CARS microscopy for the monitoring of lipid storage in C. elegans

After several years of proof-of-principle measurements and focus on technological development, it is timely to make full use of the capabilities of CARS microscopy within the biosciences. We have here identified an urgent biological problem, to which CARS microscopy provides unique insights and consequently may become a widely accepted experimental procedure. In order to improve present understanding of mechanisms underlying dysfunctional metabolism regulation reported for many of our most wide-spread diseases (obesity, diabetes, cardio-vascular diseases etc.), we have monitored genetic and environmental impacts on cellular lipid storage in the model organism C. elegans in vivo in a full-scale biological study. Important advantages of CARS microscopy could be demonstrated compared to present technology, i.e. fluorescence microscopy of labelled lipid stores. The fluorescence signal varies not only with the presence of lipids, but also with the systemic distribution of the fluorophore and the chemical properties of the surrounding medium. By instead probing high-density regions of CH bonds naturally occurring in the sample, the CARS process was shown to provide a consistent representation of the lipid stores. The increased accumulation of lipid stores in mutants with deficiencies in the insulin and transforming growth factor signalling pathways could hereby be visualized and quantified. Furthermore, spectral CARS microscopy measurements in the C-H bond region of 2780-2930 cm-1 provided the interesting observation that this accumulation comes with a shift in the ordering of the lipids from gel- to liquid phase. The present study illustrates that CARS microscopy has a strong potential to become an important instrument for systemic studies of lipid storage mechanisms in living organisms, providing new insights into the phenomena underlying metabolic disorders.