Mediators of SARS-CoV-2 entry are preferentially enriched in cardiomyocytes

Background The coronavirus disease 2019 (COVID-19) has spread rapidly around the world. In addition to common respiratory symptoms such as cough and fever, some patients also have cardiac injury, however, the mechanism of cardiac injury is not clear. In this study, we analyzed the RNA expression atlases of angiotensin-converting enzyme 2(ACE2), cathepsin B (CTSB) and cathepsin L (CTSL) in the human embryonic heart at single-cell resolution. Results The results showed that ACE2 was preferentially enriched in cardiomyocytes. Interestingly, serine protease transmembrane serine protease 2 (TMPRSS2) had less expression in cardiomyocytes, but CTSB and CTSL, which belonged to cell protease, could be found to be enriched in cardiomyocytes. The results of enrichment analysis showed that differentially expressed genes (DEGs) in ACE2-positive cardiomyocytes were mainly enriched in the processes of cardiac muscle contraction, regulation of cardiac conduction, mitochondrial respiratory chain, ion channel binding, adrenergic signaling in cardiomyocytes and viral transcription. Conclusions Our study suggests that both atrial and ventricular cardiomyocytes are potentially susceptible to severe acute respiratory syndrome coronavirus-2(SARS-CoV-2), and SARS-CoV-2 may enter ventricular cardiomyocytes using CTSB/CTSL for S protein priming. This may be the partial cellular mechanism of cardiac injury in patients with COVID-19.

Glutathione and Nitric Oxide: Key Team Players in Use and Disuse of Skeletal Muscle

Glutathione (GSH) is the main non-enzymatic antioxidant playing an important role in detoxification, signal transduction by modulation of protein thiols redox status and direct scavenging of radicals. The latter function is not only performed against reactive oxygen species (ROS) but GSH also has a fundamental role in buffering nitric oxide (NO), a physiologically-produced molecule having-multifaceted functions. The efficient rate of GSH synthesis and high levels of GSH-dependent enzymes are characteristic features of healthy skeletal muscle where, besides the canonical functions, it is also involved in muscle contraction regulation. Moreover, NO production in skeletal muscle is a direct consequence of contractile activity and influences several metabolic myocyte pathways under both physiological and pathological conditions. In this review, we will consider the homeostasis and intersection of GSH with NO and then we will restrict the discussion on their role in processes related to skeletal muscle function and degeneration.

Abstract 270: The Core Function of Calcineurin

Background: Recent evidence demonstrates that not only NFAT, but also calcineurin is translocated into the nucleus upon hypertrophic stimulation. Previously it was also demonstrated that calpain-mediated degradation caused a constitutive active calcineurin. We hypothesised that nuclear calcineurin is an intranuclear Ca 2+ sensor hypertrophied myocardium and that inhibition of nuclear translocation of calcineurin is a therapeutic strategy to prevent hypertrophy. Methods: Employing a transgene mouse model with conditional calpastatin overexpression (”tet-off”, resulting in calpain inhibition), different adenoviral calcineurin mutants and confocal microscopy in isolated adult cardiac myocytes we investigated calcineurin translocation and nuclear Ca 2+ transients. Assessment of cardiac function if transgenic animals was performed by 7T MRI. Results: We could demonstrate that chronic Ang II stimulation of mice caused calpain-mediated degradation of calcineurin resulting in a constitutive active calcineurin with nuclear translocation. The constitutive active calcineurin in the nucleus escaped further degradation by the UPS and sustained an ongoing hypertrophic response, even after removal of Ang II. Inhibition of nuclear translocation of activated calcineurin by a small inhibitory peptide prevented myocardial hypertrophy in vivo. Transgenic inhibition of calpain activity by calpastatin overexpression prevented proteolysis of calcineurin and allowed for relocation of calcineurin from the nucleus back to the cytosol and regression hypertrophy after removal of Ang II. We were also able to demonstrate that Ang II increases nuclear Ca 2+ transients via InsP3 receptors and that calcineurin is able to act as nuclear Ca 2+ sensor detecting local Ca 2+ release from the nuclear envelope via InsP3R. Nuclear calcineurin mutants that are defective for Ca 2+ activation failed to activate NFAT dependent transcription. Conclusion: This provides an explanation how Ca 2+ and calcineurin can regulate transcription in cardiomyocytes in response to neurohumoral signals apart from Ca 2+ changes in contraction regulation.

TMEM16A Protein: A New Identity for Ca2+-Dependent Cl− Channels

Ca+-dependent Cl− channels (CaCCs) play a variety of physiological roles in different organs and tissues, including transepithelial Cl− secretion, smooth muscle contraction, regulation of neuronal excitability, and transduction of sensory stimuli. The recent identification of TMEM16A protein as an important component of CaCCs should allow a better understanding of their physiological role, structure-function relationship, and regulatory mechanisms.