ZBTB20 Regulates SERCA2a Activity and Myocardial Contractility Through Phospholamban.

BACKGROUND: Intracellular Ca2+ cycling determines myocardial contraction and relaxation in response to physiological demands. SERCA2a (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2a) is responsible for the sequestration of cytosolic Ca2+ into intracellular stores during cardiac relaxation, and its activity is reversibly inhibited by PLN (phospholamban). However, the regulatory hierarchy of SERCA2a activity remains unclear. METHODS: Cardiomyocyte-specific ZBTB20 knockout mice were generated by crossing ZBTB20flox mice with Myh6-Cre mice. Echocardiography, blood pressure measurements, Langendorff perfusion, histological analysis and immunohistochemistry, quantitative reverse transcription-PCR, Western blot analysis, electrophysiological measurements, and chromatin immunoprecipitation assay were performed to clarify the phenotype and elucidate the molecular mechanisms. RESULTS: Specific ablation of ZBTB20 in cardiomyocyte led to a significant increase in basal myocardial contractile parameters both in vivo and in vitro, accompanied by an impairment in cardiac reserve and exercise capacity. Moreover, the cardiomyocytes lacking ZBTB20 showed an increase in sarcoplasmic reticular Ca2+ content and exhibited a remarkable enhancement in both SERCA2a activity and electrically stimulated contraction. Mechanistically, PLN expression was dramatically reduced in cardiomyocytes at the mRNA and protein levels by ZBTB20 deletion or silencing, and PLN overexpression could largely restore the basal contractility in ZBTB20-deficient cardiomyocytes. CONCLUSIONS: These data point to ZBTB20 as a fine-tuning modulator of PLN expression and SERCA2a activity, thereby offering new perspective on the regulation of basal contractility in the mammalian heart.

ZBTB20 is essential for cochlear maturation and hearing in mice.

The mammalian cochlear epithelium undergoes substantial remodeling and maturation before the onset of hearing. However, very little is known about the transcriptional network governing cochlear late-stage maturation and particularly the differentiation of its lateral nonsensory region. Here, we establish ZBTB20 as an essential transcription factor required for cochlear terminal differentiation and maturation and hearing. ZBTB20 is abundantly expressed in the developing and mature cochlear nonsensory epithelial cells, with transient expression in immature hair cells and spiral ganglion neurons. Otocyst-specific deletion of Zbtb20 causes profound deafness with reduced endolymph potential in mice. The subtypes of cochlear epithelial cells are normally generated, but their postnatal development is arrested in the absence of ZBTB20, as manifested by an immature appearance of the organ of Corti, malformation of tectorial membrane (TM), a flattened spiral prominence (SP), and a lack of identifiable Boettcher cells. Furthermore, these defects are related with a failure in the terminal differentiation of the nonsensory epithelium covering the outer border Claudius cells, outer sulcus root cells, and SP epithelial cells. Transcriptome analysis shows that ZBTB20 regulates genes encoding for TM proteins in the greater epithelial ridge, and those preferentially expressed in root cells and SP epithelium. Our results point to ZBTB20 as an essential regulator for postnatal cochlear maturation and particularly for the terminal differentiation of cochlear lateral nonsensory domain.

Hepatic ELOVL3 is dispensable for lipid metabolism in mice.

Very long-chain fatty acid elongase 3 (ELOVL3) catalyzes the synthesis of C20-C24 fatty acids and is highly expressed in the liver and adipose tissues. The deficiency of Elovl3 exhibits an anti-obesity effect in mice, but the specific role of hepatic ELOVL3 in lipid metabolism remains unclear. Here we demonstrate that hepatic Elovl3 is not required for lipid homeostasis or the pathogenesis of diet-induced obesity and hepatic steatosis. We generated Elovl3 liver-specific knockout mice via Cre/LoxP approach, which maintained normal expression of ELOVL1 or ELOVL7 in the liver. Unexpectedly, the mutant mice did not show significant abnormalities in body weight, liver mass and morphology, liver triglyceride content, or glucose tolerance when fed normal chow or even a low-fat diet. Moreover, deletion of hepatic Elovl3 did not significantly affect body weight gain or hepatic steatosis induced by high-fat diet. Lipidomic analysis revealed that the lipid profiles were not significantly altered by the loss of hepatic Elovl3. Unlike its global knockouts, the mice lacking Elovl3 specifically in liver displayed normal expression of genes involved in hepatic de novo lipogenesis, lipid uptake, or beta-oxidation at the mRNA and protein levels. Collectively, our data indicate that hepatic ELOVL3 is dispensable for metabolic homeostasis or diet-induced metabolic disease.

The zinc finger and BTB domain containing protein ZBTB20 regulates plasma triglyceride metabolism by repressing lipoprotein lipase gene transcription in hepatocytes.

BACKGROUND AND AIMS: Lipoprotein lipase (LPL) is responsible for the lipolytic processing of triglyceride-rich lipoproteins, the deficiency of which causes severe hypertriglyceridemia. Liver LPL expression is high in suckling rodents but relatively low at adulthood. However, the regulatory mechanism and functional significance of liver LPL expression are incompletely understood. We have established the zinc finger protein ZBTB20 as a critical factor for hepatic lipogenesis. Here, we evaluated the role of ZBTB20 in regulating liver Lpl gene transcription and plasma triglyceride metabolism. APPROACH AND RESULTS: Hepatocyte-specific inactivation of ZBTB20 in mice led to a remarkable increase in LPL expression at the mRNA and protein levels in adult liver, in which LPL protein was mainly localized onto sinusoidal epithelial cells and Kupffer cells. As a result, the LPL activity in postheparin plasma was substantially increased, and postprandial plasma triglyceride clearance was significantly enhanced, whereas plasma triglyceride levels were decreased. The dysregulated liver LPL expression and low plasma triglyceride levels in ZBTB20-deficient mice were normalized by inactivating hepatic LPL expression. ZBTB20 deficiency protected the mice against high-fat diet-induced hyperlipidemia without causing excessive triglyceride accumulation in the liver. Chromatin immunoprecipitation and gel-shift assay studies revealed that ZBTB20 binds to the LPL promoter in the liver. A luciferase reporter assay revealed that ZBTB20 inhibits the transcriptional activity of LPL promoter. The regulation of LPL expression by ZBTB20 is liver-specific under physiological conditions. CONCLUSIONS: Liver ZBTB20 serves as a key regulator of LPL expression and plasma triglyceride metabolism and could be a therapeutic target for hypertriglyceridemia.

Hepatic neddylation targets and stabilizes electron transfer flavoproteins to facilitate fatty acid ß-oxidation.

Neddylation is a ubiquitination-like pathway that controls cell survival and proliferation by covalently conjugating NEDD8 to lysines in specific substrate proteins. However, the physiological role of neddylation in mammalian metabolism remains elusive, and no mitochondrial targets have been identified. Here, we report that mouse models with liver-specific deficiency of NEDD8 or ubiquitin-like modifier activating enzyme 3 (UBA3), the catalytic subunit of the NEDD8-activating enzyme, exhibit neonatal death with spontaneous fatty liver as well as hepatic cellular senescence. In particular, liver-specific UBA3 deficiency leads to systemic abnormalities similar to glutaric aciduria type II (GA-II), a rare autosomal recessive inherited fatty acid oxidation disorder resulting from defects in mitochondrial electron transfer flavoproteins (ETFs: ETFA and ETFB) or the corresponding ubiquinone oxidoreductase. Neddylation inhibition by various strategies results in decreased protein levels of ETFs in neonatal livers and embryonic hepatocytes. Hepatic neddylation also enhances ETF expression in adult mice and prevents fasting-induced steatosis and mortality. Interestingly, neddylation is active in hepatic mitochondria. ETFs are neddylation substrates, and neddylation stabilizes ETFs by inhibiting their ubiquitination and degradation. Moreover, certain mutations of ETFs found in GA-II patients hinder the neddylation of these substrates. Taken together, our results reveal substrates for neddylation and add insight into GA-II.

ChREBP-regulated lipogenesis is not required for the thermogenesis of brown adipose tissue.

OBJECTIVES: Brown adipose tissue (BAT) plays a critical role in energy expenditure by uncoupling protein 1 (UCP1)-mediated thermogenesis and represents an important therapeutic target for metabolic diseases. Carbohydrate response element-binding protein (ChREBP) is a key transcription factor regulating de novo lipogenesis, and its activity is associated with UCP1 expression and thermogenesis in BAT. However, the exact physiological role of endogenous ChREBP in BAT thermogenesis remains unclear. METHODS: We used the Cre/LoxP system to generate ChREBP BAT-specific knockout mice, and examined their BAT thermogenesis under acute cold exposure and long-term cold acclimation. Gene expression was analyzed at the mRNA and protein levels, and lipogenesis was examined by 3H-H2O incorporation assay. RESULTS: The mice lacking ChREBP specifically in BAT displayed a significant decrease in the expression levels of lipogenic genes and the activity of de novo lipogenesis in BAT after cold exposure, with UCP1 expression decreased under thermoneutral conditions or after acute cold exposure but not chronic cold acclimation. Unexpectedly, BAT-specific ChREBP deletion did not significantly affect body temperature as well as local temperature or morphology of BAT after acute cold exposure or chronic cold acclimation. Of note, ChREBP deletion mildly aggravated glucose intolerance induced by a high-fat diet. CONCLUSIONS: Our work indicates that ChREBP regulates de novo lipogenesis in BAT and glucose tolerance, but is not required for non-shivering thermogenesis by BAT under acute or long-term cold exposure.

Zbtb20 deficiency causes cardiac contractile dysfunction in mice.

The zinc-finger protein ZBTB20 regulates development and metabolism in multiple systems, and is essential for postnatal survival in mice. However, its potential role in the cardiovascular system remains undefined. Here, we demonstrate that ZBTB20 is critically involved in the regulation of cardiac contractility and blood pressure in mice. At the age of 16 days, the relatively healthy Zbtb20-null mice exhibited hypotension without obvious change of heart rate or other evidence for heart failure. Moreover, Zbtb20 deletion led to a marked reduction in heart size, left ventricular wall thickness, and cell size of cardiomyocytes, which was largely proportional to the decreased body growth. Notably, echocardiographic and hemodynamic analyses showed that cardiac contractility was greatly impaired in the absence of ZBTB20. Mechanistically, ZBTB20 deficiency decreased cardiac ATP contents, and compromised the enzyme activity of mitochondrial complex I in heart as well as L-type calcium current density in cardiomyocytes. Furthermore, the developmental activation of some mitochondrial function-related genes was significantly attenuated in Zbtb20-null myocardium, which included Hspb8, Ckmt2, Cox7a1, Tfrc, and Ogdhl. Put together, these results suggest that ZBTB20 plays a crucial role in the regulation of heart development, energy metabolism, and contractility.

Zbtb20 regulates the terminal differentiation of hypertrophic chondrocytes via repression of Sox9.

The terminal differentiation of hypertrophic chondrocytes is a tightly regulated process that plays a pivotal role in endochondral ossification. As a negative regulator, Sox9 is essentially downregulated in terminally differentiated hypertrophic chondrocytes. However, the underlying mechanism of Sox9 silencing is undefined. Here we show that the zinc finger protein Zbtb20 regulates the terminal differentiation of hypertrophic chondrocytes by repressing Sox9. In the developing skeleton of the mouse, Zbtb20 protein is highly expressed by hypertrophic chondrocytes from late embryonic stages. To determine its physiological role in endochondral ossification, we have generated chondrocyte-specific Zbtb20 knockout mice and demonstrate that disruption of Zbtb20 in chondrocytes results in delayed endochondral ossification and postnatal growth retardation. Zbtb20 deficiency caused a delay in cartilage vascularization and an expansion of the hypertrophic zone owing to reduced expression of Vegfa in the hypertrophic zone. Interestingly, Sox9, a direct suppressor of Vegfa expression, was ectopically upregulated at both mRNA and protein levels in the late Zbtb20-deficient hypertrophic zone. Furthermore, knockdown of Sox9 greatly increased Vegfa expression in Zbtb20-deficient hypertrophic chondrocytes. Our findings point to Zbtb20 as a crucial regulator governing the terminal differentiation of hypertrophic chondrocytes at least partially through repression of Sox9.

Regulation of plasma lipid homeostasis by hepatic lipoprotein lipase in adult mice.

LPL is a pivotal rate-limiting enzyme to catalyze the hydrolysis of TG in circulation, and plays a critical role in regulating lipid metabolism. However, little attention has been paid to LPL in the adult liver due to its relatively low expression. Here we show that endogenous hepatic LPL plays an important physiological role in plasma lipid homeostasis in adult mice. We generated a mouse model with the Lpl gene specifically ablated in hepatocytes with the Cre/LoxP approach, and found that specific deletion of hepatic Lpl resulted in a significant decrease in plasma LPL contents and activity. As a result, the postprandial TG clearance was markedly impaired, and plasma TG and cholesterol levels were significantly elevated. However, deficiency of hepatic Lpl did not change the liver TG and cholesterol contents or glucose homeostasis. Taken together, our study reveals that hepatic LPL is involved in the regulation of plasma LPL activity and lipid homeostasis.

ALCAT1 controls mitochondrial etiology of fatty liver diseases, linking defective mitophagy to steatosis.

UNLABELLED: Defective autophagy is implicated in the pathogenesis of nonalcoholic fatty liver diseases (NAFLD) through poorly defined mechanisms. Cardiolipin is a mitochondrial phospholipid required for bioenergetics and mitophagy from yeast to mammals. Here we investigated a role for ALCAT1 in the development of NAFLD. ALCAT1 is a lysocardiolipin acyltransferase that catalyzes pathological cardiolipin remodeling in several aging-related diseases. We show that the onset of diet-induced NAFLD caused autophagic arrest in hepatocytes, leading to oxidative stress, mitochondrial dysfunction, and insulin resistance. In contrast, targeted deletion of ALCAT1 in mice prevented the onset of NAFLD. ALCAT1 deficiency also restored mitophagy, mitochondrial architecture, mitochondrial DNA (mtDNA) fidelity, and oxidative phosphorylation. In support of a causative role of the enzyme in a mitochondrial etiology of the disease, hepatic ALCAT1 expression was significantly up-regulated in mouse models of NAFLD. CONCLUSION: Forced expression of ALCAT1 in primary hepatocytes led to multiple defects that are highly reminiscent of NAFLD, including steatosis, defective autophagy, and mitochondrial dysfunction, linking pathological cardiolipin remodeling by ALCAT1 to the pathogenesis of NAFLD.

Zinc finger protein ZBTB20 promotes Toll-like receptor-triggered innate immune responses by repressing IκBα gene transcription.

Toll-like receptor (TLR) signaling is critical in innate response against invading pathogens. However, the molecular mechanisms for full activation of TLR-triggered innate immunity need to be fully elucidated. The broad complex tramtrack bric-a-brac/poxvirus and zinc finger (BTB/POZ) family is a class of transcription factors involved in many biological processes. However, few BTB/POZ proteins were reported to function in innate immune response. Zinc finger and BTB domain-containing 20 (ZBTB20), a member of BTB/POZ family, functions in neurogenesis and represses α-fetoprotein gene transcription in liver. However, the immunological functions of ZBTB20 remain unknown. Here, we found that myeloid cell-specific ZBTB20 KO mice were resistant to endotoxin shock and Escherichia coli-caused sepsis. ZBTB20 deficiency attenuated TLR-triggered production of proinflammatory cytokines and type I IFN in macrophages, which attributed to higher abundance of IκBα protein and impaired activity of NF-κB. Furthermore, ChIP and next generation high-throughput DNA sequencing assay showed that ZBTB20 specifically bound to IκBα gene promoter (+1 to +60 region) after TLR activation. ZBTB20 could inhibit IκBα gene transcription, govern IκBα protein expression, and then promote NF-κB activation. Therefore, transcriptional repressor ZBTB20 is needed to promote full activation of TLR signaling and TLR-triggered innate immune response by selectively suppressing the suppressor IκBα gene transcription.

Deficiency of APPL1 in mice impairs glucose-stimulated insulin secretion through inhibition of pancreatic beta cell mitochondrial function.

AIMS/HYPOTHESIS: Adaptor protein, phosphotyrosine interaction, pleckstrin homology domain and leucine zipper containing 1 (APPL1) is an adapter protein that positively mediates adiponectin signalling. Deficiency of APPL1 in the target tissues of insulin induces insulin resistance. We therefore aimed, in the present study, to determine its role in regulating pancreatic beta cell function. METHODS: A hyperglycaemic clamp test was performed to determine insulin secretion in APPL1 knockout (KO) mice. Glucose- and adiponectin-induced insulin release was measured in islets from APPL1 KO mice or INS-1(832/13) cells with either APPL1 knockdown or overproduction. RT-PCR and western blotting were conducted to analyse gene expression and protein abundance. Oxygen consumption rate (OCR), ATP production and mitochondrial membrane potential were assayed to evaluate mitochondrial function. RESULTS: APPL1 is highly expressed in pancreatic islets, but its levels are decreased in mice fed a high-fat diet and db/db mice compared with controls. Deletion of the Appl1 gene leads to impairment of both the first and second phases of insulin secretion during hyperglycaemic clamp tests. In addition, glucose-stimulated insulin secretion (GSIS) is significantly decreased in islets from APPL1 KO mice. Conversely, overproduction of APPL1 leads to an increase in GSIS in beta cells. In addition, expression levels of several genes involved in insulin production, mitochondrial biogenesis and mitochondrial OCR, ATP production and mitochondrial membrane potential are reduced significantly in APPL1-knockdown beta cells. Moreover, suppression or overexproduction of APPL1 inhibits or stimulates adiponectin-potentiated GSIS in beta cells, respectively. CONCLUSIONS/INTERPRETATION: Our study demonstrates the roles of APPL1 in regulating GSIS and mitochondrial function in pancreatic beta cells, which implicates APPL1 as a therapeutic target in the treatment of type 2 diabetes.

A role for protein inhibitor of activated STAT1 (PIAS1) in lipogenic regulation through SUMOylation-independent suppression of liver X receptors.

Liver X receptors (LXRs) are nuclear receptors that function to modulate lipid metabolism as well as immune and inflammatory responses. Upon activation by their ligands, LXRs up-regulate a spectrum of gene transcription programs involved in cholesterol and fatty acid homeostasis. However, the mechanisms by which LXR-mediated transcriptional activation is regulated remain incompletely understood. Here, we show that PIAS1, a member of the protein inhibitor of the activated STAT family of proteins with small ubiquitin-like modifier (SUMO) E3 ligase activity, acts to suppress LXR ligand-dependent transcriptional activation of the lipogenic program in hepatocytes. We found that liver mRNA expression levels of Pias1 and Pias3 were inversely associated with those of genes involved in lipogenesis in mouse models with diet-induced or genetic obesity. Overexpression of PIAS1 in primary hepatocytes resulted in a reduction of LXR ligand-induced fatty acid synthesis and suppression of the expression of lipogenic genes, including Srebp1c and Fas. Moreover, PIAS1 was able to interact with LXRß and repress its transcriptional activity upon ligand stimulation, which did not require PIAS1-promoted SUMO modification of LXRß. In addition, PIAS1 could also interact with PGC-1ß and attenuate its association with LXRß, blunting the ability of PGC-1ß to co-activate LXRß. Importantly, PIAS1 impaired LXRß binding to its target DNA sequence. Taken together, our results suggest that PIAS1 may serve as a lipogenic regulator by negatively modulating LXRs in a SUMOylation-independent manner.

The zinc finger protein ZBTB20 regulates transcription of fructose-1,6-bisphosphatase 1 and ß cell function in mice.

BACKGROUND & AIMS: Fructose-1,6-bisphosphatase (FBP)-1 is a gluconeogenic enzyme that regulates glucose metabolism and insulin secretion in ß cells, but little is known about how its transcription is controlled. The zinc finger protein ZBTB20 regulates glucose homeostasis, so we investigated its effects on expression of FBP-1. METHODS: We analyzed gene expression using real-time reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. We generated mice with ß cell-specific disruption of Zbtb20 using Cre/LoxP technology. Expression of Zbtb20 in ß cells was reduced using small interfering RNAs, and promoter occupancy and transcriptional regulation were analyzed by chromatin immunoprecipitation and reporter assays. RESULTS: ZBTB20 was expressed at high levels by ß cells and other endocrine cells in islets of normal mice; expression levels were reduced in islets from diabetic db/db mice. Mice with ß cell-specific knockout of Zbtb20 had normal development of ß cells but had hyperglycemia, hypoinsulinemia, glucose intolerance, and impaired glucose-stimulated insulin secretion. Islets isolated from these mice had impaired glucose metabolism, adenosine triphosphate production, and insulin secretion after glucose stimulation in vitro, although insulin secretion returned to normal levels in the presence of KCl. ZBTB20 knockdown with small interfering RNAs impaired glucose-stimulated insulin secretion in the ß cell line MIN6. Expression of Fbp1 was up-regulated in ß cells with ZBTB20 knockout or knockdown; impairments to glucose-stimulated insulin secretion were restored by inhibition of FBPase activity. ZBTB20 was recruited to the Fbp1 promoter and repressed its transcription in ß cells. CONCLUSIONS: The transcription factor ZBTB20 regulates ß cell function and glucose homeostasis in mice. It might be a therapeutic target for type 2 diabetes mellitus.

TLR4 is required for the obesity-induced pancreatic beta cell dysfunction.

Obesity is an important inducing factor for type 2 diabetes. However, the mechanism underlying high-fat-(HF) diet-induced obesity in pancreatic beta cell dysfunction is still unclear. Toll-like receptor-4 (TLR4) is a key mediator of innate immunity. To investigate the effects of TLR4 in obesity-induced pancreatic beta cell dysfunction, we used male diabetic (db/db), obese (ob/ob) mice, TLR4-wild type (WT), and TLR4-knockout mice that were fed with normal diet or HF diet for 24 weeks. Immunostaining of TLR4 and TLR4 mRNA level in pancreatic islet were assessed. The results from biological characteristics, glucose tolerance test, insulin tolerance test, and insulin release test showed that the function of pancreatic islet was impaired in HF-fed TLR4 WT mice, but was protected in HF-fed TLR4 deficient (TLR4(-/-)) mice. By electron microscope detection, we observed that beta cell insulin secretory vesicles increased in HF-fed TLR4 WT mice. Ultrastructure of beta cell in HF-fed TLR4(-/-) mice was similar to that in normal chow diet-fed TLR4 WT mice. Then, glucose-stimulated insulin secretion assay by using primary pancreatic islet showed that the secretion function of pancreatic islet in HF-fed TLR4(-/-) mice was better than that in HF-fed TLR4 WT mice. Furthermore, in HF-fed TLR4(-/-) mice, the mRNA levels of IL-6, TNF-α, and MCP-1 genes in pancreatic islet were significantly lower than those in HF-fed TLR4 WT mice. Consistent with the change in gene expression, HF-fed TLR4 WT mice but not HF-fed TLR4(-/-) mice exhibited macrophage invasion in pancreatic island. Taken together, our data indicated that HF diet-induced obesity can stimulate the up-regulation of TLR4 locating on the surface of pancreatic beta cell, and subsequently lead to the recruitment of macrophage into pancreatic islet, which finally results in pancreatic beta cell dysfunction. This process is a possible mechanism involved in obesity-induced pancreatic beta cell dysfunction.

Zbtb20 is essential for the specification of CA1 field identity in the developing hippocampus.

The development of hippocampal circuitry depends on the proper assembly of correctly specified and fully differentiated hippocampal neurons. Little is known about factors that control the hippocampal specification. Here, we show that zinc finger protein Zbtb20 is essential for the specification of hippocampal CA1 field identity. We found that Zbtb20 expression was initially activated in the hippocampal anlage at the onset of corticogenesis, and persisted in immature hippocampal neurons. Targeted deletion of Zbtb20 in mice did not compromise the progenitor proliferation in the hippocampal and adjacent transitional ventricular zone, but led to the transformation of the hippocampal CA1 field into a transitional neocortex-like structure, as evidenced by cytoarchitectural, neuronal migration, and gene expression phenotypes. Correspondingly, the subiculum was ectopically located adjacent to the CA3 in mutant. Although the field identities of the mutant CA3 and dentate gyrus (DG) were largely maintained, their projections were severely impaired. The hippocampus of Zbtb20 null mice was reduced in size, and exhibited increased apoptotic cell death during postnatal development. Our data establish an essential role of Zbtb20 in the specification of CA1 field identity by repressing adjacent transitional neocortex-specific fate determination.

Hepatic but not Intestinal FBP1 Is Required for Fructose Metabolism and Tolerance.

Fructose intolerance in mammals is caused by defects in fructose absorption and metabolism. Fructose-1,6-bisphosphatase 1 (FBP1) is a key enzyme in gluconeogenesis, and its deficiency results in hypoglycemia as well as intolerance to fructose. However, the mechanism about fructose intolerance caused by FBP1 deficiency has not been fully elucidated. Here, we demonstrate that hepatic but not intestinal FBP1 is required for fructose metabolism and tolerance. We generated inducible knockout mouse models specifically lacking FBP1 in adult intestine or liver. Intestine-specific deletion of Fbp1 in adult mice does not compromise fructose tolerance, as evidenced by no significant body weight loss, food intake reduction, or morphological changes of the small intestine during 4 weeks of exposure to a high-fructose diet. By contrast, liver-specific deletion of Fbp1 in adult mice leads to fructose intolerance, as manifested by substantial weight loss, hepatomegaly, and liver injury after exposure to a high-fructose diet. Notably, the fructose metabolite fructose-1-phosphate is accumulated in FBP1-deficient liver after fructose challenge, which indicates a defect of fructolysis, probably due to competitive inhibition by fructose-1,6-bisphosphate and may account for the fructose intolerance. In conclusion, these data have clarified the essential role of hepatic but not intestinal FBP1 in fructose metabolism and tolerance.

Bile acids-mediated intracellular cholesterol transport promotes intestinal cholesterol absorption and NPC1L1 recycling.

Niemann-Pick C1-like 1 (NPC1L1) is essential for intestinal cholesterol absorption. Together with the cholesterol-rich and Flotillin-positive membrane microdomain, NPC1L1 is internalized via clathrin-mediated endocytosis and transported to endocytic recycling compartment (ERC). When ERC cholesterol level decreases, NPC1L1 interacts with LIMA1 and moves back to plasma membrane. However, how cholesterol leaves ERC is unknown. Here, we find that, in male mice, intracellular bile acids facilitate cholesterol transport to other organelles, such as endoplasmic reticulum, in a non-micellar fashion. When cholesterol level in ERC is decreased by bile acids, the NPC1L1 carboxyl terminus that previously interacts with the cholesterol-rich membranes via the A1272LAL residues dissociates from membrane, exposing the Q1277KR motif for LIMA1 recruitment. Then NPC1L1 moves back to plasma membrane. This study demonstrates an intracellular cholesterol transport function of bile acids and explains how the substantial amount of cholesterol in NPC1L1-positive compartments is unloaded in enterocytes during cholesterol absorption.

Fructose overconsumption impairs hepatic manganese homeostasis and ammonia disposal.

Arginase, a manganese (Mn)-dependent enzyme, is indispensable for urea generation and ammonia disposal in the liver. The potential role of fructose in Mn and ammonia metabolism is undefined. Here we demonstrate that fructose overconsumption impairs hepatic Mn homeostasis and ammonia disposal in male mice. Fructose overexposure reduces liver Mn content as well as its activity of arginase and Mn-SOD, and impairs the clearance of blood ammonia under liver dysfunction. Mechanistically, fructose activates the Mn exporter Slc30a10 gene transcription in the liver in a ChREBP-dependent manner. Hepatic overexpression of Slc30a10 can mimic the effect of fructose on liver Mn content and ammonia disposal. Hepatocyte-specific deletion of Slc30a10 or ChREBP increases liver Mn contents and arginase activity, and abolishes their responsiveness to fructose. Collectively, our data establish a role of fructose in hepatic Mn and ammonia metabolism through ChREBP/Slc30a10 pathway, and postulate fructose dietary restriction for the prevention and treatment of hyperammonemia.

Adipocyte Thyroid Hormone ß Receptor-Mediated Hormone Action Fine-tunes Intracellular Glucose and Lipid Metabolism and Systemic Homeostasis.

Thyroid hormone (TH) has a profound effect on energy metabolism and systemic homeostasis. Adipose tissues are crucial for maintaining whole-body homeostasis; however, whether TH regulates systemic metabolic homeostasis through its action on adipose tissues is unclear. Here, we demonstrate that systemic administration of triiodothyronine (T3), the active form of TH, affects both inguinal white adipose tissue (iWAT) and whole-body metabolism. Taking advantage of the mouse model lacking adipocyte TH receptor (TR) α or TRß, we show that TRß is the major TR isoform that mediates T3 action on the expression of genes involved in multiple metabolic pathways in iWAT, including glucose uptake and use, de novo fatty acid synthesis, and both UCP1-dependent and -independent thermogenesis. Moreover, our results indicate that glucose-responsive lipogenic transcription factor in iWAT is regulated by T3, thereby being critically involved in T3-regulated glucose and lipid metabolism and energy dissipation. Mice with adipocyte TRß deficiency are susceptible to diet-induced obesity and metabolic dysregulation, suggesting that TRß in adipocytes may be a potential target for metabolic diseases. ARTICLE HIGHLIGHTS: How thyroid hormone (TH) achieves its diverse biological activities in the regulation of metabolism is not fully understood. Whether TH regulates systemic metabolic homeostasis via its action on white adipose tissue is unclear. Adipocyte TH receptor (TR) ß mediates the triiodothyronine effect on multiple metabolic pathways by targeting glucose-responsive lipogenic transcription factor in white adipose tissue; mice lacking adipocyte TRß are susceptible to high-fat diet-induced metabolic abnormalities. TRß in white adipocytes controls intracellular and systemic metabolism and may be a potential target for metabolic diseases.