Involvement of system xc- in chronic pain of inflammatory origin

Details

Supervisors

Hermans, Emmanuel

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

Chronic pain is considered as a major public health concern mainly due to its growing prevalence and the limited efficacy of current treatments. Understanding the pathophysiology of chronic pain is therefore essential if we want to improve patients' quality of life and alleviate the physical, emotional and socio-economic burden this condition represents. The main hypothesis for the underlying mechanisms of chronic pain relies on the processes of central and peripheral sensitizations, involving increased glutamatergic transmission and persistent inflammatory state in the nervous system. In this study, we investigated system xc-, a transporter mainly expressed on glial cells and responsible for extrasynaptic glutamate release while also reportedly involved in neuroinflammatory mechanisms, as a potential therapeutic target for chronic pain. To determine the role of system xc- in chronic pain, we used a validated inflammatory chronic pain model of Complete Freund’s Adjuvant injection in the hind paw of wild-type and mice lacking xCT, the specific subunit of system xc-. We performed behavioral analyses over 21 days and noticed a reduced inflammatory oedema, mechanical allodynia and thermal hyperalgesia in xCT-/- mice as opposed to wild-types. Aiming at better understanding the role of system xc- in the onset or maintenance of chronic pain, we conducted similar studies using animals subjected to either a preventive or curative treatment with sulfasalazine, a pharmacological inhibitor of system xc-. Our behavioral results suggested a long-lasting beneficial effect of the preventive inhibition of system xc-. In parallel, we started the characterization of a newly developed model of tamoxifen-induced Cre-lox inactivation of xCT. This system would allow a reliable inducible deletion of xCT (SLC7A11, exon 2 and 3) in all cell types thanks to the ubiquitous ROSA promoter. This way, potential emergence of compensatory systems could be avoided and our behavioral results confirmed. To validate this inactivation of system xc- after tamoxifen administration, we evaluated its functionality through glutamate uptake assays as well as SLC7A11 mRNA levels by RT-qPCR. This was assessed in vitro on cultured primary xCTfl/fl Rosa-Cre+/- astrocytes previously treated with different concentrations of 4-hydroxytamoxifen. In vivo, we performed these assays on nervous tissue samples extracted from tamoxifen-treated xCTfl/fl Rosa-Cre+/- mice. We obtained promising preliminary results, with a particularly efficient decrease in mRNA levels and functional activity of xCT in vitro.