The present disclosure describes novel hybrid soluble ActRIIB-ECD polypeptides which fully retain binding affinity for myostatin and activin A but demonstrate significantly reduced binding to BMPs, especially BMP-9. The novel compositions described herein can be used to prepare novel hybrid ActRIIB ligand trap proteins, which can be used for modulating the growth of muscle, bone, cartilage, fat, fibroblast, blood and neuronal tissue to counteract muscle wasting, bone loss, anemia, inflammation and fibrosis in a therapeutically meaningful manner. Because these novel next-generation myostatin/activin inhibitors are safer and more effective molecules than the currently available myostatin inhibitors, they are useful in a wide variety of clinical indications.本揭露內容描述了新型雜合可溶ActRIIB-ECD多肽，其完全保留了對肌生成抑制蛋白(myostatin)和啟動蛋白A的結合親和力，但表現出與BMP、特別地BMP-9顯著減少的結合。本文描述的新型組合物可用於製備新型雜合ActRIIB配體陷阱蛋白，該新型雜合ActRIIB配體陷阱蛋白可用於調節肌肉、骨、軟骨、脂肪、成纖維細胞、血液和神經組織的生長，以在治療上有意義的方式對抗肌肉萎縮、骨質丟失、貧血、炎症和纖維化。因為這些新型下一代肌生成抑制蛋白/啟動蛋白抑制劑是比當前可用的肌生成抑制蛋白抑制劑更安全且更有效的分子，所以它們在非常廣泛的臨床適應症中是有用的。
