Gut Microbiome and Depression

Our overall hypothesis is that specific gut microbiome or gut-derived metabolites are associated with depression in pwMS. Mechanistically, the investigators further hypothesize that depression in pwMS is related to decreased abundance of gut bacteria with GABA-producing activities and/or with anti-inflammatory properties. AIM 1. To determine if the presence of depression in pwMS is associated with specific gut microbiome, gut-derived metabolites or peripheral blood immune profiles. The investigators will perform a cross-sectional study in clinically stable pwMS recruited at the John L. Trotter MS Center. The investigators will evaluate the presence of depression using the Quality of Life in Neurological Disorders (Neuro-Qol) depression scale, one of the 13 scales in the Neuro-Qol recently developed by the NIH using modern psychometric techniques and validated in pwMS. A total of 120 pwMS will be recruited: 60 with and 60 without depression based on the Neuro-Qol depression scale. At the study visit each participant will be asked to provide a stool sample for microbiome analyses and a blood sample for peripheral blood immunophenotyping. Potential confounders will be collected and treated as covariates in the analyses. These include: 1) degree of disability (EDSS); 2) treatment with anti-depressants and DMTs; 3) a 4-days food diary to evaluate diet composition; 4) the investigatorsight and height to calculate the BMI; 5) fatigue; 6) level of physical activity; 7) sleep quality. AIM 1A. To determine if depression will correlate with specific gut microbiome or gut-derived metabolites profiles in pwMS. Stool samples will be processed for microbiome sequencing and metabolome characterization. AIM 1B. To determine if depression will correlate with a specific peripheral blood immune-inflammatory profile in pwMS. A peripheral blood sample will be obtained from each participant to perform: 1) peripheral blood immune cell phenotyping to characterize the main immune cell subsets and their activation; 2) intracellular cytokine production to study cytokine production profiles of blood lymphocytes and monocytes. AIM 2. To quantify GABA production in pwMS with or without depression and determine gut microbiome-immune system interaction in vitro. In this aim the investigators will perform functional studies to evaluate the potential of gut microbiota from pwMS with or without depression to produce GABA and to modulate immune-inflammatory responses. AIM 2A. To quantify GABA levels in whole stool, specific stool bacterial isolates and blood of pwMS with or without depression. The investigators will evaluate GABA levels in the stool and blood of pwMS. In addition, the investigators will measure GABA production by Bacteroides ssp isolated from the gut microbiota of pwMS. Aim 2B. To evaluate the effects of whole stool and specific bacterial species from pwMS on blood immune cell phenotype and cytokine production. The investigators will test how whole gut microbiome or specific bacteria (identified in Aim 1 as associated with depression in pwMS) can modulate immune cell function. Peripheral blood mononuclear cells (PBMC) from healthy donors will be cultured in conditioning media from whole stool or bacteria of interest isolated from pwMS. PBMC phenotype and cytokine production after exposure in vitro will be characterized by flow cytometry.