ANS 124: Alveoli

Prolactin acts on what cells to induce the production of IGF-2?

Mammary Epithelial Cells

PRL is part of a group of molecules called _______________.

cytokines

What receptor does PRL use when it acts on epithelial cells?

PRL Receptor

What type of receptor is the PRL Receptor?

Transmembrane Receptor

PRL binds to its receptor on what side of the epithelial cell?

basal side

When PRL binds to its receptor, what does it initiate inside the cell? (general)

initiates a signaling cascade

What happens to the structure of the PRL receptor when PRL binds?

the two monomers of PRL Receptor dimerizes when PRL binds

When the PRL Receptor dimerizes, what does that activate inside the cell?

Janus Kinase (JAK2)

What does a kinase do?

phosphorylates (add PO4 to things)

When JAK2 is activated, what does it phosphorylate?

phosphorylates STAT

What does STAT stand for?

Signal Transducer and Activator of Transcription

What happens to STAT in the cytoplasm after it is phosphorylated by JAK2?

STAT dimerizes with another phosphorylated STAT molecule.

Where does the dimerized STAT go?

to the nucleus

In the nucleus, the dimerized STAT acts as what, to do what?

acts as a transcription factor to activate gene transcription

Specifically, when PRL binds to its receptor at the epithelial cells, it activates the transcription/translation of what?

IGF-2

What happens to IGF-2 after it is made in the epithelial cells?

it is released to do its effect on cells

Many of the genes that encode milk proteins have what type of binding sites on their gene promoters?

STAT factor binding sites

What do Prolactin, Growth Hormone, and Placental Lactogen ALL do in the mammary gland?

they all help with Alveolar Development

For Growth Hormone, although it helps with Alveolar Development, it has a bigger role for what other process in the mammary gland?

Ductal Growth (during puberty)

What is PRL's role in lactation? (general)

Lactogenesis (initiate lactation)

What is GH's role in lactation? (general)

Galactopoeisis (copious milk secretion)

What is PL's role in lactation? (general)

Lactogenesis?

(question mark was included on the lecture slide)

PRL induces the synthesis of what in the mammary gland?

Induces IGF2 in mammary gland.

GH induces the synthesis of what in the mammary gland?

Induces IGF1 in mammary gland.

PL induces the synthesis of what in the mammary gland?

Induces IGF1 in mammary gland.

What receptor does IGF-2 bind to when doing its effects on epithelial cells?

IGF-2 Receptors

When IGF-2 binds to IGF-2R, it sends a signal cascade to the nucleus to induce what?

mitosis (for alveolar development)

During pregnancy, what happens to PRL concentrations in the blood? Describe the PRL level at parturition.

[PRL] increases and peaks at parturition.

[PRL] increases during pregnancy due to what hormone?

Due to Estrogen, which is also increasing during pregnancy.

Increased Estrogen increases [PRL] during pregnancy through what 2 ways?

Increased Estrogen directly increases production of PRL by the lactotrophs in the pituitary.

Increased Estrogen increases the number of lactotrophs in the pituitary so there are more cells secreting PRL.

How were the effects of Estrogen on [PRL] discovered in a study? (give general description of what was done in the study)

Animals were given injections of estradiol and they saw that it increased [PRL] in blood, PRL synthesis, and the number of lactotrophs in the pituitary.

A major player in helping alveoli form is the production of _____________ by __________________.

production of IGF-2 by epithelial cells

When IGF-2 is produced due to PRL stimulation of epithelial cells, IGF-2 can act on cells in what 2 ways?

IGF-2 is either a paracrine stimulant (act on nearby epi cell) or an autocrine stimulant (act on itself).

What are 2 other molecules, that are made by the stroma, that can stimulate epithelial cells to divide and make alveoli?

Epidermal Growth Factor (EGF)

Transforming Growth Factor-Alpha (TGF-Alpha)

What 2 hormones stimulates the stroma to produce EGF and TGF-Alpha?

PRL and Progesterone

Epidermal Growth Factor (EGF) is a protein that binds to what receptors? On what cells?

binds to EGF Receptors on epithelial cells

Is Transforming Growth Factor-Alpha (TGF-Alpha) similar to EGF?

Yes, it is another relative of EGF.

Is Transforming Growth Factor-Alpha (TGF-Alpha) similar to TGF-Beta?

No, it is distinct from TGF-Beta.

Compare the function of TGF-Alpha and TGF-Beta in the mammary gland.

TGF-Alpha stimulates epithelial cells to divide to make alveoli.

TGF-Beta stimulates epithelial cells to divide for branching.

What are 2 cells in the Stroma that can make EGF and TGF-Alpha?

Adipose

Connective Tissue Fibroblasts

During Pregnancy, there is increasing levels of what 4 hormones in circulation?

Estrogen

Progesterone

Prolactin

Placental Lactogen

During pregnancy, where are the 4 hormones synthesized?

E&P synthesized from ovaries.

PRL synthesized from pituitary.

PL synthesized from placenta.

During pregnancy, what is Estrogen's effect on the epithelial cells?

E still increases PR production in epithelial cells (like during cycling before pregnancy).

During pregnancy, Progesterone and Prolactin work together to increase what?

increase further formation of branches and alveoli

During pregnancy, PRL acts on where to increase production of what 2 molecules?

PRL increases production of IGF2 in epithelial cells (paracrine).

PRL increases production of EGF-molecules in the stroma (paracrine).

During pregnancy, what do IGF-2 and EGF enhance?

enhance epithelial cell division forming alveoli

What antibodies are used during Immunohistochemistry to find the Basement Membrane in the mammary gland?

Antibodies for either laminin, fibronectin, or collagen.

Why are antibodies for laminin, fibronectin, or collagen used to find the Basement Membrane?

Because laminin, fibronectin, or collagen are all molecules that are in the basement membrane.

The Basement Membrane is also referred to as what name?

Extracellular Matrix

Describe the general structure of the Basement Membrane around the alveolus.

A "sheet" of proteins and complex sugars that are like a "reinforcing mesh" around the alveolus.

What 2 cells in the mammary gland rest on the Basement Membrane?

Epithelial Cells

Myoepithelial Cells

During the growth of epithelial cells, are the epithelial cells physically in contact with each other?

No, there is little epithelial cell-cell contact in both a virgin and pregnant mammary gland.

During growth of epithelial cells, are the cells polarized or oriented in a certain direction?

Cells are not polarized (don't have particular orientation).

During growth of epithelial cells, what is the cytoplasm to nuclear ratio in the cells? (general)

Low cytoplasm to nuclear ratio in the epithelial cells of ducts and growing alveoli.

How many layers does the Basement Membrane have?

3 layers

What are the 3 layers of the Basement Membrane?

Lamina Lucida

Lamina Densa

Lamina Reticular

Which layer of the basement membrane is closest to the epithelial cells?

Lamina Lucida

Describe the Lamina Lucida.

It is empty space. When cells are connected to a membrane, they tend to leave a little gap.

The Lamina Densa is derived from what?

epithelialium-derived

The Lamina Reticular is derived from what?

stroma-derived

The two layers, Lamina Lucida and Lamina Densa, together are called...

Basal Lamina

The epithelial cells are anchored to the Basement Membrane through what structure?

Integrins

Describe what 2 places the integrins are connecting.

Integrins anchor the epithelial cells to the Lamina Densa & Reticular (it reaches across the lamina lucida).

The Basement Membrane can be from _____nm thick around tip of end bud.

100 nm

The Basement Membrane can be up to _____ micron thick around ducts.

2 micron thick (20x thicker than around end buds)

Describe the set-up of an experiment that looked at how the basement membrane affects the organization of epithelial cells.

Researchers took epithelial cells and put them in a dish, one with Extracellular Matrix, and the other without.

What happened to the formation of the epithelial cells that did NOT have Extracellular Matrix?

the epithelial cells spread out in a flat, 2D formation on the bottom of the dish

What happened to the formation of the epithelial cells that DID have Extracellular Matrix?

The cells become a 3D shaped 1 layer thick spherical ball with a hollow lumen in the middle.

From the experiment with adding ECM to epithelial cells, what does that tell us about the Basement Membrane?

The basement membrane tells the cells to make the alveolus with only 1 layer of epithelial cells and the spherical shape.

When epithelial cells form the spherical shape of the alveoli in the mammary gland, what do the epithelial cells do to the basement membrane?

Epithelial cells will pull up the basement membrane around them as they form the alveoli.

How are integrins situated in the cell membrane?

they are transmembrane anchors

Integrins allow a cells to do what 2 things?

Connect to extracellular matrix proteins (ex. collagen).

Communicate to various structural proteins and signaling molecules.

Describe the subunits of Integrin.

Integrin has two different subunits (α & β) that combine together.

On the inside of the cell, Integrins are connected to what? What does this tell the cell?

connected to signaling molecules so cell knows they are anchored

What happens in mice that have the Integrin KO?

the mice can't make a full 3D alveoli (alveoli have gaps or cells that have broken away) and they can't lactate

On the time scale from start of pregnancy to end of lactation, when does "Growth of Cells as Alveoli" happen?

From start of pregnancy to a little after parturition.

On the time scale from start of pregnancy to end of lactation, when does Lactogenesis I happen?

last trimester of pregnancy

On the time scale from start of pregnancy to end of lactation, when does Lactogenesis II happen?

right before parturition

On the time scale from start of pregnancy to end of lactation, when does Galactopoiesis happen?

After parturition to the end of lactation.