All-trans Retinoic Acid Increased Transglutaminase 2 Expressions in BV-2 Cells and Cultured Astrocytes

Activation of microglia and astrocytes has been observed in Alzheimer's disease (AD). Transglutaminase 2 (TG2) is reported to be activated in AD and involved in cell proliferation, differentiation, and inflammation. Moreover, amyloid β (Aβ) aggregation is detected as a characteristic pathology in the AD brain, and is known to be a substrate of TG2. All-trans retinoic acid (ATRA) can modify cell proliferation and differentiation, and is reported to have therapeutic effects on AD pathology.

We aimed to assess the effects of ATRA in microglia and astrocytes on TG2 expression and glial functions.

After treatment with ATRA, TG2 expression and TG activity were assayed in both murine microglia BV-2 cells and cultured rat brain astrocytes. Endocytosis activity in BV-2 cells and Aβ aggregation by astrocytes conditioned medium were also assessed.

In both BV-2 cells and cultured astrocytes, ATRA increased TG2 expression and TG activity. The increase was blocked by AGN194310, an RA receptor antagonist. ATRA enhanced the endocytosis activity in BV-2 cells, and the addition of AGN194310 reversed it. The addition of cystamine, a competitive TG inhibitor, also reduced ATRA-enhanced endocytosis activity. On the other hand, Aβ aggregation was potentiated by ATRA-treated astrocytes conditioned medium compared to control astrocytes conditioned medium.

These results suggest that ATRA increased TG2 expression and TG activity via RA receptor in microglia and astrocytes. ATRA-enhanced TGs might be involved in phagocytosis and Aβ aggregation. Adequate control of TGs expression and function in microglia and astrocytes can be an important factor in AD pathology.