P21 AUTOCRINE AND PARACRINE REGULATION OF PDGF-A AND PDGF-B GENE EXPRESSION AND THE CORRESPONDING PDGF RECEPTOR IN CULTURED DERMAL PAPILLA CELLS AND FOLLICULAR     KERATINOCYTES OF THE HUMAN HAIR FOLLICLE

Kamp H., Geilen C.C., Orfanos C.E., Blume-Peytavi U.; Department of Dermatology, University Medical Center Benjamin Franklin, The Free University of Berlin, Germany

Platelet-derived growth factors (PDGF) are potent mitogens for dermal fibroblasts and other cell types, able to directly stimulate proliferation and to indirectly regulate angiogenesis by influencing VEGF expression. Mitogenic activity is mediated by two PDGF receptors which dimerize upon binding of PDGF and exert their further biological activity.

As PDGF have been reported to play in addition an important role in hair follicle formation we investigated the expression of the different PDGF isoforms as well as their corresponding receptors in cultured dermal papilla cells (DPC) and follicular keratinocytes (FK) of the human hair follicle. Furthermore we examined the regulation of PDGF by different cytokines (Il-1b, TNFa, TGFb1, IL-4 and IFNg), important for hair follicle regulation.

We demonstrated by PCR experiments and Western Blot analysis that DPC strongly express both types of PDGF receptors, a and b, whereas FK only weakly express both receptors at the gene expression level. Expression of PDGF-A mRNA could be detected in both, FK and DPC, whereas PDGF-B mRNA could only be detected with a low expression level in FK. PDGF-A mRNA expression was downregulated by IL-1b and IFNg in DPC as well as in FK; a significant  down- regulation of PDGF-B mRNA occured in FK stimulated by IL-1b.

The present study suggests an autocrine loop for PDGF-A in DPC and for PDGF-B in FK. As only FK synthesize PDGF-B a paracrine influence of DPC expressing the PDGF-receptor b has to be Considered.