Dantuma N P, Pijnenburg M A, Diederen J H, Van der Horst D J
Department of Experimental Zoology and Institute of Biomembranes, Utrecht University, The Netherlands.
J Lipid Res. 1998 Sep;39(9):1877-88.
The binding and internalization of a circulating insect lipoprotein, high density lipophorin (HDLp), by insect fat body cells was studied at the electron-microscopic level using ultrasmall gold-labeled HDLp and DiI-labeled HDLp, which were visualized by silver enhancement and diaminobenzidine photoconversion, respectively. Internalization of HDLp seems to conflict with the selective process by which the lipids are transported between HDLp and fat body cells. The pathway followed by the internalized lipoproteins was investigated. In addition, the localizations of HDLp in fat body cells of young and older adult locusts were compared because of the previously reported age-related differences in distribution of cell-associated and internalized HDLp. In the present study, internalized labeled HDLp was observed in early endosomes, late endosomes, and putative lysosomes. In older adults, these labeled structures were much less abundant than in young adults. Moreover, in these animals, the labeled endosomal/lysosomal vesicles were located close to the plasma membranes. A more intense labeling was observed in the extracellular matrix in older adults compared to young adults. In both developmental stages, an apparent accumulation of labeled HDLp was found in extracellular spaces. We propose that this entrapment of HDLp may be essential for selective lipid transport between HDLp and fat body cells.
利用超小金标记的高密度脂蛋白（HDLp）和分别通过银增强和二氨基联苯胺光转化进行可视化的DiI标记的HDLp，在电子显微镜水平上研究了循环中的昆虫脂蛋白——高密度脂蛋白（HDLp）与昆虫脂肪体细胞的结合及内化过程。HDLp的内化似乎与脂质在HDLp和脂肪体细胞之间运输的选择性过程相矛盾。研究了内化脂蛋白所遵循的途径。此外，由于先前报道的细胞相关和内化HDLp分布存在年龄相关差异，比较了年轻和老年成年蝗虫脂肪体细胞中HDLp的定位。在本研究中，在内体早期、晚期内体和假定的溶酶体中观察到内化的标记HDLp。在老年成虫中，这些标记结构比年轻成虫中少得多。此外，在这些动物中，标记的内体/溶酶体囊泡靠近质膜。与年轻成虫相比，老年成虫的细胞外基质中观察到更强的标记。在两个发育阶段，细胞外空间中均发现标记的HDLp明显积累。我们认为，HDLp的这种截留可能对HDLp和脂肪体细胞之间的选择性脂质运输至关重要。
