Xie Minyu, Zhang Guofei, Zhang Hanbin, Chen Feilong, Chen Yan, Zhuang Yuge, Huang Zicong, Zou Feng, Liu Min, An Geng, Kang Xiangjin, Chen Zhenguo
Guangdong Provincial Key Laboratory of Construction and Detection in Tissue Engineering, Department of Cell Biology, School of Basic Medical Sciences, Southern Medical University, Guangzhou, China.
Department of Urology, Nanhai Hospital, Southern Medical University, Foshan, China.
Biol Reprod. 2020 Oct 29;103(5):1121-1131. doi: 10.1093/biolre/ioaa134.
Mammalian spermatozoa are highly polarized cells characterized by compartmentalized cellular structures and energy metabolism. Adenylate kinase (AK), which interconverts two ADP molecules into stoichiometric amounts of ATP and AMP, plays a critical role in buffering adenine nucleotides throughout the tail to support flagellar motility. Yet the role of the major AK isoform, AK1, is still not well characterized. Here, by using a proteomic analysis of testis biopsy samples, we found that AK1 levels were significantly decreased in nonobstructive azoospermia patients. This result was further verified by immunohistochemical staining of AK1 on a tissue microarray. AK1 was found to be expressed in post-meiotic round and elongated spermatids in mouse testis and subsequent mature sperm in the epididymis. We then generated Ak1 knockout mice, which showed that AK1 deficiency did not induce any defects in testis development, spermatogenesis, or sperm morphology and motility under physiological conditions. We further investigated detergent-modeled epididymal sperm and included individual or mixed adenine nucleotides to mimic energy stress. When only ADP was available, Ak1 disruption largely compromised sperm motility, manifested as a smaller beating amplitude and higher beating frequency, which resulted in less effective forward swimming. The energy restriction/recover experiments with intact sperm further addressed this finding. Besides, decreased AK activity was observed in sperm of a male fertility disorder mouse model induced by cadmium chloride. These results cumulatively demonstrate that AK1 was dispensable for testis development, spermatogenesis, or sperm motility under physiological conditions, but was required for sperm to maintain a constant adenylate energy charge to support sperm motility under conditions of energy stress.
哺乳动物精子是高度极化的细胞，其特征在于具有分区化的细胞结构和能量代谢。腺苷酸激酶（AK）可将两个ADP分子转化为化学计量的ATP和AMP，在缓冲整个尾部的腺嘌呤核苷酸以支持鞭毛运动方面发挥着关键作用。然而，主要的AK同工型AK1的作用仍未得到充分表征。在这里，通过对睾丸活检样本进行蛋白质组学分析，我们发现非阻塞性无精子症患者的AK1水平显著降低。这一结果通过在组织微阵列上对AK1进行免疫组织化学染色得到了进一步验证。我们发现AK1在小鼠睾丸减数分裂后的圆形和细长精子细胞以及随后附睾中的成熟精子中表达。然后我们生成了Ak1基因敲除小鼠，结果表明在生理条件下，AK1缺乏不会诱导睾丸发育、精子发生或精子形态及运动方面的任何缺陷。我们进一步研究了用去污剂处理的附睾精子，并加入单个或混合的腺嘌呤核苷酸以模拟能量应激。当只有ADP可用时，Ak1基因敲除极大地损害了精子运动，表现为摆动幅度较小和摆动频率较高，导致向前游动效率降低。对完整精子进行的能量限制/恢复实验进一步证实了这一发现。此外，在氯化镉诱导的雄性生育障碍小鼠模型的精子中观察到AK活性降低。这些结果累积表明，在生理条件下，AK1对于睾丸发育、精子发生或精子运动并非必需，但在能量应激条件下，精子需要AK1来维持恒定的腺苷酸能量电荷以支持精子运动。
