title: Estrogen deficiency-induced Ca balance impairment is associated with decrease in expression of epithelial Ca transport proteins in aged female rats.
abstract: OBJECTIVE
  The study is designed to determine whether estrogen and vitamin D endocrine systems interact to regulate calcium (Ca) balance as well as changes in mRNA expression of epithelial Ca transport proteins involved in intestinal and renal Ca transport in aging animals in response to ovariectomy and low dietary Ca intake.
  
  
  METHODS
  Eleven-month-old female sham or ovariectomized (OVX) rats were divided into four groups and fed with either a low-Ca (LCD; 0.1% Ca, 0.65% P) or a high-Ca (HCD; 1.2% Ca, 0.65% P) diet for 12weeks. Ca balance and mRNA expression of Ca transport proteins in the intestine and kidney from rats were systematically studied.
  
  
  RESULTS
  OVX rats fed with LCD resulted in a negative Ca balance. LCD suppressed serum Ca in OVX but not sham rats, resulting in an induction of serum PTH and 1,25(OH)2D3 levels. The surge in serum 1,25(OH)2D3 levels in LCD-fed OVX rats was associated with an increase in mRNA expression of intestinal transient receptor potential cation channel (TRPV6) and calbindin D9k (CaBP9k) as well as renal vitamin D receptor (VDR), but such an induction was unable to restore Ca balance in vivo. In contrast, the negative Ca balance was associated with suppression of intestinal plasma membrane Ca pump (PMCA1b) and renal transient receptor potential cation channel (TRPV5), calbindin D28k (CaBP28k) and PMCA1b mRNA expression in aged OVX rats.
  
  
  CONCLUSIONS
  Negative Ca balance in aged female OVX rats is associated with estrogen-dependent and vitamin D-independent downregulation of epithelial Ca transport protein mRNA expression.
authors.affiliation: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China.
authors.forename: Xiao-Li
authors.initials: XL
authors.lastname: Dong
authors.affiliation: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China; Center for Systems Biomedical Sciences, University of Shanghai for Science and Technology, Shanghai 200093, People's Republic of China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, People's Republic of China; State Key Laboratory of Chinese Medicine and Molecular Pharmacology (Incubation), Shenzhen 518057, People's Republic of China. Electronic address: bcmswong@polyu.edu.hk.
authors.forename: Man-Sau
authors.initials: MS
authors.lastname: Wong
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D064092:Calbindin 1 / Q000096:biosynthesis*; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000096:biosynthesis / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000096:biosynthesis; D002352:Carrier Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D015536:Down-Regulation / Q000502:physiology; D004967:Estrogens / Q000172:deficiency*; D005260:Female; D005786:Gene Expression Regulation; D007413:Intestinal Mucosa / Q000378:metabolism; D010052:Ovariectomy / Q000379:methods; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000096:biosynthesis*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D050916:TRPV Cation Channels / Q000096:biosynthesis*
chemical_list: D064092:Calbindin 1; D015220:Calcium Channels; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D004967:Estrogens; D050916:TRPV Cation Channels; C492241:TRPV5 protein, rat; D053499:Plasma Membrane Calcium-Transporting ATPases; C506955:Atp2b1 protein, rat; D002118:Calcium
keywords: Ca balance; Epithelial Ca transport proteins; Estrogen deficiency; High Ca diet; Low Ca diet