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Mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the glomerular basement membrane.

Kikkawa Y, Virtanen I, Miner JH - J. Cell Biol. (2003)

Bottom Line: In addition, podocytes exhibited their typical arrangement in a single cell layer epithelium adjacent to the GBM, but convolution of glomerular capillaries did not occur.Finally, in vitro studies showed that integrin alpha3beta1 and the Lutheran glycoprotein mediate adhesion of mesangial cells to laminin alpha5.Our results elucidate a mechanism whereby mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the GBM.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Washington University School of Medicine, St Louis, MO 63110, USA.

ABSTRACT
In developing glomeruli, laminin alpha5 replaces laminin alpha1 in the glomerular basement membrane (GBM) at the capillary loop stage, a transition required for glomerulogenesis. To investigate domain-specific functions of laminin alpha5 during glomerulogenesis, we produced transgenic mice that express a chimeric laminin composed of laminin alpha5 domains VI through I fused to the human laminin alpha1 globular (G) domain, designated Mr51. Transgene-derived protein accumulated in many basement membranes, including the developing GBM. When bred onto the Lama5 -/- background, Mr51 supported GBM formation, preventing the breakdown that normally occurs in Lama5 -/- glomeruli. In addition, podocytes exhibited their typical arrangement in a single cell layer epithelium adjacent to the GBM, but convolution of glomerular capillaries did not occur. Instead, capillaries were distended and exhibited a ballooned appearance, a phenotype similar to that observed in the total absence of mesangial cells. However, here the phenotype could be attributed to the lack of mesangial cell adhesion to the GBM, suggesting that the G domain of laminin alpha5 is essential for this adhesion. Analysis of an additional chimeric transgene allowed us to narrow the region of the alpha5 G domain essential for mesangial cell adhesion to alpha5LG3-5. Finally, in vitro studies showed that integrin alpha3beta1 and the Lutheran glycoprotein mediate adhesion of mesangial cells to laminin alpha5. Our results elucidate a mechanism whereby mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the GBM.

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Expression of the chimeric α chains, Mr51 and Mr5G2, in transgenic mice. Micrographs show E17.5 glomeruli from Lama5 −/− (A and B), Lama5 −/−; Mr5 (C and D), Lama5 +/−; Mr51 (E and F), Lama5 −/−; Mr51 (G and H), Lama5 +/−; Mr5G2 (I and J), and Lama5 −/−; Mr5G2 (K and L) embryos. Sections were doubly stained with an antiserum to domains IIIb/IVa of laminin α5 (A, C, E, G, I, and K) and a mouse monoclonal antibody specific for human laminin α1 LG1–2 (B, D, F, H, J, and L). Although the chimeric laminins were assembled into the GBM, Lama5 −/−; Mr51 and Lama5 −/−; Mr5G2 glomeruli exhibited distended capillaries (G, H, and K). Arrowheads indicate the GBM. Bar, 50 μm.
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fig3: Expression of the chimeric α chains, Mr51 and Mr5G2, in transgenic mice. Micrographs show E17.5 glomeruli from Lama5 −/− (A and B), Lama5 −/−; Mr5 (C and D), Lama5 +/−; Mr51 (E and F), Lama5 −/−; Mr51 (G and H), Lama5 +/−; Mr5G2 (I and J), and Lama5 −/−; Mr5G2 (K and L) embryos. Sections were doubly stained with an antiserum to domains IIIb/IVa of laminin α5 (A, C, E, G, I, and K) and a mouse monoclonal antibody specific for human laminin α1 LG1–2 (B, D, F, H, J, and L). Although the chimeric laminins were assembled into the GBM, Lama5 −/−; Mr51 and Lama5 −/−; Mr5G2 glomeruli exhibited distended capillaries (G, H, and K). Arrowheads indicate the GBM. Bar, 50 μm.

Mentions: Expression of the two chimeric laminins was also widespread, as determined by staining with the anti–human α1 LG1–2 and LG4–5 domain antibodies (Kikkawa et al., 2002; Fig. 3 ; unpublished data). The Mr51 and Mr5G2 transgenes were separately mated onto the Lama5 mutant genetic background, but the resulting Lama5 −/−; Mr51 and Lama5 −/−; Mr5G2 mice were not viable. Lama5 −/−; Mr51 embryos exhibited the same defects we initially reported for Lama5 −/− embryos (Miner et al., 1998), but the incidence of exencephaly was reduced from 60% to <10%. On the other hand, although defects in digit septation were still observed, the Mr5G2 transgene improved the growth of Lama5 −/− embryos, which are usually smaller than controls (Miner et al., 1998). This indicates that the chimeric proteins have limited functions, and that the G domain of α1 cannot fully compensate for the missing α5 G domain.


Mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the glomerular basement membrane.

Kikkawa Y, Virtanen I, Miner JH - J. Cell Biol. (2003)

Expression of the chimeric α chains, Mr51 and Mr5G2, in transgenic mice. Micrographs show E17.5 glomeruli from Lama5 −/− (A and B), Lama5 −/−; Mr5 (C and D), Lama5 +/−; Mr51 (E and F), Lama5 −/−; Mr51 (G and H), Lama5 +/−; Mr5G2 (I and J), and Lama5 −/−; Mr5G2 (K and L) embryos. Sections were doubly stained with an antiserum to domains IIIb/IVa of laminin α5 (A, C, E, G, I, and K) and a mouse monoclonal antibody specific for human laminin α1 LG1–2 (B, D, F, H, J, and L). Although the chimeric laminins were assembled into the GBM, Lama5 −/−; Mr51 and Lama5 −/−; Mr5G2 glomeruli exhibited distended capillaries (G, H, and K). Arrowheads indicate the GBM. Bar, 50 μm.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172883&req=5

fig3: Expression of the chimeric α chains, Mr51 and Mr5G2, in transgenic mice. Micrographs show E17.5 glomeruli from Lama5 −/− (A and B), Lama5 −/−; Mr5 (C and D), Lama5 +/−; Mr51 (E and F), Lama5 −/−; Mr51 (G and H), Lama5 +/−; Mr5G2 (I and J), and Lama5 −/−; Mr5G2 (K and L) embryos. Sections were doubly stained with an antiserum to domains IIIb/IVa of laminin α5 (A, C, E, G, I, and K) and a mouse monoclonal antibody specific for human laminin α1 LG1–2 (B, D, F, H, J, and L). Although the chimeric laminins were assembled into the GBM, Lama5 −/−; Mr51 and Lama5 −/−; Mr5G2 glomeruli exhibited distended capillaries (G, H, and K). Arrowheads indicate the GBM. Bar, 50 μm.
Mentions: Expression of the two chimeric laminins was also widespread, as determined by staining with the anti–human α1 LG1–2 and LG4–5 domain antibodies (Kikkawa et al., 2002; Fig. 3 ; unpublished data). The Mr51 and Mr5G2 transgenes were separately mated onto the Lama5 mutant genetic background, but the resulting Lama5 −/−; Mr51 and Lama5 −/−; Mr5G2 mice were not viable. Lama5 −/−; Mr51 embryos exhibited the same defects we initially reported for Lama5 −/− embryos (Miner et al., 1998), but the incidence of exencephaly was reduced from 60% to <10%. On the other hand, although defects in digit septation were still observed, the Mr5G2 transgene improved the growth of Lama5 −/− embryos, which are usually smaller than controls (Miner et al., 1998). This indicates that the chimeric proteins have limited functions, and that the G domain of α1 cannot fully compensate for the missing α5 G domain.

Bottom Line: In addition, podocytes exhibited their typical arrangement in a single cell layer epithelium adjacent to the GBM, but convolution of glomerular capillaries did not occur.Finally, in vitro studies showed that integrin alpha3beta1 and the Lutheran glycoprotein mediate adhesion of mesangial cells to laminin alpha5.Our results elucidate a mechanism whereby mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the GBM.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine, Washington University School of Medicine, St Louis, MO 63110, USA.

ABSTRACT
In developing glomeruli, laminin alpha5 replaces laminin alpha1 in the glomerular basement membrane (GBM) at the capillary loop stage, a transition required for glomerulogenesis. To investigate domain-specific functions of laminin alpha5 during glomerulogenesis, we produced transgenic mice that express a chimeric laminin composed of laminin alpha5 domains VI through I fused to the human laminin alpha1 globular (G) domain, designated Mr51. Transgene-derived protein accumulated in many basement membranes, including the developing GBM. When bred onto the Lama5 -/- background, Mr51 supported GBM formation, preventing the breakdown that normally occurs in Lama5 -/- glomeruli. In addition, podocytes exhibited their typical arrangement in a single cell layer epithelium adjacent to the GBM, but convolution of glomerular capillaries did not occur. Instead, capillaries were distended and exhibited a ballooned appearance, a phenotype similar to that observed in the total absence of mesangial cells. However, here the phenotype could be attributed to the lack of mesangial cell adhesion to the GBM, suggesting that the G domain of laminin alpha5 is essential for this adhesion. Analysis of an additional chimeric transgene allowed us to narrow the region of the alpha5 G domain essential for mesangial cell adhesion to alpha5LG3-5. Finally, in vitro studies showed that integrin alpha3beta1 and the Lutheran glycoprotein mediate adhesion of mesangial cells to laminin alpha5. Our results elucidate a mechanism whereby mesangial cells organize the glomerular capillaries by adhering to the G domain of laminin alpha5 in the GBM.

Show MeSH
Related in: MedlinePlus