Abstract
Mutations in the MPV17 gene are associated with hepatocerebral form of mitochondrial depletion syndrome. The mechanisms through which MPV17 mutations cause respiratory chain dysfunction and mtDNA depletion is still unclear. The MPV17 gene encodes an inner membrane mitochondrial protein that was recently described to function as a non-selective channel. Although its exact function is unknown, it is thought to be important in the maintenance of mitochondrial membrane potential (ΔΨm). To obtain more information about the role of MPV17 in human disease, we investigated the effect of MPV17 knockdown and of selected known MPV17 mutations associated with MPV17 disease in vitro. We used different approaches in order to evaluate the cellular consequences of MPV17 deficiency. We found that lower levels of MPV17 were associated with impaired mitochondrial respiration and with a quiescent energetic metabolic profile. All the mutations studied destabilized the protein, resulting in reduced protein levels. We also demonstrated that different mutations caused different cellular abnormalities, including increased ROS production, decreased oxygen consumption, loss of ΔΨm, and mislocalization of MPV17 protein. Our study provides novel insight into the molecular effects of MPV17 mutations and opens novel possibilities for testing therapeutic strategies for a devastating group of disorders.
Highlights
Mitochondrial DNA depletion syndromes (MDDS) are autosomal recessive disorders characterized by a severe decrease in mitochondrial DNA copy number in affected tissues
To better understand the role of MPV17 in human disease, we investigated the effect of MPV17 knockdown in human cell lines and characterized the effect of selected MPV17 mutations associated with MDDS on cellular and organelle localization, and on mitochondrial bioenergetics
As resazurin reduction can be used as a measure of cell viability and as an indicator of overall mitochondrial function, this indicates MPV17 knockdown (MPV17KD) reduced cell viability and/or deficient mitochondrial oxidative capacity, as differences in cell proliferation were not detected by cell count (Figure 1D)
Summary
Mitochondrial DNA depletion syndromes (MDDS) are autosomal recessive disorders characterized by a severe decrease in mitochondrial DNA (mtDNA) copy number in affected tissues. Several genes are associated with MDDS, affecting mtDNA maintenance by three possible mechanisms: (i) impaired mitochondrial nucleotide (dNTP) synthesis [mutations in TK2 (Saada et al, 2001), SUCLA2 (Elpeleg et al, 2005), SUCLG1 (Ostergaard et al, 2007), RRMB2 (Bourdon et al, 2007), DGUOK (Mandel et al, 2001), TYMP (Nishino et al, 1999), ABAT (Besse et al, 2015), SLC25A4 (Echaniz-Laguna et al, 2012), and AGK (Mayr et al, 2012)]; (ii) deficient mtDNA replication [mutations in POLG (Naviaux et al, 1999), POLG2 (Young et al, 2015), TWINKLE (Sarzi et al, 2007b), TFAM (Stiles et al, 2016), RNASEH1 (Reyes et al, 2015), MGME1 (Kornblum et al, 2013), and DNA2 (Ronchi et al, 2013)], which leads to defects in mtDNA synthesis and repair; or (iii) defective mitochondrial dynamics [OPA1 (Amati-Bonneau et al, 2008), MFN2 (Rouzier et al, 2012), and FBXL4 (Antoun et al, 2015)] All these mechanisms cause deficient turnover and/or segregation of mtDNA to daughter cells, leading to a decrease in its copy number. MtDNA depletion results in inadequate synthesis of respiratory chain complexes with consequent deficient energy production and organ dysfunction (Sarzi et al, 2007a; Spinazzola et al, 2009)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
