MicroRNA-135a and -200b, potential Biomarkers for Alzheimer׳s disease, regulate β secretase and amyloid precursor protein

• MiR-135a, -200b, and -429 were downregulated in the hippocampi of APP/PS1 transgenic mice.
• MiR-135a could repress the expression and activity of BACE-1 by binding it 3′–UTR.
• MiR-200b and -429 could repress the expression of APP by binding a same seed region of its 3′–UTR.
• Aβ42 could repress miR-200b expression, which might lead to a vicious circle and result in continuous accumulation of Aβ42.
• MiR-200b was a potential biomarker for MCI and DAT.

Amyloid precursor protein (APP) and β-site amyloid precursor protein cleaving enzyme (BACE-1) play important roles in the generation of Alzheimer׳s disease (AD), a progressive neurodegenerative disorder. In the present study, microRNA (miR) microarray was used to analyze the miR expression profiles in the hippocampi from APP/PS1 transgenic and wild type mice. The miRs with significant alteration and putative targets on APP or BACE-1 were retrieved (miR-135a, -200b and -429). The deregulations of these miRs were confirmed in mice and further verified in AD patient samples by qPCR. Primary mouse hippocampal neurons, SH-SY5Y and HEK293 cells were used to study the function of miRs on APP and BACE-1. We found that miR-135a, which was downregulated significantly in hippocampi from APP/PS1 transgenic mice compared with the wild type control, directly interacted with the 3′–UTR of BACE-1 and repressed its expression and activity. On the other hand, miR-200b and -429, which were downregulated significantly in hippocampi from APP/PS1 transgenic mice compared with the wild type control, targeted the 3′–UTR of APP and repressed its expression. Furthermore, Aβ42 could downregulate miR-200b expression which may generate a vicious cycle resulted in accumulating Aβ42. The levels of miR-135a and -200b in the serum of DAT group were significantly lower than that of control groups (P<0.05). The serum miR-200b level of MCI group was higher than that of DAT group (P<0.05) and lower than that of control group (P<0.05). We also found decreased miR-135a and -200b levels in the cerebrospinal fluid of DAT group compared with the control group (P<0.05). In conclusion, these findings showed that miR-135a, -200b and -429 may take part in the progress of AD; miR-200b was of great potential as noninvasive and easily detected blood-based biomarkers of MCI and DAT patients.