Patterns of type VI collagen compared to types I, III and V collagen in human embryonic and fetal skin and in fetal skin-derived cell cultures

Abstract

The distribution of type VI collagen was examined in human embryonic and fetal skin and in cultured cells and matrix from this tissue. Frozen sections were immunolabeled with primary antibodies against type VI collagen and types I, III or V collagen, and processed further for fluorescence microscopy and immunoelectron microscopy. At 6 weeks estimated gestational age (EGA), type VI collagen was identified by positive fluorescence and by immunogold staining of filaments and fibers beneath the dermal-epidermal junction (DEJ), weaker fluorescence in the fine matrix of the dermis, and stronger fluorescence in the subcutis. At progressive stages of gestation, immunolabeling for type VI collagen increased in the dermis in parallel with increased deposition of types I and III collagen. By 15 weeks EGA, type VI collagen stained intensely throughout the dermis. At 13 weeks EGA, type VI collagen appeared diminished from the growing tips of invaginating hair buds, but as the hair peg developed, type VI collagen accumulated in adnexal sheaths. Cell cultures were derived from fetal skin at 7.5 to 12 weeks EGA. In primary explant cultures containing both keratinocytes and fibroblasts, mats of type V collagen were present beneath keratinocytes and associated with dense spots that co-labeled for both type VI and type V collagen. In passaged cultures of fibroblasts, individual cells with or without pretreatment with monensin were positive for type VI and/or types I, III or V collagen. Fibrous matrix that was labeled for type VI collagen was also immunopositive for type I or III collagen, while filamentous matrix that was type VI collagen positive tended to exclude types I and III collagen but in some areas to overlap with type V collagen. These findings support the hypothesis that type VI collagen present in both filamentous and fibrous matrix and networks of type VI collagen may serve as a fine scaffolding that facilitates the integration of types I and III collagen into developing fibrous matrix.