DECIPHERING NON-CANONICAL PATHWAYS CONTROLLED BY RETINOIC ACID IN VIVO USING SERTOLI CELLS AS A MODEL – ARESSERC
In vertebrates, all-trans retinoic acid (ATRA), the active metabolite of vitamin A, is a key mediator of cell differentiation during embryonic development, male and female reproduction and homeostatic maintenance of adult tissues. In humans, vitamin A deficiency has a plethora of clinical manifestations, ranging from growth-deficiency to susceptibility to severe infection, and ATRA and its functional analogs (referred to as retinoids) are common therapeutics for the treatment of cancers and acne. Their use are nevertheless limited due to misunderstood side effects. Therefore, it is crucial to uncover all the molecular mechanisms involved in ATRA signaling. Using genetic and pharmacological approaches in the mouse, we have demonstrated that ATRA acts in vivo, notably during embryonic development, through a signaling pathway involving nuclear receptors (NR), called RARA, RARB and RARG, heterodimerized with rexinoid receptors (RXR) (“canonical” mechanism). However, in vitro studies indicate that RAR can also exert functions via non-canonical signaling pathways including heterodimerization with NR other than RXR or with transcription factors other than NR, and non-genomic actions through kinase-dependent cascades.
Our experimental model, the seminiferous epithelium, composed of somatic cells (Sertoli cells, SC) and of germ cells, represents an excellent paradigm to investigate the pleiotropic effects of ATRA in vivo, as it integrates the problematics of stem cell renewal, cell proliferation, switching from mitotic to meiotic cell division, programmed cell death and paracrine signaling. In this system, the canonical signaling based on RAR/RXR heterodimers applies to germ cells, but quite remarkably, not to SC. Actually, by demonstrating that ablation of RARA in SC yields seminiferous epithelium defects that are distinct from those induced by RXR ablations, we have provided the first genetic evidence that non-canonical ATRA signaling pathways are also operational in vivo.
Through focusing on Sertoli cells (SC), the ARESSERC project proposes to characterize these yet unidentified signaling pathways (Alternative REtinoid Signaling in SERtoli Cells). To this aim, we contemplate to test whether RARA mediates non-genomic effects in SC and to challenge the possibilities that RARA acts in heterodimer with the SF-1 NR or with the GATA4 transcription factor. Furthermore, by combining immunoprecipitation of RARA-containing protein complexes in SC and mass spectrometry analysis, we will identify new partners interacting with RARA to transduce the ATRA signal. In addition, generating and combining RNA-seq and ChIP-seq data sets with bioinformatics will allow identifying RARA target genes in SC. Our study, which will first focus on SC lines, will then be extended in vivo thanks to the unique collection of mutant mice that we are the only in the world to have in hands.
Deciphering non-canonical alternatives for ATRA signaling is of paramount importance, as they provide potential means for coupling different signaling pathways and represent potential targets for pharmaceutical strategies aimed at modulating ATRA action, notably in pathological situations.
Monsieur Norbert GHYSELINCK (Institut de Génétique et Biologie Moléculaire et Cellulaire)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
IGBMC Institut de Génétique et Biologie Moléculaire et Cellulaire
IRSET - INSERM U1085 Institut de Recherche en Santé Environnement et Travail
Help of the ANR 421,878 euros
Beginning and duration of the scientific project: September 2016 - 36 Months