A genetic approach to decipher the role of T-type calcium channels in neuropathic pain – Pain-T

The detection and processing of painful stimuli in afferent sensory neurons is critically dependent on a wide range of different types of voltage and ligand gated ion channels, including sodium, calcium, and TRP channels, to name a few. The functions of these channels include the detection of mechanical thermal and chemical signals, the generation of action potentials and regulation of neuronal firing patterns, the initiation of neurotransmitter release at dorsal horn synapses, and the ensuing activation of neurons that project to pain centers in the brain. Long-term changes in ion channel expression are thought to contribute to chronic pain states. Many of the channels involved in the afferent pain pathways are permeable to calcium ions, suggesting modifications in cell signaling in addition to the mere generation of electrical activity. Among the calcium permeable channels, T-type channels have recently become good candidates for drug development to treat pain. Over the recent years, the consortium leader has established the pronociceptive role of Cav3.2 subunit of T-type calcium channels in peripheral sensory neurons (DRG) both using administration of specific oligodeoxynucleotide antisenses, selective pharmacology and knock-out animals. The precise implication of Cav3.2 channels in pain processing from the periphery to the spinal and central nervous system is however far from being elucidated. This will be challenged in this proposal by exploring an innovative animal model with cutting-edge and highly sensitive approaches. This animal model will be assayed in pain models that are well established in the consortium.
We aim to determine the precise contribution of Cav3.2 channel in the pain circuits and to identify the major sites of action supporting the analgesic properties of T-type channel blockers. Experiments will be performed using the Spared Nerve Injury (SNI) model and the Oxaliplatin chemotherapy Induced Neuropathy model that will be challenged by a well-defined combination of KI/cKO Cav3.2 mouse lines, selective pharmacology, optogenetics and pharmacologic approaches coupled to electrophysiological, and behavioral studies.

The project is articulated around three interconnected tasks:

Task 1: Sourcing pain: Cav3.2 in primary afferents
To perform an extensive characterization of Cav3.2 expressing DRG neurons in chronic pain

Task 2: Relaying pain: Impact of Cav3.2 in spinal cord network
To decipher Cav3.2 role at spinal level

Task 3: Integrating/modulating pain: Deciphering supra spinal role of Cav3.2
To characterize the impact of Cav3.2 in CNS nuclei of the thalamocortical and bulbar networks related to pain integration and control.

Alltogether, completion of this proposal will foster our understanding of the role of Cav3.2 channels in the pain pathways and critically help the development of innovative therapeutic strategies in pain treatment that remains an unmet medical need today. Specifically, this project will provide:
- A detailed characterization of the contribution of Cav3.2 channels in the neuropathic pain circuits
- A comprehensive view of the analgesic properties of selective T-type channel blockers
- New findings regarding the neurophysiological role of low voltage gated calcium influxes: impact in mechanotransduction (at afferent fiber receptive field), in synaptic transmission (at the presynaptic compartments in all the networks), in action potential conduction (in fibers, at the AIS)…
- Validation of a customized toolkit (mouse models and selective pharmacology) that may appear useful to study Cav3.2 channels in both physiological and pathological conditions.
- All in all, establishing T-type channel blockers as future standards to treat chronic pain.