36 research outputs found
DBA/2J Haplotype on Distal Chromosome 2 Reduces Mertk Expression, Restricts Efferocytosis, and Increases Susceptibility to AtherosclerosisHighlights
OBJECTIVE: Arch atherosclerosis 4 (Aath4) is a quantitative trait locus for atherosclerotic plaque formation in the inner curve of the aortic arch previously identified in an F2 cross of Apoe-/- mice on DBA/2J and 129S6 backgrounds. C-mer proto-oncogene tyrosine kinase (Mertk), coding for a ligand-activated transmembrane tyrosine kinase, is a candidate gene within the same chromosomal region. Our objective was to determine whether strain differences in Mertk influence plaque formation.
APPROACH AND RESULTS: To dissect the strain effects of Mertk on atherosclerosis, we first established a congenic mouse line (Aath4aDBA/DBA ) in which a 5' region of Aath4 of DBA/2J, including Mertk, was backcrossed onto a 129S6-Apoe-/- background. The resulting Aath4aDBA/DBA male mice developed significantly larger plaques compared with control mice (Aath4a129/129 ), proving that the DBA/2J allele of Aath4a is proatherogenic. Thioglycollate-elicited peritoneal macrophages from Aath4aDBA/DBA mice express less than 50% of Mertk mRNA and cell-surface MERTK protein compared with those from the control mice. Moreover, both large and small peritoneal Aath4aDBA/DBA macrophages showed reduced phagocytosis of apoptotic cells. When Mertk cDNAs from 129S6 and DBA/2J mice were overexpressed in HEK293T (human embryonic kidney 293T) cells, phagocytosis of apoptotic cells was equally enhanced in direct proportion to Mertk levels, indicating that phagocytosis is modulated by the amount of MERTK, but that it is not affected by MERTK amino acid differences between 129S6 and DBA/2J.
CONCLUSIONS: Reduced transcription of Mertk, rather than differences in MERTK protein structure, determines the reduced efficiency of apoptotic cell clearance in the Aath4aDBA/DBA mice, which, in turn, contributes to their increased susceptibility to atherosclerosis
The kallikrein–kinin system and oxidative stress
The Kallikrein-kinin system (KKS) constitutes a complex multi-enzyme cascade that produces several bioactive kinin peptides and their derivatives including bradykinin. In addition to the classical notion of the KKS as a potent vasodilator and a mediator of inflammatory responses, recent studies suggest a link between the KKS and oxidative stress. A number of established mouse model with altered levels of KKS components opened the way to evaluate precise functions of the KKS. Here we review recent findings on the role of the KKS in cardiovascular diseases and chronic kidney diseases, and discuss potential benefits of KKS activation in these diseases
Reduction of \u3ci\u3eStabilin-2\u3c/i\u3e Contributes to a Protection Against Atherosclerosis
We have previously identified a novel atherosclerosis quantitative trait locus (QTL), Arch atherosclerosis 5 (Aath5), on mouse chromosome 10 by three-way QTL analyses between Apoe−/− mice on a DBA/2J, 129S6 and C57BL/6J background. The DBA/2J haplotype at the Aath5 locus was associated with smaller plaque size. One of the candidate genes underlying Aath5 was Stabilin-2 (Stab2), which encodes a clearance receptor for hyaluronan (HA) predominantly expressed in liver sinusoidal endothelial cells (LSECs). However, the role of Stab2 in atherosclerosis is unknown. A congenic line of Apoe−/− mice carrying Aath5 covering the Stab2DBA allele on a background of 129S6 confirmed the small reductions of atherosclerotic plaque development. To further determine whether Stab2 is an underlying gene for Aath5, we generated Stab2−/−Apoe−/− mice on a C57BL/6J background. When fed with a Western diet for 8 weeks, Stab2−/−Apoe−/− males developed approximately 30% smaller plaques than Stab2+/+Apoe−/− mice. HA was accumulated in circulation but not in major organs in the Stab2 deficient mice. STAB2-binding molecules that are involved in atherosclerosis, including acLDL, apoptotic cells, heparin and vWF were not likely the direct cause of the protection in the Stab2−/−Apoe−/− males. These data indicate that reduction of Stab2 is protective against atherosclerotic plaque development, and that Stab2 is a contributing gene underlying Aath5, although its effect is small. To test whether non-synonymous amino acid changes unique to DBA/2J affect the function of STAB2 protein, we made HEK293 cell lines expressing STAB2129 or STAB2DBA proteins, as well as STAB2129 proteins carrying each of five DBA-unique replacements that have been predicted to be deleterious. These mutant cells were capable of internalizing 125I -HA and DiI-acLDL similarly to the control cells. These results indicate that the amino acid changes unique to DBA/2J are not affecting the function of STAB2 protein, and support our previous observation that the reduced transcription of Stab2 in the liver sinusoid as a consequence of the insertion of a viral-derived sequence, intracisternal A particle, is the primary contributor to the athero-protection conferred by the DBA/2J allele
Reduction of Stabilin-2 Contributes to a Protection Against Atherosclerosis
We have previously identified a novel atherosclerosis quantitative trait locus (QTL), Arch atherosclerosis 5 (Aath5), on mouse chromosome 10 by three-way QTL analyses between Apoe−/− mice on a DBA/2J, 129S6 and C57BL/6J background. The DBA/2J haplotype at the Aath5 locus was associated with smaller plaque size. One of the candidate genes underlying Aath5 was Stabilin-2 (Stab2), which encodes a clearance receptor for hyaluronan (HA) predominantly expressed in liver sinusoidal endothelial cells (LSECs). However, the role of Stab2 in atherosclerosis is unknown. A congenic line of Apoe−/− mice carrying Aath5 covering the Stab2DBA allele on a background of 129S6 confirmed the small reductions of atherosclerotic plaque development. To further determine whether Stab2 is an underlying gene for Aath5, we generated Stab2−/−Apoe−/− mice on a C57BL/6J background. When fed with a Western diet for 8 weeks, Stab2−/−Apoe−/− males developed approximately 30% smaller plaques than Stab2+/+Apoe−/− mice. HA was accumulated in circulation but not in major organs in the Stab2 deficient mice. STAB2-binding molecules that are involved in atherosclerosis, including acLDL, apoptotic cells, heparin and vWF were not likely the direct cause of the protection in the Stab2−/−Apoe−/− males. These data indicate that reduction of Stab2 is protective against atherosclerotic plaque development, and that Stab2 is a contributing gene underlying Aath5, although its effect is small. To test whether non-synonymous amino acid changes unique to DBA/2J affect the function of STAB2 protein, we made HEK293 cell lines expressing STAB2129 or STAB2DBA proteins, as well as STAB2129 proteins carrying each of five DBA-unique replacements that have been predicted to be deleterious. These mutant cells were capable of internalizing 125I -HA and DiI-acLDL similarly to the control cells. These results indicate that the amino acid changes unique to DBA/2J are not affecting the function of STAB2 protein, and support our previous observation that the reduced transcription of Stab2 in the liver sinusoid as a consequence of the insertion of a viral-derived sequence, intracisternal A particle, is the primary contributor to the athero-protection conferred by the DBA/2J allele
Atherosclerosis in Different Vascular Locations Unbiasedly Approached with Mouse Genetics
Atherosclerosis in different vascular locations leads to distinct clinical consequences, such as ischemic stroke and myocardial infarction. Genome-wide association studies in humans revealed that genetic loci responsible for carotid plaque and coronary artery disease were not overlapping, suggesting that distinct genetic pathways might be involved for each location. While elevated plasma cholesterol is a common risk factor, plaque development in different vascular beds is influenced by hemodynamics and intrinsic vascular integrity. Despite the limitation of species differences, mouse models provide platforms for unbiased genetic approaches. Mouse strain differences also indicate that susceptibility to atherosclerosis varies, depending on vascular locations, and that the location specificity is genetically controlled. Quantitative trait loci analyses in mice suggested candidate genes, including Mertk and Stab2, although how each gene affects the location-specific atherosclerosis needs further elucidation. Another unbiased approach of single-cell transcriptome analyses revealed the presence of a small subpopulation of vascular smooth muscle cells (VSMCs), which are “hyper-responsive” to inflammatory stimuli. These cells are likely the previously-reported Sca1+ progenitor cells, which can differentiate into multiple lineages in plaques. Further spatiotemporal analyses of the progenitor cells are necessary, since their distribution pattern might be associated with the location-dependent plaque development
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Ectopic expression of the Stabilin2 gene triggered by an intracisternal A particle (IAP) element in DBA/2J strain of mice
Stabilin2 (Stab2) encodes a large transmembrane protein which is predominantly expressed in the liver sinusoidal endothelial cells (LSECs) and functions as a scavenger receptor for various macromolecules including hyaluronans (HA). In DBA/2J mice, plasma HA concentration is ten times higher than in 129S6 or C57BL/6J mice, and this phenotype is genetically linked to the Stab2 locus. Stab2 mRNA in the LSECs was significantly lower in DBA/2J than in 129S6, leading to reduced STAB2 proteins in the DBA/2J LSECs. We found a retrovirus-derived transposable element, intracisternal A particle (IAP), in the promoter region of Stab2DBA which likely interferes with normal expression in the LSECs. In contrast, in other tissues of DBA/2J mice, the IAP drives high ectopic Stab2DBA transcription starting within the 5' long terminal repeat of IAP in a reverse orientation and continuing through the downstream Stab2DBA. Ectopic transcription requires the Stab2-IAP element but is dominantly suppressed by the presence of loci on 59.7-73.0 Mb of chromosome (Chr) 13 from C57BL/6J, while the same region in 129S6 requires additional loci for complete suppression. Chr13:59.9-73 Mb contains a large number of genes encoding Krüppel-associated box-domain zinc-finger proteins that target transposable elements-derived sequences and repress their expression. Despite the high amount of ectopic Stab2DBA transcript in tissues other than liver, STAB2 protein was undetectable and unlikely to contribute to the plasma HA levels of DBA/2J mice. Nevertheless, the IAP insertion and its effects on the transcription of the downstream Stab2DBA exemplify that stochastic evolutional events could significantly influence susceptibility to complex but common diseases
Insulin Elevates ID2 Expression in Trophoblasts and Aggravates Preeclampsia in Obese ASB4-Null Mice
Obesity is a risk factor for preeclampsia. We investigated how obesity influences preeclampsia in mice lacking ankyrin-repeat-and-SOCS-box-containing-protein 4 (ASB4), which promotes trophoblast differentiation via degrading the inhibitor of DNA-binding protein 2 (ID2). Asb4−/− mice on normal chow (NC) develop mild preeclampsia-like phenotypes during pregnancy, including hypertension, proteinuria, and reduced litter size. Wild-type (WT) and Asb4−/− females were placed on a high-fat diet (HFD) starting at weaning. At the age of 8–9 weeks, they were mated with WT or Asb4−/− males, and preeclamptic phenotypes were assessed. HFD-WT dams had no obvious adverse outcomes of pregnancy. In contrast, HFD-Asb4−/− dams had significantly more severe preeclampsia-like phenotypes compared to NC-Asb4−/− dams. The HFD increased white fat weights and plasma leptin and insulin levels in Asb4−/− females. In the HFD-Asb4−/− placenta, ID2 amounts doubled without changing the transcript levels, indicating that insulin likely increases ID2 at a level of post-transcription. In human first-trimester trophoblast HTR8/SVneo cells, exposure to insulin, but not to leptin, led to a significant increase in ID2. HFD-induced obesity markedly worsens the preeclampsia-like phenotypes in the absence of ASB4. Our data indicate that hyperinsulinemia perturbs the timely removal of ID2 and interferes with proper trophoblast differentiation, contributing to enhanced preeclampsia
Insulin Elevates ID2 Expression in Trophoblasts and Aggravates Preeclampsia in Obese ASB4-Null Mice
Obesity is a risk factor for preeclampsia. We investigated how obesity influences preeclampsia in mice lacking ankyrin-repeat-and-SOCS-box-containing-protein 4 (ASB4), which promotes trophoblast differentiation via degrading the inhibitor of DNA-binding protein 2 (ID2). Asb4−/− mice on normal chow (NC) develop mild preeclampsia-like phenotypes during pregnancy, including hypertension, proteinuria, and reduced litter size. Wild-type (WT) and Asb4−/− females were placed on a high-fat diet (HFD) starting at weaning. At the age of 8–9 weeks, they were mated with WT or Asb4−/− males, and preeclamptic phenotypes were assessed. HFD-WT dams had no obvious adverse outcomes of pregnancy. In contrast, HFD-Asb4−/− dams had significantly more severe preeclampsia-like phenotypes compared to NC-Asb4−/− dams. The HFD increased white fat weights and plasma leptin and insulin levels in Asb4−/− females. In the HFD-Asb4−/− placenta, ID2 amounts doubled without changing the transcript levels, indicating that insulin likely increases ID2 at a level of post-transcription. In human first-trimester trophoblast HTR8/SVneo cells, exposure to insulin, but not to leptin, led to a significant increase in ID2. HFD-induced obesity markedly worsens the preeclampsia-like phenotypes in the absence of ASB4. Our data indicate that hyperinsulinemia perturbs the timely removal of ID2 and interferes with proper trophoblast differentiation, contributing to enhanced preeclampsia
Identification of Aortic Arch-Specific Quantitative Trait Loci for Atherosclerosis by an Intercross of DBA/2J and 129S6 Apolipoprotein E-Deficient Mice
<div><p>The genetic background of apolipoprotein E (apoE) deficient mice influences atherosclerotic plaque development. We previously reported three quantitative trait loci (QTL), <i>Aath1–Aath3</i>, that affect aortic arch atherosclerosis independently of those in the aortic root in a cross between C57BL6 apoEKO mice (B6-apoE) and 129S6 apoEKO mice (129-apoE). To gain further insight into genetic factors that influence atherosclerosis at different vascular locations, we analyzed 335 F2 mice from an intercross between 129-apoE and apoEKO mice on a DBA/2J genetic background (DBA-apoE). The extent of atherosclerosis in the aortic arch was very similar in the two parental strains. Nevertheless, a genome-wide scan identified two significant QTL for plaque size in the aortic arch: <i>Aath4</i> on Chromosome (Chr) 2 at 137 Mb and <i>Aath5</i> on Chr 10 at 51 Mb. The DBA alleles of <i>Aath4</i> and <i>Aath5</i> respectively confer susceptibility and resistance to aortic arch atherosclerosis over 129 alleles. Both QTL are also independent of those affecting plaque size at the aortic root. Genome analysis suggests that athero-susceptibility of <i>Aath4</i> in DBA may be contributed by multiple genes, including <i>Mertk</i> and <i>Cd93</i>, that play roles in phagocytosis of apoptotic cells and modulate inflammation. A candidate gene for <i>Aath5</i> is <i>Stab2</i>, the DBA allele of which is associated with 10 times higher plasma hyaluronan than the 129 allele. Overall, our identification of two new QTL that affect atherosclerosis in an aortic arch-specific manner further supports the involvement of distinct pathological processes at different vascular locations.</p></div
DBA-allele dependent upregulation of Stab2 and its ligand hyaluronan.
<p>(A) Plasma hyaluronan concentrations in the wild-type male C57BL/6, 129S6 and DBA2/J mice. Box-and-whisker plots: midline, median; box, 25th and 75th percentiles; whiskers, 1.5× interquartile range; dots, outliers. Numbers of mice were indicated below the plots. (B) Plasma hyaluronan concentrations in a subset of F2 males and females of 129-apoE × DBA-apoE. Mice were grouped by the genotype of rs13480630 on Chr 10, which is located near <i>Stab2</i>. Differences were compared by Kruskal–Wallis test followed by Steel-Dwass test for (A) and (B). (C) Effects of other hyaluronan metabolic loci on plasma hyaluronan concentrations. The same set of F2 population was grouped into 129-homo, Hetero and DBA-homo according to the genotype of rs13459148 on Chr 17 (near <i>Has1</i>), rs13482628 on Chr 15 (near <i>Has2</i>), rs3667255 on Chr 8 (near <i>Has3</i>), rs13480325 on Chr 9 (near <i>Hayl1–3</i>), rs13476631 on Chr 2 (near <i>Cd44</i>), rs13479497 on Chr 7 (near <i>Lyve1</i>) and rs13480973 on Chr 11 (near <i>Hmmr</i>). Kruskal–Wallis test was used for the multiple comparison. (D) Expression levels of Stab2 in various tissues from B6 (black filled bars), 129 (gray filled bars) and DBA (open bars). Data are relative to those in the B6 liver (= 100) assessed by quantitative RT-PCR. <sup>**</sup><i>P</i> < 0.01, <sup>***</sup><i>P</i> < 0.001 vs. B6; <sup>##</sup><i>P</i> < 0.01, <sup>###</sup><i>P</i> < 0.001 vs. 129 (one-way ANOVA followed by Tukey-Kramer’s HSD test). Data were shown as the mean ± SD. Sample numbers were indicated in the bars.</p