PPARbeta/delta regulates paneth cell differentiation via controlling the hedgehog signaling pathway

Hedgehog Signalling Pathway and Its Role in Shaping the Architecture of Intestinal Epithelium

The hedgehog (Hh) signalling pathway plays a key role in both embryonic and postnatal development of the intestine and is responsible for gut homeostasis. It regulates stem cell renewal, formation of the villous-crypt axis, differentiation of goblet and Paneth cells, the cell cycle, apoptosis, development of gut innervation, and lipid metabolism. Ligands of the Hh pathway, i.e., Indian hedgehog (Ihh) and Sonic hedgehog (Shh), are expressed by superficial enterocytes but act in the mesenchyme, where they are bound by a Patched receptor localised on myofibroblasts and smooth muscle cells. This activates a cascade leading to the transcription of target genes, including those encoding G1/S-specific cyclin-D2 and -E1, B-cell lymphoma 2, fibroblast growth factor 4, and bone morphogenetic protein 4. The Hh pathway is tightly connected to Wnt signalling. Ihh is the major ligand in the Hh pathway. Its activation inhibits proliferation, while its blocking induces hyperproliferation and triggers a wound-healing response. Thus, Ihh is a negative feedback regulator of cell proliferation. There are data indicating that diet composition may affect the expression of the Hh pathway genes and proteins, which in turn, induces changes in mucosal architecture. This was shown for fat, vitamin A, haem, berberine, and ovotransferrin. The Hh signalling is also affected by the intestinal microbiota, which affects the intestinal barrier integrity. This review highlights the critical importance of the Hh pathway in shaping the intestinal mucosa and summarises the results obtained so far in research on the effect of dietary constituents on the activity of this pathway.

The Versatile Role of Peroxisome Proliferator-Activated Receptors in Immune-Mediated Intestinal Diseases

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that sense lipophilic molecules and act as transcription factors to regulate target genes. PPARs have been implicated in the regulation of innate immunity, glucose and lipid metabolism, cell proliferation, wound healing, and fibrotic processes. Some synthetic PPAR ligands are promising molecules for the treatment of inflammatory and fibrotic processes in immune-mediated intestinal diseases. Some of these are currently undergoing or have previously undergone clinical trials. Dietary PPAR ligands and changes in microbiota composition could modulate PPARs' activation to reduce inflammatory responses in these immune-mediated diseases, based on animal models and clinical trials. This narrative review aims to summarize the role of PPARs in immune-mediated bowel diseases and their potential therapeutic use.

The PPARα Regulation of the Gut Physiology in Regard to Interaction with Microbiota, Intestinal Immunity, Metabolism, and Permeability

Peroxisome proliferator-activated receptor alpha (PPARα) is expressed throughout the mammalian gut: in epithelial cells, in the villi of enterocytes and in Paneth cells of intestinal crypts, as well as in some immune cells (e.g., lamina propria macrophages, dendritic cells) of the mucosa. This review examines the reciprocal interaction between PPARα activation and intestinal microbiota. We refer to the published data confirming that microbiota products can influence PPARα signaling and, on the other hand, PPARα activation is able to affect microbiota profile, viability, and diversity. PPARα impact on the broad spectrum of events connected to metabolism, signaling (e.g., NO production), immunological tolerance to dietary antigens, immunity and permeability of the gut are also discussed. We believe that the phenomena described here play a prominent role in gut homeostasis. Therefore, in conclusion we propose future directions for research, including the application of synthetic activators and natural endogenous ligands of PPARα (i.e., endocannabinoids) as therapeutics for intestinal pathologies and systemic diseases assumed to be related to gut dysbiosis.

Pregnane X receptor (PXR) represses osteoblast differentiation through repression of the Hedgehog signaling pathway

The pregnane X receptor (PXR, NR1I2) belongs to the nuclear receptor family and functions as a xenobiotic and endobiotic sensor by binding to various molecules through its relatively flexible ligand-binding domain. In addition to these well-known canonical roles, we previously reported that PXR represses osteoblast differentiation. However, the mechanisms underlying the PXR-mediated repression of osteoblast differentiation remains unknown. In this study, we analyzed the changes in global gene expression profiles induced by PXR in calvarial osteoblasts cultured in standard fetal bovine serum (in which PXR induces repression of differentiation), and in those cultured in charcoal-stripped fetal bovine serum (in which PXR does not induce repression of differentiation). The comparison revealed that PXR attenuated the Hedgehog-mediated signaling in culture conditions that induced PXR-mediated repression of differentiation. Real-time PCR analysis showed that PXR repressed the Hedgehog signaling-induced genes such as Gli1 and Hhip, and conversely induced the Hedgehog signaling-repressed genes such as Cdon, Boc, and Gas1. Activation of Smo-mediated signaling in osteoblasts following treatment with a Smo agonist (SAG) significantly restored Gli-mediated transcriptional activity and osteoblast differentiation. Our results demonstrate the osteoblast-autonomous effects of PXR and identify a novel regulation of Hedgehog signaling by nuclear receptors.

Hedgehog Signaling in Colorectal Cancer: All in the Stroma?

Hedgehog (Hh) signaling regulates intestinal development and homeostasis. The role of Hh signaling in cancer has been studied for many years; however, its role in colorectal cancer (CRC) remains controversial. It has become increasingly clear that the “canonical” Hh pathway, in which ligand binding to the receptor PTCH1 initiates a signaling cascade that culminates in the activation of the GLI transcription factors, is mainly organized in a paracrine manner, both in the healthy colon and in CRC. Such canonical Hh signals largely act as tumor suppressors. In addition, stromal Hh signaling has complex immunomodulatory effects in the intestine with a potential impact on carcinogenesis. In contrast, non-canonical Hh activation may have tumor-promoting roles in a subset of CRC tumor cells. In this review, we attempt to summarize the current knowledge of the Hh pathway in CRC, with a focus on the tumor-suppressive role of canonical Hh signaling in the stroma. Despite discouraging results from clinical trials using Hh inhibitors in CRC and other solid cancers, we argue that a more granular understanding of Hh signaling might allow the exploitation of this key morphogenic pathway for cancer therapy in the future.

Peroxisome Proliferator-Activated Receptors as Molecular Links between Caloric Restriction and Circadian Rhythm

The circadian rhythm plays a chief role in the adaptation of all bodily processes to internal and environmental changes on the daily basis. Next to light/dark phases, feeding patterns constitute the most essential element entraining daily oscillations, and therefore, timely and appropriate restrictive diets have a great capacity to restore the circadian rhythm. One of the restrictive nutritional approaches, caloric restriction (CR) achieves stunning results in extending health span and life span via coordinated changes in multiple biological functions from the molecular, cellular, to the whole-body levels. The main molecular pathways affected by CR include mTOR, insulin signaling, AMPK, and sirtuins. Members of the family of nuclear receptors, the three peroxisome proliferator-activated receptors (PPARs), PPARα, PPARβ/δ, and PPARγ take part in the modulation of these pathways. In this non-systematic review, we describe the molecular interconnection between circadian rhythm, CR-associated pathways, and PPARs. Further, we identify a link between circadian rhythm and the outcomes of CR on the whole-body level including oxidative stress, inflammation, and aging. Since PPARs contribute to many changes triggered by CR, we discuss the potential involvement of PPARs in bridging CR and circadian rhythm.

PPARs and Microbiota in Skeletal Muscle Health and Wasting

Skeletal muscle is a major metabolic organ that uses mostly glucose and lipids for energy production and has the capacity to remodel itself in response to exercise and fasting. Skeletal muscle wasting occurs in many diseases and during aging. Muscle wasting is often accompanied by chronic low-grade inflammation associated to inter- and intra-muscular fat deposition. During aging, muscle wasting is advanced due to increased movement disorders, as a result of restricted physical exercise, frailty, and the pain associated with arthritis. Muscle atrophy is characterized by increased protein degradation, where the ubiquitin-proteasomal and autophagy-lysosomal pathways, atrogenes, and growth factor signaling all play an important role. Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family of transcription factors, which are activated by fatty acids and their derivatives. PPARs regulate genes that are involved in development, metabolism, inflammation, and many cellular processes in different organs. PPARs are also expressed in muscle and exert pleiotropic specialized responses upon activation by their ligands. There are three PPAR isotypes, viz., PPARα, -β/δ, and -γ. The expression of PPARα is high in tissues with effective fatty acid catabolism, including skeletal muscle. PPARβ/δ is expressed more ubiquitously and is the predominant isotype in skeletal muscle. It is involved in energy metabolism, mitochondrial biogenesis, and fiber-type switching. The expression of PPARγ is high in adipocytes, but it is also implicated in lipid deposition in muscle and other organs. Collectively, all three PPAR isotypes have a major impact on muscle homeostasis either directly or indirectly. Furthermore, reciprocal interactions have been found between PPARs and the gut microbiota along the gut–muscle axis in both health and disease. Herein, we review functions of PPARs in skeletal muscle and their interaction with the gut microbiota in the context of muscle wasting.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

An Update Review on the Paneth Cell as Key to Ileal Crohn's Disease

The Paneth cells reside in the small intestine at the bottom of the crypts of Lieberkühn, intermingled with stem cells, and provide a niche for their neighbors by secreting growth and Wnt-factors as well as different antimicrobial peptides including defensins, lysozyme and others. The most abundant are the human Paneth cell α-defensin 5 and 6 that keep the crypt sterile and control the local microbiome. In ileal Crohn's disease various mechanisms including established genetic risk factors contribute to defects in the production and ordered secretion of these peptides. In addition, life-style risk factors for Crohn's disease like tobacco smoking also impact on Paneth cell function. Taken together, current evidence suggest that defective Paneth cells may play the key role in initiating inflammation in ileal, and maybe ileocecal, Crohn's disease by allowing bacterial attachment and invasion.

The absence of interleukin 10 affects the morphology, differentiation, granule content and the production of cryptidin-4 in Paneth cells in mice

Paneth cells (PCs) are specialized epithelial cells of the small bowel that contain multiple secretory granules filled with antimicrobial peptides and trophic factors, which are essential for the control of the microorganisms growth and maintaining intestinal integrity. Alterations in their function are associated with an imbalance of the normal microbiota, gastrointestinal infections and inflammatory processes, such as Crohn's disease (CD). One of the most common murine models for studying CD is IL-10-/- mouse. IL-10-/- mice when housed in conventional conditions and take contact with commensal microorganisms develop an acute enterocolitis mediated by a Th1 immune response. Even though, alterations in PCs function are related to CD, they had not been characterized yet in this mouse model. Here we show that in specific pathogen free conditions IL-10-/- mice have aberrant granules and a large number of immature PCs at the bottom of the crypt in the ileum of IL-10-/- mice before developing intestinal inflammation, along with a reduced expression of Indian Hedgehog. In addition, IL-10-/- Paneth cells presented a reduced expression of cryptidin-4, and a heterogeneous distribution of lysozyme+ granules. The alterations in the maturation of the PCs at the bottom of the crypt were not modified after the colonization by the conventional microbiota. On the other hand, depletion of microbiota altered the phenotype, but did not normalize PCs. Our results suggest that IL-10 could be necessary for the integrity of PCs. Moreover, our results help to explain why IL-10-/- mice develop enterocolitis in response to microorganisms.

The Intestinal Stem Cell Niche: Homeostasis and Adaptations

The intestinal epithelium is a rapidly renewing cellular compartment. This constant regeneration is a hallmark of intestinal homeostasis and requires a tightly regulated balance between intestinal stem cell (ISC) proliferation and differentiation. Since intestinal epithelial cells directly contact pathogenic environmental factors that continuously challenge their integrity, ISCs must also actively divide to facilitate regeneration and repair. Understanding niche adaptations that maintain ISC activity during homeostatic renewal and injury-induced intestinal regeneration is therefore a major and ongoing focus for stem cell biology. Here, we review recent concepts and propose an active interconversion of the ISC niche between homeostasis and injury-adaptive states that is superimposed upon an equally dynamic equilibrium between active and reserve ISC populations.

Enteric Microbiota⁻Gut⁻Brain Axis from the Perspective of Nuclear Receptors

Nuclear receptors (NRs) play a key role in regulating virtually all body functions, thus maintaining a healthy operating body with all its complex systems. Recently, gut microbiota emerged as major factor contributing to the health of the whole organism. Enteric bacteria have multiple ways to influence their host and several of them involve communication with the brain. Mounting evidence of cooperation between gut flora and NRs is already available. However, the full potential of the microbiota interconnection with NRs remains to be uncovered. Herewith, we present the current state of knowledge on the multifaceted roles of NRs in the enteric microbiota–gut–brain axis.

PPARγ Modulates Long Chain Fatty Acid Processing in the Intestinal Epithelium

Nuclear receptor PPARγ affects lipid metabolism in several tissues, but its role in intestinal lipid metabolism has not been explored. As alterations have been observed in the plasma lipid profile of ad libitum fed intestinal epithelium-specific PPARγ knockout mice (iePPARγKO), we submitted these mice to lipid gavage challenges. Within hours after gavage with long chain unsaturated fatty acid (FA)-rich canola oil, the iePPARγKO mice had higher plasma free FA levels and lower gastric inhibitory polypeptide levels than their wild-type (WT) littermates, and altered expression of incretin genes and lipid metabolism-associated genes in the intestinal epithelium. Gavage with the medium chain saturated FA-rich coconut oil did not result in differences between the two genotypes. Furthermore, the iePPARγKO mice did not exhibit defective lipid uptake and stomach emptying; however, their intestinal transit was more rapid than in WT mice. When fed a canola oil-rich diet for 4.5 months, iePPARγKO mice had higher body lean mass than the WT mice. We conclude that intestinal epithelium PPARγ is activated preferentially by long chain unsaturated FAs compared to medium chain saturated FAs. Furthermore, we hypothesize that the iePPARγKO phenotype originates from altered lipid metabolism and release in epithelial cells, as well as changes in intestinal motility.

You Are What You Eat: Linking High-Fat Diet to Stem Cell Dysfunction and Tumorigenesis

A high-fat diet is linked to elevated cancer risk, yet this link remains poorly understood. New studies in mice are now beginning to obtain mechanistic insight into how high-fat diets perturb stem cell function and cause cancers.

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.

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.

Requirement of Gαq/Gα11 Signaling in the Preservation of Mouse Intestinal Epithelial Homeostasis

BACKGROUND & AIMS

Proliferation, differentiation, and morphogenesis of the intestinal epithelium are tightly regulated by a number of molecular pathways. Coordinated action of intestine is achieved by gastrointestinal hormones, most of which exert these actions through G-protein-coupled receptors. We herein investigated the role of Gα_q/11-mediated signaling in intestinal homeostasis.

METHODS

Intestinal tissues from control (Gnaq^flox/floxGna11^+/+ ), Int-G_q knock-out (KO) (VilCre^+/-Gnaq^flox/floxGna11^+/+ ), G₁₁ KO (Gnaq^flox/floxGna11^-/- ), and Int-G_q/G₁₁ double knock-out (DKO) (VilCre^+/-Gnaq^flox/floxGna11^-/- ) mice were examined by microscopy, transmission electron microscopy, and immunohistochemistry. The effect of Gα_q/11-mediated signaling was studied in the cell lineage, proliferation, and apoptosis. Dextran sodium sulfate (DSS) colitis was induced to study the role of Gα_q/11 in colon.

RESULTS

Paneth cells were enlarged, increased in number, and mislocalized in Int-Gq/G11 DKO small intestine. Paneth cells also reacted with PAS and Muc2 antibody, indicating an intermediate character of Paneth and goblet cells. The nuclear β-catenin, T-cell factor 1, and Sox9 expression were reduced severely in the crypt base of Int-Gq/G11 DKO intestine. Proliferation was activated in the crypt base and apoptosis was enhanced along the crypt. Int-Gq/G11 DKO mice were susceptible to DSS colitis. Proliferation was inhibited in the crypt of unaffected and regenerative areas. Cystic crypts, periodic acid-Schiff-positive cells, and Muc2-positive cells were unusually observed in the ulcerative region.

CONCLUSIONS

The Gα_q/11-mediated pathway plays a pivotal role in the preservation of intestinal homeostasis, especially in Paneth cell maturation and positioning. Wnt/β-catenin signaling was reduced significantly in the crypt base in Gα_q/G₁₁-deficient mice, resulting in the defective maturation of Paneth cells, induction of differentiation toward goblet cells, and susceptibility to DSS colitis.

The PPARβ/δ Agonist GW0742 Induces Early Neuronal Maturation of Cortical Post-Mitotic Neurons: Role of PPARβ/δ in Neuronal Maturation

Increasing evidences support that signaling lipids participate in synaptic plasticity and cell survival, and that the lipid signaling is closely associated with neuronal differentiation, learning, and memory and with pathologic events, such as epilepsy and Alzheimer's disease. The Peroxisome Proliferator-Activated Receptors (PPAR) are strongly involved in the fatty acid cell signaling, as many of the natural lypophylic compounds are PPAR ligands. We have previously shown that PPARβ/δ is the main isotype present in cortical neuron primary cultures and that during neuronal maturation, PPARβ/δ is gradually increased and activated. To get more insight into the molecular mechanism by which PPARβ/δ may be involved in neuronal maturation processes, in this work a specific PPARβ/δ agonist, GW0742 was used administered alone or in association with a specific PPARβ/δ antagonist, the GSK0660, and the parameters involved in neuronal differentiation and maturation were assayed. The data obtained demonstrated the strong involvement of PPARβ/δ in neuronal maturation, triggering the agonist an anticipation of neuronal differentiation, and the antagonist abolishing the observed effects. These effects appear to be mediated by the activation of BDNF pathway.

Metabolic and Inflammatory Adaptation of Reactive Astrocytes: Role of PPARs

Astrocyte-mediated inflammation is associated with degenerative pathologies such as Alzheimer's and Parkinson's diseases and multiple sclerosis. The acute inflammation and morphological and metabolic changes that astrocytes develop after the insult are known as reactive astroglia or astrogliosis that is an important response to protect and repair the lesion. Astrocytes optimize their metabolism to produce lactate, glutamate, and ketone bodies in order to provide energy to the neurons that are deprived of nutrients upon insult. Firstly, we review the basis of inflammation and morphological changes of the different cell population implicated in reactive gliosis. Next, we discuss the more active metabolic pathways in healthy astrocytes and explain the metabolic response of astrocytes to the insult in different pathologies and which metabolic alterations generate complications in these diseases. We emphasize the role of peroxisome proliferator-activated receptors isotypes in the inflammatory and metabolic adaptation of astrogliosis developed in ischemia or neurodegenerative diseases. Based on results reported in astrocytes and other cells, we resume and hypothesize the effect of peroxisome proliferator-activated receptor (PPAR) activation with ligands on different metabolic pathways in order to supply energy to the neurons. The activation of selective PPAR isotype activity may serve as an input to better understand the role played by these receptors on the metabolic and inflammatory compensation of astrogliosis and might represent an opportunity to develop new therapeutic strategies against traumatic brain injuries and neurodegenerative diseases.

Integrative and systemic approaches for evaluating PPARβ/δ (PPARD) function

The peroxisome proliferator-activated receptors (PPARs) are a group of nuclear receptors that function as transcription factors regulating the expression of genes involved in cellular differentiation, development, metabolism and also tumorigenesis. Three PPAR isotypes (α, β/δ and γ) have been identified, among which PPARβ/δ is the most difficult to functionally examine due to its tissue-specific diversity in cell fate determination, energy metabolism and housekeeping activities. PPARβ/δ acts both in a ligand-dependent and -independent manner. The specific type of regulation, activation or repression, is determined by many factors, among which the type of ligand, the presence/absence of PPARβ/δ-interacting corepressor or coactivator complexes and PPARβ/δ protein post-translational modifications play major roles. Recently, new global approaches to the study of nuclear receptors have made it possible to evaluate their molecular activity in a more systemic fashion, rather than deeply digging into a single pathway/function. This systemic approach is ideally suited for studying PPARβ/δ, due to its ubiquitous expression in various organs and its overlapping and tissue-specific transcriptomic signatures. The aim of the present review is to present in detail the diversity of PPARβ/δ function, focusing on the different information gained at the systemic level, and describing the global and unbiased approaches that combine a systems view with molecular understanding.

Physiological functions of peroxisome proliferator-activated receptor β

The peroxisome proliferator-activated receptors, PPARα, PPARβ, and PPARγ, are a family of transcription factors activated by a diversity of molecules including fatty acids and fatty acid metabolites. PPARs regulate the transcription of a large variety of genes implicated in metabolism, inflammation, proliferation, and differentiation in different cell types. These transcriptional regulations involve both direct transactivation and interaction with other transcriptional regulatory pathways. The functions of PPARα and PPARγ have been extensively documented mainly because these isoforms are activated by molecules clinically used as hypolipidemic and antidiabetic compounds. The physiological functions of PPARβ remained for a while less investigated, but the finding that specific synthetic agonists exert beneficial actions in obese subjects uplifted the studies aimed to elucidate the roles of this PPAR isoform. Intensive work based on pharmacological and genetic approaches and on the use of both in vitro and in vivo models has considerably improved our knowledge on the physiological roles of PPARβ in various cell types. This review will summarize the accumulated evidence for the implication of PPARβ in the regulation of development, metabolism, and inflammation in several tissues, including skeletal muscle, heart, skin, and intestine. Some of these findings indicate that pharmacological activation of PPARβ could be envisioned as a therapeutic option for the correction of metabolic disorders and a variety of inflammatory conditions. However, other experimental data suggesting that activation of PPARβ could result in serious adverse effects, such as carcinogenesis and psoriasis, raise concerns about the clinical use of potent PPARβ agonists.

Loss of Sirt1 function improves intestinal anti-bacterial defense and protects from colitis-induced colorectal cancer

Dysfunction of Paneth and goblet cells in the intestine contributes to inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC). Here, we report a role for the NAD⁺-dependent histone deacetylase SIRT1 in the control of anti-bacterial defense. Mice with an intestinal specific Sirt1 deficiency (Sirt1^int−/−) have more Paneth and goblet cells with a consequent rearrangement of the gut microbiota. From a mechanistic point of view, the effects on mouse intestinal cell maturation are mediated by SIRT1-dependent changes in the acetylation status of SPDEF, a master regulator of Paneth and goblet cells. Our results suggest that targeting SIRT1 may be of interest in the management of IBD and CAC.

Role of Peroxisome Proliferator-Activated Receptor (PPAR)δ in Embryonic Stem Cell Proliferation

The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear receptor family. It is well known that PPARs function as regulators of lipid and lipoprotein metabolism and glucose homeostasis, as well as influence cellular proliferation, differentiation and apoptosis. However, the role of the PPARs with regard to embryonic stem (ES) cells remains unknown. We will review the function of the PPARδ, one of the three PPAR isoforms, α, δ (also called β/δ), and γ, in ES cells and its role in embryo development. In addition, pluripotent mouse ES cells can be expanded in large numbers in vitro due to the process of symmetrical self-renewal. Here we describe how PPARδ sustains ES cell proliferation.

Loss of Sonic hedgehog leads to alterations in intestinal secretory cell maturation and autophagy

Background

Intestinal epithelial cells express the Sonic and Indian hedgehog ligands. Despite the strong interest in gut hedgehog signaling in GI diseases, no studies have specifically addressed the singular role of intestinal epithelial cell Sonic hedgehog signaling. The aim of this study was to investigate the specific role of Sonic hedgehog in adult ileal epithelial homeostasis.

Methodology/Principal Findings

A Sonic hedgehog intestinal epithelial conditional knockout mouse model was generated. Assessment of ileal histological abnormalities, crypt epithelial cell proliferation, epithelial cell fate, junctional proteins, signaling pathways, as well as ultrastructural analysis of intracellular organelles were performed in control and mutant mice. Mice lacking intestinal epithelial Sonic Hedgehog displayed decreased ileal crypt/villus length, decreased crypt proliferation as well as a decrease in the number of ileal mucin-secreting goblet cells and antimicrobial peptide-secreting Paneth cells during adult life. These secretory cells also exhibited disruption of their secretory products in mutant mice. Ultrastructural microscopy analysis revealed a dilated ER lumen in secretory cells. This phenotype was also associated with a decrease in autophagy.

Conclusions/Significance

Altogether, these findings indicate that the loss of Sonic hedgehog can lead to ileal secretory cell modifications indicative of endoplasmic reticulum stress, accompanied by a significant reduction in autophagy.

The prognostic significance of peroxisome proliferator-activated receptor β expression in the vascular endothelial cells of colorectal cancer

OBJECTIVE

Currently, little is known regarding the role of peroxisome proliferator-activated receptor-β (PPAR β) in the vascular endothelial cells (VECs) of colorectal cancers (CRCs). The aim of this study was to investigate the relationship of PPAR β expression in the VECs of CRCs in terms of the prognosis and clinicopathological features of CRC patients.

DESIGN

The expression and localization of PPAR β in the primary cancers and the matched normal mucosal samples of 141 Swedish CRC patients were analyzed in terms of its correlation with clinicopathological features and the expression of angiogenesis-related genes. This study also included 92 Chinese CRC patients.

RESULTS

PPAR β was predominantly localized in the cytoplasm and was significantly downregulated in the VECs of CRC compared to that of the normal mucosa. The low expression levels of PPAR β in the VECs of CRC were statistically correlated with enhanced differentiation, early staging and favorable overall survival and were associated with the increased expression of VEGF and D2-40. The patients exhibiting elevated expression of PPAR β in CRC cells but reduced expression in VECs exhibited more favorable survival compared with the other patients, whereas the patients with reduced expression of PPAR β in CRC cells but increased expression in VECs exhibited less favorable prognosis.

CONCLUSIONS

PPAR β might play a tumor suppressor role in CRC cells in contrast to a tumor promoter role in the VECs of CRCs.

Understanding and modulating mammalian-microbial communication for improved human health

The molecular basis for the regulation of the intestinal barrier is a very fertile research area. A growing body of knowledge supports the targeting of various components of intestinal barrier function as means to treat a variety of diseases, including the inflammatory bowel diseases. Herein, we will summarize the current state of knowledge of key xenobiotic receptor regulators of barrier function, highlighting recent advances, such that the field and its future are succinctly reviewed. We posit that these receptors confer an additional dimension of host-microbe interaction in the gut, by sensing and responding to metabolites released from the symbiotic microbiota, in innate immunity and also in host drug metabolism. The scientific evidence for involvement of the receptors and its molecular basis for the control of barrier function and innate immunity regulation would serve as a rationale towards development of non-toxic probes and ligands as drugs.

Paneth cells expand from newly created and preexisting cells during repair after doxorubicin-induced damage

Paneth cell numbers increase following intestinal damage, but mechanisms driving this process are not understood. We hypothesized that the increase in Paneth cell numbers is due to recruitment of cells from a preexisting pool of secretory progenitors. Mice were given a single injection of doxorubicin (Dox), and intestinal tissue was collected 0-168 h after treatment. Paneth, goblet, and intermediate cells were counted and evaluated for cell morphology. Quantitative RT-PCR was used to measure expression of various genes associated with Paneth cell allocation and maturation. Paneth cells were birth dated using incorporation of thymidine analogs given before or after Dox. Staining revealed "intermediate" cells, which were rarely observed in control crypts but increased significantly in number 96 and 120 h after Dox treatment. Birth dating of intermediate cells 5 days after Dox treatment revealed that 24% of these cells took up thymidine analog given prior to Dox treatment and 36% took up thymidine analog given after Dox treatment. Quantitative RT-PCR demonstrated a significant increase in Spdef, Atoh1, Sox9, EphB3, Mist, Wnt5a, FGF-9, and FGF-18 mRNAs and a significant decrease in Indian hedgehog mRNA. Expansion of the Paneth cell compartment after Dox treatment is due to generation of new cells and recruitment of cells from an existing pool. These cells express Paneth and goblet biomarkers and are found only during repair. Expansion of these cells correlates temporally with reduced Indian hedgehog and increased FGF and Wnt mRNA. These findings are significant, as they provide a first step in understanding mechanisms of Paneth cell expansion during mucosal repair.

Knockdown of PPAR δ gene promotes the growth of colon cancer and reduces the sensitivity to bevacizumab in nude mice model

The role of peroxisome proliferator – activated receptor- δ (PPAR δ) gene in colon carcinogenesis remains highly controversial. Here, we established nude mice xenograft model using a human colon cancer cell line KM12C either with PPAR δ silenced or normal. The xenografts in PPAR δ-silenced group grew significantly larger and heavier with less differentiation, promoted cell proliferation, increased expression of vascular endothelial growth factor (VEGF) and similar apoptosis index compared with those of PPAR δ-normal group. After treated with the specific VEGF inhibitor bevacizumab, the capacities of growth and proliferation of xenografts were decreased in both groups while still significantly higher in PPAR δ-silenced group than in PPAR δ-normal group. Administration of PPAR δ agonist significantly decreased VEGF expression in PPAR δ-normal KM12C cells but not in PPAR δ-silenced cells. These findings demonstrate that, knockdown of PPAR δ promotes the growth of colon cancer by inducing less differentiation, accelerating the proliferation and VEGF expression of tumor cells in vivo, and reduces tumor sensitivity to bevacizumab. This study indicates that PPAR δ attenuates colon carcinogenesis.

PPARβ/δ affects pancreatic β cell mass and insulin secretion in mice

PPARβ/δ protects against obesity by reducing dyslipidemia and insulin resistance via effects in muscle, adipose tissue, and liver. However, its function in pancreas remains ill defined. To gain insight into its hypothesized role in β cell function, we specifically deleted Pparb/d in the epithelial compartment of the mouse pancreas. Mutant animals presented increased numbers of islets and, more importantly, enhanced insulin secretion, causing hyperinsulinemia. Gene expression profiling of pancreatic β cells indicated a broad repressive function of PPARβ/δ affecting the vesicular and granular compartment as well as the actin cytoskeleton. Analyses of insulin release from isolated PPARβ/δ-deficient islets revealed an accelerated second phase of glucose-stimulated insulin secretion. These effects in PPARβ/δ-deficient islets correlated with increased filamentous actin (F-actin) disassembly and an elevation in protein kinase D activity that altered Golgi organization. Taken together, these results provide evidence for a repressive role for PPARβ/δ in β cell mass and insulin exocytosis, and shed a new light on PPARβ/δ metabolic action.

The role of peroxisome proliferator-activated receptors in colorectal cancer

Colorectal cancer is one of the most common cancers in the world. Dietary fat intake is a major risk factor for colorectal cancer. Some nuclear hormone receptors play an important role in regulating nutrient metabolism and energy homeostasis. Among these receptors, special attention has been focused on the role of peroxisome proliferator-activated receptors (PPARs) in colorectal cancer, because PPARs are involved in regulation of lipid and carbohydrate metabolism. PPARs are ligand-activated intracellular transcription factors. The PPAR subfamily consists of three subtypes encoded by distinct genes named PPARα, PPARβ/δ, and PPARγ. PPARγ is the most extensively studied subtype of PPARs. Even though many investigators have studied the expression and clinical implications of PPARs in colorectal cancer, there are still many controversies about the role of PPARs in colorectal cancer. In this paper, the recent progresses in understanding the role of PPARs in colorectal cancer are summarized.

The role of peroxisome proliferator-activated receptors in the esophageal, gastric, and colorectal cancer

Tumors of the gastrointestinal tract are among the most frequent human malignancies and account for approximately 30% of cancer-related deaths worldwide. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that control diverse cellular functions such as proliferation, differentiation, and cell death. Owing to their involvement in so many processes, they play crucial roles also in the development and physiology of the gastrointestinal tract. Consistently, PPARs deregulation has been implicated in several pathophysiological conditions, including chronic inflammation and cancer development. This paper summarizes the current knowledge on the role that the various PPAR isoforms play in the pathogenesis of the esophageal, gastric, and intestinal cancer. Elucidation of the molecular mechanisms underlying PPARs' signaling pathways will provide insights into their possible use as predictive biomarkers in the initial stages of the process. In addition, this understanding will provide the basis for new molecular targets in cancer therapy and chemoprevention.

Recent advances in small bowel diseases: Part I

As is the case in all parts of gastroenterology and hepatology, there have been many advances in our knowledge and understanding of small intestinal diseases. Over 1000 publications were reviewed for 2008 and 2009, and the important advances in basic science as well as clinical applications were considered. In Part I of this Editorial Review, seven topics are considered: intestinal development; proliferation and repair; intestinal permeability; microbiotica, infectious diarrhea and probiotics; diarrhea; salt and water absorption; necrotizing enterocolitis; and immunology/allergy. These topics were chosen because of their importance to the practicing physician.

PPARs at the crossroads of lipid signaling and inflammation

Nuclear receptors (NRs) are ligand-dependent transcription factors whose activation affects genes controlling vital processes. Among them, the peroxisome proliferator-activated receptors (PPARs) have emerged as links between lipids, metabolic diseases, and innate immunity. PPARs are activated by fatty acids and their derivatives, many of which also signal through membrane receptors, thereby creating a lipid signaling network between the cell surface and the nucleus. Tissues that play a role in whole-body metabolic homeostasis, such as adipose tissue, liver, skeletal muscle, intestines, and blood vessel walls, are prone to inflammation when metabolism is disturbed, a complication that promotes type 2 diabetes and cardiovascular disease. This review discusses the protective roles of PPARs in inflammatory conditions and the therapeutic anti-inflammatory potential of PPAR ligands.

Dissecting the role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) in colon, breast, and lung carcinogenesis

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is a promising drug target since its agonists increase serum high-density lipoprotein; decrease low-density lipoprotein, triglycerides, and insulin associated with metabolic syndrome; improve insulin sensitivity; and decrease high fat diet-induced obesity. PPARβ/δ agonists also promote terminal differentiation and elicit anti-inflammatory activities in many cell types. However, it remains to be determined whether PPARβ/δ agonists can be developed as therapeutics because there are reports showing either pro- or anti-carcinogenic effects of PPARβ/δ in cancer models. This review examines studies reporting the role of PPARβ/δ in colon, breast, and lung cancers. The prevailing evidence would suggest that targeting PPARβ/δ is not only safe but could have anti-carcinogenic protective effects.

Control of adult stem cells in vivo by a dynamic physiological environment: diet-dependent systemic factors in Drosophila and beyond

Adult stem cells are inextricably linked to whole-body physiology and nutrient availability through complex systemic signaling networks. A full understanding of how stem cells sense and respond to dietary fluctuations will require identifying key systemic mediators, as well as elucidating how they are regulated and integrated with local and intrinsic factors across multiple tissues. Studies focused on the Drosophila germline have generated valuable insights into how stem cells are controlled by diet-dependent pathways, and increasing evidence suggests that diverse adult stem cell populations respond to nutrients through similar mechanisms. Systemic signals, including nutrients themselves and diet-regulated hormones such as Insulin/Insulin-like growth factor or steroid hormones, can directly or indirectly affect stem cell behavior by modifying local cell-cell communication or intrinsic factors. The physiological regulation of stem cells in response to nutritional status not only is a fascinating biological problem, but also has clinical implications, as research in this field holds the key to noninvasive approaches for manipulating stem cells in vivo. In addition, given the known associations between diet, stem cells, and cancer risk, this research may inspire novel anticancer therapies.

Conditional Expression of Human PPARδ and a Dominant Negative Variant of hPPARδ In Vivo

The nuclear receptor, NR1C2 or peroxisome proliferator-activated receptor (PPAR)-δ, is ubiquitously expressed and important for placental development, fatty acid metabolism, wound healing, inflammation, and tumour development. PPARδ has been hypothesized to function as both a ligand activated transcription factor and a repressor of transcription in the absence of agonist. In this paper, treatment of mice conditionally expressing human PPARδ with GW501516 resulted in a marked loss in body weight that was not evident in nontransgenic animals or animals expressing a dominant negative derivative of PPARδ. Expression of either functional or dominant negative hPPARδ blocked bezafibrate-induced PPARα-dependent hepatomegaly and blocked the effect of bezafibrate on the transcription of PPARα target genes. These data demonstrate, for the first time, that PPARδ could inhibit the activation of PPARα in vivo and provide novel models for the investigation of the role of PPARδ in pathophysiology.

High-affinity peroxisome proliferator-activated receptor β/δ-specific ligands with pure antagonistic or inverse agonistic properties

Peroxisome proliferator-activated receptor β/δ (PPARβ/δ) is a ligand-regulated nuclear receptor with essential functions in metabolism and inflammation. We have synthesized a new derivative [methyl 3-(N-(4-(hexylamino)-2-methoxyphenyl)sulfamoyl)thiophene-2-carboxylate (ST247) structurally related to the published PPARβ/δ inhibitory ligand methyl 3-(N-(2-methoxy-4-(phenylamino)phenyl)sulfamoyl)thiophene-2-carboxylate (GSK0660). ST247 has a higher affinity to PPARβ/δ than GSK0660, and at equimolar concentrations, it more efficiently 1) induces the interaction with corepressors both in vitro and in vivo, 2) inhibits the agonist-induced transcriptional activity of PPARβ/δ, and 3) down-regulates basal level expression of the peroxisome proliferator responsive element-driven PPARβ/δ target gene ANGPTL4. Methyl 3-(N-(4-(tert-butylamino)-2-methoxyphenyl)sulfamoyl)thiophene-2-carboxylate (PT-S58), another high-affinity derivative from our series, also efficiently inhibits agonist-induced transcriptional activation, but in contrast to ST247, it does not enhance the interaction of PPARβ/δ with corepressors. PT-S58 rather prevents corepressor recruitment triggered by the inverse agonist ST247. These findings classify ST247 as an inverse agonist, whereas PT-S58 is the first pure PPARβ/δ antagonist described to date. It is noteworthy that ST247 and PT-S58 are also effective on PPRE-independent functions of PPARβ/δ: in monocytic cells, both ligands modulate expression of the activation marker CCL2 in the opposite direction as an established PPARβ/δ agonist. The possibility to differentially modulate specific functions of PPARβ/δ makes these novel compounds invaluable tools to advance our understanding of PPARβ/δ biology.

Development of improved PPARβ/δ inhibitors

GSK0660 (1) is the first peroxisome proliferator-activated receptor (PPAR) β/δ-selective inhibitory ligand described in the literature. Based on its structure, we designed and synthesized a series of modified compounds to establish preliminary structure-activity relationships. Most beneficial for increased binding affinity towards the PPARβ/δ ligand binding domain was the replacement of the 4'-aminophenyl substituent by medium-length n-alkyl chains, such as n-butyl or iso-pentyl. These compounds show activity down to the one-digit nanomolar range, thus possessing up to a tenfold higher binding affinity compared with GSK0660. Additionally, the subtype-specific inhibition of PPARβ/δ was confirmed in a cell-based assay making these compounds invaluable tools for the further exploration of the functions of PPARβ/δ.

PPARgamma and PPARdelta as Modulators of Neoplasia and Cell Fate

PPARγ and PPARδ agonists represent unique classes of drugs that act through their ability to modulate gene transcription associated with intermediary metabolism, differentiation, tumor suppression, and in some instances proliferation and cell adhesion. PPARγ agonists are used by millions of people each year to treat type 2 diabetes but may also find additional utility as relatively nontoxic potentiators of chemotherapy. PPARδ agonists produce complex actions as shown by their tumor promoting effects in rodents and their cholesterol-lowering action in dyslipidemias. There is now emerging evidence that PPARs regulate tumor suppressor genes and developmental pathways associated with transformation and cell fate determination. This review discusses the role of PPARγ and PPARδ agonists as modulators of these processes.

A Role for PPARbeta/delta in Tumor Stroma and Tumorigenesis

Peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) is a transcription factor that is activated by endogenous fatty acid ligands and by synthetic agonists. Its role in the regulation of skeletal muscle fatty acid catabolism, glucose homeostasis, and cellular differentiation has been established in multiple studies. On the contrary, a role for PPARβ/δ in tumorigenesis is less clear because there are contradictory reports in the literature. However, the majority of these studies have not examined the role of PPARβ/δ in the tumor stroma. Recent evidence suggests that stromal PPARβ/δ regulates tumor endothelial cell proliferation and promotes differentiation leading to the properly orchestrated events required for tumor blood vessel formation. This review briefly summarizes the significance of these studies that may provide clues to help explain the reported discrepancies in the literature regarding the role of PPARβ/δ in tumorigenesis.

The multiple roles of autophagy in cancer

Autophagy is an evolutionarily conserved, catabolic process that involves the entrapment of cytoplasmic components within characteristic vesicles for their delivery to and degradation within lysosomes. Autophagy is regulated via a group of genes called AuTophaGy-related genes and is executed at basal levels in virtually all cells as a homeostatic mechanism for maintaining cellular integrity. The levels and cargos of autophagy can be modulated in response to a variety of intra- and extracellular cues to bring about specific and selective events. Autophagy is a multifaceted process and alterations in autophagic signalling pathways are frequently found in cancer and many other diseases. During tumour development and in cancer therapy, autophagy has paradoxically been reported to have roles in promoting both cell survival and cell death. In addition, autophagy has been reported to control other processes relevant to the aetiology of malignant disease, including oxidative stress, inflammation and both innate and acquired immunity. It is the aim of this review to describe the molecular basis and the signalling events that control autophagy in mammalian cells and to summarize the cellular functions that contribute to tumourigenesis when autophagy is perturbed.

Hedgehog signaling controls homeostasis of adult intestinal smooth muscle

The Hedgehog (Hh) pathway plays multiple patterning roles during development of the mammalian gastrointestinal tract, but its role in adult gut function has not been extensively examined. Here we show that chronic reduction in the combined epithelial Indian (Ihh) and Sonic (Shh) hedgehog signal leads to mislocalization of intestinal subepithelial myofibroblasts, loss of smooth muscle in villus cores and muscularis mucosa as well as crypt hyperplasia. In contrast, chronic over-expression of Ihh in the intestinal epithelium leads to progressive expansion of villus smooth muscle, but does not result in reduced epithelial proliferation. Together, these mouse models show that smooth muscle populations in the adult intestinal lamina propria are highly sensitive to the level of Hh ligand. We demonstrate further that Hh ligand drives smooth muscle differentiation in primary intestinal mesenchyme cultures and that cell-autonomous Hh signal transduction in C3H10T1/2 cells activates the smooth muscle master regulator Myocardin (Myocd) and induces smooth muscle differentiation. The rapid kinetics of Myocd activation by Hh ligands as well as the presence of an unusual concentration of Gli sties in this gene suggest that regulation of Myocd by Hh might be direct. Thus, these data indicate that Hh is a critical regulator of adult intestinal smooth muscle homeostasis and suggest an important link between Hh signaling and Myocd activation. Moreover, the data support the idea that lowered Hh signals promote crypt expansion and increased epithelial cell proliferation, but indicate that chronically increased Hh ligand levels do not dampen crypt proliferation as previously proposed.

Fibroblast growth factor receptor-3 (FGFR-3) regulates expression of paneth cell lineage-specific genes in intestinal epithelial cells through both TCF4/beta-catenin-dependent and -independent signaling pathways

Fibroblast growth factor receptor-3 (FGFR-3) expression in the developing intestine is restricted to the undifferentiated epithelial cells within the lower portion of the crypt. We previously showed that mice lacking functional FGFR-3 have a significant decrease in the number of Paneth cells in the small intestine. Here, we used Caco2 cells to investigate whether FGFR-3 signaling can directly modulate expression of Paneth cell differentiation markers through its effects on TCF4/β-catenin or through other signaling pathways downstream of this receptor. Caco2 cells treated with FGFR-3 ligands or expressing FGFR-3(K650E), a constitutively active mutant, resulted in a significantly increased expression of genes characteristic of mature Paneth cells, including human α-defensins 5 and 6 (HD5 and HD6) and Paneth cell lysozyme, whereas enterocytic differentiation markers were reduced. Activation of FGFR-3 signaling sustained high levels of β-catenin mRNA expression, leading to increased TCF4/β-catenin-regulated transcriptional activity in Caco2 cells. Sustained activity of the TCF4/β-catenin pathway was required for the induction of Paneth cell markers. Activation of the MAPK pathway by FGFR-3 is also required for the induction of Paneth cell markers in addition to and independent of the effect of FGFR-3 on TCF4/β-catenin activity. These studies suggest that coordinate activation of multiple independent signaling pathways downstream of FGFR-3 is involved in regulation of Paneth cell differentiation.

Defensins couple dysbiosis to primary immunodeficiency in Crohn’s disease

Antimicrobial peptides, including defensins, are essential effectors in host defence and in the maintenance of immune homeostasis. Clinical studies have linked the defective expression of both α- and β-defensin to the reduced killing of certain microorganisms by the intestinal mucosa of patients suffering from ileal and colonic Crohn’s disease (CD), respectively. Only recently have the events leading to defective expression of defensins in CD been further elucidated, and are discussed herein. These events may account for CD-associated alterations in the microbiome and may subsequently precipitate the development of granulomatous inflammatory lesions in genetically-predisposed patients. We also address how these discoveries may pave the way for the development of a molecular medicine aimed at restoring gut barrier function in CD.

Vertebrate intestinal endoderm development

The endoderm gives rise to the lining of the esophagus, stomach and intestines, as well as associated organs. To generate a functional intestine, a series of highly orchestrated developmental processes must occur. In this review, we attempt to cover major events during intestinal development from gastrulation to birth, including endoderm formation, gut tube growth and patterning, intestinal morphogenesis, epithelial reorganization, villus emergence, as well as proliferation and cytodifferentiation. Our discussion includes morphological and anatomical changes during intestinal development as well as molecular mechanisms regulating these processes.

A key role for E-cadherin in intestinal homeostasis and Paneth cell maturation

Background

E-cadherin is a major component of adherens junctions. Impaired expression of E-cadherin in the small intestine and colon has been linked to a disturbed intestinal homeostasis and barrier function. Down-regulation of E-cadherin is associated with the pathogenesis of infections with enteropathogenic bacteria and Crohn's disease.

Methods and Findings

To genetically clarify the function of E-cadherin in intestinal homeostasis and maintenance of the epithelial defense line, the Cdh1 gene was conditionally inactivated in the mouse intestinal epithelium. Inactivation of the Cdh1 gene in the small intestine and colon resulted in bloody diarrhea associated with enhanced apoptosis and cell shedding, causing life-threatening disease within 6 days. Loss of E-cadherin led cells migrate faster along the crypt-villus axis and perturbed cellular differentiation. Maturation and positioning of goblet cells and Paneth cells, the main cell lineage of the intestinal innate immune system, was severely disturbed. The expression of anti-bacterial cryptidins was reduced and mice showed a deficiency in clearing enteropathogenic bacteria from the intestinal lumen.

Conclusion

These results highlight the central function of E-cadherin in the maintenance of two components of the intestinal epithelial defense: E-cadherin is required for the proper function of the intestinal epithelial lining by providing mechanical integrity and is a prerequisite for the proper maturation of Paneth and goblet cells.

Indian hedgehog regulates intestinal stem cell fate through epithelial-mesenchymal interactions during development

BACKGROUND & AIMS

Intestinal stem cells (ISCs) are regulated by the mesenchymal environment via physical interaction and diffusible factors. We examined the role of Indian hedgehog (Ihh) in mesenchymal organization and the mechanisms by which perturbations in epithelial-mesenchymal interactions affect ISC fate.

METHODS

We generated mice with intestinal epithelial-specific disruption of Ihh. Gross and microscopic anatomical changes were determined using histologic, immunohistochemical, and in situ hybridization analyses. Molecular mechanisms were elucidated by expression profiling and in vitro analyses.

RESULTS

Deletion of intestinal epithelial Ihh disrupted the intestinal mesenchymal architecture, demonstrated by loss of the muscularis mucosae, deterioration of the extracellular matrix, and reductions in numbers of crypt myofibroblasts. Concurrently, the epithelial compartment had increased Wnt signaling, disturbed crypt polarity and architecture, defective enterocyte differentiation, and increased and ectopic proliferation that was accompanied by increased numbers of ISCs. Mechanistic studies revealed that Hh inhibition deregulates bone morphogenetic protein signaling, increases matrix metalloproteinase levels, and disrupts extracellular matrix proteins, fostering a proliferative environment for ISCs and progenitor cells.

CONCLUSIONS

Ihh regulates ISC self-renewal and differentiation. Intestinal epithelial Ihh signals to the mesenchymal compartment to regulate formation and proliferation of mesenchymal cells, which in turn affect epithelial proliferation and differentiation. These findings provide a basis for analyses of the role of the muscularis mucosae in ISC regulation.

Peroxisome proliferator-activated receptor gamma activation is required for maintenance of innate antimicrobial immunity in the colon

Crohn's disease (CD), a major form of human inflammatory bowel disease, is characterized by primary immunodeficiencies. The nuclear receptor peroxisome proliferator-activated receptor gamma (PPARgamma) is essential for intestinal homeostasis in response to both dietary- and microbiota-derived signals. Its role in host defense remains unknown, however. We show that PPARgamma functions as an antimicrobial factor by maintaining constitutive epithelial expression of a subset of beta-defensin in the colon, which includes mDefB10 in mice and DEFB1 in humans. Colonic mucosa of Ppargamma mutant animals shows defective killing of several major components of the intestinal microbiota, including Candida albicans, Bacteroides fragilis, Enterococcus faecalis, and Escherichia coli. Neutralization of the colicidal activity using an anti-mDefB10 blocking antibody was effective in a PPARgamma-dependent manner. A functional promoter variant that is required for DEFB1 expression confers strong protection against Crohn's colitis and ileocolitis (odds ratio, 0.559; P = 0.018). Consistently, colonic involvement in CD is specifically linked to reduced expression of DEFB1 independent of inflammation. These findings support the development of PPARgamma-targeting therapeutic and/or nutritional approaches to prevent colonic inflammation by restoring antimicrobial immunity in CD.