A potential new source of TrkB dysregulation: Microglia possess the machinery for BDNF receptor cleavage

The signalling pathways mediated by BDNF are impaired in Alzheimer’s disease (AD) due to the cleavage of its receptor, TrkB-FL. Amyloid-Beta peptide (Aβ) accumulation promotes the overactivation of NMDA receptors, allowing for a major calcium influx. As a consequence, calcium-dependent calpains proteases become activated, leading to TrkB-FL receptor cleavage and the formation of a new fragment, TrkB-ICD. Data from primary neuronal cultures show that TrkB-ICD is a stable fragment able to phosphorylate nuclear and axonal proteins and promotes transcriptomic and proteomic alterations. Alongside, TrkB-ICD leads to synaptic plasticity dysregulation culminating in memory deficits. Knowing that previous studies have shown that TrkB-ICD possesses a deleterious effect in neurons and that neuron-glial communication is ever-occurring, we hypothesize that this fragment may present potential harmful events on microglia. To that endeavour, we aim to investigate if these cells possess the necessary machinery for TrkB-FL cleavage to occur. Mixed glial cultures were prepared from 1-2 days-old Wild-type C57BL6 pups. After 21-days in vitro, microglia were isolated by mild trypsinization. Seventy-two hours later the isolated microglia were collected for molecular analysis. The preliminary results, using the western-blot technique, revealed the presence of both TrkB-FL and NMDA receptors alongside with calpains proteases in microglia cells. Thus, microglia cells have all the necessary machinery for TrkB-FL cleavage to occur, nevertheless, the effect that TrkB-ICD possesses on these cells remains to be elucidated.