The PI3K/AKT pathway, negatively regulated by PTEN, plays a paramount role in glucose metabolism regulation due to its activation by the insulin receptor signaling pathway. We generated a PTEN-KO mouse to evaluate the systemic effect of the overactivation of the PI3K/AKT pathway in insulin signaling and glucose homeostasis. Our results demonstrate that PTEN-KO mice show very low glucose levels in the fasted state, which poorly respond to glucose and pyruvate administration. Insulinemia decreased without alterations in pancreatic islets. Among the possible reasons, we uncover the deregulation of the expression of proximal tubule glucose transporter and consequent glycosuria. Moreover, we evidence an altered activation of hepatic gluconeogenesis-related genes. In addition, the expression of several genes related to β-oxidation showed a delayed or even absent response to fasting, suggesting that the lack of PTEN not only impairs glucose metabolism but also slows down the use of lipids as a metabolic fuel. We conclude that the inducible full PTEN-KO mice could be a good model to study the metabolic interactions between glycidic and lipidic metabolism in hypoinsulinemic hypoglycemia and that PTEN could be an important mediator in the disease and/or a potential drug target.

BACKGROUND AND AIMS Chronic kidney disease (CKD) represents an important and growing burden on health worldwide, mainly driven by the increase in the incidence of associated risk factors like diabetes. As kidney function declines, changes in mineral metabolism occur, which contribute to the increased risk of cardiovascular disease in CKD patients. In this respect, Klotho was described as an anti-ageing protein, mainly expressed in the kidney, where it acts as an obligatory co-receptor of the Fibroblast Growth Factor (FGF23), which is involved in urinary phosphate excretion. The earliest mineral metabolism change in CKD is the fall in renal and plasma Klotho levels, followed by an increase in FGF23. Klotho loss is related to inflammatory and fibrotic processes contributing not only to the progression of CKD but also to the increase in cardiovascular risk. Clinically, there is a growing interest in maintaining renal Klotho expression in patients, but the mechanisms in Klotho decline remain unknown. PTEN is the main negative regulator of PI3K-AKT-mTOR pathway. PTEN degrades PIP3 to PIP2 decreasing the activation of the canonical insulin pathway. The involvement of PTEN in cancer has been broadly investigated. Furthermore, the PI3K/PTEN signalling pathways are involved in a wide variety of diseases including cardiac hypertrophy, heart failure, hypertension and acute kidney injury. However, its potential role in CKD has not been properly assessed. The objective of this study was to investigate the role of PTEN and the PI3K/AKT/mTOR pathways in kidney Klotho levels and the modulation of phosphorus metabolism. METHOD We generated a proximal tubule conditional PTEN knockout mouse model (PT-PTEN-cKO), in which a high phosphorus diet (HPD) and rapamycin treatment were administered in order to analyse how PI3K/AKT/mTOR pathway participates in phosphorus metabolism and kidney Klotho levels. We used human proximal tubular cell (PTC) line HK-2 to knock down PTEN by means of transfection with shPTEN lentiviral vector, to study the direct effect of PTEN elimination in Klotho levels in vitro. RESULTS PT-PTEN-cKO mice present a specific activation of the PI3K/AKT/mTOR pathway in the proximal tubule. PTEN mRNA decrease correlates with a drop in kidney Klotho levels, accompanied by an increment of inflammatory and fibrotic markers. In addition, our model showed an increase in both, plasma phosphate and FGF23, with a decrease in the fractional excretion of phosphate (% FEPi). This fact can be explained by the inability of kidney cells to respond to FGF23, because of Klotho loss. Moreover, parathyroid hormone (PTH) and bone resorption were increased. We observe that PT-PTEN-KO mice in an HPD needed higher FGF23 levels in order to excrete phosphate than control mice. Rapamycin administration restored Klotho levels. In vitro, PTEN silencing in PTC, leads to an increase in PI3K/AKT/mTOR activity and also to a reduction in Klotho expression. Finally, the inhibition of mTOR phosphorylation by rapamycin reestablished Klotho expression in vitro. CONCLUSION The overactivation of PI3K/AKT/mTOR pathway, in PTC, decreases Klotho kidney levels. Our findings constitute an important breakthrough in the research of new therapeutic targets in order to maintain renal Klotho levels and it may be useful in the treatment of kidney disease patients.