Biosynthesis of neuroprotective melatonin is dysregulated in Huntington's disease.
Level 5 - mechanism / opinion, no new human data
Bench, animal model, cell culture, and human postmortem tissue mechanistic study
PubMed 37721126 · doi:10.1111/jpi.12909
What was done
The authors investigated the integrity of melatonin biosynthesis pathways, focusing on the rate-limiting enzyme aralkylamine N-acetyltransferase (AANAT), across pineal and extrapineal brain areas. Assessments were conducted using postmortem human brain samples (pineal gland and striatum) from Huntington's disease (HD) patients and controls, the R6/2 mouse model of HD (analyzing synaptosomal and nonsynaptosomal mitochondria in the forebrain), and full-length mutant huntingtin knock-in cell lines.
What was found
AANAT protein expression was significantly decreased in the pineal gland and striatum of HD patients compared to normal controls. In R6/2 mice, AANAT protein expression and melatonin levels were decreased in synaptosomal, but not nonsynaptosomal, mitochondria compared to wild-type mice. AANAT was sequestered within mutant huntingtin protein aggregates. Paradoxically, AANAT mRNA expression was increased in tissues showing decreased AANAT protein expression. No numerical values or effect sizes were reported in the abstract.
Why it matters
The study identifies a localized impairment in mitochondrial melatonin synthesis driven by AANAT sequestration in huntingtin aggregates, providing a mechanistic explanation for reduced melatonin and synaptosomal vulnerability in Huntington's disease.
Limits
The abstract reports no sample sizes (n) for human postmortem samples, animals, or cell lines, and contains no numerical data or statistical effect estimates. Human observations rely on postmortem tissue, which may reflect end-stage disease rather than causative disease onset.
Cited by
- supports Melatonin is synthesized directly inside human mitochondria.