Ethanol induces apoptotic death of beta-endorphin neurons in the rat hypothalamus by a TGF-beta 1-dependent mechanism.
BACKGROUND
We have previously shown that developing beta-endorphin neurons, in the arcuate nucleus of the hypothalamus become increasingly apoptotic when exposed to ethanol. As in the previous study we have observed an involvement in transforming growth factor beta 1 (TGF-beta1) in mediation of the apoptotic process, the present study was conducted to determine the ethanol-induced changes in this apoptotic regulatory peptide signaling in the arcuate nucleus of the hypothalamus of neonatal rats.


METHODS
Pups were exposed to 11.34% ethanol in a milk-based diet or control diet on postnatal day (PND) 3 to PND7. Two hours after the last daily feeding, brains were collected and frozen in liquid nitrogen for analysis of various apoptosis regulatory proteins in the arcuate tissue by Western blots. Some animals were fixed in 4% paraformaldehyde and analyzed immunohistochemically.


RESULTS
Ethanol exposure increased apoptotic death of beta-endorphin neurons in the arcuate nucleus of the hypothalamus. The cell death was associated with an increase in the tissue levels of TGF-beta1 in the mediobasal hypothalamus. This was correlated with a reduction in the arcuate level of retinoblastoma protein (Rb) phosphorylation. The reduced level of Rb phosphorylation was associated with an increased protein level of the cyclin dependent kinase inhibitor p27/kip but with a decreased protein level of cyclin dependent kinase 4 and cyclin D3. In addition, the apoptotic cell death was positively correlated with the level of Bclxs but negatively correlated with the level of the Bcl2.


CONCLUSIONS
These results suggest that ethanol exposure increases TGF-beta1 signaling involving Bcl2 and Rb repression that may lead to apoptotic death of cells including beta-endorphin neurons in the arcuate nucleus of the hypothalamus.
Kuhn
Peter
P
Endocrine Program, Center of Alcohol Studies and Department of Animal Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901, USA.
Sarkar
Dipak K
DK
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D000431:Ethanol / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation; D011247:Pregnancy; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016160:Retinoblastoma Protein / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology; D053773:Transforming Growth Factor beta1 / Q000502:physiology*; D001615:beta-Endorphin / Q000096:biosynthesis* / Q000235:genetics
D019253:Proto-Oncogene Proteins c-bcl-2; D016160:Retinoblastoma Protein; D053773:Transforming Growth Factor beta1; D000431:Ethanol; D001615:beta-Endorphin