What You Need To Know About Stem Cells

 

How Have Stem Cells Changed Treatment For Degenerative Diseases

Regenerative medicine, which relies on the near-magic of human stem cells, has come far in the last two decades. For medical problems that once seemed past all hope – such as leukemia and other types of cancer, degenerative diseases like osteoarthritis, or traumatic injury to the body – humanity now has a range of solutions based on actually regrowing injured or damage systems.

How Do Cells Work?

The human body comprises trillions of cells. When like cells work together, these are known as tissues. We have many types of tissue, such as nervous, cardiac, liver and so much more.

Cells are complex structures that have dedicated purposes, depending on their location and function in the body. In other words, the inner and outer structure of each cell varies with the job it does. However, they share similarities across tissue types, including an outer membrane, inner organelles (the cell’s own “organs”) and a nucleus containing our genetic code or DNA.

By dividing constantly, cells are able to maintain the functionality of muscles, organs, tissues, and blood. Over time, the older cells die off and get recycled by the body, while younger cells take their place. The result is a cycle of birth that mimics life itself. It keeps a human body going for as much as a hundred years – and maybe more.

Unfortunately, while cells are nothing short of miraculous in their machinery, most cell divisions can’t keep going forever.

Why Don’t All Cells Reproduce Forever?

Some parts of the body do produce more stem cells on their own. For instance, bone marrow is capable of producing stem cells that differentiate into various types of blood cells. For that reason, most people do not need to worry about their blood becoming compromised over time, except in cases where the cells themselves are defective (ex. sickle-cell anemia), or cases where the bone marrow itself suffers damage (ex. leukemia). Normally, though, if you have blood drawn, or even if you lose a lot of it to injury, you can make more.

Other parts of the body are not so lucky, however. We come into this world with a limited number of some types of cells. Other cell types can proliferate, but to a limited extent. When damage occurs to the heart or brain, if it is severe enough, there is usually no saving the victim.

The same is true for cartilage cells. Degenerative conditions such as osteoarthritis, in which cartilage in the joints breaks down over time, eventually result in a painful grinding of bone on bone. In some cases, surgery or over-the-counter medicine can help. In others, steroid injections may provide relief. But, few approaches (if any) can help the cartilage to grow back.

Then there is the fact that cells simply get “old.” After a certain number of divisions, the cells can start to have problems. That’s because the ends of each chromosome (strands of DNA all coiled up into compact shapes), start to unravel. These sites – called telomeres – degrade over time, resulting in worse and worse copies of your genetic information. These “senescent cells” just aren’t good anymore.

How Do Stem Cells Help?

Stem cells solve this problem of finite cell division, as well as the problem of traumatic injury to parts of the body that cannot repair themselves.

Unlike regular cells, which have a dedicated role, stem cells can turn into many types of cell. So, for instance, a muscle cell could never fill in for a blood cell or heart cell. That’s not what it’s made for. However, a stem cell could see a need in the body, head to that location (called “honing”) and become the necessary cell type through a guided transformation involving chemicals, growth factors and other complex determinants.

In addition, stem cells are the foundation of development in complex plants and animals. The embryo, or extremely early life stage, contains stem cells. As development progresses, these stem cells turn into the different cell types needed to create a fully functioning human, cow, or tree. They turn into the tissue-specific cells discussed above.

Some types of stem cells (discussed below) are only present in the earliest stages of development, while other types remain throughout the remainder of fetal development (in mammals, anyway). Still, others remain present in the body throughout an adult’s lifetime.

What Types of Stem Cells Exist?

A range of stem cells exist. The first distinction is between adult and embryonic stem cells, while the second main distinction is between the level of capability stem cells possess to turn into other types of cells. Note the overlap between the two categories.

Embryonic Stem Cells

When two gametes unite to form an embryo, new life is initiated. After 3 to five days, the embryo becomes a blastocyst composed of roughly 150 cells. During this time, embryonic stem cells start to form. Present at the earliest stages of life, embryonic stem cells can form any of the more than 200 cell types present in the human body.
Quickly, embryonic stem cells start to specialize and lose their ability to turn into any type of cell.

Adult Stem Cells

Adult stem cells are present in the human body after birth, during childhood, and throughout the adult lifespan. They exist in a number of places, including within the teeth, liver, brain, skeletal muscle, gut, ovarian epithelium, testis, heart, and a few other places. However, the most common places from which to harvest those cells today include the bone marrow, adipose tissue (fat cells), and peripheral blood.

Tissue-Specific (Multipotent) Stem Cells

Adult stem cells are tissue-specific, meaning that they can become a limited number of cell types. An example of tissue-specific stem cells includes the mesenchymal stem cells (MSCs), which can develop into many of the cells associated with the skeletal system, such as bone cells, cartilage cells, muscle cells, and fat cells. Similarly, hematopoietic stem cells (HSCs) can give rise to a wide range of blood cells, including white blood cells, platelets, red blood cells and more.
Tissue-specific stem cells are multipotent stem cells, because they can turn into many different, but not all, types of cells.

Pluripotent Stem Cells

Pluripotent stem cells are so named because they are able to turn into any cell in the body. These are found only in the earliest stages of embryonic development. In 2006, scientists also discovered a way to “induce” pluripotency, as described below in the section on induced pluripotent stem cells (iPSCs).

How Are Stem Cells Used in Medicine?

Stem cells are used in a variety of ways in medicine. For instance, when a person has a blood or bone marrow disorder, they may receive a stem cell transplant. If they have lost the ability to manufacture their own new marrow or blood cells, then replenishing their stem cells will renew that function.

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