Spinal cord injury and the gut microbiota

The gut microbiota is the community of microbes (bacteria, viruses, fungi) that live in the gastrointestinal tract and are critical for normal nutrient absorption, digestion, and immune system development. These microbes communicate with the central nervous system (CNS) through interactions with the immune system, production of neuroactive metabolites/neurotransmitters, and activation of the vagus nerve. Spinal cord injury (SCI) disrupts the autonomic nervous system (ANS) and impairs communication with organ systems throughout the body, resulting in dysautonomia. This dysautonomia contributes to the pronounced immunosuppression and gastrointestinal dysfunction seen after SCI. Combined with frequent antibiotic use, physical and psychosocial stress, and altered GI motility, SCI-induced dysautonomia likely also causes an imbalance in the composition of the gut microbiome, i.e., gut dysbiosis. Pre-clincal and clinical studies indicate that SCI-induced gut dysbiosis triggers intestinal inflammation, impairs gut motility, and alters the composition of serum metabolites. SCI not only affects the abundance of various gut microbes but also the functional potential of the gut microbiome. As gut dysbiosis develops and the metabolites produced by gut microbiota change, these changes can influence the progress or severity of various SCI-associated comorbidities including metabolic syndrome, cardiovascular disease, liver dysfunction, and depression/anxiety disorders. Therefore, the development of novel therapeutic targets to prevent and treat these comorbidities requires a better understanding of how SCI affects the emergence or reduction in key gut microbial species.