P1244MILD DIFFERENCES IN CARDIAC CALCIFICATION BETWEEN WILD TYPE AND SCLEROSTIN KNOCKOUT MICE WITH CKD

Background and Aims Ectopic soft tissue calcifications, especially cardiovascular calcifications, are frequently observed in patients with chronic kidney disease (CKD) and are associated with increased morbidity and mortality. Sclerostin, a well-known inhibitor of bone formation, shows significantly increased serum levels in CKD patients. Since the process of ectopic calcification shares many similarities with physiological bone formation, we investigated a possible role for sclerostin in ectopic calcification development. Method CKD was induced in wild type (WT) (n=21) and sclerostin knockout (Sost ko) mice (n = 21), both on a C57Bl6/J background, by the alternate administration of a 0.30% and 0.15% adenine supplemented diet, containing 1% phosphate. A normal renal function control group receiving standard mouse chow (WT C57Bl6/J n = 8) was also included in the study. Serum creatinine and phosphate levels were measured at the start and end of the study to assess CKD development. At sacrifice, the calcium content of the kidneys, heart and aorta was determined by flame atomic absorption spectrometry. Results The adenine-supplemented diet led to a clear induction of CKD in both the Sost ko and wild type mice, as reflected by increased serum creatinine (0.38 ± 0.09 mg/dL in control mice vs 0.65 ± 0.18 mg/dL in adenine-exposed mice, p<0.0001) and phosphate levels (9.12 ± 1.16 mg/dL in control mice vs 19.03 ± 3.11 mg/dL in adenine-exposed mice, p<0.0001). The Sost ko and WT mice receiving the adenine diet, developed the same degree of renal failure, since there were no differences in serum levels of creatinine (p=0.0507) and phosphate (p=0.4890). Significantly higher amounts of calcium were measured in the kidney (0.05 ± 0.01 mg/g wet tissue vs 3.70 ± 2.00 mg/g wet tissue, p<0.0001) and the heart (0.03 ± 0.01 mg/g wet tissue vs 0.07 ± 0.04 mg/g wet tissue, p<0.0001) of adenine-exposed mice, compared to mice receiving the control diet. Furthermore, Sost ko mice had a significantly higher calcium content in the heart compared to the WT mice with renal failure (0.05 ± 0.03 mg/g wet tissue in WT mice vs 0.08 ± 0.05 mg/g wet tissue in Sost ko mice, p = 0.0029). No differences were observed in aortic calcium content between control mice and mice with renal failure. Conclusion In this study we managed to develop a mouse model of CKD-induced soft tissue calcification in the heart and kidneys of the animals, however no calcifications developed in the aorta. The higher calcium content that was observed in the heart of Sost ko mice compared to WT mice, might be an indication of a protective function of sclerostin during ectopic cardiac calcification