Defects in optineurin and myosin VI mediated cellular trafficking in amyotrophic lateral sclerosis.

Human molecular genetics

PubMedID: 25859013

Sundaramoorthy V, Walker AK, Tan V, Fifita JA, McCann EP, Williams KL, Blair IP, Guillemin GJ, Farg MA, Atkin JD. Defects in optineurin and myosin VI mediated cellular trafficking in amyotrophic lateral sclerosis. Hum Mol Genet. 2015;.
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder primarily affecting motor neurons. Mutations in optineurin cause a proportion of familial ALS cases, and wildtype optineurin is misfolded and forms inclusions in sporadic ALS patient motor neurons. However it is unknown how optineurin mutation or misfolding leads to ALS. Optineurin acts an adaptor protein connecting the molecular motor myosin VI to secretory vesicles and autophagosomes. Here we demonstrate that ALS-linked mutations p. Q398X and p. E478G disrupt the association of optineurin with myosin VI, leading to an abnormal diffuse cytoplasmic distribution, inhibition of secretory protein trafficking, endoplasmic reticulum (ER) stress and Golgi fragmentation in motor neuron-like NSC-34 cells. We also provide further insight into the role of optineurin as an autophagy receptor. Wildtype optineurin associated with lysosomes and promoted autophagosome fusion to lysosomes in neuronal cells, implying it mediates trafficking of lysosomes during autophagy in association with myosin VI. However, either expression of ALS mutant optineurin or siRNA-mediated knockdown of endogenous optineurin blocked lysosome fusion to autophagosomes, resulting in autophagosome accumulation. Together these results indicate that ALS-linked mutations in optineurin disrupt myosin VI-mediated intracellular trafficking processes. In addition, in control human patient tissues optineurin displayed its normal vesicular localization but in sporadic ALS patient tissues, vesicles were present in a significantly decreased proportion of motor neurons. Optineurin binding to myosin VI was also decreased in tissue lysates from sporadic ALS spinal cords. This study therefore links several previously described pathological mechanisms in ALS, including defects in autophagy, fragmentation of the Golgi, and induction of ER stress, to disruption of optineurin function. These findings also indicate that optineurin-myosin VI dysfunction is a common feature of both sporadic and familial ALS.