Journal of Endocrinology

Effects of thyroid hormone on microglia (reproduced with permission from Mori et al. 2015). Schematic representation of possible signal transduction pathways activated by T₃. Microglia contain various TH transporters (LAT2, OATP4a1 and MCT10) and TH receptors. Intracellular T₃ activates intracellular TRs (TRα1 and possibly TRβ1) and appears to also couple to various other factors, such as nitric oxide synthase (NOS), G_i/o-protein, PI3K and MAP/ERK. The receptors for gamma-aminobutyric acid (GABA) A and B are also involved in T₃-induced microglial migration but not in T₃-induced phagocytosis, the mechanism of which is unclear. The reverse mode of the Na⁺/Ca²⁺ exchanger (NCX) may be activated by Na⁺ influx by the Na⁺/K⁺ pump, resulting in Ca²⁺ influx, which in turn activates small-conductance Ca²⁺-dependent K⁺ channels (SK). This subsequently induces microglial migration and phagocytosis, possibly due to membrane hyperpolarization. Hypothetical signalling pathways for phagocytosis are indicated by the dotted line. Reproduced, with permission, from Mori Y, Tomonaga D, Kalashnikova A, Furuya F, Akimoto N, Ifuku M, Okuno Y, Beppu K, Fujita K, Katafuchi T, et al. (2015) Effects of 3,3’,5-triiodothyronine on microglial functions, Glia, volume 63, pages 906–920. Copyright (2015) Wiley Periodicals, Inc.