Thursday, April 30, 2015

The Avengers: Is It Possible Someone Could Turn Into A Hulk?

"The Avengers: Age of Ultron" has finally arrived, reuniting fans with their favorite superheroes and introducing them to new ones to cheer on, like Quicksilver.  

Judging from the never-ending string of successful superhero films, it seems safe to say that we're obsessed with champions of justice who harbor extraordinary abilities. No doubt we've shared this fascination with superpowers since the beginning. Some of us are born faster, stronger, smarter - causing the rest of us to wonder whether we can tap into some hidden superpower within ourselves. We love hearing stories of genius and watching talent shows, just to catch a glimpse of someone crossing the threshold of what we thought was the boundary of human capability.

Stanford biologist Sebastian Alvarado is no exception, but he is endeavoring to put some scientific plausibility behind some of our favorite superheroes. Take the Hulk, for instance. The Hulk is the muscular green beast that scrawny scientist Bruce Banner transforms into whenever he gets enraged.

A lot of scientists can identify with Dr. Banner’s plight, and I have seen many undergo an analogous transformation while reading their grant reviews.
How did Dr. Banner gain this blessing and curse? As a scientist, he was researching how people summoned these unusual bursts of strength. Using himself as a guinea pig, he exposed himself to gamma radiation in an attempt to become stronger. There was no noticeable effect at first, but when Dr. Banner got angry, his skin turned green and his muscles burst out of his shirt. Since Dr. Banner is a good guy, the Hulk is generally a good beast, although somewhat messy. When the anger subsides, Dr. Banner returns to his modest, wimpy self and heads to the store to buy new clothes.

The comic book tale prompted Dr. Alvarado to wonder:  is this even remotely possible? He addresses the question in the video below.

Let’s clarify a few of these points for those who might be less familiar with the concepts. First, gamma radiation blasts your DNA (chromosomes) apart. As Dr. Alvarado mentioned, there are enzymes that will “heal” the DNA, but it doesn’t always heal correctly, which might result in new genes (and the loss of other genes). Second, we are learning more and more that genes are regulated in a surprising number of ways. They are not merely binary switches that turn on and off, but rather they are controlled more like volume knobs. Epigenetics refers to the factors in your cells that have their fingers on those volume knobs.

We discussed epigenetics in a previous article covering Ozzy Osbourne’s genome; in the case of the Hulk, epigenetics provides an attractive means to account for how Dr. Banner can switch between Hulk and normal guy. Between transformations, Dr. Banner’s genes are not changing, but which ones are active – and the degree they are active – is changing. For example, epigenetic factors can crank up genes controlling muscle development when they receive a signal in the form of a stress hormone that increases during temper tantrums. As this hormone subsides, other epigenetic factors return the volume of those genes to their normal level. You can think of genes as the selection of music, but epigenetic factors are the DJs.
So what kinds of epigenetic factors are there? We are discovering a dizzying array of cellular components that can alter gene expression, which can result in changes in physical appearance, behavior, mental abilities, and more. It has long been known that chemical modification (i.e. methylation, delivered by enzymes called DNMTs – DNA methyltransferases) of DNA itself can shut down genes. DNA methylation marks are like orange construction cones blocking the highway. Scientists then discovered that histone proteins, which congregate in bundles of 8 to form nucleosomes, could also be chemically modified in several different ways. The nucleosomes give DNA the “beads on a string" appearance shown below.

This is your DNA, not a pearl necklace! The DNA "string" wraps around the "beads", which are nucleosomes composed of 8 histone proteins. Once thought to merely help package DNA, we now know these nucleosomes are major contributors to the regulation of genes on the DNA.

These proteins were long thought to be just scaffolding components for the DNA, but now we know they play a major role in directing the activity level of nearby genes. Numerous chemical modifications, such as acetylation, methylation, phosphorylation (and more), can take place on multiple places of each histone protein. These may alter the binding between nucleosomes and DNA, making certain genes more accessible, or these modifications may form a cellular “code” that can affect gene expression levels.

Histones can also be moved, replaced, or evicted by epigenetic factors called SWI/SNF ATPases. As the name implies, these enzymes require energy from ATP to affect gene expression. More recently, it has also been found that small non-coding RNA molecules can regulate genes.

A summary of the major epigenetic factors that can regulate the "volume" of gene expression.

While these complex methods a cell employs to influence gene expression offer a potential explanation for how someone could temporarily become a Hulk, it is by no means probable. Most massive gamma radiation doses would destroy genes that are essential to survival. But it is fun to use cutting-edge science to put just a tiny hint of credence behind the superpowers. And even more fun to think that with enough knowledge we may be able to modulate epigenetic factors to treat disease or maximize human potential.

Contributed by:  Bill Sullivan
Follow Bill on Twitter.

Falkenberg KJ, & Johnstone RW (2014). Histone deacetylases and their inhibitors in cancer, neurological diseases and immune disorders. Nature reviews. Drug discovery PMID: 25131830

Haggarty P, Hoad G, Harris SE, Starr JM, Fox HC, Deary IJ, & Whalley LJ (2010). Human intelligence and polymorphisms in the DNA methyltransferase genes involved in epigenetic marking. PloS one, 5 (6) PMID: 20593030

Tuesday, April 28, 2015

Quicksilver: The Avenger With Mutations For Speed

Quicksilver can run really fast. People can’t really
see him, but he can see everything that is going on
and make sense of it even though his speed is
phenomenal. He’s fast enough to have been in an
X-Men movie last year and an Avengers movie
this year.
May 1st brings yet another movie of comic book characters to life. I think we went about two weeks without one. The Avengers: Age of Ultron brings back our favorite superheroes – Iron Man, Black Widow, Hawkeye, Hulk, Thor, and Captain America – but adds some new characters as well.

Brother and sister duo of Pietro and Wanda Maximoff become reluctant Avengers in the new film. They have been characters in the comic books for years, and are two of the most promiscuous characters in terms of which stories they enter. Pietro has appeared in X-Men, Fantastic Four, and even the DC Comics Justice League of America.

Wanda (Scarlett Witch) and Pietro (Quicksilver) are different kinds of Avengers. They don’t have fancy toys like Iron Man; they don’t have as much martial training as Natasha Romanov or Hawkeye. They aren’t gods from another planet like Thor, but they do have some similarities to Hulk and Captain America.

Dr. Banner was a victim of gamma radiation–induced mutation during his research and Captain America had his body altered via science. The Maximoffs’ are mutants, but they were born with their individual mutations – heck, Magneto is their father.

Quicksilver’s mutations let him run amazingly fast, up to Mach 4 (4x the speed of sound, about 3044 mph) in some iterations of his character. He’s strong too, some websites say he can bench press about 1000 pounds. This is pretty amazing stuff, and I’m wondering how these feats might come about. 

How would Quicksilver’s physiology have to be altered in order for him to achieve faster than normal speeds? Believe it or not, science has identified mutations that could account for at least some of his abilities.

Mercury is the only metal that is liquid at room
temperature. The Greeks called it Hydragyrum (water
silver); that’s why it’s element symbol is Hg. The other
name, quicksilver, is from English, where "quick" means
living (ie. the quick and the dead). Therefore,
quicksilver means living silver.
First of all, Quicksilver would have to have some changes in his physiology other than just fast, strong muscles – muscles don’t mean anything if you can’t supply them with what they need. To go really fast, he would need cardiovascular and oxygen utilization systems that could get oxygenated blood to his muscles faster and in larger volume than anyone else.

But it is true that Quicksilver would need large muscles and muscles that would move quickly. Mammals have two basic types of skeletal muscle fibers, slow twitch (red, type I) and fast twitch (Type II, white). Slow twitch are good for endurance. They use oxygen well and have lots of myoglobin (an oxygen carrier like hemoglobin). Fast twitch are for speed and they come in two flavors. Type IIa are good for speed and endurance, and Type IIx are for pure, short-term speed.

People are born with a mixture of Type I and Type II fibers, usually around 50:50. Sprinters usually have more Type II fibers, maybe 60:40. Quicksilver must be 99:01 or more; Usain Bolt is 90:10 fast twitch and I don’t see him coming close to the speed of sound.

A ridiculously high fast twitch ratio is genetic, not a mutation per se, but it would be mighty unusual. My guess is that Quicksilver would be mostly Type IIa, since he can run fast for hours, Bolt maxes out at about 200 meters.

There is a certain mutation might help Pietro increase his fast twitch fibers. In a 2015 study, knocking out a gene called Fnip1 (codes for folliculin interacting protein-1) led to an increase in slow twitch fibers. Fnip works with follicullin (imagine that) in the area of energy and nutrient sensing. If having less Fnip1 leads to more slow twitch, then maybe more Fnip1 might call for making more energy in the cell, which would tend to support Type II fiber development.

Myostatin-induced muscular hypertrophy makes body
builders out toddlers. It isn’t just the increased muscle
mass, it’s the lower adipose levels (muscle requires
energy, so there is less fat). The muscle doesn’t create a
problem – it’s usually the parents that are the problem.
So being fast twitch makes him fast, but Quicksilver would need more – he would need a whole lot of Type IIa muscle fibers. We’ve got a mutation for that too. The protein myostatin is a regulator of muscle growth; it’s function is to limit the growth of muscle. With a mutation that prevents function of myostatin, you end up with myostatin-induced muscular hypertrophy - a huge amount of muscle and very little body fat. Maybe this isn’t such a bad mutation to have; it would certainly get Quicksilver closer to his onscreen abilities.

Other mutations can affect muscle performance as well. The gene for angiotensin converting enzyme (ACE) comes in several forms. One form, termed D, is associated with increased speed in athletes. The normal form is called I; but in a study of Japanese runners, people with I/D or D/D (you have two copies, one from mom and one from dad) were much faster. This is just one of many studies to conclude that the D allele is associated with speedy muscles.

There is another protein called alpha-actinin 3. If a person has a specific mutation in the gene for this protein, called the X allele, then the individual will have more muscular endurance, and perhaps more speed, according to a 2014 study.

More than 10 other genes have polymorphisms (small changes) that can be associated with promoting or inhibiting speed and endurance. There is no study showing an athlete with all the polymorphisms that make you faster or stronger – but Quicksilver would likely need them all if he wants to approach Mach 4.

Aside from muscle mass and speed, our Avenger of interest would need the oxygen and carbohydrates to power those muscles – certainly much more than you or I need. Oxygen is taken from the air by the lungs and the oxygen is carried to the muscles by the blood. When sugar and oxygen get to the muscle, they are used to produce ATP in the mitochondria. Quicksilver needs more oxygen, more blood flow, more carbohydrate and more mitochondria if he wants to be really fast. We’ve got mutations for that.

Heat shock protein 72 (HSP72) usually works in protecting proteins from damage, but it can have other functions. A 2014 study showed that activating HSP72 increases contraction of the heart, oxygen usage, and mitochondria number in cells. There are mutations that gives constitutively active HSPs (working all the time). It is these forms that could increase energy production in muscle.

Even superheroes need to be in shape. Running requires
you to put more oxygen into your blood and blow off
more CO2, so you breathe harder. Eventually, you get to
a point when you don’t have enough oxygen and you start
anaerobic metabolism. You’re going to panting for a
while to catch up.
Another way to increase blood flow and cellular activity would be to increase the basal metabolic rate. A 2014 paper described a mutation in a Japanese family that led to hyperthyroidism. Increased thyroid function leads to increased cardiac output, stroke volume (amount of blood moved with each heartbeat) and heart rate. We better give Quicksilver one of these mutations as well.

He needs more oxygen, so we also better provide Pietro with a mutation in growth hormone receptor. A 1998 study showed that increased growth hormone (GH) in adolescent males was associated with higher VO2 (amount of oxygen moved to blood). A recent study indicates that if you knock out the growth hormone receptor (GHRP) protein in mice, it is also associated with higher VO2. This suggests that GHRP mutations result in more circulating GH, and higher levels of GH lead to increased VO2 via some receptor-independent mechanism.

Finally, Quicksilver has to get more carbohydrates to the cells, which means he has to take in more carbohydrate as well. A mutation in the primary cilia of the POMC neurons of the hypothalamus (in the brain) leads to dysregulation of appetite (see this post). If you have this mutation, you’re always hungry, a condition called hyperphagia. This would lead to more calories and more energy for those strong muscles.

This could also be accomplished by mutations in the appetite hormones ghrelin and/or leptin. Leptin tells you when you are full, so a mutation that reduces its function would make you hungry, as would a mutation that increases the levels or function of the hunger hormone, ghrelin.

Neo could slow time down. Is it because he could increase
his metabolism and processing speed? Quicksilver has to
be able to do the same thing, or else everything would be
a blur as he sped by. That’s not good for avoiding
obstacles and catching the bad guy.
There is a final mutation that Quicksilver will need. Not so much to be speedy, but to keep from running into things. Brain processing speed is fast, but perhaps not fast enough for you to know what’s in front of you when you’re moving 3000 miles an hour. A recent study shows that the brain can visualize and recognize an image in just 13 milliseconds, but Quicksilver will need a serious upgrade to his operating system to go as fast as he is reputed to run.

Or will he? Another study shows that small animals have high metabolic rates, and higher metabolic rates are associated with faster brain processing speeds. Like Neo in The Matrix, perhaps Quicksilver’s increased metabolic rate due to thyroid mutations (see above) will make time slow down for him. This is how houseflies keep from being swatted (see this post), so it could work for him too.

Personally, I’m wondering what kind of mutations Pietro would need to prevent the horrible chafing he would probably experience. Wouldn’t he cook himself, or at least burn his crotch to ash? I guess this is where the fiction part of the story comes in.

Contributed by Mark E. Lasbury, MS, MSEd, PhD

Reyes, N., Banks, G., Tsang, M., Margineantu, D., Gu, H., Djukovic, D., Chan, J., Torres, M., Liggitt, H., Hirenallur-S, D., Hockenbery, D., Raftery, D., & Iritani, B. (2015). Fnip1 regulates skeletal muscle fiber type specification, fatigue resistance, and susceptibility to muscular dystrophy Proceedings of the National Academy of Sciences, 112 (2), 424-429 DOI: 10.1073/pnas.1413021112

Henstridge, D., Bruce, C., Drew, B., Tory, K., Kolonics, A., Estevez, E., Chung, J., Watson, N., Gardner, T., Lee-Young, R., Connor, T., Watt, M., Carpenter, K., Hargreaves, M., McGee, S., Hevener, A., & Febbraio, M. (2014). Activating HSP72 in Rodent Skeletal Muscle Increases Mitochondrial Number and Oxidative Capacity and Decreases Insulin Resistance Diabetes, 63 (6), 1881-1894 DOI: 10.2337/db13-0967

Nakamura, A., Morikawa, S., Aoyagi, H., Ishizu, K., & Tajima, T. (2014). A Japanese family with nonautoimmune hyperthyroidism caused by a novel heterozygous thyrotropin receptor gene mutation Pediatric Research, 75 (6), 749-753 DOI: 10.1038/pr.2014.34

Westbrook, R., Bonkowski, M., Arum, O., Strader, A., & Bartke, A. (2013). Metabolic Alterations Due to Caloric Restriction and Every Other Day Feeding in Normal and Growth Hormone Receptor Knockout Mice The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 69 (1), 25-33 DOI: 10.1093/gerona/glt080

Potter, M., Wyble, B., Hagmann, C., & McCourt, E. (2013). Detecting meaning in RSVP at 13 ms per picture Attention, Perception, & Psychophysics, 76 (2), 270-279 DOI: 10.3758/s13414-013-0605-z

Gunel, T., Gumusoglu, E., Hosseini, M., Yilmazyildirim, E., Dolekcap, I., & Aydinli, K. (2014). Effect of angiotensin I-converting enzyme and α-actinin-3 gene polymorphisms on sport performance Molecular Medicine Reports DOI: 10.3892/mmr.2014.1974