Mitofusin 2 Regulated Transport of Mitochondria is Necessary for Axonal Integrity

OF THE DISSERTATION Mitofusin 2 Regulated Transport of Mitochondria is Necessary for Axonal Integrity By Albert Lawrence Misko Doctor of Philosophy in Biology and Biomedical Sciences Neurosciences Washington University in St. Louis, 2012 Professor Robert Baloh, Chairperson The ubiquitous finding of axonal degeneration in a number of the most prevalent neuropathologies marks the importance of understanding axonal biology and the axonal selfdestruct mechanism. Though our understanding of axonal degeneration remains largely incomplete, several down-steam steps of the molecular cascade have been elucidated. While this insight has emerged from models of axon degeneration following physical injury or toxic insult, a more comprehensive understanding of the upstream events may be gained from studying primary axonopathies with defined genetic causes. This dissertation aims to elucidate a molecular mechanism underlying the loss of axons in Charcot-Marie-Tooth Disease type 2A, which is caused by mutations in the mitofusin 2 (MFN2) gene. Utilizing an in vitro culture system, we find that CMT2A associated MFN2 mutants disrupt the transport of axonal mitochondria in DRG neurons. Though MFN2 has a previously defined role in facilitating mitochondrial fusion, we propose a direct role for MFN2 in mediating transport based on its interaction with key components of the mitochondrial transport apparatus and perturbation of transport in MFN2 null DRG neurons. MFN2 does not provide a direct link between mitochondria and microtubule based motors, but is poised to mediate transport by a still undefined mechanism. The ability of MFN2 to mediate transport is separate from its ability to mediate fusion as MFN2 disease mutants, that have been shown to retain their ability to fuse mitochondria, cannot rescue the transport deficit in MFN2 null neurons. Additionally, loss of mitochondrial fusion by knockdown of opa-1 is not sufficient to disrupt mitochondrial transport