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Loeys-Dietz syndrome (LDS) is a connective tissue disorder that is characterized by a high risk for aneurysm and dissection throughout the arterial tree and phenotypically resembles Marfan syndrome. LDS is caused by heterozygous missense mutations in either TGF-β receptor gene (TGFBR1 or TGFBR2), which are predicted to result in diminished TGF-β signaling; however, aortic surgical samples from patients show evidence of paradoxically increased TGF-β signaling. We generated 2 knockin mouse strains with LDS mutations in either Tgfbr1 or Tgfbr2 and a transgenic mouse overexpressing mutant Tgfbr2. Knockin and transgenic mice, but not haploinsufficient animals, recapitulated the LDS phenotype. While heterozygous mutant cells had diminished signaling in response to exogenous TGF-β in vitro, they maintained normal levels of Smad2 phosphorylation under steady-state culture conditions, suggesting a chronic compensation. Analysis of TGF-β signaling in the aortic wall in vivo revealed progressive upregulation of Smad2 phosphorylation and TGF-β target gene output, which paralleled worsening of aneurysm pathology and coincided with upregulation of TGF-β1 ligand expression. Importantly, suppression of Smad2 phosphorylation and TGF-β1 expression correlated with the therapeutic efficacy of the angiotensin II type 1 receptor antagonist losartan. Together, these data suggest that increased TGF-β signaling contributes to postnatal aneurysm progression in LDS.

Skeletal muscle has the ability to achieve rapid repair in response to injury or disease 1 . Many individuals with Marfan syndrome (MFS), caused by a deficiency of extracellular fibrillin-1, exhibit myopathy and often are unable to increase muscle mass despite physical exercise. Evidence suggests that selected manifestations of MFS reflect excessive signaling by transforming growth factor (TGF)-β (refs. 2 , 3 ). TGF-β is a known inhibitor of terminal differentiation of cultured myoblasts; however, the functional contribution of TGF-β signaling to disease pathogenesis in various inherited myopathic states in vivo remains unknown 4 , 5 . Here we show that increased TGF-β activity leads to failed muscle regeneration in fibrillin-1–deficient mice. Systemic antagonism of TGF-β through administration of TGF-β–neutralizing antibody or the angiotensin II type 1 receptor blocker losartan normalizes muscle architecture, repair and function in vivo . Moreover, we show TGF-β–induced failure of muscle regeneration and a similar therapeutic response in a dystrophin-deficient mouse model of Duchenne muscular dystrophy. NOTE: In the version of this article initially published, the same panels were inadvertently used to show negative pSmad2/3 and periostin staining in muscle of Fbn1 C1039G/+ mice treated with TGF-β‐neutralizing antibody in both the steady-state (Fig. 1a, right column, second and third rows, respectively) and muscle-regeneration (Fig. 1b, right column, third and fourth rows, respectively) experiments. In reality, these images only relate to the steady-state experiment (Fig. 1a). The intended images for Figure 1b are provided (red, pSmad2/3 staining; green, periostin staining). As both sets of images show negative staining in neutralizing antibody–treated Fbn1 C1039G/+ mice, this does not alter any observations or conclusions discussed in the manuscript. The error has been corrected in the HTML and PDF versions of the article.

The mechanism by which disruption of reading frame can influence pre-messenger RNA (pre-mRNA) processing is poorly understood. We assessed the role of factors essential for nonsense-mediated mRNA decay (NMD) in nonsense-mediated altered splicing (NAS) with the use of RNA interference (RNAi) in mammalian cells. Inhibition of rent1/hUpf1 expression abrogated both NMD and NAS of nonsense T cell receptor β transcripts. In contrast, inhibition of rent2/hUpf2 expression did not disrupt NAS despite achieving comparable stabilization of nonsense transcripts. We also demonstrate that NAS and NMD are genetically separable functions of rent1/hUpf1. Additionally, rent1/hUpf1 enters the nucleus where it may directly influence early events in mRNA biogenesis. This provides compelling evidence that NAS relies on a component of the nonsense surveillance machinery but is not an indirect consequence of NMD.

The Fibroblast Growth Factor (FGF) signaling pathway is reported to stimulate glioblastoma (GBM) growth. In this work we evaluated the effect of FGF2, FGF receptor (FGFR), and small molecule inhibition on GBM cells grown in traditional media, or cultured directly in stem-cell media. These lines each expressed the FGFR1, FGFR3 and FGFR4 receptors. Addition of FGF2 ligand showed significant growth stimulation in 8 of 10 cell lines. Disruption of FGF signaling by a neutralizing FGF2 monoclonal antibody and FGFR1 suppression by RNA interference both partially inhibited cell proliferation. Growth inhibition was temporally correlated with a reduction in MAPK signaling. A receptor tyrosine kinase inhibitor with known FGFR/VEGFR activity, PD173074, showed reproducible growth inhibition. Possible mechanisms of growth suppression by PD173074 were implicated by reduced phosphorylation of AKT and MAPK, known oncogenic signal transducers. Subsequent reduction in the cyclin D1, cyclin D2 and CDK4 cell cycle regulators was also observed. Our results indicate that FGF signaling pathway inhibition as a monotherapy will slow, but not arrest growth of glioblastoma cells.

Loeys-Dietz syndrome (LDS) is a connective tissue disorder that is characterized by a high risk for aneurysm and dissection throughout the arterial tree and phenotypically resembles Marfan syndrome. LDS is caused by heterozygous missense mutations in either TGF-β receptor gene (TGFBR1 or TGFBR2), which are predicted to result in diminished TGF-bgr; signaling. In this paper, the authors generated 2 knockin mouse strains with LDS mutations in either Tgfbr1 or Tgfbr2 and a transgenic mouse overexpressing mutant Tgfbr2. Knockin and transgenic mice, but not haploinsufficient animals, recapitulated the LDS phenotype. The analysis of TGF-β signaling in the aortic wall in vivo revealed progressive upregulation of Smad2 phosphorylation and TGF-β target gene output, which paralleled worsening of aneurysm pathology and coincided with upregulation of TGF-β1 ligand expression. Importantly, the suppression of Smad2 phosphorylation and TGF-β1 expression correlated with the therapeutic efficacy of the angiotensin II type 1 receptor antagonist losartan.