RESUMEN
OBJECTIVE: The purpose of this study was to identify rare APOA5 variants in 130 severe hypertriglyceridemic patients by sequencing, and to test their functionality, since no patient recall was possible. METHODS AND RESULTS: We studied the impact in vitro on LPL activity and receptor binding of 3 novel heterozygous variants, apoAV-E255G, -G271C, and -H321L, together with the previously reported -G185C, -Q139X, -Q148X, and a novel construct -Delta139 to 147. Using VLDL as a TG-source, compared to wild type, apoAV-G255, -L321 and -C185 showed reduced LPL activation (-25% [P=0.005], -36% [P<0.0001], and -23% [P=0.02]), respectively). ApoAV-C271, -X139, -X148, and Delta139 to 147 had little affect on LPL activity, but apoAV-X139, -X148, and -C271 showed no binding to LDL-family receptors, LR8 or LRP1. Although the G271C proband carried no LPL and APOC2 mutations, the H321L carrier was heterozygous for LPL P207L. The E255G carrier was homozygous for LPL W86G, yet only experienced severe hypertriglyceridemia when pregnant. CONCLUSIONS: The in vitro determined function of these apoAV variants only partly explains the high TG levels seen in carriers. Their occurrence in the homozygous state, coinheritance of LPL variants or common APOA5 TG-raising variant in trans, appears to be essential for their phenotypic expression.
Asunto(s)
Apolipoproteínas A/metabolismo , Hipertrigliceridemia/metabolismo , Lipoproteína Lipasa/metabolismo , Mutación Missense , Receptores de LDL/metabolismo , Adulto , Apolipoproteína A-V , Apolipoproteínas A/genética , Análisis Mutacional de ADN , Europa (Continente) , Femenino , Heterocigoto , Homocigoto , Humanos , Hidrólisis , Hipertrigliceridemia/enzimología , Hipertrigliceridemia/genética , Lipoproteínas VLDL/metabolismo , Masculino , Modelos Moleculares , Fenotipo , Embarazo , Complicaciones del Embarazo/genética , Complicaciones del Embarazo/metabolismo , Unión Proteica , Conformación Proteica , Proteínas Recombinantes/metabolismo , Índice de Severidad de la Enfermedad , Relación Estructura-Actividad , Resonancia por Plasmón de Superficie , Triglicéridos/sangreAsunto(s)
Apolipoproteínas/genética , Dieta , Aceites de Pescado/farmacología , Hígado/efectos de los fármacos , Hígado/metabolismo , Triglicéridos/sangre , Animales , Apolipoproteína A-V , Apolipoproteínas/sangre , Regulación de la Expresión Génica/efectos de los fármacos , Masculino , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Ratas , Ratas Wistar , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
AIMS/HYPOTHESIS: Apolipoprotein AV (apoAV) is a recently discovered apolipoprotein with a triglyceride-lowering effect in genetically modified mice. Transcription of the human gene encoding apoAV (APOA5) is suppressed by insulin and stimulated by fibrates. Our goal was to study the expression of Apoa5, in comparison with Apoa4 and Apoc3, in hypertriglyceridaemic, obese and insulin-resistant Zucker rats receiving the insulin sensitiser rosiglitazone and/or a fish oil diet to lower triglycerides. METHODS: Hepatic Apoa5, Apoa4 and Apo3 mRNA and liver and plasma apoAV were measured in lean and obese Zucker rats receiving rosiglitazone while on a coconut oil or fish oil diet. RESULTS: Basal hepatic Apoa5 expression was similar in obese and lean Zucker rats. Unexpectedly, obese Zucker rats tended to have higher plasma apoAV levels despite their hypertriglyceridaemic state. Both rosiglitazone and the fish oil diet significantly increased Apoa5 mRNA, by about 70%, but tended to lower liver and plasma apoAV. Rosiglitazone had no effect on Apoa5 mRNA in cultured rat hepatocytes. No intact PPAR (peroxisome proliferator-activated receptor) response element was identified in the rat Apoa5 promoter. CONCLUSIONS/INTERPRETATION: Our data indicate that apoAV does not contribute to the hypertriglyceridaemia of obese Zucker rats or to the hypolipidaemic effect of rosiglitazone or a fish oil diet. The divergent changes of Apoa5 mRNA and apoAV levels suggest co- or post-translational regulation. The increase in Apoa5 mRNA induced by rosiglitazone is not directly mediated by peroxisome proliferator-activated receptor gamma.
