Minireview: Glucocorticoid-Leptin Crosstalk: Role of Glucocorticoid-Leptin Counterregulation in Metabolic Homeostasis and Normal Development.

Glucocorticoids and leptin are two important hormones that regulate metabolic homeostasis by controlling appetite and energy expenditure in adult mammals. Also, glucocorticoids and leptin strongly counterregulate each other, such that chronic stress-induced glucocorticoids upregulate the production of leptin and leptin suppresses glucocorticoid production directly via action on endocrine organs and indirectly via action on food intake. Altered glucocorticoid or leptin levels during development can impair organ development and increase the risk of chronic diseases in adults, but there are limited studies depicting the significance of glucocorticoid-leptin interaction during development and its impact on developmental programming. In mammals, leptin-induced suppression of glucocorticoid production is critical during development, where leptin prevents stress-induced glucocorticoid production by inducing a period of short-hyporesponsiveness when the adrenal glands fail to respond to certain mild to moderate stressors. Conversely, reduced or absent leptin signaling increases glucocorticoid levels beyond what is appropriate for normal organogenesis. The counterregulatory interactions between leptin and glucocorticoids suggest the potential significant involvement of leptin in disorders that occur from stress during development.

Reduced male fertility of an Antarctic mite following extreme heat stress could prompt localized population declines.

Climate change is leading to substantial global thermal changes, which are particularly pronounced in polar regions. Therefore, it is important to examine the impact of heat stress on the reproduction of polar terrestrial arthropods, specifically, how brief extreme events may alter survival. We observed that sublethal heat stress reduces male fecundity in an Antarctic mite, yielding females that produced fewer viable eggs. Females and males collected from microhabitats with high temperatures showed a similar reduction in fertility. This impact is temporary, as indicated by recovery of male fecundity following return to cooler, stable conditions. The diminished fecundity is likely due to a drastic reduction in the expression of male-associated factors that occur in tandem with a substantial increase in the expression of heat shock proteins. Cross-mating between mites from different sites confirmed that heat-exposed populations have impaired male fertility. However, the negative impacts are transient as the effect on fertility declines with recovery time under less stressful conditions. Modeling indicated that heat stress is likely to reduce population growth and that short bouts of non-lethal heat stress could have substantial reproductive effects on local populations of Antarctic arthropods.

Characterization of a novel corticosterone response gene in Xenopus tropicalis tadpole tails.

Corticosteroids are critical for development and for mediating stress responses across diverse vertebrate taxa. Study of frog metamorphosis has made significant breakthroughs in our understanding of corticosteroid signaling during development in non-mammalian vertebrate species. However, lack of adequate corticosterone (CORT) response genes in tadpoles make identification and quantification of CORT responses challenging. Here, we characterized a CORT-response gene frzb (frizzled related protein) previously identified in Xenopus tropicalis tadpole tail skin by an RNA-seq study. We validated the RNA-seq results that CORT and not thyroid hormone induces frzb in the tails using quantitative PCR. Further, maximum frzb expression was achieved by 100-250 nM CORT within 12-24 hours. frzb is not significantly induced in the liver and brain in response to 100 nM CORT. We also found no change in frzb expression across natural metamorphosis when endogenous CORT levels peak. Surprisingly, frzb is only induced by CORT in X. tropicalis tails and not in Xenopus laevis tails. The exact downstream function of increased frzb expression in tails in response to CORT is not known, but the specificity of hormone response and its high mRNA expression levels in the tail render frzb a useful marker of exogenous CORT-response independent of thyroid hormone for exogenous hormone treatments and in-vivo endocrine disruption studies.

Development and metamorphosis in frogs deficient in the thyroid hormone transporter MCT8.

Precisely regulated thyroid hormone (TH) signaling within tissues during frog metamorphosis gives rise to the organism-wide coordination of developmental events among organs required for survival. This TH signaling is controlled by multiple cellular mechanisms, including TH transport across the plasma membrane. A highly specific TH transporter has been identified, namely monocarboxylate transporter 8 (MCT8), which facilitates uptake and efflux of TH and is differentially and dynamically expressed among tissues during metamorphosis. We hypothesized that loss of MCT8 would alter tissue sensitivity to TH and affect the timing of tissue transformation. To address this, we used CRISPR/Cas9 to introduce frameshift mutations inslc16a2, the gene encoding MCT8, inXenopus laevis. We produced homozygous mutant tadpoles with a 29-bp mutation in the l-chromosome and a 20-bp mutation in the S-chromosome. We found that MCT8 mutants survive metamorphosis with normal growth and development of external morphology throughout the larval period. Consistent with this result, the expression of the pituitary hormone regulating TH plasma levels (tshb) was similar among genotypes as was TH response gene expression in brain at metamorphic climax. Further, delayed initiation of limb outgrowth during natural metamorphosis and reduced hindlimb and tail TH sensitivity were not observed in MCT8 mutants. In sum, we did not observe an effect on TH-dependent development in MCT8 mutants, suggesting compensatory TH transport occurs in tadpole tissues, as seen in most tissues in all model organisms examined.

cyp21a2 Knockout Tadpoles Survive Metamorphosis Despite Low Corticosterone.

Corticosteroids are so vital for organ maturation that reduced corticosteroid signaling during postembryonic development causes death in terrestrial vertebrates. Indeed, death occurs at metamorphosis in frogs lacking proopiomelanocortin (pomc) or the glucocorticoid receptor (GR; nr3c1). Some residual corticosteroids exist in pomc mutants to activate the wild-type (WT) GR and mineralocorticoid receptor (MR), and the elevated corticosteroids in GR mutants may activate MR. Thus, we expected a more severe developmental phenotype in tadpoles with inactivation of 21-hydroxylase, which should eliminate all interrenal corticosteroid biosynthesis. Using CRISPR/Cas9 in Xenopus tropicalis, we produced an 11-base pair deletion in cyp21a2, the gene encoding 21-hydroxylase. Growth and development were delayed in cyp21a2 mutant tadpoles, but unlike the other frog models, they survived metamorphosis. Consistent with an absence of 21-hydroxylase, mutant tadpoles had a 95% reduction of aldosterone in tail tissue, but they retained some corticosterone (∼40% of WT siblings), an amount, however, too low for survival in pomc mutants. Decreased corticosteroid signaling was evidenced by reduced expression of corticosteroid-response gene, klf9, and by impaired negative feedback in the hypothalamus-pituitary-interrenal axis with higher messenger RNA expression levels of crh, pomc, star, and cyp11b2 and an approximately 30-fold increase in tail content of progesterone. In vitro tail-tip culture showed that progesterone can transactivate the frog GR. The inadequate activation of GR by corticosterone in cyp21a2 mutants was likely compensated for by sufficient corticosteroid signaling from other GR ligands to allow survival through the developmental transition from aquatic to terrestrial life.

Targeting the succinate receptor effectively inhibits periodontitis.

Periodontal disease (PD) is one of the most common inflammatory diseases in humans and is initiated by an oral microbial dysbiosis that stimulates inflammation and bone loss. Here, we report an abnormal elevation of succinate in the subgingival plaque of subjects with severe PD. Succinate activates succinate receptor-1 (SUCNR1) and stimulates inflammation. We detected SUCNR1 expression in the human and mouse periodontium and hypothesize that succinate activates SUCNR1 to accelerate periodontitis through the inflammatory response. Administration of exogenous succinate enhanced periodontal disease, whereas SUCNR1 knockout mice were protected from inflammation, oral dysbiosis, and subsequent periodontal bone loss in two different models of periodontitis. Therapeutic studies demonstrated that a SUCNR1 antagonist inhibited inflammatory events and osteoclastogenesis in vitro and reduced periodontal bone loss in vivo. Our study reveals succinate's effect on periodontitis pathogenesis and provides a topical treatment for this disease.

Impaired negative feedback and death following acute stress in glucocorticoid receptor knockout Xenopus tropicalis tadpoles.

Blood glucocorticoid levels are regulated by the hypothalamo-pituitary-adrenal/interrenal axis (HPA axis in mammals, HPI axis in amphibians), and negative feedback by glucocorticoid signaling is a key player in that regulation. Glucocorticoid and mineralocorticoid receptors (GR and MR) mediate negative feedback in mammals, but little is known about nuclear receptor-mediated feedback in amphibians. Because amphibians have only one corticosteroidogenic cell type responsible for glucocorticoid and mineralocorticoid production, we hypothesized that GR knockout (GRKO) tadpoles have elevated levels of glucocorticoids and mineralocorticoids as well as axis components regulating their production. We also examined the response to stress and potential for increased aldosterone signaling in GRKO tadpoles. We found that GRKO tadpoles have severe hyperactivity of the HPI axis, namely high mRNA expression levels of pomc, cyp17a1, cyp21a2, cyp11b2, and star, and high tissue content of corticosterone, aldosterone, 17-hydroxyprogesterone, 21-deoxycortisol, and progesterone. Such aberrant HPI activity was accompanied by reduced survival after acute temperature shock and shaking stress. Like mammalian models of HPA hyperactivity, GRKO tadpoles have high MR mRNA expression levels in brain, kidney, heart, and skin and high levels of the inflammatory cytokine tnf-α and the profibrotic factor tgf-ß in kidneys. This study showed GR is critical for negative feedback to the amphibian HPI axis and for survival from acute stressors. This study also showed GRKO tadpoles exhibit altered expression/overproduction of regulators of salt-water homeostasis and associated biomarkers of kidney disease.

Thyroid and Corticosteroid Signaling in Amphibian Metamorphosis.

In multicellular organisms, development is based in part on the integration of communication systems. Two neuroendocrine axes, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-adrenal/interrenal axes, are central players in orchestrating body morphogenesis. In all vertebrates, the hypothalamic-pituitary-thyroid axis controls thyroid hormone production and release, whereas the hypothalamic-pituitary-adrenal/interrenal axis regulates the production and release of corticosteroids. One of the most salient effects of thyroid hormones and corticosteroids in post-embryonic developmental processes is their critical role in metamorphosis in anuran amphibians. Metamorphosis involves modifications to the morphological and biochemical characteristics of all larval tissues to enable the transition from one life stage to the next life stage that coincides with an ecological niche switch. This transition in amphibians is an example of a widespread phenomenon among vertebrates, where thyroid hormones and corticosteroids coordinate a post-embryonic developmental transition. The review addresses the functions and interactions of thyroid hormone and corticosteroid signaling in amphibian development (metamorphosis) as well as the developmental roles of these two pathways in vertebrate evolution.

Intrahepatic microbes govern liver immunity by programming NKT cells.

The gut microbiome shapes local and systemic immunity. The liver is presumed to be a protected sterile site. As such, a hepatic microbiome has not been examined. Here, we showed a liver microbiome in mice and humans that is distinct from that of the gut and is enriched in Proteobacteria. It undergoes dynamic alterations with age and is influenced by the environment and host physiology. Fecal microbial transfer experiments revealed that the liver microbiome is populated from the gut in a highly selective manner. Hepatic immunity is dependent on the microbiome, specifically the bacteroidetes species. Targeting bacteroidetes with oral antibiotics reduced hepatic immune cells by approximately 90%, prevented antigen-presenting cell (APC) maturation, and mitigated adaptive immunity. Mechanistically, our findings are consistent with presentation of bacteroidetes-derived glycosphingolipids to NKT cells promoting CCL5 signaling, which drives hepatic leukocyte expansion and activation, among other possible host-microbe interactions. Collectively, we reveal a microbial/glycosphingolipid/NKT/CCL5 axis that underlies hepatic immunity.

Microbial population shift and metabolic characterization of silver diamine fluoride treatment failure on dental caries.

The objective of this pilot study was to describe the microbial profiles present in the plaque and saliva of children who continued to develop new carious lesions following treatment with silver diamine fluoride ("nonresponders") compared to caries active, caries-free, and children immediately receiving SDF treatment for untreated caries in order to identify potential microbial differences that may relate to a re-incidence of caries. Saliva and plaque samples from infected and contralateral sites were obtained from twenty children who were either caries free, had active carious lesions, were caries active and received SDF treatment immediately before sampling, or had previously received SDF treatment and developed new caries. In total, 8,057,899 Illumina-generated sequence reads from 60 samples were obtained. Reads were processed using the Quantitative Insights Into Microbial Ecology pipeline. Group differences were assessed using Analysis of Variance Models and Tukey Honest Significant Differences. To identify significant taxa between treatment groups, Linear discriminant analysis Effect Size (LefSe) and Analysis of Differential Abundance Taking Sample Variation Into Account were used. Differential abundant analysis indicated that members of the Lachnospiraceae family were significantly enriched in non-responders and the genus Tannerella and species Granulicatella adiances were also highly abundant in this group. LefSe analysis between non-responders and SDF-treated groups revealed that genera Leptotrichia and Granulicatella were enriched in non-responders. We observed the highest abundance of phosphotransferase system and lowest abundance of lipopolysaccharide synthesis in non-responders. The microbiome in dental biofilms is responsible for initiation and progression of dental caries. SDF has been shown to be effective in arresting the progression carious lesions, in part due to its antimicrobial properties. Findings suggest that the differential abundance of select microbiota and specific pathway functioning in individuals that present with recurrent decay after SDF treatment may contribute to a potential failure of silver diamine fluoride to arrest dental caries. However, the short duration of sample collection following SDF application and the small sample size emphasize the need for further data and additional analysis.

Predicting Treatment Nonresponse in Hispanic/Latino Children Receiving Silver Diamine Fluoride for Caries Arrest: A Pilot Study Using Machine Learning.

Objectives: Silver diamine fluoride (SDF) is a nonsurgical therapy for the arrest and prevention of dental caries with demonstrated clinical efficacy. Approximately 20% of children receiving SDF fail to respond to treatment. The objective of this study was to develop a predictive model of treatment non-response using machine learning. Methods: An observational pilot study (N = 20) consisting of children with and without active decay and who did and did not respond to silver diamine fluoride provided salivary samples and plaque from infected and contralateral sites. 16S rRNA genes from samples were amplified and sequenced on an Illumina Miseq and analyzed using QIIME. The association between operational taxonomic units and treatment non-response was assessed using lasso regression and artificial neural networks. Results: Bivariate group comparisons of bacterial abundance indicate a number of genera were significantly different between non-responders and those who responded to SDF therapy. No differences were found between non-responders and caries-active subjects. Prevotella pallens and Veillonella denticariosi were retained in full lasso models and combined with clinical variables in a six-input multilayer perceptron. Discussion: The acidogenic and acid-tolerant nature of retained bacterial species may overcome the antimicrobial effects of SDF. Further research to validate the model in larger external samples is needed.

Comparative Effects of E-Cigarette Aerosol on Periodontium of Periodontitis Patients.

Introduction: Tobacco use is one of the main causes of periodontitis. E-cigarette are gaining in popularity, and studies are needed to better understand the impact of e-cigarettes on oral health. Objective: To perform a longitudinal study to evaluate the adverse effects of e-cigarettes on periodontal health. Methods: Naïve E-cigarette users, cigarette smokers, and non-smokers were recruited using newspaper and social media. Age, gender, and ethnicity, were recorded. Participants were scheduled for two visits 6 months apart. At each visit, we collected data on the frequency and magnitude of e-cigarette and cigarette use, and alcohol consumption. Carbon monoxide (CO) levels, cotinine levels, salivary flow rate, periodontal probing depth (PD), bleeding on probing (BoP), and clinical attachment loss (CAL) were also determined at both baseline and follow-up visits and compared between groups with two-way repeated measures ANOVA. Periodontal diagnosis and other categorical variables were compared between groups with the chi-square statistic and logistic regression. Results: We screened 159 subjects and recruited 119 subjects. One-hundred-one subjects (31 cigarette smokers, 32 e-cigarette smokers, and 38 non-smokers) completed every assessment in both visits. The retention and compliance rate of subjects was 84.9%. The use of social media and craigslist was significant in recruiting e-cigarette subjects. Ethnicity and race differed between groups, as did average age in the male subjects. Carbon monoxide and salivary cotinine levels were highest among cigarette smokers. Bleeding on probing and average PDs similarly increased over time in all three groups, but CAL uniquely increased in e-cigarette smokers. Rates of severe periodontal disease were higher in cigarette smokers and e-cigarette users than non-smokers, but interpretation is confounded by the older age of the cigarette smokers. Conclusion: Among the recruited participants, CAL after 6 months was significantly worse only in the e-cigarette smokers. This study design and protocol will assist in future larger studies on e-cigarette and oral health.

The Influences of Bioinformatics Tools and Reference Databases in Analyzing the Human Oral Microbial Community.

There is currently no criterion to select appropriate bioinformatics tools and reference databases for analysis of 16S rRNA amplicon data in the human oral microbiome. Our study aims to determine the influence of multiple tools and reference databases on α-diversity measurements and ß-diversity comparisons analyzing the human oral microbiome. We compared the results of taxonomical classification by Greengenes, the Human Oral Microbiome Database (HOMD), National Center for Biotechnology Information (NCBI) 16S, SILVA, and the Ribosomal Database Project (RDP) using Quantitative Insights Into Microbial Ecology (QIIME) and the Divisive Amplicon Denoising Algorithm (DADA2). There were 15 phyla present in all of the analyses, four phyla exclusive to certain databases, and different numbers of genera were identified in each database. Common genera found in the oral microbiome, such as Veillonella, Rothia, and Prevotella, are annotated by all databases; however, less common genera, such as Bulleidia and Paludibacter, are only annotated by large databases, such as Greengenes. Our results indicate that using different reference databases in 16S rRNA amplicon data analysis could lead to different taxonomic compositions, especially at genus level. There are a variety of databases available, but there are no defined criteria for data curation and validation of annotations, which can affect the accuracy and reproducibility of results, making it difficult to compare data across studies.

Electronic Cigarette Aerosol Modulates the Oral Microbiome and Increases Risk of Infection.

The trend of e-cigarette use among teens is ever increasing. Here we show the dysbiotic oral microbial ecology in e-cigarette users influencing the local host immune environment compared with non-smoker controls and cigarette smokers. Using 16S rRNA high-throughput sequencing, we evaluated 119 human participants, 40 in each of the three cohorts, and found significantly altered beta-diversity in e-cigarette users (p = 0.006) when compared with never smokers or tobacco cigarette smokers. The abundance of Porphyromonas and Veillonella (p = 0.008) was higher among vapers. Interleukin (IL)-6 and IL-1ß were highly elevated in e-cigarette users when compared with non-users. Epithelial cell-exposed e-cigarette aerosols were more susceptible for infection. In vitro infection model of premalignant Leuk-1 and malignant cell lines exposed to e-cigarette aerosol and challenged by Porphyromonas gingivalis and Fusobacterium nucleatum resulted in elevated inflammatory response. Our findings for the first time demonstrate that e-cigarette users are more prone to infection.

Targeting cellular metabolism to reduce head and neck cancer growth.

Head and neck squamous cell carcinoma (HNSCC) presents a major public health concern because of delayed diagnosis and poor prognosis. Malignant cells often reprogram their metabolism in order to promote their survival and proliferation. Aberrant glutaminase 1 (GLS1) expression enables malignant cells to undergo increased glutaminolysis and utilization of glutamine as an alternative nutrient. In this study, we found a significantly elevated GLS1 expression in HNSCC, and patients with high expression levels of GLS1 experienced shorter disease-free periods after therapy. We hypothesized that the GLS1 selective inhibitor, bis-2-(5-phenylacetamido-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES), which curtails cells' glutamine consumption, may inhibit HNSCC cell growth. Our results support the idea that BPTES inhibits HNSCC growth by inducing apoptosis and cell cycle arrest. Considering that metformin can reduce glucose consumption, we speculated that metformin would enhance the anti-neoplasia effect of BPTES by suppressing malignant cells' glucose utilization. The combination of both compounds exhibited an additive inhibitory effect on cancer cell survival and proliferation. All of our data suggest that GLS1 is a promising therapeutic target for HNSCC treatment. Combining BPTES with metformin might achieve improved anti-cancer effects in HNSSC, which sheds light on using novel therapeutic strategies by dually targeting cellular metabolism.

The Effects of Combinatorial Genistein and Sulforaphane in Breast Tumor Inhibition: Role in Epigenetic Regulation.

Dietary compounds that possess the properties of altering epigenetic processes are gaining popularity as targets for cancer prevention studies. These compounds when administered at optimal concentrations and especially in combination can have enhanced effects in cancer prevention or therapy. It is important to study the interaction of two or more compounds in order to assess their role in enhancing prevention. Genistein (GEN), found in soy, has been extensively studied for its role as an epigenetic modifier especially as a DNA methyltransferase (DNMT) inhibitor and sulforaphane (SFN), found in cruciferous vegetables, is known as a histone deacetylase (HDAC) inhibitor. However, very little is known about the effects of these two compounds in conjunction in breast cancer prevention or therapy. In our current study, we determined that, at certain doses, the compounds have synergistic effects in decreasing cellular viability of breast cancer cell lines. Our results indicate that the combination of GEN and SFN is much more effective than their single doses in increasing the rate of apoptosis and lowering the colony forming potential of these cells. We determined that these compounds inhibit cell cycle progression to G2 phase in MDA-MB-231 and G1 phase in MCF-7 breast cancer cell lines. Additionally, we determined that the combination is effective as an HDAC and histone methyltransferase (HMT) inhibitor. Furthermore, we demonstrated that this combination downregulates the levels of HDAC2 and HDAC3 both at the mRNA and protein levels. We also found that these compounds have the potential to downregulate KLF4 levels, which plays an important role in stem cell formation. The combination of GEN and SFN is also effective in downregulating hTERT levels, which is known to be activated when KLF4 binds to its promoter region. Our hypothesis is further strengthened by in vivo studies, where the combination is administered to transgenic mice in the form of genistein and SFN-enriched broccoli sprouts. We have demonstrated that the combination is more effective in preventing or treating mammary cancer via extending tumor latency and reducing tumor volumes/sizes than either of these dietary components administered alone. These results are consistent with our in vitro study suggesting potential preventive and therapeutic effects of this novel dietary combinatorial approach against breast cancer.

Withaferin A and sulforaphane regulate breast cancer cell cycle progression through epigenetic mechanisms.

Little is known about the effects of combinatorial dietary compounds on the regulation of epigenetic mechanisms involved in breast cancer prevention. The human diet consists of a multitude of components, and there is a need to elucidate how certain compounds interact in collaboration. Withaferin A (WA), found in the Indian winter cherry and documented as a DNA methyltransferase (DNMT) inhibitor, and sulforaphane (SFN), a well-known histone deacetylase (HDAC) inhibitor found in cruciferous vegetables, are two epigenetic modifying compounds that have only recently been studied in conjunction. The use of DNMT and HDAC inhibitors to reverse the malignant expression of certain genes in breast cancer has shown considerable promise. Previously, we found that SFN + WA synergistically promote breast cancer cell death. Herein, we determined that these compounds inhibit cell cycle progression from S to G2 phase in MDA-MB-231 and MCF-7 breast cancer. Furthermore, we demonstrate that this unique combination of epigenetic modifying compounds down-regulates the levels of Cyclin D1 and CDK4, and pRB; conversely, the levels of E2F mRNA and tumor suppressor p21 are increased independently of p53. We find these events coincide with an increase in unrestricted histone methylation. We propose SFN + WA-induced breast cancer cell death is attributed, in part, to epigenetic modifications that result in the modulated expression of key genes responsible for the regulation of cancer cell senescence.

Impact of genistein on the gut microbiome of humanized mice and its role in breast tumor inhibition.

Since dietary polyphenols can have beneficial effects in prevention and treatment of cancer, we tested the hypothesis that breast cancer patients' intestinal microbiota is modulated by genistein (GE), an isoflavone found in soy, and that microbial alterations may offset the side effects brought about by chemotherapy. We demonstrated successful humanization of germ-free mice by transplanting fecal samples from breast cancer patients before and after chemotherapy. Mice were then grouped based on chemotherapy status and GE or control diet. We did not find any significant differences between pre-chemotherapy and post-chemotherapy bacterial composition and abundances. Germ-free mice on a GE diet showed differences in microbial composition as compared to mice on control diet. Four weeks after introduction of the customized GE diet, there was distinct clustering of GE-fed mice as compared to the control-fed group. In the gut microbiome of GE-treated humanized mice, there was an increase in abundance of genera Lactococcus and Eubacterium. Phylum Verrucomicrobia showed statistically significant (p = 0.02) differences in abundances between the GE-fed and control-fed groups. There was an increase in bacteria belonging to family Lachnospiraceae and Ruminococcaceae in GE-fed mice. Marked changes were observed in GE catabolism in mice humanized with fecal material from two of three patients' post-chemotherapy with complete disappearance of 4-ethylphenol and 2-(4-hydroxyphenol) propionic acid conjugates. The post-tumor samples did not show any distinct clustering of the gut microbiota between the two diet groups. There was an increase in latency of about 25% for tumor growth of the humanized mice that were on a GE diet as compared to humanized mice on a control diet. The average tumor size for the GE group was significantly decreased compared to the non-GE group. Collectively, our results suggest that the intestinal microbiota becomes altered with a GE diet before induction of tumor. Our findings indicate that GE modulates the microbiome in humanized mice that may contribute to its effects on increasing the latency of breast tumor and reducing tumor growth.

Influences of diet and the gut microbiome on epigenetic modulation in cancer and other diseases.

Epigenetic modulation of gene activity occurs in response to non-genetic factors such as body weight status, physical activity, dietary factors, and environmental toxins. In addition, each of these factors is thought to affect and be affected by the gut microbiome. A primary mechanism that links these various factors together in mediating control of gene expression is the production of metabolites that serve as critical cofactors and allosteric regulators of epigenetic processes. Here, we review the involvement of the gut microbiota and its interactions with dietary factors, many of which have known cellular bioactivity, focusing on particular epigenetic processes affected and the influence they have on human health and disease, particularly cancer and response to treatment. Advances in DNA sequencing have expanded the capacity for studying the microbiome. Combining this with rapidly improving techniques to measure the metabolome provides opportunities to understand complex relationships that may underlie the development and progression of cancer as well as treatment-related sequelae. Given broad reaching and fundamental biology, both at the cellular and organismal levels, we propose that interactive research programs, which utilize a wide range of mutually informative experimental model systems-each one optimally suited for answering particular questions-provide the best path forward for breaking ground on new knowledge and ultimately understanding the epigenetic significance of the gut microbiome and its response to dietary factors in cancer prevention and therapy.