1. Lysosomes and Lysosomal Storage Diseases
August 30, 2018
Tom Gallagher
CTRE room 234
Extension 64850

2. Biogenesis and Function of Lysosomes
Five Introductory Slides

3. Lysosomes are acidic organelles that contain hydrolytic enzymes and mediate intracellular digestion
transporters for sugars, amino acids, purines, pyrimidines , and other building blocks of protoplasm

4. Endosomes evolve into lysosomes as they move to the cell interior and acquire hydrolytic enzymes

5. The hydrolytic enzymes feed into lysosomes from the Golgi apparatus
phosphorylation of mannose residues on lysosomal enzymes

6. The substrates (lysosome “food”) are delivered from both extracellular and cytoplasmic sources

7. Lysosomes are defined by a common set of properties rather than by appearance
a luminal pH of about 4.5;
the presence of active forms of lysosomal hydrolases ; and
the presence of a unique set of lysosomal membrane proteins (LAMPs).
Morphologically diverse
Black arrow: Lysosome (lead phosphate stain)
Blue arrow: Mitochondrion
Red arrows: Small lysosomes A B C

8. How are hydrolytic enzymes transported to lysosomes?

9. Lysosomal enzymes are phosphorylated on mannose residues in the cis-Golgi network

10. The transport of enzymes to the lysosomes involves mannose 6-phosphate receptors

11. Cleavage of lysosomal pro-proteins into active enzymatic forms

12. Lysosomal enzymes that are secreted are recovered by receptor-mediated endocytosis
Allen Frankfater

13. (2) How are “unwanted” cell membrane proteins brought to lysosomes for degradation?

14. Lysosomes degrade membrane proteins via multivesicular bodies
Terminate cell signaling by degrading receptors in lysosomes

15. Side note: Many endocytosed proteins will avoid lysosomal degradation via recycling and transcytosis.

16. Recycling can sort membrane proteins to distinct domains (at right)

17. Babies get protective maternal antibodies via transcytosis

18. (3) How are large organelles and “old” cells brought to lysosomes for degradation?

19. Autophagy engulfs cytosol and organelles for degradation
Note the double membrane surrounding two senescent organelles.
This autophagosome has not yet fused with a lysosome.

20. A macrophage phagocytosing two red blood cells
The arrows point to the edges of macrophage pseudopodia.
The RBC membrane contains phosphosphingolipids, glycosphingolipids, glycerol- containing phospholipids and carbohydrate-containing proteins.

21. The carbohydrate-rich glycocalyx is continously remodeled via endocytosis and eventual lysosomal degradation
Left Panel: Eukaryotic cell surface showing the glycocalyx.
Right Panel: Lysosomes containing extracellular matrix constituents.

22. (4) Some of the macromolecules brought into lysosomes are hard to digest.

23. N-glycans are sequentially degraded in lysosomes
Swainsonine in “loco-weed”:
Accumulation of alpha-mannosidase substrates:
CNS dysfunction

24. N-acetylgalactosamine 4-sulfatase
Ordered degradation of glycosaminoglycans GAGs):
Buildup of GAG degradation intermediates:
Example:
Hurler’s Disease
Example: Hurler Disease

25. (6) What are some of the lysosomal storage diseases?

26. What are Lysosomal Storage Diseases?
genetic conditions due to lysosomal enzyme deficiencies with the corresponding accumulation of substrates within lysosomes.
individually rare, but with ~ 50 described deficiencies, a collective incidence of about 1 in 6,000
autosomal recessive, except for Hunter syndrome and Fabry disease, which are X-linked recessive
onset of clinical symptoms usually occurs very early in life, but variants exist with onsets in adulthood
not all tissues are equally affected, and depends in part on the tissue distribution of the relevant substrate

27. Stored Substrate(s) and Clinical Symptoms
The stored substrates can classify lysosomal storage diseases
Type
Stored Substrate(s) and Clinical Symptoms
Mucopolysaccharidoses
GLYCOSAMINOGLYCANS (GAGs)
Dysmorphic features, cardiovascular and skeletal abnormalities, mental retardation and early death
Ex.; Hunter Syndrome
Oligosaccharidoses
GLYCANS AND OLIGOSACCHARIDES
Symptoms resemble those seen with the mucopolysaccharidoses 
Sphingolipidoses
SPHINGOLIPIDS
Severe neurological degeneration leading to loss of intellectual abilities, motor function, awareness of the surroundings, and death
Ex.; ; Fabry, Neimann-Pick, Gaucher, Metachromatic
Leukodystrophy , and Tay-Sachs
Mucolipidoses
SEVERAL STORED SUBSTRATES (due to loss of the phosphotransferase necessary to direct hydrolytic enzymes to lysosomes).
Ex.;; I-cell disease or mucolipidosis type II.

28. Hurler Disease (Mucopolysaccharidosis I)
Recessive mutation of α-L-Iduronidase
Buildup of dermatan sulfate and heparan sulfate glycosaminoglycans;
carbohydrate –containing glycosphingolipids may also build up in lysosomes
Disease severity varies with allelic heterogeneity (Hurler is worse than Scheie)
Skeletal deformities (reduced stature), coarse facial features, prominent forehead, enlarged liver and spleen, and cardiac abnormalities, neuropathies in severe cases (mental retardation and loss of hearing and vision). A C
Foam cells containing lysosomes engorged with stored glycosaminoglycans
Zebra bodies (arrows), which are lysosomes that also contain glycolipids
Child with Hurler disease B

29. Fabry Disease (Sphingolipidosis)
X-linked mutation in the enzyme ‑galactosidase
Accumulation of the glycosphingolipid ceramide trihexoside
First symptoms include tingling, numbness and/or burning sensations in the hands and feet, with periodic episodes of excruciating burning pain
Vascular lesions appear on the skin
Undegraded glycosphingolipid accumulates in heart, kidney and brain can lead to congestive heart failure, deteriorating renal function and neurological deficits; death due to uremia, myocardial infarction or pulmonary congestion by age
Can now be treated by enzyme replacement therapy A B
Brain pathology:
widespread segmental (torpedo-like swelling of axons
B) neuronal ballooning due to the storage of undegraded glyhcosphingolipid.

30. I-Cell Disease (Mucolipidosis II )
Recessive disorder
Defect in the Phosphotransferase that Creates the M-6-P Lysosomal Targeting Signal
Impaired turnover of extracellular matix constituents is noticed first
Dense inclusions in fibroblast cytoplasm
Lysosomal enzymes secrete into extracellular fluids (elevated plasma and urinary enzymes)
Skeletal deformation, enlarged liver and other soft tissues, coarse facial features (e.g. enlarged lips, thick skin), low nasal bridge, progressive growth retardation and intellectual regression, and death in early childhood A B
Fibroblasts containing numerous dense cytoplasmic inclusions
Facial features of I-Cell Disease

31. Additional signs and symptoms may be observedC A B
Cyst-like lytic lesions in bone from a Gaucher patient
Cherry red spot on the retina of an infant with Tay-Sachs disease
C. Angiokeratoma in Fabry disease – skin capillary lesions that give the appearance of a rash

32. (7) What are possible treatments for lysosomal storage diseases?

33. Enzyme Replacement Therapy (ERT) for the Treatment of Non-neurologic forms of some Lysosomal Storage Diseases
Mannose-6-Phosphate
receptors

34. A girl born to parents of eastern Mediterranean Jewish descent is brought to the pediatric neurology clinic. She appeared normal at birth and is now 6 months of age. There is a loss of peripheral vision and an abnormal startle response to auditory stimuli. She has suddenly shown a loss of coordination and has lost some responsiveness to her environment. She has a cherry-red spot on her macula. Treatments to cure this disease might focus on developing therapies that would do which one of the following?
A. Stimulate ganglioside GM2 production
B. Stimulate GM2 synthesis in the rough endoplasmic reticulum (RER)
C. Stimulate hexosaminidase production
D. Stimulate transport of ganglioside GM2 to the lysosome
E. Remove mannose 6-phosphate from hexosaminidase.