GFAP and sarcopenia: However, aged microglia, together with a weakened BBB, lead to an increase in circulating IL-6 [159,160], TNF-α [161], intercellular adhesion molecule-1 (ICAM-1), the tissue inhibitor of metalloproteinases 1 (TIMP-1), and glial fibrillary acidic protein (GFAP), which are associated with sarcopenia and physical frailty [162].