Regulation of glomerular basement membrane collagen expression by LMX1B contributes to renal disease in nail patella syndrome

Abstract

Basement membrane (BM) morphogenesis is critical for normal kidney function. Heterotrimeric type IV collagen, composed of different combinations of six alpha-chains (1-6), is a major matrix component of all BMs (ref. 2). Unlike in other BMs, glomerular BM (GBM) contains primarily the alpha 3(IV) and alpha 4(IV) chains, together with the alpha 5(IV) chain. A poorly understood, coordinated temporal and spatial switch in gene expression from ubiquitously expressed alpha 1(IV) and alpha 2(IV) collagen to the alpha 3(IV), alpha 4(IV) and alpha 5(IV) chains occurs during normal embryogenesis of GBM (ref. 4). Structural abnormalities of type IV collagen have been associated with diverse biological processes including defects in molecular filtration in Alport syndrome, cell differentiation in hereditary leiomyomatosis, and autoimmunity in Goodpasture syndrome; however, the transcriptional and developmental regulation of type IV collagen expression is unknown. Nail patella syndrome (NPS) is caused by mutations in LMX1B, encoding a LIM homeodomain transcription factor. Some patients have nephrosis-associated renal disease characterized by typical ultrastructural abnormalities of GBM (refs. 8,9). In Lmx1b(-/-) mice, expression of both alpha(3)IV and alpha(4)IV collagen is strongly diminished in GBM, whereas that of alpha1, alpha2 and alpha5(IV) collagen is unchanged. Moreover, LMX1B binds specifically to a putative enhancer sequence in intron 1 of both mouse and human COL4A4 and upregulates reporter constructs containing this enhancer-like sequence. These data indicate that LMX1B directly regulates the coordinated expression of alpha 3(IV) and alpha 4(IV) collagen required for normal GBM morphogenesis and that its dysregulation in GBM contributes to the renal pathology and nephrosis in NPS.

Loss of α3/α4(IV) Collagen from the Glomerular Basement Membrane Induces a Strain-Dependent Isoform Switch to α5α6(IV) Collagen Associated with Longer Renal Survival in Col4a3 −/− Alport Mice

“…To distinguish between these alternatives, we examined the distribution of collagen IV chains in the kidneys of newborn Lmx1b mutant mice by indirect immunofluorescence staining with chain-specific mAb ( Figure 2). In Lmx1b Ϫ/Ϫ kidneys, the staining for ␣3 and ␣4(IV) chains was faint and segmental, but ␣5(IV) chain persisted in the GBM, in agreement with previous reports (16). Importantly, ␣6(IV) collagen co-localized with ␣5(IV) collagen not only in Bowman's capsule basement membrane (as expected) but also in the GBM of Lmx1b Ϫ/Ϫ mice.…”

“…mice, preventing the expression of ␣3 and ␣4(IV) collagen chains, yet the ␣5(IV) chain persists in the mutant GBM (16). This paradoxical uncoupling between the ␣5(IV) chain and ␣3/␣4(IV) chains challenges the current paradigm of the specific assembly and tissue-restricted expression of collagen IV chains.…”

Genotype–phenotype studies in nail-patella syndrome show that LMX1B mutation location is involved in the risk of developing nephropathy

“…13,14 NPS nephropathy is a disease of both the podocytes and the GBM, with irregular thickening and electron lucent areas as consistent ultrastructural hallmarks of the GBM. 7,15,16 Interestingly, abnormal collagen expression has been observed in human NPS renal biopsy specimens 15 and in Lmx1b À/À murine kidneys 5 and corneal stroma. 6 The molecular mechanisms underlying the phenotypic aspects of this disorder, however, are as yet unclear.…”

The identification of transcription factors expressed in the notochord of Ciona intestinalis adds new potential players to the brachyury gene regulatory network

“…The dreher mouse carries a mutation in Lmx1a which is responsible for numerous abnormalities, including skeletal defects such as a short tail (Bergstrom et al, 1999). Mutation of Lmx1b leads to aberrant collagen fibril formation in mouse corneas (Pressman et al, 2000) and also to a decrease in the levels of type IV collagens in glomerular basement membranes of the kidney (Morello et al, 2001). Given the involvement of Lmx1b in the expression and maturation of collagen in different tissues and the expression of various collagen genes in the Ciona notochord (Wada et al, 2006;Kugler et al, 2010), it is possible that Ci-Lmx-like could play an analogous role in the formation of the notochordal sheath, a possibility that has yet to be explored in any chordate.…”