Developmental regulation of intestinal epithelial hydrolase activity in human fetal jejunal xenografts maintained in severe-combined immunodeficient mice

NF-kappa-B activation unveils the presence of inflammatory hotspots in human gut xenografts

The single-epithelial cell layer of the gut mucosa serves as an essential barrier between the host and luminal microflora and plays a major role in innate immunity against invading pathogens. Nuclear factor kB (NF-κB), a central component of the cellular signaling machinery, regulates immune response and inflammation. NF-κB proteins are activated by signaling pathways downstream to microbial recognition receptors and cytokines receptors. Highly regulated NF-κB activity in intestinal epithelial cells (IEC) is essential for normal gut homeostasis; dysregulated activity has been linked to a number of disease states, including inflammatory bowel diseases (IBD) such as Crohn's Disease (CD). Our aim was to visualize and quantify spatial and temporal dynamics of NF-κB activity in steady state and inflamed human gut. Lentivirus technology was used to transduce the IEC of human gut xenografts in SCID mice with a NF-κB luminescence reporter system. NF-κB signaling was visualized and quantified using low resolution, intravital imaging of the whole body and high resolution, immunofluorescence microscopic imaging of the tissues. We show that NF-κB is activated in select subset of IEC with low "leaky" NF-κB activity. These unique inflammatory epithelial cells are clustered in the gut into discrete hotspots of NF-κB activity that are visible in steady state and selectively activated by systemic LPS and human TNFα or luminal bacteria. The presence of inflammatory hotspots in the normal and inflamed gut might explain the patchy mucosal lesions characterizing CD and thus could have important implications for diagnosis and therapy.

Differential Expression of the Activator Protein 1 Transcription Factor Regulates Interleukin-1ß Induction of Interleukin 6 in the Developing Enterocyte

The innate immune response is characterized by activation of transcription factors, nuclear factor kappa B and activator protein-1 and their downstream targets, the pro-inflammatory cytokines including interleukin 1β and interleukin 6. Normal development of this response in the intestine is critical to survival of the human neonate and delays can cause the onset of devastating inflammatory diseases such as necrotizing enterocolitis. Previous studies have addressed the role of nuclear factor kappa B in the development of the innate immune response in the enterocyte, however despite its central role in the control of multiple pro-inflammatory cytokine genes, little is known on the role of Activator Protein 1 in this response in the enterocyte. Here we show that the canonical Activator Protein 1 members, cJun and cFos and their upstream kinases JNK and p38 play an essential role in the regulation of interleukin 6 in the immature enterocyte. Our data supports a model whereby the cFos/cJun heterodimer and the more potent cJun homodimer downstream of JNK are replaced by less efficient JunD containing dimers, contributing to the decreased responsiveness to interleukin 1β and decreased interleukin 6 secretion observed in the mature enterocyte. The tissue specific expression of JunB in colonocytes and colon derived tissues together with its ability to repress Interleukin-1β induction of an Interleukin-6 gene reporter in the NCM-460 colonocyte suggests that induction of JunB containing dimers may offer an attractive therapeutic strategy for the control of IL-6 secretion during inflammatory episodes in this area of the intestine

The role of gut microbiota in programming the immune phenotype

The human fetus lives in a germ-free intrauterine environment and enters the outside world containing microorganisms from several sources, resulting in gut colonization. Full-term, vaginally born infants are completely colonized with a diverse array of bacterial families in clusters (Phyla) and species (>1000) by the first year of life. Colonizing bacteria communicating with the gut epithelium and underlying lymphoid tissues ('bacterial-epithelial crosstalk') result in a functional immune phenotype and no expression of disease (immune homeostasis). Appropriate colonization is influenced by the prebiotic effect of breast milk oligosaccharides. Adequate colonization results in an innate and adaptive mucosal immune phenotype via communication between molecular patterns on colonizing bacteria and pattern-recognition receptors (e.g., toll-like receptors) on epithelial and lymphoid cells. This ontogeny affects the immune system's capacity to develop oral tolerance to innocuous bacteria and benign antigens. Inadequate intestinal colonization with premature delivery, delivery by Cesarean section and excessive use of perinatal antibiotics results in the absence of adequate bacterial-epithelial crosstalk and an increased incidence of immune-mediated diseases [e.g., asthma, allergy in general and necrotizing enterocolitis (NEC)]. Fortunately, infants with inadequate intestinal colonization can be restored to a bacterial balance with the intake of probiotics. This has been shown to prevent debilitating diseases such as NEC. Thus, understanding the role of gut microbiota in programming of the immune phenotype may be important in preventing disease expression in later childhood and adulthood.

Stem cells and biopharmaceuticals: vital roles in the growth of tissue-engineered small intestine

Tissue engineering currently constitutes a complex, multidisciplinary field exploring ideal sources of cells in combination with scaffolds or delivery systems in order to form a new, functional organ to replace native organ lack or loss. Short bowel syndrome (SBS) is a life-threatening condition with high morbidity and mortality rates in children. Current therapeutic strategies consist of costly and risky allotransplants that demand lifelong immunosuppression. A promising alternative is the implantation of autologous organoid units (OU) to create a tissue-engineered small intestine (TESI). This strategy is proven to be stem cell and mesenchyme dependent. Intestinal stem cells (ISCs) are located at the base of the crypt and are responsible for repopulating the cycling mucosa up to the villus tip. The stem cell niche governs the biology of ISCs and, together with the rest of the epithelium, communicates with the underlying mesenchyme to sustain intestinal homeostasis. Biopharmaceuticals are broadly used in the clinic to activate or enhance known signaling pathways and may greatly contribute to the development of a full-thickness intestine by increasing mucosal surface area, improving blood supply, and determining stem cell fate. This review will focus on tissue engineering as a means of building the new small intestine, highlighting the importance of stem cells and recombinant peptide growth factors as biopharmaceuticals.

Human tissue-engineered colon forms from postnatal progenitor cells: an in vivo murine model

AIM

Loss of colon reservoir function after colectomy can adversely affect patient outcomes. In previous work, human fetal intestinal cells developed epithelium without mesenchyme following implantation in mice. However, for humans, postnatal tissue would be the preferred donor source. We generated tissue-engineered colon (TEC) from postnatal human organoid units.

MATERIALS & METHODS

Organoid units were prepared from human colon waste specimens, loaded onto biodegradable scaffolds and implanted into immunocompromised mice. After 4 weeks, human TEC was harvested. Immunofluorescence staining confirmed human origin, identified differentiated epithelial cell types and verified the presence of supporting mesenchyme.

RESULTS

Human TEC demonstrated a simple columnar epithelium. Immunofluorescence staining demonstrated human origin and the three differentiated cell types of mature colon epithelium. Key mesenchymal components (smooth muscle, intestinal subepithelial myofibroblasts and ganglion cells) were seen.

CONCLUSION

Colon can form from human progenitor cells on a scaffold in a mouse host. This proof-of-concept experiment is an important step in transitioning TEC to human therapy.

Human tissue-engineered small intestine forms from postnatal progenitor cells

PURPOSE

Tissue-engineered small intestine (TESI) represents a potential cure for short bowel syndrome (SBS). We previously reported full-thickness intestine formation using an organoid units-on-scaffold approach in rodent and swine models. Transplanted intestinal xenografts have been documented to survive from human fetal tissue but not from postnatal tissue. We now present the first report of human TESI from postnatal tissue.

METHODS

Organoid units (OU) were prepared from human small bowel resection specimens, loaded onto biodegradable scaffolds and implanted into NOD/SCID gamma chain-deficient mice. After 4 weeks, TESI was harvested and immunostained for β2-microglobulin to identify human tissue, villin for enterocytes, lysozyme for Paneth cells, chromogranin-A for enteroendocrine cells, mucin-2 for goblet cells, smooth muscle actin and desmin to demonstrate muscularis, and S-100 for nerves.

RESULTS

All TESI was of human origin. Immunofluorescence staining of human TESI reveals the presence of all four differentiated cell types of mature human small intestine, in addition to the muscularis and the supporting intestinal subepithelial myofibroblasts. Nerve tissue is also present.

CONCLUSIONS

Our technique demonstrates survival, growth, and differentiation of postnatally derived human small intestinal OU into full thickness TESI in murine hosts. This regenerative medicine strategy may eventually assist in the treatment of SBS.

Glucocorticoid responsiveness in developing human intestine: possible role in prevention of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a major inflammatory disease of the premature human intestine that can be prevented by glucocorticoids if given prenatally before the 34th wk of gestation. This observation suggests that a finite period of steroid responsiveness exists as has been demonstrated in animal models. Human intestinal xenografts were used to determine whether a glucocorticoid responsive period exists in the developing human intestine. Developmental responsiveness was measured by lactase activity and inflammatory responsiveness by IL-8, IL-6, and monocyte chemotactic protein-1 (MCP-1) induction after an endogenous (IL-1 beta) or exogenous (LPS) proinflammatory stimulus, respectively. Functional development of ileal xenografts were monitored for 30 wk posttransplantation, and the lactase activity recapitulated that predicted by in utero development. Cortisone acetate accelerated the ontogeny of lactase at 20 wk (immature) but the effect was lost by 30 wk (mature) posttransplant. Concomitant with accelerated maturation, the IL-8 response to both IL-1 beta and LPS was significantly dampened (from 6- to 3-fold) by glucocorticoid pretreatment in the immature but not mature xenografts. The induction of IL-8 was reflected at the level of IL-8 mRNA, suggesting transcriptional regulation. The excessive activation of IL-8 in the immature gut was mediated by a prolonged activation of ERK and p38 kinases and nuclear translocation of NF-kappa B due to low levels of I kappa B. Steroid pretreatment in immature intestine dampens activation of all three signaling pathways in response to proinflammatory stimuli. Therefore, accelerating intestinal maturation by glucocorticoids within the responsive period by accelerating functional and inflammatory maturation may provide an effective preventive therapy for NEC.

The Dynamic Effects of Breastfeeding on Intestinal Development and Host Defense

In this review, evidence is provided to support the hypothesis that human milk provides a link between the mother and her newborn infant in the extrauterine environment in a manner similar to the placental link between mother and fetus in utero. In addition, breastfeeding helps prevent age-related diseases affecting the gastrointestinal tract during the newborn period. To provide evidence to support this hypothesis, anecdotal clinical studies are sited to suggest that human milk contains factors that may be missing in inherited diseases of inborn errors in metabolism and provide passive protective factors that lessen the expression of neonatal allergic and infectious diseases. In some instances, by providing the missing factor in an inherited disease, the newborn may be protected from serious damage to its developing brain. A second line of evidence to support this hypothesis is the observation that the composition of human milk varies with the infant's needs. To illustrate this principal, the composition of milk from mothers delivering prematurely and milk of mothers of full-term infants were compared, and the differences in trophic and protective factors in colostrum versus mature milk from mothers delivering full-term are cited. Finally, using observations from the laboratory that define the immaturities in neonatal and premature human intestinal defenses as the neonate's host defense deficiency, the specific effect that anti-inflammatory and maturational factors in human milk has on these immaturities is discussed. The active stimulus of maternal milk on the rapid development of host defenses is underscored. These cited examples of human milk effects in the newborn help support the stated hypothesis. Additional studies of human immature gut function along with translational and clinical studies are necessary to provide further objective evidence in support of breastfeeding for all neonates, particularly premature neonates.

Breaking the species barrier: use of SCID mouse-human chimeras for the study of human infectious diseases

Mouse-human chimeras have become a novel way to model the interactions between microbial pathogens and human cells, tissues or organs. Diseases studied with human xenografts in severe combined immunodeficient (SCID) mice include Pseudomonas aeruginosa infection in cystic fibrosis, group A streptococci and impetigo, bacillary and amoebic dysentery, and AIDS. In many cases, disease in the human xenograft appears to accurately reproduce the disease in humans, providing a powerful model for identifying virulence factors, host responses to infection and the effects of specific interventions on disease. In this review, we summarize recent studies that have used mouse-human chimeras to understand the pathophysiology of specific bacterial and protozoan infections.

Normal and glucocorticoid-induced development of the human small intestinal xenograft

The aim of this study was to determine whether intestinal xenografts could recapitulate human in utero development by using disaccharidases as markers. Twenty-week-old fetal intestine was transplanted into immunocompromised mice and was followed. At 20-wk of gestation, the fetal human intestine was morphologically developed with high sucrase and trehalase but had low lactase activities. By 9-wk posttransplantation, jejunal xenografts were morphologically and functionally developed and were then monitored for </=6 mo. Both sucrase and trehalase activities remained unchanged, but lactase activity increased in a manner similar to that described in in utero development. Changes in sucrase and lactase activities were paralleled by protein levels. Cortisone acetate treatment at 20-wk posttransplantation accelerated the ontogeny of lactase but did not alter sucrase and trehalase activities. Biopsies from 1- and 2-yr-old infant intestine showed that all activities, except trehalase in the proximal intestine, corresponded to the levels found in jejunal xenografts at 24 wk posttransplantation. These studies suggest that 20-wk-old fetal intestine has the extrauterine developmental potential to follow normal intrauterine ontogeny as a xenograft.

Developmental patterns of mucin gene expression in human fetal small intestinal xenografts maintained in severe-combined immunodeficient mice

The lack of a suitable animal model that expresses human intestinal mucin genes limits the study of mucin function. The aim of this study was to examine whether human fetal intestinal xenografts, known to model host-restricted interactions with human-specific pathogens, express mucin genes in an appropriate developmental pattern when transplanted into severe-combined immunodeficient (scid) mice. Expression profiles for eight mucin genes were examined in human fetal ileal xenografts transplanted ectopically into scid mice for 10 wk. In situ hybridization was performed on fetal, xenograft, and adult intestinal tissue sections with 35S-labeled oligonucleotides specific to human tandem repeat sequences for MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, MUC6, and MUC7. Hybridization patterns observed with the MUC2, MUC3, MUC4, and MUC5AC probes demonstrated that mucin gene expression in xenografted fetal intestine was comparable to third trimester fetal and/or adult tissues. MUC2 and MUC5AC were expressed in a developmental-specific fashion. MUC5AC, expressed in first and early second trimester fetal bowel, was never detected in intestinal xenografts. MUC2 expression displayed a late fetal and/or adult-type hybridization pattern. MUC3 and MUC4 were not developmentally expressed. Appropriate developmental regulation of known intestinal mucin genes was recorded in ectopically grafted human fetal intestinal xenografts. Adult-like patterns of mucin gene expression in this model system will permit future studies aimed at characterizing cis/trans-acting factors that regulate mucin gene expression and function during development, disease, and wound healing and also in mucin-pathogen interactions during host defense.