Environmental epigenetics is a branch of epigenetics that studies the effects of external environmental factors on the gene expression of a developing embryo. These factors do not alter the genetic code, but genes affected may be passed down from parent to offspring through epigenetic modifications.
During development, exposure to certain environmental factors can influence epigenetic modifications, which can be harmful to offspring and increase the risk of developmental disorders or disease. Epigenetic modifications such as DNA methylation and histone modification, alter how genes are expressed through turning on or off specific genes, ultimately affecting the embryo's phenotype.
These environmental factors are referred to as triggers and can involve anything that influences normal gene expression without changing the DNA sequence itself. Some of the most common environmental triggers leading to epigenetic change include diet, temperature, lifestyle choices, stress, exposure to chemicals, and exposure to industrial pollutants. These triggers can cause low birth weight, neurological disorders, cancers, autoimmune diseases, and many other malformations.
Anyone with a Genome is Predisposed to Epigenetic Effects
But, who's most at risk?
Environmental exposures primarily affect embryos and children, but exposure can occur throughout your lifetime, and the effects can be lifelong and passed on.
Due to the complexity of fertilization, it is not completely known how the germline mechanism works throughout generations, but epigenetic reprogramming is well known. Epigenetic reprogramming occurs to ensure totipotency and reduce the number of negative gene modifications and mutations. Although this reprogramming occurs in the germ line cells, some modifications will be passed on to the 3rd generation.
A common example of this phenomenon is a grandparent's chemical exposure to the insecticide DDT and materials, like plastic, containing bisphenol A, increasing a grandchild's risk of experiencing early puberty, obesity, and fertility issues. Once a child is born, their genome can be modified by toxins and stress exposure can cause offspring epigenome to rearrange, resulting in disease later in life de Magalhães-Barbosa, M. C., Prata-Barbosa, A., & da Cunha, A. J. L. A. (2022). Toxic stress, epigenetics and child development. Jornal de Pediatria, 98, S13–S18. https://doi.org/10.1016/j.jped.2021.09.007
Examples of Triggers
Nutrients Offspring can experience phenotypic changes depending on their access to nutrients. When nutrients are limited during pregnancy, the offspring's phenotypic expression can be disrupted. Nutrient intake is also important during lactation for the purpose of transferring nutrients to the offspring.
Stress during pregnancy Pregnancy is a significant life event that brings many hormonal changes. Stress during pregnancy can have adverse effects on both humans and animals. These stressors can be emotional or physical and have an impact not only on the mother but on the offspring as well. Understanding the causes and effects of stressors during pregnancy is important for managing the well-being of both mother and offspring.
Exposure to maternal stressors can increase the likelihood of either overexpressing or suppressing DNA expression. When high levels of depression or stress are experienced in animals, it can result in smaller litter sizes and lower birth rates. This is believed to be due to decreased hormone production. Without adequate hormone production, ovulation may be affected, leading to fewer eggs and reduced potential offspring. Hormones also regulate the nutrients available to the offspring and assist in building the immune system. Reduced hormone levels can lead to miscarriages, underdevelopment, and weak offspring.
Oxidative stress in offspring can come from environmental factors or actions. Drinking and smoking are some of the leading causes of birth defects in humans. Drinking during pregnancy can have a significant effect on an unborn child. Brain abnormalities and stunted growth are only two of the numerous impacts of Fetal Alcohol Spectrum Disorder. Smoking during pregnancy is another major oxidative stressor, causing changes in growth genes, and has been linked to premature, undersized babies that may also have cognitive issues throughout life. Smoking is not the only cause of oxidative stress through inhalation; air pollution can also alter gene methylation, potentially increasing the offspring's risk of early-onset vascular disease.
Extreme stress during pregnancy can cause changes in the baby's stress response gene (NR3C1), which regulates cortisol levels in the body. These changes can cause sensitivity to stress later on in life. This can lead to anxiety, depression, and attention deficits in both children and adults. Early stress can also impact brain development, leading to long-lasting effects on mental health and behavior.
There are many clinically proven ways to manage stress during pregnancy. Meditation, yoga, and breathing exercises have been proven to lower stress hormone levels and can decrease prenatal depression and anxiety. When the expectant mother experiences less stress, it also reduces stress for the baby, leading to better health outcomes for both mother and child.
Temperature Changes in temperature can have varied effects on an organism. DNA methylation can be impacted by temperature when the temperature deviates from its normal value, preventing regular processes from taking place. Temperature can be considered a stressor in environmental epigenetics since it has the potential to change how offspring respond and react to their environment. Monarch butterflies are an example of how temperature can impact the survival and fitness of an organism. If exposed to stressors such as varying temperatures, these butterflies may express coloring that deviates from their normal color.
Lifestyle choices Epigenetic marks can result from a number of exposures and choices made by an individual in their lifetime. Exposure to environmental pollutants, psychological stress, dietary choices or restrictions, working habits, and consumption of drugs or alcohol all influence the epigenetics of an individual and what may be passed down to future offspring. Such exposures can affect important processes of epigenetics such as DNA methylation and histone acetylation, influencing the risk for noncommunicable diseases such as obesity.
Physical Activity
Physical activity plays a pivotal role in shaping gene expression through key epigenetic mechanisms, including DNA methylation, histone modifications, and non-coding RNA activity. Regular exercise induces specific changes in DNA methylation patterns, particularly in genes related to metabolism, inflammation, and muscle adaptation, thereby regulating critical physiological pathways without altering the genetic code itself. For instance, both acute and long-term physical activity remodels promoter methylation in human skeletal muscle, improving glucose uptake, insulin sensitivity, and mitochondrial function.
Moreover, exercise promotes beneficial histone modifications, such as increased histone acetylation, which relaxes chromatin structure and facilitates the transcription of genes involved in muscle growth, endurance, and energy metabolism. Additionally, physical activity influences non-coding RNAs like microRNAs, modulating post-transcriptional gene regulation related to muscle repair, cardiovascular function, and immune response.
Exposure Exposure to certain materials or chemicals can cause an epigenetic reaction. The epigenetic causing substances cause issues like altered DNA methylation, CpG islands, chromatin, along with other transcription factors. Environmental epigenetics aims to relate such environmental triggers or substances to phenotypic variation. Numerous studies have demonstrated how exposure to environmental pollutants, such as heavy metals, pesticides, and air pollutants, can induce epigenetic changes in various organisms. For example, research has shown that exposure to pollutants like biphenol A (BPA) and polycyclic aromatic hydrocarbons (PAHs) can lead to DNA methylation changes and histone modifications in plants, animals, and humans.
Epigentic mechanisms play a role in the adaptation of species of changing environmental conditions, including climate change. Studies have shown that organisms can exhibit phenotypic plasticity through epigenetic modifications in response to environmental stressors such as temperature fluctuation, drought, and habitat loss.
Environmental epigenetics has revealed the potential for transgenerational effects, where environmental exposures experienced by one generation can influence the phenotypes and health outcomes of subsequent generations through epigenetic inheritance mechanisms. Studies in various organisms, including plants, insects, and mammals, have shown transgenerational epigenetic effects resulting from parental exposure to stressors such as toxins, dietary changes, and environmental contaminants. Epigenetic modifications can influence gene expression and phenotypic traits in organisms across different trophic levels, with implications for ecosystem stability.
Lemon sharks A real-world example of environmental effects on DNA can be seen in lemon sharks (Negaprion brevirostris) in the Bahamas. After a dredging event, where machinery scrapes mud and debris from the ocean floor, these sharks were exposed to toxic metals like manganese and other pollutants. Scientists found that this pollution caused changes in the shark's DNA Methylation, a process that helps control gene activity. Essentially, the sharks' genes started behaving differently than normal, likely due to the stress of dredging and the toxins in their habitat. This case shows how human activities, like dredging, don't just harm the environment, but they can also trigger hidden changes in animals' DNA, potentially affecting their health and survival.
Plants Plants require certain metals in small amounts for healthy growth, but excessive amounts can become toxic. While plants naturally absorb beneficial metals from soil, they can't distinguish these from harmful metals like mercury, so they take up both. When metal concentrations get too high, they damage plants in two main ways. First, they cause direct harm through oxidative stress, which creates destructive chemical reactions that damage plant cells. Second, they cause indirect harm by occupying spaces where plants normally absorb nutrients, blocking essential elements from entering the plant. The amount of mercury a plant absorbs depends on various factors including soil acidity and the specific plant species, making this a complex environmental issue.
Many types of heavy metals are toxic to plants, such as lead. Typically, land plants absorb lead(Pb) from the soil, most retaining it in their roots with some evidence of foliage uptakes and potential distribution to other plant parts. Calcium and phosphorus can reduce the uptake of lead, a common and toxic soil element that impacts the plant, growth structure, and photosynthesis of the plant. Lead, in particular, inhibits the process by which a plant grows from a seed into a seedling, known as seed germination in various species, by interfering with crucial enzymes. Studies have shown that lead acetate reduces protease and amylase activity in rice endosperm considerably. This interferes with early seeding growth across plant species such as soybean, rice, tomato, barley, maize, and some legumes.