Cell-surface sensors for real-time probing of cellular environments

Abstract

The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell biology and developing effective therapeutics. However, it is not yet possible to monitor the interaction of cells with their environments in real time. Here, we show that a fluorescent sensor attached to a cell membrane can detect signalling molecules in the cellular environment. The sensor is an aptamer (a short length of single-stranded DNA) that binds to platelet-derived growth factor (PDGF) and contains a pair of fluorescent dyes. When bound to PDGF, the aptamer changes conformation and the dyes come closer to each other, producing a signal. The sensor, which is covalently attached to the membranes of mesenchymal stem cells, can quantitatively detect with high spatial and temporal resolution PDGF that is added in cell culture medium or secreted by neighbouring cells. The engineered stem cells retain their ability to find their way to the bone marrow and can be monitored in vivo at the single-cell level using intravital microscopy.

Aptamer photoregulation in vivo

“…Aptamers can fold into well-defined conformations and are more resistant to enzymatic degradation than other oligonucleotides (7)(8)(9). Aptamers have been suggested for imaging applications because their relatively small size and molecular mass (∼10 kDa) allow fast tissue penetration and clearance from blood (10,11). The same characteristics make aptamers promising for effective delivery of diagnostic and therapeutic agents to tissues or organs.…”

Aptamer-based molecular imaging

“…The PDGF aptamer probes could quantify PDGF concentra-© Higher Education Press and Springer-Verlag Berlin Heidelberg 2012 tion added in cell culture medium and secreted by neighboring cells with single-cell resolution. The aptamer probe-coupled stem cells still retained their homing ability to bone marrow, indicating the feasibility for the cell-surface coupled aptamer sensors for in vivo tracking and quantification of extracellular signaling molecules (Zhao et al, 2011). Tc-labeled aptamer could image inflammation with peak signal/noise ratio of 4.3 ± 0.6 at 2 h, which was superior to IgG with peak signal/noise ratio of 3.1 ± 0.1 at 3 h (Charlton et al, 1997).…”

Adult mesenchymal stem cells and the NO pathways

“…The role played by NO in this regard is unstudied, although molecules such as PDGF-BB and VEFG-A seem to be obligatory. This is clearly documented in real-time in vivo sensing of PDGF secretion by sensor-engineered MSCs (11).…”