Défense publique de thèse - Louise PIERRE

Study of the role of AMPK in autophagic and lysosomal alterations in renal proximal tubular epithelial cells upon lipotoxicity

Renal proximal tubules are a primary site of injury in metabolic diseases. In obese patients and animal models, proximal tubular epithelial cells (PTECs) display dysregulated lipid metabolism, organelle dysfunctions, and oxidative stress that contribute to interstitial inflammation, fibrosis and ultimately end-stage renal failure. Our research group previously highlighted the importance of AMP-activated protein kinase (AMPK) in obesity-induced chronic kidney disease. Decline in AMPK activity has been shown to mediate the development of the renal disease while its reactivation provides renal benefits and alleviates signs of PTEC injury. Because PTECs display high autophagic activity and rely heavily on their endo-lysosomal system, we investigated the effect of lipotoxicity on autophagy and lysosomes in these cells. Additionally, we were interested to decipher the role of AMPK dysregulation in these pathways. We first developed and characterized a model of palmitate-induced lipotoxicity in primary murine PTECs (mPTECs). These primary cells allow the study of cellular and molecular events as well as some PTEC features recapitulated in vitro due to high differentiation degree. We identified impaired lysosomal acidification as an early event of lipotoxicity in mPTECs exposed to palmitate. It subsequently leads to the accumulation of non-degraded substrates among which autophagosomes. In response to palmitate-induced lysosomal damage, lysosomal quality control pathways are initiated but fail to restore acidic pH which finally drive PTEC dedifferentiation. When palmitate-induced AMPK inhibition was prevented with AMPK activators, lysosomal acidification and the differentiation profile of mPTECs are preserved. Altogether, our data placed lysosomes at the cornerstone of cell physiology and the lipotoxic phenotype in PTECs. We demonstrate the relevance of maintaining lysosomal function to protect these cells from the harmful consequences of lipotoxicity and further show the benefits of AMPK pharmacological activation in this regard. Overall, findings of the present work support that proximal tubules are deleteriously impacted by dysregulated lipid metabolism and provide new insights about the underlying mechanisms.

Contact : Louise PIERRE - 081725710 - louise.pierre@unamur.be
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