Human Dorsal Root Ganglia are Either Preserved or Completely Lost After Deafferentation by Brachial Plexus Injury
Paper Title: Human Dorsal Root Ganglia Are Either Preserved or Completely Lost After Deafferentation by Brachial Plexus Injury
Authors:
Annemarie Sodmann, Johannes Degenbeck, Annemarie Aue, Magnus Schindehütte, Felicitas Schlott, Panagiota Arampatzi, Thorsten Bischler, Max Schneider, Alexander Brack, Camelia M. Monoranu, Tom Gräfenhan, Michael Bohnert, Mirko Pham, Gregor Antoniadis, Robert Blum, Heike L. Rittner
Journal:
British Journal of Anaesthesia, 133(6): 1250-1262 (2024)
DOI:
10.1016/j.bja.2024.09.004
Publication Date:
11 October 2024
Abstract
Background:
Brachial plexus injury (BPI) results in lifelong suffering from flaccid paralysis, sensory loss, and intractable pain. Regenerative medicine concepts hold high expectations for addressing this clinical problem. However, little is known about how dorsal root ganglia (DRG) are affected by accidental deafferentation.
Methods:
This study phenotyped DRG from a clinically and MRI-characterized cohort of 13 patients with brachial plexus injury. Avulsed DRG were collected during reconstructive nerve surgery, and control DRG were obtained from forensic autopsies. The cellular composition of DRG was analyzed using histopathological slices with multicolor high-resolution immunohistochemistry, tile microscopy, and deep-learning-based bioimage analysis. Bulk RNA sequencing of corresponding DRG slices was also performed.
Results:
In about half of the patients, the typical DRG units consisting of neurons and satellite glial cells (SGCs) were lost and replaced by mesodermal/connective tissue. In the remaining patients, the cellular units were well preserved. Preoperative plexus MRI neurography could not distinguish between the two types. Patients with “neuronal preservation” had less maximum pain than those with “neuronal loss.” Arm function improved after nerve reconstruction, but severe pain persisted. Transcriptome analysis of preserved DRGs revealed expression of subtype-specific sensory neuron marker genes but downregulation of neuronal attributes. Additionally, signs of ongoing inflammation and connective tissue remodeling were observed.
Conclusions:
Patients with brachial plexus injury can be divided into two groups based on either neuronal preservation or neuronal loss. The former group may benefit from anti-inflammatory therapy, while the latter group requires further exploration of mechanisms of neuronal loss, especially for regenerative approaches.
Clinical Trial Registration:
DRKS00017266
Keywords:
Deafferentation, Dorsal Root Ganglia, Nerve Injury, Neuropathic Pain, RNA-seq, Sensory Neuron, Transcriptome
Introduction
Brachial plexus injury, primarily resulting from traffic accidents, leads to profound functional impairments. Typically, ventral and dorsal roots are avulsed at the dorsal root entry zone, disconnecting the axonal projections of sensory neurons in the DRG from their natural targets. In upper supraclavicular brachial plexus injury, 69-84% of patients with total palsy report pain, often resulting in lifelong disability. Surgical interventions, such as neurolysis, nerve grafting, and nerve transfer, aim to restore motor function, but sensory function and pain are rarely improved.
Little is known about the fate of DRG after plexus injury in humans. Previous studies have provided some insights into gene expression changes after injury, but the cellular composition and fate of DRG units remain largely unknown. This study aims to investigate the molecular and cellular changes in DRG after brachial plexus injury to inform future therapeutic strategies.
Methods
Patient Recruitment:
The study was approved by the local ethical committee and registered at the German Clinical Trials Registry (DRKS00017266). The cohort included 13 patients with brachial plexus injury, mostly due to motorcycle accidents. Control DRG were obtained from seven forensic autopsy cases.
Preoperative MRI Neurography:
Patients underwent 3T MRI neurography to visualize the injury extent and affected roots.
Tissue Preparation and Staining:
DRG were harvested during reconstructive surgery, fixed, and sectioned for histopathological analysis. Immunofluorescence staining was performed to label sensory neurons, SGCs, and macrophages.
RNA Sequencing:
RNA was isolated from DRG slices, and bulk RNA sequencing was performed to analyze gene expression changes.
Statistical Analysis:
Data were analyzed using GraphPad Prism software, with detailed methods provided in the supplementary material.
Results
Study Overview:
The study investigated the molecular and cellular phenotype of DRG in patients with brachial plexus injury. Preoperative MRI determined the injury extent, and DRG were harvested during reconstructive surgery. Histological analysis revealed that about half of the patients had lost typical DRG units, leading to categorization into “neuronal preservation” and “neuronal loss” groups.
Clinical Characterization:
Patients with brachial plexus injury reported moderate to severe pain, with neuropathic symptoms and significant impairment in daily life. Preoperative MRI could not distinguish between DRG preservation and loss.
Neuronal Loss vs. Neuronal Preservation:
In patients with “neuronal loss,” DRG were replaced by fat cells and connective tissue, with no evidence of neurons or SGCs. In contrast, patients with “neuronal preservation” had well-preserved DRG structures.
Transcriptome Analysis:
RNA sequencing revealed upregulated genes related to inflammation and extracellular matrix organization in preserved DRGs, while neuronal processes were downregulated. Marker genes for sensory neuron subtypes were preserved, but neuronal function was impaired.
Discussion
The study found that brachial plexus injury leads to two distinct outcomes in DRG: neuronal preservation or neuronal loss. Patients with neuronal preservation had less severe pain and may benefit from anti-inflammatory therapy. In contrast, patients with neuronal loss require further investigation into the mechanisms of neuronal loss to develop regenerative approaches.
The findings highlight the importance of early intervention to protect DRG and suggest that future MRI techniques may help non-invasively assess DRG status. The study provides a foundation for personalized treatment strategies and regenerative medicine approaches for brachial plexus injury.
Conclusion
In summary, DRG respond to nerve injury in different ways depending on the injury’s location, mechanism, and extent. Future research should focus on improving MRI methods to quantify DRG cell body-rich areas and understand when and why neuron/SGC units are lost. This could lead to personalized treatments and regenerative approaches for patients with brachial plexus injury.
Authors’ Contributions
- Conception and study design: AA, AS, GA, TG, MB, MP, MS, RB, HLR
- Acquisition of data: AA, AS, JD, PA, TB, FS, MS, MB, GA, RB, HLR
- Analysis and interpretation of data: All authors
- Writing initial draft: AS, JD, RB, HLR
- Critical revision of the manuscript: All authors
- Study supervision: RB, HLR
Acknowledgements
The authors thank all patients and their physicians for participating in the study. They also acknowledge technical support from Olivia Rudtke and the staff of the Peripheral Nerve Surgery Unit, University of Ulm.
Declarations of Interest
HLR received consultant fees from Grünenthal and Orion, and financial support for a study by Algiax. All other authors declare no conflicts of interest.
Funding
The study was supported by the Evangelisches Studienwerk Villigst, the Graduate School of Life Sciences, University of Würzburg, the Interdisciplinary Center for Clinical Research Würzburg, and the German Research Foundation.
Data Availability Statement
Images, segmentation data, and deep learning models are available at Zenodo. RNA-seq data will be available through the European Genome-Phenome Archive or upon request.
Supplementary Data
Supplementary data can be found online at https://doi.org/10.1016/j.bja.2024.09.004.