The Mitochondrial Ca²⁺ import complex is altered in ADPKD

Mutations in either of the polycystic kidney disease genes, PKD1 or PKD2, engender the growth of cysts, altering renal function. Cystic growth is supported by major changes in cellular metabolism, some of which involve the mitochondrion, a major storage site for Ca²⁺ and a key organelle in cellular Ca²⁺ signaling. The goal here was to understand the role of components of the mitochondrial Ca²⁺ uptake complex in PC1-mutant cells in autosomal dominant polycystic kidney disease (ADPKD). We found that the mitochondrial Ca²⁺ uniporter (MCU) and voltage-dependent anion channels 1& 3 (VDAC) were down-regulated in different mouse and cell models of ADPKD along with the Ca²⁺-dependent enzyme, pyruvate dehydrogenase phosphatase (PDHX). The release of Ca²⁺ from the endoplasmic reticulum, and Ca²⁺ uptake by the mitochondria were upregulated in PC1(polycystin)-null cells. We also observed an enhanced staining with MitoTracker Red CMXRos in PC1-null cultured cells than in PC1-containing cells and a substantially higher increase in response to ER Ca²⁺ release. Increased colocalization of the Ca²⁺ sensitive dye, rhodamine2, with MitoTracker Green suggested an increase Ca²⁺ entry into the mitochondria in PC1 null cells subsequent to Ca²⁺ release from the ER or from Ca²⁺ entry from the extracellular solution. These data clearly demonstrate abnormal release of Ca²⁺ by the ER and corresponding alterations in Ca²⁺ uptake by the mitochondria in PC1^-null cells. Importantly, inhibiting mitochondrial Ca²⁺ uptake with the specific inhibitor Ru360 inhibited cyst growth and altered both apoptosis and cell proliferation. We further show that the decrease in mitochondrial proteins and abnormally high Ca²⁺ signaling can be reversed by application of the cystic fibrosis (CFTR) corrector, VX-809. We conclude that enhanced Ca²⁺ signaling and alterations in proteins association with the mitochondrial Ca²⁺ uptake complex are associated with malfunction of PC1. Finally, our results identify novel therapeutic targets for treating ADPKD.