The laminin-binding integrins regulate nuclear factor kappaB-dependent epithelial cell polarity and inflammation

The main laminin-binding integrins alpha3beta1, alpha6beta1 and alpha6beta4 are co-expressed in the developing kidney collecting duct system. We previously showed that deleting the integrin alpha3 or alpha6 subunit in the ureteric bud, which gives rise to the kidney collecting system, caused either a mild or no branching morphogenesis phenotype, respectively. To determine whether these two integrin subunits cooperate in kidney collecting duct development, we deleted alpha3 and alpha6 in the developing ureteric bud. The collecting system of the double knockout phenocopied the alpha3 integrin conditional knockout. However, with age, the mice developed severe inflammation and fibrosis around the collecting ducts, resulting in kidney failure. Integrin alpha3alpha6-null collecting duct epithelial cells showed increased secretion of pro-inflammatory cytokines and displayed mesenchymal characteristics, causing loss of barrier function. These features resulted from increased nuclear factor kappa-B (NF-kappaB) activity, which regulated the Snail and Slug (also known as Snai1 and Snai2, respectively) transcription factors and their downstream targets. These data suggest that laminin-binding integrins play a key role in the maintenance of kidney tubule epithelial cell polarity and decrease pro-inflammatory cytokine secretion by regulating NF-kappaB-dependent signaling.