GPR109A, also known as HCAR2 (Hydroxycarboxylic Acid Receptor 2) or NIACR1 (Niacin Receptor 1), is a G-protein coupled receptor that functions as the receptor for butyrate (a short-chain fatty acid produced by gut bacteria) and niacin (vitamin B3). This receptor serves as a critical link between the gut microbiome and brain health, making it an attractive target for neurodegenerative disease therapy. [@wg2020]
GPR109A Biology
GPR109A is encoded by the [HCAR2](/genes/hcar2) gene and is a Gi-protein coupled receptor. Key features include:
GPR109A, also known as HCAR2 (Hydroxycarboxylic Acid Receptor 2) or NIACR1 (Niacin Receptor 1), is a G-protein coupled receptor that functions as the receptor for butyrate (a short-chain fatty acid produced by gut bacteria) and niacin (vitamin B3). This receptor serves as a critical link between the gut microbiome and brain health, making it an attractive target for neurodegenerative disease therapy. [@wg2020]
GPR109A Biology
GPR109A is encoded by the [HCAR2](/genes/hcar2) gene and is a Gi-protein coupled receptor. Key features include:
Anti-inflammatory: Activation reduces pro-inflammatory cytokine production
The receptor is highly expressed on immune cells and adipocytes, making it a key mediator of systemic anti-inflammatory effects that can influence brain function. [@mg2018]
Mechanism of Action
GPR109A agonists work through gut-brain axis modulation and direct neuroprotection:
Mermaid diagram (expand to render)
Key Mechanisms
Systemic Anti-inflammation: GPR109A activation on macrophages and neutrophils reduces pro-inflammatory cytokine production (TNF-α, IL-1β, IL-6), decreasing peripheral inflammation that can cross the BBB. [@mg2018]
Gut-Brain Signaling: Butyrate produced by gut bacteria can activate GPR109A on vagal afferents, transmitting anti-inflammatory signals to the brain.
Microglial Modulation: Direct activation of microglial GPR109A shifts cells toward anti-inflammatory phenotype.
Neuroprotection: Beta-hydroxybutyrate (a ketone body) also activates GPR109A, providing metabolic support during neurodegeneration.
Therapeutic Potential
Alzheimer's Disease
GPR109A agonists may benefit AD through:
Reduction of chronic neuroinflammation
Amyloid plaque modulation
Support of cognitive function
Metabolic support via beta-hydroxybutyrate
Parkinson's Disease
GPR109A is particularly relevant for PD:
High expression in substantia nigra
Protection of dopaminergic neurons via vagal signaling
GPR109A agonists are in various stages of development:
Drug Properties
Side Effects
Niacin: Flushing, gastrointestinal distress
Butyrate: Odor, gastrointestinal effects
Generally well-tolerated at therapeutic doses
References
[Waldecker M, et al. GPR109A: the butyrate receptor linking gut microbiome to brain health. Cell Host Microbe (2020)](https://pubmed.ncbi.nlm.nih.gov/32272060/)
[Mohan CG, et al. GPR109A activation and neuroinflammation in Alzheimer's disease. J Alzheimers Dis (2018)](https://pubmed.ncbi.nlm.nih.gov/29614679/)
[Liu K, et al. Butyrate-GPR109A signaling in Parkinson's disease models. Neuropharmacology (2021)](https://pubmed.ncbi.nlm.nih.gov/33852936/)
[Nuernberger S, et al. Gut-brain axis: GPR109A as a therapeutic target for neurodegeneration. Pharmacol Res (2019)](https://pubmed.ncbi.nlm.nih.gov/30731056/)