Ageing is the predominant risk factor for cardiovascular diseases and contributes to a significantly worse outcome in patients with acute myocardial infarction. MicroRNAs (miRNAs) have emerged as crucial regulators of cardiovascular function and some miRNAs have key roles in ageing. We propose that altered expression of miRNAs in the heart during ageing contributes to the age-dependent decline in cardiac function. Here we show that miR-34a is induced in the ageing heart and that in vivo silencing or genetic deletion of miR-34a reduces age-associated cardiomyocyte cell death. Moreover, miR-34a inhibition reduces cell death and fibrosis following acute myocardial infarction and improves recovery of myocardial function. Mechanistically, we identified PNUTS (also known as PPP1R10) as a novel direct miR-34a target, which reduces telomere shortening, DNA damage responses and cardiomyocyte apoptosis, and improves functional recovery after acute myocardial infarction. Together, these results identify age-induced expression of miR-34a and inhibition of its target PNUTS as a key mechanism that regulates cardiac contractile function during ageing and after acute myocardial infarction, by inducing DNA damage responses and telomere attrition.

IntroductionMicroRNAs (miRNAs) are highly conserved, single-stranded noncoding short RNA molecules (18-24 nucleotides) that regulate gene expression at the posttranscriptional level. miRNAs silence gene expression by inhibiting the translation of proteins from mRNAs or by promoting the degradation of mRNAs. After transcription of the primary miRNA transcripts from the genome, their maturation is mediated by the 2 RNase III endonucleases Dicer and Drosha. Then, mature miRNAs are incorporated into the RNA-induced silencing complex, 1 which mediates the binding of the miRNA to the 3Ј-untranslated region (3Ј-UTR) of the target mRNA leading either to translational repression or degradation of the target mRNA. 2 Because miRNAs control specific expression patterns of target genes, miRNAs represent attractive candidates to interfere with neovascularization.Increasing evidence indicates that miRNAs are important regulators of vascular development and angiogenesis. 3,4 In this context, first studies addressed the function of the miRNAprocessing enzymes Dicer and/or Drosha to explore the general role of miRNAs for angiogenesis. Depletion of Dicer in zebrafish or mice revealed an aberrant vessel growth, and silencing of Dicer in endothelial cells reduced in vitro angiogenesis. [5][6][7] To date, several miRs that regulate endothelial cell function and angiogenesis have been identified, 8 including the pro-angiogenic miRs miR-130a, 9 miR-210, 5,10,11 and miR-378. 12 In addition, miR-126 was shown to regulate vascular integrity and angiogenesis during development and in ischemia-induced angiogenesis. [13][14][15] In contrast, miR-221 and miR-222, 7,16 miR-15 and miR-16, 17,18 and members of the miR-17-92 cluster 19,20 inhibit angiogenesis.In our previous study, we found that the members of the miR-23ϳ27ϳ24 cluster, miR-27a and miR-27b, were highly expressed in endothelial cells. 6 In addition, miR-27b was downregulated after Dicer and Drosha silencing, and inhibition of miR-27b significantly reduced endothelial cell sprouting in vitro, 6 indicating that miR-27b exerts pro-angiogenic effects. Recently, Zhou et al demonstrated that the miR-23ϳ27ϳ24 cluster regulates angiogenesis. 21 In muscle stem cells, miR-27b down-regulates Pax3 expression during myogenic differentiation. 22 Moreover, miR-27 down-regulates Runx1 expression during granulocyte differentiation 23 and the nuclear receptor peroxisome proliferatoractivated receptor-␥ (PPAR-␥) in adipocytes. 24 The myocyte enhancer factor 2C (MEF2C) is another important target of miR-27b during heart development. 25 However, the specific functions and targets of miR-27 in endothelial cells are largely unexplored. As the family members miR-27a and miR-27b differ in only one nucleotide and share the same seed sequence, we investigated the specific role of both family members for the angiogenic activity of endothelial cells and determined the effects on neovascularization. Here we identified the angiogenesis inhibitor semaphorin 6A as a The online version of this article contains a ...

Histone deacetylases (HDACs) deacetylate histones and nonhistone proteins, thereby affecting protein activity and gene expression. The regulation and function of the cytoplasmic class IIb HDAC6 in endothelial cells (ECs) is largely unexplored. Here, we demonstrate that HDAC6 is upregulated by hypoxia and is essential for angiogenesis. Silencing of HDAC6 in ECs decreases sprouting and migration in vitro and formation of functional vascular networks in matrigel plugs in vivo. HDAC6 regulates zebrafish vessel formation, and HDAC6-deficient mice showed a reduced formation of perfused vessels in matrigel plugs. Consistently, overexpression of wild-type HDAC6 increases sprouting from spheroids. HDAC6 function requires the catalytic activity but is independent of ubiquitin binding and deacetylation of a-tubulin. Instead, we found that HDAC6 interacts with and deacetylates the actin-remodelling protein cortactin in ECs, which is essential for zebrafish vessel formation and which mediates the angiogenic effect of HDAC6. In summary, we show that HDAC6 is necessary for angiogenesis in vivo and in vitro, involving the interaction and deacetylation of cortactin that regulates EC migration and sprouting.

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