Research

Correlational analysis for identifying genes whose regulation contributes to chronic neuropathic pain

Anna-Karin Persson^1* , Mathias Gebauer^2* , Suzana Jordan² , Christiane Metz-Weidmann² , Anke M Schulte² , Hans-Christoph Schneider² , Danping Ding-Pfennigdorff² , Jonas Thun¹ , Xiao-Jun Xu³ , Zsuzsanna Wiesenfeld-Hallin³ , Ariel Darvasi⁴ , Kaj Fried¹ and Marshall Devor⁵

¹  Center for Oral Biology, Novum, Karolinska Institutet, S-141 04 Huddinge, Sweden

²  Discovery Research, Sanofi-Aventis Deutschland GmbH, 65926 Frankfurt am Main, Germany

³  Department of Clinical Neuroscience, Section of Clinical Neurophysiology, Karolinska Institute, S-141 86 Stockholm, Sweden

⁴  Department of Genetics, Institute of Life Sciences and Center for Research on Pain, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

⁵  Department of Cell & Animal Biology, Institute of Life Sciences and Center for Research on Pain, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

author email corresponding author email* Contributed equally

Molecular Pain 2009, 5:7doi:10.1186/1744-8069-5-7

Published:	19 February 2009

Abstract

Background

Nerve injury-triggered hyperexcitability in primary sensory neurons is considered a major source of chronic neuropathic pain. The hyperexcitability, in turn, is thought to be related to transcriptional switching in afferent cell somata. Analysis using expression microarrays has revealed that many genes are regulated in the dorsal root ganglion (DRG) following axotomy. But which contribute to pain phenotype versus other nerve injury-evoked processes such as nerve regeneration? Using the L5 spinal nerve ligation model of neuropathy we examined differential changes in gene expression in the L5 (and L4) DRGs in five mouse strains with contrasting susceptibility to neuropathic pain. We sought genes for which the degree of regulation correlates with strain-specific pain phenotype.

Results

In an initial experiment six candidate genes previously identified as important in pain physiology were selected for in situ hybridization to DRG sections. Among these, regulation of the Na⁺ channel α subunit Scn11a correlated with levels of spontaneous pain behavior, and regulation of the cool receptor Trpm8 correlated with heat hypersensibility. In a larger scale experiment, mRNA extracted from individual mouse DRGs was processed on Affymetrix whole-genome expression microarrays. Overall, 2552 ± 477 transcripts were significantly regulated in the axotomized L5DRG 3 days postoperatively. However, in only a small fraction of these was the degree of regulation correlated with pain behavior across strains. Very few genes in the "uninjured" L4DRG showed altered expression (24 ± 28).

Conclusion

Correlational analysis based on in situ hybridization provided evidence that differential regulation of Scn11a and Trpm8 contributes to across-strain variability in pain phenotype. This does not, of course, constitute evidence that the others are unrelated to pain. Correlational analysis based on microarray data yielded a larger "look-up table" of genes whose regulation likely contributes to pain variability. While this list is enriched in genes of potential importance for pain physiology, and is relatively free of the bias inherent in the candidate gene approach, additional steps are required to clarify which transcripts on the list are in fact of functional importance.