Study of oxidative-inflammatory aging (oxi-inflammaging) in the rat ovary : from mechanism to retardation of ovarian aging using Chinese medicine erxian decoction

Abstract

Ovarian aging-induced estrogen deficiency is the major cause of the menopausal syndrome that torments females. Hormone replacement therapy (HRT) relieves menopausal syndrome, but has serious side effects. Deeper insights into mechanisms of ovarian aging and management for ovarian aging-induced diseases are imperative for bettering the quality of life in women.

Ovarian aging is a systematic and age-dependent process. Iron overload and related chronic inflammation and oxidation induce aging, but remain largely unclear, especially in aging ovaries. In this study, novel findings on the mechanism of aberrant up-regulation of ovarian transferrin and ferritin associated with aging was unraveled via a systematic approach, two-dimensional electrophoresis (2DE)-based proteomic analysis, and investigated in ovaries of 3-, 9-, 12-, 16-18- and 22-month-old Sprague-Dawley (SD) rats. With aging, up-regulated ferritin revealed the iron-overload occurred in ovaries of naturally aged rats. Iron-overload could be induced by aberrant up-regulation of ovarian transferrin, ferritin light/heavy chain and iron regulatory protein 2 (IRP2)-mediated transferrin receptor 1 (TfR1). Meanwhile, oxidative stress markers, 3-nitrotyrosine (3-NT) and 4-hydroxy-2-nonenal (HNE) accumulated in aging ovaries. It is demonstrated that activated NF-κB associated with aging possibly induced up-regulation of oxidative and inflammatory factors iNOS and tumor necrosis factor α (TNFα). Down-regulation of an anti-oxidative and anti-inflammatory factor nuclear factor-erythroid 2–related factor 2 (Nrf2) mediated by up-regulated Kelch-like ECH associated protein 1 (Keap1) possibly contributed to a decrease of glutathione peroxidase (GPX)-4. Hence, aberrant up-regulation of transferrin and ferritin via up-regulated TfR1, revealed iron overload, thereby associated with NF-κB-iNOS-mediated ovarian oxi-inflamm-aging and estrogen deficiency in naturally aged rats. This is the first report that the age of 12 months was probably at the final step of ovarian aging in rats and much earlier than the age of 15-18 months which has been well-accepted. Importantly, our discovery could largely promote clinical studies on iron metabolism and ovarian aging and related disease.

Ovarian aging can be systematically regulated by small RNAs via modulating the transcription, translation and decay of RNAs. Systematic approaches, next generation sequencing and bioinformatics analysis, showed that ovarian aging was associated with not only significantly modulated regulatory small RNAs, including sixty-one microRNAs (miRNAs) comprised of forty mature, twenty-eight hairpin, and 3 not-well processed miRNAs, six PIWI-interacting RNAs (piRNAs), five miscellaneous RNAs (miscRNAs) and three small nucleolar RNAs (snoRNAs), but also significantly decreased infrastructural housekeeping transcripts, eleven mitochondrial transfer RNAs (Mt tRNAs) transcripts and one 5S ribosomal RNAs (rRNAs) transcript. The differently expressed mature MicroRNAs, including up-regulated rno-miR-1247-3p, rno-miR-205, rno-miR-341, rno-miR-370-3p, rno-miR-127-3p, etc, and down-regulated rno-miR-185-5p, rno-miR-34c-3p, rno-miR-183-5p, rno-miR-484, rno-miR-196c-5p, etc, possibly play a major role in ovarian aging via inflammation-related pathways, and cancer-related pathways, etc.

Erxian decoction (EXD), a traditional Chinese medicine (TCM) formula, is widely clinically used and has holistic effects on relieving ovarian aging-related disease without obvious side effects. In this study, 2DE-based proteomic analysis revealed that EXD may holistically relieve ovarian aging via promoting steroidogenesis and anti-oxidation, inhibiting progesterone degradation and apoptosis, etc. (481 words)