Precise Labeling and Tracking of Lipid Droplets in Adipocytes Using a Luminescent ZnSalen Complex

Abstract

Designing two-photon probes for precise labeling of lipid droplets (LDs) and monitoring LD dynamics in adipocytes is of great significance to understand LD homeostasis. We herein report that a luminescent metal complex LD-TPZn can specifically image LDs in adipose cells and tissue using one- or two-photon fluorescence microscopy. Importantly, LD-TPZn exhibited higher specificity to LDs than the commercial dyes Nile Red and Bodipy 493/503, probably due to different cellular uptake pathways, that is, clathrin-mediated endocytosis and non-selectively passive diffusion, respectively. More importantly, LD-TPZn can be applied as a two-photon LD probe to image adipose tissue, one of the most challengeable tissues for traditional one-photon fluorescence microscope imaging due to the strong light scattering. Most importantly, LD-TPZn can be used to monitor LD growth during adipogenesis of preadipocytes, which is highly desirable to unravel the relationship between LD homeostasis and metabolic diseases.

A BODIPY-Based Fluorogenic Probe for Specific Imaging of Lipid Droplets

“…BODIPY 493/503 is reported to have limited photostability [17], which compromises its application for spatial and temporal resolution. Although, new fluorescent probes for the visualization of LDs have been developed, including aggregation-induced emission (AIE) fluorophores [18][19][20][21], merocyanines [22], fluoranthenes [23], and solvatochromic dyes [24][25][26], turn-on LD-specific dyes are very limited, especially for emitting in red to the NIR region [22,[27][28][29]. Most recently, a family of turn-on LD markers were developed on the basis of merocyanine, which showed high signal-to-noise imaging of LDs in cells and tissues; however, they were used for a prolonged incubation time (3 h) probably due to their poor membrane-penetration properties [22].…”

Specific Two-Photon Imaging of Live Cellular and Deep-Tissue Lipid Droplets by Lipophilic AIEgens at Ultralow Concentration

“…Great efforts have been made to develop novel lipid droplets dyes to solve these problems. [12][13][14][15][16][17][18][19][20][21] Because the normal concentration used for lipid droplets staining falls in the range of 5-10 μM or even higher, these dyes show weak emission due to the aggregation-caused quenching (ACQ) effect. 22 Few dyes have been synthesized for lipid droplets imaging and function at nano-molar concentrations.…”

A guide to studying human dermal adipocytes in situ

“…To quantify changes in lipid accumulation in DAs, fluorescent lipid stains on cryosections such as BODIPY 493/503 (Figure F) or LipidTOX (Figure ) can be used as an alternative to ORO. BODIPY 493/503 and LipidTOX are cell‐permeable lipophilic neutral dyes that can be employed for both microscopy and flow cytometry . In our studies, BODIPY (Figure F) appears superior in terms of fluorescence intensity given that LipidTOX rapidly bleaches and does not display the lipid droplet morphology described in other studies (Figure ) …”