Impairment of spermatogenesis and enhancement of testicular germ cell apoptosis induced by exogenous all-trans-retinoic acid in adult lizard Podarcis sicula

In mammals retinoic acid is involved in the regulation of testicular function by interaction with two families of nuclear receptors, retinoic acid receptor (RAR) and retinoid X receptor (RXR), each with three isoforms , , and . In this paper we focused our attention on lizard Podarcis sicula in order to evaluate the effect of exogenous all-trans-retinoic acid (atRA) on spermatogenesis of a non-mammalian seasonal reproducer. atRA or atRA plus testosterone (atRA+T) were injected intraperitoneally every day for a time of 15 days, and the effects on spermatogenetic cells were compared with controls (saline or testosterone injected). In atRA-treated lizards seminiferous tubules were markedly reduced in cross-area due to collapse of seminiferous epithelium, which showed a variety of cellular damage ranging from sensible reduction in the number of germ cells to disruption in normal epithelial organization. In atRA+T-treated lizards the loss of germinal cells achieved was significantly less than that after atRA treatment. The loss of germ cells observed in both experimental groups results from an induction of apoptotic process, as revealed by TUNEL analysis. Although in low numbers, apoptotic germ cells were also observed in the control groups (saline- and T-treated lizard), where the main germ cells undergoing apoptosis are primary spermatocytes (most frequent) and some spermatogonia. Furthermore, using Northern blot cDNA hybridization we verified that lizard testicular cells express only RAR(3.7 kb) and RAR (3.4 kb) mRNAs, among RAR isoforms. In conclusion, the results presented here show that in lizard retinoic acid has deleterious effect on spermatogenesis determining a severe depletion of seminiferous epithelium, probably via induction of apoptotic processes. These effects are not completely inhibited by simultaneous administration of testosterone, although this hormone once injected is able to stimulate spermatogenesis and protect germinal cells from apoptotic cell death.