Research

Epigenetic inheritance of cancer

Family history is one of the most important risk factors for cancer. However germline mutations in high penetrance genes only explain a portion of cancer susceptibility. Genome-wide association studies (GWAS) of variants have been able to account for a small fraction of familial cancer predisposition, but much of the “missing” cancer heritability remains unexplained. Accumulating evidence suggests that parental life experiences can affect the progeny’s disease predisposition and our lab studies whether epigenetic inheritance plays a role in cancer predisposition.

Adult cancers

The most established research line in our lab focuses on non-genetic inheritance of adult cancers. We were the first to report that maternal exposures to specific nutritional factors and endocrine disrupting chemicals (which can interfere with the body’s hormones) in pregnancy cause transgenerational predisposition to breast cancer in up to three generations of offspring via both the male and female lineages (de Assis et al, 2012). We also showed that this epigenetic predisposition to cancer was associated with DNA methylation changes in stem cell genes in the offspring’s mammary tissues. More recently,  we began to investigate not only how environmentally-induced predisposition to breast cancer can be passed from one generation to the next but also on expanding the concept of epigenetic inheritance to other malignancies. 

To address the question of how environmentally-induced information is passed from one generation to the next, we chose to concentrate on paternal exposures and the male germline to avoid the confounding of pregnancy associated with maternal exposures and the technical difficulties of obtaining enough female germ cells. Our lab was the first to show that paternal obesity and malnutrition alter the sperm non-coding RNAs and predispose the progeny to breast cancer (Fontelles et al, 2016a, Fontelles et al, 2016 b, Fontelles et al, 2021 and da Cruz et al, 2018). In these studies, we showed that paternal factors not only program breast cancer predisposition in daughters, but also alter their tumor metabolism via the AMPK/mTOR axis and the amino-acid, particularly glutamine, utilization. That suggests the molecular characteristics of a tumor can be determined by ancestral exposures and may explain why cancer outcomes differ between populations with different ethnic or social backgrounds. 

We expanded the concept of epigenetic inheritance to other adult malignancies and showed that parental obesity leads to early onset pancreatic ductal adenocarcinoma (PDAC) in offspring (da Cruz et al, 2019). PDAC is a lethal disease with an overall 5-year survival rate of about 9%. This dismal prognosis is due to lack of early detection methods, effective therapies and our poor understanding of the risk factors for this disease that could be used for preventive measures. Our study is the first to show that parental obesity is associated with accelerated development of PDAC in the next generation. One interesting aspect of our study on pancreatic cancer is while parental obesity increased PDAC development in both genders though acinar-to-ductal reprogramming, PDAC development is accelerated in male offspring of obese fathers compared to females. 

More recently, we have turned our attention to epigenetic inheritance of cancer induced by environmental toxicants. Epidemiologic studies suggest that DDT exposure in early development is associated with a five-fold increase in breast cancer risk in women as well metabolic dysfunction. Our data generated in a mouse model, show that female offspring of fathers exposed to the pesticide DDT develop breast tumors that grow substantially faster than those in controls. We also found that offspring’s phenotype is functionally linked to DDT-induced reprogramming of the paternal sperm small RNA load.  This aspect of my research program is addressing an area of critical unmet need and trying to understand the mechanisms by which environmentally-induced epigenetic susceptibility to cancer is transmitted between generations.  If confirmed in humans, our research could lead to a better understanding of non-genetic transmission of cancer susceptibility and what drives tumor growth in a sub-set of patients, resulting in better preventive and therapeutic approaches. Our studies also have an important social justice aspect. In humans, obesity and malnutrition are more prevalent in minority populations. According to the Center for Disease Control and Prevention (CDC), minorities and disadvantaged populations such as African Americans and Mexican-Americans also have the highest circulating concentrations of DDT and other environmental toxicants in the U.S. 

Pediatric cancers

Through an intramural collaboration with Dr. Joanna Kitlinska, a faculty in the Department of Biochemistry and Molecular & Cellular Biology, in addition to adult cancers, we have began to expand the concept of epigenetic inheritance to pediatric cancers. Our study is examining whether epigenetic inheritance plays a role on the incidence and aggressiveness of neuroblastoma (NB), a pediatric tumor of the sympathetic nervous system. While NB appears to have a genetic background, its etiology cannot be explained solely by genetic factors, suggesting that the environment has a role. We propose that parental stress around the time of conception interferes with proper neuronal development in their children and promotes neuroblastoma formation. Our initial studies found that paternal stress accelerates neuroblastoma development in a gender specific manner, but affects tumor aggressiveness in both genders. 

The role of metabolic dysfunction in epigenetic inheritance of cancer

Metabolic dysfunction, namely hyperglycemia and hyperinsulinemia, are known risk factor for many cancers and other chronic diseases. In our studies investigating epigenetic inheritance of cancer, we have consistently observed that metabolic dysfunction in offspring result from a number of paternal exposures. We recently showed that systemic alterations in fact play an important role in cancer predisposition in offspring of obese fathers (Fontelles et al, 2021). We also reported that predisposition to cancer and metabolic dysfunction could also be passed down to the grandchildren (Fontelles et al, 2021)).

Our ongoing studies, show that the propensity to metabolic dysfunction can be inherited in a gender-specific manner, with males developing glucose intolerance and insulin resistance earlier than females. We found that those phenotypes are linked to abnormalities in fetal and placenta development (see next section).

Mechanisms underlying epigenetic predisposition to disease

Our findings discussed above have raised additional questions that we are currently addressing.

The functional role of sperm non-coding RNAs on epigenetic inheritance of cancer

A key question we have been trying to answer is how environmentally induced non-genetic predisposition to cancer is transmitted between generations. Our studies have shown that sperm non-coding RNAs play a role. We found that embryonic microinjection of sperm RNAs from DDT-exposed fathers can replicate the effects of the original paternal exposures on offspring’s cancer phenotypes. Our findings also point to a specific sperm miRNA family that can also recapitulate both the metabolic dysfunction and mammary phenotypes observed in offspring of DDT-exposed males. This aspect of my research program has potentially important clinical implications: Environmentally-induced sperm alterations may be reversible. We found that the DDT-induced sperm RNAs can be reversed by treatment with a hepatic enzyme inducer. If confirmed in humans, specific sperm non-coding RNAs could prove to be useful as biomarkers of exposure in males of reproductive age.

The placenta as a mediator of paternally-induced epigenetic inheritance

Given their short half-life, it is likely that environmentally-induced sperm non-coding RNAs act very early during embryonic development. We are currently addressing what embryonic and, later, fetal changes occur in response to paternal sperm RNA content upon fertilization. We have been examining the potential impact of pre-conception paternal DDT exposure on fetal growth and found that both fetal and placenta size of DDT offspring are significantly smaller compared to controls. The underlying molecular mechanisms behind those findings involve reduced expression of the nutrient sensors in placental tissue. We also found that paternal DDT-associated molecular changes are gender-specific and more pronounced in placentas of DDT male offspring. Our findings likely explain the gender-specific differences in cancer and metabolic phenotypes described in the previous sections.

How does sperm acquire environmentally-induced information?

Another question we are addressing in a newly funded project is how sperm acquires its small non-coding RNA upon environmental exposures given that mature sperm is transcriptionally inactive. Work by other research groups suggest that sperm cells acquire their RNA load as they transit to the reproductive systems. We are examining the mechanisms by which environmentally relevant doses of DDT and its metabolite, DDE, alter the miRNA content in paternal sperm using both in vitro and in vivo systems. While we are using DDT and metabolites in our studies, our findings could prove to be relevant many other environmental toxicants.