The in vivo role of the nuclear receptor SHP in feedback regulation of bile acid synthesis was examined. Loss of SHP in mice caused abnormal accumulation and increased synthesis of bile acids due to derepression of rate-limiting CYP7A1 and CYP8B1 hydroxylase enzymes in the biosynthetic pathway. Dietary bile acids induced liver damage and restored feedback regulation. A synthetic agonist of the nuclear receptor FXR was not hepatotoxic and had no regulatory effects. Reduction of the bile acid pool with cholestyramine enhanced CYP7A1 and CYP8B1 expression. We conclude that input from three negative regulatory pathways controls bile acid synthesis. One is mediated by SHP, and two are SHP independent and invoked by liver damage and changes in bile acid pool size.

Isolation and characterization of a human cDNA demonstrated a novel lipoprotein receptor designated apolipoprotein E receptor 2 (apoER2). The new receptor consists of five functional domains resembling the low density lipoprotein (LDL) and very low density lipoprotein (VLDL) receptors. LDL receptor deficient Chinese hamster ovary cells expressing human apoER2 bound apoE rich ␤-migrating VLDL with high affinity and internalized. LDL was bound with much lower affinity to these cells. The 4.5-and 8.5-kb mRNAs for the receptor were most highly expressed in human brain and placenta. In rabbit tissues, multiple species of the mRNA with 4, 4.5, 5.5, 8.5, and 11 kb were detected most intensely in brain and testis and, to a much lesser extent, in ovary, but were undetectable in other tissues. In rat adrenal pheochromocytoma PC12 cells, the receptor mRNA was induced by treatment of the cells with nerve growth factor. The receptor transcripts were detectable most intensely in the cerebellar cortex, choroid plexus, ependyma, hippocampus, olfactory bulb and, to a much lesser extent, in the cerebral cortex as revealed by in situ hybridization histochemistry. In the cerebellar cortex, the receptor transcripts were densely deposited in Purkinje cell somata.Receptor-mediated endocytosis of plasma lipoproteins plays an important role in the metabolism of cholesterol and triglyceride in the body. The low density lipoprotein (LDL) 1 receptor, one of the best characterized cell surface receptors, mediates cholesterol homeostasis in the body (1). The LDL receptor binds apolipoprotein B-100 containing LDL and apolipoprotein E (apoE)-containing lipoproteins, whereas the recently found very low density lipoprotein (VLDL) receptor binds only apoEcontaining lipoproteins (2, 3). Both the LDL receptor (4 -7) and VLDL receptor (2, 8 -14) consist of five functional domains: (i) an amino-terminal ligand binding domain composed of multiple cysteine-rich repeats; (ii) an epidermal growth factor (EGF) precursor homology domain, which mediates the acid-dependent dissociation of the ligands from the LDL receptor (15); (iii) an O-linked sugar domain; (iv) a transmembrane domain; and (v) a cytoplasmic domain with a coated pit targeting signal (16). Genetic deficiencies of the LDL receptor give rise to familial hypercholesterolemia, one of the most common genetic diseases in humans (17). Mutations in the chicken VLDL receptor gene lead to the failure to produce offspring (13, 18).Lipoprotein metabolism in the central nervous system (CNS) has been poorly understood, despite the importance of lipids in some specialized neural membranes, such as myelin. Most of lipids in the CNS are actively synthesized in the CNS itself and deposited in large amounts during the early phase of development (19, 20). The rate of cholesterol and fatty acid synthesis in the brain is high during the myelinating period and declines thereafter (19,20). Although most of lipids in the brain are believed to be synthesized within the brain itself, small amounts of cholesterol (21)...

Cytoglobin/stellate cell activation-associated protein (Cygb/STAP) consists of a new class of hexacoordinate globin superfamily, which was recently discovered by a proteome analysis on the rat hepatic stellate cells. Unlike haemoglobin, myoglobin, and neuroglobin, Cygb/STAP is ubiquitously expressed in several organs, although its detailed localization has not been clarified. Immunohistochemistry and immunoelectron microscopy revealed that Cygb/STAP is uniquely localized in fibroblast-like cells in splanchnic organs, namely the vitamin A-storing cell lineage, but neither in epithelial cells, endothelial cells, muscle cells, blood cells, macrophages, nor dermal fibroblasts. The expression of Cygb/STAP was upregulated in fibrotic lesions of the pancreas and kidney in which activated fibroblast-like cells or myofibroblasts are known to increase in number. In cultured hepatic stellate cells, Cygb/STAP expression was augmented by the stimulation with sera, platelet-derived growth factor-BB, and transforming growth factor-beta 1. Overexpression of Cygb/STAP in NIH 3T3 cells induced the cells to lessen migratory activities and increase the expression of collagen alpha1(I) mRNA. These results indicate that Cygb/STAP is a tissue globin uniquely localized in splanchnic fibroblastic cell lineage and may play a role in fibrotic organ disorder.

Lactobacilli and bifidobacteria are probiotic bacteria that modify host defense systems and have the ability to extend the lifespan of the nematode Caenorhabditis elegans. Here, we attempted to elucidate the mechanism by which bifidobacteria prolong the lifespan of C. elegans. When the nematode was fed Bifidobacterium infantis (BI) mixed at various ratios with the standard food bacterium Escherichia coli strain OP50 (OP), the mean lifespan of worms was extended in a dose-dependent manner. Worms fed BI displayed higher locomotion and produced more offspring than control worms. The growth curves of nematodes were similar regardless of the amount of BI mixed with OP, suggesting that BI did not induce prolongevity effects through caloric restriction. Notably, feeding worms the cell wall fraction of BI alone was sufficient to promote prolongevity. The accumulation of protein carbonyls and lipofuscin, a biochemical marker of aging, was also lower in worms fed BI; however, the worms displayed similar susceptibility to heat, hydrogen peroxide, and paraquat, an inducer of free radicals, as the control worms. As a result of BI feeding, loss-of-function mutants of daf-16, jnk-1, aak-2, tol-1, and tir-1 exhibited a longer lifespan than OP-fed control worms, but BI failed to extend the lifespan of pmk-1, skn-1, and vhp-1 mutants. As skn-1 induces phase 2 detoxification enzymes, our findings suggest that cell wall components of bifidobacteria increase the average lifespan of C. elegans via activation of skn-1, regulated by the p38 MAPK pathway, but not by general activation of the host defense system via DAF-16.

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