Ligand-dependent contribution of RXRβ to cholesterol homeostasis in Sertoli cells

We show that mice expressing retinoid X receptor β (RXRβ) impaired in its transcriptional activation function AF-2 (Rxrb^af20 mutation) do not display the spermatid release defects observed in RXRβ-null mutants, indicating that the role of RXRβ in spermatid release is ligand-independent. In contrast, like RXRβ-null mutants, Rxrb^af20 mice accumulate cholesteryl esters in Sertoli cells (SCs) due to reduced ABCA1 transporter-mediated cholesterol efflux. We provide genetic and molecular evidence that cholesterol homeostasis in SCs does not require PPARα and β, but depends upon the TIF2 coactivator and RXRβ/LXRβ heterodimers, in which RXRβ AF-2 is transcriptionally active. Our results also indicate that RXRβ may be activated by a ligand distinct from 9-cis retinoic acid.