Microglial NLRP3 inflammasome activation-mediated inflammation promotes prolactinoma development

Abstract

Prolactinomas have harmful effects on human health, and the pathogenesis is still unknown. Furthermore, 25% of prolactinoma patients do not respond to the therapy of dopamine receptor agonist in the clinic. Thus, it is important to reveal the pathogenesis and develop new therapeutic methods for prolactinomas. Herein, two animal models of prolactinomas, namely oestrogen-treated rats and transgenic D2 dopamine receptor-deficient mice, were used. PET/CT imaging detection showed that translocator protein-mediated microglia activation and inflammation significantly increased in the pituitary glands of prolactinomas rats. Messenger RNA microarrays were used to analyze and compare the differential gene and signal pathways of the pituitary glands between control and prolactinomas rats. Statistical results pertaining to gene enrichment showed that the innate immune response genes were upregulated in the pituitary glands of prolactinoma rats. This suggested that the innate immune response was activated. We analyzed the NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) inflammasome that is one of the most important members of the innate immune system in mammals and found that the expressions of NLRP3, Caspase-1, apoptosis-associated speck-like, interleukin 1B (IL1B) and IL18 proteins of pituitary glands in prolactinomas rats were increased considerably compared with those in control rats. This suggested the activation of the NLRP3 inflammasome during the emergence and evolution of prolactinomas. Immunohistochemistry results also confirmed that the NLRP3 expression was elevated in human prolactinoma tissues, and the microglia marker-ionised calcium binding adaptor molecule-1 was co-located with the NLRP3 protein in prolactinomas by immunofluorescence assay. Finally, compared with the WT mice, NLRP3−/− mice had smaller pituitary glands (weight/body weight) and diminished prolactin (PRL) expressions and secretions. These findings were associated with a reduction in the caspase-1 activation and maturation of IL1B. Furthermore, MCC950 decreased the PRL expression and secretion following the inhibition of NLRP3 inflammasome activation in GH3 cells stimulated with lipopolysaccharide and nigericin. And MCC950 inhibited the pituitary tumor overgrowth and PRL expression and secretion in prolactinoma rats. These data confirm that the microglial NLRP3 inflammasome activation upregulates the inflammatory cytokines IL1/IL18 in the pituitary glands and induces prolactinomas. Our findings showed that microglial NLRP3 inflammasome activation-mediated IL1B-related inflammation promoted the development of prolactinomas and identified the inflammasome as a new therapeutic target for prolactinomas.