MicroRNA-25 aggravates Aß1-42-induced hippocampal neuron injury in Alzheimer's disease by downregulating KLF2 via the Nrf2 signaling pathway in a mouse model.

Recently, numerous microRNAs (miRNAs) have been considered as key players in the regulation of neuronal processes. The purpose of the present study is to explore the effect of miR-25 on hippocampal neuron injury in Alzheimer's disease (AD) induced by amyloid ß (Aß) peptide fragment 1 to 42 (Aß1-42) via Kruppel-like factor 2 (KLF2) through the nuclear factor-E2-related factor 2 (Nrf2) signaling pathway. A mouse model of AD was established through Aß1-42 induction. The underlying regulatory mechanisms of miR-25 were analyzed through treatment of miR-25 mimics, miR-25 inhibitors, or small interfering RNA (siRNA) against KLF2 in hippocampal tissues and cells isolated from AD mice. The targeting relationship between miR-25 and KLF2 was predicted using a target prediction program and verified by luciferase activity determination. MTT assay was used to evaluate the proliferative ability and flow cytometry to detect cell cycle distribution and apoptosis. KLF2 was confirmed as a target gene of miR-25. When the mice were induced by Aß1-42, proliferation was suppressed while apoptosis was promoted in hippocampal neurons as evidenced by lower levels of KLF2, Nrf2, haem oxygenase, glutathione S transferase α1, glutathione, thioredoxin, and B-cell lymphoma-2 along with higher bax level. However, such alternations could be reversed by treatment of miR-25 inhibitors. These findings indicate that miR-25 may inhibit hippocampal neuron proliferation while promoting apoptosis, thereby aggravating hippocampal neuron injury through downregulation of KLF2 via the Nrf2 signaling pathway.

Mitochondrial Effects of PGC-1alpha Silencing in MPP+ Treated Human SH-SY5Y Neuroblastoma Cells.

The dopaminergic neuron degeneration and loss that occurs in Parkinson's disease (PD) has been tightly linked to mitochondrial dysfunction. Although the aged-related cause of the mitochondrial defect observed in PD patients remains unclear, nuclear genes are of potential importance to mitochondrial function. Human peroxisome proliferator-activated receptor γ coactivator-1alpha (PGC-1α) is a multi-functional transcription factor that tightly regulates mitochondrial biogenesis and oxidative capacity. The goal of the present study was to explore the potential pathogenic effects of interference by the PGC-1α gene on N-methyl-4-phenylpyridinium ion (MPP+)-induced SH-SY5Y cells. We utilized RNA interference (RNAi) technology to probe the pathogenic consequences of inhibiting PGC-1α in the SH-SY5Y cell line. Remarkably, a reduction in PGC-1α resulted in the reduction of mitochondrial membrane potential, intracellular ATP content and intracellular H2O2 generation, leading to the translocation of cytochrome c (cyt c) to the cytoplasm in the MPP+-induced PD cell model. The expression of related proteins in the signaling pathway (e.g., estrogen-related receptor α (ERRα), nuclear respiratory factor 1 (NRF-1), NRF-2 and Peroxisome proliferator-activated receptor γ (PPARγ)) also decreased. Our finding indicates that small interfering RNA (siRNA) interference targeting the PGC-1α gene could inhibit the function of mitochondria in several capacities and that the PGC-1α gene may modulate mitochondrial function by regulating the expression of ERRα, NRF-1, NRF-2 and PPARγ. Thus, PGC-1α can be considered a potential therapeutic target for PD.

Overexpression of PGC-1α Influences Mitochondrial Signal Transduction of Dopaminergic Neurons.

Parkinson's disease (PD) is a common neurodegenerative disease in the elderly. Mitochondrial dysfunction plays an important role in the pathogenesis of PD. Peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) is a powerful transcription factor, interacting with multiple transcription factors and widely involving in the regulation of mitochondrial biogenesis, oxidative stress, and other processes. The present study investigated the neuroprotective effects and signal transduction mechanisms of the overexpression of PGC-1α on N-methyl-4-phenylpyridinium ion (MPP(+))-induced mitochondrial damage in SH-SY5Y cell, establishing the cell model of overexpression of PGC-1α and the cell model of PD by using adenoviral vectors and MPP(+). 3-(4,5-Dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide thiazolyl blue (MTT) assay was used to investigate the effects of MPP(+) and adenovirus on the cell viability of SH-SY5Y cells and the cell viability of experimental groups. Western blot and real-time PCR analysis were used to detect the expression of PGC-1α. Flow cytometry and ELISA were used to detect mitochondrial membrane potential and the level of cytochrome C, respectively. The level of intracellular ATP and H2O2 was measured by multifunctional fluorescence microplate. Western blot analysis and real-time PCR were used to observe the expression of estrogen-related receptor α (ERRα), peroxisome proliferator-activated receptor γ (PPARγ), nuclear respiratory factor (NRF)-1, and NRF-2. Confocal fluorescence analysis was used to observe subcellular localization of PGC-1α in SH-SY5Y cells under the intervention of MPP(+). The expression of PGC-1α messenger RNA and protein significantly increased in Adv-PGC-1α + GFP groups, compared with the control and Adv-GFP groups (P < 0.01). The overexpression of PGC-1α could increase mitochondrial membrane potential, reduce the release of mitochondrial cytochrome C, inhibit H2O2 production, and improve the level of ATP in SH-SY5Y cells. The trend of expression of ERRα, PPARγ, and NRF-1 was more consistent with PGC-1α, the most remarkable change is ERRα, but the expression of NRF-2 has no significant changes. Under the gradually increasing concentration of MPP(+), microscale PGC-1α gradually appeared in the cytoplasm of SH-SY5Y cells. The overexpression of PGC-1α can inhibit MPP(+)-induced mitochondrial damage in SH-SY5Y cells, and PGC-1α may realize the neuroprotective effects via the ERRα, PPARγ, and NRF-1 pathway.