The studies proposed in this MERIT extension applicafion address the molecular mechanisms by which age-induced changes in the microenvironment of Leydig cells, the cells responsible for tesficular 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, resulfing 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 oxidafive stress elicit reducfions in cAMP and testosterone producfion in aged Leydig cells. We will test the hypothesis that in response to increased oxidafive stress, there is defecfive coupling of LH receptors (LHR) to Gs proteins, resulfing in reduced cAMP in response to LH stimulafion.
The second aim will test the hypothesis that as a consequence of the blunted ability of LH to sfimulate cAMP producfion in aged Leydig cells, there are reduced levels of translocator protein (TSPO) and steroidogenic acute regualtory 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 intratesficular 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 producfion and in the anfioxidant defense system, and examine proteins and lipids damaged by changes in the pro/anfioxidant.balance using fixed fissue.
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 undertying molecular basis for age-related funcfional changes in the Leydig celts, and might provide approaches for their prevention or reversal.
|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 inÂ 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|
|Beattie, M C; Adekola, L; Papadopoulos, V et al. (2015) Leydig cell aging and hypogonadism. Exp Gerontol 68:87-91|
|Chen, Haolin; Guo, Jingjing; Ge, Renshan et al. (2015) Steroidogenic fate of the Leydig cells that repopulate the testes of young and aged Brown Norway rats after elimination of the preexisting Leydig cells. Exp Gerontol 72:8-15|
|Musicki, Biljana; Zhang, Yuxi; Chen, Haolin et al. (2015) Mechanism of testosterone deficiency in the transgenic sickle cell mouse. PLoS One 10:e0128694|
|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|
|Papadopoulos, Vassilios; Aghazadeh, Yasaman; Fan, Jinjiang et al. (2015) Translocator protein-mediated pharmacology of cholesterol transport and steroidogenesis. Mol Cell Endocrinol 408:90-8|
|Odeh, Hana M; Kleinguetl, Colin; Ge, Renshan et al. (2014) Regulation of the proliferation and differentiation of Leydig stem cells in the adult testis. Biol Reprod 90:123|
|Zhou, Liang; Beattie, Matthew C; Lin, Chieh-Yin et al. (2013) Oxidative stress and phthalate-induced down-regulation of steroidogenesis in MA-10 Leydig cells. Reprod Toxicol 42:95-101|
Showing the most recent 10 out of 25 publications