Effects of TNFα challenge on sensory neuron ion channel expression and temperature sensitivity

Abstract

Chronic neuropathic pain is a major worldwide cause of disability with over 116 million adults affected in the US alone. In many cases, direct neuronal effects of cytokines are thought to contribute to the associated temperature and mechanical hypersensitivity. In a previous report we showed that the resting membrane potential of TNFα treated dorsal root ganglion (DRG) neurons was hyperpolarized compared to controls, when measured at 30°C. In this study we extended this work to measure TNFα (24hr, 10ng/ml) induced changes in underlying ion channel biomarker mRNA abundance (with qPCR), absolute resting action potential (AP) frequency and on its temperature sensitivity (using cell‐attached patch, action current recording). DRG neurons were isolated and prepared as described previously [1]. Analysis of whole DRG, glial cell depleted cultures revealed that several ion channels were differentially transcribed following TNFα treatment. Interestingly, there was a statistically significant switch from TRPV4 (transient receptor potential cation channel, subfamily V, member 4) to TRPM2 (transient receptor potential cation channel, subfamily M, member 2) transcript (TRPM2 up >3 fold, TRPV4 down >2 fold; both p<0.001) and significant shifts from KCNA1/2 to KCND2/3). For patch‐clamp experiments, only small DRG neurons (<35pF) were chosen, since they exhibit predominantly temperature and nociceptive phenotypes. Whilst we found that resting action current frequency was lower in TNFα treated neurons than controls, we found that the increase in action current frequency following a +15°C temperature challenge was significantly greater in TNFα treated neurons (1.6 fold increase in control vs 3.5 fold increase after TNFα challenge). These changes are generally smaller than previously reported. Following mathematical simulations, we conclude that this may be due to our use of cell‐attached AP frequency recording. This technique will allow native cellular control of intracellular Ca2+ and may allow endogenous feedback control that may be lost when using conventional whole‐cell patch‐clamp recording.Support or Funding InformationThe authors wish to acknowledge the D‐Board project, which has received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under grant agreement No. 305815