Equine maternal aging affects oocyte lipid content, metabolic function and developmental potential

Abstract

Advanced maternal age is associated with a decline in fertility and oocyte quality. We used novel metabolic microsensors to assess effects of mare age on single oocyte and embryo metabolic function, which has not yet been similarly investigated in mammalian species. We hypothesized that equine maternal aging affects the metabolic function of oocytes and in vitro-produced early embryos, oocyte mitochondrial DNA (mtDNA) copy number, and relative abundance of metabolites involved in energy metabolism in oocytes and cumulus cells. Samples were collected from preovulatory follicles from young (≤14 years) and old (≥20 years) mares. Relative abundance of metabolites in metaphase II oocytes (MII) and their respective cumulus cells, detected by liquid and gas chromatography coupled to mass spectrometry, revealed that free fatty acids were less abundant in oocytes, and more abundant in cumulus cells from old versus young mares. Quantification of aerobic and anaerobic metabolism, respectively measured as oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in a microchamber containing oxygen and pH microsensors, demonstrated reduced metabolic function and capacity in oocytes and day-2 embryos originating from oocytes of old when compared to young mares. In mature oocytes, mtDNA was quantified by real-time PCR, was not different between the age groups and not indicative of mitochondrial function. Significantly more sperm-injected oocytes from young than old mares resulted in blastocysts. Our results demonstrate a decline in oocyte and embryo metabolic activity that potentially contributes to the impaired developmental competence and fertility in aged females.

Oocyte metabolic function, lipid composition, and developmental potential are altered by diet in older mares

“…The development of microsensors that can measure real-time fluctuations in oxygen and pH allows us the ability to deduce single-oocyte aerobic and anaerobic metabolism and quantify them as oxygen consumption rate (OCR) and extracellular acidification rate (ECAR), respectively ( Obeidat et al 2018 , 2019 ). Utilizing this technology, we recently confirmed less-efficient aerobic and anaerobic metabolism in oocytes collected from the dominant, maturing follicles of old compared to young mares, and impaired oocyte metabolism was associated with a significant reduction in developmental potential ( Catandi et al 2019 , 2021 ). The effect of diet on the metabolism of individual oocytes has not been studied.…”

“…Mitochondrial DNA (mtDNA) content of single oocyte (COB, n = 16 and RSS1, n = 18) was quantified by real-time PCR (qPCR) as previously described ( Pasquariello et al 2019 , Catandi et al 2021 ). Kits and supplies from one source (Qiagen) were used unless noted.…”

Maternal age affects equine Day 8 embryo gene expression both in trophoblast and inner cell mass

“…Moreover, after in vitro maturation, higher spindle instability is observed in old versus young mares' oocytes, resulting in increased risks of chromosome misalignment leading to embryo aneuploidy [18][19][20] . Controversial effects of mare age on mitochondria degeneration have been also reported 16,[21][22][23] .…”

Maternal parity affects Day 8 embryo gene expression in old mares

“…Several reproductive parameters are affected by age and mares older than 10 years old can be considered as already old for reproduction as their fertility has already started to progressively decline [for review 4]. Oocytes are particularly affected by maternal age with alterations of spindle stability [5][6][7], altered gene expression [8,9], and altered metabolism [8,[10][11][12] being reported, all suggesting that oocyte developmental potential is reduced in old mares. The resulting embryos were smaller at the same developmental age in most studies [13][14][15][16][17][18][19][20][21][22][23] with altered gene expression [23] and metabolism [11,12], suggesting impaired development that has mainly been related to the oocyte quality.…”

“…Oocytes are particularly affected by maternal age with alterations of spindle stability [5][6][7], altered gene expression [8,9], and altered metabolism [8,[10][11][12] being reported, all suggesting that oocyte developmental potential is reduced in old mares. The resulting embryos were smaller at the same developmental age in most studies [13][14][15][16][17][18][19][20][21][22][23] with altered gene expression [23] and metabolism [11,12], suggesting impaired development that has mainly been related to the oocyte quality. The reproductive tract, however, is also affected by maternal age.…”