The studies proposed in this MERIT extension application address the molecular mechanisms by which age-induced changes in the microenvironment of Leydig cells, the cells responsible for testicular androgen biosynthesis, lead to reduced testosterone formation. We propose the following: (i) Changes in the balance between reactive oxygen accumulation and the antioxidant defense system result in increased oxidative stress which, in turn, results in damage to the signal transduction cascade at the plasma membrane and thus in reduced responsiveness of aged Leydig cells to luteinizing hormone (LH). (ii) As a consequence, aged cells produce less cAMP than young cells, resulting in reduced intracellular cholesterol transport into the mitochondria and therefore reduced substrate availability for testosterone.
The first aim i s to determine the mechanism by which increased oxidative stress elicit reductions in cAMP and testosterone production in aged Leydig cells. We will test the hypothesis that in response to increased oxidative stress, there is defective coupling of LH receptors (LHR) to Gs proteins, resulting in reduced cAMP in response to LH stimulation.
The second aim will test the hypothesis that as a consequence of the blunted ability of LH to simulate cAMP production in aged Leydig cells, there are reduced levels of translocator protein (TSPO) and steroidogenic acute regulatory protein (STAR)-mobilized cholesterol, and thus less efficient transfer of cholesterol to the inner mitochondrial membrane. We further hypothesize that the reduced expression of TSPO in aged cells results from that reduced expression of Natural Antisense Transcripts (NATs).
The third aim i s to determine how the age-related changes in Brown Norway rat Leydig cells compare to those in aging human testes. With this aim, we will translate our findings in the rat to the human. To this end, we will measure testosterone and ROS levels in intratesticular fluid from young and aged men, capture Leydig cells from testicular biopsies to analyze steroidogenic enzyme expression and the expression of proteins involved in reactive oxygen production and in the antioxidant defense system, and examine proteins and lipids damaged by changes in the pro/antioxidant balance using fixed tissue.
Serum testosterone levels decline as men age. This decline has relevance to quality of life issues in men, including osteoporosis, cognition and libido. Studying how testosterone decreases will provide new insights into how Leydig cells cope with stressors that are present (or increase) with aging, shed tight on the underlying molecular basis for age-related functional changes in the Leydig cells, and might provide approaches for their prevention or reversal..
|Nanjappa, M K; Medrano, T I; Prins, G S et al. (2017) Transdifferentiation of adult rat stem Leydig cells into prostatic and uterine epithelium, but not epidermis. Andrology 5:1165-1173|
|Papadopoulos, Vassilios; Fan, Jinjiang; Zirkin, Barry (2017) Translocator protein (18 kDa): an update on its function in steroidogenesis. J Neuroendocrinol :|
|Wang, Yiyan; Chen, Fenfen; Ye, Leping et al. (2017) Steroidogenesis in Leydig cells: effects of aging and environmental factors. Reproduction 154:R111-R122|
|Traore, Kassim; Martinez-Arguelles, Daniel B; Papadopoulos, Vassilios et al. (2016) Repeated exposures of the male Sprague Dawley rat reproductive tract to environmental toxicants: Do earlier exposures to di-(2-ethylhexyl)phthalate (DEHP) alter the effects of later exposures? Reprod Toxicol 61:136-41|
|Chen, Haolin; Jin, Shiying; Huang, Shengsong et al. (2016) Transplantation of alginate-encapsulated seminiferous tubules and interstitial tissue into adult rats: Leydig stem cell differentiation in vivo? Mol Cell Endocrinol 436:250-8|
|Li, Xiaoheng; Wang, Zhao; Jiang, Zhenming et al. (2016) Regulation of seminiferous tubule-associated stem Leydig cells in adult rat testes. Proc Natl Acad Sci U S A 113:2666-71|
|Salehi, Sajad; Adeshina, Ikeoluwa; Chen, Haolin et al. (2015) Developmental and endocrine regulation of kisspeptin expression in mouse Leydig cells. Endocrinology 156:1514-22|
|Musicki, Biljana; Zhang, Yuxi; Chen, Haolin et al. (2015) Mechanism of testosterone deficiency in the transgenic sickle cell mouse. PLoS One 10:e0128694|
|Beattie, M C; Adekola, L; Papadopoulos, V et al. (2015) Leydig cell aging and hypogonadism. Exp Gerontol 68:87-91|
|Chen, Haolin; Jin, Shiying; Guo, Jingjing et al. (2015) Knockout of the transcription factor Nrf2: Effects on testosterone production by aging mouse Leydig cells. Mol Cell Endocrinol 409:113-20|
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