Abstract Body (Do not enter title and authors here): Introduction: Polycystin-1 (PC1) is a large transmembrane protein expressed across the body. While PC1 mutations are responsible for ~85% of autosomal dominant polycystic kidney disease (ADPKD) cases, PC1 is increasingly recognized as a key regulator of hypertrophic growth in cardiomyocytes following mechanical stress. The exact role of PC1 in human cardiomyocyte hypertrophy remains unclear.

Goal: We utilized induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) to investigate the role of PC1 in regulating molecular mechanisms underlying hypertrophic growth in human cells.

Methods: iPSC-CMs were differentiated through temporal modulation of Wnt pathway signaling. Cyclic stretch was applied to iPSC-CM monolayers using IonOptix C-Stretch. Gene expression was analyzed via bulk RNA-seq. Additionally, LacZ and the C-terminus of PC1 (PC1-CT) were overexpressed using adenovirus.

Results: Endogenously expressed PC1-CT localizes to the plasma membrane and within sarcomere structures in adult mouse ventricular cardiomyocytes and iPSC-CMs. Silencing of PC1 blunted the early hypertrophic response to cyclic stretch in iPSC-CMs. To determine whether the PC1-CT mediates hypertrophic remodeling, we overexpressed this fragment using an adenovirus. RNA-sequencing revealed that PC1-CT overexpression in iPSC-CMs increased the expression of protein synthesis-associated genes, while hypertrophy-associated genes remained unchanged. Similarly, unchanged levels were observed for the hypertrophic markers NPPA and NPPB, which were further confirmed via qPCR. Western blotting indicated that PC1-CT overexpression activates Akt and partially mTOR, evidenced by increases in p-S6K1 and p-S6, but not p-4EPB1. Other pathways, including p38, JNK, Creb, or insulin-receptor/insulin-receptor-like signaling, were unaffected. Additionally, the PI3K inhibitor LY294002 blunted Akt and S6 phosphorylation induced by PC1-CT overexpression.

Conclusions: Our data indicate that PC1 regulates stretch-induced hypertrophic remodeling in iPSC-CMs. PC1-CT overexpression activates Akt/mTOR/S6K1/S6, impacting gene expression of protein synthesis pathways. Considering the lack of classical hypertrophic gene activation and the unique localization exhibited, PC1-CT may regulate a local sub-pool of Akt relegated to or near sarcomeric structures. Additionally, our results suggest that other protein domains within PC1 are required to promote hypertrophic remodeling in cardiomyocytes.