Pleiotropic Role of TRPV1 in Psoriasis Inflammation

Widely expressed in the sensory nerve endings of the skin, Transient Receptor Potential Vanilloid 1 (TRPV1) is a receptor that plays an important role in the perception of pain and pruritus but also in skin inflammation, primarily by inducing the local release of several neuropeptides. Although the mechanisms by which TRPV1-sensitizing inflammatory mediators in damaged skin have received considerable attention, the role of TRPV1 in psoriasis has so far been little explored. However, two studies have reported that ablation of sensory nerves expressing TRPV1 reduced psoriasiform skin inflammation, demonstrating the neuronal contribution to inflammation in psoriasis. However, the expression of TRPV1 is not limited to neurons alone. TRPV1 is also expressed by epidermal keratinocytes and skin microvessels. For example, in 2018, transcriptomic analysis of psoriatic patient skins (by definition devoid of neuron nuclei) revealed that TRPV1 expression was increased in the skin of psoriatic patients suffering from itching (pruritus). Regarding human keratinocytes, it is recognized that the activation of TRPV1 present on their surface induces the release of pro-inflammatory factors such as cyclooxygenase-2. In addition, the investigators have demonstrated that TRPV1 has a pivotal role in the keratinocyte production of inflammatory mediators, which is mediated by the protease-activated receptor-2 (PAR-2). However, the role of vascular TRPV1 in inflammation is not described. The investigators hypothesize that in addition to neuronal TRPV1, non-neuronal TRPV1 receptors of non-neuronal cells (keratinocytes and endothelial cells) may be involved in the vicious circle of the inflammatory process characteristic of psoriasis. Putting TRPV1 at the center of the deregulation of the homeostatic balance including epithelial, neuronal and vascular inflammation in psoriasis is totally innovative.