2. Academic Validation
  3. Loss of MYO5B Leads to Reductions in Na+ Absorption With Maintenance of CFTR-Dependent Cl- Secretion in Enterocytes

Loss of MYO5B Leads to Reductions in Na+ Absorption With Maintenance of CFTR-Dependent Cl- Secretion in Enterocytes

  • Gastroenterology. 2018 Dec;155(6):1883-1897.e10. doi: 10.1053/j.gastro.2018.08.025.
Amy C Engevik 1,  Izumi Kaji 1,  Melinda A Engevik 2,  Anne R Meyer 3,  Victoria G Weis 1,  Anna Goldstein 4,  Michael W Hess 5,  Thomas Müller 6,  Hermann Koepsell 7,  Pradeep K Dudeja 8,  Matthew Tyska 3,  Lukas A Huber 9,  Mitchell D Shub 10,  Nadia Ameen 11,  James R Goldenring 12
Affiliations

Affiliations

  • 1 Departments of Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee; Epithelial Biology Center, Vanderbilt University School of Medicine, Nashville, Tennessee.
  • 2 Department of Pathology and Immunology, Baylor College of Medicine, Houston, Texas; Department of Pathology, Texas Children's Hospital, Houston, Texas.
  • 3 Epithelial Biology Center, Vanderbilt University School of Medicine, Nashville, Tennessee; Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee.
  • 4 Departments of Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee; Epithelial Biology Center, Vanderbilt University School of Medicine, Nashville, Tennessee; Nashville Veterans Affairs Medical Center, Nashville, Tennessee.
  • 5 Division of Histology and Embryology, Innsbruck Medical University, Innsbruck, Austria.
  • 6 Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria.
  • 7 Department of Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, University of Würzburg, Würzburg, Germany.
  • 8 Department of Medicine, University of Illinois, Chicago and the Jesse Brown Veterans Affairs Medical Center, Chicago, Illinois.
  • 9 Division of Cell Biology, Biocenter and Innsbruck Medical University, Innsbruck, Austria; Austrian Drug Screening Institute, Innsbruck, Austria.
  • 10 Division of Gastroenterology and Phoenix Children's Hospital and the Department of Child Health, University of Arizona College of Medicine-Phoenix, Phoenix, Arizona.
  • 11 Department of Pediatrics, Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut.
  • 12 Departments of Surgery, Vanderbilt University School of Medicine, Nashville, Tennessee; Epithelial Biology Center, Vanderbilt University School of Medicine, Nashville, Tennessee; Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee; Nashville Veterans Affairs Medical Center, Nashville, Tennessee. Electronic address: jim.goldenring@vanderbilt.edu.
PMID: 30144427 DOI: 10.1053/j.gastro.2018.08.025
Abstract

Background & aims: Inactivating mutations in MYO5B cause microvillus inclusion disease (MVID), but the physiological cause of the diarrhea associated with this disease is unclear. We investigated whether loss of MYO5B results in aberrant expression of apical enterocyte transporters.

Methods: We studied alterations in apical membrane transporters in MYO5B-knockout mice, as well as mice with tamoxifen-inducible, intestine-specific disruption of Myo5b (VilCreERT2;Myo5bflox/flox mice) or those not given tamoxifen (controls). Intestinal tissues were collected from mice and analyzed by immunostaining, immunoelectron microscopy, or cultured enteroids were derived. Functions of brush border transporters in intestinal mucosa were measured in Ussing chambers. We obtained duodenal biopsy specimens from individuals with MVID and individuals without MVID (controls) and compared transporter distribution by immunocytochemistry.

Results: Compared to intestinal tissues from littermate controls, intestinal tissues from MYO5B-knockout mice had decreased apical localization of SLC9A3 (also called NHE3), SLC5A1 (also called SGLT1), Aquaporin (AQP) 7, and sucrase isomaltase, and subapical localization of intestinal Alkaline Phosphatase and CDC42. However, CFTR was present on apical membranes of enterocytes from MYO5B knockout and control mice. Intestinal biopsies from patients with MVID had subapical localization of NHE3, SGLT1, and AQP7, but maintained apical CFTR. After tamoxifen administration, VilCreERT2;Myo5bflox/flox mice lost apical NHE3, SGLT1, DRA, and AQP7, similar to germline MYO5B knockout mice. Intestinal tissues from VilCreERT2;Myo5bflox/flox mice had increased CFTR in crypts and CFTR localized to the apical membranes of enterocytes. Intestinal mucosa from VilCreERT2;Myo5bflox/flox mice given tamoxifen did not have an intestinal barrier defect, based on Ussing chamber analysis, but did have decreased SGLT1 activity and increased CFTR activity.

Conclusions: Although trafficking of many apical transporters is regulated by MYO5B, trafficking of CFTR is largely independent of MYO5B. Decreased apical localization of NHE3, SGLT1, DRA, and AQP7 might be responsible for dysfunctional water absorption in enterocytes of patients with MVID. Maintenance of apical CFTR might exacerbate water loss by active secretion of chloride into the intestinal lumen.

Keywords

Aquaporin; Mislocalization; Mouse Model; Sodium Hydrogen Exchanger.

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