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Objectives Scavenger receptor BI (SR-BI) is a key regulator of high density lipoprotein (HDL) metabolism. Recent studies showed that mice deficient in SR-BI exhibit impaired erythropoiesis and it has been proposed that the high cholesterol environment plays a major role in the abnormal erythropoiesis. In this study, we observed the effect of SR-BI deficiency and hypercholesterolemia on erythropoiesis. Methods Three animal models were utilised to evaluate the role of SR-BI and hypercholesterolemia in erythropoiesis. 1. First, we used a high fat diet-induced hypercholesterolemia model. High fat diet caused a 2-fold increase in plasma cholesterol levels in SR-BI +/+ (170 mg/dl to 352 mg/dl) and SR-BI -/- mice (315 mg/dl to 718 mg/dl). 2. Then, we used SR-BI/LDLR double knockout mice to further elucidate the contribution of hypercholesterolemia to erythropoiesis. 3. Finally, we investigated the contribution of hepatic SR-BI using ScarbI I179N mutant mice, whose hepatic SR-BI expression has been knocked down by 90% and therefore has a 1.7-fold increase in plasma cholesterol levels compared to wild type controls. Results The high fat diet treatment markedly exacerbated the impaired erythropoiesis in SR-BI -/- mice as shown by 4-fold increase in reticulocyte percentage and 2.5-fold increase in early-to-late erythroblast ratio. Unexpectedly, high fat feeding did not induce abnormal erythropoiesis in SR-BI +/+ mice despite of hypercholesterolemia in these mice. SR-BI/LDLR double knockout mice had 2-fold increase in plasma cholesterol levels and exhibited severer impaired erythropoiesis, similar to high fat-fed SR-BI -/- mice. Interestingly, despite of hyperlipidemia, LDLR single knockout mice did not display impaired erythropoiesis. ScarbI I179N mice displayed normal erythropoiesis, similar to wild type controls. These findings indicate that hypercholesterolemia does not cause abnormal erythropoiesis in the presence of SR-BI, but markedly impairs erythropoiesis in the absence of SR-BI. Conclusions Our study suggest that SR-BI is essential for normal erythropoiesis, and that hypercholesterolemia and SR-BI deficiency synergistically exacerbated impaired erythropoiesis .

Objectives To identify the major tyrosine-phosphorylated proteins in the normal artery and their changes after balloon injury. Methods The normal and balloon-injured carotid arteries, the aorta, and other tissues from Sprague-Dawley rats were perfused with sodium vanadate, excised, and then homogenised in detergent-containing lysis buffer. The clarified tissue lysate was subjected to immunoprecipitation with anti-phosphotyrosine antibody, and then analysed by Western blot with antibodies against focal adhesion kinase (FAK), paxillin, and phosphotyrosine. Results Western blot analyses with three different antibodies against phosphotyrosine revealed that pp68 and pp125 were the two major tyrosine-phosphorylated proteins present in the normal carotid artery and the aorta. Reprobing with various antibodies identified these proteins was paxi1lin and FAK. Immunodepletion with antiphosphotyrosine removed FAK and paxillin, which suggested that most of these proteins were tyrosinephosphorylated in the artery. The artery contained greater amount of tyrosine-phosphorylated FAK than that in the other tissues examined, including the inferior vena cava and the heart. The content of FAK and paxillin was decreased following the balloon injury of the carotid artery, but not after endothelial denudation ex vivo. Conclusions The findings suggest that FAK and paxillin may play an important role in the maintenance of the normal structure and function, and in the response to balloon injury of the artery.