Aminoguanidine Mitigates Methylglyoxal Induced Tau Hyperphosphorylation In SK-N-SH Cells

BackgroundAmong many reactive carbonyl compounds and advanced glycation end products (AGEs) precursors, methylglyoxal (MG) is most likely to contribute to intracellular AGEs formation. Previous studies have reported that AGEs are involved in the pathogenesis of Alzheimer's disease (AD), characterized by formation of neurofibrillary tangles (NFT) which is composed of the hyperphosphorylated tau. The study has reported that MG levels in AD patients were two fold higher than in controls, and the concentrations of MG was five to seven times higher in cerebrospinal fluid than in plasma. Glyoxalase I, for detoxifying specifically MG, has been reported to decrease in the early stage of AD, but increase in the middle and late stage of AD. Another study demonstrated that Glyoxalase I was elevated significantly in P301L mutant tau transgenic mice which developed hyperphosphorylated tau, suggesting a underlying link between MG and tau. MG, the highly active precursor of AGEs, probably plays a critical role in AD which causes the pathological changes of tau protein. So what's the mechanism about MG in tau hyperphosphorylation becomes the most significant to further understanding AD and finding a new way to prevent and treat AD.ObjectiveExplore the phosphorylation of tau protein mediated by MG and its mechanism.MethodsSK-N-SH cells were treated with several different concentrations of MG for different time. Then the optimal concentration and time of MG, when the activity of cells had not changed, were determined as experimental protocol of MG. Under this condition, tau phosphorylation in the MG-treated cells was detected by western blotting and immunofluorescence. The activities of the kinase and phosphatase which associated with tau phosphorylation were also detected to find out their role in MG-induced tau phosphorylation. The inhibitors of relative kinase and aminoguanidine were used to clarify the possible mechanism about MG impact of tau hyperphosphorylation.Results1. We found that there is no significant impact on cells activity which treated with less than 5 mM MG for 1 hour, or 1 mM MG for less than 4 hours.2. We observed that MG could induce the different phosphorylation sites of tau protein when SK-N-SH cells were treated with different concentrations of MG for 1 hour or with 1.0 mM MG for different time.3. The activity of GSK-3βand p38 were increased after treatment MG.4. MG had no effect on activity of JNK, Erk1/2 and cdk5 when MG-induced tau hyperphosphorylation.5. The activity of PP2Ac had no significant change when MG-induced tau hyperphosphorylation.6. The inhibitions of GSK-3βor p38 attenuate the MG-induced tau hyperphosphorylation.7. AG could restore the MG-induced tau hyperphosphorylation.ConclusionsMG can induce AD- like tau hyperphosphorylation and AG can prevent MG induced tau hyperphosphorylation, GSK-3βand p38 involve in the MG-induced tau hyperphosphorylation in vitro.