Hippo-YAP/TAZ signalling coordinates adipose plasticity and energy balance by uncoupling leptin expression from fat mass.

Adipose tissues serve as an energy reservoir and endocrine organ, yet the mechanisms that coordinate these functions remain elusive. Here, we show that the transcriptional coregulators, YAP and TAZ, uncouple fat mass from leptin levels and regulate adipocyte plasticity to maintain metabolic homeostasis. Activating YAP/TAZ signalling in adipocytes by deletion of the upstream regulators Lats1 and Lats2 results in a profound reduction in fat mass by converting mature adipocytes into delipidated progenitor-like cells, but does not cause lipodystrophy-related metabolic dysfunction, due to a paradoxical increase in circulating leptin levels. Mechanistically, we demonstrate that YAP/TAZ-TEAD signalling upregulates leptin expression by directly binding to an upstream enhancer site of the leptin gene. We further show that YAP/TAZ activity is associated with, and functionally required for, leptin regulation during fasting and refeeding. These results suggest that adipocyte Hippo-YAP/TAZ signalling constitutes a nexus for coordinating adipose tissue lipid storage capacity and systemic energy balance through the regulation of adipocyte plasticity and leptin gene transcription.

The Hepatokine Orosomucoid 2 Mediates Beneficial Metabolic Effects of Bile Acids.

Bile acids (BAs) are pleiotropic regulators of metabolism. Elevated levels of hepatic and circulating BAs improve energy metabolism in peripheral organs, but the precise mechanisms underlying the metabolic benefits and harm still need to be fully understood. In the current study, we identified orosomucoid 2 (ORM2) as a liver-secreted hormone (i.e., hepatokine) induced by BAs and investigated its role in BA-induced metabolic improvements in mouse models of diet-induced obesity. Contrary to our expectation, under a high-fat diet (HFD), our Orm2 knockout (Orm2-KO) exhibited a lean phenotype compared with C57BL/6J control, partly due to the increased energy expenditure. However, when challenged with a HFD supplemented with cholic acid, Orm2-KO eliminated the antiobesity effect of BAs, indicating that ORM2 governs BA-induced metabolic improvements. Moreover, hepatic ORM2 overexpression partially replicated BA effects by enhancing insulin sensitivity. Mechanistically, ORM2 suppressed interferon-γ/STAT1 activities in inguinal white adipose tissue depots, forming the basis for anti-inflammatory effects of BAs and improving glucose homeostasis. In conclusion, our study provides new insights into the molecular mechanisms of BA-induced liver-adipose cross talk through ORM2 induction.

Circadian dysfunction induces NAFLD-related human liver cancer in a mouse model.

BACKGROUND & AIMS: Chronic circadian dysfunction increases the risk of non-alcoholic fatty liver disease (NAFLD)-related hepatocellular carcinoma (HCC), but the underlying mechanisms and direct relevance to human HCC have not been established. In this study, we aimed to determine whether chronic circadian dysregulation can drive NAFLD-related carcinogenesis from human hepatocytes and human HCC progression. METHODS: Chronic jet lag of mice with humanized livers induces spontaneous NAFLD-related HCCs from human hepatocytes. The clinical relevance of this model was analysed by biomarker, pathological/histological, genetic, RNA sequencing, metabolomic, and integrated bioinformatic analyses. RESULTS: Circadian dysfunction induces glucose intolerance, NAFLD-associated human HCCs, and human HCC metastasis independent of diet in a humanized mouse model. The deregulated transcriptomes in necrotic-inflammatory humanized livers and HCCs bear a striking resemblance to those of human non-alcoholic steatohepatitis (NASH), cirrhosis, and HCC. Stable circadian entrainment of hosts rhythmically paces NASH and HCC transcriptomes to decrease HCC incidence and prevent HCC metastasis. Circadian disruption directly reprogrammes NASH and HCC transcriptomes to drive a rapid progression from hepatocarcinogenesis to HCC metastasis. Human hepatocyte and tumour transcripts are clearly distinguishable from mouse transcripts in non-parenchymal cells and tumour stroma, and display dynamic changes in metabolism, inflammation, angiogenesis, and oncogenic signalling in NASH, progressing to hepatocyte malignant transformation and immunosuppressive tumour stroma in HCCs. Metabolomic analysis defines specific bile acids as prognostic biomarkers that change dynamically during hepatocarcinogenesis and in response to circadian disruption at all disease stages. CONCLUSION: Chronic circadian dysfunction is independently carcinogenic to human hepatocytes. Mice with humanized livers provide a powerful preclinical model for studying the impact of the necrotic-inflammatory liver environment and neuroendocrine circadian dysfunction on hepatocarcinogenesis and anti-HCC therapy. IMPACT AND IMPLICATIONS: Human epidemiological studies have linked chronic circadian dysfunction to increased hepatocellular carcinoma (HCC) risk, but direct evidence that circadian dysfunction is a human carcinogen has not been established. Here we show that circadian dysfunction induces non-alcoholic steatohepatitis (NASH)-related carcinogenesis from human hepatocytes in a murine humanized liver model, following the same molecular and pathologic pathways observed in human patients. The gene expression signatures of humanized HCC transcriptomes from circadian-disrupted mice closely match those of human HCC with the poorest prognostic outcomes, while those from stably circadian entrained mice match those from human HCC with the best prognostic outcomes. Our studies establish a new model for defining the mechanism of NASH-related HCC and highlight the importance of circadian biology in HCC prevention and treatment.

Vitamin B2 enables regulation of fasting glucose availability.

Flavin adenine dinucleotide (FAD) interacts with flavoproteins to mediate oxidation-reduction reactions required for cellular energy demands. Not surprisingly, mutations that alter FAD binding to flavoproteins cause rare inborn errors of metabolism (IEMs) that disrupt liver function and render fasting intolerance, hepatic steatosis, and lipodystrophy. In our study, depleting FAD pools in mice with a vitamin B2-deficient diet (B2D) caused phenotypes associated with organic acidemias and other IEMs, including reduced body weight, hypoglycemia, and fatty liver disease. Integrated discovery approaches revealed B2D tempered fasting activation of target genes for the nuclear receptor PPARα, including those required for gluconeogenesis. We also found PPARα knockdown in the liver recapitulated B2D effects on glucose excursion and fatty liver disease in mice. Finally, treatment with the PPARα agonist fenofibrate activated the integrated stress response and refilled amino acid substrates to rescue fasting glucose availability and overcome B2D phenotypes. These findings identify metabolic responses to FAD availability and nominate strategies for the management of organic acidemias and other rare IEMs.

LRH-1 induces hepatoprotective nonessential amino acids in response to acute liver injury.

Acute hepatic injury is observed in response to various stressors, including trauma, ingestion of hepatic toxins, and hepatitis. Investigations to date have focused on extrinsic and intrinsic signals required for hepatocytes to proliferate and regenerate the liver in response to injury, though there is a more limited understanding of induced stress responses promoting hepatocyte survival upon acute injury. In this issue of the JCI, Sun and colleagues detail a mechanism by which local activation of the nuclear receptor liver receptor homolog-1 (LRH-1; NR5A2) directly induces de novo asparagine synthesis and expression of asparagine synthetase (ASNS) in response to injury and show that this response restrains hepatic damage. This work opens up several avenues for inquiry, including the potential for asparagine supplementation to ameliorate acute hepatic injury.

Aryl hydrocarbon receptor maintains hepatic mitochondrial homeostasis in mice.

OBJECTIVE: Mitophagy removes damaged mitochondria to maintain cellular homeostasis. Aryl hydrocarbon receptor (AhR) expression in the liver plays a crucial role in supporting normal liver functions, but its impact on mitochondrial function is unclear. Here, we identified a new role of AhR in the regulation of mitophagy to control hepatic energy homeostasis. METHODS: In this study, we utilized primary hepatocytes from AhR knockout (KO) mice and AhR knockdown AML12 hepatocytes. An endogenous AhR ligand, kynurenine (Kyn), was used to activate AhR in AML12 hepatocytes. Mitochondrial function and mitophagy process were comprehensively assessed by MitoSOX and mt-Keima fluorescence imaging, Seahorse XF-based oxygen consumption rate measurement, and Mitoplate S-1 mitochondrial substrate utilization analysis. RESULTS: Transcriptomic analysis indicated that mitochondria-related gene sets were dysregulated in AhR KO liver. In both primary mouse hepatocytes and AML12 hepatocyte cell lines, AhR inhibition strongly suppressed mitochondrial respiration rate and substrate utilization. AhR inhibition also blunted the fasting response of several essential autophagy genes and the mitophagy process. We further identified BCL2 interacting protein 3 (BNIP3), a mitophagy receptor that senses nutrient stress, as an AhR target gene. AhR is directly recruited to the Bnip3 genomic locus, and Bnip3 transcription was enhanced by AhR endogenous ligand treatment in wild-type liver and abolished entirely in AhR KO liver. Mechanistically, overexpression of Bnip3 in AhR knockdown cells mitigated the production of mitochondrial reactive oxygen species (ROS) and restored functional mitophagy. CONCLUSIONS: AhR regulation of the mitophagy receptor BNIP3 coordinates hepatic mitochondrial function. Loss of AhR induces mitochondrial ROS production and impairs mitochondrial respiration. These findings provide new insight into how endogenous AhR governs hepatic mitochondrial homeostasis.

The rheumatoid arthritis drug auranofin lowers leptin levels and exerts antidiabetic effects in obese mice.

Low-grade, sustained inflammation in white adipose tissue (WAT) characterizes obesity and coincides with type 2 diabetes mellitus (T2DM). However, pharmacological targeting of inflammation lacks durable therapeutic effects in insulin-resistant conditions. Through a computational screen, we discovered that the FDA-approved rheumatoid arthritis drug auranofin improved insulin sensitivity and normalized obesity-associated abnormalities, including hepatic steatosis and hyperinsulinemia in mouse models of T2DM. We also discovered that auranofin accumulation in WAT depleted inflammatory responses to a high-fat diet without altering body composition in obese wild-type mice. Surprisingly, elevated leptin levels and blunted beta-adrenergic receptor activity achieved by leptin receptor deletion abolished the antidiabetic effects of auranofin. These experiments also revealed that the metabolic benefits of leptin reduction were superior to immune impacts of auranofin in WAT. Our studies uncover important metabolic properties of anti-inflammatory treatments and contribute to the notion that leptin reduction in the periphery can be accomplished to treat obesity and T2DM.

A COP1-GATA2 axis suppresses AR signaling and prostate cancer.

Androgen receptor (AR) signaling is crucial for driving prostate cancer (PCa), the most diagnosed and the second leading cause of death in male patients with cancer in the United States. Androgen deprivation therapy is initially effective in most instances of AR-positive advanced or metastatic PCa. However, patients inevitably develop lethal castration-resistant PCa (CRPC), which is also resistant to the next-generation AR signaling inhibitors. Most CRPCs maintain AR expression, and blocking AR signaling remains a main therapeutic approach. GATA2 is a pioneer transcription factor emerging as a key therapeutic target for PCa because it promotes AR expression and activation. While directly inhibiting GATA2 transcriptional activity remains challenging, enhancing GATA2 degradation is a plausible therapeutic strategy. How GATA2 protein stability is regulated in PCa remains unknown. Here, we show that constitutive photomorphogenesis protein 1 (COP1), an E3 ubiquitin ligase, drives GATA2 ubiquitination at K419/K424 for degradation. GATA2 lacks a conserved [D/E](x)xxVP[D/E] degron but uses alternate BR1/BR2 motifs to bind COP1. By promoting GATA2 degradation, COP1 inhibits AR expression and activation and represses PCa cell and xenograft growth and castration resistance. Accordingly, GATA2 overexpression or COP1 mutations that disrupt COP1-GATA2 binding block COP1 tumor-suppressing activities. We conclude that GATA2 is a major COP1 substrate in PCa and that COP1 promotion of GATA2 degradation is a direct mechanism for regulating AR expression and activation, PCa growth, and castration resistance.

Hepatic PPARα Is Destabilized by SIRT1 Deacetylase in Undernourished Male Mice.

The nutrient sensing nuclear receptor peroxisome proliferator-activated receptor-α (PPARα) regulates the host response to short-term fasting by inducing hepatic transcriptional programming of ketogenesis, fatty acid oxidation and transport, and autophagy. This adaptation is ineffective in chronically undernourished individuals, among whom dyslipidemia and hepatic steatosis are common. We recently reported that hepatic PPARα protein is profoundly depleted in male mice undernourished by a low-protein, low-fat diet. Here, we identify PPARα as a deacetylation target of the NAD-dependent deacetylase sirtuin-1 (SIRT1) and link this to the decrease in PPARα protein levels in undernourished liver. Livers from undernourished male mice expressed high levels of SIRT1, with decreased PPARα acetylation and strongly decreased hepatic PPARα protein. In cultured hepatocytes, PPARα protein levels were decreased by transiently transfecting constitutively active SIRT1 or by treating cells with the potent SIRT1 activator resveratrol, while silencing SIRT1 increased PPARα protein levels. SIRT1 expression is correlated with increased PPARα ubiquitination, suggesting that protein loss is due to proteasomal degradation. In accord with these findings, the dramatic loss of hepatic PPARα in undernourished male mice was completely restored by treating mice with the proteasome inhibitor bortezomib. Similarly, treating undernourished mice with the SIRT1 inhibitor selisistat/EX-527 completely restored hepatic PPARα protein. These data suggest that induction of SIRT1 in undernutrition results in hepatic PPARα deacetylation, ubiquitination, and degradation, highlighting a new mechanism that mediates the liver's failed adaptive metabolic responses in chronic undernutrition.

A phospholipid mimetic targeting LRH-1 ameliorates colitis.

Phospholipids are ligands for nuclear hormone receptors (NRs) that regulate transcriptional programs relevant to normal physiology and disease. Here, we demonstrate that mimicking phospholipid-NR interactions is a robust strategy to improve agonists of liver receptor homolog-1 (LRH-1), a therapeutic target for colitis. Conventional LRH-1 modulators only partially occupy the binding pocket, leaving vacant a region important for phospholipid binding and allostery. Therefore, we constructed a set of molecules with elements of natural phospholipids appended to a synthetic LRH-1 agonist. We show that the phospholipid-mimicking groups interact with the targeted residues in crystal structures and improve binding affinity, LRH-1 transcriptional activity, and conformational changes at a key allosteric site. The best phospholipid mimetic markedly improves colonic histopathology and disease-related weight loss in a murine T cell transfer model of colitis. This evidence of in vivo efficacy for an LRH-1 modulator in colitis represents a leap forward in agonist development.

Oleic acid is an endogenous ligand of TLX/NR2E1 that triggers hippocampal neurogenesis.

Neural stem cells, the source of newborn neurons in the adult hippocampus, are intimately involved in learning and memory, mood, and stress response. Despite considerable progress in understanding the biology of neural stem cells and neurogenesis, regulating the neural stem cell population precisely has remained elusive because we have lacked the specific targets to stimulate their proliferation and neurogenesis. The orphan nuclear receptor TLX/NR2E1 governs neural stem and progenitor cell self-renewal and proliferation, but the precise mechanism by which it accomplishes this is not well understood because its endogenous ligand is not known. Here, we identify oleic acid (18:1ω9 monounsaturated fatty acid) as such a ligand. We first show that oleic acid is critical for neural stem cell survival. Next, we demonstrate that it binds to TLX to convert it from a transcriptional repressor to a transcriptional activator of cell-cycle and neurogenesis genes, which in turn increases neural stem cell mitotic activity and drives hippocampal neurogenesis in mice. Interestingly, oleic acid-activated TLX strongly up-regulates cell cycle genes while only modestly up-regulating neurogenic genes. We propose a model in which sufficient quantities of this endogenous ligand must bind to TLX to trigger the switch to proliferation and drive the progeny toward neuronal lineage. Oleic acid thus serves as a metabolic regulator of TLX activity that can be used to selectively target neural stem cells, paving the way for future therapeutic manipulations to counteract pathogenic impairments of neurogenesis.

MAPK4 promotes triple negative breast cancer growth and reduces tumor sensitivity to PI3K blockade.

About 15-20% of breast cancer (BCa) is triple-negative BCa (TNBC), a devastating disease with limited therapeutic options. Aberrations in the PI3K/PTEN signaling pathway are common in TNBC. However, the therapeutic impact of PI3K inhibitors in TNBC has been limited and the mechanism(s) underlying this lack of efficacy remain elusive. Here, we demonstrate that a large subset of TNBC expresses significant levels of MAPK4, and this expression is critical for driving AKT activation independent of PI3K and promoting TNBC cell and xenograft growth. The ability of MAPK4 to bypass PI3K for AKT activation potentially provides a direct mechanism regulating tumor sensitivity to PI3K inhibition. Accordingly, repressing MAPK4 greatly sensitizes TNBC cells and xenografts to PI3K blockade. Altogether, we conclude that high MAPK4 expression defines a large subset or subtype of TNBC responsive to MAPK4 blockage. Targeting MAPK4 in this subset/subtype of TNBC both represses growth and sensitizes tumors to PI3K blockade.

MAPK6-AKT signaling promotes tumor growth and resistance to mTOR kinase blockade.

Mitogen-activated protein kinase 6 (MAPK6) is an atypical MAPK. Its function in regulating cancer growth remains elusive. Here, we reported that MAPK6 directly activated AKT and induced oncogenic outcomes. MAPK6 interacted with AKT through its C34 region and the C-terminal tail and phosphorylated AKT at S473 independent of mTORC2, the major S473 kinase. mTOR kinase inhibitors have not made notable progress in the clinic. Our identified MAPK6-AKT axis may provide a major resistance pathway. Besides repressing growth, inhibiting MAPK6 sensitized cancer cells to mTOR kinase inhibitors. MAPK6 overexpression is associated with decreased overall survival and the survival of patients with lung adenocarcinoma, mesothelioma, uveal melanoma, and breast cancer. MAPK6 expression also correlated with AKT phosphorylation at S473 in human cancer tissues. We conclude that MAPK6 can promote cancer by activating AKT independent of mTORC2 and targeting MAPK6, either alone or in combination with mTOR blockade, may be effective in cancers.

A human liver chimeric mouse model for non-alcoholic fatty liver disease.

BACKGROUND & AIMS: The accumulation of neutral lipids within hepatocytes underlies non-alcoholic fatty liver disease (NAFLD), which affects a quarter of the world's population and is associated with hepatitis, cirrhosis, and hepatocellular carcinoma. Despite insights gained from both human and animal studies, our understanding of NAFLD pathogenesis remains limited. To better study the molecular changes driving the condition we aimed to generate a humanised NAFLD mouse model. METHODS: We generated TIRF (transgene-free Il2rg -/-/Rag2 -/-/Fah -/-) mice, populated their livers with human hepatocytes, and fed them a Western-type diet for 12 weeks. RESULTS: Within the same chimeric liver, human hepatocytes developed pronounced steatosis whereas murine hepatocytes remained normal. Unbiased metabolomics and lipidomics revealed signatures of clinical NAFLD. Transcriptomic analyses showed that molecular responses diverged sharply between murine and human hepatocytes, demonstrating stark species differences in liver function. Regulatory network analysis indicated close agreement between our model and clinical NAFLD with respect to transcriptional control of cholesterol biosynthesis. CONCLUSIONS: These NAFLD xenograft mice reveal an unexpected degree of evolutionary divergence in food metabolism and offer a physiologically relevant, experimentally tractable model for studying the pathogenic changes invoked by steatosis. LAY SUMMARY: Fatty liver disease is an emerging health problem, and as there are no good experimental animal models, our understanding of the condition is poor. We here describe a novel humanised mouse system and compare it with clinical data. The results reveal that the human cells in the mouse liver develop fatty liver disease upon a Western-style fatty diet, whereas the mouse cells appear normal. The molecular signature (expression profiles) of the human cells are distinct from the mouse cells and metabolic analysis of the humanised livers mimic the ones observed in humans with fatty liver. This novel humanised mouse system can be used to study human fatty liver disease.

CAR directs T cell adaptation to bile acids in the small intestine.

Bile acids are lipid-emulsifying metabolites synthesized in hepatocytes and maintained in vivo through enterohepatic circulation between the liver and small intestine1. As detergents, bile acids can cause toxicity and inflammation in enterohepatic tissues2. Nuclear receptors maintain bile acid homeostasis in hepatocytes and enterocytes3, but it is unclear how mucosal immune cells tolerate high concentrations of bile acids in the small intestine lamina propria (siLP). CD4+ T effector (Teff) cells upregulate expression of the xenobiotic transporter MDR1 (encoded by Abcb1a) in the siLP to prevent bile acid toxicity and suppress Crohn's disease-like small bowel inflammation4. Here we identify the nuclear xenobiotic receptor CAR (encoded by Nr1i3) as a regulator of MDR1 expression in T cells that can safeguard against bile acid toxicity and inflammation in the mouse small intestine. Activation of CAR induced large-scale transcriptional reprogramming in Teff cells that infiltrated the siLP, but not the colon. CAR induced the expression of not only detoxifying enzymes and transporters in siLP Teff cells, as in hepatocytes, but also the key anti-inflammatory cytokine IL-10. Accordingly, CAR deficiency in T cells exacerbated bile acid-driven ileitis in T cell-reconstituted Rag1-/- or Rag2-/- mice, whereas pharmacological activation of CAR suppressed it. These data suggest that CAR acts locally in T cells that infiltrate the small intestine to detoxify bile acids and resolve inflammation. Activation of this program offers an unexpected strategy to treat small bowel Crohn's disease and defines lymphocyte sub-specialization in the small intestine.

Ube2i deletion in adipocytes causes lipoatrophy in mice.

OBJECTIVE: White adipose tissue (WAT) expansion regulates energy balance and overall metabolic homeostasis. The absence or loss of WAT occurring through lipodystrophy and lipoatrophy contributes to the development of hepatic steatosis and insulin resistance. We previously demonstrated that sole small ubiquitin-like modifier (SUMO) E2-conjugating enzyme Ube2i represses human adipocyte differentiation. The role of Ube2i during WAT development remains unknown. METHODS: To determine how Ube2i impacts body composition and energy balance, we generated adipocyte-specific Ube2i knockout mice (Ube2ia-KO). CRISPR/Cas9 gene editing inserted loxP sites flanking exons 3 and 4 at the Ube2i locus. Subsequent genetic crosses to Adipoq-Cre transgenic mice allowed deletion of Ube2i in white and brown adipocytes. We measured multiple metabolic endpoints that describe energy balance and carbohydrate metabolism in Ube2ia-KO and littermate controls during postnatal growth. RESULTS: Surprisingly, Ube2ia-KO mice developed hyperinsulinemia and hepatic steatosis. Global energy balance defects emerged from dysfunctional WAT marked by pronounced local inflammation, loss of serum adipokines, hepatomegaly, and near absence of major adipose tissue depots. We observed progressive lipoatrophy that commences in the early adolescent period. CONCLUSIONS: Our results demonstrate that Ube2i expression in mature adipocytes allows WAT expansion during postnatal growth. Deletion of Ube2i in fat cells compromises and diminishes adipocyte function that induces WAT inflammation and ectopic lipid accumulation in the liver. Our findings reveal an indispensable role for Ube2i during white adipocyte expansion and endocrine control of energy balance.

MAPK4 promotes prostate cancer by concerted activation of androgen receptor and AKT.

Prostate cancer (PCa) is the second leading cause of cancer death in American men. Androgen receptor (AR) signaling is essential for PCa cell growth/survival and remains a key therapeutic target for lethal castration-resistant PCa (CRPC). GATA2 is a pioneer transcription factor crucial for inducing AR expression/activation. We recently reported that MAPK4, an atypical MAPK, promotes tumor progression via noncanonical activation of AKT. Here, we demonstrated that MAPK4 activated AR by enhancing GATA2 transcriptional expression and stabilizing GATA2 protein through repression of GATA2 ubiquitination/degradation. MAPK4 expression correlated with AR activation in human CRPC. Concerted activation of both GATA2/AR and AKT by MAPK4 promoted PCa cell proliferation, anchorage-independent growth, xenograft growth, and castration resistance. Conversely, knockdown of MAPK4 decreased activation of both AR and AKT and inhibited PCa cell and xenograft growth, including castration-resistant growth. Both GATA2/AR and AKT activation were necessary for MAPK4 tumor-promoting activity. Interestingly, combined overexpression of GATA2 plus a constitutively activated AKT was sufficient to drive PCa growth and castration resistance, shedding light on an alternative, MAPK4-independent tumor-promoting pathway in human PCa. We concluded that MAPK4 promotes PCa growth and castration resistance by cooperating parallel pathways of activating GATA2/AR and AKT and that MAPK4 is a novel therapeutic target in PCa, especially CRPC.

Vertical sleeve gastrectomy confers metabolic improvements by reducing intestinal bile acids and lipid absorption in mice.

Vertical sleeve gastrectomy (VSG) is one of the most effective and durable therapies for morbid obesity and its related complications. Although bile acids (BAs) have been implicated as downstream mediators of VSG, the specific mechanisms through which BA changes contribute to the metabolic effects of VSG remain poorly understood. Here, we confirm that high fat diet-fed global farnesoid X receptor (Fxr) knockout mice are resistant to the beneficial metabolic effects of VSG. However, the beneficial effects of VSG were retained in high fat diet-fed intestine- or liver-specific Fxr knockouts, and VSG did not result in Fxr activation in the liver or intestine of control mice. Instead, VSG decreased expression of positive hepatic Fxr target genes, including the bile salt export pump (Bsep) that delivers BAs to the biliary pathway. This reduced small intestine BA levels in mice, leading to lower intestinal fat absorption. These findings were verified in sterol 27-hydroxylase (Cyp27a1) knockout mice, which exhibited low intestinal BAs and fat absorption and did not show metabolic improvements following VSG. In addition, restoring small intestinal BA levels by dietary supplementation with taurocholic acid (TCA) partially blocked the beneficial effects of VSG. Altogether, these findings suggest that reductions in intestinal BAs and lipid absorption contribute to the metabolic benefits of VSG.

Mitophagy deficiency increases NLRP3 to induce brown fat dysfunction in mice.

Although macroautophagy/autophagy deficiency causes degenerative diseases, the deletion of essential autophagy genes in adipocytes paradoxically reduces body weight. Brown adipose tissue (BAT) plays an important role in body weight regulation and metabolic control. However, the key cellular mechanisms that maintain BAT function remain poorly understood. in this study, we showed that global or brown adipocyte-specific deletion of pink1, a Parkinson disease-related gene involved in selective mitochondrial autophagy (mitophagy), induced BAT dysfunction, and obesity-prone type in mice. Defective mitochondrial function is among the upstream signals that activate the NLRP3 inflammasome. NLRP3 was induced in brown adipocyte precursors (BAPs) from pink1 knockout (KO) mice. Unexpectedly, NLRP3 induction did not induce canonical inflammasome activity. Instead, NLRP3 induction led to the differentiation of pink1 KO BAPs into white-like adipocytes by increasing the expression of white adipocyte-specific genes and repressing the expression of brown adipocyte-specific genes. nlrp3 deletion in pink1 knockout mice reversed BAT dysfunction. Conversely, adipose tissue-specific atg7 KO mice showed significantly lower expression of Nlrp3 in their BAT. Overall, our data suggest that the role of mitophagy is different from general autophagy in regulating adipose tissue and whole-body energy metabolism. Our results uncovered a new mitochondria-NLRP3 pathway that induces BAT dysfunction. The ability of the nlrp3 knockouts to rescue BAT dysfunction suggests the transcriptional function of NLRP3 as an unexpected, but a quite specific therapeutic target for obesity-related metabolic diseases.Abbreviations: ACTB: actin, beta; BAPs: brown adipocyte precursors; BAT: brown adipose tissue; BMDMs: bone marrow-derived macrophages; CASP1: caspase 1; CEBPA: CCAAT/enhancer binding protein (C/EBP), alpha; ChIP: chromatin immunoprecipitation; EE: energy expenditure; HFD: high-fat diet; IL1B: interleukin 1 beta; ITT: insulin tolerance test; KO: knockout; LPS: lipopolysaccharide; NLRP3: NLR family, pyrin domain containing 3; PINK1: PTEN induced putative kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; RD: regular diet; ROS: reactive oxygen species; RT: room temperature; UCP1: uncoupling protein 1 (mitochondrial, proton carrier); WT: wild-type.

The bile acid induced hepatokine orosomucoid suppresses adipocyte differentiation.

Bile acids have recently emerged as key metabolic hormones with beneficial impacts in multiple metabolic diseases. We previously discovered that hepatic bile acid overload distally modulates glucose and fatty acid metabolism in adipose tissues to exert anti-obesity effects. However, the detailed mechanisms that explain the salutary effects of serum bile acid elevation remain unclear. Here, proteomic profiling identified a new hepatokine, Orosomucoid (ORM) that governs liver-adipose tissue crosstalk. Hepatic ORMs were highly induced by both genetic and dietary bile acid overload. To address the direct metabolic effects of ORM, purified ORM proteins were administered during adipogenic differentiation of 3T3-L1 cells and mouse stromal vascular fibroblasts. ORM suppressed adipocyte differentiation and strongly inhibited gene expression of adipogenic transcription factors such as C/EBPß, KLF5, C/EBPα, and PPARγ. Taken together, our data clearly suggest that bile acid-induced ORM secretion from the liver blocks adipocyte differentiation, potentially linked to anti-obesity effect of bile acids.