How cells program other cells

When I look at my body I notice that 100 trillion cells are cooperating. How do they sync their actions? How do they communicate? I have been assuming they must pass RNA back and forth among themselves, communicating important information. I pleased to read that this apparently happens:

Other subcellular packages drawing attention are exosomes — tiny membrane-enclosed sacs that form inside the cell and are later spat out. These nanoscale vessels were discovered in the 1980s and then ignored for about a decade — considered a way of bagging up cellular rubbish. “People thought they were junk, basically,” says Jan Lötvall, a clinical allergist at the University of Gothenburg in Sweden.

Interest in exosomes picked up in 1996, when Graça Raposo, a cell biologist now at the Curie Institute and the National Centre for Scientific Research in Paris, and her colleagues scrutinized exosomes spat out by B cells, a type of white blood cell. Although the technology to examine them — electron microscopy — wasn’t new, it wasn’t very popular at the time because “it was just old-fashioned”, says Raposo. Using it and other techniques, the team reported that the humble vessels might do something useful: display scraps of pathogen protein on their surfaces, spurring immune cells to mount defences against an infection13. Scientists became even more intrigued when Lötvall’s team reported in 2007 that exosomes could carry messenger RNA14, some of which could be picked up and translated in a recipient cell. This suggested that the shipments might allow cells to affect protein production in their neighbours. The study “really showed that exosomes were a vehicle of communicating important information between cells”, says Clotilde Théry, a cell biologist who is also at the Curie Institute.

Researchers are now trying to use exosomes to deliver drugs to specific parts of the body — with the hope that, because exosomes are ‘natural’, they might be less likely to be toxic or provoke an immune response than other vessels, such as artificial lipid sacs or protein shells. This year, Matthew Wood, a neuroscientist at the University of Oxford, UK, and his colleagues reported15 an attempt in mice: the team loaded exosomes with artificial RNA intended to hinder production of a protein involved in Alzheimer’s disease and tagged them with a molecule directing them to neurons and the blood–brain barrier. The exosomes successfully delivered their cargo and reduced production of the protein with no obvious ill effects, the team found. Other scientists are trying to fish exosomes out of body fluids and analyse their contents to diagnose cancer or deploy exosomes to provoke immune responses against tumours.