Date Published: April 19, 2019
Publisher: Public Library of Science
Author(s): Rashin Ghaffari, Kristin R. Di Bona, Christopher L. Riley, John H. Richburg, Suresh Yenugu.
An imbalance in copper (Cu) tissue homeostasis has a degenerative effect on spermatogenesis and male fertility. The high-affinity Cu transporter 1 (CTR1; SLC31A1) is the major protein responsible for Cu acquisition in eukaryotes and is highly expressed in mouse testes. Studies on yeast and Drosophila have demonstrated the conserved essential function of Cu and CTR1 for meiosis and fertility, implying that CTR1 may play an essential function in mammalian spermatogenesis. In mice, spermatogenesis takes place within the seminiferous epithelium, where tight junctions between somatic Sertoli cells (SCs) create a specialized microenvironment for the development of meiotic germ cells (GCs) by tightly regulating the free transport of metabolites and ions to reach these cells. Here, it is demonstrated that within the seminiferous epithelium, CTR1 is expressed on the membrane of primary pachytene spermatocytes and SCs. To examine the physiological significance of CTR1 in spermatogenesis, mice with a GC-specific (Ctr1ΔGC) and SC-specific (Ctr1ΔSC) disruption of the Ctr1 gene were generated. The testis of Ctr1ΔGC mice exhibits a severe progressive loss of GCs starting at postnatal day (PND) 28 leading to testis hypoplasia by adulthood. No spermatogenic recovery was observed in Ctr1ΔGC testis beyond PND 41, despite the presence of FOXO-1 expressing undifferentiated spermatogonial cells. However, Ctr1ΔSC mice displayed functional spermatogenesis and were fertile, even though testicular Cu levels and Cu-dependent cellular activities were significantly reduced. These results reveal, for the first time, the importance of CTR1 expression by GCs for maintaining functional spermatogenesis.
Copper (Cu) is an essential trace metal that is required for all organisms due to its important roles in growth and development. Cu serves as an important co-factor for enzymes that carryout fundamental biological processes including respiration (cytochrome c oxidase), elimination of free radicals (superoxide dismutase), iron metabolism (ceruloplasmin), connective tissue formation (lysyl oxidase) and many others [1,2]. On the other hand, excess Cu can create a toxic environment in the host cell by producing reactive oxygen species [3,4]. Consequently, alterations of Cu levels and the activities of Cu-dependent enzymes lead to disease and pathophysiological conditions including Wilson’s and Menke’s disease, and ataxia [1,3]. The importance of Cu in spermatogenesis has been documented in various animal studies . Induced Cu deficiencies in male rats, goat and rams result in reduced sperm counts and motility, poor semen quality and an abnormal germinal epithelium [6–8]. These effects were reversible upon Cu supplementation indicating the importance of Cu in the maintenance of male fertility and spermatogenesis [6–8].
The expression pattern of the Ctr1 gene and protein has been demonstrated in mice testis, but the physiological significance of CTR1 localization within the cell types of seminiferous tubules has not been identified [15,22]. In order to interrogate and differentiate the physiological significance of CTR1 protein in functional spermatogenesis, we developed and characterized both GC- specific (Ctr1ΔGC) and SC-specific (Ctr1ΔSC) Ctr1 knockout mice.