The TEX44-CPT1B axis regulates mitochondrial sheath assembly and fatty acid oxidation in sperm
Erlei Zhi, Haowei Bai, Chuan Ren, Yue Dong, Jintao Zhang, Yanzhi Xu et al. · 2025 · 7 citationsRead the paper
Mitochondrial fatty acid β-oxidation (FAO) is essential for energy production and cellular homeostasis, yet its role in sperm function has remained unclear. Through whole-exome sequencing (WES) of 800 patients with asthenozoospermia, we identified biallelic Testis-Expressed Protein 44 (TEX44) variants in six individuals, all of whom exhibited defective mitochondrial sheath assembly and impaired sperm motility. Using Tex44 knockout mice, we show that TEX44 interacts with carnitine palmitoyltransferase 1B (CPT1B) to form a mitochondrial glue, anchoring adjacent mitochondria and facilitating the assembly of the sperm-specific mitochondrial sheath. In vitro, we show that purified TEX44 protein can modulate CPT1B enzymatic activity, limiting the conversion of long-chain fatty acids such as palmitic acid and myristic acid into acyl-carnitines, thereby reducing reactive oxygen species (ROS) production. Loss of TEX44 disrupts this regulatory mechanism, leading to unregulated FAO, excessive ROS generation, and severe oxidative damage to sperm DNA and flagellar structure. Additionally, germ cell-specific Cpt1b knockout mice exhibit phenotypes similar to TEX44 deficiency, including mitochondrial sheath defects and reduced sperm motility. These findings reveal a sperm-specific mechanism by which TEX44 regulates CPT1B activity to balance FAO and ROS generation, providing critical insights into energy metabolism, mitochondrial integrity, and male infertility.
What the full text shows
Working prototype- Biallelic TEX44 variants cause asthenozoospermia and defective mitochondrial sheath assembly. — 0.75% (6/800) of patients (Human cohort with idiopathic asthenozoospermia)
- TEX44 inhibits CPT1B enzymatic activity to limit the production of long-chain acyl-carnitines. (In vitro purified protein assay)
- Loss of TEX44 leads to unregulated fatty acid oxidation and increased ROS production. (Tex44 knockout mice sperm in palmitoyl-CoA media)
- TEX44 and CPT1B form a 'mitochondrial glue' that anchors adjacent mitochondria to assemble the sperm mitochondrial sheath. (HeLa cells and mouse sperm)
- Germ cell-specific Cpt1b knockout results in similar phenotypes to TEX44 deficiency, including reduced sperm motility and sheath defects. (Cpt1b gKO mice)
- ICSI can overcome infertility associated with TEX44 loss. (Tex44 knockout mice and human probands)
- Setup
- 800 human patients with asthenozoospermia, 157 healthy controls, and C57BL/6 mouse models.
- How
- The study used whole-exome sequencing of human patients, generated Tex44 knockout and Cpt1b germ cell-specific knockout mice, and performed Co-IP, IP-MS, and in vitro enzymatic assays. Mitochondrial structure was analyzed via TEM, SEM, and immunofluorescence, while FAO and ROS were measured via metabolomics and fluorometric assays.
- Limitations
- Lack of a mouse model specifically mimicking the p.Gln79Arg missense variant. · Low confidence (pLDDT) in AlphaFold3 predicted structures for the TEX44 protein. · Mitochondrial count per spermatozoon was not quantified.
Summarized by Gemma 4 from the open-access full text · 8 Oct 2026. Read it