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ABCC6 deficiency promotes ectopic calcification; however, circumstantial evidence suggested that ABCC6 may also influence atherosclerosis. The present study addressed the role of ABCC6 in atherosclerosis using Ldlr−/− mice and pseudoxanthoma elasticum (PXE) patients. Mice lacking the Abcc6 and Ldlr genes were fed an atherogenic diet for 16 weeks before intimal calcification, aortic plaque formation and lipoprotein profile were evaluated. Cholesterol efflux and the expression of several inflammation, atherosclerosis and cholesterol homeostasis-related genes were also determined in murine liver and bone marrow-derived macrophages. Furthermore, we examined plasma lipoproteins, vascular calcification, carotid intima-media thickness and atherosclerosis in a cohort of PXE patients with ABCC6 mutations and compared results to dysmetabolic subjects with increased cardiovascular risk. We found that ABCC6 deficiency causes changes in lipoproteins, with decreased HDL cholesterol in both mice and humans, and induces atherosclerosis. However, we found that the absence of ABCC6 does not influence overall vascular mineralization induced with atherosclerosis. Decreased cholesterol efflux from macrophage cells and other molecular changes such as increased pro-inflammation seen in both humans and mice are likely contributors for the phenotype. However, it is likely that other cellular and/or molecular mechanisms are involved. Our study showed a novel physiological role for ABCC6, influencing plasma lipoproteins and atherosclerosis in a haploinsufficient manner, with significant penetrance.

Chronic hepatitis C infection is a major cause of liver cancer in the United States. Hawai‘i’s incidence of liver cancer consistently ranks among the highest in the US, due in part to the high prevalence of hepatitis B in the state. To better understand the factors associated with liver cancer among patients in Hawai‘i with hepatitis C virus (HCV) infection, the patient database of Kaiser Permanente’s Hawai’i region was used to identify a cohort of 3198 patients with a history of chronic HCV infection, of whom 159 (5%) were diagnosed with liver cancer between the years 2004-2020. Multiple logistic regression was used to identify factors independently associated with liver cancer. Male sex (AOR 2.02, 95% CI 1.34-3.06), Asian race (AOR 1.78, 1.16 - 2.74) and hepatitis B core antibody (HBCAB) positivity (AOR 1.76, 95% CI 1.25 - 2.49) emerged as independent predictors of liver cancer among patients with chronic HCV infection. A history of diabetes (AOR 1.56, 1.07 - 2.27) and older age at the time of HCV diagnosis (AOR 1.19, 1.09-1.29) also emerged as significant associations. HBCAB-positive individuals did not differ significantly from those who were HBCAB-negative in regards to demographics or 5-year survival rate. In this cohort of patients with chronic HCV, a positive HBCAB without evidence of active hepatitis B infection was associated with 1.76 increased odds of liver cancer compared to those with negative HBCAB. This finding may have important implications for screening algorithms among individuals with hepatitis C infection.

Pure ethane ices (C2H6) were irradiated at 10, 30, and 50 K under contamination-free, ultrahigh vacuum conditions with energetic electrons generated in the track of galactic cosmic-ray (GCR) particles to simulate the interaction of GCRs with ethane ices in the outer solar system. The chemical processing of the samples was monitored by a Fourier transform infrared spectrometer and a quadrupole mass spectrometer during the irradiation phase and subsequent warm-up phases on line and in situ in order to extract qualitative (products) and quantitative (rate constants and yields) information on the newly synthesized molecules. Six hydrocarbons, methane (CH4), acetylene (C2H2), ethylene (C2H4), and the ethyl radical (C2H5), together with n-butane (C4H10) and butene (C4H8), were found to form at the radiation dose reaching 1.4 eV per molecule. The column densities of these species were quantified in the irradiated ices at each temperature, permitting us to elucidate the temperature and phase-dependent production rates of individual molecules. A kinetic reaction scheme was developed to fit column densities of those species produced during irradiation of amorphous/crystalline ethane held at 10, 30, or 50 K. In general, the yield of the newly formed molecules dropped consistently for all species as the temperature was raised from 10 K to 50 K. Second, the yield in the amorphous samples was found to be systematically higher than in the crystalline samples at constant temperature. A closer look at the branching ratios indicates that ethane decomposes predominantly to ethylene and molecular hydrogen, which may compete with the formation ofn-butane inside the ethane matrix. Among the higher molecular products, n-butane dominates. Of particular relevance to the atmosphere of Saturn’s moon Titan is the radiation-induced methane production from ethane—an alternative source of replenishing methane into the atmosphere. Finally, we discuss to what extent the n-butane could be the source of “higher organics” on Titan’s surface thus resembling a crucial sink of condensed ethane molecules.

Introduction: Vascular calcification is associated with aging and common conditions such as hypercholesterolemia and certain genetic disorders. A molecular pathway inhibiting ectopic calcification is initiated by ABCC6, a membrane transporter primarily expressed in liver. ABCC6 facilitates the cellular efflux of ATP from hepatocytes, which is rapidly converted into pyrophosphate (PPi) in the liver vasculature. ABCC6 is responsible for the majority of the PPi release from the liver, and ~60% of plasma PPi in both in humans and mice. As PPi is a major inhibitor of calcification, mutations in ABCC6 underlie the currently incurable calcification disorder pseudoxanthoma elasticum (PXE), some cases of generalized arterial calcification of infancy (GACI). Hypothesis: Multiple lines of evidence have suggested a pathological synergy between ABCC6 and hyperlipidemia. Methods: We examined crosses between Abcc6-/- and Ldlr-/- mice and serum samples from human PXE patients. Three mouse genotypes were generated Ldlr-/-, Ldlr-/-xAbcc6-/- and Ldlr-/- xAbcc6+/-. Results: When subjected to a high fat diet, mice with reduced or no Abcc6 expression displayed a 2-fold increase of atherosclerotic plaque area (p=0.0001). Interestingly, atherosclerotic plaque was also found in Abcc6-deficient mice fed a normal diet but not in control Ldlr-/- animals. Aortic calcification was not significantly affected by Abcc6 expression except in Ldlr-/-xAbcc6-/- mice fed regular chow (p=0.0001). We observed an increased proliferation of smooth muscle cells of but no increase in monocyte-macrophage infiltration in the plaque of Ldlr-/-xAbcc6-/- mice. Importantly, we determined that the cholesterol efflux from isolated macrophages towards HDL (mediated by ABCG1) was significantly decreased (-28%, p=0.006) in Ldlr-/-xAbcc6-/- mice while the efflux towards ApoA1 (mediated by ABCA1) was unchanged. The analysis of high-density lipoprotein (HDL) and low-density lipoprotein (LDL) fractions in these mice showed altered profiles similar to those found with human PXE plasma samples. Conclusions: Our results indicated that, in addition to being an important inhibitor of vascular calcification, ABCC6 inhibits atherogenesis by modulating reverse cholesterol transport.

International audience; Pseudoxanthoma elasticum (PXE) is a heritable disease characterized by calcified elastic fibers in cutaneous, ocular, and vascular tissues. PXE is caused by mutations in ABCC6, which encodes a protein of the ATP-driven organic anion transporter family. The inability of this transporter to secrete its substrate into the circulation is the likely cause of PXE. Vitamin K plays a role in the regulation of mineralization processes as a co-factor in the carboxylation of calcification inhibitors such as Matrix Gla Protein (MGP). Vitamin K precursor or a conjugated form has been proposed as potential substrate(s) for ABCC6. We investigated whether an enriched diet of vitamin K1 or vitamin K2 (MK4) could stop or slow the disease progression in Abcc6 (-/-) mice. Abcc6 (-/-) mice were placed on a diet of either vitamin K1 or MK4 at 5 or 100 mg/kg at prenatal, 3 weeks or 3 months of age. Disease progression was quantified by measuring the calcium content of one side of the mouse muzzle skin and histological staining for calcium of the opposing side. Raising the vitamin K1 or MK4 content of the diet increased the concentration of circulating MK4 in the serum. However, this increase did not significantly affect the MGP carboxylation status or reduce its abnormal abundance, the total calcium content or the pathologic calcification in the whiskers of the 3 treatment groups compared to controls. Our findings showed that raising the dietary intake of vitamin K1 or MK4 was not beneficial in the treatment of PXE and suggested that the availability of vitamin K may not be a limiting factor in this pathology.

Mutations in the ABCC6 gene cause soft-tissue calcification in pseudoxanthoma elasticum (PXE) and, in some patients, generalized arterial calcification of infancy (GACI). PXE is characterized by late onset and progressive mineralization of elastic fibers in dermal, ocular, and cardiovascular tissues. GACI patients present a more severe, often prenatal arterial calcification. We have tested 10 frequent disease-causing ABCC6 missense mutants for the transport activity by using Sf9 (Spodoptera frugiperda) cells, characterized the subcellular localization in MDCKII (Madin–Darby canine kidney (cell line)) cells and in mouse liver, and tested the phenotypic rescue in zebrafish. We aimed at identifying mutants with preserved transport activity but with improper plasma membrane localization for rescue by the chemical chaperone 4-phenylbutyrate (4-PBA). Seven of the mutants were transport-competent but mislocalized in mouse liver. The observed divergence in cellular localization of mutants in MDCKII cells versus mouse liver underlined the limitations of this 2D in vitro cell system. The functionality of ABCC6 mutants was tested in zebrafish, and minimal rescue of the morpholino-induced phenotype was found. However, 4-PBA, a drug approved for clinical use, restored the plasma membrane localization of four ABCC6 mutants (R1114P, S1121W, Q1347H, and R1314W), suggesting that allele-specific therapy may be useful for selected patients with PXE and GACI.