Deficiency in AK9 causes asthenozoospermia and male infertility by destabilising sperm nucleotide homeostasis

BACKGROUND

Asthenozoospermia is the primary cause of male infertility; however, its genetic aetiology remains poorly understood. Adenylate kinase 9 (AK9) is highly expressed in the testes of humans and mice and encodes a type of adenosine kinase that is functionally involved in cellular nucleotide homeostasis and energy metabolism. We aimed to assess whether AK9 is involved in asthenozoospermia.

METHODS

One-hundred-and-sixty-five Chinese men with idiopathic asthenozoospermia were recruited. Whole-exome sequencing (WES) and Sanger sequencing were performed for genetic analyses. Papanicolaou staining, Haematoxylin and eosin staining, scanning electron microscopy, and transmission electron microscopy were used to observe the sperm morphology and structure. Ak9-knockout mice were generated using CRISPR-Cas9. Sperm adenosine was detected by liquid chromatography-mass spectrometry. Targeted sperm metabolomics was performed. Intracytoplasmic sperm injection (ICSI) was used to treat patients.

FINDINGS

We identified five patients harbouring bi-allelic AK9 mutations. Spermatozoa from men harbouring bi-allelic AK9 mutations have a decreased ability to sustain nucleotide homeostasis. Moreover, bi-allelic AK9 mutations inhibit glycolysis in sperm. Ak9-knockout male mice also presented similar phenotypes of asthenozoospermia. Interestingly, ICSI was effective in bi-allelic AK9 mutant patients in achieving good pregnancy outcomes.

INTERPRETATION

Defects in AK9 induce asthenozoospermia with defects in nucleotide homeostasis and energy metabolism. This sterile phenotype could be rescued by ICSI.

FUNDING

The National Natural Science Foundation of China (82071697), Medical Innovation Project of Fujian Province (2020-CXB-051), open project of the NHC Key Laboratory of Male Reproduction and Genetics in Guangzhou (KF202004), Medical Research Foundation of Guangdong Province (A2021269), Guangdong Provincial Reproductive Science Institute Innovation Team grants (C-03), and Outstanding Young Talents Program of Capital Medical University (B2205).

Endothelial cells cope with hypoxia-induced depletion of ATP via activation of cellular purine turnover and phosphotransfer networks

Intravascular ATP and adenosine have emerged as important regulators of endothelial barrier function, vascular remodeling and neovascularization at various pathological states, including hypoxia, inflammation and oxidative stress. By using human umbilical vein endothelial cells (HUVEC) and bovine vasa vasorum endothelial cells (VVEC) as representatives of macro- and microvessel phenotypes, this study was undertaken to evaluate cellular mechanisms contributing to physiological adaptation of vascular endothelium to hypoxia, with a particular emphasis on ectoenzymatic purine-converting activities and their link to intracellular ATP homeostasis and signaling pathways. Nucleoside triphosphate diphosphohydrolase-1 (NTPDase1/CD39), ecto-5'-nucleotidase/CD73 and ecto-adenylate kinase activities were determined by thin-layer chromatography (TLC) with ³H-labelled nucleotide substrates. Exposure of HUVEC and VVEC to 1% O₂ for 4-24 h triggered rather moderate activation of ATP breakdown into adenosine via the CD39-CD73 axis. Additional TLC analysis of salvage pathways revealed the enhanced ability of hypoxic HUVEC to convert cell-incorporated [³H]adenosine into [³H]ADP/ATP. Furthermore, following a period of hypoxia, HUVEC underwent concurrent changes in intracellular signaling manifested in the depletion of putative ATP stores and targeted up-regulation of phospho-p53, p70S6K/mTOR and other tyrosine kinases. The revealed complex implication of both extrinsic and intrinsic mechanisms into a tuned hypoxia-induced control of purine homeostasis and signaling may open up further research for the development of pharmacological treatments to improve endothelial cell function under disease conditions associated with a loss of cellular ATP during oxygen deprivation.