Analyses of the effects of 17β-estradiol on skeletal muscle and global gene expression following acute eccentric exercise

Abstract

<p> Introduction: 17β-estradiol (E2) has proposed anti-oxidant and membrane stabilizing properties that may attenuate exercise-induced damage, inflammation and alter gene expression. The purpose of this thesis was to determine if acute E2 supplementation would affect the oxidative stress, membrane damage, inflammation and global mRNA expression induced by eccentric exercise. Methods: 18 healthy young males were randomly assigned to 8 days of placebo (CON) or E2 (EXP) supplementation. Blood and muscle samples were collected at baseline (BL), following supplementation (PS), +3 hours (3H) and +48 hours (48H) after 150 single-leg eccentric contractions. Blood samples were analyzed for hormone concentration, creatine kinase (CK) activity and total antioxidant capacity (T AC). Inflammation was quantified by neutrophil and macrophage infiltration. Genes selected a priori for oxidative stress defense, membrane homeostasis and growth were analyzed with real-time RT-PCR. High density oligonucleotide based microarrays were screened for novel differences in mRNA expression. Results: A primary finding was that increased serum E2 did not affect anti-oxidant capacity, creatine kinase efflux or mRNA content of genes related to oxidative stress defence and membrane homeostasis. E2 did attenuate neutrophil infiltration into muscle but did not affect macrophage density. Microarray analysis revealed that exercise induced differential expression of 611 genes at 3H and confirmed that E2 did not affect mRNA content. Genes were manually clustered into biological categories and from this dataset the signaling pathways for RhoA and NF AT were identified as transcriptionally active. Both pathways regulate hypertrophic signaling through the AP-1 transcription factor complex. Conclusions and significance: A major contribution ofthis thesis is that E2 may affect exercise induced inflammation through mechanisms that that do not affect oxidative stress or membrane stability. Additionally, the transcriptional activation ofSTARS/RhoA/APl and NFAT/APl indicates that both are important for early repair and remodelling signaling after a single bout of unaccustomed eccentric exercise. </p>