Spatiotemporally Mapping Thermodynamics of Lysosomes and Mitochondria using Cascade Organelle-Targeting Upconversion Nanoparticles

Abstract

The intracellular metabolism of organelles, like lysosomes and mitochondria, are highly coordinated spatiotemporally and functionally. The activities of lysosomal enzymes significantly rely on the cytoplasmic temperature, and heat is constantly released by mitochondria as the byproduct of ATP generation during active metabolism. Here, we develop temperature-sensitive LysoDots and MitoDots to monitor the in situ thermodynamics of lysosomes and mitochondria. The design is based on upconversion nanoparticles (UCNPs) with high-density surface modifications to achieve the exceptionally high sensitivity of 2.7% K-1 and accuracy of 0.8 K for nanothermometry to be used in living cells. We show the measurement is independent of the intracellular ion concentrations- and pH values. With Ca2+ ion shock, the temperatures of both lysosomes and mitochondria increased by 2~4 C. Intriguingly, with Chloroquine treatment, the lysosomal temperature was observed to decrease by up to ~3 C, while mitochondria remained relatively stable. Lastly, with oxidative phosphorylation inhibitor treatment, we observed a 3~7 C thermal increase and transition from mitochondria to lysosomes. These observations indicate different metabolic pathways and thermal transitions between lysosomes and mitochondria inside HeLa cells. The nanothermometry probes provide a powerful tool for multi-modality functional imaging of subcellular organelles and interactions with high spatial, temporal and thermal dynamics resolutions.

How much heat does non-photochemical quenching produce?

“…In mammalian cells, recently developed nanothermometry probes enable the measurement of intracellular temperature. It is revealed that the mitochondrial temperature could increase by 10°C by stimulating respiration, which is 10 5 times higher than the theoretical estimation (Chretien et al, 2018;Di et al, 2022). Whereas typical animal cells with a radius of 10 μm generate 1 nW of heat per cell (Hong et al, 2020) by consuming sugars and lipids, a plant cell of the same cross-section area can continue to generate 10 times as much heat by NPQ under continuous solar illumination (314.2 μm 2 × 63.9 W m -2 = 20.1 nW).…”