Biochemistry Of Bone Formaton (Exam V) Flashcards by Annabella Moody

Q

The four phases of skeletal development:

A

1- Migration of preskeletal cells to sites of future skeletogenesis
2- Interaction of these cells with epithelial cells
3- Mesenchymal condensation
4- Cell differentiation to chondroblasts or osteoblasts

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Q

During skeletal development the pre-skeletal cells of mesenchymal origin travel to:

A

Sites of future skeletogenesis

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Q

During skeletal development the interactions of what types of cells leads to mesenchymal condensation:

A

Epithelial-mesenchymal interaction

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Q

Following the condensation phase of skeletal development, what can the cells differentiate into:

A

Chondroblasts or osteoblasts

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Q

Indirect method of forming bone

A

Endochondral bone formation

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Q

During endochondral bone formation, what does the mesenchyme first form:

A

Cartilage template

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Q

In endochondral bone formation the cartilage template forms in what shape:

A

Shape of the future bone

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Q

In endochondral bone formation the cartilage template will later be replaced by:

A

Mineralized bone tissue

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Q

What type of bone formation occurs in most bones of the skeleton especially bones that bear weight and have joints:

A

Endochondral bone formation

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Q

Type of bone formation that occurs during fracture repair:

A

Both endochondral & intramembranous

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Q

Long bones & bones with joints undergo _____ bone formation

A

Endochondral

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Q

Direct transformation of mesenchymal cells to osteoblasts:

A

Intramembranous bone formation

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Q

Type of bone formation that does not involve a cartilage intermediate

A

Intramembranous bone formation

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Q

Type of bone formation that is restricted to the cranial vault, some facial bones & parts of the mandible & clavicle:

A

Intramembranous

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Q

During endochondral bone formation-

The mesenchymal cells will intially condense to form a _____ that shows the _______ of the bone

A

Cartilage model
Future shape

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Q

During endochondral bone formation-

Following the condensation of mesenchymal cells to form the cartilage model, what occurs?

A

Differentiation & formation of mineralized collar

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Q

During endochondral bone formation-

Where does the differentiation & formation create the mineralized collar?

A

On outside of bone

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Q

During endochondral bone formation-

What is the first mineral to form?

A

Mineralized collar on outside of bone

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Q

During endochondral bone formation-

The formation of the mineralized collar on the outside of the bone causes:

A

The chondrocytes in the center to undergo hypertrophy

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Q

During endochondral bone formation-

What happens when the chondrocytes in the center of the bone undergo hypertrophy?

A

swell up
change gene expression pattern
start to calcify
secrete VEGF

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Q

During endochondral bone formation-

What produces & secretes VEGF?

A

Hypertrophic chondrocytes

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Q

During endochondral bone formation-

What does the secretion of VEGF by the hypertrophic chondrocytes accomplish?

A

Attracts blood vessels into the central area

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Q

During endochondral bone formation-

What comes in following the invasion of blood vessels into the central area via VEGF?

A

Osteogenic precursor cells
Osteoclasts

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Q

During endochondral bone formation-

The osteogenic precursor cells and osteoclasts brought in during the process of blood vessels invading the cartilage template are from what lineage?

A

Hemopoetic cell lineage

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During endochondral bone formation- Following the addition of the osteogenic precursor cells and osteoclasts (brought in by the blood vessels) what does the osteoclasts do?

The osteoclast will resorb the mineralized cartilage matrix in the middle

During endochondral bone formation- Following the addition of the osteogenic precursor cells and osteoclasts (brought in by the blood vessels) what do the osteogenic precursor cells do?

The osteogenic precursor cells cause osteogenesis to occur

During endochondral bone formation, the chondrocytes secrete _____ which attracts ______ into the center which further recruits ______ & ______

VEGF Blood vessels Osteogenic precursors Osteoclasts

During endochondral bone formation- Following the osteoclasts resorbing the mineralized matrix in the center, and the osteogenic precursors initiating osteogenesis what is the next step to take place?

Formation of a marrow cavity

During endochondral bone formation- What forms after the marrow cavity?

Trabecular bone

During endochondral bone formation- Following the trabecular bone formation what will occur late on:

Secondary ossification center

Endochondral bone formation 1. Mesenchymal cells will initially condense to form ______ that takes on the shape of the bone 2. Differentiation & formation of the ______ on the outside of the bone 3. The collar mineralization cause the chondrocytes in the center to ________ 4. The hypertrophic chondrocytes secrete _______ 5. VEGF attracts ___ to enter the central canal 6. Blood vessels invade cartilage template and recruit _____ & _____ 7. The osteoclasts will ____ the mineralized cartilage matrix in the middle, while the osteogenic precursor cells cause ____ to occur 8. Next formation of _____ occurs 9. Following ______ formation begins

1. Cartilage 2. Mineralized collar 3. Undergo hypertrophy 4. VEGF 5. Blood vessels 6. Osteogenic precursor cells & Osteoclasts 7. Resorb; osteogenesis 8. Marrow cavity 9. Trabecular bone

The area between two bony regions that is left with cartilage

Growth plate

During endochondral bone formation, the secondary ossification center leads to:

A second are of bone formation on either end of the bone

The growth plate is extremely important in:

Longitudinal bone growth

Around what age does fusion of the growth plate occur?

Age 14-20

When fusion of the growth plate occurs what is essentially happening and what does this cause?

Cartilage dissapears; bone is no longer able to grow

What factors play a role in the timing of fusion of the growth plate:

Age & gender

During intramembranous bone formation- ______ cells condense to produce _____

Mesenchymal cells Osteoblasts

What does intramembranous bone formation lack when compared to endochondral bone formation?

A cartilage intermediate

During intramembranous bone formation- Following the mesenchymal cell condensation and resulting osteoblast production, what do the osteoblasts do?

Deposit osteoid bone matrix

The osteoid bone matrix deposited by the osteoblasts is:

Unmineralized

During intramembranous bone formation- Following the deposition of osteoid matrix what happens?

The osteoid matrix calcifies & osteoblasts become arranged along the calcified region of the matrix

During intramembranous bone formation- What happens to some of the osteoblasts lining the calcified region of the osteoid matrix?

They get trapped in the bone matrix

During intramembranous bone formation- When osteoblasts get trapped within the bone matrix they ultimately become:

Osteocytes

First type of bone produced developmentally:

Woven bone

Type of bone that is considered immature bone

Woven bone

Primary bone

Woven bone

Bone that is produced when osteoblasts need to form bone rapidly

woven bone

In what situations would osteoblasts may need to form bone rapidly: (3)

Embryonic development Fracture healing Disease states

What is an example of a disease state that may require rapid bone formation?

Paget’s syndrome

Immature woven bone will later be:

Remodeled and replaced with lamellar bone

Secondary bone

Lamellar bone

Type of bone that is considered mature

Lamellar bone

Name the type of bone this describes: Disorganized in structure

Woven bone

Name the type of bone this describes: Randomly oriented collagen fibers

Woven bone

Name the type of bone this describes: Mechanically stronger

Lamellar bone

Name the type of bone this describes: Highly organized

Lamellar bone

Name the type of bone this describes: More birefringence with polarized light

Lamellar bone

Name the type of bone this describes: Lower birefringence with polarized light

Woven bone

Name the type of bone this describes: Collagen fibers oriented parallel

Lamellar bone

Name the type of bone this describes: Increased cell density

Woven bone

Name the type of bone this describes: Reduced mineral content

Woven bone

Name the type of bone this describes: Contain concentrical arrangements around central canal that houses the blood vessels and nerves

Lamellar bone

Name the type of bone this describes: Contain Haversian canals

Lamellar bone

Lamellar bone can further be classified into:

Compact (cortical) bone Cancellous (trabecular/spongy) bone

Lamellar bone that is classified as compact is also referred to as:

Cortical

Lamellar bone that is classified as cancellous is also referred to as:

Trabecular/spongy

Refers to the bone that you find in the cortex, that is full of haversian systems and thick concentric rings of bone:

Compact bone

Bone that tends to be more commonly found in the marrow cavity where its also providing a support role but there are plenty of gaps in between the bony trabeculae that allow for space for the marrow to reside:

Cancellous bone

The gaps in between the bony trabeculae of cancellous bone allow space for:

Marrow to reside

What would happen if the bony trabeculae was filled with compact bone?

It would be extremely heavy

Labels the following image

1- bone marrow 2- blood vessels 3- compact bone 4- spongy bone

Label the following image

1- canaliculi 2- osteocyte lacunae 3- osteon 4- Haversian canals 5- osteon

Giant multinucleated cells that form from the fusion of monocyte/macrophage lineage

Osteoclasts

What is the origin of osteoclasts:

Hemopoietic origin

What do osteoclasts do?

Resorb bone

How do osteoclasts resorb bone?

By producing acid and enzymes that digest away and remove bone

Cuboidal cells located on the surface of bone which secrete collagen & other matrix components to generate the bone matrix

Osteoblasts

Osteoblasts that become trapped/embedded on the surface of bone to form a network

Osteocytes

Osteocytes look similar in appearance to:

Neurons

Osteocytes are connected to eachother and other:

Osteoblasts

Label the types of cells in the image

1- osteoclasts 2- osteoblasts 3- osteocytes

Determine the types of bone cells in the following image:

1- osteoclasts 2- osteoblasts 3- osteocytes

What types of cells all differentiate from a common mesenchymal precursor? (4)

1- osteoblasts 2- chondrocytes 3- myoblasts 4- adipocytes

Type of cell condensation that pattern where the bone is going to form

Mesenchymal

Cells that dependent on what signals they are subjected to controls what will differentiate into (many options)

Multipotent

Because mesenchymal cells can give rise to numerous different cell types they are classified as:

Multipotent

When a mesenchymal cell receives signals to differentiate into a myoblast- it will ultimately give rise to:

Myocytes

When a mesenchymal cell receives signals to differentiate into a pre-adipocyte- it will ultimately give rise to:

Adipocytes

When a mesenchymal cell receives signals to differentiate into a pre chondrocytes- it will ultimately give rise to:

Hypertrophic chondrocytes

When a mesenchymal cell receives signals to differentiate into a a pre-osteoblast- it will ultimately give rise to:

Osteoblasts

Bone forming cells

Osteoblasts

Osteoblasts are derived from:

Mesenchymal stem cells

Describe shape of osteoblasts

Plump, cuboidal

What specific extracellular matrix protein do osteoblasts produce large amounts of:

Collagen type I

Lifespan of osteoblasts:

Weeks

What happens when osteoblasts reach the end of their lifespan?

Terminal differentiation to become an osteocyte or cell death

What are the osteoblast marker proteins are transcription factors (2):

Runx2 Osterix

What osteoblast marker protein is an enzyme:

Alkaline phosphatase

What osteoblast marker proteins are extracellular matrix proteins: (4)

Type I collagen Osteopontin Osteocalcin Bone sialoprotein (BSP)

When we refer to specific proteins as osteoblasts marker proteins- what does this mean?

These are the genes that differentiate osteoblasts from other types of cells

Proteins that regulate gene expression

Transcription factors

An enzyme expressed by osteoclasts that is very important in the mineralization process:

Alkaline phosphatase

Key transcriptional regulators of osteoblast differentiation: It is imperative that the RUNX2, osterix, & beta-catenin

at the appropriate time in an appropriate amount

Key transcriptional regulators of osteoblast differentiation: What transcriptional regulator functions to push the osteogenic precursor to the immature osteoblast?

RUNX2 Beta-catenin

Key transcriptional regulators of osteoblast differentiation: If Beta-catenin acts on the mesenchymal cells too early in proliferation what will result?

Inhibit the transition from mesenchymal stem cells to osteochondrogenic precursors

Key transcriptional regulators of osteoblast differentiation: What transcriptional regulators function to push the immature osteoblast to the mature (matrix producing) osteoblast during the maturation stage?

Osterix & Beta-catenin

Key transcriptional regulators of osteoblast differentiation: If RUNX2 is acts on the immature osteoblast for too long during the maturation phase what is the result?

It will prevent further differentiation

Key transcriptional regulators of osteoblast differentiation: What transcription factor is responsible for the transition from mature (matrix producing) osteoblast to the terminally differentiated states?

Beta-catenin

What are the terminally different states the osteoblast?

Osteocyte Lining cell Apoptosis

Label the boxes with the appropriate TF factors acting at the various stages of osteoblast differentiation

1. RUNX2 & Beta-Catenin 2. Osterix & Beta-Catenin 3. Beta-catenin

Label the following stages of osteoblast differentiation

1. Proliferation 2. Maturation 3. Terminal differentiation

Label the following types of cells in the various state os osteoblast differentiation:

1. Mesenchymal stem cells 2. Osteochondrogenic precursors 3. Immature osteoblast 4. Mature osteoblast 5. Differentiated cell states- osteocytes, lining cells, apoptosis

Beta-catenin is involved in:

The WNT signaling pathway

_____ comes on at an early stage pushing the precursors from the osteogenic to the osteoblastic phenotype

RUNX2

____ comes on at a later stage pushing an immature osteoblast to a mature osteoblast

Osterix

If take a mouse & KO the RUNX2 gene- you end up with a mouse that has:

an only cartilaginous skeleton that will not mineralize

In humans with complete KO of RUNX2- this will result in:

a fetus that is not compatible with life

A heterozygous mutation of RUNX2 in humans results in:

Cleidocranial dysplasia (CCD)

RUNX2 is a master transcription factor essential for:

bone & tooth development

Cleidocranial dysplasia is caused by what type of mutation?

Autosomal dominant

CCD results from ______ in RUNX2

haploinsufficiency

Inactivating mutation/deletion in one allele

haploinsifficiency

Disease characterized by delayed ossification of midline structures of the body (especially in membranous bone)

Cleidocranial dysplasia

In CCD: 1. _____ are partly or completely missing 2. late closing of _____ 3. describe teeth: 4. ____ mandible due to ____ of maxilla

1. clavicles 2. fontanelle 3. supernumerary teeth 4. prognathic (protruding); hypoplasia

what transcription factor is downstream of RUNX2

Osterix

What transcription factor does RUNX2 produce?

osterix

Mice lacking osterix have:

impaired osteoblast formation

Gene name for osterix

SP7

Osterix controls expression of what osteoblast genes?

Type I Collagen Osteocalcin Osteopontin

Human mutations in SP7 (osterix) are associated with:

Osteogenesis imperfecta type xii

What are two important key signaling pathways that regulate osteoblast differentiation:

BMPs WNT/Beta-catenin signaling

What important key signaling pathway comes first when regulation osteoblast differentiation?

BMP2,7

If signaling of WNT/Beta-catenin pathways occurs too early what will occur?

Inhibit the mesenchymal cells from differentiation into osteechondrogenic precurosurs

Originally purified from bone extracts that induce bone formation when implanted in muscle (ectopic bone assay)

BMPs

BMPs required for ______ of adult bone homeostasis

skeletal development/maintenance

BMPs promote differentiation from:

early osteoprogenitor cells

Important in fracture healing

BMPs

KO of specific BMPs leads to

skeletal defects

Naturally occurring mutations in BMPs or their receptors result in:

inherited skeletal disorders in humans

A disease characterized by heterotopic bone formation:

Fibrodyplasia ossificans progressiva

Stone man syndrome

Fibrodysplasia ossificans progressiva

Where does the bone form in fibrodysplasia ossificans progressiva?

soft tissues

In FOP cases surgical treatment is not an option because?

Bone forms in response to tissue trauma

what mutation in what gene causes fibrodysplasia ossificans progressiva

Mutation in BMP type I receptor (single amino acid mutation) gene: ACVR1

The mutation involved in FOP causes mild _______ & _______ with BMP ligand binding and overreaction with BMP ligand binding

constitutive activation

In addition to the constitutive activation & over activation with BMP ligand binding in FOP, there is also acquired responsiveness to:

Activin A

What potential treatments have been looked into regarding FOP?

antibodies against activin A & Kinase inhibitors selective for mutant receptor

WNT/Beta-catenin signaling pathway: In normal circumstances when there is no WNT to stimulate its receptor, the Beta-catenin will be:

phosphorylated by GSK-3-Beta

WNT/Beta-catenin signaling pathway: When Beta-Catenin is phosphorylated by GSK-3-Beta what results:

Beta-catenin will go to be degraded in cell

WNT/Beta-catenin signaling pathway: Describe the receptor for the WNT ligand:

LRP5 + LRP6 + Frizzled

WNT/Beta-catenin signaling pathway: When WNT comes in & binds its receptor complex, that will then come in and phosphorylate the GSK-3-beta which will then:

release the beta-catenin

WNT/Beta-catenin signaling pathway: When the GSK-3-Beta releases the B-catenin, it allows for the beta-catenin to go to the _____ & interact with a protein called _____ & then initiate ______

nucleus TCF Gene transcription

WNT/Beta-catenin signaling pathway: When the Beta-catenin is able to get inside the nucleus to interact with TCF & initiate gene transcription it will ultimately lead to:

bone formation (osteogenesis)

Signaling pathway important in determining bone mass

Wnt-B-catenin pathway

Activating mutations in Lrp5 leads to:

High bone mass in humans

Inactivating mutations of Lrp5 leads to:

Low bone mass in humans

_____ mutations in Lrp5 lead to high bone mass while ______ mutations in Lrp5 lead to low bone mass

activating inactivating

Mechanism of bone mineralization: The first phase of mineralization is initiated by:

Matrix vesicles released by the cell surface of mineralizing cell types

Mechanism of bone mineralization: The second phase of mineralization involves:

Propogation of mineralization on collagen fibers

Mechanism of bone mineralization: Extracellular membrane bound vesicles produced by osteoclasts:

matrix vesicles

Mechanism of bone mineralization: The size of matrix vesicles is:

30-1000nm in diameter

Mechanism of bone mineralization: What is located in the membrane of the matrix vesicles? (3)

1. calcium transporters 2. phosphate transporters 3. enzymes that generate phosphate

Mechanism of bone mineralization: What do the matrix vesicles create in the second phase (propogation of mineralization on collagen fibers)

seating crystals- formed by calcium & phosphate

Mechanism of bone mineralization: The seating crystals fill the matrix vesicle & eventually ______

puncture it

Mechanism of bone mineralization: After puncturing the matrix vesicles, the crystal then act as ________

nucleation sites (seed points)

Mechanism of bone mineralization: when acting as nucleation sites (following the puncturing of the matrix vesicles) this is allowing for:

further propagation of mineral deposition on collagen

Enzyme highly expressed in osteoblasts/odontoblasts

alkaline phosphatase

Enzyme that is a marker gene for mature osteoblasts & plays a role in bone mineralization by hydrolyzing pyrophosphate (PPI) a natural inhibitor mineralization

alkaline phosphatase

When alkaline phosphatase hydrolyzes PPI this results in:

Increased local concentration of phosphate Promotes mineralization

Mice lacking alkaline phosphatase gene (TNAP) have:

impaired mineralization

Humans with a mutation in the gene for alkaline phosphatase (TNSALP) this is association with _______ a disease of impaired mineralization

hypophosphatasia

a disease characterized by impaired mineralization due to mutation in gene for alkaline phosphatase

hypophosphatasia

Rare heritable rickets/osteomalacia is caused by a mutation in:

Hypophosphatasia

They type of mutation most common in the rare heritable rickets/osteomalacia (HPP) is due to

missense mutation in human alkaline phosphatase gene

The mutation in alkaline phosphatase gene in HPP render:

reduced activity of alkaline phosphatase

Symptoms of what disease include: impaired mineralization of skeleton/dentition, leg bowing, rachitic rosary, early tooth loss, waddling gait, muscle weakness & seizures

Hypophosphatasia (rare heritable rickets/osteomalacia)

Hypophosphatasia varies in severity from perinatal-lethal to adult mild onset forms only affecting the dentition. The varying severity is dependent on:

degree of loss of function of alkaline phosphatase

Treatments for hypophosphatasia:

Bone targeted enzyme replacement therapy TNSALP

In the mineralization process, mutations in ENPP1 are associated with:

syndrome of sponteneous infantile arterial & periarticular calcification

In the mineralization process, mutations ion TNSALP are associated with:

Hypophosphatasia

In the mineralization process, mutations in Anx5 don't abnormal skeletal development. This is likely due to:

compensation from other annexing family members

PHOSPHO1 deletion in mice causes:

impaired mineralization, including in MV

Key roles of osteocytes:

1- regulation of activity of osteoblast & osteoclast 2- major role in mechanosensation 3- role in phosphate homeostasis 4- endocrine function

Make up over 90% of all been cells

osteocytes

Lifespan of osteocytes:

decades

No master transcription factors have been discovered in osteocytes but _____ may play a role:

Mef2c

E11/gp38 are markers of:

early osteocyte

SOST (Sclerostin) is a marker of:

late/mature osteocyte

Highly expressed by osteocytes & acts as a naturally occurring inhibitor of bone formation by inhibiting the WNT-beta catenin signaling

sclerostin

Currently a target for the development of bone metabolic drugs

sclerostin

If a drug was found to inhibit sclerotin it would result in:

promotion of bone formation