Effect of downregulated citrate synthase on oxidative phosphorylation signaling pathway in HEI-OC1 cells

Background Citrate Synthase (Cs) gene mutation (locus ahL4) has been found to play an important role in progressive hearing loss of A/J mice. HEI-OC1 cells have been widely used as an in vitro system to study cellular and molecular mechanisms related to hearing lose. We previously reported the increased apoptosis and the accumulation of reactive oxygen species in shRNACs-1429 cells, a Cs low-expressed cell model from HEI-OCI. The details of the mechanism of ROS production and apoptosis mediated by the abnormal expression of Cs needed to research furtherly. Methods iTRAQ proteomics was utilized to detect the differentially expressed proteins (DEPs) caused by low expression of Cs. The GO and KEGG pathways analysis were performed for annotation of the differentially expressed proteins. Protein-protein interaction network was constructed by STRING online database. Immunoblotting was utilized to confirm the protein levels of the the differentially expressed proteins. Results The differentially expressed proteins were significantly enriched in various signaling pathways mainly related to mitochondrial dysfunction diseases including Parkinson's disease, Alzheimer's disease, Huntington's disease, et al. Most noteworthy, the oxidative phosphorylation pathway was most significantly suppressed in the shRNACs-1429 cells,, in which a total of 10 differentially expressed proteins were enriched and were all downregulated by the abnormal expression of Cs. The downregulations of Ndufb5, Ndufv1 and Uqcrb were confirmed by immunoblotting. Meanwhile, the ATP levels of shRNACs-1429 cells were also reduced. Conclusions These results suggest that low level expression of Cs induces the inhibition of oxidative phosphorylation pathway, which is responsible for the high level production of reactive oxygen species and low level of ATP, leading to the apoptosis of cochlear cells. This study may provide new theories for understanding and therapy of progressive hearing loss.