Summary
In Huntington's disease mouse models, M1 ipRGCs degenerate and melanopsin expression declines before motor symptoms appear, disrupting the ipRGC-SCN pathway and impairing circadian photoentrainment. These findings suggest that circadian lighting interventions may need to compensate for compromised retinal light input in neurodegenerative diseases, and that ipRGC health could serve as an early biomarker of disease progression.
Key Findings
- Melanopsin expression was reduced in R6/2 and N171-82Q HD mouse models before the onset of motor deficits, indicating circadian disruption is an early, pre-motor symptom.
- M1 ipRGC numbers were specifically reduced in R6/2 mice via apoptosis, while non-M1 ipRGCs were relatively resilient to HD progression.
- Reduced M1 ipRGC innervation of the SCN was associated with diminished light-induced c-fos and vasoactive intestinal peptide (VIP) expression in the suprachiasmatic nuclei.
- Suppression of retinal T-box brain 2 (Tbr2), a transcription factor essential for ipRGC survival, by mutant Huntingtin was identified as a likely mediator of ipRGC loss.
Categories
The Science of Light: Examines ipRGC subtypes, melanopsin expression, and the ipRGC-SCN pathway in the context of neurodegeneration.
Sleep & Circadian Health: Demonstrates that loss of M1 ipRGCs disrupts circadian photoentrainment by reducing light-induced signaling in the SCN.
Dementia & Elder Care: Provides mechanistic insight into circadian disruption in Huntington's disease, a neurodegenerative condition, with parallels to Alzheimer's and aging.
Author(s)
MS Lin, PY Liao, HM Chen, CP Chang
Publication Year
2019
Number of Citations
23
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