Inactivation of PI3Kδ induces vascular injury and promotes aneurysm development by upregulating the AP-1/MMP-12 pathway in macrophages

Objective: An aneurysm is an inflammatory vascular condition. Phosphatidylinositol 3-kinases δ is highly expressed in leukocytes, and play a key role in innate immunity. However, the link between phosphatidylinositol 3-kinases δ and aneurysm development has not yet been elucidated.

Approach and results: Carotid ligation unexpectedly induced characteristic aneurysm formation beneath the ligation point in p110δ(D910A/D910A) mice (n=25; P<0.001 versus wild-type). Besides, p110δ inactivation exacerbated CaCl2-induced abdominal aortic aneurysms development. A reverse transcription polymerase chain reaction microarray revealed significant extracellular matrix components degradation and Matrix Metalloproteinases (MMPs) upregulation in the abdominal aorta of p110δ(D910A/D910A) mice. Similarly, the expression of both collagen I and IV was significantly decreased (n=10; P<0.05 versus wild-type) in carotid artery. Western blot assay confirmed that MMP-12 was significantly upregulated in arteries of p110δ(D910A/D910A) mice (n=10; P<0.01 versus wild-type). In vitro, p110δ inactivation marked increase peritoneal macrophages recruitment and synergistically enhance tumor necrosis factor-α-induced recruitment. A specific phosphatidylinositol 3-kinases δ inhibitor (IC87114) or genetic p110δ inactivation upregulated MMP-12 expression and c-Jun phosphorylation (n=6; P<0.05 versus wild-type macrophages). IC87114 also increased activator protein-1 DNA-binding activity (n=6; P<0.001 versus control) and enhanced the effect of tumor necrosis factor-α on activator protein-1-binding activity (n=5; P<0.01 versus tumor necrosis factor-α treatment groups). Knockdown of c-Jun suppressed the effect of the IC87114 and tumor necrosis factor-α on MMP-12 mRNA expression (n=5 in each group; P<0.01 versus scrRNA treatment groups).

Conclusions: Our findings demonstrate that p110δ inactivation leads to extracellular matrix degradation in vessels and promotes aneurysm development by inducing macrophages migration and upregulating the activator protein-1/MMP-12 pathway in macrophages.