Neuroprotection mediated by glutamate carboxypeptidase II (NAALADase) inhibition requires TGF-beta

Inhibition of glutamate carboxypeptidase (GCP) II (EC 3.4.17.21), also term ed N-acetylated alpha-linked acidic dipeptidase (NAALADase), has been shown to protect against ischemic injury presumably via decreasing glutamate and increasing N-acetylaspartyl-glutamate (NAAG). NAAG is a potent and selecti ve mGlu(3) receptor agonist. Activation of glial mGlu(3) receptors has been shown to protect against NMDA toxicity by releasing transforming growth fa ctors, TGF-betas. We hypothesized that GCP II inhibition could be neuroprot ective also via TGF-betas, due to increased NAAG. To verify this, Enzyme-Li nked Immunosorbent Assays (ELISAs) were performed on media from both contro l and ischemic cultures treated with the GCP II inhibitor, 2-(phosphonometh yl)-pentanedioic acid (2-PMPA). We found that 2-PMPA attenuated ischemia-in duced declines in TGF-P. To further assess the role of TGF-betas in 2-PMPA- mediated neuroprotection, a neutralizing antibody to TGF-beta (TGF-beta Ab) was used. In both in vitro and in vivo models of cerebral ischemia, TGF-be ta Ab reversed the neuroprotection by 2-PMPA. Antibodies to other growth fa ctors had no effect. Data suggests that neuroprotection by GCP II inhibitio n may be partially mediated by promoting TGF-beta release. (C) 2001 Elsevie r Science B.V. All rights reserved.