Disorders of the Cytoskeleton of the Enterocyte

Microvillus inclusion disease: a subtotal enterectomy as a bridge to transplantation

BACKGROUND

Microvillus inclusion disease (MVID) is a known congenital cause of intractable diarrhea resulting in permanent intestinal failure. There is need for a lifelong total parenteral nutrition (TPN) from diagnosis and the prognosis is poor. Most patients die by the second decade of life as a result of complications of parenteral alimentation including liver failure or sepsis. The only available treatment at this moment is a small bowel transplantation. But before that moment, the patients often suffer from a persistent failure to thrive and electrolyte disturbances despite continuous TPN.

METHODS AND RESULTS

We report what we believe is a first case of an extensive small bowel resection in a 5-month-old boy with proven MVID to act as a bridge to (liver-) intestinal transplantation to treat failure to thrive and intractable diarrhea.

CONCLUSIONS

An extensive small bowel resection can be done to enhance the chance of survival leading up to the transplantation by managing fluid and electrolyte imbalance. It facilitates medical management of these patients and makes a bowel transplantation possible at a later stage.

Bowel "dissection" in microvillus inclusion disease

A preterm male neonate was diagnosed as having microvillus inclusion disease based on the characteristics of histological and ultrastructural findings. The peripheral blood sample also revealed MYO5B mutation. He had been on long-term parenteral nutrition. However, a bowel segment was seen in the baby's diaper during hospitalization when he was 5 months old. Serial abdominal ultrasound demonstrated progressive dissection of the bowel wall with detached mucosa in real-time. Small intestinal epithelia were seen on the histology of the detached bowel segment. He died 2 weeks after the episode; postmortem autopsy showed diffuse detachment of mucosa of small bowels without perforation. This is the first report of an infant with microvillus inclusion disease that presented with bowel "dissection". Weakened adhesion and integrity of intestinal epithelial cells caused by MYO5B mutation was speculated to result in the dissection and detachment of the epithelia of the gastrointestinal tract.

Loss-of-function of MYO5B is the main cause of microvillus inclusion disease: 15 novel mutations and a CaCo-2 RNAi cell model

Autosomal recessive microvillus inclusion disease (MVID) is characterized by an intractable diarrhea starting within the first few weeks of life. The hallmarks of MVID are a lack of microvilli on the surface of villous enterocytes, occurrence of intracellular vacuoles lined by microvilli (microvillus inclusions), and the cytoplasmic accumulation of periodic acid-Schiff (PAS)-positive vesicles in enterocytes. Recently, we identified mutations in MYO5B, encoding the unconventional type Vb myosin motor protein, in a first cohort of nine MVID patients. In this study, we identified 15 novel nonsense and missense mutations in MYO5B in 11 unrelated MVID patients. Fluorescence microscopy, Western blotting, and electron microscopy were applied to analyze the effects of MYO5B siRNA knock-down in polarized, brush border possessing CaCo-2 cells. Loss of surface microvilli, increased formation of microvillus inclusions, and subapical enrichment of PAS-positive endomembrane compartments were induced in polarized, filter-grown CaCo-2 cells, following MYO5B knock-down. Our data indicate that MYO5B mutations are a major cause of microvillus inclusion disease and that MYO5B knock-down recapitulates most of the cellular phenotype in vitro, thus independently showing loss of MYO5B function as the cause of microvillus inclusion disease.

Microvillous inclusion disease (microvillous atrophy)

Microvillous inclusion disease (MVID) or microvillous atrophy is a congenital disorder of the intestinal epithelial cells that presents with persistent life-threatening watery diarrhea and is characterized by morphological enterocyte abnormalities. MVID manifests either in the first days of life (early-onset form) or in the first two months (late-onset form) of life. MVID is a very rare disorder of unknown origin, probably transmitted as an autosomal recessive trait. To date, no prevalence data are available. Ultrastructural analyses reveal: 1) a partial to total atrophy of microvilli on mature enterocytes with apical accumulation of numerous secretory granules in immature enterocytes; 2) the highly characteristic inclusion bodies containing rudimentary or fully differentiated microvilli in mature enterocytes. Light microscopy shows accumulation of PAS-positive granules at the apical pole of immature enterocytes, together with atrophic band indicating microvillus atrophy and, in parallel, an intracellular PAS or CD10 positive line (marking the microvillous inclusion bodies seen on electron microscopy). Intestinal failure secondary to diarrhea is definitive. To date, no curative therapy exists and children with MVID are totally dependent on parenteral nutrition. Long-term outcome is generally poor, due to metabolic decompensation, repeated states of dehydration, infectious and liver complications related to the parenteral nutrition. As MVID is a very rare disorder, which is extremely difficult to diagnose and manage, children with MVID should be transferred to specialized pediatric gastro-intestinal centers, if possible, a center equipped to perform small bowel transplantation. Early small bowel transplantation resulting in intestinal autonomy gives new hope for disease management and outcome.

Unusual ultrastructural features in microvillous inclusion disease: A report of two cases

Microvillous Inclusion Disease (MID) is an inherited disorder characterized by intractable diarrhea in infancy. Ultrastructural detection of pathognomonic microvillous inclusions in the enterocytes is essential for diagnosis. The aim of this research is to contribute to the knowledge of MID studying enterocytes and goblet cells (gc). Samples of duodenal mucosa from two young infants with MID (aged 75 days and 3 months, respectively) were studied by light and electron microscopy. Detection in the intestinal villi of immature gc (with microvilli) in one of the cases led us to seek them in control samples. The total number of gc with microvilli (immature) and without microvilli (mature) were counted. In both MID specimens, light microscopy showed atrophy of villi and PAS-positive material in the enterocyte cytoplasm. The ultrastructure of villous enterocytes was characterized by brush-border abnormalities, microvillous inclusions, dense apical granules, and lysosomes. Intermediate structures between microvillous inclusions and lysosomes were also detected within a cell, as were rare microvilli on the lateral membrane of the enterocytes. In one MID specimen, immature gc were also identified in the absorptive compartment. Only mature gc were observed in the controls. The significance of the latter finding requires further studies.

Microvilli defects in retinas of ezrin knockout mice

Ezrin, a member of the ezrin/moesin/radixin (ERM) family, localizes to microvilli of epithelia in vivo, where it functions as a bridge between actin filaments and plasma membrane proteins. In the eye, ezrin has been localized to both apical microvilli of Müller cells and retinal pigment epithelium (RPE) apical microvilli and basal infoldings. In the present study, we analyze these structures in the eyes of early postnatal ezrin knockout mice. This analysis indicates that the loss of ezrin leads to substantial reductions in the apical microvilli and basal infoldings in RPE cells and in the Müller cell apical microvilli. The absence of apical microvilli in the RPE is accompanied by the presence of microvilli-like inclusions (MIs) in the RPE cytoplasm. Finally, photoreceptors in the ezrin knockout animals show substantial retardation in development as compared to their wild type littermates.

Monolayer and three-dimensional cell culture and living tissue culture of gallbladder epithelium

Several models for preparing and isolating human and animal gallbladder epithelial cells, including low-grade gallbladder carcinoma cells, as well as proposed systems for culturing these isolated epithelial cells are reviewed here. Several reports concerning tissue culture of the gallbladder are also reviewed. The cell culture systems are divided into monolayer cell culture on collagen-coated or uncoated culture dishes or other culture substrate and three-dimensional cell culture in collagen gel. To prepare and isolate gallbladder epithelial cells, digestion of the gallbladder mucosa, abrasion of the mucosal epithelial cells, and excision of epithelial outgrowth of mucosal explants are applied. In monolayer cell culture, most of the specific biological features of isolated and cultured cells characteristic to the gallbladder are gradually lost after several passages, though quantitative and objective analyses of the pathophysiology of cultured cells and their secretory substances can be performed. Tissue culture using explants of the gallbladder has mainly been used for physiological studies of the gallbladder, such as investigating the transport of water and electrolytes. In this tissue culture system, quantitative assessment is difficult, though the original and specific biological and histological characteristics of the gallbladder are retained. Three-dimensional collagen gel culture could be an ideal model combining monolayer cell culture and tissue culture systems, and create controllable conditions or environments when several biologically active substances, such as growth factors, proinflammatory cytokines and adhesion molecules, are added to the culture medium. Advantages and shortcomings of individual cultivation models are discussed, and selecting the culture model most appropriate to the purpose of the study will facilitate investigations of the biology and pathogenetic mechanisms of gallbladder diseases such as cholelithiasis.

Reestablishment of rabbit gallbladder epithelial cells in collagen gel culture and their alterations by cytochalasin B and transforming growth factor beta-1. A morphologic study

We previously developed a model in which rabbit gall bladder epithelial cells in collagen gels proliferated and formed multicellular spherical cysts after 2 to 4 days. In the present study, we examined in depth the dynamic processes of loss and reestablishment of cell polarity of rabbit gallbladder epithelial cells isolated and cultured in collagen gel. Six hours after being place in culture, the isolated epithelial cells had lost the morphologic features and phenotypic markers inherent in the in vivo gallbladder mucosa, and autophagic vacuoles appeared transiently, reflecting epithelial cell injury, or remodelling, or both. After 12 hours, mucin dots appeared in clumps of epithelial cells and gradually became larger, and the epithelial cell clumps were transformed into multicellular cysts after 1 to 2 days. The luminal surfaces of the mucin dots (intracytoplasmic inclusions or small lumens sealed by several epithelial cells) and multicellular cysts were covered by microvilli and presented profiles of mucus glycoprotein and carbohydrate residues shared with the in vivo gallbladder mucosa. The presence of cellular adhesion structures and the distribution of cellular organelles toward the luminal surface implied the reestablishment of epithelial cell polarity. The addition of cytochalasin B induced many mucin-positive cytoplasmic inclusions covered by microvilli in the epithelial cells of the multicellular cysts, while the addition of transforming growth factor beta 1 promoted maturation of the multicellular cysts. This short term culture is useful for the analysis of the polarity of biliary epithelial cells and for examining disorders in this polarity.

Intestinal microvillous dystrophy: a variant of microvillous inclusion disease or a new entity?

We report three patients with intestinal microvillous dystrophy, two of whom were siblings. The relatively delayed clinical presentation and the lack of classical microvillous inclusions distinguish these cases from the previously described microvillous inclusion disease (MVID). There appears to be an underrecognized spectrum of microvillous disorders leading to fatal intractable secretory diarrhea in infants. In our three cases the diagnosis was suggested by periodic acid-Schiff (PAS) and alkaline phosphatase preparations of a jejunal biopsy specimen showing thinning or absence of brush border staining, which was confirmed by electron microscopy. The latter showed poorly developed and haphazardly arranged microvilli with intracytoplasmic vesicular bodies but no true inclusions. As in MVID, the prognosis of intestinal microvillous dystrophy is poor. The occurrence of the disease in two siblings of consanguinous parents suggests an autosomal recessive inheritance, and like MVID, genetic counselling of affected families is essential.

Siblings with microvillous inclusion disease

Two male siblings from a consanguinous Pakistani family had fatal diarrhoea with an onset at 24 and 48 hours after birth. A diagnosis of microvillous inclusion disease (MVID) was established by showing characteristic light and electron microscopic features in the small intestinal biopsy specimen on day 6 of life in case 1. The typical abnormalities of MVID were also demonstrated retrospectively in case 2 by examining archival appendicular tissue from 10 years previously. These cases are consistent with an autosomal recessive inheritance for MVID. Retrospective diagnosis of MVID is possible by examining appropriate archival material, which may aid genetic counselling and future research.

Alterations in epithelial polarity and the pathogenesis of disease states

The establishment and maintenance of epithelial-cell polarity are prerequisites for normal epithelial-cell and organ function. Knowledge of the processes involved in cell polarity has provided insight into the mechanisms of cell dysfunction and the pathogenesis of several diseases. These insights should lead to the development of specific strategies aimed at preventing or minimizing the progression of these diseases.

Intractable diarrhoea in infancy: a continuing challenge for the paediatric gastroenterologist

Intractable diarrhoea of infancy is a syndrome of severe chronic diarrhoea, associated with malnutrition, which is not easily resolved by conventional management. Application of small bowel biopsy and colonoscopy with biopsy to children with this syndrome has identified specific entities, such as autoimmune enteropathy and microvillus atrophy. There remains a group of children with unexplained small intestinal enteropathy and idiopathic enterocolitis who pose a considerable problem for diagnosis and management.

Disease processes in epithelia: the role of the actin cytoskeleton and altered surface membrane polarity

The establishment and maintenance of cell polarity is essential for normal epithelial function. Disruption of the underlying processes, either as a primary inborn defect or as a secondary result of other pathologic processes, can lead to loss of epithelial polarity and further cellular and organ-level dysfunction. Continued elucidation of the processes involved may prove fruitful both in the understanding of basic cell biology and in the understanding and treatment of a variety of disease states.

Uptake and transport of macromolecules by the intestine: possible role in clinical disorders (an update)

The intestine is exposed to a wide variety of macromolecules. Because macromolecules are antigenic, mechanisms have evolved in the gastrointestinal tract to regulate their absorption. Macromolecular uptake can be beneficial in delivering essential factors for growth and in sampling the antigenic milieu of the gastrointestinal tract. Specific transport mechanisms exist to execute this physiological absorption. However, inappropriate and uncontrolled antigen transport may occur in disease states or as a prelude to disease states in the gastrointestinal tract. Such transport may result in immune responses that are harmful. This review examines physiological transport of macromolecules through epithelia and through M cells. It also considers uncontrolled transport and its relation to disease states. The review concludes with an examination of the interrelationship between antigen transport and an altered immune system in the establishment of gastrointestinal disease.

Microvillus inclusion disease. In vitro jejunal electrolyte transport

Microvillus inclusion disease is an inherited intestinal brush border membrane defect that causes severe fluid and electrolyte malabsorption. In an infant with microvillus inclusion disease (confirmed by electron microscopic evaluation of rectal, jejunal, and gallbladder mucosae), basal stool output was massive (greater than 125 mL . kg-1 . day-1) and was not altered by treatment with clonidine or octreotide. A proximal jejunostomy with mucous fistula was placed, allowing separation of proximal from distal tract outputs (60 mL . kg-1 . day-1 and 100 mL . kg-1 . day-1, respectively). A 10-cm jejunal segment was excised during surgery and mounted in Ussing chambers for determination of transepithelial Na+ and Cl fluxes. Compared with intestine of normal infants, this infant's epithelium showed transmural conductance and unidirectional ion fluxes that were only 30% of normal. With respect to both Na+ and Cl, the excised jejunum was in a net secretory state. Theophylline (5 mmol/L) increased net Cl secretion slightly. In response to mucosal D-glucose (30 mmol/L), jejunal mucosal-to-serosal Na+ flux doubled. In the infant, glucose-electrolyte solution administered intrajejunally did not significantly change stool output, suggesting that all of the solution (40 mL/kg) was absorbed. Subtotal enterocolectomy, in theory, could have decreased purging by 66% in this infant with microvillus inclusion disease, but diarrhea would still have been significant.