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Human neonatal keratinocytes have very high levels of cellular vitamin A-binding proteins
Insights
Newborn skin has high levels of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein (CRABP) in epidermal cells. Dermal fibroblasts show low CRABP, and CRBP levels suggest another cell type is responsible for dermal CRBP.
Area of Science:
- Biochemistry
- Dermatology
- Cell Biology
Background:
- Cellular retinol-binding proteins (CRBP) and cellular retinoic acid-binding proteins (CRABP) are crucial for vitamin A's role in epidermal differentiation.
- Understanding the distribution of these binding proteins in skin layers is essential for elucidating vitamin A metabolism and function.
Purpose of the Study:
- To quantify the levels of CRBP and CRABP in the epidermis and dermis of newborn human foreskin.
- To compare these levels with those found in primary cultures of keratinocytes and fibroblasts.
Main Methods:
- Ligand binding assays were employed using radiolabeled all-trans-retinol and all-trans-retinoic acid.
- Cytosols from skin layers and cultured cells (keratinocytes, fibroblasts) were analyzed for binding protein quantification.
Main Results:
- Epidermal CRABP and CRBP levels in newborn foreskin were significantly higher than in adult epidermis but comparable to neonatal keratinocyte cultures.
- CRABP levels were substantially lower in the dermis compared to the epidermis, consistent with fibroblast cultures.
- Cultured dermal fibroblasts exhibited very low CRBP levels, indicating another dermal cell type likely contributes significantly to dermal CRBP.
Conclusions:
- Neonatal epidermis and keratinocytes possess high concentrations of CRABP and CRBP.
- Dermal fibroblasts have low CRABP levels, while their low CRBP levels suggest a non-fibroblast source for dermal CRBP.
- These findings highlight differential expression of vitamin A binding proteins in skin compartments and cell types.
Abstract:
Since cellular retinol- and retinoic acid-binding proteins (CRBP and CRABP) mediate the effects of vitamin A on epidermal differentiation, the levels of these binding proteins were measured in the epidermal and dermal layers of newborn, human foreskin as well as in primary cultures of keratinocytes and fibroblasts from these layers. Ligand binding assays with saturating concentrations of all trans-[3H]retinol or of all trans-[11-3H]retinoic acid were used to quantitate amounts of binding proteins in cytosols prepared from these skin layers or cultured cells. The epidermal levels of CRABP and CRBP (60.9 +/- 14.4 and 7.3 +/- 1.7 pmol per mg cytosol protein, respectively) were markedly higher than that reported for adult epidermis but were comparable to levels in keratinocytes cultured from neonatal foreskin epidermis (61.8 +/- 7.8 and 10.7 +/- 2.5, respectively). The levels of CRABP were much lower in the foreskin dermis than in the epidermis and the levels measured in the fibroblasts cultured from this dermis were consistent with the dermal levels. However, CRBP levels in cultured dermal fibroblasts were very low and could not account for the dermal CRBP levels, suggesting that another dermal cell type has high levels of CRBP.