Metabolic rewiring prevents neurodegeneration caused by chronic mitochondrial dysfunction

Area of Science:

• Neuroscience
• Cell Biology
• Genetics

Background:

• The mitochondrial fission-fusion cycle is vital for neuronal health but poorly understood in long-lived neurons.
• Dysfunction in this cycle is implicated in neurodegenerative diseases.
• Mutations in the human mitochondrial fusion gene Opa1 cause optic atrophy.

Purpose of the Study:

• To investigate the roles of mitochondrial fission and fusion in Drosophila neurons.
• To characterize the molecular response to mitochondrial fusion defects, particularly Opa1.
• To identify mechanisms protecting neurons from age-dependent degeneration caused by fusion impairment.

Main Methods:

• Utilized cell-type-specific CRISPR to knock out fission and fusion genes in Drosophila neurons.
• Performed transcriptomic analysis to study age-dependent responses to Opa1 knockout.
• Employed a double knockout strategy to assess the role of Lactate dehydrogenase (Ldh) and ATF4.

Main Results:

• Neither mitochondrial fission nor fusion is essential for basic neuronal survival and function.
• Mitochondrial fusion defects, especially Opa1 knockout, had a greater impact than fission defects, particularly in older neurons.
• Opa1 knockout induced an age-dependent transcriptomic shift resembling cancer cells, including Ldh upregulation.
• Ldh upregulation was found to be neuroprotective, essential for maintaining ATP levels and preventing degeneration.
• The transcription factor ATF4 mediates the neuroprotective upregulation of Ldh.

Conclusions:

• Mitochondrial fusion is more critical than fission for neuronal viability, especially with age.
• Impaired mitochondrial fusion triggers a metabolic reprogramming (akin to the Warburg effect in cancer) for neuronal survival.
• Targeting Ldh offers a potential therapeutic strategy against age-dependent neurodegeneration caused by mitochondrial dysfunction.