Tissue kallikrein alleviates glutamate-induced neurotoxicity by activating ERK1

Glutamate-induced neurotoxicity consequent to N-methyl-D-aspartic acid (NMDA) and 2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl) propionic acid (AMPA) receptor activation underlies the pathogenesis of a wide range of central nervous system disorders, including brain ischemia. Prevention of ischemia/reperfusion (I/R)-induced neuronal injury has long been regarded as an effective therapeutic strategy for ischemia. Human tissue kallikrein (TK) gene transfer has been shown to protect neurons against cerebral I/R-induced apoptosis and oxidative stress, via activation of the brandykinin B2 receptor (B2R). However, little is known about the role of TK on glutamate-induced neurotoxicity. Here we report that pretreatment of cultured cortical neurons with TK largely prevented glutamate-induced morphological changes and cell death. We found that TK pretreatment alleviated glutamate-induced oxidative stress by inhibiting neuronal nitric oxide synthase (nNOS) activity, thereby reducing the generation of nitric oxide (NO) and reactive oxygen species (ROS). Blockage of NMDA and AMPA receptors by their specific antagonists MK801 and CNQX had effects similar to those of TK administration. Furthermore, we found that the extracellular signal-regulated kinase 1/2 cascade (ERK1/2), particularly ERK1, and nuclear factor-kappaB (NF-kappaB) were involved in TK neuroprotection against glutamate-induced neurotoxicity. TK pretreatment activated ERK1 and NF-kappaB, leading to enhanced expression of brain-derived neurotrophic factor (BDNF) mRNA and antiapoptotic gene Bcl-2 protein. Collectively, these findings demonstrate that TK attenuates glutamate-induced apoptosis through an intracellular signaling pathway including activation of B2R, ERK1/2, and NF-kappaB and up-regulation of BDNF and Bcl-2 expression. Thus, TK represents a promising therapeutic strategy for ischemic stroke.