SAA1 deletion ameliorates cardiac injury after myocardial infarction by promoting macrophage transformation to reparative subtype.

BACKGROUND

The regulation of M1/M2 macrophage phenotypic conversion is an effective therapeutic strategy for post-myocardial infarction (MI). Serum Amyloid A1 (SAA1) is an acute-phase protein that plays an important role in regulating inflammatory responses. However, its function in modulating macrophage polarization post-MI remains unclear.

METHODS

To achieve macrophage-specific manipulation of SAA1 expression in vivo, adeno-associated virus 9 (AAV9) vectors driven by a macrophage-specific promoter (F4/80) were used to either knockdown (AAV9-F4/80-sh-SAA1) or overexpress (AAV9-F4/80-SAA1) SAA1. Two weeks after the virus injection, mice underwent MI and ischemia-reperfusion (I/R) surgery. Each group included six mice. Immunofluorescence (IF), western blotting, and quantitative real-time polymerase chain reaction were performed to explore the mechanisms underlying SAA1-induced macrophage polarization and cardiac injury after MI and I/R. SAA1 was overexpressed and knocked down in lipopolysaccharide-stimulated bone marrow-derived macrophages in vitro using plasmids and siRNA. IF, western blotting, and quantitative real-time polymerase chain reaction were used to measure macrophage polarization and inflammatory responses.

RESULTS

We detected a significant increase in SAA1 levels in human and mouse peripheral blood mononuclear cells after MI and I/R. Following SAA1 knockout, left ventricular ejection fraction (64.33 ± 2.35 % versus 40.97 ± 8.36 %) was significantly improved and infarcted size (93.95 ± 3.79 % versus 29.76 ± 17.05 %) was markedly reduced in MI+AAV-9-F4/80-Sh-SAA1 compared with MI+AAV-9-F4/80-Sh-NC. Similarly, the accumulation of M1 macrophages in the infarcted tissues was reduced by SAA1 deletion. Mechanistically, these effects were partially mediated by inhibition of via the p38 MAPK signaling pathway.

CONCLUSION

SAA1 activated the p38 MAPK pathway to contribute to macrophage polarization and the release of inflammatory factors and subsequently exacerbated cardiac injury and inflammatory response post-MI and I/R.