Tipping the PARylation scale: Dysregulation of PAR signaling in Huntington and neurodegenerative diseases.

Poly(ADP-ribosyl)ation (PARylation), a crucial post-translational modification, is catalyzed by ADP-ribosyltransferases (ARTs) and has significant implications in various cellular processes, including DNA damage response, cell signaling, and immune processes. Aberrant PAR signaling is implicated in numerous neurodegenerative diseases, including Alzheimer, Parkinson, amyotrophic lateral sclerosis, and cerebellar ataxia, where increased PAR levels and PARP1 activity are commonly observed. However, Huntington disease exhibits a unique characteristic: reduced PAR levels and impaired PARP1 activity even in prodromal phase. This finding challenges the prevailing understanding of PAR's role in neurodegeneration and suggests that dysregulation of PAR signaling, whether through overactivation or suppression, can lead to neuronal dysfunction. Herein, we discuss how this balance may impact neurodegenerative diseases, and possible connections between PAR signaling and emerging modifiers of disease onset identified by HD genome-wide association studies (GWAS).