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Low-molecular mass protein 7 (LMP7) is a proteolytic subunit of the immunoproteasome that is involved in regulating inflammatory responses. However, the role of LMP7 in the pathogenesis of abdominal aortic aneurysm (AAA) remains unknown. In this study, ApoE knockout (KO) or LMP7/ApoE double KO (dKO) mice were infused with angiotensin II (Ang II, 1000 ng/kg per minute) for up to 28 d. We found that LMP7 expression was significantly upregulated in AAA tissues from ApoE KO mice and human patients. Moreover, Ang II infusion markedly increased the incidence and severity of AAA in ApoE KO mice, which was considerably reduced in LMP7/ApoE dKO mice. Histological alterations, including aortic wall thickening, collagen deposition, elastin fragmentation, and vascular smooth muscle cell apoptosis in AAA tissue of ApoE KO mice, were also significantly attenuated in LMP7/ApoE dKO mice. Interestingly, LMP7/ApoE dKO mice showed a marked reduction of infiltration of CD3+ T cells, especially CD4+ T cells in AAA tissues compared with ApoE KO mice. Moreover, ablation of LMP7 substantially inhibited the differentiation of CD4+ T cells into Th1 and Th17 cells by reducing the activation of multiple transcriptional factors. We also investigated the effects of an LMP7-specific inhibitor PR-957 (also known as ONX 0914) on AAA formation in ApoE KO mice. PR-957 treatment could reduce the AAA incidence and severity. In conclusion, our results provide, to our knowledge, novel evidence that ablation or pharmacological inhibition of LMP7 attenuates Ang II-induced AAA formation, and LMP7 might be a novel therapeutic target for treating AAA in humans. [ABSTRACT FROM AUTHOR]

BACKGROUND: The recruitment of leukocytes to the vascular wall is a key step in hypertension development. Chemokine receptor CXCR2 mediates inflammatory cell chemotaxis in several diseases. However, the role of CXCR2 in hypertension development and the underlying mechanisms remain unknown. METHODS: Angiotensin II (490 ng x kg-1 x min-1) or deoxycorticosterone acetate (DOCA) salt-induced mouse hypertensive models in genetic ablation, pharmacologic inhibition of CXCR2, and adoptive bone marrow transfer mice were used to determine the role of CXCR2 in hypertension (measured by radiotelemetry and tail-cuff system), inflammation (verified by flow cytometry and quantitative real-time polymerase chain reaction [PCR] analysis), vascular remodeling (studied by haematoxylin and eosin and Masson's trichrome staining), vascular dysfunction (assessed by aortic ring), and oxidative stress (indicated by nicotinamide adenine dinucleotide phosphate [NADPH] oxidase activity, dihydroethidium staining, and quantitative real-time PCR analysis). Moreover, the blood CXCR2+ cells in normotensive controls and hypertension patients were analyzed by flow cytometry. RESULTS: Angiotensin II significantly upregulated the expression of CXCR2 mRNA and protein and increased the number of CD45+ CXCR2+ cells in mouse aorta (n=8 per group). Selective CXCR2 knockout (CXCR2-/-) or pharmacological inhibition of CXCR2 markedly reduced angiotensin II- or DOCA-salt-induced blood pressure elevation, aortic thickness and collagen deposition, accumulation of proinflammatory cells into the vascular wall, and expression of cytokines (n=8 per group). CXCR2 inhibition also ameliorated angiotensin II-induced vascular dysfunction and reduced vascular superoxide formation, NADPH activity, and expression of NADPH oxidase subunits (n=6 per group). Bone marrow reconstitution of wild-type mice with CXCR2-/- bone marrow cells also significantly abolished angiotensin II-induced responses (n=6 per group). It is important to note that CXCR2 blockade reversed established hypertension induced by angiotensin II or DOCA-salt challenge (n=10 per group). Furthermore, we demonstrated that CXCR2+ proinflammatory cells were higher in hypertensive patients (n=30) compared with normotensive individuals (n=20). CONCLUSIONS: Infiltration of CXCR2+ cells plays a pathogenic role in arterial hypertension and vascular dysfunction. Inhibition of CXCR2 pathway may represent a novel therapeutic approach to treat hypertension. [ABSTRACT FROM AUTHOR]