Time-lapse FRET analysis reveals the ability of Bax dimer to trigger mitochondrial outer membrane permeabilization

Protective Effects and Mechanisms of Dendrobium nobile Lindl. Alkaloids on PC12 Cell Damage Induced by Aβ 25-35

Background

Aβ deposition abnormally in the mitochondria can damage the mitochondrial respiratory chain and activate the mitochondrial-mediated apoptosis pathway, resulting in AD-like symptoms.

Objective

To observe the protective effects of Dendrobium nobile Lindl. alkaloids (DNLA) on Aβ_25-35-induced oxidative stress and apoptosis in PC12 cells explore its possible protective mechanisms.

Methods

PC12 cells were treated with DNLA with different concentrations (0.035 mg/L, 0.3 mg/L, and 3.5 mg/L) for 6 h, followed by administration with Aβ_25-35 (10 μM) for 24 h. MTT assay and flow cytometer observe the effect of DNLA on Aβ_25-35-induced cytotoxicity and apoptosis of PC12 cell. Based on the mitochondrial apoptosis pathway to study the antiapoptotic effect of DNLA on this model and its relationship with oxidative stress, flow cytometer detected the level of reactive oxygen species (ROS), and ELISA kits were used to detect superoxide dismutase activity (SOD) and glutathione (GSH) content in cells. The JC-1 fluorescent staining observed the effect of DNLA on the mitochondrial membrane potential (MMP) with inverted immunofluorescence microscopy. Western blot was used to detect the levels of mitochondrial apoptosis pathway-related protein and its major downstream proteins Bax, Bcl-2, cleaved-caspase-9, and cleaved-caspase-3.

Results

DNLA can significantly improve the viability and apoptosis rate of PC12 cell damage induced by Aβ_25-35. It also can restore the reduced intracellular ROS content and MMP, while SOD activity and GSH content increase significantly. The expression of apoptosis-related protein Bax, cleaved-caspase-9, and cleaved-caspase-3 decreased when the Bcl-2 protein expression was significantly increased.

Conclusion

These findings suggest that it can significantly inhibit the apoptosis of PC12 cell damage induced by Aβ_25-35. The mechanism may reduce the level of cellular oxidative stress and thus inhibit the mitochondrial-mediated apoptosis pathway.

Co-expression of Mcl-1 and Bak induces mitochondrial swelling

We here used fluorescence imaging to explore the effect of co-overexpression of Mcl-1 and Bak/BH3-only proteins on mitochondrial morphology. The cells co-expressing CFP-Mcl-1 and YFP-Bak/BimL/Puma/tBid showed co-localization of Mcl-1 with Bak/Puma/BimL/tBid and also showed the inhibitory action of Mcl-1 on the Bak-, BimL-, Puma- or tBid-mediated cell death. Co-expression of Mcl-1 and Bak but not BH3-only proteins induced time-dependent mitochondrial swelling. Fluorescence resonance energy transfer (FRET) imaging proved the direct binding of Mcl-1 to Bak, BimL, Puma and tBid, respectively. In addition, Mcl-1 prevented Bak oligomerization by retrotranslocating Bak from mitochondria into cytoplasm. Moreover, Mcl-1-Bak complex exhibited a good co-localization with mitochondria, and co-expression of Mcl-1 and Bak for more than 24 h not only induced mitochondrial swelling but also impaired mitochondrial membrane potential. Collectively, co-expression of Mcl-1 and Bak but not BH3-only proteins significantly induced mitochondrial swelling and subsequent loss of mitochondrial membrane potential.