Beta-amyloid protein regulates miR-15a and activates Bag5 to influence neuronal apoptosis in Alzheimer's disease.

Objectives: The prevalence of Alzheimer's disease (AD) is increasing globally, however its pathogenesis is still unclear. The evidence showed that the progression of AD was closely related to the apoptosis of nerve cells. This study amis to explore the role and specific mechanism of miR-15a and Bag5 in the apoptosis of nerve cells induced by beta-amyloid protein (Aβ) in AD.

Methods: The AD rat model was constructed by injecting Aβ42 into SD rat brain and the AD cell model was constructed by treating SH-SY5Y cells with Aβ42. The learning and memory ability of rats was detected by Morris Water Maze. Hematoxylin and eosin (HE) staining was used to detect the pathological changes of brain tissues. Nissl staining was used to detect the changes of cell morphology and number in brain tissues. The upstream miRNA that interacted with Bag5 were screened by bioinformatics analysis. Methyl thiazolyl tetrazolium (MTT) assay was used to detect cell proliferation. Flow cytometry was used to detect the apoptosis rate of cells. Real-time reverse transcription PCR (real-time RT-PCR) was used to detect the mRNA levels of miR-15a and Bag5. Western blotting was used to detect the protein expression levels of Bag5, Bax and Caspase-3. MiR-15a knockdown or overexpression vectors or Bag5 knockdown vectors were transfected into AD rat model and AD cell models, respectively. Luciferase reporter assay was used to verify the binding relationship between miR-15a and Bag5.

Results: Morris Water Maze, HE staining and Nissl staining showed that the rat model of AD was established successfully, and Aβ could induce neuronal apoptosis and inhibit the expression of miR-15a in AD rats. Compared with normal cells, Aβ treatment significantly increased apoptosis rate and Bag5 expression, and weakened cell proliferation and miR-15a (all P<0.01). Overexpression of miR-15a further enhanced the effect of Aβ on cell proliferation and apoptosis, while knockdown of miR-15a expression had the opposite effect (all P<0.01). Luciferase reporter assay confirmed that there was a negative targeting relationship between miR-15a and Bag5. Compared with Bag5 knockdown alone, the co-transfection of miR-15a inhibitor and si-Bag5 significantly increased the cell proliferation ability and mRNA and protein levels of Bag5, and significantly reduced the cell apoptosis rate and the expression of Bax and Caspase-3, animal studies have also shown consistent results (all P<0.01).

Conclusions: Aβ can inhibit the expression of miR-15a, thereby inducing the expression of Bag5 and activating the protective mechanism of Bag5 against Aβ induced apoptosis.