Erythropoietin receptor expression is concordant with erythropoietin but not with common β chain expression in the rat brain throughout the life span

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Brain effects of erythropoietin (Epo) are proposed to involve a heteromeric receptor comprising the classical Epo receptor (Epo-R) and the common β chain (βc). However, data documenting the pattern of βc gene expression in the healthy brain, in comparison with that of the Epo-R gene, are still lacking. The present study is the first to investigate at the same time βc, Epo-R, and Epo gene expression within different rat brain areas throughout the life span, from neonatal to elderly stages, using quantitative RT-PCR for transcripts. Corresponding proteins were localized by using immunohistochemistry. We demonstrate that the βc transcript level does not correlate with that of Epo-R or Epo, whereas the Epo-R transcript level strongly correlates with that of Epo throughout the life span in all brain structures analyzed. Both Epo and Epo-R were detected primarily in neurons. In the hippocampus, the greatest Epo-R mRNA levels were measured during the early postnatal period and in middle-aged rats, associated with an intense neuronal immunolabeling. Conversely, βc protein was barely detectable in the brain at all ages, even in neurons expressing high levels of Epo-R. Finally, βc transcript could not be detected in PC12 cells, even after nerve growth factor-induced neuritogenesis, which is a condition that dramatically enhances Epo-R transcript level. Altogether, our data suggest that most neurons are likely to express high levels of Epo-R but low, if not null, levels of βc. Given that Epo protects extended populations of neurons after injury, a yet-to-be-identified receptor heterocomplex including Epo-R may exist in the large population of brain neurons that does not express βc. J. Comp. Neurol. 514:403–414, 2009. © 2009 Wiley-Liss, Inc.

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