Abstract
Changes in brain energy metabolism in diabetes mellitus, including increased insulin resistance and mitochondrial dysfunction, are critically involved in diabetes-related neurodegeneration, and associate with early cognitive impairment as well. The aim of this study is to detect the specific phosphorylated-Thr485- AMP-activated protein kinase (AMPK-α2), regulated by cyclin-dependent kinase 5 (Cdk5) paly the inhibitory functional role of AMPK-α2, Which is maybe the link to the accelerated diabetic brain damage progression. Here, we used GK rats, the type 2 diabetic animal model for in vivo studies and performed In vitro kinase assay, high glucose treatment, -phosphorylated mutation and protein expression in both HEK-293T and HT-22 cell lines. In vitro, the results show that murine wild-type AMPK-α2 was phosphorylated by Cdk5 at a (S/T)PX(K/H/R) phosphorylation consensus sequence, which was associated with decreased AMPK-α2 activity. Surprisingly, mutation of Thr485 to alanine in AMPK-α2 results in the abolished Cdk5 effects, demonstrating that Thr485-phosphorylation is critical to AMPK-α2 inhibition by Cdk5. In addition, these alterations in AMPK-α2-phosphorylation and -activity induced by Cdk5 is specific at Thr485. Furthermore, in GK rats, the increased phosphorylated- Thr 485 of AMPK-α2 results in the decreased AMPK-α2 activity, which is correlated with the apoptosis of neurons in hippocamps. After high glucose treatment, the decreased survival showed in AMPK-α2T485A HT-22 cells compared to AMPK-α2WT. The down-regulated of p-CREB, SNAP25, synaptophysin as well as synapsin-1were shown in both GK rats and HT-22 cell line. Meanwhile, pre-treated with either the specific Cdk5-inhibitor (roscovitine) or the antidiabetic AMPK-α2-inhibitor (metformin) could restore the alterations in neuronal protein expression. Our results suggest that Cdk5-mediated phosphorylated- Thr485 in AMPK-α2 may be involved in the pathogenesis of diabetic brain damage.