Human Central Nervous System (CNS) ApoE Isoforms Are Increased by Age, Differentially Altered by Amyloidosis, and Relative Amounts Reversed in the CNS Compared with Plasma.

The risk of Alzheimer's disease (AD) is highly dependent on apolipoprotein-E (apoE) genotype. The reasons for apoE isoform-selective risk are uncertain; however, both the amounts and structure of human apoE isoforms have been hypothesized to lead to amyloidosis increasing the risk for AD. To address the hypothesis that amounts of apoE isoforms are different in the human CNS, we developed a novel isoform-specific method to accurately quantify apoE isoforms in clinically relevant samples. The method utilizes an antibody-free enrichment step and isotope-labeled physiologically relevant lipoprotein particle standards produced by immortalized astrocytes. We applied this method to a cohort of well characterized clinical samples and observed the following findings. The apoE isoform amounts are not different in cerebrospinal fluid (CSF) from young normal controls, suggesting that the amount of apoE isoforms is not the reason for risk of amyloidosis prior to the onset of advanced age. We did, however, observe an age-related increase in both apoE isoforms. In contrast to normal aging, the presence of amyloid increased apoE3, whereas apoE4 was unchanged or decreased. Importantly, for heterozygotes, the apoE4/apoE3 isoform ratio was increased in the CNS, although the reverse was true in the periphery. Finally, CSF apoE levels, but not plasma apoE levels, correlated with CSF ß-amyloid levels. Collectively, these findings support the hypothesis that CNS and peripheral apoE are separate pools and differentially regulated. Furthermore, these results suggest that apoE mechanisms for the risk of amyloidosis and AD are related to an interaction between apoE, aging, and the amount of amyloid burden.

El ratón deficiente en apolipoproteína E, un modelo traslacional para el estudio de la aterosclerosis / Apolipoprotein E–deficient mouse, a translational model for the study of atherosclerosi

INTRODUCCIÓN: La aterosclerosis es una de las principales causas de morbimortalidad en países desarrollados que presenta varias similitudes histopatológicas con la inflamación crónica. Los ratones deficientes en apolipoproteína E (apoE-/−) son ampliamente utilizados en el estudio de los mecanismos implicados en el inicio y el progreso de las lesiones ateroscleróticas. OBJETIVO: Evaluar el impacto en la formación de la placa de ateroma de una dieta aterogénica en el ratón apoE-/−. MATERIAL Y MÉTODOS: Ratones apoE-/− de 2 meses de edad fueron sometidos o no a una dieta hipercolesterolémica (10,8% de grasa, 0,75% en colesterol) durante 2 meses adicionales. Se determinó el perfil lipídico, la lesión y el contenido en macrófagos, linfocitos, colágeno, células de la musculatura lisa vascular (CMLV) y core necrótico por técnicas histológicas e inmunohistoquímicas. Cuantificación de las interacciones leucocito-endotelio por microscopia intravital en la microcirculación cremastérica. RESULTADOS: Los ratones apoE-/− sometidos a dieta hipercolesterolémica mostraron elevados niveles circulantes de colesterol total y triglicéridos frente aquellos sometidos a dieta control. Estos efectos fueron acompañados de un claro desarrollo de lesión aterosclerótica en la aorta caracterizada por un mayor contenido en macrófagos (Mac3+), linfocitos (CD3+), colágeno, core necrótico y CMLV. Paralelamente hubo una mayor adhesividad de los leucocitos al endotelio arteriolar en aquellos animales sometidos a dieta grasa. CONCLUSIÓN: El modelo de aterosclerosis que se desarrolla en el ratón apoE-/− sometido a dieta aterogénica presenta numerosas similitudes con la lesión humana, y constituye un adecuado modelo para la detección de nuevas dianas terapéuticas y ensayo de nuevos fármacos

INTRODUCTION: Atherosclerosis is one of the leading causes of morbidity and mortality in Western countries and bears several histopathological similarities to chronic inflammation. Mice deficient in apolipoprotein E (apoE-/−) are widely used in the study of the mechanisms involved in the onset and progression of the atherosclerotic lesion. OBJECTIVE: To evaluate the impact of an atherogenic diet in lesion formation in apoE-/− mice. MATERIAL AND METHODS: Two month-old apoE-/− mice were subjected, or not (controls), to a high fat/high cholesterol diet (10.8% fat, .75% cholesterol) for two months. Lipid profile, lesion formation, and macrophage, lymphocyte, collagen, vascular smooth muscle cells (VSMC), and necrotic core content, were determined within the lesion using histological and immunohistochemical techniques. Leukocyte-endothelial cell interactions were quantified by intravital microscopy in the cremaster microcirculation. RESULTS: apoE-/− mice subjected to a hypercholesterolemic diet showed increased circulating levels of total cholesterol and triglycerides compared to those subjected to a control diet. These effects were accompanied by a clear development of atherosclerotic lesion in the aorta, which was characterized by enhanced macrophage (Mac3+), lymphocyte (CD3+) collagen, VSMC and necrotic core content. In parallel, increased adhesiveness of leukocytes to the arteriolar endothelium in those animals subjected to an atherogenic diet was also detected. CONCLUSION: The atherosclerosis model in apoE-/− mice subjected to an atherogenic diet shares common features with the human atherosclerotic lesion, and constitutes an appropriate model to detect new therapeutic targets and evaluate novel developed drugs

Proteomic analysis of mice expressing human ApoE demonstrates no differences in global protein solubility between APOE 3 and APOE 4 young mice.

Apolipoprotein E (ApoE) is a major lipid carrier protein. In humans, ApoE is expressed in three polymorphic isoforms, which are encoded by three different alleles APOE2, APOE3, and APOE4. In the brains of Alzheimer's disease (AD) patients, each one of these three allelic isoforms is found in several "isoelectric" protein isoforms (qPI), i.e. protein isoforms resulting from PTMs altering the net charge (q) of the polypeptide. AD is a complex disease in which multiple causes and several risk factors affect the onset and disease outcome. A major risk factor for AD is ApoE4; therefore, it is important to characterize the different ApoE qPIs. We have implemented a detergent-based method for isolation and quantitation of protein isoforms, and we found differences in the solubility of protein isoforms depending on the type of solvent used. In this manuscript, we describe these methods and applied them to young human-ApoE targeted replacement mice. Our results indicate that there are no significant differences in the hippocampus proteome of these mice as a function of the APOE genotype.