N-Glycosylation is Required for Secretion-Competent Human Plasma Phospholipid Transfer Protein

An engineered miniACE2 protein secreted by mesenchymal stromal cells effectively neutralizes multiple SARS-CoV- 2 variants in vitro

SARS-CoV- 2 continues to evolve, producing novel Omicron subvariants through recombinant lineages that acquire new mutations, undermining existing antiviral strategies. The viral fitness and adaptive potential of SARS-CoV- 2 present significant challenges to emergency treatments, particularly monoclonal antibodies, which demonstrate reduced efficacy with the emergence of each new variant. Consequently, immunocompromised individuals, who are more susceptible to severe manifestations of COVID- 19 and face heightened risks of critical complications and mortality, remain vulnerable in the absence of effective emergency treatments. To develop translational approaches that can benefit this at-risk population and establish broader therapeutic strategies applicable across variants, we previously designed and engineered in silico miniACE2 decoys (designated BP2, BP9, and BP11). These decoys demonstrated promising efficacy in neutralizing Omicron subvariants. In this study, we leveraged the therapeutic potential of mesenchymal stromal cells (MSCs) for tissue repair and immunomodulation in lung injuries and used these cells as a platform for the secretion of BP2. Our innovative assays, which were conducted with the BP2 protein secreted into the culture supernatant of BP2-MSCs, demonstrated the potential for neutralizing SARS-CoV- 2, including Omicron subvariants. The development of these advanced therapeutic platforms holds significant promise for scalability to effectively mitigate the impact of severe COVID- 19, contributing to broader and more resilient treatment strategies against the evolving landscape of SARS-CoV- 2 variants.

Impact of protein glycosylation on lipoprotein metabolism and atherosclerosis

Protein glycosylation is a post-translational modification consisting in the enzymatic attachment of carbohydrate chains to specific residues of the protein sequence. Several types of glycosylation have been described, with N-glycosylation and O-glycosylation being the most common types impacting on crucial biological processes, such as protein synthesis, trafficking, localization, and function. Genetic defects in genes involved in protein glycosylation may result in altered production and activity of several proteins, with a broad range of clinical manifestations, including dyslipidaemia and atherosclerosis. A large number of apolipoproteins, lipoprotein receptors, and other proteins involved in lipoprotein metabolism are glycosylated, and alterations in their glycosylation profile are associated with changes in their expression and/or function. Rare genetic diseases and population genetics have provided additional information linking protein glycosylation to the regulation of lipoprotein metabolism.

Impact of site-specific N-glycosylation on cellular secretion, activity and specific activity of the plasma phospholipid transfer protein

The plasma phospholipid transfer protein (PLTP) plays a key role in lipid and lipoprotein metabolism. It has six potential N-glycosylation sites. To study the impact of these sites on PLTP secretion and activity, six variants containing serine to alanine point mutations were prepared by site-directed mutagenesis and expressed in Chinese hamster ovary Flp-In cells. The apparent size of each of the six PLTP mutants was slightly less than that of wild type by Western blot, indicating that all six sites are glycosylated or utilized. The size of the carbohydrate at each N-glycosylation site ranged from 3.14 to 4.2kDa. The effect of site-specific N-glycosylation removal on PLTP secretion varied from a modest enhancement (15% and 60%), or essentially no effect, to a reduction in secretion (8%, 14% and 32%). Removal of N-glycosylation at any one of the six glycosylation sites resulted in a significant 35-78% decrease in PLTP activity, and a significant 29-80% decrease in PLTP specific activity compared to wild type. These data indicate that although no single N-linked carbohydrate chain is a requirement for secretion or activity, the removal of the carbohydrate chains had a quantitative impact on cellular secretion of PLTP and its phospholipid transfer activity.

Effects of aging, body mass index, plasma lipid profiles, and smoking on human plasma N-glycans

Protein glycosylation affects nearly all molecular interactions at the cell surface and in the intercellular space. Many of the physiological variations which are part of homeostatic mechanisms influence glycosylation. However, a comprehensive overview of changes in glycosylation caused by aging and common lifestyle parameters is still lacking. After analyzing N-glycans in the plasma of 1914 individuals from the Croatian islands of Vis and Korcula, we performed a comprehensive analysis of the dependence of different glycosylation features (position of fucose, level of galactosylation, sialylation and branching) on aging, smoking, body fat and plasma lipid status. A number of statistically significant associations were observed. Glycosylation changes with aging were especially evident in females, mostly in association with the transition from pre-menopausal to post-menopausal age. Levels of core-fucosylated, non-galactosylated, digalactosylated and disialylated biantennary glycans were shown to be mainly age dependent, but the level of branching and higher levels of galactosylation were found to correlate with lipid status. For the majority of glycans which we analyzed, all examined parameters explained up to 5% of the variance. The only notable exception were non-galactosylated glycans where 20% of the variance was explained mostly by age and blood pressure. In general, only a small fraction of the variability in glycan levels observed in a population was explained by age and other measured parameters, indicating that even in the absence of a genetic template, glycan levels are mostly determined by genetic background and/or specific pathophysiological processes.