Spanheimer R G, Bird T A, Peterkofsky B
Arch Biochem Biophys. 1986 Apr;246(1):33-41. doi: 10.1016/0003-9861(86)90446-7.
Previous studies suggested that decreased type I collagen synthesis in calvaria of ascorbate-deficient guinea pigs was correlated with weight loss rather than defective proline hydroxylation. The generality of this correlation was examined in articular cartilage, which synthesizes mainly type II collagen, by measuring collagen synthesis and proline hydroxylation in vitro in tissue from ascorbate-supplemented and scorbutic guinea pigs. Ascorbate concentrations in tissues were almost completely depleted after 1 week of deficiency, but proline hydroxylation remained normal until after approximately 3 weeks, when it had decreased only by 10%. At that point collagen synthesis had decreased to about 50% of the control value. There was little additional effect on proline hydroxylation but collagen synthesis decreased further to 20% of normal. Procollagen mRNA levels in cartilage, as measured by dot-blot hybridization with a type II-specific cDNA probe, were unchanged after 2 weeks of scurvy, which correlated with the lack of effect on collagen synthesis during that period. Thereafter, during the period when collagen synthesis decreased, procollagen mRNA levels decreased to 20% of control values. Refeeding ascorbate to acutely scorbutic animals led to reversal of defective proline hydroxylation within 24 h with a slower increase in collagen synthesis and mRNA levels. Collagen synthesis returned to the normal level after 4 days with no further increase, while mRNA levels continued to increase to 2.7 times the control values after 7 days. Thus the major mechanism for regulation of collagen synthesis in articular cartilage during scurvy and ascorbate repletion occurs independently of the effect on proline hydroxylation and is associated with changes in mRNA levels. The lack of precise coordination between collagen synthesis and mRNA levels during repletion, however, suggests that there may be additional regulation through post-transcriptional mechanisms.
先前的研究表明，抗坏血酸缺乏的豚鼠颅骨中I型胶原蛋白合成减少与体重减轻相关，而非脯氨酸羟化缺陷。通过测量补充抗坏血酸和患坏血病的豚鼠组织的体外胶原蛋白合成和脯氨酸羟化，在主要合成II型胶原蛋白的关节软骨中检验了这种相关性的普遍性。缺乏抗坏血酸1周后，组织中的抗坏血酸浓度几乎完全耗尽，但脯氨酸羟化在大约3周后才保持正常，此时仅下降了10%。此时胶原蛋白合成已降至对照值的约50%。对脯氨酸羟化几乎没有额外影响，但胶原蛋白合成进一步降至正常的20%。用II型特异性cDNA探针通过斑点印迹杂交测量，软骨中的前胶原mRNA水平在坏血病2周后没有变化，这与该期间对胶原蛋白合成缺乏影响相关。此后，在胶原蛋白合成下降期间，前胶原mRNA水平降至对照值的20%。给急性患坏血病的动物重新喂食抗坏血酸导致24小时内脯氨酸羟化缺陷逆转，胶原蛋白合成和mRNA水平增加较慢。4天后胶原蛋白合成恢复到正常水平且不再增加，而mRNA水平在7天后继续增加至对照值的2.7倍。因此，坏血病和抗坏血酸补充期间关节软骨中胶原蛋白合成调节的主要机制独立于对脯氨酸羟化的影响而发生，并且与mRNA水平的变化相关。然而，补充期间胶原蛋白合成和mRNA水平之间缺乏精确协调表明可能存在通过转录后机制的额外调节。
