SUMMARY The microbiome is being characterized by large-scale sequencing efforts, yet it is not known whether it regulates host metabolism in a general versus tissue-specific manner or which bacterial metabolites are important. Here, we demonstrate that microbiota have a strong effect on energy homeostasis in the colon compared to other tissues. This tissue specificity is due to colonocytes utilizing bacterially-produced butyrate as their primary energy source. Colonocytes from germfree mice are in an energy-deprived state and exhibit decreased expression of enzymes that catalyze key steps in intermediary metabolism including the TCA cycle. Consequently, there is a marked decrease in NADH/NAD+, oxidative phosphorylation, and ATP levels, which results in AMPK activation, p27kip1 phosphorylation, and autophagy. When butyrate is added to germfree colonocytes, it rescues their deficit in mitochondrial respiration and prevents them from undergoing autophagy. The mechanism is due to butyrate acting as an energy source rather than as an HDAC inhibitor.

SUMMARY Widespread changes in gene expression drive tumorigenesis, yet our knowledge of how aberrant epigenomic and transcriptome profiles arise in cancer cells is poorly understood. Here, we demonstrate that metabolic transformation plays an important role. Butyrate is the primary energy source of normal colonocytes and is metabolized to acetyl-CoA, which was shown to be important not only for energetics but also for HAT activity. Due to the Warburg effect, cancerous colonocytes rely on glucose as their primary energy source so butyrate accumulated and functioned as an HDAC inhibitor. Although both mechanisms increased histone acetylation, different target genes were upregulated. Consequently, butyrate stimulated the proliferation of normal colonocytes and cancerous colonocytes when the Warburg effect was prevented from occurring, whereas it inhibited the proliferation of cancerous colonocytes undergoing the Warburg effect. These findings link a common metabolite to epigenetic mechanisms that are differentially utilized by normal and cancerous cells because of their inherent metabolic differences.

Kidney cancer (or renal cell carcinoma [RCC]) is known as “the internist’s tumor” because it has protean systemic manifestations suggesting it utilizes complex, non-physiologic metabolic pathways. Given the increasing incidence of this cancer and its lack of effective therapeutic targets, we undertook an extensive analysis of human RCC tissue employing combined grade-dependent proteomics and metabolomics analysis to determine how metabolic reprogramming occurring in this disease allows it to escape available therapeutic approaches. After validation experiments in RCC cell lines that were wild-type or mutant for the VHL tumor suppressor, in characterizing higher grade tumors we found that the Warburg effect is relatively more prominent at the expense of the tricarboxylic acid cycle and oxidative metabolism in general. Further, we found that the glutamine metabolism pathway acts to inhibit reactive oxygen species, as evidenced by an upregulated glutathione pathway, while the β-oxidation pathway is inhibited leading to increased fatty acyl-carnitines. In support of findings from previous urine metabolomics analyses, we also documented tryptophan catabolism associated with immune suppression, which was highly represented in RCC compared to other metabolic pathways. Together, our results offer a rationale to evaluate novel anti-metabolic treatment strategies being developed in other disease settings as therapeutic strategies in RCC.

It is controversial whether dietary fiber protects against colorectal cancer because of conflicting results from human epidemiologic studies. However, these studies and mouse models of colorectal cancer have not controlled the composition of gut microbiota, which ferment fiber into short-chain fatty acids such as butyrate. Butyrate is noteworthy because it has energetic and epigenetic functions in colonocytes and tumorsuppressive properties in colorectal-cancer cell lines. We utilized gnotobiotic mouse models colonized with wild-type or mutant strains of a butyrate-producing bacterium to demonstrate that fiber does have a potent tumor-suppressive effect but in a microbiota- and butyrate-dependent manner. Furthermore, due to the Warburg effect, butyrate was metabolized less in tumors where it accumulated and functioned as an HDAC inhibitor to stimulate histone acetylation and affect apoptosis and cell proliferation. To support the relevance of this mechanism in human cancer, we demonstrate that butyrate and histone-acetylation levels are elevated in colorectal adenocarcinomas compared to normal colonic tissues.

Diet and energy metabolism affect gene expression, which influences human health and disease. Here, we discuss the role of epigenetics as a mechanistic link between energy metabolism and control of gene expression. A number of key energy metabolites including SAM, acetyl-CoA, NAD+, and ATP serve as essential co-factors for many, perhaps most, epigenetic enzymes that regulate DNA methylation, posttranslational histone modifications, and nucleosome position. The relative abundance of these energy metabolites allows a cell to sense its energetic state. And as co-factors, energy metabolites act as rheostats to modulate the activity of epigenetic enzymes and upregulate/downregulate transcription as appropriate to maintain homeostasis.

A prodigious number of microbes inhabit the human body, especially in the lumen of the gastrointestinal (GI) tract, yet our knowledge of how they regulate metabolic pathways within our cells is rather limited. To investigate the role of microbiota in host energy metabolism, we analyzed ATP levels and AMPK phosphorylation in tissues isolated from germfree and conventionally-raised C57BL/6 mice. These experiments demonstrated that microbiota are required for energy homeostasis in the proximal colon to a greater extent than other segments of the GI tract that also harbor high densities of bacteria. This tissue-specific effect is consistent with colonocytes utilizing bacterially-produced butyrate as their primary energy source, whereas most other cell types utilize glucose. However, it was surprising that glucose did not compensate for butyrate deficiency. We measured a 3.5-fold increase in glucose uptake in germfree colonocytes. However, 13C-glucose metabolic-flux experiments and biochemical assays demonstrated that they shifted their glucose metabolism away from mitochondrial oxidation/CO2 production and toward increased glycolysis/lactate production, which does not yield enough ATPs to compensate. The mechanism responsible for this metabolic shift is diminished pyruvate dehydrogenase (PDH) levels and activity. Consistent with perturbed PDH function, the addition of butyrate, but not glucose, to germfree colonocytes ex vivo stimulated oxidative metabolism. As a result of this energetic defect, germfree colonocytes exhibited a partial block in the G1-to-S-phase transition that was rescued by a butyrate-fortified diet. These data reveal a mechanism by which microbiota regulate glucose utilization to influence energy homeostasis and cell-cycle progression of mammalian host cells.

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Proinflammatory cytokines impact islet ␤-cell mass and function by altering the transcriptional activity within pancreatic ␤-cells, producing increases in intracellular nitric oxide abundance and the synthesis and secretion of immunomodulatory proteins such as chemokines. Herein, we report that IL-1␤, a major mediator of inflammatory responses associated with diabetes development, coordinately and reciprocally regulates chemokine and insulin secretion. We discovered that NF-B controls the increase in chemokine transcription and secretion as well as the decrease in both insulin secretion and proliferation in response to IL-1␤. Nitric oxide production, which is markedly elevated in pancreatic ␤-cells exposed to IL-1␤, is a negative regulator of both glucose-stimulated insulin secretion and glucose-induced increases in intracellular calcium levels. By contrast, the IL-1␤-mediated production of the chemokines CCL2 and CCL20 was not influenced by either nitric oxide levels or glucose concentration. Instead, the synthesis and secretion of CCL2 and CCL20 in response to IL-1␤ were dependent on NF-B transcriptional activity. We conclude that IL-1␤-induced transcriptional reprogramming via NF-B reciprocally regulates chemokine and insulin secretion while also negatively regulating ␤-cell proliferation. These findings are consistent with NF-B as a major regulatory node controlling inflammation-associated alterations in islet ␤-cell function and mass. chemokine; inflammation; insulin secretion; interleukin-1; nitric oxide THE PROGRESSION TO BOTH TYPE 1 (T1DM) and type 2 diabetes mellitus (T2DM) proceeds via immune cell-associated alterations in islet ␤-cell mass and function. Alterations in islet ␤-cell mass and function are two major determinants controlling the total amount of insulin produced and secreted in response to physiological stimuli (e.g., glucose). Proinflammatory cytokines such as IL-1␤ and IFN␥ contribute significantly to losses in islet ␤-cell viability and insulin secretion. Islet