Association of growth differentiation factor 11/8, putative anti-ageing factor, with cardiovascular outcomes and overall mortality in humans: analysis of the Heart and Soul and HUNT3 cohorts

GDF-11 prevents cardiomyocyte hypertrophy by maintaining the sarcoplasmic reticulum-mitochondria communication

Growth differentiation factor 11 (GDF11) is a novel factor with controversial effects on cardiac hypertrophy both in vivo and in vitro. Although recent evidence has corroborated that GDF11 prevents the development of cardiac hypertrophy, its molecular mechanism remains unclear. In our previous work, we showed that norepinephrine (NE), a physiological pro-hypertrophic agent, increases cytoplasmic Ca²⁺ levels accompanied by a loss of physical and functional communication between sarcoplasmic reticulum (SR) and mitochondria, with a subsequent reduction in the mitochondrial Ca²⁺ uptake and mitochondrial metabolism. In order to study the anti-hypertrophic mechanism of GDF11, our aim was to investigate whether GDF11 prevents the loss of SR-mitochondria communication triggered by NE. Our results show that: a) GDF11 prevents hypertrophy in cultured neonatal rat ventricular myocytes treated with NE. b) GDF11 attenuates the NE-induced loss of contact sites between both organelles. c) GDF11 increases oxidative mitochondrial metabolism by stimulating mitochondrial Ca²⁺ uptake. In conclusion, the GDF11-dependent maintenance of physical and functional communication between SR and mitochondria is critical to allow Ca²⁺ transfer between both organelles and energy metabolism in the cardiomyocyte and to avoid the activation of Ca²⁺-dependent pro-hypertrophic signaling pathways.

Growth differentiation factor 11 is involved in isoproterenol‑induced heart failure

The present study aimed to investigate the potential effects of growth differentiation factor 11 (GDF11) on isoproterenol (ISO)-induced heart failure (HF) and identify the underlying molecular mechanisms. A rat model of HF was induced in vivo by intraperitoneally administering ISO (5 mg/kg/day) for 7 days. After 4 weeks following establishment of the HF model, hemodynamic analysis demonstrated that ISO induced a significant increase in the left ventricular end-diastolic pressure and a decrease in the left ventricular systolic pressure and maximum contraction velocity. The plasma levels of myocardial injury markers, including lactate dehydrogenase (LDH), creatine kinase (CK), CK-muscle/brain which were determined using the corresponding assay kits and plasma brain natriuretic peptide which was detected by an ELISA kit, an important biomarker of HF, increased following ISO treatment. Furthermore, levels of GDF11 expression and protein, which were estimated using reverse transcription-quantitative polymerase chain reaction and an ELISA kit in plasma and western blotting in the heart tissue, respectively, significantly increased following ISO treatment. To demonstrate the effects of ISO on GDF11 production in cardiomyocytes, H9C2 cells (a cardiomyoblast cell line derived from embryonic rat heart tissue) were treated with ISO (50 nM) for 24 h in vitro; it was revealed that GDF11 protein and mRNA expression levels significantly increased following ISO treatment. In addition, recombinant GDF11 (rGDF11) administered to ISO-treated H9C2 cells resulted in decreased proliferation, which was detected via a CCK-8 assay, and increased LDH levels and cell apoptosis of cells, which was determined using Caspase-3 activity and Hoechst 33258 staining. Additionally, rGDF11 increased the levels of reactive oxygen species and malondialdehyde due to the upregulation of nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) following rGDF11 treatment. Conversely, GDF11 knockdown reduced ISO-induced apoptosis by inhibiting oxidative stress injury. The results suggested that GDF11 production was upregulated in ISO-induced rats with HF and in ISO-treated H9C2 cells, and that rGDF11 treatment increased ISO-induced oxidative stress injury by upregulating Nox4 in H9C2 cells.

Activin type II receptor signaling in cardiac aging and heart failure

Activin type II receptor (ActRII) ligands have been implicated in muscle wasting in aging and disease. However, the role of these ligands and ActRII signaling in the heart remains unclear. Here, we investigated this catabolic pathway in human aging and heart failure (HF) using circulating follistatin-like 3 (FSTL3) as a potential indicator of systemic ActRII activity. FSTL3 is a downstream regulator of ActRII signaling, whose expression is up-regulated by the major ActRII ligands, activin A, circulating growth differentiation factor-8 (GDF8), and GDF11. In humans, we found that circulating FSTL3 increased with aging, frailty, and HF severity, correlating with an increase in circulating activins. In mice, increasing circulating activin A increased cardiac ActRII signaling and FSTL3 expression, as well as impaired cardiac function. Conversely, ActRII blockade with either clinical-stage inhibitors or genetic ablation reduced cardiac ActRII signaling while restoring or preserving cardiac function in multiple models of HF induced by aging, sarcomere mutation, or pressure overload. Using unbiased RNA sequencing, we show that activin A, GDF8, and GDF11 all induce a similar pathologic profile associated with up-regulation of the proteasome pathway in mammalian cardiomyocytes. The E3 ubiquitin ligase, Smurf1, was identified as a key downstream effector of activin-mediated ActRII signaling, which increased proteasome-dependent degradation of sarcoplasmic reticulum Ca2+ ATPase (SERCA2a), a critical determinant of cardiomyocyte function. Together, our findings suggest that increased activin/ActRII signaling links aging and HF pathobiology and that targeted inhibition of this catabolic pathway holds promise as a therapeutic strategy for multiple forms of HF.

Adult Cardiac Stem Cell Aging: A Reversible Stochastic Phenomenon?

Aging is by far the dominant risk factor for the development of cardiovascular diseases, whose prevalence dramatically increases with increasing age reaching epidemic proportions. In the elderly, pathologic cellular and molecular changes in cardiac tissue homeostasis and response to injury result in progressive deteriorations in the structure and function of the heart. Although the phenotypes of cardiac aging have been the subject of intense study, the recent discovery that cardiac homeostasis during mammalian lifespan is maintained and regulated by regenerative events associated with endogenous cardiac stem cell (CSC) activation has produced a crucial reconsideration of the biology of the adult and aged mammalian myocardium. The classical notion of the adult heart as a static organ, in terms of cell turnover and renewal, has now been replaced by a dynamic model in which cardiac cells continuously die and are then replaced by CSC progeny differentiation. However, CSCs are not immortal. They undergo cellular senescence characterized by increased ROS production and oxidative stress and loss of telomere/telomerase integrity in response to a variety of physiological and pathological demands with aging. Nevertheless, the old myocardium preserves an endogenous functionally competent CSC cohort which appears to be resistant to the senescent phenotype occurring with aging. The latter envisions the phenomenon of CSC ageing as a result of a stochastic and therefore reversible cell autonomous process. However, CSC aging could be a programmed cell cycle-dependent process, which affects all or most of the endogenous CSC population. The latter would infer that the loss of CSC regenerative capacity with aging is an inevitable phenomenon that cannot be rescued by stimulating their growth, which would only speed their progressive exhaustion. The resolution of these two biological views will be crucial to design and develop effective CSC-based interventions to counteract cardiac aging not only improving health span of the elderly but also extending lifespan by delaying cardiovascular disease-related deaths.

Inhibitory effects of growth differentiation factor 11 on autophagy deficiency-induced dedifferentiation of arterial smooth muscle cells

Growth differentiation factor (GDF)11 has been reported to reverse age-related cardiac hypertrophy in mice and cause youthful regeneration of cardiomyocytes. The present study attempted to test a hypothesis that GDF11 counteracts the pathologic dedifferentiation of mouse carotid arterial smooth muscle cells (CASMCs) due to deficient autophagy. By real-time RT-PCR and Western blot analysis, exogenously administrated GDF11 was found to promote CASMC differentiation with increased expression of various differentiation markers (α-smooth muscle actin, myogenin, myogenic differentiation, and myosin heavy chain) as well as decreased expression of dedifferentiation markers (vimentin and proliferating cell nuclear antigen). Upregulation of the GDF11 gene by trichostatin A (TSA) or CRISPR-cas9 activating plasmids also stimulated the differentiation of CASMCs. Either GDF11 or TSA treatment blocked 7-ketocholesterol-induced CASMC dedifferentiation and autophagosome accumulation as well as lysosome inhibitor bafilomycin-induced dedifferentiation and autophagosome accumulation. Moreover, in CASMCs from mice lacking the CD38 gene, an autophagy deficiency model in CASMCs, GDF11 also inhibited its phenotypic transition to dedifferentiation status. Correspondingly, TSA treatment was shown to decrease GDF11 expression and reverse CASMC dedifferentiation in the partial ligated carotid artery of mice. The inhibitory effects of TSA on dedifferentiation of CASMCs were accompanied by reduced autophagosome accumulation in the arterial wall, which was accompanied by attenuated neointima formation in partial ligated carotid arteries. We concluded that GDF11 promotes CASMC differentiation and prevents the phenotypic transition of these cells induced by autophagosome accumulation during different pathological stimulations, such as Western diet, lysosome function deficiency, and inflammation. NEW & NOTEWORTHY The present study demonstrates that growth differentiation factor (GDF)11 promotes autophagy and subsequent differentiation in carotid arterial smooth muscle cells. Upregulation of GDF11 counteracts dedifferentiation under different pathological conditions. These findings provide novel insights into the regulatory role of GDF11 in the counteracting of sclerotic arterial diseases and also suggest that activation or induction of GDF11 may be a new therapeutic strategy for the treatment or prevention of these diseases.

Novel biomolecules of ageing, sex differences and potential underlying mechanisms of telomere shortening in coronary artery disease

Telomere length (TL), growth differentiate factor (GDF)11, insulin growth factor (IGF)1, sirtuin (SIRT)1 and inflammatory processes have been related to ageing and age-related diseases, like coronary artery disease (CAD). We aimed to investigate the associations between leukocyte TLs (LTLs), chronological age, sex and comorbidities in CAD patients. Any covariations between LTL, GDF11, IGF1, SIRT-1 and pro-inflammatory cytokines were further assessed.

METHODS

In 300 patients with stable CAD (age 36-81 years, 20% females), DNA and RNA were isolated from whole blood for PCR analysis and relative quantification of LTLs and gene-expression of GDF11, IGF1,SIRT1, IL-12, IL-18 and IFNƴ, respectively. Serum was prepared for the analyses of circulating IL-18, IL-12, IL-6 and TNFα.

RESULTS

Patients with previous myocardial infarction (MI) presented with 20% shorter LTLs vs. patients without (p = 0.019) indicating LTLs to be of importance for CAD severity. The observation however, was only observed in men (p = 0.009, n = 115), in which the upper LTL quartile associated with 64% lower frequency of previous MI compared to quartile 1-3 (p = 0.005, adjusted). LTLs were not differently distributed according to sex or comorbidities such as hypertension, diabetes type 2 and metabolic syndrome. LTLs and GDF11 were inversely correlated to age (r = -0.17; p = 0.007 and r = -0.16; p = 0.010, respectively), however, separated in gender, LTL only in women (r = -0.37) and GDF11 only in men (r = -0.19) (p = 0.006, both). GDF11 and SIRT1 were strongly inter-correlated (r = 0.56, p ≤ 0.001), suggesting common upstream regulators. LTLs were moderately correlated to GDF11 and SIRT1 in overweight women (BMI ≥ 25 kg/m²) (r = 0.41; p = 0.027 and 0.43; p = 0.020, respectively), which may reflect common life-style influences on LTLs and these markers. In all women, we observed further that the highest LTL quartile associated with higher GDF11 and SIRT expression and lower circulating levels of IL-12, IL-18 and TNFα, as compared to quartile 1, which may indicate lifestyle influences on female LTLs. In men, the highest LTL quartile associated with lower IFNƴ expression and lower circulating TNFα. Overall, the results indicate an association between chronic low-grade inflammation and LTLs.

CONCLUSIONS

Shorter LTLs in CAD patients with previously suffered MI may indicate telomere attrition as part of its pathophysiology in men. The inverse association between LTLs and age exclusively in women underpins the previously reported decline in attrition rate in men with increasing age. As elevated GDF11 and SIRT1 along with attenuated pro-inflammatory cytokines seem to positively affect LTL in women, we hypothesize a potential sex-dimorphism in LTL regulation, which may implicate sex- adjusted health-preventive therapies.

Iron metabolism under conditions of ineffective erythropoiesis in β-thalassemia

β-Thalassemia (BT) is an inherited genetic disorder that is characterized by ineffective erythropoiesis (IE), leading to anemia and abnormal iron metabolism. IE is an abnormal expansion of the number of erythroid progenitor cells with unproductive synthesis of enucleated erythrocytes, leading to anemia and hypoxia. Anemic patients affected by BT suffer from iron overload, even in the absence of chronic blood transfusion, suggesting the presence of ≥1 erythroid factor with the ability to modulate iron metabolism and dietary iron absorption. Recent studies suggest that decreased erythroid cell differentiation and survival also contribute to IE, aggravating the anemia in BT. Furthermore, hypoxia can also affect and increase iron absorption. Understanding the relationship between iron metabolism and IE could provide important insights into the BT condition and help to develop novel treatments. In fact, genetic or pharmacological manipulations of iron metabolism or erythroid cell differentiation and survival have been shown to improve IE, iron overload, and anemia in animal models of BT. Based on those findings, new therapeutic approaches and drugs have been proposed; clinical trials are underway that have the potential to improve erythrocyte production, as well as to reduce the iron overload and organ toxicity in BT and in other disorders characterized by IE.

Regenerative Capacity of Endogenous Factor: Growth Differentiation Factor 11; a New Approach of the Management of Age-Related Cardiovascular Events

Aging is a complicated pathophysiological process accompanied by a wide array of biological adaptations. The physiological deterioration correlates with the reduced regenerative capacity of tissues. The rejuvenation of tissue regeneration in aging organisms has also been observed after heterochronic parabiosis. With this model, it has been shown that exposure to young blood can rejuvenate the regenerative capacity of peripheral tissues and brain in aged animals. An endogenous compound called growth differentiation factor 11 (GDF11) is a circulating negative regulator of cardiac hypertrophy, suggesting that raising GDF11 levels could potentially treat or prevent cardiac diseases. The protein GDF11 is found in humans as well as animals. The existence of endogenous regulators of regenerative capacity, such as GDF11, in peripheral tissues and brain has now been demonstrated. It will be important to investigate the mechanisms with therapeutic promise that induce the regenerative effects of GDF11 for a variety of age-related diseases.

Pregnancy protects the kidney from acute ischemic injury

A complex analysis of acute kidney injury (AKI) in pregnant women shows that it is caused by the interaction of gestation-associated pathologies and beneficial signaling pathways activated by pregnancy. Studies report an increase in the regeneration of some organs during pregnancy. However, the kidney response to the injury during pregnancy has not been addressed. We investigated the mechanisms of the pregnancy influence on AKI. During pregnancy, the kidneys were shown to be more tolerant to AKI. Pregnant animals showed remarkable preservation of kidney functions after ischemia/reperfusion (I/R) indicated by the decrease of serum creatinine levels. The pregnant rats also demonstrated a significant decrease in kidney injury markers and an increase in protective markers. Two months after the I/R, group of pregnant animals had a decreased level of fibrosis in the kidney tissue. These effects are likely linked to increased cell proliferation after injury: using real-time cell proliferation monitoring we demonstrated that after ischemic injury, cells isolated from pregnant animal kidneys had higher proliferation potential vs. control animals; it was also supported by an increase of proliferation marker PCNA levels in kidneys of pregnant animals. We suggest that these effects are associated with hormonal changes in the maternal organism, since hormonal pseudopregnancy simulated effects of pregnancy.

GDF11 induces differentiation and apoptosis and inhibits migration of C17.2 neural stem cells via modulating MAPK signaling pathway

GDF11, a member of TGF-β superfamily, has recently received widespread attention as a novel anti-ageing/rejuvenation factor to reverse age-related dysfunctions in heart and skeletal muscle, and to induce angiogenesis and neurogenesis. However, these positive effects of GDF11 were challenged by several other studies. Furthermore, the mechanism is still not well understood. In the present study, we evaluated the effects of GDF11 on C17.2 neural stem cells. GDF11 induced differentiation and apoptosis, and suppressed migration of C17.2 neural stem cells. In addition, GDF11 slightly increased cell viability after 24 h treatment, showed no effects on proliferation for about 10 days of cultivation, and slightly decreased cumulative population doubling for long-term treatment (p < 0.05). Phospho-proteome profiling array displayed that GDF11 significantly increased the phosphorylation of 13 serine/threonine kinases (p < 0.01), including p-p38, p-ERK and p-Akt, in C17.2 cells, which implied the activation of MAPK pathway. Western blot validated that the results of phospho-proteome profiling array were reliable. Based on functional analysis, we demonstrated that the differentially expressed proteins were mainly involved in signal transduction which was implicated in cellular behavior. Collectively, our findings suggest that, for neurogenesis, GDF11 might not be the desired rejuvenation factor, but a potential target for pharmacological blockade.

The aging heart

As the elderly segment of the world population increases, it is critical to understand the changes in cardiac structure and function during the normal aging process. In this review, we outline the key molecular pathways and cellular processes that underlie the phenotypic changes in the heart and vasculature that accompany aging. Reduced autophagy, increased mitochondrial oxidative stress, telomere attrition, altered signaling in insulin-like growth factor, growth differentiation factor 11, and 5'- AMP-activated protein kinase pathways are among the key molecular mechanisms underlying cardiac aging. Aging promotes structural and functional changes in the atria, ventricles, valves, myocardium, pericardium, the cardiac conduction system, and the vasculature. We highlight the factors known to accelerate and attenuate the intrinsic aging of the heart and vessels in addition to potential preventive and therapeutic avenues. A greater understanding of the processes involved in cardiac aging may facilitate our ability to mitigate the escalating burden of CVD in older individuals and promote healthy cardiac aging.

GDF11 Modulates Ca2+-Dependent Smad2/3 Signaling to Prevent Cardiomyocyte Hypertrophy

Growth differentiation factor 11 (GDF11), a member of the transforming growth factor-β family, has been shown to act as a negative regulator in cardiac hypertrophy. Ca²⁺ signaling modulates cardiomyocyte growth; however, the role of Ca²⁺-dependent mechanisms in mediating the effects of GDF11 remains elusive. Here, we found that GDF11 induced intracellular Ca²⁺ increases in neonatal rat cardiomyocytes and that this response was blocked by chelating the intracellular Ca²⁺ with BAPTA-AM or by pretreatment with inhibitors of the inositol 1,4,5-trisphosphate (IP₃) pathway. Moreover, GDF11 increased the phosphorylation levels and luciferase activity of Smad2/3 in a concentration-dependent manner, and the inhibition of IP₃-dependent Ca²⁺ release abolished GDF11-induced Smad2/3 activity. To assess whether GDF11 exerted antihypertrophic effects by modulating Ca²⁺ signaling, cardiomyocytes were exposed to hypertrophic agents (100 nM testosterone or 50 μM phenylephrine) for 24 h. Both treatments increased cardiomyocyte size and [³H]-leucine incorporation, and these responses were significantly blunted by pretreatment with GDF11 over 24 h. Moreover, downregulation of Smad2 and Smad3 with siRNA was accompanied by inhibition of the antihypertrophic effects of GDF11. These results suggest that GDF11 modulates Ca²⁺ signaling and the Smad2/3 pathway to prevent cardiomyocyte hypertrophy.

Endoplasmic Reticulum Stress Induces Myostatin High Molecular Weight Aggregates and Impairs Mature Myostatin Secretion

Sporadic inclusion body myositis (sIBM) is the most prevalent acquired muscle disorder in the elderly with no defined etiology or effective therapy. Endoplasmic reticulum stress and deposition of myostatin, a secreted negative regulator of muscle growth, have been implicated in disease pathology. The myostatin signaling pathway has emerged as a major target for symptomatic treatment of muscle atrophy. Here, we systematically analyzed the maturation and secretion of myostatin precursor MstnPP and its metabolites in a human muscle cell line. We find that increased MsntPP protein levels induce ER stress. MstnPP metabolites were predominantly retained within the endoplasmic reticulum (ER), also evident in sIBM histology. MstnPP cleavage products formed insoluble high molecular weight aggregates, a process that was aggravated by experimental ER stress. Importantly, ER stress also impaired secretion of mature myostatin. Reduced secretion and aggregation of MstnPP metabolites were not simply caused by overexpression, as both events were also observed in wildtype cells under ER stress. It is tempting to speculate that reduced circulating myostatin growth factor could be one explanation for the poor clinical efficacy of drugs targeting the myostatin pathway in sIBM.

Growth differentiation factor 11 improves neurobehavioral recovery and stimulates angiogenesis in rats subjected to cerebral ischemia/reperfusion

The recent suggestion that growth differentiation factor 11 (GDF11) acts as a rejuvenation factor has remained controversial. However, in addition to its role in aging, the relationship between GDF11 and cerebral ischemia is still an important area that needs more investigation. Here we examined effects of GDF11 on angiogenesis and recovery of neurological function in a rat model of stroke. Exogenous recombinant GDF11 (rGDF11) at different doses were directly injected into the tail vein in rats subjected to cerebral ischemia/reperfusion (I/R). Neurobehavioral tests were performed, the proliferation of endothelial cells (ECs) and GDF11 downstream signal activin-like kinase 5 (ALK5) were assessed, and functional microvessels were measured. Results showed that rGDF11 at a dosage of 0.1 mg/kg/day could effectively activate cerebral angiogenesis in vivo. In addition, rGDF11 improved the modified neurological severity scores and the adhesive removal somatosensory test, promoted proliferation of ECs, induced ALK5 and increased vascular surface area and the number of vascular branch points in the peri-infarct cerebral cortex after cerebral I/R. These effects were suppressed by blocking ALK5. Our novel findings shed new light on the role of GDF11. Our results strongly suggest that GDF11 improves neurofunctional recovery from cerebral I/R injury and that this effect is mediated partly through its proangiogenic effect in the peri-infarct cerebral cortex, which is associated with ALK5. Thus, GDF11/ALK5 may represent new therapeutic targets for aiding recovery from stroke.

GDF11 administration does not extend lifespan in a mouse model of premature aging

GDF11 has recently emerged as a powerful anti-aging candidate, found in young blood, capable of rejuvenating a number of aged tissues, such as heart, skeletal muscle and brain. However, recent reports have shown contradictory data questioning its capacity to reverse age-related tissue dysfunction. The availability of a mouse model of accelerated aging, which shares most of the features occurring in physiological aging, gives us an excellent opportunity to test in vivo therapies aimed at extending lifespan both in pathological and normal aging. On this basis, we wondered whether the proposed anti-aging functions of GDF11 would have an overall effect on longevity. We first confirmed the existence of a reduction in GDF11/8 levels in our mouse model of accelerated aging compared with wild-type littermates. However, we show herein that GDF11 daily administration does not extend lifespan of premature-aged mice.

Decline in cellular function of aged mouse c-kit+ cardiac progenitor cells

KEY POINTS

While autologous stem cell-based therapies are currently being tested on elderly patients, there are limited data on the function of aged stem cells and in particular c-kit⁺ cardiac progenitor cells (CPCs). We isolated c-kit⁺ cells from young (3 months) and aged (24 months) C57BL/6 mice to compare their biological properties. Aged CPCs have increased senescence, decreased stemness and reduced capacity to proliferate or to differentiate following dexamethasone (Dex) treatment in vitro, as evidenced by lack of cardiac lineage gene upregulation. Aged CPCs fail to activate mitochondrial biogenesis and increase proteins involved in mitochondrial oxidative phosphorylation in response to Dex. Aged CPCs fail to upregulate paracrine factors that are potentially important for proliferation, survival and angiogenesis in response to Dex. The results highlight marked differences between young and aged CPCs, which may impact future design of autologous stem cell-based therapies.

ABSTRACT

Therapeutic use of c-kit⁺ cardiac progenitor cells (CPCs) is being evaluated for regenerative therapy in older patients with ischaemic heart failure. Our understanding of the biology of these CPCs has, however, largely come from studies of young cells and animal models. In the present study we examined characteristics of CPCs isolated from young (3 months) and aged (24 months) mice that could underlie the diverse outcomes reported for CPC-based therapeutics. We observed morphological differences and altered senescence indicated by increased senescence-associated markers β-galactosidase and p16 mRNA in aged CPCs. The aged CPCs also proliferated more slowly than their young counterparts and expressed lower levels of the stemness marker LIN28. We subsequently treated the cells with dexamethasone (Dex), routinely used to induce commitment in CPCs, for 7 days and analysed expression of cardiac lineage marker genes. While MEF2C, GATA4, GATA6 and PECAM mRNAs were significantly upregulated in response to Dex treatment in young CPCs, their expression was not increased in aged CPCs. Interestingly, Dex treatment of aged CPCs also failed to increase mitochondrial biogenesis and expression of the mitochondrial proteins Complex III and IV, consistent with a defect in mitochondria complex assembly in the aged CPCs. Dex-treated aged CPCs also had impaired ability to upregulate expression of paracrine factor genes and the conditioned media from these cells had reduced ability to induce angiogenesis in vitro. These findings could impact the design of future CPC-based therapeutic approaches for the treatment of older patients suffering from cardiac injury.

Role of growth differentiation factor 11 in development, physiology and disease

Growth differentiation factor (GDF11) is a member of TGF-β/BMP superfamily that activates Smad and non-Smad signaling pathways and regulates expression of its target nuclear genes. Since its discovery in 1999, studies have shown the involvement of GDF11 in normal physiological processes, such as embryonic development and erythropoiesis, as well as in the pathophysiology of aging, cardiovascular disease, diabetes mellitus, and cancer. In addition, there are contradictory reports regarding the role of GDF11 in aging, cardiovascular disease, diabetes mellitus, osteogenesis, skeletal muscle development, and neurogenesis. In this review, we describe the GDF11 signaling pathway and its potential role in development, physiology and disease.

Emerging Affinity-Based Proteomic Technologies for Large-Scale Plasma Profiling in Cardiovascular Disease

Plasma biomarkers that reflect molecular states of the cardiovascular system are central for clinical decision making. Routinely used plasma biomarkers include troponins, natriuretic peptides, and lipoprotein particles, yet interrogate only a modest subset of pathways relevant to cardiovascular disease. Systematic profiling of a larger portion of circulating plasma proteins (the plasma proteome) will provide opportunities for unbiased discovery of novel markers to improve diagnostic or predictive accuracy. In addition, proteomic profiling may inform pathophysiological understanding and point to novel therapeutic targets. Obstacles for comprehensive proteomic profiling include the immense size and structural heterogeneity of the proteome, and the broad range of abundance levels, as well. Proteome-wide, untargeted profiling can be performed in tissues and cells with tandem mass spectrometry. However, applications to plasma are limited by the need for complex preanalytical sample preparation stages limiting sample throughput. Multiplexing of targeted methods based on capture and detection of specific proteins are therefore receiving increasing attention in plasma proteomics. Immunoaffinity assays are the workhorse for measuring individual proteins but have been limited for proteomic applications by long development times, cross-reactivity preventing multiplexing, specificity issues, and incomplete sensitivity to detect proteins in the lower range of the abundance spectrum (below picograms per milliliter). Emerging technologies to address these issues include nucleotide-labeled immunoassays and aptamer reagents that can be automated for efficient multiplexing of thousands of proteins at high sample throughput, coupling of affinity capture methods to mass spectrometry for improved specificity, and ultrasensitive detection systems to measure low-abundance proteins. In addition, proteomics can now be integrated with modern genomics tools to comprehensively relate proteomic profiles to genetic variants, which may both influence binding of affinity reagents and serve to validate the target specificity of affinity assays. The application of deep quantitative proteomic profiling to large cohorts has thus become increasingly feasible with emerging affinity methods. The aims of this article are to provide the broad readership of Circulation with a timely overview of emerging methods for affinity proteomics and recent progress in cardiovascular medicine based on such methods.

Quantitation of circulating GDF-11 and β2-MG in aged patients with age-related impairment in cognitive function

Growth differentiation factor 11 (GDF-11) has been implicated in reverse effects of ageing on the central nervous system of humans. β2-microglobulin (β2-MG) has been reported to negatively regulate cognition. However, there is a lot of controversy about the role of GDF-11 and β2-MG in ageing and cognitive regulation. To examine the involvement of GDF-11 and β2-MG in the ageing process and cognitive dysfunction, a total of 51 healthy subjects and 41 elderly patients with different degrees of age-related cognitive impairment participated in the study. We measured plasma GDF-11 and β2-MG levels using ELISA and immunoturbidimetry, respectively. The results were statistically analyzed to evaluate the associations between levels of GDF-11 and β2-MG, and ageing and cognitive impairments. Circulating GDF-11 levels did not decline with age or correlate with ageing in healthy Chinese males. We did not detect differences in circulating GDF-11 levels amongst the healthy advanced age and four cognitive impairment groups. β2-MG levels increased with age, but there was no significant difference between healthy elderly males and advanced age males. Increased levels of β2-MG were observed in the dementia group compared with the healthy advanced age group. Our results suggest that circulating GDF-11 may not exert a protective effect during the ageing process or on cognitive function, and β2-MG may play a role in ageing and cognitive impairment. However, it is possible that the relatively small sample size in the present study affected the quality of the statistical analysis, and future studies are needed to further validate our findings.

The Growth Differentiation Factor 11 (GDF11) and Myostatin (MSTN) in tissue specific aging

Growth differentiation factor 11 (GDF11) and myostatin (MSTN) are evolutionarily conserved homologues proteins which are closely related members of the transforming growth factor β superfamily. They are often perceived to serve similar or overlapping roles. Recently, GDF11 has been identified as playing a role during aging, however there are conflicting reports as to the nature of this role. In this review, we will discuss the literature regarding functions of GDF11 and myostatin in the heart, brain, and skeletal muscle during aging. Consequently we expect to develop a deeper understanding about the function of these two proteins in organismal aging and disease.

Decrease in an anti-ageing factor, growth differentiation factor 11, in chronic obstructive pulmonary disease

RATIONALE

Cellular senescence is observed in the lungs of patients with COPD and may contribute to the disease pathogenesis. Growth differentiation factor 11 (GDF11) belongs to the transforming growth factor β superfamily and was recently reported to be a circulating protein that may have rejuvenating effects in mice. We aimed to investigate the amounts of GDF11 in the plasma and the lungs of patients with COPD and elucidate the possible roles of GDF11 in cellular senescence.

METHODS

The plasma levels of GDF11 were investigated in two separate cohorts by western blotting. The localisation and expression of GDF11 in the lungs were investigated by immunohistochemistry and quantitative reverse transcription PCR, respectively. The effects of GDF11 on both cigarette smoke extract (CSE)-induced cellular senescence in vitro and on elastase-induced cellular senescence in vivo were investigated.

RESULTS

The levels of plasma GDF11 in the COPD group were decreased compared with the control groups in the two independent cohorts. The levels of plasma GDF11 were significantly positively correlated with pulmonary function data. The mRNA expression of GDF11 in mesenchymal cells from the COPD group was decreased. Chronic exposure to CSE decreased the production of GDF11. Treatment with GDF11 significantly inhibited CSE-induced cellular senescence and upregulation of inflammatory mediators, partly through Smad2/3 signalling in vitro. Daily GDF11 treatment attenuated cellular senescence and airspace enlargement in an elastase-induced mouse model of emphysema.

CONCLUSIONS

The decrease in GDF11 may be involved in the cellular senescence observed in COPD.

The versatility and paradox of GDF 11

In addition to its roles in embryonic development, Growth and Differentiation Factor 11 (GDF 11) has recently drawn much interest about its roles in other processes, such as aging. GDF 11 has been shown to play pivotal roles in the rescue of the proliferative and regenerative capabilities of skeletal muscle, neural stem cells and cardiomyocytes. We would be remiss not to point that some controversy exists regarding the role of GDF 11 in biological processes and whether it will serve as a therapeutic agent. The latest studies have shown that the level of circulating GDF 11 correlates with the outcomes of patients with cardiovascular diseases, cancer and uremia. Based on these studies, GDF 11 is a promising candidate to serve as a novel biomarker of diseases. This brief review gives a detailed and concise view of the regulation and functions of GDF 11 and its roles in development, neurogenesis and erythropoiesis as well as the prospect of using this protein as an indicator of cardiac health and aging.

Eating the Dead to Keep Atherosclerosis at Bay

Atherosclerosis is the primary cause of coronary heart disease (CHD), ischemic stroke, and peripheral arterial disease. Despite effective lipid-lowering therapies and prevention programs, atherosclerosis is still the leading cause of mortality in the United States. Moreover, the prevalence of CHD in developing countries worldwide is rapidly increasing at a rate expected to overtake those of cancer and diabetes. Prominent risk factors include the hardening of arteries and high levels of cholesterol, which lead to the initiation and progression of atherosclerosis. However, cell death and efferocytosis are critical components of both atherosclerotic plaque progression and regression, yet, few currently available therapies focus on these processes. Thus, understanding the causes of cell death within the atherosclerotic plaque, the consequences of cell death, and the mechanisms of apoptotic cell clearance may enable the development of new therapies to treat cardiovascular disease. Here, we review how endoplasmic reticulum stress and cholesterol metabolism lead to cell death and inflammation, how dying cells affect plaque progression, and how autophagy and the clearance of dead cells ameliorates the inflammatory environment of the plaque. In addition, we review current research aimed at alleviating these processes and specifically targeting therapeutics to the site of the plaque.

GDF11 Protects against Endothelial Injury and Reduces Atherosclerotic Lesion Formation in Apolipoprotein E-Null Mice

Growth differentiation factor 11 (GDF11) reduces cardiac hypertrophy, improves cerebral vasculature and enhances neurogenesis in ageing mice. Higher growth differentiation factor 11/8 (GDF11/8) is associated with lower risk of cardiovascular events in humans. Here, we showed that adeno-associated viruses-GDF11 and recombinant GDF11 protein improve endothelial dysfunction, decrease endothelial apoptosis, and reduce inflammation, consequently decrease atherosclerotic plaques area in apolipoprotein E-/- mice. Moreover, adeno-associated viruses-GDF11 and recombinant GDF11 stabilize atherosclerotic plaques by selectively decreasing in macrophages and T lymphocytes, while increasing in collagen and vascular smooth muscle cells within plaques. In addition, GDF11 inhibit palmitic acid-induced endothelial apoptosis and ameliorate palmitic acid-induced inflammatory response in RAW264.7 macrophages in vitro. Mechanistically, GDF11 activates the TGF-β/Smad2/3, AMPK/endothelial nitricoxide synthase (eNOS) while suppresses JNK and NF-κB pathways. In humans, circulating GDF11/8 is positively associated with flow-mediated endothelium-dependent dilation in overweight subjects. We concluded that adeno-associated viruses-GDF11 and recombinant GDF11 protect against endothelial injury and reduce atherosclerosis in apolipoprotein E-/- mice, thus may be providing a novel approach to the treatment of atherosclerosis.

GDF11 improves tubular regeneration after acute kidney injury in elderly mice

The GDF11 expression pattern and its effect on organ regeneration after acute injury in the elderly population are highly controversial topics. In our study, GDF11/8 expression increased after kidney ischemia–reperfusion injury (IRI), and the relatively lower level of GDF11/8 in the kidneys of aged mice was associated with a loss of proliferative capacity and a decline in renal repair, compared to young mice. In vivo, GDF11 supplementation in aged mice increased vimentin and Pax2 expression in the kidneys as well as the percentage of 5-ethynyl-2′-deoxyuridine (EdU)-positive proximal tubular epithelial cells. GDF11 improved the renal repair, recovery of renal function, and survival of elderly mice at 72 h after IRI. Moreover, the addition of recombinant GDF11 to primary renal epithelial cells increased proliferation, migration, and dedifferentiation by upregulating the ERK1/2 pathway in vitro. Our study indicates that GDF11/8 in the kidney decreases with age and that GDF11 can increase tubular cell dedifferentiation and proliferation as well as improve tubular regeneration after acute kidney injury (AKI) in old mice.

GDF11 decreases bone mass by stimulating osteoclastogenesis and inhibiting osteoblast differentiation

Osteoporosis is an age-related disease that affects millions of people. Growth differentiation factor 11 (GDF11) is a secreted member of the transforming growth factor beta (TGF-β) superfamily. Deletion of Gdf11 has been shown to result in a skeletal anterior-posterior patterning disorder. Here we show a role for GDF11 in bone remodelling. GDF11 treatment leads to bone loss in both young and aged mice. GDF11 inhibits osteoblast differentiation and also stimulates RANKL-induced osteoclastogenesis through Smad2/3 and c-Fos-dependent induction of Nfatc1. Injection of GDF11 impairs bone regeneration in mice and blocking GDF11 function prevents oestrogen-deficiency-induced bone loss and ameliorates age-related osteoporosis. Our data demonstrate that GDF11 is a previously unrecognized regulator of bone remodelling and suggest that GDF11 is a potential target for treatment of osteoporosis.

Biochemistry and Biology of GDF11 and Myostatin: Similarities, Differences, and Questions for Future Investigation

Growth differentiation factor 11 (GDF11) and myostatin (or GDF8) are closely related members of the transforming growth factor β superfamily and are often perceived to serve similar or overlapping roles. Yet, despite commonalities in protein sequence, receptor utilization and signaling, accumulating evidence suggests that these 2 ligands can have distinct functions in many situations. GDF11 is essential for mammalian development and has been suggested to regulate aging of multiple tissues, whereas myostatin is a well-described negative regulator of postnatal skeletal and cardiac muscle mass and modulates metabolic processes. In this review, we discuss the biochemical regulation of GDF11 and myostatin and their functions in the heart, skeletal muscle, and brain. We also highlight recent clinical findings with respect to a potential role for GDF11 and/or myostatin in humans with heart disease. Finally, we address key outstanding questions related to GDF11 and myostatin dynamics and signaling during development, growth, and aging.

Is Growth Differentiation Factor 11 a Realistic Therapeutic for Aging-Dependent Muscle Defects?

This "Controversies in Cardiovascular Research" article evaluates the evidence for and against the hypothesis that the circulating blood level of growth differentiation factor 11 (GDF11) decreases in old age and that restoring normal GDF11 levels in old animals rejuvenates their skeletal muscle and reverses pathological cardiac hypertrophy and cardiac dysfunction. Studies supporting the original GDF11 hypothesis in skeletal and cardiac muscle have not been validated by several independent groups. These new studies have either found no effects of restoring normal GDF11 levels on cardiac structure and function or have shown that increasing GDF11 or its closely related family member growth differentiation factor 8 actually impairs skeletal muscle repair in old animals. One possible explanation for what seems to be mutually exclusive findings is that the original reagent used to measure GDF11 levels also detected many other molecules so that age-dependent changes in GDF11 are still not well known. The more important issue is whether increasing blood [GDF11] repairs old skeletal muscle and reverses age-related cardiac pathologies. There are substantial new and existing data showing that GDF8/11 can exacerbate rather than rejuvenate skeletal muscle injury in old animals. There is also new evidence disputing the idea that there is pathological hypertrophy in old C57bl6 mice and that GDF11 therapy can reverse cardiac pathologies. Finally, high [GDF11] causes reductions in body and heart weight in both young and old animals, suggestive of a cachexia effect. Our conclusion is that elevating blood levels of GDF11 in the aged might cause more harm than good.

Development and Validation of a Protein-Based Risk Score for Cardiovascular Outcomes Among Patients With Stable Coronary Heart Disease

IMPORTANCE

Precise stratification of cardiovascular risk in patients with coronary heart disease (CHD) is needed to inform treatment decisions.

OBJECTIVE

To derive and validate a score to predict risk of cardiovascular outcomes among patients with CHD, using large-scale analysis of circulating proteins.

DESIGN, SETTING, AND PARTICIPANTS

Prospective cohort study of participants with stable CHD. For the derivation cohort (Heart and Soul study), outpatients from San Francisco were enrolled from 2000 through 2002 and followed up through November 2011 (≤11.1 years). For the validation cohort (HUNT3, a Norwegian population-based study), participants were enrolled from 2006 through 2008 and followed up through April 2012 (5.6 years).

EXPOSURES

Using modified aptamers, 1130 proteins were measured in plasma samples.

MAIN OUTCOMES AND MEASURES

A 9-protein risk score was derived and validated for 4-year probability of myocardial infarction, stroke, heart failure, and all-cause death. Tests, including the C statistic, were used to assess performance of the 9-protein risk score, which was compared with the Framingham secondary event model, refit to the cohorts in this study. Within-person change in the 9-protein risk score was evaluated in the Heart and Soul study from paired samples collected 4.8 years apart.

RESULTS

From the derivation cohort, 938 samples were analyzed, participants' median age at enrollment was 67.0 years, and 82% were men. From the validation cohort, 971 samples were analyzed, participants' median age at enrollment was 70.2 years, and 72% were men. In the derivation cohort, C statistics were 0.66 for refit Framingham, 0.74 for 9-protein, and 0.75 for refit Framingham plus 9-protein models. In the validation cohort, C statistics were 0.64 for refit Framingham, 0.70 for 9-protein, and 0.71 for refit Framingham plus 9-protein models. Adding the 9-protein risk score to the refit Framingham model increased the C statistic by 0.09 (95% CI, 0.06-0.12) in the derivation cohort, and in the validation cohort, the C statistic was increased by 0.05 (95% CI, 0.02-0.09). Compared with the refit Framingham model, the integrated discrimination index for the 9-protein model was 0.12 (95% CI, 0.08-0.16) in the derivation cohort and 0.08 (95% CI, 0.05-0.10) in the validation cohort. In analysis of paired samples among 139 participants with cardiovascular events after the second sample, absolute within-person annualized risk increased more for the 9-protein model (median, 1.86% [95% CI, 1.15%-2.54%]) than for the refit Framingham model (median, 1.00% [95% CI, 0.87%-1.19%]) (P = .002), while among 375 participants without cardiovascular events, both scores changed less and similarly (P = .30).

CONCLUSIONS AND RELEVANCE

Among patients with stable CHD, a risk score based on 9 proteins performed better than the refit Framingham secondary event risk score in predicting cardiovascular events, but still provided only modest discriminative accuracy. Further research is needed to assess whether the score is more accurate in a lower-risk population.

Quantification of GDF11 and Myostatin in Human Aging and Cardiovascular Disease

Growth and differentiation factor 11 (GDF11) is a transforming growth factor β superfamily member with a controversial role in aging processes. We have developed a highly specific LC-MS/MS assay to quantify GDF11, resolved from its homolog, myostatin (MSTN), based on unique amino acid sequence features. Here, we demonstrate that MSTN, but not GDF11, declines in healthy men throughout aging. Neither GDF11 nor MSTN levels differ as a function of age in healthy women. In an independent cohort of older adults with severe aortic stenosis, we show that individuals with higher GDF11 were more likely to be frail and have diabetes or prior cardiac conditions. Following valve replacement surgery, higher GDF11 at surgical baseline was associated with rehospitalization and multiple adverse events. Cumulatively, our results show that GDF11 levels do not decline throughout aging but are associated with comorbidity, frailty, and greater operative risk in older adults with cardiovascular disease.

Serum Levels of Growth Differentiation Factor 11 Are Independently Associated with Low Hemoglobin Values in Hemodialysis Patients

Circulating levels of growth differentiation factor 11 (GDF11) have been shown to decrease with age in several mammalian species, and supplementation of GDF11 by heterochronic parabiosis or systemic administration reverses age-related organ damage. However, there is some controversy about the pathophysiological role of GDF11 in aging-associated organ damage. Since aging process is accelerated in uremia, we compared serum levels of GDF11 in hemodialysis (HD) patients with those in age-matched healthy controls, and then determined the independent clinical correlates of GDF11 in HD subjects. Sixty-two maintenance HD patients (34 male and 28 female; mean age, 52.6 years; mean duration of HD, 7.7 months) were enrolled in the present study. Twenty-nine age-matched subjects were used as a control. GDF11 was measured by a commercially available enzyme-linked immunosorbent assay kit. Serum GDF11 levels in HD patients were significantly higher than those in controls (9.4 ± 5.1 pg/mL vs. 7.3 ± 5.9 pg/mL). A statistical significance was demonstrated between GDF11 and hemoglobin (inversely). Multiple stepwise regression analysis revealed that hemoglobin (p < 0.001) was a sole independent correlate of GDF11 levels in HD patients (R² = 0.168). Our present study suggests that kinetics and regulation of circulating GDF11 may differ between normal physiological aging process and accelerated pathological aging conditions, such as uremia. Given that GDF11 has been shown to inhibit erythroid maturation in mice, elevation of GDF11 levels may be involved in erythropoietin-resistant anemia in HD patients.

Molecular circuitry of stem cell fate in skeletal muscle regeneration, ageing and disease

Satellite cells are adult myogenic stem cells that repair damaged muscle. The enduring capacity for muscle regeneration requires efficient satellite cell expansion after injury, their differentiation to produce myoblasts that can reconstitute damaged fibres and their self-renewal to replenish the muscle stem cell pool for subsequent rounds of injury and repair. Emerging studies indicate that misregulation of satellite cell fate and function can contribute to age-associated muscle dysfunction and influence the severity of muscle diseases, including Duchenne muscular dystrophy (DMD). It has also become apparent that satellite cell fate during muscle regeneration and ageing, and in the context of DMD, is governed by an intricate network of intrinsic and extrinsic regulators. Targeted manipulation of this network may offer unique opportunities for muscle regenerative medicine.

Circulating Concentrations of Growth Differentiation Factor 11 Are Heritable and Correlate With Life Span

Growth differentiation factor 11 (GDF11) is member of the transforming growth factor β (TGF-β) superfamily of proteins. Circulating GDF11 concentrations appear to decline with age, and its depletion is associated with cardiac hypertrophy and other morbidities. Knowledge of GDF11 regulation is limited, and the effects of natural genetic variation on GDF11 levels are currently undefined. We tested whether genetic background determines serum GDF11 concentrations using two classical inbred mouse strains: C57BL/6J (B6) and BALB/cByJ (BALB). B6 mice exhibited significantly higher GDF11 levels than BALB mice, and these strain differences were consistent throughout the life span. Overall, interactions between age and genetic background determined GDF11 concentrations, which were unaffected by sex. We then surveyed a panel of 22 genetically diverse inbred mouse strains and discovered a sixfold range in GDF11 levels at middle age. We estimated that 74.52% of phenotypic variation in GDF11 levels was attributable to genetic background. We used the Mouse Phenome Database to screen for phenotypes that correlate with GDF11. Interestingly, GDF11 levels predicted median strain life spans. This study revealed high heritability of GDF11 levels. Furthermore, our correlative data suggest that GDF11 may serve as a novel predictor of mammalian life span.

Circulating Growth Differentiation Factor 11/8 Levels Decline With Age

RATIONALE

Growth differentiation factor 11 (GDF11) and GDF8 are members of the transforming growth factor-β superfamily sharing 89% protein sequence homology. We have previously shown that circulating GDF11 levels decrease with age in mice. However, a recent study by Egerman et al reported that GDF11/8 levels increase with age in mouse serum.

OBJECTIVE

Here, we clarify the direction of change of circulating GDF11/8 levels with age and investigate the effects of GDF11 administration on the murine heart.

METHODS AND RESULTS

We validated our previous finding that circulating levels of GDF11/8 decline with age in mice, rats, horses, and sheep. Furthermore, we showed by Western analysis that the apparent age-dependent increase in GDF11 levels, as reported by Egerman et al, is attributable to cross-reactivity of the anti-GDF11 antibody with immunoglobulin, which is known to increase with age. GDF11 administration in mice rapidly activated SMAD2 and SMAD3 signaling in myocardium in vivo and decreased cardiac mass in both young (2-month-old) and old (22-month-old) mice in a dose-dependent manner after only 9 days.

CONCLUSIONS

Our study confirms an age-dependent decline in serum GDF11/8 levels in multiple mammalian species and that exogenous GDF11 rapidly activates SMAD signaling and reduces cardiomyocyte size. Unraveling the molecular basis for the age-dependent decline in GDF11/8 could yield insight into age-dependent cardiac pathologies.

Matters of context guide future research in TGFβ superfamily signaling

The highly conserved wiring of the SMAD-dependent transforming growth factor β (TGFβ) superfamily signaling pathway has been mapped over the last 20 years after molecular discovery of its component parts. Numerous alternative TGFβ-activated signaling pathways that elicit SMAD-independent biological responses also exist. However, the molecular mechanisms responsible for the renowned context dependency of TGFβ signaling output remains an active and often confounding area of research, providing a prototype relevant to regulation of other signaling pathways. Highlighting discoveries presented at the 9th FASEB meeting, The TGFβ Superfamily: Signaling in Development and Disease (July 12-17th 2015 in Snowmass, Colorado), this Review outlines research into the rich contextual nature of TGFβ signaling output and offers clues for therapeutic advances.