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Background: Obesity increases the risk for human abdominal aortic aneurysms (AAAs) and enhances Ang II (angiotensin II)–induced AAA formation in C57BL/6J mice. Obesity is also associated with increases in perivascular fat that expresses proinflammatory markers including SAA (serum amyloid A). We previously reported that deficiency of SAA significantly reduces Ang II–induced inflammation and AAA in hyperlipidemic apoE-deficient mice. In this study. we investigated whether adipose tissue-derived SAA plays a role in Ang II–induced AAA in obese C57BL/6J mice. Methods: The development of AAA was compared between male C57BL/6J mice (wild type), C57BL/6J mice lacking SAA1.1, SAA2.1, and SAA3 (TKO); and TKO mice harboring a doxycycline-inducible, adipocyte-specific SAA1.1 transgene (TKO-Tg fat ; SAA expressed only in fat). All mice were fed an obesogenic diet and doxycycline to induce SAA transgene expression and infused with Ang II to induce AAA. Results: In response to Ang II infusion, SAA expression was significantly increased in perivascular fat of obese C57BL/6J mice. Maximal luminal diameters of the abdominal aorta were determined by ultrasound before and after Ang II infusion, which indicated a significant increase in aortic luminal diameters in wild type and TKO-TG fat mice but not in TKO mice. Adipocyte-specific SAA expression was associated with MMP (matrix metalloproteinase) activity and macrophage infiltration in abdominal aortas of Ang II–infused obese mice. Conclusions: We demonstrate for the first time that SAA deficiency protects obese C57BL/6J mice from Ang II–induced AAA. SAA expression only in adipocytes is sufficient to cause AAA in obese mice infused with Ang II.

Objectives: Serum Amyloid A (SAA) is a family of proteins whose plasma levels increase > 1000-fold in acute inflammatory states such as sepsis. We and others have demonstrated that SAA plays a causal role in mouse models of atherosclerosis. However, SAA may not be a valid therapeutic target if it is needed for host defense in inflammation. Here, we investigated the role of SAA in sepsis using mice deficient in all three acute-phase SAA isoforms (TKO). Approach and results: SAA deficiency significantly increased mortality rates in three experimental sepsis models. Survival rates in TKO and wild-type (WT) mice were: 25% and 55% after cecal ligation and puncture (CLP; p=0.02; n=10 each strain/gender); 0% and 45% after cecal slurry injection (pProz, Dbp, Cxcl1, Cxcl2, Arg1 and Ackr1 . Gene ontology analysis revealed a significant enrichment of differentially expressed genes associated with chemokine production, chemokine and cytokine-mediated signaling, neutrophil chemotaxis and neutrophil migration in TKO lung tissues compared to WT tissues (p Conclusions: SAA protects mice against sepsis-induced mortality, potentially by protecting the lung from tissue damage. Thus, the risk of infection should be considered when targeting SAA to ameliorate atherosclerosis.

Obesity increases the risk for abdominal aortic aneurysms (AAA) in humans, and enhances angiotensin II (AngII)-induced AAA formation in C57BL/6 mice. Obesity is also associated with increases in serum amyloid A (SAA). We previously reported that deficiency of SAA significantly reduces AngII-induced inflammation and AAA in apoE-deficient mice. In this study we investigated whether SAA plays a role in progression of an established AAA in obese C57BL/6 mice. Approach and Results: Male C57BL/6 mice were fed a high fat diet (60% kcal as fat) throughout the study. After 4 months of diet the mice were infused with angiotensin II (AngII) at 1000ng/kg/min until the end of the study. Ultrasound (US) was performed in all mice before and after 28 days of AngII infusion, and mice that had at least a 25% increase in the luminal diameter of the abdominal aorta were stratified by luminal diameter into 3 groups. Group 1 was killed to establish baseline AAA. Groups 2 and 3 continued to receive AngII for a further 8 weeks along with an antisense oligonucleotide (ASO) that suppresses all 3 acute phase SAA isoforms (SAA-ASO), or a control ASO (5 mg/kg/wk). US was repeated at study end to assess AAA progression. Plasma SAA at the end of the experiment was 89.2±83.2 mg/L in the control ASO group, and 18.6±0.7 mg/L in the SAA-ASO group (mean±SD , p=0.008). There was no impact of SAA suppression on body weight, body fat, or blood pressure. After the first 4 weeks of AngII infusion, the average luminal diameter in all mice was 1.81±0.40 mm (mean±SD). Mice that received the control ASO had continued aortic dilation (average luminal aortic diameter 2.06±0.42 mm), whereas the mice that received the SAA-ASO had a significant reduction in progression of aortic dilation (average luminal diameter 1.64±0.43 mm, p=0.0015 for interaction between time and group). Conclusions: We demonstrate for the first time that suppression of SAA protects obese C57BL/6 mice from progression of AngII-induced AAA. Suppression of SAA may be a therapeutic approach to limit AAA progression.

Purpose of review Acute phase serum amyloid A (SAA) is persistently elevated in chronic inflammatory conditions, and elevated levels predict cardiovascular risk in humans. More recently, murine studies have demonstrated that over-expression of SAA increases and deficiency/suppression of SAA attenuates atherosclerosis. Thus, beyond being a biomarker, SAA appears to play a causal role in atherogenesis. The purpose of this review is to summarize the data supporting SAA as a key player in atherosclerosis development. Recent findings A number of pro-inflammatory and pro-atherogenic activities have been ascribed to SAA. However, the literature is conflicted, as recombinant SAA, and/or lipid-free SAA, used in many of the earlier studies, do not reflect the activity of native human or murine SAA, which exists largely lipid-associated. Recent literatures demonstrate that SAA activates the NLRP3 inflammasome, alters vascular function, affects HDL function, and increases thrombosis. Importantly, SAA activity appears to be regulated by its lipid association, and HDL may serve to sequester and limit SAA activity. Summary SAA has many pro-inflammatory and pro-atherogenic activities, is clearly demonstrated to affect atherosclerosis development, and may be a candidate target for clinical trials in cardiovascular diseases.

Objective— SAA (serum amyloid A) is a family of acute-phase reactants that have proinflammatory and proatherogenic activities. SAA is more lipophilic than apoA-I (apolipoprotein A-I), and during an acute-phase response, Approach and Results— Delipidated human SAA was incubated with SAA-free human lipoproteins; then, samples were reisolated by fast protein liquid chromatography, and SAA analyzed by ELISA and immunoblot. Both in vitro and in vivo, we show that SAA associates with any lipoprotein and does not remain in a lipid-free form. Although SAA is preferentially found on high-density lipoprotein, it can exchange between lipoproteins. In the presence of CETP (cholesterol ester transfer protein), there is greater exchange of SAA between lipoproteins. Subjects with diabetes mellitus, but not those with metabolic syndrome, showed altered SAA lipoprotein distribution postprandially. Proteoglycan-mediated lipoprotein retention is thought to be an underlying mechanism for atherosclerosis development. SAA has a proteoglycan-binding domain. Lipoproteins containing SAA had increased proteoglycan binding compared with SAA-free lipoproteins. Conclusions— Thus, SAA is an exchangeable apolipoprotein and increases apoB-containing lipoproteins’ proteoglycan binding. We and others have previously reported the presence of SAA on low-density lipoprotein in individuals with obesity, diabetes mellitus, and metabolic syndrome. We propose that the presence of SAA on apoB-containing lipoproteins may contribute to cardiovascular disease development in these populations.

Serum amyloid A (SAA) is a family of acute phase reactants that are elevated in chronic inflammatory conditions such as obesity and diabetes. SAA promotes atherosclerosis in mice. Although SAA is generally thought to be exclusively an HDL apolipoprotein, we and others have detected SAA on apoB-containing lipoproteins in obese/diabetic mice and humans. The goal of this study was to investigate mechanisms underlying SAA exchange between lipoprotein fractions. Obese humans with or without metabolic syndrome or type 2 diabetes were recruited. Plasma samples were collected fasting and hourly for 8h after consumption of a high fat drink. Whereas SAA was found predominantly on HDL in fasting samples, in diabetic subjects SAA shifted from HDL to VLDL and LDL in post prandial samples. Postprandial LDL and VLDL containing SAA had increased proteoglycan binding compared to fasting LDL and VLDL from the same subject. We previously reported that HDLs remodeled by CETP release lipid-free SAA. To determine if CETP facilitates SAA exchange between particles, HDL-containing SAA was incubated with SAA-free VLDL in the presence of increasing amounts of CETP. Even in the absence of CETP, 16±3% of HDL-associated SAA shifted to VLDL; in samples with CETP, 19-28% of total SAA was found on VLDL and up to 17% was lipid-poor/lipid-free. To investigate whether CETP promotes SAA exchange in vivo, SAA-deficient mice that lack CETP were injected with HDL containing SAA and then bled at 1, 3, 6 and 24 hours. Essentially all SAA was found on HDL at each time point. In contrast, in SAA-deficient mice expressing CETP by adenoviral vector, approximately 50% and 20% of SAA was associated with the VLDL and LDL fractions, respectively, 1h after injection of HDL-containing SAA. Thus, increased CETP activity in diabetes may promote the transfer of SAA from HDL to apoB-containing lipoproteins, leading to increased retention in the vasculature.

Serum Amyloid A (SAA) is traditionally thought to be only found with HDL; however, recently several groups have found that SAA is found on apoB-containing lipoproteins (LDL and VLDL) under some circumstances. The goal of this study was to determine the relative lipoprotein association of SAA. Native human acute phase SAA was isolated from acute phase plasma collected from patients undergoing cardiovascular bypass surgery; the SAA was purified and delipidated. Plasma was collected from a group of healthy, non-obese humans with low levels of SAA (< 2 mg/L) and lipoproteins (VLDL, LDL and HDL) were isolated by density gradient ultracentrifugation. The delipidated SAA (at 2 concentrations) was incubated in vitro with the various lipoprotein preparations then samples were re-isolated by fast protein liquid chromatography and SAA was analyzed by ELISA and immunoblot. When SAA was incubated with any single lipoprotein all of the SAA was found associated with that lipoprotein and none remained in a lipid-free form. When SAA was incubated with a mixture of VLDL, LDL and HDL (based on equal protein and corresponding to concentrations in plasma) a majority of SAA (50-60%) was found on HDL with the remaining SAA found on VLDL and LDL. When SAA first complexed to HDL was added to a mixture of SAA-free LDL and VLDL the majority of SAA remained with the HDL (76-86%) but 5-10% of the SAA was found on each of LDL and VLDL. When SAA first complexed to either apoB-containing lipoprotein was then added to a mixture of HDL and the other apoB-containing lipoprotein most SAA moved to HDL (55-70%) but the remainder was found on the apoB-containing particles. Thus, SAA can move between lipoprotein particles in vitro. To determine if the presence of SAA on apoB-containing lipoproteins had a functional effect we evaluated lipoprotein-proteoglycan binding affinity. Proteoglycan mediated lipoprotein retention in the vessel wall is thought to be one of the key steps in initiation of atherosclerosis. Compared to SAA-free LDL or VLDL, the presence of SAA on apoB-containing lipoproteins caused increased proteoglycan binding affinity. Thus, SAA is not simply an HDL lipoprotein, but SAA can move between lipoprotein particles, and the presence of SAA on apoB particles may increase their atherogenicity.

Acute phase serum amyloid (SAA) is a family of evolutionarily conserved, secreted proteins that exerts innate functions relevant to vascular disease. In humans, two SAA isoforms (SAA1 and SAA2) are highly induced in the liver and extrahepatic tissues under the regulation of inflammatory cytokines. During severe inflammation, SAA1/2 levels can increase ≥1000-fold in plasma, where it is found associated with HDL. Mice produce an additional acute phase SAA, SAA3, which is thought to be produced mainly by adipocytes and macrophages and has not previously been found circulating on HDL. The goal of this study was to investigate whether SAA3 serves as a third liver-derived, HDL-associated acute phase SAA in mice. Using isoform-specific oligonucleotide primers for qRT-PCR, we determined that SAA3 is transcriptionally induced to a similar extent (~2500-fold) compared to SAA1.1/2.1 (~6000-fold) in livers of C57BL/6 mice 19 hr after lipopolysaccharide (LPS) injection (100 μg/mouse). SAAs were also robustly induced in fat tissue (SAA1/2~100-fold; SAA3~400-fold). The analysis of primary mouse hepatocytes and in situ hybridization of mouse liver sections indicated that liver-derived SAAs are produced by hepatocytes and not other stromal cells, including Kupffer cells. All 3 SAA isoforms were detected in plasma of LPS-injected mice, although SAA3 levels were ~20% of SAA1/2. After separation by FPLC, virtually all of plasma SAA1/2 eluted with the HDL fraction, whereas ~15% of plasma SAA3 appeared to be lipid poor/free. HDL isolated from acute phase mouse plasma by density gradient ultracentrifugation was subjected to isoelectric focusing to determine the relative recovery of the various SAA isoforms. Whereas the bulk of plasma SAA1.1 was found in the d=1.063-1.21 fraction, only ~50% of SAA2.1 and ~10% of SAA3 was recovered after ultracentrifugation. These findings suggest that SAA3 may be more loosely associated with HDL compared to SAA1.1/2.1, which may give rise to lipid poor/free SAA3 that is susceptible to more rapid clearance in vivo. We conclude that SAA3 is a major hepatic acute phase SAA in mice that may produce systemic effects during inflammation. Future studies investigating SAA pathobiology in mice must take into account the previously under-studied SAA3.

Objective— Although elevated plasma concentrations of serum amyloid A (SAA) are associated strongly with increased risk for atherosclerotic cardiovascular disease in humans, the role of SAA in the pathogenesis of lesion formation remains obscure. Our goal was to determine the impact of SAA deficiency on atherosclerosis in hypercholesterolemic mice. Approach and Results— Apolipoprotein E–deficient (apoE −/− ) mice, either wild type or deficient in both major acute phase SAA isoforms, SAA1.1 and SAA2.1, were fed a normal rodent diet for 50 weeks. Female mice, but not male apoE−/− mice deficient in SAA1.1 and SAA2.1, had a modest increase (22%; P ≤0.05) in plasma cholesterol concentrations and a 53% increase in adipose mass compared with apoE−/− mice expressing SAA1.1 and SAA2.1 that did not affect the plasma cytokine levels or the expression of adipose tissue inflammatory markers. SAA deficiency did not affect lipoprotein cholesterol distributions or plasma triglyceride concentrations in either male or female mice. Atherosclerotic lesion areas measured on the intimal surfaces of the arch, thoracic, and abdominal regions were not significantly different between apoE−/− mice deficient in SAA1.1 and SAA2.1 and apoE−/− mice expressing SAA1.1 and SAA2.1 in either sex. To accelerate lesion formation, mice were fed a Western diet for 12 weeks. SAA deficiency had effect neither on diet-induced alterations in plasma cholesterol, triglyceride, or cytokine concentrations nor on aortic atherosclerotic lesion areas in either male or female mice. In addition, SAA deficiency in male mice had no effect on lesion areas or macrophage accumulation in the aortic roots. Conclusions— The absence of endogenous SAA1.1 and 2.1 does not affect atherosclerotic lipid deposition in apolipoprotein E–deficient mice fed either normal or Western diets.

The “response-to-retention” hypothesis of atherogenesis states that atherogenic lipoproteins, such as low density lipoprotein (LDL), are retained in vessels by proteoglycans and undergo proatherosclerotic modifications. Transforming growth factor (TGF)-β1 has been identified in atherosclerotic vessels and has been shown to stimulate the synthesis of chondroitin sulfate– and dermatan sulfate–containing proteoglycans by arterial smooth muscle cells (ASMCs), but whether it promotes lipid retention has not been addressed. We investigated whether TGF-β1 modulates the biosynthesis of proteoglycans by ASMCs in a manner that promotes binding to LDL. Proteoglycans isolated from TGF-β1–treated ASMCs exhibited enhanced binding to native LDL compared with the binding of proteoglycans isolated from control cultures ( K d 18 μg/mL LDL versus 81 μg/mL LDL, respectively). The increase in proteoglycan-LDL binding caused by TGF-β1 could be attributed primarily to the glycosaminoglycan portion of the proteoglycans, since the glycosaminoglycan chains liberated from the core proteins of these proteoglycans synthesized in the presence of TGF-β1 exhibited increased LDL binding as well. Furthermore, glycosaminoglycan chains initiated on xyloside (an initiator of glycosaminoglycan synthesis) in the presence of TGF-β1 were longer and displayed enhanced binding to LDL compared with the LDL binding of xyloside-initiated glycosaminoglycan chains from control cultures. These results indicate that TGF-β1 promotes LDL-proteoglycan interaction primarily by its effects on the glycosaminoglycan synthetic machinery of the ASMCs. Therefore, this study supports a proatherogenic role for TGF-β1.

Atherosclerosis is the leading cause of death worldwide. As outlined in the Response to Retention hypothesis proteoglycan mediated lipid retention in the vascular wall is thought to be a major cause of atherosclerosis. We and others demonstrated co-localization of the vascular wall matrix proteoglycan biglycan with apoB containing lipoproteins within lesions. Furthermore, we have previously shown that increased biglycan leads to increased atherosclerosis. Thus we hypothesized that biglycan deficiency would attenuate the development of atherosclerosis. Biglycan deficient mice on a mixed genetic background were crossed with LDL receptor deficient mice (C57Bl6). Biglycan deficient and wildtype LDLr-/- mice were fed a 0.12% cholesterol diet for 26 weeks. There were no differences in blood glucose, blood pressure, or triglycerides between genotypes. Total cholesterol progressively increased in both groups over the course of the study and was significantly higher in biglycan deficient compared to wildtype mice at 26 weeks (p

Inflammation is involved in all stages of the development of an atherosclerotic plaque. Serum amyloid A (SAA), a marker of inflammation, is a well-known predictor of increased cardiovascular risk. Although elevated levels of plasma SAA have been associated with increased atherosclerosis, the role of SAA in the pathogenesis of atherosclerosis remains obscure. To investigate the impact of endogenous SAA in the etiology of atherosclerosis we bred mice lacking both major acute phase SAA isoforms SAA1.1 and SAA2.1 to apoE-/- mice. Both strains were in the C57BL/6 background. For ease of terminology we refer to these mice as SAAKO and apoE-/- mice. Aortic atherosclerotic lesion areas were quantified by en face analysis in male and female mice fed normal chow for 12 months. Although female mice weighed less and had lower plasma lipid levels than male mice, the absence of SAA did not affect plasma lipid concentrations or lipoprotein-cholesterol profiles or the size of aortic atherosclerotic lesions of apoE-/- mice. To accelerate lesion formation, male and female apoE-/- and SAAKO mice were fed a Western diet for 12 weeks. We observed gender-related differences in body weight, weight gain and plasma lipid concentrations. However, absence of SAA in apoE-/- mice fed a diet enriched in saturated fat had no discernable effect on plasma lipid concentrations, lipoprotein-cholesterol profiles or the size of the aortic atherosclerotic lesions. Lesions in the aortic root of male mice, quantitated by oil red O staining, was also not affected by genotype. We conclude that absence of endogenous acute phase SAA does not impact atherosclerotic lesion development in apoE-/- mice fed normal or fat-enriched diets.

Background Proteoglycans play a critical role in the development of atherosclerosis due to their ability to bind and retain atherogenic lipoproteins. Of all the vascular proteoglycans, biglycan has been shown to be the one most closely associated with apolipoprotein B. Our previous studies showed that angII increases vascular biglycan content and predisposes to diet-induced atherosclerosis in Ldlr null mice. The purpose of this study was to determine whether biglycan deficiency protected against angII induced atherosclerosis in vivo. Methods and Results Bgn KO or WT mice, crossed to Ldlr null (C57B/6 background), were infused with angII (1000 ng/kg/min) or saline for 28 days followed by 6-week western diet feeding. Bgn KO mice showed no difference in atherosclerotic lesion area at either aortic sinus or en face surface. Unexpectedly, Bgn KO mice exhibited a striking mortality (77% for males and 48% for females) due to aortic rupture upon angII infusion. Thus, a lower dose of angII was then infused to mice to study atherosclerosis. There was no difference in lesion area between Bgn KO or WT mice under angII (500 ng/kg/min) infusion followed by 6-week western diet feeding or under one-year normal chow feeding without angII infusion. However, angII (500 ng/kg/min) still induced greater aortic rupture in Bgn KO mice (30% for males and 13% for females) than in WT mice (0% for both gender). Besides rupture, 7 Bgn KO mice out of 35 also developed aneurysm at mid-thoracic aorta whereas only 1 Bgn WT mouse out of 25 developed abdominal aneurysm after angII (500 ng/kg/min) infusion. Therefore, our study demonstrated that biglycan deficiency did not affect atherosclerotic lesion development, but induced a striking aneurysm phenotype upon angII infusion.

Serum amyloid A (SAA), along with high sensitivity C- Reactive Protein, is a clinical marker of atherosclerosis, the leading cause of death in westernized countries. SAA is modestly but chronically elevated in several diseases such as diabetes and obesity that confer greater risk to developing atherosclerosis. It was recently reported that elevated SAA is pro-atherogenic in a murine model, although the mechanisms remain unclear. As outlined in the response to retention hypothesis, proteoglycan mediated lipoprotein retention is thought to be a key step in the initiation of atherosclerosis. We previously demonstrated in vitro that vascular smooth muscle cells treated with SAA had increased vascular biglycan synthesis with increased LDL binding affinity. We further demonstrated that SAA stimulation of biglycan was mediated via induction of TGF-β. To evaluate the pro-atherogenic effects of SAA in vivo, ApoE-/- male mice were injected with an adenovirus carrying the gene for human SAA1 (adSAA), a null control (adNull) or saline and maintained on chow for 16 weeks. SAA was elevated immediately after injection of adSAA but returned to baseline by 10 days. Although the SAA elevation was short, mice injected with adSAA had increased vascular biglycan content and significantly increased atherosclerosis at the aortic sinus (p

Clinical studies demonstrate less atherosclerosis in pre-menopausal women compared to age-matched men, but an equalization in atherosclerosis burden and cardiovascular event rates between genders following menopause. Conversely, using the LDLR−/− mouse model we and others have previously demonstrated that young female mice develop accelerated atherosclerosis compared to age matched males. Whether this difference is due to sex hormones or differences in metabolic factors is not clear. To determine if estrogen mediated the alterations in atherosclerosis in the female mice, female mice were ovariectomized (Ovx). Ovx mice had a marked reduction in uterus weight (Sham: 86 ± 1 vs Ovx: 26 ± 1mg, P < 0.001) and both Ovx females and males had greater body weight gain when fed a lard-enriched diet (10% kcal from fat, D12451 , Research Diets) for 17 weeks compared to sham females. Ovariectomy resulted in an increase in fasting glucose concentrations, which was comparable to males. Cholesterol and triglyceride concentrations were higher in both sham and Ovx females compared to males; primarily distributed in increased VLDL and LDL particles. Interestingly, ovariectomy had no significant effect on extent of atherosclerotic lesion formation in female mice and the extent of atherosclerotic lesion area in both female groups was significantly increased compared to male mice. These data suggest that gender specific differences in lipids and atherosclerotic lesion formation in female LDL-R deficient mice fed a diet enriched in lard are not mediated by estrogen.