Stem Cell Exam 3

Wingert Stem cell exam 3 content

Skeletal muscle

voluntary; enables movements, supports body; metabolism goes to energy storage and generate heat

Skeletal muscle cell shape

long, multinucleated tubes that contain hundreds of nuclei pushed to the periphery, next to the cell membrane (also known as the sarcomere)

Skeletal cell striations

striped appearance is indicative of muscle protein assemblies; myofibrils

Cardiac muscle

involuntary, heart muscle; branched cell shape with 1-2 nuclei and striations

Smooth muscle

involuntary; wrap organs and vessels in the body; fusiform (spindle) cell shape with 1 nucleus and no striations though contain myofibrils

All muscles exhibit contractility due to

myofibrils

Myofibrils

comprised of thin and thick filaments made up of several proteins; they are stably anchored in the cell membrane via discrete complexes with the scaffolding protein named dystrophin

Skeletal muscle has a remarkable capacity to adapt

to physiological cues

Skeletal muscle responds to

hormones; drives growth in adolescence for example

Skeletal muscle responds to usage

endurance or resistance training versus inaction like bed rest/prolonged illness

Hypertrophy

cells get bigger with more myofibrils; increased load

Atrophy

cells shrink and disassembly; decreased load

Skeletal muscle responds to injury

with robust regeneration; heals after cell compression due to a crush injury, tearing of cell membrane or ischemia

Ischemia

lack/interruption of oxygen availability

Mauro and Katz

satellite cells revealed due to microscopy advance

Satellite cells and TEM

the invention and application of the microscopy goes resolving power over traditional compound microscope enables visualization of cell membranes and subcellular structures (ultrastructure) in great detail

Satellite cells and mononucleated cells

delineates mononucleated cells wedged outside the cell membrane of skeletal muscle syncytium, but nestled within the basal lamina that surrounds each muscle cell

Satellite cell frequency

rare in mature muscle cells

Satellite cell ratio

high nuclear to cytoplasm ratio

Satellite cell descent

from the paraxial mesoderm from myoblasts which are highly proliferative and migratory to spontaneous cell fusion creates skeletal muscle syncytia and then the unfused myoblasts become satellite cells

Satellite cell numbers

much higher at birth and this population supports normal muscle growth

Satellite cell decline

with progressive age to 2-4% of muscle mass

Satellite cells at rest

mitotically quiescent and dormant with abundant heterochromatin compared to typical cell or a skeletal muscle cell nucleus

Satellite cell heterochromatin

densely packed DNA in which gene expression is largely silenced/suppressed due to the tight packing; this also helps to maintain genome stability like preventing transposable elements from moving around

Satellite cell regeneration

when activated reenter cell cycle and extend long cytoplasmic processes which produces highly proliferative and migratory offspring that mimic myoblast behavior in development

Satellite cell histology analysis

the myoblast behavior is viewed as hypercelluarity and the offspring undergo migration to sites of muscle cell injury which leads to spontaneous fusion to existing, damaged cells and the nuclei that are located in middle of cell initially (hallmark of cell regeneration)

Satellite cells when activated are capable of

making new skeletal muscle cells; they generate entirely new muscle cells de novo by spontaneous fusion and control innervation to form neuromuscular junctions

Satellite cell time course of muscle regeneration

varies across muscles of the body; can be as fast as ~2 weeks or as protracted as 40-50 weeks to complete

Satellite cell inherent variation

seen in proliferation rate of the cells and offspring across body muscles

Satellite cells during muscle development

governed by slightly different genetic programs

Muscle disorders

affect strength and function of skeletal muscle and can lead to atrophy and typically increase in connective tissues such as adipose

Muscle disorder can arise from

defects in the skeletal muscle as well as nervous system issues or other origins

Sarcopenia

loss of muscle mass and strength with age

Myopathy

general term for diseases that affect muscle strength

muscular dystrophy

mutations in the dystrophin scaffolding protein which destabilizes myofibrils leads to compromises in cell integrity among muscle cells of the body

mdx mutant mouse model of muscular dystrophy

reduced satellite cell number leads to overtaxed satellite cell usage due to constant need to regenerate the destabilized muscle cells

Transplantation of satellite cells (mdx mutant)

sufficient to restore muscle mass, support functional improvement, and reseed satellite cell compartment

mdx mutant therapeutic prospects

delivery across body, to each major muscle group, number of times and number of cells, satellite cells from which muscle of origin. long-term functionality of muscle, long-term self-renewal of stem cell compartment

Friedenstein experiment 1

transplantation of bone marrow to under kidney capsule to ectopic bone forms

Friedenstein experiment 2

bone marrow cultured to adherent cells to colony forming unit (CFU) fibroblasts

CFU fibroblast

highly prolific, maintain identity= self-renew indefinitely

CFU fibrolasts exhibit trilineage potential can be differentiated into

chondrocytes, adipocytes, and osteolasts

Chondrocytes

cartilage producing cells

adipocytes

fat storing cells

osteoblasts

bone producing cells

Friedenstein experiment 3

CFU fibroblasts to under kidney capsule to ectopic bone forms; cell of origin thus traced to the CFU-fibroblast

Studies of chick limb bud in culture

(Caplan) perform cell culture studies in which cells were isolated from developing limb buds and observed over time leads to finding a population of multipotential cells can be isolated

Chick limb bud cells characteristics

these multipotential cells display a spindle or stellate shape; central nucleus; exhibit trilineage potential to form cartiliage, fat, or bone cells; named MSC

MSCs

mesenchymal stem cells

MSC tissue/organ source

bone marrow, liver, heart, adipose, skin (dermis), placenta, umbilical cord

MSC secretion/fluid source

blood, amniotic fluid, endometrial lining, menstrual blood, mother’s milk

MSC trilineage

initial definition as trilineage potential is outdated and does not apply to all MSCs

MSC developmental origin mystery

include mesoderm=paraxial; ectoderm=neural crest

MSC vast heterogeneity

even within the same tissue like bone marrow

MSC specific location in the body mystery

associate with vessels like pericytes and nearby (perivascular niche)

MSC nomenclature mystery

rainbow of names= propagates confusion about identity and properties

Stiffness of substrate triggers MSCs

to differentiate into neuron, muscle, or bone

MSC matrix interaction

leads to mechanical transduction events at focal adhesion complexes

Mechanical transduction and cell signaling events

orchestrates adoption of alternative differentiation fates depending on the qualities of the matrix

Focal adhesion complex proteins

integrin proteins in cell membrane interact with fibronectin matrix protein, and integrin associates with actin cytoskeleton.

Focal adhesion myosin

Non muscle myosin motor proteins associated with the actin filaments physically deform and leads to a tug on actin in the course of their conformational changes as ATP is hydrolyzed

As cell differentiate, they become

further specialized to have different numbers of focal adhesion complexes and cytoskeleton, presumably to interact with nich in an appropriate way

Tooth crown

layers of ossified mineral deposits; outer layer of tough enamel; inner softer dentin layer

Tooth root

anchored in jaw, surrounded by peridontal ligament and ginggiva

gingiva

gum; fleshy epithelium sitting on underlying connective tissue

Dental pulp

center of tooth that receives vascular supply and innervation (via roots)

MSC tooth source location

dental pulp, peridontal ligament, tip of root, gingiva

MSC tooth sources age

deciduous (baby), emergent (erupting from gum), adult

MSC teeth heterogeneity

with regard to the type of offspring and mineralized deposits the offspring make

Teeth’s reliance on MSC

Teeth that grow continuously (like rodent incisor) rely on them to produce transit amplifying progenitors that make various tooth-producing cells (that secrete the various mineralized deposits)

Tooth engineering in vitro

seeks to mimic endogenous tooth production by culturing epithelial cells and MSCs to make tooth primordia for transplantation

Interest in using teeth

often regarded as source of bio waste, but can sources MSCs for research and medical applications

MSC clinical trials

less than 1000 examining ability of MSCs to be used in various applications

MSC as a cell source

potentially for engineering replacement tissues in vitro

MSC when transplanted in vivo

do not necessarily produce all the cell types that can be cultivated in the cell culture but instead maintain their stemness and secrete factors and exhibit the property of trafficking to locations of injury where there is inflammation

Caplan wants to change MSCs to

medicinal signaling cells since they are a source of bioactive factors

MSC perform signaling

paracrine; secrete many growth factors and cytokines (ie promote angiogenesis)

MSCs are very strong modulators

of immune cells and can repress/alleviate inflammation response

Kidneys are highly complex

mesodermally derived organs with over 40 cell types

Each kidney is comprised of

nephron structural and functional units that cleanse blood and balance many physiological parameters like water levels

Nephrons are specialized

epithelial structures surrounded by a basement membrane and located in the cortex and medulla

Nephron structure

blood filter and tubule that reabsorbs and secretes materials into the urine stream

Interstitium

places between nephrons that house diverse cell types; dynamic sites where cells enter/exit from bloodstream and lymphatics

The other functionalities of the kidney lie in

the interstitium, example is hormone secretion

Several kidney forms are made during

vertebrae development from the intermediate mesoderm

pronephros

first kidney, linear array of nephrons and vestigial (non-functional) in humans

mesonephros

second kidney, made of dozens of linear arrays of nephrons; functions during gestation; degrades and some parts repurposed

metanephros

third kidney, arborized array of nephrons (thousands to mil) with centralized drainage system

Metanephric mesenchyme (MM)

self-renewing renal stem cells that make the nephrons

Nephric duct gives rise to the ureteric bud (UB)

UB undergoes branching morphogenesis to construct an interconnected series of passageways that ultimately converge on the renal pelvis to collect the urine stream from all the nephrons

Nephrogenesis

making nephrons from renal stem cells is completed during gestation in humans (between 5-36 weeks) and no more nephrons mades as MM is used up in a final round of cortical nephrogenesis

Cortical nephrogenesis

nephron production around the outermost perimeter of the organ

nephron endowment

number of nephrons varies widely across humans and low number is a major risk factor for kidney disease, particularly as we progress in lifespan

Blood filter

renal corpuscle

Bowman’s capsule

epithelial cells of kidney that form a glove around the ball of blood vessels that interacts with a nephron

Glomerulus

ball of capillaries surrounded by podocytes

podocytes

specialized epithelial kidney cells

Blood filtration control

by podocytes, capillaries, and their intervening glomerular basement membrane; detachment of podocytes (effacement) leads to nephron dysfunction and destruction

Parietal epithelial cells (PECs)

make up the wall of the Bowman’s capsule; are stem cells that exhibit self-renewing capacity in early post natal stages and produce new podocytes

PECs maladaptive response

at later stages, undergo response due to loss of podocytes and produce proliferating fibroblast like cells that deposit extracellular matrix within the blood filter