IMPORTANCE: Alzheimer disease (AD) is the most common neurodegenerative disorder and lacks effective disease-modifying therapies. In 2001, we initiated a clinical trial of nerve growth factor (NGF) ...gene therapy in AD, the first effort at gene delivery in an adult neurodegenerative disorder. This program aimed to determine whether a nervous system growth factor prevents or reduces cholinergic neuronal degeneration in patients with AD. We present postmortem findings in 10 patients with survival times ranging from 1 to 10 years after treatment. OBJECTIVE: To determine whether degenerating neurons in AD retain an ability to respond to a nervous system growth factor delivered after disease onset. DESIGN, SETTING, AND PARTICIPANTS: Patients in this anatomicopathological study were enrolled in clinical trials from March 2001 to October 2012 at the University of California, San Diego, Medical Center in La Jolla. Ten patients with early AD underwent NGF gene therapy using ex vivo or in vivo gene transfer. The brains of all 8 patients in the first phase 1 ex vivo trial and of 2 patients in a subsequent phase 1 in vivo trial were examined. MAIN OUTCOMES AND MEASURES: Brains were immunolabeled to evaluate in vivo gene expression, cholinergic neuronal responses to NGF, and activation of NGF-related cell signaling. In 2 patients, NGF protein levels were measured by enzyme-linked immunosorbent assay. RESULTS: Among 10 patients, degenerating neurons in the AD brain responded to NGF. All patients exhibited a trophic response to NGF in the form of axonal sprouting toward the NGF source. Comparing treated and nontreated sides of the brain in 3 patients who underwent unilateral gene transfer, cholinergic neuronal hypertrophy occurred on the NGF-treated side (P < .05). Activation of cellular signaling and functional markers was present in 2 patients who underwent adeno-associated viral vectors (serotype 2)–mediated NGF gene transfer. Neurons exhibiting tau pathology and neurons free of tau expressed NGF, indicating that degenerating cells can be infected with therapeutic genes, with resultant activation of cell signaling. No adverse pathological effects related to NGF were observed. CONCLUSIONS AND RELEVANCE: These findings indicate that neurons of the degenerating brain retain the ability to respond to growth factors with axonal sprouting, cell hypertrophy, and activation of functional markers. Sprouting induced by NGF persists for 10 years after gene transfer. Growth factor therapy appears safe over extended periods and merits continued testing as a means of treating neurodegenerative disorders.
Although Aβ peptides are causative agents in Alzheimer's disease (AD), the underlying mechanisms are still elusive. We report that Aβ42 induces a translational block by activating AMPK, thereby ...inhibiting the mTOR pathway. This translational block leads to widespread ER stress, which activates JNK3. JNK3 in turn phosphorylates APP at T668, thereby facilitating its endocytosis and subsequent processing. In support, pharmacologically blocking translation results in a significant increase in Aβ42 in a JNK3-dependent manner. Thus, JNK3 activation, which is increased in human AD cases and a familial AD (FAD) mouse model, is integral to perpetuating Aβ42 production. Concomitantly, deletion of JNK3 from FAD mice results in a dramatic reduction in Aβ42 levels and overall plaque loads and increased neuronal number and improved cognition. This reveals AD as a metabolic disease that is under tight control by JNK3.
► JNK3 activation is integral to the development of AD pathology ► JNK3 regulates APP endocytosis ► Ab42 activates AMPK ► Ab42 inhibits the mTOR pathway
Yoon et al. find that, in a mouse model of Alzheimer's disease, preventing JNK3 activation dramatically reduces toxic plaque accumulation in the brain. Since JNK3 is similarly activated in Alzheimer's disease patients, these results suggest that JNK3 is a potential therapeutic target.
We determined whether rehabilitation after cortical injury also drives dynamic dendritic and spine changes in functionally distinct subsets of neurons, resulting in functional recovery. Moreover, ...given known requirements for cholinergic systems in mediating complex forms of cortical plasticity, including skilled motor learning, we hypothesized that cholinergic systems are essential mediators of neuronal structural and functional plasticity associated with motor rehabilitation. Adult rats learned a skilled forelimb grasping task and then, underwent destructive lesions of the caudal forelimb region of the motor cortex, resulting in nearly complete loss of grasping ability. Subsequent intensive rehabilitation significantly enhanced both dendritic architecture and spine number in the adjoining rostral forelimb area compared with that in the lesioned animals that were not rehabilitated. Cholinergic ablation markedly attenuated rehabilitation-induced recovery in both neuronal structure and motor function. Thus, rehabilitation focused on an affected limb robustly drives structural compensation in perilesion cortex, enabling functional recovery.
Abstract Previously we reported that templated agarose scaffolds can orient and guide local spinal cord axons after injury. In the present study we examined whether growth of long-projecting spinal ...cord axons could also be promoted into, and then beyond, templated agarose scaffolds placed into a spinal cord lesion site. Ascending spinal cord dorsal column sensory axons were transected at the C4 level. Animals were then subjected to combinatorial therapies consisting of: 1) templated agarose scaffolds implanted into the lesion site, seeded with autologous bone marrow stromal cells expressing a growth factor, neurotrophin-3 (NT-3), 2) lentiviral vectors expressing NT-3 beyond the lesion site (to promote axonal emergence from the scaffold along chemotropic gradients of growth factors), and 3) priming lesions (“conditioning lesions”) of the sensory neuronal cell body to stimulate the endogenous growth state of the injured neuron. Control groups received either non-organized, NT-3-expressing cell suspension grafts in the lesion site, or templated scaffolds plus one of the two components of the combination therapy. Among groups that received templated agarose scaffolds, long-tract sensory axonal regeneration occurred into the spinal cord lesion site, and the growth of these axons was remarkably organized and linear compared to non-organized cell suspension grafts. Axonal penetration was maximal in subjects that received combination therapies; further, 83 + 13% of axons entering the scaffolds in combination-treated subjects continued to grow the full length of the lesion cavity to reach the distal aspect of the scaffold, over a 2 mm distance. In contrast, axons regenerating into cell suspension grafts lacking guidance scaffolds exhibited a parabolic decay of growth as a function of distance, and only 22 + 6% of axons extended the length of the lesion cavity. Moreover, axonal regeneration beyond the lesion site occurred only among subjects that received full combinatorial treatments ( p < 0.05). However, axon growth beyond the scaffold was constrained to a reactive cell layer that formed between the distal aspect of the scaffold and host tissue, and did not continue further to re-penetrate the host spinal cord. Thus, templated agarose scaffolds substantially enhance the organization and distance over which long-tract axons extend through a spinal cord lesion site in the presence of combinatorial therapies, but host-scaffold reactive interfaces limit axon re-penetration of the host. Further development must reduce reactive cellular interfaces to support effective axonal penetration of host parenchyma.
Chondroitin sulfate proteoglycans (CSPGs) are extracellular matrix (ECM) molecules that are widely expressed throughout the developing and adult CNS. In vitro studies demonstrate their potential to ...restrict neurite outgrowth, and it is believed that CSPGs also inhibit axonal regeneration after CNS injury in vivo. Previous studies demonstrated that CSPGs are generally upregulated after spinal cord injury, and more recent reports have begun to identify individual proteoglycans that may play dominant roles in limiting axonal regeneration. The current study systematically examined the extended deposition patterns after CNS injury of four putatively inhibitory CSPGs that have not been extensively investigated previously in vivo: neurocan, brevican, phosphacan, and versican. After spinal cord injury, neurocan, brevican, and versican immunolabeling increased within days in injured spinal cord parenchyma surrounding the lesion site and peaked at 2 weeks. Neurocan and versican were persistently elevated for 4 weeks postinjury, and brevican expression persisted for at least 2 months. On the other hand, phosphacan immunolabeling decreased in the same region immediately following injury but later recovered and then peaked after 2 months. Combined glial fibrillary acidic protein (GFAP) immunohistochemistry and in situ hybridization demonstrated that GFAP astrocytes constituted a source of neurocan production after spinal cord injury. Thus, the production of several CSPG family members is differentially affected by spinal cord injury, overall establishing a CSPG-rich matrix that persists for up to 2 months following injury. Optimization of strategies to reduce CSPG expression to enhance regeneration may need to target several different family members over an extended period following injury.
Neural progenitor cells (NPCs) grafted to sites of spinal cord injury (SCI) extend numerous axons over long distances and form new synaptic connections with host neurons. In the present study we ...examined the myelination of axons emerging from NPC grafts. Rat embryonic day 14 (E14) multipotent NPCs constitutively expressing GFP were grafted into adult C5 spinal cord hemisection lesions; 3months later we examined graft-derived axonal diameter and myelination using transmission electron microscopy. 104 graft-derived axons were characterized. Axon diameter ranged from 0.15 to 1.70μm, and 24% of graft-derived axons were myelinated by host oligodendrocytes caudal to the lesion. The average diameter of myelinated axons (0.72±0.3μm) was significantly larger than that of non-myelinated axons (0.61±0.2μm, p<0.05). Notably, the G-ratio of myelinated graft-derived axons (0.77±0.01) was virtually identical to that of the normal, intact spinal cord described in published reports. These findings indicate that axons emerging from early stage neural grafts into the injured spinal cord recapitulate both the small/medium size range and myelin thickness of intact spinal cord axons.
•24% of axons emerging from neural progenitor cell grafts becomes myelinated by host oligodendrocytes.•Graft-derived axons of large diameter are more likely to be myelinated.•The G-ratio of NPC-derived axons equals that of the intact spinal cord.
Guidance molecules in axon regeneration Giger, Roman J; Hollis, 2nd, Edmund R; Tuszynski, Mark H
Cold Spring Harbor perspectives in biology
2, Številka:
7
Journal Article
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The regenerative capacity of injured adult mammalian central nervous system (CNS) tissue is very limited. Disease or injury that causes destruction or damage to neuronal networks typically results in ...permanent neurological deficits. Injury to the spinal cord, for example, interrupts vital ascending and descending fiber tracts of spinally projecting neurons. Because neuronal structures located proximal or distal to the injury site remain largely intact, a major goal of spinal cord injury research is to develop strategies to reestablish innervation lost as a consequence of injury. The growth inhibitory nature of injured adult CNS tissue is a major barrier to regenerative axonal growth and sprouting. An increasing complexity of molecular players is being recognized. CNS inhibitors fall into three general classes: members of canonical axon guidance molecules (e.g., semaphorins, ephrins, netrins), prototypic myelin inhibitors (Nogo, MAG, and OMgp) and chondroitin sulfate proteoglycans (lecticans, NG2). On the other end of the spectrum are molecules that promote neuronal growth and sprouting. These include growth promoting extracellular matrix molecules, cell adhesion molecules, and neurotrophic factors. In addition to environmental (extrinsic) growth regulatory cues, cell intrinsic regulatory mechanisms exist that greatly influence injury-induced neuronal growth. Various degrees of growth and sprouting of injured CNS neurons have been achieved by lowering extrinsic inhibitory cues, increasing extrinsic growth promoting cues, or by activation of cell intrinsic growth programs. More recently, combination therapies that activate growth promoting programs and at the same time attenuate growth inhibitory pathways have met with some success. In experimental animal models of spinal cord injury (SCI), mono and combination therapies have been shown to promote neuronal growth and sprouting. Anatomical growth often correlates with improved behavioral outcomes. Challenges ahead include testing whether some of the most promising treatment strategies in animal models are also beneficial for human patients suffering from SCI.
Increased expression of certain extracellular matrix (ECM) molecules after CNS injury is believed to restrict axonal regeneration. The chondroitin sulfate proteoglycans (CSPGs) are one such class of ...ECM molecules that inhibit neurite outgrowth in vitro and are upregulated after CNS injury. We examined growth responses of several classes of axons to this inhibitory environment in the presence of a cellular fibroblast bridge in a spinal cord lesion site and after a growth factor stimulus at the lesion site (fibroblasts genetically modified to secrete NGF). Immunohistochemical analysis showed dense labeling of the CSPGs NG2, brevican, neurocan, versican, and phosphacan at the host-lesion interface after spinal cord injury (SCI). Furthermore, robust expression of NG2, and to a lesser extent versican, was also observed throughout grafts of control and NGF-secreting fibroblasts. Despite this inhibitory milieu, several axonal classes penetrated control fibroblast grafts, including dorsal column sensory, rubrospinal, and nociceptive axons. Axon growth was amplified more in the presence of NGF-secreting grafts. Confocal microscopy demonstrated that axon growth was, paradoxically, preferentially associated with NG2-rich substrates in both graft types. NG2 expression also increased after sciatic nerve injury, wherein axons successfully regenerate. Cellular sources of NG2 in SCI and peripheral nerve lesion sites included Schwann cells and endothelial cells. Notably, these same cellular sources in lesion sites produced the cell adhesion molecules L1 and laminin, and these molecules all colocalized. Thus, axons grow along substrates coexpressing both inhibitory and permissive molecules, suggesting that regeneration is successful when local permissive signals balance and exceed inhibitory signals.
Although axonal regeneration after CNS injury is limited, partial injury is frequently accompanied by extensive functional recovery. To investigate mechanisms underlying spontaneous recovery after ...incomplete spinal cord injury, we administered C7 spinal cord hemisections to adult rhesus monkeys and analyzed behavioral, electrophysiological and anatomical adaptations. We found marked spontaneous plasticity of corticospinal projections, with reconstitution of fully 60% of pre-lesion axon density arising from sprouting of spinal cord midline-crossing axons. This extensive anatomical recovery was associated with improvement in coordinated muscle recruitment, hand function and locomotion. These findings identify what may be the most extensive natural recovery of mammalian axonal projections after nervous system injury observed to date, highlighting an important role for primate models in translational disease research.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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