BACKGROUND Heart failure is a growing cause of morbidity and mortality worldwide. Transforming growth factor beta (TGF-β1) promotes cardiac fibrosis, but also activates counterregulatory pathways that serve to regulate TGF-β1 activity in heart failure. Bone morphogenetic protein 9 (BMP9) is a member of the TGFβ family of cytokines and signals via the downstream effector protein Smad1. Endoglin is a TGFβ coreceptor that promotes TGF-β1 signaling via Smad3 and binds BMP9 with high affinity. We hypothesized that BMP9 limits cardiac fibrosis by activating Smad1 and attenuating Smad3, and, furthermore, that neutralizing endoglin activity promotes BMP9 activity. METHODS We examined BMP9 expression and signaling in human cardiac fibroblasts and human subjects with heart failure. We used the transverse aortic constriction-induced model of heart failure to evaluate the functional effect of BMP9 signaling on cardiac remodeling. RESULTS BMP9 expression is increased in the circulation and left ventricle (LV) of human subjects with heart failure and is expressed by cardiac fibroblasts. Next, we observed that BMP9 attenuates type I collagen synthesis in human cardiac fibroblasts using recombinant human BMP9 and a small interfering RNA approach. In BMP9-/- mice subjected to transverse aortic constriction, loss of BMP9 activity promotes cardiac fibrosis, impairs LV function, and increases LV levels of phosphorylated Smad3 (pSmad3), not pSmad1. In contrast, treatment of wild-type mice subjected to transverse aortic constriction with recombinant BMP9 limits progression of cardiac fibrosis, improves LV function, enhances myocardial capillary density, and increases LV levels of pSmad1, not pSmad3 in comparison with vehicle-treated controls. Because endoglin binds BMP9 with high affinity, we explored the effect of reduced endoglin activity on BMP9 activity. Neutralizing endoglin activity in human cardiac fibroblasts or in wild-type mice subjected to transverse aortic constriction-induced heart failure limits collagen production, increases BMP9 protein levels, and increases levels of pSmad1, not pSmad3. CONCLUSIONS Our results identify a novel functional role for BMP9 as an endogenous inhibitor of cardiac fibrosis attributable to LV pressure overload and further show that treatment with either recombinant BMP9 or disruption of endoglin activity promotes BMP9 activity and limits cardiac fibrosis in heart failure, thereby providing potentially novel therapeutic approaches for patients with heart failure.

中文翻译：

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骨形态发生蛋白9可减少心脏纤维化并改善心力衰竭的心脏功能。

背景技术心力衰竭是世界范围内发病率和死亡率的日益增长的原因。转化生长因子β（TGF-β1）促进心脏纤维化，但也激活了用于调节心力衰竭中TGF-β1活性的反调节途径。骨形态发生蛋白9（BMP9）是TGFβ细胞因子家族的成员，并通过下游效应蛋白Smad1发出信号。内皮糖蛋白是一种TGFβ共受体，可通过Smad3促进TGF-β1信号传导，并以高亲和力结合BMP9。我们假设BMP9通过激活Smad1和减弱Smad3来限制心脏纤维化，此外，中和内皮糖蛋白的活性可促进BMP9的活性。方法我们检查了人心脏成纤维细胞和患有心力衰竭的人类受试者中BMP9的表达和信号传导。我们使用横向主动脉缩窄诱发的心力衰竭模型来评估BMP9信号传导对心脏重塑的功能作用。结果BMP9表达在患有心力衰竭的人类受试者的循环和左心室（LV）中增加，并由心脏成纤维细胞表达。接下来，我们观察到BMP9使用重组人BMP9和小干扰RNA方法减弱了人心脏成纤维细胞中的I型胶原蛋白合成。在遭受横向主动脉缩窄的BMP9-/-小鼠中，BMP9活性的丧失促进了心脏纤维化，损害了LV功能，并增加了磷酸化Smad3（pSmad3）而非pSmad1的LV水平。相比之下，用重组BMP9治疗受主动脉横向狭窄的野生型小鼠会限制心脏纤维化的进程，改善左室功能，与媒介物处理的对照相比，可增强心肌毛细血管密度，并增加pSmad1而非pSmad3的LV水平。因为内皮糖蛋白以高亲和力结合BMP9，所以我们探讨了内皮糖蛋白活性降低对BMP9活性的影响。在人心脏成纤维细胞中或在遭受横向主动脉缩窄引起的心力衰竭的野生型小鼠中，内皮糖蛋白活性的中和限制了胶原蛋白的产生，增加了BMP9蛋白的水平，并增加了pSmad1而不是pSmad3的水平。结论我们的结果确定了BMP9作为一种可归因于LV压力超负荷的心脏纤维化的内源性抑制剂的新功能，并进一步表明，重组BMP9或内皮糖蛋白活性的破坏均可促进BMP9活性并限制心力衰竭中的心脏纤维化，