Modulation of apolipoprotein D expression and translocation under specific stress conditions

Endotoxin-binding affinity of sevelamer: a potential novel anti-inflammatory mechanism

Chronic inflammation is highly prevalent in patients with chronic kidney disease (CKD), and is associated with increased cardiovascular morbidity and mortality. There are numerous causes of inflammation in CKD, including the potential exposure to bacterial lipopolysaccharide (LPS) in the bloodstream from the intestinal tract as a result of uremia-related increases in intestinal permeability. Sevelamer, a commonly prescribed non-calcium, non-metal-based phosphate binder in CKD, also possesses putative anti-inflammatory properties, as its use has been associated with a reduction in systemic markers of inflammation. Emerging studies have provided direct evidence that sevelamer shows in vitro LPS-binding properties. Indirect clinical evidence suggests that sevelamer might also limit translocation of LPS from the intestinal lumen into the bloodstream. This review focuses on bacterial LPS as a source of chronic inflammation in CKD, and proposes that sevelamer might possess novel anti-inflammatory properties as a result of LPS binding in the intestinal tract. The proposed hypothesis that intestinal LPS-binding by sevelamer may lower circulating LPS, and in turn systemic inflammation, requires further evaluation in a clinical trial.

Increase in placental apolipoprotein D as an adaptation to human gestational diabetes

The expression of apolipoprotein D (apo D), a lipocalin involved in defense mechanisms against oxidative stress, in placental tissue samples of pregnancies with gestational diabetes mellitus (GDM) was compared to non-diabetic controls. We have investigated the relationship of apo D with 4-HNE, a major propagation product of lipid peroxidation, in stressed tissues. We included 20 pregnant women with GDM and 30 women with normal ongoing pregnancies as the control group. Placentas were collected and frozen for Western blot or included in paraffin for immunohistochemistry. The intensity of immunostaining was higher for apo D and 4-HNE in GDM samples; however, the differences in expression between the groups was more intense for apo D. Positive signals for both antibodies was detected in the villous trophoblast and adventitia tunica around the large blood vessels for all groups. Specific immunostaining for apo D was noted in some mesenchymal and macrophagic-like cells and this signal increased in diabetic placentas. Densitometry analysis of Western blots showed no significant difference for 4-HNE, but was significantly more intense for apo D in diabetic women. The contradictory results for 4-HNE could be due to changes which are too small and are masked in tissue homogenates. The results for apo D showed a strong relationship with GDM in the placenta that may reflect its suggested function in defense mechanisms against oxidative stress.

Modulation of Apolipoprotein D levels in human pregnancy and association with gestational weight gain

BACKGROUND

Apolipoprotein D (ApoD) is a lipocalin involved in several processes including lipid transport, but its modulation during human pregnancy was never examined.

METHODS

We investigated the changes in the levels of ApoD in the plasma of pregnant women at the two first trimesters of gestation and at delivery as well as in the placenta and in venous cord blood. These changes were studied in 151 women classified into 9 groups in relation to their prepregnancy body mass index (BMI) and gestational weight gain (GWG).

RESULTS

Plasma ApoD levels decrease significantly during normal uncomplicated pregnancy. ApoD is further decreased in women with excessive GWG and their newborns. In these women, the ApoD concentration was tightly associated with the lipid parameters. However, the similar ApoD levels in low cholesterol (LC) and high cholesterol (HC) women suggest that the plasma ApoD variation is not cholesterol dependant. A tight regulation of both placental ApoD transcription and protein content is most probably at the basis of the low circulating ApoD concentrations in women with excessive GWG. After delivery, the plasma ApoD concentrations depended on whether the mother was breast-feeding or not, lactation favoring a faster return to baseline values.

CONCLUSION

It is speculated that the decrease in plasma ApoD concentration during pregnancy is an adaptive response aimed at maintaining fetal lipid homeostasis. The exact mechanism of this adaptation is not known.

Co-expression of estrogen receptor alpha and Apolipoprotein D in node positive operable breast cancer--possible relevance for survival and effects of adjuvant tamoxifen in postmenopausal patients

BACKGROUND

Estrogen receptor-alpha (ERalpha) is an important prognostic and predictive marker in breast cancer. ERalpha signaling normally down-regulates expression of Apolipoprotein D (ApoD), a lipocalin that binds, transports or chelates lipophilic ligands, including tamoxifen (TAM). Hence, the co-expression of ApoD may therefore identify clinical relevant subgroups of ERalpha positive breast cancer patients.

MATERIAL AND METHODS

ApoD, ERalpha, and progesterone receptor (PR) protein expressions were determined by immunohistochemistry (IHC) in primary tumors of 290 patients with operable breast cancer. The median follow-up was 12 years. Patients were stratified according to age, nodal stage and the expression of ERalpha and the combined cytoplasm and nuclear staining of ApoD (ApoD(CN)).

RESULTS

In elderly women (> or =70 years) (n = 76), ApoD(CN) expression identified different prognostic subgroups in ERalpha positive patients (Trend: p < 0.0001). Multivariate analysis in this age group (n = 72), showed that the ERalpha-positive /ApoD(CN)-negative subgroup had a better breast cancer specific survival (BCSS) compared with the ERalpha-positive/ApoD(CN)-positive group (hazard ratio (HR) = 4.3; 95% CI = 1.6-11.9; p = 0.005). This difference was predominantly seen in the node positive patients (n = 30) (HR = 10.5; 95% CI = 2.3-47.6; p = 0.002). In a subset of postmenopausal ERalpha-positive/node positive patients (n = 60) previously enrolled in a trial on 2 year adjuvant TAM 20 mg vs. placebo, a better BCSS was observed in ApoD(CN) negative patients compared to placebo (p = 0.02). In ApoD(CN) positive patients, adjuvant TAM did not provide any survival benefit.

DISCUSSION

ERalpha and ApoD(CN) co-expression seems to be of prognostic importance in node positive elderly patients with operable breast cancer. In addition, we hypothesize that ApoD(CN) expression may be a novel marker and/or mechanism of TAM resistance in postmenopausal node positive patients. Thus, when targeting the ERalpha pathway in these patients, the ApoD status of the tumor may be of clinical relevance.

Human apolipoprotein D overexpression in transgenic mice induces insulin resistance and alters lipid metabolism

Apolipoprotein D (apoD), a widely expressed lipocalin, has the capacity to transport small hydrophobic molecules. Although it has been proposed that apoD may have multiple tissue-specific, physiological ligands and functions, these have yet to be identified. To gain insight in some of its functions, we generated transgenic mice overexpressing human apoD (H-apoD) under the control of neuron-specific promoters. In Thy-1/apoD and NSE/apoD mice, expression of H-apoD was strong in the nervous system although weakly detected in peripheral organs such as the liver and blood cells. These mice displayed not entirely anticipated metabolic defects. Although they are not obese and have normal lipid concentration in circulation, Thy-1/apoD and NSE/apoD mice are glucose intolerant, insulin resistant, and develop hepatic steatosis. The steatosis and its associated insulin resistance are correlated with impairments in hepatic lipogenesis. However, they are not strongly related with inflammation. This impaired insulin response is not caused by a decrease in circulating leptin or a modulation of adiponectin and resistin levels. These results suggest that variations in the levels and/or sites of apoD expression influence the lipid and glucose metabolism, consolidating apoD as a target for insulin-resistance-related disorders.

Apolipoprotein D modulates F2-isoprostane and 7-ketocholesterol formation and has a neuroprotective effect on organotypic hippocampal cultures after kainate-induced excitotoxic injury

Apolipoprotein D (apoD), a member of the lipocalin family of transporter proteins binds a number of small lipophilic molecules including arachidonic acid and cholesterol. Recent studies showed a protective function of mammalian apoD as well as its insect and plant homologs against oxidative stress. In this study we investigated the effect of direct addition of exogenous human apoD protein purified from breast cystic fluid to rat hippocampal slice cultures after excitotoxic injury induced by the glutamate analog kainate. ApoD at a concentration of 10 microg/ml partially prevented loss of MAP2 immunostaining and LDH release from injured hippocampal neurons after kainate injury. ApoD also attenuated the increase in oxidative products of arachidonic acid and cholesterol, F(2)-isoprostanes and 7-ketocholesterol, respectively, after kainate treatment. In view of the molecular structure of apoD which consists of an eight stranded beta barrel that forms a binding pocket for a number of small hydrophobic molecules, we propose that apoD promotes its neuroprotective effects by binding to arachidonic acid and cholesterol thus preventing their oxidation to neurotoxic products such as 4-hydroxynonenal (4-HNE) and 7-ketocholesterol.

PLTP is present in the nucleus, and its nuclear export is CRM1-dependent

Phospholipid transfer protein (PLTP), one of the key lipid transfer proteins in plasma and cerebrospinal fluid, is nearly ubiquitously expressed in cells and tissues. Functions of secreted PLTP have been extensively studied. However, very little is known about potential intracellular PLTP functions. In the current study, we provide evidence for PLTP localization in the nucleus of cells that constitutively express PLTP (human neuroblastoma cells, SK-N-SH; and human cortical neurons, HCN2) and in cells transfected with human PLTP (Chinese hamster ovary and baby hamster kidney cells). Furthermore, we have shown that incubation of these cells with leptomycin B (LMB), a specific inhibitor of nuclear export mediated by chromosome region maintenance 1 (CRM1), leads to intranuclear accumulation of PLTP, suggesting that PLTP nuclear export is CRM1-dependent. We also provide evidence for entry of secreted PLTP into the cell and its translocation to the nucleus, and show that intranuclear PLTP is active in phospholipid transfer. These findings suggest that PLTP is involved in novel intracellular functions.

Neuroprotective effect of apolipoprotein D against human coronavirus OC43-induced encephalitis in mice

Apolipoprotein D (apoD) is a lipocalin upregulated in the nervous system after injury or pathologies such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. We previously demonstrated that apoD protects against neuropathology by controlling the level of peroxidated lipids. Here, we further investigated the biological function of apoD in a mouse model of acute encephalitis. Our results show that apoD transcript and protein are upregulated during acute encephalitis induced by the human coronavirus OC43 (HCoV-OC43) infection. The apoD upregulation coincides with glial activation, and its expression returns to normal levels when the virus is cleared, concomitantly to a resolved glial reactivity. In addition, the overexpression of human apoD in the neurons of Thy-1/ApoD transgenic mice results in a threefold increase of the number of mice surviving to HCoV-OC43 infection. This increased survival rate is correlated with an upregulated glial activation associated with a limited innate immune response (cytokines, chemokines) and T-cell infiltration into infected brains. Moreover, the protection seems to be associated with a restricted phospholipase A2 activity. These data reveal a role for apoD in the regulation of inflammation and suggest that it protects from HCoV-OC43-induced encephalitis, most likely through the phospholipase A2 signaling pathways.

Human ApoD, an apolipoprotein up-regulated in neurodegenerative diseases, extends lifespan and increases stress resistance in Drosophila

Apolipoprotein D (ApoD) expression increases in several neurological disorders and in spinal cord injury. We provide a report of a physiological role for human ApoD (hApoD): Flies overexpressing hApoD are long-lived and protected against stress conditions associated with aging and neurodegeneration, including hyperoxia, dietary paraquat, and heat stress. We show that the fly ortholog, Glial Lazarillo, is strongly up-regulated in response to these extrinsic stresses and also can protect in vitro-cultured cells in situations modeling Alzheimer's disease (AD) and Parkinson's disease (PD). In adult flies, hApoD overexpression reduces age-associated lipid peroxide accumulation, suggesting a proximal mechanism of action. Similar data obtained in the mouse [Ganfornina, M.D., et al., (2008) Apolipoprotein D is involved in the mechanisms regulating protection from oxidative stress. Aging Cell 10.1111/j.1474-9726.2008.00395.] as well as in plants (Charron et al., personal communication) suggest that ApoD and its orthologs play an evolutionarily conserved role in response to stress, possibly managing or preventing lipid peroxidation.

Beetle immunity: Identification of immune-inducible genes from the model insect Tribolium castaneum

The red flour beetle, Tribolium castaneum, is an established genetically tractable model insect for evolutionary and developmental studies. Therefore, it may also represent a valuable model for comparative analysis of insect immunity. Here, we used the suppression subtractive hybridization method to identify Tribolium genes that are transcriptionally induced in response to injection of crude lipopolysaccharide (LPS). Determined genes encode proteins that share sequence similarities with counterparts from other insects known to mediate sensing of infection (e.g. Toll and PGRP) or to represent potential antimicrobial effectors (e.g. ferritin, c-type lysozyme, serine proteinase inhibitors, and defensins). Especially significant is the identification of thaumatin-like peptides, representing ancient antifungal peptides originally reported from plants, that are absent from the genomes of many other insects such as Drosophila, Anopheles, and Apis. We produced recombinant thaumatin-1 in bacteria and we found that it represents an antimicrobial peptide against filamentous fungi in Tribolium. Additionally, septic injury induces expression of genes involved in stress adaptation (e.g. heat-shock proteins) or insecticide resistance (e.g. cytochrome P450s) in Tribolium, suggesting that there may be crosstalk between the immune and stress responses.