Differential role of MLKL in alcohol-associated and non-alcohol-associated fatty liver diseases in mice and humans

Hepatocellular death contributes to progression of alcohol-associated (ALD-associated) and non-alcohol-associated (NAFL/NASH) liver diseases. However, receptor-interaction protein kinase 3 (RIP3), an intermediate in necroptotic cell death, contributes to injury in murine models of ALD but not NAFL/NASH. We show here that a differential role for mixed-lineage kinase domain-like protein (MLKL), the downstream effector of RIP3, in murine models of ALD versus NAFL/NASH and that RIP1-RIP3-MLKL can be used as biomarkers to distinguish alcohol-associated hepatitis (AH) from NASH. Phospho-MLKL was higher in livers of patients with NASH compared with AH or healthy controls (HCs). MLKL expression, phosphorylation, oligomerization, and translocation to plasma membrane were induced in WT mice fed diets high in fat, fructose, and cholesterol but not in response to Gao-binge (acute on chronic) ethanol exposure. Mlkl-/- mice were not protected from ethanol-induced hepatocellular injury, which was associated with increased expression of chemokines and neutrophil recruitment. Circulating concentrations of RIP1 and RIP3, but not MLKL, distinguished patients with AH from HCs or patients with NASH. Taken together, these data indicate that MLKL is differentially activated in ALD/AH compared with NAFL/NASH in both murine models and patients. Furthermore, plasma RIP1 and RIP3 may be promising biomarkers for distinguishing AH and NASH

Role of the Chemokine System in Liver Fibrosis: A Narrative Review

BACKGROUND AND OBJECTIVE: Liver fibrosis is a disease with characteristics of an aberrant wound healing response. Fibrosis is commonly the end-stage for chronic liver diseases like alcohol-associated liver disease (ALD), metabolic-associated liver disease, viral hepatitis, and hepatic autoimmune disease. Innate immunity contributes to the progression of many diseases through multiple mechanisms including production of pro-inflammatory mediators, leukocyte infiltration and tissue injury. Chemokines and their receptors orchestrate accumulation and activation of immune cells in tissues and are associated with multiple liver diseases; however, much less is known about their potential roles in liver fibrosis. This is a narrative review of current knowledge of the relationship of chemokine biology to liver fibrosis with insights into potential future therapeutic opportunities that can be explored in the future. METHODS: A comprehensive literature review was performed searching PubMed for relevant English studies and texts regarding chemokine biology, chronic liver disease and liver fibrosis published between 1993 and 2021. The review was written and constructed to detail the intriguing chemokine biology, the relation of chemokines to tissue injury and resolution, and identify areas of discovery for fibrosis treatment. KEY CONTENT AND FINDINGS: Chemokines are implicated in many chronic liver diseases, regardless of etiology. Most of these diseases will progress to fibrosis without appropriate treatment. The contributions of chemokines to liver disease and fibrosis are diverse and include canonical roles of modulating hepatic inflammation as well as directly contributing to fibrosis via activation of hepatic stellate cells (HSCs). Limited clinical evidence suggests that targeting chemokines in certain liver diseases might provide a therapeutic benefit to patients with hepatic fibrosis. CONCLUSIONS: The chemokine system of ligands and receptors is a complex network of inflammatory signals in nearly all diseases. The specific sources of chemokines and cellular targets lend unique pathophysiological consequences to chronic liver diseases and established fibrosis. Although most chemokines are pro-inflammatory and contribute to tissue injury, others likely aid in the resolution of established fibrosis. To date, very few targeted therapies exist for the chemokine system and liver disease and/or fibrosis, and further study could identify viable treatment options to improve outcomes in patients with end-stage liver disease

Anaphylatoxin Receptors C3aR and C5aR1 Are Important Factors That Influence the Impact of Ethanol on the Adipose Secretome

Background and aims: Chronic ethanol exposure results in inflammation in adipose tissue; this response is associated with activation of complement as well as the development of alcohol-related liver disease (ALD). Adipose communicates with other organs, including liver, via the release of soluble mediators, such as adipokines and cytokines, characterized as the “adipose secretome.” Here we investigated the role of the anaphaylatoxin receptors C3aR and C5aR1 in the development of adipose tissue inflammation and regulation of the adipose secretome in murine ALD (mALD).Methods: Wild-type C57BL/6 (WT), C3aR−/−, and C5aR1−/− mice were fed Lieber-DeCarli ethanol diet for 25 days (6% v/v, 32% kcal) or isocaloric control diets; indicators of inflammation and injury were assessed in gonadal adipose tissue. The adipose secretome was characterized in isolated adipocytes and stromal vascular cells.Results: Ethanol feeding increased the expression of adipokines, chemokines and leukocyte markers in gonadal adipose tissue from WT mice; C3aR−/− were partially protected while C5aR1−/− mice were completely protected. In contrast, induction of CYP2E1 and accumulation of TUNEL-positive cells in adipose in response to ethanol feeding was independent of genotype. Bone marrow chimeras, generated with WT and C5aR1−/− mice, revealed C5aR1 expression on non-myeloid cells, likely to be adipocytes, contributed to ethanol-induced adipose inflammation. Chronic ethanol feeding regulated both the quantity and distribution of adipokines secreted from adipocytes in a C5aR1-dependent mechanism. In WT mice, chronic ethanol feeding induced a predominant release of pro-inflammatory adipokines from adipocytes, while the adipose secretome from C5aR1−/− mice was characterized by an anti-inflammatory/protective profile. Further, the cargo of adipocyte-derived extracellular vesicles (EVs) was distinct from the soluble secretome; in WT EVs, ethanol increased the abundance of pro-inflammatory mediators while EV cargo from C5aR1−/− adipocytes contained a greater diversity and more robust expression of adipokines.Conclusions: C3aR and C5aR1 are potent regulators of ethanol-induced adipose inflammation in mALD. C5aR1 modulated the impact of chronic ethanol on the content of the adipose secretome, as well as influencing the cargo of an extensive array of adipokines from adipocyte-derived EVs. Taken together, our data demonstrate that C5aR1 contributes to ethanol-mediated changes in the adipose secretome, likely contributing to intra-organ injury in ALD

A switchable light-input, light-output system modelled and constructed in yeast

<p>Abstract</p> <p>Background</p> <p>Advances in synthetic biology will require spatio-temporal regulation of biological processes in heterologous host cells. We develop a light-switchable, two-hybrid interaction in yeast, based upon the Arabidopsis proteins PHYTOCHROME A and FAR-RED ELONGATED HYPOCOTYL 1-LIKE. Light input to this regulatory module allows dynamic control of a light-emitting LUCIFERASE reporter gene, which we detect by real-time imaging of yeast colonies on solid media.</p> <p>Results</p> <p>The reversible activation of the phytochrome by red light, and its inactivation by far-red light, is retained. We use this quantitative readout to construct a mathematical model that matches the system's behaviour and predicts the molecular targets for future manipulation.</p> <p>Conclusion</p> <p>Our model, methods and materials together constitute a novel system for a eukaryotic host with the potential to convert a dynamic pattern of light input into a predictable gene expression response. This system could be applied for the regulation of genetic networks - both known and synthetic.</p

Non-coding RNA crosstalk with nuclear receptors in liver disease

The dysregulation of nuclear receptors (NRs) underlies the pathogenesis of a variety of liver disorders. Non-coding RNAs (ncRNAs) are defined as RNA molecules transcribed from DNA but not translated into proteins. MicroRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are two types of ncRNAs that have been extensively studied for regulating gene expression during diverse cellular processes. NRs as therapeutic targets in liver disease have been exemplified by the successful application of their pharmacological ligands in clinics. MiRNA-based reagents or drugs are emerging as flagship products in clinical trials. Advancing our understanding of the crosstalk between NRs and ncRNAs is critical to the development of diagnostic and therapeutic strategies. This review summarizes recent findings on the reciprocal regulation between NRs and ncRNAs (mainly on miRNAs and lncRNAs) and their implication in liver pathophysiology, which might be informative to the translational medicine of targeting NRs and ncRNAs in liver disease

MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases.

Low-grade systemic inflammation is often associated with metabolic syndrome, which plays a critical role in the development of the obesity-associated inflammatory diseases, including insulin resistance and atherosclerosis. Here, we investigate how Toll-like receptor-MyD88 signaling in myeloid and endothelial cells coordinately participates in the initiation and progression of high fat diet-induced systemic inflammation and metabolic inflammatory diseases. MyD88 deficiency in myeloid cells inhibits macrophage recruitment to adipose tissue and their switch to an M1-like phenotype. This is accompanied by substantially reduced diet-induced systemic inflammation, insulin resistance, and atherosclerosis. MyD88 deficiency in endothelial cells results in a moderate reduction in diet-induced adipose macrophage infiltration and M1 polarization, selective insulin sensitivity in adipose tissue, and amelioration of spontaneous atherosclerosis. Both in vivo and ex vivo studies suggest that MyD88-dependent GM-CSF production from the endothelial cells might play a critical role in the initiation of obesity-associated inflammation and development of atherosclerosis by priming the monocytes in the adipose and arterial tissues to differentiate into M1-like inflammatory macrophages. Collectively, these results implicate a critical MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases

Alternatively spliced exon regulates context-dependent MEF2D higher-order assembly during myogenesis

: During muscle cell differentiation, the alternatively spliced, acidic β-domain potentiates transcription of Myocyte-specific Enhancer Factor 2 (Mef2D). Sequence analysis by the FuzDrop method indicates that the β-domain can serve as an interaction element for Mef2D higher-order assembly. In accord, we observed Mef2D mobile nuclear condensates in C2C12 cells, similar to those formed through liquid-liquid phase separation. In addition, we found Mef2D solid-like aggregates in the cytosol, the presence of which correlated with higher transcriptional activity. In parallel, we observed a progress in the early phase of myotube development, and higher MyoD and desmin expression. In accord with our predictions, the formation of aggregates was promoted by rigid β-domain variants, as well as by a disordered β-domain variant, capable of switching between liquid-like and solid-like higher-order states. Along these lines, NMR and molecular dynamics simulations corroborated that the β-domain can sample both ordered and disordered interactions leading to compact and extended conformations. These results suggest that β-domain fine-tunes Mef2D higher-order assembly to the cellular context, which provides a platform for myogenic regulatory factors and the transcriptional apparatus during the developmental process

Diagnostic and Prognostic Significance of Complement in Patients with Alcohol-associated Hepatitis

BACKGROUND and AIMS: Given the lack of effective therapies and high mortality in acute alcohol-associated hepatitis (AH), it is important to develop rationally-designed biomarkers for effective disease management. Complement, a critical component of the innate immune system, contributes to uncontrolled inflammatory responses leading to liver injury, but is also involved in hepatic regeneration. Here we investigated if a panel of complement proteins and activation products would provide useful biomarkers for severity of AH and aid in predicting 90 days mortality. APPROACH and RESULTS: Plasma samples collected at time of diagnosis from 254 patients with moderate and severe AH recruited from four medical centers and 31 healthy individuals were used to quantify complement proteins by ELISA and Luminex arrays. Components of the classical and lectin pathways, including complement factors C2, C4b and C4d, as well as complement factor I (CFI) and C5, were reduced in AH patients compared to healthy individuals. In contrast, components of the alternative pathway, including complement factor Ba (CFBa) and factor D (CFD), were increased. Markers of complement activation were also differentially evident, with C5a increased and the soluble terminal complement complex (sC5b9) decreased in AH. Mannose binding lectin (MBL), C4b, CFI, C5 and sC5b9 were negatively correlated with model for end-stage liver disease (MELD) score, while CFBa and CFD were positively associated with disease severity. Lower CFI and sC5b9 were associated with increased 90-day mortality in AH. CONCLUSIONS: Taken together, these data indicate that AH is associated with a profound disruption of complement. Inclusion of complement, especially CFI and sC5b9, along with other laboratory indicators, could improve diagnostic and prognostic indications of disease severity and risk of mortality for AH patients