For these purposes, I'm going to assume everyone knows what DNA is and what we (as living things) use it for. If you don't know those things... Wikipedia, people. However, since this is getting into some fairly heavy molecular genetics, something I'm pretty geeky about, I might ramble off down some obscure bio-geeky rabbit-hole. If that happens, just whack me on the head (preferably in the comments).
Ok, first things first. Telomeres are important because of the role they play in DNA replication, so we're gonna talk about that real quick. Whenever a cell divides, it's got to duplicate all its bits, including the DNA that carries the instructions for all those bits. It does this in a very specific way (and every single organism on the planet does it the exact same way) in order to ensure the accuracy of the copies. DNA is a double-helix, which means it's two strands that are twisted around each other. The entire strand (humans have 23 separate strands) is tightly coiled together to make a rod-shaped structure called a chromosome. To make a copy, the two strands unzip and cellular machinery copies each strand. This allows each parent strand to serve as a template for the new one. It forms two 'daughter' double-helices that each contain one strand from the parent helix and one brand-new strand (semi-conservative). Once the whole chromosome is copied, the two helices are still connected at the middle, forming the X-shaped structure that's characteristic of chromosomes during cell division. That's DNA replication in a nutshell.
Each strand of DNA is directional, meaning it has a 'front' end and a 'back' end (or right and left, if that's easier) that are molecularly distinct from one another. The two strands in the double-helix line up front-to-back (anti-parallel). The backbone of each strand is made up of ribose sugars, the carbon atoms in which are numbered. The ends of the strands are named for the carbon atom that is sticking out: 3' or 5' (3-prime or 5-prime). For our purposes, let's call the 3' end the front and the 5' end the back.
The DNA replication machinery (a protein called DNA polymerase) only moves one direction: 3' to 5', or front to back. If the whole DNA molecule would just open up, the machinery could just start at each 3' end and zip on down. Unfortunately, single-stranded DNA is very unstable and the cell's own defenses attack and destroy it immediately. So, the DNA only unzips the tiny portion where the machinery is actually working. This means that one side will still get to just zip on down, but the other side will have to be a bit more clever. The strand that can replicate in the 'right' direction is called the leading strand and is, for our purposes, uninteresting. The side that is having to replicate in the 'wrong' direction is the one causing all the problems. The machinery can still only copy in a front-to-back direction, so replication occurs in short fragments (in the right direction) that are later glued together. A kind of leap-frog motion allows a small fragment to be copied, the machinery to hop backward and begin again behind the fragment it just created as a new area of the double-helix is unzipped. The spots where the machinery re-binds are marked by little pieces of RNA binding to the DNA (called primers). Another machine comes in later to replace the little RNA primers with DNA... but this can only happen if there is DNA on either side of the RNA primer. This isn't a problem until it gets to the very end. Because there isn't any DNA on the other side of the very last spot the machinery needs to bind, that RNA primer can't be replaced with DNA, so it eventually falls off, leaving a small piece of single-stranded DNA exposed. Remember what I said about the cell really not liking single-stranded DNA hanging around? The cell's defenses come in and chop off that little piece of DNA and dispose of it.
BUT HANG ON A SECOND. Our chromosome just got 20 bases shorter! Isn't that stuff important? Don't we need that? That happens every single time the cell divides?!
I'm so glad you asked.
This is what biologists refer to as the 'end replication problem'. This is where telomeres come in.
Telomeres are long sections of repetitive DNA (in mammals, it's a bunch of repeats of TTAGGG) at the ends of the chromosomes that don't contain any genes. Their sole purpose is to protect the important stuff (the genes) from replication-induced degradation. So, the replication machinery copies the DNA all the way down the chromosome, and all the way to the end of the telomere. When that small piece of single-stranded DNA gets cut off, it's the non-coding telomeric repeats that get chopped and not the important stuff. It serves as a buffer, like the plastic cap on the end of a shoelace. As a side benefit, the repetitive nature of telomeres also makes them curl up, which protects the ends from over-zealous cellular vigilantes that fix double-strand breaks by fusing chromosomes together. The centromere is another area of non-coding, repetitive DNA that serves a mechanic purpose and not an instructional one. It allows the chromosomes to be pulled apart during cell division.
So. The telomeres get a little shorter every time the cell divides. There does come a time when the telomere gets 'used up'. Usually at this point the cell stops dividing. Depending on its genetic history and cell type, it may enter a state of senescence (it keeps on doing its thing, but doesn't divide), or it may commit suicide (known as apoptosis or programmed cell death). When a lot of cells in the body get to this stage, as you may guess, the body itself isn't looking so good. Many of the ailments of old age can be attributed to shortened telomeres and the resulting decrease in cell division. Cells divide for lots of reasons, the most prominent being to repair damage (injury) and to mount an immune response (illness). With decreased cell division, an organism doesn't heal from injury as quickly and is more susceptible to infection. As undesirable as these things are, they're just a result of 'normal' wear and tear. However, sometimes when the telomeres are exhausted, the cell doesn't stop dividing. It begins chopping off ends of important genes and those genes now code for faulty or non-functional proteins. DNA damage like this has been linked to several forms of cancer typically associated with old age.
BUT. If the telomeres get shorter every time a cell divides, aren't we passing on progressively shorter and shorter telomeres to our offspring? Why haven't we died out yet??
Good question. We aren't, which is why we haven't. There is a protein called telomerase that builds the telomeres back up. It's active in stem cells during early development, so we can get from a fertilized egg to a multi-cellular person without losing a bunch of our telomeres. It's also active in... you guessed it! Gametes. Sperm and eggs. So rest assured, you're equipping your kids with a full set of telomeres.
So, why can't we just turn telomerase back on and keep those cells dividing without damaging the DNA? Fountain of youth, right here! I feel a Nobel Prize coming on...
Because unregulated telomerase activity basically turns cells immortal... and we have a word for immortal cells: Cancer. The other major place where telomerase is active is within tumor cells... 90% of cancers have active telomerase. A cancer is basically just a group of cells that have lost all their inhibitions and continually divide. The normal mechanisms that tell cells to stop dividing because we have enough lung for now, thanks have either been permanently switched off or damaged. Tumors are just areas of unrestrained cell growth.
So yes, telomerase has some pretty powerful implications for the ageing process and its associated discomforts... but our cells keep it on a short leash for a very good reason.
Ok, so now you're ready for the article. It's here.
In a nutshell, cells were treated with a small piece of messenger RNA (the RNA that transcribes DNA genes and takes the info out of the nucleus so it can be made into a protein) that codes for the 'active ingredient' in telomerase (telomere extension reverse transcriptase, or TERT). The new and awesome part of this procedure is that it's transient. Remember what unrestrained telomerase does? Bad stuff. So, here, they've restrained it. The RNA 'signal' only persists in the cell for about 48 hours. Then it's gone and the telomeres (newly lengthened) begin to shorten again like normal. Fortunately, the researchers think that the procedure would reverse telomere shortening equivalent to about 10 years in humans. This means that any treatments developed from this procedure could be administered less frequently than a tetanus booster.
This new transient application of TERT would reduce the risk of cancer resulting from treatments like this, and the need for repeated treatments doesn't seem prohibitive. Therapies could be generalized to treat general old age symptoms or very specific to treat diseases associated with age (like diabetes and heart disease) and prematurely shortened telomeres (like progeria, liver pulmonary fibrosis and liver cirrhosis).
Pretty cool, huh?
