Molecular cloning and regional distribution of rat brain cyclophilin

Cyclosporine A (CsA) is a potent immunosuppressive drug that has widespread clinical uses in organ transplantation and the treatment of autoimmune disorders. However, the drug's clinical applications are on an empiric basis with a poor understanding of the basic mechanism(s) of action. CsA may exert some of its effects by binding to a cellular receptor protein--the cyclosporine receptor (also called cyclophilin). Cyclophilin (CyP) is an ubiquitous, soluble, cytoplasmic 17 kDa protein which has recently been shown to be a peptide-prolyl isomerase. CsA specifically binds to this protein and inhibits its isomerase activity. A rat cyclophilin cDNA clone was isolated from a rat brain lambda gt11 cDNA library. Northern blot analysis shows a single 1 kb messenger RNA in rat brain. In order to determine the regional distribution of the Cyp mRNA in situ hybridization was performed. The Cyp mRNA appeared to be expressed throughout the brain but there were particularly high levels in the cerebral cortex and hippocampus compared to the relatively low levels in white matter areas and tracts. At the cellular level, the Cyp mRNA is expressed at much higher levels in neurons than in glia. The high levels of Cyp in cortical (neuronal) areas may, in part, explain the global encephalopathic symptoms clinically observed in CsA neurotoxicity.