Journal Article

Respiratory dysfunction by AFG3L2 deficiency causes decreased mitochondrial calcium uptake via organellar network fragmentation

Francesca Maltecca, Diego De Stefani, Laura Cassina, Francesco Consolato, Michal Wasilewski, Luca Scorrano, Rosario Rizzuto and Giorgio Casari

in Human Molecular Genetics

Volume 21, issue 17, pages 3858-3870
Published in print September 2012 | ISSN: 0964-6906
Published online June 2012 | e-ISSN: 1460-2083 | DOI: http://dx.doi.org/10.1093/hmg/dds214

Show Summary Details

Preview

The mitochondrial protein AFG3L2 forms homo-oligomeric and hetero-oligomeric complexes with paraplegin in the inner mitochondrial membrane, named m-AAA proteases. These complexes are in charge of quality control of misfolded proteins and participate in the regulation of OPA1 proteolytic cleavage, required for mitochondrial fusion. Mutations in AFG3L2 cause spinocerebellar ataxia type 28 and a complex neurodegenerative syndrome of childhood. In this study, we demonstrated that the loss of AFG3L2 in mouse embryonic fibroblasts (MEFs) reduces mitochondrial Ca2+ uptake capacity. This defect is neither a consequence of global alteration in cellular Ca2+ homeostasis nor of the reduced driving force for Ca2+ internalization within mitochondria, since cytosolic Ca2+ transients and mitochondrial membrane potential remain unaffected. Moreover, experiments in permeabilized cells revealed unaltered mitochondrial Ca2+ uptake speed in Afg3l2−/− cells, indicating the presence of functional Ca2+ uptake machinery. Our results show that the defective Ca2+ handling in Afg3l2−/− cells is caused by fragmentation of the mitochondrial network, secondary to respiratory dysfunction and the consequent processing of OPA1. This leaves a number of mitochondria devoid of connections to the ER and thus without Ca2+ elevations, hampering the proper Ca2+ diffusion along the mitochondrial network. The recovery of mitochondrial fragmentation in Afg3l2−/− MEFs by overexpression of OPA1 rescues the impaired mitochondrial Ca2+ buffering, but fails to restore respiration. By linking mitochondrial morphology and Ca2+ homeostasis, these findings shed new light in the molecular mechanisms underlining neurodegeneration caused by AFG3L2 mutations.

Journal Article.  7091 words.  Illustrated.

Subjects: Genetics and Genomics

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.