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Phase separation into liquid-like compartments is an emerging property of proteins containing prion-like domains (PrLDs), yet the in vivo roles of phase separation remain poorly understood. TIA proteins contain a C-terminal PrLD, and mutations in the PrLD are associated with several diseases. Here, we show that the C. elegans TIAR-2/TIA protein functions cell autonomously to inhibit axon regeneration. TIAR-2 undergoes liquid-liquid phase separation in vitro and forms granules with liquid-like properties in vivo. Axon injury induces a transient increase in TIAR-2 granule number. The PrLD is necessary and sufficient for granule formation and inhibiting regeneration. Tyrosine residues within the PrLD are important for granule formation and inhibition of regeneration. TIAR-2 is also serine phosphorylated in vivo. Non-phosphorylatable TIAR-2 variants do not form granules and are unable to inhibit axon regeneration. Our data demonstrate an in vivo function for phase-separated TIAR-2 and identify features critical for its function in axon regeneration.

Abstract Central nervous system (CNS) neurons typically fail to regenerate their axons after injury leading to neurological impairment. Axonal regeneration is a highly energy-demanding cellular program that requires local mitochondria to supply most energy within injured axons. Recent emerging lines of evidence have started to reveal that injury-triggered acute mitochondrial damage and local energy crisis contribute to the intrinsic energetic restriction that accounts for axon regeneration failure in the CNS. Characterizing and reprogramming bioenergetic signaling and mitochondrial maintenance after axon injury-ischemia is fundamental for developing therapeutic strategies that can restore local energy metabolism and thus facilitate axon regeneration. Therefore, establishing reliable and reproducible neuronal model platforms is critical for assessing axonal energetic metabolism and regeneration capacity after injury-ischemia. In this focused methodology article, we discuss recent advances in applying cutting-edge microfluidic chamber devices in combination with state-of-the-art live-neuron imaging tools to monitor axonal regeneration, mitochondrial transport, bioenergetic metabolism, and local protein synthesis in response to injury-ischemic stress in mature CNS neurons.

Central nervous system (CNS) neurons typically fail to regenerate their axons after injury leading to neurological impairment. Axonal regeneration is a highly energy-demanding cellular program that requires local mitochondria to supply most energy within injured axons. Recent emerging lines of evidence have started to reveal that injury-triggered acute mitochondrial damage and local energy crisis contribute to the intrinsic energetic restriction that accounts for axon regeneration failure in the CNS. Characterizing and reprogramming bioenergetic signaling and mitochondrial maintenance after axon injury-ischemia is fundamental for developing therapeutic strategies that can restore local energy metabolism and thus facilitate axon regeneration. Therefore, establishing reliable and reproducible neuronal model platforms is critical for assessing axonal energetic metabolism and regeneration capacity after injury-ischemia. In this focused methodology article, we discuss recent advances in applying cutting-edge microfluidic chamber devices in combination with state-of-the-art live-neuron imaging tools to monitor axonal regeneration, mitochondrial transport, bioenergetic metabolism, and local protein synthesis in response to injury-ischemic stress in mature CNS neurons. [ABSTRACT FROM AUTHOR]

Abstract 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.

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.

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. [ABSTRACT FROM AUTHOR]

Most projection neurons, including retinal ganglion cells (RGCs), undergo cell death after axotomy proximal to the cell body. Specific RGC subtypes, such as ON-OFF direction selective RGCs (ooDSGCs) are particularly vulnerable, whereas intrinsically photosensitive RGCs (ipRGCs) exhibit resilience to axonal injury. Through the application of RNA sequencing and fluorescent in situ hybridization, we show that the expression of chloride intracellular channel protein 1 and 4 (Clic1 and Clic4) are highly increased in the ooDSGCs after axonal injury. Toward determining a gene's role in RGCs, we optimized the utility and efficacy of adenovirus associated virus (AAV)-retro expressing short hairpin RNA (shRNA). Injection of AAV2-retro into the superior colliculus results in efficient shRNA expression in RGCs. Incorporating histone H2B gene fused with mGreenLantern results in bright nuclear reporter expression, thereby enhancing single RGC identification and cell quantitation in live retinas. Lastly, we demonstrate that AAV2-retro mediated knockdown of both Clic1 and Clic4 promotes RGC survival after injury. Our findings establish an integrated use of AAV2-retro-shRNA and real-time fundus imaging and reveal CLICs' contribution to RGC death. • Expression of Clic1 and Clic4 are upregulated in RGCs after axonal injury. • Optimization of AAV2-retro for RGC labeling and gene manipulation. • Integrated use of the AAV2-retro-shRNA and longitudinal retinal fundus imagining. • Concomitant knockdown of Clic1 and Clic4 promotes RGC survival. [ABSTRACT FROM AUTHOR]

Macroautophagy/autophagy is essential for maintaining cellular homeostasis through the degradation of organelles and proteins. It also has a prominent role in modulating aging. However, the role of autophagy in the neuronal response to axon injury and axon regeneration, particularly in the context of aging, remains largely unknown. Our candidate genetic screen for axon regeneration regulators has identified genes in the autophagy pathway. Using a reporter that monitors autophagosomes and autolysosomes, we were able to monitor the dynamics of autophagy during axon regeneration. In response to axon injury, there was a significant increase in the number of autophagic vesicles. Injury-triggered autophagy activation and axon regeneration capacity undergo an age-dependent decline, and autophagy-activating agents partially rescued these declines. We found that DLK-1 was both required and sufficient for injury-induced autophagy activation. Autophagic vesicles co-localized with the NOTCH4 ortholog, LIN-12 receptor, a previously identified inhibitor of axon regeneration. Epistasis analyses indicate that LIN-12 might be a target of autophagy in axon regeneration. Together, our data suggest that DLK-mediated injury signaling can activate autophagy, which might limit the level of LIN-12 and NOTCH proteins to promote axon regeneration. Our findings reveal that autophagy activation can promote axon regeneration in neurons that lack maximal regrowth capacity, providing a promising therapeutic strategy for axon injury. Abbreviations: 3-MA: 3-methyladenine; ALs: autolysosomes; APs: autophagosomes; ARF-6: ADP-Ribosylation Factor related 6; ATG-9: AuTophaGy (yeast Atg homolog) 9; ATG9A: autophagy related 9A; BA1: bafilomycin A1; BEC-1: BEClin (human autophagy) homolog; BECN1: beclin 1; C. elegans: Caenorhabditis elegans; CEBP-1: C/EBP (CCAAT/enhancer-binding protein) homolog; CNS: central nervous system; DLK-1: Dual-Leucine zipper Kinase; DMSO: dimethyl sulfoxide; DRG: dorsal root ganglion; FOS: Fos proto-oncogene, AP-1 transcription factor subunit; GABA: gamma-aminobutyric acid; GFP: green fluorescent protein; HDA-3: Histone DeAcetylase; IP3: inositol trisphosphate; ITR-1: Inositol Triphosphate Receptor; KLF-2: Kruppel-Like Factor (zinc finger protein) 2; LGG-1: LC3, GABARAP and GATE-16 family; MAK-2: MAP kinase Activated protein Kinase; MAP kinase: mitogen-activated protein kinase; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MKK-4: mitogen activated protein kinase kinase 4; MTOR: mechanistic target of rapamycin kinase; NGM: nematode growth medium; NICD: Notch intracellular domain; NOTCH: notch receptor; PLM: posterior lateral microtubule; PMK-3: P38 Map kinase family; PNS: peripheral nervous system; SCG10: superior cervical ganglion protein 10; SCI: spinal cord injury; UNC-51: UNCoordinated 51; ULK1: unc-51 like autophagy activating kinase 1; wnd: wallenda [ABSTRACT FROM AUTHOR]

The optic nerve, predominantly constituted by the axons of retinal ganglion cells (RGCs), lacks the ability to regenerate and re-establish function after injury. RGCs are crucial for visual function, and thus, RGC death contributes to the development of numerous progressive neurodegenerative optic neuropathies including glaucoma, ischemic optic neuropathy, and optic neuritis. Regenerating optic nerve axons poses numerous challenges due to factors such as the intricate and inhibitory conditions that exist within their environment, intrinsic breaks to regeneration, and the geometric tortuosity that offers physical hindrance to axon growth. However, recent research advancements offer hope for clinically meaningful regeneration for those who suffer from optic nerve damage. In this review, we highlight the current treatment approaches for optic nerve axon regeneration. [Display omitted] [ABSTRACT FROM AUTHOR]

In contrast to central nervous system neurons, dorsal root ganglia (DRG) neurons can switch to a regenerative state after peripheral axotomy. In a screen for chromatin regulators of the regenerative responses in this conditioning lesion paradigm, we identified Tet methylcytosine dioxygenase 3 (Tet3) as upregulated in DRG neurons, along with increased 5-hydroxymethylcytosine (5hmC). We generated genome-wide 5hmC maps in adult DRG, which revealed that peripheral and central axotomy (leading to no regenerative effect) triggered differential 5hmC changes that are associated with distinct signaling pathways. 5hmC was altered in a large set of regeneration-associated genes (RAGs), including well-known RAGs, such as Atf3, Bdnf, and Smad1, that regulate axon growth potential of DRG neurons, thus supporting its role for RAG regulation. Our analyses also predicted HIF-1, STAT, and IRF as potential transcription factors that may collaborate with Tet3 for 5hmC modifications. Intriguingly, central axotomy resulted in widespread 5hmC modifications that had little overlap with those of peripheral axotomy, thus potentially constituting a roadblock for regeneration. Our study revealed 5hmC dynamics as a previously unrecognized epigenetic mechanism underlying the divergent responses after axonal injury.

Axon regeneration after injury is a conserved biological process that involves a large number of molecular pathways, including rapid calcium influx at injury sites, retrograde injury signaling, epigenetic transition, transcriptional reprogramming, polarized transport, and cytoskeleton reorganization. Despite the numerous efforts devoted to understanding the underlying cellular and molecular mechanisms of axon regeneration, the search continues for effective target molecules for improving axon regeneration. Although there have been significant historical efforts towards characterizing pro-regenerative factors involved in axon regeneration, the pursuit of intrinsic inhibitors is relatively recent. EFA6 (exchange factor for ARF6) has been demonstrated to inhibit axon regeneration in different organisms. EFA6 inhibition could be a promising therapeutic strategy to promote axon regeneration and functional recovery after axon injury. This review summarizes the inhibitory role on axon regeneration through regulating microtubule dynamics and through affecting ARF6 (ADP-ribosylation factor 6) GTPase-mediated integrin transport.

After an injury in the adult mammalian central nervous system (CNS), lesioned axons fail to regenerate. This failure to regenerate contrasts with axons' remarkable potential to grow during embryonic development and after an injury in the peripheral nervous system (PNS). Several intracellular mechanisms—including cytoskeletal dynamics, axonal transport and trafficking, signaling and transcription of regenerative programs, and epigenetic modifications—control axon regeneration. In this review, we describe how manipulation of intrinsic mechanisms elicits a regenerative response in different organisms and how strategies are implemented to form the basis of a future regenerative treatment after CNS injury. [ABSTRACT FROM AUTHOR]

In both the central nervous system (CNS) and the peripheral nervous system (PNS), axonal injury induces changes in neuronal gene expression. In the PNS, a relatively well-characterized alteration in transcriptional activation is known to promote axonal regeneration. This transcriptional cascade includes the neurotrophin Bdnf and the transcription factor Sox11. Although both molecules act to facilitate successful axon regeneration in the PNS, this process does not occur in the CNS. The present study examines the differential expression of Sox11 and Bdnf mRNA isoforms in the PNS and CNS using three experimental paradigms at different time points: (i) the acutely injured CNS (retina after optic nerve crush) and PNS (dorsal root ganglion after sciatic nerve crush), (ii) a CNS regeneration model (retina after optic nerve crush and induced regeneration); and (iii) the retina during a chronic form of central neurodegeneration (the DBA/2J glaucoma model). We find an initial increase of Sox11 in both PNS and CNS after injury; however, the expression of Bdnf isoforms is higher in the PNS relative to the CNS. Sustained upregulation of Sox11 is seen in the injured retina following regeneration treatment, while the expression of two Bdnf mRNA isoforms is suppressed. Furthermore, two isoforms of Sox11 with different 3′UTR lengths are present in the retina, and the long isoform is specifically upregulated in later stages of glaucoma. These results provide insight into the molecular cascades active during axonal injury and regeneration in mammalian neurons.

In both the central nervous system (CNS) and the peripheral nervous system (PNS), axonal injury induces changes in neuronal gene expression. In the PNS, a relatively well-characterized alteration in transcriptional activation is known to promote axonal regeneration. This transcriptional cascade includes the neurotrophin Bdnf and the transcription factor Sox11. Although both molecules act to facilitate successful axon regeneration in the PNS, this process does not occur in the CNS. The present study examines the differential expression of Sox11 and Bdnf mRNA isoforms in the PNS and CNS using three experimental paradigms at different time points: (i) the acutely injured CNS (retina after optic nerve crush) and PNS (dorsal root ganglion after sciatic nerve crush), (ii) a CNS regeneration model (retina after optic nerve crush and induced regeneration); and (iii) the retina during a chronic form of central neurodegeneration (the DBA/2J glaucoma model). We find an initial increase of Sox11 in both PNS and CNS after injury; however, the expression of Bdnf isoforms is higher in the PNS relative to the CNS. Sustained upregulation of Sox11 is seen in the injured retina following regeneration treatment, while the expression of two Bdnf mRNA isoforms is suppressed. Furthermore, two isoforms of Sox11 with different 30UTR lengths are present in the retina, and the long isoform is specifically upregulated in later stages of glaucoma. These results provide insight into the molecular cascades active during axonal injury and regeneration in mammalian neurons. [ABSTRACT FROM AUTHOR]

Intraorbital optic nerve crush in rodents is widely used as a model to study axon regeneration in the adult mammalian central nervous system. Recent studies using appropriate genetic manipulations have revealed remarkable abilities of mature retinal ganglion cell (RGC) axons to regenerate after optic nerve injury, with some studies demonstrating that axons can then go on to re-innervate a number of central visual targets with partial functional restoration. However, one confounding factor inherent to optic nerve crush injury is the potential incompleteness of the initial lesion, leaving spared axons that later on could erroneously be interpreted as regenerating distal to the injury site. Careful examination of axonal projection pattern and morphology may facilitate separating spared from regenerating RGC axons. Here we discuss morphological criteria and strategies that may be used to differentiate spared versus regenerated axons in the injured mammalian optic nerve. [ABSTRACT FROM AUTHOR]

ABSTRACT In the adult mammalian central nervous system (CNS), axonal damage often triggers neuronal cell death and glial activation, with very limited spontaneous axon regeneration. In this study, we performed optic nerve injury in adult naked mole-rats, the longest living rodent, with a maximum life span exceeding 30 years, and found that injury responses in this species are quite distinct from those in other mammalian species. In contrast to what is seen in other mammals, the majority of injured retinal ganglion cells (RGCs) survive with relatively high spontaneous axon regeneration. Furthermore, injured RGCs display activated signal transducer and activator of transcription-3 (STAT3), whereas astrocytes in the optic nerve robustly occupy and fill the lesion area days after injury. These neuron-intrinsic and -extrinsic injury responses are reminiscent of those in 'cold-blooded' animals, such as fish and amphibians, suggesting that the naked mole-rat is a powerful model for exploring the mechanisms of neuronal injury responses and axon regeneration in mammals. J. Comp. Neurol. 525:380-388, 2017. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Maintaining neuronal connectivity in the face of injury and disease is a major challenge for the nervous system. The great length of axons makes them particularly vulnerable to insult with dire consequences for neuronal function. In the peripheral nervous system there is a program of axonal regeneration that can reestablish connectivity. In the mammalian central nervous system, however, injured axons have little or no capacity to regenerate. The molecular mechanisms that promote axon regeneration have begun to be identified and many of the implicated pathways are evolutionarily conserved. Here we discuss Drosophila models of axonal regrowth, describe insights derived from these studies, and highlight future directions in the use of the fly for dissecting the mechanisms of axonal regeneration. [ABSTRACT FROM AUTHOR]

Abstract: Severed axons in adult mammals do not regenerate appreciably after central nervous system (CNS) injury due to developmentally determined reductions in neuron-intrinsic growth capacity and extracellular environment for axon elongation. Chondroitin sulfate proteoglycans (CSPGs), which are generated by reactive scar tissues, are particularly potent contributors to the growth-limiting environment in mature CNS. Thus, surmounting the strong inhibition by CSPG-rich scar is an important therapeutic goal for achieving functional recovery after CNS injuries. As of now, the main in vivo approach to overcoming inhibition by CSPGs is enzymatic digestion with locally applied chondroitinase ABC (ChABC), but several disadvantages may prevent using this bacterial enzyme as a therapeutic option for patients. A better understanding of the molecular mechanisms underlying CSPG action is needed in order to develop more effective therapies to overcome CSPG-mediated inhibition of axon regeneration and/or sprouting. Because of their large size and dense negative charges, CSPGs were thought to act by non-specifically hindering the binding of matrix molecules to their cell surface receptors through steric interactions. Although this may be true, recent studies indicate that two members of the leukocyte common antigen related (LAR) phosphatase subfamily, protein tyrosine phosphatase σ (PTPσ) and LAR, are functional receptors that bind CSPGs with high affinity and mediate CSPG inhibitory effects. CSPGs also may act by binding to two receptors for myelin-associated growth inhibitors, Nogo receptors 1 and 3 (NgR1 and NgR3). If confirmed, it would suggest that CSPGs have multiple mechanisms by which they inhibit axon growth, making them especially potent and difficult therapeutic targets. Identification of CSPG receptors is not only important for understanding the scar-mediated growth suppression, but also for developing novel and selective therapies to promote axon sprouting and/or regeneration after CNS injuries, including spinal cord injury (SCI). [Copyright &y& Elsevier]

Axons in the adult mammalian central nervous system fail to regenerate after spinal cord injury. Neurons lose their capacity to regenerate during development, but the intracellular processes underlying this loss are unclear. We found that critical components of the presynaptic active zone prevent axon regeneration in adult mice. Transcriptomic analysis combined with live-cell imaging revealed that adult primary sensory neurons downregulate molecular constituents of the synapse as they acquire the ability to rapidly grow their axons. Pharmacogenetic reduction of neuronal excitability stimulated axon regeneration after adult spinal cord injury. Genetic gain- and loss-of-function experiments uncovered that essential synaptic vesicle priming proteins of the presynaptic active zone, but not clostridial-toxin-sensitive VAMP-family SNARE proteins, inhibit axon regeneration. Systemic administration of Baclofen reduced voltage-dependent Ca2+ influx in primary sensory neurons and promoted their regeneration after spinal cord injury. These findings indicate that functional presynaptic active zones constitute a major barrier to axon regeneration. [Display omitted] • Axon growth-competent adult neurons downregulate critical components of the synapse • Pharmacogenetic reduction of neuronal excitability stimulates axon regeneration • The presynaptic active zone proteins Munc13 and RIM suppress axon growth • Systemic Baclofen treatment promotes regeneration after adult spinal cord injury Combining genetic, pharmacogenetic, pharmacological, and transcriptomic approaches with live-cell, super-resolution, and 3-dimensional two-photon imaging, Hilton et al. demonstrate that critical components of the presynaptic transmitter release machinery actively inhibit axon growth. Munc13, a presynaptic active zone protein essential for synaptic transmission, suppresses axon regeneration following adult CNS injury. [ABSTRACT FROM AUTHOR]

Axon regeneration after injury is a conserved biological process that involves a large number of molecular pathways, including rapid calcium influx at injury sites, retrograde injury signaling, epigenetic transition, transcriptional reprogramming, polarized transport, and cytoskeleton reorganization. Despite the numerous efforts devoted to understanding the underlying cellular and molecular mechanisms of axon regeneration, the search continues for effective target molecules for improving axon regeneration. Although there have been significant historical efforts towards characterizing pro-regenerative factors involved in axon regeneration, the pursuit of intrinsic inhibitors is relatively recent. EFA6 (exchange factor for ARF6) has been demonstrated to inhibit axon regeneration in different organisms. EFA6 inhibition could be a promising therapeutic strategy to promote axon regeneration and functional recovery after axon injury. This review summarizes the inhibitory role on axon regeneration through regulating microtubule dynamics and through affecting ARF6 (ADP-ribosylation factor 6) GTPase-mediated integrin transport. [ABSTRACT FROM AUTHOR]

Autophagy is a conserved pathway that plays a key role in cell homeostasis in normal settings, as well as abnormal and stress conditions. Autophagy dysfunction is found in various neurodegenerative diseases, although it remains unclear whether autophagy impairment is a contributor or consequence of neurodegeneration. Axonal injury is an acute neuronal stress that triggers autophagic responses in an age-dependent manner. In this study, we investigate the injury-triggered autophagy response in a C. elegans model of tauopathy. We found that transgenic expression of pro-aggregant Tau, but not the anti-aggregant Tau, abolished axon injury-induced autophagy activation, resulting in a reduced axon regeneration capacity. Furthermore, axonal trafficking of autophagic vesicles were significantly reduced in the animals expressing pro-aggregant F3ΔK280 Tau, indicating that Tau aggregation impairs autophagy regulation. Importantly, the reduced number of total or trafficking autophagic vesicles in the tauopathy model was not restored by the autophagy activator rapamycin. Loss of PTL-1, the sole Tau homologue in C. elegans, also led to impaired injury-induced autophagy activation, but with an increased basal level of autophagic vesicles. Therefore, we have demonstrated that Tau aggregation as well as Tau depletion both lead to disruption of injury-induced autophagy responses, suggesting that aberrant protein aggregation or microtubule dysfunction can modulate autophagy regulation in neurons after injury. [ABSTRACT FROM AUTHOR]

Injured axons fail to regenerate in the adult CNS, which contrasts with their vigorous growth during embryonic development. We explored the potential of re-initiating axon extension after injury by reactivating the molecular mechanisms that drive morphogenetic transformation of neurons during development. Genetic loss- and gain-of-function experiments followed by time-lapse microscopy, in vivo imaging, and whole-mount analysis show that axon regeneration is fueled by elevated actin turnover. Actin depolymerizing factor (ADF)/cofilin controls actin turnover to sustain axon regeneration after spinal cord injury through its actin-severing activity. This pinpoints ADF/cofilin as a key regulator of axon growth competence, irrespective of developmental stage. These findings reveal the central role of actin dynamics regulation in this process and elucidate a core mechanism underlying axon growth after CNS trauma. Thereby, neurons maintain the capacity to stimulate developmental programs during adult life, expanding their potential for plasticity. Thus, actin turnover is a key process for future regenerative interventions. • Elevated actin turnover is essential for regenerative growth • ADF/cofilin activity increases during conditioning-mediated regeneration • ADF/cofilin is necessary and sufficient for axon regeneration • The severing activity of ADF/cofilin is critical for axon regeneration Tedeschi et al. identify ADF/cofilin as a key driver of axon regeneration in adult dorsal root ganglion neurons. Specifically, enhanced actin turnover by the ADF/cofilin severing function controls axon regeneration in the adult CNS. [ABSTRACT FROM AUTHOR]

Neuronal subtypes show diverse injury responses, but the molecular underpinnings remain elusive. Using transgenic mice that allow reliable visualization of axonal fate, we demonstrate that intrinsically photosensitive retinal ganglion cells (ipRGCs) are both resilient to cell death and highly regenerative. Using RNA sequencing (RNA-seq), we show genes that are differentially expressed in ipRGCs and that associate with their survival and axon regeneration. Strikingly, thrombospondin-1 (Thbs1) ranked as the most differentially expressed gene, along with the well-documented injury-response genes Atf3 and Jun. THBS1 knockdown in RGCs eliminated axon regeneration. Conversely, RGC overexpression of THBS1 enhanced regeneration in both ipRGCs and non-ipRGCs, an effect that was dependent on syndecan-1, a known THBS1-binding protein. All structural domains of the THBS1 were not equally effective; the trimerization and C-terminal domains promoted regeneration, while the THBS type-1 repeats were dispensable. Our results identify cell-type-specific induction of Thbs1 as a novel gene conferring high regenerative capacity. • ipRGCs survive and regenerate axons well after injury • RNA-seq reveals unique sets of genes enriched in injured ipRGCs, including Thbs1 and Sdc1 • Neural THBS1 promotes axon regeneration in various RGC types • Neural THBS1 promotes axon regeneration in a syndecan1-dependent manner Here, Bray et al. used a variety of transgenic mice to demonstrate high survival and regenerative ability of one neuronal type in the retina and show several factors within these neurons, including thrombospondin-1 and syndecan-1 that confer high regenerative capacity. [ABSTRACT FROM AUTHOR]