Lysine Malonylation Regulates Human Sperm Motility

Kmal levels were significantly elevated in asthenozoospermic men and inversely correlated with progressive motility across 94 participants

Journal: Communications Biology | Published: 2026-02-09 | Type: Journal Article | PMID: 41663573 Authors: Cheng Yimin, Tian Yan, Chen Houyang, Peng Shenglin, Chen Ying, Peng Zhen, Luo Tao (Yichun University; Jiangxi Medical College; Jiangxi Maternal and Child Health Hospital — all Jiangxi province, China) Funding/COI: Funding not disclosed. Authors declare no competing interests.

Summary

Lysine malonylation (Kmal) is a chemical modification that attaches to proteins after they're made — a type of molecular tag that can change how those proteins function. This study found that Kmal is concentrated in sperm tail proteins and is markedly elevated in men with asthenozoospermia (poor sperm motility) compared to men with normal motility. When the researchers artificially elevated Kmal in healthy sperm using sodium malonate, motility dropped — pointing toward a causal relationship, not just a correlation.

Claims

• Kmal modifications are localized primarily to sperm flagella (tail) proteins, confirmed by two independent imaging methods: laser scanning confocal microscopy and super-resolution structured illumination microscopy
• Kmal levels were significantly higher in asthenozoospermic sperm (n=41) than normozoospermic sperm (n=53), with a negative correlation to progressive motility
• Asthenozoospermic samples had reduced SIRT5 protein levels (the proposed Kmal "eraser"), lower ATP, and inhibited glycolysis compared to controls
• In vitro induction of Kmal via sodium malonate in normozoospermic samples reduced progressive motility, penetration ability, intracellular Ca²⁺, ATP, cAMP, and PKA activity, and suppressed glycolysis
• P300 acetyltransferase and SIRT5 are proposed as the writer and eraser, respectively, of Kmal in human sperm — supported by inhibitor experiments but not definitively proven
• CATSPER current (responsible for sperm hyperactivation) was unaffected by elevated Kmal, suggesting the motility effect runs through a different pathway

Study Quality

This is a mechanistic laboratory study, not a clinical trial. The human cohort — 53 normozoospermic and 41 asthenozoospermic men aged 20–39, recruited from a single hospital in Yichun, China between March 2022 and December 2024 — used WHO 5th Edition criteria for semen classification and excluded confounders including varicocele, prostatitis, and endocrine disorders. Sample size was determined by a priori power calculation via G*Power 3.0, which is more methodological rigor than most studies in this space bother with.

The causal claim rests primarily on in vitro sodium malonate experiments: spike Kmal, watch motility fall. That's a meaningful intervention, but sodium malonate isn't a physiological Kmal inducer — it's a metabolic disruptor with off-target effects (it inhibits succinate dehydrogenase), so the mechanism can't be attributed cleanly to Kmal alone. The authors acknowledge that future work is needed to confirm whether Kmal directly modifies PKA or whether reduced ATP/cAMP is doing the work.

Red Flags

• Funding source is entirely absent — unusual for a Nature portfolio paper and a non-trivial gap in transparency
• Single geographic recruitment site limits generalizability; all samples from one hospital in Jiangxi province
• Sodium malonate is not a clean Kmal-specific tool — it disrupts the TCA cycle independently, complicating mechanistic attribution
• The proposed P300/SIRT5 writer-eraser system is characterized as "potential" — the inhibitor data is suggestive but the paper stops short of definitive proof
• No longitudinal data: whether reducing Kmal in asthenozoospermic men would restore motility is untested
• The correlation between Kmal and progressive motility is reported without the actual correlation coefficient or p-value in the abstract

Strengths

• Human sperm, not a mouse model — directly relevant to male infertility
• Dual imaging modalities (LSCM and SIM) for protein localization add technical credibility
• Prospective power calculation is rare and welcome
• Multiple independent outcome measures (ATP, Ca²⁺, cAMP, PKA activity, glycolysis, motility, penetration) all pointing the same direction
• Exclusion criteria appropriately remove common confounders

Verdict

This paper identifies a plausible new molecular player in asthenozoospermia using solid methodology for a mechanistic study. The association between Kmal and poor motility is well-documented here; the causal claim is directionally supported but not airtight — the sodium malonate model carries enough off-target risk to keep "Kmal causes asthenozoospermia" in the hypothesis column, not the finding column. The missing funding disclosure is a yellow flag on an otherwise credible piece of work. Worth watching if SIRT5 activators ever reach clinical research, but this is foundational science, not a treatment signal.