ABSTRACT
RATIONALE: Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor-ß super family of secreted factors. A recent study showed that reduced GDF11 blood levels with aging was associated with pathological cardiac hypertrophy (PCH) and restoring GDF11 to normal levels in old mice rescued PCH. OBJECTIVE: To determine whether and by what mechanism GDF11 rescues aging dependent PCH. METHODS AND RESULTS: Twenty-four-month-old C57BL/6 mice were given a daily injection of either recombinant (r) GDF11 at 0.1 mg/kg or vehicle for 28 days. rGDF11 bioactivity was confirmed in vitro. After treatment, rGDF11 levels were significantly increased, but there was no significant effect on either heart weight or body weight. Heart weight/body weight ratios of old mice were not different from 8- or 12-week-old animals, and the PCH marker atrial natriuretic peptide was not different in young versus old mice. Ejection fraction, internal ventricular dimension, and septal wall thickness were not significantly different between rGDF11 and vehicle-treated animals at baseline and remained unchanged at 1, 2, and 4 weeks of treatment. There was no difference in myocyte cross-sectional area rGDF11 versus vehicle-treated old animals. In vitro studies using phenylephrine-treated neonatal rat ventricular myocytes, to explore the putative antihypertrophic effects of GDF11, showed that GDF11 did not reduce neonatal rat ventricular myocytes hypertrophy, but instead induced hypertrophy. CONCLUSIONS: Our studies show that there is no age-related PCH in disease-free 24-month-old C57BL/6 mice and that restoring GDF11 in old mice has no effect on cardiac structure or function.
Subject(s)
Aging/pathology , Bone Morphogenetic Proteins/pharmacology , Cardiomegaly/prevention & control , Growth Differentiation Factors/pharmacology , Myocytes, Cardiac/drug effects , Ventricular Remodeling/drug effects , Adrenergic alpha-1 Receptor Agonists/pharmacology , Age Factors , Aging/metabolism , Animals , Bone Morphogenetic Proteins/administration & dosage , Cardiomegaly/metabolism , Cardiomegaly/pathology , Cardiomegaly/physiopathology , Cells, Cultured , Drug Administration Schedule , Fibroblasts/drug effects , Fibroblasts/metabolism , Fibroblasts/pathology , Fibrosis , Growth Differentiation Factors/administration & dosage , Injections, Intraperitoneal , Male , Mice, Inbred C57BL , Myocytes, Cardiac/metabolism , Myocytes, Cardiac/pathology , Recombinant Proteins/pharmacology , Time Factors , Ventricular Function, Left/drug effects , Ventricular Pressure/drug effectsABSTRACT
Growth differentiation factor-11 (GDF11) and myostatin (MSTN) are highly related transforming growth factor-ß (TGF-ß) ligands with 89% amino acid sequence homology. They have different biologic activities and diverse tissue distribution patterns. However, the activities of these ligands are indistinguishable in in vitro assays. SMAD2/3 signaling has been identified as the canonical pathway for GDF11 and MSTN, However, it remains unclear which receptor heterodimer and which antagonists preferentially mediate and regulate signaling. In this study, we investigated the initiation and regulation of GDF11 and MSTN signaling at the receptor level using a novel receptor dimerization detection technology. We used the dimerization platform to link early receptor binding events to intracellular downstream signaling. This approach was instrumental in revealing differential receptor binding activity within the TGF-ß family. We verified the ActR2b/ALK5 heterodimer as the predominant receptor for GDF11- and MSTN-induced SMAD2/3 signaling. We also showed ALK7 specifically mediates activin-B signaling. We verified follistatin as a potent antagonist to neutralize both SMAD2/3 signaling and receptor dimerization. More remarkably, we showed that the two related antagonists, growth and differentiation factor-associated serum protein (GASP)-1 and GASP2, differentially regulate GDF11 (and MSTN) signaling. GASP1 blocks both receptor dimerization and downstream signaling. However, GASP2 blocks only downstream signaling without interference from receptor dimerization. Our data strongly suggest that physical binding of GDF11 (and MSTN) to both ActR2b and ALK5 receptors is required for initiation of signaling.
Subject(s)
Receptors, Transforming Growth Factor beta/metabolism , Transforming Growth Factor beta/metabolism , Actin-Related Protein 2/chemistry , Actin-Related Protein 2/metabolism , Bone Morphogenetic Proteins/metabolism , Growth Differentiation Factors/metabolism , Hep G2 Cells , Humans , Myostatin/metabolism , Protein Binding , Protein Multimerization , Protein Serine-Threonine Kinases/chemistry , Protein Serine-Threonine Kinases/metabolism , Protein Structure, Quaternary , Receptor, Transforming Growth Factor-beta Type I , Receptors, Transforming Growth Factor beta/chemistry , Signal Transduction , Smad2 Protein/metabolism , Smad3 Protein/metabolism , Substrate SpecificityABSTRACT
Loss of skeletal muscle mass and function results in loss of mobility for elderly patients. Novel therapies that can protect and/or restore muscle function during aging would have profound effects on the quality of life for this population. Growth differentiation factor 11 (GDF11) has been proposed as a "youthful" circulating factor that can restore cardiac, neural, and skeletal muscle functions in aging animals. However, conflicting data has been recently published that casts doubt on these assertions. We used a complex rat model of skeletal muscle injury that physiologically mimics injuries seen in patients; to investigate the ability of GDF11 and to enhance skeletal muscle regeneration after injury in older rats. Our data showed that GDF11 treatment resulted in a significant increase in tissue fibrosis, accompanied by attenuated functional recovery, as compared to animals treated with vehicle alone. GDF11 impaired the recovery of skeletal muscle function in older rats after injury.