Structural basis for potency differences between GDF8 and GDF11.

BACKGROUND: Growth/differentiation factor 8 (GDF8) and GDF11 are two highly similar members of the transforming growth factor β (TGFβ) family. While GDF8 has been recognized as a negative regulator of muscle growth and differentiation, there are conflicting studies on the function of GDF11 and whether GDF11 has beneficial effects on age-related dysfunction. To address whether GDF8 and GDF11 are functionally identical, we compared their signaling and structural properties. RESULTS: Here we show that, despite their high similarity, GDF11 is a more potent activator of SMAD2/3 and signals more effectively through the type I activin-like receptor kinase receptors ALK4/5/7 than GDF8. Resolution of the GDF11:FS288 complex, apo-GDF8, and apo-GDF11 crystal structures reveals unique properties of both ligands, specifically in the type I receptor binding site. Lastly, substitution of GDF11 residues into GDF8 confers enhanced activity to GDF8. CONCLUSIONS: These studies identify distinctive structural features of GDF11 that enhance its potency, relative to GDF8; however, the biological consequences of these differences remain to be determined

A TagSNP in <i>SIRT1</i> Gene Confers Susceptibility to Myocardial Infarction in a Chinese Han Population

<div><p><i>SIRT1</i> exerts protective effects against endothelial cells dysfunction, inflammation and atherosclerosis, indicating an important role on myocardial infarction (MI) pathogenesis. Nonetheless, the effects of <i>SIRT1</i> variants on MI risk remain poorly understood. Here we aimed to investigate the influence of <i>SIRT1</i> polymorphisms on individual susceptibility to MI. Genotyping of three tagSNPs (rs7069102, rs3818292 and rs4746720) in <i>SIRT1</i> gene was performed in a Chinese Han population, consisting of 287 MI cases and 654 control subjects. In a logistic regression analysis, we found that G allele of rs7069102 had increased MI risk with odds ratio (OR) of 1.57 [95% confidence interval (CI) = 1.15–2.16, Bonferroni corrected <i>P</i> (<i>P_c</i>) = 0.015] after adjustment for conventional risk factors compared to C allele. Similarly, the combined CG/GG genotypes was associated with the increased MI risk (OR = 1.64, 95% CI = 1.14–2.35, <i>P_c</i> = 0.021) compared to the CC genotype. Further stratified analysis revealed a more significant association with MI risk among younger subjects (≤ 55 years old). Consistent with these results, the haplotype rs7069102G-rs3818292A-rs4746720T containing the rs7069102 G allele was also associated with the increased MI risk (OR = 1.41, 95% CI = 1.09–1.84, <i>P_c</i> = 0.040). However, we did not detect any association of rs3818292 and rs4746720 with MI risk. Our study provides the first evidence that the tagSNP rs7069102 and haplotype rs7069102G-rs3818292A-rs4746720T in <i>SIRT1</i> gene confer susceptibility to MI in the Chinese Han population.</p></div

Circulating Growth Differentiation Factor 11/8 Levels Decline with Age

Rationale: Growth differentiation factor 11 (GDF11) and GDF8 are members of the transforming growth factor-β superfamily sharing 89% protein sequence homology. We have previously shown that circulating GDF11 levels decrease with age in mice. However, a recent study by Egerman et al reported that GDF11/8 levels increase with age in mouse serum. Objective: Here, we clarify the direction of change of circulating GDF11/8 levels with age and investigate the effects of GDF11 administration on the murine heart. Methods and Results: We validated our previous finding that circulating levels of GDF11/8 decline with age in mice, rats, horses, and sheep. Furthermore, we showed by Western analysis that the apparent age-dependent increase in GDF11 levels, as reported by Egerman et al, is attributable to cross-reactivity of the anti-GDF11 antibody with immunoglobulin, which is known to increase with age. GDF11 administration in mice rapidly activated SMAD2 and SMAD3 signaling in myocardium in vivo and decreased cardiac mass in both young (2-month-old) and old (22-month-old) mice in a dose-dependent manner after only 9 days. Conclusions: Our study confirms an age-dependent decline in serum GDF11/8 levels in multiple mammalian species and that exogenous GDF11 rapidly activates SMAD signaling and reduces cardiomyocyte size. Unraveling the molecular basis for the age-dependent decline in GDF11/8 could yield insight into age-dependent cardiac pathologies

Multivariate associations of the three tagSNPs in <i>SIRT1</i> gene with the risk of MI.

<p><i>P</i>_<i>c</i>, Bonferroni corrected <i>P</i>; NS, not significant.</p><p>^a Adjusted for age, sex, BMI, smoking, drinking, hypertension, diabetes and hyperlipidemia.</p><p>^b<i>P</i>_<i>c</i> values under 0.05 were indicated in bold font.</p><p>Multivariate associations of the three tagSNPs in <i>SIRT1</i> gene with the risk of MI.</p

Association between haplotypes of the three tagSNPs in <i>SIRT1</i> gene with the risk of MI.

<p><i>P</i>_<i>c</i>, Bonferroni corrected <i>P</i>; NS, not significant.</p><p>^<i>a</i> The allelic sequence in the haplotypes is in the following order: rs7069102, rs3818292, rs4746720.</p><p>^b<i>P</i>_<i>c</i> values under 0.05 were indicated in bold font.</p><p>Association between haplotypes of the three tagSNPs in <i>SIRT1</i> gene with the risk of MI.</p

The characteristics of MI cases and controls.

<p>BMI, body mass index; FPG, fasting plasma glucose; TG, triglyceride; TC, total cholesterol; HDLC, high density lipoprotein cholesterol; LDLC, low density lipoprotein cholesterol.</p><p>^a Two-sided chi-square test or independent-samples <i>t</i>-test.</p><p>^b<i>P</i> values under 0.05 were indicated in bold font.</p><p>The characteristics of MI cases and controls.</p

Multivariate associations of the rs7069102 in <i>SIRT1</i> gene with the risk of MI by further stratification for age.

<p><i>P</i>_<i>c</i>, Bonferroni corrected <i>P</i>; NS, not significant.</p><p>^a Adjusted for sex, BMI, smoking, drinking, hypertension, diabetes and hyperlipidemia.</p><p>^b<i>P</i>_<i>c</i> values under 0.05 were indicated in bold font.</p><p>Multivariate associations of the rs7069102 in <i>SIRT1</i> gene with the risk of MI by further stratification for age.</p

Additional file 1: Table S1. of Structural basis for potency differences between GDF8 and GDF11

Analysis of GDF8 and GDF11 activity in HEK293, HepG2 and LβT2 cells [57, 94–96]. (DOC 30 kb

Additional file 2: Figure S1. of Structural basis for potency differences between GDF8 and GDF11

Potency of recombinant GDF8 and GDF11 from different sources. Luciferase reporter gene assay ((CAGA)12 promoter) following titration of GDF8 (blue) and GDF11 (orange) ligands in HEK293 cells. Luciferase activity was assessed 18–24 h post ligand treatment. The calculated EC50 value for each ligand source using non-linear regression with variable slope is shown in the table below the graph. Data information: Data are presented as percent GDF11 activation after background subtraction (0 nM ligand concentration). Each point is the mean ± SEM of three to four independent experiments. Ligand sources are indicated in the graph. (TIF 750 kb