Advances in small molecule two-photon fluorescent trackers for lipid droplets in live sample imaging

Abstract

Two-photon fluorescent trackers for monitoring of lipid droplets (LDs) would be highly effective for illustrating the critical roles of LDs in live cells or tissues. Although a number of one-photon fluorescent trackers for labeling LDs have been developed, their usability remains constrained in live sample imaging due to photo damage, shallow imaging depth, and auto-fluorescence. Recently, some two-photon fluorescent trackers for LDs have been developed to overcome these limitations. In this mini-review article, the advances in two-photon fluorescent trackers for monitoring of LDs are summarized. We summarize the chemical structures, two-photon properties, live sample imaging, and biomedical applications of the most recent representative two-photon fluorescent trackers for LDs. Additionally, the current challenges and future research trends for the two-photon fluorescent trackers of LDs are discussed.

Keywords: lipid droplet; lipid metabolism; live sample imaging; organelle tracker; two-photon microscopy.

FIGURE 1

(A) Illustration for monitoring the dynamics of LDs in live sample by TPM imaging using TP fluorescent tracker. (B) Chemical structures of the representative small molecule TP trackers for LDs. (C) Schematic plot for the emission maxima and TPA values of 1–10.

FIGURE 2

(A) Co-localization experiments of 5 (Green, LDs), Hoechst 33,342 (Blue, nucleus), and Mito Tracker Deep Red (Red, mitochondria). Reproduced with permission from Guo et al., 2018. Copyright 2018 American Chemical Society. (B) Ex vivo two-photon images of live mice liver tissue incubated with or without 6, and the reconstructed 3D image. Reproduced with permission from Niu et al., 2018. Copyright 2018 American Chemical Society. (C) Representative images of hepatic LDs using 8 in the liver of anesthetized mice after normal feeding or fasting. Reproduced with permission from Moon and Kim, 2021. Copyright 2021 The Korean Society of Lipid and Atherosclerosis. (D) Reconstructed 3D TPM images of normal mouse liver tissue and fatty liver disease mouse tissue stained with 9. Reproduced with permission from Han et al., 2022. Copyright 2022 Royal Society of Chemistry. (E) Merged images of dual-color TPM experiments of LDs (Red, 10) and lysosomes (Green, BLT) in the liver of normal mice and MCD diets mice for various time periods. Reproduced with permission from Lee et al., 2022. Copyright 2022 American Chemical Society.