Background-Stromal cell-derived factor-1␣ (SDF-1␣) binding to its cognate receptor, CXCR4, regulates a variety of cellular functions such as stem cell homing, trafficking, and differentiation. However, the role of the SDF-1␣-CXCR4 axis in modulating myocardial ischemia/reperfusion injury is unknown. Methods and Results-In mice subjected to ischemic preconditioning, myocardial SDF-1␣ mRNA was found to be increased 3 hours later (PϽ0.05). Myocardial SDF-1␣ and CXCR4 mRNA and protein were found to be expressed in both cardiac myocytes and fibroblasts. SDF-1␣ production increased significantly after 1 or 4 hours of hypoxia and 18 hours of reoxygenation in cultured myocytes (PϽ0.05) but did not change in fibroblast cultures. In isolated myocytes, CXCR4 activation by SDF-1␣ resulted in increased phosphorylation of both ERK 1/2 and AKT and decreased phosphorylation of JNK and p38. Cultured myocytes pretreated with SDF-1␣ were resistant to hypoxia/reoxygenation damage, exhibiting less lactate dehydrogenase release, trypan blue uptake, and apoptotic cell death (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay) (PϽ0.05). This protective effect was blocked by the CXCR4 selective antagonist AMD3100. In vivo, administration of SDF-1␣ before 30 minutes of coronary occlusion followed by 4 hours of reperfusion decreased infarct size (PϽ0.05). The decrease in infarct size with SDF-1␣ administration also was blocked by AMD3100. Conclusions-We conclude that SDF-1␣ and its receptor, CXCR4, constitute a paracrine or autocrine axis in cardiac myocytes that is activated in response to preconditioning and hypoxic stimuli, recruiting the antiapoptotic kinases ERK and AKT and promoting an antiapoptotic program that confers protection against ischemia/reperfusion damage.

Pseudoxanthoma elasticum (PXE) is a heritable disorder of connective tissue, affecting mainly skin, eye and the cardiovascular system. PXE is characterized by dystrophic mineralization of elastic fibres. The condition is caused by loss of function mutations in ABCC6. We generated Abcc6 deficient mice (Abcc6-/-) by conventional gene targeting. As shown by light and electron microscopy Abcc6-/- mice spontaneously developed calcification of elastic fibres in blood vessel walls and in Bruch's membrane in the eye. No clear abnormalities were seen in the dermal extracellular matrix. Calcification of blood vessels was most prominent in small arteries in the cortex of the kidney, but in old mice, it occurred also in other organs and in the aorta and vena cava. Newly developed monoclonal antibodies against mouse Abcc6 localized the protein to the basolateral membranes of hepatocytes and the basal membrane in renal proximal tubules, but failed to show the protein at the pathogenic sites. Abcc6-/- mice developed a 25% reduction in plasma HDL cholesterol and an increase in plasma creatinine levels, which may be due to impaired kidney function. No changes in serum mineral balance were found. We conclude that the phenotype of the Abcc6-/- mouse shares calcification of elastic fibres with human PXE pathology, which makes this model a useful tool to further investigate the aetiology of PXE. Our data support the hypothesis that PXE is in fact a systemic disease.

Artificial intelligence with automated analysis of imaging biomarkers allows personalized prediction of AMD progression. Moreover, pathways of progression may be specific in respect to the neovascular/atrophic type.

M RP6 (ABCC6) is a member of the subfamily of the multidrug resistance proteins (MRPs, reviewed by Borst et al, 2000), but its putative role in multidrug resistance (MDR, reviewed by Moscow et al, 1997) is still under investigation. Closely related proteins such as MDR1 P-glycoprotein (P-gp, ABCB1, reviewed by Ambudkar et al, 1999), breast cancer resistance protein (BCRP, ABCG2;Doyle et al, 1998), and MRP1, -2, and -3 (ABCC1-3) are established MDR transporters. The exact range of substrates for MRP6 has not yet been determined, but a preliminary report suggested that MRP6 may be involved in the transport of certain anticancer agents, including anthracyclines and epipodophyllotoxins (M.G. Belinsky et al, Proceedings of the AACR, abstract 1510, 2001). Recently it was found that mutations in the MRP6 gene cause pseudoxanthoma elasticum (PXE), an inheritable disorder of the connective tissue involving impaired visual acuity, skin lesions, and cardiovascular complications (Bergen et al, 2000). The expression of MRP6 in normal human tissues has only been studied at the mRNA level. High MRP6 mRNA levels were reported in liver and kidney, whereas low expression was found in a range of other tissues, including lung, intestines, retina, skin, and vessel walls (Bergen et al, 2000;Kool et al, 1999).To study MRP6 at the protein level, three rat Mabs (M 6 II-7, M 6 II-21, and M 6 II-31) were generated from rats immunized with a fusion protein containing amino acids 764 to 964 of human MRP6 (FP M 6 II), according to described methods (Scheffer et al, 2000 Detection of the approximately 65 kD MRP6-MBP fusion protein and full length MRP6 from protein preparations of MRP6-transfected HEK 293 cells, using anti-MRP6 Mab M 6 II-7. The approximately 180,000 kD MRP6 migrates slightly faster than MRP2, as shown by control lanes stained for MRP2, using M 2 III-6 and MRP2-transfected cells. Total cell lysates were made as previously described (Scheffer et al, 2000). Ten to forty g of cell lysates or fusion proteins were fractionated on a 7% polyacrylamide slab gel and transferred onto a nitrocellulose membrane by electroblotting. After blocking, the membrane was incubated for 2 hours with primary antibody in the appropriate dilution. Horseradish peroxidase (HRP)-labeled-anti-rat or -mouse serum (1:1000; Dako, Copenhagen, Denmark) was used as a secondary antibody. Enhanced chemoluminescence (Amersham, Buckinghamshire, United Kingdom) was used to detect Mab binding.

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