Isolation of a Ubiquitous Cholesteryl Ester Spectral Signature

Area of Science:

• Biophysics
• Molecular Spectroscopy
• Metabolic Biochemistry

Background:

• Lipid droplet (LD) composition is crucial for metabolic regulation and disease, but quantitative analysis is challenging.
• Spectral overlap between triacylglycerols (TAGs) and cholesteryl esters (CEs) hinders accurate differentiation due to similar acyl chain structures.

Purpose of the Study:

• To develop a method for distinguishing and quantifying cholesteryl esters (CEs) within lipid droplets (LDs).
• To overcome spectral overlap limitations in analyzing LD composition using stimulated Raman scattering (SRS).

Main Methods:

• Utilized stimulated Raman scattering (SRS) microscopy to analyze lipid droplet composition.
• Developed gradient-based residual iterative minimization (GRIM) for spectral unmixing.
• Identified a conserved spectral signature, the 'CE-core', for cholesteryl esters.

Main Results:

• Isolated a ubiquitous and conserved 'CE-core' spectral signature, independent of acyl chain identity.
• Demonstrated minimal spectral overlap between the 'CE-core' signature and TAG spectra.
• Successfully quantified TAG-to-CE ratios and resolved LD heterogeneity in varied cellular conditions.

Conclusions:

• The conserved 'CE-core' spectral signature enables specific differentiation and quantification of cholesteryl esters.
• The GRIM framework provides a powerful tool for spectral unmixing in complex biological systems.
• This approach advances quantitative chemical analysis of lipid droplets, aiding metabolic research and disease understanding.