Role of keratinocyte-derived protease-activated receptor-2 in neuro-epidermal communication

• Applicant: Professor Dr. Timo Buhl
• Subject Area: Dermatology
• Term: from 2013 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 239914971

In atopic dermatitis (AD), major hallmarks of the disease comprise significant inflammation, impaired barrier function, and severe pruritus. While the cellular interaction between mast cells and nerves is well understood using histamine, tryptase or nerve growth factor (NGF) as transmitters, the mediators that exert the communication between keratinocytes and nerves are poorly investigated. Of note, nerval innervation and concentration of neuromediators are enhanced and correlate with severity of AD. Thus, neuro-epidermal communication and dysregulation may play an essential role in the pathophysiology of itch and AD. Strong evidence indicates that the interaction between exogenous and endogenous proteases, protease-activated receptors (PARs) and protease inhibitors is critically involved in itch, immune regulation, skin barrier function, and AD. Based on these profound findings, the aim of my study at the University of California in San Francisco (UCSF) will be to elucidate the mechanisms that underlie neuro-epidermal communication; in particular I will study the role of keratinocyte-derived proteases and PAR receptors for the regulation of sensory nerves and pruritic inflammatory skin diseases. Therefore, I will use a murine model that conditionally overexpresses protease-activated receptor 2 in keratinocytes (KC-PAR2 OE) and compare its function using PAR2 gene-deficient mice (PAR2 KO) and wildtype (WT) mice. Of note, KC-PAR2 OE mice spontaneously develop atopic-like dermatitis with intense pruritus. Thus, my analysis will attribute infiltration of inflammatory cells, development of pruritus, nerve sprouting into the skin, neuronal activation and probably central sensitization that leads to chronic itch. In support of that, preliminary data from the Steinhoff and Coughlin lab at UCSF revealed enhanced scratching behavior associated with increased cutaneous innervation by sensory nerves in KC-PAR2 OE mice. Therefore, histological approaches (IHC, IF) along with gene expression analyzes (qRTPCR), and flow cytometry will be used to reveal the transmitters that keratinocytes release upon protease stimulation to mediate inflammation and pruritus. Moreover, I will study the impact of KC-derived proteases on immune cell infiltration and to clarify the role of the Th2-like cell responses for keratinocyte-neuronal communication in KC-PAR2 OE mice. Hyperknesis and alloknesis approaches as well as electrophysiological studies will be conducted to clarify the impact of KC-PAR2 overexpression for neuronal activation and signaling. New insights into the dysregulated interaction between keratinocytes and terminal nerve endings could possibly identify new specific targets for intervention; hopefully this approach may be transferable to patients with AD and other eczematous diseases in the future.

• DFG Programme: Research Fellowships
• International Connection: USA
• Hosts: Professor Dr. Shaun R. Coughlin; Professor Dr. Martin Steinhoff