Induction of Ikaros Transcription Factors during Neuronal Hypoxia
T-R Kiehl, N Chaudary, RP Hill, S Ezzat, SL Asa. University Health Network, Toronto, ON, Canada; University of Toronto, Toronto, ON, Canada; Ontario Cancer Institute/Princess Margaret Hospital, Toronto, ON, Canada; Mount Sinai Hospital, Toronto, ON, Canada
Background: During stroke, injury or global cerebral hypoperfusion, the amount of oxygen available to neurons of the brain is markedly reduced. Adaptation mechanisms to neuronal hypoxia may include the suppression of energy metabolism, global alterations in gene expression and ultimately the activation or repression of stress-responsive genes. Prolonged periods of hypoxia eventually lead to cell cycle arrest, apoptosis, and necrosis. Our preliminary observations have indicated that Ikaros (Ik), a family of zinc-finger transcription factors that is essential in the development and function of leukocytes and the pituitary, is expressed in neuronal cells under hypoxic-ischemic conditions.
Design: A neuronal cell culture model was established. P19 embryonal carcinoma cells were differentiated into mature neuronal cells by treatment with retinoic acid for 96h. Cells were then placed into a nearly anoxic environment of 0.2 % oxygen for 1, 2, 4, 6, 12 and 24h. They were assessed for Ik expression by immunohistochemistry, qRT-PCR and western blotting. For assessment in vivo, adult wild-type mice were subjected to low oxygen concentrations (5%) for up to 6 hours.
Results: Ik expression levels were markedly elevated in P19 cells after more than 12h in the ultra-low oxygen environment. Ik was also detected in the brains of mice that were subjected to low oxygen concentrations for over 4 hours. Cortical neurons, hippocampal neurons and cerebellar Purkinje cells all displayed strong nuclear and mild cytoplasmic Ik-immunoreactivity when compared to controls at normoxia. Highly similar observations were made in human brain tissue from neurosurgical procedures that showed morphologic evidence of hypoxia-ischemia.
Conclusions: Our finding that hypoxic states strongly induce Ik in several neuronal systems adds novelty to the still limited knowledge of the epigenetic events that occur in response to hypoxia. A better understanding of these chromatin changes could improve the treatment of stroke and CNS trauma. Future studies will clarify whether this response is limited to neuronal cells or whether it may represent a general cellular adaptation mechanism to a low oxygen environment.
Tuesday, March 10, 2009 9:30 AM
Poster Session III # 207, Tuesday Morning