Saturday, June 7, 2025
6/7/2025
Metabolic control of porphyrin biosynthesis by mTOR signaling - PROJECT SUMMARY/ABSTRACT Acute porphyrias are potentially life-threatening disorders caused by inherited mutations in enzymes of the evolutionarily conserved heme biosynthesis pathway. The resulting bottleneck effect leads to a buildup of toxic heme precursors, including the neurotoxin 5-aminolevulinic acid (ALA) and molecules called porphyrins that generate free radicals when exposed to light. Conditions that upregulate the first, and rate-limiting pathway enzyme, 5-aminolevulinic acid synthase (ALAS), can trigger rapid accumulation of ALA and porphyrins, leading to symptomatic “attacks” characterized by seizures, paralysis, and extreme light sensitivity. One common trigger of acute attacks is dieting or fasting. The overall goal of this project is to characterize the molecular mechanisms involved in metabolic control of porphyrin/heme biosynthesis, with an emphasis on determining the role of the key cellular energy sensor mechanistic target of rapamycin (mTOR). The research plan utilizes planarian flatworms as an experimentally tractable porphyria disease model. Planarians have a natural bottleneck in the heme biosynthesis pathway, leading to porphyrin accumulation in the pigment cells of their skin, and exhibit elevated ALAS expression, porphyrin levels, and light sensitivity in response to reduced nutrient intake, just like many human patients. Preliminary results show knockdown of mTOR by RNA interference (RNAi) also leads to an increase in porphyrins, raising the possibility that mTOR signaling in response to feeding acts as a negative regulator of ALAS expression. This hypothesis will be tested in the first aim, using RNAi, qRT-PCR, and a liquid chromatography assay for ALAS activity. Additional RNAi experiments in planarians will identify upstream and downstream components of this signaling pathway, while studies involving siRNA and drug treatments in cultured human hepatocytes will determine whether this mechanism is evolutionarily conserved and amenable to pharmacological manipulation. Completion of these experiments will improve our understanding of the pathogenesis of acute porphyrias and may reveal new avenues for treating these disorders. Additionally, the work will provide high-level research experiences for undergraduate students interested in pursuing biomedical career paths in the INBRE state of New Hampshire.
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