School of Molecular Biosciences and Center for Reproductive Biology, Washington State University, Pullman, Washington, USA.
Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.
Biol Reprod. 2019 Feb 1;100(2):547-560. doi: 10.1093/biolre/ioy200.
Despite the essential role of the active metabolite of vitamin A, all-trans retinoic acid (atRA) in spermatogenesis, the enzymes, and cellular populations responsible for its synthesis in the postnatal testis remain largely unknown. The aldehyde dehydrogenase 1A (ALDH1A) family of enzymes residing within Sertoli cells is responsible for the synthesis of atRA, driving the first round of spermatogenesis. Those studies also revealed that the atRA required to drive subsequent rounds of spermatogenesis is possibly derived from the ALDH1A enzymes residing within the meiotic and post-meiotic germ cells. Three ALDH1A isozymes (ALDH1A1, ALDH1A2, and ALDH1A3) are present in the testis. Although, ALDH1A1 is expressed in adult Sertoli cells and is suggested to contribute to the atRA required for the pre-meiotic transitions, ALDH1A2 is proposed to be the essential isomer involved in testicular atRA biosynthesis. In this report, we first examine the requirement for ALDH1A2 via the generation and analysis of a conditional Aldh1a2 germ cell knockout and a tamoxifen-induced Aldh1a2 knockout model. We then utilized the pan-ALDH1A inhibitor (WIN 18446) to test the collective contribution of the ALDH1A enzymes to atRA biosynthesis following the first round of spermatogenesis. Collectively, our data provide the first in vivo evidence demonstrating that animals severely deficient in ALDH1A2 postnatally proceed normally through spermatogenesis. Our studies with a pan-ALDH1A inhibitor (WIN 18446) also suggest that an alternative source of atRA biosynthesis independent of the ALDH1A enzymes becomes available to maintain atRA levels for several spermatogenic cycles following an initial atRA injection.
尽管维生素 A 的活性代谢物全反式视黄酸（atRA）在精子发生中起着至关重要的作用，但负责其在出生后睾丸中合成的酶和细胞群在很大程度上仍然未知。醛脱氢酶 1A（ALDH1A）家族的酶位于支持细胞内，负责 atRA 的合成，推动第一轮精子发生。这些研究还表明，驱动随后几轮精子发生所需的 atRA 可能来自位于减数分裂和减数分裂后生殖细胞内的 ALDH1A 酶。睾丸中有三种 ALDH1A 同工酶（ALDH1A1、ALDH1A2 和 ALDH1A3）。虽然 ALDH1A1 在成年支持细胞中表达，并被认为有助于前减数分裂转变所需的 atRA，但 ALDH1A2 被认为是参与睾丸 atRA 生物合成的必需同工酶。在本报告中，我们首先通过生成和分析条件性 Aldh1a2 生殖细胞敲除和他莫昔芬诱导的 Aldh1a2 敲除模型来检查 ALDH1A2 的需求。然后，我们利用泛 ALDH1A 抑制剂（WIN 18446）来测试在第一轮精子发生后，ALDH1A 酶对 atRA 生物合成的集体贡献。总的来说，我们的数据提供了第一个体内证据，证明出生后严重缺乏 ALDH1A2 的动物能够正常通过精子发生。我们用泛 ALDH1A 抑制剂（WIN 18446）进行的研究也表明，在初始 atRA 注射后，一种独立于 ALDH1A 酶的替代 atRA 生物合成来源可用于维持几个精子发生周期的 atRA 水平。
