Deficiency in reverse cholesterol transport in mice augments sepsis

BackgroundSepsis claims over 215,000 lives and costs $16.7 billion per year in America alone. Recent studies revealed that HDL receptor scavenger receptor BI (SR-BI or Scarb1) plays a critical protective role in sepsis. Using Scarb1I179N mice, a mutant SR-BI mouse model with 90% depletion in hepatic SR-BI, we previously reported that the mutant mice are susceptible to cecal ligation and puncture (CLP)-induced sepsis. However, using a hypo-AlbCreSR-BIfl/fl mouse model, Hubys group showed that the liver-specific SR-BI KO mice are not more susceptible to CLP-induced sepsis. In this study, we generated a new floxed SR-BI mouse model to clarify the contribution of hepatic SR-BI in sepsis. SR-BI is known as a receptor that plays a key role in reverse cholesterol transport (RCT) by uptaking cholesterol to the liver. So, our established AlbCreSR-BIfl/fl mice (liver-specific SR-BI KO) is an RCT deficiency mice model that can be used to understand the mechanisms of RCT protecting against sepsis and may provide new insight into the pathogenesis of sepsis. Methods and ResultsWe generated SR-BIfl/fl mice by flanking exon 2. We bred the floxed mice with AlbCre mice to generate AlbCreSR-BIfl/fl mice (liver-specific SR-BI KO mice), then the mice were backcrossed to C57BL/6J for 10 generations. As shown in Fig 1, the liver SR-BI expression was normal in SR-BIfl/fl mice as compared to C57BL/6J (B6) mice, but completely depleted in AlbCreSR-BIfl/fl mice. Using this liver-specific SR-BI KO model, we observed that a deficiency in RCT rendered the mice highly susceptible to CLP-induced sepsis as shown by 80% and 14.3% survival of SR-BIfl/fl and AlbCreSR-BIfl/fl mice, respectively. We found aggravated inflammatory cytokine production, altered leukocyte recruitment and slightly increased in the blood and peritoneal bacteria. Moreover, we found RCT deficiency mice increased both free and total cholesterol levels in serum and showed severer hemolysis in AlbCreSR-BIfl/fl mice than SR-BIfl/fl mice during CLP-induced sepsis. Importantly, when we fed AlbCreSR-BIfl/fl mice with probucol to decrease the cholesterol level in serum before performing CLP, the survival rate of AlbCreSR-BIfl/fl mice improved to 88.9%. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=94 SRC="FIGDIR/small/051250v1_fig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@80f819org.highwire.dtl.DTLVardef@12064dborg.highwire.dtl.DTLVardef@1bd8e72org.highwire.dtl.DTLVardef@1d30b5e_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFig. 1.C_FLOATNO Mice deficient in hepatic SR-BI are susceptible to CLP-induced septic death. A, PCR genotyping of AlbCreSR-BIfl/fl mice using tail DNA. B, Western blot analysis of SR-BI expression in the liver; C, survival analysis. AlbCreSR-BIfl/fl (n = 14) and SR-BIfl/fl mice (n = 10) were treated with CLP (23G needle, half ligation) and survival was observed for 7 days. The data were expressed as the percentage of mice surviving at indicated times, and survival was analyzed by Log-Rank x2 test. D, AlbCreSR-BIfl/fl and SR-BIfl/fl mice were treated with CLP for the indicated times, and kidney injury was assessed by measuring blood urea nitrogen (BUN) levels; and E, liver injury was assessed by measuring serum alanine aminotransferase (ALT) levels. n = 6 - 7 each group, mean {+/-} SEM. C_FIG ConclusionsDeficiency RCT resulting in abnormal metabolism of cholesterol and lipid metabolism is a risk factor in sepsis and maintain normal metabolism of cholesterol may provide a new insight for sepsis therapies.