High-fat diet enhances stemness and tumorigenicity of intestinal progenitors

Biological Mechanisms for the Effect of Obesity on Cancer Risk: Experimental Evidence

Multiple epidemiological studies demonstrated that overweight and obesity significantly increase the risk of several types of cancer. As the prevalence of obesity is dramatically rising, it is expected that it will represent one of the major lifestyle-associated risk factors for cancer development in the near future. Numerous recent studies expanded knowledge about key players and pathways, which are deregulated in the obese state and potentially promote cancer initiation, progression and aggressiveness via remote and local effects. These players include (but are not limited to) insulin/IGF, adipokines and inflammatory signaling molecules as well as metabolites. Nevertheless, the detailed mechanisms linking obesity and malignant transformation at the systemic, cellular and molecular level still demand further investigation. Additionally, dysfunctional molecular metabolic pathways appear to be specific for distinct cancer entities, thereby yet precluding definition of a common principle. This chapter will present an overview of the current knowledge of molecular nodes linking obesity and cancer and will briefly touch upon potential therapy options addressing metabolic cancer etiologies.

Pigs, Unlike Mice, Have Two Distinct Colonic Stem Cell Populations Similar to Humans That Respond to High-Calorie Diet prior to Insulin Resistance

Basal colonic crypt stem cells are long lived and play a role in colon homeostasis. Previous evidence has shown that high-calorie diet (HCD) enhances colonic stem cell numbers and expansion of the proliferative zone, an important biomarker for colon cancer. However, it is not clear how HCD drives dysregulation of colon stem cell/colonocyte proliferative kinetics. We used a human-relevant pig model and developed an immunofluorescence technique to detect and quantify colonic stem cells. Pigs (n = 8/group) were provided either standard diet (SD; 5% fat) or HCD (23% fat) for 13 weeks. HCD- and SD-consuming pigs had similar total calorie intake, serum iron, insulin, and glucose levels. However, HCD elevated both colonic proliferative zone (KI-67) and stem cell zone (ASCL-2 and BMI-1). Proliferative zone correlated with elevated innate colonic inflammatory markers TLR-4, NF-κB, IL6, and lipocalin-2 (r ≥ 0.62, P = 0.02). Elevated gut bacterial phyla proteobacteria and firmicutes in HCD-consuming pigs correlated with proliferative and stem cell zone. Colonic proteome data revealed the upregulation of proteins involved in cell migration and proliferation and correlated with proliferative and stem cell zone expansion. Our study suggests that pig colon, unlike mice, has two distinct stem cells (ASCL-2 and BMI-1) similar to humans, and HCD increases expansion of colonic proliferative and stem cell zone. Thus, pig model can aid in the development of preventive strategies against gut bacterial dysbiosis and inflammation-promoted diseases, such as colon cancer. Cancer Prev Res; 10(8); 442-50. ©2017 AACR.

Apc inactivation, but not obesity, synergizes with Pten deficiency to drive intestinal stem cell-derived tumorigenesis

Obesity is a major risk factor for colorectal cancer and can accelerate Lgr5+ intestinal stem cell (ISC)-derived tumorigenesis after the inactivation of Apc However, whether non-canonical pathways involving PI3K-Akt signaling in ISCs can lead to tumor formation, and if this can be further exacerbated by obesity is unknown. Despite the synergy between Pten and Apc inactivation in epithelial cells on intestinal tumor formation, their combined role in Lgr5+-ISCs, which are the most rapidly dividing ISC population in the intestine, is unknown. Lgr5+-GFP mice were provided low-fat diet (LFD) or high-fat diet (HFD) for 8 months, and the transcriptome was evaluated in Lgr5+-ISCs. For tumor studies, Lgr5+-GFP and Lgr5+-GFP-Pten^flox/flox mice were tamoxifen treated to inactivate Pten in ISCs and provided LFD or HFD until 14-15 months of age. Finally, various combinations of Lgr5+-ISC-specific, Apc- and Pten-deleted mice were generated and evaluated for histopathology and survival. HFD did not overtly alter Akt signaling in ISCs, but did increase other metabolic pathways. Pten deficiency, but not HFD, increased BrdU-positive cells in the small intestine (P < 0.05). However, combining Pten and Apc deficiency synergistically increased proliferative markers, tumor pathology and mortality, in a dose-dependent fashion (P < 0.05). In summary, we show that HFD alone fails to drive Akt signaling in ISCs and that Pten deficiency is dispensable as a tumor suppressor in Lgr5+-ISCs. However, combining Pten and Apc deficiency in ISCs synergistically increases proliferation, tumor formation and mortality. Thus, aberrant Wnt/β-catenin, rather than PI3K-Akt signaling, is requisite for obesity to drive Lgr5+ ISC-derived tumorigenesis.

In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis

In vivo interrogation of the function of genes implicated in tumorigenesis is limited by the need to generate and cross germline mutant mice. Here we describe approaches to model colorectal cancer (CRC) and metastasis, which rely on in situ gene editing and orthotopic organoid transplantation in mice without cancer-predisposing mutations. Autochthonous tumor formation is induced by CRISPR-Cas9-based editing of the Apc and Trp53 tumor suppressor genes in colon epithelial cells and by orthotopic transplantation of Apc-edited colon organoids. ApcΔ/Δ;KrasG12D/+;Trp53Δ/Δ (AKP) mouse colon organoids and human CRC organoids engraft in the distal colon and metastasize to the liver. Finally, we apply the orthotopic transplantation model to characterize the clonal dynamics of Lgr5+ stem cells and demonstrate sequential activation of an oncogene in established colon adenomas. These experimental systems enable rapid in vivo characterization of cancer-associated genes and reproduce the entire spectrum of tumor progression and metastasis.

PPAR-delta modulates membrane cholesterol and cytokine signaling in malignant B cells

A deeper understanding of the mechanisms that underlie aberrant signal transduction in B-cell cancers such as chronic lymphocytic leukemia (CLL) may reveal new treatment strategies. The lipid-activated nuclear receptor peroxisome proliferator-activated receptor delta (PPARδ) accounts for a number of properties of aggressive cancers and was found to enhance Janus kinase (JAK)-mediated phosphorylation of signal transducer and activator of transcription (STAT) proteins in B lymphoma cell lines and primary CLL cells. Autocrine production of cytokines such as IL10 and interferon-beta was not increased by PPARδ but signaling responses to these cytokines were amplified and associated with increased cholesterol biosynthesis and plasma membrane levels. Plasmalemmal cholesterol and STAT phosphorylation from type 1 interferons (IFNs) were increased by PPARδ agonists, transgenes and exogenous cholesterol, and decreased by cyclodextrin, PPARD deletion and chemical PPARδ inhibitors. Functional consequences of PPARδ-mediated perturbation of IFN signaling included impaired upregulation of co-stimulatory molecules. These observations suggest PPARδ modulates signaling processes in malignant B cells in part by altering cholesterol metabolism and changes the outcomes of signaling from cytokines such as IFNs. PPARδ antagonists may have therapeutic activity as anti-leukemic signal transduction modulators.

The Research Progress on Intestinal Stem Cells and Its Relationship with Intestinal Microbiota

The intestine is home to trillions of microorganisms, and the vast diversity within this gut microbiota exists in a balanced state to protect the intestinal mucosal barrier. Research into the association of the intestinal microbiota with health and disease (including diet, nutrition, obesity, inflammatory bowel disease, and cancer) continues to expand, with the field advancing at a rapid rate. Intestinal stem cells (ISCs) are the fundamental component of the mucosal barrier; they undergo continuous proliferation to replace the epithelium, which is also intimately involved in intestinal diseases. The intestinal microbiota, such as Lactobacillus, communicates with ISCs both directly and indirectly to regulate the proliferation and differentiation of ISCs. Moreover, Salmonella infection significantly decreased the expression of intestinal stem cell markers Lgr5 and Bmi1. However, the detailed interaction of intestinal microbiota and ISCs are still unclear. This review considers the progress of research on the model and niches of ISCs, as well as the complex interplay between the gut microbiota and ISCs, which will be crucial for explaining the mechanisms of intestinal diseases related to imbalances in the intestinal microbiota and ISCs.

Body mass index and risk of colorectal carcinoma subtypes classified by tumor differentiation status

Previous studies suggest that abnormal energy balance status may dysregulate intestinal epithelial homeostasis and promote colorectal carcinogenesis, yet little is known about how host energy balance and obesity influence enterocyte differentiation during carcinogenesis. We hypothesized that the association between high body mass index (BMI) and colorectal carcinoma incidence might differ according to tumor histopathologic differentiation status. Using databases of the Nurses' Health Study and Health Professionals Follow-up Study, and duplication-method Cox proportional hazards models, we prospectively examined an association between BMI and the incidence of colorectal carcinoma subtypes classified by differentiation features. 120,813 participants were followed for 26 or 32 years and 1528 rectal and colon cancer cases with available tumor pathological data were documented. The association between BMI and colorectal cancer risk significantly differed depending on the presence or absence of poorly-differentiated foci (P_{heterogeneity} = 0.006). Higher BMI was associated with a higher risk of colorectal carcinoma without poorly-differentiated foci (≥30.0 vs. 18.5-22.4 kg/m²: multivariable-adjusted hazard ratio, 1.87; 95% confidence interval, 1.49-2.34; P_trend < 0.001), but not with risk of carcinoma with poorly-differentiated foci (P_trend = 0.56). This differential association appeared to be consistent in strata of tumor microsatellite instability or FASN expression status, although the statistical power was limited. The association between BMI and colorectal carcinoma risk did not significantly differ by overall tumor differentiation, mucinous differentiation, or signet ring cell component (P_{heterogeneity} > 0.03, with the adjusted α of 0.01). High BMI was associated with risk of colorectal cancer subtype containing no poorly-differentiated focus. Our findings suggest that carcinogenic influence of excess energy balance might be stronger for tumors that retain better intestinal differentiation throughout the tumor areas.

Effect of essential amino acids on enteroids: Methionine deprivation suppresses proliferation and affects differentiation in enteroid stem cells

We investigated the effects of essential amino acids on intestinal stem cell proliferation and differentiation using murine small intestinal organoids (enteroids) from the jejunum. By selectively removing individual essential amino acids from culture medium, we found that 24 h of methionine (Met) deprivation markedly suppressed cell proliferation in enteroids. This effect was rescued when enteroids cultured in Met deprivation media for 12 h were transferred to complete medium, suggesting that Met plays an important role in enteroid cell proliferation. In addition, mRNA levels of the stem cell marker leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5) decreased in enteroids grown in Met deprivation conditions. Consistent with this observation, Met deprivation also attenuated Lgr5-EGFP fluorescence intensity in enteroids. In contrast, Met deprivation enhanced mRNA levels of the enteroendocrine cell marker chromogranin A (ChgA) and markers of K cells, enterochromaffin cells, goblet cells, and Paneth cells. Immunofluorescence experiments demonstrated that Met deprivation led to an increase in the number of ChgA-positive cells. These results suggest that Met deprivation suppresses stem cell proliferation, thereby promoting differentiation. In conclusion, Met is an important nutrient in the maintenance of intestinal stem cells and Met deprivation potentially affects cell differentiation.

Metabolic Teamwork in the Stem Cell Niche

Nearby cells can support stem cell differentiation, but the metabolic activities in stem cell niches are unknown. A recent study (Rodríguez-Colman et al., 2017) reveals a metabolic partnership in the intestinal stem cell niche: glycolysis in niche Paneth cells provides lactate to drive mitochondrial oxidative phosphorylation in intestinal stem cells.

Insights into the role of the intestinal microbiota in colon cancer

The intestinal microbiota consists of a dynamic organization of bacteria, viruses, archaea, and fungal species essential for maintaining gut homeostasis and protecting the host against pathogenic invasion. When dysregulated, the intestinal microbiota can contribute to colorectal cancer development. Though the microbiota is multifaceted in its ability to induce colorectal cancer, this review will focus on the capability of the microbiota to induce colorectal cancer through the modulation of immune function and the production of microbial-derived metabolites. We will also explore an experimental technique that is revolutionizing intestinal research. By elucidating the interactions of microbial species with epithelial tissue, and allowing for drug screening of patients with colorectal cancers, organoid development is a novel culturing technique that is innovating intestinal research. As a cancer that remains one of the leading causes of cancer-related deaths worldwide, it is imperative that scientific findings are translated into the creation of effective therapeutics to treat colorectal cancer.

Prolonged Absence of Mechanoluminal Stimulation in Human Intestine Alters the Transcriptome and Intestinal Stem Cell Niche

BACKGROUND & AIMS

For patients with short-bowel syndrome, intestinal adaptation is required to achieve enteral independence. Although adaptation has been studied extensively in animal models, little is known about this process in human intestine. We hypothesized that analysis of matched specimens with and without luminal flow could identify new potential therapeutic pathways.

METHODS

Fifteen paired human ileum samples were collected from children aged 2-20 months during ileostomy-reversal surgery after short-segment intestinal resection and diversion. The segment exposed to enteral feeding was denoted as fed, and the diverted segment was labeled as unfed. Morphometrics and cell differentiation were compared histologically. RNA Sequencing and Gene Ontology Enrichment Analysis identified over-represented and under-represented pathways. Immunofluorescence staining and Western blot evaluated proteins of interest. Paired data were compared with 1-tailed Wilcoxon rank-sum tests with a P value less than .05 considered significant.

RESULTS

Unfed ileum contained shorter villi, shallower crypts, and fewer Paneth cells. Genes up-regulated by the absence of mechanoluminal stimulation were involved in digestion, metabolism, and transport. Messenger RNA expression of LGR5 was significantly higher in unfed intestine, accompanied by increased levels of phosphorylated signal transducer and activator of transcription 3 protein, and CCND1 and C-MYC messenger RNA. However, decreased proliferation and fewer LGR5+, OLFM4+, and SOX9+ intestinal stem cells (ISCs) were observed in unfed ileum.

CONCLUSIONS

Even with sufficient systemic caloric intake, human ileum responds to the chronic absence of mechanoluminal stimulation by up-regulating brush-border enzymes, transporters, structural genes, and ISC genes LGR5 and ASCL2. These data suggest that unfed intestine is primed to replenish the ISC population upon re-introduction of enteral feeding. Therefore, the elucidation of pathways involved in these processes may provide therapeutic targets for patients with intestinal failure. RNA sequencing data are available at Gene Expression Omnibus series GSE82147.

Beyond growth signaling: Paneth cells metabolically support ISCs

Single Lgr5 intestinal stem cells (ISCs) can be expanded in vitro into epithelial organoids or "mini-guts", self-organizing cellular structures that recreate the intestinal differentiation program; Paneth cells, which constitute the intestinal stem cell niche, secrete stem cell growth signals, and are thus essential for this process. In a recent paper published in Nature, Rodríguez-Colman et al. describe how Paneth cells may be supporting the metabolic state of ISCs.

Loss of Dnmt3a and Dnmt3b does not affect epidermal homeostasis but promotes squamous transformation through PPAR-γ

The DNA methyltransferase Dnmt3a suppresses tumorigenesis in models of leukemia and lung cancer. Conversely, deregulation of Dnmt3b is thought to generally promote tumorigenesis. However, the role of Dnmt3a and Dnmt3b in many types of cancer remains undefined. Here, we show that Dnmt3a and Dnmt3b are dispensable for homeostasis of the murine epidermis. However, loss of Dnmt3a-but not Dnmt3b-increases the number of carcinogen-induced squamous tumors, without affecting tumor progression. Only upon combined deletion of Dnmt3a and Dnmt3b, squamous carcinomas become more aggressive and metastatic. Mechanistically, Dnmt3a promotes the expression of epidermal differentiation genes by interacting with their enhancers and inhibits the expression of lipid metabolism genes, including PPAR-γ, by directly methylating their promoters. Importantly, inhibition of PPAR-γ partially prevents the increase in tumorigenesis upon deletion of Dnmt3a. Altogether, we demonstrate that Dnmt3a and Dnmt3b protect the epidermis from tumorigenesis and that squamous carcinomas are sensitive to inhibition of PPAR-γ.

Western Diet Deregulates Bile Acid Homeostasis, Cell Proliferation, and Tumorigenesis in Colon

Western-style diets (WD) high in fat and scarce in fiber and vitamin D increase risks of colorectal cancer. Here, we performed a long-term diet study in mice to follow tumorigenesis and characterize structural and metabolic changes in colon mucosa associated with WD and predisposition to colorectal cancer. WD increased colon tumor numbers, and mucosa proteomic analysis indicated severe deregulation of intracellular bile acid (BA) homeostasis and activation of cell proliferation. WD also increased crypt depth and colon cell proliferation. Despite increased luminal BA, colonocytes from WD-fed mice exhibited decreased expression of the BA transporters FABP6, OSTβ, and ASBT and decreased concentrations of secondary BA deoxycholic acid and lithocholic acid, indicating reduced activity of the nuclear BA receptor FXR. Overall, our results suggest that WD increases cancer risk by FXR inactivation, leading to BA deregulation and increased colon cell proliferation. Cancer Res; 77(12); 3352-63. ©2017 AACR.

Intestinal PPARδ protects against diet-induced obesity, insulin resistance and dyslipidemia

Peroxisome proliferator-activated receptor δ (PPARδ) is a ligand-activated transcription factor that has an important role in lipid metabolism. Activation of PPARδ stimulates fatty acid oxidation in adipose tissue and skeletal muscle and improves dyslipidemia in mice and humans. PPARδ is highly expressed in the intestinal tract but its physiological function in this organ is not known. Using mice with an intestinal epithelial cell-specific deletion of PPARδ, we show that intestinal PPARδ protects against diet-induced obesity, insulin resistance and dyslipidemia. Furthermore, absence of intestinal PPARδ abolished the ability of PPARδ agonist GW501516 to increase plasma levels of HDL-cholesterol. Together, our findings show that intestinal PPARδ is important in maintaining metabolic homeostasis and suggest that intestinal-specific activation of PPARδ could be a therapeutic approach for treatment of the metabolic syndrome and dyslipidemia, while avoiding systemic toxicity.

Tissue-specific tumorigenesis: context matters

How can we treat cancer more effectively? Traditionally, tumours from the same anatomical site are treated as one tumour entity. This concept has been challenged by recent breakthroughs in cancer genomics and translational research that have enabled molecular tumour profiling. The identification and validation of cancer drivers that are shared between different tumour types, spurred the new paradigm to target driver pathways across anatomical sites by off-label drug use, or within so-called basket or umbrella trials which are designed to test whether molecular alterations in one tumour entity can be extrapolated to all others. However, recent clinical and preclinical studies suggest that there are tissue- and cell type-specific differences in tumorigenesis and the organization of oncogenic signalling pathways. In this Opinion article, we focus on the molecular, cellular, systemic and environmental determinants of organ-specific tumorigenesis and the mechanisms of context-specific oncogenic signalling outputs. Investigation, recognition and in-depth biological understanding of these differences will be vital for the design of next-generation clinical trials and the implementation of molecularly guided cancer therapies in the future.

Precancer Atlas to Drive Precision Prevention Trials

Cancer development is a complex process driven by inherited and acquired molecular and cellular alterations. Prevention is the holy grail of cancer elimination, but making this a reality will take a fundamental rethinking and deep understanding of premalignant biology. In this Perspective, we propose a national concerted effort to create a Precancer Atlas (PCA), integrating multi-omics and immunity - basic tenets of the neoplastic process. The biology of neoplasia caused by germline mutations has led to paradigm-changing precision prevention efforts, including: tumor testing for mismatch repair (MMR) deficiency in Lynch syndrome establishing a new paradigm, combinatorial chemoprevention efficacy in familial adenomatous polyposis (FAP), signal of benefit from imaging-based early detection research in high-germline risk for pancreatic neoplasia, elucidating early ontogeny in BRCA1-mutation carriers leading to an international breast cancer prevention trial, and insights into the intricate germline-somatic-immunity interaction landscape. Emerging genetic and pharmacologic (metformin) disruption of mitochondrial (mt) respiration increased autophagy to prevent cancer in a Li-Fraumeni mouse model (biology reproduced in clinical pilot) and revealed profound influences of subtle changes in mt DNA background variation on obesity, aging, and cancer risk. The elaborate communication between the immune system and neoplasia includes an increasingly complex cellular microenvironment and dynamic interactions between host genetics, environmental factors, and microbes in shaping the immune response. Cancer vaccines are in early murine and clinical precancer studies, building on the recent successes of immunotherapy and HPV vaccine immune prevention. Molecular monitoring in Barrett's esophagus to avoid overdiagnosis/treatment highlights an important PCA theme. Next generation sequencing (NGS) discovered age-related clonal hematopoiesis of indeterminate potential (CHIP). Ultra-deep NGS reports over the past year have redefined the premalignant landscape remarkably identifying tiny clones in the blood of up to 95% of women in their 50s, suggesting that potentially premalignant clones are ubiquitous. Similar data from eyelid skin and peritoneal and uterine lavage fluid provide unprecedented opportunities to dissect the earliest phases of stem/progenitor clonal (and microenvironment) evolution/diversity with new single-cell and liquid biopsy technologies. Cancer mutational signatures reflect exogenous or endogenous processes imprinted over time in precursors. Accelerating the prevention of cancer will require a large-scale, longitudinal effort, leveraging diverse disciplines (from genetics, biochemistry, and immunology to mathematics, computational biology, and engineering), initiatives, technologies, and models in developing an integrated multi-omics and immunity PCA - an immense national resource to interrogate, target, and intercept events that drive oncogenesis. Cancer Res; 77(7); 1510-41. ©2017 AACR.

Interaction between epigenetic and metabolism in aging stem cells

Aging is accompanied by a decline in tissue function, regeneration, and repair. A large part of this decline is caused by the deterioration of tissue stem cell function. Understanding the mechanisms that drive stem cell aging and how to counteract them is a critical step for enhancing tissue repair and maintenance during aging. Emerging evidence indicates that epigenetic modifiers and metabolism regulators interact to impact lifespan, suggesting that this mechanism may also affect stem cell function with age. This review focuses on the interaction between chromatin and metabolism in the regulation of tissue stem cells during aging. We also discuss how these mechanisms integrate environmental stimuli such as nutrient stress to regulate stem cell function. Finally, this review examines new perspectives for regeneration, rejuvenation, and treatment of age-related decline of stem cell function.

Hepatic transcriptomic responses in mice exposed to arsenic and different fat diet

Chronic exposure to inorganic arsenic (iAs) or a high-fat diet (HFD) can produce liver injury. However, effects of HFD on risk assessment of iAs in drinking water are unclear. In this study, we examined how HFD and iAs interact to alter iAs-induced liver injury in C57BL/6 mice. Mice fed low-fat diet (LFD) or HFD were exposed to 3 mg/L iAs or deionized water for 10 weeks. Results showed that HFD changed intake and excretion of iAs by mice. Then, HFD increased the amount of iAs-induced hepatic DNA damage and amplified changes in pathways related to cell death and growth, signal transduction, lipid metabolism, and insulin signaling. Compared to gene expression profiles caused by iAs alone or HFD alone, insulin signaling pathway might play important roles in the interactive effects of iAs and HFD. Our data suggest that HFD increases sensitivity of mice to iAs in drinking water, resulting in increased hepatotoxicity. This study highlight that HFD might enhance the risk of iAs hepatotoxicity in iAs-polluted regions. The diet should be considered during risk assessment of iAs in drinking water.

Sedentary lifestyle related exosomal release of Hotair from gluteal-femoral fat promotes intestinal cell proliferation

Pioneering epidemiological work has established strong association of sedentary lifestyle and obesity with the risk of colorectal cancer, while the detailed underlying mechanism remains unknown. Here we show that Hotair (HOX transcript antisense RNA) is a pro-adipogenic long non-coding RNA highly expressed in gluteal-femoral fat over other fat depots. Hotair knockout in adipose tissue results in gluteal-femoral fat defect. Squeeze of the gluteal-femoral fat induces intestinal proliferation in wildtype mice, while not in Hotair knockout mice. Mechanistically, squeeze of the gluteal-femoral fat induces exosomal Hotair secretion mainly by transcriptional upregulation of Hotair via NFκB. And increased exosomal Hotair in turn circulates in the blood and is partially endocytosed by the intestine, finally promoting the stemness and proliferation of intestinal stem/progenitor cells via Wnt activation. Clinically, obese subjects with sedentary lifestyle have much higher exosomal HOTAIR expression in the serum. These findings establish that sedentary lifestyle promotes exosomal Hotair release from the gluteal-femoral fat, which in turn facilitates intestinal stem and/or progenitor proliferation, raising a possible link between sedentary lifestyle with colorectal tumorigenesis.

Dietary Regulation of Adult Stem Cells

PURPOSE OF REVIEW

Dietary intake is a critical regulator of organismal physiology and health. Tissue homeostasis and regeneration are dependent on adult tissue stem cells that self-renew and differentiate into the specialized cell types. As stem cells respond to cues from their environment, dietary signals and nutrients influence tissue biology by altering the function and activity of adult stem cells. In this review, we highlight recent studies that illustrate how diverse diets such as caloric restriction, fasting, high fat diets, and ketogenic diets impact stem cell function and their microenvironments.

RECENT FINDINGS

Caloric restriction generally exerts positive effects on adult stem cells, notably increasing stem cell functionality in the intestine and skeletal muscle as well as increasing hematopoietic stem cell quiescence. Similarly, fasting confers protection of intestinal, hematopoietic, and neuronal stem cells against injury. High fat diets induce intestinal stem cell niche independence and stem-like properties in intestinal progenitors, while high fat diets impair hematopoiesis and neurogenesis.

SUMMARY

Caloric restriction and fasting are generally beneficial to adult stem cell function, while high fat diets impair stem cell function or create opportunities for tumorigenesis. However, the effects of each diet on stem cell biology are complex and vary greatly between tissues. Given the recent interest in developing dietary interventions or mimetics as therapeutics, further studies, including on ketogenic diets, will be essential to understand how adult stem cells respond to diet-induced signals and physiology.

Steroid Hormones and the Physiological Regulation of Tissue-Resident Stem Cells: Lessons from the Drosophila Ovary

PURPOSE OF REVIEW

Stem cells respond to local paracrine signals; more recently, however, systemic hormones have also emerged as key regulators of stem cells. This review explores the role of steroid hormones in stem cells, using the Drosophila germline stem cell as a centerpiece for discussion.

RECENT FINDINGS

Stem cells sense and respond directly and indirectly to steroid hormones, which regulate diverse sets of target genes via interactions with nuclear hormone receptors. Hormone-regulated networks likely integrate the actions of multiple systemic signals to adjust the activity of stem cell lineages in response to changes in physiological status.

SUMMARY

Hormones are inextricably linked to animal physiology, and can control stem cells and their local niches. Elucidating the molecular mechanisms of hormone signaling in stem cells is essential for our understanding of the fundamental underpinnings of stem cell biology, and for informing new therapeutic interventions against cancers or for regenerative medicine.

Adipocytes activate mitochondrial fatty acid oxidation and autophagy to promote tumor growth in colon cancer

Obesity has been associated with increased incidence and mortality of a wide variety of human cancers including colorectal cancer. However, the molecular mechanism by which adipocytes regulate the metabolism of colon cancer cells remains elusive. In this study, we showed that adipocytes isolated from adipose tissues of colon cancer patients have an important role in modulating cellular metabolism to support tumor growth and survival. Abundant adipocytes were found in close association with invasive tumor cells in colon cancer patients. Co-culture of adipocytes with colon cancer cells led to a transfer of free fatty acids that released from the adipocytes to the cancer cells. Uptake of fatty acids allowed the cancer cells to survive nutrient deprivation conditions by upregulating mitochondrial fatty acid β-oxidation. Mechanistically, co-culture of adipocytes or treating cells with fatty acids induced autophagy in colon cancer cells as a result of AMPK activation. Inhibition of autophagy attenuated the ability of cancer cells to utilize fatty acids and blocked the growth-promoting effect of adipocytes. In addition, we found that adipocytes stimulated the expression of genes associated with cancer stem cells and downregulated genes associated with intestinal epithelial cell differentiation in primary colon cancer cells and mouse tumor organoids. Importantly, the presence of adipocytes promoted the growth of xenograft tumors in vivo. Taken together, our results show that adipocytes in the tumor microenvironment serve as an energy provider and a metabolic regulator to promote the growth and survival of colon cancer cells.

Microbes and Cancer

Commensal microorganisms (the microbiota) live on all the surface barriers of our body and are particularly abundant and diverse in the distal gut. The microbiota and its larger host represent a metaorganism in which the cross talk between microbes and host cells is necessary for health, survival, and regulation of physiological functions locally, at the barrier level, and systemically. The ancestral molecular and cellular mechanisms stemming from the earliest interactions between prokaryotes and eukaryotes have evolved to mediate microbe-dependent host physiology and tissue homeostasis, including innate and adaptive resistance to infections and tissue repair. Mostly because of its effects on metabolism, cellular proliferation, inflammation, and immunity, the microbiota regulates cancer at the level of predisposing conditions, initiation, genetic instability, susceptibility to host immune response, progression, comorbidity, and response to therapy. Here, we review the mechanisms underlying the interaction of the microbiota with cancer and the evidence suggesting that the microbiota could be targeted to improve therapy while attenuating adverse reactions.

ALOX15 as a suppressor of inflammation and cancer: Lost in the link

Mounting evidence supports a mechanistic link between inflammation and cancer, especially colon cancer. ALOX15 (15-lipoxygenase-1) plays an important role in the formation of key lipid mediators (e.g., lipoxins and resolvins) to terminate inflammation. ALOX15 expression is downregulated in colorectal cancer (CRC). Intestinally-targeted transgenic expression of ALOX15 in mice inhibited dextran sodium sulfate-induced colitis from promoting azoxymethane- induced colorectal tumorigenesis, demonstrating that ALOX15 can suppress inflammation-driven promotion of carcinogen-induced colorectal tumorigenesis and therefore ALOX15 downregulation during tumorigenesis is likely to enhance the link between colitis and colorectal tumorigenesis. ALOX15 suppressed the TNF-α, IL-1β/NF-κB, and IL-6/STAT3 signaling pathways, which play major roles in promotion of colorectal cancer by chronic inflammation. Defining ALOX15's regulatory role in colitis-associated colorectal cancer could identify important molecular regulatory events that could be targeted to suppress promotion of tumorigenesis by chronic inflammation.

Environmental Impact on Intestinal Stem Cell Functions in Mucosal Homeostasis and Tumorigenesis

Multiple cell compartments at or near the base of the intestinal crypt have been identified as contributing intestinal stem cells for homeostasis of the rapidly turning over intestinal mucosa and cells that can initiate tumor development upon appropriate genetic changes. There is a strong literature establishing the importance of the frequently dividing Lgr5+ crypt base columnar cells as the fundamental cell in providing these stem cell-associated functions, but there are also clear data that more quiescent cells from other compartments can be mobilized to provide these stem cell functions upon compromise of Lgr5+ cells. We review the data that vitamin D, a pleiotropic hormone, is essential for Lgr5 stem cell functions by signaling through the vitamin D receptor. Moreover, we discuss the implications of this role of vitamin D and its impact on relatively long-lived stem cells in regards to the fact that virtually all the data on normal functioning of mouse Lgr5 stem cells is derived from mice exposed to vitamin D levels well above those that characterize the human population. Thus, there are still many questions regarding how dietary and environmental factors influence the complement of cells providing stem cell functions and the mechanisms by which this is determined, and the importance of this in human colorectal tumor development. J. Cell. Biochem. 118: 943-952, 2017. © 2016 Wiley Periodicals, Inc.

PPAR-delta promotes survival of chronic lymphocytic leukemia cells in energetically unfavorable conditions

Targeting the mechanisms that allow chronic lymphocytic leukemia (CLL) cells to survive in harsh cancer microenvironments should improve patient outcomes. The nuclear receptor peroxisome proliferator activated receptor delta (PPARδ) sustains other cancers, and in silico analysis showed higher PPARD expression in CLL cells than normal lymphocytes and other hematologic cancers. A direct association was found between PPARδ protein levels in CLL cells and clinical score. Transgenic expression of PPARδ increased the growth and survival of CD5⁺ Daudi cells and primary CLL cells in stressful conditions including exhausted tissue culture media, low extracellular glucose, hypoxia and exposure to cytotoxic drugs. Glucocorticoids and synthetic PPARδ agonists up-regulated PPARD expression and also protected Daudi and primary CLL cells from metabolic stressors. Survival in low glucose was related to increased antioxidant expression, substrate utilization and mitochondrial performance, and was reversed by genetic deletion and synthetic PPARδ antagonists. These findings suggest PPARδ conditions CLL cells to survive in harsh microenvironmental conditions by reducing oxidative stress and increasing metabolic efficiency. Targeting PPARδ may be beneficial in the treatment of CLL.

PPARβ/δ in human cancer

The nuclear receptor factor peroxisome proliferator-activated receptor (PPARβ/δ) can regulate its target genes by transcriptional activation or repression through both ligand-dependent and independent mechanism as well as by interactions with other transcription factors. PPARβ/δ exerts essential regulatory functions in intermediary metabolism that have been elucidated in detail, but clearly also plays a role in inflammation, differentiation, apoptosis and other cancer-associated processes, which is, however, mechanistically only partly understood. Consistent with these functions clinical associations link the expression of PPARβ/δ and its target genes to an unfavorable outcome of several human cancers. However, the available data do not yield a clear picture of PPARβ/δ's role in cancer-associated processes and are in fact partly controversial. This article provides an overview of this research area and discusses the role of PPARβ/δ in cancer in light of the complex mechanisms of its transcriptional regulation and its potential as a druggable anti-cancer target.

Diet, microorganisms and their metabolites, and colon cancer

Colorectal cancer is one of the so-called westernized diseases and the second leading cause of cancer death worldwide. On the basis of global epidemiological and scientific studies, evidence suggests that the risk of colorectal cancer is increased by processed and unprocessed meat consumption but suppressed by fibre, and that food composition affects colonic health and cancer risk via its effects on colonic microbial metabolism. The gut microbiota can ferment complex dietary residues that are resistant to digestion by enteric enzymes. This process provides energy for the microbiota but culminates in the release of short-chain fatty acids including butyrate, which are utilized for the metabolic needs of the colon and the body. Butyrate has a remarkable array of colonic health-promoting and antineoplastic properties: it is the preferred energy source for colonocytes, it maintains mucosal integrity and it suppresses inflammation and carcinogenesis through effects on immunity, gene expression and epigenetic modulation. Protein residues and fat-stimulated bile acids are also metabolized by the microbiota to inflammatory and/or carcinogenic metabolites, which increase the risk of neoplastic progression. This Review will discuss the mechanisms behind these microbial metabolite effects, which could be modified by diet to achieve the objective of preventing colorectal cancer in Western societies.

Rapidly cycling Lgr5+ stem cells are exquisitely sensitive to extrinsic dietary factors that modulate colon cancer risk

The majority of colon tumors are driven by aberrant Wnt signaling in intestinal stem cells, which mediates an efficient route toward initiating intestinal cancer. Natural lipophilic polyphenols and long-chain polyunsaturated fatty acids (PUFAs) generally suppress Wnt- and NF-κB- (nuclear factor-κ light-chain enhancer of activated B-cell) related pathways. However, the effects of these extrinsic agents on colonic leucine-rich repeat-containing G-protein-coupled receptor 5-positive (Lgr5⁺) stem cells, the cells of origin of colon cancer, have not been documented to date. Therefore, we examined the effect of n-3 PUFA and polyphenol (curcumin) combination on Lgr5⁺ stem cells during tumor initiation and progression in the colon compared with an n-6 PUFA-enriched control diet. Lgr5-EGFP-IRES-^creERT2 knock-in mice were fed diets containing n-6 PUFA (control), n-3 PUFA, n-6 PUFA+curcumin or n-3 PUFA+curcumin for 3 weeks, followed by 6 azoxymethane (AOM) injections, and terminated 17 weeks after the last injection. To further elucidate the effects of the dietary bioactives at the tumor initiation stage, Lgr5⁺ stem cells were also assessed at 12 and 24 h post AOM injection. Only n-3 PUFA+curcumin feeding reduced nuclear β-catenin in aberrant crypt foci (by threefold) compared with control at the progression time point. n-3 PUFA+curcumin synergistically increased targeted apoptosis in DNA-damaged Lgr5⁺ stem cells by 4.5-fold compared with control at 12 h and maximally reduced damaged Lgr5⁺ stem cells at 24 h, down to the level observed in saline-treated mice. Finally, RNAseq analysis indicated that p53 signaling in Lgr5⁺ stem cells from mice exposed to AOM was uniquely upregulated only following n-3 PUFA+curcumin cotreatment. These novel findings demonstrate that Lgr5⁺ stem cells are uniquely responsive to external dietary cues following the induction of DNA damage, providing a therapeutic strategy for eliminating damaged Lgr5⁺ stem cells to reduce colon cancer initiation.

Regulation and plasticity of intestinal stem cells during homeostasis and regeneration

The intestinal epithelium is the fastest renewing tissue in mammals and has a large flexibility to adapt to different types of damage. Lgr5⁺ crypt base columnar (CBC) cells act as stem cells during homeostasis and are essential during regeneration. Upon perturbation, the activity of CBCs is dynamically regulated to maintain homeostasis and multiple dedicated progenitor cell populations can reverse to the stem cell state upon damage, adding another layer of compensatory mechanisms to facilitate regeneration. Here, we review our current understanding of how intestinal stem and progenitor cells contribute to homeostasis and regeneration, and the different signaling pathways that regulate their behavior. Nutritional state and inflammation have been recently identified as upstream regulators of stem cell activity in the mammalian intestine, and we explore how these systemic signals can influence homeostasis and regeneration.

Long-Term Culture of Intestinal Cell Progenitors: An Overview of Their Development, Application, and Associated Technologies

PURPOSE OF REVIEW

Long-term culture of adult progenitor cells in 3D is a recently emerging technology that inhabits the space between 2D cell lines and organ slice culture.

RECENT FINDINGS

Adaptations to defined media components in the wake of advances in ES and iPS cell culture has led to the identification of conditions that maintained intestinal cell progenitors in culture. These conditions retain cellular heterogeneity of the normal or tumour tissue, and the cultures have been shown to be genetically stable, such that substantial biobanks are being created from patient derived material. This coupled with advances in analytical tools has generated a field, characterized by the term "organoid culture", that has huge potential for advancing drug discovery, regenerative medicine, and furthering the understanding of fundamental intestinal biology.

SUMMARY

In this review, we describe the approaches available for the long-term culture of intestinal cells from normal and diseased tissue, the current challenges, and how the technology is likely to develop further.

Western diet enhances intestinal tumorigenesis in Min/+ mice, associating with mucosal metabolic and inflammatory stress and loss of Apc heterozygosity

Western-type diet (WD) is a risk factor for colorectal cancer, but the underlying mechanisms are poorly understood. We investigated the interaction of WD and heterozygous mutation in the Apc gene on adenoma formation and metabolic and immunological changes in the histologically normal intestinal mucosa of Apc^Min/+ (Min/+) mice. The diet used was high in saturated fat and low in calcium, vitamin D, fiber and folate. The number of adenomas was twofold higher in the WD mice compared to controls, but adenoma size, proliferation or apoptosis did not differ. The ratio of the Min to wild-type allele was higher in the WD mice, indicating accelerated loss of Apc heterozygosity (LOH). Densities of intraepithelial CD3ε⁺ T lymphocytes and of mucosal FoxP3⁺ regulatory T cells were higher in the WD mice, implying inflammatory changes. Western blot analyses from the mucosa of the WD mice showed suppressed activation of the ERK and AKT pathways and a tendency for reduced activation of the mTOR pathway as measured in phosphoS6/S6 levels. The expression of pyruvate dehydrogenase kinase 4 was up-regulated in both mRNA and protein levels. Gene expression analyses showed changes in oxidation/reduction, fatty acid and monosaccharide metabolic pathways, tissue organization, cell fate and regulation of apoptosis. Together, our results suggest that the high-risk Western diet primes the intestine to tumorigenesis through synergistic effects in energy metabolism, inflammation and oxidative stress, which culminate in the acceleration of LOH of the Apc gene.

Signals from the gut microbiota to distant organs in physiology and disease

The ecosystem of the human gut consists of trillions of bacteria forming a bioreactor that is fueled by dietary macronutrients to produce bioactive compounds. These microbiota-derived metabolites signal to distant organs in the body, which enables the gut bacteria to connect to the immune and hormone system, to the brain (the gut-brain axis) and to host metabolism, as well as other functions of the host. This microbe-host communication is essential to maintain vital functions of the healthy host. Recently, however, the gut microbiota has been associated with a number of diseases, ranging from obesity and inflammatory diseases to behavioral and physiological abnormalities associated with neurodevelopmental disorders. In this Review, we will discuss microbiota-host cross-talk and intestinal microbiome signaling to extraintestinal organs. We will review mechanisms of how this communication might contribute to host physiology and discuss how misconfigured signaling might contribute to different diseases.

Molecular Pathways: Dietary Regulation of Stemness and Tumor Initiation by the PPAR-δ Pathway

Peroxisome proliferator-activated receptor delta (PPAR-δ) is a nuclear receptor transcription factor that regulates gene expression during development and disease states, such as cancer. However, the precise role of PPAR-δ during tumorigenesis is not well understood. Recent data suggest that PPAR-δ may have context-specific oncogenic and tumor-suppressive roles depending on the tissue, cell-type, or diet-induced physiology in question. For example, in the intestine, pro-obesity diets, such as a high-fat diet (HFD), are associated with increased colorectal cancer incidence. Interestingly, many of the effects of an HFD in the stem and progenitor cell compartment are driven by a robust PPAR-δ program and contribute to the early steps of intestinal tumorigenesis. Importantly, the PPAR-δ pathway or its downstream mediators may serve as therapeutic intervention points or biomarkers in colon cancer that arise in patients who are obese. Although potent PPAR-δ agonists and antagonists exist, their clinical utility may be enhanced by uncovering how PPAR-δ mediates tumorigenesis in diverse tissues and cell types as well as in response to diet. Clin Cancer Res; 22(23); 5636-41. ©2016 AACR.

High-fat diet feeding promotes stemness and precancerous changes in murine gastric mucosa mediated by leptin receptor signaling pathway

Obesity increases the risk for gastric cancers. However, the occurrence and mechanisms of precancerous atrophic gastritis induced by high-fat diet (HFD) remain unclear. Here, we show that HFD-associated lipotoxicity induces precancerous lesions that are accompanied by the disruption of organelle homeostasis, tissue integrity, and deregulated expression of stemness genes in the gastric epithelium mediated by leptin receptor (ObR) signaling. Following HFD feeding, ectopic fat accumulated and expression of LAMP2A in lysosome and COX IV in mitochondria increased in the gastric mucosa. HFD feeding also led to enhanced expression of activated-Notch1 and stem cell markers Lgr5, CD44, and EpCAM. In addition, HFD-fed mice showed intracellular β-catenin accumulation in the gastric mucosa with increased expression of its target genes, Nanog, Oct4, and c-Myc. These observations were abrogated in the leptin-deficient ob/ob mice and ObR-mutated db/db mice, indicating that these HFD-induced changes were responsible for effects downstream of the ObR. Consistent with this, the expression of the Class IA and III PI3Ks was increased following ObR activation in the gastric mucosa of HFD-fed mice. Together, these results suggest that HFD-induced lipotoxicity and deregulated organelle biosynthesis confer cancer stem cell-like properties to the gastric mucosa via signaling pathway mediated by leptin, PI3K and β-catenin.

Celecoxib Alters the Intestinal Microbiota and Metabolome in Association with Reducing Polyp Burden

Treatment with celecoxib, a selective COX-2 inhibitor, reduces formation of premalignant adenomatous polyps in the gastrointestinal tracts of humans and mice. In addition to its chemopreventive activity, celecoxib can exhibit antimicrobial activity. Differing bacterial profiles have been found in feces from colon cancer patients compared with those of normal subjects. Moreover, preclinical studies suggest that bacteria can modulate intestinal tumorigenesis by secreting specific metabolites. In the current study, we determined whether celecoxib treatment altered the luminal microbiota and metabolome in association with reducing intestinal polyp burden in mice. Administration of celecoxib for 10 weeks markedly reduced intestinal polyp burden in APC(Min/+) mice. Treatment with celecoxib also altered select luminal bacterial populations in both APC(Min/+) and wild-type mice, including decreased Lactobacillaceae and Bifidobacteriaceae as well as increased Coriobacteriaceae Metabolomic analysis demonstrated that celecoxib caused a strong reduction in many fecal metabolites linked to carcinogenesis, including glucose, amino acids, nucleotides, and lipids. Ingenuity Pathway Analysis suggested that these changes in metabolites may contribute to reduced cell proliferation. To this end, we showed that celecoxib reduced cell proliferation in the base of normal appearing ileal and colonic crypts of APC(Min/+) mice. Consistent with this finding, lineage tracing indicated that celecoxib treatment reduced the rate at which Lgr5-positive stem cells gave rise to differentiated cell types in the crypts. Taken together, these results demonstrate that celecoxib alters the luminal microbiota and metabolome along with reducing epithelial cell proliferation in mice. We hypothesize that these actions contribute to its chemopreventive activity. Cancer Prev Res; 9(9); 721-31. ©2016 AACR.

Retinol Promotes In Vitro Growth of Proximal Colon Organoids through a Retinoic Acid-Independent Mechanism

Retinol (ROL), the alcohol form of vitamin A, is known to control cell fate decision of various types of stem cells in the form of its active metabolite, retinoic acid (RA). However, little is known about whether ROL has regulatory effects on colonic stem cells. We examined in this study the effect of ROL on the growth of murine normal colonic cells cultured as organoids. As genes involved in RA synthesis from ROL were differentially expressed along the length of the colon, we tested the effect of ROL on proximal and distal colon organoids separately. We found that organoid forming efficiency and the expression level of Lgr5, a marker gene for colonic stem cells were significantly enhanced by ROL in the proximal colon organoids, but not in the distal ones. Interestingly, neither retinaldehyde (RAL), an intermediate product of the ROL-RA pathway, nor RA exhibited growth promoting effects on the proximal colon organoids, suggesting that ROL-dependent growth enhancement in organoids involves an RA-independent mechanism. This was confirmed by the observation that an inhibitor for RA-mediated gene transcription did not abrogate the effect of ROL on organoids. This novel role of ROL in stem cell maintenance in the proximal colon provides insights into the mechanism of region-specific regulation for colonic stem cell maintenance.

Metabolic regulation of stem cell function in tissue homeostasis and organismal ageing

Many tissues and organ systems in metazoans have the intrinsic capacity to regenerate, which is driven and maintained largely by tissue-resident somatic stem cell populations. Ageing is accompanied by a deregulation of stem cell function and a decline in regenerative capacity, often resulting in degenerative diseases. The identification of strategies to maintain stem cell function and regulation is therefore a promising avenue to allay a wide range of age-related diseases. Studies in various organisms have revealed a central role for metabolic pathways in the regulation of stem cell function. Ageing is associated with extensive metabolic changes, and interventions that influence cellular metabolism have long been recognized as robust lifespan-extending measures. In this Review, we discuss recent advances in our understanding of the metabolic control of stem cell function, and how stem cell metabolism relates to homeostasis and ageing.

Type 1 Diabetes and Dysfunctional Intestinal Homeostasis

Despite the relatively high frequency of gastrointestinal (GI) disorders in individuals with type 1 diabetes (T1D), termed diabetic enteropathy (DE), the pathogenic mechanisms of these disorders remain to be elucidated. While previous studies have assumed that DE is a manifestation of diabetic autonomic neuropathy, other contributing factors such as enteric hormones, inflammation, and microbiota were later recognized. More recently, the emerging role of intestinal stem cells (ISCs) in several GI diseases has led to a new understanding of DE. Given the absence of diagnostic methods and the lack of broadly efficacious therapeutic remedies in DE, targeting factors and pathways that control ISC homeostasis and are dysfunctional in DE may represent a new path for the detection and cure of DE.

Manipulation of DNA Repair Proficiency in Mouse Models of Colorectal Cancer

Technical and biological innovations have enabled the development of more sophisticated and focused murine models that increasingly recapitulate the complex pathologies of human diseases, in particular cancer. Mouse models provide excellent in vivo systems for deciphering the intricacies of cancer biology within the context of precise experimental settings. They present biologically relevant, adaptable platforms that are amenable to continual improvement and refinement. We discuss how recent advances in our understanding of tumorigenesis and the underlying deficiencies of DNA repair mechanisms that drive it have been informed by using genetically engineered mice to create defined, well-characterized models of human colorectal cancer. In particular, we focus on how mechanisms of DNA repair can be manipulated precisely to create in vivo models whereby the underlying processes of tumorigenesis are accelerated or attenuated, dependent on the composite alleles carried by the mouse model. Such models have evolved to the stage where they now reflect the initiation and progression of sporadic cancers. The review is focused on mouse models of colorectal cancer and how insights from these models have been instrumental in shaping our understanding of the processes and potential therapies for this disease.