Specific TRPC6 Channel Activation, a Novel Approach to Stimulate Keratinocyte Differentiation

Margarethe Müller,Kirill Essin,Kerstin Hill,Heike Beschmann,Simone Rubant,Christoph M Schempp,Maik Gollasch,W Henning Boehncke,Christian Harteneck,Walter E Müller,Kristina Leuner

doi:10.1074/jbc.m801844200

Abstract

The protective epithelial barrier in our skin undergoes constant regulation, whereby the balance between differentiation and proliferation of keratinocytes plays a major role. Impaired keratinocyte differentiation and proliferation are key elements in the pathophysiology of several important dermatological diseases, including atopic dermatitis and psoriasis. Ca(2+) influx plays an essential role in this process presumably mediated by different transient receptor potential (TRP) channels. However, investigating their individual role was hampered by the lack of specific stimulators or inhibitors. Because we have recently identified hyperforin as a specific TRPC6 activator, we investigated the contribution of TRPC6 to keratinocyte differentiation and proliferation. Like the endogenous differentiation stimulus high extracellular Ca(2+) concentration ([Ca(2+)](o)), hyperforin triggers differentiation in HaCaT cells and in primary cultures of human keratinocytes by inducing Ca(2+) influx via TRPC6 channels and additional inhibition of proliferation. Knocking down TRPC6 channels prevents the induction of Ca(2+)- and hyperforin-induced differentiation. Importantly, TRPC6 activation is sufficient to induce keratinocyte differentiation similar to the physiological stimulus [Ca(2+)](o). Therefore, TRPC6 activation by hyperforin may represent a new innovative therapeutic strategy in skin disorders characterized by altered keratinocyte differentiation.

Highlights

Ferentiation stage by expressing proteins required for the cornification like keratin 1 (K1)2 or keratin 10 (K10) and additional structural proteins that are needed for the cornification such as involucrin (IVL) or transglutaminase [1]
Hyperforin Induces Differentiation in HaCaT Keratinocytes— Because of the unclear situation of TRPC channels expressed in keratinocytes, we performed RT-PCR analyses from RNA extracted from primary keratinocytes and HaCaT cells
The detection of TRPC6-encoding mRNA in both cell types provided the rationale to use hyperforin as pharmacological tools to unravel the mechanism of keratinocyte differentiation induced by high (2 mM) extracellular calcium, which has been shown to be an endogenous trigger [1, 20]

Summary

Introduction

Ferentiation stage by expressing proteins required for the cornification like keratin 1 (K1) or keratin 10 (K10) and additional structural proteins that are needed for the cornification such as involucrin (IVL) or transglutaminase [1]. Because of the crucial role of keratinocyte differentiation for normal skin function and as relevant pathomechanism in various skin diseases, an exact knowledge of the mechanism relevant for the specific and tight sequence of events leading to keratinocytes proliferation and differentiation is very much. Stimulation of the Ca2ϩ-sensing receptor activates the phospholipase C pathway generating inositol 1,4,5triphosphate and diacylglycerol [8]. Both intracellular second messengers elevate intracellular Ca2ϩ concentration. The attempts to identify the Ca2ϩ channels playing the major role for Ca2ϩ-sensing receptor-mediated keratinocyte differentiation have been significantly hampered by the lack of pharmacological tools affecting individual TRPC channel function. TRPC6 activation by hyperforin or similar compounds represents a novel approach to pharmacologically activated keratinocyte differentiation

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Conclusion