Itch, or pruritus, is a commonly reported symptom with over 7 million clinician visits annually in the
United States. Indeed, the Global Burden of Disease Study by the World Health Organization categorized itch
in the top 50 most prevalent diseases worldwide. Itch is difficult to manage, as there are limited therapeutics.
There are also racial differences in itch in skin diseases such as atopic dermatitis (AD) and prurigo nodularis
(PN), which disproportionately affect African Americans (AA). AD is more likely to be papular, affect extensor
areas, and less likely to be associated with filaggrin loss-of-function mutations in blacks as compared to
Caucasians. This study will investigate novel itch receptors and cytokine profiles in human AD and PN patients
with respect to race to provide biomarkers and potential targets for future therapeutics.
Our first aim focuses on a recently discovered group of itch receptors, known as Mas-related G protein-
coupled receptors (Mrgprs). In humans, there are 4 Mrgpr genes (MrgprX1-4). A role for three of the MrgprX
genes in humans has been elucidated: MrgprX1 mediates chloroquine-induced itch, which disproportionally
affects AA, MrgprX2 is a regulator of pseudoallergic reactions, and our recent study demonstrated a role for
MrgprX4 as a bilirubin receptor mediating cholestatic pruritus, but the function of MrgprX3 is unknown. Based
on preliminary data showing dramatic upregulation of MrgprX3 in lesional, pruritic, PN skin and because
MrgprX3 is the most highly expressed Mrgpr in keratinocytes, this aim will determine the cellular localization,
polymorphisms, and phenotypic differences in the expression of MrgprX3 in PN and AD patients with respect
to itch intensity and race.
Our second aim will characterize upregulation of the IL-22 cytokine pathway in PN and AD patients
according to race and itch intensity. Our preliminary data reveals significant upregulation of Th22-associated
genes in lesional PN and AD skin as compared to healthy skin. Further, we found robust IL-22 expression from
human blood peripheral blood mononuclear cells in PN patients as compared to healthy controls. Thus, in this
aim we will determine circulating levels of IL-22 from plasma and peripheral blood mononuclear cells in a larger
sample of PN and AD patients with respect to race and varying itch intensity. We will also determine the
expression and cellular localization of IL-22 and Th22-associated related genes in PN and AD lesional skin.
Finally, we will test the hypothesis that MrgprX3 expression is regulated by IL-22 and Th22 associated genes.
This project will provide important insights into the role of MrpgrX3, IL-22, and the interplay between
these mediators into the pathogenesis of itch in AD and PN in African American and Caucasian patients.
Importantly, the results will be correlated with race to determine the pathogenesis and novel therapeutic targets
in specific patient populations. The knowledge gained from these studies will identify patients likely to benefit
from future treatments aimed at targeting itch in AD and PN.