Gene expression of vitamin D hydroxylase and megalin in the remnant kidney of nephrectomized rats.
BACKGROUND
Regulation of vitamin D hydroxylase genes in the early stage of chronic renal failure is not fully understood. Using nephrectomized rats, we examined changes in mRNA levels of CYP27B1 (25-hydroxyvitamin D3-1 alpha-hydroxylase), CYP24 (25-hydroxyvitamin D3-24-hydroxylase), and vitamin D receptor in relation to megalin, recently found to participate in renal vitamin D metabolism.


METHODS
A rat model of moderate renal failure was induced by 3/4 nephrectomy. Plasma parameters, including vitamin D metabolite concentrations, were measured at weeks 2, 4 and 8, and poly(A)+ RNA extracted from the remnant kidneys was subjected to Northern blot hybridization.


RESULTS
Plasma creatinine concentration at week 2 was 0.40 +/- 0.02 mg/dL in the sham-operated and 0.93 +/- 0.15 mg/dL in the nephrectomized rats, and both values remained constant up to week 8. Plasma concentrations of 25(OH)D3, 1 alpha,25(OH)2D3, and 24,25(OH)2D3 were unchanged between nephrectomized and sham-operated rats at week 8. Intact parathyroid hormone (PTH) increased at week 8 in nephrectomized rats. CYP27B1 mRNA in nephrectomized rats did not vary at week 2, but increased approximately two- and four-fold at weeks 4 and 8, respectively, compared to the sham-operated rats. CYP24 and megalin mRNAs, on the other hand, began to decline as early as at week 2 in nephrectomized rats and kept decreasing throughout the experiment. The expression of vitamin D receptor was modestly but significantly decreased only at week 8.


CONCLUSIONS
Coordinated and reciprocal alterations of the increase in CYP27B1 mRNA and the decrease in CYP24 mRNA may play a pivotal role in maintaining the plasma level of 1 alpha,25(OH)2D3 in the face of reduced nephron mass and/or megalin expression.
Takemoto
Fumi
F
Kidney Center, Toranomon Hospital, Tokyo, Japan. ftakemoto-ind@umin.ac.jp
Shinki
Toshimasa
T
Yokoyama
Keitaro
K
Inokami
Taketoshi
T
Hara
Shigeko
S
Yamada
Akira
A
Kurokawa
Kiyoshi
K
Uchida
Shunya
S
D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000235:genetics*; D000818:Animals; D015152:Blotting, Northern; D002118:Calcium / Q000097:blood; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D004195:Disease Models, Animal; D015971:Gene Expression Regulation, Enzymologic; D007668:Kidney / Q000201:enzymology*; D007676:Kidney Failure, Chronic / Q000503:physiopathology*; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000235:genetics*; D008297:Male; D009392:Nephrectomy; D010281:Parathyroid Hormone / Q000097:blood; D010758:Phosphorus / Q000097:blood; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D018167:Receptors, Calcitriol / Q000235:genetics; D013250:Steroid Hydroxylases / Q000235:genetics*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D065668:Vitamin D3 24-Hydroxylase
C116441:2-methyl-1,25-dihydroxyvitamin D3; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D010281:Parathyroid Hormone; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D014807:Vitamin D; D010758:Phosphorus; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002118:Calcium