Ponec M, Havekes L, Kempenaar J, Vermeer B J
J Invest Dermatol. 1983 Aug;81(2):125-30. doi: 10.1111/1523-1747.ep12542979.
The regulation of cholesterol synthesis in cultured human skin fibroblasts and keratinocytes was compared, the incorporation of [14C]-acetate or [14C]-octanoate into [14C]-cholesterol being taken as a measure of de novo cholesterol synthesis. The two types of cultured cells differed in the following features of the regulation of cholesterol synthesis: (1) Keratinocytes synthesized 10-fold more cholesterol/mg cell protein. (2) Keratinocytes retained a greater amount of the de novo synthesized cholesterol intracellularly, and fibroblasts released it to a much higher degree into the culture medium. (3) When the extracellular environment was deprived of cholesterol, the intracellular synthesis remained virtually unchanged in keratinocytes but increased markedly in fibroblasts. (4) The low-density lipoproteins (LDL) that enter the cells by receptor-mediated endocytosis and are then degraded in lysosomes, liberate cholesterol, which in turn interferes with the intracellular cholesterol synthesis. The lipoproteins strongly suppress cholesterol synthesis in fibroblasts, but do not have this effect in keratinocytes. (5) When added to the culture medium, nonlipoprotein cholesterol produced no effect on cholesterol synthesis in keratinocytes, whereas fibroblasts showed a marked suppression of this synthesis. The addition of 25-hydroxycholesterol to the culture medium led to a strong suppression of cholesterol synthesis in both fibroblasts and keratinocytes. These findings suggest that in both cell types the 3-hydroxy-3-methylglutaryl coenzyme A reductase activity can be suppressed by a sterol delivered to the cell in artificial nonlipoprotein form. (6) The amount of [125I]-LDL bound specifically to the cell membrane receptor and particularly the amount internalized and degraded by the cells is much lower in keratinocytes than in fibroblasts, as shown biochemically. In the ultrastructural studies no binding of LDL to keratinocytes was observed.
对培养的人皮肤成纤维细胞和角质形成细胞中胆固醇合成的调节进行了比较，将[14C]-乙酸盐或[14C]-辛酸掺入[14C]-胆固醇中作为从头合成胆固醇的指标。这两种培养细胞在胆固醇合成调节的以下特征方面存在差异：(1)角质形成细胞每毫克细胞蛋白合成的胆固醇比成纤维细胞多10倍。(2)角质形成细胞在细胞内保留了更多从头合成的胆固醇，而成纤维细胞将其释放到培养基中的程度要高得多。(3)当细胞外环境缺乏胆固醇时，角质形成细胞内的合成实际上保持不变，而成纤维细胞内的合成则显著增加。(4)通过受体介导的内吞作用进入细胞并随后在溶酶体中降解的低密度脂蛋白(LDL)会释放胆固醇，这反过来又会干扰细胞内胆固醇的合成。这些脂蛋白强烈抑制成纤维细胞中的胆固醇合成，但对角质形成细胞没有这种作用。(5)当添加到培养基中时，非脂蛋白胆固醇对角质形成细胞中的胆固醇合成没有影响，而成纤维细胞的这种合成则受到显著抑制。向培养基中添加25-羟胆固醇会导致成纤维细胞和角质形成细胞中的胆固醇合成均受到强烈抑制。这些发现表明，在这两种细胞类型中，以人工非脂蛋白形式递送至细胞的固醇可抑制3-羟基-3-甲基戊二酰辅酶A还原酶的活性。(6)如生化分析所示，角质形成细胞中与细胞膜受体特异性结合的[125I]-LDL的量，特别是细胞内化和降解的量，比成纤维细胞低得多。在超微结构研究中，未观察到LDL与角质形成细胞的结合。
