Hair Follicle Transglutaminasesa

Structural changes in epidermal scale and appendages as indicators of defective TGM1 activity

Defective transglutaminase 1 (TGM1) is a causative factor in some cases of lamellar ichthyosis (LI) and congenital ichthyosiform erythroderma (CIE) despite large differences in the phenotype between these conditions. In some of these individuals, defective cornified envelopes (CEs) have been reported by light or electron microscopic examination in epidermal scale, nail and/or hair. These findings suggest that assessment of such defects could have a diagnostic utility in distinguishing TG1-deficient versus non-deficient cases of autosomal recessive ichthyosis (ARI) . Present work (a) examines the integrity of CEs in epidermal scale and appendages in a case of TGM1-deficient CIE, (b) assesses the utility of hair/nail versus scale analysis in the diagnosis of TGM1 deficiency in vivo and (c) helps characterize the consequences of the V518M mutation in TGM1, about which conflicting reports have appeared. To this end, epidermal scale or callus, nail and hair samples from a patient with TGM1-deficient CIE, his asymptomatic family members and control subjects were extracted vigorously in sodium dodecyl sulfate and dithiothreitol and examined by light (phase contrast) and electron microscopy. Both epidermal scale and nail from the index case lacked the prominent cell borders that were visible by phase contrast microscopy after detergent extraction of control samples. (By contrast, abundant envelope structures were visible in extracted epidermal scale from patients with ichthyosis vulgaris, loricrin keratoderma and epidermolytic hyperkeratosis.) Electron microscopy confirmed the paucity of intact CEs, and revealed further that hair cuticle cells from the same subject also lacked the marginal bands that are visible in control hair samples. Such aberrations were evident neither in the samples from asymptomatic relatives of the index case nor in the hair-cuticle cells of numerous normal individuals, evidence that this defect is not a common polymorphism. These studies extend our prior work on TGM1-deficient LI to the full spectrum of TGM1-deficient patients, showing that the CIE phenotype, when attributable to a V518M heterozygous mutation in TGM1 in combination with an inactive allele, confers a cross-linking deficiency in a variety of keratinizing epithelia, as previously shown for TGM1-negative LI. These results further suggest that a non-invasive assessment of scale, nail and hair could be of diagnostic utility in distinguishing patients across a full range of phenotypes with deficiency in TGM1-encoded transglutaminase activity from other causes of ARI.

Cuticle cell defects in lamellar ichthyosis hair and anomalous hair shaft syndromes visualized after detergent extraction

BACKGROUND

The biochemical bases for fragility in most of the rare brittle hair shaft syndromes are unknown. The hypothesis being investigated in several syndromes is that the hair cuticle cells show defects in cross-linked protein features. Since transglutaminases stabilize protein structures by cross-linking them, hair from autosomal recessive lamellar ichthyosis patients lacking keratinocyte transglutaminase was examined to find whether this enzyme participates in hair shaft stabilization.

METHODS

Hair shaft samples from patients afflicted with lamellar ichthyosis or several brittle hair syndromes were examined ultrastructurally by transmission electron microscopy after vigorous extraction with detergent and reducing agent to reveal cross-linked protein features.

RESULTS

In hair cuticle cells from three patients with lamellar ichthyosis the marginal band (A layer) was present but nonuniform and subject to breakage, while in a fourth sample it was missing altogether. The exocuticle appeared less dense than in normal hair, consistent with extensive protein loss during detergent extraction. In cuticle cells from trichothiodystrophy hair, the exocuticle layer was essentially fully extractable in one sample, while in two others (from siblings) the exocuticle appeared less dense and the A layer was absent or greatly reduced in thickness. A sample of proximal trichorrhexis nodosa also displayed defects in cuticle cells, in which the endocuticle layer appeared subject to rupture. The outer cuticle cells in monilethrix hair displayed a thinning of the A layer and less dense exocuticle, while the cortex exhibited regions lacking remnant cell borders. Pili annulati hair displayed large gaps in the cortex, presumably reflecting the air-filled cavities characteristic of this syndrome, and wavy borders of some cuticle cells.

CONCLUSIONS

Observations with autosomal recessive lamellar ichthyosis hair indicate that keratinocyte transglutaminase has a major role in maturation of the cuticle but appears unnecessary for stabilization of cell borders in the cortex. Defective cross-linking was also evident in cuticle cells of trichothiodystrophy and monilethrix.

Purification and characterization of a novel transglutaminase from filarial nematode Brugia malayi

A transglutaminase (pTGase) was purified from filarial nematode, Brugia malayi. The steps used for purification were thermoprecipitation, ammonium sulfate precipitation, gel filtration on Superose 12 HR 10/30, ion-exchange chromatography on a Mono-Q column and further gel filtration on Superose 12 HR 10/30. The last step yielded an electrophoretically homogenous enzyme protein with 2200-fold purification and a reproducible yield of approximately 20%. The purified enzyme had a molecular mass of 56 kDa, specific activity of 2.25 U/mg protein and an isoelectric point of 7.2. The enzyme was active in the basic pH range with an optimum activity at pH 8.5. The pTGase activity was Ca(2+)-dependent and was inhibited by ammonia, primary amines, EDTA, and -SH group blocking reagents. The enzyme activity was also inhibited by high salt (NaCl and KCl) concentrations, detergents, metal ions, and organic solvents. Ampholine (pH 6-8) at 1% (by vol.) caused about 20% inhibition of pTGase activity but at 3% (by vol.) the inhibition increased up to 80%. Similarly, the micromolar concentrations of GTP inhibited the enzyme activity only moderately but at millimolar concentration a significant inhibition was observed. The stability of the pTGase was not affected by 0.1% SDS or other physical parameters such as freezing and thawing. Further, the pTGase was found to be highly thermostable (stable at 60 degrees C for several hours) with optimum activity observed at 55 degrees C. The distinct substrate specificity, unique N-terminal sequence along with the other physico-chemical properties studied, suggested that pTGase is a novel member of transglutaminase family.

Ultrastructural visualization of cross-linked protein features in epidermal appendages

Upon vigorous extraction with ionic detergent under reducing conditions, the macroscopic structures of mammalian hair, bird feather and horny teeth of the hagfish become swollen and flexible but were substantially preserved. In each case, removal in this way of solubilizable constituents, such as disulfide-bonded keratins and associated matrix proteins, left a residue of epsilon-(gamma-glutamyl)lysine cross-linked protein. Residual features in hair included cell envelopes in the cortex, cell envelopes and intracellular deposits in the medulla, and nearly the entire cuticle cells. In feather, extraction left largely intact the macroscopic barb structures but caused collapse of the rachis. In both rachis and barbs, considerable material resembling cell envelopes remained. In extracted hagfish teeth the cellular organization was clearly visible microscopically, including cell borders and remnant nuclei. Unlike the cornified envelopes of mature epidermal keratinocytes, which appear as doublets, reflecting their formation immediately beneath each plasma membrane of apposing cells, the borders of cells of hair cortex and hagfish teeth appeared single and continuous from one cell to the next. Thus the observed cross-linked features comprised four types: (i) condensation immediately beneath the plasma membrane (feather, hair medulla and cuticle) similar to cornified envelopes of epidermal keratinocytes; (ii) deposition between cells (hair cortex, horny teeth); (iii) cytoplasmic deposits (hair cuticle and medulla); and (iv) nuclear condensation (hair medulla, horny teeth). The results emphasize the importance of transglutaminases and their substrate proteins for the function of epidermal appendages and may provide a useful diagnostic test for perturbation of their normal structures.

Molecules of the cycling hair follicle--a tabulated review

In this review we tabulated molecules which have been experimentally identified to be associated with, or play a role in, hair follicle growth. While compiling these data we were impressed by the fact that this field is only now beginning to be developed in terms of molecular analysis. Ironically, hair was used in some of the earliest molecular approaches to biologic structure (e.g. Astbury and Street, 1931), but the field did not develop from there. From our review we have come to the following conclusions. (1) As indicated by the growing number of reports dealing with follicle-associated molecules in the past 3 years, the field of hair biology has entered a new molecular era. (2) In many reported hair biology studies not enough emphasis has been placed on the fact that the follicle is a dynamic structure. All too often a study is limited to follicles of one particular phase of the cycle or one phase of development. Students in the field have to be more sensitive to the remarkable changes that this deceptively simple structure can undergo during its cycle. (3) Although we have not been able to find any molecules unique to the follicle, some of the structural molecules come close to an ideal tool. It is our impression that even more specific molecule tags will be found. Whether this requires a subtraction library approach or gene mapping of specific mutants is not yet clear. It would appear that the large, diverse family of intermediate filament-associated proteins will prove to be an excellent source of unique follicle-labeling molecules. (4) There is an acute need for molecules which distinguish the phases of the cycle, e.g. telogen from early anagen. Telogen is by far the most difficult phase to identify morphologically since the earliest phase of anagen and the latest phase of catagen may appear structurally like telogen. That these phases are functionally distinguishable must imply a molecular difference. As the number of recognized hair follicle-associated molecules and their interactions increase, it will be essential to assemble libraries of highly specific RNA and antibody probes for localization and mapping studies. We recognize that this review, as written, is imperfect. It is particularly deficient in making any effort towards identifying unifying principles of structure and function. We look forward to returning to this subject within 3 years.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and characterization of a novel hair follicle-specific gene, Hacl-1

We have isolated a hair-follicle-specific gene, termed hacl-1, from a cDNA library of ICR mouse skin. Hacl-1 is expressed specifically in skin, and its mRNA level is correlated with the active state of hair follicles in developmental and regenerative processes of hair. Its mRNA is approximately 1 kilobase pairs (kb). Its cDNA was completely co-linear with the genomic clone, indicating that the hacl-1 gene is composed of one exon. The hacl-1 gene has an open reading frame of 579 base pairs (bp). The deduced amino acid sequence showed six direct repeats of a decapeptide on the C-terminal side. The repetitive unit contains a CQP motif, which is present in repetitive peptide sequences of some hair- and epidermal-cell-specific proteins. In situ hybridization with a 3' untranslated region of the hacl-1 cDNA as a probe showed that hacl-1 was expressed specifically in the keratogenous zone of the cortical cells of the hair shaft. No other components of hair follicles or epidermis showed a positive signal. Thus, hacl-1 is a novel, hair-follicle-specific gene.

In vivo regulation of murine hair growth: insights from grafting defined cell populations onto nude mice

The nude mouse graft model for testing the hair-forming ability of selected cell populations has considerable potential for providing insights into factors that are important for hair follicle development and proper hair formation. We have developed a minimal component system consisting of immature hair follicle buds from newborn pigmented C57BL/6 mice and adenovirus E1A-immortalized rat vibrissa dermal papilla cells. Hair follicle buds contribute to formation of hairless skin when grafted alone or with Swiss 3T3 cells, but produce densely haired skin when grafted with a fresh dermal cell preparation. The fresh dermal cell preparation represents the single cell fraction after hair follicles have been removed from a collagenase digest of newborn mouse dermis. It provides dermal papilla cells, fibroblasts, and possibly other important growth factor-producing cell types. Rat vibrissa dermal papilla cells supported dense hair growth at early passage in culture but progressively lost this potential during repeated passage in culture. Of 19 E1A-immortalized, clonally derived rat vibrissa dermal papilla cell lines, the four most positive clones supported hair growth to the extent of approximately 200 to 300 hairs per 1-2 cm2 graft area. The remaining clones were moderately positive (five clones), weakly positive (three clones), or negative (seven clones). Swiss 3T3 cells prevented contraction of the graft area but did not appear to affect the number of hairs in the graft site produced by dermal papilla cells plus hair follicle buds alone. The relatively low hair density (estimated 1-5% of normal) resulting from grafts of hair follicle buds with the most positive of the immortalized dermal papilla cell clones compared to fresh dermal cells suggests that optimal reconstitution of hair growth requires some function of dermal papilla cells partially lost during the immortalization process and possibly the contribution of other cell types present in the fresh dermal cell preparation, which is not supplied by the Swiss 3T3 cells. The current graft system, comprising hair follicle buds and immortalized dermal papilla cell clones, provides an assay for positive or negative influences on hair growth exerted by added selected cell types, growth factors, or other substances. Characterization of the phenotype of the dermal papilla cell lines, which differ in their ability to support hair growth when grafted with hair follicle buds, may provide insight into specific dermal papilla cell properties important for their function in this system.