CHI3L1 and Alzheimer disease: Inspection of possible layer-specific effects revealed that the increase in GFAP and YKL-40 levels in AD vs. CTRL astrocytes was evident throughout all cortical layers analyzed (II through VI), whereas VIM and TSPO were clearly increased only in AD astrocytes from layers V and VI, GS was clearly reduced only in AD astrocytes from layers II to IV, and EAAT1 and EAAT2 exhibited a mixed trend depending on the cortical layer (see Fig. S4a: Additional file 2).