Keratins of the Human Hair Follicle

Compartmentation of Mitochondrial and Oxidative Metabolism in Growing Hair Follicles: A Ring of Fire

Little is known about the energetics of growing hair follicles, particularly in the mitochondrially abundant bulb. Here, mitochondrial and oxidative metabolism was visualized by multiphoton and light sheet microscopy in cultured bovine hair follicles and plucked human hairs. Mitochondrial membrane potential (ΔΨ), cell viability, reactive oxygen species (ROS), and secretory granules were assessed with parameter-indicating fluorophores. In growing follicles, lower bulb epithelial cells had high viability, and mitochondria were polarized. Most epithelially generated ROS co-localized with polarized mitochondria. As the imaging plane captured more central and distal cells, ΔΨ disappeared abruptly at a transition to a nonfluorescent core continuous with the hair shaft. Approaching the transition, ΔΨ and ROS increased, and secretory granules disappeared. ROS and ΔΨ were strongest in a circumferential paraxial ring at putative sites for formation of the outer cortex/cuticle of the hair shaft. By contrast, polarized mitochondria in dermal papillar fibroblasts produced minimal ROS. Plucked hairs showed a similar abrupt transition of degranulation/depolarization near sites of keratin deposition, as well as an ROS-generating paraxial ring of fire. Hair movement out of the follicle appeared to occur independently of follicular bulb bioenergetics by a tractor mechanism involving the inner and outer root sheaths.

Characterisation of cell cycle arrest and terminal differentiation in a maximally proliferative human epithelial tissue: Lessons from the human hair follicle matrix

Human hair follicle (HF) growth and hair shaft formation require terminal differentiation-associated cell cycle arrest of highly proliferative matrix keratinocytes. However, the regulation of this complex event remains unknown. CIP/KIP family member proteins (p21^CIP1, p27^KIP1 and p57^KIP2) regulate cell cycle progression/arrest, endoreplication, differentiation and apoptosis. Since they have not yet been adequately characterized in the human HF, we asked whether and where CIP/KIP proteins localise in the human hair matrix and pre-cortex in relation to cell cycle activity and HF-specific epithelial cell differentiation that is marked by keratin 85 (K85) protein expression. K85 expression coincided with loss or reduction in cell cycle activity markers, including in situ DNA synthesis (EdU incorporation), Ki-67, phospho-histone H3 and cyclins A and B1, affirming a post-mitotic state of pre-cortical HF keratinocytes. Expression of CIP/KIP proteins was found abundantly within the proliferative hair matrix, concomitant with a role in cell cycle checkpoint control. p21^CIP1, p27^KIP1 and cyclin E persisted within post-mitotic keratinocytes of the pre-cortex, whereas p57^KIP2 protein decreased but became nuclear. These data imply a supportive role for CIP/KIP proteins in maintaining proliferative arrest, differentiation and anti-apoptotic pathways, promoting continuous hair bulb growth and hair shaft formation in anagen VI. Moreover, post-mitotic hair matrix regions contained cells with enlarged nuclei, and DNA in situ hybridisation showed cells that were >2N in the pre-cortex. This suggests that CIP/KIP proteins might counterbalance cyclin E to control further rounds of DNA replication in a cell population that has a propensity to become tetraploid. These data shed new light on the in situ-biography of human hair matrix keratinocytes on their path of active cell cycling, arrest and terminal differentiation, and showcase the human HF as an excellent, clinically relevant model system for cell cycle physiology research of human epithelial cells within their natural tissue habitat.

DELAYED GREENING 238, a Nuclear-Encoded Chloroplast Nucleoid Protein, Is Involved in the Regulation of Early Chloroplast Development and Plastid Gene Expression in Arabidopsis thaliana

Chloroplast development is an essential process for plant growth that is regulated by numerous proteins. Plastid-encoded plastid RNA polymerase (PEP) is a large complex that regulates plastid gene transcription and chloroplast development. However, many proteins in this complex remain to be identified. Here, through large-scale screening of Arabidopsis mutants by Chl fluorescence imaging, we identified a novel protein, DELAYED GREENING 238 (DG238), which is involved in regulating chloroplast development and plastid gene expression. Loss of DG238 retards plant growth, delays young leaf greening, affects chloroplast development and lowers photosynthetic efficiency. Moreover, blue-native PAGE (BN-PAGE) and Western blot analysis indicated that PSII and PSI protein levels are reduced in dg238 mutants. DG238 is mainly expressed in young tissues and is regulated by light signals. Subcellular localization analysis showed that DG238 is a nuclear-encoded chloroplast nucleoid protein. More interestingly, DG238 was co-expressed with FLN1, which encodes an essential subunit of the PEP complex. Bimolecular fluorescence complementation (BiFC) and co-immunoprecipitation (Co-IP) assays showed that DG238 can also interact with FLN1. Taken together, these results suggest that DG238 may function as a component of the PEP complex that is important for the early stage of chloroplast development and helps regulate PEP-dependent plastid gene expression.

Dermal-Epidermal Cross-Talk: Differential Interactions With Microvascular Endothelial Cells

The biological importance of circulatory blood supply and angiogenesis for hair growth is now well recognized, but the their regulatory mechanisms require more mechanistic investigation. In vitro cocultures and tricultures can be successfully employed to greatly improve our knowledge on paracrine crosstalk between cell types that populate the dermal-epidermal interface and cutaneous vasculature. Here we report that human dermal fibroblasts (NHDF) promote viability and proliferation of microvascular endothelial cells (HMVEC), while HMVEC are not mitogenic for NHDF. In triculture setup, conditioned media (CM) obtained by cocultures (HMVEC/NHDF or HMVEC/follicle fibroblasts) differently modulate growth and proliferation of keratinocytes and alter the expression of metabolic and pro-inflammatory markers. In conclusion, tricultures were successfully employed to characterize in vitro dermal-epithelial and endothelial interactions and could integrate ex vivo and in vivo approaches by the use of high-throughput and standardized protocols in controlled conditions. J. Cell. Physiol. 232: 897-903, 2017. © 2016 Wiley Periodicals, Inc.

A High-Yield Two-Hour Protocol for Extraction of Human Hair Shaft Proteins

Proteome analysis of the human hair remains challenging due to the poor solubility of hair proteins and the difficulty in their extraction. In the present study, we have developed a rapid extraction protocol for hair shaft protein using alkaline-based buffer. The new protocol accelerated the procedure by reducing the extraction time from at least a day to less than two hours and showed a protein recovery of 47.3 ± 3.72%. Further analyses of the extracted protein sample through sodium dodecyl sulfate polyacrylamide gel electrophoresis and Quadrupole-time-of-flight mass spectrometry analysis unveiled a total of 60 proteins, including 25 that were not previously reported. Identification of these proteins is anticipated to be crucial in helping to understand the molecular basis of hair for potential applications in the future.

A primer for studying cell cycle dynamics of the human hair follicle

The cell cycle is of major importance to human hair follicle (HF) biology. Not only is continuously active cell cycling required to facilitate healthy hair growth in anagen VI HFs, but perturbations in the cell cycle are likely to be of significance in HF pathology (i.e. in scarring, non-scarring, chemotherapy-induced and androgenic alopecias). However, cell cycle dynamics of the human hair follicle (HF) are poorly understood in contrast to what is known in mouse. The current Methods Review aims at helping to close this gap by presenting a primer that introduces immunohistological/immunofluorescent techniques to study the cell cycle in the human HF. Moreover, this primer encourages the exploitation of the human HF as a powerful and clinically relevant tool to investigate mammalian cell cycle biology in situ. To achieve this, we describe methods to study markers of general 'proliferation' (nuclei count, Ki-67 expression), apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labelling, cleaved caspase 3), mitosis (phospho-histone H3, 'pS780'), DNA synthesis (5-ethynyl-2'-deoxyuridine) and cell cycle regulation (cyclins) in the human HF. In addition, we provide specific examples of dual immunolabelling for instructive cell cycle analyses and for investigating the cell cycle behaviour of specific HF keratinocyte subpopulations, such as keratin 15+ stem/progenitor cells.

Birth of Four Chimeric Plastid Gene Clusters in Japanese Umbrella Pine

Many genes in the plastid genomes (plastomes) of plants are organized as gene clusters, in which genes are co-transcribed, resembling bacterial operons. These plastid operons are highly conserved, even among conifers, whose plastomes are highly rearranged relative to other seed plants. We have determined the complete plastome sequence of Sciadopitys verticillata (Japanese umbrella pine), the sole member of Sciadopityaceae. The Sciadopitys plastome is characterized by extensive inversions, pseudogenization of four tRNA genes after tandem duplications, and a unique pair of 370-bp inverted repeats involved in the formation of isomeric plastomes. We showed that plastomic inversions in Sciadopitys have led to shuffling of the remote conserved operons, resulting in the birth of four chimeric gene clusters. Our data also demonstrated that the relocated genes can be co-transcribed in these chimeric gene clusters. The plastome of Sciadopitys advances our current understanding of how the conifer plastomes have evolved toward increased diversity and complexity.

Comparative Transcriptome Analysis of Fetal Skin Reveals Key Genes Related to Hair Follicle Morphogenesis in Cashmere Goats

Cashmere goat skin contains two types of hair follicles (HF): primary hair follicles (PHF) and secondary hair follicles (SHF). Although multiple genetic determinants associated with HF formation have been identified, the molecules that determine the independent morphogenesis of HF in cashmere goats remain elusive. The growth and development of SHF directly influence the quantity and quality of cashmere production. Here, we report the transcriptome profiling analysis of nine skin samples from cashmere goats using 60- and 120-day-old embryos (E60 and E120, respectively), as well as newborns (NB), through RNA-sequencing (RNA-seq). HF morphological changes indicated that PHF were initiated at E60, with maturation from E120, while differentiation of SHF was identified at E120 until formation of cashmere occurred after birth (NB). The RNA-sequencing analysis generated over 20.6 million clean reads from each mRNA library. The number of differentially expressed genes (DEGs) in E60 vs. E120, E120 vs. NB, and E60 vs. NB were 1,024, 0 and 1,801, respectively, indicating that no significant differences were found at transcriptomic levels between E120 and NB. Key genes including B4GALT4, TNC, a-integrin, and FGFR1, were up-regulated and expressed in HF initiation from E60 to E120, while regulatory genes such as GPRC5D, PAD3, HOXC13, PRR9, VSIG8, LRRC15, LHX2, MSX-2, and FOXN1 were up-regulated and expressed in HF keratinisation and hair shaft differentiation from E120 and NB to E60. Several genes belonging to the KRT and KRTAP gene families were detected throughout the three HF developmental stages. The transcriptional trajectory analyses of all DEGs indicated that immune privilege, glycosaminoglycan biosynthesis, extracellular matrix receptor interaction, and growth factor receptors all played dominant roles in the epithelial-mesenchymal interface and HF formation. We found that the Wnt, transforming growth factor-beta/bone morphogenetic protein, and Notch family members played vital roles in HF differentiation and maturation. The DEGs we found could be attributed to the generation and development of HF, and thus will be critically important for improving the quantity and quality of fleece production in animals for fibres.

Autosomal Recessive Hypotrichosis with Woolly Hair Caused by a Mutation in the Keratin 25 Gene Expressed in Hair Follicles

Hypotrichosis is an abnormal condition characterized by decreased hair density and various defects in hair structure and growth patterns. In particular, in woolly hair, hypotrichosis is characterized by a tightly curled structure and abnormal growth. In this study, we present a detailed comparative examination of individuals affected by autosomal-recessive hypotrichosis (ARH), which distinguishes two types of ARH. Earlier, we demonstrated that exon 4 deletion in the lipase H gene caused an ARH (hypotrichosis 7; MIM: 604379) in populations of the Volga-Ural region of Russia. Screening for this mutation in all affected individuals revealed its presence only in the group with the hypotrichosis 7 phenotype. Other patients formed a separate group of woolly hair-associated ARH, with a homozygous missense mutation c.712G>T (p.Val238Leu) in a highly conserved position of type I keratin KRT25 (K25). Haplotype analysis indicated a founder effect. An expression study in the HaCaT cell line demonstrated a deleterious effect of the p.Val238Leu mutation on the formation of keratin intermediate filaments. Hence, we have identified a previously unreported missense mutation in the KRT25 gene causing ARH with woolly hair.

Combining Untargeted and Targeted Proteomic Strategies for Discrimination and Quantification of Cashmere Fibers

Cashmere is regarded as a specialty and luxury fiber due to its scarcity and high economic value. For fiber quality assessment, it is technically very challenging to distinguish and quantify the cashmere fiber from yak or wool fibers because of their highly similar physical appearance and substantial protein sequence homology. To address this issue, we propose a workflow combining untargeted and targeted proteomics strategies for selecting, verifying and quantifying biomarkers for cashmere textile authentication. Untargeted proteomic surveys were first applied to identify 174, 157, and 156 proteins from cashmere, wool and yak fibers, respectively. After marker selection at different levels, peptides turned out to afford much higher selectivity than proteins for fiber species discrimination. Subsequently, parallel reaction monitoring (PRM) methods were developed for ten selected peptide markers. The PRM-based targeted analysis of peptide markers enabled accurate determination of fiber species and cashmere percentages in different fiber mixtures. Furthermore, collective use of these peptide makers allowed us to discriminate and quantify cashmere fibers in commercial finished fabrics that have undergone heavy chemical treatments. Cashmere proportion measurement in fabric samples using our proteomic approach was in good agreement with results from traditional light microscopy, yet our method can be more readily standardized to become an objective and robust assay for assessing authenticity of fibers and textiles. We anticipate that the proteomic strategies presented in our study could be further implicated in discovery of quality trait markers for other products containing highly homologous proteomes.

Plastid RNA polymerases: orchestration of enzymes with different evolutionary origins controls chloroplast biogenesis during the plant life cycle

Chloroplasts are the sunlight-collecting organelles of photosynthetic eukaryotes that energetically drive the biosphere of our planet. They are the base for all major food webs by providing essential photosynthates to all heterotrophic organisms including humans. Recent research has focused largely on an understanding of the function of these organelles, but knowledge about the biogenesis of chloroplasts is rather limited. It is known that chloroplasts develop from undifferentiated precursor plastids, the proplastids, in meristematic cells. This review focuses on the activation and action of plastid RNA polymerases, which play a key role in the development of new chloroplasts from proplastids. Evolutionarily, plastids emerged from the endosymbiosis of a cyanobacterium-like ancestor into a heterotrophic eukaryote. As an evolutionary remnant of this process, they possess their own genome, which is expressed by two types of plastid RNA polymerase, phage-type and prokaryotic-type RNA polymerase. The protein subunits of these polymerases are encoded in both the nuclear and plastid genomes. Their activation and action therefore require a highly sophisticated regulation that controls and coordinates the expression of the components encoded in the plastid and nucleus. Stoichiometric expression and correct assembly of RNA polymerase complexes is achieved by a combination of developmental and environmentally induced programmes. This review highlights the current knowledge about the functional coordination between the different types of plastid RNA polymerases and provides working models of their sequential expression and function for future investigations.

Широкое многообразие кератинов человека

А review presents systematic data about the diversity of human keratins. The results of numerous studies concerning the structure and functions of keratins, their distribution in various cells and tissues were summarized. The role of these proteins in the development of human hereditary diseases, as well as modern approaches in use keratins in immunohistochemistry and perspectives of their further studies are discussed.

Proteomic analysis of differentially expressed skin proteins in iRhom2(Uncv) mice

A mouse homozygous for the spontaneous mutation uncovered (Uncv) has a hairless phenotype. A 309-bp non-frameshift deletion mutation in the N-terminal cytoplasmic domain of iRhom2 was identified in Uncv mice (iRhom2^Uncv) using target region sequencing. The detailed molecular basis for how the iRhom2 mutation causes the hairless phenotype observed in the homozygous iRhom2^Uncv mouse remains unknown. To identify differentially expressed proteins in the skin of wild-type and homozygous iRhom2^Uncv littermates at postnatal day 5, proteomic approaches, including two-dimensional gel electrophoresis and mass spectrometry were used. Twelve proteins were differentially expressed in the skin in a comparison between wild-type and homozygous iRhom2^Uncv mice. A selection of the proteomic results were tested and verified using qRT-PCR, western blot and immunohistochemistry. These data indicate that differentially expressed proteins, especially KRT73, MEMO1 and Coro-1, might participate in the mechanism by which iRhom2 regulates the development of murine skin. [BMB Reports 2015; 48(1): 19-24]

The proteomics of wool fibre morphogenesis

Gel and gel-free proteomic techniques have been used for the first time to directly study the proteins present in whole wool follicles and dissected portions of follicles that correlated with morphological changes in the developing fibre as determined by transmission electron microscopy. Individual wool follicles were dissected into four portions designated as the bulb, elongation, keratogenous and keratinisation portions. Gel-free proteomic analysis of dissected portions from 30 follicles showed that the first keratins to appear were K31, K35 and K85, in the bulb portion. The first epithelial KAP, trichohyalin, was detected in the bulb portion and the first cortical KAP, KAP11.1 was found in the elongation portion. Other major trichocyte keratins and cortical KAPs began to appear further up the follicle in the keratogenous and keratinisation zones. These results were consistent with what has been observed from gene expression studies and correlated well with the morphological changes observed in the follicle. Other proteins detected by this approach included the keratin anchor protein desmoplakin, as well as vimentin and epithelial keratins, histones, ribosomal proteins and collagens. Two-dimensional electrophoretic (2DE) analysis of dissected portions of 50 follicles revealed substantial changes in the position, number and intensity of the spots of the trichocyte keratins as they progressed through the follicle zones, suggesting that they are subject to modification as a result of the keratinisation process. Also present in the 2DE maps were a number of epithelial keratins, presumably from the inner and outer root sheaths, and the dermal components.

Convergent evolution of cysteine-rich proteins in feathers and hair

Background

Feathers and hair consist of cornified epidermal keratinocytes in which proteins are crosslinked via disulfide bonds between cysteine residues of structural proteins to establish mechanical resilience. Cysteine-rich keratin-associated proteins (KRTAPs) are important components of hair whereas the molecular components of feathers have remained incompletely known. Recently, we have identified a chicken gene, named epidermal differentiation cysteine-rich protein (EDCRP), that encodes a protein with a cysteine content of 36%. Here we have investigated the putative role of EDCRP in the molecular architecture and evolution of feathers.

Results

Comparative genomics showed that the presence of an EDCRP gene and the high cysteine content of the encoded proteins are conserved among birds. Avian EDCRPs contain a species-specific number of sequence repeats with the consensus sequence CCDPCQ(K/Q)(S/P)V, thus resembling mammalian cysteine-rich KRTAPs which also contain sequence repeats of similar sequence. However, differences in gene loci and exon-intron structures suggest that EDCRP and KRTAPs have not evolved from a common gene ancestor but represent the products of convergent sequence evolution. mRNA in situ hybridization demonstrated that chicken EDCRP is expressed in the subperiderm layer of the embryonic epidermis and in the barbule cells of growing feathers. This expression pattern supports the hypothesis that feathers are evolutionarily derived from the subperiderm.

Conclusions

The results of this study suggest that convergent sequence evolution of avian EDCRP and mammalian KRTAPs has contributed to independent evolution of feathers and hair, respectively.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0360-y) contains supplementary material, which is available to authorized users.

Evolutionary aspects in intermediate filament proteins

Intermediate filament (IF) proteins, together with tubulins and actins, constitute the majority of cytoskeletal proteins in metazoans. Proteins of the IF family fulfil increasingly diverse functions but share common structural features. Phylogenetic analysis within the metazoan lineage traces back their origin to a common lamin-like ancestor. Major steps in lamin evolution occurred at the base of the vertebrate radiation, while cytoplasmic IF protein subfamilies evolved independently in the major metazoan lineages.

In vitro assembly properties of human type I and II hair keratins

Multiple type I and II hair keratins are expressed in hair-forming cells but the role of each protein in hair fiber formation remains obscure. In this study, recombinant proteins of human type I hair keratins (K35, K36 and K38) and type II hair keratins (K81 and K85) were prepared using bacterial expression systems. The heterotypic subunit interactions between the type I and II hair keratins were characterized using two-dimensional gel electrophoresis and surface plasmon resonance (SPR). Gel electrophoresis showed that the heterotypic complex-forming urea concentrations differ depending on the combination of keratins. K35-K85 and K36-K81 formed relatively stable heterotypic complexes. SPR revealed that soluble K35 bound to immobilized K85 with a higher affinity than to immobilized K81. The in vitro intermediate filament (IF) assembly of the hair keratins was explored by negative-staining electron microscopy. While K35-K81, K36-K81 and K35-K36-K81 formed IFs, K35-K85 afforded tight bundles of short IFs and large paracrystalline assemblies, and K36-K85 formed IF tangles. K85 promotes lateral association rather than elongation of short IFs. The in vitro assembly properties of hair keratins depended on the combination of type I and II hair keratins. Our data suggest the functional significance of K35-K85 and K36-K81 with distinct assembly properties in the formation of macrofibrils.

Increased expression of Dkk1 by HR is associated with alteration of hair cycle in hairpoor mice

BACKGROUND

Hairless (Hr), a transcriptional corepressor expressed mainly in the skin, regulates hair follicle (HF) morphogenesis and hair cycling. Recently, we reported a new Hr mutant mouse, "Hairpoor" (Hr(Hp)), that resembles the human hair disorder Marie Unna hereditary hypotrichosis (MUHH) in the heterozygous state. The Wnt/β-catenin signaling pathway is critical for homeostasis in various adult tissues including skin and HFs. One of the Wnt inhibitors, Dickkopf (Dkk), inhibits hair growth during the hair cycle as a catagen inducer of apoptosis, resulting in HF reductions.

OBJECTIVE

To investigate regulation of Dkk1 by HR and its effect on hair formation.

METHODS

The relative expression of Dkk1 in (+)/Hr(HP) and Hr(Hp)/Hr(Hp) mice during the hair cycle was investigated using real time PCR and Western blot analysis. Immunohistochemistry was performed in order to confirm abnormal expression of Dkk1 in HFs of (+)/Hr(HP) and Hr(Hp)/Hr(Hp) mice. To determine whether Dkk1 expression was also regulated by HR in vitro, an Hr-transient transfection experiment was performed. Alteration of the hair cycle in Hr(HP) heterozygous mice was identified by determination of the hair cycle and measurement of HF length.

RESULTS

Dkk1 expression was increased in the skin of (+)/Hr(HP) and Hr(Hp)/Hr(Hp) mice, as well as in Hr-overexpressing mouse keratinocytes. Additionally, an earlier entrance of HFs into catagen and shortened HF length in (+)/Hr(HP) mice compared to wild-type mice was observed.

CONCLUSION

Study results suggested that up-regulation of Dkk1 by HR contributed to abnormal development of HFs and failure in regeneration of HFs in Hr(Hp)/Hr(Hp) mice. These findings also indicated that alteration of the hair cycle in (+)/Hr(HP) mice was related to the up-regulation of Dkk1 by HR.

Beyond expectations: novel insights into epidermal keratin function and regulation

The epidermis is a stratified epithelium that relies on its cytoskeleton and cell junctions to protect the body against mechanical injury, dehydration, and infections. Keratin intermediate filament proteins are involved in many of these functions by forming cell-specific cytoskeletal scaffolds crucial for the maintenance of cell and tissue integrity. In response to various stresses, the expression and organization of keratins are altered at transcriptional and posttranslational levels to restore tissue homeostasis. Failure to restore tissue homeostasis in the presence of keratin gene mutations results in acute and chronic skin disorders for which currently no rational therapies are available. Here, we review the recent progress on the role of keratins in cytoarchitecture, adhesion, signaling, and inflammation. By focusing on epidermal keratins, we illustrate the contribution of keratin isotypes to differentiated epithelial functions.

The possible role of dermatophyte cysteine dioxygenase in keratin degradation

Cysteine dioxygenase (CDO, EC 1.13.11.20) is a key enzyme involved in the homeostatic regulation of cysteine level and in production of important oxidized metabolites of cysteine such as pyruvate, sulphite, sulphate, hypotaurine, and taurine in all eukaryotic cells. The intracellular CDO concentration is regulated at both transcriptional and posttranslational levels. In several fungi, CDO plays an important role as a virulence factor involved in morphological transition from yeast to mycelial forms. CDO is crucial for oxidation of cysteine to cysteine sulphinic acid and therefore for sulphite production and secretion. Because sulphite cleaves disulphide bridges as a first unavoidable step in keratinolysis, it is hypothesized that in dermatophytes, CDO is a virulence factor crucial for keratin degradation.

To grow or not to grow: hair morphogenesis and human genetic hair disorders

Mouse models have greatly helped in elucidating the molecular mechanisms involved in hair formation and regeneration. Recent publications have reviewed the genes involved in mouse hair development based on the phenotype of transgenic, knockout and mutant animal models. While much of this information has been instrumental in determining molecular aspects of human hair development and cycling, mice exhibit a specific pattern of hair morphogenesis and hair distribution throughout the body that cannot be directly correlated to human hair. In this mini-review, we discuss specific aspects of human hair follicle development and present an up-to-date summary of human genetic disorders associated with abnormalities in hair follicle morphogenesis, structure or regeneration.

New facets of keratin K77: interspecies variations of expression and different intracellular location in embryonic and adult skin of humans and mice

The differential expression of keratins is central to the formation of various epithelia and their appendages. Structurally, the type II keratin K77 is closely related to K1, the prototypical type II keratin of the suprabasal epidermis. Here, we perform a developmental study on K77 expression in human and murine skin. In both species, K77 is expressed in the suprabasal fetal epidermis. While K77 appears after K1 in the human epidermis, the opposite is true for the murine tissue. This species-specific pattern of expression is also found in conventional and organotypic cultures of human and murine keratinocytes. Ultrastructure investigation shows that, in contrast to K77 intermediate filaments of mice, those of the human ortholog are not attached to desmosomes. After birth, K77 disappears without deleterious consequences from human epidermis while it is maintained in the adult mouse epidermis, where its presence has so far gone unnoticed. After targeted Krt1 gene deletion in mice, K77 is normally expressed but fails to functionally replace K1. Besides the epidermis, both human and mouse K77 are present in luminal duct cells of eccrine sweat glands. The demonstration of a K77 ortholog in platypus but not in non-mammalian vertebrates identifies K77 as an evolutionarily ancient component of the mammalian integument that has evolved different patterns of intracellular distribution and adult tissue expression in primates.

Immunolocalization of junctional proteins in human hairs indicates that the membrane complex stabilizes the inner root sheath while desmosomes contact the companion layer through specific keratins

The inner root sheath (IRS) sustains and addresses the hair shaft outside the follicle. Ultrastructural analysis of immunolabeling for beta-catenin, plakophilin-1, desmoglein-4 and keratin-17 in human hairs has indicated that adherens junctions and desmosomes initially connect cells in mature IRS and the companion layer. Beta-catenin immunolabeling for adherens junctions is only seen in sparse regions of differentiating Huxley cells, Flugelzellen cells and Henle cells, but disappears in cornified cells of the IRS. Desmoglein-4 and plakophilin-1 immunolabeling are observed in differentiating and cornified desmosomes of the Huxley and Henle layers and in the membrane complex joining these cells. Desmoglein-4 and plakophilin-1 are more frequently immunolocalized in the intracellular side of the junctions, but some labeling is also present in the delta-layer of the membrane complex. The labeling indicates a prevalent intracellular redistribution of desmoglein-4 and plakophilin-1 when the final cornification of the IRS occurs. Intense keratin-17 immunolabeling is observed in tonofilaments of the companion layer joining the plakophilin-1 rich desmosomes of the Henle layer. This suggests that this elastic type of keratin is present at desmosome junctions during the movements of the companion layer along the slippage plane of the hair shaft.

A mutation in the type II hair keratin KRT86 gene in a Han family with monilethrix

Monilethrix, a congenital disease of hair, is usually associated with mutations in keratin genes, like KRT81, KRT83 and KRT86. We conducted this study to investigate the mutation of type II human basic hair keratin hHb/KRT gene in a Han family with monilethrix and obtain information for potential pathogenic mechanism study of monilethrix. Peripheral blood samples were drawn for genomic DNA detection. Exon 1 and exon 7 of the KRT81, KRT83 and KRT86 genes were amplified by PCR. All PCR products were sequenced directly using an ABI 310 DNA sequencer. These sequences were aligned with the standard sequences in GenBank using the BLAST software. PCR products were digested with restriction endonuclease and restriction fragment length polymorphism (RFLP) analysis was performed. In this study, we identified one novel mutation, which is a heterozygous transitional mutation of G→A at position 1,289 in exon 7 of the KRT86 gene [R430Q (KRT86)]. RFLP assays for the novel mutation excluded the possibility of polymorphism. The R430Q mutation of the KRT86 gene may be pathogenic for monilethrix. Meanwhile, we did not find any novel mutation or recurrent mutation in exons 1 and 7 of KRT81 and KRT83 and exon 1 of KRT86. There is a potential pathogenic gene in the subjects and our results expand the spectrum of mutations in the hHb6 gene.

A novel control of human keratin expression: cannabinoid receptor 1-mediated signaling down-regulates the expression of keratins K6 and K16 in human keratinocytes in vitro and in situ

Cannabinoid receptors (CB) are expressed throughout human skin epithelium. CB1 activation inhibits human hair growth and decreases proliferation of epidermal keratinocytes. Since psoriasis is a chronic hyperproliferative, inflammatory skin disease, it is conceivable that the therapeutic modulation of CB signaling, which can inhibit both proliferation and inflammation, could win a place in future psoriasis management. Given that psoriasis is characterized by up-regulation of keratins K6 and K16, we have investigated whether CB1 stimulation modulates their expression in human epidermis. Treatment of organ-cultured human skin with the CB1-specific agonist, arachidonoyl-chloro-ethanolamide (ACEA), decreased K6 and K16 staining intensity in situ. At the gene and protein levels, ACEA also decreased K6 expression of cultured HaCaT keratinocytes, which show some similarities to psoriatic keratinocytes. These effects were partly antagonized by the CB1-specific antagonist, AM251. While CB1-mediated signaling also significantly inhibited human epidermal keratinocyte proliferation in situ, as shown by K6/Ki-67-double immunofluorescence, the inhibitory effect of ACEA on K6 expression in situ was independent of its anti-proliferative effect. Given recent appreciation of the role of K6 as a functionally important protein that regulates epithelial wound healing in mice, it is conceivable that the novel CB1-mediated regulation of keratin 6/16 revealed here also is relevant to wound healing. Taken together, our results suggest that cannabinoids and their receptors constitute a novel, clinically relevant control element of human K6 and K16 expression.

Expression of caspase-14 and keratin-19 in the human epidermis and appendages during fetal skin development

Caspase-14 is a seemingly non-apoptotic caspase involved in keratinocyte differentiation and cornification of the skin. Keratin-19 is an epithelial marker and a potential marker of epidermal stem cells that is expressed during human fetal skin development. We examined the immunohistochemical expression of caspase-14 in relation to CK-19 in the human fetal skin during development and perinatally, to assess their role in human skin maturation. Skin samples were received at autopsy. In the fetal epidermis, caspase-14 was predominantly expressed in the more differentiated layers, gradually disappearing from the basal layer toward term. By contrast, keratin-19 expression gradually decreased with epidermal maturation through gestation (rho = -0.949; p = 0.0001) and was a marker of the germinative layers. Keratin-19 was preserved in scarce basal cell nests at term and postnatally. Caspase-14 and keratin-19 were inversely expressed in the differentiating epidermal layers through gestation (p < 0.0001). Concerning the appendages, in hair follicles and sebaceous glands, caspase-14 located preferentially in the more differentiated layers of the inner root sheath, whereas keratin-19 was expressed in the outer sheath. Eccrine sweat glands showed a variable pattern of caspase-14 and keratin-19 expression. In conclusion, caspase-14 emerged as a marker of human skin differentiation during development, while keratin-19 marked the germinative epithelial layers in the fetal epidermis and appendages and possibly the nests of epidermal stem cells.

Evaluation of a multi-layer adipose-derived stem cell sheet in a full-thickness wound healing model

Cell sheet technology has been studied for applications such as bone, ligament and skin regeneration. There has been limited examination of adipose-derived stem cells (ASCs) for cell sheet applications. The specific aim of this study was to evaluate ASC sheet technology for wound healing. ASCs were isolated from discarded human abdominal subcutaneous adipose tissue, and ASC cell sheets were created on the surface of fibrin-grafted culture dishes. In vitro examination consisted of the histochemical characterization of the ASC sheets. In vivo experiments consisted of implanting single-layer cell sheets, triple-layer cell sheets or non-treated control onto a full-thickness wound defect (including epidermis, dermis, and subcutaneous fat) in nude mice for 3 weeks. Cell sheets were easily peeled off from the culture dishes using forceps. The single- and triple-layer ASC sheets showed complete extracellular structure via hematoxylin & eosin staining. In vivo, the injury area was measured 7, 10, 14 and 21 days post-treatment to assess wound recovery. The ASC sheet-treated groups' injury area was significantly smaller than that of the non-treated control group at all time points except day 21. The triple-layer ASC sheet treatment significantly enhanced wound healing compared to the single-layer ASC sheet at 7, 10 and 14 days. The density of blood vessels showed that ASC cell sheet treatment slightly enhanced total vessel proliferation compared to the empty wound injury treatment. Our studies indicate that ASC sheets present a potentially viable matrix for full-thickness defect wound healing in a mouse model. Consequently, our ASC sheet technology represents a substantial advance in developing various types of three-dimensional tissues.

Keratin 71 mutations: from water dogs to woolly hair

The study of rare genetic disorders of the hair follicle has resulted in the identification of many causative genes, leading to the potential for the development of novel therapeutic approaches for both inherited and acquired hair disorders. In this issue, Fujimoto et al. identify a missense mutation within the keratin 71 (KRT71) gene as the cause for autosomal dominant woolly hair/hypotrichosis in a Japanese family. This represents the first human mutation in KRT71 to be linked to a hair disorder, establishing this gene as an important determinant of mammalian hair texture. Moreover, this finding provides new insight into the relationship between similar phenotypes resulting from mutations in distinct regulatory pathways and underscores the role of the inner root sheath in human hair growth.

A splice variant in KRT71 is associated with curly coat phenotype of Selkirk Rex cats

One of the salient features of the domestic cat is the aesthetics of its fur. The Selkirk Rex breed is defined by an autosomal dominant woolly rexoid hair (ADWH) abnormality that is characterized by tightly curled hair shafts. A genome-wide case - control association study was conducted using 9 curly coated Selkirk Rex and 29 controls, including straight-coated Selkirk Rex, British Shorthair and Persian, to localize the Selkirk autosomal dominant rexoid locus (SADRE). Although the control cats were from different breed lineages, they share recent breeding histories and were validated as controls by Bayesian clustering, multi-dimensional scaling and genomic inflation. A significant association was found on cat chromosome B4 (Praw = 2.87 × 10(-11)), and a unique haplotype spanning ~600 Kb was found in all the curly coated cats. Direct sequencing of four candidate genes revealed a splice site variant within the KRT71 gene associated with the hair abnormality in Selkirk Rex.

Redefining the structure of the hair follicle by 3D clonal analysis

The hair follicle (HF) is a multi-tissue mini-organ that self-renews periodically. However, the cellular organisation of this much-studied model is not fully understood. The structures of the outer layer and of the bulb, which ensures HF growth, have not been completely established. To clarify these points, we have conducted in vivo clonal analyses with 3D imaging in mice. The upper two-thirds of the HF outer layer consists of two clonally unrelated groups of cells that exhibit different modes of growth. They correspond to the basal outer root sheath (ORS) and the companion layer (Cp). The basal ORS has an unusual anisotropic mode of growth from a suprabulbar zone, which we named the privileged proliferation zone. The Cp has a stem/transient-amplifying mode of growth and is shown to be an HF internal structure. Furthermore, we describe an additional element, the bulb outer layer, which is contiguous and shares markers (e.g. Lgr5) with the basal ORS but is formed by a separate lineage that belongs neither to the ORS nor Cp lineage. It represents a novel element with proximal cells that are contiguous with the germinative layer in the bulb. In reference to its shape and position we named it the lower proximal cup (LPC). These clonal hierarchies reveal a novel model of HF organisation and growth based on two major entities: the basal ORS and the LPC plus the seven internal layers.

Bioengineering the hair follicle

The hair follicle develops from the primitive embryonic epidermis as a result of complex epithelial-mesenchymal interactions. The full follicle, consisting of epithelial cylinders under control of a proximal lying mesenchymal papilla, grows in cycles giving rise to a new hair shaft during each cycle. The ability to cycle endows the follicle with regenerative properties. The evolution of hair follicle engineering began with the recognition in the early 1960's that hair follicles could be transplanted clinically into a foreign site and still grow a shaft typical of the donor site. Since that time, it has been found that the follicular papilla has hair follicle inducing properties and that the hair follicle houses within it epithelial stem cells that can respond to hair inductive signals. These findings have laid the foundation for isolating hair-forming cells, for expanding the cells in culture, and for forming new follicles in vivo.