Tuesday, 19 June 2012

Who needs NASA? Launching genes with lasers in space-travelled fish

promoters launch genes on DNA
Inside the cell genes are launched from promoters on our DNA.
(photo of space shuttle Atlantis)
NASA has its sights on launching rockets into space using lasers. "What if..." they're wondering, "shuttles could be sent up using laser beams to heat their fuel from the ground?"

Biophysicists in Japan have had a similar idea. They've successfully used lasers to 'launch' genes inside living creatures, with a little help from nanotechnology. If this process works in humans, future battles with cancer may be fought by remote control.

Deep within our cells, genes are launched into action from promoters, sequences of DNA where movable machinery assembles to fire copies of a gene, called messenger RNAs (mRNAs), from the nucleus to the cytoplasm.

Promoter ’launch pads’ are triggered by different things – stresses or chemicals or signals from outside the cell. Some promoters are heat sensitive, firing off mRNAs in response to fever or infection. Arriving in the cytoplasm, their mission is to build proteins to defend the cell from invaders such as viruses.

New research published recently in PNAS, describes a way of using laser light to trigger these 'heat shock' promoters from above the skin of living organisms. It's a first step towards launching our own genetic defences to disease from outside the human body.
laser-fired genes may fight cancer
Could lasers be used to fire mRNAs out from
the nucleus to fight diseases?
(photo: Space shuttle Atlantis from plane, Ryan Graff)

To develop these new pyrotechnics, Eiliro Miyako and colleagues injected carbon nanoparticles called nanohorns into medaka fish, Oryzias latipes. These fish are no strangers to laboratories. They've even been to space (and were the first Earthly vertebrates to reproduce in orbit).

Nanohorns, molecule-thin sheets of carbon folded into cone shapes, have huge potential for scooping up and delivering drugs inside cells and tissues. But it was something else about these tiny metal structures (which measure around 1/100000 cm across) that excited Dr Miyako and his team: nanohorns convert laser light energy into heat.

With a microscopic fuel source in hand the team from collaborating research institutes in Japan, set about building a DNA launch pad.

They pieced together DNA in the lab, placing the gene for a green fluorescent protein (GFP) next to a man-made heat shock promoter. After transferring the whole thing into the cells of the medaka fish, it was time for launch!

A low-powered laser beam was focused beneath the fish's skin. The carbon nanohorns absorbed the laser's energy, emitting it as heat. The surrounding tissue began to warm up. At a temperature of 42°C the heat shock promoters fired into life, launching the GFP gene. Minutes later the cells in the fish were glowing green. Genes had been successfully launched from outside a living body.

remote control gene expression
Medaka, the first vertebrate to reproduce in space.
In this study its genes were launched by remote control.
Dr Miyako writes "This work is a proof-of-principle study demonstrating that... gene expression can be mediated by the photothermal properties of nanocarbons."

 He believes that they could be used "in various biological fields, including analysis of cell signaling within organisms, investigation of genetic mechanisms, and development of unique cell therapies and tissue engineering techniques."

Makes you wonder which will come first - the fire laser-propelled rocket to the moon, or the first cancerous cell killed by remote control?

What does this mean for me?
This study was not simply about making glowing fish. As Dr Miyato says, this is a proof of principle. In the future, lasers might be used to trigger specific genes inside the human body, boosting the body's response to infection, or triggering cell death in cancer cells. This could compliment drug-based approaches aiming to manipulate genes and proteins in a similar way. The team have also used nanohorns to trigger genes inside living mice and found no signs of toxicity or adverse reaction to the particles, which is encouraging for future trials.

What does this mean for science?
Remote control of gene expression has been achieved before, but this study is the first to use near infrared light (NIR, with wavelengths between 0.7- 2.5um). NIR light lies inside the "optical window" of biological tissue (0.6- 1.1um) and is able to penetrate over 10cm deep. This study adds to the - already impressive - list of potential uses for metal nanoparticles in biology including drug delivery, tissue scaffolding,  the detection of harmful pathogens and improved MRI images.

Reference (free to download via Open Access!):

ResearchBlogging.org Miyako, E., Deguchi, T., Nakajima, Y., Yudasaka, M., Hagihara, Y., Horie, M., Shichiri, M., Higuchi, Y., Yamashita, F., Hashida, M., Shigeri, Y., Yoshida, Y., & Iijima, S. (2012). Photothermic regulation of gene expression triggered by laser-induced carbon nanohorns Proceedings of the National Academy of Sciences, 109 (19), 7523-7528 DOI: 10.1073/pnas.1204391109

Thursday, 7 June 2012

Death by metal: a hidden detonator inside cancer cells?

Our cells are wired to explode. Given the right signals they can burst open, scattering bits of crunched up DNA, shrivelled membrane and chemicals in all directions. Sometimes this is all part of the plan: controlled cell death it vital to defining the outline of our toes and fingers in the womb, and to the daily act of replacing old cells with new ones. Cell death is a part of life.

pools of iron are found in some cancer cells
Could pools of iron inside cancer cells be exploited
to trigger their demise?
Iron in Lake Khövsgöl, Mongolia
(picture credit Josefontheroad
New research has uncovered a hidden route to cell death. Death by iron, or 'ferroptosis' may be a secret weapon against some forms of cancer.

In work published recently in Cell, Scott Dixon and colleagues triggered the death  of cells in a dish using chemicals which causes a build-up of Reactive Oxygen Species (ROS). ROS are volatile and highly damaging to cells, so death within a few hours came as no surprise. What did was another observation: erastin was only effective in cells with a healthy supply of iron.

Iron absorbed from the blood stream (but not other heavy metals such as copper, nickel or cobalt) appeared to sensitise certain cells to erastin and a quick death. 

Exactly what the link is between ROS-inducing chemicals such as erastin and iron has yet to be uncovered. But the team from Columbia University, New York, found evidence that ferroptosis has a "unique genetic network" that is entirely separate from other forms of cell death such as apoptosis (the 'culling' of cells, apoptosis helped to create the gaps between our toes) and necrosis (triggered when a cell is too injured to repair).

This distinct wiring presents an intriguing opportunity: to selectively activate ferroptosis to kill certain cancer cells.

Death by Iron, targeting Ferroptosis
Can death by iron, or 'ferroptosis' be aimed at cancer?
Or blocked in nerve cells to protect the nervous system?
(Iron Maiden. ' The Trooper' (1983))
"The RAS family [of genes] is mutated in 30% of cancers," Dr Dixon writes. These mutations lead to uncontrolled cell division, but also "for better or worse... elevated levels of iron... are observed in some cancer cells".

His team believes it is possible to activate ferroptosis in RAS-mutated cancers inside the human body, using the abnormal iron levels to sensitise the cells to chemicals like erastin.

But activating ferroptosis in cancer may not be its only health benefit. There may be a use for blocking the process too.

The team successfully rescued neurons in rodent brains from cell death by blocking ferroptosis with a chemical inhibitor called ferrostatin-1. They propose that blocking ferroptosis in human brain cells following a stroke or epileptic fit (when ROS and iron levels are high) might protect the central nervous system from long-term damage.

Although the wiring inside our cells is complex (and multitasking is common), ferroptosis is a rare example of independence. Its distinct wiring may allow selective activation or inhibition of cell death, and maybe even the treatment of cancer with fewer side effects. That this metal-based killer might be used to protect life is, in more ways than one, quite ironic.

What does this mean for me?
This study might lead to a whole new line of approach for the treatment of some cancers and diseases which damage the central nervous system. High levels of iron have been reported in cases of Alzheimer's and Parkinson's disease. Understanding exactly how our cells are wired to use ferroptosis will make it easier for scientists to manipulate its effects with drugs similar to erastin or ferrostatin-1.

What does this mean for science?
The discovery of a previously unknown route to cell death shows just how much about our cells we have yet to understand. Indeed, the authors of this work suggest there may be much more "hidden" wiring  used by the cell, waiting to be discovered.


ResearchBlogging.orgDixon, S., Lemberg, K., Lamprecht, M., Skouta, R., Zaitsev, E., Gleason, C., Patel, D., Bauer, A., Cantley, A., Yang, W., Morrison, B., & Stockwell, B. (2012). Ferroptosis: An Iron-Dependent Form of Nonapoptotic Cell Death Cell, 149 (5), 1060-1072 DOI: 10.1016/j.cell.2012.03.042