Gene Editing of Swine Myosin Vb Induces Microvillus Inclusion Disease and Loss of Apical Sodium Transporters with Maintenance of CFTR in Enterocytes
Authors: Engevik Amy C , Coutts Alex , Saqui‐Salces Milena , Kaji Izumi , Medida Ramya Lekha , Williams Janice , Carlson Daniel F , Melkamu Tamene , Goldenring James R 
Published: June 2021

BackgroundThe human genetic disorder Microvillus Inclusion Disease (MVID) results from inactivating mutations in Myosin Vb (MYO5B). MVID is characterized by severe, unremitting diarrhea that typically presents shortly after birth. The necessity of implementing total parenteral nutrition (TPN) and the long‐term administration of TPN in neonates with MVID presents challenges to elucidating the complex pathogenesis of MVID in humans. Thus, a large animal model of MVID that closely recapitulates human physiology is needed. To better understand the pathophysiology of MVID we created a large animal model that closely mimics human MVID.MethodsPigs were cloned using somatic cell nuclear transfer of primary pig fibroblasts edited with TALEN to express a P663L mutation of the MYO5B gene. This swine P663L mutation, referred to as MYO5B(P663L), corresponds to the Navajo P660L mutation seen in MVID patients. Neonatal pigs were euthanized within 1 day of birth and tissue was collected for analysis and generation of intestinal enteroids.ResultsThe MYO5B(P663L) pigs developed diarrhea shortly after birth, similar to patients with MVID. Immunostaining for brush border components F‐actin, ezrin, CD10 and DPPIV showed the presence of subapical intracellular inclusions in enterocytes of MYO5B P663L pigs. Transmission electron microscopy confirmed the presence of inclusions lined with microvilli in the MYO5B(P663L) pigs. Immunostaining for NHE3 and SGLT1, drivers of intestinal sodium and water absorption, showed decreased apical expression and diffuse sub‐apical expression in the MYO5B(P663L) pigs compared to control pigs. In contrast to decreased expression of sodium transporters, CFTR was maintained on the apical membrane of MYO5B(P663L) pigs. Enteroids generated from the proximal small intestine of neonatal control and MYO5B(P663L) pigs grew at similar rates, but showed differences in the brush border. Enteroids derived from MYO5B(P663L) pigs had sub‐apical expression of intestinal alkaline phosphatase and DPPIV and decreased apical expression of NHE3 compared to control enteroids. Administration of forskolin resulted in increased swelling in MYO5B(P663L) enteroids (170.8% ± 15.9) compared to control enteroids (90.4% ± 4.6), indicative of functional Cl− secretion.ConclusionsCollectively, these data suggest that decreased apical expression of NHE3 and SGLT1, which are required for water absorption, are likely responsible for the MVID diarrhea disorder. Moreover, maintenance of functional CFTR on the apical membrane of enterocytes in the MYO5B(P663L) pig may further exacerbate the development of diarrhea by actively secreting Cl−, thus driving further water loss by facilitating fluid secretion. This novel large animal model of MVID could provide an important vehicle for testing novel therapeutic approaches for patients with MVID.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.