Introduction: Neuroinflammation is a key aspect of various injuries and diseases of the central nervous system and brain, including stroke, Alzheimer's, Parkinson's, multiple sclerosis, etc. Phoenixin-14 is a naturally occurring pleiotropic peptide involved in reproduction, anxiety, pain, and other functions.
Materials and methods: Primary astrocytes were isolated from new-born pups of c57bl/6 mice. The gene expression of GPR173, CHOP, and GADD34 was measured by real-time PCR. Protein expression was assessed by western blot analysis. Secretions of IL-1β and IL-18 were determined by ELISA.
Results: Phoenixin-14 (PNX-14) is a ligand for the G protein-coupled receptor GPR173, which we demonstrate to be expressed in astrocytes and suppressed by exposure to lipopolysaccharide (LPS). Endoplasmic reticulum (ER) stress resulting from injury or disease leads to the unfolded protein response, which is mediated by the activation of transcription factors including eIF-2α, ATF4, and CHOP, and regulated by GADD34. ER stress also leads to a robust neuroinflammatory response, which is mediated by HMGB1-induced activation of the NLRP3 inflammasome and subsequent production of IL-1β and IL-18. In the present study, we demonstrate that PNX-14 could attenuate LPS-induced ER stress response and NLRP3 inflammasome activation in mouse cerebral astrocytes. Our findings show that PNX-14 could suppress the production of ROS as well as the decrease in SOD induced by LPS. PNX-14 also inhibited HMGB1-mediated NLRP3 inflammasome activation and production of IL-1β and IL-18. Through a GPR173 siRNA knockdown experiment, we further demonstrate that GPR173 knockdown abolished the effects of PNX-14 on LPS-induced NLRP3 expression and IL-18 production.
Conclusion: These findings suggest that PNX-14 may have potential in the treatment of neuroinflammation.
Keywords: (eIF-2α)/ATF4; ATF6; Astrocytes; CHOP; Caspase-1; Caspase-11; GADD34; Lipopolysaccharide; NLRP3 inflammasome; Neuroinflammation; Phoenixin-14.