Post-Transcriptional Nature of Uremia-induced Down-Regulation of hepatic Apolipoprotein A-I production

CKD is associated with premature death from cardiovascular disease which is, in part, driven by HDL deficiency and dysfunction. One of the main causes of HDL deficiency in CKD is diminished plasma apoliprotein A-I level. Plasma ApoA-I is reduced in dialysis patients and hepatic ApoA-I mRNA is decreased in the uremic rats. This study explored the mechanism of uremia-induced down-regulation of ApoA-I. HepG2 cells were incubated in media containing whole plasma or plasma subfractionation from normal subjects and ESRD patients pre- and post-hemodialysis. Cells and culture media were isolated to measure ApoA-I protein and mRNA. ApoA-I promoter activity was measured using transfection with a luciferase promoter construct containing the −2096 to +293 segment of ApoA-I gene. Finally effect of uremic and control plasma was assessed on ApoA-I RNA stability. Exposure to uremic plasma significantly reduced ApoA-I mRNA expression and ApoA-I protein production. These effects were reversed by replacing uremic plasma with normal plasma. While no difference in ApoA-I promoter activity was found between cells exposed to uremic and normal plasma, uremic plasma significantly reduced ApoA-I RNA stability. Experiments using plasma sub-fractions revealed that the inhibitory effect of uremic plasma on ApoA-I mRNA expression resides in fractions containing molecules larger but not smaller than 30kd. The pre- and post-dialysis plasma exerted an equally potent inhibitory effect on ApoA-I mRNA abundance.Uremia lowers ApoA-I production by reducing its RNA stability. The inhibitory effect of uremic milieu on ApoA-I mRNA expression is mediated by non-dialyzable molecule(s) larger than 30 kd