[Effects of Cathepsin K on spatial learning and memory in rats]

To investigate the effects of Cathepsin K(CatK) on spatial learning and memory in rat hippocampus and its mechanisms.

Twenty male SD rats were randomly divided into Control group and CatK inhibitor group(CatKⅡ group), which were microinjected with Cathepsin K specific inhibitor(0.5 μg/μl) and artificial cerebrospinal fluid in hippocampal DG area respectively with 5 days. The cultured hippocampal neuron cells were divided into control group (CON group), negative control group(NC group), siRNA interference group(siCatK group). Three re-wells were set for each group, and samples were collected 18～20 h after siRNA transfection. Morris water maze was used to evaluate spatial learning and memory function of rats. Meanwhile, dynamic changes of glutamate(Glu) content in extracellular fluid of DG region during learning and memory were observed by microdialysis and high performance liquid chromatography in conscious rats. Western blot was used to detect CatK-mediated Notch1 activation and other signal molecules.

Animal experiments showed that compared with the control group, the spatial learning and memory ability were decreased significantly in CatKII group, and the hippocampus protein expressions of c-Notch1, p-Akt, p-CREB and BDNF were also decreased significantly(P＜0.05); the levels of Glu in DG area of control group and CatK II group were increased significantly with Morris water maze training days, but the increase of CatK II group was significantly weaker than that of control group(P＜ 0.05). The results of cell experiment showed that the expressions of CatK, c-Notch1, p-CREB and BDNF in siCatK group were significantly lower than other groups (P＜0.05).

CatK can affect the spatial learning and memory function of rats by activating Notch1 and its memory related signal protein in hippocampus.