Regulation of collagen synthesis by ascorbic acid.

Abstract

After prolonged exposure to ascorbate, collagen synthesis in cultured human skin fibroblasts increased approximately 8-fold with no significant change in synthesis ofnoncollagen protein. This effect of ascorbate appears to be unrelated to its cofactor function in collagen hydroxylation. The collagenous protein secreted in the absence of added ascorbate was normal in hydroxylysine but was mildly deficient in hydroxyproline. In parallel experiments, lysine hydroxylase (peptidyllysine, 2-oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) activity increased 3-fold in response to ascorbate administration whereas proline hydroxylase (prolyl-glycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.2) activity decreased considerably. These results suggest that collagen polypeptide synthesis, posttranslational hydroxylations, and activities of the two bydroxylases are independently regulated by ascorbate.Ascorbic acid is essential for normal collagen formation (1-3) by virtue ofthe fact that it is a required component in the synthesis of hydroxyproline and hydroxylysine in collagen (4). Hydroxyproline serves to stabilize the collagen triple helix (5, 6); its absence results in structurally unstable collagen (7, 8) which is not secreted from cells at a normal rate (9). Hydroxylysine is necessary for formation of the intermolecular crosslinks in collagen (10). In addition, specific carbohydrate residues are linked glycosidically to collagen through hydroxylysine, a process that may be important in the regulation of crosslink formation (11).It is generally believed that ascorbate modulates collagen production through its effect on prolyl hydroxylation (12). There have been indications, however, that ascorbate may have an additional role in collagen biosynthesis (13-16). Notable are the early studies by Jeffrey and Martin (13) who observed a substantial increase in the size of chicken long bones cultured in the presence of ascorbate, concomitant with an increase in the incorporation of proline into peptidyl hydroxyproline.In this study we have examined the long-term effect of ascorbate on collagen production by cultured human skin fibroblasts. The influence ofascorbate on prolyl hydroxylase (prolylglycyl-peptide, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.2) and lysyl hydroxylase (peptidyllysine, 2 oxoglutarate:oxygen 5-oxidoreductase, EC 1.14.11.4) levels was also examined simultaneously to understand better the interrelationship of collagen synthesis and posttranslational hydroxylation. The data indicate that ascorbate increases collagen synthesis by acting at a level other than hydroxylation. MATERIALS AND METHODSHuman skin fibroblasts from a normal 3-day-old boy (GM 970) were obtained from the Institute for Medical Research (Camden, NJ) and grown to confluent density in Dulbecco's modified Eagle's medium buffered with 24 mM sodium bicarbonate and 25 mM Hepes and supplemented with 20% fetal calf serum (GIBCO) which had been inactivated for 30 min at 560C. Cultures were growth arrested for 90 hr in ...

Extracellular matrix production and calcium carbonate precipitation by coral cells in vitro

“…The hydroxylation of proline involves the activation of a reactive iron-oxygen complex, and ascorbic acid is required for the reduction of Fe 3ϩ formed in this reaction (25). Previous studies have shown that the addition of ascorbic acid stimulates collagen production in many metazoans (26)(27)(28)(29)(30)(31)(32); however, its effect on collagen production in basal metazoans such as corals is not known. The addition of ascorbic acid to the culture media increased collagen production by Ϸ40% in M. digitata cell cultures (4.4 Ϯ 0.2 weight percent collagen relative to total protein without ascorbic acid compared with 6.2 Ϯ 0.5% with ascorbic acid; P Յ 0.01; Fig.…”

Hyperpolarized 13 C dehydroascorbate as an endogenous redox sensor for in vivo metabolic imaging

“…A scorbic acid (Vitamin C) is an essential cofactor in reactions catalyzed by Cu þ -dependent monooxygenases and Fe 2þ -dependent dioxygenases, required for the enzymatic biosynthesis of collagen, catecholamines, and peptide neurohormones (1)(2)(3). Vitamin C is also an effective reducing agent protecting cells from the injurious effects of reactive oxygen species (4).…”

“…Here we report the development of [1- 13 C] dehydroascorbate [DHA], the oxidized form of Vitamin C, as an endogenous redox sensor for in vivo imaging using hyperpolarized 13 C spectroscopy. In murine models, hyperpolarized [1-13 C] DHA was rapidly converted to [1][2][3][4][5][6][7][8][9][10][11][12][13] C] vitamin C within the liver, kidneys, and brain, as well as within tumor in a transgenic prostate cancer mouse. This result is consistent with what has been previously described for the DHA/Vitamin C redox pair, and points to a role for hyperpolarized [1][2][3][4][5][6][7][8][9][10][11][12][13] C] DHA in characterizing the concentrations of key intracellular reducing agents, including GSH.…”

KONJAC1 and 2 Are Key Factors for GDP-Mannose Generation and Affect l-Ascorbic Acid and Glucomannan Biosynthesis in Arabidopsis

“…Deficiency in AsA results in scurvy, since AsA is a critical cofactor in the synthesis of collagen (Murad et al, 1981). Indeed, AsA is a major antioxidant compound involved in many reactions.…”