Stem Cells
Study Notes on Stem Cells and Applications
Introduction
Stem cells are defined as cells capable of self-renewal and differentiation.
Self-renewal: The ability of cells to proliferate indefinitely without losing differentiation potential and without undergoing senescence (biological aging).
A stem cell is a precursor cell that can develop into multiple tissue types such as skin, muscle, or nerve cells.
Stem cells serve as the foundational building blocks of the human body.
Features of Stem Cells
Uniqueness: Stem cells are distinct from other cell types due to their capabilities.
Developmental Potential: They can develop into various cell types in the body, which allows for a diversity of functions.
Repair Mechanism: Stem cells act as a natural repair system, restoring functions to damaged areas.
Limitless Division: These cells can theoretically divide indefinitely to replenish various specialized cells.
Daughter Cell Potential: Upon division, the new cells can either remain stem cells or evolve into more specialized functions (e.g., muscle cell, brain cell).
Unique Properties of Stem Cells
They can self-renew and divide for extended periods.
Stem cells are unspecialized, meaning they can give rise to specialized cell types when required.
They remain uncommitted until they receive signals to differentiate into specialized cells.
Stem Cell History
1998: Researchers extract stem cells from human embryos.
1999: First successful human transplant of insulin-producing cells from cadavers.
2001: President Bush restricts federal funding for embryonic stem cell research.
2002: Juvenile Diabetes Research Foundation International initiates a $20 million fundraising effort to support stem cell research.
2004: California approves stem cell research funding, and Harvard researchers grow stem cells from embryos using private funding.
Stem Cell - Definition
Defined as a cell that can continuously divide and differentiate into various types of cells/tissues.
Characteristics of Stem Cells
Self-renewable: Ability to continuously divide.
Pluripotent: Can develop into various cell types.
Repair Function: Can restore function to damaged cells within a living organism.
Types of Stem Cells
Embryonic Stem Cells:
Source: Derived from a five to six-day-old embryo.
Capabilities: Can form virtually any cell type in the human body.
Embryonic Germ Cells:
Origin: Derived from parts of human embryos or fetuses that develop into gametes (eggs or sperm).
Adult Stem Cells:
Location: Found among specialized cells in tissues/organs after birth.
Limitations: More restricted in producing different cell types and self-renewal compared to embryonic stem cells.
Subtypes of Stem Cells
Embryonic Stem Cells: Pluripotent and derived from the inner cell mass of blastocysts.
Fetal Stem Cells, Adult Stem Cells: Include cells from various tissues such as liver, brain (CNS stem cells), fat, and bone marrow.
Amniotic Stem Cells: Derived from amniotic fluid and also possess significant regenerative potential.
Classification of Stem Cells Based on Differentiation Ability
Totipotent: Can create all cell types, including placental cells.
Pluripotent: Can differentiate into all cells from the three embryonic layers but not placental structures.
Multipotent: Limited to a finite number of cell types, primarily from adult tissues.
Unipotent: Can develop into one specific cell type.
Embryonic Stem Cells (ES Cells)
Origin: Derived from the inner cell mass of the blastocyst, approximately 4-5 days post-fertilization, comprising 50-150 cells.
Ethical concerns surrounding the isolation of inner cell mass due to destruction of embryos.
Typical size: Human ESCs measure approximately 14 µm, mouse ESCs around 8 µm.
Advantages of Embryonic Stem Cells
Flexibility: Potential to differentiate into any cell type.
Immortality: A single embryonic stem cell line can potentially provide an endless supply of predetermined cells.
Availability: Abundant sources from in vitro fertilization clinics.
Disadvantages of Embryonic Stem Cells
Difficulty in Differentiation: Uniform differentiation into target tissues can be challenging.
Immunogenicity: Risk of immune rejection after transplantation due to being derived from random embryonic donors.
Tumorigenicity: Potential for tumor formation.
Ethical Issues: Involves the destruction of developing human life.
Adult Stem Cells
Definition: Undifferentiated cells found within specialized cells in tissues/organs, responsible for maintaining and repairing these tissues.
Somatic Stem Cells: Term used interchangeably with adult stem cells, referring to non-germ cells of the body.
Differentiation Pathways of Adult Stem Cells
Neural Stem Cells: Give rise to neurons, astrocytes, and oligodendrocytes in the brain.
Epithelial Stem Cells: In the digestive tract, lead to absorptive cells, goblet cells, Paneth cells, and enteroendocrine cells.
Skin Stem Cells: Located in the basal epidermis and hair follicle bases; produce keratinocytes for skin protection.
Adult Stem Cell Advantages
Flexibility: Capable of giving rise to various cell types similar to embryonic stem cells.
Reduced Immunogenicity: Cells from the recipient's own body minimize immune rejection risk.
Ease of Procurement: Can harvest from areas like skin, muscle, marrow, and fat easily.
Non-tumorigenic: Generally, adult stem cells do not lead to tumors.
Adult Stem Cell Disadvantages
Limited Quantity: May be difficult to obtain large quantities.
Finite: May not have as long a lifespan in cultures compared to embryonic stem cells.
Less Flexibility: More difficult to reprogram to form other tissue types compared to embryonic stem cells.
Induced Pluripotent Stem Cells (iPSCs)
Description: Adult cells genetically reprogrammed to an embryonic stem cell-like state by expressing specific genes significant for maintaining pluripotent properties.
Initial discovery: Mouse iPSCs (2006) and human iPSCs (2007) demonstrated pluripotent characteristics.
Current research is ongoing to evaluate differences, if any, between iPSCs and embryonic stem cells in clinical applications.
Applications of Stem Cells
Developmental Study: Understanding organism development from fertilized eggs.
Disease Treatment: Used in treatments for extensive burns and to restore the blood system in leukemia patients.
Modeling Diseases: Stem cells engineered to carry disease genes for laboratory modeling.
Testing Medical Treatments: Enables testing new medications for safety before human trials.
Cell Therapy: Potential treatment for various diseases such as Parkinson’s, Alzheimer’s, and many others.
Regenerative Medicine: Focused on repairing damaged organs or tissues.
Ethical and Political Issues Surrounding Stem Cell Research
Ethical considerations: Concerns over the destruction of embryos for stem cells.
Regulatory challenges: Variability in stem cell research legality globally, influenced by local social and political climates.
Public perception: Model stem cell research as a promising avenue for curing diseases versus ethical concerns about embryo destruction.
Addressing Challenges in Stem Cell Research
Contamination: Both physical (bacteria, fungi) and ethical (use of animal cells for growth) concerns.
Long-term effects: Chromosomal abnormalities and mutation accumulation in stem cells during in vitro culture.
Need for precise differentiation protocols: Necessary for clinical application of stem cells.
Summary of Stem Cell Research Innovations
iPSCs offer a way to generate pluripotent cells without ethical dilemmas posed by embryonic sources.
Future strategies include non-viral delivery methods to enhance safety and effectiveness in cell therapy.
Introduction
Stem cells - cells which have capability of self-renewal and differentiation
Self-renewal - ability of cells to proliferate without the loss of differentiation potential and without undergoing senescence - biological aging
Stem cell - precursor cell - gives rise to multiple tissue types - building block of human body
Stem cell definition- cell that has the ability to continuously divide and differentiation into various other kinds of cells and tissues
Features of stem cells
Unique
Develop into several distinct cell types
Used as a repair system
Theoretically divide without limit in a living organism in order to replenish various types of cells
When a stem cell divides - new cell can either remain a stem cell or become another type of cell with a specialised function
Unique properties for stem cells only - division and self-renewal for long periods; unspecialised - therefore can give rise to specialised cell types; stem cell is uncommitted until it recieves a signal to develop into a specialised cell
Kinds of stem cells
Embryonic stem cells - from 5-6 day-old embryo - ability to form any type of cell found in human body - embryonic stem cells of the inner cell mass - pluripotent :. Able to differentiate to generate primitive ectoderm- which ultimately differentiates during gastrulation into all derivatives of the 3 primary germ layers - ectoderm, endoderm and mesoderm
Embryonic germ cells - derived from the part of a human embryo or fetus that will ultimately produce eggs or sperm
Adult stem cells - undifferentiated cells found among specialised or differentiated cells in a tissue or organ after birth - more restricted ability to produce diff cell types
Embryonic stem cells - pluripotent ; adult stem cells are multipotent
Classification of stem cells based on their ability to differentiate
Totipotent - able to generate all the cells of the organism including cells that are not part of the embryo such as the cells of the umbilical cord and placenta
Pluripotent - found in the embryo at the blastocyst stage - can differentiate into all cells from 3 embryonic layers - not able to give rise to the placenta and its supporting structures
Multipotent - can give rise to a finite number of cell types and are usually isolated from adult tissues
Unipotent - can give rise to a single type of cell
Embryonic stem cells ES cells
Pluripotent stem cells derived from inncer cell mass of blastocyst - early-stage preimplantation embryo
Human embryo reach blastocyst stage 4-5 post-fertilisation - 50-150 cells
Isolating the embryoblast or inner cell mass ICM results in destruction of the blastocyst - ethical issues - whether or not embbryos at the preimplantation stage should be considered to have the same moral or legal status as more developed human beings
Human ES cells- 14 um and mouse ES cells - 8 um
Under defined conditions ES cells are capable of propagating themselves indefinitely in an undifferentiated states and have the capacity when provided with the appropriate signals to differentiate into almost all mature cell phenotypes - useful tools for research and regenerative medicine
Advantages of ES cell:- flexible - can differentiate into many cell types; immortal; availability- embryos from in vitro fertilisation clinics
Disadvantages of ES cell:- difficult to differentiate uniformly and homogenously into target tissue ; immunogenic - embryonic stem cells from a random embryo donor are likely to be rejected after transplantation; tumourigenic - capable of forming tumours or promoting tumour formation; destruction of developing human life
Adult stem cells
Undifferentiated cell found among differentiated cells in a tissue or organ
Can renew itself and differentiate to yield some or all of the major specialised cell types of tissue or organ
Primary function- maintain and repair tissue
Also called somatic stem cells
Origin of adult stem cells in some mature tissues is still under investigation
Differentiation pathways of adult stem cells
Neural stem cells- in brain give rise to 3 major cell types - neurons, astrocytes and oligodendrocytes
Epithelial stem cells- in lining of digestive tract - absorptive cells, goblet cells, paneth cells and enteroendocrine cells
Skin stem cells - basal layer of epidermis and at base of hair follicles
Epidermal stem cells - give rise to keratinocytes
Follicular stem cells - give rise to both hair follicle and to epidermis
Advantages of adult stem cell
Adult stem cells from bone marrow and umbilical cord - flexible
Somewhat specialised
Not immunogenic
Relative ease of procurement - some are easy to harvest ex. From marrow
Non-tumourigenic
No harm done to donor
Adult stem cells are preferable to embryonic sem cells because they belong in the microenvironment of an adult body while ES cells belong in the microenvironment of the early embryo- tend to cause tumours and immune system reactions
Disadvantages
Limited quantity
Finite - may not live as long as ES cell in cultuee
Less flexible - more difficult to reprogram to form other tissue types
Induced pluripotent stem cells
Adult cells that have been genetically reprogrammed to an embryonic stem cell-like state by being forced to express genes and factors important for maintaining the defining properties of embryonic stem cells
Human iPSCs - express stem cell markers and are capable of generating cells characteristic of all 3 germ layers
iPSCs - useful tools for drug development and modelling of diseases
Source of stem cells
May be derived from autologous, allogeneic or xenogenic sources
Histocompatibility is prerequisite for transplantation of allogeneic stem cells