SynopsisThe contraction of hepatic stellate cells has been proposed to mediate fibrosis by regulating sinusoidal blood flow and extracellular matrix remodeling. Abundant data from diverse, yet complementary, experimental methods support a robust model for the regulation of contractile force generation by stellate cells. In this model, soluble factors associated with liver injury, including endothelin-1 and nitric oxide, are transduced primarily through rho signaling pathways that promote the myosin IIpowered generation of contractile force by stellate cells. The enhanced knowledge of the role and differential regulation of stellate cell contraction may facilitate the discovery of new and targeted strategies for the prevention and treatment of hepatic fibrosis. Keywordshepatic stellate cell; contraction; fibrosis; pericyte; rho-associated kinase; sinusoid IntroductionContractile force generation by hepatic stellate cells is recognized to play a key role in the liver's response to injury. This cellular behavior is consequently believed to contribute to normal healing as well as the development of hepatic fibrosis. Therefore, improved understanding of stellate cell contraction and its regulation would be predicted to facilitate development of clinical strategies for the treatment of liver disease. Despite more than 15 years of study, however, effective therapies based on targeting the generation of contractile force by stellate cells have remained elusive. This chapter will examine the current state of knowledge regarding stellate cell contraction, its role, its regulation, and its potential as a therapeutic target, by addressing three fundamental questions:1. What do we believe we know? Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. In summary, conventional wisdom holds that hepatic stellate cells are contractile, and their capacity to generate contractile force mediates the liver's injury response through modulation of sinusoidal blood flow and scar contracture (Fig. 1). This current understanding of the role of stellate cell contraction is, however, largely based on circumstantial evidence and common logic. In the following section we will dissect the scientific methods that have been employed to study stellate cell contraction, as well as discuss the model (Fig. 2) for the regulation of stellate cell contraction that is best supported by the evidence. NIH Public AccessWhat do we really know about hepatic stellate cell contraction? [20][21][22][23]. In this assay stellate cells in culture were grown to sub-confluence on a glass cover slip and visualized with transmissio...

Background & Aims-Stress signaling, both within and outside the endoplasmic reticulum, has been linked to metabolic dysregulation and hepatic steatosis. Methionine-choline-deficient (MCD) diets cause severe fatty liver disease and have the potential to cause many types of cellular stress. The purpose of this study was to characterize hepatic stress in MCD-fed mice and explore the relationship between MCD-mediated stress and liver injury.

Background Methionine-choline-deficient (MCD) diets cause steatohepatitis in rodents and are used to model fatty liver disease in human beings. Recent studies have identified sucrose as a major contributor to MCD-related liver disease through its ability to promote hepatic de novo lipogenesis. Aims To determine whether glucose and fructose, the two constitutents of sucrose, differ in their capacity to provoke steatohepatitis when incorporated individually into MCD formulas. Materials & Methods MCD and control formulas prepared with either glucose or fructose as the sole source of carbohydrate were fed to mice for 21 days. Liver injury was assessed biochemically and histologically together with hepatic gene expression and fatty acid analysis. Results Mice fed MCD formulas developed similar degrees of hepatic steatosis whether they contained glucose or fructose. By contrast, mice fed MCD-fructose developed significantly more hepatocellular injury than mice fed MCD-glucose, judged by histology, apoptosis staining and serum alanine aminotransferase. Liver injury in MCD-fructose mice coincided with an exaggerated rise in the ratio of long-chain saturated to unsaturated fatty acids in the liver. Notably, hepatic inflammation was not enhanced in mice fed MCD-fructose, correlating instead with hepatic lipid peroxidation, which was equivalent in the two MCD groups. Discussion Fructose is more cytotoxic than glucose when used as the source of carbohydrate in MCD formulas. Conclusion The data suggest the enhanced cytotoxicity of fructose in the MCD model is related to its ability to stimulate de novo lipogenesis, which yields harmful long-chain saturated fatty acids.

ObjectiveNeuronal ceroid lipofuscinosis type 2 (CLN2 disease) is a rare, progressive, fatal neurodegenerative pediatric disorder resulting from deficiencies of the lysosomal enzyme tripeptidyl peptidase 1 that are caused by mutations in TPP1. Identifying biomarkers of CLN2 disease progression will be important in assessing the efficacy of therapeutic interventions for this disorder. Neurofilament light is an intrinsic component of healthy neurons; elevated circulating extracellular neurofilament light is a biomarker of neuropathology in several adult‐onset neurological diseases. Our objective was to assess whether circulating neurofilament light is a biomarker that is responsive to enzyme replacement therapy (ERT) in CLN2 disease.MethodsUsing an ultrasensitive immunoassay, we assessed plasma neurofilament light changes during disease progression in a canine model of CLN2 disease and in ERT clinical trial CLN2 disease patients.ResultsIn tripeptidyl peptidase 1 (TPP1)‐null dogs (N = 11), but not in control dogs [N = 6 (TPP1 +/−) and N = 27 (WT)], neurofilament light levels increased more than tenfold above initial low baseline levels during disease progression. Before treatment in 21 human subjects with CLN2 disease (age range: 1.72–6.85 years), neurofilament light levels were 48‐fold higher (P < 0.001) than in 7 pediatric controls (age range: 8–11 years). Pretreatment neurofilament light did not significantly correlate with disease severity or age. In CLN2 disease subjects receiving ERT, neurofilament light levels decreased by 50% each year over more than 3 years of treatment.InterpretationOur data indicate that circulating neurofilament light is a treatment‐responsive biomarker in CLN2 disease and could contribute to understanding of the pathophysiology of this devastating pediatric disorder.