Mitochondrial dynamics and bioenergetic dysfunction is associated with synaptic alterations in mutant SOD1 motor neurons.
Mutations in Cu,Zn superoxide dismutase (SOD1) cause familial amyotrophic lateral sclerosis (FALS), a rapidly fatal motor neuron disease. Mutant SOD1 has pleiotropic toxic effects on motor neurons, among which mitochondrial dysfunction has been proposed as one of the contributing factors in motor neuron demise. Mitochondria are highly dynamic in neurons; they are constantly reshaped by fusion and move along neurites to localize at sites of high-energy utilization, such as synapses. The finding of abnormal mitochondria accumulation in neuromuscular junctions, where the SOD1-FALS degenerative process is though to initiate, suggests that impaired mitochondrial dynamics in motor neurons may be involved in pathogenesis. We addressed this hypothesis by live imaging microscopy of photo-switchable fluorescent mitoDendra in transgenic rat motor neurons expressing mutant or wild-type human SOD1. We demonstrate that mutant SOD1 motor neurons have impaired mitochondrial fusion in axons and cell bodies. Mitochondria also display selective impairment of retrograde axonal transport, with reduced frequency and velocity of movements. Fusion and transport defects are associated with smaller mitochondrial size, decreased mitochondrial density, and defective mitochondrial membrane potential. Furthermore, mislocalization of mitochondria at synapses among motor neurons, in vitro, correlates with abnormal synaptic number, structure, and function. Dynamics abnormalities are specific to mutant SOD1 motor neuron mitochondria, since they are absent in wild-type SOD1 motor neurons, they do not involve other organelles, and they are not found in cortical neurons. Together, these results suggest that impaired mitochondrial dynamics may contribute to the selective degeneration of motor neurons in SOD1-FALS.
Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, New York 10065, USA.
Jordi
J
Magrané
Mary Anne
MA
Sahawneh
Serge
S
Przedborski
Álvaro G
ÁG
Estévez
Giovanni
G
Manfredi
D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D004195:Disease Models, Animal; D004734:Energy Metabolism / Q000235:genetics; D005260:Female; D006801:Humans; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D028361:Mitochondrial Diseases / Q000235:genetics / Q000378:metabolism*; D009046:Motor Neurons / Q000378:metabolism* / Q000473:pathology; D011247:Pregnancy; D061251:Primary Cell Culture; D051381:Rats; D017207:Rats, Sprague-Dawley; D055647:Rats, Transgenic; D013482:Superoxide Dismutase / Q000172:deficiency* / Q000235:genetics; D000072105:Superoxide Dismutase-1; D013569:Synapses / Q000378:metabolism* / Q000473:pathology
C000606290:SOD1 protein, human; C000606292:Sod1 protein, rat; D013482:Superoxide Dismutase; D000072105:Superoxide Dismutase-1