SUMMARY Endothelial cells play essential roles in maintenance of vascular integrity, angiogenesis and wound repair. We show that an endothelial cell-restricted microRNA (miR-126) mediates developmental angiogenesis in vivo. Targeted deletion of miR-126 in mice causes leaky vessels, hemorrhaging, and partial embryonic lethality, due to a loss of vascular integrity and defects in endothelial cell proliferation, migration and angiogenesis. The subset of mutant animals that survives displays defective cardiac neovascularization following myocardial infarction. The vascular abnormalities of miR-126 mutant mice resemble the consequences of diminished signaling by angiogenic growth factors, such as VEGF and FGF. Accordingly, miR-126 enhances the pro-angiogenic actions of VEGF and FGF and promotes blood vessel formation by repressing the expression of Spred-1, an intracellular inhibitor of angiogenic signaling. These findings have important therapeutic implications for a variety of disorders involving abnormal angiogenesis and vascular leakage.

Apoptosis is a pivotal process in embryogenesis and postnatal cell homeostasis and involves the shedding of membranous microvesicles termed apoptotic bodies. In response to tissue damage, the CXC chemokine CXCL12 and its receptor CXCR4 counteract apoptosis and recruit progenitor cells. Here, we show that endothelial cell-derived apoptotic bodies are generated during atherosclerosis and convey paracrine alarm signals to recipient vascular cells that trigger the production of CXCL12. CXCL12 production was mediated by microRNA-126 (miR-126), which was enriched in apoptotic bodies and repressed the function of regulator of G protein (heterotrimeric guanosine triphosphate-binding protein) signaling 16, an inhibitor of G protein-coupled receptor (GPCR) signaling. This enabled CXCR4, a GPCR, to trigger an autoregulatory feedback loop that increased the production of CXCL12. Administration of apoptotic bodies or miR-126 limited atherosclerosis, promoted the incorporation of Sca-1+ progenitor cells, and conferred features of plaque stability on different mouse models of atherosclerosis. This study highlights functions of microRNAs in health and disease that may extend to the recruitment of progenitor cells during other forms of tissue repair or homeostasis.

Atherosclerosis, a hyperlipidemia-induced chronic inflammatory process of the arterial wall, develops preferentially at sites where disturbed laminar flow compromises endothelial cell (EC) function. Here we show that endothelial miR-126-5p maintains a proliferative reserve in ECs through suppression of the Notch1 inhibitor delta-like 1 homolog (Dlk1) and thereby prevents atherosclerotic lesion formation. Endothelial recovery after denudation was impaired in Mir126−/− mice because lack of miR-126-5p, but not miR-126-3p, reduced EC proliferation by derepressing Dlk1. At nonpredilection sites, high miR-126-5p levels in endothelial cells confer a proliferative reserve that compensates for the antiproliferative effects of hyperlipidemia, such that atherosclerosis was exacerbated in Mir126−/− mice. In contrast, downregulation of miR-126-5p by disturbed flow abrogated EC proliferation at predilection sites in response to hyperlipidemic stress through upregulation of Dlk1 expression. Administration of miR-126-5p rescued EC proliferation at predilection sites and limited atherosclerosis, introducing a potential therapeutic approach.

The cystic fibrosis transmembrane conductance regulator (CFTR) gene encodes a chloride channel protein that belongs to the superfamily of ATP binding cassette (ABC) transporters. Phosphorylation by protein kinase A in the presence of ATP activates the CFTR-mediated chloride conductance of the apical membranes. We have identified a novel hydrophilic CFTR binding protein, CAP70, which is also concentrated on the apical surfaces. CAP70 consists of four PDZ domains, three of which are capable of binding to the CFTR C terminus. Linking at least two CFTR molecules via cytoplasmic C-terminal binding by either multivalent CAP70 or a bivalent monoclonal antibody potentiates the CFTR chloride channel activity. Thus, the CFTR channel can be switched to a more active conducting state via a modification of intermolecular CFTR-CFTR contact that is enhanced by an accessory protein.

SummaryThe formation of new blood vessels through the process of angiogenesis is critical in vascular development and homeostasis. Aberrant angiogenesis leads to a variety of diseases, such as ischemia and cancer. Recent studies have revealed important roles for miRNAs in regulating endothelial cell (EC) function, especially angiogenesis. Mice with EC-specific deletion of Dicer, a key enzyme for generating miRNAs, display defective postnatal angiogenesis. Specific miRNAs (angiomiRs) have recently been shown to regulate angiogenesis in vivo. miRNA-126, an EC-restricted miRNA, regulates vascular integrity and developmental angiogenesis. miR-378, miR-296, and the miR-17~92 cluster, contribute to tumor angiogenesis. Manipulating angiomiRs in the settings of pathological vascularization represents a new therapeutic approach.

MicroRNAs (miRNAs) modulate complex physiological and pathological processes by repressing expression of multiple components of cellular regulatory networks. Here we demonstrate that miRNAs encoded by the miR-23∼27∼24 gene clusters are enriched in endothelial cells and highly vascularized tissues. Inhibition of miR-23 and miR-27 function by locked nucleic acid-modified anti-miRNAs represses angiogenesis in vitro and postnatal retinal vascular development in vivo. Moreover, miR-23 and miR-27 are required for pathological angiogenesis in a laser-induced choroidal neovascularization mouse model. MiR-23 and miR-27 enhance angiogenesis by promoting angiogenic signaling through targeting Sprouty2 and Sema6A proteins, which exert antiangiogenic activity. Manipulating miR-23/ 27 levels may have important therapeutic implications in neovascular age-related macular degeneration and other vascular disorders.blindness | MAP kinase signaling | semaphorins | Akt | proangiogenic T he growth of blood vessels through angiogenesis is a delicately controlled process that involves endothelial cell (EC) activation, proliferation, migration, and maturation (1). Physiological angiogenesis is required for normal vascular development as well as vascular homeostasis during adulthood. Pathological angiogenesis, commonly induced by tissue ischemia or inflammation, underlies numerous vascular disorders, such as age-related macular degeneration (AMD), a leading cause of blindness in the elderly (2). Choroidal neovascularization (CNV), which involves abnormal growth of blood vessels in the back of the eye, is a hallmark of neovascular AMD (3). Although the pathogenic mechanisms underlying AMD are still largely unknown, vascular endothelial growth factor (VEGF) has been shown to play a causal role in the development of CNV (4). Anti-VEGF agents have demonstrated efficacy in treating CNV in neovascular AMD (5, 6) but have limited efficacy and potential side effects (7,8).Recent studies have revealed important roles for microRNAs (miRNAs) in cardiovascular diseases and other disorders (9). miRNAs are small noncoding RNAs that negatively regulate gene expression by inducing mRNA degradation or inhibiting translation through binding to the 3′ untranslated region (3′UTR) of target mRNAs (10). Often, miRNAs modulate broad collections of mRNAs encoding multiple components of complex biological pathways. Several miRNAs have been implicated in angiogenesis (11,12). A group of miRNAs has also been shown to be substantially decreased in a laser-induced CNV model (13).The miR-23∼27∼24 clusters are highly expressed in ECs (14-17). Two miR-23∼27∼24 clusters exist in the vertebrate genome: an intergenic miR-23a∼27a∼24-2 cluster and an intronic miR23b∼27b∼24-1 cluster. Members of these clusters are involved in cell cycle control, proliferation, and differentiation of various cell types (18). Here, we show that inhibition of miR-23/27 impairs angiogenesis in vitro and postnatal retinal vascular development in vivo. Moreover, silencing of miR-23/27 suppresses l...

part of the spindle matrix in mitosis. Indeed, the yeast nuclear protein FIN1p contains coiled-coil domains and associates with spindles during mitosis (46). Furthermore, purified FIN1p self-assembles into 10-nm filaments resembling the cytoskeletal intermediate filaments formed in vitro (46). In interphase nuclei of vertebrate cells, LB is concentrated at the nuclear lamina and is also distributed throughout the nucleoplasm. During interphase, the lamins interact with a wide range of nuclear proteins to regulate many nuclear functions as well as nuclear structural integrity. At the onset of mitosis, lamins are phosphorylated by Cdk1, which leads to the disassembly of nuclear lamina (48, 49). The prevailing idea is that the disassembled LB is dispersed throughout the cy-toplasm during mitosis. However, a fraction of LB is associated with the mitotic spindle and/or mitotic chromosomes (19, 26-28). Our studies suggest that LB might perform functions analogous to those of the nuclear lamina to regulate spindle integrity and chromosome organization in mitosis.

Polarization of the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel, to the apical plasma membrane of epithelial cells is critical for vectorial transport of chloride in a variety of epithelia, including the airway, pancreas, intestine, and kidney. However, the motifs that localize CFTR to the apical membrane are unknown. We report that the last 3 amino acids in the COOH-terminus of CFTR (T-R-L) comprise a PDZ-interacting domain that is required for the polarization of CFTR to the apical plasma membrane in human airway and kidney epithelial cells. In addition, the CFTR mutant, S1455X, which lacks the 26 COOH-terminal amino acids, including the PDZ-interacting domain, is mispolarized to the lateral membrane. We also demonstrate that CFTR binds to ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50), an apical membrane PDZ domain-containing protein. We propose that COOH-terminal deletions of CFTR, which represent about 10% of CFTR mutations, result in defective vectorial chloride transport, partly by altering the polarized distribution of CFTR in epithelial cells. Moreover, our data demonstrate that PDZ-interacting domains and PDZ domain-containing proteins play a key role in the apical polarization of ion channels in epithelial cells.