Loss Of Sensory Neurons Research Articles

Chitosan/gelatin hydrogel and endometrial stem cells with subsequent atorvastatin injection impact in regenerating spinal cord tissue

Central nervous system trauma can cause loss of functional sensory neurons and motor functions that results in death of neuronal cells and axon degeneration. For this purpose, therapeutic approaches to enhance repair mechanisms spinal cord injury (SCI) is reflected to be a difficult task that requires thoughtful strategy. Hydrogel scaffolds in the presence of stem cells could repair damaged SCI due to their ability to support cellular viability, motility, and differentiation. In this study, we investigated the effectiveness of a biomimetic composite hydrogel of chitosan and gelatin containing endometrial stem cells (EnSCs) as a minimally invasive treatment of SCI in an animal model. Moreover, the simultaneous, effect of intraperitoneal injection of atorvastatin drug was assessed for animal models. From the results, morphological and cell viability studies demonstrated favorable seeding microenvironment and viability in the hydrogel. The transplanted hydrogel containing EnSCs into hemisected SCI rats showed recovery of sensory and motor functions by confirming locomotor activity evaluation using Basso, Beattie, and Bresnahan test. The growth of neuronal cells confirmed with immunohistochemical study. The findings in this study suggested that combination therapy using biomimetic hydrogel seeded with stem cells as well as atorvastatin injection has the potential to heal SCI through neuroinflammation attenuation, improvement of functional recovery, and limit the secondary damages.

Differential Effects of Nasal Inflammation and Odor Deprivation on Layer-Specific Degeneration of the Mouse Olfactory Bulb.

Harmful environmental agents cause nasal inflammation, and chronic nasal inflammation induces a loss of olfactory sensory neurons (OSNs) and reversible atrophy of the olfactory bulb (OB). Here, we investigated the mechanisms underlying this inflammation-induced OB atrophy by histologically and biochemically comparing the OB changes in mouse models of nasal inflammation and odor deprivation. In addition, we examined whether odor stimulation is necessary for OB recovery from atrophy. One group of adult male C57BL/6 mice was administered lipopolysaccharide (LPS) unilaterally for 10 weeks to induce nasal inflammation (control animals received saline), and a second group received unilateral naris closures (NCs) for 10 weeks of odor deprivation. The OBs atrophied in both models, but odor deprivation shrank the glomerular, external plexiform, mitral, and granule cell layers (GCLs), whereas the olfactory nerve, glomerular, and external plexiform layers (EPLs) atrophied as a result of nasal inflammation. Additionally, nasal inflammation, but not odor deprivation, caused neuroinflammation in the OB, inducing glial activation and elevated expression of interleukin-1β (IL-1β) and TNFα. After 10 weeks of nasal inflammation, mice were housed for another 10 weeks with no additional treatment or with unilateral NC. Nasal inflammation and glial activation subsided in both groups, but glomerular and EPLs recovered only in those with no additional treatment. Our findings demonstrate that nasal inflammation and odor deprivation differentially induce layer-specific degeneration in the OB, that loss of OSN activity rather than neuroinflammation is a major cause of inflammation-induced OB atrophy, and that odor stimulation is required for OB recovery from atrophy.

Neural crest and placode roles in formation and patterning of cranial sensory ganglia in lamprey.

Vertebrates possess paired cranial sensory ganglia derived from two embryonic cell populations, neural crest and placodes. Cranial sensory ganglia arose prior to the divergence of jawed and jawless vertebrates, but the developmental mechanisms that facilitated their evolution are unknown. Using gene expression and cell lineage tracing experiments in embryos of the sea lamprey, Petromyzon marinus, we find that in the cranial ganglia we targeted, development consists of placode-derived neuron clusters in the core of ganglia, with neural crest cells mostly surrounding these neuronal clusters. To dissect functional roles of neural crest and placode cell associations in these developing cranial ganglia, we used CRISPR/Cas9 gene editing experiments to target genes critical for the development of each population. Genetic ablation of SoxE2 and FoxD-A in neural crest cells resulted in differentiated cranial sensory neurons with abnormal morphologies, whereas deletion of DlxB in cranial placodes resulted in near-total loss of cranial sensory neurons. Taken together, our cell-lineage, gene expression, and gene editing results suggest that cranial neural crest cells may not be required for cranial ganglia specification but are essential for shaping the morphology of these sensory structures. We propose that the association of neural crest and placodes in the head of early vertebrates was a key step in the organization of neurons and glia into paired sensory ganglia.

Efficacy of autologous bone marrow mononuclear cell transplantation in dogs with chronic spinal cord injury.

Background:Spinal cord injury (SCI) is relatively common in dogs and is a devastating condition involving loss of sensory neurons and motor neurons. However, the main clinical protocol for the management of SCI is surgery to decompress and stabilize the vertebra. Cell transplantation therapy is a very promising strategy for the treatment of chronic SCI, but extensive preclinical and clinical research work remains.Aim:The aim of this study is to confirm the effect of bone marrow-derived mononuclear cell (BM-MNC) transplantation for chronic SCI in dogs.Methods:We tested the treatment efficiency of chronic SCI in 12 dogs using BM-MNC transplantation. Neurological evaluation used the Texas Spinal Cord Injury Scale (TSCIS). Concurrently, we characterized the transplanted cells by evaluation using quantitative real-time polymerase chain reaction, flow cytometry, and enzyme-linked immunosorbent assay.Result:All dogs had a pre-transplantation TSCIS score of 0. Two animals did not show any improvement in their final TSCIS scores. The remaining 10 dogs (83.4%) achieved improvement in the final TSCIS scores. Five of them (41.7%) regained ambulatory function with a TSCIS score greater than 10. We determined that canine BM-MNCs expressed hepatocyte growth factor (HGF) mRNA at higher levels than other cytokines, with significant increases in HGF levels in cerebrospinal fluid within 48 hours after autologous BM-MNC transplantation into the subarachnoid space of the spinal dura matter in dogs.Conclusions:BM-MNC transplantation may be effective for at least some cases of chronic SCI.

Looking into nerve damage in the cornea.

Interactions between T helper cells and the complement system promote loss of sensory neurons in the eye.

Toxoplasma gondii alters NMDAR signaling and induces signs of Alzheimer's disease in wild‐type, C57BL/6 mice

Alzheimer's disease (AD) is a progressive neurodegenerative disease associated with cognitive decline, resulting in a complete loss of basic functions. The ubiquitous apicomplexan parasite Toxoplasma gondii (T. gondii) infects up to one third of the world's population and is implicated in AD. We infected C57BL/6 wild‐type male and female mice with 10 T. gondii ME49 cysts and assessed whether infection led to behavioral and anatomical effects using immunohistochemistry, immunofluorescence, Western blotting, cell culture assays, as well as an array of mouse behavior tests. We previously reported that T. gondii infection induced two major hallmarks of AD in the brains of C57BL/6 male and female mice: beta‐amyloid (Aβ) immunoreactivity and hyperphosphorylated Tau. Infected mice showed significant neuronal death, loss of N‐methyl‐D‐aspartate receptor (NMDAR) expression, and loss of olfactory sensory neurons. T. gondii infection also caused anxiety‐like behavior, altered recognition of social novelty, altered spatial memory, and reduced olfactory sensitivity. We have new data that suggests that T. gondii might be recruiting the NMDA receptor to the parasitophorous vacuole, a structure that protects T. gondii from the phagolysosomes of its host. This indicates that T. gondii might use the NMDA receptor of the host to survive and might explain the reduction of NMDAR that we observed with T. gondii infection. Since reduced NMDAR expression coincides with Aβ immunoreactivity, it is possible that T. gondii infection leads to reduced NMDAR expression which then leads to Aβ immunoreactivity.Support or Funding InformationThis work was supported by NIH grant R01 NS063011 to M.S BynoeThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Phosphodiesterase Inhibitors Revert Axonal Dystrophy in Friedreich's Ataxia Mouse Model.

Friedreich's ataxia (FRDA) is a neurodegenerative disorder caused by an unstable GAA repeat expansion within intron 1 of the FXN gene and characterized by peripheral neuropathy. A major feature of FRDA is frataxin deficiency with the loss of large sensory neurons of the dorsal root ganglia (DRG), namely proprioceptive neurons, undergoing dying-back neurodegeneration with progression to posterior columns of the spinal cord and cerebellar ataxia. We used isolated DRGs from a YG8R FRDA mouse model and C57BL/6J control mice for a proteomic study and a primary culture of sensory neurons from DRG to test novel pharmacological strategies. We found a decreased expression of electron transport chain (ETC) proteins, the oxidative phosphorylation (OXPHOS) system and antioxidant enzymes, confirming a clear impairment in mitochondrial function and an oxidative stress-prone phenotype. The proteomic profile also showed a decreased expression in Ca2+ signaling related proteins and G protein-coupled receptors (GPCRs). These receptors modulate intracellular cAMP/cGMP and Ca2+ levels. Treatment of frataxin-deficient sensory neurons with phosphodiesterase (PDE) inhibitors was able to restore improper cytosolic Ca2+ levels and revert the axonal dystrophy found in DRG neurons of YG8R mice. In conclusion, the present study shows the effectiveness of PDE inhibitors against axonal degeneration of sensory neurons in YG8R mice. Our findings indicate that PDE inhibitors may become a future FRDA pharmacological treatment.

Abstract # 2045 Nasal inflammatory stage-associated plastic changes in the olfactory bulb neurocircuit

We are exposed to harmful environmental agents that may cause nasal inflammation. Although prolonged nasal inflammation results in long-lasting olfactory loss, little is known about the influence of chronic nasal inflammation on the olfactory bulb (OB). We made a mouse model of chronic nasal inflammation by repeatedly administering lipopolysaccharide (LPS) to nostril and histologically analyzed changes in the olfactory epithelium (OE) and OB. Mice received LPS or saline every other day (3 times per week) for 3, 10, 18 or 24 weeks. For the recovery analyses, the mice treated with LPS for 10 weeks were housed without treatment for another 10 weeks. LPS induced OE inflammation with a loss of olfactory sensory neurons (OSNs). More than 10 weeks of LPS administration caused robust OB atrophy with a complete loss of OSNs. In atrophied OB, a prominent shrinkage occurred in the external plexiform layer (EPL) in addition to the olfactory nerve and glomerular layers. The superficial layer of the EPL, in which tufted cells form dendrodendritic synapses with interneurons, underwent shrinkage in a selective manner, although neither tufted cells nor interneurons underwent cell death. The atrophied OB returned to the normal size after the 10-week period of no treatment. These indicate a particular OB circuit, in which tufted cells are involved, is vulnerable to a chronic nasal inflammation but retains high plasticity to recover from atrophy.

Loss or Gain of Function Mutations in <i>ACOX1</i> Cause Axonal Loss Via Different Mechanisms

ACOX1 (acyl-CoA oxidase 1) encodes the first and rate-limiting enzyme in very-long-chain fatty acid (VLCFA) β-oxidation in peroxisomes and produces H2O2. Unexpectedly, dACOX1 is mostly expressed and required in glia, and its loss in flies leads to developmental delay and pupal death. Flies that escape death exhibit a severely reduced lifespan, impaired synaptic transmission, and pronounced glial and axonal loss. Patients who carry a previously unidentified, de novo, heterozygous variant in ACOX1 (p.N237S) also exhibit axonal loss. However, this mutation causes increased levels of ACOX1 and reactive oxygen species in insulating glia in flies and Schwann cells in mice. Similarly, ACOX1 (p.N237S) patients exhibit a severe loss of Schwann cells, motor and sensory neurons. Treatment of flies, primary Schwann cells and a patient with an anti-oxidant suppresses these phenotypes. In summary, both loss and gain-of ACOX1 leads to glial and neuronal loss, but via different mechanisms and require different treatments.

Neuroplastic changes in the olfactory bulb associated with nasal inflammation in mice

Rhinitis and rhinosinusitis are olfactory disorders caused by inflammation of the nasal passage and paranasal sinuses. Although patients with chronic rhinosinusitis have smaller olfactory bulbs (OBs), there is limited knowledge regarding the influence of chronic nasal inflammation on OB neurons. Repeated intranasal administration of LPS that induced persistent nasal inflammation in mice caused a loss of olfactory sensory neurons (OSNs) and gliosis and synaptic loss in the OBs within 3weeks. The present study aimed to clarify the effects of long-term LPS treatment on the OB neurocircuit. LPS was repeatedly administered into a mouse nostril for up to 24weeks. For the recovery analyses, the mice received LPS for 10weeks and were subsequently maintained without additional treatment for another 10weeks. The effects of these treatments on the OBs were examined histologically. Three or more mice were analyzed per group. Long-term repeated LPS administration caused OB atrophy, particularly in the layers along which OSN axons travel and in the superficial external plexiform layer, in which tufted cells form synapses with interneurons. Interestingly, the OBs recovered from atrophy after cessation of LPS administration: OB volume and superficial external plexiform layer thickness returned to pretreatment levels after the nontreatment period. In contrast, OSN regeneration was incomplete. These results suggest that chronic nasal inflammation induces structural changes in a specific OB circuit related to tufted cells, whereas tufted cells retain a high degree of plasticity that enables recovery from structural damages after inflammation subsides.

Voluntary Exercise Modifies Olfactory Circuits in Control‐ and Fat‐Fed Mice

Consumption of a fatty diet causes loss of olfactory sensory neurons (OSNs), loss of olfactory discrimination assessed by olfactometry and electroolfactogram, and increased inflammation in the olfactory epithelium. Because of potential anti‐inflammatory properties of voluntary exercise, we hypothesized it could mitigate the detrimental effects of a fatty diet on the olfactory system. Mice with reporters for the olfactroy receptor M72 (Olfr160) and those with resistance to diet‐induced obesity (Kv1.3−/−) were challenged with control (CF) vs. moderately‐high fat (MHF) diet for 6 months upon weaning, with (running wheel; RW) and without access (sedentary; SED) to a Med Associates vertical wireless running wheel and sensor. MHF/RW mice (n=10; mean 7 month body weight = 40.1 g) gained less body weight than MHF/SED (n=10; 33.3 g, p<0.001) and were able to clear plasma glucose as efficiently as CF/SED mice. Although mice of all treatment groups ran at the same velocity, those provided MHF diet (distance run/day = 11.2 km) increased running distance compared to both CF‐fed WT (n=10) and Kv1.3−/− (n=5) mice (6.85 km/day and 8.29 km/day respectively; p=0.02). Actogram analysis demonstrated that CF‐fed Kv1.3−/− and MHF/RW spend 20.2% and 28.3%, respectively, more time running and exhibit shorter pauses in running activity than CF/RW. Whole‐mount brain images were examined to evaluate M72 staining as quantified by the pixel density of the lateral glomerulus and projections. MHF/RW M72 pixel density was twice as much as MHF/SED mice, but CF/RW pixel density was 31.6% lower than that of CF/SED mice. Our results indicate that in addition to combating weight gain and glucose intolerance, voluntary exercise may reduce the detrimental effects of a MHF diet on olfaction, but exercise may also affect the olfactory system independent of diet composition.Support or Funding InformationThis was supported by NIH grant RO1 DC013080 from the NIDCD and a Dean's Arts and Sciences Scholarship in the Chemical Senses from FSU.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Toxoplasma gondii alters NMDAR signaling and induces signs of Alzheimer\u2019s disease in wild-type, C57BL/6 mice

BackgroundAlzheimer’s disease (AD) is a progressive neurodegenerative disease associated with cognitive decline and complete loss of basic functions. The ubiquitous apicomplexan parasite Toxoplasma gondii (T. gondii) infects up to one third of the world’s population and is implicated in AD.MethodsWe infected C57BL/6 wild-type male and female mice with 10 T. gondii ME49 cysts and assessed whether infection led to behavioral and anatomical effects using immunohistochemistry, immunofluorescence, Western blotting, cell culture assays, as well as an array of mouse behavior tests.ResultsWe show that T. gondii infection induced two major hallmarks of AD in the brains of C57BL/6 male and female mice: beta-amyloid (Aβ) immunoreactivity and hyperphosphorylated Tau. Infected mice showed significant neuronal death, loss of N-methyl-d-aspartate receptor (NMDAR) expression, and loss of olfactory sensory neurons. T. gondii infection also caused anxiety-like behavior, altered recognition of social novelty, altered spatial memory, and reduced olfactory sensitivity. This last finding was exclusive to male mice, as infected females showed intact olfactory sensitivity.ConclusionsThese results demonstrate that T. gondii can induce advanced signs of AD in wild-type mice and that it may induce AD in some individuals with underlying health problems.

Brain-derived neurotrophic factor derived from sensory neurons plays a critical role in chronic pain.

Many studies support the pro-nociceptive role of brain-derived neurotrophin factor (BDNF) in pain processes in the peripheral and central nervous system. We have previously shown that nociceptor-derived BDNF is involved in inflammatory pain. Microglial-derived BDNF has also been shown to be involved in neuropathic pain. However, the distinct contribution of primary afferent-derived BNDF to chronic pain processing remains undetermined. In this study, we used Avil-CreERT2 mice to delete Bdnf from all adult peripheral sensory neurons. Conditional BDNF knockouts were healthy with no sensory neuron loss. Behavioural assays and in vivo electrophysiology indicated that spinal excitability was normal. Following formalin inflammation or neuropathy with a modified Chung model, we observed normal development of acute pain behaviour, but a deficit in second phase formalin-induced nocifensive responses and a reversal of neuropathy-induced mechanical hypersensitivity during the later chronic pain phase in conditional BDNF knockout mice. In contrast, we observed normal development of acute and chronic neuropathic pain in the Seltzer model, indicating differences in the contribution of BDNF to distinct models of neuropathy. We further used a model of hyperalgesic priming to examine the contribution of primary afferent-derived BDNF in the transition from acute to chronic pain, and found that primed BDNF knockout mice do not develop prolonged mechanical hypersensitivity to an inflammatory insult. Our data suggest that BDNF derived from sensory neurons plays a critical role in mediating the transition from acute to chronic pain.

Olfactory loss in chronic rhinosinusitis is associated with neuronal activation of c-Jun N-terminal kinase.

Olfactory inflammation in chronic rhinosinusitis (CRS) is associated with cytokines that may result in the death of olfactory sensory neurons. The principal signaling molecules involved in the apoptotic pathway are c-Jun N-terminal kinases (JNK). Although the JNK pathway has emerged as a key player in programmed cell death in neuroinflammation, its specific role in CRS-associated olfactory loss has not been thoroughly investigated. JNK activation was studied in human tissue samples from 9 control and 11 CRS patients by immunohistochemical staining for phosphorylated c-Jun. A mouse model of inducible olfactory cytokine expression was used to experimentally control inflammation and assess JNK activation over time. In patients with CRS, activation of c-Jun is significantly increased relative to non-CRS control subjects, and there is an associated loss of sensory neurons. In the olfactory inflammation mouse model, prolonged induction of inflammation results in elevation of c-Jun expression and neuronal apoptosis. Activation of neuronal JNK is a feature of chronic olfactory inflammation that is associated with neuronal apoptosis. Given that inhibition of JNK activity is neuroprotective in other settings, antagonism of this pathway may have therapeutic potential in the management of inflammatory olfactory loss or other disorders linked to olfactory neuronal apoptosis.

Lipopolysaccharide-initiated persistent rhinitis causes gliosis and synaptic loss in the olfactory bulb

The olfactory mucosa (OM) is exposed to environmental agents and therefore vulnerable to inflammation. To examine the effects of environmental toxin-initiated OM inflammation on the olfactory bulb (OB), we induced persistent rhinitis in mice and analyzed the spatial and temporal patterns of histopathological changes in the OM and OB. Mice received unilateral intranasal administration of lipopolysaccharide (LPS) or saline three times per week, and were immunohistologically analyzed at 1, 3, 7, 14 and 21 days after the first administration. LPS administration induced an inflammatory response in the OM, including the infiltration of Ly-6G-, CD11b-, Iba-1- and CD3-positive cells, the production of interleukin-1β by CD11b- and Iba-1-positive cells, and loss of olfactory sensory neurons (OSNs). In the OB, we observed activation of microglia and astrocytes and decreased expression of tyrosine hydroxylase in periglomerular cells, vesicular glutamate transporter 1, a presynaptic protein, in mitral and tufted projection neurons, and 5T4 in granule cells. Thus, the OM inflammation exerted a detrimental effect, not only on OSNs, but also on OB neurons, which might lead to neurodegeneration.

Reversible Axonal Dystrophy by Calcium Modulation in Frataxin-Deficient Sensory Neurons of YG8R Mice.

Friedreich’s ataxia (FRDA) is a peripheral neuropathy involving a loss of proprioceptive sensory neurons. Studies of biopsies from patients suggest that axonal dysfunction precedes the death of proprioceptive neurons in a dying-back process. We observed that the deficiency of frataxin in sensory neurons of dorsal root ganglia (DRG) of the YG8R mouse model causes the formation of axonal spheroids which retain dysfunctional mitochondria, shows alterations in the cytoskeleton and it produces impairment of axonal transport and autophagic flux. The homogenous distribution of axonal spheroids along the neurites supports the existence of continues focal damages. This lead us to propose for FRDA a model of distal axonopathy based on axonal focal damages. In addition, we observed the involvement of oxidative stress and dyshomeostasis of calcium in axonal spheroid formation generating axonal injury as a primary cause of pathophysiology. Axonal spheroids may be a consequence of calcium imbalance, thus we propose the quenching or removal extracellular Ca2+ to prevent spheroids formation. In our neuronal model, treatments with BAPTA and o-phenanthroline reverted the axonal dystrophy and the mitochondrial dysmorphic parameters. These results support the hypothesis that axonal pathology is reversible in FRDA by pharmacological manipulation of intracellular Ca2+ with Ca2+ chelators or metalloprotease inhibitors, preventing Ca2+-mediated axonal injury. Thus, the modulation of Ca2+ levels may be a relevant therapeutic target to develop early axonal protection and prevent dying-back neurodegeneration.

The combined strategy of mesenchymal stem cells and tissue-engineered scaffolds for spinal cord injury regeneration.

Spinal cord injury (SCI) is a traumatic lesion that can result in the loss of motor or sensory neurons. Stem cell (SC)-based therapies have been demonstrated to promote neuronal regeneration following SCI, by releasing a range of trophic factors that support endogenous repair or by differentiating into neurons, or glial cells in order to replace the damaged cells. However, numerous limitations remain for therapies based on SC transplantion alone, including a low rate of survival/engraftment. Nevertheless, scaffolds are 3-dimentional substrates that have revealed to support cell survival, proliferation and differentiation in vivo, by mimicking a more favorable endogenous microenvironment. A multidisciplinary approach, which combines engineered scaffolds with SCs has been proposed as a promising strategy for encouraging spinal cord regeneration. The present review has focused on the regenerative potential of mesenchymal SCs isolated from different sources and combined with various scaffold types, in preclinical and clinical SCI studies.

N-Acetylcysteine Prevents Retrograde Motor Neuron Death after Neonatal Peripheral Nerve Injury.

Neuronal death may be an overlooked and unaddressed component of disability following neonatal nerve injuries, such as obstetric brachial plexus injury. N-acetylcysteine and acetyl-L-carnitine improve survival of neurons after adult nerve injury, but it is unknown whether they improve survival after neonatal injury, when neurons are most susceptible to retrograde neuronal death. The authors' objective was to examine whether N-acetylcysteine or acetyl-L-carnitine treatment improves survival of neonatal motor or sensory neurons in a rat model of neonatal nerve injury. Rat pups received either a sciatic nerve crush or transection injury at postnatal day 3 and were then randomized to receive either intraperitoneal vehicle (5% dextrose), N-acetylcysteine (750 mg/kg), or acetyl-L-carnitine (300 mg/kg) once or twice daily. Four weeks after injury, surviving neurons were retrograde-labeled with 4% Fluoro-Gold. The lumbar spinal cord and L4/L5 dorsal root ganglia were then harvested and sectioned to count surviving motor and sensory neurons. Transection and crush injuries resulted in significant motor and sensory neuron loss, with transection injury resulting in significantly less neuron survival. High-dose N-acetylcysteine (750 mg/kg twice daily) significantly increased motor neuron survival after neonatal sciatic nerve crush and transection injury. Neither N-acetylcysteine nor acetyl-L-carnitine treatment improved sensory neuron survival. Proximal neonatal nerve injuries, such as obstetric brachial plexus injury, produce significant retrograde neuronal death after injury. High-dose N-acetylcysteine significantly increases motor neuron survival, which may improve functional outcomes after obstetrical brachial plexus injury.

54. Prevention of Sensory Ataxia in a Novel Mouse Model of Friedreich Ataxia Using Gene Therapy Approach

Friedreich's ataxia (FRDA), the most common autosomal recessive ataxia, is characterized by a sensory and spinocerebellar ataxia, hypertrophic cardiomyopathy and increase incidence of diabetes. FRDA is caused by reduced levels of frataxin (FXN), an essential mitochondrial protein involved in the biosynthesis of iron-sulfur (Fe-S) clusters. Impaired mitochondrial oxidative phosphorylation, bioenergetics imbalance, deficit of Fe-S cluster enzymes and mitochondrial iron overload occur in individuals with FRDA. Proprioceptive neurons within the dorsal root ganglia (DRG) and cardiomyocytes are the most affected tissues in FRDA patients. To date there are not effective treatment for FRDA. We have previously established the primary proof-of-concept for developing gene therapy of FRDA cardiomyopathy and showed that adeno-associated virus (AAV) rh. 10 vector expressing human FXN injected intravenously not only prevented the onset of the cardiac disease in a faithful FRDA cardiac mouse model, but also, when administered at the time of heart failure, rapidly and completely reversed the cardiac disease. To date, there were unfortunately no adequate neuronal mouse model to address the possibility of gene therapy for the neuronal aspects of FRDA. We therefore recently generated a novel mouse model that recapitulates faithfully the sensory ataxia associated to FRDA using the conditional approach to delete frataxin specifically in the proprioceptive neurons of the DRG. By behavioural analysis, the mice exhibit an ataxic phenotype beginning at 3 weeks of age, which is rapidly progressive. Electrophysiological studies reveal a significant decrease of sensory wave already at 4.5 weeks and almost a complete loss at 8 weeks of age. A significant loss of sensory neurons within dorsal root ganglia is observed at 17.5 weeks of age compare to age matched controls. Ultrastructural analysis of sciatic and saphenous nerves showed abnormalities at early time points. Using this mouse model, we have developed an AAV gene therapy approach based on an intravenous delivery of AAV9-CAG-hFXN-HA vector at an early symptomatic stage of the disease. Mice displayed a complete prevention of the ataxic phenotype and electrophysiological analysis showed maintenance of the sensory wave in the treated animals. Histological studies revealed a complete prevention of neuronal loss in the DRG as well as a normal ultrastructure of saphenous and sciatic nerve. As results are encouraging, we plan to evaluate the potential therapeutical effect at a more advanced stage of the disease.

Neuronal death in the dorsal root ganglion after sciatic nerve injury does not depend on sortilin

Injury to the sciatic nerve induces loss of sensory neurons in the affected dorsal root ganglia (DRGs). Previous studies have suggested the involvement of the neurotrophin receptors p75 neurotrophin receptor (p75NTR) and sortilin, proposing that sensory neuron subpopulations undergo proneurotrophin-induced apoptosis in a similar manner to what can be observed in the CNS following injury. To further investigate this hypothesis we induced sciatic nerve injury in sortilin-deficient mice, thereby preventing apoptotic signaling of proneurotrophins via the sortilin-p75NTR receptor complex. Using an unbiased stereological approach we found that loss of sortilin did not prevent the injury-induced loss of DRG neurons. This result demonstrates that previous findings linking p75NTR and proneurotrophins to loss of sensory neurons need to involve sortilin-independent pathways and suggests that proneurotrophins may elicit different functions in the CNS and PNS.