The overall goals of our research are to investigate the role of acid ceramidase (AC) in sphingolipid metabolism, sphingolipid-mediated signal transduction, and the pathogenesis of Farber disease. Towards this end, we have: a) isolated the full-length cDNAs and genes encoding human and murine AC, b) developed an overexpression/purification system for the large-scale production of the human enzyme, c) extensively characterized the recombinant enzyme, revealing a multienzyme complex consisting of AC, acid sphingomyelinase, and at least one other enzyme involved in ceramide metabolism, and d) constructed the first knock-out mouse model of AC activity. In these latter experiments, no homozygous, affected (ACKO-/-) embryos were found at day E8.5 or later. We now propose to extend these findings by pursuing the following four specific aims: 1) Examine the expression of AC in early mouse development and investigate the mechanism explaining the absence of ACKO-/- embryos. We will document the expression pattern of AC in normal mouse embryos, obtain preimplantation embryos from ACKO+/- intercrosses for genotype analysis and biochemical/morphological characterization, and study the gametes from ACKO+/- animals to uncover potential abnormalities in mutant gametes that might affect fertilization, 2) Construct and characterize AC conditional knock-out mice. We have already constructed an AC gene targeting vector that can be used to produce conditional KO mice. We will next obtain mice that are homozygous for this targeting sequence, and breed them to transgenic mice expressing Cre recombinase under the control of inducible, macrophage-specific, and Purkinje cell-specific promoters. Resulting animals will be characterized clinically, pathologically, and biochemically. 3) Investigate the interaction of AC, acid sphingomyelinase and other lipid hydrolases in a multienzyme complex. We will use novel, sphingolipid affinity ligands to obtain large quantities of the multienzyme complex, and identify new components by a proteomics approach and/or by functional assays, and study the formation and intracellular trafficking of the complex under cell growth conditions known to stimulate sphingolipid-mediated cell signaling, and 4) Use AC-specific inhibitors to investigate the "forward" and "reverse" AC activities, and for the treatment of Farber disease. We will continue to characterize the inhibitory effects of novel sphingolipid analogues in vitro and in situ, and evaluate their use for chaperone therapy of Farber disease.