Abstract Body: Background: Ischemic stroke is the most common cerebrovascular disease worldwide and the leading cause of permanent disability, which imposes a heavy burden on society and families. Currently, there are still limited treatments for improving long-term recovery after cerebral infarction. Recent studies have found that the development and prognosis after stroke are closely related to abnormal tryptophan metabolism. In this study, we aimed to identify tryptophan metabolites with ischemic protective effects in stroke patients and animal models and determine their mechanisms of action.
Methods: Metabolomics analysis using liquid chromatography-mass spectrometry was performed to identify differentially bioactive metabolites in plasma samples from 46 acute ischemic stroke (AIS) patients and 35 healthy controls and validated in experimental animals, identifying decreased levels of 3-hydroxy-kynurenamine (3-HKA) after stroke. We then examined the role of 3-HKA in stroke mice and performed proteomic analysis to elucidate the molecular mechanisms of 3-HKA.
Results: Supplementation of 3-HKA improves long-term sensory and motor recovery in ischemic stroke and increases ipsilateral cerebral blood flow. 3-HKA can also promote angiogenesis, stimulate the formation of functional blood vessels, and repair the blood-brain barrier, thereby enhancing post-stroke remodeling. Meanwhile, 3-HKA inhibits the activation of neurotoxic (A1-like) astrocytes but promotes the polarization of neuroprotective (A2-like) astrocytes. Mechanistically, 3-HKA inhibited the activation of AIM2 inflammasomes, and AIM2 expression was increased mainly in astrocytes at 7 and 14 days after stroke, suggesting that 3-HKA may regulate astrocyte-mediated vascular remodeling. Consistently, in primary mouse brain microvascular endothelial cells and astrocyte co-culture, 3-HKA promoted angiogenesis after oxygen-glucose deprivation (OGD). In astrocytes, the effects of 3-HKA on enhancing vascular remodeling in vitro and in vivo were abolished after lentiviral or AAV overexpression of AIM2. Overexpression of AIM2 in astrocytes by lentivirus or AAV counteracted the effect of 3-HKA on augmenting vascular remodeling in vitro and in vivo.
Conclusions: Our results suggest that tryptophan metabolism is disturbed after stroke, with decreased 3-HKA levels. Supplementation of 3-HKA may foster vascular remodeling by regulating the activation of A1/A2 astrocytes after stroke, thereby improving long-term neurological recovery.