Molecular heterogeneity of the dystrophin-associated protein complex in the mouse kidney nephron: differential alterations in the absence of utrophin and dystrophin

The dystrophin-associated protein complex (DPC) consisting of syntrophin, dystrobrevin, and dystroglycan isoforms is associated either with dystrophin or its homolog utrophin. It is present not only in muscle cells, but also in numerous tissues, including kidney, liver, and brain. Using high-resolution immunofluorescence imaging and Western blotting, we have investigated the effects of utrophin and dystrophin gene deletion on the formation and membrane anchoring of the DPC in kidney epithelial cells, which co-express utrophin and low levels of the C-terminal dystrophin isoform Dp71. We show that multiple, molecularly distinct DPCs co-exist in the nephron; these DPCs have a segment-specific distribution and are only partially associated with utrophin in the basal membrane of tubular epithelial cells. In utrophin-deficient mice, a selective reduction of beta2-syntrophin has been observed in medullary tubular segments, whereas alpha1-syntrophin and beta1-syntrophin are retained, concomintant with an upregulation of beta-dystroglycan, beta-dystrobrevin, and Dp71. These findings suggest that beta2-syntrophin is dependent on utrophin for association with the DPC, and that loss of utrophin is partially compensated by Dp71, allowing the preservation of the DPC in kidney epithelial cells. This hypothesis is confirmed by the almost complete loss of all DPC proteins examined in mice lacking full-length utrophin and all C-terminal dystrophin isoforms (utrophin(0/0)/mdx(3Cv)). The DPC thus critically depends on these proteins for assembly and/or membrane localization in kidney epithelial cells.