Increased left ventricular fibrosis has been reported in patients hospitalized with coronavirus disease 2019 (COVID-19). It is unclear whether this fibrosis is a consequence of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection or a risk factor for severe disease progression. We observed increased fibrosis in the left ventricular myocardium of deceased COVID-19 patients, compared with matched controls. We also detected increased mRNA levels of soluble interleukin-1 receptor-like 1 (sIL1-RL1) and transforming growth factor β1 (TGF-β1) in the left ventricular myocardium of deceased COVID-19 patients. Biochemical analysis of blood sampled from patients admitted to the emergency department (ED) with COVID-19 revealed highly elevated levels of TGF-β1 mRNA in these patients compared to controls. Left ventricular strain measured by echocardiography as a marker of pre-existing cardiac fibrosis correlated strongly with blood TGF-β1 mRNA levels and predicted disease severity in COVID-19 patients. In the left ventricular myocardium and lungs of COVID-19 patients, we found increased neuropilin-1 (NRP-1) RNA levels, which correlated strongly with the prevalence of pulmonary SARS-CoV-2 nucleocapsid. Cardiac and pulmonary fibrosis may therefore predispose these patients to increased cellular viral entry in the lung, which may explain the worse clinical outcome observed in our cohort. Our study demonstrates that patients at risk of clinical deterioration can be identified early by echocardiographic strain analysis and quantification of blood TGF-β1 mRNA performed at the time of first medical contact.

Adrenergic stimulation, while being the central mechanism of cardiac positive inotropy, is a universally acknowledged inductor of undesirable sarcoplasmic reticulum (SR) Ca²⁺ leak. However, the exact mechanisms for this remained unspecified so far. This study shows that Ca²⁺/calmodulin‐dependent protein kinase II (CaMKII)‐specific phosphorylation of ryanodine receptor type 2 at Ser‐2814 is the pivotal mechanism by which SR Ca²⁺ leak develops downstream of β1‐adrenergic stress by increase of the leak/load relationship. Cardiomyocytes with a Ser‐2814 phosphoresistant mutation (S2814A) were protected from isoproterenol‐induced SR Ca²⁺ leak and consequently displayed improved postrest potentiation of systolic Ca²⁺ release under adrenergic stress compared to littermate wild‐type cells.

The current study shows that activation of CaMKIIδ through Met281/282 oxidation is neither required for CaMKII-dependent recovery of Ca²⁺ transients during acidosis nor relevant for the occurrence of postacidic cellular arrhythmias. Despite a usually prooxidant increase in cytosolic Na⁺, acidosis reduces the cytosolic glutathione redox state within cardiac myocytes. This novel finding suggests that oxidation of cytosolic proteins is less likely to occur during acidosis.

Background: Diabetic cardiomyopathy (DbCM) preclinical studies have used animal models from different species and implicated altered redox regulation and reactive oxygen species (ROS) in this disease. However hyperglycaemia‐induced ROS signalling may differ in ventricular myocytes from different species, and here we compare mice, rats, rabbits and humans with respect to hyperglycaemia‐induced ROS production. Methods: Using the chemical sensor H₂DCFDA and genetically encoded redox sensors, we measured time‐dependent ROS signals in response to high glucose (HiGlu). Live cell confocal imaging was used to determine redox and glucose levels, contractility and Ca²⁺ transients in isolated cardiomyocytes. Western blotting and activity assays were used to evaluate superoxide dismutase (SOD) expression and activity. Results: Consistent with our prior mouse studies, HiGlu exposure in rat and human ventricular myocytes increased cytosolic (not mitochondrial) ROS production via a mechanism involving Ca‐calmodulin‐dependent protein kinase (CaMKII) O‐GlcNAcylation (at Ser280) and NADPH oxidase 2 (NOX2) activation. However in rabbit ventricular myocytes HiGlu alone did not induce significant ROS production, unless complemented by low levels of angiotensin II and inhibition of the enzyme that reverses O‐GlcNAcylation using 100 nM Thiamet G, where both cytosolic and mitochondrial ROS accumulation were involved by more complex signalling networks. Conclusion: Acute hyperglycaemia readily induces robust ROS production in mouse, rat and human ventricular myocytes, but rabbit myocytes are intrinsically better protected from this HiGlu‐induced ROS responses. In most regards rabbit are much more human‐like than rodents for many aspects of myocyte function, but this surprisingly is not the case for HiGlu‐induced ROS production. image Key points: In mouse ventricular myocytes we previously showed that acute hyperglycaemia (HiGlu) induced increase in reactive oxygen species (ROS) mediated by O‐GlcNAcylation of Ca‐calmodulin‐dependent protein kinase at Ser280 and consequent NADPH oxidase 2 (NOX2) activation. Here we demonstrate that this same pathway is functional in human and rat ventricular myocytes but not in rabbit ventricular myocytes. In rat and human myocytes HiGlu induced an increase in cytosolic, but not mitochondrial, ROS production. In rabbit myocytes HiGlu only produced increased ROS (cytosolic and mitochondrial) only when it was accompanied by both low concentration angiotensin II and an O‐GlcNAcylase inhibitor (that individually did not promote ROS production). This direct HiGlu‐induced ROS production in cardiac myocytes may contribute to pathological signalling in diabetes.