Non-alcoholic Fatty Liver Disease and Liver Fibrosis during Aging

Bile acid metabolism in health and ageing-related diseases

Bile acids (BAs) have surpassed their traditional roles as lipid solubilizers and regulators of BA homeostasis to emerge as important signalling molecules. Recent research has revealed a connection between microbial dysbiosis and metabolism disruption of BAs, which in turn impacts ageing-related diseases. The human BAs pool is primarily composed of primary BAs and their conjugates, with a smaller proportion consisting of secondary BAs. These different BAs exert complex effects on health and ageing-related diseases through several key nuclear receptors, such as farnesoid X receptor and Takeda G protein-coupled receptor 5. However, the underlying molecular mechanisms of these effects are still debated. Therefore, the modulation of signalling pathways by regulating synthesis and composition of BAs represents an interesting and novel direction for potential therapies of ageing-related diseases. This review provides an overview of synthesis and transportion of BAs in the healthy body, emphasizing its dependence on microbial community metabolic capacity. Additionally, the review also explores how ageing and ageing-related diseases affect metabolism and composition of BAs. Understanding BA metabolism network and the impact of their nuclear receptors, such as farnesoid X receptor and G protein-coupled receptor 5 agonists, paves the way for developing therapeutic agents for targeting BA metabolism in various ageing-related diseases, such as metabolic disorder, hepatic injury, cardiovascular disease, renal damage and neurodegenerative disease.

STING promotes homeostatic maintenance of tissues and confers longevity with aging

Local immune processes within aging tissues are a significant driver of aging associated dysfunction, but tissue-autonomous pathways and cell types that modulate these responses remain poorly characterized. The cytosolic DNA sensing pathway, acting through cyclic GMP-AMP synthase (cGAS) and Stimulator of Interferon Genes (STING), is broadly expressed in tissues, and is poised to regulate local type I interferon (IFN-I)-dependent and independent inflammatory processes within tissues. Recent studies suggest that the cGAS/STING pathway may drive pathology in various in vitro and in vivo models of accelerated aging. To date, however, the role of the cGAS/STING pathway in physiological aging processes, in the absence of genetic drivers, has remained unexplored. This remains a relevant gap, as STING is ubiquitously expressed, implicated in multitudinous disorders, and loss of function polymorphisms of STING are highly prevalent in the human population (>50%). Here we reveal that, during physiological aging, STING-deficiency leads to a significant shortening of murine lifespan, increased pro-inflammatory serum cytokines and tissue infiltrates, as well as salient changes in histological composition and organization. We note that aging hearts, livers, and kidneys express distinct subsets of inflammatory, interferon-stimulated gene (ISG), and senescence genes, collectively comprising an immune fingerprint for each tissue. These distinctive patterns are largely imprinted by tissue-specific stromal and myeloid cells. Using cellular interaction network analyses, immunofluorescence, and histopathology data, we show that these immune fingerprints shape the tissue architecture and the landscape of cell-cell interactions in aging tissues. These age-associated immune fingerprints are grossly dysregulated with STING-deficiency, with key genes that define aging STING-sufficient tissues greatly diminished in the absence of STING. Changes in immune signatures are concomitant with a restructuring of the stromal and myeloid fractions, whereby cell:cell interactions are grossly altered and resulting in disorganization of tissue architecture in STING-deficient organs. This altered homeostasis in aging STING-deficient tissues is associated with a cross-tissue loss of homeostatic tissue-resident macrophage (TRM) populations in these tissues. Ex vivo analyses reveal that basal STING-signaling limits the susceptibility of TRMs to death-inducing stimuli and determines their in situ localization in tissue niches, thereby promoting tissue homeostasis. Collectively, these data upend the paradigm that cGAS/STING signaling is primarily pathological in aging and instead indicate that basal STING signaling sustains tissue function and supports organismal longevity. Critically, our study urges caution in the indiscriminate targeting of these pathways, which may result in unpredictable and pathological consequences for health during aging.

Associated factors with liver fibrosis in rheumatoid arthritis patients treated with methotrexate

INTRODUCTION

There are conflicting findings on the link between liver fibrosis and cumulative methotrexate dosages. We aimed to determine the frequency of liver fibrosis in rheumatoid arthritis patients treated with methotrexate and to identify its associated factors.

METHODS

We conducted a cross-sectional study over 9 months (April-December 2021), including rheumatoid arthritis patients treated with methotrexate. Demographic and clinical data were collected. Liver stiffness was assessed by FibroScan. Fibrosis and significant liver fibrosis were defined as liver stiffness higher than 6 and 7.2 kPa, respectively. Liver tests, albuminemia, lipid profile, and blood glycemia were measured. Metabolic syndrome was also evaluated. Statistical analyses were performed using SPSS.

RESULTS

We included 21 men and 47 women. The mean age was 51.60 ± 1.82 years. The mean disease duration was 8.29 ± 6.48 years. The mean weekly intake of methotrexate was 13.76 ± 3.91 mg. The mean methotrexate duration was 4.67 ± 4.24 years. The mean cumulative dose was 3508.87 ± 3390.48 mg. Hypoalbuminemia and metabolic syndrome were found in 34% and 25% of cases. We noted increased alkaline phosphatase levels in four cases. The mean liver stiffness was 4.50 ± 1.53 kPa. Nine patients had liver fibrosis, and four had significant fibrosis. Associated factors with liver fibrosis were as follows: age ≥ 60 years (OR:22.703; 95%CI [1.238-416.487]; p = 0.035), cumulated dose of methotrexate ≥ 3 g (OR: 76.501; 95%CI [2.383-2456.070]; p = 0.014), metabolic syndrome (OR: 42.743; 95%CI [1.728-1057.273]; p = 0.022), elevated alkaline phosphatase levels (OR: 28.252; 95%CI [1.306-611.007]; p = 0.033), and hypoalbuminemia (OR: 59.302; 95%CI [2.361-1489.718]; p = 0.013).

CONCLUSION

Cumulating more than 3 g of methotrexate was associated with liver fibrosis in rheumatoid arthritis patients. Having a metabolic syndrome, higher age, hypoalbuminemia, and elevated alkaline phosphatase levels were also likely to be independently associated with liver fibrosis. Key points • Rheumatoid arthritis patients require monitoring hepatic fibrosis when the cumulated dose of methotrexate is above 3 g. • Metabolic syndrome is a risk factor for liver fibrosis, suggesting that its management is necessary to prevent this complication. • Hypoalbuminemia and elevated alkaline phosphatase levels (twice the upper limit) in rheumatoid arthritis patients treated with methotrexate were associated with liver fibrosis.

PCSK9: an emerging player in cardiometabolic aging and its potential as a therapeutic target and biomarker

Proprotein convertase subtilisin/kexin type 9 (PCSK9), renowned for its pivotal role in low-density lipoprotein (LDL) regulation, has emerged as a compelling regulator of cardiometabolic aging. Beyond its well-established involvement in cholesterol metabolism, PCSK9's multifaceted influence on the aging processes of the cardiovascular and metabolic systems is garnering increasing attention. This review delves into the evolving landscape of PCSK9 in the context of cardiometabolic aging, offering fresh insights into its potential implications. Drawing inspiration from pioneering research conducted by the Pacher laboratory (Arif et al., Geroscience, 2023, PMID: 37726433), we delve into the intricate interplay of PCSK9 within the aging heart and liver, shedding light on its newfound significance. Recent studies underscore PCSK9's pivotal role in liver aging, suggesting intriguing connections between hepatic aging, lipid metabolism, and cardiovascular health. Additionally, we explore the therapeutic potential of PCSK9 as both a target and a biomarker, within the context of age-related cardiovascular disease.

Vitamin D ameliorates age-induced nonalcoholic fatty liver disease by increasing the mitochondrial contact site and cristae organizing system (MICOS) 60 level

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease. Despite intensive research, considerable information on NAFLD development remains elusive. In this study, we examined the effects of vitamin D on age-induced NAFLD, especially in connection with mitochondrial abnormalities. We observed the prevention of NAFLD in 22-month-old C57BL/6 mice fed a vitamin D3-supplemented (20,000 IU/kg) diet compared with mice fed a control (1000 IU/kg) diet. We evaluated whether vitamin D3 supplementation enhanced mitochondrial functions. We found that the level of mitochondrial contact site and cristae organizing system (MICOS) 60 (Mic60) level was reduced in aged mice, and this reduction was specifically restored by vitamin D3. In addition, depletion of Immt, the human gene encoding the Mic60 protein, induced changes in gene expression patterns that led to fat accumulation in both HepG2 and primary hepatocytes, and these alterations were effectively prevented by vitamin D3. In addition, silencing of the vitamin D receptor (VDR) decreased the Mic60 levels, which were recovered by vitamin D treatment. To assess whether VDR directly regulates Mic60 levels, we performed chromatin immunoprecipitation and reporter gene analysis. We discovered that VDR directly binds to the Immt 5' promoter region spanning positions -3157 to -2323 and thereby upregulates Mic60. Our study provides the first demonstration that a reduction in Mic60 levels due to aging may be one of the mechanisms underlying the development of aging-associated NAFLD. In addition, vitamin D3 could positively regulate Mic60 expression, and this may be one of the important mechanisms by which vitamin D could ameliorate age-induced NAFLD.

Aging aggravates liver fibrosis through downregulated hepatocyte SIRT1-induced liver sinusoidal endothelial cell dysfunction

BACKGROUND

Aging increases the susceptibility to chronic liver diseases and hastens liver fibrosis deterioration, but the underlying mechanisms remain partially understood. The aim of this study was to investigate the effect of aging and chronic liver diseases on hepatocyte Sirtuin 1 (SIRT1) and LSECs and their contribution to liver fibrosis pathogeneses.

METHODS

Young (8-12 wk) and aged (18-20 mo) mice were subjected to carbon tetrachloride-induced liver fibrosis. Primary HSCs and LSECs were isolated and cocultured for in vitro experiments. Liver tissues and blood samples from healthy controls and patients with liver fibrosis were analyzed.

RESULTS

Downregulated hepatocytes SIRT1 in aged mice increased high mobility group box 1 acetylation, cytoplasmic translocation, and extracellular secretion, causing LSECs dysfunction by means of the toll-like receptor 4/AK strain transforming (AKT)/endothelial nitric oxide synthase pathway, ultimately activating HSCs and increasing susceptibility to liver injury and fibrosis. Adeno-associated virus-mediated overexpression of SIRT1 in hepatocytes suppressed the abovementioned alterations and attenuated carbon tetrachloride-induced liver injury and fibrosis in liver fibrosis mice, and there were no significant differences in liver injury and fibrosis indicators between young and aged mice after SIRT1 overexpression treatment. In vitro experiments demonstrated that SIRT1 overexpression and endothelial nitric oxide synthase agonist YC-1 improved LSECs function and inhibited HSCs activation, mediated by nitric oxide. Similarly, downregulated hepatocytes SIRT1 and LSECs dysfunction were observed in the livers of aged individuals compared to young individuals and were more pronounced in aged patients with liver fibrosis.

CONCLUSIONS

Aging aggravates liver fibrosis through downregulated hepatocytes SIRT1-induced LSECs dysfunction, providing a prospective curative approach for preventing and treating liver fibrosis.

A nomogram based on psoas muscle index predicting long-term cirrhosis incidence in non-cirrhotic patients with HBV-related acute‑on‑chronic liver failure

There is a lack of scoring system to predict the occurrence of cirrhosis in individuals with acute-on-chronic liver failure (ACLF) in the absence of cirrhosis. The goal of this study was to develop a psoas muscle index (PMI)-based nomogram for cirrhosis risk in non-cirrhotic patients with HBV-related ACLF. We included 274 non-cirrhotic HBV-ACLF patients who were randomly assigned to training and validation groups. Logistic analyses were performed to identify risk factors for cirrhosis. A nomogram was then constructed. The predictive performance of the nomogram was assessed using the area under the receiver operating characteristic curve (AUROC), calibration curve, and decision curve analysis (DCA). During the 360-day follow-up, 44.5% (122/274) of non-cirrhotic HBV-ACLF patients developed cirrhosis. A higher PMI at the L3 level was correlated with a decreased risk of long-term cirrhosis occurrence (OR 0.677, 95% CI 0.518-0.885, P = 0.004). The nomogram incorporating PMI, age, neutrophil-to-lymphocyte ratio (NLR), and international normalized ratio (INR), indicated satisfactory predictive performance for cirrhosis risk stratification in ACLF population. The nomograms had an AUROC of 0.812 (95% CI 0.747-0.866) and 0.824 (95% CI 0.730-0.896) in the training and validation cohorts, respectively. The calibration curves displayed excellent predictive accuracy of the nomogram in both sets. In both cohorts, the DCA verified the nomogram's clinical efficacy. In non-cirrhotic HBV-ACLF patients, a greater PMI appears to protect against long-term cirrhosis occurrence. Strong predictive performance has been demonstrated by PMI-based nomograms in assessing the likelihood of 1-year cirrhosis in those with HBV-ACLF.

Single- and combined-phthalate exposures are associated with biological ageing among adults

BACKGROUND

Previous research has emphasized the effects of lifestyle and genetics on ageing. However, the association between exposure to phthalates, which are extensively used in cosmetics and personal care products, and ageing is still unclear.

METHOD

Data for 4711 subjects from the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2010 were incorporated in the present study. The acceleration of the Klemera-Doubal method-biological age (KDM-BA) and phenotypic Age (PhenoAge) were measured by the composite of 13 biomarkers. Multiple-linear and weighted-quantile sum (WQS) regression models were constructed to explore the relationships of single- and combined-phthalate exposures, as indicated by urinary phthalate metabolites, with KDM-BA and PhenoAge. A generalized additive model (GAM) was fitted to explore the potential nonlinear relationships among the above variables.

RESULTS

Except for mono-(carboxynonyl), all urinary phthalate metabolites were associated with biological ageing, with correlation coefficients ranging from 0.241 to 0.526; however, mono-ethyl presented a negative correlation. The WQS models revealed mixed effects of combined urinary phthalate metabolites on ageing, with a 0.22-year ((95 % CI) 0.09, 0.32) increase in KDM-BA acceleration and a 0.27-year ((95 % CI) 0.13, 0.37) increase in PhenoAge acceleration for each decile increase in urinary phthalate metabolites. Moreover, MCPP, MEOHP, and MBzP seemed to be the top three phthalates in terms of biological ageing, with weights of 33.3 % and 32.2 %, 29.2 % and 17.2 %, and 21.5 % and 30.1 % in KDM-BA and PhenoAge acceleration, respectively.

CONCLUSION

Single-phthalate exposure was mostly associated with the ageing process, and combined-phthalate exposure presented mixed effects on biological ageing, emphasizing phthalate exposure as a significant risk factor for ageing.

The silent burden of non-alcoholic fatty liver disease in the elderly: A global burden of disease analysis

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) represents a significant health threat worldwide. The growing trend towards an aging population, along with an alarming rise in obesity and diabetes, may have significant implications for the burden of NAFLD.

AIM

To assess the impact of NAFLD on the elderly.

METHODS

We utilised data from the Global Burden of Disease study between 2010 and 2019 to conduct a comprehensive analysis of the prevalence, mortality, and disability-adjusted life years (DALYs) associated with NAFLD in the elderly (65-89 years), stratified by region, nation, sociodemographic Index and sex.

RESULTS

Globally, there were an estimated 228 million cases, 87,230 deaths and 1.46 million DALYs attributed to NAFLD in the elderly. Geographically, the Western Pacific region had the highest burden of NAFLD in the elderly. From 2010 to 2019, there was an increasing prevalence rate in all areas, with the most pronounced change observed in the Western Pacific region (annual percentage change (APC) +0.95%, p < 0.001). Over the study period, there was a more rapid increase in NAFLD prevalence in men (APC +0.74%, p < 0.001) than in women (APC +0.63%, p < 0.001). In most regions, death and DALYs rates have declined, with the exception of the Americas, where there was a slight increase (APC +0.25%, p = 0.002 and 0.38%, p < 0.001, respectively).

CONCLUSION

Over the past decade, the burden of NAFLD in the elderly has been increasing, necessitating immediate and inclusive measures to tackle the rising burden.

Inhibition of the mTORC1 pathway alleviates adipose tissue fibrosis

Background

Adipose fibrosis is a major factor of adipose dysfunction, which causes metabolic dysfunction during obesity, but its molecular mechanisms are poorly understood. This study investigated the role and potential mechanisms of mTORC1 in obesity-induced adipose fibrosis.

Methods

ob/ob mice were injected with rapamycin or the same volume of normal saline. The level of fibrosis in epididymal adipose tissue (EAT) was detected by observing aberrant deposition of extracellular matrix. Expression of fibrotic related genes was analysed using RNA-seq. 3T3-L1 preadipocytes were treated with cobalt chloride (CoCl2) and TGF-β1 to induce preadipocyte fibrosis. The fibrosis-related gene expression and protein levels were determined by RT-PCR, WB, and immunofluorescence in two types of fibrotic preadipocytes with or without rapamycin.

Results

Compared with vehicle treatment, EAT fibrosis-related aberrant deposition of extracellular matrix proteins and fibrotic gene expression were reduced in ob/ob mice treated with rapamycin. Both CoCl2-induced hypoxia and TGF-β1 successfully promoted adipocyte fibrosis, and the upregulated fibrosis-related genes expression was inhibited after the mTORC1 pathway was inhibited by rapamycin.

Conclusion

Inhibition of the mTORC1 pathway ameliorates adipose fibrosis by suppressing fibrosis-related genes in hypoxia- and TGF-β-induced fibrotic preadipocytes.

The Surreptitious Burden of Nonalcoholic Fatty Liver Disease in the Elderly in the Asia-Pacific Region: An Insight from the Global Burden of Disease Study 2019

Nonalcoholic fatty liver disease (NAFLD) represents a significant health threat worldwide. The aging population and a rise in metabolic syndrome in Asia might influence the epidemiology of NAFLD among the elderly. However, there is a lack of understanding of the burden and recommendations for NAFLD in this group. Our study sought to investigate the trends in the NAFLD burden among the elderly in the Asia-Pacific region. We employed data from the Global Burden of Disease 2019 study for an in-depth analysis of the prevalence and disability-adjusted life years (DALYs) along with age-standardized rate (ASR) associated with NAFLD in elderly populations (age 65-89 years) across the Asia-Pacific region, including the Southeast Asia (SEA) and Western Pacific (WP) regions, from 2010 to 2019. This study also examined the trends and disparities in NAFLD burden across different nations and sexes. In 2019, there were over 120 million cases of NAFLD in the elderly in the Asia-Pacific region. The ASR of prevalence was higher in SEA compared to WP (36,995.37 vs. 32,821.78 per 100,000). ASR of prevalence increased with annual percentage change (APC) +0.95% in the WP while it increased by +0.87% in SEA. During the study period, the ASR of DALYs decreased in SEA (APC -0.41%) but remained stable in the WP region. The burden of NAFLD in the elderly population in Asia-Pacific has increased, underscoring the timely intervention to tackle this high and rising burden.

Chaperone-mediated autophagy dysregulation during aging impairs hepatic fatty acid oxidation via accumulation of NCoR1

OBJECTIVE

Alterations in lipid metabolism are associated with aging and age-related diseases. Chaperone-mediated autophagy (CMA) is a lysosome-dependent process involved in specific protein degradation. Heat shock cognate 71 kDa protein (Hsc70) recognizes cytosolic proteins with KFERQ motif and allows them to enter the lysosome via lysosome-associated membrane glycoprotein 2 isoform A (LAMP2A). CMA deficiency is associated with dysregulated lipid metabolism in the liver. In this study, we examined the effect of CMA on lipid metabolism in the aged liver.

METHODS

12-week-old and 88-week-old mice were employed to assess the effect of aging on hepatic CMA activity. We generated CMA-deficient mouse primary hepatocytes using siRNA for Lamp2a and liver-specific LAMP2A knockdown mice via adeno-associated viruses expressing short hairpin RNAs to investigate the influence of CMA on lipid metabolism.

RESULTS

We noted aging-induced progression toward fatty liver and a decrease in LAMP2A levels in total protein and lysosomes. The expression of genes associated with fatty acid oxidation was markedly downregulated in the aged liver, as verified in CMA-deficient mouse primary hepatocytes. In addition, the aged liver accumulated nuclear receptor corepressor 1 (NCoR1), a negative regulator of peroxisome proliferator-activated receptor α (PPARα). We found that Hsc70 binds to NCoR1 via the KFERQ motif. Lamp2a siRNA treatment accumulated NCoR1 and decreased the fatty acid oxidation rate. Pharmacological activation of CMA by AR7 treatment increased LAMP2A expression, leading to NCoR1 degradation. A liver-specific LAMP2A knockdown via adeno-associated viruses expressing short hairpin RNAs caused NCoR1 accumulation, inactivated PPARα, downregulated the expression of fatty acid oxidation-related genes and significantly increased liver triglyceride levels.

CONCLUSIONS

Our results elucidated a novel PPARα regulatory mechanism involving CMA-mediated NCoR1 degradation during aging. These findings demonstrate that CMA dysregulation is crucial for the progression of aging-related fatty liver diseases.

PM2.5 induced liver lipid metabolic disorders in C57BL/6J mice

PM2.5 can cause adverse health effects via several pathways, such as inducing pulmonary and systemic inflammation, penetration into circulation, and activation of the autonomic nervous system. In particular, the impact of PM2.5 exposure on the liver, which plays an important role in metabolism and detoxification to maintain internal environment homeostasis, is getting more attention in recent years. In the present study, C57BL/6J mice were randomly assigned and treated with PM2.5 suspension and PBS solution for 8 weeks. Then, hepatic tissue was prepared and identified by metabolomics analysis and transcriptomics analysis. PM2.5 exposure can cause extensive metabolic disturbances, particularly in lipid and amino acids metabolic dysregulation.128 differential expression metabolites (DEMs) and 502 differently expressed genes (DEGs) between the PM2.5 exposure group and control group were detected. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that DEGs were significantly enriched in two disease pathways, non-alcoholic fatty liver disease (NAFLD) and type II diabetes mellitus (T2DM), and three signaling pathways, which are TGF-beta signaling, AMPK signaling, and mTOR signaling. Besides, further detection of acylcarnitine levels revealed accumulation in liver tissue, which caused restricted lipid consumption. Furthermore, lipid droplet accumulation in the liver was confirmed by Oil Red O staining, suggesting hepatic steatosis. Moreover, the aberrant expression of three key transcription factors revealed the potential regulatory effects in lipid metabolic disorders, the peroxisomal proliferative agent-activated receptors (PPARs) including PPARα and PPARγ is inhibited, and the activated sterol regulator-binding protein 1 (SREBP1) is overexpressed. Our results provide a novel molecular and genetic basis for a better understanding of the mechanisms of PM2.5 exposure-induced hepatic metabolic diseases, especially in lipid metabolism.

Multi-omics Analysis of Aging Liver Reveals Changes in Endoplasmic Stress and Degradation Pathways in Female Nonhuman Primates

The liver is critical for functions that support metabolism, immunity, digestion, detoxification, and vitamin storage. Aging is associated with severity and poor prognosis of various liver diseases such as nonalcoholic fatty liver disease (NAFLD). Previous studies have used multi-omic approaches to study liver diseases or to examine the effects of aging on the liver. However, to date, no studies have used an integrated omics approach to investigate aging-associated molecular changes in the livers of healthy female nonhuman primates. The goal of this study was to identify molecular changes associated with healthy aging in the livers of female baboons ( Papio sp., n=35) by integrating multiple omics data types (transcriptomics, proteomics, metabolomics) from samples across the adult age span. To integrate omics data, we performed unbiased weighted gene co-expression network analysis (WGCNA), and the results revealed 3 modules containing 3,149 genes and 33 proteins were positively correlated with age, and 2 modules containing 37 genes and 216 proteins were negatively correlated with age. Pathway enrichment analysis showed that unfolded protein response (UPR) and endoplasmic reticulum (ER) stress were positively associated with age, whereas xenobiotic metabolism and melatonin and serotonin degradation pathways were negatively associated with age. The findings of our study suggest that UPR and a reduction in reactive oxygen species generated from serotonin degradation could protect the liver from oxidative stress during the aging process in healthy female baboons.

Identifying a distinct fibrosis subset of NAFLD via molecular profiling and the involvement of profibrotic macrophages

BACKGROUND

There are emerging studies suggesting that non-alcoholic fatty liver disease (NAFLD) is a heterogeneous disease with multiple etiologies and molecular phenotypes. Fibrosis is the key process in NAFLD progression. In this study, we aimed to explore molecular phenotypes of NAFLD with a particular focus on the fibrosis phenotype and also aimed to explore the changes of macrophage subsets in the fibrosis subset of NAFLD.

METHODS

To assess the transcriptomic alterations of key factors in NAFLD and fibrosis progression, we included 14 different transcriptomic datasets of liver tissues. In addition, two single-cell RNA sequencing (scRNA-seq) datasets were included to construct transcriptomic signatures that could represent specific cells. To explore the molecular subsets of fibrosis in NAFLD based on the transcriptomic features, we used a high-quality RNA-sequencing (RNA-seq) dataset of liver tissues from patients with NAFLD. Non-negative matrix factorization (NMF) was used to analyze the molecular subsets of NAFLD based on the gene set variation analysis (GSVA) enrichment scores of key molecule features in liver tissues.

RESULTS

The key transcriptomic signatures on NAFLD including non-alcoholic steatohepatitis (NASH) signature, fibrosis signature, non-alcoholic fatty liver (NAFL) signature, liver aging signature and TGF-β signature were constructed by liver transcriptome datasets. We analyzed two liver scRNA-seq datasets and constructed cell type-specific transcriptomic signatures based on the genes that were highly expressed in each cell subset. We analyzed the molecular subsets of NAFLD by NMF and categorized four main subsets of NAFLD. Cluster 4 subset is mainly characterized by liver fibrosis. Patients with Cluster 4 subset have more advanced liver fibrosis than patients with other subsets, or may have a high risk of liver fibrosis progression. Furthermore, we identified two key monocyte-macrophage subsets which were both significantly correlated with the progression of liver fibrosis in NAFLD patients.

CONCLUSION

Our study revealed the molecular subtypes of NAFLD by integrating key information from transcriptomic expression profiling and liver microenvironment, and identified a novel and distinct fibrosis subset of NAFLD. The fibrosis subset is significantly correlated with the profibrotic macrophages and M2 macrophage subset. These two liver macrophage subsets may be important players in the progression of liver fibrosis of NAFLD patients.

Role of Liver CD38 in the Regulation of Metabolic Pathways during Cold-Induced Thermogenesis in Mice

Boosting NAD⁺ levels are considered a promising means to promote healthy aging and ameliorate dysfunctional metabolism. The expression of CD38, the major NAD⁺-consuming enzyme, is downregulated during thermogenesis in both brown and white adipose tissues (BAT and WAT). Moreover, BAT activation and WAT "browning" were enhanced in Cd38^-/- mice. In this study, the role of CD38 in the liver during thermogenesis was investigated, with the liver being the central organ controlling systemic energy metabolism. Wild-type mice and Cd38^-/- mice were exposed to cold temperatures, and levels of metabolites and enzymes were measured in the livers and plasma. During cold exposure, CD38 expression was downregulated in the liver, as in BAT and WAT, with a concomitant increase in NAD(H) and a marked decrease in NADPH levels. Glucose-6-phosphate dehydrogenase and the malic enzyme, along with enzymes in the glycolytic pathway, were downregulated, which is in line with glucose-6-P being re-directed towards glucose release. In Cd38^-/- mice, the cross-regulation between glycolysis and glucose release was lost, although this did not impair the glucose release from glycogen. Glycerol levels were decreased in the liver from Cd38^-/- animals upon cold exposure, suggesting that glyceroneogenesis, as gluconeogenesis, was not properly activated in the absence of CD38. SIRT3 activity, regulating mitochondrial metabolism, was enhanced by cold exposure, whereas its activity was already high at a warm temperature in Cd38^-/- mice and was not further increased by the cold. Notably, FGF21 and bile acid release was enhanced in the liver of Cd38^-/- mice, which might contribute to enhanced BAT activation in Cd38^-/- mice. These results demonstrate that CD38 inhibition can be suggested as a strategy to boost NAD⁺ and would not negatively affect hepatic functions during thermogenesis.

Rejuvenation: Turning Back Time by Enhancing CISD2

The aging human population with age-associated diseases has become a problem worldwide. By 2050, the global population of those who are aged 65 years and older will have tripled. In this context, delaying age-associated diseases and increasing the healthy lifespan of the aged population has become an important issue for geriatric medicine. CDGSH iron-sulfur domain 2 (CISD2), the causative gene for Wolfram syndrome 2 (WFS2; MIM 604928), plays a pivotal role in mediating lifespan and healthspan by maintaining mitochondrial function, endoplasmic reticulum integrity, intracellular Ca²⁺ homeostasis, and redox status. Here, we summarize the most up-to-date publications on CISD2 and discuss the crucial role that this gene plays in aging and age-associated diseases. This review mainly focuses on the following topics: (1) CISD2 is one of the few pro-longevity genes identified in mammals. Genetic evidence from loss-of-function (knockout mice) and gain-of-function (transgenic mice) studies have demonstrated that CISD2 is essential to lifespan control. (2) CISD2 alleviates age-associated disorders. A higher level of CISD2 during natural aging, when achieved by transgenic overexpression, improves Alzheimer's disease, ameliorates non-alcoholic fatty liver disease and steatohepatitis, and maintains corneal epithelial homeostasis. (3) CISD2, the expression of which otherwise decreases during natural aging, can be pharmaceutically activated at a late-life stage of aged mice. As a proof-of-concept, we have provided evidence that hesperetin is a promising CISD2 activator that is able to enhance CISD2 expression, thus slowing down aging and promoting longevity. (4) The anti-aging effect of hesperetin is mainly dependent on CISD2 because transcriptomic analysis of the skeletal muscle reveals that most of the differentially expressed genes linked to hesperetin are regulated by hesperetin in a CISD2-dependent manner. Furthermore, three major metabolic pathways that are affected by hesperetin have been identified in skeletal muscle, namely lipid metabolism, protein homeostasis, and nitrogen and amino acid metabolism. This review highlights the urgent need for CISD2-based pharmaceutical development to be used as a potential therapeutic strategy for aging and age-associated diseases.