Exploratory analysis of estrogen-mediated gene expression of relaxin in the hypothalamus

Introduction: Women are eight times more likely to sustain ACL injuries than men, often attributed to hormonal fluctuations. Estrogen and relaxin, a hormone influencing ligament laxity, may contribute to this disparity. Relaxin's role in altering collagen properties suggests a potential link between estrogen-regulated relaxin expression and increased injury susceptibility, particularly during the menstrual cycle's follicular phase.

Objective: This study investigates estrogen's role in modulating relaxin and its receptors (RXFP-1 and RXFP-3) in the hypothalamic arcuate nucleus (ARC) and paraventricular nucleus (PVN). We aim to explore whether high estrogen phases of the menstrual cycle correlate with increased relaxin expression, potentially explaining heightened ligament injury risk in females.

Methods: Adult female Sprague-Dawley rats (n=6) underwent bilateral ovariectomy, followed by a seven-day recovery. Rats were injected with estrogen (10 μg, n=3) or oil vehicle (n=3) for three days and terminated on day four. Brain punches from ARC and PVN underwent RNA extraction and microarray analysis (Rat Clariom S Assay). Data were analyzed using Transcriptome Analysis Console (TAC) Software 4.0.

Results: Preliminary findings indicate that estrogen increases relaxin signaling. RXFP-1 expression in the ARC of estrogen-treated rats showed a five-fold increase compared to controls. While relaxin expression in the ARC doubled under estrogen treatment, the difference was not statistically significant. In the PVN, relaxin receptor RXFP-3 expression was two-fold higher in estrogen-treated rats (p=0.07). These results suggest a potential role for estrogen in relaxin-mediated ligament laxity, particularly during the late follicular or ovulatory phase.

Discussion: Our findings indicate that estrogen enhances relaxin secretion and receptor expression in the hypothalamus, contributing to ligament laxity. These insights may explain the increased susceptibility of female athletes to ligament injuries during high-estrogen phases of the menstrual cycle. However, the small sample size limits definitive conclusions.

Conclusion: This exploratory study demonstrates a potential link between estrogen levels and relaxin-mediated effects on ligament integrity. Future research should include largersample sizes and investigate the systemic roles of relaxin receptors to establish robust connections between estrogen, relaxin, and injury risk.