Paraoxonase 2 protects against the CML mediated mitochondrial dysfunction through modulating JNK pathway in human...

Paraoxonase 2 (PON2) a known anti-apoptotic protein, has not been explored against N^ε-(carboxymethyl)lysine (CML), induced mitochondrial dysfunction and apoptosis in human retinal cells. Hence this present study aims to investigate the potential role of PON2 in mitigating CML-induced mitochondrial dysfunction in these cells.

PON2 protein was quantified in HRECs (Human retinal endothelial cells), ARPE-19 (Retinal pigment epithelial cells) cells upon CML treatment and also in cadaveric diabetic retina vs respective controls. ROS production, mitochondrial membrane potential (MMP), mitochondrial permeability transition pore (mPTP) opening, the release of Cyt-c, Bax, Caspase-3, Fis1, Mfn1, Mfn2, mitochondrial morphology, and the signaling pathway was assessed using DCFDA, JC-1, CoCl₂, immunofluorescence or western blotting analysis in both loss-of-function or gain-of-function experiments.

PON2 protein was downregulated in HREC and ARPE-19 cells upon CML treatment as well as in the diabetic retina (p = 0.035). Decrease in PON2 augments Fis1 expression resulting in fragmentation of mitochondria and enhances the ROS production, decreases MMP, facilitates mPTP opening, and induces the release of Cyt-c, which activates the pro-apoptotic pathway. Whereas PON2 overexpression similar to SP600125 (a specific JNK inhibitor) was able to decrease Fis1 (p = 0.036) and reverse the Bcl-2 and Bax ratio, and inhibit the JNK1/2 signaling pathway.

Our results confirm that PON2 has an anti-apoptotic role against the CML mediated mitochondrial dysfunction and inhibits apoptosis through the JNK-Fis1 axis.

We hypothesis that enhancing PON2 may provide a better therapeutic potential against diabetic vascular disease.