The role of neuroinflammation in cell death and cell survival after neonatal hypoxia-ischemia.

摘要

Many developmental, neurological and psychiatric disorders (i.e. cerebral palsy, mental retardation, and learning disabilities) have been linked to birth trauma, disruption in the maternal-placental-fetal system and hypoxia-ischemia (HI) in early life. HI leads to significant neuroinflammation as evidenced by increased microglial activation, proinflammatory cytokine release, increased matrix metalloproteinase activity and profuse neuronal cell loss. The tetracycline derivative doxycycline (DOXY) has anti-inflammatory actions independent of its antimicrobial effects and has been reported to be neuroprotective in adult animal models of cerebral ischemia. To investigate the role of neuroinflammation in cell death and cell survival after neonatal HI and the consequences of DOXY administration, a timecourse study was run such that neonatal rats received DOXY (10 mg/kg) or vehicle (VEH) (n≥6) in clinically relevant dosing regimes. Pups were euthanized 30 minutes to 7d post-HI. Immunochemical methods were used to detect specific cell markers, inflammatory cytokines, markers of cell genesis, and cell death signaling proteins. High performance liquid chromatography was used to determine levels of DOXY in brain parenchyma and concentrations of amino acid neurotransmitters. In addition to showing that DOXY significantly penetrates the blood-brain barrier, the studies presented here demonstrate that neuronal cell loss and evidence of neuroinflammation was present throughout the brain of all HI pups. Treatment with DOXY significantly attenuated this cell loss, robustly inhibited microglial activation, decreased the levels of interleukin-1beta and tumor necrosis factor alpha, augmented the levels of brain derived neurotrophic factor, and decreased cleaved caspase-3 protein expression (all p0.05). HI also significantly altered brain levels of the amino acids investigated including glutamate, gamma-aminobutyric acid, alanine, serine, and glycine. Treatment with DOXY significantly normalized levels of alanine, serine, and glycine in every region examined, 4h post-HI (p0.05). Compared to VEH-treated pups, DOXY-treated pups had fewer 2-bromo-5-deoxyuridine positive cells in the subventricular zone immediately following HI, but DOXY administration did not persistently affect the timecourse of neurogenesis in the subventricular zone or dentate gyrus 7d post-HI. This thesis highlights the complex role of activated microglia in cell survival and cell death following HI and a putative role for DOXY in the treatment of the brain damage associated with HI.