Mitochondrial transformation occurs in cultured adipocytes, but fails to increase adipose tissue metabolic activity in mice in vivo.

A large number of studies in recent years have aimed to devise novel therapeutic strategies to increase adipose tissue metabolic activity and fight the global obesity epidemics. Growing evidence suggests that cells are able to accept isolated mitochondria by a simple coincubation in a process known as mitochondrial transformation. Therefore, we aimed to test whether mitochondrial transformation occurs in mature adipocytes, and whether this phenomenon could be utilized as a therapeutic approach to increase adipose tissue mitochondrial content and improve metabolic control. We provide evidence that both brown and white adipocytes are able to rapidly accept a large amount of brown adipocyte-derived mitochondria, which remain functional for several days and significantly contribute to cellular respiration in vitro. However, we did not find any evidence that internalization of exogenous mitochondria would trigger transcriptional changes in the recipient cells. Moreover, injection of a large amount of brown adipocyte-derived mitochondria into the inguinal fat of C57BL/6 mice failed to increase whole-body energy expenditure, and reduce body weight gain under obesogenic conditions. This might be due to activation of immune response and rapid removal of administered mitochondria. Altogether, our study adds information on the usability of mitochondrial transformation in the treatment of metabolic disease.