Background: Obesity is a risk factor of hypertension and abdominal aortic aneurysm (AAA). Melanocortin 4 receptor (MC4R) is activated by α-melanocyte-stimulating hormone (α-MSH) to mediate most of the anorectic effects of leptin. In humans, deficiency or mutation of MC4R is the most common monogenic form of obesity. However, it remains unknown whether MC4R signaling affects the development of obesity-associated hypertension, vascular vulnerability and aortic aneurysm.

Methods and Results: MC4R-knockout (KO) mice fed a high-fat/high-sucrose diet (HF/HS) for 20 weeks displayed obesity associated with hyperleptinemia compared to HF/HS-fed wild type (WT) mice. MC4R-KO mice exhibited hypertension, increase of medial thickness and elastic lamina destruction, and elevation of inflammatory and fibrosis-related genes including TGF-β and osteopontin (OPN) in aortae. MC4R-KO mice showed higher incidence of angiotensin II (Ang II, 500 ng/kg/min)-induced AAA (73%) than WT mice (8%). MC4R-KO mice with ob/ob background exhibited lower incidence of Ang II-induced AAA (50%) than MC4R-KO mice, but higher than ob/ob mice (12.5%). Treatment of OPN-blocking antibody decreased Ang II-induced AAA incidence in HF/HS-fed MC4R-KO mice. In vascular smooth muscle cells (VSMCs), leptin (100 ng/ml) significantly upregulated OPN gene expression. α-MSH suppressed AngII-induced TGF-β gene expression in VSMCs, and LPS/IFN-γ-induced iNOS gene expression in peritoneal macrophages. However, these effects of α-MSH were abolished in primary macrophages from MC4R-KO mice and RAW264.7 cells pretreated with MC4R antagonist HS024.

Conclusion: Our observation indicates that deficiency of MC4R promotes the vascular vulnerability in mice. It suggests that, not only hyperleptinemia, but also impairment of α-MSH-MC4R signaling in VSMCs and macrophages, may also promote the vascular vulnerability.


K. Mori: None. K. Tsuchiya: None. S. Nakamura: None. K. Shiba: None. Y. Miyachi: None. Y. Ogawa: None. K. Kitamura: None.

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