A Human Integrin-α3 Mutation Confers Major Renal Developmental Defects

<div><p>The development of the mammalian kidney is a highly complex process dependent upon the interplay of various cell types, secreted morphogens, and the extra-cellular matrix (ECM). Although integrins are the most important receptors for ECM proteins and are ubiquitously expressed during kidney development, mice lacking expression of integrin α3 (Itga3) do not demonstrate a reduced number of nephrons, but mostly a disorganized GBM (glomerular basement membrane) leading to proteinuria. Thus, ITGA3 is considered mostly a passive GBM stabilizer and not an active player in nephrogenesis. Recently, mutations in the human <i>ITGA3</i> were shown to cause congenital nephrotic syndrome, epidermolysis bullosa and interstitial lung disease, otherwise termed NEP syndrome (<b>N</b>ephrotic syndrome, <b>E</b>pidermolysis bullosa and <b>P</b>ulmonary disease). Herein, we performed histological and molecular analysis on the kidneys of a single patient from the initial cohort harboring an <i>ITGA3</i> mutation, to illuminate the role of <i>ITGA3</i> in human renal development. We show the patient to harbor a unique phenotype at birth, including severe unilateral renal hypodysplasia. Interrogation of global gene expression in the hypodysplastic kidney versus three controls (fetal, child and adult kidneys) revealed perturbed expression in several renal developmental pathways implicated in hypodysplasia, including the Wnt, BMP (bone morphogenetic protein) and TGF (transforming growth factor) pathways. Moreover, the affected kidney showed upregulation of early embryonic genes (e.g. <i>OCT4</i> and <i>PAX8</i>) concomitant with downregulated kidney differentiation markers, implying a defect in proper renal differentiation. In conclusion, we show for the first time that ITGA3 is not merely a passive anchor for renal ECM proteins, as predicted by mouse models. Instead, our results may suggest it plays a central role in the interplay of cells, morphogens and ECM, required for proper nephrogenesis, thus adding <i>ITGA3</i> to the list of CAKUT (congenital anomalies of the kidney and urinary tract)-causing genes.</p></div

Clinical and histological features of the index patient.

<p>(A) A pedigree presenting the patient, born to healthy consanguineous parents, as the only affected child among nine siblings. (B) Renal ultrasound examination, demonstrating a small hyper-echogenic left kidney and an enlarged right kidney. (C) H&E staining of the patient's right kidney demonstrating a typical nephrotic syndrome phenotype including global sclerosis and mesangial proliferation. (D) The patient's left kidney presents histology consistent with renal hypodysplasia including the presence of cartilage, stroma and renal lesions of nephrotic syndrome similar to those observed in the right kidney.</p

Immuno-localization and interrogation of global gene expression of the patient's kidney.

<p>(A) Immunohistochemical staining for integrin α3 reveals a widespread expression pattern in the developing human fetal kidney (hFK), with localization to early duct precursors, ureteric buds and their differentiated derivatives and basement membrane of assembled fetal glomeruli. Integrin α3 expression was absent in the patient's kidneys. (B) Heat-map comparison of gene expression profile between the patient's kidney (PK) and an age matched control (CK) kidney. Unsupervised hierarchical clustering demonstrates that the PK is more similar genetically to human fetal kidney (hFK) than to the human adult kidney counterpart (hAK). (C) Microarray expression analysis of selected genes demonstrated altered expression in the PK of genes crucial for normal nephron formation, including the Wnt and TGFβ signaling pathways, early developmental genes and renal differentiation genes.</p