Ultrastructural identification of extension aminopropeptides of type I and III collagens in human skin.

Abstract

Human skin was labeled with purified antibodies against type I and m collagens and against their extension aminopropeptides by using the ferritin technique. Both aminopropeptides were visualized mainly along thin collagenous fibrils (diameter, 20-40 nm) and rarely in nonfibrillar regions of the skin. The labeling showed a periodicity of 60-65 nm resembling the D (67 nm) stagger of collagen molecules. Blocking of antibodies with aminopropeptides and treatment of tissues with procollagen NH2-terminal protease abolished labeling. Antibodies against type I collagen uniformly labeled -80% of the fibrils (diameter, 20-80 nm), while reaction with antibodies against type m collagen was restricted to thin fibrils. It is currently thought that the aminopropeptides of procollagen molecules are cleaved after they are released from the cell and before fibril formation. Our data indicate that aminopropeptides are removed at the fibrillar level and that fibril growth can be regulated by extracellular procollagen processing. Type I and III collagens are major components of the dermis and are organized into fibrils varying considerably in diameter. Distinct growth of fibrils is observed during development and may be disturbed in certain skin diseases (1). The mechanism of controlling this process is unknown. It has also not been established whether type I and III collagens are present in the same fibrils. Both collagens can form D-staggered fibrils in vitro showing identical cross-striations when examined in the electron microscope (2). Because specific antibodies against various collagens and procollagens are available (3, 4), it is feasible to identify distinct types of collagenous proteins at the ultrastructural level in situ, as was recently done for type III collagen (5).Interstitial collagens are synthesized in the form of procollagens that possess additional extension amino-and carboxypropeptides. Each precursor-specific peptide is removed by specific proteases (procollagen NH2-terminal and COOH-terminal proteases) presumably after release of procollagens from the cell (6). Cell and organ culture studies indicated different kinetics in the processing of type I and III procollagens (7-9). After cleavage, the aminopropeptides persist for some time in the extracellular space, as shown by immunofluorescence staining with antibodies against these peptides (3, 4).A functional role for extension aminopropeptides in the control of fibril growth was first suggested in studies of dermatosparactic animals, which, due to a defective NH2-terminal protease, accumulate an intermediate form of type I procollagen (pN-collagen) in the skin and other organs (10, 11). The collagenous fibrils appeared thin and hieroglyphic (12, 13) and could be stained with antibodies against the aminopropeptide by using a ferritin label (13). Small amounts of type I and III pN-collagens could also be extracted from the skin of growing animals (14-18). It was suggested (3, 14, 19) that these aminopropeptides are structural elements ofimmature or th...

Increase in types IV and VI collagen in cherry haemangiomas

“…In accordance with previous studies [9,44,29], type III collagen and hyaluronic acid stained intensely in the normal subpapillary connective tissue surrounding the haemangidmas and in the connective tissue matrix between the capillary loops. In contrast to this, staining for type III collagen was very weak in the thickened vascular wall of the haemangioma capillaries; in these areas there were also ultrastructurally only a few scattered collagen fibrils with a periodicity of 67 nm.…”

A role for glycosaminoglycans in the development of collagen fibrils

“…It has been suggested that the duration of the so-called 'lag (or nucleation) phase' of fibril growth, which is altered by the presence of different GAGS, would directly affect the number-density of collagen fibrils so formed, in that collagen fibrils of smaller diameters would be produced when the nucleation phase was long and those of larger diameters when the nucleation phase was short [7][8][9]131. However, other experiments have shown that collagen molecules are capable of aggregating into fibrils in the absence of any of the GAGS [4,7,11] and that fibril diameter may be dependent upon glycoprotein content [ 141, parameters such as pH, ionic strength and temperature [3,, the distribution and number of glycosylated residues along the length of the collagen molecule [ 191, the degree of copolymerisation in some tissues of types I and III collagen , collagen-fibronectin interactions [22] and the amount of collagen extension aminopropeptides remaining in the fibril [23].…”

Immunochemical properties of the aminopropeptide of procollagen type III

“…They are liberated during the conversion of the precursor into collagen [1,2] and are considered to play important roles in regulating collagen synthesis [3] and fibril formation [4,5]. The amino acid sequence of the aminopropeptides of procollagen I and 111 has been elucidated [2, 6,7] supporting previous evidence on three structurally and conformationally distinct domains [8 -101 in each peptide segment.…”

“…Similar data are still lacking for the homologous segment of procollagen 111. However, antibodies against this peptide have been of value for studying its matrix function [4] and for developing sensitive radioimmunoassays for quantifying circulating antigens under clinical conditions [I 71. The latter approach indicated different affinities for the intact aminopropeptide and smaller antigenic fra'gments which may arise in the body due to physiologic dcgradation [I 7 -191.…”