Treatment with the Bacterial Toxin CNF1 Selectively Rescues Cognitive and Brain Mitochondrial Deficits in a Female Mouse Model of Rett Syndrome Carrying a MeCP2-Null Mutation

Abstract

Rett syndrome (RTT) is a rare neurological disorder caused by mutations in the X-linked MECP2 gene and a major cause of intellectual disability in females. No cure exists for RTT. We previously reported that the behavioural phenotype and brain mitochondria dysfunction are widely rescued by a single intracerebroventricular injection of the bacterial toxin CNF1 in a RTT mouse model carrying a truncating mutation of the MeCP2 gene (MeCP2-308 mice). Given the heterogeneity of MECP2 mutations in RTT patients, we tested the CNF1 therapeutic efficacy in a mouse model carrying a null mutation (MeCP2-Bird mice). CNF1 selectively rescued cognitive defects, without improving other RTT-related behavioural alterations, and restored brain mitochondrial respiratory chain complex activity in MeCP2-Bird mice. To shed light on the molecular mechanisms underlying the differential CNF1 effects on the behavioural phenotype, we compared treatment effects on relevant signalling cascades in the brain of the two RTT models. CNF1 provided a significant boost of the mTOR activation in MeCP2-308 hippocampus, which was not observed in the MeCP2-Bird model, possibly explaining the differential effects of CNF1. These results demonstrate that CNF1 efficacy depends on the mutation beared by MeCP2-mutated mice, stressing the need of testing potential therapeutic approaches across RTT models.

Excitation and Inhibition Imbalance in Rett Syndrome

“…Through these effects, CNF1 modulates actin cytoskeleton dynamics and enhances synaptic transmission and plasticity (Amir et al, 1999;Diana et al, 2007). Mecp2 KO and HET mice treated with CNF1 show a significant improvement in cognition and motor function (308/Y and Bird line) (De Filippis et al, 2012;Urbinati et al, 2021). CNF1 treatment also prevents an enhancement of GluN2B-tyrosine phosphorylation and facilitates LTP induction in hippocampal CA1 of Mecp2 HET mice.…”

Effects of the Rho GTPase‐activating toxin CNF1 on fibroblasts derived from Rett syndrome patients: A pilot study

“…It is interesting to note that the modulation of Rho GTPases by CNF1 has been described to rescue mitochondrial dysfunctions in Mecp2‐308 mice and null mice 12,25 . Various lines of evidence point to mitochondria dysfunction as a possible contributing factor in RTT pathogenesis.…”

“…Several metabolic components contribute to the phenotypical manifestations of RTT, 16 , 35 thus making difficult the analysis of RTT development and progression. Rho GTPases modulation by the bacterial product CNF1 has been reported to ameliorate the cognitive deficits and to rescue the mitochondrial defects in in vivo models of RTT, 12 , 18 , 25 thus suggesting CNF1 as a promising therapeutic drug. However, the molecular and cellular mechanisms which underlie the beneficial effects observed in the RTT models after exposure to CNF1 were still unclear.…”

“…It is interesting to note that the modulation of Rho GTPases by CNF1 has been described to rescue mitochondrial dysfunctions in Mecp2‐308 mice and null mice. 12 , 25 Various lines of evidence point to mitochondria dysfunction as a possible contributing factor in RTT pathogenesis. In the last years, several reports documented an altered mitochondrial structure, as well as deficiencies in mitochondrial enzyme activity in different RTT‐derived cells or tissues.…”

“…In particular, CNF1 reshapes the actin cytoskeleton and enhances neurotransmission and synaptic plasticity in mouse brains 18 . Interestingly, CNF1 also counteracts the RTT‐related mitochondrial defects restoring the mitochondrial respiratory chain complexes and ATP synthase activities, known to be crucial players for the cell energy production 12,19,25 . As a whole, these preclinical data suggest a potential role for Rho GTPases as therapeutic targets for RTT.…”