Concomitant western diet and chronic-binge alcohol dysregulate hepatic metabolism

BACKGROUND AND AIMS

There is significant overlap between non-alcoholic fatty liver disease (NAFLD) and alcohol-associated liver disease (ALD) with regards to risk factors and disease progression. However, the mechanism by which fatty liver disease arises from concomitant obesity and overconsumption of alcohol (syndrome of metabolic and alcohol-associated fatty liver disease; SMAFLD), is not fully understood.

METHODS

Male C57BL6/J mice were fed chow diet (Chow) or high-fructose, high-fat, high-cholesterol diet (FFC) for 4 weeks, then administered either saline or ethanol (EtOH, 5% in drinking water) for another 12 weeks. The EtOH treatment also consisted of a weekly 2.5 g EtOH/kg body weight gavage. Markers for lipid regulation, oxidative stress, inflammation, and fibrosis were measured by RT-qPCR, RNA-seq, Western blot, and metabolomics.

RESULTS

Combined FFC-EtOH induced more body weight gain, glucose intolerance, steatosis, and hepatomegaly compared to Chow, EtOH, or FFC. Glucose intolerance by FFC-EtOH was associated with decreased hepatic protein kinase B (AKT) protein expression and increased gluconeogenic gene expression. FFC-EtOH increased hepatic triglyceride and ceramide levels, plasma leptin levels, hepatic Perilipin 2 protein expression, and decreased lipolytic gene expression. FFC and FFC-EtOH also increased AMP-activated protein kinase (AMPK) activation. Finally, FFC-EtOH enriched the hepatic transcriptome for genes involved in immune response and lipid metabolism.

CONCLUSIONS

In our model of early SMAFLD, we observed that the combination of an obesogenic diet and alcohol caused more weight gain, promoted glucose intolerance, and contributed to steatosis by dysregulating leptin/AMPK signaling. Our model demonstrates that the combination of an obesogenic diet with a chronic-binge pattern alcohol intake is worse than either insult alone.

Global-run on sequencing identifies Gm11967 as an Akt-dependent long noncoding RNA involved in insulin sensitivity

The insulin responsive Akt and FoxO1 signaling axis is a key regulator of the hepatic transcriptional response to nutrient intake. Here, we used global run-on sequencing (GRO-seq) to measure the nascent transcriptional response to fasting and refeeding as well as define the specific role of hepatic Akt and FoxO1 signaling in mediating this response. We identified 599 feeding-regulated transcripts, as well as over 6,000 eRNAs, and mapped their dependency on Akt and FoxO1 signaling. Further, we identified several feeding-regulated lncRNAs, including the lncRNA Gm11967, whose expression was dependent upon the liver Akt-FoxO1 axis. Restoring Gm11967 expression in mice lacking liver Akt improved insulin sensitivity and induced glucokinase protein expression, indicating that Akt-dependent control of Gm11967 contributes to the translational control of glucokinase. More broadly, we have generated a unique genome-wide dataset that defines the feeding and Akt/FoxO1-dependent transcriptional changes in response to nutrient availability.

Acute Deletion of the FOXO1-dependent Hepatokine FGF21 Does not Alter Basal Glucose Homeostasis or Lipolysis in Mice

The hepatic transcription factor forkhead box O1 (FOXO1) is a critical regulator of hepatic and systemic insulin sensitivity. Previous work by our group and others demonstrated that genetic inhibition of FOXO1 improves insulin sensitivity both in genetic and dietary mouse models of metabolic disease. Mechanistically, this is due in part to cell nonautonomous control of adipose tissue insulin sensitivity. However, the mechanisms mediating this liver-adipose tissue crosstalk remain ill defined. One candidate hepatokine controlled by hepatic FOXO1 is fibroblast growth factor 21 (FGF21). Preclinical and clinical studies have explored the potential of pharmacological FGF21 as an antiobesity and antidiabetic therapy. In this manuscript, we performed acute loss-of-function experiments to determine the role of hepatocyte-derived FGF21 in glucose homeostasis and insulin tolerance both in control and mice lacking hepatic insulin signaling. Surprisingly, acute deletion of FGF21 did not alter glucose tolerance, insulin tolerance, or adipocyte lipolysis in either liver-specific FGF21KO mice or mice lacking hepatic AKT-FOXO1-FGF21, suggesting a permissive role for endogenous FGF21 in the regulation of systemic glucose homeostasis and insulin tolerance in mice. In addition, these data indicate that liver FOXO1 controls glucose homeostasis independently of liver-derived FGF21.

Activation of Liver mTORC1 Protects Against NASH via Dual Regulation of VLDL-TAG Secretion and De Novo Lipogenesis

BACKGROUND & AIMS

Dysregulation of liver lipid metabolism is associated with the development and progression of nonalcoholic fatty liver disease, a spectrum of liver diseases including nonalcoholic steatohepatitis (NASH). In the liver, insulin controls lipid homeostasis by increasing triglyceride (TAG) synthesis, suppressing fatty acid oxidation, and enhancing TAG export via very low-density lipoproteins. Downstream of insulin signaling, the mechanistic target of rapamycin complex 1 (mTORC1), is a key regulator of lipid metabolism. Here, we define the role of hepatic mTORC1 activity in mouse models of NASH and investigate the mTORC1-dependent mechanisms responsible for protection against liver damage in NASH.

METHODS

Utilizing 2 rodent NASH-promoting diets, we demonstrate that hepatic mTORC1 activity was reduced in mice with NASH, whereas under conditions of insulin resistance and benign fatty liver, mTORC1 activity was elevated. To test the beneficial effects of hepatic mTORC1 activation in mouse models of NASH, we employed an acute, liver-specific knockout model of TSC1 (L-TSC-KO), a negative regulator of mTORC1.

RESULTS

L-TSC-KO mice are protected from and have improved markers of NASH including reduced steatosis, decreased circulating transaminases, and reduced expression of inflammation and fibrosis genes. Mechanistically, protection from hepatic inflammation and fibrosis by constitutive mTORC1 activity occurred via promotion of the phosphatidylcholine synthesizing enzyme, CCTα, and enhanced very low-density lipoprotein-triglyceride export. Additionally, activation of mTORC1 protected from hepatic steatosis via negative feedback of the mTORC2-AKT-FOXO-SREBP1c lipogenesis axis.

CONCLUSIONS

Collectively, this study identifies a protective role for liver mTORC1 signaling in the initiation and progression of NASH in mice via dual control of lipid export and synthesis.

AKT controls protein synthesis and oxidative metabolism via combined mTORC1 and FOXO1 signalling to govern muscle physiology

BACKGROUND

Skeletomuscular diseases result in significant muscle loss and decreased performance, paralleled by a loss in mitochondrial and oxidative capacity. Insulin and insulin-like growth factor-1 (IGF-1) are two potent anabolic hormones that activate a host of signalling intermediates including the serine/threonine kinase AKT to influence skeletal muscle physiology. Defective AKT signalling is associated with muscle pathology, including cachexia, sarcopenia, and disuse; however, the mechanistic underpinnings remain unresolved.

METHODS

To elucidate the role of AKT signalling in muscle mass and physiology, we generated both congenital and inducible mouse models of skeletal muscle-specific AKT deficiency. To understand the downstream mechanisms mediating AKT's effects on muscle biology, we generated mice lacking AKT1/2 and FOXO1 (M-AKTFOXO1TKO and M-indAKTFOXO1TKO) to inhibit downstream FOXO1 signalling, AKT1/2 and TSC1 (M-AKTTSCTKO and M-indAKTTSCTKO) to activate mTORC1, and AKT1/2, FOXO1, and TSC1 (M-QKO and M-indQKO) to simultaneously activate mTORC1 and inhibit FOXO1 in AKT-deficient skeletal muscle. Muscle proteostasis and physiology were assessed using multiple assays including metabolic labelling, mitochondrial function, fibre typing, ex vivo physiology, and exercise performance.

RESULTS

Here, we show that genetic ablation of skeletal muscle AKT signalling resulted in decreased muscle mass and a loss of oxidative metabolism and muscle performance. Specifically, deletion of muscle AKT activity during development or in adult mice resulted in a significant reduction in muscle growth by 30-40% (P  < 0.0001; n = 12-20) and 15% (P < 0.01 and P < 0.0001; n = 20-30), respectively. Interestingly, this reduction in muscle mass was primarily due to an ~40% reduction in protein synthesis in both M-AKTDKO and M-indAKTDKO muscles (P < 0.05 and P < 0.01; n = 12-20) without significant changes in proteolysis or autophagy. Moreover, a significant reduction in oxidative capacity was observed in both M-AKTDKO (P < 0.05, P < 0.01 and P < 0.001; n = 5-12) and M-indAKTDKO (P < 0.05 and P < 0.01; n = 4). Mechanistically, activation and inhibition of mTORC1/FOXO1, respectively, but neither alone, were sufficient to restore protein synthesis, muscle oxidative capacity, and muscle function in the absence of AKT in vivo. In a mouse model of disuse-induced muscle loss, simultaneous activation of mTORC1 and inhibition of FOXO1 preserved muscle mass following immobilization (~5-10% reduction in casted M-indFOXO1TSCDKO muscles vs. ~30-40% casted M-indControl muscles, P < 0.05 and P < 0.0001; n = 8-16).

CONCLUSIONS

Collectively, this study provides novel insights into the AKT-dependent mechanisms that underlie muscle protein homeostasis, function, and metabolism in both normal physiology and disuse-induced muscle wasting.

Hepatic AKT orchestrates adipose tissue thermogenesis via FGF21-dependent and -independent mechanisms

Organismal stressors such as cold exposure require a systemic response to maintain body temperature. Brown adipose tissue (BAT) is a key thermogenic tissue in mammals that protects against hypothermia in response to cold exposure. Defining the complex interplay of multiple organ systems in this response is fundamental to our understanding of adipose tissue thermogenesis. In this study, we identify a role for hepatic insulin signaling via AKT in the adaptive response to cold stress and show that liver AKT is an essential cell-nonautonomous regulator of adipocyte lipolysis and BAT function. Mechanistically, inhibition of forkhead box O1 (FOXO1) by AKT controls BAT thermogenesis by enhancing catecholamine-induced lipolysis in the white adipose tissue (WAT) and increasing circulating fibroblast growth factor 21 (FGF21). Our data identify a role for hepatic insulin signaling via the AKT-FOXO1 axis in regulating WAT lipolysis, promoting BAT thermogenic capacity, and ensuring a proper thermogenic response to acute cold exposure.

Shared PPARα/γ Target Genes Regulate Brown Adipocyte Thermogenic Function

Brown adipose tissue (BAT) generates heat to maintain body temperature and suppress obesity. Agonists for nuclear receptors PPARα and PPARγ both affect brown adipocyte function, yet the interplay between these factors in BAT is uncertain. Here, we report that PPARα shares most genomic binding sites with PPARγ, and these common binding sites are more related to BAT function than PPARγ-selective sites without PPARα. Integrating PPARα and PPARγ genomic occupancy with cold-responsive BAT transcriptomes identifies a subset of 16 genes with potential relevance to BAT function. Among these, we focused on the lysosomal protease cathepsin Z (CTSZ) and showed it is necessary for mitochondrial respiration in both mouse and human brown adipocytes. Thus, CTSZ is a shared PPARα/γ target gene in BAT and a regulator of brown adipocyte thermogenic function.

Early B Cell Factor Activity Controls Developmental and Adaptive Thermogenic Gene Programming in Adipocytes

Brown adipose tissue (BAT) activity protects animals against hypothermia and represents a potential therapeutic target to combat obesity. The transcription factor early B cell factor-2 (EBF2) promotes brown adipocyte differentiation, but its roles in maintaining brown adipocyte fate and in stimulating BAT recruitment during cold exposure were unknown. We find that the deletion of Ebf2 in adipocytes of mice ablates BAT character and function, resulting in cold intolerance. Unexpectedly, prolonged exposure to cold restores the thermogenic profile and function of Ebf2 mutant BAT. Enhancer profiling and genetic assays identified EBF1 as a candidate regulator of the cold response in BAT. Adipocyte-specific deletion of both Ebf1 and Ebf2 abolishes BAT recruitment during chronic cold exposure. Mechanistically, EBF1 and EBF2 promote thermogenic gene transcription through increasing the expression and activity of ERRα and PGC1α. Together, these studies demonstrate that EBF proteins specify the developmental fate and control the adaptive cold response of brown adipocytes.

YAP1 enhances NF-κB-dependent and independent effects on clock-mediated unfolded protein responses and autophagy in sarcoma

Terminal differentiation opposes proliferation in the vast majority of tissue types. As a result, loss of lineage differentiation is a hallmark of aggressive cancers, including soft tissue sarcomas (STS). Consistent with these observations, undifferentiated pleomorphic sarcoma (UPS), an STS subtype devoid of lineage markers, is among the most lethal sarcomas in adults. Though tissue-specific features are lost in these mesenchymal tumors they are most commonly diagnosed in skeletal muscle, and are thought to develop from transformed muscle progenitor cells. We have found that a combination of HDAC (Vorinostat) and BET bromodomain (JQ1) inhibition partially restores differentiation to skeletal muscle UPS cells and tissues, enforcing a myoblast-like identity. Importantly, differentiation is partially contingent upon downregulation of the Hippo pathway transcriptional effector Yes-associated protein 1 (YAP1) and nuclear factor (NF)-κB. Previously, we observed that Vorinostat/JQ1 inactivates YAP1 and restores oscillation of NF-κB in differentiating myoblasts. These effects correlate with reduced tumorigenesis, and enhanced differentiation. However, the mechanisms by which the Hippo/NF-κB axis impact differentiation remained unknown. Here, we report that YAP1 and NF-κB activity suppress circadian clock function, inhibiting differentiation and promoting proliferation. In most tissues, clock activation is antagonized by the unfolded protein response (UPR). However, skeletal muscle differentiation requires both Clock and UPR activity, suggesting the molecular link between them is unique in muscle. In skeletal muscle-derived UPS, we observed that YAP1 suppresses PERK and ATF6-mediated UPR target expression as well as clock genes. These pathways govern metabolic processes, including autophagy, and their disruption shifts metabolism toward cancer cell-associated glycolysis and hyper-proliferation. Treatment with Vorinostat/JQ1 inhibited glycolysis/MTOR signaling, activated the clock, and upregulated the UPR and autophagy via inhibition of YAP1/NF-κB. These findings support the use of epigenetic modulators to treat human UPS. In addition, we identify specific autophagy, UPR, and muscle differentiation-associated genes as potential biomarkers of treatment efficacy and differentiation.