The Peter Bullock Lab
PML, a human demyelinating disease caused by the JC virus
Progressive Multifocal Leukoencephalopthy (PML) is an often-fatal demyelinating disease of the central nervous system that is caused by the JC polyomavirus (JCV). The disease occurs primarily in immuno-compromised individuals, such as transplant patients on immunosuppressive medications, AIDS patients, those taking certain types of drugs (e.g., Tysabri for multiple sclerosis) and individuals suffering from hematological malignancies. Moreover, a possible association between JC virus and human brain and non-central system tumors has also been reported.
Development of a model system for studies of PML
The principal CNS targets for JCV infection are oligodendrocytes (the brain cells that produce myelin). A stable human oligodendrocyte cell line for studies of JCV dependent PML was, however, not previously available. Therefore, we were delighted to report in Peterson et al, 2017 that a human stem cell line termed G144 (Pollard et al, 2009) undergoes differentiation by removal of growth factors (Fig. 1A), express oligodendrocyte specific surface markers (Fig. 1B), has a rapid doubling time (3-5 days) and is stable during passage. Furthermore, we reported that G144 cells support robust levels of JCV DNA replication and infection by JC virus. Thus, we have established the first oligodendrocyte based model system for studies of JCV dependent PML.
Figure 1. Characteristics of the G144 oligodendrocyte cell line. A. Bright field images confirming that G144 cells undergo differentiation upon growth factor removal. B. Immunofluorescence based evidence that G144 cells express characteristic surface markers.
Utilizing the G144 based model system to understand the molecular basis for PML
We are now engaged in a number of studies designed to determine how infection of oligodendrocytes with JC virus leads to the death of these cells and demyelination of neurons. For instance, we want to confirm recent data indicating that infection of G144 cells with JC virus causes the cells to die via a Caspase-3 dependent pathway.
Building on our previous studies of JC virus
We anticipate that our previous studies of the initiation of JCV DNA replication, including our structural studies of JCV T-antigen (Meinke et al, 2016), will be very useful in terms of understanding the molecular basis of JCV dependent PML. For instance, we want to use Cas9 based techniques to identify the oligodendrocyte specific factors that bind to the viral regulatory region, that also includes binding sites for JCV T-antigen, and thereby determine the tropism of JCV for oligodendrocytes.
A possible approach for treating PML
In Peterson et al. (2017) we also reported that Akt is required for JCV DNA replication. Thus, we are continuing to test the hypothesis that drugs that target the PI3K-Akt- mTOR pathway will serve as inhibitors of JCV infections.