The translocator protein (18 kDa) (TSPO) is a five transmembrane domain protein that is localized primarily in the outer mitochondrial membrane and is expressed predominantly in steroid-synthesizing tissues, including the brain. TSPO is involved in the translocation of cholesterol from the outer to the inner mitochondrial membrane, which is the rate-limiting step in the synthesis of steroids and neurosteroids. TSPO is currently under investigation as a biomarker of brain inflammation and reactive gliosis that are associated with various neuropathologies. Although TSPO is expressed in many organs, the highest levels are found in tissues containing steroidsynthesizing cells, such as adrenal, gonad and brain cells. As a major component of the outer mitochondrial membrane, TSPO mediates various mitochondrial functions, including cholesterol transport and steroid hormone synthesis, mitochondrial respiration, mitochondrial permeability transition (mPT) pore opening, apoptosis, and cell proliferation.


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