High factor VIII concentrations interfere with glycoprotein VI-mediated platelet activation in vitro

BACKGROUND

The recruitment of activated factor VIII (FVIII) at the surface of activated platelets is a key step toward the burst of thrombin and fibrin generation during thrombus formation at the site of vascular injury. It involves binding to phosphatidylserine and, possibly, to fibrin-bound αIIbβ3. Seminal work had shown the binding of FVIII to resting platelets, yet without a clear understanding of a putative physiological relevance.

OBJECTIVES

To characterize the effects of FVIII-platelet interaction and its potential modulation of platelet function.

METHODS

FVIII was incubated with washed platelets. The effects on platelet activation (spontaneously or triggered by collagen and thrombin) were studied by flow cytometry and light transmission aggregometry. We explored the involvement of downstream pathways by studying phosphorylation profiles (Western blot). The FVIII-glycoprotein (GP) VI interaction was investigated by ELISA, confocal microscopy, and proximity ligation assay.

RESULTS

FVIII bound to the surface of resting and activated platelets in a dose-dependent manner. FVIII at supraphysiological concentrations did not induce platelet activation but rather specifically inhibited collagen-induced platelet aggregation and altered glycoprotein VI (GPVI)-dependent phosphorylation. FVIII, freed of its chaperone protein von Willebrand factor (VWF), interacted in close proximity with GPVI at the platelet surface.

CONCLUSION

We showed that VWF-free FVIII binding to, or close to, GPVI modulates platelet activation in vitro. This may represent an uncharacterized negative feedback loop to control overt platelet activation. Whether locally activated FVIII concentrations achieved during platelet accumulation and thrombus formation at the site of vascular injury in vivo are compatible with such a function remains to be determined.

Cholesterol transport and beyond: Illuminating the versatile functions of HDL apolipoproteins through structural insights and functional implications

High-density lipoproteins (HDLs) play a vital role in lipid metabolism and cardiovascular health, as they are intricately involved in cholesterol transport and inflammation modulation. The proteome of HDL particles is indeed complex and distinct from other components in the bloodstream. Proteomics studies have identified nearly 285 different proteins associated with HDL; however, this review focuses more on the 15 or so traditionally named "apo" lipoproteins. Important lipid metabolizing enzymes closely working with the apolipoproteins are also discussed. Apolipoproteins stand out for their integral role in HDL stability, structure, function, and metabolism. The unique structure and functions of each apolipoprotein influence important processes such as inflammation regulation and lipid metabolism. These interactions also shape the stability and performance of HDL particles. HDLs apolipoproteins have multifaceted roles beyond cardiovascular diseases (CVDs) and are involved in various physiological processes and disease states. Therefore, a detailed exploration of these apolipoproteins can offer valuable insights into potential diagnostic markers and therapeutic targets. This comprehensive review article aims to provide an in-depth understanding of HDL apolipoproteins, highlighting their distinct structures, functions, and contributions to various physiological processes. Exploiting this knowledge holds great potential for improving HDL function, enhancing cholesterol efflux, and modulating inflammatory processes, ultimately benefiting individuals by limiting the risks associated with CVDs and other inflammation-based pathologies. Understanding the nature of all 15 apolipoproteins expands our knowledge of HDL metabolism, sheds light on their pathological implications, and paves the way for advancements in the diagnosis, prevention, and treatment of lipid and inflammatory-related disorders.

A Commentary on the Development and Validation of novel automatable assay for cholesterol efflux capacity

The determination of functionality or quality of HDL is assuming a central stage in the prediction of cardiovascular diseases (CVD). To assess HDL quality, several attempts have been made to develop an automated, cost-effective CEC system with few operational steps that might be used in clinical settings for large throughput testing. The work of Dr. Ohkawa and co-workers seems to address this issue and provide a solution for the same (Bioscience Reports (2023) 43 BSR20221519, https://doi.org/10.1042/BSR20221519). Earlier work from the author's lab utilized a radioisotope and cell-free CEC assay known as the immobilized liposome-bound gel beads (ILGs) method. However, this assay required a centrifugation step to separate the cells and was not suitable for automation. To overcome these limitations, two very important changes were made (i) magnetic beads were used instead of gel beads which allowed them to avoid the centrifugation process that would allow ease of setting up an autonomous analyzer; (ii) porous magnetic beads were coated with liposomes containing fluorescently tagged cholesterol instead radiolabeled cholesterol. These two changes can be considered not only significant but also novel as they were highly suitable for CEC testing. The authors reported the successful development of a simple Immobilized liposome-based magnetic beads (ILM) automated system to measure CEC which provided both consistent performance and satisfactory correlation with the other methods.  Thus, we feel this study will open newer avenues for measuring the quality of HDL in addition to the quantity of HDL-cholesterol in clinical settings in a more robust way.

Delineating the impact of pathogenic mutations on the conformational dynamics of HDL's vital protein ApoA1: a combined computational and molecular dynamic simulation approach

Apolipoprotein A1 (ApoA1), is the important component of high-density lipoproteins (HDL), that has key role in HDL biogenesis, cholesterol trafficking, and reverse cholesterol transport (RCT). Non-synonymous Single Nucleotide Polymorphisms (nsSNPs) in ApoA1 have been linked to cardiovascular diseases and amyloidosis as they alter the protein's native structure and function. Therefore in this study, we attempted to understand the molecular pathogenicity profile of nsSNPs of ApoA1 using various computational approaches. We used state-of-the-art computational methods to thoroughly investigate the 295 ApoA1 nsSNPs at sequence and structural levels. Seven nsSNPs (L13R, L84R, L84P, L99P, R173P, L187P, and L238P) out of 295 were classified as the most deleterious and destabilizing. In order to estimate the effect of such destabilizing mutations on the protein conformation, all-atom molecular dynamics simulations (MDS) of ApoA1 wild-type (WT), L99P and R173P for 100 ns, was carried out using GROMACS 5.0.1 package. The MD simulation investigation revealed significant structural alterations in L99P and R173P. In addition, they had changed principal component analysis and electrostatic surface potential, decreased structural compactness, and intramolecular hydrogen bonds, which supported the rationale underpinning ApoA1 dysfunction with such mutations. This work sheds light on ApoA1 dysfunction due to single amino acid alterations, and offers new insight into the molecular basis of ApoA1-related diseases progression.Communicated by Ramaswamy H. Sarma.

Leveraging knowledge of HDLs major protein ApoA1: Structure, function, mutations, and potential therapeutics

Apolipoprotein A1 (ApoA1) is a member of the Apolipoprotein family of proteins. It's a vital protein that helps in the production of high-density lipoprotein (HDL) particles, which are crucial for reverse cholesterol transport (RCT). It also has anti-inflammatory, anti-atherogenic, anti-apoptotic, and anti-thrombotic properties. These functions interact to give HDL particles their cardioprotective characteristics. ApoA1 has recently been investigated for its potential role in atherosclerosis, diabetes, neurological diseases, cancer, and certain infectious diseases. Since ApoA1's discovery, numerous mutations have been reported that affect its structural integrity and alter its function. Hence these insights have led to the development of clinically relevant peptides and synthetic reconstituted HDL (rHDL) that mimics the function of ApoA1. As a result, this review has aimed to provide an organized explanation of our understanding of the ApoA1 protein structure and its role in various essential pathways. Furthermore, we have comprehensively reviewed the important ApoA1 mutations (24 mutations) that are reported to be involved in various diseases. Finally, we've focused on the therapeutic potentials of some of the beneficial mutations, small peptides, and synthetic rHDL that are currently being researched or developed, since these will aid in the development of novel therapeutics in the future.