Hepatic acyl-coenzyme a:cholesterol acyltransferase-2 expression is decreased in mice with hyperhomocysteinemia

Neural tube defects and epigenetics: role of histone post-translational histone modifications

Neural tube defects (NTDs) are the most common congenital anomalies of the CNS. It is widely appreciated that both genetic and environmental factors contribute to their etiology. The inability to ascribe clear genetic patterns of inheritance to various NTD phenotypes suggests it is possible that epigenetic mechanisms are involved in the etiology of NTDs. In this context, the contribution of DNA methylation as an underlying contributing factor to the etiology of NTDs has been extensively reviewed. Here, an updated accounting of the evidence linking post-translational histone modifications to these birth defects, relying heavily upon studies in humans, and the possible molecular implications inferred from reports based on cellular and animal models, are presented.

Ability of dietary factors to affect homocysteine levels in mice: a review

Homocysteine is associated with several diseases, and a series of dietary factors are known to modulate homocysteine levels. As mice are often used as model organisms to study the effects of dietary hyperhomocysteinemia, we collected data about concentrations of vitamin B₁₂, vitamin B₆, folate, methionine, cystine, and choline in mouse diets and the associated plasma/serum homocysteine levels. In addition, we more closely examined the composition of the control diet, the impact of the mouse strain, sex and age, and the duration of the dietary intervention on homocysteine levels. In total, 113 out of 1103 reviewed articles met the inclusion criteria. In the experimental and control diets, homocysteine levels varied from 0.1 to 280 µmol/l. We found negative correlations between dietary vitamin B₁₂ (rho = − 0.125; p < 0.05), vitamin B₆ (rho = − 0.191; p < 0.01) and folate (rho = − 0.395; p < 0.001) and circulating levels of homocysteine. In contrast, a positive correlation was observed between dietary methionine and homocysteine (methionine: rho = 0.146; p < 0.05). No significant correlations were found for cystine or choline and homocysteine levels. In addition, there was no correlation between the duration of the experimental diets and homocysteine levels. More importantly, the data showed that homocysteine levels varied widely in mice fed control diets as well. When comparing control diets with similar nutrient concentrations (AIN-based), there were significant differences in homocysteine levels caused by the strain (ANOVA, p < 0.05) and age of the mice at baseline (r = 0.47; p < 0.05). When comparing homocysteine levels and sex, female mice tended to have higher homocysteine levels than male mice (9.3 ± 5.9 µmol/l vs. 5.8 ± 4.5 µmol/l; p = 0.069). To conclude, diets low in vitamin B₁₂, vitamin B₆, or folate and rich in methionine are similarly effective in increasing homocysteine levels. AIN recommendations for control diets are adequate with respect to the amounts of homocysteine-modulating dietary parameters. In addition, the mouse strain and the age of mice can affect the homocysteine level.

Homocysteine levels associate with subtle changes in leukocyte DNA methylation: an epigenome-wide analysis

AIM

Homocysteine (Hcy) is a sensitive marker of one-carbon metabolism. Higher Hcy levels have been associated with global DNA hypomethylation. We investigated the association between plasma Hcy and epigenome-wide DNA methylation in leukocytes.

METHODS

Methylation was measured using Illumina 450 k arrays in 2035 individuals from six cohorts. Hcy-associated differentially methylated positions and regions were identified using meta-analysis.

RESULTS

Three differentially methylated positions cg21607669 (SLC27A1), cg26382848 (AJUBA) and cg10701000 (KCNMA1) at chromosome 19, 14 and 10, respectively, were significantly associated with Hcy. In addition, we identified 68 Hcy-associated differentially methylated regions, the most significant of which was a 1.8-kb spanning domain (TNXB/ATF6B) at chromosome 6.

CONCLUSION

We identified novel epigenetic loci associated with Hcy levels, of which specific role needs to be further validated.

The association and significance of H3K27me3 and a folate metabolic gene ACat2 in neural tube defects

AIM

To study the association between the expression of H3K27me3 and ACat2 (a folate metabolic protein), in order to elucidate the protective mechanism of folic acid (FA) in neural tube defects (NTDs).

METHODS

Eighteen female SD rats were randomly divided into normal, NTD and FA group. NTD group was induced by all-trans retinoic acid (ATRA) at E10d. FA group was fed with FA supplementation since 2 weeks before pregnancy, followed by ATRA induction. At E15d, FA level in the embryonic neural tube was determined by ELISA. Neural stem cells (NSCs) were isolated. Cell proliferation was compared by CCK-8 assay. The differentiation potency was assessed by immunocytochemical staining. H3K27me3 expression was measured by immunofluorescence method and Western blot. ACat2 mRNA expression was detected by qRT-PCR.

RESULTS

Cultured NSCs formed numerous Nestin-positive neurospheres. After 5 days, they differentiated into NSE-positive neurons and GFAP-positive astrocytes. When compared with controls, the FA level in NTD group was significantly lower, the ability of cell proliferation and differentiation was significantly reduced, H3K27me3 expression was increased, and ACat2 mRNA expression was decreased (P <0.05). The intervention of FA notably reversed these changes (P <0.05). H3K27me3 expression was negatively correlated with the FA level (rs = -0.908, P <0.01) and ACat2 level (rs = -0.879, P <0.01) in the neural tube.

CONCLUSION

The increased H3K27me3 expression might cause a disorder of folate metabolic pathway by silencing ACat2 expression, leading to reduced proliferation and differentiation of NSCs, and ultimately the occurrence of NTD. FA supplementation may reverse this process.

Homocysteine and DNA methylation: a review of animal and human literature

Homocysteine (Hcy) is a sulfur-containing non-protein forming amino acid, which is synthesized from methionine as an important intermediate in the one-carbon pathway. High concentrations of Hcy in a condition called hyperhomocysteinemia (HHcy) are an independent risk factor for several disorders including cardiovascular diseases and osteoporotic fractures. Since Hcy is produced as a byproduct of the methyltransferase reaction, alteration in DNA methylation is studied as one of the underlying mechanisms of HHcy-associated disorders. In animal models, elevated Hcy concentrations are induced either by diet (high methionine, low B-vitamins, or both), gene knockouts (Mthfr, Cbs, Mtrr or Mtr) or combination of both to investigate their effects on DNA methylation or its markers. In humans, most of the literature involves case-control studies concerning patients. The focus of this review is to study existing literature on HHcy and its role in relation to DNA methylation. Apart from this, a few studies investigated the effect of Hcy-lowering trials on restoring DNA methylation patterns, by giving a folic acid or B-vitamin supplemented diet. These studies which were conducted in animal models as well as humans were included in this review.

Epigenetic regulation of cholesterol homeostasis

Although best known as a risk factor for cardiovascular disease, cholesterol is a vital component of all mammalian cells. In addition to key structural roles, cholesterol is a vital biochemical precursor for numerous biologically important compounds including oxysterols and bile acids, as well as acting as an activator of critical morphogenic systems (e.g., the Hedgehog system). A variety of sophisticated regulatory mechanisms interact to coordinate the overall level of cholesterol in cells, tissues and the entire organism. Accumulating evidence indicates that in additional to the more “traditional” regulatory schemes, cholesterol homeostasis is also under the control of epigenetic mechanisms such as histone acetylation and DNA methylation. The available evidence supporting a role for these mechanisms in the control of cholesterol synthesis, elimination, transport and storage are the focus of this review.