A defect in the peroxisomal biogenesis in germ cells induces a spermatogenic arrest at the round spermatid stage in mice

Ann-Kristin Brauns,Klaus Tödter,Udo Schumacher,Georg H Lüers,Eveline Baumgart-Vogt,Markus Heine

doi:10.1038/s41598-019-45991-6

Abstract

Peroxisomes are involved in the degradation of very long-chain fatty acids (VLCFAs) by β-oxidation. Besides neurological defects, peroxisomal dysfunction can also lead to testicular abnormalities. However, underlying alterations in the testes due to a peroxisomal defect are not well characterized yet. To maintain all metabolic functions, peroxisomes require an import machinery for the transport of matrix proteins. One component of this translocation machinery is PEX13. Its inactivation leads to a peroxisomal biogenesis defect. We have established a germ cell-specific KO of Pex13 to study the function of peroxisomes during spermatogenesis in mice. Exon 2 of floxed Pex13 was specifically excised in germ cells prior to meiosis by using a transgenic mouse strain carrying a STRA8 inducible Cre recombinase. Germ cell differentiation was interrupted at the round spermatid stage in Pex13 KO mice with formation of multinucleated giant cells (MNCs) and loss of mature spermatids. Due to a different cellular content in the germinal epithelium of Pex13 KO testes compared to control, whole testes biopsies were used for the analyses. Thus, differences in lipid composition and gene expression are only shown for whole testicular tissue but cannot be limited to single cells. Gas chromatography revealed an increase of shorter fatty acids and a decrease of n-6 docosapentaenoic acid (C22:5n-6) and n-3 docosahexaenoic acid (C22:6n-3), the main components of sperm plasma membranes. Representative genes of the metabolite transport and peroxisomal β-oxidation were strongly down-regulated. In addition, structural components of the blood-testis barrier (BTB) were altered. To conclude, defects in the peroxisomal compartment interfere with normal spermatogenesis.

Highlights

Peroxisomes are ubiquitous eukaryotic cell organelles that are essential to maintain cellular function and homeostasis
Our results show that truncated PEX13 abolished peroxisomal biogenesis leading to an impaired import of peroxisomal matrix proteins
Whereas the green fluorescent protein (GFP)-peroxisomal targeting signal type 1 (PTS1) fluorescence pattern within the germinal epithelium of control mice showed characteristic peroxisomal structures (Fig. 7a,c,g,i), we found a typical expression of the GFP-PTS1 transgene in peritubular myoid cells, in the basal epithelium and in Leydig cells but not in multinucleated giant cells (MNCs) of gcPex13∆ex2/∆ex2/Stra8-Cre+/− mice (Fig. 7d,f,j,l)

Summary

Introduction

Peroxisomes are ubiquitous eukaryotic cell organelles that are essential to maintain cellular function and homeostasis. One of their major functions is the degradation of VLCFAs and their derivatives via β-oxidation. Even though still under debate, they at least partially contribute to the synthesis of steroids and cholesterol[1] They are involved in the biosynthesis of glycerolipids and bile acids, the catabolism of purines and polyamines, as well as the degradation of reactive oxygen species (ROS)[1]. We hypothesize that peroxisomal dysfunction in germ cells interferes with normal spermatogenesis, as peroxisomes provide essential metabolites to maintain cellular function. Peroxisomal genes involved in the metabolite transport, β-oxidation, ether lipid synthesis as well as retinoid and ROS metabolism were differently regulated in the Pex[13] KO. We provide initial data demonstrating that peroxisomes are necessary for spermiogenesis and indispensable for the maintenance of the tight junction barrier

Methods

Results

Conclusion