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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 laminin β chains in glomeruli. Sections of E17.5 control (A and E), Lama5 −/− (B and F), Lama5 −/−; Mr51 (C and G) and Lama5 −/−; Mr5G2 (D and H) kidneys were stained with specific antibodies to laminin β1 (A–D) and β2 (E–H). Arrowheads indicate GBM. Laminin β2 was almost undetectable in Lama5 −/−; Mr51 GBM (G), but Mr5G2 increased β2 accumulation (H), though it was somewhat lower than that in the control (E). Bar, 50 μm.
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fig7: Expression of laminin β chains in glomeruli. Sections of E17.5 control (A and E), Lama5 −/− (B and F), Lama5 −/−; Mr51 (C and G) and Lama5 −/−; Mr5G2 (D and H) kidneys were stained with specific antibodies to laminin β1 (A–D) and β2 (E–H). Arrowheads indicate GBM. Laminin β2 was almost undetectable in Lama5 −/−; Mr51 GBM (G), but Mr5G2 increased β2 accumulation (H), though it was somewhat lower than that in the control (E). Bar, 50 μm.

Mentions: The distended capillaries observed upon substitution of Mr51 transgene–derived protein for endogenous α5 could result from secondary defects in basement membrane composition. For example, Kostka et al. (2001) recently reported that 10–40% of glomeruli in fibulin-1–deficient mice exhibit a similar capillary malformation. Thus, the distended capillaries in Lama5 −/−; Mr51 glomeruli could be secondary to the failure of fibulin-1 to incorporate into the GBM. To investigate whether deposition of fibulin-1 or other GBM components was altered in Lama5 −/−; Mr51 glomeruli, we stained E17.5 kidney sections from control and Lama5 −/−; Mr51 fetuses with a panel of antibodies to GBM proteins (Fig. 6 ; unpublished data). Fibulin-1 was detected in both the GBM and the mesangial matrix on the Lama5 −/−; Mr51 background, suggesting that the distended capillary loops were not secondary to the absence of fibulin-1. We also examined the expression of fibulin-2, agrin, nidogen-1/entactin-1, nephronectin, perlecan, and the collagen α3(IV) and α4(IV) chains, and in no case was there a significant difference between control and Lama5 −/−; Mr51 glomeruli (Fig. 6). Again, this suggested that the defects observed in Lama5 −/−; Mr51 glomeruli are not due to the disappearance of other GBM or mesangial matrix components. However, we did find greatly reduced levels of the laminin β2 chain (Fig. 7, E and G) , whereas laminin β1 was present in both control and Lama5 −/−; Mr51 maturing glomeruli (Fig. 7, A and C).


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 laminin β chains in glomeruli. Sections of E17.5 control (A and E), Lama5 −/− (B and F), Lama5 −/−; Mr51 (C and G) and Lama5 −/−; Mr5G2 (D and H) kidneys were stained with specific antibodies to laminin β1 (A–D) and β2 (E–H). Arrowheads indicate GBM. Laminin β2 was almost undetectable in Lama5 −/−; Mr51 GBM (G), but Mr5G2 increased β2 accumulation (H), though it was somewhat lower than that in the control (E). Bar, 50 μm.
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Related In: Results  -  Collection

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fig7: Expression of laminin β chains in glomeruli. Sections of E17.5 control (A and E), Lama5 −/− (B and F), Lama5 −/−; Mr51 (C and G) and Lama5 −/−; Mr5G2 (D and H) kidneys were stained with specific antibodies to laminin β1 (A–D) and β2 (E–H). Arrowheads indicate GBM. Laminin β2 was almost undetectable in Lama5 −/−; Mr51 GBM (G), but Mr5G2 increased β2 accumulation (H), though it was somewhat lower than that in the control (E). Bar, 50 μm.
Mentions: The distended capillaries observed upon substitution of Mr51 transgene–derived protein for endogenous α5 could result from secondary defects in basement membrane composition. For example, Kostka et al. (2001) recently reported that 10–40% of glomeruli in fibulin-1–deficient mice exhibit a similar capillary malformation. Thus, the distended capillaries in Lama5 −/−; Mr51 glomeruli could be secondary to the failure of fibulin-1 to incorporate into the GBM. To investigate whether deposition of fibulin-1 or other GBM components was altered in Lama5 −/−; Mr51 glomeruli, we stained E17.5 kidney sections from control and Lama5 −/−; Mr51 fetuses with a panel of antibodies to GBM proteins (Fig. 6 ; unpublished data). Fibulin-1 was detected in both the GBM and the mesangial matrix on the Lama5 −/−; Mr51 background, suggesting that the distended capillary loops were not secondary to the absence of fibulin-1. We also examined the expression of fibulin-2, agrin, nidogen-1/entactin-1, nephronectin, perlecan, and the collagen α3(IV) and α4(IV) chains, and in no case was there a significant difference between control and Lama5 −/−; Mr51 glomeruli (Fig. 6). Again, this suggested that the defects observed in Lama5 −/−; Mr51 glomeruli are not due to the disappearance of other GBM or mesangial matrix components. However, we did find greatly reduced levels of the laminin β2 chain (Fig. 7, E and G) , whereas laminin β1 was present in both control and Lama5 −/−; Mr51 maturing glomeruli (Fig. 7, A and C).

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