What Are Mesenchymal Stem Cells And Why Are They Important for Arthritis?

Mesenchymal stem cells, also known as MSCs, are cells that can differentiate into a number of cell types.

The distinction here should be made between the term "multipotent" and the term "pluripotent."

Stem cells (SCs) obtained from an adult are multipotent. While they can differentiate into a number of different cell types, their ability to differentiate is somewhat limited. That makes them different from embryonic stem cells. These are SCs obtained from fetuses. Embryonic SCs are "pluripotent" meaning they can differentiate into virtually any type of cell. While this makes them almost ideal for tissue repair, there are potential problems. The first is the ethical one that is still being debated in many quarters. The second is that while their power to differentiate is unquestioned, the ability to turn them off at the right time is a concern.

Adult MSCs can differentiate into various types of connective tissue which makes them valuable as a potential source of regenerative tissue for the treatment of disorders such as arthritis. In fact, adult MSCs are often referred to as "repair" SCs.

MSCs are found in the bone marrow, synovium (lining of the joint), the pulp of deciduous (baby) teeth, fat, and muscle.

Another source of MSCs is the umbilical cord.

Researchers are now discovering the various factors that cause MSCs to home in different areas of disease and damage.

Small proteins called chemokines apparently attract MSCs because these cells have receptors for chemokines on their surface. When a tissue is damaged or diseased, there is a release of chemokines which then travel via the bloodstream. When these chemokines bind to receptors on the surface of MSCs, they cause the stem cells to migrate to the site of injury.

In addition, other substances, called adhesion molecules, also present on the surface of MSCs play a role in cell migration to an area of injury.

To date, multiple methods for introducing SCs have been used. For example, orthopedic surgeons tout the benefits of microfracture. While short term benefit may be derived, microfracture surgery requires lengthy recuperation. Also, studies have demonstrated that the type of cartilage produced by microfracture is weaker fibrocartilage as opposed to the more desirable and stronger hyaline cartilage.

Recently, some studies have demonstrated the effectiveness of MSCs in combination with fat and platelet rich plasma in the treatment of osteoarthritis. Further studies need to be done to corroborate the early research.

What is unknown at the present are the following:

How many MSCs are required for repair of large areas of damage such as is found in osteoarthritis?

What is the role of MSCs in modulating immune system function? Some studies indicate these SCs have immunomodulatory effects.

While marrow contains a large number of MSCs, fat actually has a greater number per unit volume. Therefore, what is the role of fat in tissue regeneration?

Is there a method for inducing the chemokine and adhesion molecule functioning so as to enhance stem cell repair?

What is the optimal environment which permits SC reparative function?