Longitudinal bone growth is determined by endochondral ossification that occurs as chondrocytes in the cartilaginous growth plate undergo proliferation, hypertrophy, cell death, and osteoblastic replacement. The natriuretic peptide family consists of three structurally related endogenous ligands, atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP), and is thought to be involved in a variety of homeostatic processes. To investigate the physiological significance of CNP in vivo, we generated mice with targeted disruption of CNP (Nppc ؊/؊ mice). The Nppc ؊/؊ mice show severe dwarfism as a result of impaired endochondral ossification. They are all viable perinatally, but less than half can survive during postnatal development. The skeletal phenotypes are histologically similar to those seen in patients with achondroplasia, the most common genetic form of human dwarfism. Targeted expression of CNP in the growth plate chondrocytes can rescue the skeletal defect of Nppc ؊/؊ mice and allow their prolonged survival. This study demonstrates that CNP acts locally as a positive regulator of endochondral ossification in vivo and suggests its pathophysiological and therapeutic implication in some forms of skeletal dysplasia.

Achondroplasia is the most common genetic form of human dwarfism, for which there is presently no effective therapy. C-type natriuretic peptide (CNP) is a newly identified molecule that regulates endochondral bone growth through GC-B, a subtype of particulate guanylyl cyclase. Here we show that targeted overexpression of CNP in chondrocytes counteracts dwarfism in a mouse model of achondroplasia with activated fibroblast growth factor receptor 3 (FGFR-3) in the cartilage. CNP prevented the shortening of achondroplastic bones by correcting the decreased extracellular matrix synthesis in the growth plate through inhibition of the MAPK pathway of FGF signaling. CNP had no effect on the STAT-1 pathway of FGF signaling that mediates the decreased proliferation and the delayed differentiation of achondroplastic chondrocytes. These results demonstrate that activation of the CNP-GC-B system in endochondral bone formation constitutes a new therapeutic strategy for human achondroplasia.

Angiotensin (Ang) II has two major receptor isoforms, AT1 and AT2. Currently, AT1 antagonists are undergoing clinical trials in patients with cardiovascular diseases. Treatment with AT1 antagonists causes elevation of plasma Ang II which selectively binds to AT2 and exerts as yet undefined effects. Cardiac AT2 level is low in adult hearts, whereas its distribution ratio is increased during cardiac remodeling and its action is enhanced by application of AT1 antagonists. Although in AT2 knock-out mice sensitivity to the pressor action of Ang II was increased, underlying mechanisms remain undefined. Here, we report the unexpected finding that cardiac-specific overexpression of the AT2 gene using alpha-myosin heavy chain promoter resulted in decreased sensitivity to AT1-mediated pressor and chronotropic actions. AT2 protein undetectable in the hearts of wild-type mice was overexpressed in atria and ventricles of the AT2 transgenic (TG) mice and the proportions of AT2 relative to AT1 were 41% in atria and 45% in ventricles. No obvious morphological change was observed in the myocardium and there was no significant difference in cardiac development or heart to body weight ratio between wild-type and TG mice. Infusion of Ang II to AT2 TG mice caused a significantly attenuated increase in blood pressure response and the change was completely blocked by pretreatment with AT2 antagonist. This decreased sensitivity to Ang II-induced pressor action was mainly due to the AT2-mediated strong negative chronotropic effect and exerted by circulating Ang II in a physiological range that did not stimulate catecholamine release. Isolated hearts of AT2 transgenic mice perfused using a Langendorff apparatus also showed decreased chronotropic responses to Ang II with no effects on left ventricular dp/dt max values, and Ang II-induced activity of mitogen-activated protein kinase was inhibited in left ventricles in the transgenic mice. Although transient outward K+ current recorded in cardiomyocytes from AT2 TG mice was not influenced by AT2 activation, this study suggested that overexpression of AT2 decreases the sensitivity of pacemaker cells to Ang II. Our results demonstrate that stimulation of cardia AT2 exerts a novel antipressor action by inhibiting AT1-mediated chronotropic effects, and that application of AT1 antagonists to patients with cardiovascular diseases has beneficial pharmacotherapeutic effects of stimulating cardiac AT2.

Background-Mitochondrial oxidative stress and damage play major roles in the development and progression of left ventricular (LV) remodeling and failure after myocardial infarction (MI). We hypothesized that overexpression of the mitochondrial antioxidant, peroxiredoxin-3 (Prx-3), could attenuate this deleterious process. Methods and Results-We created MI in 12-to 16-week-old, male Prx-3-transgenic mice (TGϩMI, nϭ37) and nontransgenic wild-type mice (WTϩMI, nϭ39) by ligating the left coronary artery. Prx-3 protein levels were 1.8 times higher in the hearts from TG than WT mice, with no significant changes in other antioxidant enzymes. At 4 weeks after MI, LV thiobarbituric acid-reactive substances in the mitochondria were significantly lower in TGϩMI than in WTϩMI mice (meanϮSEM, 1.5Ϯ0.2 vs 2.2Ϯ0.2 nmol/mg protein; nϭ8 each, PϽ0.05). LV cavity dilatation and dysfunction were attenuated in TGϩMI compared with WTϩMI mice, with no significant differences in infarct size (56Ϯ1% vs 55Ϯ1%; nϭ6 each, PϭNS) and aortic pressure between groups. Mean LV end-diastolic pressures and lung weights in TGϩMI mice were also larger than those in WTϩsham-operated mice but smaller than those in WTϩMI mice. Improvement in LV function in TGϩMI mice was accompanied by a decrease in myocyte hypertrophy, interstitial fibrosis, and apoptosis in the noninfarcted LV. Mitochondrial DNA copy number and complex enzyme activities were significantly decreased in WTϩMI mice, and this decrease was also ameliorated in TGϩMI mice. Conclusions-Overexpression of Prx-3 inhibited LV remodeling and failure after MI. Therapies designed to interfere with mitochondrial oxidative stress including the antioxidant Prx-3 might be beneficial in preventing cardiac failure.

Background-The involvement of Ca 2ϩ -dependent tyrosine kinase PYK2 in the Akt/endothelial NO synthase pathway remains to be determined. Methods and Results-Blood flow recovery and neovessel formation after hind-limb ischemia were impaired in PYK2

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SUMMARYThe aim of this study was to assess the acute effects of clonazepam and clonidine on rhythmic masticatory muscle activity in young adults with primary sleep bruxism, as well as accompanying effects on sleep architecture and cardiac activity. This study used a double-blind, crossover, placebo-controlled design. Polysomnography was performed on 19 subjects [nine men and 10 women; mean age (AESE): 25.4 AE 2.7 years] for 5 nights. The first 2 nights were used for the habituation and diagnosis of sleep bruxism. The other 3 nights were randomly assigned for clonazepam (1.0 mg), clonidine (0.15 mg) or placebo (all administered 30 min before bedtime). Sleep, oromotor activity and cardiac activity variables were assessed and compared among the three drug conditions. Clonidine significantly reduced the median percentage of time spent in the rapid eye movement sleep stage compared with placebo and clonazepam. The number of rhythmic masticatory muscle activity episodes was reduced with clonidine by >30% compared with placebo and clonazepam. The reduction of rhythmic masticatory muscle activity index by clonidine was associated with an increase of mean RR intervals (slower heart rate) during quiet sleep periods and during a 70-s period before the onset of rhythmic masticatory muscle activity episodes. However, no changes in cardiac activity variables were observed for clonazepam. In young adults with primary sleep bruxism, clonidine was significantly more effective in suppressing sleep bruxism than clonazepam. The acute effects of clonidine on rhythmic masticatory muscle activity episodes may be mediated by suppression of autonomic nervous system activity and nonrapid eye movement-rapid eye movement sleep processes.