GDF11: An emerging therapeutic target for liver diseases and fibrosis.

Growth differentiation factor 11 (GDF11), also known as bone morphogenetic protein 11 (BMP11), has been identified as a key player in various biological processes, including embryonic development, aging, metabolic disorders and cancers. GDF11 has also emerged as a critical component in liver development, injury and fibrosis. However, the effects of GDF11 on liver physiology and pathology have been a subject of debate among researchers due to conflicting reported outcomes. While some studies suggest that GDF11 has anti-aging properties, others have documented its senescence-inducing effects. Similarly, while GDF11 has been implicated in exacerbating liver injury, it has also been shown to have the potential to reduce liver fibrosis. In this narrative review, we present a comprehensive report of recent evidence elucidating the diverse roles of GDF11 in liver development, hepatic injury, regeneration and associated diseases such as non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), liver fibrosis and hepatocellular carcinoma. We also explore the therapeutic potential of GDF11 in managing various liver pathologies.

The Effect of Liraglutide on Axon Regeneration and Functional Recovery after Peripheral Nerve Lesion.

Peripheral nerve injuries inflict severe consequences, necessitating innovative therapeutic strategies. This study investigates the potential of liraglutide, a glucagon-like peptide-1 receptor agonist, in mitigating the consequences of peripheral nerve injury. The existing treatment methods for such injuries underscore the importance of ongoing translational research efforts. Thirty adult Wistar rats underwent sciatic nerve dissection and repair surgery. The nerves were surgically transected using micro scissors at a precise location located 1.5 cm proximal to the trifurcation site. The study included a control group and two experimental groups, one treated with saline (placebo group) and the other with liraglutide (experimental group) for 12 weeks. Motor function, electromyography (EMG), and biochemical and histopathological analyses were performed after 12 weeks of treatment. Electrophysiological assessments revealed that liraglutide improved the compound muscle action potential (CMAP) amplitude and motor function compared to the saline-treated group. Histological and immunohistochemical analyses demonstrated increased NGF expression, total axon number, and diameter and reduced fibrosis in the liraglutide group. Biochemical analyses illustrated liraglutide's antioxidative properties, evidenced by reduced malondialdehyde (MDA) levels. Galectin-3 levels were suppressed and GDF-11 levels were modulated by liraglutide, indicating anti-inflammatory and anti-apoptotic effects. Liraglutide is a promising therapeutic intervention for peripheral nerve injuries, promoting functional recovery and histopathological improvement. Its multifaceted positive impact, beyond glycemic control, suggests constructive effects on the acute and chronic inflammatory processes associated with peripheral neuropathy. These findings warrant further research to elucidate molecular mechanisms and facilitate clinical translation. The study contributes valuable insights to the growing understanding of GLP-1 receptor agonists' neuroprotective properties in the context of peripheral nerve injuries.

Growth differentiation factor 11 regulates high glucose-induced cardiomyocyte pyroptosis and diabetic cardiomyopathy by inhibiting inflammasome activation.

BACKGROUND: Diabetic cardiomyopathy (DCM) is a crucial complication of long-term chronic diabetes that can lead to myocardial hypertrophy, myocardial fibrosis, and heart failure. There is increasing evidence that DCM is associated with pyroptosis, a form of inflammation-related programmed cell death. Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor ß superfamily, which regulates oxidative stress, inflammation, and cell survival to mitigate myocardial hypertrophy, myocardial infarction, and vascular injury. However, the role of GDF11 in regulating pyroptosis in DCM remains to be elucidated. This research aims to investigate the role of GDF11 in regulating pyroptosis in DCM and the related mechanism. METHODS AND RESULTS: Mice were injected with streptozotocin (STZ) to induce a diabetes model. H9c2 cardiomyocytes were cultured in high glucose (50 mM) to establish an in vitro model of diabetes. C57BL/6J mice were preinjected with adeno-associated virus 9 (AAV9) intravenously via the tail vein to specifically overexpress myocardial GDF11. GDF11 attenuated pyroptosis in H9c2 cardiomyocytes after high-glucose treatment. In diabetic mice, GDF11 alleviated cardiomyocyte pyroptosis, reduced myocardial fibrosis, and improved cardiac function. Mechanistically, GDF11 inhibited pyroptosis by preventing inflammasome activation. GDF11 achieved this by specifically binding to apoptosis-associated speck-like protein containing a CARD (ASC) and preventing the assembly and activation of the inflammasome. Additionally, the expression of GDF11 during pyroptosis was regulated by peroxisome proliferator-activated receptor α (PPARα). CONCLUSION: These findings demonstrate that GDF11 can treat diabetic cardiomyopathy by alleviating pyroptosis and reveal the role of the PPARα-GDF11-ASC pathway in DCM, providing ideas for new strategies for cardioprotection.

GDF11 (Protein of Juvenility) and GDF15 (Protein of Senility) in the Plasma of Patients with Sleep Apnea Syndrome: a Pilot Study.

We performed a matched-pair analysis of the content of GDF11 and GDF15 proteins in the plasma of patients (56 middle-aged men) with obstructive sleep apnea syndrome (OSAS) and healthy volunteers (27 men with no complaints of sleep disorders). The groups were comparable in terms of age and presence of chronic diseases. No statistically significant differences in GDF11 content in the studied groups were revealed, while the content of GDF15 in the OSAS group was 1.3 times higher. These results require further research from the viewpoint of geriatric somnology and molecular biology.

GDF-11 downregulates placental human chorionic gonadotropin expression by activating SMAD2/3 signaling.

BACKGROUND: The production of human chorionic gonadotropin (hCG) by the placental trophoblast cells is essential for maintaining a normal pregnancy. Aberrant hCG levels are associated with reproductive disorders. The protein of hCG is a dimer consisting of an α subunit and a ß subunit. The ß subunit is encoded by the CGB gene and is unique to hCG. Growth differentiation factor-11 (GDF-11), a member of the transforming growth factor-ß (TGF-ß) superfamily, is expressed in the human placenta and can stimulate trophoblast cell invasion. However, whether the expression of CGB and the production of hCG are regulated by GDF-11 remains undetermined. METHODS: Two human choriocarcinoma cell lines, BeWo and JEG-3, and primary cultures of human cytotrophoblast (CTB) cells were used as experimental models. The effects of GDF-11 on CGB expression and hCG production, as well as the underlying mechanisms, were explored by a series of in vitro experiments. RESULTS: Our results show that treatment of GDF-11 downregulates the expression of CGB and the production of hCG in both BeWo and JEG-3 cells as well as in primary CTB cells. Using a pharmacological inhibitor and siRNA-mediated approach, we reveal that both ALK4 and ALK5 are required for the GDF-11-induced downregulation of CGB expression. In addition, treatment of GDF-11 activates SMAD2/3 but not SMAD1/5/8 signaling pathways. Moreover, both SMAD2 and SMAD3 are involved in the GDF-11-downregulated CGB expression. ELISA results show that the GDF-11-suppressed hCG production requires the ALK4/5-mediated activation of SMAD2/3 signaling pathways. CONCLUSIONS: This study not only discovers the biological function of GDF-11 in the human placenta but also provides important insights into the regulation of the expression of hCG. Video Abstract.

GDF11 Improves Ischemia-Reperfusion-Induced Acute Kidney Injury via Regulating Macrophage M1/M2 Polarization.

INTRODUCTION: Acute kidney injury (AKI) is a clinical emergency caused by the rapid decline of renal function caused by various etiologies. Growth differentiation factor 11 (GDF11) can promote renal tubular regeneration and improve kidney function in AKI, but the specific mechanism remains unclear. Herein, we investigated the effect and mechanisms of GDF11 in ameliorating AKI induced by ischemia-reperfusion (I/R). METHODS: An animal model of AKI was established by I/R method, and the changes of serum urea nitrogen and creatinine were measured to evaluate the AKI. Enzyme-linked immunosorbent assay (ELISA) was used to measure cytokines, malondialdehyde, superoxide dismutase, nitric oxide synthase, and arginase 1 levels. Flow cytometry was used to count the M1/M2 macrophages. IHC, WB, and q-PCR experiments were used to evaluate the expression of GDF11. RESULTS: The changes in serum levels of urea nitrogen and creatinine after I/R suggest that an animal model of AKI induced by I/R was successfully established. AKI caused by I/R significantly changed the M1/M2 macrophage polarization balance, with an increase in M2 being significantly higher than M1 as well as increased oxidative stress. Treatment with GDF11 after I/R significantly increased the differentiation of M2 cells and inhibited the differentiation of M1 macrophages, as well as decreased oxidative stress. CONCLUSION: GDF11 can promote the repair of AKI caused by I/R by regulating the balance of M1/M2 polarization in macrophages and oxidative stress.

GDF11 promotes wound healing in diabetic mice via stimulating HIF-1ɑ-VEGF/SDF-1ɑ-mediated endothelial progenitor cell mobilization and neovascularization.

Non-healing diabetic wounds (DW) are a serious clinical problem that remained poorly understood. We recently found that topical application of growth differentiation factor 11 (GDF11) accelerated skin wound healing in both Type 1 DM (T1DM) and genetically engineered Type 2 diabetic db/db (T2DM) mice. In the present study, we elucidated the cellular and molecular mechanisms underlying the action of GDF11 on healing of small skin wound. Single round-shape full-thickness wound of 5-mm diameter with muscle and bone exposed was made on mouse dorsum using a sterile punch biopsy 7 days following the onset of DM. Recombinant human GDF11 (rGDF11, 50 ng/mL, 10 µL) was topically applied onto the wound area twice a day until epidermal closure (maximum 14 days). Digital images of wound were obtained once a day from D0 to D14 post-wounding. We showed that topical application of GDF11 accelerated the healing of full-thickness skin wounds in both type 1 and type 2 diabetic mice, even after GDF8 (a muscle growth factor) had been silenced. At the cellular level, GDF11 significantly facilitated neovascularization to enhance regeneration of skin tissues by stimulating mobilization, migration and homing of endothelial progenitor cells (EPCs) to the wounded area. At the molecular level, GDF11 greatly increased HIF-1ɑ expression to enhance the activities of VEGF and SDF-1ɑ, thereby neovascularization. We found that endogenous GDF11 level was robustly decreased in skin tissue of diabetic wounds. The specific antibody against GDF11 or silence of GDF11 by siRNA in healthy mice mimicked the non-healing property of diabetic wound. Thus, we demonstrate that GDF11 promotes diabetic wound healing via stimulating endothelial progenitor cells mobilization and neovascularization mediated by HIF-1ɑ-VEGF/SDF-1ɑ pathway. Our results support the potential of GDF11 as a therapeutic agent for non-healing DW.

Celastrol assuages oxygen-glucose deprivation and reoxygenation-induced damage in human brain microvascular endothelial cells through the circDLGAP4/miR-6085/GDF11 pathway.

The effect of Celastrol on cerebral ischemia-reperfusion remains unknown. The study aims to explore the role of circular RNA DLGAP4 (circDLGAP4) in cerebral ischemia-reperfusion and the underlying mechanism. Ischemia-reperfusion (I/R) injury of human brain microvascular endothelial cells (HBMECs) was induced by oxygen-glucose deprivation and reoxygenation (OGD/R). Reverse transcription quantitative real-time PCR (RT-qPCR) and western blotting analysis were performed to detect the expression of circDLGAP4, microRNA-6085 (miR-6085), growth differentiation factor 11 (GDF11), B-cell lymphoma-2 (BCL2) and BCL2-associated x protein (BAX). Cell viability, proliferation, and apoptosis were analyzed by cell counting kit-8, 5-Ethynyl-2'-deoxyuridine and flow cytometry analysis. Oxidative stress was analyzed by evaluating the levels of Malondialdehyde (MDA) and Reactive Oxygen Species (ROS) and the activity of Superoxide Dismutase (SOD). The associations among circDLGAP4, miR-6085 and GDF11 were identified by dual-luciferase reporter, RNA immunoprecipitation (RIP) and RNA pull-down assays. Celastrol reduced OGD/R-induced inhibition of circDLGAP4 expression in HBMECs. Celastrol treatment protected HBMECs from OGD/R-induced cell proliferation inhibition and apoptosis and oxidative stress promotion; however, circDLGAP4 depletion attenuated these effects. CircDLGAP4 acted as a sponge for miR-6085, and miR-6085 mimics restored circDLGAP4-mediated effects in OGD/R-stimulated HBMECs. In addition, GDF11 was identified as a targte of miR-6085, and participated in the regulation of miR-6085 to OGD/R-induced HBMEC damage. Further, circDLGAP4 absence inhibited GDF11 expression by interacting with miR-6085 under Celastrol treatment. Celastrol ameliorated OGD/R-induced HBMEC apoptosis and oxidative stress by circDLGAP4/miR-6085/GDF11 pathway, supporting the use of Celastrol as a therapeutic agent for cerebral infarction.

GDF11 promotes osteogenesis as opposed to MSTN, and follistatin, a MSTN/GDF11 inhibitor, increases muscle mass but weakens bone.

Growth and differentiation factor 11 (GDF11) and myostatin (MSTN) are closely related transforming growth factor ß (TGF-ß) family members, but their biological functions are quite distinct. While MSTN has been widely shown to inhibit muscle growth, GDF11 regulates skeletal patterning and organ development during embryogenesis. Postnatal functions of GDF11, however, remain less clear and controversial. Due to the perinatal lethality of Gdf11 null mice, previous studies used recombinant GDF11 protein to prove its postnatal function. However, recombinant GDF11 and MSTN proteins share nearly identical biochemical properties, and most GDF11-binding molecules have also been shown to bind MSTN, generating the possibility that the effects mediated by recombinant GDF11 protein actually reproduce the endogenous functions of MSTN. To clarify the endogenous functions of GDF11, here, we focus on genetic studies and show that Gdf11 null mice, despite significantly down-regulating Mstn expression, exhibit reduced bone mass through impaired osteoblast (OB) and chondrocyte (CH) maturations and increased osteoclastogenesis, while the opposite is observed in Mstn null mice that display enhanced bone mass. Mechanistically, Mstn deletion up-regulates Gdf11 expression, which activates bone morphogenetic protein (BMP) signaling pathway to enhance osteogenesis. Also, mice overexpressing follistatin (FST), a MSTN/GDF11 inhibitor, exhibit increased muscle mass accompanied by bone fractures, unlike Mstn null mice that display increased muscle mass without fractures, indicating that inhibition of GDF11 impairs bone strength. Together, our findings suggest that GDF11 promotes osteogenesis in contrast to MSTN, and these opposing roles of GDF11 and MSTN must be considered to avoid the detrimental effect of GDF11 inhibition when developing MSTN/GDF11 inhibitors for therapeutic purposes.

Inhibitor Design Strategy for Myostatin: Dynamics and Interaction Networks Define the Affinity and Release Mechanisms of the Inhibited Complexes.

Myostatin, an important negative regulator of muscle mass, is a therapeutic target for muscle atrophic disorders such as muscular dystrophy. Thus, the inhibition of myostatin presents a strategy to treat these disorders. It has long been established that the myostatin prodomain is a strong inhibitor of the mature myostatin, and the minimum peptide of the prodomain-corresponding to the α1-helix of its lasso-region-responsible for the inhibitory efficiency was defined and characterized as well. Here we show that the minimum peptide segment based on the growth differentiation factor 11 (GDF11), which we found to be more helical in its stand-alone solvated stfate than the similar segment of myostatin, is a promising new base scaffold for inhibitor design. The proposed inhibitory peptides in their solvated state and in complex with the mature myostatin were analyzed by in silico molecule modeling supplemented with the electronic circular dichroism spectroscopy measurements. We defined the Gaussian-Mahalanobis mean score to measure the fraction of dihedral angle-pairs close to the desired helical region of the Ramachandran-plot, carried out RING analysis of the peptide-protein interaction networks and characterized the internal motions of the complexes using our rigid-body segmentation protocol. We identified a variant-11m2-that is sufficiently ordered both in solvent and within the inhibitory complex, forms a high number of contacts with the binding-pocket and induces such changes in its internal dynamics that lead to a rigidified, permanently locked conformation that traps this peptide in the binding site. We also showed that the naturally evolved α1-helix has been optimized to simultaneously fulfill two very different roles: to function as a strong binder as well as a good leaving group. It forms an outstanding number of non-covalent interactions with the mature core of myostatin and maintains the most ordered conformation within the complex, while it induces independent movement of the gate-keeper ß-hairpin segment assisting the dissociation and also results in the least-ordered solvated form which provides extra stability for the dissociated state and discourages rebinding.

Pathophysiological levels of GDF11 activate Smad2/Smad3 signaling and induce muscle atrophy in human iPSC-derived myocytes.

Skeletal muscle mass is negatively regulated by several TGF-ß superfamily members. Myostatin (MSTN) is the most prominent negative regulator of muscle mass. Recent studies show that in addition to MSTN, GDF11, which shares a high sequence identity with MSTN, induces muscle atrophy in vitro and in vivo at supraphysiological levels, whereas controversy regarding its roles exists. Furthermore, higher circulating GDF11 levels associate with frailty in humans. On the other hand, little is known about the effect of pathophysiological levels of GDF11 on muscle atrophy. Here we seek to determine whether pathophysiological levels of GDF11 are sufficient to activate Smad2/Smad3 signaling and induce muscle atrophy using human iPSC-derived myocytes (hiPSC myocytes). We first show that incubating hiPSC myocytes with pathophysiological concentrations of GDF11 significantly reduces myocyte diameters. We next demonstrate that pathophysiological levels of GDF11 are sufficient to activate Smad2/3 signaling. Finally, we show that pathophysiological levels of GDF11 are capable of inducing the expression of Atrogin-1, an atrophy-promoting E3 ubiquitin ligase and that FOXO1 blockage reverses the GDF11-induced Atrogin-1 expression and atrophic phenotype. Collectively, our results suggest that GDF11 induces skeletal muscle atrophy at the pathophysiological levels through the GDF11-FOXO1 axis.

Neuroprotective effects of TRPV1 by targeting GDF11 in the Mpp+/MPTP-induced Parkinson's disease model.

Protecting dopaminergic neurons is a key approach in the prevention of Parkinson's disease (PD). Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel that is widely distributed in the mammalian nervous system. In this study, we designed experiments to investigate the effect and mechanisms of TRPV1 against DA neurons damage of PD. Our results showed that trpv1-deficient mice showed a significant loss of TH + neurons than PD mice after MPTP intraperitoneal injection, in addition, a significant decline in motor function was observed in trpv1-deficient mice versus the MPTP model. In addition, our study indicated that GDF11 overexpression inhibited MPP + - induced oxidative stress, cell senescence, and apoptosis in neurons. Results also showed that TRPV1 prevented the down-regulation of GDF11 expression in PD model, gdf11 knockdown blocks the effects of TRPV1 on the antioxidant, antiaging, and antiapoptotic activities of dopaminergic neurons. Consequently, our findings indicate that TRPV1 protects dopaminergic neurons from injury by promoting GDF11 expression in PD model.

Growth differentiation factor-11 downregulates steroidogenic acute regulatory protein expression through ALK5-mediated SMAD3 signaling pathway in human granulosa-lutein cells.

BACKGROUND: Growth differentiation factor-11 (GDF-11) belongs to the transforming growth factor-ß (TGF-ß) superfamily. To date, the expression of GDF-11 in the ovary and its role in regulating ovarian function are completely unknown. Ovarian granulosa cell-mediated steroidogenesis plays a pivotal role in maintaining normal female reproductive function. GDF-11 and GDF-8 share high sequence similarity and exhibit many similar features and functions. Steroidogenic acute regulatory protein (StAR) regulates the rate-limiting step in steroidogenesis and its expression can be downregulated by GDF-8. Polycystic ovary syndrome (PCOS) is the most common cause of female infertility. The expression levels of GDF-8 are upregulated in the human follicular fluid and granulosa-lutein (hGL) cells of PCOS patients. However, whether similar results can be observed for the GDF-11 needs to be determined. METHODS: The effect of GDF-11 on StAR expression and the underlying molecular mechanisms were explored by a series of in vitro experiments in a primary culture of hGL cells obtained from patients undergoing in vitro fertilization (IVF) treatment. Human follicular fluid samples were obtained from 36 non-PCOS patients and 36 PCOS patients. GDF-11 levels in follicular fluid were measured by ELISA. RESULTS: GDF-11 downregulates StAR expression, whereas the expression levels of the P450 side-chain cleavage enzyme (P450scc) and 3ß-hydroxysteroid dehydrogenase (3ß-HSD) are not affected by GDF-11 in hGL cells. Using pharmacological inhibitors and a siRNA-mediated approach, we reveal that ALK5 but not ALK4 mediates the suppressive effect of GDF-11 on StAR expression. Although GDF-11 activates both SMAD2 and SMAD3 signaling pathways, only SMAD3 is involved in the GDF-11-induced downregulation of StAR expression. In addition, we show that SMAD1/5/8, ERK1/2, and PI3K/AKT signaling pathways are not activated by GDF-11 in hGL cells. RT-qPCR and ELISA detect GDF-11 mRNA expression in hGL cells and GDF-11 protein expression in human follicular fluid, respectively. Interestingly, unlike GDF-8, the expression levels of GDF-11 are not varied in hGL cells and follicular fluid between non-PCOS and PCOS patients. CONCLUSIONS: This study increases the understanding of the biological function of GDF-11 and provides important insights into the regulation of ovarian steroidogenesis.

GDF-11 promotes human trophoblast cell invasion by increasing ID2-mediated MMP2 expression.

BACKGROUND: Growth differentiation factor-11 (GDF-11), also known as bone morphogenetic protein-11, belongs to the transforming growth factor-beta superfamily. GDF-11 was first identified as an important regulator during embryonic development. Increasing evidence has demonstrated that GDF-11 regulates the development of various organs and its aberrant expressions are associated with the risk of cardiovascular diseases and cancers. Extravillous trophoblast (EVT) cells invasion is a critical event for placenta development and needs to be finely regulated. However, to date, the biological function of GDF-11 in the human EVT cells remains unknown. METHODS: HTR-8/SVneo, a human EVT cell line, and primary cultures of human EVT cells were used to examine the effect of GDF-11 on matrix metalloproteinase 2 (MMP2) expression. Matrigel-coated transwell invasion assay was used to examine cell invasiveness. A series of in vitro experiments were applied to explore the underlying mechanisms that mediate the effect of GDF-11 on MMP2 expression and cell invasion. RESULTS: Treatment with GDF-11 stimulates MMP2 expression, in the HTR-8/SVneo and primary human EVT cells. Using a pharmacological inhibitor and siRNA-mediated knockdown approaches, our results demonstrated that the stimulatory effect of GDF-11 on MMP2 expression was mediated by the ALK4/5-SMAD2/3 signaling pathways. In addition, the expression of inhibitor of DNA-binding protein 2 (ID2) was upregulated by GDF-11 and that was required for the GDF-11-stimulated MMP2 expression and EVT cell invasion. CONCLUSIONS: These findings discover a new biological function and underlying molecular mechanisms of GDF-11 in the regulation of human EVT cell invasion. Video Abstract.

Dietary intake of GDF11 delays the onset of several biomarkers of aging in male mice through anti-oxidant system via Smad2/3 pathway.

Current studies have generated controversy over the age-related change in concentration of growth differentiation factor 11 (GDF11) and its role in the genesis of rejuvenation conditions. In this study, we displayed rGDF11 on the surface of Yarrowic Lipolytica (Y. lipolytica), and proved the bioavailability of the yeast-displayed rGDF11 by oral delivery in aged male mice. On the basis of these findings, we started to explore the anti-aging activity and underlying mechanisms of displayed rGDF11. It was found that dietary intake of displayed rGDF11 had little influence on the body weight and biochemical parameters of aged male mice, but delayed the occurrence and development of age-related biomarkers such as lipofuscin (LF) and senescence-associated-ß-galactosidase, and to some extent, prolonged the lifespan of aged male mice. Moreover, we demonstrated once again that dietary intake of displayed rGDF11 enhanced the activity of anti-oxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPX), reduced the reactive oxygen species (ROS) level, and slowed down the protein oxidation and lipid peroxidation. Importantly, we showed for the first time that rGDF11 enhanced the activity of CAT, SOD and GPX through activation of the Smad2/3 signaling pathway. Our study also provided a simple and safe route for delivery of recombinant GDF11, facilitating its therapeutic application in the future.

Structural characterization of an activin class ternary receptor complex reveals a third paradigm for receptor specificity.

TGFß family ligands, which include the TGFßs, BMPs, and activins, signal by forming a ternary complex with type I and type II receptors. For TGFßs and BMPs, structures of ternary complexes have revealed differences in receptor assembly. However, structural information for how activins assemble a ternary receptor complex is lacking. We report the structure of an activin class member, GDF11, in complex with the type II receptor ActRIIB and the type I receptor Alk5. The structure reveals that receptor positioning is similar to the BMP class, with no interreceptor contacts; however, the type I receptor interactions are shifted toward the ligand fingertips and away from the dimer interface. Mutational analysis shows that ligand type I specificity is derived from differences in the fingertips of the ligands that interact with an extended loop specific to Alk4 and Alk5. The study also reveals differences for how TGFß and GDF11 bind to the same type I receptor, Alk5. For GDF11, additional contacts at the fingertip region substitute for the interreceptor interactions that are seen for TGFß, indicating that Alk5 binding to GDF11 is more dependent on direct contacts. In support, we show that a single residue of Alk5 (Phe84), when mutated, abolishes GDF11 signaling, but has little impact on TGFß signaling. The structure of GDF11/ActRIIB/Alk5 shows that, across the TGFß family, different mechanisms regulate type I receptor binding and specificity, providing a molecular explanation for how the activin class accommodates low-affinity type I interactions without the requirement of cooperative receptor interactions.

The relationship between transforming growth factor ß superfamily members (GDF11 and BMP4) and lumbar spine bone mineral density in postmenopausal Chinese women.

PURPOSE: The relationship between transforming growth factor ß superfamily members (GDF11 and BMP4) and bone metabolism remains controversial. The aim of this study was to investigate the association between serum GDF11 and BMP4 levels and lumbar spine bone mineral density (LBMD) in a cohort of postmenopausal Chinese women. METHODS: This was a non-prospective cross-sectional study of 350 postmenopausal women with a mean age of 63.13 ± 8.66 years who came from Shenyang, China. LBMD was measured using dual-energy X-ray absorptiometry. Serum GDF11 and BMP4 concentrations were detected using a sandwich enzyme immunoassay kit. Pearson's correlation analysis and regression analyses were carried out to investigate the relationships between LBMD and serum GDF11 and BMP4 levels. RESULTS: A linear association between LBMD and serum LgGDF11 concentration was observed after adjusting for numerous confounders (P = 0.018). In addition, the osteoporosis (OP) was inversely related to LgGDF11 and the odds ratios for postmenopausal women with lumbar OP in LgGDF11 quartile group 2, group 3, and group 4 were 0.46 (95% CI 0.23-0.90, P < 0.05), 0.41 (95% CI 0.20-0.84, P < 0.05), and 0.30 (95% CI 0.14-0.63, P < 0.01), respectively (P = 0.001 for the trend), when compared to the highest quartile of LgGDF11 after adjustments for many confounding variables in this study. CONCLUSIONS: This study showed that serum GDF11 levels were linearly related to LBMD, and it was also revealed that serum GDF11 levels were significantly associated with lumbar OP in postmenopausal women. However, serum BMP4 levels were not associated with LBMD and lumbar OP.

Multifaceted Benefits of GDF11 Treatment in Spinal Cord Injury: In Vitro and In Vivo Studies.

Traumatic spinal cord injury (SCI) initiates a series of cellular and molecular events that include both primary and secondary injury cascades. This secondary cascade provides opportunities for the delivery of therapeutic intervention. Growth differentiation factor 11 (GDF11), a member of the transforming growth factor-ß (TGF-ß) superfamily, regulates various biological processes in mammals. The effects of GDF11 in the nervous system were not fully elucidated. Here, we perform extensive in vitro and in vivo studies to unravel the effects of GDF11 on spinal cord after injury. In vitro culture studies showed that GDF11 increased the survival of both neuronal and oligodendroglial cells but decreased microglial cells. In stressed cultures, GDF11 effectively inhibited LPS stimulation and also protected neurons from ischemic damage. Intravenous GDF11 administration to rat after eliciting SCI significantly improved hindlimb functional restoration of SCI rats. Reduced neuronal connectivity was evident at 6 weeks post-injury and these deficits were markedly attenuated by GDF11 treatment. Furthermore, SCI-associated oligodendroglial alteration were more preserved by GDF11 treatment. Taken together, GDF11 infusion via intravenous route to SCI rats is beneficial, facilitating its therapeutic application in the future.

The role of GDF11 in aging and skeletal muscle, cardiac and bone homeostasis.

GDF11 is a secreted factor in the TGFß family of cytokines. Its nearest neighbor evolutionarily is myostatin, a factor discovered as being a negative regulator of skeletal muscle growth. High profile studies several years ago suggested that GDF11 declines with age, and that restoration of systemic GDF11 to 'youthful' levels is beneficial for several age-related conditions. Particularly surprising was a report that supplementation of GDF11 aided skeletal muscle regeneration, as its homolog, myostatin, has the opposite role. Given this apparent contradiction in functionality, multiple independent labs sought to discern differences between the two factors and better elucidate age-related changes in circulating GDF11, with most failing to reproduce the initial finding of declining GDF11 levels, and, importantly, all subsequent studies examining the effects of GDF11 on skeletal muscle described an inhibitory effect on regeneration - and that higher doses induce skeletal muscle atrophy and cachexia. There have also been several studies examining the effect of GDF11 and/or the downstream ActRII pathway on cardiac function, along with several interesting reports on bone. A review of the GDF11 literature, as it relates in particular to aging and skeletal muscle, cardiac and bone biology, is presented.

GDF11 prevents the formation of thoracic aortic dissection in mice: Promotion of contractile transition of aortic SMCs.

Thoracic aortic dissection (TAD) is an aortic disease associated with dysregulated extracellular matrix composition and de-differentiation of vascular smooth muscle cells (SMCs). Growth Differentiation Factor 11 (GDF11) is a member of transforming growth factor ß (TGF-ß) superfamily associated with cardiovascular diseases. The present study attempted to investigate the expression of GDF11 in TAD and its effects on aortic SMC phenotype transition. GDF11 level was found lower in the ascending thoracic aortas of TAD patients than healthy aortas. The mouse model of TAD was established by ß-aminopropionitrile monofumarate (BAPN) combined with angiotensin II (Ang II). The expression of GDF11 was also decreased in thoracic aortic tissues accompanied with increased inflammation, arteriectasis and elastin degradation in TAD mice. Administration of GDF11 mitigated these aortic lesions and improved the survival rate of mice. Exogenous GDF11 and adeno-associated virus type 2 (AAV-2)-mediated GDF11 overexpression increased the expression of contractile proteins including ACTA2, SM22α and myosin heavy chain 11 (MYH11) and decreased synthetic markers including osteopontin and fibronectin 1 (FN1), indicating that GDF11 might inhibit SMC phenotype transition and maintain its contractile state. Moreover, GDF11 inhibited the production of matrix metalloproteinase (MMP)-2, 3, 9 in aortic SMCs. The canonical TGF-ß (Smad2/3) signalling was enhanced by GDF11, while its inhibition suppressed the inhibitory effects of GDF11 on SMC de-differentiation and MMP production in vitro. Therefore, we demonstrate that GDF11 may contribute to TAD alleviation via inhibiting inflammation and MMP activity, and promoting the transition of aortic SMCs towards a contractile phenotype, which provides a therapeutic target for TAD.