Ciguatera Fish Poisoning (CFP) is a widespread tropical intoxication consecutive to ciguatoxin (CTX) ingestion, which is characterized by persistent neuro-cutaneous disturbances, including an intense pruritus (itch). Currently, there is no specific treatment. The primary target of CTXs is the voltage dependent sodium channel (Nav), which is largely expressed in sensory nerves and, to a lesser extent, in keratinocytes. By activating Nav, CTXs induce neuronal hyper-excitability but the downstream molecular mechanisms leading to sensory disorders are poorly understood. Recent advances in dermatology reveal protease-activated receptor-2 (PAR-2) involvement in itch pathophysiology. Interestingly, this receptor is expressed in sensory neurons and keratinocytes. To better understand the pathophysiology of CFP pruritus, the purpose of the present study was to identify cellular and molecular actors involved in the substance P (SP) release elicited by P-CTX-2 from cocultured sensory neurons and keratinocytes.
First, P-CTX-2 is able to induce calcium signal in both sensory neurons and keratinocytes.
We show that antagonism of PAR-2 significantly inhibited the P-CTX-2-evoked calcium signal in both cells. Then, our results demonstrate the synergistic role of keratinocytes in the SP release elicited by P-CTX-2 in the coculture. The P-CTX-2-induced SP was almost completely abolished by PAR-2 or cathepsin S (Cat S) antagonists, and Cat S activity was significantly increased after P-CTX-2 treatment. Finally, P-CTX-2 is able to internalise PAR-2 in keratinocytes. Taken together, this work reveals that keratinocytes, PAR-2 and Cat S are novel actors in the P-CTX-2-induced release of SP, suggesting those are promising pharmacological targets for specifically treating CFP neuro-cutaneous disorders.

Involvement of cathepsin S and protease-activated receptor-2 in ciguatoxin-induced substance P release: new promising targets to treat ciguatera pruritus