The Effect of a Novel c.820C>T (Arg274Trp) Mutation in the Mitofusin 2 Gene on Fibroblast Metabolism and Clinical Manifestation in a Patient

Abstract

Charcot-Marie-Tooth disease type 2A (CMT2A) is an autosomal dominant axonal peripheral neuropathy caused by mutations in the mitofusin 2 gene (MFN2). Mitofusin 2 is a GTPase protein present in the outer mitochondrial membrane and responsible for regulation of mitochondrial network architecture via the fusion of mitochondria. As that fusion process is known to be strongly dependent on the GTPase activity of mitofusin 2, it is postulated that the MFN2 mutation within the GTPase domain may lead to impaired GTPase activity, and in turn to mitochondrial dysfunction. The work described here has therefore sought to verify the effects of MFN2 mutation within its GTPase domain on mitochondrial and endoplasmic reticulum morphology, as well as the mtDNA content in a cultured primary fibroblast obtained from a CMT2A patient harboring a de novo Arg274Trp mutation. In fact, all the parameters studied were affected significantly by the presence of the mutant MFN2 protein. However, using the stable model for mitofusin 2 obtained by us, we were next able to determine that the Arg274Trp mutation does not impact directly upon GTP binding. Such results were also confirmed for GTP-hydrolysis activity of MFN2 protein in patient fibroblast. We therefore suggest that the biological malfunctions observable with the disease are not consequences of impaired GTPase activity, but rather reflect an impaired contribution of the GTPase domain to other MFN2 activities involving that region, for example protein-protein interactions.

[Retracted] Protective Effects of Hydrogen on Myocardial Mitochondrial Functions in Septic Mice

“…Mitochondrial fission begins with the induction of Drp1. Mitochondrial fusion is a complex physiological process that involves optic atrophy 1 in the outer membrane and Mfn2 in the inner membrane [29] and depends on the MMP and hydrolysis of guanosine-5′-triphosphate [30]. e present investigation demonstrated reduced cardiac mitochondrial function in septic Nrf2 − /− mice as compared with that in their WT counterparts.…”

Molecular modelling of mitofusin 2 for a prediction for Charcot-Marie-Tooth 2A clinical severity

“…Membrane fusion is a GTP-dependent process that depends on mitofusin 2 GTPase activity and consists of the following sequence of events: (i) binding of GTP to the GTPase domain leading to conformational changes of the GTP binding site; (ii) dimerization of two adjacent MFN2 molecules, which facilitates membrane proximity and their tethering and (iii) GTP-dependent outer membrane fusion associated with proper closure of mitofusin 2 10 . Several studies have demonstrated that MFN2 mutations affecting its GTPase domain (95–339 aa) alter mitochondria fusion, leading to changes in the mitochondrial shape from tubular to more oval 9 , 11 . Moreover, in mitofusin 2-mutant cells, mitochondria seem to extensively aggregate around nucleus and are nonfunctional for fusion 9 , 12 .…”

“…Moreover, in mitofusin 2-mutant cells, mitochondria seem to extensively aggregate around nucleus and are nonfunctional for fusion 9 , 12 . Mitochondrial network dysfunctions were also accompanied by reticular stress, diminished respiratory capacity and changes in mtDNA in patient–derived fibroblasts 11 – 13 . Another report suggested that mitochondrial network dysfunction is associated with impaired GTPase activity 9 while we have recently reported that p.Arg274Trp mutation does not influence GTP binding or GTPase activity 11 .…”

“…Mitochondrial network dysfunctions were also accompanied by reticular stress, diminished respiratory capacity and changes in mtDNA in patient–derived fibroblasts 11 – 13 . Another report suggested that mitochondrial network dysfunction is associated with impaired GTPase activity 9 while we have recently reported that p.Arg274Trp mutation does not influence GTP binding or GTPase activity 11 . All these indicate significant functional heterogeneity of MFN2 mutants that underlie CMT2A.…”

“…Patients carrying mutations within GTPase domain present wide range of symptoms starting from classical form of CMT2A and ending with impairment of the central nervous system 2 . Moreover, significant differences in symptoms are also noticeable when distinct amino acid substitutions occurs at the same position 11 , 14 . Therefore, given that it is difficult to establish a categorical genotype - phenotype correlation, we have investigated whether the protein structure alterations caused by mutations in the MFN2 gene can inform the diseases phenotypes.…”