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Evaluation of apoptotic pathways in dorsal root ganglion neurons following peripheral nerve injury
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
2018 (English)In: NeuroReport, ISSN 0959-4965, E-ISSN 1473-558X, p. 779-785Article in journal (Refereed) Published
Abstract [en]

Peripheral nerve injuries induce significant sensory neuronal cell death in the dorsal root ganglia (DRG); however, the role of specific apoptotic pathways is still unclear. In this study, we performed peripheral nerve transection on adult rats, after which the corresponding DRGs were harvested at 7, 14, and 28 days after injury for subsequent molecular analyses with quantitative reverse transcription-PCR, western blotting, and immunohistochemistry. Nerve injury led to increased levels of caspase-3 mRNA and active caspase-3 protein in the DRG. Increased expression of caspase-8, caspase-12, caspase-7, and calpain suggested that both the extrinsic and the endoplasmic reticulum (ER) stress-mediated apoptotic pathways were activated. Phosphorylation of protein kinase R-like ER kinase further implied the involvement of ER-stress in the DRG. Phosphorylated protein kinase R-like ER kinase was most commonly associated with isolectin B4 (IB4)-positive neurons in the DRG and this may provide an explanation for the increased susceptibility of these neurons to die following nerve injury, likely in part because of an activation of the ER-stress response.

Place, publisher, year, edition, pages
Lippincott Williams & Wilkins, 2018. p. 779-785
National Category
Cell and Molecular Biology Neurosciences
Identifiers
URN: urn:nbn:se:umu:diva-127356DOI: 10.1097/WNR.0000000000001031ISI: 000433096700013PubMedID: 29659443OAI: oai:DiVA.org:umu-127356DiVA, id: diva2:1045418
Note

Originally included in thesis in manuscript form.

Available from: 2016-11-09 Created: 2016-11-09 Last updated: 2018-06-25Bibliographically approved
In thesis
1. An exploration of the mechanisms behind peripheral nerve injury
Open this publication in new window or tab >>An exploration of the mechanisms behind peripheral nerve injury
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Despite surgical innovation, the sensory and motor outcome after peripheral nerve injury is incomplete. In this thesis, the biological pathways potentially responsible for the poor functional recoveries were investigated in both the distal nerve stump/target organ, spinal motoneurons and dorsal root ganglia (DRG). The effect of delayed nerve repair was determined in a rat sciatic nerve transection model. There was a dramatic decline in the number of regenerating motoneurons and myelinated axons found in the distal nerve stumps of animals undergoing nerve repair after a delay of 3 and 6 months. RT-PCR of the distal nerve stumps showed a decline in expression of Schwann cells (SC) markers, with a progressive increase in fibrotic and proteoglycan scar markers, with increased delayed repair time. Furthermore, the yield of SC which could be isolated from the distal nerve segments progressively fell with increased delay in repair time. Consistent with the impaired distal nerve stumps the target medial gastrocnemius (MG) muscles at 3- and 6-months delayed repair were atrophied with significant declines in wet weights (61% and 27% compared with contralateral sides). The role of myogenic transcription factors, muscle specific microRNAs and musclespecific E3 ubiquitin ligases in the muscle atrophy was investigated in both gastrocnemius and soleus muscles following either crush or nerve transection injury. In the crush injury model, the soleus muscle showed significantly increased recovery in wet weight at days 14 and 28 (compared with day 7) which was not the case for the gastrocnemius muscle which continued to atrophy. There was a significantly more pronounced up-regulation of MyoD expression in the denervated soleus muscle compared with the gastrocnemius muscle. Conversely, myogenin was more markedly elevated in the gastrocnemius versus soleus muscles. The muscles also showed significantly contrasting transcriptional regulation of the microRNAs miR-1 and miR-206. MuRF1 and Atrogin-1 showed the highest levels of expression in the denervated gastrocnemius muscle. Morphological and molecular changes in spinal motoneurons were compared after L4-L5 ventral root avulsion (VRA) and distal peripheral nerve axotomy (PNA). Neuronal degeneration was indicated by decreased immunostaining for microtubule-associated protein-2 in dendrites and synaptophysin in presynaptic boutons after both VRA and PNA. Immunostaining for ED1-reactive microglia and GFAPpositive astrocytes was significantly elevated in all experimental groups. qRT-PCR analysis and Western blotting of the ventral horn from L4-L5 spinal cord segments revealed a significant upregulation of apoptotic cell death mediators including caspases-3 and -8 and a range of related death receptors following VRA. In contrast, following PNA, only caspase-8 was moderately upregulated. The mechanisms of primary sensory neuron degeneration were also investigated in the DRG following peripheral nerve axotomy, where several apoptotic pathways including those involving the endoplasmic reticulum were shown to be upregulated. In summary, these results show that the critical time point after which the outcome of regeneration becomes too poor appears to be 3-months. Both proximal and distal injury affect spinal motoneurons morphologically, but VRA induces motoneuron degeneration mediated through both intrinsic and extrinsic apoptotic pathways. Primary sensory neuron degeneration involves several different apoptotic pathways, including the endoplasmic reticulum.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. p. 53
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1853
Keywords
Peripheral nerve injury, target organ, spinal motoneurons, primary sensory neurons, degeneration
National Category
Cell and Molecular Biology
Research subject
Human Anatomy
Identifiers
urn:nbn:se:umu:diva-127357 (URN)978-91-7601-591-9 (ISBN)
Public defence
2016-12-02, Sal KB3A9, KBC-huset, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2016-11-11 Created: 2016-11-09 Last updated: 2018-06-09Bibliographically approved

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Wiberg, RebeccaNovikova, Liudmila NKingham, Paul J.

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