Astrocytes produce and secrete FGF-1, which promotes the production of apoE-HDL in a manner of autocrine action

The astrocytes prepared by 1 week secondary culture after 1 month primary culture of rat brain cells (M/W cells) synthesized and secreted apolipoprotein E (apoE) and cholesterol more than the astrocytes prepared by conventional 1 week primary and 1 week secondary culture (W/W cells) (Ueno, S., J. Ito, Y. Nagayasu, T. Furukawa, and S. Yokoyama. 2002. 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. Biochim. Biophys. Acta. 1589: 261-272). M/W cells also highly expressed fibroblast growth factor-1 (FGF-1) mRNA. FGF-1 was identified in the cell lysate of both cell types, but M/W cells released more of it into the medium. Immunostaining of FGF-1 and apoE revealed that both localized in the cells that produce glial fibrillary acidic protein. The conditioned media of M/W cells and FGF-1 stimulated W/W cells to release apoE and cholesterol to generate more HDL. Pretreatment with a goat anti-FGF-1 antibody or heparin depleted the stimulatory activity of M/W cell-conditioned medium. The presence of the anti-FGF-1 antibody in the medium suppressed apoE secretion by M/W cells. Differential inhibition of signaling pathways suggested that FGF-1 stimulates apoE synthesis via the phosphoinositide 3-OH kinase for PI3K/Akt pathway. Thus, astrocytes release FGF-1, which promotes apoE-HDL production by an autocrine mechanism. These results are consistent with our in vivo observation that astrocytes produce FGF-1 before the increase of apoE in the postinjury lesion of the mouse brain (Tada, T., J. Ito, M. Asai, and S. Yokoyama. 2004. Fibroblast growth factor 1 is produced prior to apolipoprotein E in the astrocytes after cryo-injury of mouse brain. Neurochem. Int. 45: 23-30).     

Estrogen increases hepatic lipase levels in inbred strains of mice: A possible mechanism for estrogen-dependent lowering of high density lipoprotein

We have shown mouse to be an useful animal model for studies on the estrogen-mediated synthesis and secretion of lipoproteins since, unlike in rats, low density lipoprotein receptors are not upregulated in mice [3]. This results into the elevation of plasma levels of apolipoprotein (apo) B and apoE, and lowering of apoA-I-containing particles. The mechanisms of apoB and apoE elevation by estrogen have been elucidated [6], but the mechanism of lowering of plasma levels of HDL is still not known. Among other factors, apoA-I, cholesterol ester transfer protein (CETP), scavenger receptor B1 (SR-B1), and hepatic lipase are potential candidates that modulate plasma levels of HDL. Since estrogen treatment increased hepatic apoA-I mRNA and apoA-I synthesis, and mouse express undetectable levels of CETP, we tested the hypothesis that estradiol-mediated lowering of HDL in mice may occur through modulation of hepatic lipase (HL). Four mouse strains (C57L, C57BL, BALB, C3H) were administered supraphysiological doses of estradiol, and plasma levels of HDL as well as HL mRNA were quantitated. In all 4 strains estradiol decreased plasma levels of HDL by 30%, and increased HL mRNA 2–3 fold. In a separate experiment groups of male C57BL mouse were castrated or sham-operated, and low and high doses of estradiol administered. We found 1.4–2.5 fold elevation of HL mRNA with concomitant lowering of HDL levels. Ten other mouse strains examined also showed estradiol-induced elevation of HL mRNA, but the extent of elevation was found to be strain-specific. Based on these studies, we conclude that hepatic lipase is an important determinant of plasma levels of HDL and that HL mRNA is modulated by estrogen which in turn may participate in the lowering of plasma levels of HDL.     

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.     

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.     

A liver X receptor and retinoid X receptor heterodimer mediates apolipoprotein E expression, secretion and cholesterol homeostasis in astrocytes

Apolipoprotein E (apoE) is an important protein involved in lipoprotein clearance and cholesterol redistribution. ApoE is abundantly expressed in astrocytes in the brain and is closely linked to the pathogenesis of Alzheimer's disease (AD). We report here that small molecule ligands that activate either liver X receptors (LXR) or retinoid X receptor (RXR) lead to a dramatic increase in apoE mRNA and protein expression as well as secretion of apoE in a human astrocytoma cell line (CCF-STTG1 cells). Examination of primary mouse astrocytes also revealed significant induction of apoE mRNA, and protein expression and secretion following incubation with LXR/RXR agonists. Moreover, treatment of mice with a specific synthetic LXR agonist T0901317 resulted in up-regulation of apoE mRNA and protein in both hippocampus and cerebral cortex, indicating that apoE expression in brain can be up-regulated by LXR agonists in vivo. Along with a dramatic induction of ABCA1 cholesterol transporter expression, these ligands effectively mediate cholesterol efflux in both CCF-STTG1 cells and mouse astrocytes in the presence or absence of apolipoprotein AI (apoAI). Our studies provide strong evidence that small molecule LXR/RXR agonists can effectively mediate apoE synthesis and secretion as well as cholesterol homeostasis in astrocytes. LXR/RXR agonists may have significant impact on the pathogenesis of multiple neurological diseases, including AD.     

Cholesterol homeostasis in rat astrocytoma cells GA-1

Astrocytes play a key role in cholesterol metabolism in central nervous system. We have shown that fetal rat astrocytes in primary culture secrete cholesterol-rich HDL with the endogenous apolipoprotein (apo) E and generate cholesterol-poor HDL with exogenous apoE and apoA-I [Ito et al. (1999) J. Neurochem. 72, 2362]. In order to study these reactions in relation to the stage of cell differentiation, we examined generation of HDL by rat astrocytoma cells. Lack of apoE secretion was found in three astrocytoma cell lines, human T98G, rat C6, and GA-1 [Kano-Tanaka et al. (1986) Proc. Jpn. Acad. Ser. B 62, 109]. GA-1 produced apoE at very low level and therefore generated much less HDL by itself than the astrocytes in primary culture. In contrast, GA-1 interacted with exogenous apoE and apoA-I to produce cholesterol-rich HDL while the astrocytes produced cholesterol-poor HDL with these apolipoproteins. Cholesterol biosynthesis rate measured from mevalonate was higher and down-regulated more by LDL in the astrocytes than GA-1. On the other hand, the cellular cholesterol level, uptake of LDL, and cyclodextrin-mediated non-specific diffusion of cholesterol from cell surface were same between these two cells. Treatment of GA-1 with acidic fibroblast growth factor influenced neither the production of apoE nor the baseline lipid secretion, but increased the cholesterol synthesis from mevalonate and the magnitude of its down-regulation by LDL, and decreased cholesterol content in the HDL produced by exogenous apoA-I. In conclusion, suppression of apoE biosynthesis in the undifferentiated astrocytes GA-1 resulted in poor secretion of cholesterol-rich HDL and in turn more production of HDL with exogenous apolipoprotein. Cellular cholesterol homeostasis was altered accordingly.     

Reactivity of astrocytes to fibroblast growth factor-1 for biogenesis of apolipoprotein E-high density lipoprotein is down-regulated by long-time secondary culture

We previously showed that astrocytes produce and release fibroblast growth factor-1 (FGF-1) upon 1-month primary and 1-week secondary culture (M/W cells) and stimulate themselves by an autocrine manner to produce apoE-high-density lipoproteins (HDL), closely associated with their generation of apoE-HDL in brain injury. Astrocytes prepared by 1-week primary and 1-month secondary culture (W/M cells), however, expressed FGF-1 as much as M/W cells but produce apoE-HDL much less. The W/M cells conditioned medium in fact contained FGF-1 activity to stimulate astrocytes prepared by 1-week primary and 1-week-secondary culture (W/W cells). FGF-1 did not stimulate W/M cells for apoE-HDL biogenesis while it stimulated W/W cells. Phosphorylation of Akt, ERK and MEK were induced by FGF-1 in W/W cells but not in W/M cells. Finally, fibroblast growth factor receptor-1 in the membrane decreased in W/M cells in comparison to W/W cells. Interestingly, the reactivity of astrocytes to FGF-1 was recovered when W/M cells were transferred to the tertiary culture of 1 week. We concluded that astrocytes decrease their reactivity to FGF-1 for apoE-HDL biogenesis in certain conditions. The findings indicate astrocyte FGF-1 enhances biogenesis of apoE-HDL also by a paracrine mechanism.     

Dietary phytosterols modulate T-helper immune response but do not induce apparent anti-inflammatory effects in a mouse model of acute, aseptic inflammation

Although most studies have focused on the cholesterol-lowering activity of phytosterols, other biological actions have been ascribed to these plant sterol compounds, one of which is a potential immune modulatory effect. To gain insight into this issue, we used a mouse model of acute, aseptic inflammation induced by a single subcutaneous turpentine injection. Hypercholesterolemic apolipoprotein E-deficient (apoE(-/-)) mice, fed with or without a 2% phytosterol supplement, were treated with turpentine or saline and euthanized 48 h later. No differences were observed in spleen lymphocyte subsets between phytosterol- and control-fed apoE(-/-) mice. However, cultured spleen lymphocytes of apoE(-/-) mice fed with phytosterols and treated with turpentine showed increased IL-2 and IFN-gamma secretion (T-helper type1, Th1 lymphocyte cytokines) compared with turpentine-treated, control-fed animals. In contrast, there was no change in Th2 cytokines IL-4 and IL-10. Phytosterols also inhibit intestinal cholesterol absorption in wild-type C57BL/6J mice but, in this case, without decreasing plasma cholesterol. Spleen lymphocytes of turpentine-treated C57BL/6J mice fed with phytosterols also showed increased IL-2 production, but IFN-gamma, IL-4 and IL-10 production was unchanged. The Th1/Th2 ratio was significantly increased both in phytosterol-fed apoE(-/-) and C57BL/6J mice. We conclude that phytosterols modulate the T-helper immune response in vivo, in part independently of their hypocholesterolemic effect in a setting of acute, aseptic inflammation. Further study of phytosterol effects on immune-based diseases characterized by an exacerbated Th2 response is thus of interest.     

Low and high density lipoprotein metabolism in primary cultures of hepatic cells from normal and apolipoprotein E knockout mice.

Apolipoprotein E (apoE) plays a major role in lipoprotein metabolism by mediating the binding of apoE-containing lipoproteins to receptors. The role of hepatic apoE in the catabolism of apoE-free lipoproteins such as low density lipoprotein (LDL) and high density lipoprotein-3 (HDL(3)) is however, unclear. We analyzed the importance of hepatic apoE by comparing human LDL and HDL(3) metabolism in primary cultures of hepatic cells from control C57BL/6J and apoE knockout (KO) mice. Binding analysis showed that the maximal binding capacity (Bmax) of LDL, but not of HDL(3), is increased by twofold in the absence of apoE synthesis/secretion. Compared to control hepatic cells, LDL and HDL(3) holoparticle uptake by apoE KO hepatic cells, as monitored by protein degradation, is reduced by 54 and 77%, respectively. Cleavage of heparan sulfate proteoglycans (HSPG) by treatment with heparinase I reduces LDL association by 21% in control hepatic cells. Thus, HSPG alone or a hepatic apoE-HSPG complex is partially involved in LDL association with mouse hepatic cells. In apoE KO, but not in normal hepatic cells, the same treatment increases LDL uptake/degradation by 2.4-fold suggesting that in normal hepatic cells, hepatic apoE increases LDL degradation by masking apoB-100 binding sites on proteoglycans. Cholesteryl ester (CE) association and CE selective uptake (CE/protein association ratio) from LDL and HDL(3) by mouse hepatic cells were not affected by the absence of apoE expression. We also show that 69 and 72% of LDL-CE hydrolysis in control and apoE KO hepatic cells, respectively, is sensitive to chloroquine revealing the importance of a pathway linked to lysosomes. In contrast, HDL(3)-CE hydrolysis is only mediated by a nonlysosomal pathway in both control and apoE KO hepatic cells. Overall, our results indicate that hepatic apoE increases the holoparticle uptake pathway of LDL and HDL(3) by mouse hepatic cells, that HSPG devoid of apoE favors LDL binding/association but impairs LDL uptake/degradation and that apoE plays no significant role in CE selective uptake from either human LDL or HDL(3) lipoproteins.     

Fibroblast Growth Factor-2 (FGF-2) Induces Vascular Endothelial Growth Factor (VEGF) Expression in the Endothelial Cells of Forming Capillaries: An Autocrine Mechanism Contributing to Angiogenesis

FGF-2 and VEGF are potent angiogenesis inducers in vivo and in vitro. Here we show that FGF-2 induces VEGF expression in vascular endothelial cells through autocrine and paracrine mechanisms. Addition of recombinant FGF-2 to cultured endothelial cells or upregulation of endogenous FGF-2 results in increased VEGF expression. Neutralizing monoclonal antibody to VEGF inhibits FGF-2–induced endothelial cell proliferation. Endogenous 18-kD FGF-2 production upregulates VEGF expression through extracellular interaction with cell membrane receptors; high-M_r FGF-2 (22–24-kD) acts via intracellular mechanism(s). During angiogenesis induced by FGF-2 in the mouse cornea, the endothelial cells of forming capillaries express VEGF mRNA and protein. Systemic administration of neutralizing VEGF antibody dramatically reduces FGF-2-induced angiogenesis. Because occasional fibroblasts or other cell types present in the corneal stroma show no significant expression of VEGF mRNA, these findings demonstrate that endothelial cell-derived VEGF is an important autocrine mediator of FGF-2-induced angiogenesis. Thus, angiogenesis in vivo can be modulated by a novel mechanism that involves the autocrine action of vascular endothelial cell-derived FGF-2 and VEGF.     

Unique lipoproteins secreted by primary astrocytes from wild type, apoE (-/-), and human apoE transgenic mice.

Composition of central nervous system lipoproteins affects the metabolism of lipoprotein constituents within the brain. The epsilon4 allele of apolipoprotein E (apoE) is a risk factor for Alzheimer's disease via an unknown mechanism(s). As glia are the primary central nervous system cell type that synthesize apoE, we characterized lipoproteins secreted by astrocytes from wild type (WT), apoE (-/-), and apoE transgenic mice expressing human apoE3 or apoE4 in a mouse apoE (-/-) background. Nondenaturing size exclusion chromatography demonstrates that WT, apoE3, and apoE4 astrocytes secrete particles the size of plasma high density lipoprotein (HDL) composed of phospholipid, free cholesterol, and protein, primarily apoE and apoJ. However, the lipid:apoE ratio of particles containing human apoE is significantly lower than WT. ApoE localizes across HDL-like particle sizes. ApoJ localizes to the smallest HDL-like particles. ApoE (-/-) astrocytes secrete little phospholipid or free cholesterol despite comparable apoJ expression, suggesting that apoE is required for normal secretion of astrocyte lipoproteins. Further, particles were not detected in apoE (-/-) samples by electron microscopy. Nondenaturing immunoprecipitation experiments indicate that apoE and apoJ reside predominantly on distinct particles. These studies suggest that apoE expression influences the unique structure of astrocyte lipoproteins, a process further modified by apoE species.     

NAD(P)H quinone oxidoreductase 1 regulates neutrophil elastase-induced mucous cell metaplasia

Mucous cell metaplasia (MCM) and neutrophil-predominant airway inflammation are pathological features of chronic inflammatory airway diseases. A signature feature of MCM is increased expression of a major respiratory tract mucin, MUC5AC. Neutrophil elastase (NE) upregulates MUC5AC in primary airway epithelial cells by generating reactive oxygen species, and this response is due in part to upregulation of NADPH quinone oxidoreductase 1 (NQO1) activity. Delivery of NE directly to the airway triggers inflammation and MCM and increases synthesis and secretion of MUC5AC protein from airway epithelial cells. We hypothesized that NE-induced MCM is mediated in vivo by NQO1. Male wild-type and Nqo1-null mice (C57BL/6 background) were exposed to human NE (50 μg) or vehicle via oropharyngeal aspiration on days 1, 4, and 7. On days 8 and 11, lung tissues and bronchoalveolar lavage (BAL) samples were obtained and evaluated for MCM, inflammation, and oxidative stress. MCM, inflammation, and production of specific cytokines, granulocyte-macrophage colony-stimulating factor, macrophage inflammatory protein-2, interleukin-4, and interleukin-5 were diminished in NE-treated Nqo1-null mice compared with NE-treated wild-type mice. However, in contrast to the role of NQO1 in vitro, we demonstrate that NE-treated Nqo1-null mice had greater levels of BAL and lung tissue lipid carbonyls and greater BAL iron on day 11, all consistent with increased oxidative stress. NQO1 is required for NE-induced inflammation and MCM. This model system demonstrates that NE-induced MCM directly correlates with inflammation, but not with oxidative stress.     

Deficiency of ABCA1 impairs apolipoprotein E metabolism in brain

ABCA1 is a cholesterol transporter that is widely expressed throughout the body. Outside the central nervous system (CNS), ABCA1 functions in the biogenesis of high-density lipoprotein (HDL), where it mediates the efflux of cholesterol and phospholipids to apolipoprotein (apo) A-I. Deficiency of ABCA1 results in lack of circulating HDL and greatly reduced levels of apoA-I. ABCA1 is also expressed in cells within the CNS, but its roles in brain lipid metabolism are not yet fully understood. In the brain, glia synthesize the apolipoproteins involved in CNS lipid metabolism. Here we demonstrate that glial ABCA1 is required for cholesterol efflux to apoA-I and plays a key role in facilitating cholesterol efflux to apoE, which is the major apolipoprotein in the brain. In both astrocytes and microglia, ABCA1 deficiency reduces lipid efflux to exogenous apoE. The impaired ability to efflux lipids in ABCA1-/- glia results in lipid accumulation in both astrocytes and microglia under normal culture conditions. Additionally, apoE secretion is compromised in ABCA1-/- astrocytes and microglia. In vivo, deficiency of ABCA1 results in a 65% decrease in apoE levels in whole brain, and a 75-80% decrease in apoE levels in hippocampus and striatum. Additionally, the effect of ABCA1 on apoE is selective, as apoJ levels are unchanged in brains of ABCA1-/- mice. Taken together, these results show that glial ABCA1 is a key influence on apoE metabolism in the CNS.     

Circulating adhesion molecules in apoE-deficient mouse strains with different atherosclerosis susceptibility

Recruitment of inflammatory cells in the arterial wall by vascular adhesion molecules plays a key role in development of atherosclerosis. Apolipoprotein E-deficient (apoE(-/-)) mice have spontaneous hyperlipidemia and develop all phases of atherosclerotic lesions. We sought to examine plasma levels of soluble vascular cell adhesion molecule-1 (sVCAM-1) and sP-selectin in two apoE(-/-) strains C57BL/6 (B6) and BALB/c with early or advanced lesions. Mice were fed chow or a Western diet containing 42% fat, 0.15% cholesterol, and 19.5% casein. On either diet, BALB/c.apoE(-/-) mice developed much smaller atherosclerotic lesions and displayed significantly lower levels of sVCAM-1 and sP-selectin than B6.apoE(-/-) mice. The Western diet significantly elevated sVCAM-1 levels in both strains and sP-selectin levels in B6.apoE(-/-) mice. BALB/c.apoE(-/-) mice exhibited 2-fold higher HDL cholesterol levels on the chow diet and 15-fold higher HDL levels on the Western diet than B6.apoE(-/-) mice, although the two strains had comparable levels of total cholesterol and triglyceride. Thus, increased atherosclerosis is accompanied by increases in circulating VCAM-1 and P-selectin levels in the two apoE(-/-) mouse strains, and the high HDL level may protect against atherosclerosis by inhibiting the expression of adhesion molecules in BALB/c.apoE(-/-) mice.     

Differential cellular FGF-2 upregulation in the rat facial nucleus following axotomy, functional electrical stimulation and corticosterone: a possible therapeutic target to Bell's palsy

Background

The etiology of Bell's palsy can vary but anterograde axonal degeneration may delay spontaneous functional recovery leading the necessity of therapeutic interventions. Corticotherapy and/or complementary rehabilitation interventions have been employed. Thus the natural history of the disease reports to a neurotrophic resistance of adult facial motoneurons leading a favorable evolution however the related molecular mechanisms that might be therapeutically addressed in the resistant cases are not known. Fibroblast growth factor-2 (FGF-2) pathway signaling is a potential candidate for therapeutic development because its role on wound repair and autocrine/paracrine trophic mechanisms in the lesioned nervous system.

Methods

Adult rats received unilateral facial nerve crush, transection with amputation of nerve branches, or sham operation. Other group of unlesioned rats received a daily functional electrical stimulation in the levator labii superioris muscle (1 mA, 30 Hz, square wave) or systemic corticosterone (10 mgkg^-1). Animals were sacrificed seven days later.

Results

Crush and transection lesions promoted no changes in the number of neurons but increased the neurofilament in the neuronal neuropil of axotomized facial nuclei. Axotomy also elevated the number of GFAP astrocytes (143% after crush; 277% after transection) and nuclear FGF-2 (57% after transection) in astrocytes (confirmed by two-color immunoperoxidase) in the ipsilateral facial nucleus. Image analysis reveled that a seven days functional electrical stimulation or corticosterone led to elevations of FGF-2 in the cytoplasm of neurons and in the nucleus of reactive astrocytes, respectively, without astrocytic reaction.

Conclusion

FGF-2 may exert paracrine/autocrine trophic actions in the facial nucleus and may be relevant as a therapeutic target to Bell's palsy.     

PDAPP转基因小鼠脑组织内反应性星形胶质细胞的活化程度明显升高

目的　研究PDAPP转基因小鼠脑组织内反应性星形胶质细胞的活化程度。方法　通过免疫组织化学染色方法检测小鼠脑组织内反应性星形胶质细胞表达胶质纤维酸性蛋白 (GFAP)的情况 ,比较PDAPP转基因小鼠和C5 7 BL非转基因小鼠脑组织反应性星形胶质细胞的活化程度。结果　PDAPP转基因小鼠脑组织内反应性星形胶质细胞表达GFAP的水平明显高于C5 7 BL非转基因小鼠。结论　PDAPP转基因小鼠脑组织内存在明显的神经炎症反应     

Phospholipid transfer protein

A role for phospholipid transfer protein (PLTP) in HDL remodelling and in the formation of pre-beta-HDL is now well established, both in vivo and in vitro. Over-expression of human PLTP in C57BL6 mice lowers plasma HDL levels, probably because of increased HDL catabolism. Despite these low HDL levels, plasma from these mice mitigates cholesterol accumulation in macrophages and has increased potential for pre-beta-HDL formation. Plasma HDL concentration is also decreased in PLTP knockout mice. These intriguing observations can be explained by recent studies that indicate that PLTP is not only involved in remodelling of HDL subfractions but also in VLDL turnover. The role of PLTP in atherogenesis and VLDL synthesis was demonstrated in transgenic mouse models with increased susceptibility for the development of atherosclerosis, bred into PLTP knockout mice. The data clearly show that PLTP can be proatherogenic. As mentioned above, however, PLTP may have antiatherogenic potential in wild-type C57BL6 mice. Information regarding the role and regulation of PLTP in human (patho)physiology is still relatively sparse but accumulating rapidly. PLTP activity is elevated in diabetes mellitus (both type 1 and type 2), obesity and insulin resistance.     

Situs inversus in the developing mouse: proteins affected by the iv mutation (genocopy) and the teratogen retinoic acid (phenocopy)

To decipher genes that are important in the determination of laterality, we compared two-dimensional protein gels from wild-type C57BL/6J mice and C57BL/6J mice that carried the iv mutation, which confers random determination of visceral situs. To span the time period(s) during which laterality determination occurs, we compared computer-analyzed two-dimensional protein gels from wild-type mouse embryos and iv/iv mouse embryos at 7.5, 8.0, and 8.5 days post-coitum. One polypeptide that was expressed only on day 8.0 of development and only in wild-type embryos represents a particular candidate for determination of laterality. Day 8.5 postcoitum represents the earliest time in murine development that laterality is manifest. Two-dimensional gels were compared from 8.5 day embryos that were C57BL/6J wild-type, C57BL/6J iv/iv, or C57BL/6J wild-type and exposed to the teratogen retinoic acid late on day 7. Reproducible alterations of protein synthesis were observed in both the iv genocopy and retinoic acid phenocopy, yielding abnormal laterality determination. The intersection of these peptide changes identifies a protein likely to play a role in the determination of laterality.