Women's age do not face age-related mitochondrial mutation. A new study led by Kateryna Makova at Penn State University and Barbara Arbeithuber at Johannes Kepler University Linz suggests that human egg cells or oocytes, may be uniquely protected against certain age-related mutations. It also offered a new look into how women maintain their fertility in the later stage of their lives. Unlike the most body cells, which accumulate genetic changes over time, oocytes appear to keep their mitochondrial DNA stable, even when the women age. The study is published in Science Advances and is titled 'Allele frequency selection and no age-related increase in human oocyte mitochondrial mutations'. Mitochondria is known as the 'powerhouse' of the cell and are responsible for producing energy. Each mitochondria carries its own DNA, inherited by mothers. While most mitochondrial DNA (mtDNA) mutations are harmless, some can also impair energy production including muscle and nerve cell. Up until now, scientists have thought that mtDNA mutations would accumulate in eggs as women grow older, which also affects fertility and offspring health. However, new research suggests otherwise. How Was The Study Conducted?The researchers collected 80 eggs from 22 women from age 20 to 42, alongside blood and saliva samples from the same participants. They then applied high-precision DNA sequencing to examine the prevalence of mitochondrial mutation. The study found that while mtDNA mutations increased in blood and saliva with age, the same did not occur in oocytes. Human eggs showed 17-to-24 fold fewer mutations. However, even then, they were less likely to appear in regions of the mitochondrial genome which is responsible for the vital cellular functions .“When we think about age-related mutations, we often assume that older cells carry more mutations than younger ones. But expectation is not necessarily the truth,” says Makova. “Human egg cells seem to be protected against some age-related mutations, which could help explain why women can reproduce later in life.”Were Anything Like This Found Before?These findings actually align with the earlier observation in macaques, where the researchers did find that mitochondrial mutations in eggs increased up to animals' reproductive prime and then plateaued. This hinted that evolutionary mechanism would safeguard reproductive cells. It appears that oocytes have evolved to lower their mutation burden, preserving energy production and genetic integrity,” says Makova.Why Is This Discovery So Important?This discovery opens new doors in the fertility research, as more women now choose to delay child birth. This can help one understand how oocytes maintain their mitochondrial health. It can also inform strategies to preserve fertility and improve reproductive outcomes. While the study only examined a small sample, the conclusions are robust. They reveal that human eggs have unique protective mechanisms against age-related mitochondrial mutations. Further research, especially in younger women and larger cohorts, could confirm whether this resilience is universal and uncover the exact molecular processes behind it.
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