Epigenetic Mechanisms and Hypertension

DNA N6-methyladenine modification in hypertension

DNA methylation has a role in the pathogenesis of essential hypertension. DNA N6-methyladenine (6mA) modification as a novel adenine methylation exists in human tissues, but whether it plays a role in hypertension development remains unclear. Here, we reported that the global 6mA DNA level in leukocytes was significantly reduced in patients with hypertension and was reversed with successful treatment. Age, systolic blood pressure, and serum total cholesterol and high-density lipoprotein levels were associated with decreased leukocyte 6mA DNA level. Elevated ALKBH1 (AlkB homolog 1), a demethylase of 6mA, level mediated this dynamic change in 6mA level in leukocytes and vascular smooth muscle cells in hypertension mouse and rat models. Knockdown of ALKBH1 suppressed angiotensin II-induced vascular smooth muscle phenotype transformation, proliferation and migration. ALKBH1-6mA directly and negatively regulated hypoxia inducible factor 1 α (HIF1α), which responded to angiotensin II-induced vascular remodeling. Collectively, our results demonstrate a potential epigenetic role for ALKBH1-6mA regulation in hypertension development, diagnosis and treatment.

Machine learning and clinical epigenetics: a review of challenges for diagnosis and classification

BACKGROUND

Machine learning is a sub-field of artificial intelligence, which utilises large data sets to make predictions for future events. Although most algorithms used in machine learning were developed as far back as the 1950s, the advent of big data in combination with dramatically increased computing power has spurred renewed interest in this technology over the last two decades.

MAIN BODY

Within the medical field, machine learning is promising in the development of assistive clinical tools for detection of e.g. cancers and prediction of disease. Recent advances in deep learning technologies, a sub-discipline of machine learning that requires less user input but more data and processing power, has provided even greater promise in assisting physicians to achieve accurate diagnoses. Within the fields of genetics and its sub-field epigenetics, both prime examples of complex data, machine learning methods are on the rise, as the field of personalised medicine is aiming for treatment of the individual based on their genetic and epigenetic profiles.

CONCLUSION

We now have an ever-growing number of reported epigenetic alterations in disease, and this offers a chance to increase sensitivity and specificity of future diagnostics and therapies. Currently, there are limited studies using machine learning applied to epigenetics. They pertain to a wide variety of disease states and have used mostly supervised machine learning methods.

DNA damage and expression of DNA methylation modulators in urine-derived cells of patients with hypertension and diabetes

Diabetes and hypertension have become the primary causes of chronic kidney disease worldwide. However, there are no established markers for early diagnosis or predicting renal prognosis. Here, we investigated the expression profiles of DNA repair and DNA methylation factors in human urine-derived cells as a possible diagnostic or renal prognosis-predicting marker. A total of 75 subjects, aged 63.3 ± 1.9 years old, were included in this study. DNA and RNA were extracted from 50 mL of urine samples. We evaluated DNA double-strand breaks (DSBs) by the quantitative long distance-PCR method and performed real-time RT-PCR analysis to analyze the expression of renal cell-specific markers, DNA DSB repair factor KAT5, DNA methyltransferases DNMTs, and demethylation enzymes TETs. In patients with hypertension and diabetes, DNA DSBs of the nephrin gene increased with decreased urine KAT5/nephrin expression, consistent with our previous study (Cell Rep 2019). In patients with hypertension, DNA DSBs of the AQP1 gene were increased with elevated urine DNMTs/AQP1 and TETs/AQP1 expression. Moreover, urine DNMTs/AQP1 expression was significantly correlated with the annual eGFR decline rate after adjustment for age, baseline eGFR, the presence of diabetes and the amount of albuminuria, suggesting a possible role as a renal prognosis predictor.

Histone methylation and vascular biology

The vasculature not only transports oxygenated blood, metabolites, and waste products but also serves as a conduit for hormonal communication between distant tissues. Therefore, it is important to maintain homeostasis within the vasculature. Recent studies have greatly expanded our understanding of the regulation of vasculature development and vascular-related diseases at the epigenetic level, including by protein posttranslational modifications, DNA methylation, and noncoding RNAs. Integrating epigenetic mechanisms into the pathophysiologic conceptualization of complex and multifactorial vascular-related diseases may provide promising therapeutic approaches. Several reviews have presented detailed discussions of epigenetic mechanisms not including histone methylation in vascular biology. In this review, we primarily discuss histone methylation in vascular development and maturity, and in vascular diseases.

B6.Rag1 Knockout Mice Generated at the Jackson Laboratory in 2009 Show a Robust Wild-Type Hypertensive Phenotype in Response to Ang II (Angiotensin II)

A key finding supporting a causal role of the immune system in the pathogenesis of hypertension is the observation that RAG1 knockout mice on a C57Bl/6J background (B6.Rag1^-/-), which lack functional B and T cells, develop a much milder hypertensive response to Ang II (angiotensin II) than control C57Bl/6J mice. Here, we report that we never observed any Ang II resistance of B6.Rag1^-/- mice purchased directly from the Jackson Laboratory as early as 2009. B6.Rag1^-/- mice displayed nearly identical blood pressure increases monitored via radiotelemetry and hypertensive end-organ damage in response to different doses of Ang II and different levels of salt intake (0.02%, 0.3%, and 3% NaCl diet). Similarly, restoration of T-cell immunity by adoptive cell transfer did not affect the blood pressure response to Ang II in B6.Rag1^-/- mice. Full development of the hypertension-resistant phenotype in B6.Rag1^-/- mice appears to depend on the action of yet unidentified nongenetic modifiers in addition to the absence of functional T cells.

Preterm birth is associated with epigenetic programming of transgenerational hypertension in mice

Renal and cardiovascular complications of prematurity are well established, notably the development of hypertension in adulthood. However, the underlying molecular mechanisms remain poorly understood. Our objective was to investigate the impact of prematurity on the ontogenesis of renal corticosteroid pathways, to evaluate its implication in perinatal renal complications and in the emergence of hypertension in adulthood. Swiss CD1 pregnant mice were injected with lipopolysaccharides at 18 days of gestation (E18) to induce prematurity at E18.5. Pups were sacrificed at birth, 7 days and 6 months of life. Second (F2) and third (F3) generations, established by mating prematurely born adult females with wild-type males, were also analyzed. Former preterm males developed hypertension at M6 (P < 0.0001). We found robust activation of renal corticosteroid target gene transcription at birth in preterm mice (αENaC (+45%), Gilz (+85%)), independent of any change in mineralocorticoid or glucocorticoid receptor expression. The offspring of the preterm group displayed increased blood pressure in F2 and F3, associated with increased renal Gilz mRNA expression, despite similar MR or GR expression and plasma corticosteroid levels measured by LC-MS/MS. Gilz promoter methylation measured by methylated DNA immunoprecipitation-qPCR was reduced with a negative correlation between methylation and expression (P = 0.0106). Our study demonstrates prematurity-related alterations in renal corticosteroid signaling pathways, with transgenerational inheritance of blood pressure dysregulation and epigenetic Gilz regulation up to the third generation. This study provides a better understanding of the molecular mechanisms involved in essential hypertension, which could partly be due to perinatal epigenetic programming from previous generations.

A propensity towards high blood pressure may be passed down through several generations from adults who were born preterm. People who are born prematurely often suffer from kidney (renal) problems, high blood pressure and cardiovascular disease as they age. Recent research suggests adults born prematurely can pass dysregulated blood pressure to their children. Laetitia Martinerie at INSERM Unit 1185, Le Kremlin Bicêtre and Robert Debré Hospital in Paris, France, and co-workers studied generations of mice to explore how epigenetic alterations, DNA modifications that do not change the DNA code, affect blood pressure from birth through to adulthood. The team identified tissue-specific alterations in renal signaling pathways in premature mice. They also traced the associated overexpression of a gene called Gilz, known to play a role in blood pressure maintenance, through second and third generation mice born to the first generation preterms.

Comparative and Functional Genomic Resource for Mechanistic Studies of Human Blood Pressure-Associated Single Nucleotide Polymorphisms

The objective of the current study is to use comparative and functional genomic analysis to help to understand the biological mechanism mediating the effect of single nucleotide polymorphisms (SNPs) on blood pressure. We mapped 26 585 SNPs that are in linkage disequilibrium with 1071 human blood pressure-associated sentinel SNPs to 9447 syntenic regions in the mouse genome. Approximately 21.8% of the 1071 linkage disequilibrium regions are located at least 10 kb from any protein-coding gene. Approximately 300 blood pressure-associated SNPs are expression quantitative trait loci for a few dozen known blood pressure physiology genes in tissues including specific kidney regions. Blood pressure-associated sentinel SNPs are significantly enriched for expression quantitative trait loci for blood pressure physiology genes compared with randomly selected SNPs (P<0.00023, Fisher exact test). Using a newly developed deep learning method and other methods, we identified SNPs that were predicted to influence the conservation of CTCF (CCCTC-binding factor) binding across cell types, transcription factor binding, mRNA splicing, or secondary structures of RNA including long noncoding RNA. The SNPs were more likely to be located in CTCF-binding regions than what would be expected from the whole genome (P=4.90×10^-7, Pearson χ² test). One example synonymous SNP rs9337951 was predicted to influence the secondary structure of its host mRNA JCAD (junctional cadherin 5 associated) and was experimentally validated to influence JCAD protein expression. These findings provide an extensive comparative and functional genomic resource for developing experiments to test the functional significance of human blood pressure-associated SNPs in human cells and animal models.