Unit 4 BHS: Stem Cells & Ageing

Question 1

Identify and explain the 4 types of stem cell potencies

Answer 1

1. totipotent: can give rise to all cell types, including structures that support the developing foetus. Cells of embryonic morula.
2. pluripotent: all derive into all types of cells but not supporting structures. Cells of inner cell mass of the blastocyst.
3. multipotency: can give rise to a number of cell types. e.g. Bone marrow
4. unipotency: follows only one cell lineage.

Question 2

Explain the mechanism by which stem cells renew itself

Answer 2

Asymmetric divison: giving rise to one identical daughter cell and another partially defined progenitor cell. This way, the stem cell pool remains the same size.

Question 3

Explain the therapeutic potential of stem cells

Answer 3

1. mesenchymal cells can differentiate into adipocytes, chondrocytes, osteoblasts, neurons and muscle cells. They have potential to be used in treating cartilage, bone, neural and muscular related disorders.
2. adult stem cells: haematopoeitic cells can be harvested from a patient, it can be cultured in laboratory settings and these cells can be injected back into the patient to treat blood disorders.
3. umbilical stem cells: vascular cells can be isolated from the umbilical cord, after undergoing tissue engineering, these cells can be surgically implanted into the patient to treat conditions such as congenital heart diseases.
4. induced pluripotent cells (iPs): terminally differentiated skin fibroblast cells can be reversed into pluripotency by the addition of 4 genes (transcription factors). These cells can be redirected into a different specialisation, thus have the potential of treating a number of diseases.

Question 4

The use of stem cells in medicine and medical research

Answer 4

1. test drugs on human cells in culture
2. study cell differentiation
3. understand birth defects

Question 5

Explain how adult stem cells are affected by ageing

Answer 5

The stem cell hypothesis of ageing: living organisms are as old as their adult stem cells. Stem cell function declines with age and can undergo age-related change. Stem cell ageing mirrors the ageing of other tissues, marked by inflammatory responses, stress responses, and substantial alterations in the regulation of chromatin structure.

Adult stem cells interact with the environment. Locally within the niche, stem cells respond to ECM, and other stem cells and their paracrine factors. Within a tissue, stem cell niche is influenced by soluble factors derived from mesenchymal cells, which in turn are influenced by systemic immunological and endocrine signals. Thus external factors filter down through the various levels to influence stem cell function.

Question 6

Explain how ageing affects the functionality of stem cells

Answer 6

1. Muscular system: repair of muscle after injury is affected by intrinsic stem cell ageing; ageing of local microenvironment or stem cell niche; and the ageing of systemic environments.
2. Neural system: neurogenesis decline with age. Number of neural stem cells decline. This results in impaired ability to repair olfactory cells (sense of smell diminishes).

Question 7

Can stem cells renew the physiology of ageing?

Answer 7

If we find a way to keep stem cells young, they may regenerate aged tissues more efficiently. In order to achieve this we need to understand the molecules and processes that enable the self-renewal, division and differentiation of adult stem cells.

Current research:

1) reverse ageing by suppressing the accumulation of retrotransposon transcripts
2) injection of stem cells in to mice model of progeria resulted in improved health and increased lifespan
3) injection of embryonic stem cell-dervived retinal pigment epithelial cells to reverse effects of age-related macular degeneration (AMD)
4) turning back the molecular clock of dysfunctional cells in-vivo
5) sirtuin (SIRT3) prolongs lifespan of yeast, and when injected into mice, production of adult stem cells increased.