When ceramides meet immune senescence, a GIMAP5 connection

Capillarization, lack of liver sinusoidal endothelial cell (LSEC) fenestration, and formation of an organized basement membrane not only precedes fibrosis, but is also permissive for hepatic stellate cell activation and fibrosis. Thus, dysregulation of the LSEC phenotype is a critical step in the fibrotic process. Both a vascular endothelial growth factor (VEGF)-stimulated, nitric oxide (NO)-independent pathway and a VEGF-stimulated NO-dependent pathway are necessary to maintain the differentiated LSEC phenotype. The NO-dependent pathway is impaired in capillarization and activation of this pathway downstream from NO restores LSEC differentiation in vivo. Restoration of LSEC differentiation in vivo promotes HSC quiescence, enhances regression of fibrosis, and prevents progression of cirrhosis.

The BB (BioBreeding) rat is one of the best models of spontaneous autoimmune diabetes and is used to study non-MHC loci contributing to Type 1 diabetes. Type 1 diabetes in the diabetes-prone BB (BBDP) rat is polygenic, dependent upon mutations at several loci. Iddm1, on chromosome 4, is responsible for a lymphopenia (lyp) phenotype and is essential to diabetes. In this study, we report the positional cloning of the Iddm1/lyp locus. We show that lymphopenia is due to a frameshift deletion in a novel member (Ian5) of the Immune-Associated Nucleotide (IAN)-related gene family, resulting in truncation of a significant portion of the protein. This mutation was absent in 37 other inbred rat strains that are nonlymphopenic and nondiabetic. The IAN gene family, lying within a tight cluster on rat chromosome 4, mouse chromosome 6, and human chromosome 7, is poorly characterized. Some members of the family have been shown to be expressed in mature T cells and switched on during thymic T-cell development, suggesting that Ian5 may be a key factor in T-cell development. The lymphopenia mutation may thus be useful not only to elucidate Type 1 diabetes, but also in the function of the Ian gene family as a whole.