BPS2026 – Transport mechanism of polyamines in mitochondria

Mitochondrial polyamines, such as spermine and spermidine, are essential for bioenergetics, calcium signaling, and cell survival. Recent studies have further highlighted key importance of polyamines in enhancing T cell function to defend against cancer. However, the molecular mechanisms underlying their transport into the mitochondrial matrix remain unclear. To address this knowledge gap, we characterize mitochondrial uptake of 14C-labeled spermine in HEK 293 cells. We observed large accumulation of spermine within mitochondria, and that this process is inhibited by Mg 2+ . As spermine is known to bind membranes, it is crucial to reduce signals originating from spermine’s membrane association. Accordingly, we applied tobramycin, an organic cation with strong membrane affinity, to block spermine binding to membranes. This approach strongly enhanced the signal-to-noise level of our assay. We next examined the role of mitochondrial membrane potential by treating mitochondria with the uncoupler FCCP. The results showed that mitochondrial spermine uptake did not differ significantly between control and FCCP-treated conditions, indicating that mitochondrial spermine uptake is independent of the membrane potential. We then expanded our investigation to mitochondria isolated from different organs to determine whether mitochondria exhibit tissue-specific spermine uptake activity. This study will provide insight into tissue-specific adaptations of polyamine metabolism. In conclusion, our study establishes an experimental framework for analyzing mitochondrial spermine uptake and provides mechanistic insights into this membrane-transport pathway and further studies will enhance our understanding of mitochondrial polyamine regulation and may reveal new opportunities for boosting immunity and cancer treatments.