Towards understanding microvillus inclusion disease

Antibacterial polypeptide-bioparticle for oral administration: Powder formulation, palatability and in vivo toxicity approach

The upsurge of bacterial resistance to conventional antibiotics turned a well-recognized public health threat. The need of developing new biomaterials of effective practical use in order to tackle bacterial resistance became urgent. In this study, a submicrometric bioparticle of known antibacterial activity was produced in powder form with suitable texture and appealing characteristics for effective oral administration. Through complex coacervating a natural-source antimicrobial polypeptide with chitosan-N-arginine and alginate, the bioactive polypeptide was physically incorporated to the bioparticle whose structure positively responds to the pH variations found in gastrointestinal tract. The powder formulation presented high palatability that was evaluated using fish as in vivo animal model. A thorough survey of the fish intestinal tissues, following a systematic oral administration, revealed high penetration potential of the biomaterial through epithelial cells and deeper intestine layers. Despite, no cytotoxic effect was observed in analyzing the tissues through different histology methods. The absence of intestinal damage was corroborated by immune histochemistry, being the integrity of epithelial motor myosin Vb and related traffic proteins preserved. Hematology further endorsed absence of toxicity in blood cells whose morphology was evaluated in detail. The study evidenced the applicability potential of a new biomaterial of appealing and safe oral administration of antibacterial polypeptide.

[Ultrastructure of pathologic deposits and cellular inclusions]

Intra- and extracellular depositions and inclusions occur in a wide range of diseases with exogenous (e.g. infectious, environmental and toxic) or endogenous (e.g. genetic, inflammatory, neoplastic and degenerative) aetiology. The noxious agent and the pathogenesis influence the organ of manifestation, the subcellular localisation and the ultrastructural appearance of the depositions. Whereas some of the inclusions like pathogens, foreign material (e.g. asbestos) or microvilli have an almost pathognomonic morphology, other inclusions are present in lower amounts also under normal conditions (e.g. lipid vacuoles and glycogen). Therefore, the interpretation of ultrastructural findings makes a correlation with the histological features and clinical constellation necessary. Auxiliary investigations by electron energy loss spectroscopy (EELS) or electron spectroscopic imaging (ESI) provide additional information about the chemical composition of the material and are therefore especially helpful for the identification of foreign substances. This review focuses on a selection of deposits and inclusions relevant to diagnostic pathology.

Pathogenic STX3 variants affecting the retinal and intestinal transcripts cause an early-onset severe retinal dystrophy in microvillus inclusion disease subjects

Biallelic STX3 variants were previously reported in five individuals with the severe congenital enteropathy, microvillus inclusion disease (MVID). Here, we provide a significant extension of the phenotypic spectrum caused by STX3 variants. We report ten individuals of diverse geographic origin with biallelic STX3 loss-of-function variants, identified through exome sequencing, single-nucleotide polymorphism array-based homozygosity mapping, and international collaboration. The evaluated individuals all presented with MVID. Eight individuals also displayed early-onset severe retinal dystrophy, i.e., syndromic-intestinal and retinal-disease. These individuals harbored STX3 variants that affected both the retinal and intestinal STX3 transcripts, whereas STX3 variants affected only the intestinal transcript in individuals with solitary MVID. That STX3 is essential for retinal photoreceptor survival was confirmed by the creation of a rod photoreceptor-specific STX3 knockout mouse model which revealed a time-dependent reduction in the number of rod photoreceptors, thinning of the outer nuclear layer, and the eventual loss of both rod and cone photoreceptors. Together, our results provide a link between STX3 loss-of-function variants and a human retinal dystrophy. Depending on the genomic site of a human loss-of-function STX3 variant, it can cause MVID, the novel intestinal-retinal syndrome reported here or, hypothetically, an isolated retinal dystrophy.

MYO5B Pathogenic Variants Found to Cause Intestinal Symptoms Without Microvillus Inclusion Disease in a Child Who Previously Underwent Liver Transplantation for PFIC-like Cholestasis

Myosin 5B (MYO5B ) pathogenic variants are associated with microvillus inclusion disease (MVID), a congenital disorder of the enterocyte characterized by intractable diarrhea (5 ). A subset of MVID patients also have cholestatic liver disease. Conversely, some patients may have isolated cholestasis without gastrointestinal symptoms (2 ). Such patients have been described to have a progressive familial intrahepatic cholestasis (PFIC)-like phenotype with normal serum gamma-glutamyl transferase. We report a novel case in which MYO5B pathogenic variants were discovered by whole exome sequencing in a post-liver transplant patient who originally presented with PFIC-like cholestasis and chronic intermittent diarrhea without ultrastructural evidence of microvillus inclusion disease.

SNAREs and developmental disorders

Members of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family mediate membrane fusion processes associated with vesicular trafficking and autophagy. SNAREs mediate core membrane fusion processes essential for all cells, but some SNAREs serve cell/tissue type-specific exocytic/endocytic functions, and are therefore critical for various aspects of embryonic development. Mutations or variants of their encoding genes could give rise to developmental disorders, such as those affecting the nervous system and immune system in humans. Mutations to components in the canonical synaptic vesicle fusion SNARE complex (VAMP2, STX1A/B, and SNAP25) and a key regulator of SNARE complex formation MUNC18-1, produce variant phenotypes of autism, intellectual disability, movement disorders, and epilepsy. STX11 and MUNC18-2 mutations underlie 2 subtypes of familial hemophagocytic lymphohistiocytosis. STX3 mutations contribute to variant microvillus inclusion disease. Chromosomal microdeletions involving STX16 play a role in pseudohypoparathyroidism type IB associated with abnormal imprinting of the GNAS complex locus. In this short review, I discuss these and other SNARE gene mutations and variants that are known to be associated with a variety developmental disorders, with a focus on their underlying cellular and molecular pathological basis deciphered through disease modeling. Possible pathogenic potentials of other SNAREs whose variants could be disease predisposing are also speculated upon.

Challenges of Microvillus Inclusion Disease in the NICU

Mutations in the myosin 5β, syntaxin-binding protein 2, and syntaxin 3 genes lead to microvillus inclusion disease (MVID), an autosomal recessive congenital enteropathy. This rare disease is characterized by lack of microvilli on the surface of enterocytes in the small intestine, the presence of pathognomonic intracellular microvillus inclusions, and vesicular bodies within these enterocytes. This pathology leads to the characteristic intractable, life-threatening, watery diarrhea. In the more common early-onset form, affected patients present in the first few days after birth, whereas in the late-onset form, clinical manifestations appear at approximately 2 to 3 months of age. Genetic testing can confirm the diagnosis, but the infant's medical history, clinical presentation, and small intestinal biopsy results are strongly suggestive of the diagnosis. The prevalence of MVID is thought to be higher in countries with a high degree of consanguinity. Patients with MVID cannot tolerate feedings and require continuous total parenteral nutrition. Mortality is extremely high in the early-onset type with reports of survival in patients treated with small intestinal transplantation. Medical counseling for parents of infants with MVID needs to reflect our current understanding of the various genetic forms of this disease, the feasible management, and anticipated outcomes.

Microvillus Inclusion Disease: A Rare Mutation of STX3 in Exon 9 Causing Fatal Congenital Diarrheal Disease

Inherited diarrheal disorders cause serious morbidity resulting in dependence on intensive care and parenteral nutrition. Microvillus inclusion disease (MVID) has been classically described and results from mutations in the gene coding myosin Vb, which is responsible for enterocyte polarization. Newer reports of mutations resulting in truncated syntaxin 3 (STX3) and Munc18-2 (STXBP2) proteins have been elucidated as causative. To date, five cases of STX3 abnormalities resulting in MVID have been described. We report an infant who presented with congenital diarrhea and was determined to have a rare mutation of STX3. This new finding would be beneficial in future functional genotype–phenotype correlation studies.

Recent advances in understanding and managing malabsorption: focus on microvillus inclusion disease

Microvillus inclusion disease (MVID) is a rare congenital severe malabsorptive and secretory diarrheal disease characterized by blunted or absent microvilli with accumulation of secretory granules and inclusion bodies in enterocytes. The typical clinical presentation of the disease is severe chronic diarrhea that rapidly leads to dehydration and metabolic acidosis. Despite significant advances in our understanding of the causative factors, to date, no curative therapy for MVID and associated diarrhea exists. Prognosis mainly relies on life-long total parenteral nutrition (TPN) and eventual small bowel and/or liver transplantation. Both TPN and intestinal transplantation are challenging and present with many side effects. A breakthrough in the understanding of MVID emanated from seminal findings revealing mutations in MYO5B as a cause for MVID. During the last decade, many studies have thus utilized cell lines and animal models with knockdown of MYO5B to closely recapitulate the human disease and investigate potential therapeutic options in disease management. We will review the most recent advances made in the research pertaining to MVID. We will also highlight the tools and models developed that can be utilized for basic and applied research to increase our understanding of MVID and develop novel and effective targeted therapies.

Congenital diarrhea in a newborn infant: A case report

BACKGROUND

Microvillus inclusion disease (MVID) is a rare autosomal recessive cause of severe congenital diarrhea with significant morbidity and mortality. Definitive treatment involves bowel transplant. The diagnosis of this condition can be challenging and a few genetic panels are available for the identification of the most common mutations. We present the case of an infant with MVID due to a mutation not reported in the literature before.

CASE SUMMARY

We report the case of an infant transferred to our institution with severe diarrhea of unknown etiology, failure to thrive, and significant metabolic derangements. An extensive work-up including stool studies for common gastrointestinal pathogens, abdominal ultrasound, esophagogastroduodenoscopy with duodenal biopsy and flexible sigmoidoscopy failed to reveal a diagnosis. Multiple dietary and formula regimens were introduced but all resulted in voluminous diarrhea. She remained on total parenteral nutrition (TPN) for the duration of her hospital stay. Genetic testing was done and she was subsequently found to have a novel mutation in the MYO5B gene [homozygous mutation for MYO5B c.1462del, p. (Ile488Leufs*93)] giving us the diagnosis of MVID. She remains on TPN while awaiting bowel transplant at the time of the compilation of this case report.

CONCLUSION

We report a novel mutation involved in MVID and highlight the importance of considering this disease when faced with a newborn presenting with life threatening diarrhea. At the time of this publication, 232 allelic variations of this gene (MIM#606540) exist in National Center for Biotechnology Information's database. Our patient's mutation has not been reported in literature as a cause of MVID.

Physiology of Electrolyte Transport in the Gut: Implications for Disease

We now have an increased understanding of the genetics, cell biology, and physiology of electrolyte transport processes in the mammalian intestine, due to the availability of sophisticated methodologies ranging from genome wide association studies to CRISPR-CAS technology, stem cell-derived organoids, 3D microscopy, electron cryomicroscopy, single cell RNA sequencing, transgenic methodologies, and tools to manipulate cellular processes at a molecular level. This knowledge has simultaneously underscored the complexity of biological systems and the interdependence of multiple regulatory systems. In addition to the plethora of mammalian neurohumoral factors and their cross talk, advances in pyrosequencing and metagenomic analyses have highlighted the relevance of the microbiome to intestinal regulation. This article provides an overview of our current understanding of electrolyte transport processes in the small and large intestine, their regulation in health and how dysregulation at multiple levels can result in disease. Intestinal electrolyte transport is a balance of ion secretory and ion absorptive processes, all exquisitely dependent on the basolateral Na⁺ /K⁺ ATPase; when this balance goes awry, it can result in diarrhea or in constipation. The key transporters involved in secretion are the apical membrane Cl^- channels and the basolateral Na⁺ -K⁺ -2Cl^- cotransporter, NKCC1 and K⁺ channels. Absorption chiefly involves apical membrane Na⁺ /H⁺ exchangers and Cl^- /HCO₃ ^- exchangers in the small intestine and proximal colon and Na⁺ channels in the distal colon. Key examples of our current understanding of infectious, inflammatory, and genetic diarrheal diseases and of constipation are provided. © 2019 American Physiological Society. Compr Physiol 9:947-1023, 2019.

A V0-ATPase-dependent apical trafficking pathway maintains the polarity of the intestinal absorptive membrane

Intestine function relies on the strong polarity of intestinal epithelial cells and the array of microvilli forming a brush border at their luminal pole. Combining a genetic RNA interference (RNAi) screen with in vivo super-resolution imaging in the Caenorhabditis elegans intestine, we found that the V0 sector of the vacuolar ATPase (V0-ATPase) controls a late apical trafficking step, involving Ras-related protein 11 (RAB-11)⁺ endosomes and the N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) synaptosome-associated protein 29 (SNAP-29), and is necessary to maintain the polarized localization of both apical polarity modules and brush border proteins. We show that the V0-ATPase pathway also genetically interacts with glycosphingolipids and clathrin in enterocyte polarity maintenance. Finally, we demonstrate that silencing of the V0-ATPase fully recapitulates the severe structural, polarity and trafficking defects observed in enterocytes from individuals with microvillus inclusion disease (MVID) and use this new in vivo MVID model to follow the dynamics of microvillus inclusions. Thus, we describe a new function for V0-ATPase in apical trafficking and epithelial polarity maintenance and the promising use of the C. elegans intestine as an in vivo model to better understand the molecular mechanisms of rare genetic enteropathies.

Early Diagnosis and Management of Aggressive Posterior Vitreoretinopathy Presenting in Premature Neonates

BACKGROUND AND OBJECTIVE

Aggressive posterior vitreoretinopathy (APVR) manifests with a broad area of retinal avascularity, progressive neovascularization, and/or tractional retinal detachment during the neonatal period.

PATIENTS AND METHODS

A multicenter, retrospective, observational, consecutive case series study was performed to evaluate the retinal findings and structural retinal outcomes in patients treated for APVR within the first 3 months of life.

RESULTS

Three premature neonates with a non-retinopathy of prematurity (ROP) APVR identified during routine ROP screening exams exhibited relatively severe, rapidly progressive retinal vascular abnormalities. Immediate laser photocoagulation of the avascular retina and vitrectomy for traction retinal detachment within several days to weeks improved or stabilized the retinal anatomy in all cases.

CONCLUSIONS

This series describes clinical features in APVR in premature infants and suggests that early diagnosis and intervention may mitigate the typical aggressive course and poor prognosis of this condition. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:201-207.].

Microvillus inclusion disease, a diagnosis to consider when abnormal stools and neurological impairments run together due to a rare syntaxin 3 gene mutation

BACKGROUND

Microvillus Inclusion Disease (MVID) was first described in the literature in 1978 with presentation of severe watery diarrhea, failure to thrive, and metabolic acidosis. Mutations in the myosin Vb (MYO5B) gene have been identified as causative for MVID, but other clinical manifestations and associations with novel mutations are lacking.

METHODS

We report a full-term infant admitted to the neonatal intensive care unit (NICU) with abdominal distension and inability to sustain full enteral feeds. A retrospective chart review and review of the literature was performed.

RESULTS

An infant with abnormal, mucoid-like stringy stools was incidentally found to have severe metabolic acidosis on routine lab monitoring. Acidosis corrected with total parenteral nutrition (TPN), but the infant experienced recurrent episodes of acidosis with enteral feeds. He was also noted to have abnormal ocular movements, fluctuating tonicity, and staring spells. He underwent an extensive workup and the diagnosis of microvillus inclusion disease was made by findings on electron microscopy. The diagnosis was confirmed with whole exome sequencing, showing a rare homozygous mutation in the syntaxin 3 (STX3) gene. This is the fifth reported patient with microvillus inclusion disease with a mutation in this gene, and the first with abnormal neurologic findings.

CONCLUSION

It is important to consider MVID in the differential diagnosis of a neonate or infant with abnormal stools, metabolic acidosis, with and without neurologic symptoms for prompt referral and treatment.

Dynamic Formation of Microvillus Inclusions During Enterocyte Differentiation in Munc18-2-Deficient Intestinal Organoids

BACKGROUND & AIMS

Microvillus inclusion disease (MVID) is a congenital intestinal malabsorption disorder caused by defective apical vesicular transport. Existing cellular models do not fully recapitulate this heterogeneous pathology. The aim of this study was to characterize 3-dimensional intestinal organoids that continuously generate polarized absorptive cells as an accessible and relevant model to investigate MVID.

METHODS

Intestinal organoids from Munc18-2/Stxbp2-null mice that are deficient for apical vesicular transport were subjected to enterocyte-specific differentiation protocols. Lentiviral rescue experiments were performed using human MUNC18-2 variants. Apical trafficking and microvillus formation were characterized by confocal and transmission electron microscopy. Spinning disc time-lapse microscopy was used to document the lifecycle of microvillus inclusions.

RESULTS

Loss of Munc18-2/Stxbp2 recapitulated the pathologic features observed in patients with MUNC18-2 deficiency. The defects were fully restored by transgenic wild-type human MUNC18-2 protein, but not the patient variant (P477L). Importantly, we discovered that the MVID phenotype was correlated with the degree of enterocyte differentiation: secretory vesicles accumulated already in crypt progenitors, while differentiated enterocytes showed an apical tubulovesicular network and enlarged lysosomes. Upon prolonged enterocyte differentiation, cytoplasmic F-actin-positive foci were observed that further progressed into classic microvillus inclusions. Time-lapse microscopy showed their dynamic formation by intracellular maturation or invagination of the apical or basolateral plasma membrane.

CONCLUSIONS

We show that prolonged enterocyte-specific differentiation is required to recapitulate the entire spectrum of MVID. Primary organoids can provide a powerful model for this heterogeneous pathology. Formation of microvillus inclusions from multiple membrane sources showed an unexpected dynamic of the enterocyte brush border.

Engineered Glycocalyx Regulates Stem Cell Proliferation in Murine Crypt Organoids

At the base of the intestinal crypt, long-lived Lgr5⁺ stem cells are intercalated by Paneth cells that provide essential niche signals for stem cell maintenance. This unique epithelial anatomy makes the intestinal crypt one of the most accessible models for the study of adult stem cell biology. The glycosylation patterns of this compartment are poorly characterized, and the impact of glycans on stem cell differentiation remains largely unexplored. We find that Paneth cells, but not Lgr5⁺ stem cells, express abundant terminal N-acetyllactosamine (LacNAc). Employing an enzymatic method to edit glycans in cultured crypt organoids, we assess the functional role of LacNAc in the intestinal crypt. We discover that blocking access to LacNAc on Paneth cells leads to hyperproliferation of the neighboring Lgr5⁺ stem cells, which is accompanied by the downregulation of genes that are known as negative regulators of proliferation.

Abnormal Rab11-Rab8-vesicles cluster in enterocytes of patients with microvillus inclusion disease

Microvillus inclusion disease (MVID) is a congenital enteropathy characterized by accumulation of vesiculo-tubular endomembranes in the subapical cytoplasm of enterocytes, historically termed "secretory granules." However, neither their identity nor pathophysiological significance is well defined. Using immunoelectron microscopy and tomography, we studied biopsies from MVID patients (3× Myosin 5b mutations and 1× Syntaxin3 mutation) and compared them to controls and genome-edited CaCo2 cell models, harboring relevant mutations. Duodenal biopsies from 2 patients with novel Myosin 5b mutations and typical clinical symptoms showed unusual ultrastructural phenotypes: aberrant subapical vesicles and tubules were prominent in the enterocytes, though other histological hallmarks of MVID were almost absent (ectopic intra-/intercellular microvilli, brush border atrophy). We identified these enigmatic vesiculo-tubular organelles as Rab11-Rab8-positive recycling compartments of altered size, shape and location harboring the apical SNARE Syntaxin3, apical transporters sodium-hydrogen exchanger 3 (NHE3) and cystic fibrosis transmembrane conductance regulator. Our data strongly indicate that in MVID disrupted trafficking between cargo vesicles and the apical plasma membrane is the primary cause of a defect of epithelial polarity and subsequent facultative loss of brush border integrity, leading to malabsorption. Furthermore, they support the notion that mislocalization of transporters, such as NHE3 substantially contributes to the reported sodium loss diarrhea.

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.

Complex Polarity: Building Multicellular Tissues Through Apical Membrane Traffic

The formation of distinct subdomains of the cell surface is crucial for multicellular organism development. The most striking example of this is apical-basal polarization. What is much less appreciated is that underpinning an asymmetric cell surface is an equally dramatic intracellular endosome rearrangement. Here, we review the interplay between classical cell polarity proteins and membrane trafficking pathways, and discuss how this marriage gives rise to cell polarization. We focus on those mechanisms that regulate apical polarization, as this is providing a number of insights into how membrane traffic and polarity are regulated at the tissue level.