Maternal inflammation leads to impaired glutamate homeostasis and up-regulation of glutamate carboxypeptidase II in activated microglia in the fetal/newborn rabbit brain

Abstract

Astrocyte dysfunction and excessive activation of glutamatergic systems has been implicated in a number of neurologic disorders, including periventricular leukomalacia (PVL) and cerebral palsy (CP). However, the role of chorioamnionitis on glutamate homeostasis in the fetal and neonatal brains is not clearly understood. We have previously shown that intrauterine endotoxin administration results in intense microglial ‘activation’ and increased pro-inflammatory cytokines in the periventricular region (PVR) of the neonatal rabbit brain. In this study, we assessed the effect of maternal inflammation on key components of the glutamate pathway and its relationship to astrocyte and microglial activation in the fetal and neonatal New Zealand white rabbit brain. We found that intrauterine endotoxin exposure at gestational day 28 (G28) induced acute and prolonged glutamate elevation in the PVR of fetal (G29, 1 day post-injury) and postnatal day 1 (PND1, 3 days post-injury) brains along with prominent morphological changes in the astrocytes (soma hypertrophy and retracted processes) in the white matter tracts. There was a significant increase in glutaminase and N-Methyl-D-Aspartate receptor (NMDAR) NR2 subunits expression along with decreased glial L-glutamate transporter 1 (GLT1) in the PVR at G29, that would promote acute dysregulation of glutamate homeostasis. This was accompanied with significantly decreased TGF-β1 at PND1 in CP kits indicating ongoing neuroinflammation. We also show for the first time that glutamate carboxypeptidase II (GCPII) was significantly increased in the activated microglia at the periventricular white matter area in both G29 and PND1 CP kits. This was confirmed by in vitro studies demonstrating that LPS activated primary microglia markedly upregulate GCPII enzymatic activity. These results suggest that maternal intrauterine endotoxin exposure results in early onset and long-lasting dysregulation of glutamate homeostasis, which may be mediated by impaired astrocyte function and GCPII upregulation in activated microglia.

Unique Molecular Regulation of Higher-Order Prefrontal Cortical Circuits: Insights into the Neurobiology of Schizophrenia

“…146 Conversely, maternal inflammation has been shown to increase microglial GCPII expression in neonate brain, which would reduce endogenous mGluR3 stimulation by NAAG. 187 Taken together, these studies suggest that various DNC mechanisms that normally serve to inhibit feedforward cAMP–calcium signaling in dlPFC layer III microcircuits may be reduced in schizophrenia subjects.…”

FOLH1/GCPII is elevated in IBD patients, and its inhibition ameliorates murine IBD abnormalities

“…With regard to site of action, although the increased expression in IBD patients has been reported in epithelial cells (6) it is also possible that inhibition of FOLH1/ GCPII may affect the enteric nervous system or infiltrating immune cells. Of interest, our laboratory recently found that GCPII is highly upregulated in microglial cells (e.g., the immune cells of the brain) following inflammation and its inhibition prevents neurological damage (27). With respect to enzymatic mechanism, to date there are 3 known FOLH1 /GCPII substrates that could be implicated as possible mediators of the therapeutic effect, including N-acetylaspartylglutamate (NAAG) (28), folate polyglutamate (29–31), and laminin-derived peptides (32, 33).…”

Scalable synthesis and validation of PAMAM dendrimer‐N‐acetyl cysteine conjugate for potential translation

“…Experimental procedures were approved by the Johns Hopkins University Animal Care and Use Committee (IACUC). After one week of acclimation, the pregnant rabbits underwent laparotomy on gestational day 28 (G28) and received a total of 4,800 EU of LPS ( E. coli serotype O127:B8, Sigma‐Aldrich, St. Louis, MO) injection along the wall of the uterus as previously described . The kits were induced on G30 with intravenous injection of Pitocin (0.2 unit/kg) and kept in incubators with the temperature of ∼32–35°C and relative humidity of ∼50–60%.…”