RESUMEN
Low density lipoprotein receptor-related protein (LRP) participates in the uptake and degradation of several ligands implicated in neuronal pathophysiology including apolipoprotein E (apoE), activated alpha(2) -macroglobulin (alpha(2)M*) and beta-amyloid precursor protein (APP). The receptor is expressed in a variety of tissues. In the brain LRP is present in pyramidal-type neurons in cortical and hippocampal regions and in astrocytes that are activated as a result of injury or neoplasmic transformation. As LRP is expressed in the monocyte/macrophage cell system, we were interested in examining whether LRP is expressed in microglia. We isolated glial cells from the brain of neonatal rats and LRP was immunodetected both in microglial cells and in astrocytes expressing glial fibrillar acidic protein (GFAP). Microglial cells were able to bind and internalize LRP-specific ligand, alpha(2)M*. The internalization was inhibitable by RAP, with a Kd of 1.7 nM. The expression of LRP was up-regulated by dexamethasone, and down-regulated by lipopolysaccharide (LPS), gamma interferon (IFN-gamma) or a combination of both. LRP was less sensitive to dexamethasone in activated astrocytes than in microglia. We provided the first analysis of LRP expression and regulation in microglia. Our results open the possibility that microglial cells could be related to the participation of LRP and its ligands in different pathophysiological states in brain.
Asunto(s)
Microglía/metabolismo , Receptores Inmunológicos/biosíntesis , Receptores de LDL/biosíntesis , Enfermedad de Alzheimer/metabolismo , Enfermedad de Alzheimer/patología , Animales , Animales Recién Nacidos , Western Blotting , Células Cultivadas , Dexametasona/farmacología , Regulación hacia Abajo/efectos de los fármacos , Técnica del Anticuerpo Fluorescente , Glucocorticoides/farmacología , Inmunohistoquímica , Interferón gamma/farmacología , Cinética , Ligandos , Lipopolisacáridos/farmacología , Proteína 1 Relacionada con Receptor de Lipoproteína de Baja Densidad , Neuroglía/metabolismo , Pruebas de Precipitina , Ratas , Regulación hacia Arriba/efectos de los fármacosRESUMEN
We studied the expression of the mannose receptor (ManR) in rat microglial cells. Microglial cells are the central nervous system resident macrophages, key participants of the innate immune response. ManR is a differentiation marker and a relevant glycoprotein for the phagocytic and endocytic function of macrophages. Because there is evidence suggesting that ManR could mediate some of the nonenzymatic effects of acetilcholinesterase (AchE) and the enzyme seems to be involved in Alzheimer's disease (AD), we looked for ManR in microglia, evaluating the functionality of the receptor. We isolated microglial cells from the brain of 2-day-old neonatal rats. Microglial cells, identified by their specific staining with the lectin Griffonia simplicifolia, expressed ManR, being detected by immunocytochemistry, Western blot, and immunoprecipitation. Microglial ManR was downregulated by lipopolysaccharide (LPS) and upregulated by dexamethasone, as described for peripheral macrophages. Microglial ManR was functional and able to internalize horseradish peroxidase (HRP), a known ManR ligand, in a mannan-inhibitable manner. The presence of a functional ManR in microglia opens the possibility that ManR could participate in multiple physiologic and pathologic conditions in the central nervous system (CNS), including inflammation, ischaemia, and neurodegenerative diseases such as AD.
Asunto(s)
Lectinas Tipo C , Lectinas de Unión a Manosa , Microglía/metabolismo , Lectinas de Plantas , Receptores de Superficie Celular/metabolismo , Acetilcolinesterasa/metabolismo , Animales , Animales Recién Nacidos , Anticuerpos Monoclonales , Encéfalo/citología , Encéfalo/metabolismo , Células Cultivadas , Dexametasona/farmacología , Regulación hacia Abajo/efectos de los fármacos , Peroxidasa de Rábano Silvestre/farmacocinética , Humanos , Lectinas , Lipopolisacáridos/farmacología , Macrófagos/metabolismo , Receptor de Manosa , Microglía/citología , Ratas , Receptores de Superficie Celular/genética , Regulación hacia Arriba/efectos de los fármacosRESUMEN
A significant amount of biliary cholesterol is carried in unilamellar-phospholipid (lecithin) vesicles, in both supersaturated human hepatic bile and unsaturated rat bile. This fact supports the concept that biliary cholesterol is normally secreted in phospholipid vesicles from the hepatocyte into the canaliculus. The fundamental aspects of biliary lipid secretion relate first to the quantitative determinants of hepatocytic cholesterol secretion into the bile and, second, to the cell biology of this process. There is a tight curvilinear coupling between the rates of bile acids and biliary lipid secretion in all animal species. The hydrophobicity of the bile acid pool may modify this cosecretory mechanism in that more hydrophobic bile acids recruit more phospholipid and cholesterol per mole of bile acid secreted into the bile. The quantitative significance of this effect, however, is relatively minor. In contrast, intrahepatic determinants, such as the rates of hepatic cholesterol esterification and very low density lipoprotein production modulated by dietary factors, may markedly change the amount of cholesterol carried in vesicles into the bile. Recent studies provide strong evidence to support the concept that biliary cholesterol output is also modulated by the amount of free cholesterol available in specific regions of the endoplasmic reticulum for recruitment by the bile acid cosecretory mechanism. The origin of biliary lipids is in the smooth endoplasmic reticulum membranes. The intracellular transport and the canalicular secretory mechanism of the precursor of biliary lipid vesicles is mostly unknown. Two theories related to the cell biology of biliary lipid secretion are discussed in this article, the fusion-budding model and the exocytotic model.
Asunto(s)
Bilis/metabolismo , Metabolismo de los Lípidos , Hígado/metabolismo , Animales , Ácidos y Sales Biliares/sangre , Transporte Biológico , Colesterol/metabolismo , Humanos , Hígado/citología , Circulación Hepática , Modelos BiológicosRESUMEN
The liver represents the principal pathway for sterol excretion from the organism. In addition, the major proportion of serum lipoproteins is catabolized in the liver. It is known that diosgenin and bean diet markedly induce biliary cholesterol output. In this series of studies we characterized the catabolism of several lipoprotein particles in animals fed diosgenin or a bean-rich diet (biliary cholesterol output is increased greater than 300% in these animals). Human low density lipoprotein (hLDL) and rat high density lipoprotein apo-E free (rHDL) were labeled with 125I. Rat chylomicrons were labeled with cholesterol-(3H)-oleate. hLDL clearance increased from 381 +/- 39 to 628 +/- 44 (microliters/h x 100 g body wt) (p less than 0.005) in bean-fed rats. The half life (t1/2) decreased from 12.4 +/- 1 to 9.8 +/- 0.7 h (p less than 0.005) in these rats. The clearance of rHDL apo-E free increased from 579 +/- 8 to 680 +/- 36 (microliters/h x 100 g body wt) (p less than 0.05) in diosgenin-fed animals. The t1/2 significantly decreased from 8.2 +/- 0.7 h to 7.0 +/- 0.3 h (p less than 0.05) in these rats. In contrast, chylomicron clearance and t1/2 were not modified by the diosgenin or bean diets. These results are consistent with the hypothesis that the number and/or affinity of the B/E and A-I receptors, but not E receptors are increased in rats fed biliary cholesterol hypersecretory diets. These studies suggests the presence of a functional inter-relationship between the biliary and sinusoidal pathways of hepatic cholesterol.