The potential mechanism for glutamine-induced collagen biosynthesis in cultured human skin fibroblasts

Although glutamine (Gln) is known as an important stimulator of collagen bi osynthesis in collage n-producing cells, the mechanism and endpoints by whi ch it regulate the process remain largely unknown. Intermediates of Gln int erconversion: glutamate (Glu) and pyrroline-5-carboxylate (P5C stimulate co llagen biosynthesis in cultured cells but evoke different maxima of collage n biosynthesis stimulating activity at different times of incubation. P5C w as found to be the most potent stimulator of collagen biosynthesis after 6 h of incubation (approx. three-fold increase); after 12 h, it induced incre ase in collagen biosynthesis to 260%, while at 24 h, the process was decrea sed to approximately 80% of control values. Glu. induced increase in collag en biosynthesis to approximately 180%, 400% and 120% of control values, aft er 6, 12 and 24 h, respectively, suggesting that after 12 h of incubation, Glu was the most potent stimulator of collagen biosynthesis. Glu was also t he most potent stimulator of type I procollagen expression at this time. Af ter 6, 12 and 24 h incubation, Gln induced collagen biosynthesis to approxi mately 112, 115 and 230% of control values, respectively. Since prolidase i s known to be involved in collagen metabolism, the enzyme activity assay wa s performed in fibroblasts cultured in the presence of Gln, Glu and P5C. Wh ile Gln and Glu required 24 h for maximal stimulation of prolidase activity . P5C induced it after 6-12 h. The data suggest that P5C induced collagen b iosynthesis and prolidase activity in a shorter time than Gln and Glu. We c onsidered that P5C directly stimulates the processes, while Gln acts throug h its intermediate-P5C. Reduction of P5C to proline is coupled to the conve rsion of glucose-6-phosphate (G6P) to 6-phospho-gluconate, catalyzed by G6P dehydrogenase. We have found that dehydroepiandrosterone (DHEA), a potent inhibitor of G6P dehydrogenase, inhibited a stimulatory effect of P5C on co llagen synthesis, expression of type I collagen and prolidase activity. Our results postulate a potential mechanism of glutamine-induced collagen bios ynthesis through its intermediate - P5C. P5C-dependent activation of nucleo tide biosynthesis, prolidase activity and P5C conversion into proline may c ontribute to the stimulation of collagen biosynthesis. (C) 2001 Elsevier Sc ience Inc. All rights reserved.