Fructose consumption has risen dramatically in recent decades due to use of sucrose and high fructose corn syrup in beverages and processed foods 1 , contributing to rising rates of obesity and non-alcoholic fatty liver disease (NAFLD) 2 – 4 . Fructose intake triggers hepatic de novo lipogenesis (DNL) 4 – 6 , which is initiated from acetyl-CoA. ATP-citrate lyase (ACLY) cleaves cytosolic citrate to generate acetyl-CoA and is upregulated upon carbohydrate consumption 7 . Ongoing clinical trials are pursuing ACLY inhibition for treatment of metabolic diseases 8 . Nevertheless, the route from dietary fructose to hepatic acetyl-CoA and lipids remains unproven. Here we show, using in vivo isotope tracing, that liver-specific deletion of Acly fails to suppress fructose-induced DNL in mice. Dietary fructose is converted by the gut microbiome into acetate 9 , which supplies lipogenic acetyl-CoA independently of ACLY 10 . Depletion of the microbiome or silencing of hepatic ACSS2, which generates acetyl-CoA from acetate, potently suppresses conversion of a fructose bolus into hepatic acetyl-CoA and fatty acids, bypassing ACLY. When fructose is consumed more gradually to facilitate its absorption in the small intestine, both citrate cleavage and microbial acetate contribute to lipogenesis. The DNL transcriptional program, on the other hand, is activated in response to fructose in a manner independent of acetyl-CoA metabolism. These data reveal a two-pronged mechanism regulating hepatic DNL, in which fructolysis within hepatocytes provides a signal to promote DNL gene expression, while microbial acetate generation feeds lipogenic acetyl-CoA pools.

It is becoming clear that the manner by which the immune response resolves or contains infection by a pathogen varies according to the tissue that is affected. Unlike many peripheral cell types, CNS neurons are generally non-renewable. Thus, the cytolytic and inflammatory strategies that are effective in controlling infections in the periphery could be damaging if deployed in the CNS. Perhaps for this reason, the immune response to some CNS viral infections favours maintenance of neuronal integrity and non-neurolytic viral control. This modified immune response — when combined with the unique anatomy and physiology of the CNS — provides an ideal environment for the maintenance of viral genomes, including those of RNA viruses. Therefore, it is possible that such viruses can reactivate long after initial viral exposure, contributing to CNS disease.

Acetyl-CoA is a vitally important and versatile metabolite used for many cellular processes including fatty acid synthesis, ATP production, and protein acetylation. Recent studies have shown that cancer cells upregulate acetyl-CoA synthetase 2 (ACSS2), an enzyme that converts acetate to acetyl-CoA, in response to stresses such as low nutrient availability and hypoxia. Stressed cancer cells use ACSS2 as a means to exploit acetate as an alternative nutrient source. Genetic depletion of ACSS2 in tumors inhibits the growth of a wide variety of cancers. However, there are no studies on the use of an ACSS2 inhibitor to block tumor growth. In this study, we synthesized a small-molecule inhibitor that acts as a transition-state mimetic to block ACSS2 activity in vitro and in vivo. Pharmacologic inhibition of ACSS2 as a single agent impaired breast tumor growth. Collectively, our findings suggest that targeting ACSS2 may be an effective therapeutic approach for the treatment of patients with breast cancer. Significance: These findings suggest that targeting acetate metabolism through ACSS2 inhibitors has the potential to safely and effectively treat a wide range of patients with cancer.

BACKGROUND: Recent studies have suggested that fatty acid oxidation (FAO) is a key metabolic pathway for the growth of triple negative breast cancers (TNBCs), particularly those that have high expression of MYC. However, the underlying mechanism by which MYC promotes FAO remains poorly understood. METHODS: We used a combination of metabolomics, transcriptomics, bioinformatics, and microscopy to elucidate a potential mechanism by which MYC regulates FAO in TNBC. RESULTS: We propose that MYC induces a multigenic program that involves changes in intracellular calcium signalling and fatty acid metabolism. We determined key roles for fatty acid transporters (CD36), lipases (LPL), and kinases (PDGFRB, CAMKK2, and AMPK) that each contribute to promoting FAO in human mammary epithelial cells that express oncogenic levels of MYC. Bioinformatic analysis further showed that this multigenic program is highly expressed and predicts poor survival in the claudin-low molecular subtype of TNBC, but not other subtypes of TNBCs, suggesting that efforts to target FAO in the clinic may best serve claudin-low TNBC patients. CONCLUSION: We identified critical pieces of the FAO machinery that have the potential to be targeted for improved treatment of patients with TNBC, especially the claudin-low molecular subtype.

Sodium 4-phenylbutyrate (4PBA) improves the intracellular trafficking of ⌬F508-CFTR in cystic fibrosis (CF) epithelial cells. The underlying mechanism is uncertain, but 4PBA modulates the expression of some cytosolic molecular chaperones. To identify other 4PBA-regulated proteins that might regulate ⌬F508-CFTR trafficking, we performed a differential display RT-PCR screen on IB3-1 CF bronchiolar epithelial cells exposed to 4PBA. One transcript up-regulated by 4PBA encoded ERp29, a luminal resident of the endoplasmic reticulum (ER) thought to be a novel molecular chaperone. We tested the hypothesis that ERp29 is a 4PBA-regulated ER chaperone that influences ⌬F508-CFTR trafficking. ERp29 mRNA and protein expression was significantly increased (ϳ1.5-fold) in 4PBA-treated IB3-1 cells. In Xenopus oocytes, ERp29 overexpression increased the functional expression of both wild-type and ⌬F508-CFTR over 3-fold and increased wild-type cystic fibrosis transmembrane conductance regulator (CFTR) plasma membrane expression. In CFBE41o؊ WT-CFTR cells, expression of and short circuit currents mediated by CFTR decreased upon depletion of ERp29 as did maturation of newly synthesized CFTR. In IB3-1 cells, ⌬F508-CFTR co-immunoprecipitated with endogenous ERp29, and overexpression of ERp29 led to increased ⌬F508-CFTR expression at the plasma membrane. These data suggest that ERp29 is a 4PBA-regulated ER chaperone that regulates WT-CFTR biogenesis and can promote ⌬F508-CFTR trafficking in CF epithelial cells.

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Genomic material from many neurotropic RNA viruses (e.g., measles virus [MV], West Nile virus [WNV], Sindbis virus [SV], rabies virus [RV], and influenza A virus [IAV]) remains detectable in the mouse brain parenchyma long after resolution of the acute infection. The presence of these RNAs in the absence of overt central nervous system (CNS) disease has led to the suggestion that they are viral remnants, with little or no potential to reactivate. Here we show that MV RNA remains detectable in permissive mouse neurons long after challenge with MV and, moreover, that immunosuppression can cause RNA and protein synthesis to rebound, triggering neuropathogenesis months after acute viral control. Robust recrudescence of viral transcription and protein synthesis occurs after experimental depletion of cells of the adaptive immune response and is associated with a loss of T resident memory (Trm) lymphocytes within the brain. The disease associated with loss of immune control is distinct from that seen during the acute infection: immune cell-depleted, long-term-infected mice display severe gait and motor problems, in contrast to the wasting and lethal disease that occur during acute infection of immunodeficient hosts. These results illuminate the potential consequences of noncytolytic, immune-mediated viral control in the CNS and demonstrate that what were once considered “resolved” RNA viral infections may, in fact, induce diseases later in life that are distinct from those caused by acute infection. IMPORTANCE Viral infections of neurons are often not cytopathic; thus, once-infected neurons survive, and viral RNAs can be detected long after apparent viral control. These RNAs are generally considered viral fossils, unlikely to contribute to central nervous system (CNS) disease. Using a mouse model of measles virus (MV) neuronal infection, we show that MV RNA is maintained in the CNS of infected mice long after acute control and in the absence of overt disease. Viral replication is suppressed by the adaptive immune response; when these immune cells are depleted, viral protein synthesis recurs, inducing a CNS disease that is distinct from that observed during acute infection. The studies presented here provide the basis for understanding how persistent RNA infections in the CNS are controlled by the host immune response, as well as the pathogenic consequences of noncytolytic viral control.

In permissive mouse central nervous system (CNS) neurons, measles virus (MV) spreads in the absence of hallmark viral budding or neuronal death, with transmission occurring efficiently and exclusively via the synapse. MV infection also initiates a robust type I interferon (IFN) response, resulting in the synthesis of a large number of genes, including bone marrow stromal antigen 2 (Bst2)/tetherin/CD317. Bst2 restricts the release of some enveloped viruses, but to date, its role in viral infection of neurons has not been assessed. Consequently, we investigated how Bst2 was induced and what role it played in MV neuronal infection. The magnitude of induction of neuronal Bst2 RNA and protein following IFN exposure and viral infection was notably higher than in similarly treated mouse embryo fibroblasts (MEFs). Bst2 synthesis was both IFN and Stat1 dependent. Although Bst2 prevented MV release from nonneuronal cells, its deletion had no effect on viral pathogenesis in MV-challenged mice. Our findings underscore how cell-type-specific differences impact viral infection and pathogenesis. IMPORTANCE Viral infections of the central nervous system can lead to debilitating disease and death. Moreover, it is becoming increasingly clear that nonrenewable cells, including most central nervous system neurons, combat neurotropic viral infections in fundamen-tally different ways than other rapidly dividing and renewable cell populations. Here we identify type I interferon signaling as a key inducer of a known antiviral protein (Bst2) in neurons. Unexpectedly, the gene is dispensable for clearance of neurotropic viral infection despite its well-defined contribution to limiting the spread of enveloped viruses in proliferating cells. A deeper appreciation of the importance of cell type heterogeneity in antiviral immunity will aid in the identification of unique therapeutic targets for life-threatening viral infections. Many of the foundational principles in immunology have resulted from basic observations of virus-cell interactions, including the induction and antiviral function of both type I and type II interferons (IFNs) (reviewed in references 1, 2, and 3). Viral infection of a cell typically results in cellular production and secretion of type I IFNs, which can then bind to cell surface receptors in a paracrine and autocrine fashion, leading to synthesis of interferon-stimulated genes (ISGs). These ISGs, in turn, aid in clearing the viral infection by directly cleaving viral nucleic acids, triggering cellular apoptosis, inducing autophagy, upregulating major histocompatibility complex (MHC) class I expression to aid in CD8 ϩ T cell-mediated cytotoxicity, and preventing viral egress. Moreover, the induction of type I IFN contributes to the recruitment of adaptive immune effectors to infected sites, which further promotes viral clearance.One ISG that is highly induced following infection by many viruses, and in response to both type I and II IFN signaling, is the gene for bone marrow stromal antigen 2 (Bst2; also known a...