A Humanized In Vitro Model of Innervated Skin for Transdermal Analgesic Testing

Sensory innervation of the skin is essential for its function, homeostasis and wound healing mechanisms. Thus, to adequately model the cellular microenvironment and function of native skin, in vitro human skin equivalents (hSE) containing a sensory neuron population began to be researched. In this work, we established a fully human three-dimensional (3D) platform of hSE innervated by induced pluripotent stem cell-derived nociceptors neurospheres (hNNs), mimicking the native mode of innervation. Both the hSE and nociceptor population exhibited morphological and phenotypical characteristics resembling their native counterparts, such as epidermal and dermal layer formation and nociceptor marker exhibition, respectively. In the co-culture platform, neurites developed from the hNNs and navigated in 3D to innervate the hSE from a distance. To probe both skin and nociceptor functionality, we applied a clinically available capsaicin patch (Qutenza™) directly over the hSE section and analyzed neuron reaction. Application of the patch caused an exposure time-dependent neurite regression and degeneration. In platforms absent of hSE, axonal degeneration was further increased, highlighting the role of the skin construct as a barrier. In sum, we established an in vitro tool of functional innervated skin with high interest for preclinical research. This article is protected by copyright. All rights reserved.