Molecular Mechanisms of the Microbiota–Gut–Brain Axis in the Onset and Progression of Stroke

The bidirectional relationship between the brain and gut microbiota has led to the concept of the microbiota-gut-brain axis. It refers to a system of bilateral communication that integrates neuronal, immunological, and metabolic signals, whose disruption has been linked to the pathogenesis of digestive, metabolic, and neurological disorders, among others. Intestinal dysbiosis (an imbalance in the gut microbiota) can promote a proinflammatory and prothrombotic state, as well as dyslipidaemia and dysglycemia, that increase atherogenic risk and consequently the risk of stroke. Dysbiosis can also lead to neuroinflammatory and neurodegenerative effects, compromising the integrity of the blood-brain barrier and exacerbating brain injury after stroke. Specific bacterial profiles have been associated with varying levels of stroke risk, emphasising the role of gut microbiota-derived vasoactive metabolites such as Trimethylamine N-Oxide (TMAO), phenylacetylglnutamine (PAGln), and short-chain fatty acids (SCFAs), which may serve as biomarkers for stroke risk and severity. Gut microbiota also influences neurotrophic factors such as brain-derived neurotrophic factor (BDNF) and glial cell-derived neurotrophic factor (GDNF), involved in recovery after stroke. Research has explored the potential to modify the gut microbiota to either prevent stroke (by reducing risk) or improve outcomes (by decreasing severity and sequelae). Current scientific evidence supports the role of gut microbiota as a potential diagnostic and prognostic biomarker, as well as a therapeutic target.