ABSTRACT
Tripartite motif (TRIM) 31 has been implicated in diverse biological and pathological conditions. However, whether TRIM31 plays a role in ischemic stroke progression is not clarified. Here we demonstrated that TRIM31 was significantly downregulated in the ischemic brain and the deficiency of TRIM31 alleviated brain injury induced by middle cerebral artery occlusion by reducing reactive oxygen species production and maintaining mitochondrial homeostasis. Mechanistically, we found that TRIM31 is an E3 ubiquitin ligase for TP53-induced glycolysis and apoptosis regulator (TIGAR), which confers protection against brain ischemia by increasing the pentose phosphate pathway flux and preserving mitochondria function. TRIM31 interacted with TIGAR and promoted the polyubiquitination of TIGAR, consequently facilitated its degradation in a proteasome-dependent pathway. Furthermore, TIGAR knockdown effectively abolished the protective effect of TRIM31 deficiency after cerebral ischemia. In conclusion, we identified that TRIM31 was a novel E3 ubiquitin ligase for TIGAR, played a critical role in regulating its protein level, and subsequently involved in the ischemic brain injury, suggesting TRIM31 as a potential therapeutic target for ischemic stroke.
Subject(s)
Apoptosis Regulatory Proteins/metabolism , Brain Injuries , Phosphoric Monoester Hydrolases/metabolism , Tripartite Motif Proteins/genetics , Ubiquitin-Protein Ligases/genetics , Animals , Apoptosis , Glycolysis , Male , Mice, Inbred C57BL , Ubiquitin-Protein Ligases/metabolism , UbiquitinationABSTRACT
G protein-coupled receptor 120 (GPR120) has been shown to negatively regulate inflammation and apoptosis, but its role in cerebral ischemic injury remains unclear. Using an in vivo model of middle cerebral artery occlusion (MCAO) and an in vitro model of oxygen-glucose deprivation (OGD), we investigated the potential role and molecular mechanisms of GPR120 in focal cerebral ischemic injury. Increased GPR120 expression was observed in microglia and neurons following MCAO-induced ischemia in wild type C57BL/6 mice. Treatment with docosahexaenoic acid (DHA) inhibited OGD-induced inflammatory response in primary microglia and murine microglial BV2 cells, whereas silencing of GPR120 strongly exacerbated the inflammation induced by OGD and abolished the anti-inflammatory effects of DHA. Mechanistically, DHA inhibited OGD-induced inflammation through GPR120 interacting with ß-arrestin2. In addition to its anti-inflammatory function, GPR120 also played a role in apoptosis as its knockdown impaired the antiapoptotic effect of DHA in OGD-induced rat pheochromocytoma (PC12) cells. Finally, using MCAO mouse model, we demonstrated that GPR120 activation protected against focal cerebral ischemic injury by preventing inflammation and apoptosis. Our study indicated that pharmacological targeting of GPR120 may provide a novel approach for the treatment of patients with ischemic stroke.
Subject(s)
Apoptosis , Brain Ischemia/prevention & control , Inflammation/prevention & control , Receptors, G-Protein-Coupled/metabolism , Transcriptional Activation , Animals , Disease Models, Animal , Docosahexaenoic Acids/pharmacology , Gene Silencing , Male , Mice , Mice, Inbred C57BL , Microglia/drug effects , PC12 Cells , Rats , Receptors, G-Protein-Coupled/genetics , Stroke/prevention & controlABSTRACT
BACKGROUND: In Parkinson's disease (PD), loss of striatal dopaminergic (DA) terminals and degeneration of DA neurons in the substantia nigra (SN) are associated with inflammation. Nucleotide-binding oligomerization domain-containing protein (NOD)2, one of the first discovered NOD-like receptors, plays an important role in inflammation. However, the role of NOD2 has not been elucidated in PD. METHODS: NOD2 mRNA and protein expression in the SN and the striatum of C57BL/6 mice treated with 6-hydroxydopamine (6-OHDA) was measured. We next investigated the potential contribution of the NOD2-dependent pathway to 6-OHDA-induced DA degeneration using NOD2-deficient (NOD2-/-) mice. Assays examining DA degeneration and inflammation include HPLC, Western blot, immunohistochemistry, TUNEL staining, and cytometric bead array. To further explore a possible link between NADPH oxidase 2 (NOX2) and NOD2 signaling in PD, microglia were transfected with shRNA specific to NOX2 in vitro and apocynin were given to mice subjected to 6-OHDA and muramyl dipeptide (MDP) striatal injection. RESULTS: The expression of NOD2 was upregulated in an experimental PD model induced by the neurotoxin 6-OHDA. NOD2 deficiency resulted in a protective effect against 6-OHDA-induced DA degeneration and neuronal death, which was associated with the attenuated inflammatory response. Moreover, silencing of NOX2 in microglia suppressed the expression of NOD2 and the inflammatory response induced by 6-OHDA and attenuated the toxicity of conditioned medium from 6-OHDA or MDP-stimulated microglia to neuronal cells. Furthermore, apocynin treatment inhibited NOD2 upregulation and DA degeneration in the SN of WT mice induced by 6-OHDA and MDP. CONCLUSION: This study provides the direct evidence that NOD2 is related to 6-OHDA-induced DA degeneration through NOX2-mediated oxidative stress, indicating NOD2 is a novel innate immune signaling molecule participating in PD inflammatory response.
