STEM CELLS

Stem cells have been a very controversial topic since they were discovered in the mid 1970s. The use of embryonic stem cells has caused many moral and practical dilemmas. Embryonic stem cell research requires the creation, usage, and destruction of human embryos. But today scientists are researching new ways to cure diseases without the use of embryonic stem cells.

Glossary

Stem cells: cells with the ability to divide for indefinite periods in culture and to give rise to specialized cells

Embryonic stem cells: undifferentiated cells derived from a 5-day preimplantation embryo that are capable of dividing without differentiating for a prolonged period in culture and are known to develop into cells and tissues of the three primary germ layers

Induced pluripotent stem cells (iPSC): a pluripotent stem cells artificially derived from a non-pluripotent cell, typically a somatic cell, by inducing a forced expression of specific genes which preprograms the cell to enter and embryonic stem cell-like state

Adult stem cells (somatic stem cells): a relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation

Pluripotency: the capacity to morph into any tissue in the body

Preimplantation: embryo has not yet implanted in the wall of the uterus

Some depth

Stem cells have the potential to develop into many different cell types in the body during early life and growth. They may for tissues that serve as a sort of internal repair system, dividing essentially without limit to replenish other cells. Each new stem cell, when it’s dividing, has the potential to either remain and stem cell or become another type of cell with a more specialized function. Two fundamental properties of stem cells are that they are capable of renewing themselves through cell division, sometimes after long periods of inactivity, and they can be induced to become tissue-specific or organ-specific cells with specialized functions, under certain experimental conditions.

iPSCs demonstrate important characteristics of pluripotent stem cells. They include the expression of stem cell markers, the formation of tumors contain cells from all three germ layers, and the ability to contribute to many different tissues when injected.

Somatic cells vs. embryonic stem cells: Both types of stem cells have potential for cell-based regenerative therapies. However, there are some major differences. Embryonic stems cells are pluripotent. Somatic stem cells are thought to be more limited to differentiating into different cell types of their tissue of origin. Embryonic stems cells can be grown relatively easily in culture while somatic stem cells are rare. Embryonic stem cells have a higher chance of rejection than somatic stem cells because somatic stem cells contain the host’s DNA so they are perfect matches as opposed to an embryo.

Medical experiments

Parkinson’s disease: Researches have created embryonic stem cells to become the types of cells damaged by this neurodegenerative disease and grafted them into the appropriate brain area of mice (who were injected with a deficit similar to Parkinson’s disease). Results showed that the neurons integrated themselves into the mice’s tissue and made proper connections. However, some cells were cancerous because they had a high potential to divide.

Spinal cord injury: Researches grafted human neural stem cells into mice with spinal cord injuries. The results produced appropriately differentiated cells and helped the mice recover motor function. But this stem cell therapy will take years before a clinical therapy is available for humans.

Experimental heart repair: Stem cells are currently used in a human clinical trial to repair the heart muscle that was damaged or destroyed during heart attacks. These stem cells come from bone marrow and circulating blood. Data suggests that these cells may help make moderate repairs, but there is no significant date to make a conclusion yet.

Differentiation

Scientists can harvest and maintain stem cells and they can cause stem cells to differentiate in to many different lineages, but some types of differentiation are hard to control. For example, the proper differentiation and growth of neurons are still difficult to perform, whereas the differentiation to muscle is easier. Scientists use growth additives to encourage differentiation. For example sonic hedgehog and retinoic acid are used to tell cells what to do. Also, activin is similar in function to sonic hedgehog. Hormonal environments also affect the path a stem cell can take in its differentiation.