Metabolic rewiring prevents neurodegeneration caused by chronic mitochondrial dysfunction

The mitochondrial fission-fusion cycle is often disrupted in neurodegenerative diseases, but this important, dynamic process is not well characterized in healthy long-lived neurons of animals. We used an efficient cell-type-specific CRISPR strategy to knock out key fission and fusion genes in specific Drosophila neurons. Neither process is essential for neuronal survival and function, but the fusion knockouts had a larger impact than that of fission, especially in older animals. Mutations in the human mitochondrial inner membrane fusion gene Opa1 often cause the disease optic atrophy. Importantly, knockout of Opa1 in neurons causes a dramatic age-dependent transcriptomic response. This response resembles those of cancer cells and includes the upregulation of glycolytic genes, including Lactate dehydrogenase (Ldh). A novel double knockout strategy indicates that Ldh enhances the reduced ATP levels of the fusion mutants and is essential to prevent age-dependent neurodegeneration. This neuroprotective upregulation of Ldh is largely mediated by the transcription factor ATF4. The identified relationship-dysfunctional mitochondrial fusion alters metabolism-is reminiscent of Warburg's original cancer hypothesis, albeit in neurons. These data underscore the similarity of the two molecular programs, which promote growth in cancer and viability in the case of neurodegeneration.