Chondrocalcinosis is an arthropathy that is characterized by the deposition of calcium-containing crystals in the joint spaces of affected individuals. For patients suffering from the deposition of a specific calcium crystal type, calcium pyrophosphate dihydrate (CPPD), a long history of biochemical analyses of fibroblasts and lymphoblasts from patients has established a strong relationship between abnormalities in inorganic pyrophosphate (PPi) metabolism and transport with the disease presentation. Our study of autosomal dominant familial Chondrocalcinosis (specifically, calcium pyrophosphate dihydrate deposition disease, CPPD disease) identified mutations in a gene, termed ANKH, that are responsible for the disease in at least five CPPD disease families. The ANKH gene codes for a 492 amino acid protein (ANK) that appears to function in the regulation of transport of the inorganic pyrophosphate (PPi). Interestingly, we have also observed that ANK gene expression is sensitive to oxygen. We hypothesize that this property may provide a mechanism by which ANK-regulated transport of PPi is relevant to idiopathic Chondrocalcinosis. In order to better understand the function of ANK in regulating the elaboration of PPi, we propose the following specific aims: (1) we will express wild type and mutant ANK (mutations are derived from our familial studies) in stably transduced cell lines to facilitate evaluation of the impact of mutant ANK on the generation of PPi, (2) we will examine the impact of oxygen on the expression of ANK and on the generation of PPi in an in vitro chondrogenesis model system and in primary chondrocytes; and (3) we will use specific and selective anion transport inhibitors to explore the possibility that ANK functions via calcium-activated chloride currents and to generate additional tools to for the study of transport function. These studies will enable us to understand the role that ANK plays in the transport of PPi, will provide information about the role of ANK in both familial and idiopathic Chondrocalcinosis and, ultimately, will facilitate the development of specific therapeutic agents. ? ?
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