Fathers exposed to chemicals in plastics can affect the metabolic health of their offspring for two generations, a University of California, Riverside, mouse study reports.

Plastics, which are now ubiquitous, contain endocrine disrupting chemicals, or EDCs, that have been linked to increased risk of many chronic diseases; parental exposure to EDCs, for example, has been shown to cause metabolic disorders, including obesity and diabetes, in the offspring.

Most studies have focused on the impact of maternal EDC exposure on the offspring’s health. The current study, published in the journal Environment International, focused on the effects of paternal EDC exposure.

Led by Changcheng Zhou, a professor of biomedical sciences in the School of Medicine, the researchers investigated the impact of paternal exposure to a phthalate called dicyclohexyl phthalate, or DCHP, on the metabolic health of first-generation (F1) and second-generation (F2) offspring in mice. Phthalates are chemicals used to make plastics more durable.

The researchers found paternal DCHP exposure for four weeks led to high insulin resistance and impaired insulin signaling in F1 offspring. The same effect, but weaker, was seen in F2 offspring.

“We found paternal exposure to endocrine disrupting phthalates may have intergenerational and transgenerational adverse effects on the metabolic health of their offspring,” Zhou said. “To the best of our knowledge, our study is the first to demonstrate this.”

In the case of paternal exposure in the study, intergenerational effects are changes that occur due to direct exposure to a stressor, such as exposure to DCHP of fathers (F0 generation) and his developing sperm (F1 generation). Transgenerational effects are changes passed down to offspring that are not directly exposed to the stressor (for example, F2 generation).

Zhou’s team focused on sperm, specifically, its small-RNA molecules that are responsible for passing information down generations. The researchers used “PANDORA-seq method,” an innovative method that showed DCHP exposure can lead to small-RNA changes in sperm. These changes are undetected by traditional RNA-sequencing methods, which lack the comprehensive overview of the small-RNA profile that PANDORA-seq provides. 

The study used only F1 males to breed with unexposed female mice to generate F2 offspring. The team found that paternal DCHP exposure induced metabolic disorders, such as impaired glucose tolerance, in both male and female F1 offspring, but these disorders were seen only in female F2 offspring. The study did not examine F3 offspring.

“This suggests that paternal DCHP exposure can lead to sex-specific transgenerational effects on the metabolic health of their progenies,” Zhou said. “At this time, we do not know why the disorders are not seen in male F2 offspring.”

Zhou stressed that the impact of exposure to DCHP on human health is not well understood, even though DCHP is widely used in a variety of plastic products and has been detected in food, water, and indoor particulate matter. DCHP has also been found in human urinary and blood samples. Indeed, the U.S. Environmental Protection Agency recently designated DCHP as one of 20 high-priority substances for risk evaluation.

“It’s best to minimize our use of plastic products,” Zhou said. “This can also help reduce plastic pollution, one of our most pressing environmental issues.”

Zhou, whose earlier mouse study showed exposure to DCHP leads to increased plasma cholesterol levels, was joined in the current study by Jingwei Liu, Junchao Shi, Rebecca Hernandez, Xiuchun Li, Pranav Konchadi, Yuma Miyake, and Qi Chen of UCR; and Tong Zhou of University of Nevada, Reno School of Medicine.

The study was partially supported by grants from the National Institutes of Health and American Heart Association. Hernandez was supported by a National Institutes of Health training grant and an American Heart Association predoctoral fellowship.

The title of the paper is “Paternal phthalate exposure-elicited offspring metabolic disorders are associated with altered sperm small RNAs in mice.”

Researchers identified two miRNAs that are downregulated in the disease and an uncommon situation that occurs in which multiple miRNAs regulate the same set of genes. CREDIT Reiko Matsushita

A group of researchers from the Graduate School of Medicine at Nagoya University in Japan have discovered the impact of microRNA (miRNA) on inflammation in lupus in mice. They identified two miRNAs that are downregulated in the disease and an uncommon situation that occurs in which multiple miRNAs regulate the same set of genes.  

Although the human body has many types of RNA, the most important is messenger RNA, which is involved in the creation of proteins in the body. The body also contains miRNA, which binds to regions of the messenger RNA to inhibit protein production and regulate several important bodily functions such as development, growth, and metabolism. Problems with miRNA are associated with several diseases including cancer and HIV. Now, the Nagoya University research group has identified the role of miRNA in systemic lupus erythematosus, a disease in which the human immune system attacks itself. They published their findings in BMC Biology.  

Pairing with the correct messenger RNA target is determined by the ‘seed’ of miRNA, a sequence that determines whether the miRNA can bind or not. The seed is like a ‘key’ to the messenger RNA’s ‘lock.’ However, this is complicated by the nature of miRNA’s interaction with messenger RNA as a single particle of messenger RNA may be regulated by multiple miRNAs and the miRNA-messenger RNA pairs do not have to be an exact match to exert an effect. 

As the effects of a single miRNA on a binding receptor site tend to be modest, stronger effects are often regulated by multiple miRNAs working in concert. This occurs through two processes. The first of these processes is ‘neighborhood’ miRNA co-targeting, where two nearby miRNAs affect messenger RNA. The second, is ‘seed overlap’ miRNA co-targeting, which is similar to the neighborhood type except both have similar nucleotides, so they bind to messenger RNA in such a way that some of their nucleotides overlap.  

Given that altered miRNA expression has been reported in lupus disease, researchers have long suspected a connection. Now, a group of scientists, headed by Professor Hiroshi Suzuki at the Department of Molecular Oncology, and Lecturer Noritoshi Kato and Researcher Hiroki Kitai at the Department of Nephrology at the Nagoya University Graduate School of Medicine, have performed miRNA expression profiling using mice with lupus to investigate the role of miRNA in the disease.  

The researchers found that two microRNAs, miR-128 and miR-148a, were down-regulated in plasmacytoid dendritic cells in lupus patients. As plasmacytoid dendritic cells play a crucial role in antiviral immunity and antibody production, they have been implicated in the initiation and development of several autoimmune and inflammatory diseases, including lupus. Both miR-128 and miR-148a target a gene called KLF4, which is associated with inflammatory control and the production of cytokines that regulate the activity of the immune system. 

“Assuming that the expression levels of the other miRNA are maintained, the downregulation of one miRNA can be compensated for by the other microRNA,” Suzuki explains. “However, when two miRNAs decrease simultaneously, as in lupus disease, alterations in their target — in this case KLF4 — emerge.” 

One of the most important findings of the study was that as miR-128 and miR-148a share common nucleotides, they can bind to messenger RNA using ‘seed overlap’ miRNA co-targeting.  “miR-128 and miR-148a target KLF4 through extensive ‘seed overlap’ miRNA cotargeting. In this case, it negatively regulates the production of inflammatory cytokines,” says Suzuki. “Therefore, this study collectively suggests the complexity of different modes of miRNA cotargeting and the importance of their perturbations in human diseases.” 

The researchers also performed integrative analyses, discovering that “seed overlap” miRNA cotargeting of KLF4 is a prevalent feature in other species. “We found that the conserved overlap site of KLF4 is the same in most species between humans and Coelacanths,” said Suzuki. “Therefore, we expanded these findings by integratively analyzing seed overlap patterns of all miRNAs and the conservation patterns of ‘seed overlap’ target sites.” 

Suzuki and the research team discovered two main conservation classes of miRNA target sites. The first was shared by eutherian mammals, including animals that have a placenta. The second was shared by other animals, including humans and Coelacanths, and has a stronger association with both “seed overlap” and “neighborhood” miRNA cotargeting.  

“Our study provides a comprehensive view of ‘seed overlap’ miRNA cotargeting, which is very important for the process by which lupus develops from the viewpoint of gene regulation and miRNA evolution. These findings highlight the importance of miRNA co-targeting in human pathology and the unique evolutionary aspects of miRNA co-targeting and miRNA target site conservation,” Suzuki explains.  

Suzuki also sees the potential of his research in treating lupus patients: “Testing for downregulation of the two miRNAs may help identify patients with high level of inflammation who may benefit from specific therapeutic development,” he says.