Apolipoprotein A-II is catabolized in the kidney as a function of its plasma concentration.

We investigated in vivo catabolism of apolipoprotein A-II (apo A-II), a major determinant of plasma HDL levels. Like apoA-I, murine apoA-II (mapoA-II) and human apoA-II (hapoA-II) were reabsorbed in the first segment of kidney proximal tubules of control and hapoA-II-transgenic mice, respectively. ApoA-II colocalized in brush border membranes with cubilin and megalin (the apoA-I receptor and coreceptor, respectively), with mapoA-I in intracellular vesicles of tubular epithelial cells, and was targeted to lysosomes, suggestive of degradation. By use of three transgenic lines with plasma hapoA-II concentrations ranging from normal to three times higher, we established an association between plasma concentration and renal catabolism of hapoA-II. HapoA-II was rapidly internalized in yolk sac epithelial cells expressing high levels of cubilin and megalin, colocalized with cubilin and megalin on the cell surface, and effectively competed with apoA-I for uptake, which was inhibitable by anti-cubilin antibodies. Kidney cortical cells that only express megalin internalized LDL but not apoA-II, apoA-I, or HDL, suggesting that megalin is not an apoA-II receptor. We show that apoA-II is efficiently reabsorbed in kidney proximal tubules in relation to its plasma concentration.

Klebsiella oxytoca as an agent of antibiotic-associated hemorrhagic colitis.

BACKGROUND & AIMS: Klebsiella oxytoca has been isolated from stools and colonic biopsy specimens of patients with Clostridium difficile-negative antibiotic-associated hemorrhagic colitis (AAHC), but the pathogenic role of the germ has not been established. The purpose of this study was to investigate the presence of K. oxytoca in patients with AAHC from a prospective cohort of patients with acute colitis, and to test the cytotoxicity on HEp-2 cells of K. oxytoca strains from patients with AAHC and healthy carriers. METHODS: Colonic biopsy specimens and a sample of colonic fluid from 93 consecutive patients with acute colitis were cultured on selective media for 7 established pathogens and K. oxytoca. The 2 K. oxytoca strains isolated in the 4 patients with C. difficile-negative AAHC of this cohort and 105 additional K. oxytoca strains from patients with C. difficile-negative AAHC (n = 15) and healthy carriers (n = 90) were tested for cytotoxicity using a HEp-2 cell culture assay. RESULTS: K. oxytoca was isolated in 50% (2 of 4) of the patients of the prospective cohort with C. difficile-negative AAHC compared with 2% (1 of 41) of the patients with acute colitis caused by established pathogens (P = 0.02). The rate of cytotoxic strains of K. oxytoca was higher in patients with AAHC (82%) than in healthy carriers (42%, P = 0.003). CONCLUSIONS: We conclude that K. oxytoca is isolated with a significant high rate in patients with C. difficile-negative AAHC, and that K. oxytoca strains from patients with AAHC are cytotoxic more frequently on HEp-2 cells than strains from healthy carriers. These results strengthen the hypothesis of a causative role of K. oxytoca in some of the patients with AAHC.

Restriction of apolipoprotein A-IV gene expression to the intestine villus depends on a hormone-responsive element and parallels differential expression of the hepatic nuclear factor 4alpha and gamma isoforms.

The apoA-I/C-III/A-IV gene cluster, like most intestine-specific genes, displays a specific pattern of expression along the intestinal cephalocaudal and crypt-to-villus axes. We have shown that this specific pattern of expression requires the distal apoA-IV promoter and the apoC-III enhancer. Using a new set of transgenic mice, we demonstrate here that the restriction of apoA-IV gene transcription to villus enterocytes requires a hormone-responsive element (HRE) located within the apoA-IV distal promoter. We showed, using nuclear extracts from villus or crypt epithelial cells, that this HRE bound the transcription factor hepatic nuclear factor 4 (HNF-4). We also found that the HNF-4gamma isoform was produced only in the villus, whereas the HNF-4alpha isoform was produced along the entire length of the crypt-to-villus axis. Our results demonstrate that the HRE of the distal apoA-IV promoter is responsible for the restriction of gene expression to villus epithelial cells and that this HRE binds HNF-4 isoforms. The in vivo observation of parallel gradients for apoA-IV and HNF-4gamma gene expression raises questions concerning whether this transcription factor plays a specific role in the control of enterocyte differentiation.