FRI295 Prolactin Exerts Anti- And Pro-inflammatory Actions In Joint Tissues That Are Cytokine-Dependent

Abstract Disclosure: J.F. García Rodrigo: None. G. Ortiz: None. O. Martínez Díaz: None. X. Ruiz Herrera: None. M. Ledesma Colunga: None. G. Martínez de la Escalera: None. C. Clapp: None. The close association between rheumatoid arthritis (RA), sex, reproductive state, and stress have long-linked the sexually dimorphic, reproductive, stress-related hormone prolactin (PRL) to disease progression. However, this role is questioned by the fact that PRL has both pro-inflammatory and anti-inflammatory outcomes in RA with mechanisms that are unclear. Here, we show that PRL modifies in an opposite manner the inflammatory action of IL-1β and TNF-α in mouse synovial fibroblasts (SF) in culture and in joints in vivo. SF isolated from the knee joint of male C57BL/6 mice were incubated with or without IL-1β (1 ng/mL) or TNF-α (10 ng/mL) in the presence or absence of PRL (2.3 μg/mL). Both, IL-1β and TNF-α upregulated the metabolic activity (MTT assay) and the RT-qPCR expression of pro-inflammatory mediators (IL-1β, IL-6, iNOS) via the activation of the NF-κB signaling pathway (immunocytofluorescence, Western blot). However, IL-1β increased and TNF-α decreased the levels of the long PRL receptor isoform (RT-qPCR, Western blot) and this opposite action associated with contrasting effects of PRL in these cells. PRL decreased the IL-1β upregulation of metabolic activity and expression of pro-inflammatory mediators by blocking the degradation of NF-κB inhibitors kB-beta (Iκ-Bβ) and alpha (Iκ-Bα) and, thereby, interfering with the nuclear translocation of NF-κB. By contrast, PRL increased TNF-α-induced stimulation of metabolic activity and expression of pro-inflammatory mediators by promoting the nuclear translocation of NF-κB led by the increased degradation of Iκ-Bβ and Iκ-Bα. The double-faceted regulatory role of PRL against the two cytokines also manifested in vivo. IL-1β (80 ng) or TNF-α (300 ng) with or without PRL (2 μg) were injected into the intra-articular space of the knee joint of mice and, after 24 h, joint inflammation was monitored through the expression of pro-inflammatory mediators (IL-1β and iNOS). Both IL-1β and TNF-α upregulated the expression of IL-1β and iNOS in the joint. However, PRL inhibited the joint proinflammatory effect of IL-1β on IL-1β and iNOS, but not that of TNF-α. We conclude that the outcome of PRL actions on joint inflammation is dependent on its interaction with specific inflammatory cytokines, the level of the PRL receptor, and the activation of NF-κB signaling. We speculate that the opposite effects of PRL help balance joint inflammation in RA and that determining the mechanisms underlying dual actions provide insights into the pathophysiology of RA and the development of new treatments. Supported by UNAM (DGAPA-PAPIIT IN202321). Presentation: Friday, June 16, 2023