Aberrantly up-regulated expression of transferrin and ferritin induces iron overload and thereby ovarian aging in Sprague-Dawley rats

Abstract

BACKGROUND: The World Health Organization predicted that the total population of postmenopausal women in the world will reach 1200 million in 2030. Ovarian aging is the root cause of menopausal symptoms including skin aging, hot flashes, osteoporosis, mood changes, night sweat, and insomnia. Menopausal symptoms are conventionally treated with hormone replacement therapy which may induce side effects, such as the risk of breast cancer and stroke. However, the mechanism of ovarian aging has not been fully understood. Result from our proteomics study indicated that iron overload is possibly correlated to ovarian aging. But few studies have been performed to investigate the effects of iron overload on ovarian aging. OBJECTIVES: To investigate the effects of iron overload on the process of ovarian aging and unveil it’s the mechanism. METHODS: Naturally aging female SD-rats at different ages including 3, 9, 17 and 22 months old (n=3-4) were used as an animal model of spontaneous aging. The experiments had been approved by the Committee on the Use of Live Animals in Teaching and Research (CULATR Ref. 3203-14) of the Li Ka Shing Faculty of Medicine, the University of Hong Kong. ~10 mg ovarian tissue was homogenized thoroughly in 150 μl ice-cooled PBS (pH=7.4). The tissue homogenates were centrifuged (10,000 g) at 4 ℃ for 20 min. Then the supernatants were retained and used for determination of protein content, iron level and nitrate/nitrite level. Protein concentration was determined using the Bradford assay (Bio-rad, USA) at 595 nm with a microplate reader (Bio-rad, USA). Ovarian iron level was determined with QuantiChromTM Iron Assay Kit (DIFE-250, BioAssay Systems, USA) according to the manufacturer’s instruction. For nitrate/nitrite detection, the tissues homogenates were ultrafiltered with Nanosep 10K Omega Centrifugal Devices (P/N OD010C33, Pall the Corporation, USA) at 14,000 g for 20 min at 4℃, then nitrate/nitrite level was quantified with Nitrate/Nitrite Colorimetric Assay Kit (78001, Cayman Chemical, USA) following the manufacturer’s manual.The levels of the antioxidant enzyme SOD and iron metabolism related proteins including transferrin, ferritin heavy/light chain and transferrin receptor were determined with Western blotting analysis. RESULTS AND DISCUSSION: The ovarian iron levels were significantly higher in the 17 and 22 months old SD rats than those in the 3 and 9 months old one. Similarly, the nitrate/nitrite (final products of NO) level increased with aging, which possibly caused an oxidative stress, and thereby tissue degeneration. However, the level of the antioxidant enzyme SOD decreased with aging, though no significant difference was detected. The levels of proteins associated with iron metabolism including transferrin, ferritin heavy/light chain and transferrin receptor demonstrated a significant increase with aging. CONCLUSION: This study demonstrated that the aberrant up-regulation of transferrin and ferritin induced an iron-overload via transferin receptor 1, thereby oxidative stress, thus inducing ovarian aging. It is worthwhile to conduct further studies on the mechanism of iron homeostasis and the development of a platform for screening of drugs to chelate the excess iron and thereby retarding ovarian aging.