Our adenine treated animals exhibited increased BUN aprox
Our adenine-treated animals exhibited increased BUN (aprox 5-fold), creatinine (aprox 2-fold), and urine volume (aprox 6-fold). These changes are characteristic of patients with predominant tubule-interstitial damage in early-middle stages. Other authors have made similar approaches by studying animals fed with AMG-176 for 1–2 week, as they were interested in inflammation as the initial event in the development of renal damage in this model , or in the prevention of the progression of the disease . Longer treatment times, between 3 and 8 weeks, were selected by other authors more devoted to the analysis of established fibrosis [42,43]. Because we were interested both in the analysis of the mechanism of development/progression and in the prevention of the disease, we selected 2 to 6 weeks of treatment. The functional changes previously mentioned, together with the structural abnormalities in the tubules showed in the Results section were observed in our adenine-fed animals, which exhibited a progressive increase in renal ILK content and activity. Similarly, increased levels of ILK were also observed in a wide variety of chronic kidney diseases in both experimental and clinical settings [16,18,20,21]. We observed that ILK overexpression was not the consequence of a direct effect of adenine on cells, as ILK protein content and activity did not change in tubular cells incubated directly with adenine, but probably of the complex interaction that took place at tubular level after DHOA crystal deposition. ILK can be a very interesting target to be analyzed during the progression of renal disease. Its involvement in the modulation of key mechanisms implicated in CKD, such as TGF-β expression and ECM protein accumulation [, , ,44], EMT induction [, , , , , , , ,26], and activation of local inflammatory responses, as has been shown in vitro and in vivo by us and others . Additionally, ILK is activated by the interaction of integrins with ECM proteins [27,29], accumulated during chronic renal fibrosis, and it could be proposed as a key molecule that determines and auto-perpetuates the mechanisms that contribute to CKD progression. In adenine-fed mice, we demonstrated the activation of many of the above-mentioned mechanisms and their inhibition conditioned by ILK depletion. Our excellent correlations between renal ILK content and the different parameters tested reinforce the hypothesis that ILK can be considered a good therapeutic target. Several authors have observed that ILK regulating action of EMT is mediated by its protein kinase activity, because an ILK kinase-dead mutant and specific kinase inhibitor block TGF-β-mediated EMT in vitro or renal interstitial fibrosis in obstructive nephropathy [15,16,19]. Our results do not clarify whether the loss of ILK scaffolding function or its kinase activity is responsible for the blockade of the pathogenic mechanisms previously mentioned. Before our study, other groups attempted to inhibit ILK at kidney level, which becomes a complex methodological problem; ILK has no safe pharmacological inhibitors available. Li and coauthors  tested the effect of a potential candidate molecule, QLT-0267, but on a short-term basis. Transgenic mice with specific podocytes ILK deletion exhibited a progressive focal segmental glomerulosclerosis, massive proteinuria and premature death . Our present work used an adult transgenic model of general ILK depletion, which showed a sustained decrease in ILK in kidney cells (from 1 to 3 months after 5 days of tamoxifen treatment) with normal renal function that includes normal histological appearance of renal structures and urine protein excretion [25,32]. The possibility that tamoxifen, and not ILK, could be responsible for renal function improvement seems improbable because the treatment with tamoxifen given to CKD was discontinued and adequate excluding control experiments were performed .