Hippo cooperates with p53 to maintain foregut homeostasis and suppress the malignant transformation of foregut basal progenitor cells

Basal progenitor cells serve as a stem cell pool to maintain the homeostasis of the epithelium of the foregut, including the esophagus and the forestomach. Aberrant genetic regulation in these cells can lead to carcinogenesis, such as squamous cell carcinoma (SCC). However, the underlying molecular mechanisms regulating the function of basal progenitor cells remain largely unknown. Here, we use mouse models to reveal that Hippo signaling is required for maintaining the homeostasis of the foregut epithelium and cooperates with p53 to repress the initiation of foregut SCC. Deletion of Mst1/2 in mice leads to epithelial overgrowth in both the esophagus and forestomach. Further molecular studies find that Mst1/2-deficiency promotes epithelial growth by enhancing basal cell proliferation in a Yes-associated protein (Yap)-dependent manner. Moreover, Mst1/2 deficiency accelerates the onset of foregut SCC in a carcinogen-induced foregut SCC mouse model, depending on Yap. Significantly, a combined deletion of Mst1/2 and p53 in basal progenitor cells sufficiently drives the initiation of foregut SCC. Therefore, our studies shed light on the collaborative role of Hippo signaling and p53 in maintaining squamous epithelial homeostasis while suppressing malignant transformation of basal stem cells within the foregut.

Pharmacological Improvement of CFTR Function Rescues Airway Epithelial Homeostasis and Host Defense in Children with Cystic Fibrosis

RATIONALE

Pharmacological improvement of CFTR function with elexacaftor/tezacaftor/ivacaftor (ETI) provides unprecedented improvements in lung function and other clinical outcomes to patients with cystic fibrosis (CF). However, ETI effects on impaired mucosal homeostasis and host defense at the molecular and cellular level in the airways of CF patients remain unknown.

OBJECTIVES

To investigate effects of ETI on the transcriptiome of nasal epithelial and immune cells from children with CF at the single cell level.

METHODS

Nasal swabs from 13 children with CF and at least one F508del allele aged 6 to 11 years were collected at baseline and three months after initiation of ETI, subjected to scRNA-seq and compared to swabs from 12 age-matched healthy children.

MEASUREMENTS AND MAIN RESULTS

Proportions of CFTR-positive cells were decreased in epithelial basal, club and goblet cells, but not in ionocytes from children with CF at baseline and were restored on ETI therapy to near healthy levels. Single cell transcriptomics revealed an impaired interferon signalling and reduced expression of MHC I and II encoding genes in epithelial cells of CF children at baseline, which was partially restored by ETI. Additionally, ETI therapy markedly reduced the inflammatory phenotype of immune cells, particularly of neutrophils and macrophages.

CONCLUSIONS

Pharmacological improvement of CFTR function improves innate mucosal immunity and reduces immune cell inflammatory responses in the upper airways of children with CF at the single cell level, highlighting the potential to restore epithelial homeostasis and host defense in CF airways by early initiation of ETI therapy. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Apical extrusion prevents apoptosis from activating an acute inflammatory program in epithelia

Apoptosis is traditionally considered to be an immunologically silent form of cell death. Multiple mechanisms exist to ensure that apoptosis does not stimulate the immune system to cause inflammation or autoimmunity. Against this expectation, we now report that epithelia are programmed to provoke, rather than suppress, inflammation in response to apoptosis. We found that an acute inflammatory response led by neutrophils occurs in zebrafish and cell culture when apoptotic epithelial cells cannot be expelled from the monolayer by apical extrusion. This reflects an intrinsic circuit where ATP released from apoptotic cells stimulates epithelial cells in the immediate vicinity to produce interleukin-8 (IL-8). Apical extrusion therefore prevents inappropriate epithelial inflammation by physically eliminating apoptotic cells before they can activate this pro-inflammatory circuit. This carries the implication that epithelia may be predisposed to inflammation, elicited by sporadic or induced apoptosis, if apical extrusion is compromised.

Cytoplasmic division cycles without the nucleus and mitotic CDK/cyclin complexes

Cytoplasmic divisions are thought to rely on nuclear divisions and mitotic signals. We demonstrate in Drosophila embryos that cytoplasm can divide repeatedly without nuclei and mitotic CDK/cyclin complexes. Cdk1 normally slows an otherwise faster cytoplasmic division cycle, coupling it with nuclear divisions, and when uncoupled, cytoplasm starts dividing before mitosis. In developing embryos where CDK/cyclin activity can license mitotic microtubule (MT) organizers like the spindle, cytoplasmic divisions can occur without the centrosome, a principal organizer of interphase MTs. However, centrosomes become essential in the absence of CDK/cyclin activity, implying that the cytoplasm can employ either the centrosome-based interphase or CDK/cyclin-dependent mitotic MTs to facilitate its divisions. Finally, we present evidence that autonomous cytoplasmic divisions occur during unperturbed fly embryogenesis and that they may help extrude mitotically stalled nuclei during blastoderm formation. We postulate that cytoplasmic divisions occur in cycles governed by a yet-to-be-uncovered clock mechanism autonomous from CDK/cyclin complexes.

Role of E6 in Maintaining the Basal Cell Reservoir during Productive Papillomavirus Infection

Papillomaviruses exclusively infect stratified epithelial tissues and cause chronic infections. To achieve this, infected cells must remain in the epithelial basal layer alongside their uninfected neighbors for years or even decades. To examine how papillomaviruses achieve this, we used the in vivo MmuPV1 (Mus musculus papillomavirus 1) model of lesion formation and persistence. During early lesion formation, an increased cell density in the basal layer, as well as a delay in the infected cells' commitment to differentiation, was apparent in cells expressing MmuPV1 E6/E7 RNA. Using cell culture models, keratinocytes exogenously expressing MmuPV1 E6, but not E7, recapitulated this delay in differentiation postconfluence and also grew to a significantly higher density. Cell competition assays further showed that MmuPV1 E6 expression led to a preferential persistence of the cell in the first layer, with control cells accumulating almost exclusively in the second layer. Interestingly, the disruption of MmuPV1 E6 binding to MAML1 protein abrogated these phenotypes. This suggests that the interaction between MAML1 and E6 is necessary for the lower (basal)-layer persistence of MmuPV1 E6-expressing cells. Our results indicate a role for E6 in lesion establishment by facilitating the persistence of infected cells in the epithelial basal layer, a mechanism that is most likely shared by other papillomavirus types. Interruption of this interaction is predicted to impede persistent papillomavirus infection and consequently provides a novel treatment target. IMPORTANCE Persistent infection with high-risk HPV types can lead to development of HPV-associated cancers, and persistent low-risk HPV infection causes problematic diseases, such as recurrent respiratory papillomatosis. The management and treatment of these conditions pose a considerable economic burden. Maintaining a reservoir of infected cells in the basal layer of the epithelium is critical for the persistence of infection in the host, and our studies using the mouse papillomavirus model suggest that E6 gene expression leads to the preferential persistence of epithelial cells in the lower layers during stratification. The E6 interaction with MAML1, a component of the Notch pathway, is required for this phenotype and is linked to E6 effects on cell density and differentiation. These observations are likely to reflect a common E6 role that is preserved among papillomaviruses and provide us with a novel therapeutic target for the treatment of recalcitrant lesions.

Colonizing Microbes, IL-10 and IL-22: Keeping the Peace at the Mucosal Surface

Our world is filled with microbes. Each multicellular organism has developed ways to interact with this microbial environment. Microbes do not always pose a threat; they can contribute to many processes that benefit the host. Upon colonization both host and microbes adapt resulting in dynamic ecosystems in different host niches. Regulatory processes develop within the host to prevent overt inflammation to beneficial microbes, yet keeping the possibility to respond when pathogens attempt to adhere and invade tissues. This review will focus on microbial colonization and the early (innate) host immune response, with special emphasis on the microbiota-modifying roles of IL-10 and IL-22 in the intestine. IL-10 knock out mice show an altered microbial composition, and spontaneously develop enterocolitis over time. IL-22 knock out mice, although not developing enterocolitis spontaneously, also have an altered microbial composition and increase of epithelial-adherent bacteria, mainly caused by a decrease in mucin and anti-microbial peptide production. Recently interesting links have been found between the IL-10 and IL-22 pathways. While IL-22 can function as a regulatory cytokine at the mucosal surface, it also has inflammatory roles depending on the context. For example, lack of IL-22 in the IL-10–/– mice model prevents spontaneous colitis development. Additionally, the reduced microbial diversity observed in IL-10–/– mice was also reversed in IL-10/IL-22 double mutant mice (Gunasekera et al., 2020). Since in early life, host immunity develops in parallel and in interaction with colonizing microbes, there is a need for future studies that focus on the effect of the timing of colonization in relation to the developmental phase of the host. To illustrate this, examples from zebrafish research will be compared with studies performed in mammals. Since zebrafish develop from eggs and are directly exposed to the outside microbial world, timing of the development of host immunity and subsequent control of microbial composition, is different from mammals that develop in utero and only get exposed after birth. Likewise, colonization studies using adult germfree mice might yield different results from those using neonatal germfree mice. Lastly, special emphasis will be given to the need for host genotype and environmental (co-housing) control of experiments.

Regulation of Paneth Cell Function by RNA-Binding Proteins and Noncoding RNAs

Paneth cells are specialized intestinal epithelial cells that are located at the base of small intestinal crypts and play a vital role in preserving the gut epithelium homeostasis. Paneth cells act as a safeguard from bacterial translocation across the epithelium and constitute the niche for intestinal stem cells in the small intestine by providing multiple niche signals. Recently, Paneth cells have become the focal point of investigations defining the mechanisms underlying the epithelium-microbiome interactions and pathogenesis of chronic gut mucosal inflammation and bacterial infection. Function of Paneth cells is tightly regulated by numerous factors at different levels, while Paneth cell defects have been widely documented in various gut mucosal diseases in humans. The post-transcription events, specific change in mRNA stability and translation by RNA-binding proteins (RBPs) and noncoding RNAs (ncRNAs) are implicated in many aspects of gut mucosal physiology by modulating Paneth cell function. Deregulation of RBPs and ncRNAs and subsequent Paneth cell defects are identified as crucial elements of gut mucosal pathologies. Here, we overview the posttranscriptional regulation of Paneth cells by RBPs and ncRNAs, with a particular focus on the increasing evidence of RBP HuR and long ncRNA H19 in this process. We also discuss the involvement of Paneth cell dysfunction in altered susceptibility of the intestinal epithelium to chronic inflammation and bacterial infection following disrupted expression of HuR and H19.

Collective ERK/Akt activity waves orchestrate epithelial homeostasis by driving apoptosis-induced survival

Cell death events continuously challenge epithelial barrier function yet are crucial to eliminate old or critically damaged cells. How such apoptotic events are spatio-temporally organized to maintain epithelial homeostasis remains unclear. We observe waves of extracellular-signal-regulated kinase (ERK) and AKT serine/threonine kinase (Akt) activity pulses that originate from apoptotic cells and propagate radially to healthy surrounding cells. This requires epidermal growth factor receptor (EGFR) and matrix metalloproteinase (MMP) signaling. At the single-cell level, ERK/Akt waves act as spatial survival signals that locally protect cells in the vicinity of the epithelial injury from apoptosis for a period of 3-4 h. At the cell population level, ERK/Akt waves maintain epithelial homeostasis (EH) in response to mild or intense environmental insults. Disruption of this spatial signaling system results in the inability of a model epithelial tissue to ensure barrier function in response to environmental insults.

Key Elements of Gingival Epithelial Homeostasis upon Bacterial Interaction

Epithelia are structurally integral elements in the fabric of oral mucosa with significant functional roles. Similarly, the gingival epithelium performs uniquely critical tasks in responding to a variety of external stimuli and dangers through the regulation of specific built-in molecular mechanisms in a context-dependent fashion at cellular levels. Gingival epithelial cells form an anatomic architecture that confers defense, robustness, and adaptation toward external aggressions, most critically to colonizing microorganisms, among other functions. Accordingly, recent studies unraveled previously uncharacterized response mechanisms in gingival epithelial cells that are constructed to rapidly exert biocidal effects against invader pathobiotic bacteria, such as Porphyromonas gingivalis, through small danger molecule signaling. The host-adapted bacteria, however, have developed adroit strategies to 1) exploit the epithelia as privileged growth niches and 2) chronically target cellular bactericidal and homeostatic metabolic pathways for successful bacterial persistence. As the overgrowth of colonizing microorganisms in the gingival mucosa can shift from homeostasis to dysbiosis or a diseased state, it is crucial to understand how the innate modulatory molecules are intricately involved in antibacterial pathways and how they shape susceptibility versus resistance in the epithelium toward pathogens. Thus, in this review, we highlight recent discoveries in gingival epithelial cell research in the context of bacterial colonizers. The current knowledge outlined here demonstrates the ability of epithelial cells to possess highly organized defense machineries, which can jointly regulate host-derived danger molecule signaling and integrate specific global responses against opportunistic bacteria to combat microbial incursion and maintain host homeostatic balance. These novel examples collectively suggest that the oral epithelia are equipped with a dynamically robust and interconnected defense system encompassing sensors and various effector molecules that arrange and achieve a fine-tuned and advanced response to diverse bacteria.

RNA-binding proteins and long noncoding RNAs in intestinal epithelial autophagy and barrier function

The intestinal autophagy and barrier function are crucial for maintaining the epithelium homeostasis and tightly regulated through well-controlled mechanisms. RNA-binding proteins (RBPs) and long noncoding RNAs (lncRNAs) modulate gene expression at the posttranscription level and are intimately involved in different physiological processes and diverse human diseases. In this review, we first highlight the roles of several RBPs and lncRNAs in the regulation of intestinal epithelial autophagy and barrier function, particularly focusing on the emerging evidence of RBPs and lncRNAs in the control of mRNA stability and translation. We additionally discuss recent findings that the interactions between RBPs and lncRNAs alter the fate of their target transcripts and thus influence gut epithelium host defense in response to stressful environments. These exciting advances in understanding the posttranscriptional control of the epithelial autophagy and barrier function by RBPs and lncRNAs provide a strong rationale for developing new effective therapeutics based on targeting RBPs and/or lncRNAs to preserve the intestinal epithelial integrity in patients with critical illnesses.

Interaction between HuR and circPABPN1 Modulates Autophagy in the Intestinal Epithelium by Altering ATG16L1 Translation

Intestinal epithelial autophagy is crucial for host defense against invasive pathogens, and defects in this process occur frequently in patients with inflammatory bowel disease (IBD) and other mucosal disorders, but the exact mechanism that activates autophagy is poorly defined. Here, we investigated the role of RNA-binding protein HuR (human antigen R) in the posttranscriptional control of autophagy-related genes (ATGs) in the intestinal epithelium. We found that targeted deletion of HuR in intestinal epithelial cells (IECs) specifically decreased the levels of ATG16L1 in the intestinal mucosa. Intestinal mucosa from patients with IBD exhibited reduced levels of both HuR and ATG16L1. HuR directly interacted with Atg16l1 mRNA via its 3' untranslated region and enhanced ATG16L1 translation, without affecting Atg16l1 mRNA stability. Circular RNA circPABPN1 blocked HuR binding to Atg16l1 mRNA and lowered ATG16L1 production. HuR silencing in cultured IECs also prevented rapamycin-induced autophagy, which was abolished by overexpressing ATG16L1. These findings indicate that HuR regulates autophagy by modulating ATG16L1 translation via interaction with circPABPN1 in the intestinal epithelium.

Intestinal epithelial deletion of the glucocorticoid receptor NR3C1 alters expression of inflammatory mediators and barrier function

Glucocorticoids (GCs) are important hormones involved in the regulation of multiple physiologic functions. GCs are also widely used in anti-inflammatory/immunosuppressant drugs. GCs are synthesized by the adrenal cortex as part of the hypothalamus-pituitary-adrenal axis and also by intestinal epithelial cells, among other peripheral sites. GCs are one of the main therapy choices for the exacerbations of inflammatory bowel disease, but they are not useful to prolong remission, and development of tolerance with secondary treatment failure is frequent. Thus, GC actions at the intestinal epithelial level are of great importance, both physiologically and pharmacologically. We generated a tamoxifen-inducible nuclear receptor subfamily 3 group C member 1 (NR3C1)^ΔIEC mouse model to study the effects of GCs on epithelial cells in vivo. Nr3c1 deletion in epithelial cells of the small intestine and colon was associated with limited colonic inflammation at 1 wk postdeletion, involving augmented epithelial proliferation and mucus production, plus local and systemic immune/inflammatory changes. This phenotype regressed substantially, but not completely, after 2 wk. The mechanism may involve augmented inflammatory signaling by epithelial cells or defective barrier function. We conclude that the epithelial GC receptor plays a significant role in colonic homeostasis in basal conditions, but its deficiency can be compensated in the short term. Future studies are required to assess the impact of Nr3c1 deletion in other conditions such as experimental colitis.-Aranda, C. J., Arredondo-Amador, M., Ocón, B., Lavín, J. L., Aransay, A. M., Martínez-Augustin, O., Sánchez de Medina, F. Intestinal epithelial deletion of the glucocorticoid receptor NR3C1 alters expression of inflammatory mediators and barrier function.

Differential Homeostasis of Sessile and Pendant Epithelium Reconstituted in a 3D-Printed "GeminiChip"

Local mechanical cues can affect crucial fate decisions of living cells. Transepithelial stress has been discussed in the context of epithelial monolayers, but the lack of appropriate experimental systems leads current studies to approximate it simply as an in-plane stress. To evaluate possible contribution of force vectors acting in other directions, double epithelium in a 3D-printed "GeminiChip" containing a sessile and a pendant channel is reconstituted. Intriguingly, the sessile epithelia is prone to apoptotic cell extrusion upon crowding, whereas the pendant counterpart favors live cell delamination. Transcriptome analyses show upregulation of RhoA, BMP2, and hypoxia-signaling genes in the pendant epithelium, consistent with the onset of an epithelial-mesenchymal transition program. HepG2 microtumor spheroids also display differential spreading patterns in the sessile and pendant configuration. Using this multilayered GeminiChip, these results uncover a progressive yet critical role of perpendicular force vectors in collective cell behaviors and point at fundamental importance of these forces in the biology of cancer.

Innate lymphoid cells, mediators of tissue homeostasis, adaptation and disease tolerance

Innate lymphoid cells (ILC) are a recently identified group of tissue-resident innate lymphocytes. Available data support the view that ILC or their progenitors are deposited and retained in tissues early during ontogeny. Thereby, ILC become an integral cellular component of tissues and organs. Here, we will review the intriguing relationships between ILC and basic developmental and homeostatic processes within tissues. Studying ILC has already led to the appreciation of the integral roles of immune cells in tissue homeostasis, morphogenesis, metabolism, regeneration, and growth. This area of immunology has not yet been studied in-depth but is likely to reveal important networks contributing to disease tolerance and may be harnessed for future therapeutic approaches.

Drosophila intestinal stem and progenitor cells are major sources and regulators of homeostatic niche signals

Epithelial homeostasis requires the precise balance of epithelial stem/progenitor proliferation and differentiation. While many signaling pathways that regulate epithelial stem cells have been identified, it is probable that other regulators remain unidentified. Here, we use gene-expression profiling by targeted DamID to identify the stem/progenitor-specific transcription and signaling factors in the Drosophila midgut. Many signaling pathway components, including ligands of most major pathways, exhibit stem/progenitor-specific expression and have regulatory regions bound by both intrinsic and extrinsic transcription factors. In addition to previously identified stem/progenitor-derived ligands, we show that both the insulin-like factor Ilp6 and TNF ligand eiger are specifically expressed in the stem/progenitors and regulate normal tissue homeostasis. We propose that intestinal stem cells not only integrate multiple signals but also contribute to and regulate the homeostatic signaling microenvironmental niche through the expression of autocrine and paracrine factors.

KMT2D regulates p63 target enhancers to coordinate epithelial homeostasis

In this study, Lin-Shiao et al. identify a novel role for KMT2D, an epigenetic regulator, in coordinating self-renewal, proliferation, and differentiation, as depletion of KMT2D from undifferentiated epidermal keratinocytes results in reduced proliferation, premature spurious activation of terminal differentiation genes, and disorganized epidermal stratification. Their results reveal a critical role for KMT2D in the control of epithelial enhancers and p63 target gene expression, including the requirement of KMT2D for the maintenance of epithelial progenitor gene expression and the coordination of proper terminal differentiation.

Epithelial tissues rely on a highly coordinated balance between self-renewal, proliferation, and differentiation, disruption of which may drive carcinogenesis. The epigenetic regulator KMT2D (MLL4) is one of the most frequently mutated genes in all cancers, particularly epithelial cancers, yet its normal function in these tissues is unknown. Here, we identify a novel role for KMT2D in coordinating this fine balance, as depletion of KMT2D from undifferentiated epidermal keratinocytes results in reduced proliferation, premature spurious activation of terminal differentiation genes, and disorganized epidermal stratification. Genome-wide, KMT2D interacts with p63 and is enriched at its target enhancers. Depletion of KMT2D results in a broad loss of enhancer histone modifications H3 Lys 4 (H3K4) monomethylation (H3K4me1) and H3K27 acetylation (H3K27ac) as well as reduced expression of p63 target genes, including key genes involved in epithelial development and adhesion. Together, these results reveal a critical role for KMT2D in the control of epithelial enhancers and p63 target gene expression, including the requirement of KMT2D for the maintenance of epithelial progenitor gene expression and the coordination of proper terminal differentiation.

Chromofungin Ameliorates the Progression of Colitis by Regulating Alternatively Activated Macrophages

Ulcerative colitis (UC) is characterized by a functional dysregulation of alternatively activated macrophage (AAM) and intestinal epithelial cells (IECs) homeostasis. Chromogranin-A (CHGA) secreted by neuroendocrine cells is implicated in intestinal inflammation and immune dysregulation. CHGA undergoes proteolytic processing to generate CHGA-derived peptides. Chromofungin (CHR: CHGA_47–66) is a short CHGA-derived peptide encoded by CHGA Exon-IV and is involved in innate immune regulation, but the basis is poorly investigated. We investigated the expression of CHR in colonic tissue of patients with active UC and assessed the effects of the CHR in dextran sulfate sodium (DSS) colitis in mice and on macrophages and human colonic epithelial cells. We found that mRNA expression of CHR correlated positively with mRNA levels of AAM markers and gene expression of tight junction (TJ) proteins and negatively with mRNA levels of interleukin (IL)-8, IL-18, and collagen in patients with active UC. Moreover, AAM markers correlated positively with gene expression of TJ proteins and negatively with IL-8, IL-18, and collagen gene expression. Experimentally, intracolonic administration of CHR protected against DSS-induced colitis by priming macrophages into AAM, reducing colonic collagen deposition, and maintaining IECs homeostasis. This effect was associated with a significant increase of AAM markers, reduction of colonic IL-18 release and conservation of gene expression of TJ proteins. In vitro, CHR enhanced AAM polarization and increased the production of anti-inflammatory mediators. CHR-treated AAM conditioned medium increased Caco-2 cell migration, viability, proliferation, and mRNA levels of TJ proteins, and decreased oxidative stress-induced apoptosis and proinflammatory cytokines release. Direct CHR treatments had the same effect. In conclusion, CHR treatment reduces the severity of colitis and the inflammatory process via enhancing AAM functions and maintaining IECs homeostasis. CHR is involved in the pathogenesis of inflammation in experimental colitis. These findings provide insight into the mechanisms of colonic inflammation and could lead to new therapeutic strategies for UC.

Non-Cell-Autonomous Regulation of Prostate Epithelial Homeostasis by Androgen Receptor

Prostate inflammation has been suggested as an etiology for benign prostatic hyperplasia (BPH). We show that decreased expression of the androgen receptor (AR) in luminal cells of human BPH specimens correlates with a higher degree of regional prostatic inflammation. However, the cause-and-effect relationship between the two events remains unclear. We investigated specifically whether attenuating AR activity in prostate luminal cells induces inflammation. Disrupting luminal cell AR signaling in mouse models promotes cytokine production cell-autonomously, impairs epithelial barrier function, and induces immune cell infiltration, which further augments local production of cytokines and chemokines including Il-1 and Ccl2. This inflammatory microenvironment promotes AR-independent prostatic epithelial proliferation, which can be abolished by ablating IL-1 signaling or depleting its major cellular source, the macrophages. This study demonstrates that disrupting luminal AR signaling promotes prostate inflammation, which may serve as a mechanism for resistance to androgen-targeted therapy for prostate-related diseases.

Reserve stem cells: Differentiated cells reprogram to fuel repair, metaplasia, and neoplasia in the adult gastrointestinal tract

It has long been known that differentiated cells can switch fates, especially in vitro, but only recently has there been a critical mass of publications describing the mechanisms adult, postmitotic cells use in vivo to reverse their differentiation state. We propose that this sort of cellular reprogramming is a fundamental cellular process akin to apoptosis or mitosis. Because reprogramming can invoke regenerative cells from mature cells, it is critical to the long-term maintenance of tissues like the pancreas, which encounter large insults during adulthood but lack constitutively active adult stem cells to repair the damage. However, even in tissues with adult stem cells, like the stomach and intestine, reprogramming may allow mature cells to serve as reserve ("quiescent") stem cells when normal stem cells are compromised. We propose that the potential downside to reprogramming is that it increases risk for cancers that occur late in adulthood. Mature, long-lived cells may have years of exposure to mutagens. Mutations that affect the physiological function of differentiated, postmitotic cells may lead to apoptosis, but mutations in genes that govern proliferation might not be selected against. Hence, reprogramming with reentry into the cell cycle might unmask those mutations, causing an irreversible progenitor-like, proliferative state. We review recent evidence showing that reprogramming fuels irreversible metaplastic and precancerous proliferation in the stomach and pancreas. Finally, we illustrate how we think reprogrammed differentiated cells are likely candidates as cells of origin for cancers of the intestine.

Cleavage of transmembrane junction proteins and their role in regulating epithelial homeostasis

Epithelial tissues form a selective barrier that separates the external environment from the internal tissue milieu. Single epithelial cells are densely packed and associate via distinct intercellular junctions. Intercellular junction proteins not only control barrier properties of the epithelium but also play an important role in regulating epithelial homeostasis that encompasses cell proliferation, migration, differentiation and regulated shedding. Recent studies have revealed that several proteases target epithelial junction proteins during physiological maturation as well as in pathologic states such as inflammation and cancer. This review discusses mechanisms and biological consequences of transmembrane junction protein cleavage. The influence of junction protein cleavage products on pathogenesis of inflammation and cancer is discussed.

SIRT1 inhibits the mouse intestinal motility and epithelial proliferation

Sirtuin 1 (SIRT1), a NAD(+)-dependent histone deacetylase, is involved in a wide array of cellular processes including glucose homeostasis, energy metabolism, proliferation and apoptosis, and immune response. However, it is unknown whether SIRT1 plays any physiological role in the regulation of intestinal homeostasis and motility. Thus the aim was to define SIRT1 expression and function in the gastrointestinal (GI) tract under physiological conditions. Forty 12-14-wk-old SIRT1 knockout (KO) and wild-type (WT) mice were fasted 21 h and/or refed 3 h. Fasted mice were injected intraperitoneally with bromodeoxyuridine (120 mg/kg body wt) 2 h before euthanasia. SIRT1 protein was localized to gastric and intestinal epithelial nuclei and was responsive to the nutritional status. SIRT1 was required for intestinal epithelial homeostasis. The SIRT1 KO mice showed enhanced crypt proliferation and suppressed villous apoptosis, resulting in increased intestinal villous height. In the SIRT1 KO intestine, the abundance of Forkhead box protein O1 and p53 protein decreased, whereas the subcellular localization of β-catenin protein accumulated mainly in the crypts. The SIRT1 KO mice showed accelerated gastric emptying rate with increased abundance of ghrelin mRNA and protein in the stomach. Moreover, the SIRT1 KO mouse intestine showed enhanced ex vivo spontaneous contraction. We concluded that, SIRT1 plays a critical role in the control of intestinal homeostasis (by promoting apoptosis and inhibiting proliferation) and gastrointestinal motility (by reducing gastric emptying and intestinal contractile activity), implicating a novel role for SIRT1.

NF-κB in the regulation of epithelial homeostasis and inflammation

The IκB kinase/NF-κB signaling pathway has been implicated in the pathogenesis of several inflammatory diseases. Increased activation of NF-κB is often detected in both immune and non-immune cells in tissues affected by chronic inflammation, where it is believed to exert detrimental functions by inducing the expression of proinflammatory mediators that orchestrate and sustain the inflammatory response and cause tissue damage. Thus, increased NF-κB activation is considered an important pathogenic factor in many acute and chronic inflammatory disorders, raising hopes that NF-κB inhibitors could be effective for the treatment of inflammatory diseases. However, ample evidence has accumulated that NF-κB inhibition can also be harmful for the organism, and in some cases trigger the development of inflammation and disease. These findings suggested that NF-κB signaling has important functions for the maintenance of physiological immune homeostasis and for the prevention of inflammatory diseases in many tissues. This beneficial function of NF-κB has been predominantly observed in epithelial cells, indicating that NF-κB signaling has a particularly important role for the maintenance of immune homeostasis in epithelial tissues. It seems therefore that NF-κB displays two faces in chronic inflammation: on the one hand increased and sustained NF-κB activation induces inflammation and tissue damage, but on the other hand inhibition of NF-κB signaling can also disturb immune homeostasis, triggering inflammation and disease. Here, we discuss the mechanisms that control these apparently opposing functions of NF-κB signaling, focusing particularly on the role of NF-κB in the regulation of immune homeostasis and inflammation in the intestine and the skin.

Bifidobacterium bifidum reduces apoptosis in the intestinal epithelium in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease of neonates, and clinical studies suggest the beneficial effect of probiotics in NEC prevention. Recently, we have shown that administration of Bifidobacterium bifidum protects against NEC in a rat model. Intestinal apoptosis can be suppressed by activation of cyclooxygenase-2 (COX-2) and increased production of prostaglandin E(2) (PGE(2)). The present study investigates the effect of B. bifidum on intestinal apoptosis in the rat NEC model and in an intestinal epithelial cell line (IEC-6), as a mechanism of protection against mucosal injury. Premature rats were divided into the following three groups: dam fed, hand fed with formula (NEC), or hand fed with formula supplemented with B. bifidum (NEC + B. bifidum). Intestinal Toll-like receptor-2 (TLR-2), COX-2, PGE(2), and apoptotic regulators were measured. The effect of B. bifidum was verified in IEC-6 cells using a model of cytokine-induced apoptosis. Administration of B. bifidum increased expression of TLR-2, COX-2, and PGE(2) and significantly reduced apoptosis in the intestinal epithelium of both in vivo and in vitro models. The Bax-to-Bcl-w ratio was shifted toward cell survival, and the number of cleaved caspase-3 positive cells was markedly decreased in B. bifidum-treated rats. Experiments in IEC-6 cells showed anti-apoptotic effect of B. bifidum. Inhibition of COX-2 signaling blocked the protective effect of B. bifidum treatment in both in vivo and in vitro models. In conclusion, oral administration of B. bifidum activates TLR-2 in the intestinal epithelium. B. bifidum increases expression of COX-2, which leads to higher production of PGE(2) in the ileum and protects against intestinal apoptosis associated with NEC. This study indicates the ability of B. bifidum to downregulate apoptosis in the rat NEC model and in IEC-6 cells by a COX-2-dependent matter and suggests a molecular mechanism by which this probiotic reduces mucosal injury and preserves intestinal integrity.

Epidermal growth factor reduces autophagy in intestinal epithelium and in the rat model of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating intestinal disease of premature infants. Epidermal growth factor (EGF) is one of the most promising candidates in NEC prophylaxis. Autophagy regulates cell homeostasis, but uncontrolled activation of autophagy may lead to cellular injury. The aim was to evaluate the effects of EGF on intestinal autophagy in epithelial cells and in the rat NEC model and measure autophagy in NEC patients. Intestinal epithelial cells (IEC-6) and the rat NEC model were used to study the effect of EGF on intestinal autophagy. Protein levels of Beclin 1 and LC3II were measured in the intestinal epithelium in both in vivo and in vitro models. Ultrastructural changes in intestinal epithelium were studied by electron microscopy. Expression of Beclin 1, LC3II, and p62 protein was evaluated in biopsies from NEC patients. Autophagy was induced in IEC-6 cells and inhibited by adding EGF into the culture. In the rat NEC model, EGF treatment of NEC reduced expression of Beclin 1 and LC3II in ileal epithelium. Morphologically, typical signs of autophagy were observed in the epithelium of the NEC group, but not in the EGF group. A strong signal for Beclin 1 and LC3II was detected in the intestine from patients with NEC. Autophagy is activated in the intestinal epithelium of NEC patients and in the ileum of NEC rats. Supplementation of EGF blocks intestinal autophagy in both in vivo and in vitro conditions. Results from this study indicate that EGF-mediated protection against NEC injury is associated with regulation of intestinal autophagy.

Alterations in epithelial and mesenchymal intestinal gene expression during doxorubicin-induced mucositis in mice

In the current study we aimed to gain insight into epithelial-mesenchymal cross-talk and progenitor compartment modulation during doxorubicin (DOX)-induced mucositis in mice. Intestinal segments were collected on various days after DOX treatment. DOX-induced damage at day 1-2 was characterized by increased epithelial proliferation and apoptosis and a decrease in the expression of epithelial differentiation markers. Concurrently, T-cell factor-4 (TCF4) levels increased and the epithelial differentiation enhancing factor, bone morphogenic protein-4 (BMP4), decreased. During severe damage (day 3), BMP4 levels were significantly increased, which inversely correlated with epithelial proliferation. At the same time, the expression of the epithelial differentiation markers was increasing again. At day 7, BMP4 levels were down-regulated, while the levels of the epithelial differentiation markers and TCF4 were normalized again. These data suggest that in response to DOX-induced damage, BMP4 and TCF4 are modulated in such a way that homeostasis of the progenitor compartment is partly preserved.