Vitamin A homeostasis by hepatic stellate cells

维生素A是一种脂溶性维生素，许多生理功能都需要维生素A，包括视力、生殖、胚胎发育和上皮细胞的维持。人体血液中的维生素A水平保持在2 μM左右。日本七鳃鳗（Lethenteron japonicum）富含维生素a。我们克隆了细胞视黄醇结合蛋白（CRBP）的cDNA。克隆的CRBP不与视网膜结合。CRBP mRNA在肠内表达量最高。成年七鳃鳗可能不需要与视网膜结合CRBP才能有效地从鱼血中吸收维生素A。因此，七鳃鳗CRBP可能失去了对视网膜的亲和力，而保留了对视黄醇的亲和力。

Vitamin A is a fat-soluble vitamin needed for many physiological functions including vision, reproduction, embryonic development, and epithelial maintenance. Vitamin A levels in the bloodstream are kept within a range around 2 μM in humans. The Japanese lamprey, Lethenteron japonicum, stores a high concentration of vitamin A. We have cloned a lamprey cDNA for cellular retinolbinding protein (CRBP). The cloned CRBP did not bind to retinal. The CRBP mRNA showed the highest expression within the intestine. Adult lamprey may not require CRBP binding to retinal in order to effectively absorb vitamin A from fish blood. As a result, lamprey CRBP may have lost the affinity for retinal, while retaining the affinity for retinol.