Reports suggest a role of endothelial dysfunction and loss of endothelial barrier function in COVID-19. It is well established that the endothelial glycocalyx-degrading enzyme heparanase contributes to vascular leakage and inflammation. Low molecular weight heparins (LMWH) serve as an inhibitor of heparanase. We hypothesize that heparanase contributes to the pathogenesis of COVID-19, and that heparanase may be inhibited by LMWH. To test this hypothesis, heparanase activity and heparan sulfate levels were measured in plasma of healthy controls (n = 10) and COVID-19 patients (n = 48). Plasma heparanase activity and heparan sulfate levels were significantly elevated in COVID-19 patients. Heparanase activity was associated with disease severity including the need for intensive care, lactate dehydrogenase levels, and creatinine levels. Use of prophylactic LMWH in non-ICU patients was associated with a reduced heparanase activity. Since there is no other clinically applied heparanase inhibitor currently available, therapeutic treatment of COVID-19 patients with low molecular weight heparins should be explored.

Reports suggest a role of endothelial dysfunction and loss of endothelial barrier function in COVID-19. It is well established that the endothelial glycocalyx-degrading enzyme heparanase contributes to vascular leakage and inflammation. Low molecular weight heparins (LMWH) serve as an inhibitor of heparanase. We hypothesize that heparanase contributes to the pathogenesis of COVID-19, and that heparanase may be inhibited by LMWH. Heparanase activity and heparan sulfate levels were measured in plasma of healthy controls (n=10) and COVID-19 patients (n=48). Plasma heparanase activity and heparan sulfate levels were significantly elevated in COVID-19 patients. Heparanase activity associated with disease severity including the need for intensive care and mechanical ventilation, lactate dehydrogenase levels and creatinine levels. Use of prophylactic LMWH in non-ICU patients was associated with a reduced heparanase activity. Since there is no other clinically applied heparanase inhibitor currently available, therapeutic treatment of COVID-19 patients with low molecular weight heparins should be explored.

Mg2؉ is an essential ion for many cellular processes, including protein synthesis, nucleic acid stability, and numerous enzymatic reactions. Mg 2؉ homeostasis in mammals depends on the equilibrium between intestinal absorption, renal excretion, and exchange with bone. To maintain a physiological extra-and intracellular Mg 2ϩ concentration is of great importance to keep the accurate function of more than 300 enzymatic systems and the subsequent various biological and physiological processes (1-4). The kidney is the principal organ responsible for the regulation of the body Mg 2ϩ balance. Around 80% of the total plasma Mg 2ϩ is ultrafiltered through the glomeruli and subsequently reabsorbed passively in the proximal tubule and the thick ascending limb of Henle's loop (5 Ϫ/Ϫ mice that survived had neural tube defects (9). TRPM6 and its closest homologue TRPM7 uniquely combine an ion channel pore-forming region with a serine/ threonine protein kinase domain. It is located at the carboxyl terminus and has similarities with members of the ␣-kinase family (10,11). Previous studies demonstrated that receptor for activated C-kinase 1 (RACK1) and repressor of estrogen receptor activity (REA) interact with this domain and inhibit channel activity in an (auto)phosphorylation-dependent manner (12, 13). Moreover, modulation of TRPM6 channel activity by intracellular ATP requires the ATP-binding motif in the ␣-kinase domain (14). Although the phosphorylation activity of the TRPM6/7 ␣-kinase domains has been well determined, the role of these domains in regulating channel activity remains elusive (12,(15)(16)(17)(18).Over the last years, several studies have implicated TRPM channels in ischemia (19,20). Sun et al. (21) showed that decreased TRPM7 channel expression significantly reduced neuronal cell death after global ischemia. Furthermore, TRPM4 channel activation in vascular smooth muscle has been shown to contribute to cell death of vascular cells during ischemic injury, and TRPM2 has been well studied in relation to oxidative stress (22)(23)(24)(25). Accumulating evidence suggests that reactive oxygen species are not only harmful side products of cellular metabolism but also central players in cell signaling and regulation (26 -29). Interestingly, renal DCT cells contain the largest number of mitochondria. However, the effect of oxidative stress on the epithelial Mg 2ϩ channel TRPM6, expressed at the apical membrane of the DCT, has not been studied.The aim of the present study was to investigate the role of the ␣-kinase domain in TRPM6 channel activity by the identification of associated proteins. To this end, the Ras recruitment system (RRS), a novel yeast two-hybrid screening system, which is designed to screen for partners of plasma membrane proteins, was applied (30). Here, we identified methionine sulfoxide reductase B1 (MsrB1) as a TRPM6-associated protein, bind-

The thiazide-sensitive NaCl cotransporter (NCC) plays a key role in renal salt reabsorption and the determination of systemic BP, but the molecular mechanisms governing the regulation of NCC are not completely understood. Here, through pull-down experiments coupled to mass spectrometry, we found that ␥-adducin interacts with the NCC transporter. ␥-Adducin colocalized with NCC to the distal convoluted tubule.22 Na ϩ uptake experiments in the Xenopus laevis oocyte showed that ␥-adducin stimulated NCC activity in a dose-dependent manner, an effect that occurred upstream from With No Lysine (WNK) 4 kinase. The binding site of ␥-adducin mapped to the N terminus of NCC and encompassed three previously reported phosphorylation sites. Supporting this site of interaction, competition with the N-terminal domain of NCC abolished the stimulatory effect of ␥-adducin on the transporter. ␥-Adducin failed to increase NCC activity when these phosphorylation sites were constitutively inactive or active. In addition, ␥-adducin bound only to the dephosphorylated N terminus of NCC. Taken together, our observations suggest that ␥-adducin dynamically regulates NCC, likely by amending the phosphorylation state, and consequently the activity, of the transporter. These data suggest that ␥-adducin may influence BP homeostasis by modulating renal NaCl transport.

Highlights d PBMCs of COVID-19 patients show increased responses to Toll-like receptor ligands d Trained immunity is modeled in vitro using Candida-trained PBMCs d Hydroxychloroquine inhibits changes in lipidome and histone modifications d Hydroxychloroquine dampens the trained response to interferons and viral stimuli