Intraperitoneal injection of JNK-specific inhibitor SP600125 inhibits the expression of presenilin-1 and Notch signaling in mouse brain without induction of apoptosis.

Presenilin-1 (PS1) is a multifunctional protein involved in many cellular functions including the processing of type 1 membrane proteins such as β-amyloid precursor protein (APP) and Notch 1 receptor. PS1 acts as the catalytic subunit of the γ-secretase complex, and participates in Notch 1 processing to release Notch intracellular domain (NICD) in the cytoplasm. NICD subsequently migrates to the nucleus and causes Notch signaling by increasing the expression of the Hes1 gene. We have previously shown that inhibition of basal activity of c-jun-NH2-terminal kinase (JNK) with JNK-specific inhibitor SP600125 represses the expression of PS1 and γ-secretase activity by increasing p53 level in SK-N-SH cell line in vitro (Lee and Das, 2008, 2010). However, it is largely unknown whether PS1 can be effectively suppressed in vivo in adult mouse brains. In this report we showed that intraperitoneal (i.p) injection of JNK-specific inhibitor SP600125 decreased p-JNK level, and reduced PS1 expression by increasing p53 level in adult mouse brains. We also showed that suppression of PS1 expression by SP600125 reduced γ-secretase activity which decreased Notch 1 processing to reduce NICD in mouse brains. Furthermore, inhibition of Notch 1 processing by SP600125 decreased Notch 1 signaling by reducing the expression of the NICD target Hes1 gene in mouse brains without induction of apoptosis. These results provide insights for further study on PS1-mediated reduction of Notch 1 and APP processing for the treatment of Alzheimer's disease.