A new study examines how male cannabis use may have an inherited effect on male fertility.
Study: Changes in sperm DNA methylation due to exposure to cannabis extracts are evident in offspring. Image credit: Christoph Burgstedt/Shutterstock
Previous studies have shown how inherited epigenetic changes occur after toxic exposure. The best known of these is sperm DNA modification, which is a stable and heritable covalent change in gene expression without any change in the actual codons. DNA methylation is a key component of sperm formation and maturation, but it can also lead to potentially adverse environmental effects.
Cannabis use during pregnancy has been associated with neurological, musculoskeletal, and cardiovascular developmental problems in offspring. Previous studies have shown changes in sperm methylation after cannabis use in people with partial reversal after stopping the drug. These results are supported by animal experiments using the most potent cannabis derivative, tetrahydrocannabidiol (THC), which have shown hereditary effects of candidate gene methylation on autism, as well as problems with synaptic transmission, voluntary movement, and cognitive impairment.
The current study, published online in the journal Epigenetics and Chromatism, focuses on the consequences of paternal cannabis use pre-conception in terms of persistent changes in methylation throughout the epigenome of the offspring.
Using bisulfite whole genome sequencing (WGBS), a rat study examined exposure to cannabis extract (CE) for 28 days followed by 56 days of withdrawal (early exposure, EE); 28-day CE exposure after the first 56 days of vehicle use (Late Exposure, LE); and control group. All were observed during the same period. The period of 56 days corresponds to one cycle of spermatogenesis.
What did the study show?
Late impact, permanent change
The study showed differences in the degree of epigenetic modification by methylation depending on the time of exposure, although the direction of the changes was the same in both cases. However, under both treatments, mean differences in methylation showed a strong correlation.
The 56-day washout period in the EE rat group was associated with a marked reduction in methylation changes. “This supports the hypothesis that cessation of exposure for at least one semen cycle is effective in minimizing many of the epigenetic effects induced by EC in semen.”
The magnitude of the change was greater with late exposure compared to early exposure, whether hypo- or hypermethylation. An average difference of 15.5% at hypomethylated sites in the LE group contrasts with an 8.5% difference at the same sites in the EE group. For hypermethylated sites, the corresponding differences were 14% versus 7.5%, respectively.
The EE group showed methylation changes in some genes in sperm and brain DNA compared to controls, which were not found in the LE group.
The damage may involve spermatogonial stem cells, which transmit the resulting methylation modification to the spermatozoa derived from them. Spermatozoa obtained from later stage spermatogonia may have been resorbed during the washout period, which explains the above result.
This may indicate persistent or even permanent changes after early exposure to the self-renewing pool of spermatogonial stem cell progenitors, despite a washout period. The finding of very similar methylation profiles in the sperm and some brain tissues of the offspring of EC-exposed rats may indicate that methylation changes associated with paternal exposure to EC before conception may be passed down from generation to generation.
Interestingly, most of the affected genes were involved in development.
These changes in sperm DNA methylation have been confirmed to be hereditary. Sperm from offspring born from EC-exposed males (LE group) showed a marked loss of methylation compared to control offspring. In the EE group, the results were not significant.
The same loss of methylation was also observed in the Mtss1 group in the hippocampus and nucleus accumbens (NAc) compared to control progeny with hypomethylation at 4/9 of the sites analyzed. This gene controls changes in synaptic transmission, indicating the importance of even small changes in methylation due to the extremely strong impact on gene expression.
Changes in gene expression depending on sex
However, this did not lead to a uniform effect on the expression of these genes. Gender analysis revealed a negative relationship in men in the control group and a positive relationship in women. In EC-exposed offspring, a positive association was observed in males and a slight negative association in females.
Interestingly, the inverted patterns of association between gene coding and methylation levels observed between male and female offspring of male rats exposed to EC reflect actual physiological differences in behavioral and cognitive patterns between the offspring of both sexes after paternal exposure to EC.
EC-exposed offspring showed an increase in heart mass in both groups, but when analyzed separately, females showed significant increases in both groups and males only in the EE group. Overall, the effect was only significant in women.
What are the conclusions?
The study demonstrates heritable epigenetic changes in sperm DNA methylation in male rats exposed to EC. She then shows that these changes are passed on to offspring in sperm, as well as in areas of the brain involved in development. Despite the elimination period corresponding to the cycle of spermatogenesis, some of these changes persisted. Previous research suggests that this may be due to stress-induced changes in sperm that affect their differentiation and maturation.
The study also showed cardiomegaly in male and female offspring of male rats exposed to EC prior to conception.
Taken together, these results suggest that paternal exposure to cannabis prior to conception influences intergenerational outcomes. As cannabis legalization expands and consumption increases, it is critical to better understand how one generation’s exposure can affect the health and disease of future generations.”
Further research is needed in the many areas covered by this study, such as the mechanism of heredity, the role of the placenta in transmitting the effects of paternal exposure to offspring, the mechanism of cardiomegaly in the offspring of exposed rats, and whether offspring exhibit other neurodevelopmental or behavioral effects associated with changes gene expression.