Selective impairment of gene expression and assembly of nephrin in human diabetic nephropathy.
BACKGROUND
Recent disclosure of podocyte proteins has unraveled previously rather mysterious mechanisms that govern glomerular perm-selectivity in health and disease. Here we addressed the role of nephrin, CD2-associated protein (CD2AP), and podocin together with the integrity of the slit diaphragm in the pathogenesis of proteinuria of patients with diabetes and nephropathy.


METHODS
Nephrin mRNA and protein expression were evaluated in parallel in adult diabetic patients by in situ hybridization and immunohistochemistry. For comparison, nondiabetic patients with minimal change nephrosis and normal control patients were evaluated. CD2AP and podocin expression by immunohistochemistry was also assessed. The filtration slit was analyzed by morphometry and transmission electron microscopy.


RESULTS
Extracellular nephrin mRNA and protein were markedly reduced in diabetic patients. No changes were found in patients with minimal change versus controls. CD2AP and podocin were comparable in all subjects. Ultrastructural analysis showed in diabetic patients a remarkable reduction in the percentage of electron dense slit diaphragms, despite a frequency of the filtration slits comparable to control patients.


CONCLUSIONS
Down-regulation of nephrin and loss of the electron dense structure of slit diaphragm indicate a novel mechanism accounting for proteinuria in diabetic nephropathy. To the extent that glomerular protein trafficking contributes to renal disease progression, our findings may have clinical relevance. Reduction of nephrin in the context of normal expression of CD2AP and podocin can be taken reasonably as a specific marker of renal disease in diabetes. Therapies targeted at correcting podocyte nephrin might be of value for diabetic medicine.
Benigni
Ariela
A
Mario Negri Institute for Pharmacological Research, Negri Bergamo Laboratories, Bergamo, Italy.
Gagliardini
Elena
E
Tomasoni
Susanna
S
Abbate
Mauro
M
Ruggenenti
Piero
P
Kalluri
Raghu
R
Remuzzi
Giuseppe
G
D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D016022:Case-Control Studies; D003598:Cytoskeletal Proteins / Q000378:metabolism; D003928:Diabetic Nephropathies / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D005260:Female; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D047908:Intracellular Signaling Peptides and Proteins; D007668:Kidney / Q000378:metabolism / Q000473:pathology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D008875:Middle Aged; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C114545:CD2-associated protein; D003598:Cytoskeletal Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; C407223:NPHS2 protein; D011506:Proteins; D012333:RNA, Messenger; C113267:nephrin