Lon-PDH axis

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SUMMARY From the parent grant R01 GM136905-01 entitled, “Mitochondrial metabolism and the Lon-PDH axis”. The human Lon protease is a master regulator of mitochondrial proteostasis, which is essential for regulating mitochondrial energy metabolism and mitigating cell stress. We recently identified a novel pathogenic variant in the LONP1 gene encoding Lon, in two siblings with profound neurologic impairment, cerebral and cerebellar atrophy, in which proline at position 761 was replaced by leucine (Lon-P761L). Primary skin fibroblasts from these siblings, showed substantially reduced activity of pyruvate dehydrogenase (PDH). Our results demonstrated that PDH deficiency was caused by the failure of Lon-P761L to degrade the phosphorylated E1a subunit of PDH, which accumulates and inhibits PDH activity. PDH is the central gatekeeper linking glycolysis to the tricarboxylic acid (TCA) cycle and a key regulatory node for glucose and fatty acid catabolism. Neurons generate ATP almost exclusively by glucose oxidation, thus fully active PDH is crucial. We hypothesize that wild type Lon regulates the activity and architecture of the PDH complex and is crucial for calibrating mitochondrial metabolism and energetics. In this project, we will employ patient- and parent- derived fibroblasts, and also induced pluripotent stem cells (iPSCs), which have been generated from these fibroblasts. The patient- and parent- derived iPSCs will be differentiated into neurons and astrocytes. Using these cells, Aim 1 will test the hypothesis that Lon-mediated degradation regulates the architecture and activity of the PDH complex. Aim 2 will identify the up- and down- stream modulators of the Lon-PDH axis, which are altered in cells expressing wild type Lon versus Lon-P761L. In Aim 3, we will investigate the regulation of PDH by Lon in iPSCs differentiated into neurons and astrocytes. Our investigation will establish new molecular mechanisms for the Lon-dependent regulation of PDH. The knowledge gained will also help to identify potential therapeutic protein targets, pharmacologic and dietary interventions for increasing PDH activity and/or for treating PDH deficiency associated with Lon dysfunction. These outcomes have a broader impact for understanding how PDH activity and mitochondrial metabolism can be calibrated in both rare and more common disorders such as heart disease, cancer and neurodegeneration.