Hepatocyte caveolin-1 modulates metabolic gene profiles and functions in non-alcoholic fatty liver disease

In search of epigenetic hallmarks of different tissues: an integrative omics study of horse liver, lung, and heart

DNA methylation and microRNA (miRNA) expression are epigenetic mechanisms essential for regulating tissue-specific gene expression and metabolic processes. However, high-resolution transcriptome, methylome, or miRNAome data is only available for a few model organisms and selected tissues. Up to date, only a few studies have reported on gene expression, DNA methylation, or miRNA expression in adult equine tissues at the genome-wide level. In the present study, we used RNA-Seq, miRNA-seq, and reduced representation bisulfite sequencing (RRBS) data from the heart, lung, and liver tissues of healthy cold-blooded horses to identify differentially expressed genes (DEGs), differentially expressed miRNA (DE miRNA) and differentially methylated sites (DMSs) between three types of horse tissues. Additionally, based on integrative omics analysis, we described the observed interactions of epigenetic mechanisms with tissue-specific gene expression alterations. The obtained data allowed identification from 4067 to 6143 DMSs, 9733 to 11,263 mRNAs, and 155 to 185 microRNAs, differentially expressed between various tissues. We pointed out specific genes whose expression level displayed a negative correlation with the level of CpG methylation and miRNA expression and revealed biological processes that they enrich. Furthermore, we confirmed and validated the accuracy of the Next-Generation Sequencing (NGS) results with bisulfite sequencing PCR (BSP) and quantitative PCR (qPCR). This comprehensive analysis forms a strong foundation for exploring the epigenetic mechanisms involved in tissue differentiation, especially the growth and development of the equine heart, lungs, and liver.

Caveolin-1 ameliorates hepatic injury in non-alcoholic fatty liver disease by inhibiting ferroptosis via the NOX4/ROS/GPX4 pathway

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease globally, with a complex and contentious pathogenesis. Caveolin-1 (CAV1) is an important regulator of liver function and can mitigate liver injury by scavenging reactive oxygen species (ROS). Evidence suggests that NOX4 is a source of ROS production, that oxidative stress and ferroptosis are closely related, and that both are involved in the onset and progression of NAFLD. However, whether CAV1 attenuates liver injury in NAFLD caused by high-fat diet via the NOX4/ROS/GPX4 pathway remains unclear. An in vivo fatty liver model was established by feeding mice with a high-fat diet for 16 weeks. In addition, an in vitro fatty liver model was established by incubating AML-12 cells with free fatty acids for 24 h using an in vitro culture method. In our study, it was observed that a high-fat diet induces mitochondrial damage and worsens oxidative stress in NAFLD. This diet also hinders GPX4 expression, leading to an escalation of ferroptosis and lipid accumulation. To counteract these effects, intraperitoneal administration of CSD peptide in mice attenuated the high-fat diet-induced liver mitochondrial damage and ferroptosis. Likewise, overexpression of CAV1 resulted in an increase in GPX4 expression and a reduction in levels of ROS-mediated iron metamorphosis, thus mitigating the progression of the disease. However, the effects of CAV1 on GPX4-mediated ferroptosis and lipid deposition could be reversed by CAV1 small interfering RNA (SiRNA). Finally, NOX4 inhibitor (GLX351322) treatment increased CAV1 siRNA-mediated GPX4 expression and decreased the level of ROS-mediated ferroptosis. These findings suggest a potential mechanism underlying the protective role of CAV1 against high-fat diet-induced hepatotoxicity in NAFLD, shedding new light on the interplay between CAV1, GPX4, and ferroptosis in liver pathology.

Multiple Machine Learning Identifies Key Gene PHLDA1 Suppressing NAFLD Progression

Non-alcoholic fatty liver disease (NAFLD) poses a serious global health threat, with its progression mechanisms not yet fully understood. While several molecular markers for NAFLD have been developed in recent years, a lack of robust evidence hampers their clinical application. Therefore, identifying novel and potent biomarkers would directly aid in the prediction, prevention, and personalized treatment of NAFLD. We downloaded NAFLD-related datasets from the Gene Expression Omnibus (GEO). Differential expression analysis and functional analysis were initially conducted. Subsequently, Weighted Gene Co-expression Network Analysis (WGCNA) and multiple machine learning strategies were employed to screen and identify key genes, and the diagnostic value was assessed using Receiver Operating Characteristic (ROC) analysis. We then explored the relationship between genes and immune cells using transcriptome data and single-cell RNA sequencing (scRNA-seq) data. Finally, we validated our findings in cell and mouse NAFLD models. We obtained 23 overlapping differentially expressed genes (DEGs) across three NAFLD datasets. Enrichment analysis revealed that DEGs were associated with Apoptosis, Parathyroid hormone synthesis, secretion and action, Colorectal cancer, p53 signaling pathway, and Biosynthesis of unsaturated fatty acids. After employing machine learning strategies, we identified one gene, pleckstrin homology like domain family A member 1 (PHLDA1), downregulated in NAFLD and showing high diagnostic accuracy. CIBERSORT analysis revealed significant associations of PHLDA1 with various immune cells. Single-cell data analysis demonstrated downregulation of PHLDA1 in NAFLD, with PHLDA1 exhibiting a significant negative correlation with macrophages. Furthermore, we found PHLDA1 to be downregulated in an in vitro hepatic steatosis cell model, and overexpression of PHLDA1 significantly reduced lipid accumulation, as well as the expression of key molecules involved in hepatic lipogenesis and fatty acid uptake, such as FASN, SCD-1, and CD36. Additionally, gene set enrichment analysis (GSEA) pathway enrichment analysis suggested that PHLDA1 may influence NAFLD progression through pathways such as Cytokine Cytokine Receptor Interaction, Ecm Receptor Interaction, Parkinson's Disease, and Ribosome pathways. Our conclusions were further validated in a mouse model of NAFLD. Our study reveals that PHLDA1 inhibits the progression of NAFLD, as overexpression of PHLDA1 significantly reduces lipid accumulation in cells and markedly decreases the expression of key molecules involved in liver lipogenesis and fatty acid uptake. Therefore, PHLDA1 may emerge as a novel potential target for future prediction, diagnosis, and targeted prevention of NAFLD.

Context-specific fatty acid uptake is a finely-tuned multi-level effort

Fatty acids (FAs) are essential nutrients that play multiple roles in cellular activities. To meet cell-specific needs, cells exhibit differential uptake of FAs in diverse physiological or pathological contexts, coordinating to maintain metabolic homeostasis. Cells tightly regulate the localization and transcription of CD36 and other key proteins that transport FAs across the plasma membrane in response to different stimuli. Dysregulation of FA uptake results in diseases such as obesity, steatotic liver, heart failure, and cancer progression. Targeting FA uptake might provide potential therapeutic strategies for metabolic diseases and cancer. Here, we review recent advances in context-specific regulation of FA uptake, focusing on the regulation of CD36 in metabolic organs and other cells.

Mechanism of Metabolic Dysfunction-associated Steatotic Liver Disease: Important role of lipid metabolism

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease, has a high global prevalence and can progress to metabolic dysfunction-associated steatohepatitis, cirrhosis, and hepatocellular carcinoma. The pathogenesis of MASLD is primarily driven by disturbances in hepatic lipid metabolism, involving six key processes: increased hepatic fatty acid uptake, enhanced fatty acid synthesis, reduced oxidative degradation of fatty acids, increased cholesterol uptake, elevated cholesterol synthesis, and increased bile acid synthesis. Consequently, maintaining hepatic lipid metabolic homeostasis is essential for effective MASLD management. Numerous novel molecules and Chinese proprietary medicines have demonstrated promising therapeutic potential in treating MASLD, primarily by inhibiting lipid synthesis and promoting lipid oxidation. In this review, we summarized recent research on MASLD, elucidated the molecular mechanisms by which lipid metabolism disorders contribute to MASLD pathogenesis, and discussed various lipid metabolism-targeted therapeutic approaches for MASLD.

Identification and multicentric validation of soluble CDCP1 as a robust serological biomarker for risk stratification of NASH in obese Chinese

The definitive diagnosis of non-alcoholic steatohepatitis (NASH) currently relies on invasive and labor-intensive liver biopsy. Here, we identified soluble CUB domain-containing protein 1 (sCDCP1) as a top-ranked non-invasive biomarker for NASH using Olink-based proteomics in 238 obese individuals with liver biopsies. Both the circulating concentration and hepatic mRNA abundance of sCDCP1 were significantly elevated in patients with NASH and correlated closely with each histological feature of NASH. In the pooled multicenter validation cohort, sCDCP1 as a standalone biomarker achieved an area under the receiver operating characteristic (AUROC) of 0.838 (95% confidence interval [CI] 0.789-0.887) for diagnosing NASH, which is better than those achieved with cytokeratin-18 and other non-invasive tests. Furthermore, the C-DAG model established by the combination of sCDCP1 with diabetes, aspartate aminotransferase (AST), and gender accurately rules in and rules out both NASH and fibrotic NASH (gray zones <20%). Thus, sCDCP1-based non-invasive tests can be potentially implemented for screening and early diagnosis of NASH and for ruling out low-risk individuals to avoid unnecessary liver biopsies.

Caveolin-1 is critical for hepatic iron storage capacity in the development of nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with disordered lipid and iron metabolism. Our previous study has substantiated the pivotal role of Caveolin-1 (Cav-1) in protecting hepatocytes and mediating iron metabolism in the liver. This study aimed to explore the specific mechanisms underlying the regulation of iron metabolism by Cav-1 in NAFLD.

METHODS

Hepatocyte-specific Cav-1 overexpression mice and knockout mice were used in this study. Cav-1-knockdown of RAW264.7 cells and mouse primary hepatocytes were performed to verify the changes in vitro. Moreover, a high-fat diet and palmitic acid plus oleic acid treatment were utilized to construct a NAFLD model in vivo and in vitro, respectively, while a high-iron diet was used to construct an in vivo iron overload model. Besides, iron concentration, the expression of Cav-1 and iron metabolism-related proteins in liver tissue or serum were detected using iron assay kit, Prussian blue staining, Western blotting, immunofluorescence staining, immunohistochemical staining and ELISA. The related indicators of lipid metabolism and oxidative stress were evaluated by the corresponding reagent kit and staining.

RESULTS

Significant disorder of lipid and iron metabolism occurred in NAFLD. The expression of Cav-1 was decreased in NAFLD hepatocytes (P < 0.05), accompanied by iron metabolism disorder. Cav-1 enhanced the iron storage capacity of hepatocytes by activating the ferritin light chain/ferritin heavy chain pathway in NAFLD, subsequently alleviating the oxidative stress induced by excess ferrous ions in the liver. Further, CD68+CD163+ macrophages expressing Cav-1 were found to accelerate iron accumulation in the liver, which was contrary to the effect of Cav-1 in hepatocytes. Positive correlations were also observed between the serum Cav-1 concentration and the serum iron-related protein levels in NAFLD patients and healthy volunteers (P < 0.05).

CONCLUSIONS

These findings confirm that Cav-1 is an essential target protein that regulates iron and lipid metabolic homeostasis. It is a pivotal molecule for predicting and protecting against the development of NAFLD.

Invasion by exogenous RNA: cellular defense strategies and implications for RNA inference

Exogenous RNA poses a continuous threat to genome stability and integrity across various organisms. Accumulating evidence reveals complex mechanisms underlying the cellular response to exogenous RNA, including endo-lysosomal degradation, RNA-dependent repression and innate immune clearance. Across a variety of mechanisms, the natural anti-sense RNA-dependent defensive strategy has been utilized both as a powerful gene manipulation tool and gene therapy strategy named RNA-interference (RNAi). To optimize the efficiency of RNAi silencing, a comprehensive understanding of the whole life cycle of exogenous RNA, from cellular entry to its decay, is vital. In this paper, we review recent progress in comprehending the recognition and elimination of foreign RNA by cells, focusing on cellular entrance, intracellular transportation, and immune-inflammatory responses. By leveraging these insights, we highlight the potential implications of these insights for advancing RNA interference efficiency, underscore the need for future studies to elucidate the pathways and fates of various exogenous RNA forms, and provide foundational information for more efficient RNA delivery methods in both genetic manipulation and therapy in different organisms.

Caveolin-1 protects against liver damage exacerbated by acetaminophen in non-alcoholic fatty liver disease by inhibiting the ERK/HIF-1α pathway

Acetaminophen (APAP) is a common antipyretic and analgesic drug that can cause long-term liver damage after an overdose. Non-alcoholic fatty liver disease (NAFLD) increases susceptibility to APAP. In NAFLD, excessive accumulation of lipids leads to an abnormal increase in hypoxia-inducible factor-1α (HIF-1α). Caveolin-1 (CAV1) may protect against NAFLD by inhibiting HIF-1α. This research aimed to determine whether CAV1 could attenuate APAP-exacerbated liver injury in NAFLD by inhibiting oxidative stress involving HIF-1α. In this study, 7-week-old C57BL/6 mice were fed a high-fat diet (HFD) for eight weeks, followed by the instillation of APAP. Levels of oxidative stress and liver lipid deposition were determined, and p-ERK1/2 and HIF-1α protein expression were measured by the Western blot (WB) method. In the APAP-treated group, the level of CAV1 was decreased, while the levels of HIF-1α and reactive oxygen species (ROS) were significantly increased. AML12 cells were treated with a mixture of palmitic acid (PA) and oleic acid (OA) (1:2 mix) for 48 h, and APAP was added for the last 24 h. Overexpression of CAV1 in AML12 cells significantly inhibited the expression of ROS and HIF-1α. And the results of immunofluorescence after treatment with CAV1-SiRNA showed that the HIF-1α levels were significantly increased in mitochondria. In conclusion, our experimental results suggest that CAV1 has a protective function in the fatty liver based on preventing oxidative stress, which involves HIF-1α. Thus, upregulation of CAV1 may attenuate APAP-exacerbated liver injury in NAFLD.

Role of caveolin-1 in metabolic programming of fetal brain

Mice lacking caveolin-1 (Cav1), a key protein of plasma membrane, exhibit brain aging at an early adult stage. Here, integrative analyses of metabolomics, transcriptomics, epigenetics, and single-cell data were performed to test the hypothesis that metabolic deregulation of fetal brain due to the ablation of Cav1 is linked to brain aging in these mice. The results of this study show that lack of Cav1 caused deregulation in the lipid and amino acid metabolism in the fetal brain, and genes associated with these deregulated metabolites were significantly altered in the brain upon aging. Moreover, ablation of Cav1 deregulated several metabolic genes in specific cell types of the fetal brain and impacted DNA methylation of those genes in coordination with mouse epigenetic clock. The findings of this study suggest that the aging program of brain is confounded by metabolic abnormalities in the fetal stage due to the absence of Cav1.

Omics data analysis reveals common molecular basis of small cell lung cancer and COVID-19

The impact of COVID-19 infection on individuals with small cell lung cancer (SCLC) poses a serious threat. Unfortunately, the molecular basis of this severe comorbidity has yet to be elucidated. The present study addresses this gap utilizing publicly available omics data of COVID-19 and SCLC to explore the key molecules and associated pathways involved in the convergence of these diseases. Findings revealed 402 genes, that exhibited differential expression patterns in SCLC patients and also play a pivotal role in COVID-19 pathogenesis. Subsequent functional enrichment analyses identified relevant ontologies and pathways that are significantly associated with these genes, revealing important insights into their potential biological, molecular and cellular functions. The protein-protein interaction network, constructed under four combinatorial topological assessments, highlighted SMAD3, CAV1, PIK3R1, and FN1 as the primary components to this comorbidity. Our results suggest that these components significantly regulate this cross-talk triggering the PI3K-AKT and TGF-β signaling pathways. Lastly, this study made a multi-step computational attempt and identified corylifol A and ginkgetin from natural sources that can potentially inhibit these components. Therefore, the outcomes of this study offer novel perspectives on the common molecular mechanisms underlying SCLC and COVID-19 and present future opportunities for drug development.Communicated by Ramaswamy H. Sarma.

Comprehensive Strategy for Identifying Extracellular Vesicle Surface Proteins as Biomarkers for Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a liver disorder that has become a global health concern due to its increasing prevalence. There is a need for reliable biomarkers to aid in the diagnosis and prognosis of NAFLD. Extracellular vesicles (EVs) are promising candidates in biomarker discovery, as they carry proteins that reflect the pathophysiological state of the liver. In this review, we developed a list of EV proteins that could be used as diagnostic biomarkers for NAFLD. We employed a multi-step strategy that involved reviewing and comparing various sources of information. Firstly, we reviewed papers that have studied EVs proteins as biomarkers in NAFLD and papers that have studied circulating proteins as biomarkers in NAFLD. To further identify potential candidates, we utilized the EV database Vesiclepedia.org to qualify each protein. Finally, we consulted the Human Protein Atlas to search for candidates' localization, focusing on membrane proteins. By integrating these sources of information, we developed a comprehensive list of potential EVs membrane protein biomarkers that could aid in diagnosing and monitoring NAFLD. In conclusion, our multi-step strategy for identifying EV-based protein biomarkers for NAFLD provides a comprehensive approach that can also be applied to other diseases. The protein candidates identified through this approach could have significant implications for the development of non-invasive diagnostic tests for NAFLD and improve the management and treatment of this prevalent liver disorder.

Lower adiposity does not protect beta-2 syntrophin null mice from hepatic steatosis and inflammation in experimental non-alcoholic steatohepatitis

Visceral adiposity is strongly associated with liver steatosis, which predisposes to the development of non-alcoholic steatohepatitis (NASH). Mice with loss of the molecular adapter protein beta-2 syntrophin (SNTB2) have greatly reduced intra-abdominal fat mass. Hepatic expression of proteins with a role in fatty acid metabolism such as fatty acid synthase was nevertheless normal. This was also the case for proteins regulating cholesterol synthesis and uptake. Yet, a slight induction of hepatic cholesterol was noticed in the mutant mice. When mice were fed a methionine choline deficient (MCD) diet to induce NASH, liver cholesteryl ester content was induced in the wild type but not the mutant mice. Serum cholesterol of the mice fed a MCD diet declined and this was significant for the SNTB2 null mice. Though the mutant mice lost less fat mass than the wild type animals, hepatic triglyceride levels were similar between the groups. Proteins involved in fatty acid or cholesterol metabolism such as fatty acid synthase, apolipoprotein E and low-density lipoprotein receptor did not differ between the genotypes. Hepatic oxidative stress and liver inflammation of mutant and wild type mice were comparable. Mutant mice had lower hepatic levels of secondary bile acids and higher cholesterol storage in epididymal fat, and this may partly prevent hepatic cholesterol deposition. In summary, the current study shows that SNTB2 null mice have low intra-abdominal fat mass and do not accumulate hepatic cholesteryl esters when fed a MCD diet. Nevertheless, the SNTB2 null mice develop a similar NASH pathology as wild type mice suggesting a minor role of intra-abdominal fat and liver cholesteryl esters in this model.

A caveolin-1 dependent glucose-6-phosphatase trafficking contributes to hepatic glucose production

OBJECTIVE

Deregulation of hepatic glucose production is a key driver in the pathogenesis of diabetes, but its short-term regulation is incompletely deciphered. According to textbooks, glucose is produced in the endoplasmic reticulum by glucose-6-phosphatase (G6Pase) and then exported in the blood by the glucose transporter GLUT2. However, in the absence of GLUT2, glucose can be produced by a cholesterol-dependent vesicular pathway, which remains to be deciphered. Interestingly, a similar mechanism relying on vesicle trafficking controls short-term G6Pase activity. We thus investigated whether Caveolin-1 (Cav1), a master regulator of cholesterol trafficking, might be the mechanistic link between glucose production by G6Pase in the ER and glucose export through a vesicular pathway.

METHODS

Glucose production from fasted mice lacking Cav1, GLUT2 or both proteins was measured in vitro in primary culture of hepatocytes and in vivo by pyruvate tolerance tests. The cellular localization of Cav1 and the catalytic unit of glucose-6-phosphatase (G6PC1) were studied by western blotting from purified membranes, immunofluorescence on primary hepatocytes and fixed liver sections and by in vivo imaging of chimeric constructs overexpressed in cell lines. G6PC1 trafficking to the plasma membrane was inhibited by a broad inhibitor of vesicular pathways or by an anchoring system retaining G6PC1 specifically to the ER membrane.

RESULTS

Hepatocyte glucose production is reduced at the step catalyzed by G6Pase in the absence of Cav1. In the absence of both GLUT2 and Cav1, gluconeogenesis is nearly abolished, indicating that these pathways can be considered as the two major pathways of de novo glucose production. Mechanistically, Cav1 colocalizes but does not interact with G6PC1 and controls its localization in the Golgi complex and at the plasma membrane. The localization of G6PC1 at the plasma membrane is correlated to glucose production. Accordingly, retaining G6PC1 in the ER reduces glucose production by hepatic cells.

CONCLUSIONS

Our data evidence a pathway of glucose production that relies on Cav1-dependent trafficking of G6PC1 to the plasma membrane. This reveals a new cellular regulation of G6Pase activity that contributes to hepatic glucose production and glucose homeostasis.

Caveolin-1 ameliorates acetaminophen-aggravated inflammatory damage and lipid deposition in non-alcoholic fatty liver disease via the ROS/TXNIP/NLRP3 pathway

The overuse of acetaminophen (APAP) may cause more severe hepatotoxicity in patients with non-alcoholic fatty liver disease (NAFLD). Caveolin-1 (CAV1), is an essential regulator of metabolic function, which can alleviate liver damage by scavenging reactive oxygen species (ROS). Evidence suggests that the NOD-like receptor family pyrin domain-containing 3 (NLRP3) -mediated pyroptosis is involved in the development of NAFLD. Moreover, thioredoxin-interactive protein (TXNIP) activation is a key event linking ROS to NLRP3 inflammasome. However, whether CAV1 alleviates APAP-aggravated hepatotoxicity in NAFLD via the ROS/TXNIP/NLRP3 pathway remains unclear. An in vivo fatty liver model was established by feeding mice a high-fat diet for 56 days. Additionally, using in vitro approach, AML-12 cells were incubated with free fatty acids for 48 h and APAP was added during the last 24 h. We found that the overuse of APAP in NAFLD not only induced oxidative stress, but also increased TXNIP expression, NLRP3-mediated pyroptosis, and lipid deposition. In addition to inhibiting ROS generation and lipid deposition, overexpression of CAV1 reduced the elevated levels of TXNIP expression and NLRP3-mediated pyroptosis. However, the effect of CAV1 on TXNIP expression, NLRP3-mediated pyroptosis, and lipid deposition was reversed by CAV1 small interfering RNA (siRNA) intervention. Finally, N-acetyl cysteine (NAC) treatment reduced CAV1 siRNA-mediated changes in TXNIP expression and NLRP3-mediated pyroptosis levels. These results demonstrate that the inhibitory effect of CAV1 on NLRP3-mediated pyroptosis may be mediated through the ROS/TXNIP axis. Moreover, the current study provides novel mechanistic insights into the protective effects of CAV1 on APAP-aggravated hepatotoxicity in NAFLD.

Mitochondria-endoplasmic reticulum contacts in sepsis-induced myocardial dysfunction

Mitochondrial and endoplasmic reticulum (ER) are important intracellular organelles. The sites that mitochondrial and ER are closely related in structure and function are called Mitochondria-ER contacts (MERCs). MERCs are involved in a variety of biological processes, including calcium signaling, lipid synthesis and transport, autophagy, mitochondrial dynamics, ER stress, and inflammation. Sepsis-induced myocardial dysfunction (SIMD) is a vital organ damage caused by sepsis, which is closely associated with mitochondrial and ER dysfunction. Growing evidence strongly supports the role of MERCs in the pathogenesis of SIMD. In this review, we summarize the biological functions of MERCs and the roles of MERCs proteins in SIMD.

Adeno-associated virus-based caveolin-1 delivery via different routes for the prevention of cholesterol gallstone formation

BACKGROUND

Hepatic caveolin-1 (CAV1) is reduced in cholesterol gallstone disease (CGD). Mice with CAV1 deficiency were prone to develop CGD. However, it remains unknown whether restored hepatic CAV1 expression prevents the development of CGD.

METHODS

C57BL/6 mice were injected with adeno-associated virus 2/8 (AAV2/8) vectors carrying the CAV1 gene (^AAV2/8CAV1) via intravenous (i.v.) or intraperitoneal (i.p.) route and then subjected to a lithogenic diet (LD) for 8 weeks. Uninjected mice were used as controls. The functional consequences of rescuing CAV1 expression by either i.v. or i.p. ^AAV2/8CAV1 treatment for CGD prevention and its subsequent molecular mechanisms were examined.

RESULTS

CAV1 expression was reduced in the liver and gallbladder of LD-fed CGD mice. We discovered that ^AAV2/8CAV1 i.p. delivery results in higher transduction efficiency in the gallbladder than tail vein administration. Although either i.v. or i.p. injection of ^AAV2/8CAV1 improved liver lipid metabolic abnormalities in CGD mice but did not affect LD feeding-induced bile cholesterol supersaturation. In comparison with i.v. administration route, i.p. administration of ^AAV2/8CAV1 obviously increased CAV1 protein levels in the gallbladder of LD-fed mice, and i.p. delivery of ^AAV2/8CAV1 partially improved gallbladder cholecystokinin receptor (CCKAR) responsiveness and impeded bile cholesterol nucleation via the activation of adenosine monophosphate-activated protein kinase (AMPK) signaling, which induced a reduction in gallbladder mucin-1 (MUC1) and MUC5ac expression and gallbladder cholesterol accumulation.

CONCLUSION

CGD prevention by i.p. ^AAV2/8CAV1 injection in LD-fed mice was associated with the improvement of gallbladder stasis, which again supported the notion that supersaturated bile is required but not sufficient for the formation of cholesterol gallstones. Additionally, AAV treatment via the local i.p. injection offers particular advantages over the systemic i.v. route for much more effective gallbladder gene delivery, which will be an excellent tool for conducting preclinical functional studies on the maintenance of normal gallbladder function to prevent CGD.

Targeting oxidized phospholipids by AAV-based gene therapy in mice with established hepatic steatosis prevents progression to fibrosis

Oxidized phosphatidylcholines (OxPCs) are implicated in chronic tissue damage. Hyperlipidemic LDL-R--deficient mice transgenic for an OxPC-recognizing IgM fragment (scFv-E06) are protected against nonalcoholic fatty liver disease (NAFLD). To examine the effect of OxPC elimination at different stages of NAFLD progression, we used cre-dependent, adeno-associated virus serotype 8-mediated expression of the single-chain variable fragment of E06 (AAV8-scFv-E06) in hepatocytes of albumin-cre mice. AAV8-induced expression of scFv-E06 at the start of FPC diet protected mice from developing hepatic steatosis. Independently, expression of scFv-E06 in mice with established steatosis prevented the progression to hepatic fibrosis. Mass spectrometry-based oxophospho-lipidomics identified individual OxPC species that were reduced by scFv-E06 expression. In vitro, identified OxPC species dysregulated mitochondrial metabolism and gene expression in hepatocytes and hepatic stellate cells. We demonstrate that individual OxPC species independently affect disease initiation and progression from hepatic steatosis to steatohepatitis, and that AAV-mediated expression of scFv-E06 is an effective therapeutic intervention.

Bone morphogenetic protein 6-mediated crosstalk between endothelial cells and hepatocytes recapitulates the iron-sensing pathway in vitro

Liver sinusoidal endothelial cell–derived bone morphogenetic protein 6 (BMP6) and the BMP6–small mothers against decapentaplegic homolog (SMAD) signaling pathway are essential for the expression of hepcidin, the secretion of which is considered the systemic master switch of iron homeostasis. However, there are continued controversies related to the strong and direct suppressive effect of iron on hepatocellular hepcidin in vitro in contrast to in vivo conditions. Here, we directly studied the crosstalk between endothelial cells (ECs) and hepatocytes using in vitro coculture models that mimic hepcidin signaling in vivo. Huh7 cells were directly cocultured with ECs, and EC conditioned media (CM) were also used to culture Huh7 cells and primary mouse hepatocytes. To explore the reactions of ECs to surrounding iron, they were grown in the presence of ferric ammonium citrate and heme, two iron-containing molecules. We found that both direct coculture with ECs and EC-CM significantly increased hepcidin expression in Huh7 cells. The upstream SMAD pathway, including phosphorylated SMAD1/5/8, SMAD1, and inhibitor of DNA binding 1, was induced by EC-CM, promoting hepcidin expression. Efficient blockage of this EC-mediated hepcidin upregulation by an inhibitor of the BMP6 receptor ALK receptor tyrosine kinase 2/3 or BMP6 siRNA identified BMP6 as a major hepcidin regulator in this coculture system, which highly fits the model of hepcidin regulation by iron in vivo. In addition, EC-derived BMP6 and hepcidin were highly sensitive to levels of not only ferric iron but also heme as low as 500 nM. We here establish a hepatocyte–endothelial coculture system to fully recapitulate iron regulation by hepcidin using EC-derived BMP6.

Effects of Lingonberry (Vaccinium vitis-idaea L.) Supplementation on Hepatic Gene Expression in High-Fat Diet Fed Mice

The prevalence of nonalcoholic fatty liver disease (NAFLD) is growing worldwide in association with Western-style diet and increasing obesity. Lingonberry (Vaccinium vitis-idaea L.) is rich in polyphenols and has been shown to attenuate adverse metabolic changes in obese liver. This paper investigated the effects of lingonberry supplementation on hepatic gene expression in high-fat diet induced obesity in a mouse model. C57BL/6N male mice were fed for six weeks with either a high-fat (HF) or low-fat (LF) diet (46% and 10% energy from fat, respectively) or HF diet supplemented with air-dried lingonberry powder (HF + LGB). HF diet induced a major phenotypic change in the liver, predominantly affecting genes involved in inflammation and in glucose and lipid metabolism. Lingonberry supplementation prevented the effect of HF diet on an array of genes (in total on 263 genes) associated particularly with lipid or glucose metabolic process (such as Mogat1, Plin4, Igfbp2), inflammatory/immune response or cell migration (such as Lcn2, Saa1, Saa2, Cxcl14, Gcp1, S100a10) and cell cycle regulation (such as Cdkn1a, Tubb2a, Tubb6). The present results suggest that lingonberry supplementation prevents HF diet-induced adverse changes in the liver that are known to predispose the development of NAFLD and its comorbidities. The findings encourage carrying out human intervention trials to confirm the results, with the aim of recommending the use of lingonberries as a part of healthy diet against obesity and its hepatic and metabolic comorbidities.

Synapsin-Promoted Caveolin-1 Overexpression Maintains Mitochondrial Morphology and Function in PSAPP Alzheimer's Disease Mice

Mitochondrial dysfunction plays a pivotal role in the Alzheimer's Disease (AD) pathology. Disrupted mitochondrial dynamics (i.e., fusion/fission balance), which are essential for normal mitochondria structure and function, are documented in AD. Caveolin-1 (Cav-1), a membrane/lipid raft (MLR) scaffolding protein regulates metabolic pathways in several different cell types such as hepatocytes and cancer cells. Previously, we have shown decreased expression of Cav-1 in the hippocampus of 9-month (m) old PSAPP mice, while hippocampal overexpression of neuron-targeted Cav-1 using the synapsin promoter (i.e., SynCav1) preserved cognitive function, neuronal morphology, and synaptic ultrastructure in 9 and 12 m PSAPP mice. Considering the central role of energy production in maintaining normal neuronal and synaptic function and survival, the present study reveals that PSAPP mice exhibit disrupted mitochondrial distribution, morphometry, and respiration. In contrast, SynCav1 mitigates mitochondrial damage and loss and enhances mitochondrial respiration. Furthermore, by examining mitochondrial dynamics, we found that PSAPP mice showed a significant increase in the phosphorylation of mitochondrial dynamin-related GTPase protein (DRP1), resulting in excessive mitochondria fragmentation and dysfunction. In contrast, hippocampal delivery of SynCav1 significantly decreased p-DRP1 and augmented the level of the mitochondrial fusion protein, mitofusin1 (Mfn1) in PSAPP mice, a molecular event, which may mechanistically explain for the preserved balance of mitochondria fission/fusion and metabolic resilience in 12 m PSAPP-SynCav1 mice. Our data demonstrate the critical role for Cav-1 in maintaining normal mitochondrial morphology and function through affecting mitochondrial dynamics and explain a molecular and cellular mechanism underlying the previously reported neuroprotective and cognitive preservation induced by SynCav1 in PSAPP mouse model of AD.

Human Glioblastoma Visualization: Triple Receptor-Targeting Fluorescent Complex of Dye, SIWV Tetra-Peptide, and Serum Albumin Protein

Fluorescence guided surgery (FGS) has been highlighted in the clinical site for guiding surgical procedures and providing the surgeon with a real-time visualization of the operating field. FGS is a powerful technique for precise surgery, particularly tumor resection; however, clinically approved fluorescent dyes have often shown several limitations during FGS, such as non-tumor-targeting, low in vivo stability, insufficient emission intensity, and low blood-brain barrier penetration. In this study, we disclose a fluorescent dye complex, peptide, and protein for the targeted visualization of human glioblastoma (GBM) cells and tissues. Our noble triple receptor-targeting fluorescent complex (named BSA-OXN-SIWV) consists of (i) dipolar oxazepine dye (OXN), which has high stability, low cytotoxicity, bright fluorescence, and two-photon excitable, (ii) tetra-peptide (SIWV) for the targeting of the caveolin-1 receptor, and (iii) bovine serum-albumin (BSA) protein for the targeting of albondin (gp60) and secreted protein acidic and rich in cysteine receptor. The photophysical properties and binding mode of BSA-OXN-SIWV were analyzed, and the imaging of GBM cell lines and human clinical GBM tissues were successfully demonstrated in this study. Our findings hold great promise for the application of BSA-OXN-SIWV to GBM identification and the surgery at clinical sites, as a new FGS agent.

Hepatic cholesterol transport and its role in non-alcoholic fatty liver disease and atherosclerosis

Non-alcoholic fatty liver disease (NAFLD) is a quickly emerging global health problem representing the most common chronic liver disease in the world. Atherosclerotic cardiovascular disease represents the leading cause of mortality in NAFLD patients. Cholesterol metabolism has a crucial role in the pathogenesis of both NAFLD and atherosclerosis. The liver is the major organ for cholesterol metabolism. Abnormal hepatic cholesterol metabolism not only leads to NAFLD but also drives the development of atherosclerotic dyslipidemia. The cholesterol level in hepatocytes reflects the dynamic balance between endogenous synthesis, uptake, esterification, and export, a process in which cholesterol is converted to neutral cholesteryl esters either for storage in cytosolic lipid droplets or for secretion as a major constituent of plasma lipoproteins, including very-low-density lipoproteins, chylomicrons, high-density lipoproteins, and low-density lipoproteins. In this review, we describe decades of research aimed at identifying key molecules and cellular players involved in each main aspect of hepatic cholesterol metabolism. Furthermore, we summarize the recent advances regarding the biological processes of hepatic cholesterol transport and its role in NAFLD and atherosclerosis.

How does hepatic lipid accumulation lead to lipotoxicity in non-alcoholic fatty liver disease?

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD), characterized as excess lipid accumulation in the liver which is not due to alcohol use, has emerged as one of the major health problems around the world. The dysregulated lipid metabolism creates a lipotoxic environment which promotes the development of NAFLD, especially the progression from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH).

PURPOSEAND AIM

This review focuses on the mechanisms of lipid accumulation in the liver, with an emphasis on the metabolic fate of free fatty acids (FFAs) in NAFLD and presents an update on the relevant cellular processes/mechanisms that are involved in lipotoxicity. The changes in the levels of various lipid species that result from the imbalance between lipolysis/lipid uptake/lipogenesis and lipid oxidation/secretion can cause organellar dysfunction, e.g. ER stress, mitochondrial dysfunction, lysosomal dysfunction, JNK activation, secretion of extracellular vesicles (EVs) and aggravate (or be exacerbated by) hypoxia which ultimately lead to cell death. The aim of this review is to provide an overview of how abnormal lipid metabolism leads to lipotoxicity and the cellular mechanisms of lipotoxicity in the context of NAFLD.

Exogenous Liposomal Ceramide-C6 Ameliorates Lipidomic Profile, Energy Homeostasis, and Anti-Oxidant Systems in NASH

In non-alcoholic steatohepatitis (NASH), many lines of investigation have reported a dysregulation in lipid homeostasis, leading to intrahepatic lipid accumulation. Recently, the role of dysfunctional sphingolipid metabolism has also been proposed. Human and animal models of NASH have been associated with elevated levels of long chain ceramides and pro-apoptotic sphingolipid metabolites, implicated in regulating fatty acid oxidation and inflammation. Importantly, inhibition of de novo ceramide biosynthesis or knock-down of ceramide synthases reverse some of the pathology of NASH. In contrast, cell permeable, short chain ceramides have shown anti-inflammatory actions in multiple models of inflammatory disease. Here, we investigated non-apoptotic doses of a liposome containing short chain C6-Ceramide (Lip-C6) administered to human hepatic stellate cells (hHSC), a key effector of hepatic fibrogenesis, and an animal model characterized by inflammation and elevated liver fat content. On the basis of the results from unbiased liver transcriptomic studies from non-alcoholic fatty liver disease patients, we chose to focus on adenosine monophosphate activated kinase (AMPK) and nuclear factor-erythroid 2-related factor (Nrf2) signaling pathways, which showed an abnormal profile. Lip-C6 administration inhibited hHSC proliferation while improving anti-oxidant protection and energy homeostasis, as indicated by upregulation of Nrf2, activation of AMPK and an increase in ATP. To confirm these in vitro data, we investigated the effect of a single tail-vein injection of Lip-C6 in the methionine-choline deficient (MCD) diet mouse model. Lip-C6, but not control liposomes, upregulated phospho-AMPK, without inducing liver toxicity, apoptosis, or exacerbating inflammatory signaling pathways. Alluding to mechanism, mass spectrometry lipidomics showed that Lip-C6-treatment reversed the imbalance in hepatic phosphatidylcholines and diacylglycerides species induced by the MCD-fed diet. These results reveal that short-term Lip-C6 administration reverses energy/metabolic depletion and increases protective anti-oxidant signaling pathways, possibly by restoring homeostatic lipid function in a model of liver inflammation with fat accumulation.