Bone morphogenetic proteins (BMPs) belong to the TGF-β family, whose 33 members regulate multiple aspects of morphogenesis. TGF-β family members are secreted as procomplexes containing a small growth factor dimer associated with two larger prodomains. As isolated procomplexes, some members are latent, whereas most are active; what determines these differences is unknown. Here, studies on pro-BMP structures and binding to receptors lead to insights into mechanisms that regulate latency in the TGF-β family and into the functions of their highly divergent prodomains. The observed open-armed, nonlatent conformation of pro-BMP9 and pro-BMP7 contrasts with the cross-armed, latent conformation of pro-TGF-β1. Despite markedly different arm orientations in pro-BMP and pro-TGF-β, the arm domain of the prodomain can similarly associate with the growth factor, whereas prodomain elements N-and C-terminal to the arm associate differently with the growth factor and may compete with one another to regulate latency and stepwise displacement by type I and II receptors. Sequence conservation suggests that pro-BMP9 can adopt both crossarmed and open-armed conformations. We propose that interactors in the matrix stabilize a cross-armed pro-BMP conformation and regulate transition between cross-armed, latent and open-armed, nonlatent pro-BMP conformations.

Le VP, Knutsen RH, Mecham RP, Wagenseil JE. Decreased aortic diameter and compliance precedes blood pressure increases in postnatal development of elastin-insufficient mice. Am J Physiol Heart Circ Physiol 301: H221-H229, 2011. First published May 2, 2011; doi:10.1152/ajpheart.00119.2011.-Increased arterial stiffness and blood pressure are characteristic of humans and adult mice with reduced elastin levels caused by aging or genetic disease. Direct associations have been shown between increased arterial stiffness and hypertension in humans, but it is not known whether changes in mechanical properties or increased blood pressure occur first. Using genetically modified mice with elastin haploinsufficiency (Eln ϩ/Ϫ ), we investigated the temporal relationship between arterial mechanical properties and blood pressure throughout postnatal development. Our results show that some mechanical properties are maintained constant regardless of elastin amounts. The peak diameter compliance for both genotypes occurs near the physiologic pressure at each age, which acts to provide maximum pulse dampening. The stress-strain relationships are similar between genotypes and become nonlinear near the systolic pressure for each age, which serves to limit distension under high pressure. Our results also show that some mechanical properties are affected by reduced elastin levels and that these changes occur before measurable changes in blood pressure. Eln ϩ/Ϫ mice have decreased aortic diameter and compliance in ex vivo tests that are significant by postnatal day 7 and increased blood pressure that is not significant until postnatal day 14. This temporal relationship suggests that targeting large arteries to increase diameter or compliance may be an effective treatment for human hypertension. extracellular matrix; vasculature; vessels THE CONDUCTING ARTERIES IN vertebrates are composed of a specialized extracellular matrix (ECM) that is designed to provide elastic recoil that dampens the pulse pressure in distal arteries and reduces the work of the heart. The major ECM components are elastin and collagen, and the ratio of these proteins primarily determines the passive mechanical behavior of the large elastic arteries. Collagen is 100 -1,000 times stiffer than elastin; hence, vessels become stiffer and their elastic recoil function is compromised as the ratio of elastin to collagen is decreased (5). Arterial wall stiffness, as measured by pulse wave velocity (PWV), is independently associated with hypertension in humans and is increased even at the very early stages of the disease, suggesting that it may be a causative factor and not a resulting symptom of essential hypertension (18).Elastin amounts in humans are decreased through elastic fiber fragmentation in normal aging or through genetic mutations that affect elastin synthesis. Genetic mutations that lead to functional elastin haploinsufficiency have been linked to two inherited diseases, supravalvular aortic stenosis and Williams syndrome (7,19). The cardiovascular phenotypes of...

Aortic aneurysms are life-threatening and often associated with defects in connective tissues and mutations in smooth muscle cell (SMC) contractile proteins. Despite recent advances in understanding altered signaling in aneurysms of Marfan syndrome, the underlying mechanisms and options for pharmacological treatment for other forms of aneurysms are still under investigation. We previously showed in mice that deficiency in the fibulin-4 gene in vascular SMCs (Fbln4SMKO) leads to loss of the SMC contractile phenotype, hyperproliferation and ascending aortic aneurysms. Here, we report that abnormal upregulation of angiotensin converting enzyme (ACE) in SMCs and subsequent activation of angiotensin II (AngII) signaling is involved in the onset of aortic aneurysms in Fbln4SMKO mice. In this model, aneurysm formation was completely prevented by inhibition of the AngII pathway with losartan or captopril within a narrow therapeutic window during the first month of life, even though the altered mechanical properties of blood vessel walls were not reversed by the pharmacological treatment. The therapeutic effects of losartan in Fbln4SMKO mice do not require the AngII receptor type 2 (Agtr2) but likely require both type 1a (Agtr1a) and 1b (Agtr1b) receptors. The results indicate that fibulin-4 is a vascular matrix component required for regulation of local angiotensin signaling, aortic aneurysms, and development and maintenance of the SMC phenotype.

Specific uptake through dopamine transporter (DAT) followed by the inhibition of the mitochondrial complex-I have been accepted as the cause of the specific dopaminergic toxicity of MPP+. However, MPP+ is taken up into many cell types through other transporters suggesting that in addition to the efficient uptake, intrinsic vulnerability of dopaminergic cells may also contribute to their high sensitivity to MPP+ and similar toxins. To test this possibility, two simple cyanines were employed in a comparative study based on their unique characteristics and structural similarity to MPP+. Here we show that they freely accumulate in dopaminergic (MN9D and SH-SY5Y) as well as in liver (HepG2) cells, but are specifically and highly toxic to dopaminergic cells with IC50s in the range of 50–100 nM demonstrating that they are about 1000 fold more toxic than MPP+ under similar experimental conditions. They cause mitochondrial depolarization non-specifically, but increase the ROS specifically in dopaminergic cells leading to the apoptotic cell death parallel to MPP+. These and other findings suggest that the specific dopaminergic toxicity of these cyanines is due to the inherent vulnerability of dopaminergic cells towards mitochondrial toxins that lead to the excessive production of ROS. Therefore the specific dopaminergic toxicity of MPP+ must also at least be partly due to the specific vulnerability of dopaminergic neurons. Thus, these cyanines could be stronger in vivo dopaminergic toxins than MPP+ and their in vivo toxicities must be evaluated.

Seaweed-derived polysaccharides including agar and alginate, have found widespread applications in biomedical research and medical therapeutic applications including wound healing, drug delivery, and tissue engineering. Given the recent increases in the incidence of diabetes, obesity and hyperlipidemia, there is a pressing need for low cost therapeutics that can economically and effectively slow the progression of atherosclerosis. Marine polysaccharides have been consumed by humans for millennia and are available in large quantities at low cost. Polysaccharides such as fucoidan, laminarin sulfate and ulvan have shown promise in reducing atherosclerosis and its accompanying risk factors in animal models. However, others have been tested in very limited context in scientific studies. In this review, we explore the current state of knowledge for these promising therapeutics and discuss the potential and challenges of using seaweed derived polysaccharides as therapies for atherosclerosis.

A major factor in the progression to heart failure in humans is the inability of the adult heart to repair itself after injury. We recently demonstrated that the early postnatal mammalian heart is capable of regeneration following injury through proliferation of preexisting cardiomyocytes 1,2 and that Meis1, a three amino acid loop extension (TALE) family homeodomain transcription factor, translocates to cardiomyocyte nuclei shortly after birth and mediates postnatal cell cycle arrest 3 . Here we report that Hoxb13 acts as a cofactor of Meis1 in postnatal cardiomyocytes. Cardiomyocyte-specific deletion of Hoxb13 can extend the postnatal window of cardiomyocyte proliferation and reactivate the cardiomyocyte cell cycle in the adult heart. Moreover, adult Meis1-Hoxb13 doubleknockout hearts display widespread cardiomyocyte mitosis, sarcomere disassembly and improved left ventricular systolic function following myocardial infarction, as demonstrated by echocardiography and magnetic resonance imaging. Chromatin

Modulating transcription factors is crucial to executing sophisticated gene expression programs. The silent information regulator 2 (Sir2) family of NAD-dependent protein deacetylases influences transcription by targeting proteins such as histones, p53 and forkhead-box family transcription factors. Although apparently cytoplasmic, both mammalian SIRT2 and its yeast orthologue Hst2 have been implicated in transcriptional regulation. Here, we show that Hst2 moves between the nucleus and cytoplasm, but is largely cytoplasmic owing to efficient nuclear export. This nuclear exclusion is mediated by the exportin chromosomal region maintenance 1 (Crm1) and a putative leucine-rich nuclear export sequence in Hst2, which overlaps a unique autoregulatory helix. Disruption of Hst2 export shows that nuclear exclusion inhibits the activity of Hst2 as a transcriptional repressor. Our identification of putative nuclear export sequences in numerous vertebrate SIRT2 proteins shows that active nuclear export can be a conserved mechanism for regulating Sir2 homologues.

Growth differentiation factor 8 (GDF8)/myostatin is a latent TGF-β family member that potently inhibits skeletal muscle growth. Here, we compared the conformation and dynamics of precursor, latent, and Tolloid-cleaved GDF8 pro-complexes to understand structural mechanisms underlying latency and activation of GDF8. Negative stain electron microscopy (EM) of precursor and latent pro-complexes reveals a V-shaped conformation that is unaltered by furin cleavage and sharply contrasts with the ring-like, cross-armed conformation of latent TGF-β1. Surprisingly, Tolloid-cleaved GDF8 does not immediately dissociate, but in EM exhibits structural heterogeneity consistent with partial dissociation. Hydrogen-deuterium exchange was not affected by furin cleavage. In contrast, Tolloid cleavage, in the absence of prodomain-growth factor dissociation, increased exchange in regions that correspond in pro-TGF-β1 to the α1-helix, latency lasso, and β1-strand in the prodomain and to the β6'- and β7'-strands in the growth factor. Thus, these regions are important in maintaining GDF8 latency. Our results show that Tolloid cleavage activates latent GDF8 by destabilizing specific prodomain-growth factor interfaces and primes the growth factor for release from the prodomain.