*Article* **Hair Histology and Glycosaminoglycans Distribution Probed by Infrared Spectral Imaging: Focus on Heparan Sulfate Proteoglycan and Glypican-1 during Hair Growth Cycle**

**Charlie Colin-Pierre 1,2,3,† , Valérie Untereiner 4,† , Ganesh D. Sockalingum <sup>5</sup> , Nicolas Berthélémy <sup>3</sup> , Louis Danoux <sup>3</sup> , Vincent Bardey <sup>3</sup> , Solène Mine <sup>3</sup> , Christine Jeanmaire <sup>3</sup> , Laurent Ramont 1,2,6,‡ and Stéphane Brézillon 1,2,\* ,‡**


**Abstract:** The expression of glypicans in different hair follicle (HF) compartments and their potential roles during hair shaft growth are still poorly understood. Heparan sulfate proteoglycan (HSPG) distribution in HFs is classically investigated by conventional histology, biochemical analysis, and immunohistochemistry. In this report, a novel approach is proposed to assess hair histology and HSPG distribution changes in HFs at different phases of the hair growth cycle using infrared spectral imaging (IRSI). The distribution of HSPGs in HFs was probed by IRSI using the absorption region relevant to sulfation as a spectral marker. The findings were supported by Western immunoblotting and immunohistochemistry assays focusing on the glypican-1 expression and distribution in HFs. This study demonstrates the capacity of IRSI to identify the different HF tissue structures and to highlight protein, proteoglycan (PG), glycosaminoglycan (GAG), and sulfated GAG distribution in these structures. The comparison between anagen, catagen, and telogen phases shows the qualitative and/or quantitative evolution of GAGs as supported by Western immunoblotting. Thus, IRSI can simultaneously reveal the location of proteins, PGs, GAGs, and sulfated GAGs in HFs in a reagentand label-free manner. From a dermatological point of view, IRSI shows its potential as a promising technique to study alopecia.

**Keywords:** hair follicle growth; glycosaminoglycans; infrared spectral imaging; *k*-means clustering; immunohistochemistry
