Transection Site Research Articles

Efect of longitudinally oriented collagen conduit combined with nerve growth factor on nerve regeneration after dog sciatic nerve injury.

The research on artificial nerve conduits has become a focus of study in peripheral nerve reconstruction so as a possible replacement for the treatment of autologous nerve grafts in clinics. In this study, we used longitudinally oriented collagen conduit (LOCC) combined with nerve growth factor (NGF) to reconstruct long distance of sciatic nerve defects (35 mm) in adult dog model. The long term follow-up evaluation demonstrated that the LOCC/NGF conduit allowed functional and morphological nerve regeneration at the transection site of the injured sciatic nerve. Furthermore, the functional study confirmed that when NGF was loaded onto LOCC it promoted a better recovery of regenerated axons than LOCC alone. The gastrocnemius muscle mass in the LOCC/NGF group was significantly greater than in the LOCC alone group. The results indicated that when LOCC conduit combined with NGF it would provide a preferential environment for sciatic nerve regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2131-2139, 2018.

Postinjury Induction of Activated ErbB2 Selectively Hyperactivates Denervated Schwann Cells and Promotes Robust Dorsal Root Axon Regeneration.

Following nerve injury, denervated Schwann cells (SCs) convert to repair SCs, which enable regeneration of peripheral axons. However, the repair capacity of SCs and the regenerative capacity of peripheral axons are limited. In the present studies we examined a potential therapeutic strategy to enhance the repair capacity of SCs, and tested its efficacy in enhancing regeneration of dorsal root (DR) axons, whose regenerative capacity is particularly weak. We used male and female mice of a doxycycline-inducible transgenic line to induce expression of constitutively active ErbB2 (caErbB2) selectively in SCs after DR crush or transection. Two weeks after injury, injured DRs of induced animals contained far more SCs and SC processes. These SCs had not redifferentiated and continued to proliferate. Injured DRs of induced animals also contained far more axons that regrew along SC processes past the transection or crush site. Remarkably, SCs and axons in uninjured DRs remained quiescent, indicating that caErbB2 enhanced regeneration of injured DRs, without aberrantly activating SCs and axons in intact nerves. We also found that intraspinally expressed glial cell line-derived neurotrophic factor (GDNF), but not the removal of chondroitin sulfate proteoglycans, greatly enhanced the intraspinal migration of caErbB2-expressing SCs, enabling robust penetration of DR axons into the spinal cord. These findings indicate that SC-selective, post-injury activation of ErbB2 provides a novel strategy to powerfully enhance the repair capacity of SCs and axon regeneration, without substantial off-target damage. They also highlight that promoting directed migration of caErbB2-expressing SCs by GDNF might be useful to enable axon regrowth in a non-permissive environment.SIGNIFICANCE STATEMENT Repair of injured peripheral nerves remains a critical clinical problem. We currently lack a therapy that potently enhances axon regeneration in patients with traumatic nerve injury. It is extremely challenging to substantially increase the regenerative capacity of damaged nerves without deleterious off-target effects. It was therefore of great interest to discover that caErbB2 markedly enhances regeneration of damaged dorsal roots, while evoking little change in intact roots. To our knowledge, these findings are the first demonstration that repair capacity of denervated SCs can be efficaciously enhanced without altering innervated SCs. Our study also demonstrates that oncogenic ErbB2 signaling can be activated in SCs but not impede transdifferentiation of denervated SCs to regeneration-promoting repair SCs.

Combining Constitutively Active Rheb Expression and Chondroitinase Promotes Functional Axonal Regeneration after Cervical Spinal Cord Injury

After spinal cord injury (SCI), severed axons in the adult mammalian CNS are unable to mount a robust regenerative response. In addition, the glial scar at the lesion site further restricts the regenerative potential of axons. We hypothesized that a combinatorial approach coincidentally targeting these obstacles would promote axonal regeneration. We combined (1) transplantation of a growth-permissive peripheral nerve graft (PNG) into an incomplete, cervical lesion cavity; (2) transduction of neurons rostral to the SCI site to express constitutively active Rheb (caRheb; a Ras homolog enriched in brain), a GTPase that directly activates the growth-promoting pathway mammalian target of rapamycin (mTOR) via AAV-caRheb injection; and (3) digestion of growth-inhibitory chondroitin sulfate proteoglycans within the glial scar at the distal PNG interface using the bacterial enzyme chondroitinase ABC (ChABC). We found that expressing caRheb in neurons post-SCI results in modestly yet significantly more axons regenerating across a ChABC-treated distal graft interface into caudal spinal cord than either treatment alone. Excitingly, we found that caRheb+ChABC treatment significantly potentiates the formation of synapses in the host spinal cord and improves the animals' ability to use the affected forelimb. Thus, this combination strategy enhances functional axonal regeneration following a cervical SCI.

Involvement of MAPK, Akt/GSK-3β and AMPK/mTOR signaling pathways in protection of remote glial cells from axotomy-induced necrosis and apoptosis in the isolated crayfish stretch receptor.

Severe mechanical nerve injury such as axotomy can lead to neuron degeneration and death of surrounding glial cells. We showed that axotomy not only mechanically injures glial cells at the cutting location, but also induces necrosis or apoptosis of satellite glial cells remote from the transection site. Therefore, axon integrity is necessary for survival of surrounding glial cells. We used the crayfish stretch receptor that consists of a single mechanoreceptor neuron enveloped by satellite glial cells as a simple, but informative model object in the study of the role of various signaling proteins in axotomy-induced death of remote glial cells. After axon transection, stretch receptors were isolated and incubated in saline in the presence or without specific inhibitors of various signaling proteins. Inhibition of MEK1/2, p38, Akt, GSK-3β and mTOR increased axotomy-induced apoptosis of remote glial cells, whereas inhibition of ERK1/2 and GSK-3β enhanced necrosis. This suggests the involvement of these signaling proteins in protective, antiapoptotic and antinecrotic processes in the remote satellite glia surrounding the axotomized mechanoreceptor neuron.

Adipose-derived stem cell sheets functionalized by hybrid baculovirus for prolonged GDNF expression and improved nerve regeneration.

Peripheral nerve regeneration requires coordinated functions of supporting cells (e.g. Schwann cells) and neurotrophic factors such as glial cell line-derived neurotrophic factor (GDNF), but nerve regeneration is usually far from complete. Here we constructed a Cre/loxP-based hybrid baculovirus (BV) vector which enabled intracellular formation of episomal DNA minicircle for effective transduction of rat adipose-derived stem cells (ASCs) and prolonged expression of functional GDNF capable of recruiting Schwann cells. The GDNF expression persisted for >20 days with the peak level (≈128ng/ml) tremendously exceeding the picogram levels of GDNF secreted by neuroprogenitor cells. We further developed a facile method to fabricate and transduce cell sheets composed of undifferentiated ASCs in 2 days, without the need of thermo-responsive polymer commonly used for cell sheet fabrication. Implantation of the hybrid BV-engineered, GDNF-expressing ASCs sheets into sciatic nerve transection site in rats significantly improved the nerve repair, as judged from the enhanced functional recovery, nerve reinnervation, electrophysiological functionality, Schwann cells proliferation/infiltration, axon regeneration, myelination and angiogenesis. The hybrid BV is able to functionalize ASCs sheets by intracellular episomal DNA minicircle formation that circumvents undesired gene integration, and the ASCs sheets fabrication is rapid and simple. These data and features implicate the potentials of ASCs sheets functionalized by the hybrid BV for peripheral nerve regeneration.

Lanthionine ketimine ester promotes locomotor recovery after spinal cord injury by reducing neuroinflammation and promoting axon growth

The mammalian central nervous system (CNS) has limited regenerative ability after injury, largely due to scar formation and axonal growth inhibitors. Experimental suppression of neuroinflammation encourages recovery from spinal cord injury (SCI), yet practical means for pharmacologically treating SCI have remained elusive. Lanthionine ketimine (LK) is a natural brain sulfur amino acid metabolite with demonstrated anti-neuroinflammatory and neurotrophic activities. LK and its synthetic brain-penetrating ethyl ester (LKE) promote growth factor-dependent neurite extension in cultured cell and suppress microglial activation in animal models of neurodegeneration. Thus far however, LKE has not been explored as a potential therapy for SCI. The present study investigated the hypothesis that systemic LKE could improve motor functional recovery after SCI in a mouse model. Intraperitoneal administration of LKE (100 mg/kg/d) after near-complete transect of spinal cord at the T7 level significantly improved motor function over a 4-week time course. Vehicle-treated mice, in contrast, demonstrated negligible functional recovery. In terms of histology, LKE treatment reduced pro-neuroinflammatory microglia/macrophage activation evidenced by quantitative Iba1 labeling and shifted the microglial phenotype toward a more neurotrophic M2 character evidenced by changes in the M2 marker arginase-1. This was correlated with less dense scar formation and more extensive axonal regrowth across the transection site demonstrated by 5-hydroxytryptamine (5HT) immunolabeling of raphespinal tract axons. These data provide evidence that LKE or similar compounds have potential therapeutic value for recovery after certain forms of SCI.

Lymphatic Contribution to the Cellular Niche in Heterotopic Ossification

The objective of this study was to determine the contribution of lymphatic tissue to heterotopic ossification (HO). HO is the pathologic development of ectopic bone within soft tissues often following severe trauma. Characterization of the tissue niche supporting HO is critical to identifying therapies directed against this condition. Lymphangiogenesis is upregulated during incidents of trauma, thereby coincident with the niche supportive of HO. We hypothesized that lymphatic tissues play a critical role in HO formation. Mice underwent hindlimb Achilles' tendon transection and dorsal burn injury (burn/tenotomy) to induce HO. The popliteal and inguinal lymph nodes were excised ipsilateral to the tenotomy site. Flow cytometry and immunostaining were used to quantify and localize lymphoendothelium. MicroCT was used to quantify HO. Enrichment of mature lymphatic tissues was noted 2 weeks after injury at the tendon transection sites when compared with the contralateral, intact tendon based on LYVE1+ tubules (10.9% vs 0.8%, P < 0.05). Excision of the inguinal and popliteal nodes with draining popliteal lymphatic vessel significantly decreased the presence of mature lymphoendothelium 2 weeks after injury (10.9% vs 3.3%, P < 0.05). Bone-cartilage-stromal progenitor cells (CD105+/AlphaV+/Tie2-/CD45-/CD90-/BP1-) were also significantly decreased after lymph node excision (10.2% vs 0.5%, P < 0.05). A significant decrease was noted in the volume of de novo HO present within the soft tissues (0.12 mm vs 0.02 mm). These findings suggest that lymphatic vessels are intimately linked with the de novo formation bone within soft tissues following trauma, and their presence may facilitate bone formation.

Poster

Poster

Role of c-Jun N-terminal kinase in late nerve regenerationmonitored by invivo imaging of thy1-yellow fluorescent protein transgenic mice.

The restoration of function to injured peripheral nerves separated by a gap requires regeneration across it and reinnervation to target organs. To elucidate these processes, we have established an invivo monitoring system of nerve regeneration in thy1-yellow fluorescent protein transgenic mice expressing a fluorescent protein in their nervous system. Here we demonstrated that motor and sensory nerves were regenerated in a coordinated fashion across the gap and that the functional recovery of the response to mechanical stimuli correlated well with sensory innervation to the foot. Among the mitogen-activated protein kinase inhibitors examined, only the c-Jun N-terminal kinase (JNK) inhibitors delayed functional recovery. Although it did not affect the reinnervation of the muscle, the JNK inhibitor delayed sensory nerve innervation to the skin for over 8weeks and increased the expression of activatng transcription factor 3 (ATF3), a neuronal injury marker, in the dorsal root ganglion over the same time period. Antibodies against nerve growth factor, glia-derived neurotrophic factor, and brain-derived neurotrophic factor applied to the transection site delayed the functional recovery in this order of potency. These neurotrophic factors enhanced neurite outgrowth from cultured dorsal root ganglion neurons, and the JNK inhibitor reversed their stimulatory effects. These results suggest that JNK played roles in nerve regeneration at both early and late phases. Taken together, the present study demonstrated that neurotrophic factors released from the distal nerve may accelerate motor and sensory nerve regeneration across the gap in a coordinated fashion and reinnervation of the target organs independently. The model characterized here has the advantage of invivo monitoring of the evaluation of morphological and functional recovery in the same mice for a long period of time.

Repositioning again of zonisamide for nerve regeneration.

Repositioning again of zonisamide for nerve regeneration.

Zonisamide Enhances Neurite Elongation of Primary Motor Neurons and Facilitates Peripheral Nerve Regeneration In Vitro and in a Mouse Model.

No clinically applicable drug is currently available to enhance neurite elongation after nerve injury. To identify a clinically applicable drug, we screened pre-approved drugs for neurite elongation in the motor neuron-like NSC34 cells. We found that zonisamide, an anti-epileptic and anti-Parkinson’s disease drug, promoted neurite elongation in cultured primary motor neurons and NSC34 cells in a concentration-dependent manner. The neurite-scratch assay revealed that zonisamide enhanced neurite regeneration. Zonisamide was also protective against oxidative stress-induced cell death of primary motor neurons. Zonisamide induced mRNA expression of nerve growth factors (BDNF, NGF, and neurotrophin-4/5), and their receptors (tropomyosin receptor kinase A and B). In a mouse model of sciatic nerve autograft, intragastric administration of zonisamide for 1 week increased the size of axons distal to the transected site 3.9-fold. Zonisamide also improved the sciatic function index, a marker for motor function of hindlimbs after sciatic nerve autograft, from 6 weeks after surgery. At 8 weeks after surgery, zonisamide was protective against denervation-induced muscle degeneration in tibialis anterior, and increased gene expression of Chrne, Colq, and Rapsn, which are specifically expressed at the neuromuscular junction. We propose that zonisamide is a potential therapeutic agent for peripheral nerve injuries as well as for neuropathies due to other etiologies.

The lh3 Glycosyltransferase Directs Target-Selective Peripheral Nerve Regeneration

Functional PNS regeneration requires injured axons to return to their original synaptic targets, yet the mechanisms underlying target-selective regeneration have remained elusive. Using live-cell imaging in zebrafish we find that regenerating motor axons exhibit a strong preference for their original muscle territory and that axons probe both correct and incorrect trajectories extensively before selecting their original path. We show that this process requires the glycosyltransferase lh3 and that post-injury expression of lh3 in Schwann cells is sufficient to restore target-selective regeneration. Moreover, we demonstrate that Schwann cells neighboring the transection site express the lh3 substrate collagen4a5 and that during regeneration collagen4a5 destabilizes axons probing inappropriate trajectories to ensure target-selective regeneration, possibly through the axonal repellant slit1a. Our results demonstrate that selective ECM components match subpopulations of regenerating axons with their original targets and reveal a previously unappreciated mechanism that conveys synaptic target selection to regenerating axons invivo. VIDEO ABSTRACT.

Enabling dual cellular destinations of polymeric nanoparticles for treatment following partial injury to the central nervous system

Following neurotrauma, oxidative stress is spread via the astrocytic syncytium and is associated with increased aquaporin 4 (AQP4), inflammatory cell infiltration, loss of neurons and glia and functional deficits. Herein we evaluate multimodal polymeric nanoparticles functionalized with an antibody to an extracellular epitope of AQP4, for targeted delivery of an anti-oxidant as a therapeutic strategy following partial optic nerve transection. Using fluorescence microscopy, spectrophotometry, correlative nanoscale secondary ion mass spectrometry (NanoSIMS) and transmission electron microscopy, in vitro and in vivo, we demonstrate that functionalized nanoparticles are coated with serum proteins such as albumin and enter both macrophages and astrocytes when administered to the site of a partial optic nerve transection in rat. Antibody functionalized nanoparticles synthesized to deliver the antioxidant resveratrol are effective in reducing oxidative damage to DNA, AQP4 immunoreactivity and preserving visual function. Non-functionalized nanoparticles evade macrophages more effectively and are found more diffusely, including in astrocytes, however they do not preserve the optic nerve from oxidative damage or functional loss following injury. Our study highlights the need to comprehensively investigate nanoparticle location, interactions and effects, both in vitro and in vivo, in order to fully understand functional outcomes.

Laparoscopic and Endoscopic Near‐infrared Perfusion Assessment of in situ ileoileal, ileocolic, colocolic, colorectal and ileoanal anastomosis during intestinal operation for benign and malignant disease: A Video Vignette

As detailed in this supplement, near-infrared laparoscopy and endoscopy can be used to provide an intraoperative indocyanine green (ICG) perfusion angiogram of the small and large intestine both before and after anastomotic construction 1-3. This may aid efficiency in operative dissection and confirm dynamically and in situ the technical adequacy of the anastomosis providing reassurance about its vascular sufficiency and the absence of significant tension. This series of videos shows it's applicablility and usefulness as an aid to intraoperative decision-making by both laparoscopic and endoscopic (i.e. transanal) access in a variety of anastomosis including ileoileal, ileocolic, colocolic, colorectal and ileoanal. In general, 3–5 ml of ICG (2.5 mg/ml) was administered via a peripheral venous cannula at each intraoperative timepoint of interest usually either or both before intracorporeal intestinal transection or/and immediately after anastomotic construction. A commercially available laparoscope (PINPOINT, Novadaq) was used to assess both white-light (standard) and also near-infrared appearances either laparoscopically or endoscopically with false colour overlay by rapid sequencing allowing dual modality, augmented reality intraoperative visualisation. In addition to the experiences described in the supplement, we ourselves have employed the technique in 25 consectutive patients undergoing ileal, colonic and rectal resection with anastomosis for both benign and malignant disease over the past 6 months. In three cases, the technique encouraged reselection of a more proximal site of transection during anterior resection while all constructed anastomoses were thereafter dynamically shown to be technically satisfactory (as evidenced by observing the anastomosis's fluorescence filling and persistance in comparison to the positive control of that occuring in non-operated intestine). There were no postoperative anastomotic complications. The authors have no conflicts of interest to declare. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Antisense Morpholino Oligonucleotides Reduce Neurofilament Synthesis and Inhibit Axon Regeneration in Lamprey Reticulospinal Neurons.

The sea lamprey has been used as a model for the study of axonal regeneration after spinal cord injury. Previous studies have suggested that, unlike developing axons in mammal, the tips of regenerating axons in lamprey spinal cord are simple in shape, packed with neurofilaments (NFs), and contain very little F-actin. Thus it has been proposed that regeneration of axons in the central nervous system of mature vertebrates is not based on the canonical actin-dependent pulling mechanism of growth cones, but involves an internal protrusive force, perhaps generated by the transport or assembly of NFs in the distal axon. In order to assess this hypothesis, expression of NFs was manipulated by antisense morpholino oligonucleotides (MO). A standard, company-supplied MO was used as control. Axon retraction and regeneration were assessed at 2, 4 and 9 weeks after MOs were applied to a spinal cord transection (TX) site. Antisense MO inhibited NF180 expression compared to control MO. The effect of inhibiting NF expression on axon retraction and regeneration was studied by measuring the distance of axon tips from the TX site at 2 and 4 weeks post-TX, and counting the number of reticulospinal neurons (RNs) retrogradely labeled by fluorescently-tagged dextran injected caudal to the injury at 9 weeks post-TX. There was no statistically significant effect of MO on axon retraction at 2 weeks post-TX. However, at both 4 and 9 weeks post-TX, inhibition of NF expression inhibited axon regeneration.

Toward a standard technique for laparoscopic distal pancreatectomy? Synthesis of the 2013 ACHBT Spring workshop

Laparoscopic distal pancreatectomy is currently a commonly performed procedure. Twenty-five retrospective studies comparing laparotomy and laparoscopy have dealt with the feasibility of this approach for localized benign and malignant tumors. However, these studies report several different techniques. The aim of this review was to determine if a standardized procedure could be proposed. Based on the literature and the experience of surgeons in the French Association of Hepatobiliary Surgery and Liver Transplantation (ACBHT-Association française de chirurgie hépato-biliaire et de transplantation hépatique), we recommend primary control of the splenic artery, use of linear staplers for pancreatic transection, splenic vein control either at its end or its origin, and, depending on local conditions, preservation of the splenic vessels when splenic preservation is envisioned. Current data do not allow establishment of any definitive recommendations as to the ideal site of pancreatic transection, operative patient position, or the direction of dissection, which mainly depends on local practices. Control of the splenic vein remains the critical point of this procedure, and impacts the intra-operative strategy.

Quantitative Assessment of Tendon Healing by Using MR T2 Mapping in a Rabbit Achilles Tendon Transection Model Treated with Platelet-rich Plasma.

To determine if magnetic resonance (MR) imaging T2 mapping can be used to quantify histologic tendon healing by using a rabbit Achilles tendon transection model treated with platelet-rich plasma (PRP). Experiments were approved by the Institutional Animal Care and Use Committee. The Achilles tendons of 24 New Zealand white rabbits (48 limbs) were surgically transected, and PRP (in the test group) or saline (in the control group) was injected into the transection site. The rabbits were sacrificed 2, 4, 8, and 12 weeks after surgery. Thereafter, T2 mapping and histologic evaluations were performed by using the Bonar scale. A mixed-model multivariate analysis of variance was used to test the effects of time and PRP treatment on the T2 value and Bonar grade, respectively. The correlation between the T2 value and Bonar grade was also assessed by using the Spearman correlation coefficient. The Bonar scale values decreased in both groups during tendon healing. The T2 value also shortened over time (P < .001 for both groups). The T2 values were positively correlated with the Bonar grade (ρ = 0.78, P < .001). Both the T2 value and Bonar scale value were lower in the PRP group than in the control group at 4, 8, and 12 weeks; however, there was no significant effect of PRP treatment on the T2 value or Bonar grade. The T2 value changes reflected histologic tendon healing. While T2 and Bonar grade were lower at all time points in tendons treated with PRP, there was no significant difference between the treatment and control tendons.

The influence of transection site on the development of pancreatic fistula in patients undergoing distal pancreatectomy: A review of 294 consecutive cases

Pancreatic fistula (PF) is a significant cause of morbidity in patients undergoing distal pancreatectomy (DP), with an incidence of 15-40%. It remains unclear if the location of pancreatic transection affects the rate of PF occurrence. This study examines the correlation between the transection site of the pancreas during DP and the incidence of PF. All cases of DP from October 2005 to January 2012 were reviewed retrospectively from an institutional review board-approved database at the Thomas Jefferson University Hospital. Patient demographics and perioperative outcomes were analyzed. The pancreatic transection location was determined by review of operative reports, and then dichotomized into 2 groups: neck/body or tail. PF were graded following the International Study Group on Pancreatic Fistula guidelines. During the study period, 294 DP were performed with 244 pancreas transections at the neck/body and 50 at the tail. Of the 294 patients, 52 (17.7%) developed a postoperative PF. The incidence of PF after transection at the tail of the pancreas was higher (28%) when compared with transection at the neck/body (15.6%; P = .04). When stratified by PF grade, grade A PF occurred more commonly when transection of the gland was at the tail (22% tail vs 8.2% neck/body; P = .007); however, no difference was found for grade B/C PF (6% tail vs 7.4% neck/body; P = 1). Our data suggest that PF occurs more often when the tail is transected during DP, although the majority are low grade and of minimal clinical significance. More severe PF occurred equally between the transection sites.

Positive effects of bFGF modified rat amniotic epithelial cells transplantation on transected rat optic nerve.

PurposeEffective therapy for visual loss caused by optic nerve injury or diseases has not been achieved even though the optic nerve has the regeneration potential after injury. This study was designed to modify amniotic epithelial cells (AECs) with basic fibroblast growth factor (bFGF) gene, preliminarily investigating its effect on transected optic nerve.MethodsA human bFGF gene segment was delivered into rat AECs (AECs/hbFGF) by lentiviral vector, and the gene expression was examined by RT-PCR and ELISA. The AECs/hbFGF and untransfected rat AECs were transplanted into the transected site of the rat optic nerve. At 28 days post transplantation, the survival and migration of the transplanted cells was observed by tracking labeled cells; meanwhile retinal ganglion cells (RGCs) were observed and counted by employing biotin dextran amine (BDA) and Nissl staining. Furthermore, the expression of growth associated protein 43 (GAP-43) within the injury site was examined with immunohistochemical staining.ResultsThe AECs/hbFGF was proven to express bFGF gene and secrete bFGF peptide. Both AECs/hbFGF and AECs could survive and migrate after transplantation. RGCs counting implicated that RGCs numbers of the cell transplantation groups were significantly higher than that of the control group, and the AECs/hbFGF group was significantly higher than that of the AECs group. Moreover GAP-43 integral optical density value in the control group was significantly lower than that of the cell transplantation groups, and the value in the AECs/hbFGF group was significantly higher than that of the AECs group.ConclusionsAECs modified with bFGF could reduce RGCs loss and promote expression of GAP-43 in the rat optic nerve transected model, facilitating the process of neural restoration following injury.

Dynamic Regulation of Schwann Cell Enhancers after Peripheral Nerve Injury

Myelination of the peripheral nervous system is required for axonal function and long term stability. After peripheral nerve injury, Schwann cells transition from axon myelination to a demyelinated state that supports neuronal survival and ultimately remyelination of axons. Reprogramming of gene expression patterns during development and injury responses is shaped by the actions of distal regulatory elements that integrate the actions of multiple transcription factors. We used ChIP-seq to measure changes in histone H3K27 acetylation, a mark of active enhancers, to identify enhancers in myelinating rat peripheral nerve and their dynamics after demyelinating nerve injury. Analysis of injury-induced enhancers identified enriched motifs for c-Jun, a transcription factor required for Schwann cells to support nerve regeneration. We identify a c-Jun-bound enhancer in the gene for Runx2, a transcription factor induced after nerve injury, and we show that Runx2 is required for activation of other induced genes. In contrast, enhancers that lose H3K27ac after nerve injury are enriched for binding sites of the Sox10 and early growth response 2 (Egr2/Krox20) transcription factors, which are critical determinants of Schwann cell differentiation. Egr2 expression is lost after nerve injury, and many Egr2-binding sites lose H3K27ac after nerve injury. However, the majority of Egr2-bound enhancers retain H3K27ac, indicating that other transcription factors maintain active enhancer status after nerve injury. The global epigenomic changes in H3K27ac deposition pinpoint dynamic changes in enhancers that mediate the effects of transcription factors that control Schwann cell myelination and peripheral nervous system responses to nerve injury.