Homeoprotein neuroprotection of embryonic neuronal cells

ABSTRACT

Most homeoprotein transcription factors have a highly conserved internalization domain used in intercellular transfer. Internalization of homeoproteins ENGRAILED1 or ENGRAILED2 promotes the survival of adult dopaminergic cells, whereas that of OTX2 protects adult retinal ganglion cells. Here we characterize the in vitro neuroprotective activity of several homeoproteins in response to H₂O₂. Protection is observed with ENGRAILED1, ENGRAILED2, OTX2, GBX2 and LHX9 on midbrain and striatal embryonic neurons whereas cell-permeable c-MYC shows no protective effects. Therefore, five homeoproteins belonging to 3 different classes (ANTENNAPEDIA, PAIRED and LIM) share the ability to protect embryonic neurons from midbrain and striatum. Because midbrain and striatal neurons do not express the same repertoire of the 4 proteins, a lack of neuronal specificity together with a general protective activity can be proposed. Interestingly, hEN1 and GBX2 provided protection to primary midbrain astrocytes but not to non-neural cells including mouse embryo fibroblasts, macrophages or HeLa cells. For the 4 proteins, protection against cell-death correlated with a reduction in the number of H₂O₂-induced DNA break foci in midbrain and striatal neurons. In conclusion, within the limit of the number of cell types and homeoproteins tested, homeoprotein protection against oxidative stress-induced DNA breaks and death is specific to neurons and astrocytes but shows no homeoprotein or neuronal type specificity.

SIGNIFICANCE STATEMENT Homeoproteins are DNA binding proteins regulating gene expression throughout life. Many of them transfer between cells and are thus internalized by live cells. This has allowed for their use as therapeutic proteins in animal models of Parkinson disease and glaucoma. Part of their therapeutic activity is through a protection against neuronal death. Here we show that internalized homeoproteins from three different classes protect embryonic ventral midbrain and striatal neurons from oxidative stress, both at the level of DNA damage and survival. The interest of this finding is that it lends weight to the possibility that many homeoproteins play a role in neuroprotection through shared mechanisms involving, in particular, DNA protection against stress-induced breaks.