involucrin and Alopecia

The role for 1,25-dihydroxyvitamin D3 and/or calcium in hair follicle cycling is not clear despite their impact on keratinocyte differentiation. We found that calbindin-D9k null (knockout) pups generated from calbindin-D9k knockout females fed a vitamin D-deficient, low-calcium (0.47%) diet develop transient alopecia. The pups appear phenotypically normal until 13 days of age, after which the hair progressively sheds in a caudocephalic direction, resulting in truncal alopecia totalis by 20-23 days, with spontaneous recovery by 28 days. Histological studies showed markedly dystrophic hair follicles, loss of hair shafts with increased apoptosis, and hyperplastic epidermis during this time. Ha1 expression is lost during catagen in all mice but recovers more slowly in the knockout pups on the vitamin D-deficient, low-calcium diet. Keratin 1 expression is reduced throughout days 19-28. The expressions of involucrin, loricrin, and cathepsin L is initially increased by day 19 but subsequently falls below those of controls by day 23, as does that of desmoglein 3. Feeding the mothers a high-vitamin D/high-calcium (2%)/lactose (20%) diet lessens the phenotype, and knockout pups fostered to mothers fed a normal diet do not develop alopecia. Our results show that in calbindin-D9k knockout pups, a maternal vitamin D-deficient/low-calcium diet leads to transient noncicatricial alopecia.

Topics: Alopecia; Animals; Apoptosis; Calcium, Dietary; Cathepsin L; Cell Differentiation; Desmoglein 3; Epidermis; Female; Hair Follicle; Immunohistochemistry; Keratin-1; Keratinocytes; Male; Membrane Proteins; Mice; Mice, Inbred C57BL; Mice, Knockout; Phenotype; Protein Precursors; Receptors, Calcitriol; Vitamin D

The biological effects of 1,25-dihydroxyvitamin D3 are mediated by a nuclear receptor, the vitamin D receptor (VDR). Targeted ablation of the VDR in mice results in hypocalcemia, hypophosphatemia, hyperparathyroidism, rickets, osteomalacia, and alopecia. Normalization of mineral ion homeostasis prevents these abnormalities with the exception of the alopecia. Because 1,25(OH)2D3 has been shown to play a role in keratinocyte proliferation and differentiation, we undertook studies in primary keratinocytes and skin isolated from VDR null mice to determine if a keratinocyte abnormality could explain the alopecia observed. The basal proliferation rate of the VDR null and wild-type keratinocytes was identical both under proliferating and differentiating conditions. Assessment of in vivo keratinocyte proliferation at 4 days of age confirmed that VDR ablation did not have a significant effect. There was no difference in the basal expression of markers of keratinocyte differentiation (keratin 1, involucrin, and loricrin) in the keratinocytes isolated from VDR-ablated mice when compared with those isolated from control littermates. Similarly, in vivo expression of these genes was not altered at 4 days of age. When anagen was induced by depilation at 18 days of age, the VDR null mice had a profound impairment in initiation of the hair cycle. These data suggest that the alopecia in the VDR null mice is not attributable to an intrinsic defect in keratinocyte proliferation or differentiation, but rather to an abnormality in initiation of the hair cycle.

Topics: Alopecia; Animals; Calcitriol; Calcium; Cell Differentiation; Cell Division; Cells, Cultured; Keratinocytes; Keratins; Membrane Proteins; Mice; Mice, Hairless; Mice, Knockout; Mutation; Protein Precursors; Receptors, Calcitriol

Involucrin is a precursor of the keratinocyte cornified envelope that is specifically expressed in the suprabasal layers of the epidermis and other stratifying squamous epithelia. To study involucrin gene expression and the function of involucrin, we expressed a 6 kb DNA fragment of the human involucrin gene, containing approximately 2.5 kb of upstream sequence and 0.5 kb of downstream sequence, in transgenic mice. The transgene produces a 68 kDa protein that is detected by a human involucrin-specific antibody, and is expressed in a tissue-specific and differentiation-appropriate manner (i.e., expression is confined to the suprabasal layers of the epidermis, extocervix, trachea, esophagus and conjunctiva). Soluble involucrin levels are two to four times higher in transgenic epidermal keratinocytes compared to human foreskin keratinocytes. Newborn heterozygous animals have a normal birth weight and a normal appearing epidermis and hair growth begins at 4 to 5 days of age (i.e., the same time as hair growth in non-transgenic animals). In a subpopulation of the newborn homozygous animals birth weight is reduced, the epidermis is scaly and hair growth begins late, at around 9 to 10 days of age. In addition, the hair tends to stand erect on both heterozygous and homozygous adult animals giving the appearance of diffuse alopecia. Immunofluorescent and electron microscopy localize involucrin in the hair follicle and cornified envelope, respectively. These results suggest that overexpression of involucrin may cause abnormalities in hair follicle structure/function and cornified envelope structure. These animals provide a new model for the study of cornified envelope structure and function.

Topics: Alopecia; Amino Acid Sequence; Animals; Animals, Newborn; Cell Differentiation; Disease Models, Animal; DNA, Complementary; Epidermis; Female; Gene Expression Regulation; Genotype; Hair; Humans; Keratinocytes; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Molecular Sequence Data; Organ Specificity; Phenotype; Protein Precursors; Recombinant Proteins