AIM (apoptosis Inhibitor expressed by Macrophages)
AIM is a novel member of the Scavenger-Receptor Cysteine-Rich (SRCR) superfamily, which we initially identified as an apoptosis inhibitory factor. AIM displays amino-acid sequence of a secreted molecule containing a typical signal sequence and no transmembrane region. Expression of AIM is solely restricted in macrophages, and its gene-regulation appears to require some specific microenvironment in vivo. By analyzing knockout and transgenic mice of AIM as well as by in vitro experiments using recombinant AIM protein, we have found a variety of functions of AIM related to inflammation, autoimmunity, innate immunology, and more recently, atherosclerosis. We are trying to clarify the molecular mechanisms of how AIM is physiologically involved in these diseases.
Gene manipulation in NOD-derived Embryonic Stem (ES) cells.
The NOD (non-obese diabetes) mouse is a best animal model for human type I diabetes, which is an autoimmune disease characterized by destruction of insulin-secreting b-cells of the Langerhans islets in the pancreas via infiltrating leukocytes leading to overt diabetes. To date, many candidate genes responsible to the disease have been proposed and are extensively studied mainly by backcrossing NOD mice and the mutant mice of the gene of interest. This, however, provokes a problem of genetic contamination of non-NOD genes, which often confuses the interpretation of outcomes. In order to avoid this, we have established gene manipulation in ES cells, which were established from NOD mice. The AIM gene was successfully disrupted in the cells, and the pure AIM-null NOD mice are being generated. In the NOD-ES cells, we are targeting other genes seemingly susceptible to diabetes, which mutant mice were not appropriate to crossbreed with NOD mice due to their gene localization.
Genes essential for positive/negative selection of T cells in the thymus.
Understanding the molecular mechanism of positive/negative selection of T cells in the thymus must be one of the most important and attractive questions in immunology. We have been studying the role of a zinc-finger transcription factor, Egr-1, in positive/negative selection. Overexpression of Egr-1 within thymocytes does modulate thymic selection in Egr-1 transgenic mice: it allows positive selection of thymocytes even by extremely low avidity of T cell receptor/MHC interaction. In other words, high Egr-1 expression lowers the threshold of avidity of T cell receptor/ MHC interaction required for positive selection. Similarly, under the overexpression of Egr-1, negative selection of thymocytes can be achieved by much lower avidity of T cell receptor/ MHC interaction than that normally required. By using micro-array and gene-tip technique, we are identifying the down-stream genes of Egr-1, which should be ?the? genes for positive/negative selection of thymocytes.
Towards the development of a novel genetic therapy for Propionic Acidemia (PA).
Propionic Acidemia is a life-threatening disease of newborns, which is caused by a genetic dysfunction of the Propionyl-CoA carboxylase (PCC) via variable mutations in its responsible gene locus. We have successfully generated mouse model for PA by knocking out the PCC-a subunit gene (PCCA). In addition, we observed that genetic supplementation of only a low level of PCC-activity solely in the liver was sufficient for the rescue the mutant mice from the lethal phenotype. Based on these, we are attempting to establish a new style of therapy for PA via transplantation of stem cells into the liver aiming to generate chimeric liver organ. Transplanted normal cells will supply the PCC-activity hopefully leading to a release from the disease.
