Lysine glutarylation in human sperm is associated with progressive motility

Study question: Is there a role for lysine glutarylation (Kglu), a newly identified protein post-translational modification (PTM), in human sperm?

Summary answer: Kglu occurs in several proteins located in the tail of human sperm, and it was reduced in asthenozoospermic (A) men and positively correlated with progressive motility of human sperm, indicating its important role in maintaining sperm motility.

What is known already: Since mature sperm are almost transcriptionally silent, PTM is regarded as an important pathway in regulating sperm function. However, only phosphorylation has been extensively studied in mature sperm to date. Protein lysine modification (PLM), a hot spot of PTMs, was rarely studied except for a few reports on lysine methylation and acetylation. As a newly identified PLM, Kglu has not been well characterized, especially in mature sperm.

Study design, size, duration: Sperm samples were obtained from normozoospermic (N) men and A men who visited the reproductive medical center between February 2016 and January 2018. In total, 61 N men and 59 A men were recruited to participate in the study.

Participants/Materials, setting, methods: Kglu was examined by immunoblotting and immunofluorescence assays using a previously qualified pan-anti-glutaryllysine antibody that recognizes glutaryllysine in a wide range of sequence contexts (both in histones and non-histone substrates) but not the structurally similar malonyllysine and succinyllysine. The immunofluorescence assay was imaged using laser scanning confocal microscopy and super-resolution structured illumination microscopy. Sperm motility parameters were examined by computer-assisted sperm analysis.

Main results and the role of chance: Kglu occurs in several proteins (20-150 kDa) located in the tail of human sperm, especially in the middle piece and the latter part of the principal piece. Sperm Kglu was modulated by regulatory systems (enzymes and glutaryl-CoA) similar to those in HeLa cells. The mean level of sperm Kglu was significantly reduced in A men compared with N men (P < 0.001) and was positively correlated with progressive motility (P < 0.001). The sodium glutarate-induced elevation of Kglu levels in A men with lower Kglu levels in sperm significantly improved the progressive motility (P < 0.001). Furthermore, the reduced sperm Kglu levels in A men was accompanied by an increase in sperm glutaryl-CoA dehydrogenase (a regulatory Enzyme of Kglu).

Large scale data: N/A.

Limitations, reasons for caution: Although the present study indicated the involvement of sperm Kglu in maintaining progressive motility of human sperm, the underlying mechanism needs to be investigated further.

Wider implications of the findings: The findings of this study provide an insight into the novel role of Kglu in human sperm and suggest that abnormality of sperm PLMs may be one of the causes of asthenozoospermia.

Study funding/competing interest(s): National Natural Science Foundation of China (81 771 644 to T.L.; 31 671 204 to X.Z. and 81 871 207 to H.C.); National Basic Research Program of China (973 Program, 2015CB943003 to X.Z.); Natural Science Foundation of Jiangxi, China (20171ACB21006 and 20161BAB204167 to T.L.; 20165BCB18001 to X.Z.). The authors have no conflicts of interest to declare.