Multidrug resistance transporter-1 dysfunction perturbs meiosis and Ca2+ homeostasis in oocytes

Abstract

MDR-1 is a transmembrane ATP-dependent effluxer present in organs that transport a variety of xenobiotics and byproducts. Previous findings by our group demonstrated that this transporter is also present in the oocyte mitochondrial membrane and that its mutation led to abnormal mitochondrial homeostasis. Considering the importance of these organelles in the female gamete, we assessed the impact of MDR-1 dysfunction on mouse oocyte quality, with a particular focus on the meiotic spindle organization, aneuploidies, Ca2+ homeostasis, ATP production and mtDNA mutations. Our results demonstrate that young Mdr1 mutant mice produce oocytes characterized by lower quality, with a significant delay in the germinal vesicle (GV) to germinal vesicle breakdown (GVBD) transition, an increased percentage of symmetric divisions, chromosome mis-alignments and a severely altered meiotic spindle shape compared to the wild types. Mutant oocytes exhibit 7000 more single nucleotide polymorphisms (SNPs) in the exomic DNA and twice the amount of mitochondrial DNA SNPs compared to the wild-type ones. Ca2+ analysis revealed the inability of MDR-1 mutant oocytes to manage Ca2+ storage content and oscillations in response to several stimuli and ATP quantification shows that mutant oocytes trend towards lower ATP levels compared to wild types. Finally, 1-year-old mutant ovaries express a lower amount of Sirt1, Sirt3, Sirt5, Sirt6 and Sirt7 compared to wild type levels. These results, together emphasize the importance of MDR-1 in mitochondrial physiology and highlight the influence of MDR-1 on oocyte quality and ovarian aging.

Mechanisms of mitochondrial dysfunction in ovarian aging and potential interventions

“…Moreover, the deletion of spindle defective protein 3 (SPD3) located on the outer membrane of mitochondria directly leads to the abnormal pairing of homologous chromosomes in the meiosis of Caenorhabditis elegans , which may be caused by the inhibition of mitochondrial function ( 132 ). Other proteins that regulate mitochondrial function, such as multidrug resistance protein 1 (MDR1) ( 133 ), regulate ROS efflux from the inner mitochondrial membrane, and RAB7 specific deletion regulates DRP1 phosphorylation ( 134 ), resulting in mitochondrial dysfunction, abnormal spindle shape, and increase of oocyte meiosis chromosome errors. In addition, SIRT3-/- mice aging oocyte exhibited spindle assembly interruption ( 55 ).…”

“… Mitochondria and meiosis in the oocyte (the figure was created with ) MCU mediates the rapid entry of Ca 2+ into mitochondria and provides high energy in an instant ( 129 ). MDR1 regulate ROS efflux from the inner mitochondrial membrane to maintain mitochondrial function ( 133 ). SPD3 may affect the abnormal pairing of homologous chromosomes which may be caused by the inhibition of mitochondrial function ( 132 ).…”

Ex ovo omnia—why don’t we know more about egg quality via imaging?

“…The results showed more than a 3-fold increase in aneuploidies, more abnormal meiotic spindles in the mutant compared to the wildtype, and twice the amount of mitochondrial single nucleotide polymorphisms in mutant compared to wild type mice oocytes ( Figure 4 ). The mutant mouse also displayed lower adenosine triphosphate levels compared to wild type, demonstrating the importance of MDR-1 in oocyte mitochondrial physiology [ 71 ].…”

“… Whole mounted mutant oocytes stained with anti-tubulin antibody (magenta) and DAPI (cyan) to reveal chromosomes and spindle alignment. The bottom left image shows misaligned chromosomes in mutants (34%) compared to wt (15%) [ 71 ]. …”