Comparison of DNA methylation patterns across tissue types in infants with tetralogy of Fallot.

BACKGROUND: Environmental factors may influence the development of tetralogy of Fallot (TOF), and DNA methylation patterns may reveal specific chemical signatures of perturbations during cardiac development. We investigated whether blood and buccal cells could be viable surrogates for myocardium. METHODS: We measured epigenome-wide DNA methylation at 866,895 5'-cytosine-phosphate-guanine-3' (CpG) sites in blood (n=3), buccal cells (n=3), and right ventricular myocardium (n=4) collected from infants with TOF and compared the percent of differentially methylated CpG sites across tissue types. Gene-specific DNA methylation profiles were also analyzed for ten representative genes associated with heart development. Welch's ANOVAs compared general methylation between tissue types. RESULTS: Comparison of DNA methylation profiles across blood, buccal, and myocardium suggested myocardium and buccal samples were most similar, differing in DNA methylation at only 1.3% (11,386) of CpG sites whereas myocardium and blood were most dissimilar, having 146,857 statistically dissimilar methylated CpG sites (~17% dissimilarity; adjusted p < 0.01 for each site). Buccal swabs were significantly more variable (p < .001) than either blood or myocardial samples. In gene-specific analyses, SCO2, GATA4, NOTCH4, WNT7A, and DKK2 showed conserved DNA methylation profiles across tissue types, while HAND1, JAG1, NKX2-5, TBX5 and TBX20 showed more distinctive tissue-specific patterns of DNA methylation. CONCLUSIONS: Compared with blood, buccal tissue more closely mirrors the myocardial methylome, with >10-fold similarity. Nevertheless, both buccal and blood tissue capture highly conserved DNA methylation patterns at specific genetic loci related to cardiac development. Buccal cheek swabs may be a useful surrogate tissue type for future investigations of TOF-specific epigenetic profiles.

Experimental Modal Analysis of an In-situ Clavicle.

Clavicle fractures are widespread, and the understanding of their mechanism of occurrence via dynamic loading is important for prevention and design of protection systems. The proposed work will find the natural frequencies and mode shapes of the human clavicles in-situ, by employing experimental modal analysis (EMA) techniques on cadaver clavicles. The clavicle response to impact depends on mechanical energy transmission to the bone and requires an understanding of bone modal characteristics (natural frequencies and mode shapes), as well as the frequency content of the impact force. These dynamic forces include blunt trauma (sport injury or gun stock impact) or falls (i.e. motorcycle accidents) and exhibit a wide frequency spectrum. Clavicle modes are not well understood, and while researchers performed whole body or individual clavicle EMA, no in-situ EMA has been reported. Since an in-situ clavicle features its natural boundary conditions, mode estimation via EMA was more accurate than one performed for an isolated clavicle.The clavicle EMA used instrumented excitation sources (i.e. impact hammer) and sensors (i.e. triaxial accelerometers). The accelerometer responses gathered at several locations along the cadaver clavicle bone and the exciting force was recorded and through time-frequency transformations, the natural frequencies and mode shapes were identified. Mode shape visualization was performed in ModalView software. While material properties of cadaver clavicles may be influenced by embalming, the results, which include natural frequencies, modes and damping constants, would be more relevant than those obtained for isolated clavicles. These results would be used to design protection systems, define global material properties, and calibrate existing analytical models.