title: Effect of aging on EGF-induced proliferative response in primary cultured periportal and perivenous hepatocytes.
abstract: 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.
authors.affiliation: Department of Radiopharmacy, Tohoku Pharmaceutical University, 4-4-1, Komatsushima, Aoba-ku, Sendai, Miyagi 981-8558, Japan. y-ohtake@tohoku-pharm.ac.jp
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Ohtake
authors.forename: Akiko
authors.initials: A
authors.lastname: Maruko
authors.forename: Nao
authors.initials: N
authors.lastname: Ohishi
authors.forename: Manabu
authors.initials: M
authors.lastname: Fukumoto
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Ohkubo
mesh_terms: 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
chemical_list: D004815:Epidermal Growth Factor; D004247:DNA; D066246:ErbB Receptors