Fusion between Hematopoietic and Epithelial Cells in Adult Human Intestine

Following transplantation of hematopoietic lineage cells, genetic markers unique to the transplanted cells have been detected in non-hematopoietic recipient cells of human liver, vascular endothelium, intestinal epithelium and brain. The underlying mechanisms by which this occurs are unclear. Evidence from mice suggests it is due in part to fusion between cells of hematopoietic and non-hematopoietic origins; however, direct evidence for this in humans is scant. Here, by quantitative and statistical analysis of X- and Y-chromosome numbers in epithelial and non-epithelial intestinal cells from gender-mismatched hematopoietic cell transplant patients, we provide evidence that transplanted cells of the hematopoietic lineage incorporate into human intestinal epithelium through cell fusion. This is the first definitive identification of cell fusion between hematopoietic cells and any epithelial cell type in humans, and provides the basis for further understanding the physiological and potential pathological consequences of cell fusion in humans.     

Nucleocytoplasmic movement of fluorescent tracers microinjected into living salivary gland cells

The permeability of the nuclear envelop of a somatic cell, the C. thummi larval salivary gland cell, was studied by intracellular microinjection of fluorescent molecular tracers. As shown previously in oocytes (4,5,15,16), the envelop is permeable to a wide variety of materials, including molecules which are large enough to possess condiderable biological specificities and to play important roles in regulation of cellular activities. The envelop exhibits transport selectivity on the basis of size in the range of naturally occurring intracellular materials and it may thus perform important controlling functions in nucleocytoplasmic exchange. The nucleus to cytoplasm movement of in vivo ribonucleoprotein particulates in these synthetically active cells probably requires conformational changes in the particulates and/or the envelope pore complexes; morphological evidence exists for such processess in these cells (20).     

Lymphocyte recirculation and the gut: the cellular basis of humoral immunity in the intestine

During the last 15 years evidence has accumulated which shows that the B immunoblasts generated in the gut associated lymphoid tissue (GALT) in response to antigenic stimuli from the intestinal tract are discharged into the intestinal lymph. The lymph stream carries them to the blood but most of them soon extravasate in the gut (and some other mucosae) and develop into plasma cells which synthesise secretory immunoglobulins. In sheep, there is some evidence that these cells may be derived initially from a sub-set of small lymphocytes which circulate preferentially through the GALT, but the situation in rodents is less clear. However, in most species it is becoming clear that although some of the antibodies produced by the sub-mucosal plasma cells are secreted directly into the lumen of the gut many find their way, via the lymph, into the blood and, if in the form of polymeric IgA, they are rapidly and actively transported by the hepatocytes into the bile and thus gain direct access to the duodenum in concert with the entry of freshly ingested food and bacteria.     

Enterocyte chloride and water secretion into the small intestine after enterotoxin challenge: Unifying hypothesis or intellectual dead end?

Many forms of diarrhoeal disease, particularly so called “secretory” diarrhoeal disease are thought to arise by the active secretion of chloride ion from the enterocytes, creating an osmotic gradient for fluid movement into the small intestinal lumen. This model implies that normally occurring intestinal secretion is catastrophically enhanced by bacterial enterotoxins. This review advocates that neither normal nor abnormal intestinal secretion from the enterocytes occurs and that no competent proof for chloride secretion exists. Prior to 1970, the physiological evidence failed to support the concept of the formation of intestinal juice as a normal intestinal event. support the concept of the formation of intestinal juice as a normal intestinal event. The concept was later revived to explain the high rate of fluid entry into the lumen after exposure to cholera toxin. Much evidence has been advanced for the chloride secretion hypothesis, the dominant secretory paradigm after 1974, but is the evidence sufficiently compelling for it to be regarded as proving the chloride secretory model? The evidence falls into four categories and a fifth conjectural argument that proposes that an abnormal chloride ion channel in cystic fibrotic sufferers confers a natural selective advantage by preventing diarrhoeal disease. Secretion is putatively demonstrated by 1) showing that mass transfer of fluid is into the lumen (secretion) and not merely a failure to transport out of the lumen (failed absorption). Support is offered by 2) chloride ion flux measurementsin vitro in Ussing chambers and by 3) shortcircuit current measurements that are consistent with and purport to show chloride ion movement into the lumen. In addition, 4) pharmacological agents are identified that affect short-circuit current and these are assumed to be anti-secretory, consistent with the biochemical mechanism for secretion, confirmed wherever possible by mouse knock-out models. Finally, the proxy methods used to study water movement such as elevated short-circuit current measurements show these to be absent in cystic fibrotic patients. The enterocyte secretion hypothesis is challenged here on the basis of an examination of the methods used to show secretion, particularly after exposing the small intestine to heat stable enterotoxin (STa) fromE. coli. STa is thought to be secretory because fluid entry into the lumen is claimed, enhanced isotopic flux of chloride ion towards the lumen occurs, an increase in short-circuit current is found, preventable by various drugs that are deemed likely to be anti-secretory and also because the short-circuit current changes after STa are not seen in cystic fibrotic patients. Using volume recoveryin vivo, STa is found not to be secretory but only anti-absorptive. Hence, other techniques used to show secretion are not fit for that purpose. If STa is identified as secretory and yet no secretion occurs, how reliable is the evidence for other toxins being secretory when these methods are used? This review concludes that chloride ion secretion is unproven. A review of the literature indicates that secretion occurs not because epithelial cells actively pump water but by interdiction of fluid absorption, increased conductivity through tight junctions and an increased hydrostatic driving force through elevated capillary pressure. The exclusive focus on chloride secretion may explain the failure to develop antisecretory drugs over the last three decades.     

肠道菌群：肠道干细胞增殖分化的调节者

肠道干细胞(intestinal stem cells, ISCs)是肠道各类上皮细胞的来源,通过平衡增殖与分化维持肠道稳态。同时,肠道菌群及其代谢物在维持宿主肠道稳态中也发挥着重要作用。随着技术的发展,研究者认识到ISCs与肠道菌群之间存在相互作用。研究表明,ISCs对上皮细胞亚型的调控影响肠道菌群的组成,并且肠道菌群及其代谢物也影响ISCs介导的上皮发育。本文阐述了ISCs分化对肠道菌群的影响,重点总结了肠道菌群及其代谢物调控ISCs增殖分化的研究进展,从菌群调控ISCs的角度探讨肠道损伤的治疗思路,并对未来可能的研究方向进行讨论。     

Vasopressin-induced intracellular redistribution of protein kinase D in intestinal epithelial cells

The spatio-temporal changes of signaling molecules in response to G protein-coupled receptors (GPCR) stimulation is a poorly understood process in intestinal epithelial cells. Here we investigate the dynamic mechanisms associated with GPCR signaling in living rat intestinal epithelial cells by characterizing the intracellular translocation of protein kinase D (PKD), a serine/threonine protein kinase involved in mitogenic signaling in intestinal epithelial cells. Analysis of the intracellular steady-state distribution of green fluorescent protein (GFP)-tagged PKD indicated that in non-stimulated IEC-18 cells, GFP-PKD is predominantly cytoplasmic. However, cell stimulation with the GPCR agonist vasopressin induces a rapid translocation of GFP-PKD from the cytosol to the plasma membrane that is accompanied by its activation via protein kinase C (PKC)-mediated process and posterior plasma membrane dissociation. Subsequently, active PKD is imported into the nuclei where it transiently accumulates before being exported into the cytosol by a mechanism that requires a competent Crm1 nuclear export pathway. These findings provide evidence for a mechanism by which PKC coordinates in intestinal epithelial cells the translocation and activation of PKD in response to vasopressin-induced GPCR activation.     

Numb modulates intestinal epithelial cells toward goblet cell phenotype by inhibiting the Notch signaling pathway

Numb was originally identified as an important cell fate determinant that is asymmetrically inherited during mitosis and controls the fate of sibling cells by inhibiting the Notch signaling pathway in neural tissue. The small intestinal epithelium originates from the division of stem cells that reside in the crypt, which further differentiate into goblet cells, absorptive cells, paneth cells, and enteroendocrine cells. However, Numb's involvement in the differentiation process of intestinal epithelium is largely unknown. In the present study, we confirm that both the Numb mRNA and protein isoforms are expressed in adult mouse intestinal mucosa. Numb protein is ubiquitously expressed throughout the crypt–villus axis of the small intestinal epithelium and is mainly localized to the cytoplasmic membrane. Down-regulation of endogenous Numb using RNA interference in cultured intestinal LS174T cells increased Notch signaling, leading to the up-regulation of Hes1 and the down-regulation of Hath1. Knockdown of Numb alleviated MUC2 protein expression and led to loss of the goblet cell phenotype in LS174Tl cells. Our results provide the first evidence that Numb, an important cell fate determinant, modulates intestinal epithelial cells towards the goblet cell phenotype by inhibiting the Notch signaling pathway.     

Gut bacteria in health and disease: a survey on the interface between intestinal microbiology and colorectal cancer

A healthy human body contains at least tenfold more bacterial cells than human cells and the most abundant and diverse microbial community resides in the intestinal tract. Intestinal health is not only maintained by the human intestine itself and by dietary factors, but is also largely supported by this resident microbial community. Conversely, however, a large body of evidence supports a relationship between bacteria, bacterial activities and human colorectal cancer. Symbiosis in this multifaceted organ is thus crucial to maintain a healthy balance within the host-diet-microbiota triangle and accordingly, changes in any of these three factors may drive a healthy situation into a state of disease. In this review, the factors that sustain health or drive this complex intestinal system into dysbiosis are discussed. Emphasis is on the role of the intestinal microbiota and related mechanisms that can drive the initiation and progression of sporadic colorectal cancer (CRC). These mechanisms comprise the induction of pro-inflammatory and pro-carcinogenic pathways in epithelial cells as well as the production of (geno)toxins and the conversion of pro-carcinogenic dietary factors into carcinogens. A thorough understanding of these processes will provide leads for future research and may ultimately aid in development of new strategies for CRC diagnosis and prevention.     

EARLY STAGES OF INTESTINAL ABSORPTION OF SPECIFIC ANTIBODIES IN THE NEWBORN : An Ultrastructural, Cytochemical, and Immunological Study in the Pig, Rat, and Rabbit

In mammals, passive immunity is transferred from mother to offspring by transplacental passage or by intestinal absorption. The rabbit receives antibodies exclusively across the placenta, whereas intestinal absorption is the principal source of antibodies for the new-born pig. In the rat, passive immunity is transferred by both pathways. The role of the jejunal absorptive cells was investigated in these three species, by the use of specific immune globulins as tracers of protein absorption. Rabbit anti-peroxidase and anti-ferritin antibodies were injected into the jejunum of newborn pigs, rats, and rabbits, and absorption was studied over the first 2 hr. The specific antibodies were detected in glutaraldehyde-fixed tissues after in vitro treatment with the antigens, and in sera by immunological methods. Intact antibodies are transferred into the circulation of the pig and the rat, but not into that of the rabbit. In the three species, the jejunal absorptive cells take up antibodies by endocytosis. In the pig, the antibodies are transported across the epithelium in vacuoles. In the rabbit, the endocytosis of antibodies triggers a lysosomal response and all absorbed antibodies are trapped in lysosomes. In the rat, both situations are found; there is no evidence of transfer of antibody fragments into the circulation.     

Biopolymer particulate turnover in biological waste treatment systems: a review

Microorganisms — the major component in most biological waste treatment processes and a number of industrial fermentations — are not able to directly assimilate biopolymeric particulate material. Such organic particulates must first be solubilized into soluble polymers or monomers before they can diffuse through the capsular slime layer surrounding most bacteria, then transported across the cell membrane, to be used as either a carbon, energy or other essential nutrient source. Throughout these events, new cells are synthesized, which are themselves biopolymer particulates.The turnover of biopolymer particulates in biological treatment systems has not been examined with respect to its impact on system performance and culture physiology. The aim of this paper is to review the observations of particulate turnover in various biological treatment systems and to identify those fundamental mechanisms which govern microbial conversion of biopolymer particulates.Current address: Department of Chemical Engineering, California, Institute of Technology, Pasadena, Ca 91125 USA     

Structure,Ultrastructure and Function of the Neural Gland Complex of Ascidia interrupta (Chordata,Ascidiacea): Clarification of Hypotheses Regarding the Evolution of the Vertebrate Anterior Pituitary

Abstract The neural gland complex of Ascidia interrupta consists of three parts: dorsal tubercle, ciliated duct, and neural gland. The dorsal tubercle protrudes above the pharyngeal lining and bears a ciliated funnel. The funnel opens into a ciliated duct which opens into the neural gland, a blind sac in a blood sinus below the brain. Funnel and duct cells are joined by adhaerens junctions and, apically, by putative tight junctions. The neural gland wall is a loose, irregular, non-ciliated epithelium of phagocytes. Adhaerens, but not tight, junctions join the cells. Secretory cells were not observed. Tracers delivered onto the dorsal tubercle and dissolved in seawater around undissected animals are transported unidirectionally inward into the neural gland. The continuous ciliary incurrent moves the tracers across the wall of the neural gland and into the pharyngeal blood vessels. Small particulates and large macromolecules, however, are removed from the water stream by endocytosis on neural gland cells. Large particulates delivered onto the dorsal tubercle do not enter the system but rather are rejected by cilia on the surface of the tubercle. The neural gland complex is interpreted as an organ of blood volume regulation that consists of a pump (cilia) and coarse (tubercle) and fine (gland) filters. Analogous and homologous systems are discussed.     

Shiga toxin 1 interaction with enterocytes causes apical protein mistargeting through the depletion of intracellular galectin-3

Shiga toxins (Stx) 1 and 2 are responsible for intestinal and systemic sequelae of infection by enterohemorrhagic Escherichia coli (EHEC). However, the mechanisms through which enterocytes are damaged remain unclear. While secondary damage from ischemia and inflammation are postulated mechanisms for all intestinal effects, little evidence excludes roles for more primary toxin effects on intestinal epithelial cells. We now document direct pathologic effects of Stx on intestinal epithelial cells. We study a well-characterized rabbit model of EHEC infection, intestinal tissue and stool samples from EHEC-infected patients, and T84 intestinal epithelial cells treated with Stx1. Toxin uptake by intestinal epithelial cells in vitro and in vivo causes galectin-3 depletion from enterocytes by increasing the apical galectin-3 secretion. This Shiga toxin-mediated galectin-3 depletion impairs trafficking of several brush border structural proteins and transporters, including villin, dipeptidyl peptidase IV, and the sodium-proton exchanger 2, a major colonic sodium absorptive protein. The mistargeting of proteins responsible for the absorptive function might be a key event in Stx1-induced diarrhea. These observations provide new evidence that human enterocytes are directly damaged by Stx1. Conceivably, depletion of galectin-3 from enterocytes and subsequent apical protein mistargeting might even provide a means whereby other pathogens might alter intestinal epithelial absorption and produce diarrhea.     

The iron cycle and oxidative stress in the lung

Iron is critical for many aspects of cellular function, but it can also generate reactive oxygen species that can damage biological macromolecules. To limit oxidative stress, iron acquisition and its distribution must be tightly regulated. In the lungs, which are continuously exposed to the atmosphere, the risk of oxidative damage is particularly high because of the high oxygen concentration and the presence of significant amounts of catalytically active iron in atmospheric particulates. An effective system of metal detoxification must exist to minimize the associated generation of oxidative stress in the lungs. Here we summarize the evidence that a number of specific proteins that control iron uptake in the gastrointestinal tract are also employed in the lung to transport iron into epithelial cells and sequester it in a catalytically inactive form in ferritin. Furthermore, these and other proteins facilitate ferritin release from lung cells to the epithelial and bronchial lining fluids for clearance by the mucociliary system or to the reticuloendothelial system for long-term storage of iron. These pathways seem to be the primary mechanism for control of oxidative stress presented by iron in the respiratory tract.     

Generating human intestinal tissue from pluripotent stem cells in vitro

Here we describe a protocol for generating 3D human intestinal tissues (called organoids) in vitro from human pluripotent stem cells (hPSCs). To generate intestinal organoids, pluripotent stem cells are first differentiated into FOXA2(+)SOX17(+) endoderm by treating the cells with activin A for 3 d. After endoderm induction, the pluripotent stem cells are patterned into CDX2(+) mid- and hindgut tissue using FGF4 and WNT3a. During this patterning step, 3D mid- or hindgut spheroids bud from the monolayer epithelium attached to the tissue culture dish. The 3D spheroids are further cultured in Matrigel along with prointestinal growth factors, and they proliferate and expand over 1-3 months to give rise to intestinal tissue, complete with intestinal mesenchyme and epithelium comprising all of the major intestinal cell types. To date, this is the only method for efficiently directing the differentiation of hPSCs into 3D human intestinal tissue in vitro.     

Precardiac cell migration: fibronectin localization at mesoderm-endoderm interface during directional movement

The pathway of directional movement of chick precardiac mesoderm cells was studied by indirect immunofluorescence and by scanning electron microscopy. Directional movement of the precardiac cells begins at stage 6 from the lateral sides of the embryo at the level of Hensen's node. The cells move anteriorly in an arc to the embryo's midline. By stage 8 the cells arrive at the lateral sides of the anterior intestinal portal and movement ceases. The interval of this directional movement is approximately 10 hr. During migration the precardiac cells are in close association with the underlying endoderm. As migration proceeds, the cells encounter increasing amounts of fibrils in the substratum at the mesoderm-endoderm interface. Concomitant with increasing fibril formation there is an increase in fibronectin (FN) in the heart-forming region. During stage 5 FN first appears in the lateral heart-forming regions and increases in amount during the period of cell migration. By stage 7 a concentration difference of FN is apparent in the lateral regions with more FN cephalad and decreasing amounts caudad. At stages 7 and 8 large amounts of extracellular FN-associated fibrils are observed at the lateral sides of the anterior intestinal portal where the cells stop moving. The precardiac cells moving into this region are oriented perpendicular to the anterior intestinal portal and in close association with these fibrils. There is no evidence that the fibrillar meshwork forming the substratum of the precardiac mesoderm cells is physically oriented as a guide for directional movement. The correlations between FN distribution at the mesoderm-endoderm interface and directional cell movement suggest that the precardiac cells may migrate by haptotaxis, i.e., by moving along the substratum toward areas of greater adhesiveness.     

肠道干细胞和潘氏细胞在肠道稳态和疾病中的作用

肠道是最复杂的器官之一,负责营养的吸收和消化。肠道具有多层结构保护整个肠道免受病原体的侵害。肠道上皮是由单层柱状上皮细胞组成,是抵抗病原体的第一道屏障。因此,肠上皮必须保持完整性以保护肠免受感染和毒性剂的侵害。上皮细胞分为两个谱系(吸收型与分泌型),并且每隔3~4天脱落至肠腔中。细胞的快速更替是由于肠道干细胞的存在,肠道干细胞排列在隐窝底部终极分化的潘氏细胞之间并沿隐窝绒毛轴分化成不同的上皮细胞。一旦肠道干细胞受到损伤,潘氏细胞将通过提供WNT配体和Notch刺激来补充肠道干细胞。因此,潘氏细胞充当辅助细胞以维持干细胞微环境,即生态位。该综述探讨了干细胞和潘氏细胞之间的相互作用,进一步探讨了维持肠道稳态的信号通路。     

Epithelial cells transdifferentiation into bladder urothelium in experiments in vivo

Atoplastic surgery using intestinal tissue has been used for the reconstructive therapy of the urinary tract since the mid-20th century; however, cell mechanisms of the urothelium engraftment are still unclear. Intestinal stem cells possess plasticity and, after autoplastic surgery, are presumably able to transdifferentiate into mature cells of the urinary tract. Using the preliminarily developed model for evaluating of the transdifferentiaion of somatic cells into urothelium in vivo, we found that, in syngeneic C57BL mice, epithelial Gfp-producing intestinal cells transdifferentiate into the cryoinjured bladder urothelium. Gfp was detected in the bladder tissue of recipient mice using reverse polymerase chain reaction, fluorescence and immunofluorescence. Colocalization of Her-4 protein revealed by common urothelium expression pattern and Gfp was demonstrated in few urothelial cells by double immunohistochemical staining of the bladder tissue with specific antibodies. The results obtained suggest that epithelial intestinal cells are able to transdifferentiate into bladder urothelium; however, the level of transdifferentiation is low and, presumably, cannot ensure the full functional urothelium engraftment in the case of autoplastic bladder surgery using intestinal tissue.     

Intestinal epithelial cells modulate CD4 T cell responses via the thymus leukemia antigen

The intestinal epithelium is comprised of a monolayer of intestinal epithelial cells (IEC), which provide, among other functions, a physical barrier between the high Ag content of the intestinal lumen and the sterile environment beyond the epithelium. IEC express a nonclassical MHC class I molecule known as the thymus leukemia (TL) Ag. TL is known to interact with CD8αα-expressing cells, which are abundant in the intestinal intraepithelial lymphocyte compartment. In this report, we provide evidence indicating that expression of TL by IEC modulates the cytokine profile of CD4(+) T cells favoring IL-17 production. We show in an adoptive transfer model of colitis that donor-derived cells become more pathogenic when TL is expressed on IEC in recipient animals. Moreover, TL(+)IEC promote development of IL-17-mediated responses capable of protecting mice from Citrobacter rodentium infection. We also show that modulation of IL-17-mediated responses by TL(+)IEC is controlled by the expression of CD8α on CD4(+) T cells. Overall, our results provide evidence for an important interaction between IEC and CD4(+) T cells via TL, which modulates mucosal immune responses.     

Inducible lymphoid tissues in the adult gut: recapitulation of a fetal developmental pathway?

The intestinal immune system faces an extraordinary challenge from the large numbers of commensal bacteria and potential pathogens that are restrained by only a single layer of epithelial cells. Here, I discuss evidence that the intestinal immune system develops an extensive network of inducible, reversible lymphoid tissues that contributes to the vital equilibrium between the gut and the bacterial flora. I propose that this network is induced by cryptopatches, which are small clusters of dendritic cells and lymphoid cells that are identical to fetal inducers of lymph-node and Peyer's-patch development.