Paneth cells in intestinal homeostasis and tissue injury

Adult stem cell niches are often co-inhabited by cycling and quiescent stem cells. In the intestine, lineage tracing has identified Lgr5(+) cells as frequently cycling stem cells, whereas Bmi1(+), mTert(+), Hopx(+) and Lrig1(+) cells appear to be more quiescent. Here, we have applied a non-mutagenic and cell cycle independent approach to isolate and characterize small intestinal label-retaining cells (LRCs) persisting in the lower third of the crypt of Lieberkühn for up to 100 days. LRCs do not express markers of proliferation and of enterocyte, goblet or enteroendocrine differentiation, but are positive for Paneth cell markers. While during homeostasis, LR/Paneth cells appear to play a supportive role for Lgr5(+) stem cells as previously shown, upon tissue injury they switch to a proliferating state and in the process activate Bmi1 expression while silencing Paneth-specific genes. Hence, they are likely to contribute to the regenerative process following tissue insults such as chronic inflammation.     

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.     

A genetic study of the role of the Wnt/beta-catenin signalling in Paneth cell differentiation

Wnt/β-catenin signalling plays a key role in the homeostasis of the intestinal epithelium. Whereas its role in the maintenance of the stem cell compartment has been clearly demonstrated, its role in the Paneth cell fate remains unclear. We performed genetic studies to elucidate the functions of the Wnt/β-catenin pathway in Paneth cell differentiation. We analysed mice with inducible gain-of-function mutations in the Wnt/β-catenin pathway and mice with a hypomorphic β-catenin allele that have not been previously described. We demonstrated that acute activation of Wnt/β-catenin signalling induces de novo specification of Paneth cells in both the small intestine and colon and that colon cancers resulting from Apc mutations expressed many genes involved in Paneth cell differentiation. This suggests a key role for the Wnt/β-catenin pathway in Paneth cell differentiation. We also showed that a slight decrease in β-catenin gene dosage induced a major defect in Paneth cell differentiation, but only a modest effect on crypt morphogenesis. Overall, our findings show that a high level of β-catenin activation is required to determine Paneth cell fate and that fine tuning of β-catenin signalling is critical for correct Paneth cell lineage.     

Canonical Wnt signalling requires the BMP pathway to inhibit oligodendrocyte maturation

OLs (oligodendrocytes) are the myelinating cells of the CNS (central nervous system), wrapping axons in conductive sheathes to ensure effective transmission of neural signals. The regulation of OL development, from precursor to mature myelinating cell, is controlled by a variety of inhibitory and inductive signalling factors. The dorsal spinal cord contains signals that inhibit OL development, possibly to prevent premature and ectopic precursor differentiation. The Wnt and BMP (bone morphogenic protein) signalling pathways have been identified as dorsal spinal cord signals with overlapping temporal activity, and both have similar inhibitory effects on OL differentiation. Both these pathways feature prominently in many developmental processes and demyelinating events after injury, and they are known to interact in complex inductive, inhibitive and synergistic manners in many developing systems. The interaction between BMP and Wnt signalling in OL development, however, has not been extensively explored. In the present study, we examine the relationship between the canonical Wnt and BMP pathways. We use pharmacological and genetic paradigms to show that both Wnt3a and BMP4 will inhibit OL differentiation in vitro. We also show that when the canonical BMP signalling pathway is blocked, neither Wnt3a nor BMP4 have inhibitory effects on OL differentiation. In contrast, abrogating the Wnt signalling pathway does not alter the actions of BMP4 treatment. Our results indicate that the BMP signalling pathway is necessary for the canonical Wnt signalling pathway to exert its effects on OL development, but not vice versa, suggesting that Wnt signals upstream of BMP.     

Paneth cells, antimicrobial peptides and maintenance of intestinal homeostasis

Building and maintaining a homeostatic relationship between a host and its colonizing microbiota entails ongoing complex interactions between the host and the microorganisms. The mucosal immune system, including epithelial cells, plays an essential part in negotiating this equilibrium. Paneth cells (specialized cells in the epithelium of the small intestine) are an important source of antimicrobial peptides in the intestine. These cells have become the focus of investigations that explore the mechanisms of host-microorganism homeostasis in the small intestine and its collapse in the processes of infection and chronic inflammation. In this Review, we provide an overview of the intestinal microbiota and describe the cell biology of Paneth cells, emphasizing the composition of their secretions and the roles of these cells in intestinal host defence and homeostasis. We also highlight the implications of Paneth cell dysfunction in susceptibility to chronic inflammatory bowel disease.     

Optimality in the development of intestinal crypts

Intestinal crypts in mammals are comprised of long-lived stem cells and shorter-lived progenies. These two populations are maintained in specific proportions during adult life. Here, we investigate the design principles governing the dynamics of these proportions during crypt morphogenesis. Using optimal control theory, we show that a proliferation strategy known as a "bang-bang" control minimizes the time to obtain a mature crypt. This strategy consists of a surge of symmetric stem cell divisions, establishing the entire stem cell pool first, followed by a sharp transition to strictly asymmetric stem cell divisions, producing nonstem cells with a delay. We validate these predictions using lineage tracing and single-molecule fluorescence in?situ hybridization of intestinal crypts in infant mice, uncovering small crypts that are entirely composed of Lgr5-labeled stem cells, which become a minority as crypts continue to grow. Our approach can be used to uncover similar design principles in other developmental systems.     

Drugging Wnt signalling in cancer

Aberrant regulation of the Wnt signalling pathway has emerged as a prevalent theme in cancer biology. This chapter summarizes the research that provides a proof of concept for inhibiting Wnt signalling in cancer, the potential means by which this could be achieved, and some recent advances towards this goal. A brief discussion of molecular diagnostics and possible safety concerns is also provided.     

Rapid loss of intestinal crypts upon conditional deletion of the Wnt/Tcf-4 target gene c-Myc

Inhibition of the mutationally activated Wnt cascade in colorectal cancer cell lines induces a rapid G1 arrest and subsequent differentiation. This arrest can be overcome by maintaining expression of a single Tcf4 target gene, the proto-oncogene c-Myc. Since colorectal cancer cells share many molecular characteristics with proliferative crypt progenitors, we have assessed the physiological role of c-Myc in adult crypts by conditional gene deletion. c-Myc-deficient crypts are lost within weeks and replaced by c-Myc-proficient crypts through a fission process of crypts that have escaped gene deletion. Although c-Myc(-/-) crypt cells remain in the cell cycle, they are on average much smaller than wild-type cells, cycle slower, and divide at a smaller cell size. c-Myc appears essential for crypt progenitor cells to provide the necessary biosynthetic capacity to successfully progress through the cell cycle.     

Paneth cells: the hub for sensing and regulating intestinal flora

The complex interplay between symbiotic bacteria and host immunity plays a key role in shaping intestinal homeostasis and maintaining host health. Paneth cells, as one of the major producers of antimicrobial peptides in the intestine under steady-state conditions, play a vital role in regulating intestinal flora. Many studies on inflammatory bowel disease (IBD)-associated genes have put Paneth cells at the center of IBD pathogenesis. In this perspective, we focus on mechanistic studies of different cellular processes in Paneth cells that are regulated by various IBD-associated susceptibility genes, and we discuss the hypothesis that Paneth cells function as the central hub for sensing and regulating intestinal flora in the maintenance of intestinal homeostasis.     

Kinetic dimensions of cells and crypts in irradiated intestinal epithelium of mice]

The average value of axial cryptal section area and cell section area on it were studied during 8 days after total X-ray irradiation of male mice (400 rad). A small reducing of cryptal area (20%) during destructive period (1-2 days) is followed by a big overshoot (60%) during regenerative time (3-7 days). The cryptal sizes in regenerative period deviate from a steady state more than during destructive time. There are two high waves of abnormal growth of cell sizes above the steady level: the first one during destructive time and the second one during regeneration. This level seems to be near to minimal sizes of cryptal proliferative cells which are necessary for proliferation. It means that normal intestinal epithelium is a very economical and stabilized system. It is possible to evaluate quantitatively the associated with proliferation flow of substance per crypt cell for normal and irradiated intestine by means of index Iv where I is mitotical index and v - the cell volume. Cell hypertrophy at the time of regeneration on the 4th-7th days and later after irradiation (130-160%), was revealed. The crypt cell hypertrophy is the factor of destabilization of irradiated intestinal epithelium.     

Wnt signaling in adult intestinal stem cells and cancer

Signaling initiated by secreted glycoproteins of the Wnt family regulates many aspects of embryonic development and it is involved in homeostasis of adult tissues. In the gastrointestinal (GI) tract the Wnt pathway maintains the self-renewal capacity of epithelial stem cells. The stem cell attributes are conferred by mutual interactions of the stem cell with its local microenvironment, the stem cell niche. The niche ensures that the threshold of Wnt signaling in the stem cell is kept in physiological range. In addition, the Wnt pathway involves various feedback loops that balance the opposing processes of cell proliferation and differentiation. Today, we have compelling evidence that mutations causing aberrant activation of the Wnt pathway promote expansion of undifferentiated progenitors and lead to cancer.The review summarizes recent advances in characterization of adult epithelial stem cells in the gut. We mainly focus on discoveries related to molecular mechanisms regulating the output of the Wnt pathway. Moreover, we present novel experimental approaches utilized to investigate the epithelial cell signaling circuitry in vivo and in vitro. Pivotal aspects of tissue homeostasis are often deduced from studies of tumor cells; therefore, we also discuss some latest results gleaned from the deep genome sequencing studies of human carcinomas of the colon and rectum.     

Wnt信号在胚胎干细胞自我更新和分化中的作用

胚胎干细胞分离自胚泡内细胞团,具有无限自我更新和多向分化潜能,有很大的医学应用前景。Wnt家族是一类分泌型的细胞信号传导蛋白,可以通过复杂的信号传递通路调控胚胎的早期发育,对细胞的分化、增殖及生长具有重要的调节作用。该文就Wnt信号通路调节胚胎干细胞的自我更新和分化作一综述。     

HIV induces maturation of monocyte-derived dendritic cells and Langerhans cells

In HIV infection, dendritic cells (DCs) may play multiple roles, probably including initial HIV uptake in the anogenital mucosa, transport to lymph nodes, and subsequent transfer to T cells. The effects of HIV-1 on DC maturation are controversial, with several recent conflicting reports in the literature. In this study, microarray studies, confirmed by real-time PCR, demonstrated that the genes encoding DC surface maturation markers were among the most differentially expressed in monocyte-derived dendritic cells (MDDCs), derived from human blood, treated with live or aldrithriol-2-inactivated HIV-1(BaL). These effects translated to enhanced cell surface expression of these proteins but differential expression of maturation markers was only partial compared with the effects of a conventional potent maturation stimulus. Such partially mature MDDCs can be converted to fully mature cells by this same potent stimulus. Furthermore, live HIV-1 stimulated greater changes in maturation marker surface expression than aldrithriol-2-inactivated HIV-1 and this enhanced stimulation by live HIV-1 was mediated via CCR5, thus suggesting both viral replication-dependent and -independent mechanisms. These partially mature MDDCs demonstrated enhanced CCR7-mediated migration and are also able to stimulate interacting T cells in a MLR, suggesting DCs harboring HIV-1 might prepare CD4 lymphocytes for transfer of HIV-1. Increased maturation marker surface expression was also demonstrated in native DCs, ex vivo Langerhans cells derived from human skin. Thus, HIV initiates maturation of DCs which could facilitate subsequent enhanced transfer to T cells.