Pseudoxanthoma elasticum (PXE), a pleiotropic heritable disorder, is characterized by ectopic mineralization of the connective tissues. This disease is caused by mutations in the ABCC6 gene, which is expressed primarily in the baso-lateral surface of hepatocytes, and Abcc6 ؊/؊ mice develop progressive mineralization mimicking human PXE. To investigate the hypothesis that PXE is a metabolic disorder, potentially caused by the absence of antimineralization factor(s) in circulation, we used parabiotic pairing, ie, surgical joining of two mice, to create a shared circulation between various Abcc6 genotypic mice. To prevent immune reaction between the parabiotic animals, all mice were bred to be Rag1 Shared circulation between the parabiotic animals was confirmed by Evans blue dye injection and by quantitative PCR of blood cell genotypes. Pairing of Abcc6؊/؊ mice with their wild-type counterparts halted the connective tissue mineralization in the knockout mice. Homogenetic wild-type and heterozygous pairings serving as controls were phenotypically unaffected by parabiosis. Consequently , the observations on the parabiotic mice support the notion that PXE is a metabolic disease , potentially due to absence of systemic antimineralization factor(s). These observations suggest that reintroduction of the critical antimineralization factors into circulation could provide a potential treatment for this , currently intractable , disease.

The pathologic hallmark of pseudoxanthoma elasticum (PXE) is ectopic mineralization of soft connective tissues. Recent studies have suggested that PXE is a metabolic disease, and perturbations in a number of circulatory factors have been postulated. One of them is fetuin-A, a 60-kDa glycoprotein synthesized in the liver and secreted into blood. Observations in targeted mutant mice (Ahsg−/−) and in cell culture model systems have demonstrated that fetuin-A is a powerful anti-mineralization factor in circulation, and the serum levels of fetuin-A both in patients with PXE as well as in a mouse model of PXE (Abcc6−/−) have been shown to be reduced by up to 30 percent. In this study, we tested the hypothesis that over-expression of fetuin-A in Abcc6−/− mice counteracts the ectopic mineralization. Delivery of a construct containing full-length mouse fetuin-A cDNA, linked to a His-tag, to the liver of these mice resulted in elevated serum levels of this protein. As a consequence, soft tissue mineralization, a characteristic of Abcc6−/− mice, was reduced by ~70 percent at 12 weeks of age. The results suggest that normalization of serum fetuin-A, either through gene therapy approaches or by direct protein delivery to the circulation, may offer novel strategies to treat PXE and perhaps other heritable disorders of soft tissue mineralization.

Phenolic glycolipids (PGLs) are cell wall components of a subset of pathogenic mycobacteria, with immunomodulatory properties. Here, we show that in addition, PGLs exert antibactericidal activity by limiting the production of nitric oxide synthase (iNOS) in mycobacteria-infected macrophages. PGL-mediated downregulation of iNOS was complement receptor 3-dependent and comparably induced by bacterial and purified PGLs. Using Mycobacterium leprae PGL-1 as a model, we found that PGLs dampen the toll-like receptor (TLR)4 signaling pathway, with macrophage exposure to PGLs leading to significant reduction in TIR-domain-containing adapter-inducing interferon-β (TRIF) protein level. PGL-driven decrease in TRIF operated posttranscriptionally and independently of Src-family tyrosine kinases, lysosomal and proteasomal degradation. It resulted in the defective production of TRIF-dependent IFN-β and CXCL10 in TLR4-stimulated macrophages, in addition to iNOS. Our results unravel a mechanism by which PGLs hijack both the bactericidal and inflammatory responses of host macrophages. Moreover, they identify TRIF as a critical node in the crosstalk between CR3 and TLR4.