Sustained axon regeneration induced by a synergy of PTEN and SOCS3 deletion
ABSTRACT: A formidable challenge in neural repair in the adult central nervous system (CNS) is the long distances that regenerating axons often need to travel in order to reconnect with their targets. Thus, a sustained capacity for axon regeneration is critical for achieving functional restoration. Although deletion of either Phosphatase and tensin homolog (PTEN), a negative regulator of mammalian target of rapamycin (mTOR), or suppressor of cytokine signaling 3 (SOCS3), a negative regulator of Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, in adult retinal ganglion cells (RGCs) individually promoted significant optic nerve regeneration, such regrowth tapered off around two weeks after the crush injury. Remarkably, we now find that simultaneous deletion of both PTEN and SOCS3 enable robust and sustained axon regeneration. We further show that PTEN and SOCS3 regulate two independent pathways that act synergistically to promote enhanced axon regeneration. Gene expression analyses suggest that double deletion not only result in the induction of many growth-related genes, but also allow RGCs to maintain the expression of a repertoire of genes at the physiological level after injury. Our results reveal concurrent activation of mTOR and STAT3 pathways as a key for sustaining long-distance axon regeneration in adult CNS, a crucial step toward functional recovery. RNAs were extracted from FACS sorted YFP positive mouse retinal cells, and gene-profiled using affymetrix 1.0 ST expression arrays. Three hybridizations were performed for each group (Wild type after crush, PTEN Knockout+crush, SOCS3 Knockout+crush, and PTEN/SOCS3 double knockout+crush) with RNA samples collected from three independent FACS purifications. Data were analyzed using dChIP and SAM.
Project description:At least 30 types of retinal ganglion cell (RGC) send distinct messages through the optic nerve to the brain. Strategies for promoting regeneration of RGC axons following injury act on only some of these types. Here we tested the hypothesis that over-expressing developmentally important transcription factors in adult RGCs could reprogram them to a “youthful” growth-competent state and promote regeneration of other types. From a screen of transcription factors expressed by developing RGCs, we found one, Sox11, that induced substantial axon regeneration. Transcriptome profiling confirmed that Sox11 activates genes involved in cytoskeletal remodeling and axon growth. Remarkably, alpha-RGCs, which preferentially regenerate following treatments such as PTEN deletion, were killed by Sox 11. Thus, Sox 11 promotes regeneration of non-alpha RGCs, which are refractory to PTEN. We conclude that Sox11 can reprogram adult RGCs to a growth-competent state and that different growth-promoting interventions act on distinct neuronal types. Overall design: We compared transcriptomes of retinal ganglion cells between AAV-Control retinas, and retinas treated with AAV-Sox11 overexpression. We then performed optic nerve crush, and 3 days later purified RGCs using FACS. RGCs were marked with Thy1-PE-Cy7 antibody and with live/dead cell staining. We performed sample preparations in full triplicate, and in each replicate we always performed Control and Sox11 on the same day, in alternating order.
Project description:Retinal ganglion cell (RGC) death is the final consequence of many blinding diseases, where there is considerable variation in the time course and severity of RGC loss. Indeed, this process appears to be influenced by a wide variety of genetic and environmental factors. In this study we explored the genetic basis for differences in ganglion cell death in two inbred strains of mice. We found that RGCs are more susceptible to death following optic nerve crush in C57BL/6J mice (54% survival) than in DBA2/J mice (62% survival). Using the Illumina Mouse-6 microarray, we identified 1,580 genes with significant change in expression following optic nerve crush in these two strains of mice. Our analysis of the changes occurring after optic nerve crush demonstrated that the greatest amount of change (44% of the variance) was due to the injury itself. This included changes associated with ganglion cell death, reactive gliosis, and abortive regeneration. The second pattern of gene changes (23% of the variance) was primarily related to differences in gene expressions observed between the C57BL/6J and DBA/2J mouse strains. The remaining changes in gene expression represent interactions between the effects of optic nerve crush and the genetic background of the mouse. We extracted one genetic network from this dataset that appears to be related to tissue remodeling. One of the most intriguing sets of changes included members of the crystallin family of genes, which may represent a signature of pathways modulating the susceptibility of cells to death. Differential responses to optic nerve crush between two widely used strains of mice were used to define molecular networks associated with ganglion cell death and reactive gliosis. These results form the basis for our continuing interest in the modifiers of retinal injury. 18 Samples: 9 per strain (C57BL/6J & DBA/2J); 3 conditions per strain
Project description:It is well-established that neurons in the adult mammalian central nervous system are terminally differentiated and, if injured, will be unable to regenerate their connections. In contrast to mammals, zebrafish and other teleosts display a robust neuroregenerative response. Following optic nerve crush (ONX), retinal ganglion cells (RGC) regrow their axons to synapse with topographically correct targets in the optic tectum, such that vision is restored in ~21 days. What accounts for these differences between teleostean and mammalian responses to neural injury is not fully understood. A time course analysis of global gene expression patterns in the zebrafish eye after optic nerve crush can help to elucidate cellular and molecular mechanisms that contribute to a successful neuroregeneration. We used microarrays to detail the global gene expression patterns underlying a successful regeneration or the optic nerve following injury. Experiment Overall Design: Microarray analysis was performed on total RNA extracted from whole eye following optic nerve crush (ONX) or sham surgery at defined intervals (4, 12, & 21 days).
Project description:Unlike adult mammals, adult frogs regrow and regenerate their optic nerve following a crush injury. Using Translational Ribosome Affinity Purification (TRAP), a method to isolate mRNAs actively undergoing translation in a target cell population, we have generated a transcriptional profile by RNA-Seq for retinal ganglion cells (RGC) during the period of recovery following an optic nerve injury. Based on bioinformatics analysis using the JGI 9.1 Xenopus laevis gene models, our results reveal a profound shift in the composition of actively translating mRNAs during the early stages of RGC regeneration: as factors involved in cell signaling are rapidly downregulated, and those involved in core metabolism are upregulated. We identified one highly upregulated gene in response to injury, uchl1, which coupled to downregulation of the synucleins (snca, scng), was previously implicated in neurodegenerative diseases. Our injury-screen in Xenopus identified a previously unknown gene, gng8, as being associated with the regenerative process. Our generated online database provides the Xenopus community a valuable resource for the identification of genes involved in the regeneration process to target for future functional studies. Overall design: To investigate the changes in gene expression that occur as retinal ganglion cells (RGCs) recover and regrow following injury, we have used the TRAP method. With TRAP we are able to isolate the actively translating pool of mRNAs from a specific cell type, in this case RGCs. To do this, we created lines of transgenic frogs which express an eGFP-tagged variant of the large ribosomal protein rpl10a under the control of an RGC-specific promoter from the islet2b locus. In our experimental framework, we quantify gene expression changes in RGCs recovering from optic nerve crush by comparing mRNA levels in samples collected from the eye undergoing a surgical crush (right) to the contralateral eye (left). At discrete time points following optic nerve crush in the left eye, both eyes are rapidly dissected and the ribosome-associated RNAs purified from tissue extracts using eGFP antibodies conjugated to magnetic beads. To control for the effects of surgery on RGCs, gene expression was also quantified in animals that underwent sham surgeries with no optic nerve crush ("sham" samples). To control for the systemic effects of the surgical procedure per se, gene expression was also quantified in animals that did not undergo any surgery ("naive" sample). These mRNA pools were used to construct libraries for RNA-Seq using poly(A) selection and 2x multiplexing.
Project description:In adult mammals, retinal ganglion cells (RGCs) fail to regenerate their axons when damaged. As a result, RGCs die after acute injury and in progressive degenerative diseases such as glaucoma; such damage can lead to permanent vision loss and blindness. Little is known about the roles of lipids in axon injury and repair despite their fundamental importance in composition of cell membranes, myelin sheaths and mediation of signaling pathways. Study of the lipidome in the biology of optic nerve (ON) regeneration has been largely neglected. A better understanding of the roles that lipids play in RGC biology may enhance understanding of RGC-related diseases and point to novel treatments. Established experimental models of ON regeneration allow exploration of molecular determinants of RGC axon regenerative success and failure. In this study, we used high-resolution liquid chromatography-tandem mass spectrometry to analyze lipidomic profiles of the ON and retina in an ON crush model with and without intravitreal Zymosan injections to enhance regeneration. Our results reveal profound remodeling of retina and ON lipidomes that occur after injury. In the retina, Zymosan treatment largely abrogates widespread lipidome alterations. In the ON, Zymosan induces lipid profiles that are distinct from those observed in naïve and vehicle-injected crush controls. We have identified a number of lipid species, classes and fatty acids that may be involved in the mechanisms of axon damage and repair. Lipids upregulated during RGC regeneration may be interesting candidates for further functional studies.
Project description:Adult mammalian CNS neurons undergo a developmental switch in intrinsic axon growth ability associated with their failure to regenerate axons after injury. Krüppel-like transcription factors (KLF) regulate intrinsic axon growth ability, but signaling regulation upstream and downstream is poorly understood. Here we find that suppressing expression of KLF9, an axon growth suppressor normally upregulated 250-fold in retinal ganglion cell (RGC) development, promotes long-distance optic nerve regeneration in vivo. We identify a novel binding partner, MAPK10/JNK3, critical for KLF9’s axon growth suppressive activity. Additionally, by screening genes regulated by KLFs in RGCs, we identify dual-specificity phosphatase 14 (Dusp14) as key to limiting axon growth and regenerative ability downstream of KLF9, associated with its dephosphorylation of MAPKs critical to neurotrophic signaling of RGC axon elongation. These results now link intrinsic and extrinsic regulation of axon growth and suggest new therapeutic strategies to promote axon regeneration in the adult CNS. Overall design: RGCs from early postnatal rats were purified and KLF9, -16, -7, and -11 genes and control, FLAG-tagged mCherry gene were transduced using lentivirus. RNA was then extracted using RNEasy (Qiagen) and processed for hybridization onto Affymetrix Rat Genome 230 2.0 Arrays.
Project description:Reactive gliosis is a complex process that involves profound changes in gene expression. We used microarray to indentify differentially expressed genes and to investigate the molecular mechanisms of reactive gliosis in optic nerve head in response to optic nerve crush injury. C57Bl/6 female mice were 6-8 weeks old at the time of optic nerve crush surgery. The optic nerve in the left eye was crush 1 mm behind the globe for 10 seconds and the right eye served as contralateral control. The animals were allowed to recover for 1 day, 3 day, 1 week, 3 weeks and 3 months before the optic nerve heads were collected. The naive control mice did not receive any surgery in either eye. Due to the small tissue size of the mouse optic nerve head, two optic nerve heads were pooled together for each microarray chip. The left eyes and the right eyes of two mice were combined respectively to form one pair of experiment and control samples. There were five biological replicates (10 mice) for each condition.
Project description:Retinal ganglion cell (RGC) death is the final consequence of many blinding diseases, where there is considerable variation in the time course and severity of RGC loss. Indeed, this process appears to be influenced by a wide variety of genetic and environmental factors. In this study we explored the genetic basis for differences in ganglion cell death in two inbred strains of mice. We found that RGCs are more susceptible to death following optic nerve crush in C57BL/6J mice (54% survival) than in DBA2/J mice (62% survival). Using the Illumina Mouse-6 microarray, we identified 1,580 genes with significant change in expression following optic nerve crush in these two strains of mice. Our analysis of the changes occurring after optic nerve crush demonstrated that the greatest amount of change (44% of the variance) was due to the injury itself. This included changes associated with ganglion cell death, reactive gliosis, and abortive regeneration. The second pattern of gene changes (23% of the variance) was primarily related to differences in gene expressions observed between the C57BL/6J and DBA/2J mouse strains. The remaining changes in gene expression represent interactions between the effects of optic nerve crush and the genetic background of the mouse. We extracted one genetic network from this dataset that appears to be related to tissue remodeling. One of the most intriguing sets of changes included members of the crystallin family of genes, which may represent a signature of pathways modulating the susceptibility of cells to death. Differential responses to optic nerve crush between two widely used strains of mice were used to define molecular networks associated with ganglion cell death and reactive gliosis. These results form the basis for our continuing interest in the modifiers of retinal injury. Overall design: 18 Samples: 9 per strain (C57BL/6J & DBA/2J); 3 conditions per strain
Project description:Suppressor of cytokine signaling 3 (SOCS3) down-regulates several signaling pathways in multiple cell types, and previous data suggest that SOCS3 may shut off cytokine activation at the early stages of liver regeneration. We developed hepatocyte-specific Socs3 knockout (Socs3 h-KO) mice to directly study the role of SOCS3 during liver regeneration after 2/3 partial hepatectomy (PH). Socs3 h-KO mice demonstrate marked enhancement of DNA replication and liver weight restoration after 2/3 PH in comparison with littermate controls. Without SOCS3, signal transducer and activator of transcription 3 (STAT3) phosphorylation is prolonged, and activation of the mitogenic kinases extracellular signal-regulated kinase 1/2 (ERK1/2) is enhanced after PH. In vitro, we show that SOCS3 deficiency enhances hepatocyte proliferation in association with enhanced STAT3 and ERK activation after epidermal growth factor (EGF) or interleukin 6 (IL-6) stimulation. Microarray analyses show that SOCS3 modulates a distinct set of genes after PH, which fall into diverse physiologic categories. Using a model of chemical-induced carcinogenesis, we found that Socs3 h-KO mice develop hepatocellular carcinoma (HCC) at an accelerated rate. By acting on cytokines and multiple proliferative pathways, SOCS3 modulates both physiologic and neoplastic proliferative processes in the liver, and may act as a tumor suppressor. Keywords: SOCS3, liver regeneration Overall design: Hepatocyte-specific excision of the Socs3 gene was achieved by breeding Socs3 fl/fl mice with mice expressing the Cre recombinase transgene under control of the albumin promoter (Alb-Cre+), yielding Socs3 h-KO mice. Socs3 fl/fl, Alb-Cre- littermates were used as controls for all experiments, and are henceforth referred to as littermates. All mice (C57BL/6) were free of Helicobacter species, housed in a specific pathogen free facility with 12-h light/dark cycles with free access to standard food and water. 2/3 PH and sham operations were performed as previously described (15, 50) (n=3-6 mice per genotype per time point). Liver remnants were weighed after removal of necrotic stumps and sutures, and compared to post-operative body weight. For HCC experiments, a single i.p. injection of DEN (5mg/kg, Sigma) was performed 12-14 d after birth. For short time points, a single injection of DEN (100mg/kg) (31) was given to 4 wk old mice. At indicated time points, mice were sacrificed by CO2 inhalation. All animal studies were carried out under approved IACUC protocols at the University of Washington.