Stem Cells

Explain the role of stem cells in therapies and as therapeutic targets:

• can be a target of negative drug side effects (i.e. dexamethasone → reduces replication of stem cells needed for replacing blood cells)

• also positive drug targeting (i.e. PGE₂ → stimulates adult blood somatic stem cell replication → more stem cells, better engraftment

Characteristics of stem cells:

• can renew (self-replicate) many to an indefinite number of times

• typically have relatively high telomerase levels

• responsible for tissue replenishment/repair

• has a range of potency

unipotent

produces only 1 cell type (i.e. epidermis skin cells)

multipotent

can produce multiple but few cell types (i.e. bone marrow)

pluripotent

can produce cells of any tissue or body layer (i.e. blastocyst inner cell mass cells)

totipotent

generates ALL cells and tissue types INCLUDING embryonic ones

• found in earliest stages of embryonic development

embryonic stem cells (ESC)

• derived from inner cell mass

• can be totipotent or pluripotent

What do ICM pluripotent cells give rise to?

• endoderm: lungs, GI tract, bladder

• mesoderm: bone marrow, muscle, bone

• ectoderm: skin, eyes, brain

somatic stem cells (adults)

• specialized self renewing tissue

• unipotent with little variety in progeny but can also be multipotent

hematopoietic stem cells

• multipotent cell renewal

• there’s no changing once committed

• CLP and CMP

committed lymphoid precursor (CLP)

hematopoietic stem cell that’s progressed past multipotent and only gives rise to lymphoid cells

• T cells

• B cells

committed myeloid precursor (CMP)

hematopoietic stem cell that’s progressed past multipotent and only gives rise to myeloid cells

• RBCs

• megakaryocytes

• basophils/neutrophils/macrophages

How does self-renewal work in epithelial crypts?

intestinal stem cell (ISC) divide to produce 1 ISC and 1 transient amplifying (TA) cell → TA cells differentiate into goblet cells and enterocytes

adenomatous polyposis coli (APC)

mutation in multifunctional tumor suppressor gene that causes most colon cancers and some others like liver

• affects gene expression, adhesion to ECM, and migration

adenoma

a mass of over-proliferating epithelial cells; a tumor but is NOT cancer

Explain the embryonic cell therapy using a mouse model:

mouse ES cells differentiated into insulin-secreting clusters similar to pancreatic islet B cells

• clusters in petri dish responded to glucose by secreting insulin

• insulin amounts were lower than those secreted by normal islet cells

**overall result: insulin production REDUCED mouse hyperglycemia

induced pluripotent stem cells (iPS)

adult cells genetically reprogrammed to pluripotent state like embryonic stem cells

• iPS cells injected into early embryo contribute to ALL types of embryonic tissues

What are the 4 different genes that are inserted into adult cell genome?

• OCT4

• c-MYC

• SOX2

• KLF4

What results from reprogramming genes?

proteins from these genes cause loss of adult cell-specific function and gain pluripotency

What are some issues with achieving iPS cells?

• low gene delivery efficiency: must deliver all 4 genes to SAME cell simultaneously

• insertion need for transcription may cause mutation in genome

Summarize patient therapy using iPS cells:

samples taken from patient → skin biopsy with OCT4, c-MYC, SOX2, KLF4 → recDNA inserts functional gene to replace mutated → repaired iPS cells specializes healthy cells → transplant back to patient

Summarize drug discovery screening with iPS cells:

samples taken from patient → skin biopsy with OCT4, c-MYC, SOX2, KLF4 → iPS cells specializes to neurons with same defect as pt’s cells → screen new drug compound library → cell response in petri dish = model for pt response