cPKCγ-Modulated Autophagy Contributes to Ischemic Preconditioning-Induced Neuroprotection in Mice with Ischemic Stroke via mTOR-ULK1 Pathway

Neuron-specific conventional protein kinase C (cPKC)γ mediates cerebral hypoxic preconditioning (HPC). In parallel, autophagy plays a prosurvival role in ischemic preconditioning (IPC) against ischemic stroke. However, the effect of cPKCγ on autophagy in IPC still remains to be addressed. In this study, adult and postnatal 1-day-old C57BL/6 J wild-type (cPKCγ+/+) and knockout (cPKCγ-/-) mice were used to establish in vivo and in vitro IPC models. The results showed that IPC pretreatment alleviated neuronal damage caused by lethal ischemia, which could be suppressed by autophagy inhibitor 3-MA or bafilomycin A1. Meanwhile, cPKCγ knockout blocked IPC-induced neuroprotection, accompanied by significant increase of LC3-I to LC3-II conversion and Beclin 1 protein level, and a significant decrease in p62 protein level. Immunofluorescent staining results showed a decrease of LC3 puncta numbers in IPC-treated cPKCγ+/+ neurons with fatal ischemia, which was reversed in cPKCγ-/- neurons. In addition, cPKCγ-modulated phosphorylation of mTOR at Ser 2448 and ULK1 at Ser 555, rather than p-Thr-172 AMPK, was detected in IPC-pretreated neurons upon lethal ischemic exposure. The present data demonstrated that cPKCγ-modulated autophagy via the mTOR-ULK1 pathway likely modulated IPC-induced neuroprotection.

cPKCγ Deficiency Exacerbates Autophagy Impairment and Hyperphosphorylated Tau Buildup through the AMPK/mTOR Pathway in Mice with Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (T1DM)-induced cognitive dysfunction is common, but its underlying mechanisms are still poorly understood. In this study, we found that knockout of conventional protein kinase C (cPKC)γ significantly increased the phosphorylation of Tau at Ser214 and neurofibrillary tangles, but did not affect the activities of GSK-3β and PP2A in the hippocampal neurons of T1DM mice. cPKCγ deficiency significantly decreased the level of autophagy in the hippocampal neurons of T1DM mice. Activation of autophagy greatly alleviated the cognitive impairment induced by cPKCγ deficiency in T1DM mice. Moreover, cPKCγ deficiency reduced the AMPK phosphorylation levels and increased the phosphorylation levels of mTOR in vivo and in vitro. The high glucose-induced Tau phosphorylation at Ser214 was further increased by the autophagy inhibitor and was significantly decreased by an mTOR inhibitor. In conclusion, these results indicated that cPKCγ promotes autophagy through the AMPK/mTOR signaling pathway, thus reducing the level of phosphorylated Tau at Ser214 and neurofibrillary tangles.