Background: Duchenne muscular dystrophy (DMD) is caused by loss of dystrophin expression and leads to severe ambulatory and cardiac function decline. However, the dystrophin-deficient mdx murine model of DMD only develops a very mild form of the disease. Our group and others have shown vascular abnormalities in animal models of MD, a likely consequence of the fact that blood vessels express the same dystrophin-associated glycoprotein complex (DGC) proteins as skeletal muscles. Methods: To test the blood vessel contribution to muscle damage in DMD, mdx 4cv mice were given elevated lipid levels via apolipoprotein E (ApoE) gene knockout combined with normal chow or lipid-rich Western diets. Ambulatory function and heart function (via echocardiogram) were assessed at 4 and 7 months of age. After sacrifice, muscle histology and aortic staining were used to assess muscle pathology and atherosclerosis development, respectively. Plasma levels of total cholesterol, high-density lipoprotein (HDL), triglycerides, and creatine kinase (CK) were also measured. Results: Although there was an increase in left ventricular heart volume in mdx-ApoE mice compared to that in mdx mice, parameters of heart function were not affected. Compared with wild-type and ApoE-null, only mdx-ApoE KO mice showed significant ambulatory dysfunction. Despite no significant difference in plasma CK, histological analyses revealed that elevated plasma lipids in chow-and Western diet-fed mdx-ApoE mice was associated with severe exacerbation of muscle pathology compared to mdx mice: significant increase in myofiber damage and fibrofatty replacement in the gastrocnemius and triceps brachii muscles, more reminiscent of human DMD pathology. Finally, although both ApoE and mdx-ApoE groups displayed increased plasma lipids, mdx-ApoE exhibited atherosclerotic plaque deposition equal to or less than that of ApoE mice. Conclusions: Since others have shown that lipid abnormalities correlate with DMD severity, our data suggest that plasma lipids could be primary contributors to human DMD severity and that the notoriously mild phenotype of mdx mice might be attributable in part to their endogenously low plasma lipid profiles. Hence, DMD patients may benefit from lipid-lowering and vascular-targeted therapies.

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Marfan syndrome (MFS) is a connective tissue disorder caused by mutations in fibrillin-1 (Fbn1). Although aortic rupture is the major cause of mortality in MFS, patients also experience pulmonary complications, which are poorly understood. Loss of basal nitric oxide (NO) production and vascular integrity has been implicated in MFS aortic root disease, yet their contribution to lung complications remains unknown. Because of its capacity to potentiate the vasodilatory NO/cyclic guanylate monophosphate signaling pathway, we assessed whether the phosphodiesterase-5 inhibitor, sildenafil (SIL), could attenuate aortic root remodeling and emphysema in a mouse model of MFS. Despite increasing NO-dependent vasodilation, SIL unexpectedly elevated mean arterial blood pressure, failed to inhibit MFS aortic root dilation, and exacerbated elastic fiber fragmentation. In the lung, early pulmonary artery dilation observed in untreated MFS mice was delayed by SIL treatment, and the severe emphysema-like alveolar destruction was prevented. In addition, improvements in select parameters of lung function were documented. Subsequent microarray analyses showed changes to gene signatures involved in the inflammatory response in the MFS lung treated with SIL, without significant down-regulation of connective tissue or transforming growth factor-b signaling genes. Because phosphodiesterase-5 inhibition leads to improved lung histopathology and function, the effects of SIL against emphysema warrant further investigation in the settings of MFS despite limited efficacy on aortic root remodeling.