Chronic Stress and the Immune Response's Impact on Ghrelin and its Role in the Development of Cardiovascular Disease.

Abstract

The purpose of this study was to investigate how the chronic ‘stress of life’ and stress- induced changes in immune reactivity plays a role in the development of cardio-vascular disorders with an emphasis on the appetite hormone, ghrelin. Ghrelin is pertinent as it has been found to be an anti-inflammatory and cardio-protective peptide hormone. Chronic stress more often affects poorer and medically underserved communities which consists of about three- fourths of Georgia’s counties. Additionally, the state ranks fifteenth in death rates due to cardio-vascular disease in the U.S. This study could provide further insight as to how poorer and stressed-out Georgians’ health are significantly affected by the stress in their lives. In our murine model of chronic stress, we infected a group of mice with murine herpes virus (MHV) 4 Strain 68, as viruses have been implicated in cardiovascular related diseases. Half of infected and half of the uninfected animals were subjected to different stressors for 30-day period. Data analysis was performed with Jamovi v2.3 (The jamovi project http://www.jamovi.org) and SigmaPlot (Systat Software, Inc., CA) statistical software. One- and Two-Way ANOVA and ANOVA on Ranks followed by the post-hoc t-test were used to determine statistical significance in observed changes. Throughout the study the mice and their food were weighed at regular intervals to track how the stress and/or viral infection affected their food consumption and weight. After the month of stress, the mice were sacrificed, and key organs (heart, brain, spleen, and stomach) were collected to evaluate tissue-specific expression of genes of interest. Additionally, blood was drawn to characterize the systemic distribution of leukocytes via flow cytometry. Plasma was separated from the blood for analysis of systemic levels for markers of the endocrine (cortisol) and immune (cytokine) responses. Post-stress challenge statistically significant differences in leukocyte subset distribution were observed between the non-infected and infected animals. Additionally, a significant decrease in overall food intake throughout the stress period between the stressed and non-stressed groups based on viral infections as well as the viral and non-virally infected groups based on stress. Differences in gene expression for genes encoding Atrial Natriuretic Peptide, Brain Natriuretic Peptide, Vascular Endothelial Growth Factor Alpha, and Endothelial Nitric Oxide Synthase along with both Ghrelin and its receptor, Growth Hormone Secretagogue Receptor within the heart. Changes in gene expression were also observed for the Growth Hormone Secretagogue Receptor within the brain in addition to changes in Ghrelin mRNA levels in both the brain and stomach. Altered plasma levels of cytokines were observed in groups subjected to stress and/or viral challenges in comparison to control group. Collected data suggests chronic stress in the setting of the immune stress response negatively impacts the heart and decreases Ghrelin expression in the heart.