Microbiota-derived metabolite-GPCR signalling in neurodegeneration.

The gut microbiome acts as a primary regulator of host homeostasis, influencing the entire body through bidirectional communication along the gut-brain axis (GBA). Dysbiosis, which is defined as a state of microbial imbalance involving alterations in community composition and function, can disrupt the synthesis of important microbiota-derived metabolites, such as short-chain fatty acids (SCFAs), bile acids and neurotransmitter precursors. This can lead to impaired essential host signalling pathways. There is growing evidence that metabolic alterations associated with dysbiosis contribute to the onset and progression of neurodegenerative disorders (NDDs), including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). In this context, G protein-coupled receptors (GPCRs) act as essential molecular transducers that link microbial metabolites to intracellular signalling networks. Aberrant GPCR activation, driven by altered metabolite profiles, modulates key downstream pathways including cAMP, MAPK, PI3K/Akt, NF-κB and Ca2 + signalling. This promotes neuroinflammation, oxidative stress, mitochondrial dysfunction and pathological protein aggregation - hallmark processes underlying neurodegeneration. By identifying convergent and disease-specific signalling pathways, the review highlights mechanistic nodes of therapeutic relevance and discusses GPCR-centric emerging and other microbiome-targeted strategies aimed at restoring metabolic and signalling homeostasis in neurodegenerative disorders.