The insulin-like growth factor 1 receptor is essential for axonal regeneration in adult central nervous system neurons

From Insight to Eyesight: Unveiling the Secrets of the Insulin-Like Growth Factor Axis in Retinal Health

Insulin-like growth factor-1 (IGF-1) plays a diverse role in the retina, exerting its effects in both normal and diseased conditions. Deficiency of IGF-1 in humans leads to issues such as microcephaly, mental retardation, deafness, and postnatal growth failure. IGF-1 is produced in the retinal pigment epithelium (RPE) and activates the IGF-1 receptor (IGF-1R) in photoreceptor cells. When IGF-1R is absent in rod cells, it results in the degeneration of photoreceptors, emphasizing the neuroprotective function of IGF signaling in these cells. Contrastingly, in neovascular age-related macular degeneration (AMD), there is an overexpression of both IGF-1 and IGF-1R in RPE. The mechanisms behind this altered regulation of IGF-1 in diseased states are currently unknown. This comprehensive review provides recent insights into the role of IGF-1 in the health and disease of the retina, raising several unanswered questions that still need further investigation.

Acrylic Acid Modified Poly-ethylene Glycol Microparticles for Affinity-Based release of Insulin-Like Growth Factor-1 in Neural Applications

Sustained release of bioactive molecules via affinity-based interactions presents a promising approach for controlled delivery of growth factors. Insulin-like growth factor-1 (IGF-1) has gained increased attention due to its ability to promote axonal growth in the central nervous system. In this work, we aimed to evaluate the effect of IGF-1 delivery from polyethylene-glycol diacrylate (PEG-DA) microparticles using affinity-based sustained release on neurons. We developed PEG-DA-based microparticles with varying levels of acrylic acid (AA) as a comonomer to tune their overall charge. The particles were synthesized via precipitation polymerization under UV light, yielding microparticles (MPs) with a relatively low polydispersity index. IGF-1 was incubated with the PEG-DA particles overnight, and formulations with a higher AA content resulted in higher loading efficiency and slower release rates over 4 weeks, suggesting the presence of binding interactions between the positively charged IGF-1 and negatively charged particles containing AA. The released IGF-1 was tested in dorsal root ganglion (DRG) neurite outgrowth assay and found to retain its biological activity for up to two weeks after encapsulation. Furthermore, the trophic effect of IGF-1 was tested with stem cell-derived V2a interneurons and found to have a synergistic effect when combined with neurotrophin-3 (NT3). To assess the potential of a combinatorial approach, IGF-1-releasing MPs were encapsulated within a hyaluronic acid (HA) hydrogel and showed promise as a dual delivery system. Overall, the PEG-DA MPs developed herein deliver bioactive IGF-1 for a period of weeks and hold potential to enable axonal growth of injured neurons via sustained release.

Insulin restores retinal ganglion cell functional connectivity and promotes visual recovery in glaucoma

Dendrite pathology and synaptic loss result in neural circuit dysfunction, a common feature of neurodegenerative diseases. There is a lack of strategies that target dendritic and synaptic regeneration to promote neurorecovery. We show that daily human recombinant insulin eye drops stimulate retinal ganglion cell (RGC) dendrite and synapse regeneration during ocular hypertension, a risk factor to develop glaucoma. We demonstrate that the ribosomal protein p70S6 kinase (S6K) is essential for insulin-dependent dendritic regrowth. Furthermore, S6K phosphorylation of the stress-activated protein kinase-interacting protein 1 (SIN1), a link between the mammalian target of rapamycin complexes 1 and 2 (mTORC1/2), is required for insulin-induced dendritic regeneration. Using two-photon microscopy live retinal imaging, we show that insulin rescues single-RGC light-evoked calcium (Ca2+) dynamics. We further demonstrate that insulin enhances neuronal survival and retina-brain connectivity leading to improved optomotor reflex-elicited behaviors. Our data support that insulin is a compelling pro-regenerative strategy with potential clinical implications for the treatment and management of glaucoma.

Cytokine polarized, alternatively activated bone marrow neutrophils drive axon regeneration

The adult central nervous system (CNS) possesses a limited capacity for self-repair. Severed CNS axons typically fail to regrow. There is an unmet need for treatments designed to enhance neuronal viability, facilitate axon regeneration and ultimately restore lost neurological functions to individuals affected by traumatic CNS injury, multiple sclerosis, stroke and other neurological disorders. Here we demonstrate that both mouse and human bone marrow neutrophils, when polarized with a combination of recombinant interleukin-4 (IL-4) and granulocyte colony-stimulating factor (G-CSF), upregulate alternative activation markers and produce an array of growth factors, thereby gaining the capacity to promote neurite outgrowth. Moreover, adoptive transfer of IL-4/G-CSF-polarized bone marrow neutrophils into experimental models of CNS injury triggered substantial axon regeneration within the optic nerve and spinal cord. These findings have far-reaching implications for the future development of autologous myeloid cell-based therapies that may bring us closer to effective solutions for reversing CNS damage.

Cytokine polarized, alternatively activated bone marrow neutrophils drive axon regeneration

The adult central nervous system (CNS) possesses a limited capacity for self-repair. Severed CNS axons typically fail to regrow. There is an unmet need for treatments designed to enhance neuronal viability, facilitate axon regeneration, and ultimately restore lost neurological functions to individuals affected by traumatic CNS injury, multiple sclerosis, stroke, and other neurological disorders. Here we demonstrate that both mouse and human bone marrow (BM) neutrophils, when polarized with a combination of recombinant interleukin (IL)-4 and granulocyte-colony stimulating factor (G-CSF), upregulate alternative activation markers and produce an array of growth factors, thereby gaining the capacity to promote neurite outgrowth. Moreover, adoptive transfer of IL-4/G-CSF polarized BM neutrophils into experimental models of CNS injury triggered substantial axon regeneration within the optic nerve and spinal cord. These findings have far-reaching implications for the future development of autologous myeloid cell-based therapies that may bring us closer to effective solutions for reversing CNS damage.

Transcriptome and methylome of the supraoptic nucleus provides insights into the age-dependent loss of neuronal plasticity

The age-dependent loss of neuronal plasticity is a well-known phenomenon that is poorly understood. The loss of this capacity for axonal regeneration is emphasized following traumatic brain injury, which is a major cause of disability and death among adults in the US. We have previously shown the intrinsic capacity of magnocellular neurons within the supraoptic nucleus to undergo axonal regeneration following unilateral axotomization in an age-dependent manner. The aim of this research was to determine the age-dependent molecular mechanisms that may underlie this phenomenon. As such, we characterized the transcriptome and DNA methylome of the supraoptic nucleus in uninjured 35-day old rats and 125-day old rats. Our data indicates the downregulation of a large number of axonogenesis related transcripts in 125-day old rats compared to 35-day old rats. Specifically, several semaphorin and ephrin genes were downregulated, as well as growth factors including FGF's, insulin-like growth factors (IGFs), and brain-derived neurotrophic factor (BDNF). Differential methylation analysis indicates enrichment of biological processes involved in axonogenesis and axon guidance. Conversely, we observed a robust and specific upregulation of MHCI related transcripts. This may involve the activator protein 1 (AP-1) transcription factor complex as motif analysis of differentially methylated regions indicate enrichment of AP-1 binding sites in hypomethylated regions. Together, our data suggests a loss of pro-regenerative capabilities with age which would prevent axonal growth and appropriate innervation following injury.

Reproducible generation of human retinal ganglion cells from banked retinal progenitor cells: analysis of target recognition and IGF-1-mediated axon regeneration

The selective degeneration of retinal ganglion cells (RGCs) is a common feature in glaucoma, a complex group of diseases, leading to irreversible vision loss. Stem cell-based glaucoma disease modeling, cell replacement, and axon regeneration are viable approaches to understand mechanisms underlying glaucomatous degeneration for neuroprotection, ex vivo stem cell therapy, and therapeutic regeneration. These approaches require direct and facile generation of human RGCs (hRGCs) from pluripotent stem cells. Here, we demonstrate a method for rapid generation of hRGCs from banked human pluripotent stem cell-derived retinal progenitor cells (hRPCs) by recapitulating the developmental mechanism. The resulting hRGCs are stable, functional, and transplantable and have the potential for target recognition, demonstrating their suitability for both ex vivo stem cell approaches to glaucomatous degeneration and disease modeling. Additionally, we demonstrate that hRGCs derived from banked hRPCs are capable of regenerating their axons through an evolutionarily conserved mechanism involving insulin-like growth factor 1 and the mTOR axis, demonstrating their potential to identify and characterize the underlying mechanism(s) that can be targeted for therapeutic regeneration.

The Role of Insulin-like Growth Factor-1 and Its Receptor in the Eye: A Review and Implications for IGF-1R Inhibition

PURPOSE

FDA approval of teprotumumab for thyroid eye disease in January 2020 reinforced interest in the pharmacologic potential of insulin-like growth factor-1 (IGF-1) and its receptor, IGF-1R. Despite recent approval and adaptation for ophthalmic use, IGF-1R inhibitors are not a new therapeutic class. In 1986, Yamashita described aIR3, a monoclonal antibody to IGF-1R (anti-IGF-1R), that inhibited the effect of IGF-1 on growth hormone release. Given the widespread presence of IGF-1R, interrupting this receptor can lead to systemic physiologic effects, some adverse. We aim to review what is known about IGF-1/IGF-1R in the eye and consider the possible local side effects, unintended consequences, and potential uses of this medication class.

METHODS

A PubMed database search utilizing the keywords "insulin-like growth factor-1, eye, inhibitor, antibody, side effect" was performed to identify publications discussing IGF-1 in the human eye from January 2011 to August 2021. Criteria for acceptance included studies discussing human subjects or human tissue specifically related to the eye.

RESULTS

Out of a total of 230 articles, 47 were organized in 3 subject groups for discussion: thyroid-associated orbitopathy, cornea and the ocular surface, and the retina and neovascularization. Review of the literature demonstrated that IGF-1 affects growth and development of the eye, epithelial proliferation, retinal angiogenesis, inflammation, and is associated with thyroid-associated orbitopathy.

CONCLUSIONS

IGF-1R exists throughout in the human body, including the cornea, retina, and orbit. Research regarding ocular effects of IGF-1/IGF-1R outside thyroid eye disease is limited. Carefully designed studies and clinical assessments of patients undergoing treatment with anti-IGF-1R may identify ocular side effects and foster consideration of the role of anti-IGF-1R in ocular therapeutics. Given the increasing use of anti-IGF-1R antibodies, understanding their ocular effects, side effects, and potential systemic implications for use in disease is critical.

Insulin-like growth factor-1 stimulates retinal cell proliferation via activation of multiple signaling pathways

Insulin-like growth factor-1 (IGF-1) plays critical roles in the development of the central nervous system (CNS), including the retina, regulating cell proliferation, differentiation, and survival. Here, we investigated the role of IGF-1 on retinal cell proliferation using primary cultures from rat neural retina. Our data show that IGF-1 stimulates retinal cell proliferation and regulates the expression of neurotrophic factors, such as interleukin-4 and brain-derived neurotrophic factor. In addition, our results indicates that IGF-1-induced retinal cell proliferation requires activation of multiple signaling pathways, including phosphatidylinositol 3-kinase, protein kinase Src, phospholipase-C, protein kinase C delta, and mitogen-activated protein kinase pathways. We further show that activation of matrix metalloproteinases and epidermal growth factor receptor is also necessary for IGF-1 enhancing retinal cell proliferation. Overall, these results unveil potential mechanisms by which IGF-1 ensures retinal cell proliferation and support the notion that manipulation of IGF-1 signaling may be beneficial in CNS disorders associated with abnormal cell proliferation.

Axonal Regeneration: Underlying Molecular Mechanisms and Potential Therapeutic Targets

Axons in the peripheral nervous system have the ability to repair themselves after damage, whereas axons in the central nervous system are unable to do so. A common and important characteristic of damage to the spinal cord, brain, and peripheral nerves is the disruption of axonal regrowth. Interestingly, intrinsic growth factors play a significant role in the axonal regeneration of injured nerves. Various factors such as proteomic profile, microtubule stability, ribosomal location, and signalling pathways mark a line between the central and peripheral axons' capacity for self-renewal. Unfortunately, glial scar development, myelin-associated inhibitor molecules, lack of neurotrophic factors, and inflammatory reactions are among the factors that restrict axonal regeneration. Molecular pathways such as cAMP, MAPK, JAK/STAT, ATF3/CREB, BMP/SMAD, AKT/mTORC1/p70S6K, PI3K/AKT, GSK-3β/CLASP, BDNF/Trk, Ras/ERK, integrin/FAK, RhoA/ROCK/LIMK, and POSTN/integrin are activated after nerve injury and are considered significant players in axonal regeneration. In addition to the aforementioned pathways, growth factors, microRNAs, and astrocytes are also commendable participants in regeneration. In this review, we discuss the detailed mechanism of each pathway along with key players that can be potentially valuable targets to help achieve quick axonal healing. We also identify the prospective targets that could help close knowledge gaps in the molecular pathways underlying regeneration and shed light on the creation of more powerful strategies to encourage axonal regeneration after nervous system injury.

Subtype-specific survival and regeneration of retinal ganglion cells in response to injury

Retinal ganglion cells (RGCs) are a heterogeneous population of neurons that function synchronously to convey visual information through the optic nerve to retinorecipient target areas in the brain. Injury or disease to the optic nerve results in RGC degeneration and loss of visual function, as few RGCs survive, and even fewer can be provoked to regenerate their axons. Despite causative insults being broadly shared, regeneration studies demonstrate that RGC types exhibit differential resilience to injury and undergo selective survival and regeneration of their axons. While most early studies have identified these RGC types based their morphological and physiological characteristics, recent advances in transgenic and gene sequencing technologies have further enabled type identification based on unique molecular features. In this review, we provide an overview of the well characterized RGC types and identify those shown to preferentially survive and regenerate in various regeneration models. Furthermore, we discuss cellular characteristics of both the resilient and susceptible RGC types including the combinatorial expression of different molecular markers that identify these specific populations. Lastly, we discuss potential molecular mechanisms and genes found to be selectively expressed by specific types that may contribute to their reparative capacity. Together, we describe the studies that lay the important groundwork for identifying factors that promote neural regeneration and help advance the development of targeted therapy for the treatment of RGC degeneration as well as neurodegenerative diseases in general.

Insulin-like growth factor 1 receptor mediates photoreceptor neuroprotection

Insulin-like growth factor I (IGF-1) is a neurotrophic factor and is the ligand for insulin-like growth factor 1 receptor (IGF-1R). Reduced expression of IGF-1 has been reported to cause deafness, mental retardation, postnatal growth failure, and microcephaly. IGF-1R is expressed in the retina and photoreceptor neurons; however, its functional role is not known. Global IGF-1 KO mice have age-related vision loss. We determined that conditional deletion of IGF-1R in photoreceptors and pan-retinal cells produces age-related visual function loss and retinal degeneration. Retinal pigment epithelial cell-secreted IGF-1 may be a source for IGF-1R activation in the retina. Altered retinal, fatty acid, and phosphoinositide metabolism are observed in photoreceptor and retinal cells lacking IGF-1R. Our results suggest that the IGF-1R pathway is indispensable for photoreceptor survival, and activation of IGF-1R may be an essential element of photoreceptor and retinal neuroprotection.

Cultured dissociated primary dorsal root ganglion neurons from adult horses enable study of axonal transport

Neurological disorders are prevalent in horses, but their study is challenging due to anatomic constraints and the large body size; very few host‐specific in vitro models have been established to study these types of diseases, particularly from adult donor tissue. Here we report the generation of primary neuronal dorsal root ganglia (DRG) cultures from adult horses: the mixed, dissociated cultures, containing neurons and glial cells, remained viable for at least 90 days. Similar to DRG neurons in vivo, cultured neurons varied in size, and they developed long neurites. The mitochondrial movement was detected in cultured cells and was significantly slower in glial cells compared to DRG‐derived neurons. In addition, mitochondria were more elongated in glial cells than those in neurons. Our culture model will be a useful tool to study the contribution of axonal transport defects to specific neurodegenerative diseases in horses as well as comparative studies aimed at evaluating species‐specific differences in axonal transport and survival.

Identification of long noncoding RNAs in injury-resilient and injury-susceptible mouse retinal ganglion cells

BACKGROUND

Emerging evidence indicates that long noncoding RNAs (lncRNAs) are important regulators of various biological processes, and their expression can be altered following certain pathological conditions, including central nervous system injury. Retinal ganglion cells (RGCs), whose axons form the optic nerve, are a heterogeneous population of neurons with more than 40 molecularly distinct subtypes in mouse. While most RGCs, including the ON-OFF direction-selective RGCs (ooDSGCs), are vulnerable to axonal injury, a small population of RGCs, including the intrinsically photosensitive RGCs (ipRGCs), are more resilient.

RESULTS

By performing systematic analyses on RNA-sequencing data, here we identify lncRNAs that are expressed in ooDSGCs and ipRGCs with and without axonal injury. Our results reveal a repertoire of different classes of lncRNAs, including long intergenic noncoding RNAs and antisense ncRNAs that are differentially expressed between these RGC types. Strikingly, we also found dozens of lncRNAs whose expressions are altered markedly in response to axonal injury, some of which are expressed exclusively in either one of the types. Moreover, analyses into these lncRNAs unraveled their neighboring coding genes, many of which encode transcription factors and signaling molecules, suggesting that these lncRNAs may act in cis to regulate important biological processes in these neurons. Lastly, guilt-by-association analysis showed that lncRNAs are correlated with apoptosis associated genes, suggesting potential roles for these lncRNAs in RGC survival.

CONCLUSIONS

Overall, the results of this study reveal RGC type-specific expression of lncRNAs and provide a foundation for future investigation of the function of lncRNAs in regulating neuronal type specification and survival.

Exosomes Derived from lncRNA TCTN2-Modified Mesenchymal Stem Cells Improve Spinal Cord Injury by miR-329-3p/IGF1R Axis

Mesenchymal stem cells (MSCs)-derived exosomes play significant roles in alleviating spinal cord injury (SCI). Previous study showed that long non-coding RNA tectonic family member 2 (TCTN2) was able to relieve SCI. Herein, whether TCTN2 exerted its roles in functional recovery after SCI via exosomes derived from MSCs was explored. The SCI model was established in rats, and the neurological function was evaluated using the Basso, Beattie, and Bresnahan (BBB) scoring. Lipopolysaccharide (LPS)-induced differentiated PC12 cells were used as an in vitro model for neurotoxicity research. The expression of genes and proteins was detected by qRT-PCR and Western blot. Exosomes were isolated by ultracentrifugation and qualified by TEM and Western blot. In vitro assays were performed using CCK-8 assay, EdU assay, and flow cytometry, respectively. Dual-luciferase reporter assay and RIP assay were used to confirm the target relationship between miR-329-3p and TCTN2 or insulin-like growth factor1 receptor (IGF1R). TCTN2 expression was down-regulated in SCI model rat and lipopolysaccharide (LPS)-stimulated PC12 cells. MSCs produced exosomes and could package TCTN2 into secreted exosomes. Tail vein injection of TCTN2 exosomes into rats significantly improved functional recovery of SCI. Meanwhile, TCTN2 exosomes treatment alleviated LPS-induced neuronal apoptosis, inflammation, and oxidative stress in vitro. Additionally, TCTN2 targeted miR-329-3p and subsequently regulated the expression of its target IGF1R. Rescue assays suggested that miR-329-3p/IGF1R axis mediated the beneficial effects of TCTN2 exosomes on LPS-treated PC12 cells. In all, exosomes derived from TCTN2-modified MSCs could improve functional recovery of SCI in vivo and attenuate LPS-induced neuronal apoptosis, inflammation, and oxidative stress in vitro via miR-329-3p/IGF1R axis, suggesting a novel insight into the development of MSC-exosomes-based therapy for SCI.

The Ubiquitinated Axon: Local Control of Axon Development and Function by Ubiquitin

Ubiquitin tagging sets protein fate. With a wide range of possible patterns and reversibility, ubiquitination can assume many shapes to meet specific demands of a particular cell across time and space. In neurons, unique cells with functionally distinct axons and dendrites harboring dynamic synapses, the ubiquitin code is exploited at the height of its power. Indeed, wide expression of ubiquitination and proteasome machinery at synapses, a diverse brain ubiquitome, and the existence of ubiquitin-related neurodevelopmental diseases support a fundamental role of ubiquitin signaling in the developing and mature brain. While special attention has been given to dendritic ubiquitin-dependent control, how axonal biology is governed by this small but versatile molecule has been considerably less discussed. Herein, we set out to explore the ubiquitin-mediated spatiotemporal control of an axon's lifetime: from its differentiation and growth through presynaptic formation, function, and pruning.

Optic nerve regeneration screen identifies multiple genes restricting adult neural repair

Adult mammalian central nervous system (CNS) trauma interrupts neural networks and, because axonal regeneration is minimal, neurological deficits persist. Repair via axonal growth is limited by extracellular inhibitors and cell-autonomous factors. Based on results from a screen in vitro, we evaluate nearly 400 genes through a large-scale in vivo regeneration screen. Suppression of 40 genes using viral-driven short hairpin RNAs (shRNAs) promotes retinal ganglion cell (RGC) axon regeneration after optic nerve crush (ONC), and most are validated by separate CRISPR-Cas9 editing experiments. Expression of these axon-regeneration-suppressing genes is not significantly altered by axotomy. Among regeneration-limiting genes, loss of the interleukin 22 (IL-22) cytokine allows an early, yet transient, inflammatory response in the retina after injury. Reduced IL-22 drives concurrent activation of signal transducer and activator of transcription 3 (Stat3) and dual leucine zipper kinase (DLK) pathways and upregulation of multiple neuron-intrinsic regeneration-associated genes (RAGs). Including IL-22, our screen identifies dozens of genes that limit CNS regeneration. Suppression of these genes in the context of axonal damage could support improved neural repair.

IGF1R Deficiency Modulates Brain Signaling Pathways and Disturbs Mitochondria and Redox Homeostasis

Insulin-like growth factor 1 receptor (IGF1R)-mediated signaling pathways modulate important neurophysiological aspects in the central nervous system, including neurogenesis, synaptic plasticity and complex cognitive functions. In the present study, we intended to characterize the impact of IGF1R deficiency in the brain, focusing on PI3K/Akt and MAPK/ERK1/2 signaling pathways and mitochondria-related parameters. For this purpose, we used 13-week-old UBC-CreERT2; Igf1r^fl/fl male mice in which Igf1r was conditionally deleted. IGF1R deficiency caused a decrease in brain weight as well as the activation of the IR/PI3K/Akt and inhibition of the MAPK/ERK1/2/CREB signaling pathways. Despite no alterations in the activity of caspases 3 and 9, a significant alteration in phosphorylated GSK3β and an increase in phosphorylated Tau protein levels were observed. In addition, significant disturbances in mitochondrial dynamics and content and altered activity of the mitochondrial respiratory chain complexes were noticed. An increase in oxidative stress, characterized by decreased nuclear factor E2-related factor 2 (NRF2) protein levels and aconitase activity and increased H₂O₂ levels were also found in the brain of IGF1R-deficient mice. Overall, our observations confirm the complexity of IGF1R in mediating brain signaling responses and suggest that its deficiency negatively impacts brain cells homeostasis and survival by affecting mitochondria and redox homeostasis.

The Influence of Neuron-Extrinsic Factors and Aging on Injury Progression and Axonal Repair in the Central Nervous System

In the aging western population, the average age of incidence for spinal cord injury (SCI) has increased, as has the length of survival of SCI patients. This places great importance on understanding SCI in middle-aged and aging patients. Axon regeneration after injury is an area of study that has received substantial attention and made important experimental progress, however, our understanding of how aging affects this process, and any therapeutic effort to modulate repair, is incomplete. The growth and regeneration of axons is mediated by both neuron intrinsic and extrinsic factors. In this review we explore some of the key extrinsic influences on axon regeneration in the literature, focusing on inflammation and astrogliosis, other cellular responses, components of the extracellular matrix, and myelin proteins. We will describe how each element supports the contention that axonal growth after injury in the central nervous system shows an age-dependent decline, and how this may affect outcomes after a SCI.

Single-Cell Profiles of Retinal Ganglion Cells Differing in Resilience to Injury Reveal Neuroprotective Genes

Neuronal types in the central nervous system differ dramatically in their resilience to injury or other insults. Here we studied the selective resilience of mouse retinal ganglion cells (RGCs) following optic nerve crush (ONC), which severs their axons and leads to death of ∼80% of RGCs within 2 weeks. To identify expression programs associated with differential resilience, we first used single-cell RNA-seq (scRNA-seq) to generate a comprehensive molecular atlas of 46 RGC types in adult retina. We then tracked their survival after ONC; characterized transcriptomic, physiological, and morphological changes that preceded degeneration; and identified genes selectively expressed by each type. Finally, using loss- and gain-of-function assays in vivo, we showed that manipulating some of these genes improved neuronal survival and axon regeneration following ONC. This study provides a systematic framework for parsing type-specific responses to injury and demonstrates that differential gene expression can be used to reveal molecular targets for intervention.

IGF-1 and IGF-1R modulate the effects of IL-4 on retinal ganglion cells survival: The involvement of M1 muscarinic receptor

Trophic factors are involved in different cellular responses. Previously we demonstrated that IL-4 treatment induces an increase in retinal ganglion cell survival (RGCS) and regulates cholinergic differentiation of retinal cells in vitro. Data from literature show that IGF-1 also promotes RGCS, an effect mediated by PI-3K/AKT pathway. The aim of this study was to investigate the role of IGF-1 and IGF-1R on RGCS mediated by IL-4 treatment and the role of M1 acetylcholine receptors in this effect. Here we show that the effect of IL-4 on RGCS depends on IGF-1 and IGF-1R activation, the PI-3K/AKT and NFkB intracellular pathways and depends on M1 mAChRs activation. IGF-1 increases the levels of M1 mAChRs in 15min, 45min, 24 h and 48 h in mixed retinal cells culture, modulates the levels of IL-4, pIGF-1R, IGF-1R. IL-4 modulates IGF-1, pIGF-1R and IGF-1R levels in different time intervals. These results put in evidence a crosstalk between IL-4 and IGF-1 and a role of M1 mAChRs, IGF-1 and IGF-1R in RGCS mediated by IL-4.

Igf1R/InsR function is required for axon extension and corpus callosum formation

One of the earliest steps during the development of the nervous system is the establishment of neuronal polarity and the formation of an axon. The intrinsic mechanisms that promote axon formation have been extensively analyzed. However, much less is known about the extrinsic signals that initiate axon formation. One of the candidates for these signals is Insulin-like growth factor 1 (Igf1) that acts through the Igf1 (Igf1R) and insulin receptors (InsR). Since Igf1R and InsR may act redundantly we analyzed conditional cortex-specific knockout mice that are deficient for both Igf1r and Insr to determine if they regulate the development of the cortex and the formation of axons in vivo. Our results show that Igf1R/InsR function is required for the normal development of the embryonic hippocampus and cingulate cortex while the lateral cortex does not show apparent defects in the Igf1r;Insr knockout. In the cingulate cortex, the number of intermediate progenitors and deep layer neurons is reduced and the corpus callosum is absent at E17. However, cortical organization and axon formation are not impaired in knockout embryos. In culture, cortical and hippocampal neurons from Igf1r;Insr knockout embryos extend an axon but the length of this axon is severely reduced. Our results indicate that Igf1R/InsR function is required for brain development in a region-specific manner and promotes axon growth but is not essential for neuronal polarization and migration in the developing brain.

Neural Stem Cell Transplantation Improves Locomotor Function in Spinal Cord Transection Rats Associated with Nerve Regeneration and IGF-1 R Expression

Transplantation of neural stem cells (NSCs) is a potential strategy for the treatment of spinal cord transection (SCT). Here we investigated whether transplanted NSCs would improve motor function of rats with SCT and explored the underlying mechanism. First, the rats were divided into sham, SCT, and NSC groups. Rats in the SCT and NSC groups were all subjected to SCT in T10, and were administered with media and NSC transplantation into the lesion site, respectively. Immunohistochemistry was used to label Nestin-, TUNEL-, and NeuN-positive cells and reveal the expression and location of type I insulin-like growth factor receptor (IGF-1 R). Locomotor function of hind limbs was assessed by Basso, Beattie, Bresnahan (BBB) score and inclined plane test. The conduction velocity and amplitude of spinal nerve fibers were measured by electrophysiology and the anatomical changes were measured using magnetic resonance imaging. Moreover, expression of IGF-1 R was determined by real-time polymerase chain reaction and Western blotting. The results showed that NSCs could survive and differentiate into neurons in vitro and in vivo. SCT-induced deficits were reduced by NSC transplantation, including increase in NeuN-positive cells and decrease in apoptotic cells. Moreover, neurophysiological profiles indicated that the latent period was decreased and the peak-to-peak amplitude of spinal nerve fibers conduction was increased in transplanted rats, while morphological measures indicated that fractional anisotropy and the number of nerve fibers in the site of spinal cord injury were increased after NSC transplantation. In addition, mRNA and protein level of IGF-1 R were increased in the rostral segment in the NSC group, especially in neurons. Therefore, we concluded that NSC transplantation promotes motor function improvement of SCT, which might be associated with activated IGF-1 R, especially in the rostral site. All of the above suggests that this approach has potential for clinical treatment of spinal cord injury.

Neuroprotection: Pro-survival and Anti-neurotoxic Mechanisms as Therapeutic Strategies in Neurodegeneration

Neurotrophins (NTs) are a subset of the neurotrophic factor family. These growth factors were originally named based on the nerve growth functional assays used to identify them. NTs act as paracrine or autocrine factors for cells expressing NT receptors. The receptors and their function have been studied primarily in cells of the nervous system, but are also present in the cardiovascular, endocrine, and immune systems, as well as in many neoplastic cells. The signals activated by NTs can be varied, depending on cellular stage and context, healthy or disease states, and depending on whether the specific NTs and their receptors are expressed in the relevant cells. In the healthy central and peripheral adult nervous systems, NTs drive neuronal survival, phenotype, synaptic maintenance, and function. Deficiencies of the NT/NT receptor axis are causally associated with disease onset or disease progression. Paradoxically, NTs can also drive synaptic loss and neuronal death. In the embryonic stage this activity is essential for proper developmental pruning of the nervous system, but in the adult it can be associated with neurodegenerative disease. Given their key role in neuronal survival and death, NTs and NT receptors have long been considered therapeutic targets to achieve neuroprotection. The first neuroprotective approaches consisted of enhancing neuronal survival signals using NTs. Later strategies selectively targeted receptors to induce survival signals specifically, while avoiding activation of death signals. Recently, the concept of selectively targeting receptors to reduce neuronal death signals has emerged. Here, we review the rationale of each neuroprotective strategy with respect to the complex cell biology and pharmacology of each target receptor.

Liraglutide and its Neuroprotective Properties-Focus on Possible Biochemical Mechanisms in Alzheimer's Disease and Cerebral Ischemic Events

Liraglutide is a GLP-1 analog (glucagon like peptide-1) used primarily in the treatment of diabetes mellitus type 2 (DM2) and obesity. The literature starts to suggest that liraglutide may reduce the effects of ischemic stroke by activating anti-apoptotic pathways, as well as limiting the harmful effects of free radicals. The GLP-1R expression has been reported in the cerebral cortex, especially occipital and frontal lobes, the hypothalamus, and the thalamus. Liraglutide reduced the area of ischemia caused by MCAO (middle cerebral artery occlusion), limited neurological deficits, decreased hyperglycemia caused by stress, and presented anti-apoptotic effects by increasing the expression of Bcl-2 and Bcl-xl proteins and reduction of Bax and Bad protein expression. The pharmaceutical managed to decrease concentrations of proapoptotic factors, such as NF-κB (Nuclear Factor-kappa β), ICAM-1 (Intercellular Adhesion Molecule 1), caspase-3, and reduced the level of TUNEL-positive cells. Liraglutide was able to reduce the level of free radicals by decreasing the level of malondialdehyde (MDA), and increasing the superoxide dismutase level (SOD), glutathione (GSH), and catalase. Liraglutide may affect the neurovascular unit causing its remodeling, which seems to be crucial for recovery after stroke. Liraglutide may stabilize atherosclerotic plaque, as well as counteract its early formation and further development. Liraglutide, through its binding to GLP-1R (glucagon like peptide-1 receptor) and consequent activation of PI3K/MAPK (Phosphoinositide 3-kinase/mitogen associated protein kinase) dependent pathways, may have a positive impact on Aβ (amyloid beta) trafficking and clearance by increasing the presence of Aβ transporters in cerebrospinal fluid. Liraglutide seems to affect tau pathology. It is possible that liraglutide may have some stem cell stimulating properties. The effects may be connected with PKA (phosphorylase kinase A) activation. This paper presents potential mechanisms of liraglutide activity in conditions connected with neuronal damage, with special emphasis on Alzheimer's disease and cerebral ischemia.

Crosstalk between receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCR) in the brain: Focus on heteroreceptor complexes and related functional neurotrophic effects

Neuronal events are regulated by the integration of several complex signaling networks in which G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) are considered key players of an intense bidirectional cross-communication in the cell, generating signaling mechanisms that, at the same time, connect and diversify the traditional signal transduction pathways activated by the single receptor. For this receptor-receptor crosstalk, the two classes of receptors form heteroreceptor complexes resulting in RTKs transactivation and in growth-promoting signals. In this review, we describe heteroreceptor complexes between GPCR and RTKs in the central nervous system (CNS) and their functional effects in controlling a variety of neuronal effects, ranging from development, proliferation, differentiation and migration, to survival, repair, synaptic transmission and plasticity. In this interaction, RTKs can also recruit components of the G protein signaling cascade, creating a bidirectional intricate interplay that provides complex control over multiple cellular events. These heteroreceptor complexes, by the integration of different signals, have recently attracted a growing interest as novel molecular target for depressive disorders. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'.

The Virtuous Cycle of Axon Growth: Axonal Transport of Growth-Promoting Machinery as an Intrinsic Determinant of Axon Regeneration

Injury to the brain and spinal cord has devastating consequences because adult central nervous system (CNS) axons fail to regenerate. Injury to the peripheral nervous system (PNS) has a better prognosis, because adult PNS neurons support robust axon regeneration over long distances. CNS axons have some regenerative capacity during development, but this is lost with maturity. Two reasons for the failure of CNS regeneration are extrinsic inhibitory molecules, and a weak intrinsic capacity for growth. Extrinsic inhibitory molecules have been well characterized, but less is known about the neuron-intrinsic mechanisms which prevent axon re-growth. Key signaling pathways and genetic/epigenetic factors have been identified which can enhance regenerative capacity, but the precise cellular mechanisms mediating their actions have not been characterized. Recent studies suggest that an important prerequisite for regeneration is an efficient supply of growth-promoting machinery to the axon; however, this appears to be lacking from non-regenerative axons in the adult CNS. In the first part of this review, we summarize the evidence linking axon transport to axon regeneration. We discuss the developmental decline in axon regeneration capacity in the CNS, and comment on how this is paralleled by a similar decline in the selective axonal transport of regeneration-associated receptors such as integrins and growth factor receptors. In the second part, we discuss the mechanisms regulating selective polarized transport within neurons, how these relate to the intrinsic control of axon regeneration, and whether they can be targeted to enhance regenerative capacity. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 00: 000-000, 2018.

Multifarious Biologic Loaded Liposomes that Stimulate the Mammalian Target of Rapamycin Signaling Pathway Show Retina Neuroprotection after Retina Damage

A common event in optic neuropathies is the loss of axons and death of retinal ganglion cells (RGCs) resulting in irreversible blindness. Mammalian target of rapamycin (mTOR) signaling pathway agonists have been shown to foster axon regeneration and RGC survival in animal models of optic nerve damage. However, many challenges remain in developing therapies that exploit cell growth and tissue remodeling including (i) activating/inhibiting cell pathways synergistically, (ii) avoiding tumorigenesis, and (iii) ensuring appropriate physiological tissue function. These challenges are further exacerbated by the need to overcome ocular physiological barriers and clearance mechanisms. Here we present liposomes loaded with multiple mTOR pathway stimulating biologics designed to enhance neuroprotection after retina damage. Liposomes were loaded with ciliary neurotrophic factor, insulin-like growth factor 1, a lipopeptide N-fragment osteopontin mimic, and lipopeptide phosphatase tension homologue inhibitors for either the ATP domain or the c-terminal tail. In a mouse model of N-methyl-d-aspartic acid induced RGC death, a single intravitreal administration of liposomes reduced both RGC death and loss of retina electrophysiological function. Furthermore, combining liposomes with transplantation of induced pluripotent stem cell derived RGCs led to an improved electrophysiological outcome in mice. The results presented here show that liposomes carrying multiple signaling pathway modulators can facilitate neuroprotection and transplant electrophysiological outcome.

Integrins promote axonal regeneration after injury of the nervous system

Integrins are cell surface receptors that form the link between extracellular matrix molecules of the cell environment and internal cell signalling and the cytoskeleton. They are involved in several processes, e.g. adhesion and migration during development and repair. This review focuses on the role of integrins in axonal regeneration. Integrins participate in spontaneous axonal regeneration in the peripheral nervous system through binding to various ligands that either inhibit or enhance their activation and signalling. Integrin biology is more complex in the central nervous system. Integrins receptors are transported into growing axons during development, but selective polarised transport of integrins limits the regenerative response in adult neurons. Manipulation of integrins and related molecules to control their activation state and localisation within axons is a promising route towards stimulating effective regeneration in the central nervous system.

Serial Changes of Cytokines in Children with Cerebral Palsy Who Received Intravenous Granulocyte-colony Stimulating Factor Followed by Autologous Mobilized Peripheral Blood Mononuclear Cells

BACKGROUND

This study was performed to assess serial cytokine changes and their clinical impact in children with cerebral palsy (CP) who received granulocyte-colony stimulating factor (G-CSF) followed by infusion of autologous mobilized peripheral blood mononuclear cells (mPBMCs).

METHODS

Peripheral blood (PB) samples were collected from 16 CP children at enrollment, and 1 month and 7 months after G-CSF infusion as well as at the end of the study. Cytokine levels were measured by enzyme-linked immunosorbent assays with plasma samples.

RESULTS

There were no significant differences in cytokine levels between the mPBMC and placebo groups over 6 months. However, when clinical responders and non-responders were compared, interleukin (IL)-6 (P = 0.050) as well as G-CSF (P = 0.010) were higher in the responders than the non-responders at 1 month, while brain-derived neurotrophic factor (BDNF) (P = 0.030) and insulin-like growth factor (IGF)-1 (P = 0.001) were lower. In addition, BDNF was higher at baseline in the responders than the non-responders (P = 0.030).

CONCLUSION

The changes of G-CSF itself, as well as G-CSF-induced cytokines such as IL-6, may be associated with the clinical improvement of neurologic functions. The G-CSF-induced changes of IL-6, BDNF and IGF-1, and BDNF levels before treatment, could be used as prognostic factors in G-CSF trials in CP children.

The Hierarchy of Brain Networks Is Related to Insulin Growth Factor-1 in a Large, Middle-Aged, Healthy Cohort: An Exploratory Magnetoencephalography Study

Recently, a large study demonstrated that lower serum levels of insulin growth factor-1 (IGF-1) relate to brain atrophy and to a greater risk for developing Alzheimer's disease in a healthy elderly population. We set out to test if functional brain networks relate to IGF-1 levels in the middle aged. Hence, we studied the association between IGF-1 and magnetoencephalography-based functional network characteristics in a middle-aged population. The functional connections between brain areas were estimated for six frequency bands (delta, theta, alpha1, alpha2, beta, gamma) using the phase lag index. Subsequently, the topology of the frequency-specific functional networks was characterized using the minimum spanning tree. Our results showed that lower levels of serum IGF-1 relate to a globally less integrated functional network in the beta and theta band. The associations remained significant when correcting for gender and systemic effects of IGF-1 that might indirectly affect the brain. The value of this exploratory study is the demonstration that lower levels of IGF-1 are associated with brain network topology in the middle aged.

Mesenchymal stem cells secretome-induced axonal outgrowth is mediated by BDNF

Mesenchymal stem cells (MSCs) have been used for cell-based therapies in regenerative medicine, with increasing importance in central and peripheral nervous system repair. However, MSCs grafting present disadvantages, such as, a high number of cells required for transplantation and low survival rate when transplanted into the central nervous system (CNS). In line with this, MSCs secretome which present on its composition a wide range of molecules (neurotrophins, cytokines) and microvesicles, can be a solution to surpass these problems. However, the effect of MSCs secretome in axonal elongation is poorly understood. In this study, we demonstrate that application of MSCs secretome to both rat cortical and hippocampal neurons induces an increase in axonal length. In addition, we show that this growth effect is axonal intrinsic with no contribution from the cell body. To further understand which are the molecules required for secretome-induced axonal outgrowth effect, we depleted brain-derived neurotrophic factor (BDNF) from the secretome. Our results show that in the absence of BDNF, secretome-induced axonal elongation effect is lost and that axons present a reduced axonal growth rate. Altogether, our results demonstrate that MSCs secretome is able to promote axonal outgrowth in CNS neurons and this effect is mediated by BDNF.

Epigenetic regulation of HDAC1 SUMOylation as an endogenous neuroprotection against Aβ toxicity in a mouse model of Alzheimer's disease

Amyloid-β (Aβ) produces neurotoxicity in the brain and causes neuronal death, but the endogenous defense mechanism that is activated on Aβ insult is less well known. Here we found that acute Aβ increases the expression of PIAS1 and Mcl-1 via activation of MAPK/ERK, and Aβ induction of PIAS1 enhances HDAC1 SUMOylation in rat hippocampus. Knockdown of PIAS1 decreases endogenous HDAC1 SUMOylation and blocks Aβ induction of Mcl-1. Sumoylated HDAC1 reduces it association with CREB, increases CREB binding to the Mcl-1 promoter and mediates Aβ induction of Mcl-1 expression. Transduction of SUMO-modified lenti-HDAC1 vector to the hippocampus of APP/PS1 mice rescues spatial learning and memory deficit and long-term potentiation impairment in APP/PS1 mice. It also reduces the amount of amyloid plaque and the number of apoptotic cells in CA1 area of APP/PS1 mice. Meanwhile, HDAC1 SUMOylation decreases HDAC1 binding to the neprilysin promoter. These results together reveal an important role of HDAC1 SUMOylation as a naturally occurring defense mechanism protecting against Aβ toxicity and provide an alternative therapeutic strategy against AD.

IGF1 neuronal response in the absence of MECP2 is dependent on TRalpha 3

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder in which the MECP2 (methyl CpG-binding protein 2) gene is mutated. Recent studies showed that RTT-derived neurons have many cellular deficits when compared to control, such as: less synapses, lower dendritic arborization and reduced spine density. Interestingly, treatment of RTT-derived neurons with Insulin-like Growth Factor 1 (IGF1) could rescue some of these cellular phenotypes. Given the critical role of IGF1 during neurodevelopment, the present study used human induced pluripotent stem cells (iPSCs) from RTT and control individuals to investigate the gene expression profile of IGF1 and IGF1R on different developmental stages of differentiation. We found that the thyroid hormone receptor (TRalpha 3) has a differential expression profile. Thyroid hormone is critical for normal brain development. Our results showed that there is a possible link between IGF1/IGF1R and the TRalpha 3 and that over expression of IGF1R in RTT cells may be the cause of neurites improvement in neural RTT-derived neurons.

Primary Postnatal Dorsal Root Ganglion Culture from Conventionally Slaughtered Calves

Neurological disorders in ruminants have an important impact on veterinary health, but very few host-specific in vitro models have been established to study diseases affecting the nervous system. Here we describe a primary neuronal dorsal root ganglia (DRG) culture derived from calves after being conventionally slaughtered for food consumption. The study focuses on the in vitro characterization of bovine DRG cell populations by immunofluorescence analysis. The effects of various growth factors on neuron viability, neurite outgrowth and arborisation were evaluated by morphological analysis. Bovine DRG neurons are able to survive for more than 4 weeks in culture. GF supplementation is not required for neuronal survival and neurite outgrowth. However, exogenously added growth factors promote neurite outgrowth. DRG cultures from regularly slaughtered calves represent a promising and sustainable host specific model for the investigation of pain and neurological diseases in bovines.

The age factor in axonal repair after spinal cord injury: A focus on neuron-intrinsic mechanisms

Age is an important consideration for recovery and repair after spinal cord injury. Spinal cord injury is increasingly affecting the middle-aged and aging populations. Despite rapid progress in research to promote axonal regeneration and repair, our understanding of how age can modulate this repair is rather limited. In this review, we discuss the literature supporting the notion of an age-dependent decline in axonal growth after central nervous system (CNS) injury. While both neuron-intrinsic and extrinsic factors are involved in the control of axon growth after injury, here we focus on possible intrinsic mechanisms for this age-dependent decline.

Neuroprotective levels of IGF-1 exacerbate epileptogenesis after brain injury

Exogenous Insulin-Like Growth Factor-1 (IGF-1) is neuroprotective in animal models of brain injury, and has been considered as a potential therapeutic. Akt-mTOR and MAPK are downstream targets of IGF-1 signaling that are activated after brain injury. However, both brain injury and mTOR are linked to epilepsy, raising the possibility that IGF-1 may be epileptogenic. Here, we considered the role of IGF-1 in development of epilepsy after brain injury, using the organotypic hippocampal culture model of post-traumatic epileptogenesis. We found that IGF-1 was neuroprotective within a few days of injury but that long-term IGF-1 treatment was pro-epileptic. Pro-epileptic effects of IGF-1 were mediated by Akt-mTOR signaling. We also found that IGF-1 - mediated increase in epileptic activity led to neurotoxicity. The dualistic nature of effects of IGF-1 treatment demonstrates that anabolic enhancement through IGF-1 activation of mTOR cascade can be beneficial or harmful depending on the stage of the disease. Our findings suggest that epilepsy risk may need to be considered in the design of neuroprotective treatments for brain injury.

Elevated Serum Insulin-Like Growth Factor 1 Levels in Patients with Neurological Remission after Traumatic Spinal Cord Injury

After traumatic spinal cord injury, an acute phase triggered by trauma is followed by a subacute phase involving inflammatory processes. We previously demonstrated that peripheral serum cytokine expression changes depend on neurological outcome after spinal cord injury. In a subsequent intermediate phase, repair and remodeling takes place under the mediation of growth factors such as Insulin-like Growth Factor 1 (IGF-1). IGF-1 is a promising growth factor which is thought to act as a neuroprotective agent. Since previous findings were taken from animal studies, our aim was to investigate this hypothesis in humans based on peripheral blood serum. Forty-five patients after traumatic spinal cord injury were investigated over a period of three months after trauma. Blood samples were taken according to a fixed schema and IGF-1 levels were determined. Clinical data including AIS scores at admission to the hospital and at discharge were collected and compared with IGF-1 levels. In our study, we could observe distinct patterns in the expression of IGF-1 in peripheral blood serum after traumatic spinal cord injury regardless of the degree of plegia. All patients showed a marked increase of levels seven days after injury. IGF-1 serum levels were significantly different from initial measurements at four and nine hours and seven and 14 days after injury, as well as one, two and three months after injury. We did not detect a significant correlation between fracture and the IGF-1 serum level nor between the quantity of operations performed after trauma and the IGF-1 serum level. Patients with clinically documented neurological remission showed consistently higher IGF-1 levels than patients without neurological remission. This data could be the base for the establishment of animal models for further and much needed research in the field of spinal cord injury.

The tumor microenvironment underlies acquired resistance to CSF-1R inhibition in gliomas

Macrophages accumulate with glioblastoma multiforme (GBM) progression and can be targeted via inhibition of colony-stimulating factor-1 receptor (CSF-1R) to regress high-grade tumors in animal models of this cancer. However, whether and how resistance emerges in response to sustained CSF-1R blockade is unknown. We show that although overall survival is significantly prolonged, tumors recur in >50% of mice. Gliomas reestablish sensitivity to CSF-1R inhibition upon transplantation, indicating that resistance is tumor microenvironment-driven. Phosphatidylinositol 3-kinase (PI3K) pathway activity was elevated in recurrent GBM, driven by macrophage-derived insulin-like growth factor-1 (IGF-1) and tumor cell IGF-1 receptor (IGF-1R). Combining IGF-1R or PI3K blockade with CSF-1R inhibition in recurrent tumors significantly prolonged overall survival. Our findings thus reveal a potential therapeutic approach for treating resistance to CSF-1R inhibitors.

Regulating Axonal Responses to Injury: The Intersection between Signaling Pathways Involved in Axon Myelination and The Inhibition of Axon Regeneration

Following spinal cord injury (SCI), a multitude of intrinsic and extrinsic factors adversely affect the gene programs that govern the expression of regeneration-associated genes (RAGs) and the production of a diversity of extracellular matrix molecules (ECM). Insufficient RAG expression in the injured neuron and the presence of inhibitory ECM at the lesion, leads to structural alterations in the axon that perturb the growth machinery, or form an extraneous barrier to axonal regeneration, respectively. Here, the role of myelin, both intact and debris, in antagonizing axon regeneration has been the focus of numerous investigations. These studies have employed antagonizing antibodies and knockout animals to examine how the growth cone of the re-growing axon responds to the presence of myelin and myelin-associated inhibitors (MAIs) within the lesion environment and caudal spinal cord. However, less attention has been placed on how the myelination of the axon after SCI, whether by endogenous glia or exogenously implanted glia, may alter axon regeneration. Here, we examine the intersection between intracellular signaling pathways in neurons and glia that are involved in axon myelination and axon growth, to provide greater insight into how interrogating this complex network of molecular interactions may lead to new therapeutics targeting SCI.

Microdeletion 15q26.2qter and Microduplication 18q23 in a Patient with Prader-Willi-Like Syndrome: Clinical Findings

The small interstitial deletion in the long arm of chromosome 15 causing Prader-Willi/Angelman syndrome is well known, whereas cases that report terminal deletions in 15q in association with the Prader-Willi-like phenotype are very rare. By using GTG-banding analysis, metaphase FISH, MLPA analysis, and genome-wide array CGH, we detected an unbalanced translocation involving a microdeletion of the distal part of 15q and a microduplication of the distal part of 18q. The unbalanced translocation was found in a boy that was referred with clinical suspicion of Prader-Willi syndrome. In the 15q-deleted region, 23 genes have been identified, and 13 of them are included in the OMIM database. Among these, the deleted IGFR1, MEF2A, CHSY1, and TM2D3 genes could contribute to the patient's phenotype. Seven genes are included in the duplicated chromosome segment 18q, but only one (CTDP1) is present in the OMIM database. We suggest that the deleted chromosome segment 15q26.2qter may be responsible for the phenotype of our case and may also be a candidate locus of Prader-Willi-like syndrome.

Insulin deficiency induces rat renal mesangial cell dysfunction via activation of IGF-1/IGF-1R pathway

AIM

Diabetic nephropathy is one of the major complications of diabetes and the major cause of end-stage renal disease. In this study we investigated the insulin deficiency (ID) induced changes in renal mesangial cells (MCs) and in the kidney of STZ-induced diabetic rats.

METHODS

Cultured rat renal MCs were incubated in ID media. Cell proliferation was analyzed using BrdU incorporation assay. The expression of insulin receptor (IR), insulin-like growth factor-1 receptor (IGF-1R), phosphorylated IGF-1R, fibronectin, and collagen IV was determined with Western blot analysis. STZ-induced diabetic rats were treated with an IGF-1R antagonist picropodophyllin (PPP, 20 mg·kg(-1)·d(-1), po) for 8 weeks. After the rats were euthanized, plasma and kidneys were collected. IGF-1 levels in renal cortex were measured with RT-PCR or ELISA. The morphological changes in the kidneys were also examined.

RESULTS

Incubation in ID media significantly increased cell proliferation, the synthesis of fibronectin and collagen IV, and the expression of IGF-1 and IGF-1R and phosphorylated IGF-1R in renal MCs. Pretreatment of the cells with PPP (50 nmol/L) blocked ID-induced increases in cell proliferation and the synthesis of fibronectin and collagen IV; knockdown of IGF-1R showed a similar effect as PPP did. In contrast, treatment of the cells with IGF-1 (50 ng/mL) exacerbated ID-induced increases in cell proliferation. In the kidneys of diabetic rats, the expression of IGF-1, IGF-1R and phosphorylated IGF-1R were significantly elevated. Treatment of diabetic rats with PPP did not lower the blood glucose levels, but significantly suppressed the expression of TGF-β, fibronectin and collagen IV in the kidneys, the plasma levels of urinary nitrogen and creatinine, and the urinary protein excretion.

CONCLUSION

Insulin deficiency increases the expression of IGF-1 and IGF-1R in renal MCs and the kidney of diabetic rats, which contributes to the development of diabetic nephropathy.

Norrin mediates angiogenic properties via the induction of insulin-like growth factor-1

Norrin is an angiogenic signaling molecule that activates canonical Wnt/β-catenin signaling, and is involved in capillary formation in retina and brain. Moreover, Norrin induces vascular repair following an oxygen-induced retinopathy (OIR), the model of retinopathy of prematurity in mice. Since insulin-like growth factor (IGF)-1 is a very potent angiogenic molecule, we investigated if IGF-1 is a downstream mediator of Norrin's angiogenic properties. In retinae of transgenic mice with an ocular overexpression of Norrin (βB1-Norrin), we found at postnatal day (P)11 a significant increase of IGF-1 mRNA compared to wild-type littermates. In addition, after treatment of cultured Müller cells or dermal microvascular endothelial cells with Norrin we observed an increase of IGF-1 and its mRNA, an effect that could be blocked with DKK-1, an inhibitor of Wnt/β-catenin signaling. When OIR was induced, the expression of IGF-1 was significantly suppressed in both transgenic βB1-Norrin mice and wild-type littermates when compared to wild-type animals that were housed in room air. Furthermore, at P13, one day after the mice had returned to normoxic conditions, IGF-1 levels were significantly higher in transgenic mice compared to wild-type littermates. Finally, after intravitreal injections of inhibitory α-IGF-1 antibodies at P12 or at P12 and P14, the Norrin-mediated vascular repair was significantly attenuated. We conclude that Norrin induces the expression of IGF-1 via an activation of the Wnt/β-catenin signaling pathway, an effect that significantly contributes to the protective effects of Norrin against an OIR.

Extracellular vimentin interacts with insulin-like growth factor 1 receptor to promote axonal growth

Vimentin, an intermediate filament protein, is generally recognised as an intracellular protein. Previously, we reported that vimentin was secreted from astrocytes and promoted axonal growth. The effect of extracellular vimentin in neurons was a new finding, but its signalling pathway was unknown. In this study, we aimed to determine the signalling mechanism of extracellular vimentin that facilitates axonal growth. We first identified insulin-like growth factor 1 receptor (IGF1R) as a receptor that is highly phosphorylated by vimentin stimulation. IGF1R blockades diminished vimentin- or IGF1-induced axonal growth in cultured cortical neurons. IGF1, IGF2 and insulin were not detected in the neuron culture medium after vimentin treatment. The combined drug affinity responsive target stability method and western blotting analysis showed that vimentin and IGF1 interacted with IGF1R directly. In addition, immunoprecipitation and western blotting analyses confirmed that recombinant IGF1R bound to vimentin. The results of a molecular dynamics simulation revealed that C-terminal residues (residue number 330-407) in vimentin are the most appropriate binding sites with IGF1R. Thus, extracellular vimentin may be a novel ligand of IGF1R that promotes axonal growth in a similar manner to IGF1. Our results provide novel findings regarding the role of extracellular vimentin and IGF1R in axonal growth.

The Acquisition of Target Dependence by Developing Rat Retinal Ganglion Cells

Similar to neurons in the peripheral nervous system, immature CNS-derived RGCs become dependent on target-derived neurotrophic support as their axons reach termination sites in the brain. To study the factors that influence this developmental transition we took advantage of the fact that rat RGCs are born, and target innervation occurs, over a protracted period of time. Early-born RGCs have axons in the SC by birth (P0), whereas axons from late-born RGCs do not innervate the SC until P4-P5. Birth dating RGCs using EdU allowed us to identify RGCs (1) with axons still growing toward targets, (2) transitioning to target dependence, and (3) entirely dependent on target-derived support. Using laser-capture microdissection we isolated ∼34,000 EdU⁺ RGCs and analyzed transcript expression by custom qPCR array. Statistical analyses revealed a difference in gene expression profiles in actively growing RGCs compared with target-dependent RGCs, as well as in transitional versus target-dependent RGCs. Prior to innervation RGCs expressed high levels of BDNF and CNTFR α but lower levels of neurexin 1 mRNA. Analysis also revealed greater expression of transcripts for signaling molecules such as MAPK, Akt, CREB, and STAT. In a supporting in vitro study, purified birth-dated P1 RGCs were cultured for 24-48 h with or without BDNF; lack of BDNF resulted in significant loss of early-born but not late-born RGCs. In summary, we identified several important changes in RGC signaling that may form the basis for the switch from target independence to dependence.

Injury-induced decline of intrinsic regenerative ability revealed by quantitative proteomics

Neurons differ in their responses to injury, but the underlying mechanisms remain poorly understood. Using quantitative proteomics, we characterized the injury-triggered response from purified intact and axotomized retinal ganglion cells (RGCs). Subsequent informatics analyses revealed a network of injury-response signaling hubs. In addition to confirming known players, such as mTOR, this also identified new candidates, such as c-myc, NFκB, and Huntingtin. Similar to mTOR, c-myc has been implicated as a key regulator of anabolic metabolism and is downregulated by axotomy. Forced expression of c-myc in RGCs, either before or after injury, promotes dramatic RGC survival and axon regeneration after optic nerve injury. Finally, in contrast to RGCs, neither c-myc nor mTOR was downregulated in injured peripheral sensory neurons. Our studies suggest that c-myc and other injury-responsive pathways are critical to the intrinsic regenerative mechanisms and might represent a novel target for developing neural repair strategies in adults.