A molecular probe for the detection of polar lipids in live cells

CA Bader1, EA Carter2, S Stagni3, NH Voelcker1, PA Lay2, M Massi4, S Plush1 and DA Brooks1

  1. School of Pharmacy and Medical Science, University of South Australia, Adelaide 5001 SA, Australia
  2. Vibrational Spectroscopy Core Facility, The University of Sydney, Sydney 2006 NSW, Australia
  3. Department of Industrial Chemistry “Toso Montanari”, University of Bologna, 40126 Bologna, Italy
  4. Department of Chemistry and Nanochemistry Research Institute, Curtin University, Bentley 6102 WA, Australia

Lipids have an important role in many aspects of cell biology, including membrane architecture/compartment formation, intracellular traffic, signalling, hormone regulation, inflammation, energy storage and metabolism. Lipid biology is therefore integrally involved in major human diseases, including metabolic disorders, neurodegenerative diseases, obesity, heart disease, immune disorders and cancers; which commonly display altered lipid transport and metabolism. However, the investigation of these important cellular processes has been limited by the availability of specific tools to visualise lipids in live cells. Here we describe the potential for a molecular probe ReZolve-L1™ to localise to polar lipids in intracellular compartments, containing for example sphingomyelin and phosphatidylethanolamine. In live Drosophila fat body tissue from third instar larvae, ReZolve-L1™ interacted mainly with lipid droplets, including the core region of these organelles. The presence of polar lipids in the core of these lipid droplets was confirmed by Raman mapping and while this was consistent with the distribution of ReZolve-L1™ it did not exclude that this the molecular probe might be detecting other lipid species. In response to complete starvation conditions, ReZolve-L1™ was detected mainly in Atg8-GFP autophagic compartments, and showed reduced staining in the lipid droplets of fat body cells. The induction of autophagy by Tor inhibition also increased ReZolve-L1™ detection in autophagic compartments, whereas Atg9 knock down impaired autophagosome formation and altered the distribution of ReZolve-L1™. Finally, during Drosophila metamorphosis fat body tissues showed increased ReZolve-L1™ staining in autophagic compartments at two hours post puparium formation, when compared to earlier developmental time points. We concluded that ReZolve-L1™ is a new live cell imaging tool, which can be used as a molecular imaging reagent for the detection of polar lipids in different intracellular compartments.