Import of TAT-Conjugated Propionyl Coenzyme A Carboxylase Using Models of Propionic Acidemia

Propionic acidemia is caused by a deficiency of the enzyme propionyl coenzyme A carboxylase (PCC) located in the mitochondrial matrix. Cell-penetrating peptides, including transactivator of transcription (TAT), offer a potential to deliver a cargo into the mitochondrion. Here, we investigated the delivery of an α₆β₆ PCC enzyme into mitochondria using the HIV TAT peptide at several levels: into isolated mitochondria, in patient fibroblast cells, and in a mouse model. Results from Western blots and enzyme activity assays confirmed the import of TAT-PCC into mitochondria, as well as into patient fibroblasts, where the colocalization of imported TAT-PCC and mitochondria was also confirmed by confocal fluorescence microscopy. Furthermore, a single-dose intraperitoneal injection into PCC-deficient mice decreased the propionylcarnitine/acetylcarnitine (C3/C2) ratio toward the normal level. These results show that a cell-penetrating peptide can deliver active multimeric enzyme into mitochondria in vitro, in situ, and in vivo and push the size limit of intracellular delivery achieved so far. Our results are promising for other mitochondrion-specific deficiencies.