Nathalie LE CLEF
Promotors: Patrick C. D’Haese and Benjamin A. Vervaet
Chronic kidney disease (CKD) is a worldwide public health problem with an increasing incidence and prevalence. An episode of acute kidney injury (AKI) is an important risk factor for the development of CKD. However, thus far, there is no therapy available to halt this progression from acute to chronic renal injury. Animal models are indispensable to unravel the mechanisms underlying the AKI-to-CKD progression, and to evaluate potential or novel therapeutic strategies. Several animal models of AKI are available, however, they are often of little clinical relevance, or unsuited to study the AKI-to-CKD progression. In view of this, a physiological and clinically relevant mouse model of ischemia-reperfusion was developed and characterized as a model of acute-to-chronic kidney injury. We demonstrated in C57Bl/6J mice, by both histology and gene expression, that unilateral ischemia-reperfusion injury (UIRI) without contralateral nephrectomy is a very robust model to study the progression from acute renal injury to long-term tubulo-interstitial fibrosis, the histopathological hallmark of CKD. Furthermore, we report that the extent of renal fibrosis, in terms of collagen I, TGFβ, CCN2 and CCN3 expression and collagen I immunostaining was directly associated with body temperature during ischemia as well as duration of ischemia. In addition, we report that UIRI with contralateral nephrectomy is a model of renal repair. One of the possible pathways underlying the AKI-to-CKD progression is aberrant DNA-methylation, i.e. hyper-methylation of RASAL1, which induces the hyper-activation of fibroblasts in renal fibrosis. Therefore, it was investigated whether progression of renal fibrosis can be halted by preventing replication of the pathological DNA-methylation pattern of terminally activated fibroblasts to their daughter cells by administration of the DNA-methylation inhibitor decitabine. Even though decitabine treatment induced a significant reduction in genomic DNA-methylation, and suppressed long-term Dnmt3b gene expression, progression of fibrosis was not attenuated or prevented. Other important pathways underlying AKI-to-CKD progression are persistence of inflammation, as well as prolonged activity of the TGFβ-pathway. Hereto, it was investigated whether suppression of inflammation or antagonism of TGFβ is able to prevent the AKI-to-CKD progression. In this thesis it was demonstrated that immune suppressive treatment strategies can attenuate the development of renal fibrosis after an acute ischemic event, as evidenced by reduced collagen I gene expression and immunostaining, in combination with reduced gene expression of CCN2 and increased expression of CCN3. However, persistent treatment until near complete resolution of inflammation may be required to maintain long-term effects. On the other hand, in the model used and under the conditions tested, TGFβ antagonism had a very limited effect on the deposition of collagen I, hence fibrosis, in the ischemic kidney. Overall, it appears that, in the ischemic setting, a multi-target therapeutic strategy may be required to consistently prevent progression from acute-to-chronic renal injury.