(233) Fatty Acid Synthesis as the Central Outcome of Testosterone-Induced Metabolic Changes in Seminal Vesicle Epithelial Cells

Takahiro Yamanaka; Takashi Umehara; Masayuki Shimada

Graduate School of Integrated Sciences for Life, Hiroshima University, Higashihiroshima, Japan

Abstract Text:

Approximately 50% of infertility cases are caused by male factors. Seminal plasma, the fluid that carries sperm, plays a critical role in providing energy and supporting sperm function. For example, certain components like fructose are absent in blood but are abundant in seminal plasma, suggesting that the male accessory glands have a special synthetic mechanism. However, little is known about how the synthesis of these components is regulated. Therefore, it was hypothesized that testosterone, a key hormone in male reproduction, regulates the synthesis of specific metabolites that enhance sperm motility and fertilization capacity. This study investigated how testosterone alters the metabolism of seminal vesicle cells and how these changes affect seminal plasma composition. Since most of the seminal plasma is produced in the seminal vesicles and prostate, the effect of a secretory fluid mixture that mimics natural seminal plasma on sperm motility was analyzed. Seminal vesicle fluid increased sperm mitochondrial membrane potential measured by JC-1 and increased sperm linear motility, as evidenced by increased VSL (straight-line velocity) and LIN (linearity). This improvement in sperm was not observed when seminal vesicle secretions were collected from mice treated with flutamide, an antagonist of the androgen receptor. Histological analysis revealed that flutamide treatment induced the proliferation of seminal vesicle epithelial cells, leading to the formation of additional cell layers. It was estimated that functional changes in cells, such as cell division, occur in a testosterone-dependent manner and that this alters the quality of seminal fluid. To analyze gene expression comprehensively in these cells using RNA sequencing and quantitative PCR, the seminal vesicle epithelial cells were isolated and cultured with or without testosterone. The gene expression of Acly and Acc, which are involved in fatty acid synthesis, was significantly increased by testosterone, whereas the gene expression of the electron transport chain in mitochondria (mtNd1 and mtNd6) was significantly decreased. To further evaluate these metabolic changes, a flux analyzer was used to measure cellular metabolism. Interestingly, while the extracellular acidification rate (an indicator of glycolytic activity) increased by testosterone, mitochondrial oxygen consumption (a measure of mitochondrial activity) decreased. Additional experiments demonstrated that testosterone enhances glucose uptake via GLUT4 in seminal vesicle epithelial cells, leading to increased fatty acid synthesis. These results suggest that testosterone shifts the metabolism of seminal vesicle epithelial cells from energy release (catabolism) to the synthesis of new molecular components (anabolism). Since ATP citrate lyase (ACLY) is the rate-limiting enzyme that converts citric acid to acetyl-CoA, involved in fatty acid synthesis, this shift was thought to be due to ACLY. Therefore, ACLY in seminal vesicle epithelial cells was knocked down (KO). As a result, in ACLY KO cells, mitochondrial oxygen consumption did not decrease even in the presence of testosterone, and the amount of fatty acids secreted into the culture medium decreased. In fact, when the culture medium derived from cells treated with testosterone was added to sperm, VSL and LIN improved, but this improvement was absent with the medium from ACLY KO cells. In summary, our study demonstrates that testosterone increases fatty acid synthesis by reprogramming the metabolic pathway to fatty acid production via ACLY and increasing glucose uptake of seminal vesicle epithelial cells, thereby improving sperm motility. These findings provide a background for subsequent research on the relationship between fatty acid β-oxidation and sperm motility patterns.