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Effects of deletion of macrophage ABCA7 on lipid metabolism and the development of atherosclerosis in the presence and absence of ABCA1.

Meurs I, Calpe-Berdiel L, Habets KL, Zhao Y, Korporaal SJ, Mommaas AM, Josselin E, Hildebrand RB, Ye D, Out R, Kuiper J, Van Berkel TJ, Chimini G, Van Eck M - PLoS ONE (2012)

Bottom Line: However, single deletion of ABCA1 had a similar effect (1.8-fold, p<0.05).In conclusion, deletion of ABCA7 in bone marrow-derived cells does not affect atherogenesis in the arterial wall neither in the absence or presence of ABCA1.Interestingly, combined deletion of bone marrow ABCA1 and ABCA7 causes severe splenomegaly associated with cellular lipid accumulation, a reduction in splenic CD3+ T cells, and induced markers of erythropoeisis.

View Article: PubMed Central - PubMed

Affiliation: Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands.

ABSTRACT
ABCA7, a close relative of ABCA1 which facilitates cholesterol efflux to lipid-poor apoproteins, has been implicated in macrophage lipid efflux and clearance of apoptotic cells in in vitro studies. In the current study, we investigated the in vivo effects of macrophage ABCA7 deficiency on lipid metabolism and atherosclerosis. Chimeras with dysfunctional ABCA7 in macrophages and other blood cells were generated by transplantation of bone marrow from ABCA7 knockout (KO) mice into irradiated low-density lipoprotein receptor (LDLr) KO mice. Unexpectedly, macrophage ABCA7 deficiency did not significantly affect atherosclerosis susceptibility of LDLr KO mice after 10 weeks Western-type diet feeding. However, ABCA7 deficiency was associated with 2-fold (p<0.05) higher macrophage ABCA1 mRNA expression levels. Combined disruption of ABCA1 and ABCA7 in bone-marrow-derived cells increased atherosclerotic lesion development (1.5-fold (p>0.05) as compared to wild type transplanted mice. However, single deletion of ABCA1 had a similar effect (1.8-fold, p<0.05). Macrophage foam cell accumulation in the peritoneal cavity was reduced in ABCA1/ABCA7 dKO transplanted animals as compared to single ABCA1 KO transplanted mice, which was associated with increased ABCG1 expression. Interestingly, spleens of ABCA1/ABCA7 double KO transplanted mice were significantly larger as compared to the other 3 groups and showed massive macrophage lipid accumulation, a reduction in CD3+ T-cells, and increased expression of key regulators of erythropoiesis. In conclusion, deletion of ABCA7 in bone marrow-derived cells does not affect atherogenesis in the arterial wall neither in the absence or presence of ABCA1. Interestingly, combined deletion of bone marrow ABCA1 and ABCA7 causes severe splenomegaly associated with cellular lipid accumulation, a reduction in splenic CD3+ T cells, and induced markers of erythropoeisis. Our data indicate that ABCA7 may play a role in T cell proliferation and erythropoeisis in spleen.

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Effects of macrophage ABCA7 deficiency on plasma lipid levels, atherosclerosis and ABCA1 expression in peritoneal macrophages from LDLr KO mice reconstituted with WT and ABCA7 KO bone marrow.(A) Blood samples were drawn after an overnight fast. The concentrations of cholesterol, phospholipids and triglycerides in serum were determined using enzymatic colorimetric assays. (B) The mean lesion area (µm2) was calculated from Oil red O-stained cross-sections of the aortic root at the level of the tricuspid valves. (C) Guanidium thiocyanate-phenol was used to extract total RNA from cells and mRNA expression was determined by real-time RT-PCR. Hypoxanthine Guanine Phosphoribosyl Transferase (HPRT), β-actin, and acidic ribosomal phosphoprotein PO (36B4) were used as the standard housekeeping genes. Relative gene expression was calculated by subtracting the threshold cycle number (Ct) of the target gene from the average Ct of housekeeping genes and raising two to the power of this difference. Values represent the mean ± SEM of ≥6 mice per group. Statistically significant difference *p<0.05.
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pone-0030984-g001: Effects of macrophage ABCA7 deficiency on plasma lipid levels, atherosclerosis and ABCA1 expression in peritoneal macrophages from LDLr KO mice reconstituted with WT and ABCA7 KO bone marrow.(A) Blood samples were drawn after an overnight fast. The concentrations of cholesterol, phospholipids and triglycerides in serum were determined using enzymatic colorimetric assays. (B) The mean lesion area (µm2) was calculated from Oil red O-stained cross-sections of the aortic root at the level of the tricuspid valves. (C) Guanidium thiocyanate-phenol was used to extract total RNA from cells and mRNA expression was determined by real-time RT-PCR. Hypoxanthine Guanine Phosphoribosyl Transferase (HPRT), β-actin, and acidic ribosomal phosphoprotein PO (36B4) were used as the standard housekeeping genes. Relative gene expression was calculated by subtracting the threshold cycle number (Ct) of the target gene from the average Ct of housekeeping genes and raising two to the power of this difference. Values represent the mean ± SEM of ≥6 mice per group. Statistically significant difference *p<0.05.

Mentions: ABCA7 was selectively disrupted in hematopoietic cells, thus including macrophages, by transplantation of bone marrow from ABCA7 KO mice into LDLr KO mice, which represent a recognized model for the development of atherosclerosis. After a recovery period of 8 weeks on regular murine chow diet, the transplanted mice were challenged with a high cholesterol, high fat WTD containing 0.25% cholesterol and 15% cacao butter. No significant effect of macrophage ABCA7 deficiency was observed on serum free cholesterol (FC) levels, total cholesterol (TC), triglyceride (TG) or phospholipids (PL) (Fig. 1A). The effect on atherosclerosis susceptibility was analyzed in the aortic root of the transplanted LDLr KO mice after 10 weeks WTD feeding. Deletion of ABCA7 in macrophages did not significantly modify the lesion size (p>0.05) (Fig. 1B). Interestingly, the mRNA expression of the key lipid transporter ABCA1 was up-regulated 2-fold in ABCA7-deficient peritoneal macrophages (p = 0.028) (Fig. 1C). We have previously shown that macrophage ABCA1 overexpression inhibits atherosclerotic lesion progression in LDLr KO mice [29]. Thus, to gain further insight into the impact of ABCA7 expression on lipid metabolism and atherogenesis, the effect of combined macrophage ABCA1 and ABCA7 disruption was evaluated by means of BMT.


Effects of deletion of macrophage ABCA7 on lipid metabolism and the development of atherosclerosis in the presence and absence of ABCA1.

Meurs I, Calpe-Berdiel L, Habets KL, Zhao Y, Korporaal SJ, Mommaas AM, Josselin E, Hildebrand RB, Ye D, Out R, Kuiper J, Van Berkel TJ, Chimini G, Van Eck M - PLoS ONE (2012)

Effects of macrophage ABCA7 deficiency on plasma lipid levels, atherosclerosis and ABCA1 expression in peritoneal macrophages from LDLr KO mice reconstituted with WT and ABCA7 KO bone marrow.(A) Blood samples were drawn after an overnight fast. The concentrations of cholesterol, phospholipids and triglycerides in serum were determined using enzymatic colorimetric assays. (B) The mean lesion area (µm2) was calculated from Oil red O-stained cross-sections of the aortic root at the level of the tricuspid valves. (C) Guanidium thiocyanate-phenol was used to extract total RNA from cells and mRNA expression was determined by real-time RT-PCR. Hypoxanthine Guanine Phosphoribosyl Transferase (HPRT), β-actin, and acidic ribosomal phosphoprotein PO (36B4) were used as the standard housekeeping genes. Relative gene expression was calculated by subtracting the threshold cycle number (Ct) of the target gene from the average Ct of housekeeping genes and raising two to the power of this difference. Values represent the mean ± SEM of ≥6 mice per group. Statistically significant difference *p<0.05.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3293875&req=5

pone-0030984-g001: Effects of macrophage ABCA7 deficiency on plasma lipid levels, atherosclerosis and ABCA1 expression in peritoneal macrophages from LDLr KO mice reconstituted with WT and ABCA7 KO bone marrow.(A) Blood samples were drawn after an overnight fast. The concentrations of cholesterol, phospholipids and triglycerides in serum were determined using enzymatic colorimetric assays. (B) The mean lesion area (µm2) was calculated from Oil red O-stained cross-sections of the aortic root at the level of the tricuspid valves. (C) Guanidium thiocyanate-phenol was used to extract total RNA from cells and mRNA expression was determined by real-time RT-PCR. Hypoxanthine Guanine Phosphoribosyl Transferase (HPRT), β-actin, and acidic ribosomal phosphoprotein PO (36B4) were used as the standard housekeeping genes. Relative gene expression was calculated by subtracting the threshold cycle number (Ct) of the target gene from the average Ct of housekeeping genes and raising two to the power of this difference. Values represent the mean ± SEM of ≥6 mice per group. Statistically significant difference *p<0.05.
Mentions: ABCA7 was selectively disrupted in hematopoietic cells, thus including macrophages, by transplantation of bone marrow from ABCA7 KO mice into LDLr KO mice, which represent a recognized model for the development of atherosclerosis. After a recovery period of 8 weeks on regular murine chow diet, the transplanted mice were challenged with a high cholesterol, high fat WTD containing 0.25% cholesterol and 15% cacao butter. No significant effect of macrophage ABCA7 deficiency was observed on serum free cholesterol (FC) levels, total cholesterol (TC), triglyceride (TG) or phospholipids (PL) (Fig. 1A). The effect on atherosclerosis susceptibility was analyzed in the aortic root of the transplanted LDLr KO mice after 10 weeks WTD feeding. Deletion of ABCA7 in macrophages did not significantly modify the lesion size (p>0.05) (Fig. 1B). Interestingly, the mRNA expression of the key lipid transporter ABCA1 was up-regulated 2-fold in ABCA7-deficient peritoneal macrophages (p = 0.028) (Fig. 1C). We have previously shown that macrophage ABCA1 overexpression inhibits atherosclerotic lesion progression in LDLr KO mice [29]. Thus, to gain further insight into the impact of ABCA7 expression on lipid metabolism and atherogenesis, the effect of combined macrophage ABCA1 and ABCA7 disruption was evaluated by means of BMT.

Bottom Line: However, single deletion of ABCA1 had a similar effect (1.8-fold, p<0.05).In conclusion, deletion of ABCA7 in bone marrow-derived cells does not affect atherogenesis in the arterial wall neither in the absence or presence of ABCA1.Interestingly, combined deletion of bone marrow ABCA1 and ABCA7 causes severe splenomegaly associated with cellular lipid accumulation, a reduction in splenic CD3+ T cells, and induced markers of erythropoeisis.

View Article: PubMed Central - PubMed

Affiliation: Division of Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, Gorlaeus Laboratories, Leiden University, Leiden, The Netherlands.

ABSTRACT
ABCA7, a close relative of ABCA1 which facilitates cholesterol efflux to lipid-poor apoproteins, has been implicated in macrophage lipid efflux and clearance of apoptotic cells in in vitro studies. In the current study, we investigated the in vivo effects of macrophage ABCA7 deficiency on lipid metabolism and atherosclerosis. Chimeras with dysfunctional ABCA7 in macrophages and other blood cells were generated by transplantation of bone marrow from ABCA7 knockout (KO) mice into irradiated low-density lipoprotein receptor (LDLr) KO mice. Unexpectedly, macrophage ABCA7 deficiency did not significantly affect atherosclerosis susceptibility of LDLr KO mice after 10 weeks Western-type diet feeding. However, ABCA7 deficiency was associated with 2-fold (p<0.05) higher macrophage ABCA1 mRNA expression levels. Combined disruption of ABCA1 and ABCA7 in bone-marrow-derived cells increased atherosclerotic lesion development (1.5-fold (p>0.05) as compared to wild type transplanted mice. However, single deletion of ABCA1 had a similar effect (1.8-fold, p<0.05). Macrophage foam cell accumulation in the peritoneal cavity was reduced in ABCA1/ABCA7 dKO transplanted animals as compared to single ABCA1 KO transplanted mice, which was associated with increased ABCG1 expression. Interestingly, spleens of ABCA1/ABCA7 double KO transplanted mice were significantly larger as compared to the other 3 groups and showed massive macrophage lipid accumulation, a reduction in CD3+ T-cells, and increased expression of key regulators of erythropoiesis. In conclusion, deletion of ABCA7 in bone marrow-derived cells does not affect atherogenesis in the arterial wall neither in the absence or presence of ABCA1. Interestingly, combined deletion of bone marrow ABCA1 and ABCA7 causes severe splenomegaly associated with cellular lipid accumulation, a reduction in splenic CD3+ T cells, and induced markers of erythropoeisis. Our data indicate that ABCA7 may play a role in T cell proliferation and erythropoeisis in spleen.

Show MeSH
Related in: MedlinePlus