Upregulation of GPR109A in Parkinson's disease

PLoS One. 2014 Oct 17;9(10):e109818. doi: 10.1371/journal.pone.0109818. eCollection 2014.


Background: Anecdotal animal and human studies have implicated the symptomatic and neuroprotective roles of niacin in Parkinson's disease (PD). Niacin has a high affinity for GPR109A, an anti-inflammatory receptor. Niacin is also thought to be involved in the regulation of circadian rhythm. Here we evaluated the relationships among the receptor, niacin levels and EEG night-sleep in individuals with PD.

Methods and findings: GPR109A expression (blood and brain), niacin index (NAD-NADP ratio) and cytokine markers (blood) were analyzed. Measures of night-sleep function (EEG) and perceived sleep quality (questionnaire) were assessed. We observed significant up-regulation of GPR109A expression in the blood as well as in the substantia nigra (SN) in the PD group compared to age-matched controls. Confocal microscopy demonstrated co-localization of GPR109A staining with microglia in PD SN. Pro and anti-inflammatory cytokines did not show significant differences between the groups; however IL1-β, IL-4 and IL-7 showed an upward trend in PD. Time to sleep (sleep latency), EEG REM and sleep efficiency were different between PD and age-matched controls. Niacin levels were lower in PD and were associated with increased frequency of experiencing body pain and decreased duration of deep sleep.

Conclusions: The findings of associations among the GPR109A receptor, niacin levels and night-sleep function in individuals with PD are novel. Further studies are needed to understand the pathophysiological mechanisms of action of niacin, GPR109A expression and their associations with night-sleep function. It would be also crucial to study GPR109A expression in neurons, astrocytes, and microglia in PD. A clinical trial to determine the symptomatic and/or neuroprotective effect of niacin supplementation is warranted.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Case-Control Studies
  • Female
  • Humans
  • Male
  • Middle Aged
  • Niacin / metabolism
  • Parkinson Disease / metabolism*
  • Parkinson Disease / physiopathology
  • Receptors, G-Protein-Coupled / genetics
  • Receptors, G-Protein-Coupled / metabolism*
  • Receptors, Nicotinic / genetics
  • Receptors, Nicotinic / metabolism*
  • Sleep
  • Substantia Nigra / metabolism
  • Up-Regulation*


  • HCAR2 protein, human
  • Receptors, G-Protein-Coupled
  • Receptors, Nicotinic
  • Niacin