Transglutaminase 2 expression induced by lipopolysaccharide stimulation together with NO synthase induction in cultured astrocytes

Activation of glia has been observed in neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), multiple sclerosis and brain ischemia. Excessive production of nitric oxide (NO), as a consequence of increased inducible NO synthase (iNOS) in glia, contributes to neurodegeneration. Transglutaminase 2 (TG2) is a cross-linking enzyme, which is activated in neurodegenerative diseases such as PD, AD and Huntington's diseases. However, mechanisms contributing to the increased TG activity in neurodegenerative diseases remain to be clarified. In the present study, we examined the expression of TG2 in cultured rat hippocampal astrocytes activated with lipopolysaccharide (LPS), which is generally used for a stimulant of iNOS induction. The expressions of TG2 mRNA and protein were increased by stimulation with LPS in a dose-dependent manner. The LPS-induced TG2 expression was diminished by ammonium pyrrolidine-1-carbodithioate; an inhibitor for nuclear factor (NF)-κB activation, suggesting the factors involved. Both expressions of TG2 and iNOS induced by LPS stimulation were suppressed by an antioxidant, ethyl pyruvate, in a dose-dependent manner. Furthermore, they were also suppressed by cystamine, an inhibitor of TG activity. These results suggest that the level of TG2 expression is regulated by oxidative stress and the activity of TG itself, and that the induction of iNOS and NO production are closely associated with TG2 expression in LPS-stimulated activation of astrocytes.

Research highlights▶ Lipopolysaccharide (LPS) induced transglutaminase 2 (TG2) in cultured astrocytes, as well as iNOS. ▶ Expressions of TG2 and iNOS were inhibited by 3 different inhibitors, APDC, ethyl pyruvate, and cystamine. ▶ TG2 expression is suggested to be regulated by oxidative stress and the activity of TG itself. ▶ Induction of iNOS is closely associated with TG2 expression in activation of astrocytes.