Glycerol kinase-like proteins cooperate with Pld6 in regulating sperm mitochondrial sheath formation and male fertility

Spermatids undergo the final steps of maturation during spermiogenesis, a process that necessitates extensive rearrangement of organelles such as the mitochondria. Male infertility has been linked to mitochondrial disorder, for example, hypospermatogenesis and asthenozoospermia. However, the mechanisms that regulate mitochondrial dynamics during spermiogenesis remain largely unknown. We found the glycerol kinase (Gyk)-like proteins glycerol kinase-like 1 (Gykl1) and glycerol kinase 2 (Gk2) were specifically localized to the mitochondria in spermatids. Male mice deficient in either Gykl1 or Gk2 were infertile due to dysfunctional spermatozoa, which exhibited unregulated ATP production, disordered mitochondrial sheath formation, abnormal mitochondrial morphology, and defective sperm tail. We demonstrated that the unique C-terminal sequences found in Gykl1 and Gk2 mediated their targeting to the mitochondrial outer membrane. Furthermore, both Gykl1 and Gk2 could interact with Pld6 (MitoPLD) and induce Pld6 and phosphatidic acid (PA)-dependent mitochondrial clustering in cells. Taken together, our study has revealed previously unsuspected functions of Gyk-like proteins in spermiogenesis, providing new insight into the potential mechanisms that lead to spermatozoa dysfunction and male infertility.