Aging-related tau astrogliopathy (ARTAG) is an umbrella term that encompasses a spectrum of morphological abnormalities seen in astrocytes of the aging brain using immunostaining for pathological forms of the microtubule-associated protein tau. Morphologies of ARTAG include thorn-shaped astrocytes (TSA), and additionally granular/fuzzy astrocytes (GFA) characterized by fine granular tau immunoreactivity extending into the astrocytic processes. Thorn-shaped astrocytes can be present in the same brain in subpial, subependymal, perivascular, and white and gray matter locations together with GFAs, which are seen in the gray matter. Primary tauopathies show ARTAG-related morphologies as well, moreover, GFA has been proposed to present a conceptual link between brain ageing and primary tauopathies. Sequential distribution patterns have been recognized for subpial, white and gray matter ARTAG. This either suggests the involvement of astrocytes in the propagation of tau pathology or reflects the consequence of a long-term pathogenic process such as barrier dysfunction, local mechanical impact, or early response to neuronal degeneration. The concept of ARTAG facilitated communication among neuropathologists and researchers, informed biomarker researchers with focus on tau-related indicators and motivated further exploration of the significance of astrocytic lesions in various neurodegenerative conditions.
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