No abstract

Discovered a little over two decades ago, small interfering RNAs (siRNAs) and microRNAs (miRNAs) are noncoding RNAs with important roles in gene regulation. They have recently been investigated as novel classes of therapeutic agents for the treatment of a wide range of disorders including cancers and infections. Clinical trials of siRNA- and miRNA-based drugs have already been initiated. siRNAs and miRNAs share many similarities, both are short duplex RNA molecules that exert gene silencing effects at the post-transcriptional level by targeting messenger RNA (mRNA), yet their mechanisms of action and clinical applications are distinct. The major difference between siRNAs and miRNAs is that the former are highly specific with only one mRNA target, whereas the latter have multiple targets. The therapeutic approaches of siRNAs and miRNAs are therefore very different. Hence, this review provides a comparison between therapeutic siRNAs and miRNAs in terms of their mechanisms of action, physicochemical properties, delivery, and clinical applications. Moreover, the challenges in developing both classes of RNA as therapeutics are also discussed.

No abstract

As the first discovered gaseous signaling molecule, nitric oxide (NO) affects a number of cellular processes, including those involving vascular cells. This brief review summarizes the contribution of NO to the regulation of vascular tone and its sources in the blood vessel wall. NO regulates the degree of contraction of vascular smooth muscle cells mainly by stimulating soluble guanylyl cyclase (sGC) to produce cyclic guanosine monophosphate (cGMP), although cGMP-independent signaling [S-nitrosylation of target proteins, activation of sarco/endoplasmic reticulum calcium ATPase (SERCA) or production of cyclic inosine monophosphate (cIMP)] also can be involved. In the blood vessel wall, NO is produced mainly from l-arginine by the enzyme endothelial nitric oxide synthase (eNOS) but it can also be released non-enzymatically from S-nitrosothiols or from nitrate/nitrite. Dysfunction in the production and/or the bioavailability of NO characterizes endothelial dysfunction, which is associated with cardiovascular diseases such as hypertension and atherosclerosis.

T he historical demonstration by Furchgott and Zawadzki 1 that removal of the endothelium abrogates the in vitro vasodilator effect of acetylcholine has led to the identification 30 years ago of nitric oxide (NO) as a major endogenous local regulator of vascular tone. [2][3][4][5][6][7][8][9][10] When the ability of endothelial cells to produce NO is blunted, the ensuing vascular dysfunction sets the stage for the occurrence of cardiovascular disease in general, and atherosclerosis in particular. [11][12][13][14][15] This review focuses, stepby-step, on the bioavailability (production, action, and disposition) of endothelium-derived NO as local regulator of vascular tone in health and disease. Obviously, there is much more than NO in the control of the degree of contraction of underlying vascular smooth muscle cells exerted by the endothelial cells. Indeed, they generate also prostacyclin and hyperpolarizing signals (initiating endothelium-dependent hyperpolarization [EDH] and thus relaxation) and produce vasoconstrictor mediators (endothelium-derived contracting factors and the peptide endothelin-1); those have been discussed elsewhere in detail. 15-22 Endothelial Sources of NO NO SynthaseThree NO synthase (NOS) isozymes, which are encoded by different genes, catalyze the production of NO from l-arginine: neuronal NOS (or NOS-1), cytokine-inducible NOS (iNOS or NOS-2), and endothelial NOS (eNOS or NOS-3).6,23-25 Although iNOS can be induced (by lipopolysaccharides and inflammatory cytokines) and neuronal NOS can be present in the blood vessel

. cIMP synthesized by sGC as a mediator of hypoxic contraction of coronary arteries. Am J Physiol Heart Circ Physiol 307: H328 -H336, 2014. First published June 6, 2014; doi:10.1152/ajpheart.00132.2014cGMP is considered the only mediator synthesized by soluble guanylyl cyclase (sGC) in response to nitric oxide (NO). However, purified sGC can synthesize several other cyclic nucleotides, including inosine 3=,5=-cyclic monophosphate (cIMP). The present study was designed to determine the role of cIMP in hypoxic contractions of isolated porcine coronary arteries. Vascular responses were examined by measuring isometric tension. Cyclic nucleotides were assayed by HPLC tandem mass spectroscopy. Rho kinase (ROCK) activity was determined by measuring the phosphorylation of myosin phosphatase target subunit 1 using Western blot analysis and an ELISA kit. The level of cIMP, but not that of cGMP, was elevated by hypoxia in arteries with, but not in those without, endothelium [except if treated with diethylenetriamine (DETA) NONOate]; the increases in cIMP were inhibited by the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ). Hypoxia (PO2: 25-30 mmHg) augmented contractions of arteries with and without endothelium if treated with DETA NONOate; these hypoxic contractions were blocked by ODQ. In arteries without endothelium, hypoxic augmentation of contraction was also obtained with exogenous cIMP. In arteries with endothelium, hypoxic augmentation of contraction was further enhanced by inosine 5=-triphosphate, the precursor for cIMP. The augmentation of contraction caused by hypoxia or cIMP was accompanied by increased phosphorylation of myosin phosphatase target subunit 1 at Thr 853 , which was prevented by the ROCK inhibitor Y-27632. ROCK activity in the supernatant of isolated arteries was stimulated by cIMP in a concentration-dependent fashion. These results demonstrate that cIMP synthesized by sGC is the likely mediator of hypoxic augmentation of coronary vasoconstriction, in part by activating ROCK. soluble guanylyl cyclase; inosine 3=,5=-cyclic monophosphate; hypoxic vasoconstriction; endothelium A PREVIOUS STUDY reported that acute hypoxia caused a rapid further increase in tension of contracted canine saphenous veins (31). Subsequent findings demonstrated that such a phenomenon, termed hypoxic augmentation of vasoconstriction (5, 15), occurs in a number of blood vessel types (5,7,8,15,21,23,25,26) contracted with norepinephrine (7, 8), phenylephrine (23), PGF 2␣ (15,25), and the TP receptor agonist U-46619 (21), indicating that it is not unique for a specific vasoconstrictor. It occurs in isolated coronary arteries with but not without endothelium (5,15,25,26). The phenomenon is not affected by bosentan, a blocker of endothelin receptors (5), but is prevented by inhibitors of nitric oxide (NO) synthase (5,15,25). Hypoxic augmentation also occurs in arteries without endothelium treated with an exogenous NO donor (5) However, hypoxic augmentation is not accompanied by changes in the intracellular leve...

1 We investigated the eects of short-term exposure to physiological levels of 17b-estradiol and testosterone on vasocontractile responses in porcine coronary artery rings. 2 Concentration-response curves to endothelin-1, 5-hydroxytryptamine, the thromboxane analogue U46619 and KCl were constructed in endothelium-intact and endothelium-disrupted artery rings. 3 Thirty minutes exposure to 17b-estradiol (1 and 30 nM) signi®cantly attenuated vasoconstriction to endothelin-1, 5-hydroxytryptamine and U46619. Conversely, the same concentrations of testosterone signi®cantly potentiated responses elicited by these contractile agents. These inhibitory eects of 17b-estradiol and enhancing actions of testosterone on contractions were endotheliumindependent. KCl-mediated contractions were unaected by the presence of either sex hormones. 4 The oestrogen receptor antagonists, tamoxifen (10 mM) and ICI 182,780 (10 mM), were unable to reverse the inhibitory in¯uence 1 nM 17b-estradiol had on the agonist-mediated contractile responses. Similarly, the androgen receptor antagonists,¯utamide (10 mM) and cyproterone acetate (10 mM), failed to aect the potentiating activities of 1 nM testosterone. 5 The alteration in vasoconstrictive responses observed following acute exposure to either 1 nM 17b-estradiol and 1 nM testosterone were apparent even in the presence of the protein synthesis inhibitor cycloheximide (10 mM) and the transcription inhibitor actinomycin D (10 mM). 6 In conclusion, we report a unique type of sex hormone action on the coronary vasculature. These events occur at low nanomolar concentrations of 17b-estradiol and testosterone, are insensitive to conventional sex hormone receptor antagonists, are not blocked by de novo protein synthesis inhibitors and have rapid time-courses that are uncharacteristic of classical genomic activities.

No abstract