Advanced Glycation End-Product Precursor Methylglyoxal May Lead to Development of Alzheimer’s Disease

Abstract

Introduction

Diabetes mellitus (DM) is characterized by chronic hyperglycemia and diabetic complications. Exacerbated cortical neuronal degeneration was observed in Alzheimer’s disease (AD) patients with DM. In fact, DM is now considered a risk factor of AD, as DM-induced activation of stress responses in the central nervous system (CNS) such as oxidative stress and neuroinflammation may lead to various neurodegenerative disorders. Methylglyoxal (MG) is one of the most reactive advanced glycation end-product (AGE) precursors. Abnormal accumulation of MG is observed in the serum of diabetic patients. As MG is reported to promote brain cells impairment in the CNS, and it is found that AGEs are abnormally increased in the brains of AD patients. Therefore, the effect of MG causing subsequent symptoms of AD was investigated.

Methods

5-week-old C57BL/6 mice were intraperitoneally injected with MG solution for 11 weeks. The Morris water maze (MWM) was used to examine the spatial learning ability and cognition of mice. After MG treatment, MTT assay, real-time PCR analyses, and Western blot were performed to assess the harvested astrocytes and hippocampi.

Results

Significantly longer escape latency and reduced percentage time spent in the target quadrant were observed in the 9-week-MG-treated mice. We have found in both in vitro and in vivo models that MG induced astrogliosis, pro-inflammatory cytokines, AD-related markers, and ERK activation. Further, trend of normalization of the tested markers mRNA expressions were observed after ERK inhibition.

Conclusion

Our in vivo results suggested that MG could induce AD symptoms and in vitro results implied that ERK may regulate the promotion of inflammation and Aβ formation in MG-induced reactive astrocytes. Taken together, MG may participate in the dysfunction of brain cells resulting in possible diabetes-related neurodegeneration by promoting astrogliosis, Aβ production, and neuroinflammation through the ERK pathway. Our findings provide insight of targeting ERK as a therapeutic application for diabetes-induced AD.

Keywords:

• diabetes
• hyperglycemia
• complications
• advanced glycation end products
• astrocytes
• pathways

Abbreviations

AD, Alzheimer’s disease; AGEs, advanced glycation end products; APP, amyloid precursor protein; Aβ, beta amyloid; BACE1, beta site APP cleaving enzyme 1; CNS, central nervous system; DAPI, 4-, 6-diamidino-2-phenylindole; DM, diabetes mellitus; ERK, extracellular-signal-regulated kinase; GFAP, glial fibrillary acidic protein; IL-1β, interleukin 1 beta; IL-6, interleukin-6; JNK, C-Jun N-terminal kinases; MAPK, mitogen-activated protein kinases; MG, methylglyoxal; MTT, 3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide; MWM, Morris water maze; NFTs, neurofibrillary tangles; PS1, presenilin-1; ROS, reactive oxygen species, TGF-β, transforming growth factor beta; TNF-α, tumor necrosis factors-α.

Acknowledgments

The authors thank the staff at the Hong Kong Baptist University for helpful technical assistance.

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

This work was supported by Hong Kong Baptist University. W.Y. Li and C.Y. Lee. are supported by a studentship from the University Grant.