Abstract
Tight control of energy metabolism is essential for normal cell function and organism survival. PKM (pyruvate kinase, muscle) isoforms 1 and 2 originate from alternative splicing of PKM pre-mRNA. They are key enzymes in oxidative phosphorylation and aerobic glycolysis, respectively, and are essential for ATP generation. The PKM1:PKM2 expression ratio changes with development and differentiation, and may also vary under metabolic stress and other conditions. Until now, there have been no reports about the function and regulation of PKM isozymes in oocytes. Here, we demonstrate that PKM1 or PKM2 depletion significantly disrupts ATP levels and mitochondrial integrity, and exacerbates free-radical generation and apoptosis in mouse oocytes. We also show that KBTBD8, a female fertility factor in the KBTBD ubiquitin ligase family, selectively regulates PKM1 levels through a signaling cascade that includes Erk1/2 and Aurora A kinases as intermediates. Finally, using RNA sequencing and protein network analysis, we identify several regulatory proteins that may be govern generation of mature PKM1 mRNA. These results suggest KBTBD8 affects PKM1 levels in oocytes via a KBTBD8→Erk1/2→Aurora A axis, and may also affect other essential processes involved in maintaining oocyte quality.
Highlights
Proper energy metabolism is essential for optimal cell function
Mitochondrial membrane potential was reduced (Figures 1E and 1F), while radical oxygen species (ROS) levels increased significantly (Figures 1G and 1H). These results indicated that PKM1 expression crucially affects multiple aspects of oocyte quality
In the present study we demonstrated for the first time that PKM1 and PKM2 are critical to maintain normal ATP levels in oocytes, and identified an enzymatic cascade (KBTBD8→Erk 1/2→Aurora A) that selectively regulates PKM1 levels without affecting PKM2
Summary
ATP levels decrease with aging, a major risk factor for cardiovascular disease, cancer, diabetes, obesity, and neurodegenerative diseases. PKM (pyruvate kinase, muscle) isozymes are crucial for ATP generation. The embryonic pyruvate kinase isoform PKM2 contains exon 10, is abundant in proliferative cells (including cancer cells) and promotes aerobic glycolysis. In www.aging-us.com contrast, the adult isoform PKM1 contains exon 9, is highly expressed in differentiated cells, and promotes oxidative phosphorylation. Glucose metabolism is critically determined by both their absolute levels and the ratio of PKM1:PKM2. These vary among different cells and tissues and dysfunction or unbalanced expression of either isoform can cause growth arrest or even cell death [5,6,7]
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