Multifaceted roles of Meg3 in cellular senescence and atherosclerosis

BACKGROUND AND AIMS

Long noncoding RNAs are involved in the pathogenesis of atherosclerosis. As long noncoding RNAs maternally expressed gene 3 (Meg3) prevents cellular senescence of hepatic vascular endothelium and obesity-induced insulin resistance, we decided to examine its role in cellular senescence and atherosclerosis.

METHODS AND RESULTS

By analyzing our data and human and mouse data from the Gene Expression Omnibus database, we found that Meg3 expression was reduced in humans and mice with cardiovascular disease, indicating its potential role in atherosclerosis. In Ldlr-/- mice fed a Western diet for 12 weeks, Meg3 silencing by chemically modified antisense oligonucleotides attenuated the formation of atherosclerotic lesions by 34.9% and 20.1% in male and female mice, respectively, revealed by en-face Oil Red O staining, which did not correlate with changes in plasma lipid profiles. Real-time quantitative PCR analysis of cellular senescence markers p21 and p16 revealed that Meg3 deficiency aggravates hepatic cellular senescence but not cellular senescence at aortic roots. Human Meg3 transgenic mice were generated to examine the role of Meg3 gain-of-function in the development of atherosclerosis induced by PCSK9 overexpression. Meg3 overexpression promotes atherosclerotic lesion formation by 29.2% in Meg3 knock-in mice independent of its effects on lipid profiles. Meg3 overexpression inhibits hepatic cellular senescence, while it promotes aortic cellular senescence likely by impairing mitochondrial function and delaying cell cycle progression.

CONCLUSIONS

Our data demonstrate that Meg3 promotes the formation of atherosclerotic lesions independent of its effects on plasma lipid profiles. In addition, Meg3 regulates cellular senescence in a tissue-specific manner during atherosclerosis. Thus, we demonstrated that Meg3 has multifaceted roles in cellular senescence and atherosclerosis.

Long non-coding RNA Meg3 deficiency impairs glucose homeostasis and insulin signaling by inducing cellular senescence of hepatic endothelium in obesity

Obesity-induced insulin resistance is a risk factor for diabetes and cardiovascular disease. However, the mechanisms underlying endothelial senescence in obesity, and how it impacts obesity-induced insulin resistance remain incompletely understood. In this study, transcriptome analysis revealed that the long non-coding RNA (lncRNA) Maternally expressed gene 3 (Meg3) is one of the top differentially expressed lncRNAs in the vascular endothelium in diet-induced obese mice. Meg3 knockdown induces cellular senescence of endothelial cells characterized by increased senescence-associated β–galactosidase activity, increased levels of endogenous superoxide, impaired mitochondrial structure and function, and impaired autophagy. Moreover, Meg3 knockdown causes cellular senescence of hepatic endothelium in diet-induced obese mice. Furthermore, Meg3 expression is elevated in human nonalcoholic fatty livers and nonalcoholic steatohepatitis livers, which positively correlates with the expression of CDKN2A encoding p16, an important hallmark of cellular senescence. Meg3 knockdown potentiates obesity-induced insulin resistance and impairs glucose homeostasis. Insulin signaling is reduced by Meg3 knockdown in the liver and, to a lesser extent, in the skeletal muscle, but not in the visceral fat of obese mice. We found that the attenuation of cellular senescence of hepatic endothelium by ablating p53 expression in vascular endothelium can restore impaired glucose homeostasis and insulin signaling in obesity. In conclusion, our data demonstrate that cellular senescence of hepatic endothelium promotes obesity-induced insulin resistance, which is tightly regulated by the expression of Meg3. Our results suggest that manipulation of Meg3 expression may represent a novel approach to managing obesity-associated hepatic endothelial senescence and insulin resistance.

•LncRNA Meg3 is a top differentially expressed lncRNA in the vascular endothelium in obese mice.

•Meg3 knockdown causes cellular senescence of HUVECs and of hepatic endothelium in obese mice.

•Meg3 expression is elevated in human NAFLD and NASH Nlivers, and correlates with CDKN2A expression -a senescent marker.

•Meg3 knockdown impairs glucose homeostasis and insulin signaling in obese mice.

•Attenuation of hepatic endothelial senescence improves glucose homeostasis and insulin signaling in obese mice.

Transcriptome analysis-identified long noncoding RNA CRNDE in maintaining endothelial cell proliferation, migration, and tube formation

Obesity is a leading risk factor for type-2 diabetes. Diabetes often leads to the dysregulation of angiogenesis, although the mechanism is not fully understood. Previously, long noncoding RNAs (lncRNAs) have been found to modulate angiogenesis. In this study, we asked how the expression levels of lncRNAs change in endothelial cells in response to excessive palmitic acid treatment, an obesity-like condition. Bioinformatics analysis revealed that 305 protein-coding transcripts were upregulated and 70 were downregulated, while 64 lncRNAs were upregulated and 46 were downregulated. Gene ontology and pathway analysis identified endoplasmic reticulum stress, HIF-1 signaling, and Toll-like receptor signaling as enriched after palmitic acid treatment. Moreover, we newly report enrichment of AGE-RAGE signaling pathway in diabetic complications, IL-17 signaling, and cysteine and methionine metabolism by palmitic acid. One lncRNA, Colorectal Neoplasia Differentially Expressed (CRNDE), was selected for further investigation. Palmitic acid induces CRNDE expression by 1.9-fold. We observed that CRNDE knockdown decreases endothelial cell proliferation, migration, and capillary tube formation. These decreases are synergistic under palmitic acid stress. These data demonstrated that lncRNA CRNDE is a regulator of endothelial cell proliferation, migration, and tube formation in response to palmitic acid, and a potential target for therapies treating the complications of obesity-induced diabetes.

LncRNA Meg3 protects endothelial function by regulating the DNA damage response

The role of long non-coding RNAs (lncRNAs) in regulating endothelial function through the DNA damage response (DDR) remains poorly understood. In this study, we demonstrate that lncRNA maternally expressed gene 3 (Meg3) interacts with the RNA binding protein polypyrimidine tract binding protein 3 (PTBP3) to regulate gene expression and endothelial function through p53 signaling ─ a major coordinator of apoptosis and cell proliferation triggered by the DDR. Meg3 expression is induced in endothelial cells (ECs) upon p53 activation. Meg3 silencing induces DNA damage, activates p53 signaling, increases the expression of p53 target genes, promotes EC apoptosis, and inhibits EC proliferation. Mechanistically, Meg3 silencing reduces the interaction of p53 with Mdm2, induces p53 expression, and promotes the association of p53 with the promoters of a subset of p53 target genes. PTBP3 silencing recapitulates the effects of Meg3 deficiency on the expression of p53 target genes, EC apoptosis and proliferation. The Meg3-dependent association of PTBP3 with the promoters of p53 target genes suggests that Meg3 and PTBP3 restrain p53 activation. Our studies reveal a novel role of Meg3 and PTBP3 in regulating p53 signaling and endothelial function, which may serve as novel targets for therapies to restore endothelial homeostasis.