Effect of aging on EGF-induced proliferative response in primary cultured periportal and perivenous hepatocytes.
OBJECTIVE
Aging relates to declined proliferative capacity of the liver, but the molecular mechanism is not well understood. We examined whether functional changes of epidermal growth factor (EGF) receptor (EGFR) are involved in age-related decline in EGF-induced DNA synthesis using hepatocytes isolated in periportal and perivenous regions of the liver, which differ in the proliferative capacity.


METHODS
Periportal hepatocytes (PPH) and perivenous hepatocytes (PVH) in 7-, 30-, and 90-week-old rats were isolated using the digitonin/collagenase perfusion technique. DNA synthesis was assessed by [methyl-(3)H]thymidine incorporation. EGFR binding affinity to EGF was analyzed by Scatchard analysis using [(125)I]EGF. EGFR dimerization and phosphorylation were determined by Western blot analysis.


RESULTS
EGF-induced DNA synthesis was greater in PPH than in PVH from rats of 7 weeks, but the zonal difference disappeared with aging. [(125)I]EGF binding studies indicated that high-affinity EGFR in both subpopulations also disappeared with aging. Furthermore, EGF-induced dimerization in both subpopulations was down-regulated with aging, and the pattern of EGFR phosphorylation was parallel to that of dimerization.


CONCLUSIONS
These data suggest that age-related decline in EGF-induced DNA synthesis of PPH and PVH is caused by down-regulation of EGFR dimerization through the decrease of high-affinity EGFR.
Ohtake
Yosuke
Y
Department of Radiopharmacy, Tohoku Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan. y-ohtake@tohoku-pharm.ac.jp
Maruko
Akiko
A
Ohishi
Nao
N
Fukumoto
Manabu
M
Ohkubo
Yasuhito
Y
D000375:Aging / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D049109:Cell Proliferation / Q000187:drug effects; D002469:Cell Separation; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D019281:Dimerization; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D066246:ErbB Receptors / Q000737:chemistry / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects*; D008297:Male; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar
D004815:Epidermal Growth Factor; D004247:DNA; D066246:ErbB Receptors