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Research by Susan Murphy, PhD, Focuses on Effects of Cannabis Use, Preconception Exposures

Thursday, February 22, 2018

Recently published research by Susan Murphy, PhD, Chief of the Division of Reproductive Sciences, and an associate professor at DUMC, in conjunction with co-PI Dr. Heather Stapleton in the Nicholas School of the Environment and colleagues, notes that organophosphate flame retardants altered the methylation of many imprinted genes in human sperm. These observations indicate that the number of sperm with these methylation alterations is increased, albeit by a relatively small percentage. Nevertheless, if one of these sperm were to fertilize an egg, the potential consequences for the developing child are unknown. Research has established that at least one important class of genes, called imprinted genes, manages to escape the widespread demethylation that occurs in a newly formed embryo. All embryonic genes have two copies—one from the mother and one from the father—but for an imprinted gene, one of those copies is silenced. Because imprinted genes are not demethylated after fertilization, they can capture environmentally induced epigenetic information and transmit it to the next generation.

Dr. Murphy and colleagues used this characteristic of imprinted genes to determine how OP flame retardants could impact the methylation in sperm that then could be carried forward to the next generation.

Through a multidisciplinary effort funded by The John Templeton Foundation, Dr. Murphy and her team are now examining the impact of cannabis use on DNA methylation not just at imprinted genes, but throughout the sperm genome. In another project, they are studying the effects of tobacco use on methylation in sperm. Their initial results indicate that use of these substances is also associated with methylation changes in sperm, but they don’t yet know if these changes are transmitted to the next generation, or if the changes can be “washed out” through substance use avoidance for the duration of a spermatogenic cycle (up to 74 days in humans). As the new Chief of the Division of Reproductive Sciences, this is just one of the research areas Dr. Murphy intends to expand, as the results may reveal important information for couples planning to have a baby.

Findings about the research by Dr. Murphy and colleagues recently were published in Environmental Health Perspectives in the article "Chips off the Old Block: How a Father’s Preconception Exposures Might Affect the Health of His Children."