This study explores the proteome phenotypes of two kinds of cashmere produced in different environments to delineate and discover proteome-fibre diameter relationships. Herein, we assess the genetic and environmental influence on proteome phenotypes, identify sets of fibre diameter-related proteins and their functional themes, and highlight individual proteins with a strong association with fibre diameter. Previous comparative studies on cashmere were mostly based on genomic and transcriptomic methods[28–30]. Nevertheless, proteomic studies in cashmere are essential because regulation of gene expression occurs mainly posttranscriptionally. The first proteomic studies were focused especially on the comparison of sheep wool and were based on 2 DE-gel and subsequent mass spectrometer analysis[31]. However, this method allows only the comparison of proteins with high abundance. Advances in proteomic methods allowed the comparison of relative protein abundances and label-free quantitative proteomics used in this manuscript started to be used for protein quantitative and qualitative[32]. Our label-free proteomics investigation showed 76 proteins identified in Alxa cashmere, and 167 proteins identified in Alpas cashmere, unique proteins and peptide segments were identified between the two populations, which were involved in higher numbers of structural molecule activity and keratin filament processes, most of them are structural proteins, including keratin and keratin-associated proteins. Keratin is a non-nutritive protein with fibre properties, it is widely found in the epidermis of humans and animals. As the main component of fibre, it determines the structural characteristics of the fibre[36]. Among the proteins that were identified, some proteins(e.g., Keratin38, Keratin5, Keratin14, Keratin25, Keratin71, Keratin31, Keratin36, Keratin85) were also highlighted in other investigations on the skin of goat or other farm animals to modulating the phenotypic traits of the fibers [17, 33–35]. The protein list identified in the present study, which represents by far the broadest picture of the Inner Mongolia cashmere fibre proteome, is an improvement on the previous literature and could serve as an impetus for better understanding the processes in the average fibre diameter of cashmere is different and could therefore provide novel information about this species and its production.
The researchers used RNA sequencing to compare gene expression in skin samples from cows with different hair diameters and found that KRT14 was expressed at higher levels in the skin with thicker hair diameters and at lower levels in the skin with finer hair diameters,indicating that KRT14 is involved in regulating the formation process of hair thickness[37]. In this study, KRT14, as an up-regulated protein, had high expression in the thicker fiber of Alpas and low expression in the finer fiber of Alxa. Another study, which induced the expression of KRT14 in mice, found that defects in KRT14 may lead to reduced hair diameter and backward hairline problems in humans[38]. In this study KRT14 participated in the process of epithelial cell differentiation and protein hetero-tetramerization, involving keratin filament and intermediate filament organization, it also plays a role in structural molecule activity, speculate that KRT14 for cashmere fineness has a certain regulation effect. The effects of loss of KRT17 on hair growth and hair fineness are similar to the symptoms of hor-mone-sensitive hair loss,after the deletion of the KRT17 gene in mice, the hair fineness of mice was significantly reduced. These results suggest that KRT17 has certain effects on hair fineness and hair growth[39–41]. The effect of KRT17 on hair diameter is also supported by several studies in humans, specifically, the higher the level of KRT17 expression, the larger the hair diameter[42, 43]. In this study, KRT17 expression was higher in Alpas thicker fibers than in Alxa finer fibers. Meanwhile,it is found that KRT17 participates in the process of keratinization and intermediate filament, organization, involving keratin filament and intermediate filament organization, it also plays a role in structural molecule activity. Speculated, KRT17 plays a certain role in the regulation of fibre fineness. The expression level of KRT10 in keratinocytes is related to the thickness of the stratum corneum and affects the synthesis of cortical proteins during hair follicle cell differentiation, overexpression of KRT10 may cause excessive proliferation and differentiation of keratinocytes, resulting in larger keratinocytes in hair follicles, and thus coarser hair[44, 45], further affecting hair growth and fineness[46]. In this study, it is found that KRT10 participates in the process of peptide cross-linking and keratinocyte differentiation, plays a role in the structural constituent of the epidermis, and the expression level of KRT10 in Alpas thicker fiber was higher than that in Alxa finer fiber, it is inferred that the fineness of cashmere fiber in goats is related to its content. The researchers alhnolo-gy to knock out the KRT82 gene in the experimental sheep, and the results show the yield of cashmere was decreased, and the length and diameter of cashmere were also reduced, KRT82 may be involved in the hair growth and differentiation process by regulating the synthesis and assembly of keratin, thus affecting hair diameter[47–49]. Meanwhile, KRT82 expression was higher in Alxa finer fibers than in Alpas thicker fibers. It is found that there is a close relationship between the expression level of KRT82 and the cashmere diameter of the goat.
Studies have shown that estrogen plays an important role in regulating hair growth, development, and hair loss. Estrogen can accelerate the proliferation and division of hair mother cells and prolong the life cycle of hair follicles, thereby promoting hair growth. In addition, estrogen can also affect the activity of stromal cells, pigment cells, and glial cells, thus affecting hair diameter(Table 2). Specifically, estrogen can promote the division and proliferation of stromal cells, resulting in larger hair diameters; when estrogen levels decrease, stromal cell activity decreases, and hair diameter becomes thinner [50–52].In the results of pathway analysis, KRT14, KRT17, and KRT10 are involved in the Estrogen signaling pathway, further evidence of their role in regulating fineness in cashmere fibers.
Sulfur, an essential mineral element for animals, mainly exists in the form of organic sulfur-containing amino acids (SAAs), such as cysteine and methionine[53]. The content, form, and structure of sulfur play an important role in determining the fibre quality and directly affect the properties of cashmere,it has been shown that in fibres, higher sulfur content is associated with larger fibre diameter[53–55]. In this study, the sulfur content of KRT82 (sulfur content = 6%), KRT14 (sulfur content = 3%), KRT10 (sulfur con-tent = 2%), and KRT17 (sulfur content = 3%) is highly expressed in Alpas. In the composition of amino acids, the expression of KRT14, KRT17, KRT10, and KRT82 was further demonstrated to affect cashmere fiber, especially on fineness.
Combined with fiber diameter test results, fiber composition and expression content, protein function identification, involved pathway analysis, primary, secondary, and tertiary structure analysis, and protein interaction network, the reasons for the difference in fineness of Alpas and Alxa cashmere fibers were explained.