Activation of the interferon-gamma signaling pathway in systemic lupus erythematosus peripheral blood mononuclear cells.

OBJECTIVE: To investigate interferon-gamma (IFNgamma) signaling in peripheral blood mononuclear cells (PBMCs) from patients with systemic lupus erythematosus (SLE) by analyzing IFNgamma receptor (IFNgammaR) expression, STAT-1 expression and phosphorylation, and the regulation of IFNgamma-inducible genes. METHODS: Fluorocytometry was used to investigate expression of STAT-1, pSTAT-1, CD95, HLA-DR, class I major histocompatibility complex (MHC), IFNgamma-inducible 10-kd protein (IP-10), monokine induced by IFNgamma (Mig), and IFNgammaR in PBMCs from SLE patients and healthy individuals. STAT-1 phosphorylation was determined by fluorocytometry and Western blotting after stimulation with IFNalpha or IFNgamma. Quantitative polymerase chain reaction was used to assess messenger RNA (mRNA) expression of the IFNgamma-inducible genes IP-10 and Mig shortly after preparation or after stimulation with IFNgamma in monocytes. RESULTS: STAT-1 expression was increased in PBMCs from SLE patients and correlated significantly with disease activity and with the IFN-inducible expression of CD95 and HLA-DR. STAT-1 expression also showed a trend toward association with class I MHC expression. In addition, the expression of other IFNgamma-inducible genes, such as IP-10 or Mig, was increased in SLE monocytes. While STAT-1 phosphorylation in SLE PBMCs and PBMCs from healthy individuals was similar after IFNalpha stimulation, incubation with IFNgamma induced STAT-1 phosphorylation only in SLE lymphocytes. Moreover, SLE monocytes showed a considerably higher increase in pSTAT-1 expression upon IFNgamma stimulation than monocytes from healthy individuals. Increased responsiveness of SLE monocytes to IFNgamma was also confirmed on the mRNA level, where expression of the IFN-inducible, STAT-1-dependent genes IP-10 and Mig was more efficiently increased in SLE cells. However, IFNgammaR was similarly expressed on SLE lymphocytes and monocytes and those from healthy individuals. CONCLUSION: In addition to supporting the role of IFNs in SLE immunopathogenesis in general, the findings of the present study support a role of IFNgamma in this disease.

Implication of apoE isoforms in cholesterol metabolism by primary rat hippocampal neurons and astrocytes.

Apolipoprotein E (apoE) has been genetically linked to late-onset Alzheimer's disease. From the three common alleles (epsilon2, epsilon3 and epsilon4), epsilon4 has been suggested to promote amyloid beta (Ass) plaque fibrillation, one hallmark of Alzheimer's disease. It has been demonstrated that altered lipid content of hippocampal plasma membrane coincides with the disease. In this study, we show for the first time that the apoE dependent cholesterol metabolism in hippocampal neurons is higher than that of hippocampal astrocytes. Further, apoE-bound cholesterol is highly incorporated in membranous compartments in hippocampal neurons, whereas hippocampal astrocytes show higher intracellular distribution. This is an effect that coincides with cell-type dependent difference of low density lipoprotein receptor (LDLR) family member expression. Hippocampal neurons express high levels of the LDLR related protein (LRP), whereas hippocampal astrocytes are highly positive for LDLR. We could also demonstrate an apoE isoform (apoE2, apoE3 and apoE4) dependent cholesterol uptake in both cells types. In hippocampal neurons, we could find a decreased apoE4-bound cholesterol uptake. In contrast, hippocampal astrocytes show decreased internalization of apoE2-bound cholesterol. In addition, lipidated apoE4 is little associated with neurites in hippocampal neurons in comparison to the other two isoforms. In contrary, hippocampal astrocytes show faint apoE2 immunocytostaining intensity. Data presented indicate that the role of apoE4 in cholesterol homeostasis and apolipoprotein cell association is more pronounced in hippocampal neurons, showing significant alterations compared to the other two isoforms, suggesting that hippocampal neurons are affected by apoE4 associated altered cholesterol metabolism compared to hippocampal astrocytes.

Role of chondroitin sulphate in the uptake of beta-VLDL by brain cells.

Proteoglycans (PGs) have been suggested to work as receptors in lipoprotein uptake mechanisms. An interaction between apolipoprotein E (apoE) and glucosaminoglycans (GAG), polysaccharides linked to proteoglycans, has been proposed in this pathway. At the same time, proteoglycans, apoE as well as lipoprotein receptors have been reported to be constituents of amyloid plaques, one hallmark of Alzheimer's disease. With this study, we are the first to investigate the interaction between beta very low density lipoprotein (beta-VLDL) and a neuronal highly abundant GAG, chondroitin sulphate (CS), comparing hippocampal neurons, expressing high levels of low density lipoprotein receptor related protein (LRP) and U373 astrocytoma cells, highly positive for the low density lipoprotein receptor (LDLR). We were able demonstrate that degradation of chondroitin sulphate proteoglycans (CSPGs) with chondroitinase ABC resulted in reduced (125)I-beta-VLDL uptake. We showed that externally added CSs compete with internalization of beta-VLDL. The effect was found to be dose-dependent, but was influenced neither by cell type, nor receptor type. The position of sulphation of added CSs showed only a slight influence. The data generated suggested an interaction between apolipoproteins and soluble CSs; therefore, 3H-cholesterol linked to apoE was coadministered with CSs to the cells. The results revealed that apoE bound, but no unbound cholesterol, was reduced in cellular internalization, suggesting that CSPGs may be involved in lipoprotein uptake in the intact brain, mediated, at least in part, by apoE.

Evaluation of chondroitin sulfate bioactivity in hippocampal neurones and the astrocyte cell line U373: influence of position of sulfate groups and charge density.

Chondroitin sulfates are linear polysaccharides of alternating glucuronic acid and N-acetylgalactosamine, sulfated in varying positions. They form the extracellular framework providing the information for the structural establishment of tissues in multicellular organisms. Growth cones of neurones modulate their outgrowth according to signals received from proteoglycans. The exact molecular structures behind these functions are not fully understood, but structural details of the carbohydrate backbone are crucial. In this report we have employed quantitative cytometry on hippocampal neurite outgrowth in the presence of chondroitin sulfate added in solution to determine the influence of the position and density of the sulfate groups of the N-acetyl-D-galactosamine-residues of chondroitin sulfates. It is of profound interest whether externally added chondroitin sulfates can compete with core protein bound chondroitin sulfate to modulate the effects of tissue-synthesized matrix. In series of microscopic images 3 parameters of neuritic outgrowth activity, neurite length, number of neurites and fasciculation (thickness of neurites) are analyzed at concentrations occurring in intact tissues. Fasciculation increased and number of neurites decreased with high di-sulfation. No significant differences on process length reduction were found between the isotypes. Specificity of effects found is emphasized, as no influence on cell proliferation with U373 human astrocyte cell line is detectable, while neurones clearly are inhibited. The IC30 and IC50 values of chondroitin sulfates isoforms are presented for neurones. The data indicate that the soluble fragments from chondroitin sulfate are actively modulating cell development. Besides dosage, sulfation density and position are relevant for effects of chondroitin sulfate in neuronal regenerative activity.