Growth differentiation factor 5 is a key physiological regulator of dendrite growth during development

GDF5 as a rejuvenating treatment for age-related neuromuscular failure

Sarcopenia involves a progressive loss of skeletal muscle force, quality and mass during ageing, which results in increased inability and death; however, no cure has been established thus far. Growth differentiation factor 5 (GDF5) has been described to modulate muscle mass maintenance in various contexts. For our proof of concept, we overexpressed GDF5 by AAV vector injection in tibialis anterior muscle of adult aged (20 months) mice and performed molecular and functional analysis of skeletal muscle. We analysed human vastus lateralis muscle biopsies from adult young (21-42 years) and aged (77-80 years) donors, quantifying the molecular markers modified by GDF5 overexpression in mouse muscle. We validated the major effects of GDF5 overexpression using human immortalized myotubes and Schwann cells. We established a preclinical study by treating chronically (for 4 months) aged mice using recombinant GDF5 protein (rGDF5) in systemic administration and evaluated the long-term effect of this treatment on muscle mass and function. Here, we demonstrated that GDF5 overexpression in the old tibialis anterior muscle promoted an increase of 16.5% of muscle weight (P = 0.0471) associated with a higher percentage of 5000-6000 µm2 large fibres (P = 0.0211), without the induction of muscle regeneration. Muscle mass gain was associated with an amelioration of 26.8% of rate of force generation (P = 0.0330) and better neuromuscular connectivity (P = 0.0098). Moreover, GDF5 overexpression preserved neuromuscular junction morphology (38.5% of nerve terminal area increase, P < 0.0001) and stimulated the expression of reinnervation-related genes, in particular markers of Schwann cells (fold-change 3.19 for S100b gene expression, P = 0.0101). To characterize the molecular events induced by GDF5 overexpression during ageing, we performed a genome-wide transcriptomic analysis of treated muscles and showed that this factor leads to a 'rejuvenating' transcriptomic signature in aged mice, as 42% of the transcripts dysregulated by ageing reverted to youthful expression levels upon GDF5 overexpression (P < 0.05). Towards a preclinical approach, we performed a long-term systemic treatment using rGDF5 and showed its effectiveness in counteracting age-related muscle wasting, improving muscle function (17.8% of absolute maximal force increase, P = 0.0079), ensuring neuromuscular connectivity and preventing neuromuscular junction degeneration (7.96% of AchR area increase, P = 0.0125). In addition, in human muscle biopsies, we found the same age-related alterations than those observed in mice and improved by GDF5 and reproduced its major effects on human cells, suggesting this treatment as efficient in humans. Overall, these data provide a foundation to examine the curative potential of GDF5 drug in clinical trials for sarcopenia and, eventually, other neuromuscular diseases.

Clinical and molecular cytogenetic studies of five new patients with 20q11q12 deletion and review of the literature: Proposition of two critical regions

Deletions of the long arm of chromosome 20 (20q) are rare, with only 16 reported patients displaying a proximal interstitial 20q deletion. A 1.62 Mb minimal critical region at 20q11.2, encompassing three genes GDF5, EPB41L1, and SAMHD1, is proposed to be responsible for this syndrome. The leading clinical features include growth retardation, intractable feeding difficulties with gastroesophageal reflux, hypotonia and psychomotor developmental delay. Common facial dysmorphisms including triangular face, hypertelorism, and hypoplastic alae nasi were additionally reported. Here, we present the clinical and molecular findings of five new patients with proximal interstitial 20q deletions. We analyzed the phenotype and molecular data of all previously reported patients with 20q11.2q12 microdeletions, along with our five new cases. Copy number variation analysis of patients in our cohort has enabled us to identify the second critical region in the 20q11.2q12 region and redefine the first region that is initially identified. The first critical region spans 359 kb at 20q11.2, containing six MIM genes, including two disease-causing genes, GDF5 and CEP250. The second critical region spans 706 kb at 20q12, encompassing four MIM genes, including two disease-causing genes, MAFB and TOP1. We propose GDF5 to be the primary candidate gene generating the phenotype of patients with 20q11.2 deletions. Moreover, we hypothesize TOP1 as a potential candidate gene for the second critical region at 20q12. Of note, we cannot exclude the possibility of a synergistic role of other genes involved in the deletion, including a contiguous gene deletion syndrome or position effect affecting both critical regions. Further studies focusing on patients with proximal 20q deletions are required to support our hypothesis.

Functional and structural basis of extreme conservation in vertebrate 5' untranslated regions

The lack of knowledge about extreme conservation in genomes remains a major gap in our understanding of the evolution of gene regulation. Here, we reveal an unexpected role of extremely conserved 5' untranslated regions (UTRs) in noncanonical translational regulation that is linked to the emergence of essential developmental features in vertebrate species. Endogenous deletion of conserved elements within these 5' UTRs decreased gene expression, and extremely conserved 5' UTRs possess cis-regulatory elements that promote cell-type-specific regulation of translation. We further developed in-cell mutate-and-map (icM²), a new methodology that maps RNA structure inside cells. Using icM², we determined that an extremely conserved 5' UTR encodes multiple alternative structures and that each single nucleotide within the conserved element maintains the balance of alternative structures important to control the dynamic range of protein expression. These results explain how extreme sequence conservation can lead to RNA-level biological functions encoded in the untranslated regions of vertebrate genomes.

STRAP and NME1 Mediate the Neurite Growth-Promoting Effects of the Neurotrophic Factor GDF5

Loss of midbrain dopaminergic (mDA) neurons and their axons is central to Parkinson's disease (PD). Growth differentiation factor (GDF)5 is a potential neurotrophic factor for PD therapy. However, the molecular mediators of its neurotrophic action are unknown. Our proteomics analysis shows that GDF5 increases the expression of serine threonine receptor-associated protein kinase (STRAP) and nucleoside diphosphate kinase (NME)1 in the SH-SY5Y neuronal cell line. GDF5 overexpression increased NME1 expression in adult rat brain in vivo. NME and STRAP mRNAs are expressed in developing and adult rodent midbrain. Expression of both STRAP and NME1 is necessary and sufficient for the promotion of neurite growth in SH-SY5Y cells by GDF5. NME1 treatment increased neurite growth in both SH-SY5Y cells and cultured mDA neurons. Expression patterns of NME and STRAP are altered in PD midbrain. NME1 and STRAP are thus key mediators of GDF5's neurotrophic effects, rationalizing their future study as therapeutic targets for PD.

Multiplex Protein Imaging with Secondary Ion Mass Spectrometry Using Metal Oxide Nanoparticle-Conjugated Antibodies

In spite of recent developments in mass spectrometry imaging techniques, high-resolution multiplex protein bioimaging techniques are required to unveil the complex inter- and intracellular biomolecular interactions for accurate understanding of life phenomena and disease mechanisms. Herein, we report multiplex protein imaging with secondary ion mass spectrometry (SIMS) using metal oxide nanoparticle (MONP)-conjugated antibodies with <300 nm spatial resolution in the low ion dose without ion beam damage because of the high secondary ion yields of the MONPs, which can provide simultaneous imaging of several proteins, especially from cell membranes. We applied our new imaging technique for the study of hippocampal tissue samples from control and Alzheimer's disease (AD) model mice; the proximity of protein clusters in the hippocampus CA1 region showed intriguing dependence on aging and AD progress, suggesting that protein cluster proximity may be helpful for understanding pathological pathways in the microscopic cellular level.

First Report of Low-Rate Mosaicism for 20q11.21q12 Deletion and Delineation of the Associated Disorder

Interstitial deletions of the long arm of chromosome 20 are very rare, with only 12 reported patients harboring the 20q11.2 microdeletion and presenting a disorder characterized by psychomotor and growth delay, dysmorphisms, and brachy-/clinodactyly. We describe the first case of mosaic 20q11.2 deletion in a 5-year-old girl affected by mild psychomotor delay, feeding difficulties, growth retardation, craniofacial dysmorphisms, and finger anomalies. SNP array analysis disclosed 20% of cells with a 20q11.21q12 deletion, encompassing the 20q11.2 minimal critical region and the 3 OMIM disease-causing genes GDF5, EPB41L1, and SAMHD1. We propose a pathogenic role of other genes mapping outside the small region of overlap, in particular GHRH (growth hormone releasing hormone), whose haploinsufficiency could be responsible for the prenatal onset of growth retardation which is shared by half of these patients. Our patient highlights the utility of chromosomal microarray analysis to identify low-level mosaicism.

Growth Differentiation Factor 5 Improves Neurogenesis and Functional Recovery in Adult Mouse Hippocampus Following Traumatic Brain Injury

The aim of this study was to investigate the therapeutic effect of growth differentiation factor 5 (GDF-5) on traumatic brain injury (TBI) in mice. We utilized a controlled cortical impact to establish a mouse TBI model, and then stereotaxically administered 25 or 100 ng GDF-5 into the bilateral hippocampal dentate gyrus (DG) of each of the animals. Seven days after the injury, some of the animals were sacrificed for immunohistochemical and immunofluorescence examination of 5-bromo-2'-deoxyuridine (BrdU), Sox-2, doublecortin (DCX) and phosphorylated cAMP response element binding protein (p-CREB). Dendrite quantification was also performed using DCX positive cells. Activation of newborn neurons was assessed 35 days after the injury. The remaining animals were subjected to open field, Y maze and contextual fear conditioning tests 2 months after TBI. As a result, we found that post-injury stereotaxical administration of GDF-5 can improve neural stem cell proliferation and differentiation in the DG of the hippocampus, evidenced by the increase in BrdU, Sox-2, and DCX-labeled cells, as well as the improvement in dendrite arborization and newborn neuron activation in response to GDF-5 treatment. Mechanistically, these effects of GDF-5 may be mediated by the CREB pathway, manifested by the recovery of TBI-induced dephosphorylation of CREB upon GDF-5 administration. Behavioral tests further verified the effects of GDF-5 on improving cognitive and behavioral dysfunction after TBI. Collectively, these results reveal that direct injection of GDF-5 into the hippocampus can stimulate neurogenesis and improve functional recovery in a mouse TBI model, indicating the potential therapeutic effects of GDF-5 on TBI.

Canonical TGF-β Signaling Negatively Regulates Neuronal Morphogenesis through TGIF/Smad Complex-Mediated CRMP2 Suppression

Functional neuronal connectivity requires proper neuronal morphogenesis and its dysregulation causes neurodevelopmental diseases. Transforming growth factor-β (TGF-β) family cytokines play pivotal roles in development, but little is known about their contribution to morphological development of neurons. Here we show that the Smad-dependent canonical signaling of TGF-β family cytokines negatively regulates neuronal morphogenesis during brain development. Mechanistically, activated Smads form a complex with transcriptional repressor TG-interacting factor (TGIF), and downregulate the expression of a neuronal polarity regulator, collapsin response mediator protein 2. We also demonstrate that TGF-β family signaling inhibits neurite elongation of human induced pluripotent stem cell-derived neurons. Furthermore, the expression of TGF-β receptor 1, Smad4, or TGIF, which have mutations found in patients with neurodevelopmental disorders, disrupted neuronal morphogenesis in both mouse (male and female) and human (female) neurons. Together, these findings suggest that the regulation of neuronal morphogenesis by an evolutionarily conserved function of TGF-β signaling is involved in the pathogenesis of neurodevelopmental diseases.SIGNIFICANCE STATEMENT Canonical transforming growth factor-β (TGF-β) signaling plays a crucial role in multiple organ development, including brain, and mutations in components of the signaling pathway associated with several human developmental disorders. In this study, we found that Smads/TG-interacting factor-dependent canonical TGF-β signaling regulates neuronal morphogenesis through the suppression of collapsin response mediator protein-2 (CRMP2) expression during brain development, and that function of this signaling is evolutionarily conserved in the mammalian brain. Mutations in canonical TGF-β signaling factors identified in patients with neurodevelopmental disorders disrupt the morphological development of neurons. Thus, our results suggest that proper control of TGF-β/Smads/CRMP2 signaling pathways is critical for the precise execution of neuronal morphogenesis, whose impairment eventually results in neurodevelopmental disorders.

The Wnt Signaling Pathway Is Differentially Expressed during the Bovine Herpesvirus 1 Latency-Reactivation Cycle: Evidence That Two Protein Kinases Associated with Neuronal Survival, Akt3 and BMPR2, Are Expressed at Higher Levels during Latency

Sensory neurons in trigeminal ganglia (TG) of calves latently infected with bovine herpesvirus 1 (BoHV-1) abundantly express latency-related (LR) gene products, including a protein (ORF2) and two micro-RNAs. Recent studies in mouse neuroblastoma cells (Neuro-2A) demonstrated ORF2 interacts with β-catenin and a β-catenin coactivator, high-mobility group AT-hook 1 (HMGA1) protein, which correlates with increased β-catenin-dependent transcription and cell survival. β-Catenin and HMGA1 are readily detected in a subset of latently infected TG neurons but not TG neurons from uninfected calves or reactivation from latency. Consequently, we hypothesized that the Wnt/β-catenin signaling pathway is differentially expressed during the latency and reactivation cycle and an active Wnt pathway promotes latency. RNA-sequencing studies revealed that 102 genes associated with the Wnt/β-catenin signaling pathway were differentially expressed in TG during the latency-reactivation cycle in calves. Wnt agonists were generally expressed at higher levels during latency, but these levels decreased during dexamethasone-induced reactivation. The Wnt agonist bone morphogenetic protein receptor 2 (BMPR2) was intriguing because it encodes a serine/threonine receptor kinase that promotes neuronal differentiation and inhibits cell death. Another differentially expressed gene encodes a protein kinase (Akt3), which is significant because Akt activity enhances cell survival and is linked to herpes simplex virus 1 latency and neuronal survival. Additional studies demonstrated ORF2 increased Akt3 steady-state protein levels and interacted with Akt3 in transfected Neuro-2A cells, which correlated with Akt3 activation. Conversely, expression of Wnt antagonists increased during reactivation from latency. Collectively, these studies suggest Wnt signaling cooperates with LR gene products, in particular ORF2, to promote latency.IMPORTANCE Lifelong BoHV-1 latency primarily occurs in sensory neurons. The synthetic corticosteroid dexamethasone consistently induces reactivation from latency in calves. RNA sequencing studies revealed 102 genes associated with the Wnt/β-catenin signaling pathway are differentially regulated during the latency-reactivation cycle. Two protein kinases associated with the Wnt pathway, Akt3 and BMPR2, were expressed at higher levels during latency but were repressed during reactivation. Furthermore, five genes encoding soluble Wnt antagonists and β-catenin-dependent transcription inhibitors were induced during reactivation from latency. These findings are important because Wnt, BMPR2, and Akt3 promote neurogenesis and cell survival, processes crucial for lifelong viral latency. In transfected neuroblastoma cells, a viral protein expressed during latency (ORF2) interacts with and enhances Akt3 protein kinase activity. These findings provide insight into how cellular factors associated with the Wnt signaling pathway cooperate with LR gene products to regulate the BoHV-1 latency-reactivation cycle.

Inhibition of miR-181a promotes midbrain neuronal growth through a Smad1/5-dependent mechanism: implications for Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease, and is characterized by the progressive degeneration of nigrostriatal dopaminergic (DA) neurons. Current PD treatments are symptomatic, wear off over time and do not protect against DA neuronal loss. Finding a way to re-grow midbrain DA (mDA) neurons is a promising disease-modifying therapeutic strategy for PD. However, reliable biomarkers are required to allow such growth-promoting approaches to be applied early in the disease progression. miR-181a has been shown to be dysregulated in PD patients, and has been identified as a potential biomarker for PD. Despite studies demonstrating the enrichment of miR-181a in the brain, specifically in neurites of postmitotic neurons, the role of miR-181a in mDA neurons remains unknown. Herein, we used cell culture models of human mDA neurons to investigate a potential role for miR-181a in mDA neurons. We used a bioninformatics analysis to identify that miR-181a targets components of the bone morphogenetic protein (BMP) signalling pathway, including the transcription factors Smad1 and Smad5, which we find are expressed by rat mDA neurons and are required for BMP-induced neurite growth. We also found that inhibition of neuronal miR-181a, resulted in increased Smad signalling, and induced neurite growth in SH-SY5Y cells. Finally, using embryonic rat cultures, we demonstrated that miR-181a inhibition induces ventral midbrain (VM) and cortical neuronal growth. These data describe a new role for miR-181a in mDA neurons, and provide proof of principle that miR-181a dysresgulation in PD may alter the activation state of signalling pathways important for neuronal growth in neurons affected in PD.

Mechanisms regulating dendritic arbor patterning

The nervous system is populated by diverse types of neurons, each of which has dendritic trees with strikingly different morphologies. These neuron-specific morphologies determine how dendritic trees integrate thousands of synaptic inputs to generate different firing properties. To ensure proper neuronal function and connectivity, it is necessary that dendrite patterns are precisely controlled and coordinated with synaptic activity. Here, we summarize the molecular and cellular mechanisms that regulate the formation of cell type-specific dendrite patterns during development. We focus on different aspects of vertebrate dendrite patterning that are particularly important in determining the neuronal function; such as the shape, branching, orientation and size of the arbors as well as the development of dendritic spine protrusions that receive excitatory inputs and compartmentalize postsynaptic responses. Additionally, we briefly comment on the implications of aberrant dendritic morphology for nervous system disease.

Signaling by growth/differentiation factor 5 through the bone morphogenetic protein receptor type IB protects neurons against kainic acid-induced neurodegeneration

Growth/differentiation factor-5 (GDF-5), a member of the transforming growth factor-beta (TGF-β) superfamily, has been shown to protect rat dopaminergic neurons against insult both in embryonic neuronal culture and in Parkinson's disease models. However, whether GDF-5 exerts neuroprotective effects in hippocampal neurons is unclear. Here, we show that both mRNA levels and protein levels of GDF-5 are decreased in the mouse hippocampus upon kainic acid (KA) treatment. KA induced dramatic neuronal loss specifically in the cornu ammonis 1 (CA1) and CA3 areas of the mouse hippocampus, while intracerebral infusion of GDF-5 prevented this neuronal loss. The neuroprotective effects of GDF-5 were recapitulated by constitutively active bone morphogenetic protein type IB receptor (BMPRIB-CA) and could be blocked by BMPRI kinase inhibitor LDN-193189. Furthermore, the neuroprotective effects of GDF-5 were mediated through the prevention of apoptosis, which was indicated by terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) staining and reduced cleaved caspase 3 expression level. Thus, we conclude that GDF-5 protects hippocampal neurons against KA-induced neurodegeneration by signaling through BMPRIB, suggesting a therapeutic potential for GDF-5 in neurodegenerative diseases.

Region-specific role of growth differentiation factor-5 in the establishment of sympathetic innervation

BACKGROUND

Nerve growth factor (NGF) is the prototypical target-derived neurotrophic factor required for sympathetic neuron survival and for the growth and ramification of sympathetic axons within most but not all sympathetic targets. This implies the operation of additional target-derived factors for regulating terminal sympathetic axon growth and branching.

RESULTS

Here report that growth differentiation factor 5 (GDF5), a widely expressed member of the transforming growth factor beta (TGFβ) superfamily required for limb development, promoted axon growth from mouse superior cervical ganglion (SCG) neurons independently of NGF and enhanced axon growth in combination with NGF. GDF5 had no effect on neuronal survival and influenced axon growth during a narrow window of postnatal development when sympathetic axons are ramifying extensively in their targets in vivo. SCG neurons expressed all receptors capable of participating in GDF5 signaling at this stage of development. Using compartment cultures, we demonstrated that GDF5 exerted its growth promoting effect by acting directly on axons and by initiating retrograde canonical Smad signalling to the nucleus. GDF5 is synthesized in sympathetic targets, and examination of several anatomically circumscribed tissues in Gdf5 null mice revealed regional deficits in sympathetic innervation. There was a marked, highly significant reduction in the sympathetic innervation density of the iris, a smaller though significant reduction in the trachea, but no reduction in the submandibular salivary gland. There was no reduction in the number of neurons in the SCG.

CONCLUSIONS

These findings show that GDF5 is a novel target-derived factor that promotes sympathetic axon growth and branching and makes a distinctive regional contribution to the establishment of sympathetic innervation, but unlike NGF, plays no role in regulating sympathetic neuron survival.

Development of dendritic form and function

The nervous system is populated by numerous types of neurons, each bearing a dendritic arbor with a characteristic morphology. These type-specific features influence many aspects of a neuron's function, including the number and identity of presynaptic inputs and how inputs are integrated to determine firing properties. Here, we review the mechanisms that regulate the construction of cell type-specific dendrite patterns during development. We focus on four aspects of dendrite patterning that are particularly important in determining the function of the mature neuron: (a) dendrite shape, including branching pattern and geometry of the arbor; (b) dendritic arbor size;

Regulation of dendrite morphogenesis by extrinsic cues

Dendrites play a central role in the integration and flow of information in the nervous system. The morphogenesis and maturation of dendrites is hence an essential step in the establishment of neuronal connectivity. Recent studies have uncovered crucial functions for extrinsic cues in the development of dendrites. We review the contribution of secreted polypeptide growth factors, contact-mediated proteins, and neuronal activity in distinct phases of dendrite development. We also highlight how extrinsic cues influence local and global intracellular mechanisms of dendrite morphogenesis. Finally, we discuss how these studies have advanced our understanding of neuronal connectivity and have shed light on the pathogenesis of neurodevelopmental disorders.

A case report of amyotrophic lateral sclerosis in a patient with Klippel-Feil syndrome—a familial occurrence: a potential role of TGF-β signaling pathway

The rationale for this article is a description of a unique, familial case of a patient with amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder of unknown etiology coexisting with Klippel-Feil syndrome (KFS), a congenital malformation of cervical vertebrae, characterized by a fusion of minimum 2 cervical vertebrae. We report a 68-year-old man with moderate dysarthria, fasciculations, short neck, hearing deficit, and low posterior hairline. Definite ALS was diagnosed based on neurological abnormalities and electromyography results. Magnetic resonance imaging and computed tomography showed bony abnormalities of the craniocervical junction, fusion of 2 cervical vertebrae, and syringomyelia at the level of C6-C7. KFS phenotype was noted in 2 more family members, and patient's stepsister with KFS phenotype died due to ALS. The pedigree of our family suggests an autosomal-dominant inheritance of both syndromes. Cosegregation of ALS and KFS with an autosomal-dominant trait suggests an impairment of transforming growth factor β signaling pathway, and its potential role is discussed. Further evaluation of patients with autosomal-dominant and sporadic KFS by genetic testing, biochemical measurements, such as plasma transforming growth factor β1, and systematic follow-up electromyography seems warranted.