Artemin sensitises mouse (Mus musculus) and naked mole-rat (Heterocephalus glaber) sensory neurons in vitro

Abstract

The naked mole-rat (NMR, Heterocephalus glaber) is a subterranean rodent that exhibits a range of unusual physiological traits, including diminished inflammatory pain. For example, nerve growth factor (NGF), a key inflammatory mediator, fails to induce sensitization of sensory neurons and thermal hyperalgesia in NMRs. This lack of NGF-induced neuronal sensitization and thermal hyperalgesia results from hypofunctional signaling of the NGF receptor, tropomyosin receptor kinase A (TrkA). Like NGF-TrkA signaling, the neurotrophic factor artemin, a member of the glial cell line-derived neurotrophic factor (GDNF) family, is implicated in mediating inflammatory pain through its receptor, GDNF family receptor α3 (GFRα3), which is expressed by a subset of dorsal root ganglia (DRG) sensory neurons. Here we investigated GFRα3 expression in DRG neurons of mice and NMRs, as well as measuring the impact of artemin on DRG sensory neuron function in both species in vitro. Using immunohistochemistry, we observed a similar abundance of GFRα3 in mouse and NMR DRG sensory neurons, high coexpression with the transient receptor potential vanilloid 1 (TRPV1) ion channel suggesting that these neurons are nociceptive neurons. Using in vitro electrophysiology to record from cultured DRG sensory neurons, we observed that artemin induced depolarization of the resting membrane potential and decreased the rheobase in both species, as well as diminishing the degree of TRPV1 desensitization to multiple capsaicin stimuli. Overall, results indicate that artemin similarly sensitizes sensory neurons in both mice and NMRs, future in vivo studies being required to confirm if the conserved in vitro sensitization also occurs in vivo.

Keywords: Artemin; Naked mole-rat; Nociception; Sensory neuron; TRPV1.

Fig. 1

TRPV1 and GFRα3 show high coexpression in both mouse and NMR DRG neurons. a In NMR (N = 5, n = 21 sections, n = 1302 cells), 27.80 ± 1.94% of DRG neurons express GFRα3, 27.60 ± 2.29% express TRPV1, and 23.60 ± 2.27% express both. 84.89% of TRPV1 + ve neurons also expressing GFRα3. b In mice (N = 5, n = 23 sections, n = 1564 cells), 30.57 ± 1.41% of DRG neurons express GFRα3, 26.00 ± 1.92% express TRPV1, 23.96 ± 1.65% express both, and 93.7% of TRPV1 + ve neurons also expressing GFRα3. Scale bar in all panels, 50 μm. Data are reported as mean ± SEM

Fig. 2

Artemin sensitizes mouse and NMR DRG neurons. a–c In NMR DRG neurons, 7-minute perfusion with 100 ng/ml artemin significantly decreased rheobase a, depolarized the resting membrane potential b, and diminished TRPV1 desensitization c–e. Representative traces are shown in d, e. In mouse DRG neurons, 7-minute perfusion with 100 ng/ml artemin significantly decreased rheobase f, depolarized the resting membrane potential g, and diminished TRPV1 desensitization h–j. Paired t-tests were used to analyze RMP, rheobase, peak amplitude, half-peak duration, afterhyperpolarization amplitude, and afterhyperpolarization duration. Unpaired t-tests were applied to capsaicin response fold change analysis. * p-adj < 0.05, ** p-adj < 0.01, ***p-adj < 0.001, ****p-adj < 0.0001