ABSTRACT
The creatine transporter (CrT) maintains brain creatine (Cr) levels, but the effects of its deficiency on energetics adaptation under stress remain unclear. There are also no effective treatments for CrT deficiency, the second most common cause of X-linked intellectual disabilities. Herein, we examined the consequences of CrT deficiency in brain energetics and stress-adaptation responses plus the effects of intranasal Cr supplementation. We found that CrT-deficient (CrT-/y) mice harbored dendritic spine and synaptic dysgenesis. Nurtured newborn CrT-/y mice maintained baseline brain ATP levels, with a trend toward signaling imbalance between the p-AMPK/autophagy and mTOR pathways. Starvation elevated the signaling imbalance and reduced brain ATP levels in P3 CrT-/y mice. Similarly, CrT-/y neurons and P10 CrT-/y mice showed an imbalance between autophagy and mTOR signaling pathways and greater susceptibility to cerebral hypoxia-ischemia and ischemic insults. Notably, intranasal administration of Cr after cerebral ischemia increased the brain Cr/N-acetylaspartate ratio, partially averted the signaling imbalance, and reduced infarct size more potently than intraperitoneal Cr injection. These findings suggest important functions for CrT and Cr in preserving the homeostasis of brain energetics in stress conditions. Moreover, intranasal Cr supplementation may be an effective treatment for congenital CrT deficiency and acute brain injury.
Subject(s)
Brain Diseases, Metabolic, Inborn/genetics , Brain/metabolism , Creatine/deficiency , DNA/genetics , Membrane Transport Proteins/genetics , Mental Retardation, X-Linked/genetics , Mutation , Plasma Membrane Neurotransmitter Transport Proteins/deficiency , Animals , Animals, Newborn , Brain/ultrastructure , Brain Diseases, Metabolic, Inborn/metabolism , Brain Diseases, Metabolic, Inborn/pathology , Creatine/genetics , Creatine/metabolism , DNA Mutational Analysis , Disease Models, Animal , Homeostasis , Male , Membrane Transport Proteins/deficiency , Mental Retardation, X-Linked/metabolism , Mental Retardation, X-Linked/pathology , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Mutant Strains , Microscopy, Electron , Neurons/metabolism , Neurons/ultrastructure , Plasma Membrane Neurotransmitter Transport Proteins/genetics , Plasma Membrane Neurotransmitter Transport Proteins/metabolismABSTRACT
Traumatic brain injury (TBI) is the leading cause of death in children and adolescents in developed countries, but there are no blood-based biomarkers to support the diagnosis or prognosis of pediatric TBI to-date. Here we report that the plasma levels of osteopontin (OPN), a phosphoprotein chiefly secreted by macrophages and/or activated microglia, may contribute to this goal. In animal models of TBI, while OPN, fibrillary acidic protein (GFAP), and matrix metalloproteinase 9 (MMP-9) were all readily induced by controlled cortical impact in the brains of one-month-old mice, only OPN and GFAP ascended in the blood in correlation with high neurological severity scores (NSS). In children with TBI (three to nine years of age, n = 66), the plasma levels of OPN, but not GFAP, correlated with severe TBI (Glasgow Coma Score ≤ 8) and intracranial lesions at emergency department. In addition, the plasma OPN levels in severe pediatric TBI patients continued to ascend for 72 h and correlated with mortality and the days requiring ventilator or intensive care unit support, whereas the plasma GFAP levels lacked these properties. Together, these results suggest that plasma OPN outperforms GFAP and may be a neuroinflammation-based diagnostic and prognostic biomarker in pediatric TBI.
Subject(s)
Brain Injuries, Traumatic/diagnosis , Inflammation/diagnosis , Osteopontin/blood , Adolescent , Animals , Biomarkers/blood , Brain Injuries, Traumatic/blood , Brain Injuries, Traumatic/pathology , Child , Child, Preschool , Glial Fibrillary Acidic Protein/blood , Humans , Inflammation/etiology , Mice , Predictive Value of Tests , PrognosisABSTRACT
Clinical management of neonatal hypoxic-ischemic encephalopathy (HIE) suffers from the lack of reliable surrogate marker tests. Proteomic analysis may identify such biomarkers in blood, but there has been no proof-of-principle evidence to support this approach. Here we performed in-gel trypsin digestion of plasma proteins from four groups of 10-d-old mice [untouched and 24 h after low-dose lipopolysaccharide (LPS) exposure, hypoxia-ischemia (HI), or LPS/HI injury; n = 3 in each group) followed by liquid chromatography-tandem mass spectrometry and bioinformatics analysis to search for HI- and LPS/HI-associated brain injury biomarkers. This analysis suggested the induction of plasma osteopontin (OPN) by HI and LPS/HI, but not by sham and injury-free LPS exposure. Immunoblot confirmed post-HI induction of OPN protein in brain and blood, whereas Opn mRNA was induced in brain but not in blood. This disparity suggests brain-derived plasma OPN after HI injury. Similarly, immunostaining showed the expression of OPN by Iba1+ microglia/macrophages in HI-injured brains. Further, intracerebroventricular injection of LPS activated microglia and up-regulated plasma OPN protein. Importantly, the induction of plasma OPN after HI was greater than that of matrix metalloproteinase 9 or glial fibrillary acid protein. Plasma OPN levels at 48 h post-HI also parallel the severity of brain damage at 7-d recovery. Together, these results suggest that OPN may be a prognostic blood biomarker in HIE through monitoring brain microglial activation.