Abstract
The specific role of polyamines in the testis physiology is not fully understood. Antizymes (OAZs) and antizyme inhibitors (AZINs) are modulators of ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis and polyamine uptake. Although the three known OAZs are expressed in the testis, only OAZ3 is testis specific and has been proven to have an essential role in male fertility. Regarding the two existing AZINs, AZIN2 is the most abundantly expressed member in this gonad. Whereas previous studies suggested that AZIN2 might participate in mouse spermatogenesis, immunohistological analysis of human testicular sections revealed that AZIN2 is also detected in the steroidogenic Leydig cells but not in the germinal epithelium. In the present study, we found a close ontogenic similarity in the mRNA levels of OAZs and AZINs between mice and rats, but an opposite expression pattern of ODC activity. Further analysis of AZIN2 and OAZ3 in the testis of mice with different alterations in spermatogenesis and fertility, induced either genetically or pharmacologically, corroborated that both AZIN2 and OAZ3 are mainly expressed in the haploid germinal cells. Finally, by using transgenic mice with a truncated Azin2 gene fused to the bacterial lacZ gene, we studied the expression of Azin2 in testes, epididymides and spermatozoa. AZIN2 was detected in spermatids and spermatozoa, as well as in Leydig cells, and in epithelial epidydimal cells. Azin2 knock-out male mice were fertile; however, they showed marked decreases in testicular putrescine and plasma and testicular testosterone levels, and a dramatic reduction in the sperm motility. These results suggest an important role for AZIN2 in testicular cells by modulating polyamine concentrations, testosterone synthesis and sperm function. Overall, our data corroborate the relevance of polyamine regulation in testis functions, where both AZIN2 and OAZ3 play fundamental roles.
Highlights
The polyamines spermidine, spermine, and their precursor putrescine are small aliphatic polycations that participate in multiple cellular functions including cell growth, differentiation and apoptosis
Whereas in mice the testicular ornithine decarboxylase (ODC) activity progressively increased with age (r = 0.872, P = 0.010), reaching at the day 60 values about 90% higher than at day 5, in the rats there was a marked decrease during the same period (r = -0.9287, P = 0.0025), with values in the adult testes about 7% of those of 3-day-old rats
OAZ1 was already expressed in the testes of mice and rats during the first week of life, showing small changes during the analyzed period (Fig 2C). These results suggest that Azin2 and Oaz3 are mainly expressed in the testis during spermiogenesis
Summary
The polyamines spermidine, spermine, and their precursor putrescine are small aliphatic polycations that participate in multiple cellular functions including cell growth, differentiation and apoptosis. They are present at millimolar levels in mammalian cells, mainly associated with nucleic acids and proteins, and affecting DNA and chromatin structure, transcription, translation, cell signaling and different ion channels [1,2,3]. Two antizyme inhibitors (AZIN1 and AZIN2) have been found in mammals They share the capacity to interact with the three OAZs, but differ on tissue, cellular and subcellular location [15,16,17]
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