Lecture 24: Muscle Diseases - Stem Cell Therapies

Question 1

What treatments are currently in use that current research is trying to fix?

Answer 1

Whole organ transplants

Tissue and cell therapies

Question 2

What are the limitations of current treatments?

Answer 2

Rely on organ donors

Question 3

What are the aims of stem cell research?

Answer 3

treatments that do not rely upon organ/tissue donors

Novel therapies also needed for conditions where there is no treatment/cure

Question 4

What is the idea behind stem cell transplantation?

Answer 4

Transplantation of undifferentiated cells that are capable of both replication and differentiation

Question 5

What are the types of stem cells?

Answer 5

embryonic stem cells (eSC)

adult stem cells

inducible pluripotent stem cells (iPSCs)

Question 6

What are the types of transplantation?

Answer 6

allogenic (heterologous) transplantation involves different donor/host combination

Autologous transplantation involves a single individual

Question 7

Where are embryonic stem cells derived from?

Answer 7

The inner cell mass

Question 8

Where are stem cells derived from?

Answer 8

IVF leftovers

Question 9

What stem cells are good to get from the placenta?

Answer 9

Haemopoetic and mesenchymal stem cells

Question 10

What is the current belief regarding adult stem cells?

Answer 10

Every single tissue in the body is believed to have a population of stem cells.

Question 11

How are induced stem cells produced?

Answer 11

Stem cell pluripotency can be induced by upregulating certain genes.

*Shinaya Yamanaka

Question 12

What is the most heavily researched stem cells?

Answer 12

vast majority of stem cell trials are based around hematopoietic stem cells

Question 13

Where are skeletal muscle stem cells located?

Answer 13

between sarcolemma and basal lamina

Question 14

What is the requirement of a stem cell population?

Answer 14

Capable of renewal and differentiation into muscle

Question 15

What happens to muscle stem cell population when there is no injury?

Answer 15

They sit outside of the cell cycle in a state known as quiescence.

Question 16

How often do muscle stem cells proliferate and divide?

Answer 16

Very rarely unless there is injury

Question 17

How are muscle stem cells unique?

Answer 17

It is one of the few stem cell populations that are known to localize to aerobic conditions.

Question 18

What is another name for muscle stem cells?

Answer 18

satellite cells

Question 19

What are some other cell types that can be used for transplantation therapies?

Answer 19

Fibroadipogenic cells

Pericytes

Mesangioblasts

Mesenchymal stem cells

Bone marrow-derived stem cells

PW1 + interstitial cells

Question 20

How is the satellite cell cycle regulated?

Answer 20

Via a family of transcription factors called the myogenic regulatory factor genes.

Question 21

What does MyoD do?

Answer 21

MyoD (myogenic differentiation factor) is essential for specialization to form muscle cells

Question 22

What muscle conditions could benefit from transplant therapies?

Answer 22

Muscle injury

Genetic disorders (muscular dystrophy)

Aging

Type 2 diabetes

Question 23

What was the effect of myoblast cell transplantation in muscle of mdx mice? What happened when this was moved to clinical trials?

Answer 23

Dystrophic expression was returned

Fibrosis was decreased and was more heterogenous

Myoblast transplant was unsuccessful in clinical trials due to myoblasts dying soon after transplantation.

(Peter Law’s trials caused dystrust in scientific community)

Question 24

What effect did culturing of MuSc have on their ability to engraft into muscle tissue?

Answer 24

Freshly isolated MuSC engraft much more effectively than cultured MuSC

Question 25

Why were freshly isolated MuSCs more effectively transferred to muscle than cultured cells?

Answer 25

Cultured cells expressed MyoD which causes proliferation and as a result glycolysis. Glycolysis inhibits effective transplantation.

*Genetically ablating cells showed that freshly isolated MuSCs transplanted more efficiently due to MyoD expression in cultured cells.

Question 26

What metabolic pathway do rapidly proliferating cells such as tumours utilize?

Answer 26

Tumour cells choose to utilize glycolytic pathway because because glycolysis aids proliferation. (i.e it is a quick source of ATP)

Muscle cells don’t follow this trend. They enter the cell cycle during periods of oxidative phosphorylation

Question 27

How is metabolism manipulated in cultures to test for expressed proteins during different types of metabolism?

Answer 27

High glucose can be used to stimulate dependence on glycolysis.

Low glucose can be used to stimulate oxidative metabolism

Question 28

What did low galactose/glucose group indicate?

Answer 28

In low glucose/galactose group (i.e oxidative group) the cell cycle factors were expressed indicating that oxidative phosphorylation favors myoblast proliferation

Question 29

What happens to Pax7 and MyoD expression in single fiber cultures put at high or low carbohydrate conditions?

Answer 29

When single fibers are cultured in growth media proportion of cells expressing pax7 disappears very quickly and proportion of cells which are both MyoD+ and pax7+ decreases over time. Proportion of cells that are only MyoD+ increases over time.

This shows that when single fibers are cultured in low glucose/galactose conditions they move towards the proliferation pathway.

When cultured in high glucose/galactose conditions they are better for transplantation.

Question 30

What happens to proliferation if glucose transporter is inhibited by TXNIP?

Answer 30

Cell can be made to move to glycolytic matabolism by inhibiting glucose transporters and as a result proliferation can be favoured.

Overexpression of glucose transporter inhibitor results in senescense which is irreversible G0.

Question 31

In summary:

Answer 31

High oxidative metabolism = Quiescence

High glycolytic metabolism = Proliferation

MyoD is expressed in SCs that are proliferating

High glucose = Lots of glycolysis = Proliferation

Low glucose = lack of glycolysis = specialization

Galactose = more oxidative metabolism = Specialization

TXNIP inhibits the glucose channel and as a results favours aerobic respiration but too much inhibition by TXNIP results in permanent senescense.

Question 32

What happens when high galactose levels are used in culture?

Answer 32

High galactose levels favour oxidative metabolism and in turn specialization.