Parkin-mediated transcriptional regulation of inducible NO-synthase impacts microglial inflammatory response in Parkinson disease-related cells and mice models

Abstract Neuroinflammation and oxidative stress are central to the pathogenesis of Parkinson disease (PD). inducible Nitric Oxide Synthase (iNOS), via excessive nitric oxide (NO) production, drives dopaminergic neurodegeneration. While Parkin, an E3 ubiquitin ligase mutated in familial PD, is renowned for its role in mitochondrial quality control. Emerging evidence suggests that it also functions as a transcriptional factor. However, its involvement in neuroinflammatory pathways at the transcriptional level remains poorly understood. In this study, we investigate the role of parkin-associated transcriptional function in the control of neuroinflammation in human microglial HMC3 cells as well as in the paraquat-induced sporadic Parkinson disease mouse model. We demonstrate that parkin modulates microglial activation by regulating human and mice cell proliferation and NO production. Parkin deficiency exacerbates iNOS induction and NO release. Mechanistic analysis indicates that parkin directly binds the iNOS promoter, thereby suppressing its transcription. Parkin expression rescue attenuates iNOS activation, thus confirming its protective role. Notably, we reveal a feedback loop wherein iNOS mediates parkin nitrosylation, suggesting a functional cross-talk between these two proteins. Furthermore, the anti-inflammatory properties of parkin, both in vitro and in vivo , were strengthened by its ability to modulate both central and peripheral cytokines production in mice. Of importance, we show that endogenous parkin depletion increases iNOS mRNA levels, a phenotype fully abolished by the Parkinson disease-like inducing toxin paraquat. Overall, our study uncover a novel function of parkin as a transcriptional repressor of iNOS , that could explain the putative link between mitochondrial dysfunction, microglial activation, and nitrosative stress in PD. Targeting the parkin-iNOS axis may thus offer an original alternative potential therapeutic strategy to curb neuroinflammation and slow disease progression in Parkinson Disease.