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61 MicroRNA-216a: a cardiac-specific post-transcriptional regulator of capillary rarefaction associated with heart failure {#article-title-2} Background: While cardiomyocytes have been the main subject of extensive research in the past, the role of other cardiac cell types in the pathogenesis of heart failure received considerable less attention. Multiple other cell types, including fibroblasts, endothelial cells and vascular smooth muscle cells make up the heart and increasing evidence suggests that these cell types contribute to myocardial health and disease. Angiogenesis is an important adaptive mechanism of the myocardium to conditions of sustained increased demand. A select number of microRNAs were found to participate in post-myocardial angiogenesis but to date, it is unclear, however, if microRNAs regulate cardiac angiogenesis in the non-ischemic failing myocardium, which represents a clinically more relevant question. Purpose: Establish that non-coding RNAs are main orchestrators of vascular integrity and hemostasis in the heart and changes in expression of the non-coding RNA content in different cardiac cell types underlie defects in neovascularization and progression to heart failure. Results: To identify cardiac angiomiRs we recently completed a functional, genome-wide microRNA knockdown screen in cultured mouse cardiac microvascular endothelial cells. In this setup, we performed the scratch assay by fully automated scratch induction and image capturing and identified several candidate microRNAs. miR-216a, one of those candidates affecting endothelial cell migration, is consistently downregulated in a mouse model of cardiac pressure overload induced by transverse aortic constriction. We generated mice with a somatic gene deletion of miR-216a (miR-216-/-). Ablation of miR-216a induced dramatic effects on cardiac morphology and function. In addition to spontaneous development of pathological cardiac remodeling at baseline, miR-216-/- mice are also extremely sensitive to cardiac stress and die 1-2 weeks after pressure overload or develop severe cardiac phenotypes 3-4 weeks after myocardial infarction. Interestingly, the defects observed correlate with vascular defects including capillary rarefaction and reduced angiogen­­­­ic activity. By combining photoacoustics with high-frequency ultrasound we observed different levels of hypoxia throughout the cardiac tissue confirming lower oxygenation of the miR-216a-/- hearts. The observed effects of miR-216 modulation seem to be related to altered autophagic activity in cardiac endothelial cells. Conclusions: We identified a new angiogenesis-related gene regulatory network where miR-216a underlies the vascular changes associated with pathological cardiac remodeling and/or heart failure. # 62 Divergent effects of pre- and post-conditioning on microvascular function {#article-title-3} Background: A short period of ischemia/reperfusion (I/R) that occurs before a prolonged ischemia (preconditioning; preC) or at reflow (postconditioning; postC) reduces tissue necrosis through activation of regulatory kinases cascades, also reciprocally related, including the GPCR-PKG-PKC cascade and the RISK pathway. In this setting, an important role is played by nitric oxide (NO), which is also the main mediator of endothelium-dependent vasodilation. PreC may also protect microcirculation against I/R injury, while the impact of postC is less clear, and mechanism underlying these effects are not completely elucidated. Purpose: To study the influence of preC and postC on postichemic microcirculation, by specifically evaluating leukocyte recruitment and vasodilating reserve, and to correlate these effects with activation of regulatory kinases. Methods: In rats, cremaster muscle was prepared for in vivo videomicroscopy leaving vascular and neural connections intact. Animals were divided in 4 groups: 1- controls, in which muscle was subjected to 90 min of I and 90 min of R; 2- preC, in which preC was induced before I by 5 min of I and 10 min of R; 3- postC, in which postC was induced at R with 5 cycles of 10 seconds R and 5 seconds I; 4- sham, observed after surgery for an equivalent period of time. Leukocyte recruitment was monitored during I/R; at the end of R, vasodilating endothelium-dependent and -independent reserve was assessed by local superfusion with 10-4 µM acetylcholine and 10-5 µM sodium nitroprusside. Phosphorylation of ERK-1/2, Akt, eNOS, PKCe and GSK3β was measured by Western Blotting on muscle homogenates obtained at the end of experiment in a second set of experiments in which, to avoid possible confounding effects of acetylcholine and sodium nitroprusside on kinase activation, rats were divided in 4 groups as described above but vasodilating challenge was not performed. Results: I/R activated leukocyte recruitment (data not shown) and reduced vasodilating reserve, both endothelium-dependent and independent. Both preC and postC activated kinases and eNOS in a similar degree, and reduced leukocyte recruitment. However, only preC preserved vasodilating reserve (both endothelium-dependent and independent) (*=p