gene editing in CNS diseases

Question 1

oligodendrocytes

Answer 1

• The central function of oligodendrocytes is to generate myelin, which is an extended membrane from the cell that wraps tightly around axons.
• Due to this energy consuming process and the associated high metabolic turnover oligodendrocytes are vulnerable to cytotoxic and excitotoxic factors
• Oligodendrocytes develop from oligodendrocyte precursor cells (OPCs)

Question 2

adaptive myelination

Answer 2

characterized by changes in thickness, length, and/or number of myelin sheaths on an axon, changes in myelin protein expression and formation of new oligodendrocytes  Myelin plasticity
* Promoted by (motor) learning
* Flexibility depends on brain area

Question 3

MS and myelin

Answer 3

• In MS the myelin is eaten away by immune cells
• After this remyelination might occur but this stops as the disease progresses
• OPC and oligodendrocytes would play a central role in this
• pathology starts next to blood vessels since this is the sight of lymphocyte diapedesis

Question 4

OPC dysfuntion

Answer 4

In multiple diseases OPCs do not fully mature and thereby cannot provide adequate amounts of mature oligodendrocytes that produce myelin leading to low neuronal transmission speed

Question 5

MS - pathology timeline

Answer 5

• Before the diagnosis has been made multiple white matter lesions have already taken place (arrows) and inflammation of the brain has started –> cognition is not yet noticeable impaired
• The following years more and more lesions will form while inflammation goes up and down (relapsing-remitting MS phase) cognition will start to slowly get worse while the brain volume starts to drop slowly –> can be controlled by anti-inflammatories
• Secondary progressive phase starts after 15 years: the Brain volume decreases faster and cognition get progressively worse as large lesions form (inflammation is actually less but damage has been done) –> no treatment only symptomatic
• Treatment goal is to start remyelination using OPCs that are still fully intact
• Aims are to protect OPCs from inflammation and find out why they are not differentiation and push them to do so

Question 6

epigenetics and OPCs

Answer 6

• DNA methylation of OPCs is different in MS patients than controls
• Negative regulators like ID2/4 are highly expressed in OPCs causing low myelin expression this is normal in mature oligodendrocytes but not OPCs
• The genes that encode ID2/4 proteins are highly expressed since they are hypomethylated –> they have too few methyl groups in the CpG islands leading to overexpression
• The methylation of ID2/4 is involved in the maturation of OPCs  not only in myelin production but also essential for the cells to differentiate
• Blocking methyl transferases leads to hampering of OPC differentiation

Question 7

CRISPR/dCas and MS

Answer 7

• Using dCas CRISPR can no longer cleave DNA but can very specifically methylate DNA sites using methylating enzymes (DNMT)
• Methylation of the promoter region of negative regulators (ID2/4), means that they are not expressed anymore.
• Downregulating negative regulators in the presence of positive regulators (like SOX10) causes differentiation of OPCs  leading to (re)myelination