Chicken vigilin gene: a distinctive pattern of hypersensitive sites is characteristic for its transcriptional activity

Vigilin, a multidomain hn-ribonucleo-K-homologous protein, is part of a ribonucleoprotein complex with cognate tRNA and is found in both the nucleus and the cytoplasm. In an approach to identify genomic regions involved in regulation of the chicken vigilin gene, we carried out transfection studies with a reporter gene in suitable chicken cells. After including a distantly positioned 5'-sequence in the construct, we observed a 10.5-fold increase in luciferase (EC 1. 13.12.7) expression compared with basal promoter activity. Accordingly, chromatin analysis of freshly isolated embryonic tendon fibroblasts with high levels of vigilin mRNA expression shows a DNase-I-hypersensitive site (DHS1) localized 2.2 kb upstream of the transcriptional start site. Similarly, phytohaemagglutinin-stimulated lymphocytes with a 4-fold elevated expression of vigilin mRNA compared with resting lymphocytes also exhibited this unique DHS, having switched from that found at 3.3 kb (DHS2) in resting lymphocytes. Furthermore, using gel-retardation experiments with DNA representing either DHS1 or DHS2, a specific interaction with chicken nuclear extracts was seen.

Glycosylation of human bone collagen I in relation to lysylhydroxylation and fibril diameter

Posttranslational modifications (lysylhydroxylation, glycosylation, and crosslink formation) of collagen I and the trabecular bone volume (TBV) as well as the supramolecular organization of human vertebrae were studied by analyzing vertebral bones of 55 individuals (22-93 years of age). The degree of lysylhydroxylation of both a-chains of collagen I showed a significant inverse correlation with the TBV, while only a weak correlation between lysylhydroxylation of alpha2(I) and the age of the donor was observed. The degree of glycosylation of collagen I was significantly correlated with both the level of lysylhydroxylation and the degree of osteopenia. Electron microscopic evaluation did not show any relationship between the level of collagen glycosylation and the diameter of in vivo formed fibrils or in vitro formed fibrillar aggregates. In our study the molar ratio of the mature collagen crosslinks, pyridinoline and deoxypyridinoline, showed a slight tendency to be higher, in particular in the samples with a high level of lysylhydroxylation. This ratio was recently found to be significantly increased in avian osteoporotic bone. Our data suggest that the increased level of lysylhydroxylation in human osteopenia is related to the glycosylation of collagen I, while it seems to have little impact on the formation of the mature, non-reducible collagen crosslinks investigated. Based on our observations it appears unlikely that the different diameters of collagen fibrils contribute greatly to the reduced biomechanical stability reported for overhydroxylated, osteopenic bone tissue.

Semipreparative isolation of collagen types I, II, III and V by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electroelution

A simple method for the isolation of alpha-chains of different collagen types was developed. The procedure involves sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by electroelution of separated and defixed collagen alpha-chains. Collagen types I, II, III and V from different porcine tissues were recovered in high quantity (> 95%) and purity (> 98%) as evidenced by amino acid analysis. The procedure can be used for sample quantities smaller than required for conventional methods e.g. chromatographic procedures.

Evidence for a novel cytoplasmic tRNA-protein complex containing the KH-multidomain protein vigilin

Vigilin, a protein found predominantly in cells and tissues with a high biosynthetic capacity, was isolated in its native form from human HEp-2 cells (A.T.C.C. CCL23) by immunoaffinity chromatography. Vigilin forms part of a novel ribonucleoprotein complex that also contains additional, as yet uncharacterized, proteins. Experimental evidence suggests that the nucleic acids entrapped in this complex are protected from RNase and belong to the tRNA family. Using either a pool of total human RNA or radioactively labelled tRNA (tRNA (Asp**)) in rebinding experiments, we could show that tRNA is selectively recaptured by the RNA-depleted vigilin-containing complex.

Magnetic resonance imaging of focal liver lesions. Comparison of the superparamagnetic iron oxide resovist versus gadolinium-DTPA in the same patient

RATIONALE AND OBJECTIVES

The authors assess the efficacy of static and dynamic magnetic resonance (MR) imaging using the superparamagnetic iron oxide SHU-555A (Resovist) versus standard dose of gadolinium (Gd)-DTPA in patients with focal liver lesions.

METHODS

Magnetic resonance imaging was performed in 30 patients suffering from histopathologically verified malignant (n = 22) and benign (n = 8) liver lesions. T2-weighted conventional and fat-suppressed as well as T1-weighted sequences were used before, during, and after fast intravenous administration of Resovist (1 mL/minute) at three doses of 4, 8, and 16 mumol/kg body weight. One week before the Resovist-enhanced MR imaging study 20 patients underwent Gd-DTPA-enhanced MR imaging.

RESULTS

Detection rate was improved for metastatic lesions revealing 36 lesions unenhanced versus 53 focal lesions using Resovist-enhanced MR imaging. Gadolinium-DTPA-enhanced scans showed no additional lesion versus unenhanced and Resovist-enhanced MR imaging. Static and dynamic imaging demonstrated no measurable percentage signal intensity loss (PSIL) using Resovist-enhanced MR imaging versus a percentage enhancement of 79.7% in Gd-DTPA enhanced scans. In the dynamic T2-weighted sequences, hepatocellular carcinoma nodules (n = 4) showed a rapid decrease in signal intensity starting at 44 seconds. Postinfusion of Resovist followed by a low, constant increase in signal intensity. Gadolinium-DTPA enhanced scans showed a percentage enhancement of 73.4 focal nodular hyperplasia (FNH) and hemangioma revealed a strong and early dose-dependent PSIL 44 to 60 seconds postinfusion with a prolonged signal loss for the FNH in the late study. Statistical evaluation revealed a statistically significant superiority of Resovist-enhanced MR imaging concerning the detection and delineation of focal liver lesions compared with unenhanced and Gd-DTPA enhanced scans (P < 0.05).

CONCLUSIONS

The fast infusion of the new superparamagnetic contrast agent Resovist shows advantages for dynamic and static MR imaging of focal liver lesions.

Biochemical alterations in collagen IV induced by in vitro glycation

Non-enzymic interactions of carbohydrates and proteins are a major feature of cumulative modification in basement membranes in the course of diabetic microvascular complications. To evaluate the significance of both glycation and glycoxidation reactions for subsequent alterations of biochemical properties, we examined the effects of in vitro glycation on distinct collagen IV domains under different experimental conditions. The 7 S domain and the major triple-helical domain from human placental collagen IV were incubated for various time intervals up to 14 days at 37 degrees C in the presence of different concentrations of either glucose or ribose under oxidative and antioxidative conditions. Carbohydrate-induced non-enzymic modification in two collagen IV domains was revealed by increased cross-linking and fluorescence. In addition, these non-enzymic modifications apparently have a major impact on molecular conformation and thermal stability of collagen IV, which in turn might influence both cell-matrix interactions and matrix assembly.

Altered x-ray diffraction pattern is accompanied by a change in the mode of cross-link formation in lipodermatosclerosis

We studied the molecular packing of collagen fibrils by x-ray diffraction in skin specimens of patients with lipodermatosclerosis and in controls. A difference in the tilt angles of the collagen molecules relative to the fiber axis is suggested by a D-stagger that is 1 nm larger in sclerotic skin than in normal skin. In parallel, the collagen cross-links in the skin specimens were analyzed, and a marked increase of both hydroxylysylpyridinoline and lysylpyridinoline, the trivalent mature cross-links characteristic of skeletal tissues, was found. The content of hydroxylysylpyridinoline and lysylpyridinoline was higher in the deep layer of the affected dermis than in the superficial dermis. This increase was always accompanied by an increase in the hydroxylysylpyridinoline/lysylpyridinoline ratio, suggesting that hydroxylysylpyridinoline is a sclerosis-associated cross-link. In addition, lysyl hydroxylation was increased in affected skin, and this increase was apparently restricted to the collagen telopeptides, which are crucial anchoring structures for lysyl dependent cross-links.

Expression of vigilin in the uterus of ovariectomized steroid-treated rats and during the estrous cycle

The expression of vigilin in the uterus of rats was investigated by immunoblotting and immunohistochemistry and compared to the ultrastructural features of the endometrial cells. Vigilin could not be detected in the uteri of ovariectomized rats. Administration of estrogen, alone or in combination with progesterone, significantly stimulated the expression of vigilin, mainly in the luminal and glandular epithelial cells. Ultrastructurally, these cells show the morphological features of an increased protein synthesis. Untreated mature rats demonstrate a cyclic pattern of vigilin expression with high levels during the estrogen-dominated proestrus and early estrus stages and low levels at metestrus. The down-regulation of vigilin starts with the occurrence of apoptosis and autophagocytosis in the epithelium, but precedes the vanishing of the secretory granules. At diestrus the vigilin expression is intermediate and the vigilin staining of the epithelial cells is reduced. However, the endometrial fibroblasts show a faint staining. Morphologically, these fibroblasts are characterized by large euchromatic nuclei and dilated cisternae of the rough endoplasmic reticulum. The results suggest that in the uterus of rats the expression of vigilin is stimulated by estrogen. Under the experimental conditions chosen no influence of progesterone on vigilin expression was detected.

Liver tumors: comparison of MR imaging with Gd-EOB-DTPA and Gd-DTPA

PURPOSE

To compare the usefulness of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) and gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) in the diagnosis of focal liver lesions.

MATERIALS AND METHODS

Thirty-one patients with focal liver lesions underwent T2- and T1-weighted spin-echo magnetic resonance (MR) imaging and fast low-angle shot two-dimensional MR imaging before, during, and after intravenous administration of three different doses of Gd-EOB-DTPA (12.5, 25, and 50 mumol per kilogram body weight). Gd-DTPA-enhanced imaging (dose, 0.1 mmol per kilogram body weight) was performed in the same patients within 1 week of Gd-EOB-DTPA imaging.

RESULTS

During the perfusion phase (the 3 minutes after injection of contrast material), the dynamic enhancement characteristics seen after injection of 25 and 50 mumol of Gd-EOB-DTPA were similar to those seen with Gd-DTPA. At the lowest dose of Gd-EOB-DTPA (12.5 mumol), the dynamic enhancement characteristics were not comparable to those seen with Gd-DTPA. During the hepatobiliary phase (1.5 minutes to 4 hours after injection), Gd-EOB-DTPA-enhanced images yielded a dose-independent, statistically significant improvement in the detection rate of additional metastases, hepatocellular carcinomas, and hemangiomas compared with unenhanced and Gd-DTPA-enhanced images (P < .05).

CONCLUSION

Gd-EOB-DTPA-enhanced MR imaging enables improved detection of hepatic lesions over Gd-DTPA-enhanced MR imaging while providing comparable differential diagnostic information.

Two additional 5' exons in the human Vigilin gene distinguish it from the chicken gene and provide the structural basis for differential routes of gene expression

Vigilin, a 150-kDa protein, contains 14 tandemly arranged domains, each consisting of a KH RNA-binding motif and a spacer region. Here, we report on the physical structure of the human Vigilin gene with 29 exons, thereby outnumbering the chicken gene by two additional 5' exons. These additional exons, 1A and 1B, are alternatively though concurrently spliced to exon 1C which is homologous to the first exon in the chicken gene. None of the additional human exons code for an amino-terminal extension of Vigilin, due to in-frame stop codons. Structural features of exon 1A, however, would allow the translation of a 13-amino-acid peptide from an upstream open reading frame preceding the vigilin open reading frame. We suggest that exons 1A and 1B have been gained during evolution, allowing alternative routes of expression control of the human Vigilin gene.

Changes with age in the urinary excretion of hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP)

There is increasing evidence that the measurement of urinary hydroxylysylpyridinoline (HP or PYD) and lysylpyridinoline (LP or DPD) by HPLC (high performance liquid chromatography) is potentially useful in clinical and pharmacological studies. HP and LP are promising markers of bone resorption because their levels in urine reflect the breakdown of mature collagen fibrils mainly of skeletal tissues. HP and LP are two non-reducible cross-links of mature collagen which are formed by a sequence of post-translational modifications. HP is a derivative of three residues of hydroxylysine and is present in almost all mature tissues (e.g. tendon. vessel walls, cartilage, dentine and bone). LP is a derivative of two residues of hydroxylysine and one residue of lysine and is present mainly in dentine and bone. Neither cross-link is found in normal human skin. We have isolated and purified HP and LP from commercially available bone gelatine by a preparative reverse-phase column HPLC. These two components were used as external standards for sample analysis. In the present study we analysed the urinary excretion of HP and LP in a group of 264 male and 279 female healthy subjects aged from 6 months to 65 years. A continuous decline of both cross-link components during childhood paralleled by a decrease of the HP:LP-ratio was observed. The levels of HP and LP were 2.5-5 times higher in infants (0.5-1 year) than in children (5-10 years) and 15-20 times higher than in adults (26-65 years). After the age of 17 years, both parameters remained at low levels. These data allow a precise quantitative monitoring of bone resorption in patients with metabolic bone diseases or during pharmacological interventions.

Vigilin contains a functional nuclear localisation sequence and is present in both the cytoplasm and the nucleus

Vigilin is a member of the KH protein family and contains 14 tandemly arranged potential RNA-binding domains. Between KH domains 2 and 3 we have identified a nuclear localization sequence by cloning this sequence into the NH2-terminal region of phage T7 RNA polymerase as a reporter protein and by showing its transfer into the nucleus. Furthermore we provide experimental evidence that Vigilin is present both in the nucleus and in the cytoplasm in similar concentrations. These observations support the notion that Vigilin may shuttle between nucleus and cytoplasm presumably in contact with RNA molecules.

Superparamagnetic iron oxide--enhanced versus gadolinium-enhanced MR imaging for differential diagnosis of focal liver lesions

PURPOSE

To assess AMI-25- versus gadolinium-enhanced magnetic resonance (MR) imaging in the differential diagnosis of liver tumors.

MATERIALS AND METHODS

Twenty-nine patients with liver tumors underwent unenhanced, AMI-25-enhanced (15 micromol/kg), and gadolinium-enhanced(0.1 mmol/kg) imaging within 2 weeks.

RESULTS

A significant (P< .05) difference in percentage signal intensity loss (PSIL) was seen in benign tumors on AMI-25-enhanced proton-density-weighted images (nine focal nodular hyperplasia [FNH], 41%; one adenoma, 32.4%) versus malignant tumors. Gadolinium-enhanced T1-weighted gradient-echo images showed strong enhancement in benign lesions (seven FNH, 147.5%; one adenoma, 91.3%) and moderate enhancement in malignant tumors (eight hepatocellular carcinomas, 116.2%, 11 metastases, 39.7%). Receiver operating characteristic analysis revealed a threshold PSIL of 10% on AMI-25-enhanced images as the most essential criteria to distinguish benign from malignant lesions (sensitivity, 88%; specificity. 89%). Interobserver analysis for two observers revealed specificity of 93% for AMI-25-enhanced imaging versus 81.5% for gadolinium-enhanced MR imaging.

CONCLUSION

AMI-25 decreased the SI of benign tumors and helped differentiate benign from malignant tumors.

Transforming growth factor beta 1 influences lysyl hydroxylation of collagen I and reduces steady-state levels of lysyl hydroxylase mRNA in human osteoblast-like cells

Transforming growth factor beta 1 (TGF-beta 1) is an osteotropic growth factor that is found in substantial concentration in bone. The authors studied the influence of TGF-beta 1 on the modification of lysine residues of collagen I. The degree of lysyl hydroxylation and lysyl glycosylation of newly synthesized collagen as well as steady-state levels of mRNA for both lysyl hydroxylase and collagens I and III were determined in human osteoblast-like cells in vitro. In normal human osteoblasts lysyl hydroxylation was decreased by TGF-beta 1 particularly in the collagen alpha 2-chain. This effect was paralleled by an increase in lysyl residues, whereas glycosylation was not affected. The mRNA for lysyl hydroxylase was reduced by one-third under the influence of TGF-beta 1. Additionally, the mRNAs for both procollagen I alpha-chains were stimulated by TGF-beta 1, whereas pro alpha 1 (III)-mRNA showed a decrease. Changes in the local regulatory activity of TGF-beta 1 may play a role in matrix maturation such as collagen type production and lysyl hydroxylation, the latter being altered in various pathological conditions, e.g. in generalized osteopenia.

Experimental tissue expansion induces changes in expression of procollagen I and III messenger RNA

Experimental tissue expansion was performed in nine dogs following placement of subcutaneous silicone balloons. The balloon expander was then filled with 300 ml saline immediately after implantation. Duration of expansion varied from 3 days to 124 days. Unaffected skin and skin over an empty expander served as control tissue. Dermal procollagen I and procollagen III gene expression in response to tissue expansion was investigated by dot-blot analysis using digoxigenin-labeled RNA probes complementary to either human procollagen-alpha 1(I) mRNA or procollagen-alpha 1(III) mRNA. Cross-hybridization of human probes with canine procollagen mRNA was demonstrated by Northern blot analysis. In response to the trauma of surgery, procollagen I and III mRNA transcriptions were found to be decreased significantly within the first few days after implantation. After 9 days of expansion, increased levels of procollagen I mRNA were found, while after 16 days increased levels of procollagen III mRNA were evident. The present study is the first to demonstrate changes in dermal collagen gene expression as a reaction to tissue expansion.

Microgravity and hypergravity effects on collagen biosynthesis of human dermal fibroblasts

Astronauts experiencing long periods of space flight suffer from severe loss of bone tissue, particularly in those bones that carry the body weight under normal gravity. It is assumed that the lack of mechanical load decreases connective tissue biosynthesis in bone-forming cells. To test this assumption, quantitative and qualitative aspects of collagen synthesis under microgravity, normal gravity, and hypergravity conditions were investigated by incubating human fibroblast cultures with [3H]-proline for 4, 7, 10, and 20 h during the Spacelab D2-mission in 1993. Quantitative analysis revealed an increase of collagen synthesis under microgravity conditions, being up to 143% higher than in 1 g controls. In contrast, hypergravity samples showed a decrease in collagen synthesis with increasing g, being at the 13% level at 10 g. The relative proportion of collagen in total synthesized protein showed a slight decrease with increasing g. The secretion of collagen by the cells, proline hydroxylation of individual collagen alpha-chains, and the relative proportions of synthesized collagens I, III, and V were not affected under any of the applied conditions.

Structural and functional implications of age-related abnormal modifications in collagen II from intervertebral disc

Collagen II was isolated from annulus fibrosus of human donors, and the degree of enzymatic glycosylation and the extent of nonenzymatic modification was determined as a function of age. While enzymatic glycosylation did not alter with age, the fluorescence as a measure of nonenzymatic modification increased, in particular in those fractions containing highly cross-linked collagen molecules. The age-dependent increase of fluorescence was associated with a lower thermal stability of collagen II, being lowest (Tm = 36.9 degrees C instead of 42.1 degrees C) in a fraction of collagen II molecules isolated from tissue of a 69-year-old donor. In addition, collagen II from elderly donors showed an impaired propensity to form fibrils, using an in vitro assay, as evidenced by the facts that (1) more collagen molecules remained in solution and were not assembled into fibrils, and (2) the relative turbidity caused by the aggregates progressively decreased as the age of the donors increased. As seen on electron micrographs, these fibrillar aggregates were less densely packed and intermingled with precipitates such as unbanded filaments or discontinuous fibrils with split and frayed regions. It can be hypothesized that functional impairment of the intervertebral disc with aging may be caused in part by molecular alterations as are described here for collagen II obtained from aged donors.

Malignant liver tumors treated with MR imaging-guided laser-induced thermotherapy: technique and prospective results

PURPOSE

To evaluate magnetic resonance (MR) imaging-guided laser-induced thermotherapy (LITT) of liver metastases.

MATERIALS AND METHODS

In a phase II study, 20 patients with 33 metastases from colorectal carcinoma (75%) or other primary tumors (25%) underwent LITT. MR thermometry performed with fast low-angle shot sequences was used to monitor therapy on-line, and dynamic and static contrast material-enhanced MR images enabled estimation of the degree of resultant necrosis. Follow-up studies were performed 3 months after thermotherapy.

RESULTS

The thermosequences enabled accurate on-line monitoring in 85% of lesions. In 69% of lesions 20 mm in diameter or smaller, contrast-enhanced MR images depicted substantial necrosis, with a local tumor control rate of 69% after 6 months and 44% after 12 months. Among lesions larger than 20 mm, necrosis was frequently incomplete, with a local control rate of only 41% after 6 months and 27% after 12 months.

CONCLUSION

MR imaging-guided LITT of liver metastases is a safe and promising therapy for liver metastases.

Composition and posttranslational modification of individual collagen chains from osteosarcomas and osteofibrous dysplasias

The composition of collagen was analyzed and the degree of lysyl hydroxylation of individual collagen chains was determined in four osteosarcomas and two osteofibrous dysplasias. In addition, the tumor proliferation (number of mitoses, proliferating-nuclear-antigen-positive cells, MIB) as well as the response to chemotherapy (morphological regression grade) were checked. All tumors contained a high proportion of collagen III and, in all but one osteosarcoma, pepsin-extracted collagens I and III were overmodified. Furthermore, the proportion of diglycosides in collagen I was about four times higher than in controls. The collagen composition and modification resembled those of bones at early stages of human development. One osteosarcoma and both osteofibrous dysplasias were in the normal range of lysyl hydroxylation. There was no correlation between the collagen properties and the histopathological marker of tumor proliferation.

Hydroxylation of collagen type I: evidence that both lysyl and prolyl residues are overhydroxylated in osteogenesis imperfecta

The composition of the collagens secreted into the media of fibroblast cultures of 39 patients with osteogenesis imperfecta (OI) was the same in controls and OI cultures. An abnormal migration pattern of collagens upon SDS-PAGE was evident in one third of the cultures investigated. Lysyl and prolyl hydroxylation of HPLC-purified alpha 1(I) chains was elevated in about 60% of cultures. The degree of hydroxylation was highest in the lethal forms. The extent of lysyl and prolyl hydroxylation showed a strong correlation (r = 0.74, P < 0.001). While high levels of hydroxylation are frequently observed in OI patients, a direct correlation between lysyl or prolyl hydroxylation and fracture rate or growth retardation could not be established.

In vitro fibrillogenesis of collagen II from pig vitreous humour

Collagen from pig vitreous humour was fractionated into a soluble and an insoluble fraction by centrifugation. Most of the collagen II in the soluble fraction was present as pN-collagen II (procollagen II without the C-terminal propeptide), besides smaller quantities of procollagen II, collagen II and two as yet unidentified alpha-chains of collagen II. Other collagen types may be present only in trace amounts. Collagen II of the insoluble fraction, which is mostly deposited in fibrillar aggregates, consists of both pN-collagen II and collagen II. To determine the possible role of collagen II precursors in the formation of the extracellular matrix of the vitreous humour these collagen molecules were purified and in vitro fibrillogenesis was used to demonstrate that pN-collagen II could form fibrils in mixtures with collagen II. These fibrils have a reduced mass per unit length depending on the content of pN-collagen in the mixture. Cross-sections of the newly formed fibrillar aggregates revealed a flattened shape. The incomplete processing of the precursors of collagen II may be part of regulatory mechanisms possibly controlling the formation of a translucent scaffold as is required in the vitreous humour.

Attachment of intrinsically and extrinsically aged fibroblasts on collagen and fibronectin

In the present study we compare human dermal fibroblasts from donors of different age and from sites differing in sun exposure for their capacity to adhere to collagen or fibronectin. Attachment of cells was not dependent on the collagen concentration but was clearly dependent on the fibronectin concentration used for the coating of the plastic surfaces. Attachment of fibroblasts to collagen and fibronectin is dominated by specific integrin binding: only few cells were able to attach to collagen after inhibition with an anti-VLA 2 antibody, or to attach to fibronectin after inhibition with an anti-VLA 5 antibody. On unexposed sites, cells from old donors showed a significantly increased adhesion capacity on collagen (plus 50.7%) and on fibronectin (plus 62.4%) and an increased staining pattern of VLA 2 and VLA 5 integrins in immunohistochemistry in comparison with young donors. In contrast fibroblasts of chronically sun-exposed skin had a significantly decreased adhesion capacity both on collagen (minus 55.3%) and on fibronectin (minus 46.5%) and a poor staining pattern of the above integrins in comparison with cells from solely aged skin (unexposed sites of old donors). Adhesion of all cells could be inhibited by specific integrin antibodies showing that the employed antibodies were able to detect the epitopes responsible for attachment. Intrinsic and extrinsic aging are able to alter cellular properties of mesenchymal cells, such as adhesion to physiologically relevant macromolecules of the extracellular matrix.

Collagen synthesis in (sun-) aged human skin and in fibroblasts derived from sun-exposed and sun-protected body sites

Endogenous and sun-induced aging of the skin cause distinct morphological alterations. In this study, we have analysed the ratio of collagen III to collagen III plus I in extracts of sun-exposed (face) and sun-protected (abdomen) aged skin, as well as in collagens synthesized by fibroblasts during in vitro culture derived from actinically damaged and sun-protected skin of other subjects (face, medial aspect of the upper arm vs. abdomen, lateral aspect of the forearm). Furthermore, the amount and extent of post-translational modifications of newly synthesized collagens were determined. Chronic sun exposure of the skin does not have an impact on the quantity of collagenous proteins newly synthesized in cell culture. The proportion of collagen III in pepsin extracts of sun-damaged skin is increased relative to sun-protected skin. However, fibroblasts derived from sun-exposed skin synthesize a lower proportion of collagen III than cells from sun-protected skin. The hydroxylation of lysyl residues in newly synthesized alpha 2(I) and alpha 1(III) collagen chains is reduced by UV irradiation, whereas hydroxylation of lysyl residues in alpha 1(I) chains and of prolyl residues in alpha 1(I), alpha 2(I) and alpha 1(III) chains is unaffected by UV irradiation. These data provide circumstantial evidence to indicate that collagen synthesis is influenced independently by endogenous and sun-induced aging.