Specific attenuation of purinergic signaling during bortezomib-induced peripheral neuropathy

Human peripheral neuropathies are poorly-understood, and the availability of experimental models limits further research. The PeriTox test uses immature dorsal root ganglia (DRG)-like neurons, derived from induced pluripotent stem cells (iPSC), to assess cell death and neurite damage. Here, we explored the suitability of matured peripheral neuron cultures for detection of sub-cytotoxic endpoints, such as altered responses of pain-related P2X receptors. A 2-step differentiation protocol, involving transient expression of ectopic neurogenin-1 (NGN1), allowed for the generation of homogeneous cultures of sensory neurons. After > 38 days-of-differentiation, they showed a robust response (Ca2+-signalling) to the P2X3 ligand ,{beta}-methylene ATP. The clinical proteasome inhibitor bortezomib abolished the P2X3 signal at [≥] 5 nM, while 50-200 nM were required in the PeriTox test to identify neurite damage and cell death. A 24 h treatment with low nM concentrations of bortezomib led to moderate increases in resting cell intracellular [Ca2+], but signalling through transient receptor potential-V1 (TRPV1) receptors or depolarization-triggered Ca2+-influx remained unaffected. We interpret the specific attenuation of purinergic signalling as functional cell stress response. A reorganization of tubulin to dense structures around the cell somata confirmed a mild, non-cytotoxic stress triggered by low concentrations of bortezomib. The proteasome inhibitors carfilzomib, delanzomib, epoxomycin and MG-132 showed similar stress responses. Thus, the model presented here may be used for profiling of new proteasome inhibitors as to their side effect (neuropathy) potential, or for pharmacological studies on the attenuation of their neurotoxicity. P2X3 signalling proved useful as endpoint to assess potential neurotoxicants in peripheral neurons.