Extracellular Matrix and Adipose Tissue Flashcards
Basal Lamina Components?
Collagen type IV
Laminin and entactin
Perlecan (heparan sulfate and proteoglycan)
Basal laminae typically contain one or more of the several Type IV collagens, one or more of the laminins, and abundant proteoglycan, predominantly in the form of perlecan.
…
What is the shape that collagen type IV polymerizes into?
sheets!!! not fibrils
Laminins…. what are they?
what are they good substrate for?
- a family of glycoproteins composed of 3 polypeptides that form a cross-shaped structure
- good substrates for adhesion of epithelial cells and neurons
- different laminins are found in different basal laminae
Type IV collagen polpeptides do not polymerize in the same orientation, but rather in opposite orientations. The extension peptides or globular regions at each end of the collagens ARE NOT CLEAVED! The c-terminus of one polypeptide binds to the C-terminus of another - as a result it polymerizes into SHEETS. not fibrils
…
Laminins are not only cross shaped but they are…
modular! with multiple different binding sites
where are laminins almost exclusively found?
the basal laminae
important for binding of epithelial cells and neurons
Both collagen IV and laminin can polymerize into layers by itself!
…
what protein is always associated with laminin?
entactin
entactin has domains that bind to laminin and to collage type IV so it serves as a linker that may strengthen the basal lamina but it is not necessary for co-polymeriztaion of laminin and collagen
what is the basal lamina formed from?
co polymerization of laminin, type IV collage, and proteoglycans
type IV collagen polymerizes into flat sheets, not the linear structures like the other collagens
..
what are the four functions of the basal lamina?
support
barrier or selective filter
influences cell polarity and differentiation
promotes and guides cell migration
BL provides support and defense! IT is part of the physical barrier protecting us from environmental insults. Contact with the BL is also necessary for what of the epi cells?
survival of basal epi cells!!! If these cells detach from BL, they undergo programmed cell death
below the BL is what?
connective tissue proper consisting of cells covered with collagen fibers
BASEMENT MEMBRANE of kidney globerulus filters blood plasma, producing provisional urine. The basement membrane does not allow molecules >69,000 daltons to pass through
…
After injury, the nerve detaches from the muscle, retracts and partially degenerates. During regeneration, the nerve fiber grows back to the muscle and eventually forms a synapse in the same spot where it originally innervated the muscle.
SAME SPOT!!! HOW DOES IT KNOW?
…
Each muscle fiber is surrounded by an external lamina or basal lamina. Which laminin is distributed through this external lamina?
laminin-2! - not a specific signal that indicates the site of a neuromuscular synapse
Which laminin is only at the portion of the basal lamina associated with the neuromuscular junction?
laminin-3!
It specifically binds to motor neuron fibers and knockout of laminin-3 disrupts the formation of neuromuscular junctions
AKA laminins can be involved in direction of nerve growth
While the basal lamina has laminin and collagen type IV, the less organized layer of CT proper below it is enriched in what molecule?
fibronectin
Glycoproteins have more what?
proteins that carbs – were talking about adhesive glycoproteins and fibronectin is an example?
Fibronectin…
- connects what?
- has how many genes?
- DIMER!
- what kind of structure?
- binding sites for many ECM components
“connects fibroblasts” 1 gene dimer of virtually identical subunits modular structure binding sites for many ECM components
RGD is required for what?
Is located on fibronectin
Required to bind to different things, specifically integrin
Fibronectin is a modular structure with different globular domains that mediate distinct functions. The globular domains are connected to one another though an unstructured linker peptide, like beads on a string
…
The structure of ECM is quite variable because its components can bind to each other in many different ways
…
How many genes are there for fibronectin?
What does this imply about processing?
one gene!!
produces different polypeptides though alternative splicing!
each domain is coded by a different exon
the different alternatively spliced polypeptides for fibronectin are associated as what?
disulfide bonded dimers
Why is the RGD sequence important?
it has a key part in the cell binding activity of fibronectin
it is present in many molecules that are recognized by integrins
the tripeptide RGD, or synthetic analogs can be used to inhibit or modulate the function of fibronectin or other ECM molecules that employ the RGD binding mechanism
Summary of Fibronectin and ECM components
Many ECM components are modular, binding several other ECM components
Most ECM components are members of gene families, each member showing different tissue distributions
ECM components play key roles in physiology and development as well as structural roles
What are integrins composed of?
two polypeptides - an a and a b chain
both polypeptides are transmembrane and both contribute to ligand binding site
apart of a gene family!
For integrins, some chains interact with only one or a few partners, while others react with many… how many integrins are there?
20
What are ligands for integrins?
ECM components among other things
Some integrins are specific for a single ligand, others recognize more than one
Integrins mediate what?
binding triggers what?
signals affect what?
signals!!!
Binding of ECM component to integrin triggers tyrosine phosphorylation cascades
These signals affect gene expression, differentiation and apoptosis
LAD deficiency often has recurrent abdominal infections, umbilical cord separating late, sepsis, high leukocyte count with most of it being neutrophils, and non-suppurating ulcers
..
what is the first cel type to respond to most infections? (particularly bacterial and fungal infections)
neutrophils
they ingest microbes in the circulation and rapidly enter extravascular tissues at sites of infection, where they ingest microbes and die after a few hours
What is the first step of neutrophils leaving circulation to get into tissues?
leukocyte rolling
process of diapedesis
there are always a group of “marginating” WBCs that constantly roll on the endothelium looking for a signal to enter the cell
Tethering and rolling of leukocytes/neutrophils is done by what?
selectin-mucin binding
besides selectins, what other molecule important for diapedesis is located on leukocyte surfaces?
integrins!
Activation of integrins involves conformational changes in the extracellular domains of the alpha and beta chains….intracellular events can trigger activation of integrins.
…
The cytoplasmic domain of integrins connect to what?
the cytoskeleton
integrins play important roles in communication between cells and the extracellular matrix. the binding of matrix components to integrins alters….
gene expression!!!
in addition, integrins play important roles in cell-cell interactions during the immune response
What are activating factors for integrins?
chemoattractants that come endothelium that act on GPCR receptors on the leukocytes…. this causes intracellular signaling in the leukocyte that help to activate integrins on the leukocytes
what is a hallmark of leukocyte adhesion deficiency (LAD) syndrome?
absence of pus at sites of infection (i.e. absence of neutrophils)
In LAD, neutrophils cannot…
extravasate because they lack integrin beta2
What is the definitive test for LAD?
flow cytometric analysis of integrin expression
Several steps of leukocyte rolling and arrest could lead to phenotypes similar to LAD - and, in fact, similar symptoms can be seen in patients with no mutations in beta-2 integrin
….
LAD I has defects in integrin…
LAD II?
LAD III?
LAD II - absence of the selectin ligand
LAD III - defects in integrin actiation (GPCR activation from chemoattractants)
this is all on the leukocytes
How is the neutrophil separated from the baby?
It is separated due to the infiltration of neutrophils progressing from the edges of the umbilical area towards the center….
this infiltration finally forms a continous band producing a demarcation zone between the mummified cord stump and the vital tissues of the umbilical area of the abdominal wall from which the cord isin the process of separating
no cells other than neutrophils are present and no bacteria were seen
aka LAD also undermines separation of the umbilical cord!!
take homes from LAD notes
Neutrophil extravasation is crucial in defense against infection
Adhesion (tethering, rolling, and attachment) is essential for neutrophil extravasation
Chemoattractants released from the infection area bind to GPCRs on the leukocytes, activating integrins, thus promoting firm attachment
Defects in any of these processes (e.g. LAD I, LAD II, or LAD III) can result in severe, even fatal, disease
Integrins interact with laminins (basement membrane) and fibronectin (CT) for cell-matrix interactions… also have cell to cell interactions with ICAM on PM of another cell
…
RGD is on what molecule?
fibronectin!!
Summary from integrins?
Integrins bind many ECM components
Engagement of integrins alters gene expression and the cytoskeleton, affecting cell survival, motility, and differentiation
Integrins integrate information from extracellular and cytoplasmic environments
Where is adipose tissue derived from?
mesenchymal tissues
aka adipose tissue technically is CT!
What distinguishes adipose from normal CT material?
it is mostly cellular!! little to no matrix
Adults don’t have much BAT; BAT is mostly in in fans i nthe inter scapular region…
we have some BAT in the cervical, supraclavicular, and paravertebral regions
…
White fat = unilocular
..
Individual white fat cells are found in many CT.
Groups of adipose cells = ?
adipose tissue!!
adipose tissue has reticular fibers, nerves, and vessels
White fat is cream to yellow in color - depends on dissolved pigments… where is adipose tissue located? what is it called there?
subcutaneous layer
panniculus adiposis
Developing WAT is what?
multiocular
WAT has what appearance (shape)?
signet ring
WAT has rich vascularization and what type of nerve innervation?
sympathetic!
the pink area between fat cells is made up of cytoplasm of two adjacent cells and collagen/matrix!!
…
Scanning EM of cluster of adipocytes…. appear as spheres… almost entirely composed of a large, single droplet of fat, which is liquid at body temperature. The cells do, however, contain a nuclei, golgi, and other cellular organelles
…
Brown fat = multiocular
prevelant in?
hibernation animals and in neonates (axillae and nape of neck)
animals have to raise their body heat during the spring when they wake up!!
brown fat is highly vascularaized!!
color due to what?
abudnat capillaries and cytochromes in mitochodnria
how to differentiate multi ocular fat and mucus gland?
nuclei is in the center for BAT!
white fat functions?
energy storage
insulation
cushioning
brown fat functions?
heat regulation
fats have a very high what?
caloric value - that is, they store a significant amount of energy per unit weight
lipid droplets of white and brown fat consist of what?
fatty acids esterfied with glycerol, to form triglycerides
adipose cells lie in close proximity to blood vessels facilitating storage and mobilization of fat. fats that circulate in the blood are hydrolyzed to FA and glycerol, which can pass through the plasma membranes of the endothelial cells and adipose cell, where they are then esterified into TAGs ad incorporated into lipid droplet.
….
during mobilization of fat, TAGs are hydrolyzed and the FA pass back to the blood where they associate with albumin and are carried throughout the body
…
insulin promotes what?
fat storage!
mobilization of fat is stimulated by what?
epinephrine from the adrenal gland and/or by norepipnephrine released from sympathetic nerves that innovate adipose tissue
activates lipoprotein lipase
white fat carries out passive regulation of temperature via insulation!!
in contrast, brown fat actively warms the body via heat generation
….
how does brown fat generate heat?
uncoupling of respiration from ATP generation (UCP or thermogenin)
rich vascularization spreads heat throughout the body
important during arousal of hibernating animals and in neonates
key role in response to cold
both WAT and BAT are highly vascularized but BAT even more so
…
Some depots of white fat are not depleted during initial fasting… where are these areas? (4)
palm of hand
buttocks
orbit of eye
around kidneys
What is the largest endocrine organ in the body?
what is an important hormone that it releases?
adipose tissue! - secretes many diff hormones
leptin!! - tells you if you are “satisfied” after a meal
