#339 Thyroid hormone levels critically contribute to ADPKD progression

Abstract Background and Aims Thyroid hormone (TH) signaling plays a crucial role in the regulation of the cell differentiation state, cell cycle and metabolism in various organs. Low TH levels are observed in most patients with chronic kidney disease, and correlate with cell de-differentiation and reactivation of the cell cycle. Despite this knowledge, possible alterations of TH signaling in Autosomal Dominant Polycystic Kidney Disease (ADPKD) and the capacity of TH to modulate anti-cystogenic and renoprotective pathways have not yet been studied. In this study we aimed to (i) investigate the role of TH signaling in the pathogenesis of ADPKD in patients and experimental models, and (ii) assess whether the pharmacological modulation of this pathway with TH (T3, T4) and TH analogs could arrest or reverse ADPKD progression. Method Ninety patients with a diagnosis of ADPKD based on renal ultrasonography findings or genetic testing were included in the study and divided into five subgroups of chronic kidney disease stages, according to the KDIGO classification. Serum TH was measured using ELISA and chemiluminescent immunoassays. The correlation between TH levels and renal function parameter (eGFR) in these patients was assessed using linear regression. 3D polycystic tubules were engineered from patient-derived cells as previously described (Benedetti et al. 2016). For the in vivo experiments, PCK rats—an animal model of ADPKD—were treated with T4 (10 μg/kg) or vehicle by gavage from 4 to 11 weeks of age. Age-matched SD rats were followed for the same length of time and used as controls. Results The analysis of patients’ data showed a strong linear correlation between the levels of FT3 and eGFR, and corresponding inverse correlation between rT3 (the inactivated form of T3) and eGFR. Treating patients-derived tubules with THs strongly inhibited cyst formation and growth. Interestingly, the results were validated in engineered polycystic tubules from three ADPKD patients with different mutations (missense, splice-site and stop-gain) in the PKD1 gene, further confirming that T4 plays an essential role in the cystogenesis and, presumably, progression of the disease in humans. Treating PCK rats—an animal model of ADPKD—with T4 resulted in a significant increase in T4 serum levels and a simultaneous reduction in the size of the macrocystic area compared to vehicle-treated PCK rats. Most importantly, T4 serum levels positively correlated with a reduction in both the size of the macrocystic area and loss of protein into the urine, indicating that TH signaling plays a role in the growth of cysts, and that exogenous T4 can slow down cystogenesis and improve renal function. Interestingly, our mechanistic studies revealed that T4 exerts its anti-cystogenic effects, at least partially, by binding to the membrane receptor αvβ3 and activating the MAPK cascade. Conclusion These results suggest that TH signaling plays a role in the progression of ADPKD and timely administration of T4, ideally at a relatively early stage of the disease, could delay progression or even reverse key clinical features of ADPKD.