Mitochondria can be incorporated into mammalian cells by simple co-incubation of isolated mitochondria with cells, without the need of transfection reagents or any other type of intervention. This phenomenon was termed mitochondrial transformation and although it was discovered in 1982, currently little is known regarding its mechanism(s). Here we demonstrate that mitochondria can be transformed into recipient cells very quickly and co-localize with endogenous mitochondria. The isolated mitochondria interact directly with cells, which engulf the mitochondria with cellular extensions in a way, which may suggest the involvement of macropinocytosis or macropinocytosis-like mechanisms in mitochondrial transformation. Indeed, macropinocytosis inhibitors but not clathrin-mediated endocytosis inhibition-treatments, blocks mitochondria transformation. The integrity of the mitochondrial outer membrane and its proteins is essential for the transformation of the mitochondria into cells; cells can distinguish mitochondria from similar particles and transform only intact mitochondria. Mitochondrial transformation is blocked in the presence of the heparan sulfate molecules pentosan polysulfate and heparin, which indicate crucial involvement of cellular heparan sulfate proteoglycans in the mitochondrial transformation process.

Pathogenesis of neurodegenerative diseases involves dysfunction of mitochondria, one of the most important cell organelles in the brain, with its most prominent roles in producing energy and regulating cellular metabolism. Here we investigated the ef

Modern medicine offers no cure for mitochondrial disorders such as lipoamide dehydrogenase (LAD) deficiency. LAD is the E3 subunit shared by alpha-ketoacid dehydrogenase complexes in the mitochondrial matrix, and these complexes are crucial for the metabolism of carbohydrates and amino acids. We propose a novel concept for restoring the activity of an immense multicomponent enzymatic complex by replacing one mutated component, the LAD subunit. Our approach entails the fusing of LAD with the transactivator of transcription (TAT) peptide, which is capable of rapidly crossing biological membranes, thereby allowing TAT-LAD to be delivered into cells and their mitochondria where it can replace the mutated endogenous enzyme. Our results show that TAT-LAD is indeed delivered into the cells and their mitochondria, where it is processed, restoring LAD activity to normal values and, most importantly, increasing the activity of pyruvate dehydrogenase complex. We report here, for the first time, that TAT-mediated replacement of one mutated component restores the activity of an essential mitochondrial multicomponent enzymatic complex in cells of patients with enzyme deficiencies. We believe that this approach involving TAT-mediated enzyme replacement therapy (ERT) can be applied to the treatment of LAD deficiency as well as to other mitochondrial and metabolic disorders.

(2011). Human toxin-based recombinant immunotoxins/chimeric proteins as a drug delivery system for targeted treatment of human diseases. Expert Opinion on Drug Delivery: Vol. 8, No. 5, pp. 605-621. doi: 10.1517/17425247.2011.566269