Modeling of a Novel Patient-Based MYO5B Point Mutation Reveals Insights Into MVID Pathogenesis

A liver-specific mouse model for MYO5B-associated cholestasis reveals a toxic gain-of-function as underlying disease mechanism

Myosin Vb (MYO5B) deficiency, referring to the loss of protein expression or function, causes microvillus inclusion disease (MVID) and/or progressive familial intrahepatic cholestasis-type 10 (PFIC10) in humans. MYO5B plays a role in intracellular trafficking, but the mechanisms by which it contributes to cholestasis are not understood. The aim of this study was to generate a liver-specific mouse model and investigate the mechanism of MYO5B-associated cholestasis. In this study, we generated a liver-specific Myo5b cKO mice via CRISPR/Cas9 genome editing in conjunction with albumin-cre recombinase. Cholestatic stress was induced by dietary-administration of cholic acid (CA) or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). To investigate the frequently recurring MYO5B variant (c.2470C > T/p.(Arg824Cys)), adenoviral vectors encoding either the missense variant or blank control sequence were delivered to wild-type and Myo5b cKO mice through tail-vein injection. Serum and liver tissues were harvested from all mice for biochemical and histological analysis. Our findings indicated that loss of Myo5b expression did not cause cholestatic liver disease and did not augment CA or DDC feeding-induced cholestatic stress. By contrast, expression of the MYO5B c.2470C > T/p. (Arg824Cys) variant induced cholestasis, evidenced by elevated levels of serum alanine aminotransferase, alkaline phosphatase and bilirubin, mild hepatocellular injury, and altered bile salt export pump (Bsep) localization, resembling that observed in human PFIC10. In summary, we have developed a mouse model of MYO5B-associated cholestasis. The expression of the MYO5B-p. (Arg824Cys) variant but not the loss of Myo5b expression caused cholestasis, indicating a toxic gain-of-function as underlying disease mechanism.

Microvillus inclusion disease-causing MYO5B point mutations exert differential effects on motor function

Microvillus inclusion disease (MVID) is a rare congenital diarrheal disorder typically caused by loss of function mutations in the unconventional myosin, myosin 5b (MYO5B), which leads to the mistrafficking of apical components in enterocytes. MVID can manifest in two phenotypes: in both the intestine and liver or the liver alone. Although previous studies seeking to understand MVID disease pathology used MYO5B KO models, many patients have point mutations and thus express a dysfunctional MYO5B. How these point mutations lead to a broad spectrum of disease severity and the development of two distinct disease phenotypes is still not known. Here, we investigate the effect of MVID patient mutations on the function of the MYO5B motor domain, independent of cargo binding, using confocal imaging and fluorescence recovery after photobleaching. Patient mutations demonstrated a range of effects in these assays, from rigor-like behavior to loss of actin binding. Additionally, analysis of fluorescence recovery after photobleaching turnover kinetics suggests that some mutations negatively impact the ability of MYO5B to stay bound to actin. Collectively, our findings indicate that patient mutations affect the MYO5B motor domain in diverse ways, consistent with the spectrum of phenotypes observed in patients.

Alterations in cellular metabolic pathway and epithelial cell maturation induced by MYO5B defects are partially reversible by LPAR5 activation

Functional loss of the motor protein myosin Vb (MYO5B) induces various defects in intestinal epithelial function and causes a congenital diarrheal disorder, namely, microvillus inclusion disease (MVID). Utilizing the MVID model mice Vil1-CreERT2;Myo5bflox/flox (MYO5BΔIEC) and Vil1-CreERT2;Myo5bflox/G519R [MYO5B(G519R)], we previously reported that functional MYO5B loss disrupts progenitor cell differentiation and enterocyte maturation that result in villus blunting and deadly malabsorption symptoms. In this study, we determined that both absence and a point mutation of MYO5B impair lipid metabolism and alter mitochondrial structure, which may underlie the progenitor cell malfunction observed in the MVID intestine. Along with a decrease in fatty acid oxidation, the lipogenesis pathway was enhanced in the MYO5BΔIEC small intestine. Consistent with these observations in vivo, RNA sequencing of enteroids generated from the two MVID mouse strains showed similar downregulation of energy metabolic enzymes, including mitochondrial oxidative phosphorylation genes. In our previous studies, we reported that lysophosphatidic acid (LPA) signaling ameliorated epithelial cell defects in MYO5BΔIEC tissues and enteroids. The present study demonstrated that the highly soluble LPA receptor (LPAR)5-preferred agonist Compound-1 improved sodium transporter localization and absorptive function and tuft cell differentiation in patient-modeled MVID animals that carry independent mutations in MYO5B. Body weight loss in male MYO5B(G519R) mice was ameliorated by Compound-1. These observations suggest that Compound-1 treatment has a trophic effect on the intestine with MYO5B functional loss through epithelial cell-autonomous pathways that can accelerate the differentiation of progenitor cells and the maturation of enterocytes. Targeting LPAR5 may represent an effective therapeutic approach for the treatment of MVID symptoms induced by different point mutations in MYO5B.NEW & NOTEWORTHY This study demonstrates the importance of MYO5B for cellular lipid metabolism and mitochondria in intestinal epithelial cells, previously unexplored functions of MYO5B. The alterations may underlie the progenitor cell malfunction observed in microvillus inclusion disease (MVID) intestines. To examine the therapeutic potential of progenitor-targeted treatments, the effects of the LPAR5-preferred agonist Compound-1 were investigated utilizing several MVID model mice and enteroids. Our observations suggest that Compound-1 may provide a therapeutic approach for treating MVID.

Altered cellular metabolic pathway and epithelial cell maturation induced by MYO5B defects are partially reversible by LPAR5 activation

Functional loss of the motor protein, Myosin Vb (MYO5B), induces various defects in intestinal epithelial function and causes a congenital diarrheal disorder, microvillus inclusion disease (MVID). Utilizing the MVID model mice, Vil1-Cre ERT2 ;Myo5b flox/flox (MYO5BΔIEC) and Vil1-Cre ERT2 ;Myo5b flox/G519R (MYO5B(G519R)), we previously reported that functional MYO5B loss disrupts progenitor cell differentiation and enterocyte maturation that result in villus blunting and deadly malabsorption symptoms. In this study, we determined that both absence and a point mutation of MYO5B impair lipid metabolism and alter mitochondrial structure, which may underlie the progenitor cell malfunction observed in MVID intestine. Along with a decrease in fatty acid oxidation, the lipogenesis pathway was enhanced in the MYO5BΔIEC small intestine. Consistent with these observations in vivo , RNA-sequencing of enteroids generated from two MVID mouse strains showed similar downregulation of energy metabolic enzymes, including mitochondrial oxidative phosphorylation genes. In our previous studies, lysophosphatidic acid (LPA) signaling ameliorates epithelial cell defects in MYO5BΔIEC tissues and enteroids. The present study demonstrates that the highly soluble LPAR5-preferred agonist, Compound-1, improved sodium transporter localization and absorptive function, and tuft cell differentiation in patient-modeled MVID animals that carry independent mutations in MYO5B. Body weight loss in male MYO5B(G519R) mice was ameliorated by Compound-1. These observations suggest that Compound-1 treatment has a trophic effect on intestine with MYO5B functional loss through epithelial cell-autonomous pathways that may improve the differentiation of progenitor cells and the maturation of enterocytes. Targeting LPAR5 may represent an effective therapeutic approach for treatment of MVID symptoms induced by different point mutations in MYO5B.

NEW & NOTEWOTHY

This study demonstrates the importance of MYO5B for cellular lipid metabolism and mitochondria in intestinal epithelial cells, a previously unexplored function of MYO5B. Alterations in cellular metabolism may underlie the progenitor cell malfunction observed in microvillus inclusion disease (MVID). To examine the therapeutic potential of progenitor-targeted treatments, the effects of LPAR5-preferred agonist, Compound-1, was investigated utilizing several MVID model mice and enteroids. Our observations suggests that Compound-1 may provide a therapeutic approach for treating MVID.

Graphic Abstract

Intracellular Trafficking Defects in Congenital Intestinal and Hepatic Diseases

Enterocytes and liver cells fulfill important metabolic and barrier functions and are responsible for crucial vectorial secretive and absorptive processes. To date, genetic diseases affecting metabolic enzymes or transmembrane transporters in the intestine and the liver are better comprehended than mutations affecting intracellular trafficking. In this review, we explore the emerging knowledge on intracellular trafficking defects and their clinical manifestations in both the intestine and the liver. We provide a detailed overview including more investigated diseases such as the canonical, variant and associated forms of microvillus inclusion disease, as well as recently described pathologies, highlighting the complexity and disease relevance of several trafficking pathways. We give examples of how intracellular trafficking hubs, such as the apical recycling endosome system, the trans-Golgi network, lysosomes, or the Golgi-to-endoplasmic reticulum transport are involved in the pathomechanism and lead to disease. Ultimately, understanding these processes could spark novel therapeutic approaches, which would greatly improve the quality of life of the affected patients.

Modeling the cell biology of monogenetic intestinal epithelial disorders

Monogenetic variants are responsible for a range of congenital human diseases. Variants in genes that are important for intestinal epithelial function cause a group of disorders characterized by severe diarrhea and loss of nutrient absorption called congenital diarrheas and enteropathies (CODEs). CODE-causing genes include nutrient transporters, enzymes, structural proteins, and vesicular trafficking proteins in intestinal epithelial cells. Several severe CODE disorders result from the loss-of-function in key regulators of polarized endocytic trafficking such as the motor protein, Myosin VB (MYO5B), as well as STX3, STXBP2, and UNC45A. Investigations of the cell biology and pathophysiology following loss-of-function in these genes have led to an increased understanding of both homeostatic and pathological vesicular trafficking in intestinal epithelial cells. Modeling different CODEs through investigation of changes in patient tissues, coupled with the development of animal models and patient-derived enteroids, has provided critical insights into the enterocyte differentiation and function. Linking basic knowledge of cell biology with the phenotype of specific patient variants is a key step in developing effective treatments for rare monogenetic diseases. This knowledge can also be applied more broadly to our understanding of common epithelial disorders.

Uncovering the Relationship Between Genes and Phenotypes Beyond the Gut in Microvillus Inclusion Disease

Microvillus inclusion disease (MVID) is a rare condition that is present from birth and affects the digestive system. People with MVID experience severe diarrhea that is difficult to control, cannot absorb dietary nutrients, and struggle to grow and thrive. In addition, diverse clinical manifestations, some of which are life-threatening, have been reported in cases of MVID. MVID can be caused by variants in the MYO5B, STX3, STXBP2, or UNC45A gene. These genes produce proteins that have been functionally linked to each other in intestinal epithelial cells. MVID associated with STXBP2 variants presents in a subset of patients diagnosed with familial hemophagocytic lymphohistiocytosis type 5. MVID associated with UNC45A variants presents in most patients diagnosed with osteo-oto-hepato-enteric syndrome. Furthermore, variants in MYO5B or STX3 can also cause other diseases that are characterized by phenotypes that can co-occur in subsets of patients diagnosed with MVID. Recent studies involving clinical data and experiments with cells and animals revealed connections between specific phenotypes occurring outside of the digestive system and the type of gene variants that cause MVID. Here, we have reviewed these patterns and correlations, which are expected to be valuable for healthcare professionals in managing the disease and providing personalized care for patients and their families.

A case-control comparison of acute-phase peripheral blood gene expression in participants diagnosed with minor ischaemic stroke or stroke mimics

BACKGROUND

Past studies suggest that there are changes in peripheral blood cell gene expression in response to ischaemic stroke; however, the specific changes which occur during the acute phase are poorly characterised. The current study aimed to identify peripheral blood cell genes specifically associated with the early response to ischaemic stroke using whole blood samples collected from participants diagnosed with ischaemic stroke (n = 29) or stroke mimics (n = 27) following emergency presentation to hospital. Long non-coding RNA (lncRNA), mRNA and micro-RNA (miRNA) abundance was measured by RNA-seq, and the consensusDE package was used to identify genes which were differentially expressed between groups. A sensitivity analysis excluding two participants with metastatic disease was also conducted.

RESULTS

The mean time from symptom onset to blood collection was 2.6 h. Most strokes were mild (median NIH stroke scale score 2.0). Ten mRNAs (all down-regulated in samples provided by patients experiencing ischaemic stroke) and 30 miRNAs (14 over-expressed and 16 under-expressed in participants with ischaemic stroke) were significantly different between groups in the whole cohort and sensitivity analyses. No significant over-representation of gene ontology categories by the differentially expressed genes was observed. Random forest analysis suggested a panel of differentially expressed genes (ADGRG7 and miRNAs 96, 532, 6766, 6798 and 6804) as potential ischaemic stroke biomarkers, although modelling analyses demonstrated that these genes had poor diagnostic performance.

CONCLUSIONS

This study provides evidence suggesting that the early response to minor ischaemic stroke is predominantly reflected by changes in the expression of miRNAs in peripheral blood cells. Further work in independent cohorts particularly in patients with more severe stroke is needed to validate these findings and investigate their clinical relevance.

Patient-derived enteroids provide a platform for the development of therapeutic approaches in microvillus inclusion disease

Microvillus inclusion disease (MVID), caused by loss-of-function mutations in the motor protein myosin Vb (MYO5B), is a severe infantile disease characterized by diarrhea, malabsorption, and acid/base instability, requiring intensive parenteral support for nutritional and fluid management. Human patient-derived enteroids represent a model for investigation of monogenic epithelial disorders but are a rare resource from MVID patients. We developed human enteroids with different loss-of function MYO5B variants and showed that they recapitulated the structural changes found in native MVID enterocytes. Multiplex immunofluorescence imaging of patient duodenal tissues revealed patient-specific changes in localization of brush border transporters. Functional analysis of electrolyte transport revealed profound loss of Na+/H+ exchange (NHE) activity in MVID patient enteroids with near-normal chloride secretion. The chloride channel-blocking antidiarrheal drug crofelemer dose-dependently inhibited agonist-mediated fluid secretion. MVID enteroids exhibited altered differentiation and maturation versus healthy enteroids. γ-Secretase inhibition with DAPT recovered apical brush border structure and functional Na+/H+ exchange activity in MVID enteroids. Transcriptomic analysis revealed potential pathways involved in the rescue of MVID cells including serum/glucocorticoid-regulated kinase 2 (SGK2) and NHE regulatory factor 3 (NHERF3). These results demonstrate the utility of patient-derived enteroids for developing therapeutic approaches to MVID.

Therapy Development for Microvillus Inclusion Disease using Patient-derived Enteroids

Microvillus Inclusion Disease (MVID), caused by loss-of-function mutations in the motor protein Myosin Vb (MYO5B), is a severe infantile disease characterized by diarrhea, malabsorption, and acid-base instability, requiring intensive parenteral support for nutritional and fluid management. Human patient-derived enteroids represent a model for investigation of monogenic epithelial disorders but are a rare resource from MVID patients. We developed human enteroids with different loss-of function MYO5B variants and showed that they recapitulated the structural changes found in native MVID enterocytes. Multiplex Immunofluorescence imaging of patient duodenal tissues revealed patient-specific changes in localization of brush border transporters. Functional analysis of electrolyte transport revealed profound loss of Na + /H + exchange (NHE) activity in MVID patient enteroids with near-normal chloride secretion. The chloride channel-blocking anti-diarrheal drug, Crofelemer, dose-dependently inhibited agonist-mediated fluid secretion. MVID enteroids exhibited altered differentiation and maturation versus healthy enteroids. Inhibition of Notch signaling with the γ-secretase inhibitor, DAPT, recovered apical brush border structure and functional Na + /H + exchange activity in MVID enteroids. Transcriptomic analysis revealed potential pathways involved in the rescue of MVID cells including serum- and glucocorticoid-induced protein kinase 2 (SGK2), and NHE regulatory factor 3 (NHERF3). These results demonstrate the utility of patient-derived enteroids for developing therapeutic approaches to MVID.

Conflict-of-interest statement

The authors have declared that no conflict of interest exists.