Central Effects of BTK Inhibition in Neuroinflammation
Ross C. Gruber1, Nathalie Chretien1, Michael R. Dufault1, Jonathan Proto1, Mindy Zhang1, Michael LaMorte1, Evis Havari1, Tarek A. Samad1, Timothy Turner1, Anthony Chomyk2, Emilie Christie2, Bruce D. Trapp2, Dimitry Ofengeim1
1Sanofi, 2Cleveland Clinic
To assess the role of Bruton’s tyrosine kinase (BTK) signaling in modulating inflammatory processes in microglial cells in vitro and in vivo.
Innate immune activation in the central nervous system (CNS) has been proposed to be a key driver of disease progression in multiple sclerosis (MS). BTK is expressed in B cells and innate immune cells, including macrophages and microglia. In B cells, this kinase is an essential component of the B-cell receptor signaling pathway regulating proliferation, maturation, antigen presentation, and production of secreted immunoglobulins. We hypothesize that in addition to its role in B cells, BTK regulates microglial deleterious inflammatory signaling; therefore, inhibiting BTK with a brain-penetrant inhibitor may provide therapeutic benefit within the CNS by targeting innate immunity associated with disease progression in MS.
RNA sequencing, immunohistochemistry, and Western blotting were used to measure BTK or phospho-BTK in primary mouse microglial cell lines, mouse brains, or postmortem human MS brains.
We demonstrated basal activity of BTK in murine microglial cells in vitro that was enhanced by stimulation with immune complexes and silenced with a BTK inhibitor. Transcriptome analysis was used to generate a microglial gene expression signature of BTK signaling, identifying unique RNA biomarkers of BTK activation or inhibition. This novel BTK-dependent transcriptional profile was confirmed in vivo, using direct stereotaxic injection of aggregated IgG to mouse brain. Oral administration of a brain-penetrant BTK inhibitor downregulated the BTK-dependent gene expression signature in mouse brain. In tissue derived from autopsy specimens, immunohistochemistry studies coupled with single-nucleus RNA sequencing demonstrated that BTK was expressed in B cells as well as in microglial cells, with increased levels in MS lesion samples.
BTK-dependent inflammatory signaling in microglia can be modulated using brain-penetrant BTK inhibitors, which could abrogate microglia-driven neuroinflammation implicated in disease progression in MS.