Role and mechanisms of G-protein-coupled receptor 39 in brain injury after intracerebral hemorrhage in mice

Objective To investigate the effect and underlying mechanisms of G-protein-coupled receptor 39 (GPR39) activation on neuroinflammation and brain injury after experimental intracerebral hemorrhage in mice. Methods Mouse model of intracerebral hemorrhage (ICH) was established by intracerebral injection of autologous blood. A total of 176 male C57/BL6 mice were randomly divided into 8 groups: Sham group (n=42), ICH group (n=34), ICH+Vehicle group (n=32), ICH+TC-G 1008 group (n=44), ICH+GPR39 siRNA group (n=6), ICH+Scramble siRNA group (n=6), ICH+TC-G 1008+666-15 group (n=6), and ICH+TC-G 1008+Vehicle 2 group (n=6). GPR39-specific agonist TC-G 1008 was administered via oral gavage at 1 and 25 h post-ICH modeling. Additionally, GPR39 siRNA and cAMP response element binding protein (CREB) inhibitor 666-15 were intracerebroventricularly injected 24 h before induction of ICH to inhibit the expression levels of GPR39 and p-CREB. At 48 h after ICH, modified Garcia test, forelimb placement test and corner turn test were used to evaluate the short-term neurological deficits in mice. Brain water content was determined by wet/dry method. Immunofluorescence assay was performed to detect the co-localization of GPR39 in neurons and microglia in the brain tissue surrounding the hematoma, as well as the expression of NOD-like receptor thermal protein domain associated protein 3 (NLRP3) in neurons. ELISA was employed to measure IL-1β, TNF-α and myeloperoxidase (MPO) levels in peri-hematoma tissue. TUNEL staining was performed to quantify apoptotic neurons around the hematoma. Nissl staining was utilized to evaluate neuronal damage. Western blotting was conducted to detect the expression of GPR39, p-CREB, CREB, NLRP3, Cleaved caspase-1 (C-caspase-1), and gasdermin-D protein (GSDMD) in peri-hematoma brain tissue. Results GPR39 expression peaked at 48 h post-ICH in mice (P < 0.05), and it was expressed in both neurons and microglia. Activation of GPR39 by TC-G 1008 (24 mg/kg) significantly improved the modified Garcia score, and increased success rate of left forelimb placement and the number of left turns (P < 0.05). Brain edema in the ipsilateral basal ganglia (BG) and cortex (CX) was significantly reduced (P < 0.05). The numbers of apoptotic and damaged neurons around the hematoma were obviously decreased (P < 0.05). The expression of pyroptosis-related molecules, including NLRP3, C-caspase-1 and GSDMD and the levels of inflammation-related factors, including IL-1β, TNF-α and MPO were notably decreased (P < 0.05). However, knockdown of GPR39 and downregulation of p-CREB expression significantly increased the expression of pyroptosis related molecules and inflammatory-related factors in peri-hematoma brain tissue post-ICH in mice (P < 0.05). Conclusion GPR39 activation may inhibit neuroinflammation and brain injury after ICH in mice partly through the CREB signaling pathway. Therefore, GPR39 may be a potential therapeutic target for mitigating neuroinflammation and brain damage after ICH.