Lysosomal storage disorders Flashcards
Who discovered LSDs?
Christian de Duve
How many genes control LSDs?
One gene
Monogenic disease
What type of diseases are LSDs?
Metabolic diseases
Why do biological materials build up in LSDs?
Enzyme or membrane protein of lysosome is defective
Causes build up of proteins or substrate
What two proteins can be defective in LSDs?
Lysosomal membrane proteins
Enzymes
What is the incidence of LSDs?
Singularly rare
Many types of the disease
Combined frequency is very high
How many diseases do LSDs encompass?
More than 60 diseases
What type of mutation causes LSDs?
Many different mutations in the same or different gene causes the disease
How do the mutations influence the gravity of the symptoms in LSDs?
Mutation influences
- severity of symptoms
- onset of symptoms
Genetic analysis not enough to rule out diagnosis in patients presenting symptoms of LSD
TRUE or FALSE
TRUE
Not always a direct genotype-phenotype correlation
What two factors are used to classify LSDs?
Substrate that builds up
Gene that is mutated
Different gene mutations have similar phenotypic characteristics
TRUE or FALSE
TRUE
Same metabolic pathway is affected in the different subtypes of LSD
What are the four main roles of the lysosomes?
Endocytosis/autophagy
Apoptosis
Unfolded protein response
Mitochondrial/Ca2+ balance
What role do lysosomes play in endocytosis?
Internalisation of extracellular material through
- invagination
- formation of vesicles
Release of material into the intracellular lysosomal compartment
What is autophagy?
Normal physiological process in the body that deals with destruction of cells in the body
How does autophagy maintain homeostasis?
Protein degradation
Turnover of the destroyed cell organelles for new cell formation
What triggers autophagy?
Cell starvation
What is apoptosis?
Programmed cell death
What is the role of lysosomes in apoptosis?
Membrane of the lysosome becomes more permeable
Release proteases into the cytosol
Examples of proteases released from the lysosome into the cell during apoptosis
Cysteine
Cathepsin
What is UPR?
Unfolded protein response
Unfolded proteins must be removed from the cell environment to maintain cell homeostasis
Which two mechanisms deal with unfolded proteins in the cell environment?
Proteasomes
Chaperones
How do chaperones deal with unfolded proteins?
Break the misfolded proteins down into their primary structure
Try to fold them into the correct shape
What happens to the misfolded proteins if the aren’t folded into their correct shape by the molecular chaperones?
They are discarded in the lysosome
What happens to the misfolded proteins if they are folded into the correct shape by molecular chaperones?
Released systematically
How do mitochondria and lysosomes maintain dynamic homeostasis?
Degrade dysfuntional mitochondria
Maintain lysosomal function by acidification
Lysosomal calcium regulates mitochondrial catabolism
In which processes is calcium signalling useful for between mitochondria and lysosomes?
Autophagy
Membrane fusion
Apoptosis
What is the size of lysosomes?
1-2 micrometers
How many acid hydrolases and membrane proteins are found in lysosomes?
> 50
How is the pH maintained in lysosomes?
Actively concentrate H+ by a proton pump ATPase
In what way is the cell adapted to withstand lysosomal damage?
pH of the cytosol is around neutral
If the lysosome cell membrane breaks down the enzymes are rendered inactive by the high pH of the cytosol
Protective
What processes happen if the intracellular relationships between the lysosome and surrounding organelles is disrupted?
Dysfunctional biosynthesis and catabolism of GSLs
Accumulation of substrates
Failed trafficking
Disturbed calcium signalling
Apoptosis
Necroptosis
Macrophage activation
Disturbed autophagy
Disruption of lipid raft - receptor signaling
Why are so many organelles affected if the lysosomes become dysfunctional?
A lot of cross-talk between lysosomes and organelles
Complete disruption of the GSL pathway is incompatible with life
TRUE or FALSE
TRUE
Why are lysosomes sensitive to enzyme mutations?
The enzymes are found in this organelle
Here is where the metabolic pathways take place
When the metabolic pathways are disrupted because of a mutation, the substrate will build up in the lysosome
What are glycosphingolipids?
The metabolic pathways of glycosphingoipids are affected in LSDs
The mutated proteins are involved in these metabolic pathways
What are the components of glycosphingolipids?
Carbohydrate + ceramide
Examples of specific disorders related to the disruption of the GSL pathway
Krabbe
Gaucher
Niemann-Pick disease
Fabry
Sandhoff
Batten
Presentation of LSD varies a lot between patients
TRUE or FALSE
TRUE
The same gene can have different mutations
Mutations can affect different organs and cell types
Affected cell population can be widespread or restricted
Why are LSDs so difficult to treat?
Same disease may be caused by different mutations
How can different genetic mutations cause the same presentations?
Mutations affect the enzymatic pathway along different points
Leads to the same substrate build-up
What is a broad way to classify LSDs?
Visceral
Neurological
Clinical features of LSDs
Organomegaly
Cardiomyopathy
Respiratory manifestations
Haematological and endocrine symptoms
Bone abnormalities
Main characteristic of neuropathologies related to LSDs
Leads to premature death
What are the symptoms of neuropathology in LSD
Neurocognitive impairment
Movement disorders
Seizures
Deafness
Parkinson’s
Pathogenesis of LSDs - Krabbe disease
Metabolites from GAGs build up
These are recognised by TLRs
Causes secretion of cytokines
Apoptosis of cells
What substrate accumulated in Gaucher disease?
Glucocerebroside
What causes the substrate accumulation in Gaucher disease?
CBA gene coding for b-glucocerebroside is defective
Which cells are particularly affected in Gaucher disease?
Macrophages
Gaucher cells
What is the main symptom of Gaucher disease?
Organ enlargement
As the enlarged cells enter the organs
What is the condition where the spleen and liver become enlarged called?
Hepatosplenomegaly
How many types of Gaucher disease exist?
3 types
Describe type 1 Gaucher disease
Visceral presentation of pathology
Most common type
The b-glucocerebosidase enzyme is less efficient but still functional
Describe type 2 Gaucher disease
Acute neuropathology
Death < 2 years of age
Enzyme is affected so the active site is disrupted and completely dysfunctional
Describe type 3 Gaucher disease
Chronic neuropathy
Slow progression
What accumulates in cells during Niemann-Pick disease
CHolesterol
Sphingolipids
What two types of Niemann-Pick disease exist
Type A and B
Type C
What distinguishes the different types of Niemann-Pick disease
Genes that are mutated
What gene is mutated in types A and B Niemann-Pick disease?
SMPD1
What genes are mutated in type C Niemann-Pick disease?
NPC1 and NPC2
What does SMPD1 code for?
Enzyme
Sphingomyelinase
What do NPC1 and NPC2 code for?
Membrane proteins
Where are the manifestations of Niemann-Pick disease observed in the body?
Type A and B - viscera
Type C - viscera and nervous system
Neurodegenerative symptoms in type C Niemann-Pick disease
Delay in motor milestones
Ataxia
Psychiatric problems
Which gene mutations lead to Batten disease?
Neuronal ceroid lipofuscinoses
400 mutations in 13 different CLN genes
In Batten disease, depending on the —– affected, the —- of the disease is different
Gene
Onset
At which developmental stages can Batten disease be observed?
Infantile
Late infantile
Juvenile
Adult
Symptoms of Batten disease
Visual impairment
Seizures
Neurological symptoms
Premature death
Maculopathy and retina atrophy
What analysis is needed to diagnose LSD?
Biochemical and genetic analysis
What are sources of complication when it comes to diagnosing LSDs?
Rare disease - no routine prenatal screening
Often misdiagnosed due to the heterogeneity in symptoms
Lack of biomarkers
Examples of newborn screening to diagnose LSD
Enzymatic activity in blood spots
Detection of urinary oligosaccharides or glycosaminoglycans
Indirect biomarkers
Skin biopsy
—- diagnosis is essential for diseases with ——
Early
Neurological involvement
What are the different approaches of how to treat LSDs
Treat
- the symptoms
- cell dysfunction and cell death
- substrate storage
- enzyme or protein defect
- gene defect
LSD therapies are normally exclusive
TRUE or FALSE
FALSE
LSD therapies are normally not exclusive
What is the primary care for patients with neuropathologies?
Suppotive care for individuals and their families
What types of LSDs are particularly hard to treat?
LSDs that involve
- dysfunctional membrane proteins
- insoluble enzymes
- the BBB
What are the main therapies for LSDs?
Transplantation Substrate reduction therapy Enzyme replacement therapy Molecular chaperones Gene therapy
Procedure of transplantation
- Multipotent stem cells are obtained from the BM, peripheral blood and umbilical cord
- Bone marrow from suitable healthy donor is the therapeutic agent
- Healthy haematopoietic cells spread throughout organs
- Secrete missing enzyme
Why does haematopoietic stem cell therapy help sufferers with neurological presentation?
Microglial cells of haematopoietic origin can cross the blood-brain barrier and secrete the therapeutic enzyme in the brain
What is the main goal of stem cell therapy?
Slow or arrest neurodegeneration
Replace the defective enzyme before significant CNS injury
What are the disadvantages of stem cell therapy?
Cannot help with diseases where the condition derives from faulty intermembrane proteins
Minimal improvement is seen
No effect on CNS
What is the aim of substrate reduction therapy?
Reduce the synthesis of the accumulating substrate
Two examples of drugs involved in substrate reduction therapy
Miglustat
Eliglustat
How does Miglustat reduce the substrate concentration?
Competitively inhibits the upstream enzyme
Blocks the biosynthesis of the overproduced substrate
Diseases that Miglustat targets
Gaucher
Fabry
Advantage of Miglustat
Crosses BBB
Disadvantages of Miglustat
Causes GI problems
Disrupts metabolic pathway higher up than the overproduced substrate
Another example of a substrate reducing therapy
Eliglustat
Disadvantage of Eliglustat
Cannot cross the BBB
Drug transporter causes the compound to be pumped out of the CSF
What has been the most successful treatment of LSDs to date?
Enzyme replacement therapy
What is enzyme replacement therapy based on?
Replacement of the defective enzyme by systemically administering the recombinant protein
It is proven that partial levels of enzymatic activity might be sufficient to help stabilise symptoms of LSD
TRUE or FALSE
TRUE
How are recombinant enzymes produced?
Using recombinant DNA technology
Tagged with a moiety that allows the enzyme to enter the cells and traffic to the lysosomes
Produced in an industrial scale
What are the advantages of using recombinant enzymes as therapy for LSD?
Safe and well tolerated
Rarely causes an immune reaction
Suitable for cross-correction
What is cross-correction?
Process by which a recombinant protein can be replicated in the cell and transported to neighbouring cells
What moiety are the recombinant proteins bound to?
Mannone-6-phosphate
What cellular process do pharmacological chaperones take advantage of?
Molecular chaperones
What do molecular chaperones do?
Bind to nascent polypeptides and promote correct folding of them
Traffic mutant proteins that are not able to be folded correctly to be lysed
What condition must proteins express in order to be suitable to be corrected by chaperones?
Must possess residual enzymatic activity - the mutation cannot affect the active site
What are the aims of using molecular chaperones as therapy for LSDs?
More enzymatic activity is retained in the lysosome
Small change in enzymatic activity can affect the quality of life
What are the names of two molecular chaperones used as therapy for LSDs?
Migalastat
Arimoclol
Which condition does Migalastat treat?
Fabry disease
How does Migalastat treat Fabry?
Binds to the active site of misfolded a-galactosidase A
Which condition does Arimoclomol treat?
NPC
How does Arimoclol treat NPCs?
Co-inducer of the heat-shock response
Activates the natural cellular repair pathways
What is gene therapy?
Process by which a mutated gene that causes disease is replaced with a therapeutic copy using a viral vectors
What are two ways to perform gene therapy?
In vivo
Ex vivo
What does in vivo gene therapy involve?
Inject the vectors directly into the body where the faulty cell’s DNA is affected
What does ex vivo gene therapy involve?
Take out cells from the body
Inject the vector into the cell
Place them in the incubator
Add the cells to the body
What types of vectors can be used in gene therapy?
Non-viral
Viral
Examples of non-viral vectors
Naked DNA
Nanoparticles
Biovesicles
Examples of viral vectors
Lentivirus
Adenovirus
Adeno-associated virus
Advantages of gene therapy
Targets the CNS
Cross-correction
Liver is a good target
Long-term therapy
What is cross-correction?
Translation of beneficial proteins from genetically altered cells enter cells surrounding them
Why is the liver a good target for gene therapy?
Vectors have a great effect on hepatocytes
Genetically modified cells can produce the advantageous protein
Travel to neighbouring organs in the circulation
What are the disadvantages of gene therapy?
Gene delivery needs to be targeted to a specific cell population
Difficult to determine the concentration of protein needed and longetivity of effects
Needs to avoid the immune response
Cost
Why does the advantageous gene need to be targeted to specific cell populations?
Protein produced may be beneficial in some organs and dangerous in other
How is the long-term effectiveness of gene therapy sometimes hazardous?
If too much protein is made, past the natural concentration, pathological effects may develop
Why are AAVs used often as gene delivery vectors?
Efficient at delivering gene therapy
High titer
Causes mild immune response
Interacts with a broad number of cells
Very safe
