Whole brain delivery of an instability-prone Mecp2 transgene improves behavioral and molecular pathological defects in mouse models of Rett syndrome.

Mirko Luoni,Antonio Niro,Giuseppe Morabito,Vania Broccoli,Serena Giannelli,Angelo Iannielli,Piera Calamita,Benjamin Deverman,Luca Massimino,Silvia Gregori,Marzia Tina Indrigo,Fabio Russo,Laura Passeri

doi:10.7554/elife.52629

Abstract

Rett syndrome is an incurable neurodevelopmental disorder caused by mutations in the gene encoding for methyl-CpG binding-protein 2 (MeCP2). Gene therapy for this disease presents inherent hurdles since MECP2 is expressed throughout the brain and its duplication leads to severe neurological conditions as well. Herein, we use the AAV-PHP.eB to deliver an instability-prone Mecp2 (iMecp2) transgene cassette which, increasing RNA destabilization and inefficient protein translation of the viral Mecp2 transgene, limits supraphysiological Mecp2 protein levels. Intravenous injections of the PHP.eB-iMecp2 virus in symptomatic Mecp2 mutant mice significantly improved locomotor activity, lifespan and gene expression normalization. Remarkably, PHP.eB-iMecp2 administration was well tolerated in female Mecp2 mutant or in wild-type animals. In contrast, we observed a strong immune response to the transgene in treated male Mecp2 mutant mice that was overcome by immunosuppression. Overall, PHP.eB-mediated delivery of iMecp2 provided widespread and efficient gene transfer maintaining physiological Mecp2 protein levels in the brain.

Highlights

Rett syndrome (RTT) is a severe neurological disorder and second cause of intellectual disabilities in girls
In the vast majority of cases RTT is caused by loss-of-function mutations in the MECP2 gene, which encodes for the methyl-CpG binding protein 2 (MeCP2), a global chromatin regulator highly expressed in neurons (Bienvenu and Chelly, 2006)
We overcame these limitations by setting a novel validation assay to compare the transcriptional efficiency of different viral Mecp2 transgene cassettes directly in neuronal cultures

Summary

Introduction

Rett syndrome (RTT) is a severe neurological disorder and second cause of intellectual disabilities in girls. RTT is distinguished by a period of 6–12 month of overtly normal development followed, by a rapid regression with the loss of the purposeful motor skills and the onset of repetitive and autistic behaviors (Lombardi et al, 2015; Katz et al, 2016). In the vast majority of cases RTT is caused by loss-of-function mutations in the MECP2 gene, which encodes for the methyl-CpG binding protein 2 (MeCP2), a global chromatin regulator highly expressed in neurons (Bienvenu and Chelly, 2006). Mecp2-deficient mice recapitulate key neurological deficits observed in RTT patients offering an invaluable model where to investigate pathological mechanisms as well as test innovative therapies (Guy et al, 2001).

Methods

Results

Conclusion