Storage Diseases

Question 1

Lysosomes are:

Answer 1

single membrane organelles, heterogenous size, the main site of digestion within the cell, and are acidic inside

Question 2

Lysosomes are derived from?

Answer 2

the golgi apparatus and the plasma membrane

Question 3

Storage diseases are diseases of the ___.

Answer 3

Lysosome

Question 4

Storage diseases are caused by:

Answer 4

a defect in one of the catalytic enzymes within the lysosome which leads to a build up (i.e. storage) of the substrate for that particular enzyme within the cell

Question 5

What is the ultimate result of storage diseases?

Answer 5

cell death

Question 6

What cells are especially sensitive to storage diseases?

Answer 6

Neurons

Question 7

Name two types of lysosomal storage diseases:

Answer 7

1. Alpha-mannosidosis

2. neuronal ceroid lipofuscinoses

Question 8

Pathology of alpha-mannosidosis in guinea pigs

Answer 8

Extensive cytoplasmic vacuolization in the CNS and peripheral tissues; lysosomal enzymology in leukocytes, plasma, and skin cells

Question 9

Mannosidosis is found in:

Answer 9

goats, cattle, cats, and guinea pigs

Question 10

Mannosidosis is characterized by:

Big picture

Answer 10

skeletal deformities, retarded growth, ataxia, tremors; can also get splenomegaly (enlarged spleen) and immune deficiency and ocular problems (cloudy cornea)

Question 11

Mannosidosis is caused by:

Answer 11

mutations in the Manb gene which causes deficiency in lysosomal alpha-mannosidase activity

Question 12

What does the alpha-mannosidase enzyme do?

Answer 12

breaks alpha bonds between added mannose subunits onto oligosaccharides

Question 13

What happens without the alpha-mannosidase enzyme?

Answer 13

We get a massive build up of the oligosaccharide made up of mannose subunits because they can no longer be broken down

Question 14

Can mannosidosis be acquired (besides being genetic)?

Answer 14

Yes, ingestion of Swainsona or astragalus plants have causes mannosidosis. Swainsonine inhibits both golgi and lysosomal alpha-mannosidase

Question 15

How can you detect mannosidosis?

Answer 15

Build of oligosaccharides that can be detected in the blood and urine. Histopathology results can also show lysosomal vacuolization in nuerons and other tissues.

Question 16

Neuronal Ceroid Lipofuscinosis (NCLs) are found in:

Answer 16

Mostly dogs, but also in cats, cattle, sheep and goats

Question 17

NCLs causes:

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Answer 17

neuronal loss, cortical atrophy, cerebellar and retinal degeneration resulting in seizures, myoclonus, ataxia, and blindness

Question 18

NCLs is the result of:

Answer 18

deficiency in one of several lysosomal enzymes (palmitoyl protein thioesterase CLN1, tripeptidyl peptidase-1 CLN2, or cathepsin D CLN10)

Question 19

Enzymes that are effected in NCLs are responsible for breaking down:

Answer 19

Peptides/proteins (vs enzymes that broke down sugars in mannosidoses)

Question 20

NCLs is characterized by:

big picture

Answer 20

the build up of curvilinear storage bodies in the lysosomes that contain a mix of proteins and lipids and are fluorescent

Question 21

Pathology of NCL in Dachshund:

Answer 21

Extensive depletion of neurons in the cerebellum, cerebrum and spinal cord.
Analysis revealed curvilinear, fluorescent storage bodies characteristic of neuronal ceroid lipofuscinosis.

Question 22

Genetics of NCL in dachshund:

Answer 22

Deficiency in tripeptidyl peptidase-1 (TPP1) which is a lysosomal serine protease with N-terminal exopeptidase activity

Question 23

What is tripeptidyl peptidase-1 (TPP-1)?

Answer 23

Lysosomal serine protease with N-terminal exopeptidase activity. It is synthesized as a precursor and then autocatalytically activates itself at low pH.

Question 24

TPP1 has a specificity for peptides containing:

Answer 24

Arg-Ala-Gly

Question 25

What causes NCLs in the a dachshund?

Answer 25

single base pair deletion in exon 4 which creates a premature stop codon. This produced a truncated protein.

Question 26

How does the build up of these storage materials kill the cell in storage diseases?

Answer 26

We don’t know why, only potential models have been proposed:
Lysosomal rupture releasing digestive enzymes into the cell; the substrate itself may be toxic; disruption of membranes via lipids; ER stress

Question 27

Storage diseases: potential treatments

Answer 27

1. Gene therapy to replace the defective gene
2. Substrate-reduction therapy - biosynthetic enzyme that can chew up specific substrate
3. Enzyme replacement therapy (ERT) - recombinant enzyme that is injected and hopefully gets inside the cell

Question 28

Treatment: alpha-mannosidosis in mice

Answer 28

Treated alpha-mannosidase knockout mice with increasing amounts of recombinant human alpha-mannosidase causing a reduction of sugars in kidney and spleen, but not in the brain because of blood brain barrier. Large amounts of this enzyme had to be administered to see this result in the brain.

Question 29

Treatment: NCL in Dachshunds

Answer 29

Gave recombinant TPP1 to dachshunds homozygous for TPP1 mutation and it didn’t ameliorate the neurological defect but did reduce the build up.