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      Nephropathy in a Hypercholesterolemic Mouse Model with Streptozotocin-Induced Diabetes

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          Background/Aims: The contribution of preexisting hypercholesterolemia to diabetic nephropathy remains unclear. We assessed the impact of hypercholesterolemia on diabetic nephropathy using a double knockout (DKO) mouse, null for the low-density lipoprotein receptor (Ldlr–/–) and the apoB mRNA editing catalytic polypeptide 1 (Apobec1–/–). Methods: Wild-type (WT) and DKO mice received sham or streptozotocin injections at age 7 weeks, yielding control (WT-C, DKO-C) and diabetic (WT-D, DKO-D) groups. At sacrifice (age 40 weeks), albuminuria was determined by ELISA, and kidney sections were examined by light and electron microscopy. Results: Albuminuria increased in diabetic mice (WT-D: 82.4 ± 37.2 µg/18 h; DKO-D: 58.0 ± 45.7 µg/18 h) versusnondiabetic controls (WT-C: 10.2 ± 7.2 µg/18 h; DKO-C: 8.6 ± 5.3 µg/18 h) (p < 0.0001), but was unaffected by hypercholesterolemia. Light microscopy of kidney sections demonstrated increased collagen levels in glomeruli in WT-D mice, but not in DKO-D mice or either control group. Electron microscopy showed a thickened glomerular basement membrane in WT-D mice only. The proximal tubular basement membrane thickness was increased in both diabetic groups versusnondiabetic controls (p < 0.01); in WT-D mice this was attributable to collagen accumulation, but in DKO-D mice it was mainly caused by lipid vacuoles. Conclusions: In this animal model, preexisting hypercholesterolemia did not exacerbate either glomerular lesions of diabetes (collagen accumulation, basement membrane thickening) or albuminuria, but appeared to mitigate these effects. Furthermore, the combination of hypercholesterolemia and diabetes resulted in a significant lipid accumulation in the tubular basement membrane.

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          Most cited references 7

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          A mouse model of human familial hypercholesterolemia: markedly elevated low density lipoprotein cholesterol levels and severe atherosclerosis on a low-fat chow diet.

          Mutations in the low density lipoprotein (LDL) receptor gene cause familial hypercholesterolemia, a human disease characterized by premature atherosclerosis and markedly elevated plasma levels of LDL cholesterol and apolipoprotein (apo) B100. In contrast, mice deficient for the LDL receptor (Ldlr-/-) have only mildly elevated LDL cholesterol levels and little atherosclerosis. This difference results from extensive editing of the hepatic apoB mRNA in the mouse, which limits apoB100 synthesis in favor of apoB48 synthesis. We have generated Ldlr-/- mice that cannot edit the apoB mRNA and therefore synthesize exclusively apoB100. These mice had markedly elevated LDL cholesterol and apoB100 levels and developed extensive atherosclerosis on a chow diet. This authentic model of human familial hypercholesterolemia will provide a new tool for studying atherosclerosis.
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            Molecular basis of glomerular permselectivity.

            Recent discoveries in kidney research have given new insights into the molecular make-up of the glomerular filter and mechanisms of permselectivity. The identification of mutations in the genes for glomerular basement membrane type IV collagen has thus demonstrated the central role of the glomerular basement membrane as the structural skeleton of the glomerular capillary. Regional deterioration of this framework not only leads to proteinuria, but also to significant leakage of red blood cells into the urinary space. Tracer studies and the characterization of other glomerular basement membrane components, such as proteoglycans, have also emphasized the role of the glomerular basement membrane in the permselectivity process. However, more recent studies on nephrin, a key component of the slit diaphragm, as well as the podocyte and slit diaphragm-associated intracellular proteins, CD2-associated protein, podocin and alpha-actinin-4, have emphasized the role of the slit diaphragm as a central size-selective filtration barrier. These data have provided a completely new understanding of the mechanisms of proteinuria, both in inherited and acquired diseases. In this review, we present the recent progress made in the characterization of proteins that are important for glomerular permselectivity.
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              Phenotypic analysis of mice expressing exclusively apolipoprotein B48 or apolipoprotein B100.

              Apolipoprotein (apo)-B is found in two forms in mammals: apo-B100, which is made in the liver and the yolk sac, and apo-B48, a truncated protein made in the intestine. To provide models for understanding the physiologic purpose for the two forms of apo-B, we used targeted mutagenesis of the apo-B gene to generate mice that synthesize exclusively apo-B48 (apo-B48-only mice) and mice that synthesize exclusively apo-B100 (apo-B100-only mice). Both the apo-B48-only mice and apo-B100-only mice developed normally, were healthy, and were fertile. Thus, apo-B48 synthesis was sufficient for normal embryonic development, and the synthesis of apo-B100 in the intestines of adult mice caused no readily apparent adverse effects on intestinal function or nutrition. Compared with wild-type mice fed a chow diet, the levels of low density lipoprotein (LDL)-cholesterol and very low density lipoprotein- and LDL-triacylglycerols were lower in apo-B48-only mice and higher in the apo-B100-only mice. In the setting of apo-E-deficiency, the apo-B100-only mutation lowered cholesterol levels, consistent with the fact that apo-B100-lipoproteins can be cleared from the plasma via the LDL receptor, whereas apo-B48-lipoproteins lacking apo-E cannot. The apo-B48-only and apo-B100-only mice should prove to be valuable models for experiments designed to understand the purpose for the two forms of apo-B in mammalian metabolism.

                Author and article information

                Kidney Blood Press Res
                Kidney and Blood Pressure Research
                S. Karger AG
                19 November 2003
                : 26
                : 5-6
                : 351-361
                aDivision of Endocrinology, Diabetes, and Medical Genetics and bDepartment of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, S.C., cCorgentech Inc., Palo Alto, Calif., dAmylin Pharmaceuticals Inc., San Diego, Calif., and eSection of Endocrinology, University of Oklahoma, Oklahoma City, Okla., USA
                73942 Kidney Blood Press Res 2003;26:351–361
                © 2003 S. Karger AG, Basel

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                Figures: 8, Tables: 2, References: 40, Pages: 11
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