Exploring Inflammatory Predictors of Depressive Responses to Exercise

Morris, Benjamin

Undergraduate Honors Thesis

Exploring Inflammatory Predictors of Depressive Responses to Exercise Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/vx021g002

Abstract

Despite its prevalence and social, economic, and emotional costs, no clear causes of depression have been identified. Two factors, pro-inflammatory cytokines and hippocampal neurogenesis, have been bidirectionally linked to depressive symptoms and interact significantly with each other. As exercise influences each of these three variables, sedentary older adults were recruited to participate in a 16-week exercise intervention in either a low intensity continuous training (LICT) or moderate intensity continuous training with interval training (MICT+IT) program to better understand how these variables covary and in particular to examine the hypothesis that cytokines effect depressive symptoms through regulatory influence on hippocampal neurogenesis. Depressive symptoms as assessed by the Beck Depression Inventory (BDI), peripheral plasma concentrations of the cytokines TNFa, IL-1β, and IL-6, and hippocampal volume from a structural MRI scan were measured pre- and post-intervention. No evidence that changes in the cytokines of interest correlate with changes in hippocampal volume or changes in BDI or that changes in hippocampal volume are correlated with changes in BDI was found. As an exploratory analysis, participants’ genotype for rs16944, rs1800629, and rs1800797, three single nucleotide polymorphisms (SNPs) in the promoter regions for the IL-1β, TNFa, and IL-6 genes respectively, were assayed to investigate individual variability in depressive responses. Although no main effects of SNP genotype, exercise condition, nor genotype x exercise condition interactions were found on changes in BDI, a significant main effect of exercise condition on hippocampal volume for two of the three SNPs and a rs1800629 A-allele carrier main effect and rs1800629 A-carrier by exercise condition interaction was found. These results suggest that MICT+IT exercise may have a protective effect against hippocampal volume decrease and that A-allele carrier status with LICT exercise and Non-A-allele carrier status with MICT+IT exercise may have similar protective effects against hippocampal atrophy in older adults. More sensitive measurements of centrally-acting cytokines and development of an in vivo measure of neurogenesis could help further explore the cytokine-hippocampal neurogenesis-depression pathway.

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