Regulation of anterior/posterior patterning of the axial skeleton by growth/differentiation factor 11

Breaking constraint of mammalian axial formulae

The vertebral column of individual mammalian species often exhibits remarkable robustness in the number and identity of vertebral elements that form (known as axial formulae). The genetic mechanism(s) underlying this constraint however remain ill-defined. Here, we reveal the interplay of three regulatory pathways (Gdf11, miR-196 and Retinoic acid) is essential in constraining total vertebral number and regional axial identity in the mouse, from cervical through to tail vertebrae. All three pathways have differing control over Hox cluster expression, with heterochronic and quantitative changes found to parallel changes in axial identity. However, our work reveals an additional role for Hox genes in supporting axial elongation within the tail region, providing important support for an emerging view that mammalian Hox function is not limited to imparting positional identity as the mammalian body plan is laid down. More broadly, this work provides a molecular framework to interrogate mechanisms of evolutionary change and congenital anomalies of the vertebral column.

Vertebral column length and shape exhibits remarkable robustness within a species but diversity across species. Here the authors reveal the molecular logic constraining vertebral number in mouse and a novel role for posterior Hox genes in this context.

Growth differentiation factor 11 accelerates liver senescence through the inhibition of autophagy

The “rejuvenating” effect of growth differentiation factor 11 (GDF11) is called into question recently, and its role, as well as plausible signaling mechanisms in liver senescence, is unclear. To overexpress or knockdown GDF11, aged male mice are injected with a single dose of adeno‐associated viruses‐GDF11 or adenovirus‐small hairpin RNA‐GDF11, respectively. GDF11 overexpression significantly accelerates liver senescence in aged mice, whereas GDF11 knockdown has opposite effects. Concomitantly, autophagic flux is impaired in livers from GDF11 overexpression mice. Conversely, GDF11 knockdown increases autophagic flux. Moreover, rapamycin successfully restores the impaired autophagic flux and alleviates liver senescence in GDF11 overexpression mice, while the GDF11 knockdown‐mediated benefits are abolished by the autophagy inhibitor bafilomycin A1. GDF11 leads to a drop in lysosomal biogenesis resulting in defective autophagic flux at autophagosome clearance step. Mechanistically, GDF11 significantly activates mammalian target of rapamycin complex 1 (mTORC1) and subsequently represses transcription factor EB (TFEB), a master regulator of lysosomal biogenesis and autophagy. Inhibition of mTORC1 or TFEB overexpression rescues the GDF11‐impaired autophagic flux and cellular senescence. Hepatocyte‐specific deletion of GDF11 does not alter serum GDF11 levels and liver senescence. Collectively, suppression of autophagic activity via mTORC1/TFEB signaling may be a critical molecular mechanism by which GDF11 exacerbates liver senescence. Rather than a “rejuvenating” agent, GDF11 may have a detrimental effect on liver senescence.

Gonadal rejuvenation of mice by GDF11

Growth differentiation factor 11 (GDF11), also known as bone morphogenetic protein 11 (BMP11), has been shown to have rejuvenation and anti-aging properties, but little information is available regarding the role of GDF11 in reproductive system to date. In this study, we first confirmed the bioavailability of recombinant GDF11 (rGDF11) by oral delivery in mice. We also showed that dietary intake of rGDF11 had little influence on body and gonadal (ovary/testis) weights of recipient mice, indicating their general condition and physiology were not affected. Based on these findings, we started to test the function of rGDF11 in ovary and testis of mice and to explore the underlying mechanisms. It was found that to some extent, rGDF11 could attenuate the senescence of ovarian and testicular cells, and contribute to the recovery of ovarian and testicular endocrine functions. Moreover, rGDF11 could rescue the diminished ovarian reserve in female mice and enhance the activities of marker enzymes of testicular function (SDH and G6PD) in male mice, suggesting a potential improvement of fertility. Notably, rGDF11 markedly promoted the activities of antioxidant enzymes in the ovary and testis, and remarkably reduced the levels of lipid peroxidation, protein oxidation and ROS in the ovary and testis. Collectively, these results suggest that GDF11 can protect ovarian and testicular functions of aged mice via slowing down the generation of ROS through enhancing activities of antioxidant enzymes.

The Role of BMP Signaling in Female Reproductive System Development and Function

Bone morphogenetic proteins (BMPs) are a group of multifunctional growth factors that belong to the transforming growth factor-β (TGF-β) superfamily of proteins. Originally identified by their ability to induce bone formation, they are now known as essential signaling molecules that regulate the development and function of the female reproductive system (FRS). Several BMPs play key roles in aspects of reproductive system development. BMPs have also been described to be involved in the differentiation of human pluripotent stem cells (hPSCs) into reproductive system tissues or organoids. The role of BMPs in the reproductive system is still poorly understood and the use of FRS tissue or organoids generated from hPSCs would provide a powerful tool for the study of FRS development and the generation of new therapeutic perspectives for the treatment of FRS diseases. Therefore, the aim of this review is to summarize the current knowledge about BMP signaling in FRS development and function.

Somite development and regionalisation of the vertebral axial skeleton

A critical stage in the development of all vertebrate embryos is the generation of the body plan and its subsequent patterning and regionalisation along the main anterior-posterior axis. This includes the formation of the vertebral axial skeleton. Its organisation begins during early embryonic development with the periodic formation of paired blocks of mesoderm tissue called somites. Here, we review axial patterning of somites, with a focus on studies using amniote model systems - avian and mouse. We summarise the molecular and cellular mechanisms that generate paraxial mesoderm and review how the different anatomical regions of the vertebral column acquire their specific identity and thus shape the body plan. We also discuss the generation of organoids and embryo-like structures from embryonic stem cells, which provide insights regarding axis formation and promise to be useful for disease modelling.

GDF-11 Protects the Traumatically Injured Spinal Cord by Suppressing Pyroptosis and Necroptosis via TFE3-Mediated Autophagy Augmentation

Spinal cord injury (SCI) refers to a major worldwide cause of accidental death and disability. However, the complexity of the pathophysiological mechanism can result in less-effective clinical treatment. Growth differentiation factor 11 (GDF-11), an antiageing factor, was reported to affect the development of neurogenesis and exert a neuroprotective effect after cerebral ischaemic injury. The present work is aimed at investigating the influence of GDF-11 on functional recovery following SCI, in addition to the potential mechanisms involved. We employed a mouse model of spinal cord contusion injury and assessed functional outcomes via the Basso Mouse Scale and footprint analysis following SCI. Using western blot assays and immunofluorescence, we analysed the levels of pyroptosis, autophagy, necroptosis, and molecules related to the AMPK-TRPML1-calcineurin signalling pathway. The results showed that GDF-11 noticeably optimized function-related recovery, increased autophagy, inhibited pyroptosis, and alleviated necroptosis following SCI. Furthermore, the conducive influences exerted by GDF-11 were reversed with the application of 3-methyladenine (3MA), an autophagy suppressor, indicating that autophagy critically impacted the therapeutically related benefits of GDF-11 on recovery after SCI. In the mechanistic study described herein, GDF-11 stimulated autophagy improvement and subsequently inhibited pyroptosis and necroptosis, which were suggested to be mediated by TFE3; this effect resulted from the activity of TFE3 through the AMPK-TRPML1-calcineurin signalling cascade. Together, GDF-11 protects the injured spinal cord by suppressing pyroptosis and necroptosis via TFE3-mediated autophagy augmentation and is a potential agent for SCI therapy.

Heterozygous loss-of-function variants significantly expand the phenotypes associated with loss of GDF11

PURPOSE

Growth differentiation factor 11 (GDF11) is a key signaling protein required for proper development of many organ systems. Only one prior study has associated an inherited GDF11 variant with a dominant human disease in a family with variable craniofacial and vertebral abnormalities. Here, we expand the phenotypic spectrum associated with GDF11 variants and document the nature of the variants.

METHODS

We present a cohort of six probands with de novo and inherited nonsense/frameshift (4/6 patients) and missense (2/6) variants in GDF11. We generated gdf11 mutant zebrafish to model loss of gdf11 phenotypes and used an overexpression screen in Drosophila to test variant functionality.

RESULTS

Patients with variants in GDF11 presented with craniofacial (5/6), vertebral (5/6), neurological (6/6), visual (4/6), cardiac (3/6), auditory (3/6), and connective tissue abnormalities (3/6). gdf11 mutant zebrafish show craniofacial abnormalities and body segmentation defects that match some patient phenotypes. Expression of the patients' variants in the fly showed that one nonsense variant in GDF11 is a severe loss-of-function (LOF) allele whereas the missense variants in our cohort are partial LOF variants.

CONCLUSION

GDF11 is needed for human development, particularly neuronal development, and LOF GDF11 alleles can affect the development of numerous organs and tissues.

GDF11 expressed in the adult brain negatively regulates hippocampal neurogenesis

Growth differentiation factor 11 (GDF11) is a transforming factor-β superfamily member that functions as a negative regulator of neurogenesis during embryonic development. However, when recombinant GDF11 (rGDF11) is administered systemically in aged mice, it promotes neurogenesis, the opposite of its role during development. The goal of the present study was to reconcile this apparent discrepancy by performing the first detailed investigation into the expression of endogenous GDF11 in the adult brain and its effects on neurogenesis. Using quantitative histological analysis, we observed that Gdf11 is most highly expressed in adult neurogenic niches and non-neurogenic regions within the hippocampus, choroid plexus, thalamus, habenula, and cerebellum. To investigate the role of endogenous GDF11 during adult hippocampal neurogenesis, we generated a tamoxifen inducible mouse that allowed us to reduce GDF11 levels. Depletion of Gdf11 during adulthood increased proliferation of neural progenitors and decreased the number of newborn neurons in the hippocampus, suggesting that endogenous GDF11 remains a negative regulator of hippocampal neurogenesis in adult mice. These findings further support the idea that circulating systemic GDF11 and endogenously expressed GDF11 in the adult brain have different target cells or mechanisms of action. Our data describe a role for GDF11-dependent signaling in adult neurogenesis that has implications for how GDF11 may be used to treat CNS disease.

Limb positioning and initiation: An evolutionary context of pattern and formation

Before limbs or fins, can be patterned and grow they must be initiated. Initiation of the limb first involves designating a portion of lateral plate mesoderm along the flank as the site of the future limb. Following specification, a myriad of cellular and molecular events interact to generate a bud that will grow and form the limb. The past three decades has provided a wealth of understanding on how those events generate the limb bud and how variations in them result in different limb forms. Comparatively, much less attention has been given to the earliest steps of limb formation and what impacts altering the position and initiation of the limb have had on evolution. Here, we first review the processes and pathways involved in these two phases of limb initiation, as determined from amniote model systems. We then broaden our scope to examine how variation in the limb initiation module has contributed to biological diversity in amniotes. Finally, we review what is known about limb initiation in fish and amphibians, and consider what mechanisms are conserved across vertebrates.

Identification of Jmjd3 as an Essential Epigenetic Regulator of Hox Gene Temporal Collinear Activation for Body Axial Patterning in Mice

Body axial patterning develops via a rostral-to-caudal sequence and relies on the temporal colinear activation of Hox genes. However, the underlying mechanism of Hox gene temporal colinear activation remains largely elusive. Here, with small-molecule inhibitors and conditional gene knockout mice, we identified Jmjd3, a subunit of TrxG, as an essential regulator of temporal colinear activation of Hox genes with its H3K27me3 demethylase activity. We demonstrated that Jmjd3 not only initiates but also maintains the temporal collinear expression of Hox genes. However, we detected no antagonistic roles between Jmjd3 and Ezh2, a core subunit of PcG repressive complex 2, during the processes of axial skeletal patterning. Our findings provide new insights into the regulation of Hox gene temporal collinear activation for body axial patterning in mice.

Controlling BMP growth factor bioavailability: The extracellular matrix as multi skilled platform

Bone morphogenetic proteins (BMPs) belong to the TGF-β superfamily of signaling ligands which comprise a family of pluripotent cytokines regulating a multitude of cellular events. Although BMPs were originally discovered as potent factors extractable from bone matrix that are capable to induce ectopic bone formation in soft tissues, their mode of action has been mostly studied as soluble ligands in absence of the physiologically relevant cellular microenvironment. This micro milieu is defined by supramolecular networks of extracellular matrix (ECM) proteins that specifically target BMP ligands, present them to their cellular receptors, and allow their controlled release. Here we focus on functional interactions and mechanisms that were described to control BMP bioavailability in a spatio-temporal manner within the respective tissue context. Structural disturbance of the ECM architecture due to mutations in ECM proteins leads to dysregulated BMP signaling as underlying cause for connective tissue disease pathways. We will provide an overview about current mechanistic concepts of how aberrant BMP signaling drives connective tissue destruction in inherited and chronic diseases.

Of Necks, Trunks and Tails: Axial Skeletal Diversity among Vertebrates

The axial skeleton of all vertebrates is composed of individual units known as vertebrae. Each vertebra has individual anatomical attributes, yet they can be classified in five different groups, namely cervical, thoracic, lumbar, sacral and caudal, according to shared characteristics and their association with specific body areas. Variations in vertebral number, size, morphological features and their distribution amongst the different regions of the vertebral column are a major source of the anatomical diversity observed among vertebrates. In this review I will discuss the impact of those variations on the anatomy of different vertebrate species and provide insights into the genetic origin of some remarkable morphological traits that often serve to classify phylogenetic branches or individual species, like the long trunks of snakes or the long necks of giraffes.

Principles of the activin receptor signaling pathway and its inhibition

This review captures the anabolic and stimulatory effects observed with inhibition of the transforming growth factor β superfamily in muscle, blood, and bone. New medicinal substances that rectify activin, myostatin, and growth differentiation factor 11 signaling give hope to the many whose lives are affected by deterioration of these tissues. The review first covers the origin, structure, and common pathway of activins, myostatin, and growth differentiation factor 11 along with the pharmacodynamics of the new class of molecules designed to oppose the activin receptor signaling pathway. Current terminology surrounding this new class of molecules is inconsistent and does not infer functionality. Adopting inhibitors of the activin receptor signaling pathway (IASPs) as a generic term is proposed because it encapsulates the molecular mechanisms along the pathway trajectory. To conclude, a pragmatic classification of IASPs is presented that integrates functionality and side effects based on the data available from animals and humans. This provides researchers and clinicians with a tool to tailor IASPs therapy according to the need of projects or patients and with respect to side effects.

Longitudinal Relationship Between Growth Differentiation Factor 11 and Physical Activity in Chronic Obstructive Pulmonary Disease

BACKGROUND

Daily physical activity is reduced in patients with chronic obstructive pulmonary disease (COPD) and a reduced level of physical activity has been shown to be an important predictor for the prognosis, such as increased risk of exacerbation and mortality. However, there has not yet been a useful biomarker of the physical activity. In our previous cross-sectional study, we showed that the level of one of the possible myokines, which is an anti-aging factor, growth differentiation factor 11 (GDF11), was decreased in the plasma from patients with COPD and correlated with the physical activity. To clarify this relationship, we conducted a longitudinal evaluation of such factors.

PATIENTS AND METHODS

Twenty-four COPD patients were enrolled and prospectively followed. We measured the levels of plasma GDF11 and systemic inflammatory markers with immunoblotting or ELISA, respectively. We also evaluated lung function and daily physical activity using a triaxial accelerometer and the incidence of exacerbation.

RESULTS

The change in the plasma level of GDF11, but not systemic inflammatory markers, was positively correlated with the change in the physical activity in an intensity-dependent manner (between the change in the number of steps and GDF11; r = 0.41, p = 0.047). In the multiple regression analysis, the relationship was confirmed (β = 0.93, p < 0.001). In addition, patients who maintained their plasma level of GDF11 showed a significantly lower incidence in exacerbations of COPD than those with decreased levels of GDF11 (p = 0.041).

CONCLUSION

The longitudinal change in the plasma level of GDF11 was positively correlated with the change in the daily physical activity in COPD. GDF11 could be a useful humoral factor that reflects the physical activity in COPD.

Dynamic extrinsic pacing of the HOX clock in human axial progenitors controls motor neuron subtype specification

Rostro-caudal patterning of vertebrates depends on the temporally progressive activation of HOX genes within axial stem cells that fuel axial embryo elongation. Whether the pace of sequential activation of HOX genes, the 'HOX clock', is controlled by intrinsic chromatin-based timing mechanisms or by temporal changes in extrinsic cues remains unclear. Here, we studied HOX clock pacing in human pluripotent stem cell-derived axial progenitors differentiating into diverse spinal cord motor neuron subtypes. We show that the progressive activation of caudal HOX genes is controlled by a dynamic increase in FGF signaling. Blocking the FGF pathway stalled induction of HOX genes, while a precocious increase of FGF, alone or with GDF11 ligand, accelerated the HOX clock. Cells differentiated under accelerated HOX induction generated appropriate posterior motor neuron subtypes found along the human embryonic spinal cord. The pacing of the HOX clock is thus dynamically regulated by exposure to secreted cues. Its manipulation by extrinsic factors provides synchronized access to multiple human neuronal subtypes of distinct rostro-caudal identities for basic and translational applications.This article has an associated 'The people behind the papers' interview.

Targeting the Activin Receptor Signaling to Counteract the Multi-Systemic Complications of Cancer and Its Treatments

Muscle wasting, i.e., cachexia, frequently occurs in cancer and associates with poor prognosis and increased morbidity and mortality. Anticancer treatments have also been shown to contribute to sustainment or exacerbation of cachexia, thus affecting quality of life and overall survival in cancer patients. Pre-clinical studies have shown that blocking activin receptor type 2 (ACVR2) or its ligands and their downstream signaling can preserve muscle mass in rodents bearing experimental cancers, as well as in chemotherapy-treated animals. In tumor-bearing mice, the prevention of skeletal and respiratory muscle wasting was also associated with improved survival. However, the definitive proof that improved survival directly results from muscle preservation following blockade of ACVR2 signaling is still lacking, especially considering that concurrent beneficial effects in organs other than skeletal muscle have also been described in the presence of cancer or following chemotherapy treatments paired with counteraction of ACVR2 signaling. Hence, here, we aim to provide an up-to-date literature review on the multifaceted anti-cachectic effects of ACVR2 blockade in preclinical models of cancer, as well as in combination with anticancer treatments.

MicroRNA‑338‑3p regulates age‑associated osteoporosis via targeting PCSK5

Bone loss is a disease that is highly associated with aging. This deleterious health condition has become a public concern worldwide, and there is an urgent need to discover more novel therapeutic strategies for the development of age‑associated osteoporosis. The present study aimed to explore the association between proprotein convertase subtilisin/kexin type 5 (PCSK5) and microRNA(miR)‑338‑3p in bone‑formation and bone‑loss processes. Western blotting assay and reverse transcription‑quantitative PCR were employed to analyze PCSK5 and miR‑338‑3p expression levels in bone mesenchymal stem cells (BMSCs). Dual‑luciferase reporter and RNA pull‑down assays were used to determine the target. For osteoblastic differentiation verification, alkaline phosphatase activity, osteocalcin secretion detection, bone formation‑related indicators (osterix, runt‑related gene 2, osteopontin and bone sialoprotein), hematoxylin and eosin staining and Alizarin Red S staining were performed. The findings of the present study indicated that the expression level of PCSK5 was higher in BMSCs from young rat samples, whereas the expression level of miR‑338‑3p was higher in BMSCs from samples of old rats. Experimental results also revealed that unlike miR‑338‑3p, downregulation of PCSK5 inhibited osteoblastic differentiation and osteogenesis by inhibiting alkaline phosphatase, osteocalcin, osterix, runt‑related transcription factor 2, osteopontin, bone sialoprotein and mineralized nodule formation. Overall, the results suggested that miR‑338‑3p could suppress age‑associated osteoporosis by regulating PCSK5.

Serum growth differentiation factor 11 is closely related to metabolic syndrome in a Chinese cohort

AIMS/INTRODUCTION

Despite increasing interest in growth differentiation factor 11 (GDF11) based on its involvement in age-related disorders, clinical implications - especially for metabolic diseases - remain unclear. Therefore, we assessed the association between serum GDF11 levels and metabolic disturbance in the Chinese population.

MATERIALS AND METHODS

A total of 381 individuals from the Shanghai Nicheng Cohort Study were included. In addition to anthropometry, laboratory and ultrasonography measurements, serum concentrations of GDF11 were measured by enzyme-linked immunosorbent assay.

RESULTS

Circulating GDF11 concentrations were unchanged with age (r = -0.064, P = 0.210), but showed an inverse relationship to body mass index, waist circumference and fat-free mass index (all P < 0.05). Correlation analysis showed decreased GDF11 concentrations accompanied by elevated diastolic blood pressure, fasting and 2-h plasma glucose, triglycerides, and low-density lipoprotein cholesterol after adjusting for sex, age and body mass index, whereas variations in aspartate aminotransferase and free thyroxine were consistent with GDF11 (all P < 0.05). Furthermore, people, especially men, with abnormal glycometabolism, body mass index and/or fat accumulation in the liver had lower serum levels of GDF11 (P < 0.05); an increase in metabolic syndrome morbidity along with the circulatory decline of GDF11 was found when stratified by GDF11-level quartiles (P-trend <0.001). Logistic regression showed that serum GDF11 levels were independently correlated with the presence of metabolic syndrome (odds ratio 0.665, 95% confidence interval 0.510-0.867, P = 0.003).

CONCLUSIONS

We confirmed GDF11 as an endocrine factor playing a significant role in multiple metabolic processes and an indicator of metabolic syndrome in the Chinese population, particularly in males.

Novel myostatin-specific antibody enhances muscle strength in muscle disease models

Myostatin, a member of the transforming growth factor-β superfamily, is an attractive target for muscle disease therapy because of its role as a negative regulator of muscle growth and strength. Here, we describe a novel antibody therapeutic approach that maximizes the potential of myostatin-targeted therapy. We generated an antibody, GYM329, that specifically binds the latent form of myostatin and inhibits its activation. Additionally, via "sweeping antibody technology", GYM329 reduces or "sweeps" myostatin in the muscle and plasma. Compared with conventional anti-myostatin agents, GYM329 and its surrogate antibody exhibit superior muscle strength-improvement effects in three different mouse disease models. We also demonstrate that the superior efficacy of GYM329 is due to its myostatin specificity and sweeping capability. Furthermore, we show that a GYM329 surrogate increases muscle mass in normal cynomolgus monkeys without any obvious toxicity. Our findings indicate the potential of GYM329 to improve muscle strength in patients with muscular disorders.

Circulating plasma factors involved in rejuvenation

Aging is defined as a time-dependent functional decline that occurs in many physiological systems. This decline is the primary risk factor for prominent human pathologies such as cancer, metabolic disorders, cardiovascular disorders, and neurodegenerative diseases. Aging and age-related diseases have multiple causes. Parabiosis experiments, in which the circulatory systems of young and old mice were surgically joined, revealed that young plasma counteracts aging and rejuvenates organs in old mice, suggesting the existence of rejuvenating factors that become less abundant with aging. Diverse approaches have identified a large number of plasma proteins whose levels differ significantly between young and old mice, as well as numerous rejuvenating factors that reverse aged-related impairments in multiple tissues. These observations suggest that increasing the levels of key rejuvenating factors could promote restorative biological processes or inhibit pathological degeneration. Inspired by such findings, several companies have begun selling “young blood transfusions,” and others have tested young plasma as a treatment for Alzheimer’s disease. Here, we summarize the current findings regarding rejuvenating factors.

GDF11 induces mild hepatic fibrosis independent of metabolic health

BACKGROUND & AIMS

Growth Differentiation Factor 11 (GDF11) is an anti-aging factor, yet its role in liver diseases is not established. We evaluated the role of GDF11 in healthy conditions and in the transition from non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH).

RESULTS

GDF11 mRNA levels positively correlated with NAFLD activity score and with CPT1, SREBP, PPARγ and Col1A1 mRNA levels, and associated to portal fibrosis, in morbidly obese patients with NAFLD/NASH. GDF11-treated mice showed mildly exacerbated hepatic collagen deposition, accompanied by weight loss and without changes in liver steatosis or inflammation. GDF11 triggered ALK5-dependent SMAD2/3 nuclear translocation and the pro-fibrogenic activation of HSC.

CONCLUSIONS

GDF11 supplementation promotes mild liver fibrosis. Even considering its beneficial metabolic effects, caution should be taken when considering therapeutics that regulate GDF11.

METHODS

We analyzed liver biopsies from a cohort of 33 morbidly obese adults with NAFLD/NASH. We determined the correlations in mRNA expression levels between GDF11 and genes involved in NAFLD-to-NASH progression and with pathological features. We also exposed wild type or obese mice with NAFLD to recombinant GDF11 by daily intra-peritoneal injection and monitor the hepatic pathological changes. Finally, we analyzed GDF11-activated signaling pathways in hepatic stellate cells (HSC).

Similar sequences but dissimilar biological functions of GDF11 and myostatin

Growth differentiation factor 11 (GDF11) and myostatin (MSTN) are closely related TGFβ family members that are often believed to serve similar functions due to their high homology. However, genetic studies in animals provide clear evidence that they perform distinct roles. While the loss of Mstn leads to hypermuscularity, the deletion of Gdf11 results in abnormal skeletal patterning and organ development. The perinatal lethality of Gdf11-null mice, which contrasts with the long-term viability of Mstn-null mice, has led most research to focus on utilizing recombinant GDF11 proteins to investigate the postnatal functions of GDF11. However, the reported outcomes of the exogenous application of recombinant GDF11 proteins are controversial partly because of the different sources and qualities of recombinant GDF11 used and because recombinant GDF11 and MSTN proteins are nearly indistinguishable due to their similar structural and biochemical properties. Here, we analyze the similarities and differences between GDF11 and MSTN from an evolutionary point of view and summarize the current understanding of the biological processing, signaling, and physiological functions of GDF11 and MSTN. Finally, we discuss the potential use of recombinant GDF11 as a therapeutic option for a wide range of medical conditions and the possible adverse effects of GDF11 inhibition mediated by MSTN inhibitors.

Establishing the pattern of the vertebrate limb

The vertebrate limb continues to serve as an influential model of growth, morphogenesis and pattern formation. With this Review, we aim to give an up-to-date picture of how a population of undifferentiated cells develops into the complex pattern of the limb. Focussing largely on mouse and chick studies, we concentrate on the positioning of the limbs, the formation of the limb bud, the establishment of the principal limb axes, the specification of pattern, the integration of pattern formation with growth and the determination of digit number. We also discuss the important, but little understood, topic of how gene expression is interpreted into morphology.

Endogenous GDF11 regulates odontogenic differentiation of dental pulp stem cells

Dental stem cell‐based tooth regeneration is the futuristic treatment for missing teeth. Growth differentiation factor 11 (GDF11), a novel member of the TGF‐beta superfamily, has been reported to play a critical role in regulating stem cell differentiation. However, the role of endogenous GDF11 during dental stem cell differentiation remains unknown. Here, we have shown that GDF11 was highly expressed in dental pulp tissues in both mouse and human. Knockdown of endogenous GDF11 in human dental pulp stem cells (hDPSCs) led to comparable proliferation and migration but attenuated odontogenic differentiation as evidenced by alkaline phosphatase and Alizarin Red S staining. In addition, transcriptional levels of odontogenic‐related genes were significantly down‐regulated according to real‐time polymerase chain reaction. Mechanistically, we performed RNA sequencing analysis and found that silencing of endogenous GDF11 compromised the process of ossification and osteoblast differentiation, especially down‐regulated transcription expression of Wnt pathway‐specific genes. Immunofluorescence staining also showed diminished β‐catenin expression and nuclei accumulation after knockdown of endogenous GDF11 in hDPSCs. In summary, our results suggested that endogenous GDF11 positively regulate odontogenic differentiation of hDPSCs through canonical Wnt/β‐catenin signalling pathway.

Myelo-deception: Luspatercept & TGF-Beta ligand traps in myeloid diseases & anemia

Myelodysplastic syndromes (MDS) encompass a clinically heterogenous group of diseases defined by a clonal bone marrow failure state. Patients with lower-risk MDS primarily suffer from the consequences of anemia, with a subset having increased risks of bleeding and infection. There are few good therapeutic options for this patient population, as patients are dependent on cytokine support to improve hematopoiesis. Our review will discuss luspatercept, a transforming growth factor (TGF)-Beta ligand trap, the first new Food & Drug Administration (FDA)-approved treatment in MDS in over a decade. We will explore the different TGF-Beta ligand traps that have been developed for a number of diseases, with a focus on myeloid malignancies.

A Tgfbr1/Snai1-dependent developmental module at the core of vertebrate axial elongation

Formation of the vertebrate postcranial body axis follows two sequential but distinct phases. The first phase generates pre-sacral structures (the so-called primary body) through the activity of the primitive streak on axial progenitors within the epiblast. The embryo then switches to generate the secondary body (post-sacral structures), which depends on axial progenitors in the tail bud. Here we show that the mammalian tail bud is generated through an independent functional developmental module, concurrent but functionally different from that generating the primary body. This module is triggered by convergent Tgfbr1 and Snai1 activities that promote an incomplete epithelial to mesenchymal transition on a subset of epiblast axial progenitors. This EMT is functionally different from that coordinated by the primitive streak, as it does not lead to mesodermal differentiation but brings axial progenitors into a transitory state, keeping their progenitor activity to drive further axial body extension.

The neuroprotective and neurorestorative effects of growth differentiation factor 11 in cerebral ischemic injury

Growth differentiation factor 11 (GDF11), a member of the transforming growth factor-β (TGF-β) superfamily, regulates various biological processes in mammals. The effect of GDF11 in brain injury has not been fully elucidated. Our aim was to investigate the effects of GDF11 in cerebral ischemic injury. The expression level of GDF11 increased significantly in the peri-infarct cerebral cortex. Next, the effect of the intracerebroventricular injection of a GDF11 overexpression lentivirus or rGDF11 was investigated in middle cerebral artery occlusion (MCAO) rats. The preventative effects of the GDF11 overexpression virus on stroke were observed. The delivery of the lentivirus into rats before MCAO significantly reduced the infarct volume and the percentage of apoptotic cells and improved motor function in MCAO rats. Furthermore, it elevated the expression of p-Smad2/3 and promoted neurogenesis and angiogenesis in the ipsilateral SVZ during ischemic injury. More importantly, the therapeutic effects of rGDF11 on stroke were subsequently explored. The results in MCAO rats treated with rGDF11 were found similar to that in those treated with the GDF11 overexpression lentivirus. Together, these findings indicate that GDF11 has neuroprotective and neurorestorative effects in cerebral ischemic injury and provide new insights into the function and mechanism of GDF11 in stroke models.

Growth differentiation factor 11 attenuates liver fibrosis via expansion of liver progenitor cells

OBJECTIVE

Liver fibrosis and cirrhosis resulting from chronic liver injury represent a major healthcare burden worldwide. Growth differentiation factor (GDF) 11 has been recently investigated for its role in rejuvenation of ageing organs, but its role in chronic liver diseases has remained unknown. Here, we investigated the expression and function of GDF11 in liver fibrosis, a common feature of most chronic liver diseases.

DESIGN

We analysed the expression of GDF11 in patients with liver fibrosis, in a mouse model of liver fibrosis and in hepatic stellate cells (HSCs) as well as in other liver cell types. The functional relevance of GDF11 in toxin-induced and cholestasis-induced mouse models of liver fibrosis was examined by in vivo modulation of Gdf11 expression using adeno-associated virus (AAV) vectors. The effect of GDF11 on leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5)+ liver progenitor cells was studied in mouse and human liver organoid culture. Furthermore, in vivo depletion of LGR5+ cells was induced by injecting AAV vectors expressing diptheria toxin A under the transcriptional control of Lgr5 promoter.

RESULTS

We showed that the expression of GDF11 is upregulated in patients with liver fibrosis and in experimentally induced murine liver fibrosis models. Furthermore, we found that therapeutic application of GDF11 mounts a protective response against fibrosis by increasing the number of LGR5+ progenitor cells in the liver.

CONCLUSION

Collectively, our findings uncover a protective role of GDF11 during liver fibrosis and suggest a potential application of GDF11 for the treatment of chronic liver disease.

Cellular and Molecular Biomarkers Indicate Premature Aging in Pseudoxanthoma Elasticum Patients

The molecular processes of aging are very heterogenic and not fully understood. Studies on rare progeria syndromes, which display an accelerated progression of physiological aging, can help to get a better understanding. Pseudoxanthoma elasticum (PXE) caused by mutations in the ATP-binding cassette sub-family C member 6 (ABCC6) gene shares some molecular characteristics with such premature aging diseases. Thus, this is the first study trying to broaden the knowledge of aging processes in PXE patients. In this study, we investigated aging associated biomarkers in primary human dermal fibroblasts and sera from PXE patients compared to healthy controls. Determination of serum concentrations of the aging biomarkers eotaxin-1 (CCL11), growth differentiation factor 11 (GDF11) and insulin-like growth factor 1 (IGF1) showed no significant differences between PXE patients and healthy controls. Insulin-like growth factor binding protein 3 (IGFBP3) showed a significant increase in serum concentrations of PXE patients older than 45 years compared to the appropriate control group. Tissue specific gene expression of GDF11 and IGFBP3 were significantly decreased in fibroblasts from PXE patients compared to normal human dermal fibroblasts (NHDF). IGFBP3 protein concentration in supernatants of fibroblasts from PXE patients were decreased compared to NHDF but did not reach statistical significance due to potential gender specific variations. The minor changes in concentration of circulating aging biomarkers in sera of PXE patients and the significant aberrant tissue specific expression seen for selected factors in PXE fibroblasts, suggests a link between ABCC6 deficiency and accelerated aging processes in affected peripheral tissues of PXE patients.

Hypoxia-induced miR-1260b regulates vascular smooth muscle cell proliferation by targeting GDF11

Vascular smooth muscle cells (VSMCs) are a unique cell type that has unusual plasticity controlled by environmental stimuli. As an abnormal increase of VSMC proliferation is associated with various vascular diseases, tight regulation of VSMC phenotypes is essential for maintaining vascular homeostasis. Hypoxia is one environmental stress that stimulates VSMC proliferation. Emerging evidence has indicated that microRNAs (miRNAs) are critical regulators in the hypoxic responses of VSMCs. Therefore, we previously investigated miRNAs modulated by hypoxia in VSMCs and found that miR-1260b is one of the most upregulated miRNAs under hypoxia. However, the mechanism that underlies the regulation of VSMCs via miR-1260b in response to hypoxia has not been explored. Here we demonstrated that hypoxia-induced miR-1260b promotes VSMC proliferation. We also identified growth differentiation factor 11 (GDF11), a member of the TGF-β superfamily, as a novel target of miR-1260b. miR-1260b directly targets the 3’UTR of GDF11. Downregulation of GDF11 inhibited Smad signaling and consequently enhanced the proliferation of VSMCs. Our findings suggest that miR-1260b-mediated GDF11-Smad-dependent signaling is an essential regulatory mechanism in the proliferation of VSMCs, and this axis is modulated by hypoxia to promote abnormal VSMC proliferation. Therefore, our study unveils a novel function of miR-1260b in the pathological proliferation of VSMCs under hypoxia.

Application of Cytokines of the Bone Morphogenetic Protein (BMP) Family in Spinal Fusion - Effects on the Bone, Intervertebral Disc and Mesenchymal Stromal Cells

Low back pain is a prevalent socio-economic burden and is often associated with damaged or degenerated intervertebral discs (IVDs). When conservative therapy fails, removal of the IVD (discectomy), followed by intersomatic spinal fusion, is currently the standard practice in clinics. The remaining space is filled with an intersomatic device (cage) and with bone substitutes to achieve disc height compensation and bone fusion. As a complication, in up to 30% of cases, spinal non-fusions result in a painful pseudoarthrosis. Bone morphogenetic proteins (BMPs) have been clinically applied with varied outcomes. Several members of the BMP family, such as BMP2, BMP4, BMP6, BMP7, and BMP9, are known to induce osteogenesis. Questions remain on why hyper-physiological doses of BMPs do not show beneficial effects in certain patients. In this respect, BMP antagonists secreted by mesenchymal cells, which might interfere with or block the action of BMPs, have drawn research attention as possible targets for the enhancement of spinal fusion or the prevention of non-unions. Examples of these antagonists are noggin, gremlin1 and 2, chordin, follistatin, BMP3, and twisted gastrulation. In this review, we discuss current evidence of the osteogenic effects of several members of the BMP family on osteoblasts, IVD cells, and mesenchymal stromal cells. We consider in vitro and in vivo studies performed in human, mouse, rat, and rabbit related to BMP and BMP antagonists in the last two decades. We give insights into the effects that BMP have on the ossification of the spine. Furthermore, the benefits, pitfalls, and possible safety concerns using these cytokines for the improvement of spinal fusion are discussed.

The vertebrate tail: a gene playground for evolution

The tail of all vertebrates, regardless of size and anatomical detail, derive from a post-anal extension of the embryo known as the tail bud. Formation, growth and differentiation of this structure are closely associated with the activity of a group of cells that derive from the axial progenitors that build the spinal cord and the muscle-skeletal case of the trunk. Gdf11 activity switches the development of these progenitors from a trunk to a tail bud mode by changing the regulatory network that controls their growth and differentiation potential. Recent work in the mouse indicates that the tail bud regulatory network relies on the interconnected activities of the Lin28/let-7 axis and the Hox13 genes. As this network is likely to be conserved in other mammals, it is possible that the final length and anatomical composition of the adult tail result from the balance between the progenitor-promoting and -repressing activities provided by those genes. This balance might also determine the functional characteristics of the adult tail. Particularly relevant is its regeneration potential, intimately linked to the spinal cord. In mammals, known for their complete inability to regenerate the tail, the spinal cord is removed from the embryonic tail at late stages of development through a Hox13-dependent mechanism. In contrast, the tail of salamanders and lizards keep a functional spinal cord that actively guides the tail's regeneration process. I will argue that the distinct molecular networks controlling tail bud development provided a collection of readily accessible gene networks that were co-opted and combined during evolution either to end the active life of those progenitors or to make them generate the wide diversity of tail shapes and sizes observed among vertebrates.

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

MSTN, a member of the TGF-β family, has been widely shown to suppress muscle growth, leading to an intense effort being directed at targeting MSTN to treat patients with muscle loss. GDF11 is another TGF-β family member closely related to MSTN, but its postnatal function is less clear. Using conditional knockout techniques, we show that GDF11 enhances bone mass in contrast to MSTN, emphasizing that MSTN/GDF11 inhibitors, such as FST, can induce adverse effects on bone through GDF11 inhibition. Because most MSTN inhibitors also inhibit GDF11 due to the high sequence similarity between MSTN and GDF11, our findings suggest that their opposing roles must be carefully considered when developing MSTN inhibitors for clinical applications.

Growth and differentiation factor 11 (GDF11) and myostatin (MSTN) are closely related transforming growth factor β (TGF-β) 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.

Skeletal muscle as an experimental model of choice to study tissue aging and rejuvenation

Skeletal muscle is among the most age-sensitive tissues in mammal organisms. Significant changes in its resident stem cells (i.e., satellite cells, SCs), differentiated cells (i.e., myofibers), and extracellular matrix cause a decline in tissue homeostasis, function, and regenerative capacity. Based on the conservation of aging across tissues and taking advantage of the relatively well-characterization of the myofibers and associated SCs, skeletal muscle emerged as an experimental system to study the decline in function and maintenance of old tissues and to explore rejuvenation strategies. In this review, we summarize the approaches for understanding the aging process and for assaying the success of rejuvenation that use skeletal muscle as the experimental system of choice. We further discuss (and exemplify with studies of skeletal muscle) how conflicting results might be due to variations in the techniques of stem cell isolation, differences in the assays of functional rejuvenation, or deciding on the numbers of replicates and experimental cohorts.

Elongation during segmentation shows axial variability, low mitotic rates, and synchronized cell cycle domains in the crustacean, Thamnocephalus platyurus

Background

Segmentation in arthropods typically occurs by sequential addition of segments from a posterior growth zone. However, the amount of tissue required for growth and the cell behaviors producing posterior elongation are sparsely documented.

Results

Using precisely staged larvae of the crustacean, Thamnocephalus platyurus, we systematically examine cell division patterns and morphometric changes associated with posterior elongation during segmentation. We show that cell division occurs during normal elongation but that cells in the growth zone need only divide ~ 1.5 times to meet growth estimates; correspondingly, direct measures of cell division in the growth zone are low. Morphometric measurements of the growth zone and of newly formed segments suggest tagma-specific features of segment generation. Using methods for detecting two different phases in the cell cycle, we show distinct domains of synchronized cells in the posterior trunk. Borders of cell cycle domains correlate with domains of segmental gene expression, suggesting an intimate link between segment generation and cell cycle regulation.

Conclusions

Emerging measures of cellular dynamics underlying posterior elongation already show a number of intriguing characteristics that may be widespread among sequentially segmenting arthropods and are likely a source of evolutionary variability. These characteristics include: the low rates of posterior mitosis, the apparently tight regulation of cell cycle at the growth zone/new segment border, and a correlation between changes in elongation and tagma boundaries.

The Role of Bone Morphogenetic Protein 7 (BMP-7) in Inflammation in Heart Diseases

Bone morphogenetic protein-7 is (BMP-7) is a potent anti-inflammatory growth factor belonging to the Transforming Growth Factor Beta (TGF-β) superfamily. It plays an important role in various biological processes, including embryogenesis, hematopoiesis, neurogenesis and skeletal morphogenesis. BMP-7 stimulates the target cells by binding to specific membrane-bound receptor BMPR 2 and transduces signals through mothers against decapentaplegic (Smads) and mitogen activated protein kinase (MAPK) pathways. To date, rhBMP-7 has been used clinically to induce the differentiation of mesenchymal stem cells bordering the bone fracture site into chondrocytes, osteoclasts, the formation of new bone via calcium deposition and to stimulate the repair of bone fracture. However, its use in cardiovascular diseases, such as atherosclerosis, myocardial infarction, and diabetic cardiomyopathy is currently being explored. More importantly, these cardiovascular diseases are associated with inflammation and infiltrated monocytes where BMP-7 has been demonstrated to be a key player in the differentiation of pro-inflammatory monocytes, or M1 macrophages, into anti-inflammatory M2 macrophages, which reduces developed cardiac dysfunction. Therefore, this review focuses on the molecular mechanisms of BMP-7 treatment in cardiovascular disease and its role as an anti-fibrotic, anti-apoptotic and anti-inflammatory growth factor, which emphasizes its potential therapeutic significance in heart diseases.

Extracellular Vesicles Derived from Human Gingival Mesenchymal Stem Cells: A Transcriptomic Analysis

Human gingival mesenchymal stem cells (hGMSCs) have outstanding characteristics of proliferation and are able to differentiate into osteogenic, chondrogenic, adipogenic, and neurogenic cell lineages. The extracellular vesicles (EVs) secreted by hGMSCs contain proteins, lipids, mRNA and microRNA have emerged as important mediators of cell-to-cell communication. In this study, we analyzed the transcriptome of hGMSCs-derived EVs using Next Generation Sequencing (NGS). The functional evaluation of the transcriptome highlighted 26 structural protein classes and the presence of "non-coding RNAs". Our results showed that EVs contain several growth factors such as Transforming Growth Factor-β (TGF-β), Fibroblast Growth Factor (FGF), and Vascular Endothelial Growth Factors (VEGF) implicated in osteoblast differentiation and in angiogenetic process. Furthermore, the transcriptomic analysis showed the presence of glial cell-derived neurotrophic factor (GDNF) family ligands and neurotrophins involved in neuronal development. The NGS analysis also identified the presence of several interleukins among which some with anti-inflammatory action. Moreover, the transcriptome profile of EVs contained members of the Wnt family, involved in several biological processes, such as cellular proliferation and tissue regeneration. In conclusion, the huge amount of growth factors included in the hGMSCs-derived EVs could make them a big resource in regenerative medicine.

GASP-2 overexpressing mice exhibit a hypermuscular phenotype with contrasting molecular effects compared to GASP-1 transgenics

Muscle atrophy is associated with many diseases including genetic disorders, sarcopenia, or cachexia syndromes. Myostatin (Mstn), a transforming growth factor-beta (TGF-β) member, plays a key role in skeletal muscle homeostasis as a powerful negative regulator. Over the last decade, about 15 clinical trials aimed at inhibiting the Mstn pathway, failed to produce conclusive results. In this context, we investigated whether growth and differentiation factor-associated serum protein-1 (GASP-1) or GASP-2, two natural inhibitors of Mstn, might represent a potential therapeutic. As we previously reported, mice overexpressing Gasp-1 (Tg(Gasp-1)) present an increase of muscle mass but develop metabolic disorders with aging. Here, we showed that overexpression of Gasp-2 increases the muscular mass without metabolic defects. We also found that Tg(Gasp-2) mice displayed, like Mstn^-/- mice, a switch from slow- to fast-twitch myofibers whereas Tg(Gasp-1) mice exhibit a reverse switch. Our studies supported the fact that GASP-2 has less affinity than GASP-1 for Mstn, leading to a constitutive Mstn upregulation only in Tg(Gasp-1) mice, responsible for the observed phenotypic differences. Altogether, our findings highlighted a gene expression regulatory network of TGF-β members and their inhibitors in muscle.

Glucocorticoids counteract hypertrophic effects of myostatin inhibition in dystrophic muscle

Duchenne muscular dystrophy (DMD) is a devastating genetic muscle disease resulting in progressive muscle degeneration and wasting. Glucocorticoids, specifically prednisone/prednisolone and deflazacort, are commonly used by DMD patients. Emerging DMD therapeutics include those targeting the muscle-wasting factor, myostatin (Mstn). The aim of this study was to investigate how chronic glucocorticoid treatment impacts the efficacy of Mstn inhibition in the D2.mdx mouse model of DMD. We report that chronic treatment of dystrophic mice with prednisolone (Pred) causes significant muscle wasting, entailing both activation of the ubiquitin-proteasome degradation pathway and inhibition of muscle protein synthesis. Combining Pred with Mstn inhibition, using a modified Mstn propeptide (dnMstn), completely abrogates the muscle hypertrophic effects of Mstn inhibition independently of Mstn expression or SMAD3 activation. Transcriptomic analysis identified that combining Pred with dnMstn treatment affects gene expression profiles associated with inflammation, metabolism, and fibrosis. Additionally, we demonstrate that Pred-induced muscle atrophy is not prevented by Mstn ablation. Therefore, glucocorticoids interfere with potential muscle mass benefits associated with targeting Mstn, and the ramifications of glucocorticoid use should be a consideration during clinical trial design for DMD therapeutics. These results have significant implications for past and future Mstn inhibition trials in DMD.

Whole-genome resequencing analysis of 20 Micro-pigs

BACKGROUND

Miniature pigs have been increasingly used as mammalian model animals for biomedical research because of their similarity to human beings in terms of their metabolic features and proportional organ sizes. However, despite their importance, there is a severe lack of genome-wide studies on miniature pigs.

OBJECTIVE

In this study, we performed whole-genome sequencing analysis of 20 Micro-pigs obtained from Medi Kinetics to elucidate their genomic characteristics.

RESULTS

Approximately 595 gigabase pairs (Gb) of sequence reads were generated to be mapped to the swine reference genome assembly (Sus scrofa 10.2); on average, the sequence reads covered 99.15% of the reference genome at an average of 9.6-fold coverage. We detected a total of 19,518,548 SNPs, of which 8.7% were found to be novel. With further annotation of all of the SNPs, we retrieved 144,507 nonsynonymous SNPs (nsSNPs); of these, 5968 were found in all 20 individuals used in this study. SIFT prediction for these SNPs identified that 812 nsSNPs in 402 genes were deleterious. Among these 402 genes, we identified some genes that could potentially affect traits of interest in Micro-pigs, such as RHEB and FRAS1. Furthermore, we performed runs of homozygosity analysis to locate potential selection signatures in the genome, detecting several loci that might be involved in phenotypic characteristics in Micro-pigs, such as MSTN, GDF5, and GDF11.

CONCLUSION

In this study, we identified numerous nsSNPs that could be used as candidate genetic markers with involvement in traits of interest. Furthermore, we detected putative selection footprints that might be associated with recent selection applied to miniature pigs.

Variation in zygotic CRISPR/Cas9 gene editing outcomes generates novel reporter and deletion alleles at the Gdf11 locus

Recent advances in CRISPR/Cas gene editing technology have significantly expanded the possibilities and accelerated the pace of creating genetically engineered animal models. However, CRISPR/Cas-based strategies designed to precisely edit the genome can often yield unintended outcomes. Here, we report the use of zygotic CRISPR/Cas9 injections to generate a knock-in GFP reporter mouse at the Gdf11 locus. Phenotypic and genomic characterization of founder animals from these injections revealed a subset that contained the correct targeting event and exhibited GFP expression that, within the hematopoietic system, was restricted predominantly to lymphoid cells. Yet, in another subset of founder mice, we detected aberrant integration events at the target site that dramatically and inaccurately shifted hematopoietic GFP expression from the lymphoid to the myeloid lineage. Additionally, we recovered multiple Gdf11 deletion alleles that modified the C-terminus of the GDF11 protein. When bred to homozygosity, most of these alleles recapitulated skeletal phenotypes reported previously for Gdf11 knockout mice, suggesting that these represent null alleles. However, we also recovered one Gdf11 deletion allele that encodes a novel GDF11 variant protein ("GDF11-WE") predicted to contain two additional amino acids (tryptophan (W) and glutamic acid (E)) at the C-terminus of the mature ligand. Unlike the other Gdf11 deletion alleles recovered in this study, homozygosity for the Gdf11WE allele did not phenocopy Gdf11 knockout skeletal phenotypes. Further investigation using in vivo and in vitro approaches demonstrated that GDF11-WE retains substantial physiological function, indicating that GDF11 can tolerate at least some modifications of its C-terminus and providing unexpected insights into its biochemical activities. Altogether, our study confirms that one-step zygotic injections of CRISPR/Cas gene editing complexes provide a quick and powerful tool to generate gene-modified mouse models. Moreover, our findings underscore the critical importance of thorough characterization and validation of any modified alleles generated by CRISPR, as unintended on-target effects that fail to be detected by simple PCR screening can produce substantially altered phenotypic readouts.

Steady-state and regenerative hematopoiesis occurs normally in mice in the absence of GDF11

Tightly regulated production of mature blood cells is essential for health and survival in vertebrates and dependent on discrete populations of blood-forming (hematopoietic) stem and progenitor cells. Prior studies suggested that inhibition of growth differentiation factor 11 (GDF11) through soluble activin receptor type II (ActRII) ligand traps or neutralizing antibodies promotes erythroid precursor cell maturation and red blood cell formation in contexts of homeostasis and anemia. As Gdf11 is expressed by mature hematopoietic cells, and erythroid precursor cell expression of Gdf11 has been implicated in regulating erythropoiesis, we hypothesized that genetic disruption of Gdf11 in blood cells might perturb normal hematopoiesis or recovery from hematopoietic insult. Contrary to these predictions, we found that deletion of Gdf11 in the hematopoietic lineage in mice does not alter erythropoiesis or erythroid precursor cell frequency under normal conditions or during hematopoietic recovery after irradiation and transplantation. In addition, although hematopoietic cell-derived Gdf11 may contribute to the pool of circulating GDF11 protein during adult homeostasis, loss of Gdf11 specifically in the blood system does not impair hematopoietic stem cell function or induce overt pathological consequences. Taken together, these results reveal that hematopoietic cell-derived Gdf11 is largely dispensable for native and transplant-induced blood formation.

Relationship of Circulating Growth and Differentiation Factors 8 and 11 and Their Antagonists as Measured Using Liquid Chromatography-Tandem Mass Spectrometry With Age and Skeletal Muscle Strength in Healthy Adults

Background

Growth and differentiation factors 8 (GDF8) and 11 (GDF11) have attracted attention as targets for rejuvenating interventions. The biological activity of these proteins may be affected by circulating antagonists such as their respective prodomains, follistatin (FST315), WFIKKN1, and WFIKKN2. Reports of the relationship of GDF8 and GDF11 and their antagonists with aging and aging phenotypes such as skeletal muscle strength have been conflicting possibly because of difficulties in measuring these proteins and polypeptides.

Methods

Plasma GDF8 and GDF11 and their antagonists were measured using a multiplexed selected reaction monitoring assay and liquid chromatography-tandem mass spectrometry in 160 healthy adults aged 22-93 years. Quadriceps strength was measured by knee extensor torque using isokinetic dynamometry.

Results

Spearman correlations with age were the following: GDF11 prodomain (r = .30, p = .001), GDF11 mature protein (r = .23, p = .004), FST315 (r = .32, p < .0001), WFIKKN1 (r = -.21, p = 0.008), and WFIKKN2 (r = .18, p = .02). Independent of age, FST315 and WFIKKN1 were negatively associated with knee strength (p = .02, p = .03, respectively) in a multivariable model that included both GDF8 and GDF11 mature proteins.

Conclusions

When measured by an antibody-free selected reaction monitoring assay, GDF8, GDF11, and their antagonists are found in the circulation in the ng/mL range. In healthy adults, plasma GDF11 and antagonists FST315, WFIKKN1, and WFIKKN2 differed by age. Antagonists of GDF8 and GDF11, but not GDF8 and GDF11, were independently associated with skeletal muscle strength. Further work is needed to characterize the relationship of these protein and polypeptides with sarcopenia-related phenotypes such as physical function and walking disability.

GDF11 impairs liver regeneration in mice after partial hepatectomy

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor (TGF)-β superfamily. The rejuvenative effect of GDF11 has been called into question recently, and its role in liver regeneration is unclear. Here, we investigated the pathophysiologic role of GDF11, as well as its plausible signaling mechanisms in a mouse model of partial hepatectomy (PH). We demonstrated that both serum and hepatic GDF11 protein expression increased following PH. Treatment with adeno-associated viruses-GDF11 and recombinant GDF11 protein severely impaired liver regeneration, whereas inhibition of GDF11 activity with neutralizing antibodies significantly improved liver regeneration after PH. In vitro, GDF11 treatment significantly delayed cell proliferation and induced cell-cycle arrest in α mouse liver 12 (AML12) cells. Moreover, GDF11 activated TGF-β-SMAD2/3 signaling pathway. Inhibition of GDF11-induced SMAD2/3 activity significantly blocked GDF11-mediated reduction in cell proliferation both in vivo and in vitro. In the clinical setting, GDF11 levels were significantly elevated in patients after hepatectomy. Collectively, these results indicate that rather than a ‘rejuvenating’ agent, GDF11 impairs liver regeneration after PH. Suppression of cell-cycle progression via TGF-β-SMAD2/3 signaling pathway may be a key mechanism by which GDF11 inhibits liver regeneration.

GDF11 Implications in Cancer Biology and Metabolism. Facts and Controversies

Growth Differentiation Factor 11 (GDF11), a member of the super family of the Transforming Growth Factor β, has gained more attention in the last few years due to numerous reports regarding its functions in other systems, which are different to those related to differentiation and embryonic development, such as age-related muscle dysfunction, skin biology, metabolism, and cancer. GDF11 is expressed in many tissues, including skeletal muscle, pancreas, kidney, nervous system, and retina, among others. GDF11 circulating levels and protein content in tissues are quite variable and are affected by pathological conditions or age. Although, GDF11 biology had a lot of controversies, must of them are only misunderstandings regarding the variability of its responses, which are independent of the tissue, grade of cellular differentiation or pathologies. A blunt fact regarding GDF11 biology is that its target cells have stemness feature, a property that could be found in certain adult cells in health and in disease, such as cancer cells. This review is focused to present and analyze the recent findings in the emerging research field of GDF11 function in cancer and metabolism, and discusses the controversies surrounding the biology of this atypical growth factor.

GDF11 contributes to hepatic hepcidin (HAMP) inhibition through SMURF1-mediated BMP-SMAD signalling suppression

Hepcidin (HAMP) synthesis is suppressed by erythropoiesis to increase iron availability for red blood cell production. This effect is thought to result from factors secreted by erythroid precursors. Growth differentiation factor 11 (GDF11) expression was recently shown to increase in erythroid cells of β-thalassaemia, and decrease with improvement in anaemia. Whether GDF11 regulates hepatic HAMP production has never been experimentally studied. Here, we explore GDF11 function during erythropoiesis-triggered HAMP suppression. Our results confirm that exogenous erythropoietin significantly increases Gdf11 as well as Erfe (erythroferrone) expression, and Gdf11 is also increased, albeit at a lower degree than Erfe, in phlebotomized wild type and β-thalassaemic mice. GDF11 is expressed predominantly in erythroid burst forming unit- and erythroid colony-forming unit- cells during erythropoiesis. Exogeneous GDF11 administration results in HAMP suppression in vivo and in vitro. Furthermore, exogenous GDF11 decreases BMP-SMAD signalling, enhances SMAD ubiquitin regulatory factor 1 (SMURF1) expression and induces ERK1/2 (MAPK3/1) signalling. ERK1/2 signalling activation is required for GDF11 or SMURF1-mediated suppression in BMP-SMAD signalling and HAMP expression. This research newly characterizes GDF11 in erythropoiesis-mediated HAMP suppression, in addition to ERFE.

Analysis of Cre-mediated genetic deletion of Gdf11 in cardiomyocytes of young mice

Administration of active growth differentiation factor 11 (GDF11) to aged mice can reduce cardiac hypertrophy, and low serum levels of GDF11 measured together with the related protein, myostatin (also known as GDF8), predict future morbidity and mortality in coronary heart patients. Using mice with a loxP-flanked ("floxed") allele of Gdf11 and Myh6-driven expression of Cre recombinase to delete Gdf11 in cardiomyocytes, we tested the hypothesis that cardiac-specific Gdf11 deficiency might lead to cardiac hypertrophy in young adulthood. We observed that targeted deletion of Gdf11 in cardiomyocytes does not cause cardiac hypertrophy but rather leads to left ventricular dilation when compared with control mice carrying only the Myh6-cre or Gdf11-floxed alleles, suggesting a possible etiology for dilated cardiomyopathy. However, the mechanism underlying this finding remains unclear because of multiple confounding effects associated with the selected model. First, whole heart Gdf11 expression did not decrease in Myh6-cre; Gdf11-floxed mice, possibly because of upregulation of Gdf11 in noncardiomyocytes in the heart. Second, we observed Cre-associated toxicity, with lower body weights and increased global fibrosis, in Cre-only control male mice compared with flox-only controls, making it challenging to infer which changes in Myh6-cre;Gdf11-floxed mice were the result of Cre toxicity versus deletion of Gdf11. Third, we observed differential expression of cre mRNA in Cre-only controls compared with the cardiomyocyte-specific knockout mice, also making comparison between these two groups difficult. Thus, targeted Gdf11 deletion in cardiomyocytes may lead to left ventricular dilation without hypertrophy, but alternative animal models are necessary to understand the mechanism for these findings. NEW & NOTEWORTHY We observed that targeted deletion of growth differentiation factor 11 in cardiomyocytes does not cause cardiac hypertrophy but rather leads to left ventricular dilation compared with control mice carrying only the Myh6-cre or growth differentiation factor 11-floxed alleles. However, the mechanism underlying this finding remains unclear because of multiple confounding effects associated with the selected mouse model.