Vitamin D3 up-regulated protein-1 regulates collagen expression in mesangial cells.
BACKGROUND
Hyperglycemia is a known risk factor in the pathogenesis of nephropathy, and collagen accumulation due to an increase reactive oxygen species (ROS) has been suspected to be one of the reasons for high glucose-mediated diseases. However, molecular mechanisms that connect glucose stimulation, oxidative stress, and collagen induction are unknown.


METHODS
We examined global changes in gene expression patterns following high glucose stimulation by using DNA microarray technology in cultured human mesangial cells. The expression of vitamin D3 up-regulated protein-1 (VDUP-1), our candidate for the molecular mediator, was evaluated in the human mesangial cells, mouse mesangial cell line, and kidneys of diabetic mice by quantitative reverse transcription-polymerase chain reaction (RT-PCR). Truncated VDUP-1 proteins were used to test the effects of VDUP-1 on the biosynthesis of collagen in mesangial cells.


RESULTS
Expression of VDUP-1, which was reported as an inhibitor of thioredoxin, was induced rapidly and constantly after exposure to high concentrations of glucose upon analysis with DNA microarray. Overexpression of VDUP-1 gene in cultured mesangial cells resulted in type IV collagen alpha1 chain (COL4A1) mRNA induction and accumulation of type IV collagen protein. However, induction of COL4A1 expression was abolished with a deletion mutant of VDUP-1, which lost thioredoxin-interacting domain. Also, streptozotocin-induced diabetic mice were shown to overexpress VDUP-1 as well as COL4A1.


CONCLUSIONS
VDUP-1 mediates collagen accumulation in mesangial cells and could be the molecular mediator/marker for fibrosis in diabetic nephropathy caused by chronic hyperglycemia such as diabetes.
Kobayashi
Tsutomu
T
Banyu Tsukuba Research Institute and Merck Research Laboratories, Tsukuba, Ibaraki, Japan.
Uehara
Sayuri
S
Ikeda
Takanori
T
Itadani
Hiraku
H
Kotani
Hidehito
H
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D024141:Collagen Type IV / Q000235:genetics*; D003921:Diabetes Mellitus, Experimental / Q000473:pathology / Q000503:physiopathology; D003928:Diabetic Nephropathies / Q000473:pathology / Q000503:physiopathology*; D005355:Fibrosis; D017353:Gene Deletion; D015870:Gene Expression; D005920:Glomerular Mesangium / Q000473:pathology / Q000502:physiology*; D006801:Humans; D006943:Hyperglycemia / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D013879:Thioredoxins
D002352:Carrier Proteins; D024141:Collagen Type IV; C486715:TXNIP protein, human; D013879:Thioredoxins