Cell-specific roles of GRK2 in onset and severity of hypoxic-ischemic brain damage in neonatal mice.
The ubiquitously expressed kinase GRK2 protects against cellular overstimulation by desensitizing G protein-coupled receptors and regulating intracellular signaling. Recently, we described that hypoxia-ischemia (HI)-induced brain damage was accelerated and increased in GRK2(+/-) neonatal mice. Using Cre-Lox technology we now investigated the role of decreased GRK2 in only microglia/macrophages or forebrain neurons in development of HI brain injury. Low GRK2 in microglia/macrophages (LysM-GRK2(f/+) mice) was sufficient to accelerate onset of HI damage, without affecting the severity of brain injury at 24h post-HI as compared to LysM-GRK2(+/+) littermates. Consistently, the ipsilateral hemisphere of GRK2(+/-) mice contained microglia with a more rounded phenotype compared to WT mice at 3h post-HI. Inhibition of microglial/macrophage activity by minocycline treatment prevented the early onset of HI injury in GRK2(+/-) mice. In vitro, primary GRK2(+/-) microglia stimulated with LPS produced more TNF-alpha than WT microglia via a p38-dependent pathway. In vivo, HI-induced cerebral p38 activation and TNF-alpha production were increased in GRK2(+/-) mice or in LysM-GRK2(f/+) mice. Our findings indicate that low GRK2 in microglia/macrophages accelerates brain damage via a GRK2/p38/TNF-alpha-dependent pathway. Reduced GRK2 only in forebrain neurons (CamKIIalpha-GRK2(f/+) mice) significantly increased severity of HI brain damage without affecting the onset of brain damage. In conclusion, our data indicate that low GRK2 in microglia/macrophages facilitates activation of these cells which may contribute to the earlier onset of cerebral HI injury associated with increased p38 phosphorylation and TNF-alpha production. The level of GRK2 in neurons is crucial for determining the ultimate severity of HI damage in the newborn brain.
Nijboer
Cora H
CH
Laboratory of Psychoneuroimmunology, University Medical Center Utrecht, Utrecht, The Netherlands.
Heijnen
Cobi J
CJ
Willemen
Hanneke L D M
HL
Groenendaal
Floris
F
Dorn
Gerald W
GW
van Bel
Frank
F
Kavelaars
Annemieke
A
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D015153:Blotting, Western; D001921:Brain / Q000473:pathology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000096:biosynthesis / Q000235:genetics; D005260:Female; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000235:genetics* / Q000502:physiology*; D020925:Hypoxia-Ischemia, Brain / Q000235:genetics* / Q000401:mortality / Q000473:pathology*; D007150:Immunohistochemistry; D008264:Macrophages / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000502:physiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D014409:Tumor Necrosis Factor-alpha; C496568:GRK2 protein, mouse; D054769:G-Protein-Coupled Receptor Kinase 2; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D048051:p38 Mitogen-Activated Protein Kinases