Signification de la mort cellulaire dans l’insuffisance rénale aiguë et la fibrose causée par ischémie-reperfusion

Acute kidney injury (AKI) is a common clinical event. Ischemia-reperfusion injury (IRI) is the most important cause of AKI. The participation of programmed cell death (PCD) in the physiopathology of the AKI has been demonstrated by numerous studies. The studies of this thesis aim to elucidate the role of PCD in the different phases of IRI induced AKI. The acute phase of AKI is characterized by tubular injury, microvascular injury and inflammation. Tubular injury was considered as the key feature of the acute phase of AKI. However, mounting evidence identifies microvascular injury as a central contributor. It was documented that PCD plays a predominant role in both tubular and microvascular injury. Activation of caspase-3, the most important effector-caspase of apoptosis, has been found in both renal tubular epithelial cells (TECs) and renal endothelial cells (ECs) post-IRI. However, other studies suggest that necroptosis is the predominant PCD of TECs. To clarify the mechanisms, we created an experimental model of IRI in wild-type (WT) and caspase-3 KO mice secondary to renal artery clamping. This model demonstrated that caspase-3 deficiency protects mice against microvascular injury at all phases of IRI but worsens TEC necroptosis and IRI-induced tubular injury. The second study aimed to study the impact of anti-LG3 autoantibodies on renal IRI. Self-antigens released by damaged tissue could be recognized by their autoantibodies, causing enhanced tissue damage. LG3 is a fragment of perlecan. It has been demonstrated by Dr Hébert 's team that LG3 is released by ECs downstream of activation of caspase-3. We therefore evaluated in our IRI model the hypothesis that IRI can create permissive conditions by releasing LG3 autoantigen by damaged tissue that could be recognized by their autoantibodies, causing enhanced tissue damage. We found that anti-LG3 did not affect the function of non-IRI kidneys, but activate the complement system in microvasculature and exacerbate renal dysfunction post-IRI. The chronic phase of AKI is characterized by tubular atrophy and interstitial fibrosis. It is becoming increasingly accepted that microvascular rarefaction plays a crucial role in the chronic phase. We found that despite an increased tubular injury, caspase-3-deficient mice showed less microvascular rarefaction, less fibrosis and less tubular injury in the chronic phase; suggesting that microvascular rarefaction, caused by microvascular injury, is the driving force in the pro-fibrotic process. We also investigated the molecular mechanisms involved in fibrosis induced by microvascular depletion. The differentiation of fibroblasts in myofibroblasts is a crucial step in the pro-fibrotic process. It was shown that ROS, autophagy and senescence all participate in the development of fibrosis. The team of Dr. Hébert has already demonstrated that the serum starvation (SS) induces differentiation in myofibroblasts through the autophagy-mTORC2 pathway. In this thesis, we have shown that SS (which is used to mimic microvascular rarefaction in vitro) induces the production of ROS, which activates senescence in the way of mTORC2 - dependent autophagy. For the link between senescence and differentiation. We found a negative regulation of senescence on myofibroblastic differentiation. Together, our results demonstrate an important role of apoptosis in the regulation of microvascular integrity, the development of fibrosis and progressive renal dysfunction in the context of IRI-induced AKI.

Keyphrases: anti-LG3, Acute renal injury, Ischemia-reperfusion injury, Cell death, Apoptosis, Myofibroblastic differentiation