Date Published: February 26, 2018
Publisher: John Wiley and Sons Inc.
Author(s): B. Zhang, W. Ma, Q. Zhu, W. Xu, L. Gao, B. Xu, S. Xu, C. Gao, L. Gao, J. Liu, Y. Cui.
Approximately 40% of middle‐aged men exhibit symptoms of late‐onset hypogonadism (LOH). However, the mechanism of androgen deficiency is still currently unclear. As shown in our previous studies, the SET protein is expressed in testicular Leydig cells and ovarian granule cells. This study was designed to investigate the effect of the SET protein on androgen production in Leydig cells. The AdCMV/SET and AdH1siRNA/SET adenoviruses were individually transduced into a cultured mouse Leydig cell line (mLTC‐1) with or without human chorionic gonadotropin (HCG) stimulation in vitro. The primary mouse Leydig cells were used to confirm the main data from mLTC‐1 cells. The SET protein was expressed in the cytoplasm and nucleus of mLTC‐1 cells. Testosterone production was significantly increased in mLTC‐1 cells overexpressing the SET protein compared with the control group (p < 0.05), whereas testosterone production was significantly decreased in the SET knockdown mLTC‐1 cells (p < 0.05). Consistent with the testosterone levels, the expression levels of the steroidogenic acute regulatory (StAR) and cytochrome P450c17α‐hydroxylase (CYP17a1) mRNAs and proteins synchronously changed according to the expression level of the SET protein. Interestingly, the expression of the SET protein was significantly increased in the mLTC‐1 cells stimulated with 0.04 and 0.1 U/mL hCG. In the mLTC‐1 cells transfected with AdH1siRNA/SET and concurrently stimulated with 0.1 U/mL hCG, both testosterone production and StAR expression were significantly lower than in the cells without SET knockdown (p < 0.05). In conclusion, the SET protein participates in regulating testosterone production by increasing the expression of StAR and CYP17a1, and it may be a downstream factor of the classic luteinizing hormone (LH)/luteinizing hormone receptor (LHR) signaling pathway. This study improves our understanding of the intracellular mechanism of testicular steroidogenesis and the pathophysiological mechanism of LOH in the aging male.
Approximately 40% of middle‐aged men exhibit symptoms of late‐onset hypogonadism (LOH), also known as partial androgen deficiency in the aging male (PADAM) (Lunenfeld et al., 2005). Many symptoms are related to LOH, including a poor morning erection, erectile dysfunction, low sexual desire, sleep disturbances, and changes in moods, as well as more general symptoms such as insomnia, fatigue, loss of muscle mass, increased fat mass, decreased bone mineral density and osteoporosis, depression, and forgetfulness (Wu et al., 2010). LOH has even been shown to be related to substantially higher risks of all‐cause and cardiovascular mortality in aging males (Pye et al., 2014). The core mechanism of LOH is an absolute or relative androgen deficiency due to decreases in the number and function of testicular Leydig cells (Lunenfeld et al., 2005). However, the mechanism and pathophysiology of LOH are complicated and not completely understood at present.
The core mechanism of LOH in the aging male is the absolute or relative androgen deficiency due to the decrease in the number and function of testicular Leydig cells (Lunenfeld et al., 2005). The LH/LHR pathway is the classical pathway involved in regulating T production in Leydig cells. Many intratesticular factors and intracellular factors participate in regulating steroidogenesis (Saez, 1994). In a previous study, we observed the expression of SET protein in the testes of mice at different developmental stages (Dai et al., 2014). The expression of SET protein was found in Leydig cells. The expression level of SET protein in the aging group was significantly lower than that in the adult group (p < 0.05), while the mean of SET mRNA expression was also lower in the aging group (although p > 0.05). The expression of SET protein in Leydig cells suggests a possible role in steroidogenesis as an intracellular factor of testicular Leydig cells (Dai et al., 2014). In this study, we found that the SET protein was a potential downstream factor of LH/LHR signaling with a stimulatory effect on T production in Leydig cells by upregulating the expressions of key factors and enzymes involved in steroidogenesis, such as StAR, CYP17a1, CYP11a1, and HSD3b1. These results definitely help us understand the mechanism of androgen deficiency in aging males with LOH.
In conclusion, the SET protein is expressed in the cytoplasm and nucleus of Leydig cells and positively regulates T production by upregulating StAR and CYP17a1 expression. The potential mechanism is that the SET protein acts as a downstream factor of the LH/LHR signaling pathways. These findings advance our knowledge of the intracellular mechanism by which the SET protein promotes testicular steroidogenesis, which also helps us understand the pathophysiological mechanisms of male primary hypogonadism and androgen deficiency in the aging male with LOH.
The study was supported by grants from the National Natural Science Foundation of China (81370754, 81170559, 81401173, and 31301182) and the Jiangsu Province Special Program of Medical Science (BL2012009 and XK02200901‐NG09).
None of the authors have anything to declare.
Zhang B performed the main experiments and wrote the first draft of the manuscript. Ma W finished the experiments of the primary mouse Leydig cells. Zhu Q, Xu W, and Xu S, who are graduate students of Cui Y and Liu J, assisted Zhang in performing the experiments. Gao L and Xu B developed the AdCMV/SET and AdH1siRNA/SET vectors. Gao C and Gao L assisted with the confocal microscopy and RIA. Cui Y designed the study and revised the manuscript. All authors read and approved the final manuscript. We thank He Jing, a postdoctor in Dr Cui’s laboratory, for her help in the primary mouse Leydig cells.