Distinct surveillance pathway for immunopathology during acute infection via autophagy and SR-BI

The mechanisms protecting from immunopathology during acute bacterial infections are incompletely known. We found that in response to apoptotic immune cells and live or dead Listeria monocytogenes scavenger receptor BI (SR-BI), an anti-atherogenic lipid exchange mediator, activated internalization mechanisms with characteristics of macropinocytosis and, assisted by Golgi fragmentation, initiated autophagic responses. This was supported by scavenger receptor-induced local increases in membrane cholesterol concentrations which generated lipid domains particularly in cell extensions and the Golgi. SR-BI was a key driver of beclin-1-dependent autophagy during acute bacterial infection of the liver and spleen. Autophagy regulated tissue infiltration of neutrophils, suppressed accumulation of Ly6C(+) (inflammatory) macrophages, and prevented hepatocyte necrosis in the core of infectious foci. Perifocal levels of Ly6C(+) macrophages and Ly6C(-) macrophages were unaffected, indicating predominant regulation of the focus core. SR-BI-triggered autophagy promoted co-elimination of apoptotic immune cells and dead bacteria but barely influenced bacterial sequestration and survival or inflammasome activation, thus exclusively counteracting damage inflicted by immune responses. Hence, SR-BI-and autophagy promote a surveillance pathway that partially responds to products of antimicrobial defenses and selectively prevents immunity-induced damage during acute infection. Our findings suggest that control of infection-associated immunopathology can be based on a unified defense operation

Low density lipoprotein and liposome mediated uptake and cytotoxic effect of N4-octadecyl-1-β-D-arabinofuranosylcytosine in Daudi lymphoma cells

Low density lipoprotein (LDL) receptor-mediated uptake and cytotoxic effects of N4-octadecyl-1-beta-D-arabinofuranosylcytosine (NOAC) were studied in Daudi lymphoma cells. NOAC was either incorporated into LDL or liposomes to compare specific and unspecific uptake mechanisms. Binding of LDL to Daudi cells was not altered after NOAC incorporation (K(D) 60 nM). Binding of liposomal NOAC was not saturable with increasing concentrations. Specific binding of NOAC-LDL to Daudi cells was five times higher than to human lymphocytes. LDL receptor binding could be blocked and up- or down-regulated. Co-incubation with colchicine reduced NOAC-LDL uptake by 36%. These results suggested that NOAC-LDL is taken up via the LDL receptor pathway. In an in vitro cytotoxicity test, the IC50 of NOAC-LDL was about 160 microM, whereas with liposomal NOAC the IC50 was 40 microM. Blocking the LDL receptors with empty LDL protected 50% of the cells from NOAC cytotoxicity. The cellular distribution of NOAC-LDL or NOAC-liposomes differed only in the membrane and nuclei fraction with 13% and 6% respectively. Although it is more convenient to prepare NOAC-liposomes as compared to the loading of LDL particles with the drug, the receptor-mediated uptake of NOAC-LDL provides an interesting rationale for the specific delivery of the drug to tumours that express elevated numbers of LDL receptors

High-Density Lipoprotein Transport Through Aortic Endothelial Cells Involves Scavenger Receptor BI and ATP-Binding Cassette Transporter G1

Cholesterol efflux from macrophage foam cells is a rate-limiting step in reverse cholesterol transport. In this process cholesterol acceptors like high-density lipoproteins (HDL) and apolipoprotein (apo)A-I must cross the endothelium to get access to the donor cells in the arterial intima. Previously, we have shown that apoA-I passes a monolayer of aortic endothelial cells (ECs) from the apical to the basolateral side by transcytosis, which is modulated by the ATP-binding cassette transporter (ABC)A1. Here, we analyzed the interaction of mature HDL with ECs. ECs bind HDL in a specific and saturable manner. Both cell surface biotinylation experiments and immunofluorescence microscopy of HDL recovered approximately 30% of the cell-associated HDL intracellularly. Cultivated on inserts ECs bind, internalize, and translocate HDL from the apical to the basolateral compartment in a specific and temperature-dependent manner. The size of the translocated particle was reduced, but its protein moiety remained intact. Using RNA interference, we investigated the impact of SR-BI, ABCA1, and ABCG1 on binding, internalization, and transcytosis of HDL by ECs. HDL binding was reduced by 50% and 30% after silencing of SR-BI and ABCG1, respectively, but not at all after diminishing ABCA1 expression. Knock down of SR-BI and, even more so, ABCG1 reduced HDL transcytosis but did not affect inulin permeability. Cosilencing of both proteins did not further reduce HDL binding, internalization, or transport. In conclusion, ECs transcytose HDL by mechanisms that involve either SR-BI or ABCG1 but not ABCA1

Expression and role of cubilin in the internalization of nutrients during the peri-implantation development of the rodent embryo

Histiotrophic nutrition is essential during the peri-implantation development in rodents, but little is known about receptors involved in protein and lipid endocytosis derived from the endometrium and the uterine glands. Previous studies suggested that cubilin, a multiligand receptor for vitamin, iron, and protein uptake in the adult, might be important in this process, but the onset of its expression and function is not known. In this study, we analyzed the expression of cubilin in the pre- and early post-implantation rodent embryo and tested its potential function in protein and cholesterol uptake. Using morphological and Western blot analysis, we showed that cubilin first appeared at the eight-cell stage. It was expressed by the maternal-fetal interfaces, trophectoderm and visceral endoderm, but also by the future neuroepithelial cells and the developing neural tube. At all these sites, cubilin was localized at the apical pole of the cells exposed to the maternal environment or to the amniotic and neural tube cavities, and had a very similar distribution to megalin, a member of the LDLR gene family and a coreceptor for cubilin in adult tissues. To analyze cubilin function, we followed endocytosis of apolipoprotein A-I and HDL cholesterol, nutrients normally present in the uterine glands and essential for embryonic growth. We showed that internalization of both ligands was cubilin dependent during the early rodent gestation. In conclusion, the early cubilin expression and its function in protein and cholesterol uptake suggest an important role for cubilin in the development of the peri-implantation embryo

Thermogenic adipocytes promote HDL turnover and reverse cholesterol transport

Diabetes mellitus: pathophysiological changes and therap