Modulation of Integrin αvβ3 Activation and Signaling in BV-2 Microglial Cells and THP-1 Monocytes by Thyroid Hormones

Much evidence now indicates a direct crosstalk between thyroid hormones (THs) and the immune system. We previously showed that THs behave as anti-inflammatory agents in human leukemic THP-1 monocytes, but a potential neuroprotective effect of THs in microglia have been under-investigated. Microglia, the primary innate immune cells of the brain, play a pivotal role in the regulation of neuroinflammation and nongenomic integrin αvβ3-mediated action of THs appear to be involved. Integrin αvβ3 was highly expressed in activated BV-2 cells, while it was decreased by THs. In addition, THs facilitated wound healing in BV-2 murine microglia cells activated by lipopolysaccharide (LPS), through integrin αvβ3 and reactive oxygen species (ROS), with tetrac (a metabolite of TH) potentiated the inhibition of migration. Nitric oxide (NO) played a role with different mechanisms in the presence of either T3 or T4. Our data showed the capability of TH and analogues to modulate the M1-to-M2 microglial transition and suggest a new spectrum of actions in the central nervous system (CNS).