Bridging Mind and Gut: The Molecular Mechanisms of microRNA, Microbiota, and Cytokine Interactions in Depression

Depression is a complex psychiatric disorder that arises from various underlying biological mechanisms. In this review, the role of microRNAs (miRNAs) in modulating gut microbiotacytokine communication and their potential to unravel the pathophysiology of depression and develop novel therapeutic strategies are discussed. MiRNAs are small non-coding RNA molecules that have emerged as key regulators in the bidirectional signaling of the gut-brain axis by modulating gene expression and fine-tuning an intricate dialogue between the microbiota, immune system, and central nervous system. Results show how gut microbiota can shape miRNA expression in brain regions involved in mood regulation; conversely, evidence is accumulating, elucidating how miRNA perturbations can shape microbial ecology. Gut bacteria-derived short-chain fatty acids (SCFAs) fuel this nexus by exerting effects on neurogenesis, neurotransmitter synthesis, neuroinflammation, affective behavior alterations, and depressive-like phenotypes. Pro-inflammatory cytokines such as IL-6, TNF-α, and IL-1β are also known to be associated with depressive symptoms related to altered expression patterns of specific miRNAs across these disorders. This review exposes the novel potential biomarkers and therapeutic targets/strategies to develop innovative methods in the diagnosis and treatment of depression by exploring bidirectional relations among miRNAs, gut microbiota, and cytokines. The knowledge of these molecular networks and pathways has provided the opportunity for designing new-generation therapeutics such as phytobiotics, probiotics, psychobiotics, diet therapies, and nanomedicine based on miRNAs from a future perspective, which will revolutionize the management of mental disorders.