Up-regulation of Hrk, a regulator of cell death, in retinal ganglion cells of axotomized rat retina

Hrk, a regulator of cell death, belongs to the family of pro-apoptotic BH3-only proteins and is known to induce apoptosis in nerve tissue. We examined Hrk gene expression to clarify the role of BH3-only proteins in apoptosis of retinal ganglion cells (RGCs) after optic nerve transection in the adult rat. Reverse transcription-polymerase chain reaction showed that Hrk was up-regulated in retina from 12 h after axotomy, and continued to be elevated for 1 week. In situ hybridization histochemistry revealed that Hrk was expressed in a sub-population of axotomized RGCs. These results suggest that Hrk is involved in the induction of apoptosis in RGCs after optic nerve transection.