportal intrahepatic bile ducts and ductules as detected in mammalian livers, it lacked smooth muscles around bile ducts and portal veins. Extracellular matrices in their connective tissues had thick collagen fibers. Its innervation was restricted to intrahepatic bile ducts and portal veins in the hilum. In livers of other vertebrates, including teleosts, the innervation was broadly detectable, especially around bile ducts, hepatic arteries and portal veins (afferent vessels), but not around central veins (efferent vessels). The chondrichthyans ultrastructurally had smooth muscle tissue around bile ducts. Cilia distribution was confirmed in intrahepatic bile ducts of tetrapods and basal actinopterygians. Teleosts other than osteoglossomorphs lacked cilia in their intrahepatic bile ducts.

CONCLUSIONS

The liver architecture of the hagfish may be unique for innervation and extracellular matrices. Hepatic innervation may not have occurred in vertebrate ancestors. Hepatic innervation in bile ducts, hepatic arteries and portal veins may have been conserved among the extant jawed vertebrates. Cilia distribution in bile ducts may have changed during evolution of actinopterygians.

The Hepatic Nerves Regulated Inflammatory Effect in the Process of Liver Injury: Is Nerve the Key Treating Target for Liver Inflammation?

Liver injury is a common pathological basis for various liver diseases. Chronic liver injury is often an important initiating factor in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Currently, hepatitis A and E infections are the most common causes of acute liver injury worldwide, whereas drug toxicity (paracetamol overdose) in the USA and part of Western Europe. In recent years, chronic liver injury has become a common disease that harms human health. Meanwhile, the main causes of chronic liver injury are viral hepatitis (B, C) and long-term alcohol consumption worldwide. During the process of liver injury, massive inflammatory cytokines are stimulated by these hazardous factors, leading to a systemic inflammatory response syndrome, followed by a compensatory anti-inflammatory response, which causes immune cell dysfunction and sepsis, subsequent multi-organ failure. Cytokine release and immune cell infiltration-mediated aseptic inflammation are the most important features of the pathobiology of liver failure. From this perspective, diminishing the onset and progression of liver inflammation is of clinical importance in the treatment of liver injury. Although many studies have hinted at the critical role of nerves in regulating inflammation, there largely remains undetermined how hepatic nerves mediate immune inflammation and how the inflammatory factors released by these nerves are involved in the process of liver injury. Therefore, the purpose of this article is to summarize previous studies in the field related to hepatic nerve and inflammation as well as future perspectives on the aforementioned questions. Our findings were presented in three aspects: types of nerve distribution in the liver, how these nerves regulate immunity, and the role of liver nerves in hepatitis and liver failure.

A Novel Perspective on Neuronal Control of Anatomical Patterning, Remodeling, and Maintenance

While the nervous system may be best known as the sensory communication center of an organism, recent research has revealed a myriad of multifaceted roles for both the CNS and PNS from early development to adult regeneration and remodeling. These systems work to orchestrate tissue pattern formation during embryonic development and continue shaping pattering through transitional periods such as metamorphosis and growth. During periods of injury or wounding, the nervous system has also been shown to influence remodeling and wound healing. The neuronal mechanisms responsible for these events are largely conserved across species, suggesting this evidence may be important in understanding and resolving many human defects and diseases. By unraveling these diverse roles, this paper highlights the necessity of broadening our perspective on the nervous system beyond its conventional functions. A comprehensive understanding of the complex interactions and contributions of the nervous system throughout development and adulthood has the potential to revolutionize therapeutic strategies and open new avenues for regenerative medicine and tissue engineering. This review highlights an important role for the nervous system during the patterning and maintenance of complex tissues and provides a potential avenue for advancing biomedical applications.

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.

Downregulation of Bmal1 Expression in Celiac Ganglia Protects against Hepatic Ischemia-Reperfusion Injury

Hepatic ischemia-reperfusion injury (HIRI) significantly contributes to liver dysfunction following liver transplantation and hepatectomy. However, the role of the celiac ganglion (CG) in HIRI remains unclear. Adeno-associated virus was used to silence Bmal1 expression in the CG of twelve beagles that were randomly assigned to the Bmal1 knockdown group (KO-Bmal1) and the control group. After four weeks, a canine HIRI model was established, and CG, liver tissue, and serum samples were collected for analysis. The virus significantly downregulated Bmal1 expression in the CG. Immunofluorescence staining confirmed a lower proportion of c-fos⁺ and NGF⁺ neurons in TH⁺ cells in the KO-Bmal1 group than in the control group. The KO-Bmal1 group exhibited lower Suzuki scores and serum ALT and AST levels than the control group. Bmal1 knockdown significantly reduced liver fat reserve, hepatocyte apoptosis, and liver fibrosis, and it increased liver glycogen accumulation. We also observed that Bmal1 downregulation inhibited the hepatic neurotransmitter norepinephrine, neuropeptide Y levels, and sympathetic nerve activity in HIRI. Finally, we confirmed that decreased Bmal1 expression in CG reduces TNF-α, IL-1β, and MDA levels and increases GSH levels in the liver. The downregulation of Bmal1 expression in CG suppresses neural activity and improves hepatocyte injury in the beagle model after HIRI.

Multiple Facets of Cellular Homeostasis and Regeneration of the Mammalian Liver

Liver regeneration occurs in response to diverse injuries and is capable of functionally reestablishing the lost parenchyma. This phenomenon has been known since antiquity, encapsulated in the Greek myth where Prometheus was to be punished by Zeus for sharing the gift of fire with humanity by having an eagle eat his liver daily, only to have the liver regrow back, thus ensuring eternal suffering and punishment. Today, this process is actively leveraged clinically during living donor liver transplantation whereby up to a two-thirds hepatectomy (resection or removal of part of the liver) on a donor is used for transplant to a recipient. The donor liver rapidly regenerates to recover the lost parenchymal mass to form a functional tissue. This astonishing regenerative process and unique capacity of the liver are examined in further detail in this review.

Catecholamine induces Kupffer cell apoptosis via growth differentiation factor 15 in alcohol-associated liver disease

Chronic alcohol consumption often induces hepatic steatosis but rarely causes severe inflammation in Kupffer cells (KCs) despite the increased hepatic influx of lipopolysaccharide (LPS), suggesting the presence of a veiled tolerance mechanism. In addition to LPS, the liver is affected by several gut-derived neurotransmitters through the portal blood, but the effects of catecholamines on KCs have not been clearly explored in alcohol-associated liver disease (ALD). Hence, we investigated the regulatory roles of catecholamine on inflammatory KCs under chronic alcohol exposure. We discovered that catecholamine levels were significantly elevated in the cecum, portal blood, and liver tissues of chronic ethanol-fed mice. Increased catecholamines induced mitochondrial translocation of cytochrome P450 2E1 in perivenous hepatocytes expressing the β2-adrenergic receptor (ADRB2), leading to the enhanced production of growth differentiation factor 15 (GDF15). Subsequently, GDF15 profoundly increased ADRB2 expression in adjacent inflammatory KCs to facilitate catecholamine/ADRB2-mediated apoptosis. Single-cell RNA sequencing of KCs confirmed the elevated expression of Adrb2 and apoptotic genes after chronic ethanol intake. Genetic ablation of Adrb2 or hepatic Gdf15 robustly decreased the number of apoptotic KCs near perivenous areas, exacerbating alcohol-associated inflammation. Consistently, we found that blood and stool catecholamine levels and perivenous GDF15 expression were increased in patients with early-stage ALD along with an increase in apoptotic KCs. Our findings reveal a novel protective mechanism against ALD, in which the catecholamine/GDF15 axis plays a critical role in KC apoptosis, and identify a unique neuro-metabo-immune axis between the gut and liver that elicits hepatoprotection against alcohol-mediated pathogenic challenges.

Sensory Nerve Maintains Intervertebral Disc Extracellular Matrix Homeostasis Via CGRP/CHSY1 Axis

Sensory nerves are long being recognized as collecting units of various outer stimuli; recent advances indicate that the sensory nerve also plays pivotal roles in maintaining organ homeostasis. Here, this study shows that sensory nerve orchestrates intervertebral disc (IVD) homeostasis by regulating its extracellular matrix (ECM) metabolism. Specifically, genetical sensory denervation of IVD results in loss of IVD water preserve molecule chondroitin sulfate (CS), the reduction of CS bio-synthesis gene chondroitin sulfate synthase 1 (CHSY1) expression, and dysregulated ECM homeostasis of IVD. Particularly, knockdown of sensory neuros calcitonin gene-related peptide (CGRP) expression induces similar ECM metabolic disorder compared to sensory nerve denervation model, and this effect is abolished in CHSY1 knockout mice. Furthermore, in vitro evidence shows that CGRP regulates nucleus pulposus cell CHSY1 expression and CS synthesis via CGRP receptor component receptor activity-modifying protein 1 (RAMP1) and cyclic AMP response element-binding protein (CREB) signaling. Therapeutically, local injection of forskolin significantly attenuates IVD degeneration progression in mouse annulus fibrosus puncture model. Overall, these results indicate that sensory nerve maintains IVD ECM homeostasis via CGRP/CHSY1 axis and promotes IVD repair, and this expands the understanding concerning how IVD links to sensory nerve system, thus shedding light on future development of novel therapeutical strategy to IVD degeneration.

The Association of Measures of Cardiovascular Autonomic Function, Heart Rate, and Orthostatic Hypotension With Incident Glucose Disorders: The Cardiovascular Health Study

OBJECTIVE

The autonomic nervous system (ANS) innervates pancreatic endocrine cells, muscle, and liver, all of which participate in glucose metabolism. We tested whether measures of cardiovascular ANS function are independently associated with incident diabetes and annual change in fasting glucose (FG) levels as well as with insulin secretion and insulin sensitivity in older adults without diabetes.

RESEARCH DESIGN AND METHODS

Heart rate (HR) and measures of HR variability (HRV) were derived from 24-h electrocardiographic monitoring. Blood pressure, seated and standing, was measured. Cox proportional hazards models and linear mixed models were used to analyze the associations between HRV, HR, and orthostatic hypotension (SBP >20 mmHg decline) and incident diabetes or longitudinal FG change.

RESULTS

The mean annual unadjusted FG change was 1 mg/dL. Higher detrended fluctuation analyses (DFA) values, averaged over 4-11 (DFA1) or 12-20 beats (DFA2)-reflecting greater versus less organization of beat-to-beat intervals-were associated with less FG increase over time (per 1-SD increment: DFA1: -0.49 mg/dL/year [-0.96, -0.03]; DFA2: -0.55 mg/dL/year [-1.02, -0.09]). In mutually adjusted analyses, higher SD of the N-N interval (SDNN) was associated with less FG increase over time (per 1-SD increment: SDNN: -0.62 mg/dL/year [-1.22, -0.03]). Higher values of DFA1, DFA2, and SDNN were each associated with greater insulin secretion and insulin sensitivity but not with incident diabetes. We observed no association of HR or orthostatic hypotension with diabetes or FG change.

CONCLUSIONS

Specific measures of cardiac autonomic function are prospectively related to FG level changes and insulin secretion and action.

Neurotrophic factors stimulate the activation of hepatic stellate cells in liver fibrosis

BACKGROUND AND AIMS

Patients with liver fibrosis who have pain in the liver region may have changed nerve factors. The expression of neurokines and hepatic nerves in liver fibrosis, however, was little understood. In order to better understand how liver fibrosis develops, we plan to look into the hepatic nerve and neurokine changes and how they relate to hepatic stellate cells (HSCs).

METHODS

The expression of neurokines in liver samples from 55 chronic hepatitis B patients and the carbon tetrachloride (CCl₄) animal model were studied. The co-staining of Nissl and α-SMA allowed us to investigate the neurons and their interaction with α-SMA in fibrotic livers, as well as the expression of the glial cell marker glial fibrillary acidic protein (GFAP) and its relationship with α-SMA, a marker of HSCs. SH-SY5Y cells were treated with a fibrotic serum to imitate the hepatic microenvironment on neuronal cells. We also used brain-derived neurotrophic factor (BDNF) to stimulate mouse primary HSCs and LX2.

RESULTS

The levels of mRNA for neurokines such as BDNF, GFAP, and growth-associated protein (GAP43) are significantly increased in both human and animal liver fibrosis. As liver fibrosis advances, we found that Nissl bodies and α-SMA may co-localize, suggesting a connection between hepatic nerves and HSCs. Human fibrotic serum may increase neurkines, notably BDNF, in SH-SY5Y cells. We also found that BDNF increased pro-inflammatory cytokines and fibrogenic markers in hHSCs.

CONCLUSIONS

Patients with hepatic fibrosis had significantly higher levels of BDNF, GFAP, GAP43, and nerve fibers. HSC and nerve fibers interact, and nerves also create neurogenic substances that promote liver fibrosis and HSC activation.

Genome-wide meta-analysis identifies susceptibility loci for autoimmune hepatitis type 1

BACKGROUND AND AIMS

Autoimmune hepatitis (AIH) is a rare and chronic autoimmune liver disease. While genetic factors are believed to play a crucial role in the etiopathogenesis of AIH, our understanding of these genetic risk factors is still limited. In this study, we aimed to identify susceptibility loci to further understand the pathogenesis of this disease.

APPROACH AND RESULTS

We conducted a case-control association study of 1,622 Chinese patients with AIH type 1 and 10,466 population controls from two independent cohorts. A meta-analysis was performed to ascertain variants associated with AIH type 1. A single-nucleotide polymorphism within the human leukocyte antigen (HLA) region showed the strongest association with AIH (rs6932730: OR = 2.32; p = 9.21 × 10^-73 ). The meta-analysis also identified two non-HLA loci significantly associated with AIH: CD28/CTLA4/ICOS on 2q33.3 (rs72929257: OR = 1.31; p = 2.92 × 10^-9 ) and SYNPR on 3p14.2 (rs6809477: OR = 1.25; p = 5.48 × 10^-9 ). In silico annotation, reporter gene assays, and CRISPR activation experiments identified a distal enhancer at 2q33.3 that regulated expression of CTLA4. In addition, variants near STAT1/STAT4 (rs11889341: OR = 1.24; p = 1.34 × 10^-7 ), LINC00392 (rs9564997: OR = 0.81; p = 2.53 × 10^-7 ), IRF8 (rs11117432: OR = 0.72; p = 6.10 × 10^-6 ), and LILRA4/LILRA5 (rs11084330: OR = 0.65; p = 5.19 × 10^-6 ) had suggestive association signals with AIH.

CONCLUSIONS

Our study identifies two novel loci (CD28/CTLA4/ICOS and SYNPR) exceeding genome-wide significance and suggests four loci as potential risk factors. These findings highlight the importance of costimulatory signaling and neuro-immune interaction in the pathogenesis of AIH.

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.

Massive sympathetic nerve infiltration in advanced hepatic alveolar echinococcosis: a case report and review of the literature

Background

Alveolar echinococcosis is a zoonotic disease that mostly affects the liver, with vascular invasion and a protean clinical symptom. However, no reports of sympathetic nerve infiltration in hepatic alveolar echinococcosis have been reported. Here, we report a case of hepatic alveolar echinococcosis in a 33-year-old man. In this end-stage case, the lesion was heavily involved in the large vessels and biliary tract, and immunohistochemistry also incidentally revealed extensive nerve infiltration in the specimens after surgical treatment. Subsequently, neural classification was identified.

Case presentation

We herein report a case of advanced hepatic alveolar echinococcosis with macrovascular invasion and sympathetic nerve infiltration. In this case, inferior vena cava (IVC), the portal vein and bile duct were infiltrated. Ultimately, according to our experience, ex vivo liver resection and autotransplantation (ELRA) was the optimal treatment way to perform for this unresectable patient. Samples were collected from normal liver tissue, junction tissue and the lesion. Hematoxylin–eosin (HE) staining was used to confirm the diagnosis. Neural infiltration was observed by immunohistochemical staining with protein gene product 9.5 (PGP9.5). Fluorescence colocalization was determined with PGP9.5 and tyrosine hydroxylase (TH). These results suggest that a large amount of sympathetic nerve infiltration occurred at the junction.

Conclusion

This study suggests that advanced hepatic alveolar echinococcosis shows infiltrating growth, often invades the large vessels and biliary ducts, and may be accompanied by sympathetic nerve infiltration.

Reclassification of Hepatocellular Cancer With Neural-Related Genes

Neural infiltration is a critical component of the tumor microenvironment; however, owing to technological limitations, its role in hepatocellular cancer remains obscure. Herein, we obtained the RNA-sequencing data of liver hepatocellular carcinoma (LIHC) from The Cancer Genome Atlas database and performed a series of bioinformatic analyses, including prognosis analysis, pathway enrichment, and immune analysis, using the R software packages, Consensus Cluster Plus and Limma. LIHC could be divided into two subtypes according to the expression of neural-related genes (NRGs); moreover, there are statistic differences in the prognosis, stage, and immune regulation between the two subtypes. The prognostic model showed that high expression of NRGs correlated with a poor survival prognosis (P<0.05). Further, CHRNE, GFRA2, GFRA3, and GRIN2D was significantly correlated with LIHC clinical prognosis, clinical stage, immune infiltration, immune response, and vital signaling pathways. There was nerve-cancer crosstalk in LIHC. A reclassification of LIHC based on NRG expression may prove beneficial to clinical practice. CHRNE, GFRA2, GFRA3, and GRIN2D may serve as potential biomarker for liver cancer prognosis or immune response.

Schwann Cells in Digestive System Disorders

Proper functioning of the digestive system is ensured by coordinated action of the central and peripheral nervous systems (PNS). Peripheral innervation of the digestive system can be viewed as intrinsic and extrinsic. The intrinsic portion is mainly composed of the neurons and glia of the enteric nervous system (ENS), while the extrinsic part is formed by sympathetic, parasympathetic, and sensory branches of the PNS. Glial cells are a crucial component of digestive tract innervation, and a great deal of research evidence highlights the important status of ENS glia in health and disease. In this review, we shift the focus a bit and discuss the functions of Schwann cells (SCs), the glial cells of the extrinsic innervation of the digestive system. For more context, we also provide information on the basic findings regarding the function of innervation in disorders of the digestive organs. We find diverse SC roles described particularly in the mouth, the pancreas, and the intestine. We note that most of the scientific evidence concerns the involvement of SCs in cancer progression and pain, but some research identifies stem cell functions and potential for regenerative medicine.