P4.32 EXPRESSION OF SPARC (SECRETED PROTEIN ACIDIC RICH IN CYSTEINE) THROUGHOUT THE HAIR CYCLE IN RATS

V.E. Ferres^A, G. Nattrass^B, M. Bray^A, N. M. Penno^A and P. I. Hynd^A

^AThe University of Adelaide, and ^BSouth Australian Research and Development Institute, Livestock Systems, Roseworthy Campus, Roseworthy, South Australia, Australia

The importance of an understanding of the factors controlling the hair growth cycle in both normal and diseased states is reflected in the intensity of research interest that currently exists into the molecular and cellular regulation of the cycle. A number of candidate molecules have been implicated as key regulators of the hair cycle including follistatin, activins, bone morphogenetic proteins, and TGFb. There is also increasing evidence that a group of proteins known as matricellular proteins play an important role in cell signalling processes, particularly in tissues undergoing remodelling and repair. SPARC (osteonectin or BM40) is a 40kDa matricellular protein with attributes that suggest it may play a role in signalling transitional phases of the hair cycle. We examined the spatial and temporal changes in expression of SPARC protein and mRNA respectively throughout the hair cycle of rats using immunohistochemistry and quantitative PCR techniques.

The progeny of time-mated rats were serially slaughtered from days 15 to 30 postnatal to provide a sequence of skin samples reflecting all phases of the hair cycle. The spatial expression of SPARC throughout the cycle was visualised using an immunohistochemical technique with peroxidase/diaminobenzidine to detect antibody binding. Real time Polymerase Chain Reaction (qPCR) using SYBR Green 1 was used to quantify changes in SPARC mRNA expression.

SPARC was consistently expressed in the epidermis, sebaceous glands, reticular dermis, striated muscle, and endothelium of rat skin. During anagen, SPARC was present in the Outer Root Sheath (ORS), and Connective Tissue Sheath (CTS).  Occasionally SPARC was found in the follicle bulb and dermal papilla of anagen follicles. During catagen SPARC was present in the regressing follicle bulb, epithelial strand and ORS. In telogen, SPARC was mainly expressed in the ORS. In newly-forming anagen follicles SPARC was expressed in the ORS, Inner Root Sheath (IRS), and CTS.

Preliminary data obtained using qPCR suggest that SPARC mRNA expression was elevated during the catagen/telogen transition but not at the cusp of anagen/catagen or telogen/anagen. We conclude that SPARC is unlikely to be the initiating signalling molecule that triggers the anagen/catagen or telogen/anagen transitions of the hair cycle. It is more likely that SPARC expression is a secondary response to other signalling molecules, and reflects tissue-remodelling processes that occur throughout the hair cycle, akin to its role in wound repair.