How do stem cells know what type of cell to turn into? While scientists have known some parts of that story, new pieces of information are discovered every year. Take for example a recent study that demonstrated that sugar may play a role. Let me explain.
Stem Cells: The Body’s General Contractors of Repair
Stem cells, as I’ve mentioned many times, are the body’s primary repairmen. Taking this beyond that analogy, they are more like the general contractors of the repair process, coordinating everything from calling in specialized repair cells and influencing them to work extra hard at their job to replacing damaged mitochondria (a cell’s energy source) in a specialized cell to actually replacing an entire cell through a process called differentiation.
I covered stem cells and differentiation in a recent post, but, briefly, it’s when a stem cell detects a dying cell and then divides, making a reserve stem cell and a progenitor cell. The progenitor cell will transform into the specialized cell type that is dying. For example, if a skin cell can’t be repaired, a local stem cell can divide, and its progenitor cell can transform into the same type of skin cell and replace it.
Specialized Cells: The Cells That Aren’t Stem Cells…
What is a specialized cell? Specialized cells, or somatic cells, are any cells in the body that are not stem cells or fertilization cells (sperm, ova, gametocytes). They are specialized to perform specific functions. The list of somatic cells is very long, but it includes cells that make up every organ and system of the body, such as the circulatory system (e.g. erythrocytes, leukocytes), musculoskeletal system (e.g., osteoclasts, osteoblasts, chondrocytes), immune system (e.g., macrophages, neutrophils), nervous system (e.g., neurons, astrocytes), and so on.
So how, exactly, does a stem cell know what kind of specialized cell it can create? For example, how does a specific neural stem cell in the brain know to become an astrocyte rather than a neuron, while another neural stem cell will become a neuron? Can any stem cell become any specialized cell? Could the neural stem cell that became an astrocyte just as easily have become a neuron if it had been in the right place at the right time? It seems the answer to the final two questions, according to a new study, might be that that’s simply not how it works. Let’s review.
The Key to What Specialized Cells Stem Cells Form Is Sugar!
In the new study, researchers examined how stem cells determined what kinds of specialized cells to form. They focused on investigating specifically what led neural stem cells of the brain to form either neurons, astrocytes, or oligodendrocytes (all specialized cells of the nervous system). What did they find? Sugar was the primary player. The surface of the stem cells had specific sugar patterns that formed the common connection among each specialized cell type. For example, the sugar patterns on the stem cells that formed astrocytes were all similar but distinctly different from the sugar patterns on the stem cells that formed neurons.
So it seems the answer to how our stem cells know what cell types to form may simply be their sugar patterns. However, what to do with this information is a bit more complex. For starters, how does that sugar get there, and why do stem cells have different sugar patterns? These are topics for another day, but the goal of this study was to provide another step toward either predicting or modifying stem cell patterns to best treat injuries and diseases in the future. If we know ahead of time precisely what type of cell a stem cell will become, we can better plan treatment.
The upshot? This new study shows us that even though stem cells may look the same in a microscope, they have subtle differences that determine their final fate. By picking out stem cell sub-populations that are supposed to become the type of cell we want to repair, science may be able to make our treatments better.