Changes in mitochondrial cytochrome c oxidase mRNA levels with cataract severity in lens epithelia of Japanese patients.

We previously reported that the collapse of ATP production via mitochondrial damage causes ATPase dysfunction, resulting in the onset or progression of lens opacification in cataracts in model rats. In the present study, it was investigated whether the mRNA expression levels of the three subtypes of mitochondrial cytochrome c oxidase (MTCO)1, 2 and 3 and ATP content change with the type and severity of cataracts in human lens. Samples of lens epithelium were collected from Japanese patients during cataract surgery, and the type and severity of the cataracts (grade) were determined according to the WHO classification [cortical (COR), nuclear (NUC), posterior subcapsular (PSC) opacification]. The MTCO1‑3 mRNA expression levels in patients with grade‑1 COR, NUC and PSC opacification were significantly enhanced compared with those of normal patients. The enhanced MTCO1‑3 mRNA levels subsequently decreased in patients with COR, and the MTCO1‑3 mRNA levels and ATP levels in patients with grade‑3 COR were similar to those in normal patients. However, the mRNA expression levels of MTCO3 in patients with grade 3‑NUC opacification and MTCO1‑3 in patients with grade‑3 PSC opacification, along with the ATP content, were significantly lower than in patients without cataracts. In conclusion, it was revealed that ATP production in lens epithelium is enhanced in early‑stage cataracts (grade‑1) in Japanese patients with COR, NUC and PSC opacification. In addition, in severe cataracts (grade‑3), ATP production and content are strongly decreased in Japanese patients with PSC opacification. ATP depletion in human lens epithelium with PSC opacification may promote lens opacification by ATPase dysfunction.