Cystamine prevents haloperidol-induced decrease of BDNF/TrkB signaling in mouse frontal cortex

The role of brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology as well as treatment outcome of schizophrenia. Rodent studies indicate that several antipsychotic drugs have time-dependent (and differential) effects on BDNF levels in the brain. Earlier studies from our laboratory have indicated that long-term treatment with haloperidol (HAL) decreases BDNF, reduced GSH and anti-apoptotic marker, Bcl-xl protein levels and increases the expression of pro-apoptotic proteins in rat frontal cortex. Furthermore, findings from human as well as rodent studies suggest that treatment of schizophrenia must involve the neuroprotective strategies to improve the neuropathology and thereby clinical outcome. In the present study, we investigated the potential of cystamine (CYS), an anti-oxidant and anti-apoptotic compound, to prevent HAL-induced reduction in BDNF, GSH, and Bcl-xl protein levels in mice and the signaling mechanism(s) involved in the beneficial effects of CYS. The results indicated that CYS as well as cysteamine (the FDA-approved precursor of CYS) increased BDNF protein levels in mouse frontal cortex 7 days after treatment. CYS co-treatment prevented chronic HAL treatment-induced reduction in BDNF, GSH, and Bcl-xl protein levels. CYS treatment enhanced TrkB-tyrosine phosphorylation and activated Akt and extracellular signal-regulated kinase (ERK)1/2, downstream molecules of TrkB signaling. In addition, in vitro experiments with mouse cortical neurons showed that CYS prevented the HAL-induced reduction in neuronal cell viability and BDNF protein levels, and increase in apoptosis. BDNF-neutralizing antibody as well as K252a, a selective inhibitor of neurotrophin signaling blocked the CYS-mediated neuroprotection. Moreover, CYS-mediated neuroprotection is also blocked by LY294002, a phosphatidylinositol 3-kinase inhibitor or PD98059, a mitogen-activated protein kinase kinase (MEK) inhibitor. Thus, CYS protects cortical neurons through a mechanism involving TrkB receptor activation, and a signaling pathway involving phosphatidylinositol 3-kinase and MAPK. The findings from the present study may be helpful for the development of novel neuroprotective strategies to improve the treatment outcome of schizophrenia.