Lipid-associated macrophages' promotion of fibrosis resolution during MASH regression requires TREM2.

While macrophage heterogeneity during metabolic dysfunction-associated steatohepatitis (MASH) has been described, the fate of these macrophages during MASH regression is poorly understood. Comparing macrophage heterogeneity during MASH progression vs regression, we identified specific macrophage subpopulations that are critical for MASH/fibrosis resolution. We elucidated the restorative pathways and gene signatures that define regression-associated macrophages and establish the importance of TREM2+ macrophages during MASH regression. Liver-resident Kupffer cells are lost during MASH and are replaced by four distinct monocyte-derived macrophage subpopulations. Trem2 is expressed in two macrophage subpopulations: i) monocyte-derived macrophages occupying the Kupffer cell niche (MoKC) and ii) lipid-associated macrophages (LAM). In regression livers, no new transcriptionally distinct macrophage subpopulation emerged. However, the relative macrophage composition changed during regression compared to MASH. While MoKC was the major macrophage subpopulation during MASH, they decreased during regression. LAM was the dominant macrophage subtype during MASH regression and maintained Trem2 expression. Both MoKC and LAM were enriched in disease-resolving pathways. Absence of TREM2 restricted the emergence of LAMs and formation of hepatic crown-like structures. TREM2+ macrophages are functionally important not only for restricting MASH-fibrosis progression but also for effective regression of inflammation and fibrosis. TREM2+ macrophages are superior collagen degraders. Lack of TREM2+ macrophages also prevented elimination of hepatic steatosis and inactivation of HSC during regression, indicating their significance in metabolic coordination with other cell types in the liver. TREM2 imparts this protective effect through multifactorial mechanisms, including improved phagocytosis, lipid handling, and collagen degradation.

Heterogeneity of HSCs in a Mouse Model of NASH.

BACKGROUND AND AIMS: In clinical and experimental NASH, the origin of the scar-forming myofibroblast is the HSC. We used foz/foz mice on a Western diet to characterize in detail the phenotypic changes of HSCs in a NASH model. APPROACH AND RESULTS: We examined the single-cell expression profiles (scRNA sequencing) of HSCs purified from the normal livers of foz/foz mice on a chow diet, in NASH with fibrosis of foz/foz mice on a Western diet, and in livers during regression of NASH after switching back to a chow diet. Selected genes were analyzed using immunohistochemistry, quantitative real-time PCR, and short hairpin RNA knockdown in primary mouse HSCs. Our analysis of the normal liver identified two distinct clusters of quiescent HSCs that correspond to their acinar position of either pericentral vein or periportal vein. The NASH livers had four distinct HSC clusters, including one representing the classic fibrogenic myofibroblast. The three other HSC clusters consisted of a proliferating cluster, an intermediate activated cluster, and an immune and inflammatory cluster. The livers with NASH regression had one cluster of inactivated HSCs, which was similar to, but distinct from, the quiescent HSCs. CONCLUSIONS: Analysis of single-cell RNA sequencing in combination with an interrogation of previous studies revealed an unanticipated heterogeneity of HSC phenotypes under normal and injured states.

NADPH Oxidase 1 in Liver Macrophages Promotes Inflammation and Tumor Development in Mice.

BACKGROUND & AIMS: Although there are associations among oxidative stress, reduced nicotinamide adenine dinucleotide phosphate oxidase (NOX) activation, and hepatocellular carcinoma (HCC) development, it is not clear how NOX contributes to hepatocarcinogenesis. We studied the functions of different NOX proteins in mice after administration of a liver carcinogen. METHODS: Fourteen-day-old Nox1-/- mice, Nox4-/- mice, Nox1-/-Nox4-/- (double-knockout) mice, and wild-type (WT) C57BL/6 mice were given a single intraperitoneal injection of diethylnitrosamine (DEN) and liver tumors were examined at 9 months. We also studied the effects of DEN in mice with disruption of Nox1 specifically in hepatocytes (Nox1ΔHep), hepatic stellate cells (Nox1ΔHep), or macrophages (Nox1ΔMac). Some mice were also given injections of the NOX1-specific inhibitor ML171. To study the acute effects of DEN, 8-12-week-old mice were given a single intraperitoneal injection, and liver and serum were collected at 72 hours. Liver tissues were analyzed by histologic examination, quantitative polymerase chain reaction, and immunoblots. Hepatocytes and macrophages were isolated from WT and knockout mice and analyzed by immunoblots. RESULTS: Nox4-/- mice and WT mice developed liver tumors within 9 months after administration of DEN, whereas Nox1-/- mice developed 80% fewer tumors, which were 50% smaller than those of WT mice. Nox1ΔHep and Nox1ΔHSC mice developed liver tumors of the same number and size as WT mice, whereas Nox1ΔMac developed fewer and smaller tumors, similar to Nox1-/- mice. After DEN injection, levels of tumor necrosis factor, interleukin 6 (IL6), and phosphorylated signal transducer and activator of transcription 3 were increased in livers from WT, but not Nox1-/- or Nox1ΔMac, mice. Conditioned medium from necrotic hepatocytes induced expression of NOX1 in cultured macrophages, followed by expression of tumor necrosis factor, IL6, and other inflammatory cytokines; this medium did not induce expression of IL6 or cytokines in Nox1ΔMac macrophages. WT mice given DEN followed by ML171 developed fewer and smaller liver tumors than mice given DEN followed by vehicle. CONCLUSIONS: In mice given injections of a liver carcinogen (DEN), expression of NOX1 by macrophages promotes hepatic tumorigenesis by inducing the production of inflammatory cytokines. We propose that upon liver injury, damage-associated molecular patterns released from dying hepatocytes activate liver macrophages to produce cytokines that promote tumor development. Strategies to block NOX1 or these cytokines might be developed to slow hepatocellular carcinoma progression.

Ascorbate attenuates pulmonary emphysema by inhibiting tobacco smoke and Rtp801-triggered lung protein modification and proteolysis.

Cigarette smoking causes emphysema, a fatal disease involving extensive structural and functional damage of the lung. Using a guinea pig model and human lung cells, we show that oxidant(s) present in tobacco smoke not only cause direct oxidative damage of lung proteins, contributing to the major share of lung injury, but also activate Rtp801, a key proinflammatory cellular factor involved in tobacco smoke-induced lung damage. Rtp801 triggers nuclear factor κB and consequent inducible NOS (iNOS)-mediated overproduction of NO, which in combination with excess superoxide produced during Rtp801 activation, contribute to increased oxido-nitrosative stress and lung protein nitration. However, lung-specific inhibition of iNOS with a iNOS-specific inhibitor, N6-(1-iminoethyl)-L-lysine, dihydrochloride (L-NIL) solely restricts lung protein nitration but fails to prevent or reverse the major tobacco smoke-induced oxidative lung injury. In comparison, the dietary antioxidant, ascorbate or vitamin C, can substantially prevent such damage by inhibiting both tobacco smoke-induced lung protein oxidation as well as activation of pulmonary Rtp801 and consequent iNOS/NO-induced nitration of lung proteins, that otherwise lead to increased proteolysis of such oxidized or nitrated proteins by endogenous lung proteases, resulting in emphysematous lung damage. Vitamin C also restricts the up-regulation of matrix-metalloproteinase-9, the major lung protease involved in the proteolysis of such modified lung proteins during tobacco smoke-induced emphysema. Overall, our findings implicate tobacco-smoke oxidant(s) as the primary etiopathogenic factor behind both the noncellular and cellular damage mechanisms governing emphysematous lung injury and demonstrate the potential of vitamin C to accomplish holistic prevention of such damage.

Alcohol-Associated Liver Disease Outcomes: Critical Mechanisms of Liver Injury Progression.

Alcohol-associated liver disease (ALD) is a substantial cause of morbidity and mortality worldwide and represents a spectrum of liver injury beginning with hepatic steatosis (fatty liver) progressing to inflammation and culminating in cirrhosis. Multiple factors contribute to ALD progression and disease severity. Here, we overview several crucial mechanisms related to ALD end-stage outcome development, such as epigenetic changes, cell death, hemolysis, hepatic stellate cells activation, and hepatic fatty acid binding protein 4. Additionally, in this review, we also present two clinically relevant models using human precision-cut liver slices and hepatic organoids to examine ALD pathogenesis and progression.

Nonalcoholic Steatohepatitis and HCC in a Hyperphagic Mouse Accelerated by Western Diet.

BACKGROUND & AIMS: How benign liver steatosis progresses to nonalcoholic steatohepatitis (NASH), fibrosis, and hepatocellular carcinoma (HCC) remains elusive. NASH progression entails diverse pathogenic mechanisms and relies on complex cross-talk between multiple tissues such as the gut, adipose tissues, liver, and the brain. Using a hyperphagic mouse fed with a Western diet (WD), we aimed to elucidate the cross-talk and kinetics of hepatic and extrahepatic alterations during NASH-HCC progression, as well as regression. METHODS: Hyperphagic mice lacking a functional Alms1 gene (Foz/Foz) and wild-type littermates were fed WD or standard chow for 12 weeks for NASH/fibrosis and for 24 weeks for HCC development. NASH regression was modeled by switching back to normal chow after NASH development. RESULTS: Foz+WD mice were steatotic within 1 to 2 weeks, developed NASH by 4 weeks, and grade 3 fibrosis by 12 weeks, accompanied by chronic kidney injury. Foz+WD mice that continued on WD progressed to cirrhosis and HCC within 24 weeks and had reduced survival as a result of cardiac dysfunction. However, NASH mice that were switched to normal chow showed NASH regression, improved survival, and did not develop HCC. Transcriptomic and histologic analyses of Foz/Foz NASH liver showed strong concordance with human NASH. NASH was preceded by an early disruption of gut barrier, microbial dysbiosis, lipopolysaccharide leakage, and intestinal inflammation. This led to acute-phase liver inflammation in Foz+WD mice, characterized by neutrophil infiltration and increased levels of several chemokines/cytokines. The liver cytokine/chemokine profile evolved as NASH progressed, with subsequent predominance by monocyte recruitment. CONCLUSIONS: The Foz+WD model closely mimics the pathobiology and gene signature of human NASH with fibrosis and subsequent HCC. Foz+WD mice provide a robust and relevant preclinical model of NASH, NASH-associated HCC, chronic kidney injury, and heart failure.

Western Diet Promotes Renal Injury, Inflammation, and Fibrosis in a Murine Model of Alström Syndrome.

INTRODUCTION: Alström syndrome is a rare recessive genetic disease caused by mutations in ALMS1, which encodes a protein that is related to cilia function and intracellular endosome trafficking. The syndrome has been linked to impaired glucose metabolism and CKD. Polymorphisms in Alms1 have likewise been linked to CKD, but little is known about the modification of the phenotype by environmental factors. METHODS: To gain further insights, the fat aussie (foz) mouse strain, a genetic murine model of Alström syndrome, was exposed to a normal chow (NC) or to a Western diet (WD, 20% fat, 34% sucrose by weight, and 0.2% cholesterol) and renal outcomes were measured. RESULTS: Body weight and albuminuria were higher in foz than in wild-type (WT) mice on both diets but WD significantly increased the difference. Measurement of plasma creatinine and cystatin C indicated that glomerular filtration rate was preserved in foz versus WT independent of diet. Renal markers of injury, inflammation, and fibrosis were similar in both genotypes on NC but significantly greater in foz than in WT mice on WD. A glucose tolerance test performed in foz and WT mice on WD revealed similar basal blood glucose levels and subsequent blood glucose profiles. CONCLUSIONS: WD sensitizes a murine model of Alström syndrome to kidney injury, inflammation, and fibrosis, an effect that may not be solely due to effects on glucose metabolism. Polymorphisms in Alms1 may induce CKD in part by modulating the deleterious effects of high dietary fat and sucrose on kidney outcome.

Nitric oxide sensing by chlorophyll a.

Nitric oxide (NO) acts as a signalling molecule that has direct and indirect regulatory roles in various functional processes in biology, though in plant kingdom its role is relatively unexplored. One reason for this is the fact that sensing of NO is always challenging. There are very few probes that can classify the different NO species. The present paper proposes a simple but straightforward way for sensing different NO species using chlorophyll, the source of inspiration being hemoglobin that serves as NO sink in mammalian systems. The proposed method is able to classify NO from DETA-NONOate or (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1,2-diolate, nitrite, nitrate and S-nitrosothiol or SNO. This discrimination is carried out by chlorophyll a (chl a) at nano molar (nM) order of sensitivity and at 293 K-310 K. Molecular docking reveals the differential binding effects of NO and SNO with chlorophyll, the predicted binding affinity matching with the experimental observation. Additional experiments with a diverse range of cyanobacteria reveal that apart from the spectroscopic approach the proposed sensing module can be used in microscopic inspection of NO species. Binding of NO is sensitive to temperature and static magnetic field. This provides additional support for the involvement of the porphyrin ring structures to the NO sensing process. This also, broadens the scope of the sensing methods as hinted in the text.

Simultaneous Determination of Black Tea-Derived Catechins and Theaflavins in Tissues of Tea Consuming Animals Using Ultra-Performance Liquid-Chromatography Tandem Mass Spectrometry.

The bioavailability, tissue distribution and metabolic fate of the major tea polyphenols, catechins and theaflavins as well as their gallated derivatives are yet to be precisely elucidated on a single identification platform for assessment of their relative bioefficacy in vivo. This is primarily due to the lack of suitable analytical tools for their simultaneous determination especially in an in vivo setting, which continues to constrain the evaluation of their relative health beneficiary potential and therefore prospective therapeutic application. Herein, we report a rapid and sensitive Ultra-Performance Liquid Chromatography Tandem Mass Spectrometry (UPLC-MS/MS) based method for the simultaneous determination of the major catechins and theaflavins in black tea infusions as well as in different vital tissues and body fluids of tea-consuming guinea pigs. This method allowed efficient separation of all polyphenols within seven minutes of chromatographic run and had a lower limit of quantification (LLOQ) of ~5 ng/ml. Using this method, almost all bioactive catechins and theaflavins could be simultaneously detected in the plasma of guinea pigs orally administered 5% black tea for 14 days. Our method could further detect the majority of these polyphenols in the lung and kidney as well as identify the major catechin metabolites in the urine of the tea-consuming animals. Overall, our study presents a novel tool for simultaneous detection and quantitation of both catechins and theaflavins in a single detection platform that could potentially enable precise elucidation of their relative bioavailability and bioefficacy as well as true health beneficiary potential in vivo. Such information would ultimately facilitate the accurate designing of therapeutic strategies utilizing high efficacy formulations of tea polyphenols for effective mitigation of oxidative damage and inflammation in humans as well as prevention of associated diseases.