Enhanced podocalyxin expression alters the structure of podocyte basal surface.
Glomerular basement membrane (GBM) and podocalyxin are essential for podocyte morphology. We provide evidence of functional interconnections between basement membrane components (collagen IV and laminin), the expression of podocalyxin and the morphology of human glomerular epithelial cells (podocytes). We demonstrated that GBM and laminin, but not collagen IV, up-regulated the expression of podocalyxin. Scanning electron microscopy revealed that laminin induced a modified morphology of podocytes with process formation, which was more extensive in the presence of GBM. Under high magnification, podocytes appeared ruffled. Using transmission electron microscopy we observed that raised areas occurred in the basal cell surface. Furthermore, the presence of anti-podocalyxin antibody increased the extent of adhesion and spreading of podocytes to both collagen IV and laminin, thus podocalyxin apparently inhibits cell-matrix interactions. We also performed adhesion and spreading assays on podocytes grown under increased glucose concentration (25 mM). Under these conditions, the expression of podocalyxin was almost totally suppressed. The cells adhered and spread to basement membrane components but there was no increase in the extent of adhesion and spreading in the presence of anti-podocalyxin antibody, or ruffling of the cell edges. Additionally, in podocytes expressing podocalyxin, the presence of anti-podocalyxin antibody partially reversed the inhibition of adhesion to collagen IV provoked by anti-beta1 integrin antibody, thus podocalyxin should compete with beta1-related cell adhesion. We suggest that the observed podocalyxin-mediated inhibition of binding to the matrix could be in part responsible for the specialized conformation of the basal surface of podocytes.
Economou
Constantinos G
CG
Institute of Biology, National Center for Scientific Research, Demokritos, Agia Paraskevi, 15310 Athens, Greece.
Kitsiou
Paraskevi V
PV
Tzinia
Athina K
AK
Panagopoulou
Evridiki
E
Marinos
Evangelos
E
Kershaw
David B
DB
Kerjaschki
Dontscho
D
Tsilibary
Effie C
EC
D000599:Amino Acids, Diamino / Q000378:metabolism; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D001485:Basement Membrane / Q000502:physiology*; D015152:Blotting, Northern; D015153:Blotting, Western; D002448:Cell Adhesion; D049109:Cell Proliferation; D002469:Cell Separation; D002478:Cells, Cultured; D024141:Collagen Type IV / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D003720:Densitometry; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D005434:Flow Cytometry; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D019012:Integrin beta1 / Q000378:metabolism; D007797:Laminin / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D010750:Phosphoproteins / Q000378:metabolism; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012795:Sialoglycoproteins / Q000096:biosynthesis* / Q000378:metabolism; D015854:Up-Regulation; D062826:Zonula Occludens-1 Protein
D000599:Amino Acids, Diamino; D000911:Antibodies, Monoclonal; D024141:Collagen Type IV; D018076:DNA, Complementary; D019012:Integrin beta1; D007797:Laminin; D008565:Membrane Proteins; D010750:Phosphoproteins; D011506:Proteins; D012333:RNA, Messenger; D012795:Sialoglycoproteins; C569042:TJP1 protein, human; C569044:Tjp1 protein, rat; D062826:Zonula Occludens-1 Protein; C113267:nephrin; C001643:podocalyxin; C045397:laminine; D012313:RNA; D005947:Glucose