Hypoxic-ischemic injury induces macrophage inflammatory protein-1alpha expression in immature rat brain.
OBJECTIVE
Macrophage inflammatory protein (MIP)-1alpha is a well-characterized monocyte chemoattractant; its role in regulating monocyte and microglial recruitment and activation in the injured neonatal brain is unknown. We evaluated the impact of acute hypoxic-ischemic (HI) brain injury on the expression of MIP-1alpha in neonatal rat brain.


METHODS
To elicit forebrain ischemic injury, 7-day-old (P7) rats underwent right carotid ligation, followed by 2.5 hours of 8% oxygen exposure. We used an enzyme-linked immunosorbent assay and immunohistochemistry to detect MIP-1alpha; double-labeling immunofluorescence assays were analyzed with confocal microscopy to identify cellular sources of MIP-1alpha. Immunocytochemistry assays were also used to detect 2 MIP-1alpha receptors, CCR1 and CCR5.


RESULTS
We found marked increases in tissue concentrations of MIP-1alpha in the HI cerebral hemisphere, peaking from 8 to 72 hours after lesioning. Immunocytochemistry assays revealed that MIP-1alpha was constitutively expressed in physiologically activated microglia; from 8 to 120 hours after lesioning, MIP-1alpha immunoreactive monocytes and microglia accumulated in the lesion territory. In immunoreactive cells, MIP-1alpha was diffusely distributed throughout the cytoplasm at early post-HI time intervals; by 72 hours, MIP-1alpha immunoreactivity was typically concentrated adjacent to the nucleus, a pattern indicative of active MIP-1alpha production. In P7 to P12 brain, many cells expressed MIP-1alpha receptors; both CCR1 and CCR5 immunoreactivity were localized to endothelium and ependyma; CCR1-immunoreactive astrocytes and neurons and CCR5-immunoreactive microglia were also identified.


CONCLUSIONS
These data implicate MIP-1alpha as a mediator of the complex and sustained inflammatory response initiated by perinatal HI braininjury.
Cowell
Rita M
RM
Department of Pediatrics, University of Michigan, Ann Arbor, Mich, USA.
Xu
Haiyan
H
Galasso
John M
JM
Silverstein
Faye S
FS
D000818:Animals; D000831:Animals, Newborn; D000943:Antigens, Differentiation; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D054405:Chemokine CCL3; D054407:Chemokine CCL4; D004195:Disease Models, Animal; D018450:Disease Progression; D004797:Enzyme-Linked Immunosorbent Assay; D020925:Hypoxia-Ischemia, Brain / Q000378:metabolism* / Q000473:pathology; D007150:Immunohistochemistry; D019402:Macrophage Inflammatory Proteins / Q000096:biosynthesis*; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D054389:Receptors, CCR1; D019713:Receptors, CCR5 / Q000378:metabolism; D019707:Receptors, Chemokine / Q000378:metabolism
D000943:Antigens, Differentiation; C515302:Ccr1 protein, rat; D054405:Chemokine CCL3; D054407:Chemokine CCL4; D019402:Macrophage Inflammatory Proteins; D054389:Receptors, CCR1; D019713:Receptors, CCR5; D019707:Receptors, Chemokine