The global rise in metabolic diseases can be attributed to a complex interplay between biology, behavior and environmental factors. This article reviews the current literature concerning DNA methylation-based epigenetic inheritance (intergenerational and transgenerational) of metabolic diseases through the male germ line. Included are a presentation of the basic principles for DNA methylation in developmental programming, and a description of windows of susceptibility for the inheritance of environmentally induced aberrations in DNA methylation and their associated metabolic disease phenotypes. To this end, escapees, genomic regions with the intrinsic potential to transmit acquired paternal epigenetic information across generations by escaping the extensive programmed DNA demethylation that occurs during gametogenesis and in the zygote, are described. The ongoing descriptive and functional examinations of DNA methylation in the relevant biological samples, in conjugation with analyses of noncoding RNA and histone modifications, hold promise for improved delineation of the effect size and mechanistic background for epigenetic inheritance of metabolic diseases.

The risk of developing metabolic diseases is conferred by genetic predisposition from risk genes and by environmental exposures that can manifest in epigenetic changes. The global rise in obesity and type II diabetes has motivated a search for the epigenetic factors underlying these diseases. The possibility of transgenerational inheritance of epigenetic changes raises questions regarding how spermatozoa transmit acquired epigenetic changes that affect the metabolic health of the next generation. The purpose of this review is to describe current key literature concerning small non-coding RNA (sncRNA), specifically (1) the effects of high-fat or low-protein diets on sncRNA presence in spermatozoa; (2) sncRNA transmission from father to offspring; and (3) the functional effects of inherited sncRNA on offspring metabolic phenotype. Current research has identified alterations in the content of sncRNA subtypes, including microRNA (miRNA), Piwi-interacting RNA (piRNA), and transferRNA (tRNA)-derived small non-coding RNA (tsncRNA), in spermatozoa in response to both high-fat diets and low-protein diets. The altered content of spermatozoa sncRNA due to high-fat diets was associated with a changed phenotype in offspring, with offspring displaying insulin resistance, altered body weight, and glucose intolerance. The altered sncRNA content of spermatozoa due to a low-protein diet was associated with altered levels of lipid metabolites in offspring and decreased expression of specific genes starting in two-cell embryos. The current literature suggests that sncRNAs mediate paternal intergenerational epigenetic inheritance and thus has a direct functional importance, as well as possess biomarker potential, for metabolic diseases. Further research is urgently required to identify the specific sncRNAs with the most profound impacts.

We here characterize the usability of archival formalin-fixed paraffin-embedded (FFPE) brain tissue as a resource for genetic and DNA methylation analyses with potential relevance for brain-manifested diseases. We analyzed FFPE samples from The Brain Collection, Aarhus University Hospital Risskov, Denmark (AUBC), constituting 9479 formalin-fixated brains making it one of the largest collections worldwide. DNA extracted from brain FFPE tissue blocks was interrogated for quality and usability in genetic and DNA methylation analyses by different molecular techniques. Overall, we found that DNA quality was inversely correlated with storage time and DNA quality was insufficient for Illumina methylation arrays; data from methylated DNA immunoprecipitation, clonal bisulfite sequencing, and pyrosequencing of BDNF and ST6GALNAC1 suggested that the original methylation pattern is indeed preserved. Proof-of-principle experiments predicting sex based on the methylation status of the X-inactivated SLC9A7 gene, or genotype differences of the Y and X chromosomes, showed consistency between predicted and actual sex for a subset of FFPE samples. In conclusion, even though DNA from FFPE samples is of low quality and technically challenging, it is likely that a subset of samples can provide reliable data given that the methodology used is designed for small DNA fragments. We propose that simple PCR-based quality control experiments at the genetic and DNA methylation level, carried out at the beginning of any given project, can be used to enrich for the best-performing FFPE samples. The apparent preservation of genetic and DNA methylation patterns in archival FFPE samples may bring along new perspectives for the identification of genetic and epigenetic changes associated with brain-manifested diseases.

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