Abstract Body (Do not enter title and authors here): Background: Reduced exercise tolerance in heart failure patients with preserved ejection fraction (HFpEF) is caused by elevated left ventricular filling pressures and peripheral skeletal muscle alterations. Among a variety of molecular alterations, titin modulation is particularly interesting due to divergent regulation between myocardium and skeletal muscle. Titin expresses tissue specific isoforms, with N2BA and N2B-titin in the myocardium and N2A-titin in the skeletal muscle (SKM). While in HFpEF, myocardial titin gets hypophosphorylated, characterized by decreased N2B phosphorylation and increased PEVK-phosphorylation, the SKM titin gets hyperphosphorylated, partly due to increased PEVK phosphorylation. The aim of this study was to investigate titin phosphorylation in different HFpEF animal models and compare them to skeletal muscle biopsies of HFpEF patients.
Methods: Muscle biopsies were obtained from the OptimEx trial (ClinicalTrials.gov Identifier: NCT02078947, HFpEF patients) and the LEICA study (ClinicalTrials.gov Identifier: NCT NCT00176319, healthy controls). Snap frozen quadriceps muscle and myocardial tissue was taken from female ZSF-1 and Dahl-Salt sensitive (DSS) rats. A vertical agarose gel electrophoresis, of the homogenized muscle tissues, was performed, followed by a gel stain, to assess titin expression and phosphorylation.
Results: With respect to titin phosphorylation we observed besides well-studied hypophosphorylation in humans left ventricle (LV), a hypophosphorylation in ZSF-1 (-17.6%, p=0.01), samples, but not in DSS LV. Regarding the SKM we detected titin hyperphosphorylation in human samples (+15.5%, p<0.0001) and ZSF-1 rats (+12.9%, p=0.03), which was not observed in DSS rats. Expression of SKM titin was reduced in HFpEF patients (-9.8%, p=0.03) and ZSF-1 rats (-11.2%, p=0.03), but remained unchanged in DSS rats.
Conclusion: Our study contributes to the discussion, regarding titin phosphorylation in HFpEF, showing SKM titin hyperphosphorylation also in humans. Furthermore, we clearly show that the metabolic driven HFpEF-rats (ZSF-1) mirror the titin modulations shown in human HFpEF patients. In the purely hypertension-driven DSS rats on the other hand neither of these alterations could be found. With respect to titin phosphorylation, as a potential therapeutic target we therefore need to be aware of the differences between different HFpEF models, with the ZSF-1 rat being probably one of the best rodent HFpEF models.