Abnormal early folliculogenesis due to impeded pyruvate metabolism in mouse oocytes

Abstract

Fetal ovarian germ cells show characteristic energy metabolism status, such as enhanced mitochondrial metabolism as well as glycolysis, but their roles in early folliculogenesis are unclear. We show here that inhibition of pyruvate uptake to mitochondria by UK5099 in organ cultures of fetal mouse ovaries resulted in repressed early folliculogenesis without affecting energy production, survival of oocytes, or meiosis. In addition, the abnormal folliculogenesis by UK5099 was partially rescued by α-ketoglutarate and succinate, intermediate metabolites in the TCA cycle, suggesting the importance of those metabolites. The expression of TGFβ-related genes Gdf9 and Bmp15 in ovarian germ cells, which are crucial for folliculogenesis, was downregulated by UK5099, and the addition of recombinant GDF9 partially rescued the abnormal folliculogenesis induced by UK5099. We also found that early folliculogenesis was similarly repressed, as in the culture, in the ovaries of a germ cell-specific knockout of Mpc2, which encodes a mitochondria pyruvate carrier that is targeted by UK5099. These results suggest that insufficient Gdf9 expression induced by abnormal pyruvate metabolism in oocytes results in early follicular dysgenesis, which is a possible cause of defective folliculogenesis in humans.

Metabolic pathways regulating the development and non-genomic heritable traits of germ cells

“…Mitochondrial copy number is increased during oogenesis [ 37 ], and pyruvate and oxygen consumption gradually increase from the primary oocyte stage to the ovulation stage [ 38 ]. Consistent with these observations, the functional importance of FAO and the TCA cycle in oogenesis in pre- and perinatal mouse ovaries has been shown [ 28 ] ( Figs. 1 and 3 ).…”

“…Mitochondrial metabolism-related pathways also play a role in the subsequent developmental stages of fetal mouse germ cells. Metabolic flux analyses revealed that OXPHOS activity is higher in PGCs at E11.5 than the PGCLCs corresponding to PGCs at E9.5 [ 21 ], which gradually decreases by E18.5, but OXPHOS activity in germ cells remains significantly higher than that in gonadal somatic cells at E18.5 [ 28 ]. The evolutionary conservation of active mitochondrial metabolism in PGCs is supported by the observation that the mitochondrial copy number in a cell gradually increases from the migrating stage of human PGCs in embryos to the primordial follicle stage in adults [ 29 ].…”

“…Moreover, α-KG or succinate rescued the effects of UK5099, suggesting that regulation of DNA or histone demethylating enzyme activity by these metabolites is involved in early folliculogenesis via regulation of Gdf9 expression. The role of MPC2 in vivo was confirmed in germ cell-specific Mpc2 knockout mice, in which folliculogenesis in neonatal ovaries was affected similarly to UK5099-treated cultured ovaries [ 28 ].…”

Inheritance of environment-induced phenotypic changes through epigenetic mechanisms

“…Meanwhile, in fetal female germ cells, mitochondrial metabolism as well as protein stability are increased during differentiation, suggesting their possible importance in oogenesis [ 97 ]. Further, pyruvate and fatty acid metabolism are involved in the early steps of oocyte maturation [ 99 ], and the DNA demethylase TET1, whose cofactor is α-KG, plays an important role in regulating meiosis through DNA demethylation of a subset of meiotic genes in oocytes [ 100 ].…”

Nutritional and metabolic control of germ cell fate through O‐GlcNAc regulation

“…Intriguingly, chemical modification of macromolecules (including epigenetic modification of histones and DNA) and metabolic regulation are thought to be closely related (Hayashi & Matsui, 2022 ; Matsui & Hayashi, 2022 ), but reports describing metabolic control of PGC fate determination is limited. We previously performed integrated metabolomic and proteomic analyses of PGCs (Hayashi et al , 2017 , 2020 ; Tanaka et al , 2021 ), and found that sequential conversion of the major energy metabolic pathway from glycolysis to oxidative phosphorylation (OXPHOS) occurs during PGC differentiation and that this conversion plays an important role in reprogramming, survival, and induction of PGCs from pluripotent stem cells. In addition, a more recent study reported that an intermediate metabolite involved in the tricarboxylic acid (TCA) cycle, alpha‐ketoglutarate (α‐KG), plays a role in PGC fate determination via preservation of low H3K9me2 and high H3K27me3 in epiblast like cells (EpiLCs) (Tischler et al , 2019 ).…”