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BASICS OF

STEM CELLS: TISSUE ENGINEERING

Dr.Sandeep Agrawal!MS,DNB(Orthopedics)!Agrasen Hospital!Gondia!Maharashtra!India!www.agrasenortho.com!drsandeep123@gmail.com

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Tissue Engineering is Multidisciplinary

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What are Stem Cells?

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Stem cell division and

Differentiation 1: Symmetric stem cell division

2: Asymmetric stem cell division

3: Progenitor division

4: Terminal differentiation

A: Stem Cell

B: Progenitor Cell

C: Differentiated Cell

Symmetric Stem Cell Division

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Asymmetric division of stem cells

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Three unique properties of stem cells

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1. Stem cells are unspecialized

Does not have any tissue-specific structures that allow it to perform specialized functions.

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2.Stem cells are capable of dividing and renewing themselves for long periods.

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3.Stem cells can give rise to specialized cells

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In embryos, stem cells function to generate new organs and tissues. In adults, they function to replace cells during the natural course of cell turnover.

4.Stem cells exist in both embryos and adults.

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Distinguishing Features of Progenitor/Precursor Cells and Stem Cells.

■ A stem cell :Unspecialized cell that develops into a variety of specialized cell types.

■ Divides and gives rise to one additional stem cell and a specialized cell. !

■ A progenitor cell (a precursor cell) is unspecialized that is capable of undergoing cell division and yielding two specialized cells.

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Pluripotent stem cells

!Differentiate into any cell type, except for totipotent stem cells and the cells of the placenta.

“Pluri” from Latin plures means several or many. Have the potential to give rise to any type of cell.

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An Overview of Early Development

Fertilized egg

Totipotent stem cells

Totipotent: Can become any cell in body or placenta

Fate Decision

Pluripotent stem cells (3-5 days old)

Blastocyst

Pluripotent: Can become any cell in body

Implantation

Fate DecisionGastrulation (day 14) leads to Primary Germ Cells Endoderm (inner)!digestive tract, resp. track Mesoderm (middle)!bones, blood cells, heart Ectoderm (outer)!skin, CNS

Multipotent: Can become any cell within a specific germ layer or cell lineage

Embryonic stem cells come from inner cell mass of blastocyst.

Implantation

Fate DecisionGastrulation (day 14) leads to Primary Germ Cells Endoderm (inner)!digestive tract, resp. track Mesoderm (middle)!bones, blood cells, heart Ectoderm (outer)!skin, CNS

Multipotent: Can become any cell within a specific germ layer or cell lineage

Multipotent

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Somatic Cell

Endoderm Ectoderm Mesoderm

Liver Intestine Pancreas

Skin Hair

Nerves

Blood Muscle Bone

Cartilage

Somatic stem cell

Germ stem cell

Primitive germ cell

Gametes

Pluripotent Embryonal stem cell

Totipotent stem cells

Pluripotent stem cells

Adult Multipotent stem cell

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Embryonic Type stem cells

1.Embryonic Type

Embryonic Stem Cells  Embryonic Germ Cells

2. Adult Type

Umbilical Cord Stem Cells Placental Stem Cells Adult Stem Cells

Adult type Stem cells

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Comparison of embryonic and adult stem cells

■ Advantages of  Embryonic Stem Cell    1. Flexible - appear to have the potential to make

any cell.   2. Immortal - one embryonic stem cell line can potentially provide an endless supply of cells with defined characteristics.   3. Availability - embryos from in vitro fertilization clinics.

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Superior features of ESCs

■ Embryonic stem cells are easier to identify, isolate and harvest.

■ There are more of them. ■ They grow more quickly and easily in

the lab than adult stem cells. ■ They can be more easily manipulated

(they are more plastic)

Advantages of Embryonic Stem Cells over adult stem cells:

Embryonic S.C. Adult S.C.

“Pluripotent”(can become any cell

types present in the human body

“Multipotent”(“can become many but

not any”) E.g., blood stem cells can develop into several blood

cell types, but cannot develop into brain, kidney, or

liver cells

Stable. Can undergo many cell divisions.

Less Stable. Capacity for self-renewal is limited.

Easy to obtain but blastocyst is destroyed.

Difficult to isolate in adult tissue.

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Disadvantages of Embryonic Stem Cell

1. Difficult to differentiate uniformly and homogeneously into a target tissue.

2. Immunogenic - embryonic stem cells from a random embryo donor are likely to be rejected after transplantation

3. Tumorigenic - capable of forming tumors or promoting tumor formation.

4. Destruction of developing human life.

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Advantages of Adult Stem Cell1. Adult stem cells from bone marrow and umbilical

cords appear to be as flexible as the embryonic type 2. Somewhat specialized - inducement may be

simpler. 3. Not immunogenic - recipients who receive the

products of their own stem cells will not experience immune rejection.

4. Relative ease of procurement - some adult stem cells are easy to harvest (skin, muscle, marrow, fat)

5. Non-tumorigenic-tend not to form tumors. 6. No harm done to the donor.

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Disadvantages of Adult stem cells

 1. Limited quantity.  2. Finite - may not live as long as embryonic stem cells in culture.  3. Less flexible

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Why adult stem cells preferable to embryonic cells?

■ Naturally exist in our bodies, and they provide a natural repair mechanism for many tissues.

■ Belong in the microenvironment of adult body, while embryonic stem cells belong in the microenvironment of the early embryo, where they tend to cause tumors and immune system reactions.

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Source of Stem cells

● Autologus, allogeneic or xenogenic sources

● Foetal tissue … best current tissue source for human neural stem cells.

Embryonic Excess IVF embryos. !Fetal Aborted Fetuses !Adult stem cells Cord blood Cord (Wharton’s Jelly) Placenta Amnion, Amniotic fluid Endometrium, Menstrual blood, Milk Teeth and Wisdom teeth

DISCARDED STEM CELLS

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Mesenchymal Stem Cell (MSC)

Osteoblast Chondrocyt Myoblast Stromal Tenoblast Preadipocyt

Osteocyte Chondrocyt Myocyte Stromal Tenocyte Adipocyte

Bone Cartilage Cardiac Stroma Tendon Adipose

Benefits of mesenchymal

stem cell

No risk of rejection – used across HLA barrier

No risk of teratoma formation

Pluripotent

No ethical issues

Immune privileged

Greater potency of cultured expanded product

Lower cost of cell culture process

Efficient large scale expansion

Homogeneous population and high rate of cell division

Precise identification

Ease of isolation and scale up

Genetic stability

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Isolation & characterization of MSCs from human bone marrow

Stem Cells 2002;20:249-258

Size-sieved methods •MSCs is greater in size •MSCs is easier adhere to culture dish •MSCs is better expanded in 10%FBS-DMEM-LG •The use of culture insert with 3-µm pores !

• Also Known as Wharton’s Jelly

• Adult stem cells of infant origin

• Less invasive than bone marrow

• Greater compatibility

• Less expensive

• Obtained from cord immediately after birth.

• Rich source of haemopoietic stem cells

• These are referred to as neonatal stem cells, less mature than those found in adults bone marrow..

!Three important functions: 1. Plasticity: Potential to change into other cell types like nerve cells 2. Homing: To travel to the site of tissue damage 3. Engraftment: To unite with other tissues

Umbilical Cord Blood Stem Cells

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References• http://stemcells.nih.gov/info/scireport/2001report.htm

• http://www.ulb.ac.be/sciences/biodic/biodic/images/bio_animale/embryologie/fecondation/baefec_01_01.jpg

• http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=mboc4.figgrp.3748

• http://www.news.wisc.edu/packages/stemcells/illustration.html

• http://www.drugs.com/enc/images/images/en/17010.jpg

• http://embryology.med.unsw.edu.au/Notes/placenta.htm

• http://www.dnalc.org/stemcells.html

• http://gslc.genetics.utah.edu/units/stemcells/

• http://en.wikipedia.org/wiki/Main_Page

• Harrison Internal Medicine Edition 18

• Robbins Pathology Edition 8

Research on Stem Cells is progressing in spite of several restrictions

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DISCLAIMER

This presentation is for  doctors and students in general.". Graphics,Images and jpeg files are taken from Google and yahoo  Image  to heighten the specific points in this presentation. "• If there is any objection/or copyright violation, please inform drsandeep123@gmail.com for prompt deletion. "• It is intended for use only by the doctors of orthopaedic surgery.". Views expressed in this presentation are personal. • .For any confusion please contact the sole author for clarification. "• Every body is allowed to copy or download and use the material best suited to him. "There is no financial involvement." • For any correction or suggestion please contact drsandeep123@gmail.com."