Cardiovascular problems are the leading cause of death for patients with autosomal dominant polycystic kidney disease (ADPKD), a hereditary, systemic disease that is estimated to affects 1 per 1.000 persons. The disease leads to the formation of multiple and bilateral renal cysts and progressive loss of renal function, in addition to presenting extrarenal manifestations, such as cardiovascular changes. It is caused in the vast majority of cases by mutations in the PKD1 gene, which encodes the polycystin-1 protein, or in the PKD2 gene, which encodes polycystin-2. In the last decades, many studies were directed to the understanding of the molecular mechanisms involved in the renal cystogenesis of ADPKD. Among the mechanisms involved in the renal phenotype, metabolic defects have gained prominence in recent years. However, the molecular mechanisms involved in cardiac dysfunction associated with ADPKD are still largely unknown. In an article published in the journal Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, researchers described for the first time cardiac metabolic rewiring and mitochondrial abnormalities in an animal model orthologous to human ADPKD. Several of the observed changes may apply to human disease.

“This pioneering work proposes that metabolic alterations are involved in cardiac dysfunction associated with functional polycystin-1 deficiency, revealing common and different aspects from those described for cystic kidneys from animal models deficient in Pkd1, the gene orthologous to PKD1. This is an initial study, that opens up the possibility of proposing therapeutic interventions for several researchers. In the past, people with this disease died of kidney failure, but now, with dialysis and kidney transplantation, most deaths are due to cardiovascular changes. That would be my dream: to see this bench study maybe help patients”, said Andressa Godoy Amaral, first author of the article, who conducted the research during her doctorate, under the supervision of Professor Luiz Fernando Onuchic, responsible for the Cellular, Genetic and Molecular Nephrology Laboratory at the Faculdade de Medicina at Uiversidade de São Paulo (USP). The work was carried out in collaboration with researchers Alicia Kowaltowski and Sayuri Miyamoto groups, both from the Instituto de Química at USP and the RIDC Redoxoma. Metabolomics studies were carried out at the National Biosciences Laboratory (LNBio), in Campinas.

According to Professor Sayuri Miyamoto, whose group was responsible for the lipidomics analysis of cardiac tissue, the lipidomics data demonstrated the extensive lipid remodeling that takes place in the heart, in addition to serving as a basis for generating hypotheses about the pathways of deregulated lipid metabolism.

Metabolic rewiring

The heart is a metabolically very active organ, in which mitochondria account for 25 to 30% of the volume of the cardiomyocytes - the cardiac muscle cells - explains Andressa. And most of the energy used by the heart comes from the beta-oxidation of fatty acids, meaning the heart mainly uses fat for energy. But this only happens after birth, when the availability of oxygen is greater. The fetal heart predominantly uses glucose as a substrate for ATP production. “A characteristic of several cardiac dysfunctions is this dedifferentiation to the fetal phenotype. The heart returns to prefer alternative substrates instead of fatty acid. And we saw exactly that in this work, a metabolic reprogramming of the heart.”

To analyze the impact of polycystin-1 on cardiac metabolism, the researchers used mice named Pkd1^V/V, which are unable to cleave this protein aat the GPS site and have intensely cystic kidneys and early cardiac dysfunction. “This protein is large and complex and depends on a cleavage at the GPS site to migrate to the places where it will act”, explained the researcher. Polycystin-1 is a membrane glycoprotein and is expressed in several tissues, but its precise functions are still poorly understood. It can interact and form a complex with polycystin-2, which, in turn, functions as a calcium-permeable channel. In the primary apical cilium of renal epithelial cells, polycystin-1 acts in the regulation of intracellular calcium homeostasis.

The study showed that Pkd1^V/V hearts had lower glucose and amino acid levels and higher lipid levels than controls. This observation suggested decreased beta-oxidation of fatty acids in Pkd1^V/V hearts, which was confirmed by lower oxygen consumption by mitochondria in the presence of fatty acid. In addition, they displayed a higher density of decreased-size mitochondria, increased apoptosis (programmed cell death), and inflammation, but not hypertrophy.

The researchers performed metabolomics, by nuclear magnetic resonance spectroscopy (NMR), lipidomics, by liquid chromatography coupled to mass spectrometry (LC-MS/MS), mitochondrial function using Oroboros O2k high-resolution respirometry and the Seahorse System, in addition to using molecular biology tools. Tissues and mitochondria from the heart of animals with 15 days of life, the age at which Pkd1^V/V mice present both cardiac dysfunction and renal cysts, were analyzed. Complementarily, some analyzes were performed on cardiomyocytes isolated from neonates (0 to 3 days of age), at which age there is no presence of renal cysts, to assess cardiac alterations that are certainly independent of the renal phenotype. Comparisons were made between Pkd1^V/V animals and wild-type controls, and confirmed metabolic rearrangement.

According to the authors, this study links the cleavage of polycystin-1 to the development of the heart and the maintenance of cardiac metabolic homeostasis and can be considered a conceptual landmark in the elucidation of the cardiac dysfunction pathogenesis associated with this protein deficiency.

The article “Disruption of polycystin-1 cleavage leads to cardiac metabolic rewiring in mice” by Andressa G. Amaral, Camille C.C. da Silva, Julian D.C. Serna, Kinulpe Honorato-Sampaio, Jéssica A. Freitas, Amaro N. Duarte-Neto, Antonio C. Bloise, Laura Cassina, Marcos Y. Yoshinaga, Adriano B. Chaves-Filho, Feng Qian, Sayuri Miyamoto, Alessandra Boletta, Silvana Bordin, Alicia J. Kowaltowski and Luiz F. Onuchic, can be accessed here.