Figure 3. SIRT2 Is Undetectable in Neurons but Enriched in OLs and Released within Exosomes.

(A) Selective expression of SIRT2 in OLs but not in neurons. Mouse cortical cells at DIV7-8 were co-immunostained for SIRT2 (green), myelin basic protein (MBP, magenta), and neuron-specific βIII-tubulin (red).

(B, C) Immunoblots (B) and bar graph (C) showing development-associated expression of SIRT2 and MBP in mouse brain cortex. Brain cortical tissues were isolated from mice at indicated postnatal days (D) or months (M) of age. 10-μg homogenates were loaded and immunoblotted with the indicated antibodies (n = 2).

(D, E) Immunoblots (D) and bar graph (E) showing development-associated expression of SIRT2 and MBP in mouse cervical spinal cords. 10-μg homogenates were loaded and immunoblotted with the indicated antibodies (n = 2).

(F, G) Immunogold electron micrographs showing SIRT2-labeled MVBs (arrows) in both in vitro and in vivo OLs. Cultured primary OLs at DIV5 (F) or mouse T4 spinal cord dorsal white matter

(G) were labeled by anti-SIRT2 immunogold particles. Note a SIRT2-containing MVB in the adjacent myelin sheath (G).

(H) SIRT2-filled exosomes are released from WT but not sirt2 KO OLs. Purified OL-EXOs were co-immunostained with antibodies against SIRT2 (red) and exosome marker HSP70 (green). Right panels show an enlarged exosome.

Scale bars, 25 μm (A), 200 nm (F, G), 5 μm (H) and 500 nm (H, enlarged boxes).

See also Figure S5.