Intestinal microbiota in neurodegeneration and ageing: Mechanisms, pathways, and therapeutic interventions

The human gut microbiota represents a complex ecosystem of trillions of microorganisms with profound implications for neurological health. Emerging evidence demonstrates that dysbiosis, an imbalance in microbial composition and function, plays a crucial role in the pathogenesis of neurodegenerative diseases and age-related cognitive decline. This chapter summarizes current knowledge of the microbiota-gut-brain axis (MGBA) and elucidates how intestinal microbes and their metabolites communicate with the central nervous system via neural, immune, endocrine, and metabolic pathways. We examine the mechanistic links between gut dysbiosis and specific neurodegenerative conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), and Multiple sclerosis (MS). Furthermore, we explore age-related changes in the microbiota and their contributions to neuroinflammation, immunosenescence, and cognitive decline. Finally, we evaluate therapeutic interventions targeting the microbiota, including probiotics, prebiotics, synbiotics, and dietary modulation as promising strategies to prevent and ameliorate neurodegenerative pathology. The chapter provides a comprehensive summary of how microbiota-targeted approaches may delay ageing and neurodegeneration.