[How to model the events in cutaneous fibrosis?]

Skin fibrosis is classically seen as the consequence of chronic inflammation and altered healing response that is characterized by the differentiation of fibroblasts into secretory myofibroblasts and accumulation of connective tissue. Although fibrosis severely affects organ function and causes esthetic defects, no effective therapy is currently available to attenuate the fibrogenic process probably because the fibrogenic process is more complex than previously thought. Indeed, it might involve several interacting and mutually dependent cell types (fibroblasts, keratinocytes, endothelial cells, inflammatory cells), numerous paracrine factors, bio-active molecules and micro-environmental stimuli (growth factors, vasoactive peptides, balance between pro- and anti-inflammatory cytokines, coagulation system, reactive oxygen species, extracellular matrix...). In this perspective, the traditional approach that model individual cell response in simple cell culture system is probably inadequate and too simplistic. This article reviews the new models used to study skin fibrosis in vitro, in organotypic culture systems and in vivo and examines how these different models might be used to identify new molecular pathways involved in fibrogenesis. The monolayer cultures allow the study of fibrogenic signals induced by a single factor on a single cell type. Isolation of cells from fibrotic tissue allows to define the fibrogenic differentiation acquired in vivo. The organotypic models allow cell to cell and cell to matrix interaction and the experimental models in pigs and mice allowed studies in integrated physiological systems. These various and complementary models would also provide new tools to develop and test new drugs and treatments.