Role of glutamate and its receptors and insulin-like growth factors in hypoxia induced periventricular white matter injury.

This study investigated the glutamate concentration and cellular localization of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid glutamate receptors (AMPA GluR2, GluR3, GluR4) along with insulin-like growth factors (IGF)-1 and -2 expression in the periventricular white matter (PWM) of neonatal rats with the aim to determine their involvement in PWM injury in hypoxia. In response to hypoxia, the PWM tissue concentration of glutamate and IGF-1 as well as mRNA and protein expression of GluR2, GluR3, GluR4, IGF-1, and -2 was upregulated. Immunoexpression of GluR2/3 and GluR4 were localized in the amoeboid microglial cells (AMC) and oligodendrocytes while that of IGF-1 and -2 were confined to AMC. In primary microglial cultures subjected to hypoxia, administration of exogenous glutamate decreased IGF-1 but increased the release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) by the cells. Furthermore, silencing of the IGF-1 and -2 genes by RNA interference in primary microglial cultures and BV-2 cells downregulated the expression of these growth factors whereas production of glutamate, TNF-alpha, and IL-1beta in these cells was upregulated. It is suggested that increased IGF-1 and -2 expressions may be an early protective mechanism in attenuating the hypoxic damage in PWM but a subsequent glutamate-induced decrease of these growth factors may cause cellular injury due to excitotoxicity and increased production of inflammatory cytokines. In this connection, melatonin and edaravone were beneficial in enhancing IGF-1 and reducing glutamate release.