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Breakthrough research reveals hypoxia can cause transgenerational reproductive impairment

A team led by The Education University of Hong Kong (EdUHK) has revealed for the first time that hypoxia, a deficiency in oxygen, can cause transgenerational reproductive impairment in fish. This major breakthrough in environmental science was the result of a four-year joint project with team members from four other Hong Kong universities, and is testimony to EdUHK’s high quality research with global impact.

From 2012 to 2016, the team compared the reproductive ability of marine medaka fish and the subsequent three generations of their offspring raised in seawater under normal and low levels of oxygen (hypoxia).

This important discovery has been published in the authoritative scientific journal Nature Communications. Team leader Professor Rudolf Wu, research chair professor of biological sciences at EdUHK, said that “recent climate change has caused the sea temperature to rise and oxygen level to drop. This, together with the large amount of nutrient-rich wastewater being disposed of in the ocean has caused excessive phytoplankton growth, which has led to hypoxia.”

To determine how the imminent threat of hypoxia would affect marine life, the team put marine medaka fish into two groups: one group kept in seawater with normal levels of oxygen and the other group in seawater with low oxygen (the hypoxic group). The offspring produced by the hypoxic group were then divided into two groups, with one returned to seawater with normal oxygen and the other kept under the low oxygen condition. The team then compared the reproductive ability, epigenetics and protein and gene expression of all three groups.

The team found that the second and third generations produced by hypoxic fish had lower levels of male hormones, poorer sperm quality and lower sperm motility and fertilisation success, despite having lived in seawater with a normal oxygen level throughout their lives. The observed reproductive impairment was associated with relevant epigenetic changes and changes in gene and protein expressions. This transgenerational effect revealed is of particular importance to Hong Kong and China, where hypoxia caused by pollution commonly occurs over large areas.

This breakthrough also has significant implications for humans. There is clinic evidence showing that men suffering from sleep apnea, who experience oxygen deprivation while sleeping, have lower sex hormone levels and sex drives. Other studies have shown that people who live at high altitudes with lower oxygen levels have lower sex hormone levels than those who live in lowlands. “Since the epigenetics and sex hormone regulation mechanisms are highly conserved and similar in both fish and humans, hypoxia may also lead to transgenerational reproductive impairment in male adult humans,” said Professor Wu.

This new finding by Professor Wu’s team shows that the adverse consequences of hypoxia are much more severe than currently perceived. “Despite some people arguing that improvements in environmental quality must be cost-effective,” he said, “we must also take into account that pollution may cause permanent reproductive impairments in future generations.”

The EdUHK-led team’s findings sound a very timely warning note for us all – if appropriate environmental protection measures are not taken now, the damage to both human and marine life may well be irreversible and unbearable.

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