L21 – Molecular Composition and Functions of Glomerular barrier Flashcards

(52 cards)

1
Q

What are basement membranes?

A

Specialized ECM that underlie all epithelial cell sheets and tubes

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2
Q

What does basement membrane Provide strong connection between?

A

epithelia and underlying connective tissue

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3
Q

What three core components make up basement membrane?

A

Type IV collagen
Proteoglycans
Laminin (glycoprotein)

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4
Q

What does BM act as in glomerular?

A

Filtration barriers between parenchymal cells and connective tissue space

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5
Q

What is the normal GFR range?

A

90-140mL/min

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6
Q

What is normal Plasma / blood flow rate from renal arteries (Qp) ?

A

~700 mL/min

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7
Q

What are the 3 Structures that govern transport processes at the glomerular barrier?

A

Fenetrated glomerular endothelial surface

Glomerular Basement membrane

Podocyte foot processes

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8
Q

What is name of space between podocyte foot processes?

A

Slit Diaphragm

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9
Q

Fenestrated glomerular endothelial surface (ESL) other name?

A

Glycocalyx

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10
Q

What is ESL formed by?

A

Secreted proteoglycans

Secreted glycosaminoglycans
(GAG)

Adsorbed plasma proteins

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11
Q

What is the function of Chondroitin sulfate in ESL?

A

Negative charge on surface = barrier to prevent passage of charged molecules

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12
Q

What makes up most Proteoglycans found on ESL?

A

Syndecan core protein + Chondroitin sulfate/ Heparan Sulphate side chains

Glypican core protein + Heparan sulphate side chain + GPI anchor

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13
Q

How can podocytes produce chemicals that affect endothelial glycocalyx?

A

Podocyte produces :
ang1 >VEGFR1
VEGF > VEGFR2

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14
Q

Chemicals that allow Endothelial glycocalyx to interact with GBM?

A

a5b1, a5b3

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15
Q

How are collagen molecules arranged?

A

3 polypeptide chains (α-chains) form triple helix

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16
Q

What is aa sequence of collagen?

A

repeating triplet sequence “Gly-X-Y” (X, Y = amino acids other than glycine)

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17
Q

Why is glycine in every third position on collagen chain?

A

small enough to fit into restricted space in center of triple helix, allow tight twisting

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18
Q

What are the 4 steps to intracellular biosynthesis of Type IV collagen?

A

Pre-procollagen chains are translated

Cleavage of signal peptides to form procollagen α chains

Hydroxylation, Glycosylation

Association of nascent carboxy-terminal propeptide chain (coil around each other)

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19
Q

How is pre-procollagen translated and translocated into ER?

A

guided by signal peptides to

translocate into ER lumen for intracellular modification

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20
Q

How happens to pre-procollagen to turn into procollagen?

A

Cleavage of signal peptides (so that they do not go elsewhere after entering lumen of ER) > form procollagen α chains

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21
Q

What intracellular modifications are made before the procollagen form triple helix?

A

Hydroxylation of certain proline, lysine residues

Glycosylation (add galactose, glucose) of: hydroxylysine, asparagine residues

22
Q

How is triple helix of collagen stabilized?

A

Association of nascent carboxy-terminal
propeptide chain (coil around each other)
= stabilize with S-S bond > triple helical procollagen

23
Q

What supramolecular assembly of Type VI collagen takes place after being exported from cell? (tropocollagen to triple helical domains)

A

tropocollagens dimerize at Carboxy terminal terminals (NC1) > form tropocollagen dimers

4 tropocollagen dimers aggregate at N-terminal > form type IV collagen tetramer (7S domain)

Lateral association of triple helical domains

24
Q

What does the structure of collagen do for filtration?

A

Has big spaces in

between structures for filtration

25
What is the structure of laminin?
``` Contains A, B1 and B2 chains > join to form a 4- armed structure (= one laminin molecule) ```
26
What causes laminin molecules to join up?
In the presence of Ca2+, free ends join respective | partners at C-terminal, form polymers/network
27
What is Laminin always associated with?
Entactin | Nidogen
28
How does proteoglycan associate with Laminin and type IV collagen?
Fill spaces between laminin and collagen
29
What is the glyco- part of Basement membrane (BM)-type Proteoglycans?
heparan sulphates (HS)
30
How many Heparan Sulphates link to polypeptides?
Linked to serine residues of polypeptides, e.g.:  2 HS per agrin (spread out)  3 HS per perlecan (clustered at one end)
31
What other protein can HS form a preteoglycan with?
Chondroitin
32
How does HS on Agrin contribute to the structure of the proteoglycan?
HS has negative charge -ve charges cannot cluster, so proteoglycan extends
33
Type IV collagen, proteoglycans and Laminin form what?
BM Scaffold
34
What is the first layer of ECM?
laminin polymers anchored to membrane associated receptor proteins
35
How is Laminin polymer in ECM anchored to the membrane?
Associated receptor proteins 1. Integrins 2. α-dystroglycans 3. Sulfatides
36
How does Type IV collagen add to Laminin polymer in ECM?
 Bridged by nidogen/entactin (associated with Laminin) or  Direct interaction
37
How does proteoglycans interact with Collagen and Laminin in ECM? (think about the two types of proteoglycan and their attachments)
Proteoglycans : 1) HS + Agrin = bind to cell surface receptor proteins (e.g. sulfatides) and Laminin 2)HS + Perlecan bind to cell surface receptor proteins and interact with NC1 domain of tropocollagen dimers or Interact with 7s domain of type IV collagen tetramer
38
How does Laminin + collagen filter molecules passing by?
``` Overall negative charge Filter by size, charge:  Positive = trapped  Negative = repelled If Protein is big and negatively charged = hard to get through ```
39
What is the key component of Slit diaphragm, the space between the podocte foot processes? How can it be visualized?
Key component = nephrin molecules visualize by immunostaining technique: gold-linked antibodies bind to nephrin
40
What composes nephrin in slit diaphragm?
From inside cell to further outside cell:  Intracellular domain (C-terminal)  Fibronectin type III domain  8 immunoglobulin-like domains (N-terminal) containing 1 Spacer domain
41
What allows the immunoglobins in nephrin to be stabilized (except spacer domain)?
Cysteine forms stable S-S covalent bonds > form loops (except in spacer domain: single cysteine = no loop)
42
How does nephrin network change shape?
Receive signal: cytoskeletal proteins (actin) pull in / out the interdigitating nephrin molecules from 2 opposite foot processes
43
Mutation in what results in proteinuria/ nephrotic syndorme?
Mutations in nephrin / its intracellular interacting | partners (CD2AP, podocin)
44
Is the change in concentration of small solutes significant after filtration?
Filtration produces no significant changes in concentration of small solute
45
How does nephritis change ultrafiltration?
loss of charge selectivity | Affect nephrin, GBM components, only sort by size of molecule, not charge
46
What charge molecules are filtered more (more go through to Bowman's capsule)?
Positive charge molecules filter through more than negative charge
47
What is used to test nephritis effect on charged molecule filtration?
Dextran - neutral Dextran sulphate - -ve DEAE Dextran - +ve
48
What is Alport syndrome a deficiency in ?
Alport syndrome: deficient assembly of the a3-,4-,5- collagen type IV network
49
What does diabetic glomerulopathy affect?
Thickened GBM | Decreased HS proteoglycans
50
What does minimal change nephrotic syndrome affect ( laminin β2-deficient) ?
Reduction of polyanionic sites, HS
51
What causes urinary excretion of GBM HS proteoglycan?
Post-exercise proteinuria: | > Temporary decrease in charge of the GBM > Urinary excretion of GBM HSPG
52
How does Glomerulonephritis change BM and ECM?
thickened mesangial BM and matrix