1. ¹Department of Anatomy, Pharmacology and Forensic Medicine, University of Parma, Parma, Italy
2. ²Center for Morphology and Body Composition (CMBC), University of Parma, Parma, Italy
3. ³Terme di Sirmione, Cell Biology Laboratory, Terme di Sirmione, Brescia, Italy
4. ⁴Department of Surgery, Dermatology Division, University of Parma, Parma, Italy

Correspondence: Professor M Vitale, MD, Department of Anatomy, Pharmacology and Forensic Medicine, University of Parma, via Gramsci 14, Ospedale Maggiore, Parma 43100, Italy. E-mail: marco.vitale@unipr.it

^5*These authors equally contributed to this work.

Received 28 January 2009; Revised 28 April 2009; Accepted 4 May 2009; Published online 22 June 2009.

Abstract

The effects of exogenous hydrogen sulfide (H₂S) on normal skin-derived immortalized human keratinocytes have been investigated in detail. We show in vitro that exogenous hydrogen sulfide reduces clonal growth, cell proliferation and cell adhesion of human keratinocytes. H₂S, in fact, decreases the frequency of the putative keratinocyte stem cell subpopulation in culture, consequently affecting clonal growth, and impairs cell proliferation and adhesion of mature cells. As a mechanistic explanation of these effects, we show at the molecular level that (i) H₂S reduces the Raf/MAPK kinase/ERK signaling pathway; (ii) the reduced adhesion of sulfur-treated cells is associated to the downregulation of the expression of 4, 2 and 6 integrins that are necessary to promote cell adhesion as well as anti-apoptotic and proliferative signaling in normal keratinocytes. One specific interest of the effects of sulfurs on keratinocytes derives from the potential applications of the results, as sulfur is able to penetrate the skin and a sulfur-rich balneotherapy has been known for long to be effective in the treatment of psoriasis. Thus, the relevance of our findings to the pathophysiology of psoriasis was tested in vivo by treating psoriatic lesions with sulfurs at a concentration comparable to that most commonly found in sulfurous natural springs. In agreement with the in vitro observations, the immunohistochemical analysis of patient biopsies showed a specific downregulation of ERK activation levels, the key molecular event in the sulfur-induced effects on keratinocytes.