Investigating the Role of BTK in Microglia in Multiple Sclerosis and its Animal Models
Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) characterized by demyelination, immune cell infiltration and neurodegeneration. A class of drugs, Bruton’s tyrosine kinase (BTK) inhibitors are currently undergoing phase III clinical trials for the treatment of MS. BTK inhibitors primarily target the activity of B cells, but BTK activation is also downstream of pro-inflammatory signalling pathways in CNS myeloid cells, microglia, and macrophages. Existing research into the role of BTK signalling in microglia and macrophages is cursory, and the connection between BTK expression and pro-inflammatory activities remains to be elucidated. In this thesis, the expression of BTK was evaluated in the CNS tissue of MS and its rodent models, and the effect of BTK inhibition in the experimental autoimmune encephalomyelitis (EAE) model and on microglia in a co-culture system was investigated. In MS brain samples, we observed the expression of BTK and (the active form) pBTK in areas with a high immunoreactivity of Iba1+ microglia/macrophages. In three animal models of MS, BTK and pBTK were observed to be upregulated in the spinal cord lesions, but only pBTK expression was downregulated at later time points. Lineage tracing of CNS macrophages revealed that both microglia and macrophages express BTK and pBTK without a preference by either cell type. Treatment of MOG¬35-55 EAE mice with the BTK inhibitor GDC-0853 initiated from EAE induction day showed significant reduction in the clinical and histological pathologies. However, drug administration from clinical onset only showed marginal reductions in overall clinical signs, and immunofluorescent analyses of the spinal cord lesions did not show detectable differences in the expression of myeloid, myelin and axonal markers. In vitro, stimulation of neuron-microglia co-culture with IFN-γ and LPS resulted in robust neuronal death and elevated secretion of TNF-α, which were not attenuated with the addition of GDC-0853. Drug treatment of microglia activated with iLPS did not show reduced expression of pBTK. These results suggest that BTK inhibition may effectively reduce disease pathophysiology if treatment is initiated early, but its capacity to directly modulate microglial activities remains to be established.
multiple sclerosis, Bruton’s tyrosine kinase, neuroinflammation, microglia, animal models
Li, C. (2023). Investigating the role of BTK in microglia in multiple sclerosis and its animal models (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.