Understanding the role of TSPO in myeloid cell activation Maria Weinert1, Alexandra Phillips1, Kambiz N Alavian1, Sally A Cowley2, Paul M Matthews13, David R Owen1 1Division of Brain Sciences, Imperial College London, UK; 2Dunn School of Pathology, Oxford University, UK; 3Dementia Research Institute UK
The 18kDa Translocator Protein (TSPO) is highly expressed in macrophages and microglia and has been studied extensively as a marker for in vivo imaging of “neuroinflammation”. Furthermore, several lines of evidence suggest a beneficial effect of TSPO-specific ligands on myeloid cell phenotype. However, very little is known with respect to the function of this mitochondrial protein in myeloid cells. To understand the molecular link between TSPO function and immune modulation we used Crispr to generate TSPO knockout (KO) lines from human iPS cells. After differentiation of iPS cells into macrophages and activation with LPS, we found significantly reduced TNFα secretion in TSPO KO lines compared to wildtype controls, suggesting a role of TSPO in pro-inflammatory activation. To further understand the molecular function of TSPO after LPS activation, we performed immunoprecipitation experiments in primary human macrophages coupled to quantitative mass spectrometry to identify proteins with differential binding to TSPO after pro-inflammatory activation. We found that LPS modulates the association between TSPO and its mitochondrial interaction partner VDAC. VDAC is the main channel for metabolites crossing the mitochondrial membrane and as such it is required for the development of immune functions that rely on mitochondrial activity, such as inflammasome activation. Future experiments will aim to understand the effect of TSPO on VDAC activity in myeloid cells, the molecular requirements for interaction, and whether TSPO ligands alter interaction or activity of TSPO on VDAC.