ACTIVATION OF THE LIVER X RECEPTOR (LXR) INHIBITS INFLAMMATORY EFFECTS ASSOCIATED WITH INVOLUTION AND PROMOTES LACTOGENIC FEATURES IN MOUSE MAMMARY CELLS

EMILIA BOGNI; DIEGO GRINMAN; SABRINA VALLONE; ALBANA GATTELLI; ADALI PECCI; MEISS R; EDITH C KORDON

Buenos Aires

Congreso; Reunión Anual SAIC 2020; 2020

It is well-known that lactation is driven by glucocorticoids and prolactin (Prl) that induce milk protein expression through STAT5 activation. On the other hand, post-lactational involution is characterized by the secretion of pro-inflammatory factors that trigger mammary cell apoptosis. LXR is an anti-inflammatory transcription factor present in all developmental stages of the mouse mammary gland.The goal of this study was to determine whether LXR plays a relevant role during the lactation/involution switch. Female C57/bl6 mice were treated with the LXR agonist GW3965 (10 mg/kg) or DMSO (control) by IP injection at weaning, 48h or 96h post weaning (n=3 per group). At those times, mice were euthanized and pieces of their inguinal mammary glands were either fixed in formalin or frozen at -800C. Fixed tissue was later processed for histological studies, while proteins and RNA were extracted from frozen samples. On the other hand, we analyzed the effects of GW3965 (10-6M) compared to Dexamethasone (Dex), Dex+Prl or DMSO for 72h on HC11 mouse mammary cells in culture. Our results show that LXR activation inhibited expression of inflammatory cytokines IL-6, TNFa and LIF mRNA at 48h and 96h after weaning (by RT-qPCR), together with an increase of the anti-inflammatory tristetraprolin (TTP) protein (by Western blot analysis) at 96 hs. In addition, by immunohistochemistry, we have also found a decrease of S100A9 (a stimulator of neutrophils and their migration) expression at 96h post-weaning. In culture, we determined that GW3965 treatment induced, similarly to Dex+Prl, but differently from Dex alone, an increase of TTP and b-casein mRNA expression. Importantly, GW3965 treatment did not trigger STAT5 phosphorylation as the lactogenic hormones Dex+Prl. Taken together, these results show that activation of LXR inhibits involution associated events and promotes the lactogenic phenotype in the mammary epithelium by a Prl-Stat5 independent signaling pathway.