The IMPC is hunting unknown genes responsible for pain sensitivity by screening knockout mice
- One-third of the global population suffers from chronic pain, including 100 million people in the USA 1
- Basic science estimates that 30-80% of the variance in pain responses can be explained by genetic factors 1
- The search for novel mechanisms and targets for pain therapeutics is an urgent priority due to the current opiate use and overdose epidemic
Approach
In order to identify the function of genes, the consortium is piloting a series of protocols as described in IMPReSS (International Mouse Phenotyping Resource of Standardised Screens).
| Protocol name | IMPReSS ID | Protocol purpose |
|---|---|---|
| Formalin Challenge | In development | Assess the tonic phase of response to inflammatory pain through manual and automated scoring of video collected up to 90 minutes post-challenge. |
| Complete Freund’s Adjuvant (CFA) Challenge | JAX_EDM_001 | CFA is not a standalone assessment, but instead is an inflammatory stimulus that can be administered prior to assessing mechanical and thermal nociception. Edema is also collected as a quantitative measure of localized inflammation |
| Von Frey | HRWL_VFR_001 JAX_VFR_001 TCP_VFR_001 UCD_VFR_001 | Assess mechanical hypoalgesia, hyperalgesia and allodynia in naive or CFA challenged animals |
| Hargreaves’ | JAX_HRG_001 TCP_HRG_001 UCD_HRG_001 | Assess thermal nociception in CFA challenged animals |
| Hot Plate | HRWL_HOT_001 | Assess thermal nociception in naïve animals |
| Cage Lid Interaction | In development | Novel, passive measurement of pain behavior in mice challenged with CFA. Non-invasive, wireless capacitance measuring device is used to detect cage-lid contact time in the home-cage environment. |
| Dynamic Weight Bearing | In development | Quantify evoked pain by assessing postural equilibrium in unrestrained mice. |
Gene list
115 genes are being assessed for altered pain susceptibility phenotypes. To date, the following 86 unique candidate genes have entered Pain Phenotyping.
These genes were selected via a diverse range of discovery partners including nominations from the IMPC Portal and through synergistic interactions with an existing NIH funded Addiction Supplement. The remaining genes are extant IMPC lines highlighted as potentially pain related based on Gene Weaver selection criteria.
P2rx4 and Trpa1 knockout mice are being tested by all centres as positive controls. Existing null alleles of these genes are published as presenting with decreased pain sensitivity.
Vignettes
Reduced mechanical nociception following inflammatory stimulus using Complete Freund’s Adjuvant (CFA)
Htr3aem1(IMPC)J
Females average von Frey thresholds, baseline, 24 and 48 hrs post CFA challenge
An ethical approach
IMPC Centres breeding mice and collecting phenotyping data are guided by their own ethical review panels and licensing and accrediting bodies, reflecting the national legislation under which they operate. All phenotyping procedures were examined for potential refinements that were disseminated throughout the Consortium. Animal welfare was assessed routinely for all mice involved.
The IMPC will make experimental data freely available without restriction to facilitate research and minimize duplication. In addition, the IMPC will continue to apply the Animal Research: Reporting of In Vivo Experiments (ARRIVE) to ensure analyses can be reproduced.
[1] – Tsang et al., The Journal of Pain, 9(10) pp883-891 (2008)