The Role of Bone Morphogenetic Protein Signaling in Non-Alcoholic Fatty Liver Disease.

Non-alcoholic fatty liver disease (NAFLD) affects over 30% of adults in the United States. Bone morphogenetic protein (BMP) signaling is known to contribute to hepatic fibrosis, but the role of BMP signaling in the development of NAFLD is unclear. In this study, treatment with either of two BMP inhibitors reduced hepatic triglyceride content in diabetic (db/db) mice. BMP inhibitor-induced decrease in hepatic triglyceride levels was associated with decreased mRNA encoding Dgat2, an enzyme integral to triglyceride synthesis. Treatment of hepatoma cells with BMP2 induced DGAT2 expression and activity via intracellular SMAD signaling. In humans we identified a rare missense single nucleotide polymorphism in the BMP type 1 receptor ALK6 (rs34970181;R371Q) associated with a 2.1-fold increase in the prevalence of NAFLD. In vitro analyses revealed R371Q:ALK6 is a previously unknown constitutively active receptor. These data show that BMP signaling is an important determinant of NAFLD in a murine model and is associated with NAFLD in humans.

HDAC9 is implicated in atherosclerotic aortic calcification and affects vascular smooth muscle cell phenotype.

Aortic calcification is an important independent predictor of future cardiovascular events. We performed a genome-wide association meta-analysis to determine SNPs associated with the extent of abdominal aortic calcification (n = 9,417) or descending thoracic aortic calcification (n = 8,422). Two genetic loci, HDAC9 and RAP1GAP, were associated with abdominal aortic calcification at a genome-wide level (P < 5.0 × 10-8). No SNPs were associated with thoracic aortic calcification at the genome-wide threshold. Increased expression of HDAC9 in human aortic smooth muscle cells promoted calcification and reduced contractility, while inhibition of HDAC9 in human aortic smooth muscle cells inhibited calcification and enhanced cell contractility. In matrix Gla protein-deficient mice, a model of human vascular calcification, mice lacking HDAC9 had a 40% reduction in aortic calcification and improved survival. This translational genomic study identifies the first genetic risk locus associated with calcification of the abdominal aorta and describes a previously unknown role for HDAC9 in the development of vascular calcification.

Hepcidin Deficiency Protects Against Atherosclerosis.

Objective- Inflammatory stimuli enhance the progression of atherosclerotic disease. Inflammation also increases the expression of hepcidin, a hormonal regulator of iron homeostasis, which decreases intestinal iron absorption, reduces serum iron levels and traps iron within macrophages. The role of macrophage iron in the development of atherosclerosis remains incompletely understood. The objective of this study was to investigate the effects of hepcidin deficiency and decreased macrophage iron on the development of atherosclerosis. Approach and Results- Hepcidin- and LDL (low-density lipoprotein) receptor-deficient ( Hamp-/-/ Ldlr-/-) mice and Hamp+/+/ Ldlr-/- control mice were fed a high-fat diet for 21 weeks. Compared with control mice, Hamp-/-/ Ldlr-/- mice had decreased aortic macrophage activity and atherosclerosis. Because hepcidin deficiency is associated with both increased serum iron and decreased macrophage iron, the possibility that increased serum iron was responsible for decreased atherosclerosis in Hamp-/-/ Ldlr-/- mice was considered. Hamp+/+/ Ldlr-/- mice were treated with iron dextran so as to produce a 2-fold increase in serum iron. Increased serum iron did not decrease atherosclerosis in Hamp+/+/ Ldlr-/- mice. Aortic macrophages from Hamp-/-/ Ldlr-/- mice had less labile free iron and exhibited a reduced proinflammatory (M1) phenotype compared with macrophages from Hamp+/+/ Ldlr-/- mice. THP1 human macrophages treated with an iron chelator were used to model hepcidin deficiency in vitro. Treatment with an iron chelator reduced LPS (lipopolysaccharide)-induced M1 phenotypic expression and decreased uptake of oxidized LDL. Conclusions- In summary, in a hyperlipidemic mouse model, hepcidin deficiency was associated with decreased macrophage iron, a reduced aortic macrophage inflammatory phenotype and protection from atherosclerosis. The results indicate that decreasing hepcidin activity, with the resulting decrease in macrophage iron, may prove to be a novel strategy for the treatment of atherosclerosis.

Soluble epoxide hydrolase deficiency or inhibition enhances murine hypoxic pulmonary vasoconstriction after lipopolysaccharide challenge.

Hypoxic pulmonary vasoconstriction (HPV) is the response of the pulmonary vasculature to low levels of alveolar oxygen. HPV improves systemic arterial oxygenation by matching pulmonary perfusion to ventilation during alveolar hypoxia and is impaired in lung diseases such as the acute respiratory distress syndrome (ARDS) and in experimental models of endotoxemia. Epoxyeicosatrienoic acids (EETs) are pulmonary vasoconstrictors, which are metabolized to less vasoactive dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). We hypothesized that pharmacological inhibition or a congenital deficiency of sEH in mice would reduce the metabolism of EETs and enhance HPV in mice after challenge with lipopolysaccharide (LPS). HPV was assessed 22 h after intravenous injection of LPS by measuring the percentage increase in the pulmonary vascular resistance of the left lung induced by left mainstem bronchial occlusion (LMBO). After LPS challenge, HPV was impaired in sEH+/+, but not in sEH-/- mice or in sEH+/+ mice treated acutely with a sEH inhibitor. Deficiency or pharmacological inhibition of sEH protected mice from the LPS-induced decrease in systemic arterial oxygen concentration (PaO2 ) during LMBO. In the lungs of sEH-/- mice, the LPS-induced increase in DHETs and cytokines was attenuated. Deficiency or pharmacological inhibition of sEH protects mice from LPS-induced impairment of HPV and improves the PaO2 after LMBO. After LPS challenge, lung EET degradation and cytokine expression were reduced in sEH-/- mice. Inhibition of sEH might prove to be an effective treatment for ventilation-perfusion mismatch in lung diseases such as ARDS.

Calcification of Vascular Smooth Muscle Cells and Imaging of Aortic Calcification and Inflammation.

Cardiovascular disease is the leading cause of morbidity and mortality in the world. Atherosclerotic plaques, consisting of lipid-laden macrophages and calcification, develop in the coronary arteries, aortic valve, aorta, and peripheral conduit arteries and are the hallmark of cardiovascular disease. In humans, imaging with computed tomography allows for the quantification of vascular calcification; the presence of vascular calcification is a strong predictor of future cardiovascular events. Development of novel therapies in cardiovascular disease relies critically on improving our understanding of the underlying molecular mechanisms of atherosclerosis. Advancing our knowledge of atherosclerotic mechanisms relies on murine and cell-based models. Here, a method for imaging aortic calcification and macrophage infiltration using two spectrally distinct near-infrared fluorescent imaging probes is detailed. Near-infrared fluorescent imaging allows for the ex vivo quantification of calcification and macrophage accumulation in the entire aorta and can be used to further our understanding of the mechanistic relationship between inflammation and calcification in atherosclerosis. Additionally, a method for isolating and culturing animal aortic vascular smooth muscle cells and a protocol for inducing calcification in cultured smooth muscle cells from either murine aortas or from human coronary arteries is described. This in vitro method of modeling vascular calcification can be used to identify and characterize the signaling pathways likely important for the development of vascular disease, in the hopes of discovering novel targets for therapy.