FACI Is a Novel CREB-H-Induced Protein That Inhibits Intestinal Lipid Absorption and Reverses Diet-Induced Obesity

Cgref1 is a CREB-H-regulated hepatokine that promotes hepatic de novo lipogenesis by mediating epididymal fat insulin resistance

Rationale: Type 2 diabetes mellitus and metabolic dysfunction-associated steatotic liver disease (MASLD) are interrelated metabolic disorders that pose significant health concerns. Hepatokines and other regulatory factors implicated in these diseases are incompletely understood. Here, we report on a new hepatokine named cell growth regulator with EF-hand domain 1 (Cgref1) that modulates lipid metabolism to aggravate these conditions. Methods: Cgref1 was identified by microarray analysis of downregulated genes in liver of Creb3l3 -/- mice. Cgref1 -/- mice were subjected to transcriptomic, metabolomic and lipidomic analyses as well as metabolic assays. Gain-of-function and loss-of-function assays were performed in primary hepatocytes and cultured human and mouse cells. Results: Cgref1 expression is induced by hepatic transcription factor CREB-H. Secreted Cgref1 primarily targets epididymal white adipose tissue (eWAT), where insulin signalling and glucose uptake are suppressed. Cgref1-/- mice showed lower tendencies of developing obesity, hyperglycaemia and dyslipidaemia, associated with compromised hepatic de novo lipogenesis. Thus, Cgref1 poses an advantage to maintain the normal functioning of vital organs by preserving glucose from being absorbed into eWAT. However, in circumstances where Cgref1 expression becomes excessive, eWAT develops insulin resistance, which in turn promotes hepatic glucose production, lipogenesis and MASLD development. Conclusion: As a hepatokine that affects blood glucose levels and lipogenesis, Cgref1 is a potential target in the intervention of metabolic disorders.

C1orf115 interacts with clathrin adaptors to undergo endocytosis and induces ABCA1 to promote enteric cholesterol efflux

C1orf115 has been identified in high-throughput screens as a regulator of multidrug resistance possibly mediated through an interaction with ATP-dependent membrane transporter ABCB1. Here we show that C1orf115 not only shares structural similarities with FACI/C11orf86 to interact with clathrin adaptors to undergo endocytosis, but also induces ABCA1 transcription to promote cholesterol efflux. C1orf115 consists of an N-terminal intrinsically disordered region and a C-terminal α-helix. Its α-helix binds to phosphoinositides, and mediates C1orf115 localization to the plasma membrane, nucleolus and nuclear speckles. An acidic dileucine-like motif "ExxxIL" within C1orf115 binds with the AP2 complex and mediates its localization to clathrin-coating pits. The positively charged amphipathic α-helix undergoes acetylation, which redistributes C1orf115 from the plasma membrane and nucleolus to nuclear speckles. C1orf115 is widely expressed and most abundant in the small intestine. The ability of C1orf115 in clathrin-mediated endocytosis is required for its regulation of drug resistance, which is modulated by acetylation. RNA-seq analysis reveals that C1orf115 induces intestinal transcription of another ATP-dependent transporter ABCA1 and consequently promotes ABCA1-mediated cholesterol efflux in enterocytes. Our study provides mechanistic insight into how C1orf115 modulates drug resistance and cholesterol efflux through clathrin-mediated endocytosis and ABCA1 expression.

Age-Dependent Pathogenesis of Influenza A Virus H7N9 Mediated Through PB1-F2-Induced Mitochondrial DNA Release and Activation of cGAS-STING-NF-κB Signaling

Exactly why human infection of avian influenza A virus H7N9 causes more severe disease in the elderly remains elusive. In this study, we found that H7N9 PB1-F2 is a pathogenic factor in 15-18-month-old BALB/C mice (aged mice) but not in 6-8-week-old young adult mice (young mice). Recombinant influenza A virus with H7N9 PB1-F2-knockout was less pathogenic in aged mice as indicated with delayed weight loss. In contrast, survival of young mice infected with this virus was diminished. Furthermore, tissue damage, inflammation, proinflammatory cytokine and 2'3'-cGAMP production in the lung were less pronounced in infected aged mice despite no change in viral titer. cGAS is known to produce 2'3'-cGAMP to boost proinflammatory cytokine expression through STING-NF-κB signaling. We found that H7N9 PB1-F2 promoted interferon β (IFNβ) and chemokine gene expression in cultured cells through the mitochondrial DNA-cGAS-STING-NF-κB pathway. H7N9 PB1-F2 formed protein aggregate and caused mitochondrial cristae collapse, complex V-dependent electron transport dysfunction, reverse electron transfer-dependent oxidized mitochondrial DNA release to the cytoplasm and activation of cGAS-STING-NF-κB signaling. PB1-F2 N57 truncation, which is frequently observed in human circulating strains, mitigated H7N9 PB1-F2-mediated mitochondrial dysfunction and cGAS activation. In addition, we found that PB1-F2 of pathogenic avian influenza viruses triggered more robust cGAS activation than their human-adapted descendants. Our findings provide one explanation to age-dependent pathogenesis of H7N9 infection.

Amelioration of non-alcoholic fatty liver disease by targeting adhesion G protein-coupled receptor F1 (Adgrf1)

Background

Recent research has shown that the adhesion G protein-coupled receptor F1 (Adgrf1; also known as GPR110; PGR19; KPG_012; hGPCR36) is an oncogene. The evidence is mainly based on high expression of Adgrf1 in numerous cancer types, and knockdown Adgrf1 can reduce the cell migration, invasion, and proliferation. Adgrf1 is, however, mostly expressed in the liver of healthy individuals. The function of Adgrf1 in liver has not been revealed. Interestingly, expression level of hepatic Adgrf1 is dramatically decreased in obese subjects. Here, the research examined whether Adgrf1 has a role in liver metabolism.

Methods

We used recombinant adeno-associated virus-mediated gene delivery system, and antisense oligonucleotide was used to manipulate the hepatic Adgrf1 expression level in diet-induced obese mice to investigate the role of Adgrf1 in hepatic steatosis. The clinical relevance was examined using transcriptome profiling and archived biopsy specimens of liver tissues from non-alcoholic fatty liver disease (NAFLD) patients with different degree of fatty liver.

Results

The expression of Adgrf1 in the liver was directly correlated to fat content in the livers of both obese mice and NAFLD patients. Stearoyl-coA desaturase 1 (Scd1), a crucial enzyme in hepatic de novo lipogenesis, was identified as a downstream target of Adgrf1 by RNA-sequencing analysis. Treatment with the liver-specific Scd1 inhibitor MK8245 and specific shRNAs against Scd1 in primary hepatocytes improved the hepatic steatosis of Adgrf1-overexpressing mice and lipid profile of hepatocytes, respectively.

Conclusions

These results indicate Adgrf1 regulates hepatic lipid metabolism through controlling the expression of Scd1. Downregulation of Adgrf1 expression can potentially serve as a protective mechanism to stop the overaccumulation of fat in the liver in obese subjects. Overall, the above findings not only reveal a new mechanism regulating the progression of NAFLD, but also proposed a novel therapeutic approach to combat NAFLD by targeting Adgrf1.

Funding

This work was supported by the National Natural Science Foundation of China (81870586), Area of Excellence (AoE/M-707/18), and General Research Fund (15101520) to CMW, and the National Natural Science Foundation of China (82270941, 81974117) to SJ.

Circadian PER1 controls daily fat absorption with the regulation of PER1-PKA on phosphorylation of bile acid synthetase

Several epidemiological studies suggest a correlation between eating time and obesity. Night eating syndrome characterized by a time-delayed eating pattern is positively associated with obesity in humans as well as in experimental animals. Here, we show that oil intake at night significantly makes more fat than that at day in wild-type mice, and circadian Period 1 (Per1) contributes to this day-night difference. Per1-knockout mice are protected from high-fat diet-induced obesity, which is accompanied by a reduction in the size of the bile acid pool, and the oral administration of bile acids restores fat absorption and accumulation. We identify that PER1 directly binds to the major hepatic enzymes involved in bile acid synthesis such as cholesterol 7alpha-hydroxylase and sterol 12alpha-hydroxylase. A biosynthesis rhythm of bile acids is accompanied by the activity and instability of bile acid synthases with PER1/PKA-mediated phosphorylation pathways. Both fasting and high fat stress enhance Per1 expression, increasing the fat absorption and accumulation. Our findings reveal that Per1 is an energy regulator and controls daily fat absorption and accumulation. Circadian Per1 controls daily fat absorption and accumulation, suggesting Per1 is a potential candidate of a key regulator in stress response and the relevant obesity risk.

FACI is a novel clathrin adaptor protein 2-binding protein that facilitates low-density lipoprotein endocytosis

BACKGROUND

Cholesterol plays a vital role in multiple physiological processes. Cellular uptake of cholesterol is mediated primarily through endocytosis of low-density lipoprotein (LDL) receptor. New modifiers of this process remain to be characterized. Particularly, the role of fasting- and CREB-H-induced (FACI) protein in cholesterol homeostasis merits further investigation.

METHODS

Interactome profiling by proximity labeling and affinity purification - mass spectrometry was performed. Total internal reflection fluorescence microscopy and confocal immunofluorescence microscopy were used to analyze protein co-localization and interaction. Mutational analysis was carried out to define the domain and residues required for FACI localization and function. Endocytosis was traced by fluorescent cargos. LDL uptake in cultured cells and diet-induced hypercholesterolemia in mice were assessed.

RESULTS

FACI interacted with proteins critically involved in clathrin-mediated endocytosis, vesicle trafficking, and membrane cytoskeleton. FACI localized to clathrin-coated pits (CCP) on plasma membranes. FACI contains a conserved DxxxLI motif, which mediates its binding with the adaptor protein 2 (AP2) complex. Disruption of this motif of FACI abolished its CCP localization but didn't affect its association with plasma membrane. Cholesterol was found to facilitate FACI transport from plasma membrane to endocytic recycling compartment in a clathrin- and cytoskeleton-dependent manner. LDL endocytosis was enhanced in FACI-overexpressed AML12 cells but impaired in FACI-depleted HeLa cells. In vivo study indicated that hepatic FACI overexpression alleviated diet-induced hypercholesterolemia in mice.

CONCLUSIONS

FACI facilitates LDL endocytosis through its interaction with the AP2 complex.