PDE8B: A New Gene for Male Infertility

Presentation Number: THR-130
Date of Presentation: March 5th, 2015

Eva Szarek*1, Christopher Mercier1, Mones Abu-Asab1, Louis Dye1, Leticia F. Leal1, Edra London1, Malgorzata Kotula-Balak2, Barbara Bilinska2 and Constantine A Stratakis1
1National Institutes of Health (NIH), Bethesda, MD, 2Jagiellonian University, Krakow, Poland

Abstract

Phosphodiesterases(PDEs) play a critical role in regulating cAMP levels and PKA signaling. Among them PDE8B, a cAMP-specific PDE, is highly expressed in the testis. Genetic aberrations in cAMP-signaling predispose to endocrine tumors but they are also known to affect reproduction. We previously described that Pde8b-/- testis show regressive changes in seminiferous tubules(ST), containing increased numbers of atrophied tubules by 12 months with ST diameter significantly decreased; Atrophied tubules resembled Sertoli-cell only syndrome. We also described germ cell loss in Pde8b-/- resulted from increased apoptosis due to accumulation of spermatogonia undergoing defective spermatogenesis. The functions that PKA play and how such diversified PKA signaling is regulated during spermatogenesis remain less understood. We know that PKA regulates gene transcription and sperm motility. Here we focused on examining in more detail the ultrastucture of germ cells, Sertoli cells(SC) and mitochondria in mature testis, as well as focused on spermatogenesis and the importance of Wnt signaling for postnatal testis function; new data has shown that Wnt signaling is required at multiple stages of spermatogenesis. We examined testes isolated from wild-type(WT) and Pde8b-/- knock-out mice at 3 and 12months(n=3-8/group). At the ultrastructural level in Pde8b-/- SC and germ cells were packed with cystic-looking mitochondria without cristae and with intra-mitochondrial membranous inclusions. Some mitochondria were small and round while others thin and elongated with tubular cristae. There is clear mitochondrial dysfunction that raise an, as yet, undefined question: how do these ultrastructural defects influence spermatogenesis? Furthermore, using the Mouse Male Infertility Signaling Targets Array, we identified that in all Pde8b-/- mice there was a 4-fold increase in the spermatogenesis transcript Piwili1; aberrant expression of human PIWI orthologs has been observed in various cancers including epithelial ovarian cancer. Piwili1, an RNA binding protein, is expressed in developing spermatids and forms complexes with sperm-specific mRNAs that are distributed in the cytoplasm of spermatocytes. Additionally, transcriptional profile of key Wnt signaling components in whole mouse Pde8b-/- testis revealed a 52-fold upregulation of Fzd1, and a 5-fold down-regulated of Fgf4. Fzd1 mediates sustained activation of the Wnt/beta-catenin pathway whereas Fgf4 acts as a survival factor for germ cells. Thus, we conclude that deletion of Pde8b has a previously unknown role in SC function and proliferation; its wider role in fertility remains poorly characterized. PDE8B may be a therapeutic target for male infertility, especially that related to SC dysfunction.

 

Nothing to Disclose: ES, CM, MA, LD, LFL, EL, MK, BB, CAS