Laboratory study Plasticity of gene expression in injured human dorsal root ganglia revealed by GeneChip oligonucleotide microarrays Douglas Rabert 1,* PHD PHD, Yuanyuan Xiao 2,* PHD PHD, Yiangos Yiangou 3 PHD PHD, Dirk Kreder 1,y Lakshmi Sangameswaran 1,z PHD PHD, Mark R. Segal 4 PHD PHD, C. Anthony Hunt 2 PHD PHD, Rolfe Birch 5 FRCS FRCS, Praveen Anand 3 FRCP FRCP 1 Neurobiology Unit, Roche Bioscience, Palo Alto, CA, USA, 2 Department of Biopharmaceutical Sciences, University of California, San Francisco, CA, USA, 3 Peripheral Neuropathy Unit, Imperial College London, Hammersmith Hospital, London, UK, 4 Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA, 5 Peripheral Nerve Injury Unit, Royal National Orthopaedic Hospital, Stanmore, Middlesex, UK Summary Root avulsion from the spinal cord occurs in brachial plexus lesions. It is the practice to repair such injuries by transferring an intact neighbouring nerve to the distal stump of the damaged nerve; avulsed dorsal root ganglia (DRG) are removed to enable nerve transfer. Such avulsed adult human cervical DRG (n ¼ 10) obtained at surgery were compared to controls, for the first time, using GeneChip oligonucleotide arrays. We report 91 genes whose expression levels are clearly altered by the injury. This first study provides a global assessment of the molecular events or “gene switches” as a consequence of DRG injuries, as the tissues represent a wide range of surgical delay, from 1 to 100 days. A number of these genes are novel with respect to sensory ganglia, while others are known to be involved in neurotransmission, trophism, cytokine functions, signal transduction, myelination, transcription regulation, and apoptosis. Cluster analysis showed that genes involved in the same functional groups are largely positioned close to each other. This study represents an important step in identifying new genes and molecular mechanisms in human DRG, with potential therapeutic relevance for nerve repair and relief of chronic neuropathic pain. ª 2003 Elsevier Ltd. All rights reserved. Keywords: human, DRG, microarrays, nerve injury, pain INTRODUCTION Road traffic accidents or incidents occurring during complicated births are the most common causes of brachial plexus spinal root avulsion injuries. Usually both ventral and dorsal roots are in- volved, and the patient is subjected to paralysis and sensory dysfunction, with numbness in the limb in conjunction with in- tractable pain in adults. It is now the practice to repair spinal cord root avulsion injuries by transferring an intact neighbouring nerve to the distal stump of the damaged nerve, to restore some motor and sensory function. 1 The intercostal and accessory nerves are commonly used for this purpose. The avulsed DRG has to be removed to enable nerve transfer to the distal stump – such avulsed DRGs have been collected for our studies. There is cur- rently only limited information on the molecular level of changes that occur within the human dorsal root ganglion (DRG) following such an avulsion injury. Use of new technologies for large-scale measurements of gene expression in diseased or damaged human tissues that are available in limited quantities may yield new in- sights and treatment strategies. With the emergence of high-den- sity DNA array technology, it has become possible to investigate the range of mRNA changes that are a consequence of such in- juries. We have therefore employed GeneChip oligonucleotide arrays to study gene expression changes in avulsed human DRG from adult patients with closed brachial plexus traction injuries. While there are a number of categories of genes that may be differentially expressed in injured DRG, novel targets for chronic neuropathic pain are of particular interest. It is not possible to directly relate the changes in avulsed dorsal root ganglia to pain mechanisms in patients with spinal cord root avulsion injury, as the pain in such patients is related to de-afferentation, and the generation of abnormal impulses and other mechanisms within dorsal spinal cord. 2 A number of these patients will also have had injuries distal to the dorsal root ganglion at other spinal levels, which may contribute to their pain. However, spinal nerve root injuries occur commonly in patients with prolapsed intervertebral discs, with consequent radiating pain, which may be intractable even after surgery; our findings may be relevant to mechanisms of pain in such cases. Further, the nature of the DRG avulsion injury is different in some respects from a surgical rhizotomy, and the changes observed may share features with DRG following peripheral axotomy: there is marked displacement of the DRG, associated vascular disturbance, and an acute inflammatory re- sponse. It is known that axotomy of the central process of sensory ganglia leads to different changes within dorsal root ganglion cells, in comparison with injuries distal to the dorsal root gan- glion. For example, the expression of GAP-43 and of c-Jun in dorsal root ganglions may not be up-regulated following central axotomy, but is up-regulated following peripheral axotomy. 3;4 However, where dorsal root section was adjacent to the dorsal root ganglia, there was a small and transient increase of GAP-43 mRNA levels. 4 Classical anatomical and physiological factors provide the setting for considering the relationship of any changed genes to pathology. Three types of nerve injury have been distinguished: 5 neurapraxia – with myelin damage, with conduction block; ax- onotmesis – a degenerative lesion of the axon with basal lamina of Schwann cell intact, with no conduction; and neurotmesis – a degenerative lesion in which all elements of the nerve are Journal of Clinical Neuroscience (2004) 11(3), 289–299 0967-5868/$ - see front matter ª 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jocn.2003.05.008 Received 7 March 2003 Accepted 9 May 2003 Correspondence to: P. Anand MA MD FRCP, Peripheral Neuropathy Unit, Imperial College London, Area A, Ground Floor, Hammersmith Hospital, DuCane Road, London W12 ONN, UK. Tel.: (+44)-020-8383-3309/3319; Fax: (+44)-020-8383-3363/3364; E-mail: p.anand@imperial.ac.uk * D. Rabert and Y. Xiao contributed equally to this research. y Present address: Abgenix, Inc., 6701 Kaiser Dr, Fremont, CA 94555, USA. z Present address: Pherin Pharmaceuticals, Inc., 350 N. Bernardo Ave., Mountain View, CA 94043, USA. 289