Journal Club 2022.04.08

Mast cells instruct keratinocytes to produce thymic stromal lymphopoietin: Relevance of the tryptase/protease-activated receptor 2 axis

Davender Redhu, PhD,a Kristin Franke, PhD,a Marina Aparicio-Soto, PhD,a Vandana Kumari, PhD,a Kristijan Pazur, PhD,a Anja Illerhaus, PhD,b Karin Hartmann, MD,c,d Margitta Worm, MD,a and Magda Babina, PhDa Berlin and Cologne, Germany; and Basel, Switzerland

Background: Thymic stromal lymphopoietin (TSLP) promotes TH2 inflammation and is deeply intertwined with inflammatory dermatoses like atopic dermatitis. The mechanisms regulating TSLP are poorly defined.

Objective: We investigated whether and by what mechanisms mast cells (MCs) foster TSLP responses in the cutaneous environment.
Methods: Ex vivo and in vivo skin MC degranulation was induced by compound 48/80 in wild-type protease-activated receptor 2 (PAR-2)- and MC-deficient mice in the presence or absence of neutralizing antibodies, antagonists, or exogenous mouse MC protease 6 (mMCP6). Primary human keratinocytes and murine skin explants were stimulated with lysates/supernatants of human skin MCs, purified tryptase, or MC lysate diminished of tryptase. Chymase and histamine were also used. TSLP was quantified by ELISA, real-time quantitative PCR, and immunofluorescence staining.
Results: Mas-related G protein–coupled receptor X2 (Mrgprb2) activation elicited TSLP in intact skin, mainly in the epidermis. Responses were strictly MC dependent and relied on PAR-2. Complementarily, TSLP was elicited by tryptase in murine skin explants. Exogenous mMCP6 could fully restore responsiveness in MC-deficient murine skin explants. Conversely, PAR-2 knockout mice were unresponsive to mMCP6 while displaying increased responsiveness to other inflammatory pathways, such as IL-1a. Indeed, IL-1a acted in concert with tryptase. In primary human keratinocytes, MC-elicited TSLP generation was likewise abolished by tryptase inhibition or elimination. Chymase and histamine did not affect TSLP production, but histamine triggered IL-6, IL- 8, and stem cell factor.
Conclusion: MCs communicate with kerationocytes more broadly than hitherto suspected. The tryptase/PAR-2 axis is a crucial component of this cross talk, underlying MC-dependent stimulation of TSLP in neighboring kerationocytes. Interference specifically with MC tryptase may offer a treatment option for disorders initiated or perpetuated by aberrant TSLP, such as atopic dermatitis. (J Allergy Clin Immunol 2022;nnn:nnn-nnn.)

Key words: Atopic dermatitis, interleukin 1, keratinocytes, mast cells, PAR-2, TSLP, tryptase