Fibronectin deficiency in newborn mice leads to cyst formation in the kidney

PurposeThe ubiquitously expressed glycoprotein fibronectin (FN) is a central component of the fibrillar extracellular matrix (ECM) that is found in multiple sites throughout the body including the peritubular interstitium of the kidney. To learn more about the specific role(s) of FN in the kidney we generated and investigated FN-deficient mice. MethodsWe generated CAGG-Cre-ER/Fnfl/fl mice which carry floxed Fn alleles and ubiquitously express Cre-recombinase after tamoxifen treatment. Newborn pups were treated with tamoxifen eye drops (2.5 mg/mL) to induce FN deficiency. Conditional deletion of Fn was confirmed by quantitative real-time PCR, Western blot analysis and immunohistochemistry. The expression patterns of Fn were analyzed by in situ hybridization. Kidneys were investigated by light microscopy and immunohistochemistry. ResultsThe expression analyses and immunohistochemistry showed a significant reduction of FN at postnatal day (P) 4. Loss of FN corelated with the formation of renal cysts at the corticomedullary border, which expand with increasing age. In situ hybridization demonstrated that on P4 Fn expression extends mainly from the pelvis to the corticomedullary border, whereas in 5-6 weeks old mice it is located only in the cortex. Immunohistochemistry and light microscopy showed a loosening of the renal interstitium and additionally an appearance of ECM proteins in the cysts. ConclusionWe conclude that FN deficiency leads to the development of renal cysts, which occurs a few days after tamoxifen treatment and results in extensive loss of renal parenchyma a few weeks after birth. The results indicate an important role of FN for maintenance of kidney structure and function.