Increased mTOR and suppressed autophagic flux in the heart of a hypomorphic Pkd1 mouse model of autosomal dominant polycystic kidney disease.

Cardiac hypertrophy is common in autosomal dominant polycystic kidney disease (ADPKD) patients. We found increased heart weight in Pkd1(RC/RC) and Pkd2(WS25/+) mouse models of ADPKD. As there is a link between increased heart weight and mammalian target of rapamycin (mTOR), the aim of the study was to determine mTOR complex 1 and 2 signaling proteins in the heart in the Pkd1(RC/RC) mouse model of PKD. In 70 day old Pkd1(RC/RC) hearts, on immunoblot analysis, there was a large increase in p-AMPK(Thr172), a known autophagy inducer, and an increase in p-Akt(Ser473) and p-Akt(Thr308), but no increase in other mTORC1/2 proteins (p-S6Ser240/244, pmTOR(Ser2448)). In 150 day old Pkd1(RC/RC) hearts, there was an increase in mTORC1 (p-S6(Ser240/244)) and mTOR-related proteins (p-Akt(Thr308), p-GSK3 beta Ser9, p-AMPK(Thr172)). As the mTOR pathway is the master regulator of autophagy, autophagy proteins were measured. There was an increase in p-Beclin-1 (BECN1), an autophagy regulator and activating molecule in Beclin-1-regulated autophagy (AMBRA1), a regulator of Beclin that play a role in autophagosome formation, an early stage of autophagy. There was a defect in the later stage of autophagy, the fusion of the autophagosome with the lysosome, known as autophagic flux, as evidenced by the lack of an increase in LC3-II, a marker of autophagosomes, with the lysosomal inhibitor bafilomycin, in both 70 day old and 150 day old hearts. To determine the role of autophagy in causing increased heart weight, Pkd1(RC/RC) were treated with 2-deoxyglucose (2-DG) or Tat-Beclin1 peptide, agents known to induce autophagy. 2-DG treatment from 150 to 350 days of age, a time period when increased heart weight developed, did not reduce the increased heart weight. Unexpectedly, Tat-Beclin 1 peptide treatment from 70 to 120 days of age resulted in increased heart weight. In summary, there is suppressed autophagic flux in the heart at an early age in Pkd1(RC/RC) mice. Increased mTOR signaling in older mice is associated suppressed autophagic flux. There was a large increase in p-AMPK(Thr172), a known autophagy inducer, in both young and old mice. 2-DG treatment did not impact increased heart weight and Tat-Beclin1 peptide increased heart weight.