Endocrine Abstracts

Introduction: The importance of the liver-X receptors (LXRs) in the maintenance of cholesterol homeostasis within the testis has yet to be fully characterised. By 7 months of age, Lxrα/β double knockout male mouse (Lxrα/β DKO) develops sterility with aberrations in testosterone production and lipid homeostasis. However, the underlying testicular LXR-regulated pathways are not well understood.

Aim: The aim of this study was to further understand the importance of LXRs in the testis by investigating disruption of candidate genes and networks of cellular lipids and steroid metabolites in Lxrα/β DKO mice.

Methods: We used RNA-seq and quantitative mass spectrometry to study whole testicular tissues from 6-month old Lxrα/β DKO mice alongside age-matched littermate controls. cDNA libraries were prepared followed by sequencing using NextSeq-500. Lipid extracts from mouse testis were prepared for LC-MS analysis using SONAR acquisition, based on an m/z isolation range of the quadrupole. Results were analysed using LipidMaps and Progenesis QI for normalized quantitation.

Results: Histological assessment of testicular tissues from Lxrα/β DKO mice confirmed abnormal seminiferous tubules, germ-cell loss and lipid deposition. Quantitative lipidomic analysis confirmed statistically significant differences in 53 lipid species including triglycerides and cholesterol esters (notably 20:4 cholesteryl ester) in the Lxrα/β DKO mice. Sphingolipid species (e.g. ceramide t18:0/20:0) were also altered. The retrieved curated targets were mapped onto KEGG pathway analysis, identifying key changes in steroid hormone biosynthesis and sphingomyelin metabolism. RNA-seq analysis revealed 1161 differentially expressed genes (log2 fold change in gene expression of −3.49 to +2.17, P<0.01) in Lxrα/β DKO. Androgen biosynthesis genes (Cyp17a1, Hsd3β2, Hsd17β3), triglyceride synthesis (Acsl, Acot7) as well as genes involved in sphingolipid metabolism were altered correlating with lipidomic data.

Discussion: Our integrative approach using lipidomic analysis with mRNA transcript studies provides novel data, implicating LXRs in pathways such as sphingolipid metabolism, critical for successful spermatogenesis.