Why Heart Muscle Can’t Heal After Heart Attack: No Stem Cells?
Not sure if most people caught it, but there has been serious controversy these past few months in the scientific publishing world over whether the heart has stem cells. This has involved some major retractions of scientific papers from a famous lab and redefined how doctors think about the regenerative ability of the heart. Let me explain.
What Exactly Is a Heart Attack?
What we commonly refer to as a heart attack is termed a myocardial infarction. An infarction occurs when a tissue experiences necrosis, or death, when blood circulation is blocked to the area due to a clot. This clot can be due to a thrombus or an embolus. A thrombus is when plaque attached to the wall of a vessel builds up over time and eventually blocks the passage of blood. An embolus is when a piece of that plaque breaks free, races through the blood stream, and eventually becomes lodged in a vessel, cutting off blood supply to the tissue on the other side. A myocardial infarction (MI), therefore, is death of the heart muscle (myo- meaning muscle, and cardio- meaning heart) due to this blockage in blood supply.
After an MI, the dead heart muscle is replaced by scar tissue, which helps stabilize the structure of the heart but does not self-repair or regenerate healthy, new heart muscle. This is different from almost all other tissues in the body, in which our local stem cells take over in times of stress or injury and initiate the repair and rebuild process. So why doesn’t our body naturally repair and regenerate heart muscle after a heart attack? A new study suggests it’s because there are no local stem cells in the heart muscle. Let’s review.
The Heart Muscle Doesn’t Heal After Heart Attack Probably Because It Contains No Stem Cells
The new study set out to answer the conflicting question of whether or not cardiac stem cells really exist. They did this by using advanced technologies to map all of the cells in the heart to determine if any actually divided for the purpose of replacing damaged heart muscle tissue following a heart attack.
The result? Many different types of cells in the heart did divide following heart attack; however, none of these cells were the type that healed or regenerated the damaged and dying heart muscle. So what kinds of cells are active following a heart attack? Fibroblasts (connective tissue cells) and cardiomyocytes (heart muscle cells) for example. These, in particular, are imperative after heart muscle death as they form scar tissue over the necrotic part of the heart muscle. Without this scar tissue formation, the heart would further weaken or possibly even rupture as it did in the mice in this study.
The study also suggests that what we know as cardiac stem cells actually differentiate into blood-vessel or immune cells, not cardiac muscle. To learn more about stem cell differentiation, or how they become specialized cells throughout the body, watch my video below:
Interestingly, a prior study I covered a couple of months ago found that these blood vessel stem cells could regenerate heart muscle after a heart attack, if only they could get to the dying tissue…
Blood Vessel Stem Cells Can’t Reach Heart Muscle After Heart Attack
How could blood vessel stem cells repair dying heart muscle? One study found that in culture the stem cells that line the walls of blood vessels can differentiate, or become, beating heart muscle cells, or cardiomyocytes. The problem is that while scientists can make this happen in cultured cells, in the body, these stem cells are blocked from being able to differentiate into cardiomyocytes by the scar tissue that forms after the heart attack. So while the scar tissue may be protecting the heart muscle from further damage, it may also be blocking the stem cells from initiating repair and healing. However, now that we know there are stem cells in the area that could help following a heart attack, it will be fascinating to see how research continues to progress in this area in an attempt to find a solution.
The Big Controversy?
The big brouhaha in science circles over heart muscle stem cells involves Harvard researcher Piero Anversa and a series of retractions of his published works. The problem? Harvard claims that many of his heart muscle stem cell studies “included falsified and/or fabricated data.” Anversa claimed in 2003 to have identified adult stem cells that could regenerate cardiac muscle. Other labs and clinical trials failed to reproduce his findings.
Can Other Stem Cells Help the Heart?
Now anyone reading the science news might immediately believe that all of this means that all stem cells don't help cardiac repair after a heart attack. That would be wrong, as this meta-analysis of 34 different randomized controlled trials covering the results of more than 2,300 patients demonstrated that the stem cells derived from bone marrow improved cardiac function after an acute MI. In fact, the only thing the meta-analysis was trying to figure out was when was it best to give the cells, which turned out to be three to seven days after the event.
The upshot? So does the heart have stem cells? Probably not. Do stem cells from elsewhere (like bone marrow) help after a heart attack? Yes, bone marrow stem cells infused three to seven days after the event seem to work quite well.