Aberrant enteric neuromuscular system and dysbiosis in amyotrophic lateral sclerosis

Background: Emerging evidence has demonstrated that microbiota directly affects the enteric neuron system (ENS) and smooth muscle cell functions via metabolic products or endogenous bacterial components. Amyotrophic Lateral Sclerosis is a neuromuscular disease characterized by the progressive death of motor neurons and muscle atrophy. The GI symptoms in patients were largely ignored or underestimated, especially before the diagnosis of ALS. The relationship between enteric neuromuscular system and microbiome in ALS progression is unknown. Methods: We performed longitudinal studies on the ENS and microbiome in the ALS human-SOD1G93A transgenic G93A mice. We treated age-matched wild-type and ALS mice with bacterial product butyrate or antibiotics to investigate microbiome and neuromuscular functions. Intestinal motility, microbiome, an ENS marker GFAP, a smooth muscle marker (SMMHC), and human colonoids have been examined. The distribution of human-G93A-SOD1 (Superoxide Dismutase 1) protein was tested as an indicator of ALS progression. Results: At 2-month-old before ALS onset, G93A mice had significant lower intestinal motility, decreased grip strength, and reduced time in the rotarod. We observed increased GFAP and decreased SMMHC expression. These changes correlated with consistent increased aggregation of mutated SOD1G93A in the colon, small intestine, and spinal cord. Butyrate and antibiotic treatment showed a significantly longer latency to fall in the rotarod test, reduced SOD1G93A aggregation, and enhanced ENS and muscle function. Feces from 2-month-old SOD1G93A mice significantly enhanced SOD1G93A aggregation in human colonoids transfected with a SOD1G93A-GFP plasmid. Longitudinal studies of microbiome data further showed the altered bacterial community related with autoimmunity (e.g., Clostridium sp. ASF502, Lachnospiraceae bacterium A4), inflammation (e.g., Enterohabdus Muris,), and metabolism (e.g., Desulfovibrio fairfieldensis) at 1- and 2- month-old SOD1G93A mice, suggesting the early microbial contribution to the pathological changes. Conclusions: We have demonstrated a novel link between microbiome, hSOD1G93A aggregation, and intestinal mobility. Dysbiosis occurred at the early stage of the ALS mice before observed mutated-SOD1 aggregation, slow intestinal motility, and dysfunction of ENS. Manipulating the microbiome improves the muscle performance of SOD1G93A mice. Our study provides insights into fundamentals of intestinal neuromuscular structure/function and microbiome in ALS.