Expression of filtrin in human glomerular diseases.
BACKGROUND
Filtrin (NEPH3/KIRREL2) is a recently characterized member of the nephrin-like proteins of the immunoglobulin superfamily, and it has been suggested to participate in the maintenance of the glomerular filtration barrier in the kidney. In this study, the gene and protein expression of filtrin were examined in patients with acquired proteinuric diseases.


METHODS
Filtrin mRNA levels in renal biopsies were measured with quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in two sets of patients with proteinuria. The mRNA levels were normalized to the housekeeping gene GAPDH and also related to the podocyte-specific genes nephrin and podocin. Immunofluorescence microscopy was employed to explore changes in the glomerular distribution of filtrin.


RESULTS
Reduced glomerular expression of filtrin mRNA was observed in all studied diagnostic groups. In focal segmental glomerulosclerosis, the filtrin mRNA level was only one-tenth of the control samples (P approximately 5.0x10(-6)), and this finding was confirmed in a second set of samples. The ratios of filtrin to nephrin and podocin demonstrated a marked decrease in the expression of filtrin relative to the podocyte marker genes. However, no correlation between the expression of filtrin and the levels of serum creatinine and proteinuria was observed. Immunostaining showed changes in the expression pattern of filtrin in renal biopsies. Immunoelectron microscopic studies localized filtrin at the slit diaphragm of the podocyte foot processes.


CONCLUSIONS
Down-regulation of the filtrin gene and protein expression in the renal biopsies together with the localization to the inter-podocyte filtration slit imply a potential role for this molecule in the pathogenesis of proteinuric diseases.
Ihalmo
Pekka
P
Department of Bacteriology and Immunology, Haartman Institute, Biomedicum Helsinki, University of Helsinki, Finland, and Renal Immunopathology Laboratory, Fondazione D'Amico per la Ricerca sulle Malattie Renali, San Carlo Borromeo Hospital, Milan, Italy.
Schmid
Holger
H
Rastaldi
Maria Pia
MP
Mattinzoli
Deborah
D
Langham
Robyn G
RG
Luimula
Pauliina
P
Kilpikari
Riika
R
Lassila
Markus
M
Gilbert
Richard E
RE
Kerjaschki
Dontscho
D
Kretzler
Matthias
M
Holthöfer
Harry
H
D001706:Biopsy; D005455:Fluorescent Antibody Technique; D006801:Humans; D007136:Immunoglobulins / Q000235:genetics / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism / Q000473:pathology; D007674:Kidney Diseases / Q000150:complications / Q000378:metabolism* / Q000473:pathology; D007678:Kidney Glomerulus; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D011507:Proteinuria / Q000209:etiology / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution
D007136:Immunoglobulins; C482646:KIRREL2 protein, human; D008565:Membrane Proteins; D012333:RNA, Messenger; C113267:nephrin