Specific organ functions rely on differentiated cells. How differentiated
cells are replaced is a fundamental question in biology
with important implications for regenerative medicine.

So begins a recent paper in Cell which has shown heart cells in rodents can be stimulated to proliferate, thus repairing any damage. Typically the heart stops proliferating or regenerating shortly after birth, so any event that causes death the heart cells, like a heart attack (myocardial infarction), is currently quite irreversible. Past research on heart cell regeneration focused on trying to manipulate stem cells to differentiate into new heart muscle cells(cardiomyocytes). The breakthrough in this paper was to focus on healthy differentiated heart cells and see if any proteins could stimulate them to start dividing and repair the damage.

The scientists (Kevin Bersell, Shima Arab, Bernhard Haring, and Bernhard Kühn) tested the signaling protein, neuregulin1 (NRG1)) which is known to stimulate heart cell growth in prenatal development and even in fetal tissue. The results showed that neuregulin1 stimulated proliferation in 30% of the heart tissue as compared with 1% proliferation in control groups.

The finding  represents a major breakthrough in regenerative medicine. The protein, neuregulin1, is administered via injection, creating a noninvasive method of heart tissue repair. Kühn, one of the major investigators of the paper, is already looking for profitable potential therapies.

Bersell, K., Arab, S., Haring, B. & Kuhn, B. (2009). Neuregulin1/ErbB4 Signaling Induces Cardiomyocyte Proliferation and Repair of Heart Injury Cell

As I read the article, I found myself asking a lot of questions, that seem obvious but that I rarely think about. Questions like: How exactly does my body repair a cut on my skin? How does it know to do it? What does it have in reserve? Why doesn't it use the same mechanism to keep my skin from looking wrinkled and scathed? How do scars form?

A sample passage:

In the skin, there are stem cells that exist within the bulge of the hair follicle and also in the basal layer of the epidermis. We still don't know whether all of the cells within the basal layer can behave as stem cells or whether only a few stem cells exist that are scattered within this layer. It's an open question of where along the lineage to differentiation is the point of no return where a stem cell becomes irreversibly committed to terminally differentiate. In the skin the point of no return has definitely passed in the dead hair cells or in the enucleated squames [squamous cells] that are sloughed off the skin. But can an epidermal cell that has exited the basal layer and begun its journey to the body surface go backwards under certain circumstances and become a stem cell again?

To answer this question, we need to have a firmer grasp of the key features of a stem cell that determine stemness.

What I suddenly realized reading the article is that all these questions of regeneration are very unknown, and the medical potential of finding out is huge, and beyond that, it would be hugely satisfying as a human to really understand how the mechanics of my body works. I would love to make a working molecular model of a human one day. (In computer simulation of course) ;)

As for the potential of stem cells? Well some wikipedians have put together a good image for that: