Organization of Inner Cellular Components as Reported by a Viscosity-Sensitive Fluorescent Bodipy Probe Suitable for Phasor Approach to Flim

Recent developments in cell micro- and nano-imaging strategies prompted the rational engineering of novel fluorescent probes. We here present a new bodipy-based molecular rotor, BoMe, tailored to measuring local viscosity in the cellular context. More specifically, our probe displays sensitive dependence of its emission lifetime from the viscosity of its immediate environment. Yet, at odds with most rigidochromic fluorescent probes, the absorption and emission spectra of BoMe is poorly influenced by local polarity, thus allowing for universal viscosity measurements in different milieu. Additionally, the viscosity dependence of lifetime is conveniently monitored by the phasor approach to fluorescence lifetime imaging, a a fit-free method that overcome the main drawbacks of conventional lifetime imaging (1). In our work, BoMe rapidly permeates cells, stains cytoplasmic as well as nuclear domains, and its optical properties make it perfectly suited for widely diffused confocal microscopy imaging setups. The capability of BoMe to report on intracellular viscosity was put to the test by using a cellular model of a morbid genetic pathology (Hutchinson- Gilford progeria syndrome, HGPS) (2). Our results show that the nucleoplasm of HGPS cells display reduced viscosity as compared to normal cells. Since BoMe displays significant affinity towards DNA, as demonstrated by an in vitro essay, we hypothesize that genetic features of HGPS, namely the misassembly of lamin A protein within the nuclear lamina, modulates chromatin compaction. This hypothesis nicely agrees with recent literature data (3).