The endogenous antimicrobial cathelicidin LL37 induces platelet activation and augments thrombus formation

Abstract

Platelet-associated complications including thrombosis, thrombocytopenia, and hemorrhage are commonly observed during various inflammatory diseases such as sepsis, inflammatory bowel disease, and psoriasis. Despite the reported evidence on numerous mechanisms/molecules that may contribute to the dysfunction of platelets, the primary mechanisms that underpin platelet-associated complications during inflammatory diseases are not fully established. Here, we report the discovery of formyl peptide receptor 2, FPR2/ALX, in platelets and its primary role in the development of platelet-associated complications via ligation with its ligand, LL37. LL37 acts as a powerful endogenous antimicrobial peptide, but it also regulates innate immune responses. We demonstrate the impact of LL37 in the modulation of platelet reactivity, hemostasis, and thrombosis. LL37 activates a range of platelet functions, enhances thrombus formation, and shortens the tail bleeding time in mice. By utilizing a pharmacological inhibitor and Fpr2/3 (an ortholog of human FPR2/ALX)–deficient mice, the functional dependence of LL37 on FPR2/ALX was determined. Because the level of LL37 is increased in numerous inflammatory diseases, these results point toward a critical role for LL37 and FPR2/ALX in the development of platelet-related complications in such diseases. Hence, a better understanding of the clinical relevance of LL37 and FPR2/ALX in diverse pathophysiological settings will pave the way for the development of improved therapeutic strategies for a range of thromboinflammatory diseases.

The formyl peptide fMLF primes platelet activation and augments thrombus formation

“…Notably, the activation of platelets using 1 μg/mL cross‐linked collagen‐related peptide (CRP‐XL) increased the level of FPR1 on the surface as determined by flow cytometry (Figure AI), while the level of proteins identified by immunoblots remained unchanged (Figure AII). These data confirm the presence of FPR1 in platelets, possibly in granules or the open canalicular system or both, and their increase on the surface upon activation similar to FPR2/ALX …”

“…Recently, we have reported the presence of FPR2/ALX in human and its orthologue, Fpr2/3 in human platelets . Similarly, the expression of FPR1 in human platelets at protein level, and in megakaryocytes at transcript level, has been previously reported .…”

“…Despite numerous reports on the immune functions of FPR1, its impact upon ligation with fMLF on the modulation of hemostasis and thrombosis remains uncharacterized. Recently, we have reported the presence of FPR2/ALX in human platelets and its significance in the regulation of LL37‐induced platelet activation and thrombus formation . Here, we report the ability of fMLF to prime platelets and augment thrombus formation, and the significance of FPR1 in the regulation of platelet function in the presence and absence of fMLF.…”

A cathelicidin-related antimicrobial peptide suppresses cardiac hypertrophy induced by pressure overload by regulating IGFR1/PI3K/AKT and TLR9/AMPKα

“…The antimicrobial peptide cathelicidin (CRAMP in mouse/rat, LL-37 in human) is expressed in many immune cells, such as epithelial cells, and genital cells 10 . CRAMP was initially reported as an immunomodulatory peptide that functions in many autoimmune diseases, such as psoriasis 11 , systemic lupus erythematous 12 , arthritis 13 , atherosclerosis 14 , and type 1 diabetes 15 . Recent studies have identified a role of CRAMP in cardiovascular disease.…”

Antimicrobial action and clotting time of thin, hydrated poly(vinyl alcohol)/cellulose acetate films functionalized with LL37 for prospective wound‐healing applications

“…In an open wound, the LL37 contained within the granules of platelets is released to the local environment to support microbial clearance, activate the inflammatory response and modulate thrombosis and hemostasis. Reports have shown LL37 to promote thrombus formation, reduce the clotting time (in mice tails) and, generally, accelerate healing . The mechanisms by which LL37 intervenes in the coagulation cascade are still under investigation; however, it is clear that its presence within neutrophils, monocytes, and platelets to be extremely important during this process.…”