Mutations of C19orf12, coding for a transmembrane glycine zipper containing mitochondrial protein, cause mis-localization of the protein, inability to respond to oxidative stress and increased mitochondrial Ca2+

Abstract

Mutations in C19orf12 have been identified in patients affected by Neurodegeneration with Brain Iron Accumulation (NBIA), a clinical entity characterized by iron accumulation in the basal ganglia. By using western blot analysis with specific antibody and confocal studies, we showed that wild-type C19orf12 protein was not exclusively present in mitochondria, but also in the Endoplasmic Reticulum (ER) and MAM (Mitochondria Associated Membrane), while mutant C19orf12 variants presented a different localization. Moreover, after induction of oxidative stress, a GFP-tagged C19orf12 wild-type protein was able to relocate to the cytosol. On the contrary, mutant isoforms were not able to respond to oxidative stress. High mitochondrial calcium concentration and increased H2O2 induced apoptosis were found in fibroblasts derived from one patient as compared to controls. C19orf12 protein is a 17 kDa mitochondrial membrane-associated protein whose function is still unknown. Our in silico investigation suggests that, the glycine zipper motifs of C19orf12 form helical regions spanning the membrane. The N- and C-terminal regions with respect to the transmembrane portion, on the contrary, are predicted to rearrange in a structural domain, which is homologs to the N-terminal regulatory domain of the magnesium transporter MgtE, suggesting that C19orf12 may act as a regulatory protein for human MgtE transporters. The mutations here described affect respectively one glycine residue of the glycine zipper motifs, which are involved in dimerization of transmembrane helices and predicted to impair the correct localization of the protein into the membranes, and one residue present in the regulatory domain, which is important for protein-protein interaction.

Autophagy in childhood neurological disorders

“…In addition, overexpression of wild‐type C19orf12 increased lipidated LC3 and reduced the amount of the autophagy substrate p62. However, overexpression of mislocalized mutants failed to promote autophagy and levels of basal autophagy remained unchanged during exposure to oxidative stress in HeLa cells …”

“…Mitochondrial membrane protein‐associated neurodegeneration, also called hereditary spastic paraplegia type 43 (SPG43), is the third most common disease belonging to neurodegeneration with brain iron accumulation disorders. Patients with mitochondrial membrane protein‐associated neurodegeneration often suffer from cognitive decline, in addition to dystonia, gait and speech disturbance, or Parkinsonism . Age at onset is highly variable, but most patients present in childhood to early adulthood with slow progression .…”

Clinical and imaging characteristics of late onset mitochondrial membrane protein-associated neurodegeneration (MPAN)

“…The protein has been localized to mitochondria, endoplasmic reticula, and mitochondrial-associated membranes, and its long hydrophobic domain and glycine zipper motifs suggest that it may be a transmembrane protein (Venco et al, 2015). Mutations in C19orf12 result in a higher percentage of the protein outside the mitochondria perhaps due to inability to fit into membranes.…”

Iron chelation in the treatment of neurodegenerative diseases

“…Its physiological function and the mechanism of iron accumulation located into GP and SN are not entirely understood [82]. A case study reported no change in clinical status after chelation therapy with 30 mg/kg/day deferiprone lasting two years [83].…”