Mechanisms underlying the protective role of glycolysis in ALS

ALS is a fatal neurodegenerative disease for which there is no cure. Elucidating the molecular mechanisms underlying motor neuron dysfunction and death is imperative for devising successful therapeutic strategies. The Zarnescu Lab has developed a Drosophila model of ALS based on TDP-43, which recapitulates several aspects of disease including cytoplasmic aggregates, locomotor dysfunction and reduced lifespan. Using powerful genetic and molecular tools we have identified novel targets and protein partners of TDP-43 that modulate its toxicity in vivo. In collaboration with the Sattler Lab (Barrow Neurological Institute) we have validated our findings from flies to patient derived motor neurons and spinal cords in what we call a ?fly to man? approach. Using this strategy, we have recently discovered that degenerating motor neurons upregulate glycolysis as a compensatory mechanism. Interestingly, it has recently become clear, that contrary to what was previously thought about metabolism in the CNS, neurons are capable of glycolysis and even assemble glycolytic enzymes at synapses to handle the demands of rapid synaptic communication or to handle stress. We have found that phosphofructokinase (PFK), the rate limiting enzyme in glycolysis is significantly upregulated in a fly model of TDP-43 proteinopathy, patient derived iPSC motor neurons and spinal cords with TDP-43 pathology. Notably, over-expression of PFK is sufficient to rescue, while knocking down PFK aggravates TDP-43 dependent locomotor defects in motor neurons. Interestingly, it has been shown that PFK localizes to the neuromuscular junction of C. elegans under hypoxic stress. The clustering of PFK promotes synaptic vesicle recycling thereby maintaining synaptic function during times of high energy demand. Stressed yeast cells form glycolytic (G) bodies that contain PFK as well as chaperones, VCP and translation elongation/termination factors. Our findings about PFK in ALS and these recent reports about PFK suggest that in order to compensate for cellular energetics deficits caused by mitochondrial dysfunction, degenerating motor neurons reroute ATP production onto glycolysis to survive. We hypothesize that increased glycolysis may support the synaptic vesicle cycle and/or improve mitochondrial function via synaptic G bodies. To test this hypothesis we will: 1) Determine the mechanism by which PFK mitigates motor neuron dysfunction in ALS (i.e., improved synaptic vesicle cycle and/or mitochondrial function); 2) Determine G body composition and dynamics at synapses under normal conditions and in disease. Our ?fly to man? approach enables us to first take advantage of powerful genetic tools and accessibility of the neuromuscular junction in flies then validate key findings in patient derived motor neurons. The results from these experiments will help formulate new hypotheses about neuronal metabolism and survival in disease.