Serum amyloid A3 is pro-atherogenic

Abstract

Background and aims: Serum amyloid A (SAA) predicts cardiovascular events. Overexpression of SAA increases atherosclerosis development; however, deficiency of two of the murine acute phase isoforms, SAA1.1 and SAA2.1, has no effect on atherosclerosis. SAA3 is a pseudogene in humans, but is an expressed acute phase isoform in mice. The goal of this study was to determine if SAA3 affects atherosclerosis in mice.

Methods: ApoE^-/- mice were used as the model for all studies. SAA3 was overexpressed by an adeno-associated virus or suppressed using an anti-sense oligonucleotide approach.

Results: Over-expression of SAA3 led to a 4-fold increase in atherosclerosis lesion area compared to control mice (p = 0.01). Suppression of SAA3 decreased atherosclerosis in mice genetically deficient in SAA1.1 and SAA2.1 (p < 0.0001).

Conclusions: SAA3 augments atherosclerosis in mice. Our results resolve a previous paradox in the literature and support extensive epidemiological data that SAA is pro-atherogenic.

Keywords: Atherosclerosis; Inflammation; Murine models.

Fig. 1. SAA3 is pro-atherogenic

(A) ApoE^−/− [SAA wildtype (WT)] or apoE^−/− × SAA1.1/2.1-DKO mice were fed a western diet for 12 weeks as described in. Aortic root sections from apoE^−/− (panels 1,3) or apoE^−/− × SAA1.1/2.1-DKO (panels 2,4) mice fed a western diet for 12 weeks were stained for SAA. Shown are aortic root images representative of n=3/group magnified 10× with insets (panels 3,4) magnified 25×. Scale bars are 100 µm. Panels 5–9 are control apoE^−/− sections: IgG only, no primary, no secondary, no Ab, and SMA positive control respectively. (B) Liver sections from LPS-injected C57BL/6, SAA1.1/2.1-DKO and SAA1.1/2.1/3-TKO mice were stained for SAA. Images shown are magnified 40×; scale bars are 250 µm. (C) ApoE^−/− mice were injected with a control AAV or AAV expressing SAA3 and fed normal chow for 12 weeks. Plasma SAA3 was measured at weeks 0, 6, 12. Data shown is mean±SEM. (D) Atherosclerosis was quantified on the en face aorta, each symbol represents the atherosclerotic area for an individual mouse; horizontal lines represent the group mean. (E) apoE^−/− × SAA1.1/2.1-DKO mice were injected with a control ASO or an ASO to SAA3 and fed western diet for 12 weeks. SAA3 mRNA abundance in livers (arbitrary units, AU). Data shown is mean±SEM. (F) Atherosclerosis was quantified on the en face aorta, each symbol represents the atherosclerotic area for an individual mouse; horizontal lines represent the group mean (E).