Intramolecular Spirocyclization Enables Design of a Single Fluorescent Probe for Monitoring the Interplay between Mitochondria and Lipid Droplets

Abstract

The interplay between mitochondria and lipid droplets (LDs) plays a central role in regulating the β-oxidation and storage of fatty acids (FA) and is also engaged in responding to external stimuli such as nutrient deficiency. However, a single fluorescent probe enabling the discriminative and simultaneous visualization of the two organelles has not been reported yet, which brings limitation for the in-depth study on their interplay. In this work, utilizing the intramolecular spirocyclization reaction of rhodamine dyes that can dramatically change the optical and soluble properties, we have designed a new single fluorescent probe for labeling LDs and mitochondria in clearly separated dual-emission channels. The newly designed “biform” probe, MT-LD, presented in a ring-opened form in mitochondria to give a strong red emission, while it underwent the intramolecular spirocyclization reaction to target LDs showing an intense blue fluorescence. In this manner, MT-LD can label LDs and mitochondria in blue and red fluorescence, respectively. With this robust probe, the increase of mitochondria–LD contact and peridroplet mitochondria (PDM) amount during oleic acid treatment and starvation-induced autophagy has been successfully revealed. The interaction between the two organelles was also visualized in different tissues, which revealed an obviously higher level of mitochondria–LD contact and PDM amount in brown adipose tissue and lung tissue. This work provides a promising molecular tool to investigate the interplay between mitochondria and LDs and promotes studies on FA metabolism and autophagy.

Recent advances in fluorescent probes for lipid droplets

“…7). 24 In protic solvents, 12 displays dual absorptions at 400 nm (coumarin) and 550 nm (rhodamine); however, in aprotic solvents, 12 only shows absorption at 400 nm (coumarin). Accordingly, LDs can be imaged through the blue channel (l ex = 405 nm, l em = 425-475 nm) and mitochondria through the red channel (l ex = 561 nm, l em = 570-620 nm).…”

A Fluorescent Probe Targeting Mitochondria and Lipid Droplets for Visualization of Cell Death

“…The cationic structure form can target mitochondria, and the neutral lipophilic molecule can target LDs. We would select utilizing the spirocyclization of rhodamine dyes [14] and flavone dyes [15] (Scheme 1b). The ring‐closed rhodamine form neutral lipophilic structure and ring‐opened rhodamine form cationic structure under different physiological states.…”

Quantitative Structure–Activity Relationship Enables the Rational Design of Lipid Droplet-Targeting Carbon Dots for Visualizing Bisphenol A-Induced Nonalcoholic Fatty Liver Disease-like Changes

“…However, a fraction of the punctate red emission overlapped with the cylindrical and granular green fluorescence, indicating that these LDs were bound to the mitochondria (region 2 in Figure A). The mitochondria that were not bound to the LDs are the cytoplasmic mitochondria which can accelerate LD consumption, while the bound mitochondria are considered to be the peridroplet mitochondria which can promote LD synthesis . In order to further clarify the interaction between organelles, the dynamic process of LDs and mitochondria was studied (Figure S15A).…”

“…The mitochondria that were not bound to the LDs are the cytoplasmic mitochondria which can accelerate LD consumption, while the bound mitochondria are considered to be the peridroplet mitochondria which can promote LD synthesis. 40 In order to further clarify the interaction between organelles, the dynamic process of LDs and mitochondria was studied (Figure S15A). As shown in Figure S15B, LDs that were not bound to mitochondria have a highly dynamic nature.…”