In vitro models for investigating itch

Abstract

Itch (pruritus) is a sensation that drives a desire to scratch, a behavior observed in many animals. Although generally short-lasting and not causing harm, there are several pathological conditions where chronic itch is a hallmark symptom and in which prolonged scratching can induce damage. Finding medications to counteract the sensation of chronic itch has proven difficult due to the molecular complexity that involves a multitude of triggers, receptors and signaling pathways between skin, immune and nerve cells. While much has been learned about pruritus from in vivo animal models, they have limitations that corroborate the necessity for a transition to more human disease-like models. Also, reducing animal use should be encouraged in research. However, conducting human in vivo experiments can also be ethically challenging. Thus, there is a clear need for surrogate models to be used in pre-clinical investigation of the mechanisms of itch. Most in vitro models used for itch research focus on the use of known pruritogens. For this, sensory neurons and different types of skin and/or immune cells are stimulated in 2D or 3D co-culture, and factors such as neurotransmitter or cytokine release can be measured. There are however limitations of such simplistic in vitro models. For example, not all naturally occurring cell types are present and there is also no connection to the itch-sensing organ, the central nervous system (CNS). Nevertheless, in vitro models offer a chance to investigate otherwise inaccessible specific cell–cell interactions and molecular pathways. In recent years, stem cell-based approaches and human primary cells have emerged as viable alternatives to standard cell lines or animal tissue. As in vitro models have increased in their complexity, further opportunities for more elaborated means of investigating itch have been developed. In this review, we introduce the latest concepts of itch and discuss the advantages and limitations of current in vitro models, which provide valuable contributions to pruritus research and might help to meet the unmet clinical need for more refined anti-pruritic substances.

Characterization of human iPSC-derived sensory neurons and their functional assessment using multi electrode array

“…Although human sensory neurons from stem and other progenitor cells have to be kept for long times in culture to be used in functional assays due to the immaturity of their protein expression and electrophysiological network, our results show that the MFR observed after 4 DIV, exceeded the one observed for DRG after 14 DIV, and peaked above 10 Hz after 35 DIV (Supplementary Fig. S4 e) 12 , 25 , 31 . HiPSC-derived sensory neurons can reliably be used for recording until 64 DIV.…”

“…S1 ). Previous reviews have reported that some gene expression levels in iPSC-derived peripheral sensory neurons were lower than those of hDRG 20 , 31 . Full maturation of hiPSC derived neurons has not yet been achieved and remains a goal in the field.…”

“…It is known that itch occurs via C-fiber in www.nature.com/scientificreports/ nociceptors 30 . Recently, investigating itch has been established by using human sensory neurons from stem and other progenitor cells as in vitro model 31 . Although substances causing itch treat to their cells, their inhibitors effect aren't confirmed using hiPSC-derived sensory neurons.…”