Biomedical subjects

Shinji Yokoyama

Publications and source records attributed to Shinji Yokoyama.

42 records · Page 3Linked to original sources

PubMed2002

Apolipoprotein-mediated cellular lipid release requires replenishment of sphingomyelin in a phosphatidylcholine-specific phospholipase C-dependent manner.

When sphingomyelin is digested by sphingomyelinase in the plasma membrane of rat astrocytes, productions of sphingomyelin, diacylglycerol, and phosphatidylcholine are stimulated. D609, an inhibitor of phosphatidylcholine-specific phospholipase C, suppressed these effects. Similarly, when apolipoprotein A-I removed cellular cholesterol, phosphatidylcholine, and sphingomyelin to generate high density lipoprotein, cholesterol synthesis from acetate subsequently increased, and sphingomyelin synthesis from acetate and serine also increased. D609 inhibited these effects again. D609 also inhibited the cholesterol removal by apoA-I not only from the astrocytes but also from BALB/3T3 and RAW264 cells. D609 decreased cholesterol synthesis, although D609 did not directly inhibit hydroxymethylglutaryl-CoA reductase. ApoA-I-stimulated translocation of newly synthesized cholesterol to cytosol was also decreased by D609. A diacylglycerol analog increased the apoA-I-mediated cholesterol release, whereas ceramide did not influence it. We concluded that removal of cellular sphingomyelin by apolipoproteins is replenished by transfer of phosphorylcholine from phosphatidylcholine to ceramide, and this reaction may limit the removal of cholesterol by apoA-I. This reaction also produces diacylglycerol that potentially triggers subsequent cellular signal cascades and regulates intracellular cholesterol trafficking.

Acetates↗

PubMed2002

Cholesteryl ester transfer protein expressed in lecithin cholesterol acyltransferase-deficient mice.

OBJECTIVE: Regulation of plasma cholesteryl ester transfer protein (CETP) concentration was studied in lecithin-cholesterol acyltransferase (LCAT)-knockout mice. METHODS AND RESULTS: LCAT-knockout mice were cross-bred with CETP transgenic mice. The offspring (n=63) were classified for LCAT genotype and plasma CETP levels (no CETP, low CETP, and high CETP). High density lipoprotein (HDL) decreased as LCAT decreased in each CETP-level group. In the lcat(+/+) and lcat(+/-) mice, plasma CETP varied from 0 to 30 micro g/mL, whereas it was <10 micro g/mL in the lcat(-/-) mice. HDL cholesterol and phospholipid decreased and HDL triglyceride and apolipoprotein B increased in CETP in the lcat(+/+) and lcat(+/-) mice, whereas there was no difference in HDL between low and high CETP. An effect of CETP on HDL was not detected in the lcat(-/-) mice because of the absence of mature HDL. Genomic DNA and mRNA of CETP were correlated and were similar in the lcat(-/-) and lcat(+/+) mice. Plasma CETP was correlated with its genomic DNA and mRNA, but the slope of the increase was much lower in the lcat(-/-) mice. Whereas plasma CETP mostly associates with HDL in the lcat(+/+) mouse, it is found free in the lcat(-/-) mouse. CONCLUSIONS: Plasma CETP is posttranscriptionally downregulated in the lcat(-/-) mice, presumably by its extremely low HDL.

Animals↗

PubMed2002

An acidic fibroblast growth factor-like factor secreted into the brain cell culture medium upregulates apoE synthesis, HDL secretion and cholesterol metabolism in rat astrocytes.

Production and release of apolipoprotein (apo) E and cholesterol were highly upregulated in the astrocytes prepared by 1-week secondary culture after 1-month primary culture of rat fetal brain cells (M/W cells) in comparison to the cells prepared by a conventional method of 1-week primary and 1-week secondary culture (W/W cells). Both cell preparations were mostly composed of astrocytes with small population of other glial cells, except that type-2 astrocyte-like cells accounted for 5-15% of M/W cells indicating more activated and/or matured status. The conditioned medium of the 1-month primary culture stimulated W/W cells to increase the release of apoE and cholesterol into the medium. The treatment of W/W cells by acidic fibroblast growth factor (aFGF) similarly upregulated biosyntheses and release of apoE and cholesterol. The effect of the conditioned medium was completely inhibited by pretreatment with an anti-aFGF antibody. The increase of the aFGF message was demonstrated in the brain cells after 1-month primary culture. The findings suggested that an aFGF-like trophic factor upregulates biosynthesis and secretion of apoE-high density lipoprotein (HDL) in astrocytes probably by autocrine stimulation in this culture system. Since this cytokine is highly expressed in the development or post-injury period of the brain, it putatively activates intercellular cholesterol transport to support construction or recovery of the brain.

Animals↗

PubMed2002

Helical apolipoproteins stabilize ATP-binding cassette transporter A1 by protecting it from thiol protease-mediated degradation.

ATP-binding cassette transporter (ABC) A1 was increased by apolipoprotein A-I without an increase of its message in THP-1 cells. The pulse label study demonstrated that apoA-I retarded degradation of ABCA1. Similar changes were demonstrated by apoA-II, but the effect of high density lipoprotein was almost negligible on the basis of equivalent protein concentration. Thiol protease inhibitors (leupeptin and N-acetyl-Leu-Leu-norleucinal (ALLN)) increased ABCA1 and slowed its decay in the cells, whereas none of the proteosome-specific inhibitor lactacystin, other protease inhibitors, or the lysosomal inhibitor NH(4)Cl showed such effects. The effects of apoA-I and ALLN were additive for the increase of ABCA1, and the apoA-I-mediated cellular lipid release was enhanced by ALLN. The data suggest that ABCA1 is rapidly degraded by a thiol protease(s) in the cells unless helical apolipoproteins in their lipid-free form stabilize ABCA1 by protecting it from protease-mediated degradation.

ATP Binding Cassette Transporter 1↗

PubMed2002

Coexistence of impairment of endothelium-derived nitric oxide and platelet-derived nitric oxide in patients with coronary risk factors.

Impairment of endothelium-derived nitric oxide (EDNO) has been demonstrated in patients with coronary risk factors in some studies, as well as impaired platelet-derived nitric oxide (PDNO) in other studies. However, no study has examined whether these impairments coexist. In 24 patients with coronary risk factors, femoral vascular endothelial function was assessed with acetylcholine (ACh: 50, 100, 200 and 400 microg/min) and endothelium-independent vascular function with nitroglycerin (NTG; 50, 100, 200 microg/min) using a Doppler flow-wire technique, as well as ADP (5 micromol/L)-induced PDNO release with an NO-specific electrode. The ACh-mediated percent change in femoral vascular resistance index (% change of FVRI) and PDNO release had a significant correlation with the number of risk factors. The ACh-mediated % change of FVRI, but not that with NTG, significantly correlated with the PDNO release. Both EDNO and PDNO bioactivities are impaired in patients with coronary risk factors and there is a common mechanism.

Acetylcholine↗

PubMed2001

Apolipoprotein A-I induces translocation of cholesterol, phospholipid, and caveolin-1 to cytosol in rat astrocytes.

Intercellular cholesterol transport in the brain is carried by high density lipoprotein (HDL) generated in situ by cellular interaction with the apolipoprotein apoE, which is mainly synthesized by astrocytes, and with apoA-I secreted by cells such as endothelial cells. Rat astrocytes in fact generate HDL with extracellular apoA-I in addition to releasing HDL with endogenously synthesized apoE, seemingly by the same mechanism as the HDL assembly for systemic circulation. Relating to this reaction, apoA-I induced translocation of newly synthesized cholesterol and phospholipid to the cytosol prior to extracellular assembly of HDL, accompanied by an increase of caveolin-1 in the cytosol, activation of sterol regulatory element-binding protein, and enhancement of cholesterol synthesis. The lipid translocated into the cytosol was recovered in the fraction with a density of 1.09-1.16 g/ml as well as caveolin-1 and cyclophilin A. Cyclosporin A inhibited these apoA-I-mediated reactions and suppressed apoA-I-mediated cholesterol release. The findings suggest that such translocation of cholesterol and phospholipid into the cytosol is related to the apo A-I-mediated HDL assembly in astrocytes through functional association with caveolin-1 and a cyclosporin A-sensitive cyclophilin protein(s).

Animals↗