G-Protein–Coupled Receptor 91 and Succinate Are Key Contributors in Neonatal Postcerebral Hypoxia-Ischemia Recovery

Abstract

Objective-Prompt post-hypoxia-ischemia (HI) revascularization has been suggested to improve outcome in adults and newborn subjects. Other than hypoxia-inducible factor, sensors of metabolic demand remain largely unknown. During HI, anaerobic respiration is arrested resulting in accumulation of carbohydrate metabolic intermediates. As such succinate readily increases, exerting its biological effects via a specific receptor, G-protein-coupled receptor (GPR) 91. We postulate that succinate/GPR91 enhances post-HI vascularization and reduces infarct size in a model of newborn HI brain injury. Approach and Results-The Rice-Vannucci model of neonatal HI was used. Succinate was measured by mass spectrometry, and microvascular density was evaluated by quantification of lectin-stained cryosection. Gene expression was evaluated by real-time polymerase chain reaction. Succinate levels rapidly increased in the penumbral region of brain infarcts. GPR91 was foremost localized not only in neurons but also in astrocytes. Microvascular density increased at 96 hours after injury in wild-type animals; it was diminished in GPR91-null mice leading to an increased infarct size. Stimulation with succinate led to an increase in growth factors implicated in angiogenesis only in wild-type mice. To explain the mode of action of succinate/GPR91, we investigated the role of prostaglandin E 2 -prostaglandin E receptor 4, previously proposed in neural angiogenesis. Succinate-induced vascular endothelial growth factor expression was abrogated by a cyclooxygenase inhibitor and a selective prostaglandin E receptor 4 antagonist. This antagonist also abolished succinate-induced neovascularization. Conclusions-We uncover a dominant metabolic sensor responsible for post-HI neurovascular adaptation, notably succinate/ GPR91, acting via prostaglandin E 2 -prostaglandin E receptor 4 to govern expression of major angiogenic factors. We propose that pharmacological intervention targeting GPR91 could improve post-HI brain recovery. [20][21][22] Yet, their mode of action has generally remained inexplicable, until membrane-bound receptors that are specifically activated by these metabolites have been identified. 23 In this context, succinate has been shown to contribute to the developmental and possibly aberrant retinal neovascularization presumably through actions on G-protein-coupled receptor (GPR) 91 independent of hypoxia-inducible factor activation 24 ; accordingly, siRNAand shRNA-GPR91 interfere with developmental angiogenesis and partly with abnormal preretinal neovascularization. Nonstandard Abbreviations and Acronyms EP4prostaglandin E receptor 4 GPR G-protein-coupled receptor HI hypoxia-ischemia VEGF Vascular endothelial growth factor Figure 1. Succinate accumulates in the penumbral region after cerebral hypoxia-ischemia (HI) where G-protein-coupled receptor (GPR) 91 is expressed in neurons and astrocytes. A, GPR91 colocalizes with NeuN (i) and glial fibrillary acidic protein (GFAP) (ii) in the rat cerebral cortex. Rabbit anti-GPR91 was used to l...

Targeting the vasculature for cerebroprotection in the immature brain

“…The data using endothelial specific gene targeting in the paper supports, however, that the EP4 receptor has an important vascular role regulating cerebral perfusion in HI. The results agree with a recent publication demonstrating that the EP4 receptor in the immature brain is also critical for angiogenesis after HI (Hamel et al, 2014). Indeed, the article highlights the importance of the vascular bed in neonatal HI and brings attention to it as an attractive therapeutic target for CNS protection (Xing et al, 2012).…”

Insight into SUCNR1 (GPR91) structure and function

“…In contrast, high levels of succinate after cerebral 1R1 enhance brain vascularization and recovery by inducing expression of VEGF through SUCNR1, which is mainly expressed in neurons and astrocytes (Hamel et al, 2014). In RGC and rat cerebral astrocyte neuronal cell line (RPA), SUCNR1 upregulates VEGF via PGE 2 and prostaglandin E receptor 4 (EP 4 ), already known to promote angiogenesis (Hamel et al, 2014).…”

“…In RGC and rat cerebral astrocyte neuronal cell line (RPA), SUCNR1 upregulates VEGF via PGE 2 and prostaglandin E receptor 4 (EP 4 ), already known to promote angiogenesis (Hamel et al, 2014). Since succinate only transiently accumulates in case of brain 1R1, long-acting agonists of SUCNR1 might potentiate the recovery process (Hamel et al, 2014).…”

Metabolic Flexibility and Dysfunction in Cardiovascular Cells

“…Recent studies have elucidated the role succinate in murine models of cerebral hypoxia-ischemia revascularization and diabetic retinopathy. 48, 49 Using GPR91-deficient mice, Hamel et al 48 demonstrated increased succinate levels in close proximity to brain infarcts, and GPR91 enhanced microvascular density and reduced infarct size. The effect of succinate on VEGF release was mediated by GPR91 and prostaglandin E 2 (PGE 2 ).…”