Sodium azide induces mitochondria-mediated apoptosis in PC12 cells through Pgc-1α-associated signaling pathway

Sodium azide (NaN(3)), an inhibitor of cytochrome oxidase, induces the release of excitotoxins via an energy impairment and this, in turn, results in neurodegeneration. The present study aimed to investigate the toxic effects NaN(3) on apoptosis of PC12 cells and its mechanism of action in peroxisome proliferator-activated receptor γ co-activator 1-α (Pgc-1α)-associated signaling pathways. To induce apoptosis, PC12 cells were exposed to NaN(3) (0, 5, 10, 20, 40 and 80 mM) for 12, 24, 48 and 72 h. Cell viability was determined by CCK-8 assay. DAPI staining was employed to additionally examine apoptotic cells and their nuclear changes. Production of reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm) and apoptotic rate were also assessed by flow cytometry. Cellular ATP content was estimated by firefly luciferase assay. In addition, the expression levels of B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein (Bax), phosphorylated (p)-Ca(2+)/calmodulin-dependent protein kinase (CaMK), p-p38 mitogen-activated protein kinase (p38 MAPK), Pgc-1α, nuclear respiratory factor (Nrf)-1, mitochondrial transcription factor A (Tfam), p-extracellular signal-regulated kinase (Erk)1/2, Nrf-2 and complex IV (Cox IV) were determined by western blot analysis. The data suggested that NaN(3) may induce PC12 cell injury and dose-dependently decrease the cell viability. The expression levels of pro-apoptotic proteins Bax and cytochrome c were upregulated, while the expression levels of anti-apoptotic proteins procaspase-3 and Bcl-2 were downregulated. In addition, the phosphorylation of MAPK and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) family members including pan-calcineurin A was increased, in particular the ratios of p-p38/p38 and p-CaMKII/CaMKII. However, the expression levels of Pgc-1α and its associated proteins, including Nrf-1/2, Tfam and p-Erk1/2 were decreased. In addition, mitochondria were the target organelles of NaN(3)-induced toxicity in PC12 cells, which moderated the dissipation of ΔΨm, preserved the cellular ATP content, promoted the production of ROS and increased the apoptotic rate. These results suggested that NaN(3) induced cell death in PC12 cells via Pgc-1α-associated signaling pathways and provided a theoretical basis for additional investigation of the neurotoxic mechanism of NaN(3), with applications in neurodegenerative disorders.