Patients with myeloproliferative neoplasms and COVID-19 have increased rates of arterial thrombosis

Secondary polycythemia in acutely ill COVID-19 patients is associated with higher mortality but not markedly higher thrombotic risk

Secondary polycythemia is commonly observed among patients with chronic pulmonary diseases. However, its significance in the context of Coronavirus disease 2019 (COVID-19) is unknown. We retrospectively evaluated a total of 5872 hospitalized COVID-19 patients with mostly severe and critical symptoms, and without prior or subsequently diagnosed myeloproliferative neoplasm. Patients were stratified based on admission hemoglobin into four subgroups: anemia (hemoglobin <120 g/L for females and 130 g/L for males), normal hemoglobin, mild (hemoglobin 160-165 g/L for females and 165-185 g/L for males) and severe polycythemia (hemoglobin >165 g/L for females and >185 g/L for males). Among 5872 patients, a total of 158 (2.7%) had mild and 25 (0.4%) severe polycythemia. Polycythemia was significantly associated with higher respiratory and functional impairment, reduced plasma volume, higher serum osmolarity and comorbidity burden specific to the degree of polycythemia. Patients presenting with mild (odds ratio (OR) = 1.63, p = .003) and severe polycythemia (OR = 4.98, p < .001) had increased risk of death in comparison to patients with normal hemoglobin, whereas no significant associations with venous thromboembolism, arterial thrombosis nor major bleeding were observed. Anemia was associated with higher risk of death (OR = 1.42, p < .001), venous thromboembolism (OR = 1.34, p < .006) and major bleeding (OR = 2.27, p < .001) in comparison to normal hemoglobin. Associations of polycythemia and anemia with mortality diminished, and anemia with venous thromboembolism and major bleeding persisted, after multivariate adjustments for age, sex, comorbidities, COVID-19 severity and functional status. Secondary polycythemia in hospitalized COVID-19 patients without prior of subsequently diagnosed myeloproliferative neoplasm is rare and is associated with high mortality, increasing with degree of polycythemia, but not markedly higher thrombotic risk.

Calreticulin Regulates SARS-CoV-2 Spike Protein Turnover and Modulates SARS-CoV-2 Infectivity

Cardiovascular complications are major clinical hallmarks of acute and post-acute coronavirus disease 2019 (COVID-19). However, the mechanistic details of SARS-CoV-2 infectivity of endothelial cells remain largely unknown. Here, we demonstrate that the receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein shares a similarity with the proline-rich binding ena/VASP homology (EVH1) domain and identified the endoplasmic reticulum (ER) resident calreticulin (CALR) as an S-RBD interacting protein. Our biochemical analysis showed that CALR, via its proline-rich (P) domain, interacts with S-RBD and modulates proteostasis of the S protein. Treatment of cells with the proteasomal inhibitor bortezomib increased the expression of the S protein independent of CALR, whereas the lysosomal/autophagy inhibitor bafilomycin 1A, which interferes with the acidification of lysosome, selectively augmented the S protein levels in a CALR-dependent manner. More importantly, the shRNA-mediated knockdown of CALR increased SARS-CoV-2 infection and impaired calcium homeostasis of human endothelial cells. This study provides new insight into the infectivity of SARS-CoV-2, calcium hemostasis, and the role of CALR in the ER-lysosome-dependent proteolysis of the spike protein, which could be associated with cardiovascular complications in COVID-19 patients.