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IgA + B cells expressing programmed death ligand 1 (PD-L1) and interleukin 10 accumulate in the inflamed livers of humans and mice with non-alcoholic fatty liver disease where they promote the progression to hepatocellular carcinoma by limiting the local activation of PD-1-expressing CD8 + T cells. The role of adaptive immunity in early cancer development is controversial. Here we show that chronic inflammation and fibrosis in humans and mice with non-alcoholic fatty liver disease is accompanied by accumulation of liver-resident immunoglobulin-A-producing (IgA + ) cells. These cells also express programmed death ligand 1 (PD-L1) and interleukin-10, and directly suppress liver cytotoxic CD8 + T lymphocytes, which prevent emergence of hepatocellular carcinoma and express a limited repertoire of T-cell receptors against tumour-associated antigens. Whereas CD8 + T-cell ablation accelerates hepatocellular carcinoma, genetic or pharmacological interference with IgA + cell generation attenuates liver carcinogenesis and induces cytotoxic T-lymphocyte-mediated regression of established hepatocellular carcinoma. These findings establish the importance of inflammation-induced suppression of cytotoxic CD8 + T-lymphocyte activation as a tumour-promoting mechanism. Increased cancer risk in fatty livers Cancer progression beyond the early stages is thought to be caused in some cases by adaptive immunity, but its role remains controversial. In this study, Michael Karin and colleagues show that PD-L1-expressing IgA + B cells accumulate in the inflamed livers of humans and mice with non-alcoholic fatty liver disease. The inflammation-induced IgA + cells promote the progression to hepatocellular carcinoma by suppressing liver cytotoxic CD8 + T cells that prevent the emergence of this aggressive tumour.

The dysregulation of energy homeostasis in obesity involves multihormone resistance. Although leptin and insulin resistance have been well characterized, catecholamine resistance remains largely unexplored. Murine β3-adrenergic receptor expression in adipocytes is orders of magnitude higher compared with that of other isoforms. While resistant to classical desensitization pathways, its mRNA (Adrb3) and protein expression are dramatically downregulated after ligand exposure (homologous desensitization). β3-Adrenergic receptor downregulation also occurs after high-fat diet feeding, concurrent with catecholamine resistance and elevated inflammation. This downregulation is recapitulated in vitro by TNF-α treatment (heterologous desensitization). Both homologous and heterologous desensitization of Adrb3 were triggered by induction of the pseudokinase TRIB1 downstream of the EPAC/RAP2A/PI-PLC pathway. TRIB1 in turn degraded the primary transcriptional activator of Adrb3, CEBPα. EPAC/RAP inhibition enhanced catecholamine-stimulated lipolysis and energy expenditure in obese mice. Moreover, adipose tissue expression of genes in this pathway correlated with body weight extremes in a cohort of genetically diverse mice and with BMI in 2 independent cohorts of humans. These data implicate a signaling axis that may explain reduced hormone-stimulated lipolysis in obesity and resistance to therapeutic interventions with β3-adrenergic receptor agonists.

Liver fibrosis is characterized by the persistent deposition of extracellular matrix components by hepatic stellate cell (HSC)-derived myofibroblasts. It is the histological manifestation of progressive, but reversible wound-healing processes. An unabated fibrotic response results in chronic liver disease and cirrhosis, a pathological precursor of hepatocellular carcinoma. We report here that JQ1, a small molecule inhibitor of bromodomain-containing protein 4 (BRD4), a member of bromodomain and extraterminal (BET) proteins, abrogate cytokine-induced activation of HSCs. Cistromic analyses reveal that BRD4 is highly enriched at enhancers associated with genes involved in multiple profibrotic pathways, where BRD4 is colocalized with profibrotic transcription factors. Furthermore, we show that JQ1 is not only protective, but can reverse the fibrotic response in carbon tetrachloride-induced fibrosis in mouse models. Our results implicate that BRD4 can act as a global genomic regulator to direct the fibrotic response through its coordinated regulation of myofibroblast transcription. This suggests BRD4 as a potential therapeutic target for patients with fibrotic complications.

Fat-resident regulatory T cells (fT reg cells) accumulate in adipose tissue of mice as a function of age, but not obesity; mice without fT reg cells are protected against age-associated insulin resistance, but remain susceptible to obesity-associated insulin resistance and metabolic disease, indicating different aetiologies of age-associated versus obesity-associated insulin resistance. Detrimental role for fat T reg in insulin resistance Age-associated insulin resistance (IR) and obesity-associated IR are physiologically distinct forms of adult-onset diabetes. Although macrophage-driven inflammation drives the obesity-associated condition, the mechanisms for age-associated IR are not known. Ronald Evans and colleagues show that fat-resident regulatory T cells (fT reg cells) accumulate in adipose tissue as a function of age, but not obesity. Mice lacking fT reg cells are protected against age-associated IR, yet remain susceptible to obesity-associated IR and metabolic disease. Depletion of fT reg cells via anti-ST2 antibody treatment increases adipose tissue insulin sensitivity. Although not the main topic of this study, these findings do not support a role for fT reg cells in obesity-associated insulin resistance or in the therapeutic actions of thiazolidinedione or 'glitazone' antidiabetics. This contradicts claims that T reg cells were beneficial and necessary for restoration of insulin sensitivity in obese mice by the thiazolidinedione drug pioglitazone. Age-associated insulin resistance (IR) and obesity-associated IR are two physiologically distinct forms of adult-onset diabetes. While macrophage-driven inflammation is a core driver of obesity-associated IR 1 , 2 , 3 , 4 , 5 , 6 , the underlying mechanisms of the obesity-independent yet highly prevalent age-associated IR 7 are largely unexplored. Here we show, using comparative adipo-immune profiling in mice, that fat-resident regulatory T cells, termed fT reg cells, accumulate in adipose tissue as a function of age, but not obesity. Supporting the existence of two distinct mechanisms underlying IR, mice deficient in fT reg cells are protected against age-associated IR, yet remain susceptible to obesity-associated IR and metabolic disease. By contrast, selective depletion of fT reg cells via anti-ST2 antibody treatment increases adipose tissue insulin sensitivity. These findings establish that distinct immune cell populations within adipose tissue underlie ageing- and obesity-associated IR, and implicate fT reg cells as adipo-immune drivers and potential therapeutic targets in the treatment of age-associated IR.

Enhancers are critical genomic elements that define cellular and functional identity through the spatial and temporal regulation of gene expression. Recent studies suggest that key genes regulating cell type-specific functions reside in enhancer-dense genomic regions (i.e., super enhancers, stretch enhancers). Here we report that enhancer RNAs (eRNAs) identified by global nuclear run-on sequencing are extensively transcribed within super enhancers and are dynamically regulated in response to cellular signaling. Using Toll-like receptor 4 (TLR4) signaling in macrophages as a model system, we find that transcription of super enhancer-associated eRNAs is dynamically induced at most of the key genes driving innate immunity and inflammation. Unexpectedly, genes repressed by TLR4 signaling are also associated with super enhancer domains and accompanied by massive repression of eRNA transcription. Furthermore, we find each super enhancer acts as a single regulatory unit within which eRNA and genic transcripts are coordinately regulated. The key regulatory activity of these domains is further supported by the finding that super enhancer-associated transcription factor binding is twice as likely to be conserved between human and mouse than typical enhancer sites. Our study suggests that transcriptional activities at super enhancers are critical components to understand the dynamic gene regulatory network. Significance Super enhancers (SEs) are enhancer-dense regions found near genes that play key roles in determining cellular identity. Using global nuclear run-on sequencing (GRO-Seq), we find extensive regulation of enhancer RNAs (eRNAs) within SEs in response to lipopolysaccharide (LPS) treatment in macrophages. Both activation and repression of gene expression are associated with SEs and eRNA transcription dynamics. Furthermore, we find that each SE acts as a single regulatory unit within which eRNA and genic transcripts are coordinately regulated. We also find that transcription factor (TF) composition within an SE determines regulatory properties of each SE and associated eRNAs. We propose that signal-dependent SEs and their eRNAs function as molecular rheostats integrating the binding profiles of key regulators to produce dynamic profiles of gene expression.

Mitochondrial dysfunction is a characteristic trait of human and rodent obesity, insulin resistance and fatty liver disease. Here we show that high-fat diet (HFD) feeding causes mitochondrial fragmentation in inguinal white adipocytes from male mice, leading to reduced oxidative capacity by a process dependent on the small GTPase RalA. RalA expression and activity are increased in white adipocytes after HFD. Targeted deletion of RalA in white adipocytes prevents fragmentation of mitochondria and diminishes HFD-induced weight gain by increasing fatty acid oxidation. Mechanistically, RalA increases fission in adipocytes by reversing the inhibitory Ser637 phosphorylation of the fission protein Drp1, leading to more mitochondrial fragmentation. Adipose tissue expression of the human homolog of Drp1, DNM1L , is positively correlated with obesity and insulin resistance. Thus, chronic activation of RalA plays a key role in repressing energy expenditure in obese adipose tissue by shifting the balance of mitochondrial dynamics toward excessive fission, contributing to weight gain and metabolic dysfunction. Xia et al. show that the activity of the small GTPase RalA is increased in white adipocytes in diet-induced obese mice. RalA enhances mitochondrial fission and therefore reduces energy expenditure, which contributes to weight gain.

A fibroinflammatory stromal reaction cooperates with oncogenic signaling to influence pancreatic ductal adenocarcinoma (PDAC) initiation, progression, and therapeutic outcome, yet the mechanistic underpinning of this crosstalk remains poorly understood. Here we show that stromal cues elicit an adaptive response in the cancer cell including the rapid mobilization of a transcriptional network implicated in accelerated growth, along with anabolic changes of an altered metabolome. The close overlap of stroma-induced changes in vitro with those previously shown to be regulated by oncogenic Kras in vivo suggests that oncogenic Kras signaling—a hallmark and key driver of PDAC—is contingent on stromal inputs. Mechanistically, stroma-activated cancer cells show widespread increases in histone acetylation at transcriptionally enhanced genes, implicating the PDAC epigenome as a presumptive point of convergence between these pathways and a potential therapeutic target. Notably, inhibition of the bromodomain and extraterminal (BET) family of epigenetic readers, and of Bromodomain-containing protein 2 (BRD2) in particular, blocks stroma-inducible transcriptional regulation in vitro and tumor progression in vivo. Our work suggests the existence of a molecular “AND-gate” such that tumor activation is the consequence of mutant Kras and stromal cues, providing insight into the role of the tumor microenvironment in the origin and treatment of Ras-driven tumors.

Pharmacological fibroblast growth factor 1 (FGF1) normalizes blood glucose in diabetic mice by means of an FGF receptor signalling pathway that is independent of its mitogenic activity. Glucose-lowering activity of 'endocrine' FGF1 As a non-endocrine member of the fibroblast growth factor (FGF) family, FGF1 is known as a classic growth factor with mitogenic and angiogenic activity. This study identifies FGF1 as a powerful metabolic regulator. Injection of recombinant FGF1 (rFGF1) results in potent, insulin-dependent glucose lowering in diabetic mice, but does not lead to hypoglycaemia. Chronic pharmacological treatment with rFGF1 increases insulin-dependent glucose uptake in skeletal muscle and suppresses hepatic glucose production to achieve whole-body insulin sensitization. This work raises the possibility that FGF1 could have therapeutic potential for the treatment of insulin resistance and type 2 diabetes. Fibroblast growth factor 1 (FGF1) is an autocrine/paracrine regulator whose binding to heparan sulphate proteoglycans effectively precludes its circulation 1 , 2 . Although FGF1 is known as a mitogenic factor, FGF1 knockout mice develop insulin resistance when stressed by a high-fat diet, suggesting a potential role in nutrient homeostasis 3 , 4 . Here we show that parenteral delivery of a single dose of recombinant FGF1 (rFGF1) results in potent, insulin-dependent lowering of glucose levels in diabetic mice that is dose-dependent but does not lead to hypoglycaemia. Chronic pharmacological treatment with rFGF1 increases insulin-dependent glucose uptake in skeletal muscle and suppresses the hepatic production of glucose to achieve whole-body insulin sensitization. The sustained glucose lowering and insulin sensitization attributed to rFGF1 are not accompanied by the side effects of weight gain, liver steatosis and bone loss associated with current insulin-sensitizing therapies. We also show that the glucose-lowering activity of FGF1 can be dissociated from its mitogenic activity and is mediated predominantly via FGF receptor 1 signalling. Thus we have uncovered an unexpected, neomorphic insulin-sensitizing action for exogenous non-mitogenic human FGF1 with therapeutic potential for the treatment of insulin resistance and type 2 diabetes.

Oncogenic lesions in pancreatic ductal adenocarcinoma (PDAC) hijack the epigenetic machinery in stromal components to establish a desmoplastic and therapeutic resistant tumor microenvironment (TME). Here we identify Class I histone deacetylases (HDACs) as key epigenetic factors facilitating the induction of pro-desmoplastic and pro-tumorigenic transcriptional programs in pancreatic stromal fibroblasts. Mechanistically, HDAC-mediated changes in chromatin architecture enable the activation of pro-desmoplastic programs directed by serum response factor (SRF) and forkhead box M1 (FOXM1). HDACs also coordinate fibroblast pro-inflammatory programs inducing leukemia inhibitory factor (LIF) expression, supporting paracrine pro-tumorigenic crosstalk. HDAC depletion in cancer-associated fibroblasts (CAFs) and treatment with the HDAC inhibitor entinostat (Ent) in PDAC mouse models reduce stromal activation and curb tumor progression. Notably, HDAC inhibition (HDACi) enriches a lipogenic fibroblast subpopulation, a potential precursor for myofibroblasts in the PDAC stroma. Overall, our study reveals the stromal targeting potential of HDACi, highlighting the utility of this epigenetic modulating approach in PDAC therapeutics. The desmoplastic stroma constitutes part of the microenvironment in pancreatic ductal adenocarcinoma. Here the authors show that Class I HDACs regulate the pro-desmoplastic and pro-tumorigenic transcriptional programs to support stromal activation and tumour progression.

Peroxisome proliferator-activated receptor delta (PPARδ), a member of the nuclear receptor family, is emerging as a key metabolic regulator with pleiotropic actions on various tissues including fat, skeletal muscle, and liver. Here we show that the PPARδ agonist KD3010, but not the well-validated GW501516, dramatically ameliorates liver injury induced by carbon tetrachloride (CCl4) injections. Deposition of extracellular matrix proteins was lower in the KD3010-treated group than in the vehicle- or GW501516-treated group. Interestingly, profibrogenic connective tissue growth factor was induced significantly by GW501516, but not by KD3010, following CCl4 treatment. The hepatoprotective and antifibrotic effect of KD3010 was confirmed in a model of cholestasis-induced liver injury and fibrosis using bile duct ligation for 3 wk. Primary hepatocytes treated with KD3010 but not GW501516 were protected from starvation or CCl4-induced cell death, in part because of reduced reactive oxygen species production. In conclusion, our data demonstrate that an orally active PPARδ agonist has hepatoprotective and antifibrotic effects in animal models of liver fibrosis, suggesting a possible mechanistic and therapeutic approach in treating patients with chronic liver diseases.