Transgenerational inheritance of hepatic steatosis in mice: sperm methylome is largely reprogrammed and inherited but does not globally influence liver transcriptome

Nutritional challenges and obesity can contribute to the transmission of metabolic diseases through epigenetic mechanisms. Among them, DNA methylation stands out as a potential carrier of information because germline cytosine methylation responds to environmental factors and can be transmitted across generations. Yet, it remains unclear whether inherited DNA methylation plays an active role in the inheritance of metabolic phenotypes or solely influences expression of a few genes that cannot recapitulate the whole metabolic spectrum in the next generation offspring. Previously, we established a mouse model of childhood obesity by reducing litter size at birth. Mice raised in small litters (SL) developed obesity, insulin resistance, and hepatic steatosis. The offspring (SL-F1) and grand-offspring (SL-F2) of SL males also exhibited hepatic steatosis. Here, we aimed to investigate whether germline DNA methylation could serve as a carrier of phenotypic information, hepatic steatosis, between generations. Litter size reduction significantly altered global DNA methylation profile in the sperm of SL-F0 males. Remarkably, 8% of these methylation marks remained altered in the sperm of SL-F1 mice and in the liver of SL-F2 mice. These data suggest that germline DNA methylation is sensitive to environmental challenges and holds significant heritability, either through direct germline transmission and/or through sequential erasure and reestablishment of the marks in the following generations. Yet, DNA methylation did not strongly correlate with the hepatic transcriptome in SL-F2 mice, suggesting that it does not directly drive phenotypes in the F2. As an alternative, germline DNA methylation could potentially influence the phenotype of the next generation by modulating the expression of a reduced number of key transcription factors that, through an amplification cascade, drive phenotypic outcomes in subsequent generations.