Insights in Human Hair Curvature by Proteome Analysis of Two Distinct Hair Shapes EVELYNE MAES, FRASER BELL, CHARLES HEFER, ANCY THOMAS, DUANE HARLAND, ALASDAIR NOBLE, JEFFREY PLOWMAN, STEFAN CLERENS, and ANITA GROSVENOR , Beyond Food, AgResearch Ltd., Lincoln 7674, New Zealand (E.M., A.T., D.H., J.P., S.C., A.G.), Unilever R&D, Port Sunlight, Bebington, Wirral CH63 3JW (F.B.), United Kingdom , Knowledge and Analytics, AgResearch Ltd., Lincoln 7674, New Zealand (C.H., A.N.), Biomolecular Interaction Centre, University of Canterbury, Christchurch 8041, New Zealand (S.C.), Riddet Institute, Massey University, Palmerston North 4474, New Zealand (S.C.) Accepted for publication January 6, 2021. Synopsis Scalp hair is a universal human characteristic, and a wide range of hair shape and color variations exists. Although differences in human scalp hair shape are visually apparent, the underpinning molecular insights are yet to be fully explored. This work reports the determination of differences at the protein level between two distinct groups of hair shape: very straight samples versus very curly hair samples. An in-depth high- resolution liquid-chromatography mass spectrometry proteome analysis study was performed on hair samples from 50 individuals (pooled in 10 × 5 samples) with very curly hair and 50 subjects with very straight hair (pooled in 10 × 5 samples) to decipher differences between the two experimental groups at the protein level. Our results demonstrate that a distinction between the two experimental groups (very straight vs. very curly) can be made based on their overall protein profi les in a multivariate analysis approach. Further investigation of the protein expression levels between these two groups pinpointed 13 unique proteins which were found to be signifi cantly different between the two groups, with an adjusted p-value 0.05 and a fold change of more than two. Although differences between the very curly and the very straight hair sample groups could be identifi ed, linkage between population differences and curl phenotype is currently unknown and requires further investigation. INT RODUCTION Hum an scalp hair is an important component of personal identity, and the perception of hair quality measured by numerous visual appearance and tactile aspects is of crucial importance to consumers. Individual hair-care needs and aspirations are diverse, and Address all correspondence to Anita Grosvenor at 249 J. Cosmet. Sci., 72, 249–267 (May/June 2021)
consumers with naturally curly hair have different cosmetic needs from people with straight hair (1), thus indicating that specifi c product design is required for hair-care products to deliver optimal benefi ts to each hair type. Hai r shape can be described by consumers as straight, wavy, curly, and a number of sub- jective variations thereof. An objective classifi cation system has been developed to classify these different hair shapes based on a number of morphological and phenotypical param- eters, independent of biogeographic or genomic ancestry. This classifi cation system, based on the degree of curliness, starts at type I which refers to straight hair and goes to type VIII which is tightly curly hair (2). Man y factors have been discovered over the years that have been claimed to directly or indirectly contribute to hair curvature. One of the most prominent fi ndings was that hair curvature correlates to the morphology of the hair follicle. It has been demonstrated that curly fi bers which emerge from the follicle are generated within curved follicles, whereas straight hair emerges from collinear follicles, with bulbs tilted at almost right angles with the scalp (3). Rotation of the follicle by the arrector pili muscle has been suggested as responsible for extrusion of helical fi ber shape (4). Others have suggested that the inner root sheath, which supports the growing hair shaft, plays a role in molding curvature due to correlations between mutations to keratins K71 and K74 and high-curl disorders (5). Challenging these extrusion views are studies that correlate internal hair-shaft features in the follicle or mature fi ber with hair shape such that follicle shape is a consequence of fi ber development and not vice versa. In the follicle, these include reported differences across the hair shaft in cell division rates (6) and keratin structure development (7,8). In the mature hair, an elliptical profi le is often cited as correlated to curliness (5,9), but there are other differences across the hair shaft at the microstructural level in keratin nanostructure organization (10–12) and cortical cell remnant length (13) that also correlate with hair curvature. Two main points are that the complexity of hair growth makes discriminating between cause and effect diffi cult (14,15) and that hair curliness appears to be pro- grammed within the follicle bulb (16,17). Dat a that clarify the underpinning mechanism that connects the proteins and microstruc- ture with curvature in human hair will help us not only understand hair shape generation but more directly identify differences in damage and interventions related to hair shape. In this study, we target a comprehensive understanding of the differences in hair curva- ture at the molecular level by applying proteomic technologies to decipher differences in the proteome between two groups with distinct hair shapes. The fi rst group refl ects hair samples with very straight hair, whereas the second group contains hair samples with very high levels of curvature. MET HODS OVE RVIEW OF SAMPLES Hai r fi ber samples were sourced from 50 subjects with very straight hair, with character- istics of type I in the scale defi ned by Loussouarn and de la Mettrie et al. (18), and from 50 panelists with very curly hair, with characteristics of types V–VIII of the same scale. All subjects were aged between 18 and 55 years and had not chemically treated their hair for at least 6 weeks before sampling. JOURNAL OF COSMETIC SCIENCE 250
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