Abstract
Age-associated decline in oocyte quality is one of the dominant factors of low fertility. Aging alters several key processes, such as telomere lengthening, cell senescence, and cellular longevity of granulosa cells surrounding oocyte. To investigate the age-dependent molecular changes, we examined the expression, localization, and correlation of telomerase reverse transcriptase (TERT) and β-Klotho (KLB) in bovine granulosa cells, oocytes, and early embryos during the aging process. Herein, cumulus-oocyte complexes (COCs) obtained from aged cows (>120 months) via ovum pick-up (OPU) showed reduced expression of β-Klotho and its co-receptor fibroblast growth factor receptor 1 (FGFR1). TERT plasmid injection into pronuclear zygotes not only markedly enhanced day-8 blastocysts’ development competence (39.1 ± 0.8%) compared to the control (31.1 ± 0.5%) and D-galactose (17.9 ± 1.0%) treatment groups but also enhanced KLB and FGFR1 expression. In addition, plasmid-injected zygotes displayed a considerable enhancement in blastocyst quality and implantation potential. Cycloastragenol (CAG), an extract of saponins, stimulates telomerase enzymes and enhances KLB expression and alleviates age-related deterioration in cultured primary bovine granulosa cells. In conclusion, telomerase activation or constitutive expression will increase KLB expression and activate the FGFR1/β-Klotho pathway in bovine granulosa cells and early embryos, inhibiting age-related malfunctioning.
Highlights
The female reproductive system is more vulnerable to aging than other parts of the body, due to which women older than 35 years typically exhibit low fertility [1]
To identify the relationship between KLB and aging in bovine embryos, we administered antibodies specific for β-Klotho and its co-receptor, fibroblast growth factor receptor 1 (FGFR1), to cumulus-oocyte complexes obtained from 5-to 12 years old Hanwoo cows via ovum pick-up (OPU) (Figure 1A)
By analyzing the expression of β-Klotho and its co-receptor, FGFR1, in granulosa oocyte complexes (COCs) obtained from aged cows via OPU, we found that increasing age significantly reduced the expression of KLB
Summary
The female reproductive system is more vulnerable to aging than other parts of the body, due to which women older than 35 years typically exhibit low fertility [1]. Aging reduces the quality and quantity of granulosa cells, and as a result, the microenvironment (follicular fluid) of the oocyte deteriorates, which declines the oocyte quality [3,4]. Most aged oocytes show decreased fertilization rate, polyspermy, parthenogenesis, structural alteration, and hardening of the zona pellucida [5]. Several intra-oocyte molecular processes are affected by aging, such as chromosomal abnormalities, increased susceptibility to activating stimuli, decrease in maturation promoting factor (MEF), and mitogen-activated protein kinase (MAPK) [5]. Knowledge of molecular biology is necessary to understand age-related malfunctioning in oocytes, their surrounding granulosa cells, and early embryos
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