Aberrant Mitochondrial Dynamics and Exacerbated Response to Neuroinflammation in a Novel Mouse Model of CMT2A.

Filippos Stavropoulos,Alexia Kagiava,Su Cheong Yeom,Jae Young Lee,Ji Hyun Bae,Irene Sargiannidou,Mihalis I Panayiotidis,Kleopas A Kleopa,Louiza Potamiti

doi:10.3390/ijms222111569

Abstract

Charcot-Marie-Tooth disease type 2A (CMT2A) is the most common hereditary axonal neuropathy caused by mutations in MFN2 encoding Mitofusin-2, a multifunctional protein located in the outer mitochondrial membrane. In order to study the effects of a novel MFN2K357T mutation associated with early onset, autosomal dominant severe CMT2A, we generated a knock-in mouse model. While Mfn2K357T/K357T mouse pups were postnatally lethal, Mfn2+/K357T heterozygous mice were asymptomatic and had no histopathological changes in their sciatic nerves up to 10 months of age. However, immunofluorescence analysis of Mfn2+/K357T mice revealed aberrant mitochondrial clustering in the sciatic nerves from 6 months of age, in optic nerves from 8 months, and in lumbar spinal cord white matter at 10 months, along with microglia activation. Ultrastructural analyses confirmed dysmorphic mitochondrial aggregates in sciatic and optic nerves. After exposure of 6-month-old mice to lipopolysaccharide, Mfn2+/K357T mice displayed a higher immune response, a more severe motor impairment, and increased CNS inflammation, microglia activation, and macrophage infiltrates. Overall, ubiquitous Mfn2K357T expression renders the CNS and peripheral nerves of Mfn2+/K357T mice more susceptible to mitochondrial clustering, and augments their response to inflammation, modeling some cellular mechanisms that may be relevant for the development of neuropathy in patients with CMT2A.

Highlights

Charcot-Marie-Tooth (CMT) disease is one of the most common inherited neurological disorders, with a varying prevalence of approximately 1/2500 individuals in WesternNorway [1], 1/9804 in Western Japan [2], 1/8475 in Northern England [3], and 1/6369 in Auckland, New Zealand [4]
The novel MFN2K357T Charcot-Marie-Tooth disease type 2A (CMT2A)-causing mutation found in the CMT2A patient was introduced into the mouse endogenous Mfn2 sequence (Chr.4, exon 11 (RefSeq accession number: NM_001285922.1)), following the single-stranded oligodeoxynucleotide (ssODN)-mediated KI with CRISPR-Cas approach (Figure 1A)
The expression of the mutant Mfn2 allele (Mfn2K357T ) in the CMT2A KI mouse model is regulated by the mouse Mfn2 promoter allowing for ubiquitous expression, as is the case with the widespread expression of MFN2 mutations in CMT2A patients

Summary

Introduction

Charcot-Marie-Tooth (CMT) disease is one of the most common inherited neurological disorders, with a varying prevalence of approximately 1/2500 individuals in WesternNorway [1], 1/9804 in Western Japan [2], 1/8475 in Northern England [3], and 1/6369 in Auckland, New Zealand [4]. Involvement of adipose tissue [12,13], mitochondrial myopathy [11], and the presence of dysmorphic features accompanied by severe global developmental delay [14] have been reported. This broad CMT2A clinical spectrum, with primary involvement of the peripheral nervous system (PNS) and CNS, is explained by the ubiquitous MFN2 expression (in neuronal and non-neuronal tissues) [15,16]. The reason why MFN2 pathogenic variants preferentially target the nervous system, especially peripheral nerves with long axons, has yet to be elucidated, some mechanisms have been proposed

Methods

Results

Discussion

Conclusion