Histological assessment of the BM microenvironment in MA mice. (A) Representative 5-color immunostaining of a longitudinal tissue-wide volumetric section from a MA mouse femur (220 μm) stained for Gp1Bβ-680 (MK), Sca1-488 (arterioles), CD105-555 (sinusoids), Opn-800 (extracellular matrix), BODIPY(adipocytes), and DAPI. (B) Representative images of megakaryocytes (Gp1Bβ⁺) in young (2 months) and MA (14 months) mouse femurs (left) and quantitation of occupied volume (right). (C) Representative images of arterioles (Sca1⁺) in young (2 months) and MA (14 months) mouse femurs (left) and quantitation of occupied volume (right). (D) Representative images of sinusoids (CD105⁺) in young (2 months) and MA (14 months) mouse femurs (left) and quantitation of occupied volume (right). (E) Representative images of adipocytes (BODIPY⁺) in young (2 months) and MA (14 months) mouse femurs (left) and quantitation of occupied volume (right). (B-E) Dots represent individual mice (n = 4). MA, middle-aged; MK, megakaryocytes.