Minoxidil exerts different inhibitory effects on gene expression of lysyl hydroxylase 1, 2, and 3: implications for collagen cross-linking and treatment of fibrosis.
Collagen deposits in fibrotic lesions often display elevated levels of hydroxyallysine (pyridinoline) cross-links. The relation between the occurrence of pyridinoline cross-links and the irreversibility of fibrosis suggests that these cross-links contribute to the aberrant accumulation of collagen. Based on its inhibitory effect on lysyl hydroxylase activity minoxidil has been postulated to possess anti-fibrotic properties by limiting the hydroxylysine supply for hydroxyallysine cross-linking. However, to interfere with hydroxyallysine cross-linking specifically lysyl hydroxylation of the collagen telopeptide should be inhibited, a reaction predominantly catalysed by lysyl hydroxylase (LH) 2b. In this study, we demonstrate that minoxidil treatment of cultured fibroblasts reduces LH1>>LH2b>LH3 mRNA levels dose-and time-dependently, but has essentially no effect on the total number of pyridinoline cross-links in the collagen matrix. Still the collagen produced in the presence of minoxidil displays some remarkable features: hydroxylation of triple helical lysine residues is reduced to 50% and lysylpyridinoline cross-linking is increased at the expense of hydroxylysylpyridinoline cross-linking. These observations can be explained by our finding that LH1 mRNA levels are the most sensitive to minoxidil treatment, corroborating that LH1 has a preference for triple helical lysine residues as substrate. In addition, the non-proportional increase in cross-links (20-fold) with respect to the decrease in lysyl hydroxylation state of the triple helix (2-fold) even suggests that LH1 preferentially hydroxylates triple helical lysine residues at the cross-link positions. We conclude that minoxidil is unlikely to serve as an anti-fibroticum, but confers features to the collagen matrix, which provide insight into the substrate specificity of LH1.
Zuurmond
Anne-Marie
AM
TNO Quality of Life, Biomedical Research, Department of Tissue Repair, P.O. Box 2215, 2301 CE Leiden, The Netherlands.
van der Slot-Verhoeven
Annemarie J
AJ
van Dura
Ernst A
EA
De Groot
Jeroen
J
Bank
Ruud A
RA
D015074:2-Aminoadipic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D003094:Collagen / Q000378:metabolism*; D005355:Fibrosis / Q000188:drug therapy*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D006801:Humans; D006900:Hydroxylation; D008914:Minoxidil / Q000494:pharmacology*; D008240:Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase / Q000235:genetics* / Q000378:metabolism*
D015074:2-Aminoadipic Acid; C042487:hydroxyallysine; D008914:Minoxidil; D003094:Collagen; C475767:PLOD3 protein, human; C479138:PLOD2 protein, human; D008240:Procollagen-Lysine, 2-Oxoglutarate 5-Dioxygenase; C500142:lysyl hydroxylase 1, human