{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n Growth differentiation factor 11 (GDF11) is a multifunctional member of the transforming growth factor–β superfamily that plays diverse, context‐dependent roles in development, tissue homeostasis, and aging. In aged animals, restoration of youthful circulating GDF11 levels has been shown to reverse cardiac hypertrophy by activating SMAD2/3 signaling pathways, thereby reducing cardiomyocyte size and remodeling molecular profiles."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "3"}]}, {"type": "t", "text": " In contrast, several studies report that GDF11 can inhibit regeneration in other tissues; for example, it limits skeletal muscle regeneration by restricting satellite cell expansion and myoblast differentiation"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "4"}]}, {"type": "t", "text": "and also negatively affects terminal erythroid maturation in both normal and disease states such as β‐thalassemia."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " In the nervous system, GDF11 functions as a feedback inhibitor that limits neurogenesis by inducing cell cycle arrest in neuronal progenitors in the olfactory epithelium and by restricting the competence window for retinal ganglion cell formation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "7", "end_ref": "9"}]}, {"type": "t", "text": ""}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n During embryogenesis, GDF11 is critical for proper anterior–posterior patterning. It regulates the spatial and temporal expression of multiple Hox genes to direct axial skeletal segmentation and govern trunk‐to‐tail transitions, kidney organogenesis, and ureteric bud formation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "10", "end_ref": "13"}]}, {"type": "t", "text": " GDF11 signaling is mediated predominantly by activin receptor–like kinases (such as ALK4 and ALK5), and its bioactivity is tightly controlled by proteolytic processing – for example, cleavage by PCSK5 or by BMP1/Tolloid family metalloproteinases liberates the mature ligand from a noncovalent latent complex."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "14", "end_ref": "16"}]}, {"type": "t", "text": " Moreover, binding proteins such as WFIKKN1 and WFIKKN2 serve as endogenous antagonists by interacting with mature GDF11, thereby modulating its signaling function."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "17"}]}, {"type": "t", "text": "\n "}]}, {"type": "t", "text": "\n \n "}, {"type": "p", "children": [{"type": "t", "text": "\n Notably, controversy exists about the circulating levels and physiological relevance of GDF11 relative to other highly homologous ligands such as myostatin; some studies report age‐related declines associated with frailty and adverse cardiac outcomes"}, {"type": "fg", "children": [{"type": "fg_f", "ref": "18"}]}, {"type": "t", "text": ", whereas other work suggests that GDF11 levels are very low compared to myostatin and that its systemic impact may be limited."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "19"}]}, {"type": "t", "text": " In addition, in pancreatic development, GDF11 has been implicated in controlling the number and maturation of islet progenitor cells, thereby influencing β‐cell differentiation."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "20"}]}, {"type": "t", "text": " Collectively, these findings underscore a complex, multifaceted role for GDF11 – acting as both a rejuvenative factor in certain contexts (particularly in the aged heart) and as an inhibitory modulator of tissue regeneration and differentiation in others. \n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Francesco S Loffredo, Matthew L Steinhauser, Steven M Jay, et al. 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