Healing through the lens of immunothrombosis: Biology-inspired, evolution-tailored, and human-engineered biomimetic therapies

Biochemical and biomechanical characterization of an autologous protein-based fibrin sealant for regenerative medicine

Accidental events or surgical procedures usually lead to tissue injury. Fibrin sealants have proven to optimize the healing process but have some drawbacks due to their allogeneic nature. Autologous fibrin sealants present several advantages. The aim of this study is to evaluate the performance of a new autologous fibrin sealant based on Endoret®PRGF® technology (E-sealant). One of the most widely used commercial fibrin sealants (Tisseel®) was included as comparative Control. E-sealant´s hematological and biological properties were characterized. The coagulation kinetics and the microstructure were compared. Their rheological profile and biomechanical behavior were also recorded. Finally, the swelling/shrinkage capacity and the enzymatic degradation of adhesives were determined. E-sealant presented a moderate platelet concentration and physiological levels of fibrinogen and thrombin. It clotted 30 s after activation. The microstructure of E-sealant showed a homogeneous fibrillar scaffold with numerous and scattered platelet aggregates. In contrast, Control presented absence of blood cells and amorphous protein deposits. Although in different order of magnitude, both adhesives had similar rheological profiles and viscoelasticity. Control showed a higher hardness but both adhesives presented a pseudoplastic hydrogel nature with a shear thinning behavior. Regarding their adhesiveness, E-sealant presented a higher tensile strength before cohesive failure but their elastic stretching capacity and maximum elongation was similar. While E-sealant presented a significant shrinkage process, Control showed a slight swelling over time. In addition, E-sealant presented a high enzymatic resorption rate, while Control showed to withstand the biodegradation process in a significant way. E-sealant presents optimal biochemical and biomechanical properties suitable for its use as a fibrin sealant with regenerative purposes.

An evolutionary history of F12 gene: Emergence, loss, and vulnerability with the environment as a driver

In the context of macroevolutionary transitions, environmental changes prompted vertebrates already bearing genetic variations to undergo gradual adaptations resulting in profound anatomical, physiological, and behavioral adaptations. The emergence of new genes led to the genetic variation essential in metazoan evolution, just as was gene loss, both sources of genetic variation resulting in adaptive phenotypic diversity. In this context, F12-coding protein with defense and hemostatic roles emerged some 425 Mya, and it might have contributed in aquatic vertebrates to the transition from water-to-land. Conversely, the F12 loss in marine, air-breathing mammals like cetaceans has been associated with phenotypic adaptations in some terrestrial mammals in their transition to aquatic lifestyle. More recently, the advent of technological innovations in western lifestyle with blood-contacting devices and harmful environmental nanoparticles, has unfolded new roles of FXII. Environment operates as either a positive or a relaxed selective pressure on genes, and consequently genes are selected or lost. FXII, an old dog facing environmental novelties can learn new tricks and teach us new therapeutic avenues.

Molecular basis of clot retraction and its role in wound healing

Clot retraction is important for the prevention of bleeding, in the manifestations of thrombosis and for tissue repair. The molecular mechanisms behind clot formation are complex. Platelet involvement begins with adhesion at sites of vessel injury followed by platelet aggregation, thrombin generation and fibrin production. Other blood cells incorporate into a fibrin mesh that is consolidated by FXIIIa-mediated crosslinking and platelet contractile activity. The latter results in the asymmetric redistribution of erythrocytes into a tighter central mass providing the clot with stability and resistance to fibrinolysis. Integrin αIIbβ3 on platelets is the key player in these events, bridging fibrin and the platelet cytoskeleton. Glycoprotein VI participates in thrombus formation but not in the retraction. Rheological and environmental factors influence clot construction with retraction driven by the platelet cytoskeleton with actomyosin acting as the motor. Activated platelets provide procoagulant activity stimulating thrombin generation together with the release of a plethora of biologically active proteins and substances from storage pools; many form chemotactic gradients within the fibrin or the underlying matrix. Also released are newly synthesized metabolites and lipid-rich vesicles that circulate within the vasculature and mimic platelet functions. Platelets and their released elements play key roles in wound healing. This includes promoting stem cell and mesenchymal stromal cell recruitment, fibroblast and endothelial cell migration, angiogenesis and matrix formation. These properties have led to the use of autologous clots in therapies designed to accelerate tissue repair while offering the potential for genetic manipulation in both inherited and acquired diseases.

Evolutionary Insight into Immunothrombosis as a Healing Mechanism

Both invertebrates and vertebrates possess a cluster of immediate and local wound-sealing, pathogen-killing, and tissue healing responses known as immunoclotting and immunothrombosis, respectively, to cope with two life-threatening emergencies, namely, bleeding and microbial invasion. Despite their convergence in function, immunoclotting and immunothrombosis are deployed by different blood cells and intravascular multidomain proteins. In vertebrates, these proteins share some domains with intrinsic chemical affinities useful in generating cooperative networks such as pathogen and damage pattern recognition molecules. Moreover, many of the proteins involved in coagulation and fibrinolysis in humans are multifunctional molecules playing roles in other processes from inflammation to healing and beyond. In our modern society, however, the interaction of activated intravascular allosteric proteins with one another and with blood cells entails vulnerabilities posing a biological paradox: intravascular proteins that locally operate as tissue repair enhancers can nevertheless generate pathogenic processes by acting systemically. In this manuscript, we contextualize and frame the coagulation system and hemostasis through an evolutionary time scale, illustrating their role as dual players in the defense against exsanguination and pathogens while significantly influencing wound healing.