P300/CBP Regulates HIF-1-Dependent Sympathetic Activation and Hypertension by Intermittent Hypoxia

Obstructive sleep apnea (OSA), a widespread breathing disorder, leads to intermittent hypoxia (IH). Patients with OSA and IH-treated rodents exhibit heightened sympathetic nerve activity and hypertension. Previous studies reported transcriptional activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox) by HIF-1 (hypoxia-inducible factor-1) contribute to autonomic dysfunction in IH-treated rodents. Lysine acetylation, regulated by KATs (lysine acetyltransferases) and KDACs (lysine deacetylases), activates gene transcription and plays an important role in several physiological and pathological processes. This study tested the hypothesis that acetylation of HIF-1α by p300/CBP (CREB-binding protein) (KAT) activates Nox transcription, leading to sympathetic activation and hypertension. Experiments were performed on pheochromocytoma-12 cells and rats treated with IH. IH increased KAT activity, p300/CBP protein, HIF-1α lysine acetylation, HIF-1 transcription, and HIF-1 binding to the Nox4 gene promoter in pheochromocytoma-12 cells, and these responses were blocked by CTK7A, a selective p300/CBP inhibitor. Plasma norepinephrine (index of sympathetic activation) and blood pressures were elevated in IH-treated rats. These responses were associated with elevated p300/CBP protein, HIF-1α stabilization, transcriptional activation of Nox2 and Nox4 genes, and reactive oxygen species, and all these responses were absent in CTK7A-treated IH rats. These findings suggest lysine acetylation of HIF-1α by p300/CBP is an important contributor to sympathetic excitation and hypertension by IH.

Altered gene expression of epigenetic modifying enzymes in response to dietary supplementation with linseed oil

Recently we showed that 5% linseed oil (LSO) and 5% safflower oil (SFO) supplementation of cow's diets reduced milk fat yield by 30·38 and 32·42% respectively, accompanied by differential expression of genes and regulation by microRNAs (miRNA). This research communication addresses the hypothesis that epigenetic regulation could be involved in the observed milk fat reduction. Thus, this study investigated the gene expression pattern of major epigenetic modifying enzymes in response to dietary supplementation with LSO or SFO. Twenty-six Canadian Holstein cows in mid lactation were randomly assigned to two groups (13/group) and fed a control diet for 28 d (day -28 to -1) (control period- CP) followed by a treatment period (TP) (control diet supplemented with 5% LSO (LSO treatment) or 5% SFO (SFO treatment) of 28 d (day +1 to +28). After treatment, cows in the two groups were returned to the control diet for another 28 d (day +29 to +56) (post treatment period-PTP). Milk samples were collected on day -1 (CP), +7, +28 (TP) and +56 (PTP) for RNA isolation and measurement of the expression of thirteen epigenetic modifying genes including two DNA methytrasferases (DNMT1, DNMT3A), four histone acetylases (HAT1, KAT2A, KAT5 and CREBBP), five histone deacetylases (HDAC1, HDAC2, HDAC3, SIRT1 and SIRT2) and two histone methytransferases (EHMT2 and PRMT1) by qPCR. Linseed oil supplementation significantly repressed the expression of EHMT2, HDAC2 and HDAC3 on day +7 (P < 0·05) and KAT2A and SIRT2 on day +28 (P < 0·05) as compared with the control period (day -1) while SFO had no effect. When LSO was withdrawn, the expression of some of the genes increased slightly but did not reach control (day -1) levels at the end of the PTP. Our study demonstrated a significant role of LSO in the epigenetic regulation of fatty acid synthesis as compared to SFO. The effect of LSO may be related to its higher degree of unsaturation and might represent a different regulatory mechanism which needs further investigation.