Benson, T. | Search bioRxiv

bioRxiv2024

Attenuation of Atherosclerosis with PAR4 Deficiency: Differential Platelet Outcomes in apoE-/- vs. Ldlr-/- Mice

ObjectiveCardiovascular disease (CVD) is a significant burden globally and, despite current therapeutics, remains the leading cause of death. Platelet inhibitors are of interest in CVD treatment to reduce thrombus formation post-plaque rupture as well their contribution to inflammation throughout the progression of atherosclerosis. Protease activated receptor 4 (PAR4) is a receptor highly expressed by platelets, strongly activated by thrombin, and plays a vital role in platelet activation and aggregation. However, the role of PAR4 Approach and ResultsMice on a low-density lipoprotein receptor-deficient (Ldlr-/-) background were bred with Par4 deficient (Par4-/-) mice to create Ldlr-/-/Par4+/+ and Ldlr-/-/Par4-/- cousin lines. Mice were fed high fat (42%) and cholesterol (0.2%) Western diet for 12 weeks for all studies. Bone marrow transplant (BMT) studies were conducted by irradiating Ldlr-/-/Par4+/+ and Ldlr-/- /Par4-/- mice with 550 rads (2x, 4 hours apart) and then repopulated with Par4+/+ or Par4-/- bone marrow. To determine if the effects of thrombin were mediated solely by PAR4, the thrombin inhibitor dabigatran was added to the Western diet. Ldlr-/-/Par4-/- given dabigatran did not further decrease their atherosclerotic burden. Differences between apolipoprotein E deficient (apoE-/-) and Ldlr-/- platelets were assessed for changes in reactivity. We observed higher PAR4 abundance in arteries with atherosclerosis in human and mice versus healthy controls. PAR4 deficiency attenuated atherosclerosis in the aortic sinus and root versus proficient controls. BMT studies demonstrated this effect was due to hematopoietic cells, most likely platelets. PAR4 appeared to be acting independent of PAR1, as there werer no changes with addition of dabigatran to PAR4 deficient mice. apoE-/- platelets are hyperreactive compared to Ldlr-/- platelets. ConclusionsHematopoietic-derived PAR4, most likely platelets, plays a vital role in the development and progression of atherosclerosis. Specific targeting of PAR4 may be a potential therapeutic target for CVD. HighlightsO_LIDeficiency of protease-activated receptor 4 attenuates the development of diet-induced atherosclerosis in a Ldlr-/- mouse model. C_LIO_LIPAR4 deficiency in hematopoietic cells is atheroprotective. C_LIO_LIPAR4 deficiency accounts for the majority of thrombin-induced atherosclerosis in a Ldlr-/- mouse model. C_LIO_LIThe examination of platelet-specific proteins and platelet activation should be carefully considered before using the apoE-/- or Ldlr-/- mouse models of atherosclerosis. C_LI

pathology↗

bioRxiv2023

Platelet extracellular vesicles and their mitochondrial content significantly improve survival and cytokine levels when transfused into mice with sepsis or H1N1 infections

BACKGROUNDMitochondrial transplantation has recently gained prominence as a novel technique primarily focused on addressing ischemiareperfusion injuries and rare mitochondrial mutation diseases. Platelets, abundant in the bloodstream, play a crucial role in immune function. Upon activation, platelets release mitochondria encapsulated within extracellular vesicles, here referred to as "mitlets". These mitlets exhibit a preference for being internalized by immune cells circulating in the bloodstream, enhancing their cellular energetics. Herein, we hypothesized that the transplantation of mitlets between young animals and aged animals may exert a significant influence on the progression of infectious diseases. STUDY DESIGN AND METHODSIn this study, murine models of Influenza H1N1 infection and sepsis were employed to investigate disease dynamics. Specifically, mitlets isolated from young and healthy mice were transplanted into cohorts of mice of the same age afflicted by H1N1 infection, or into aged mice subjected to polymicrobial infection and sepsis. Survival outcomes and the quantification of cytokine levels were assessed across experimental groups to elucidate the potential therapeutic effects of mitlet transplantation. RESULTSIn the matched-age H1N1 infection model, as predicted, mitlet transplantation did not yield a statistically significant improvement in survival, although it did show a trend towards a reduction in the circulating inflammatory cytokine burden. In the young-to-old sepsis model, the transplantation of mitlets was associated with a significant enhancement in survival rates and a substantial reduction in bacterial loads and circulating cytokine levels. DISCUSSIONOur findings suggest that mitochondrial transplantation may constitute a safe and promising avenue for enhancing the immune systems capacity to counter infectious threats. This pilot investigation sets the stage for further exploration. It is plausible that in the future, immune senescence resulting from diminished mitochondrial energy production could be ameliorated through such transplantation interventions. As a consequence, this approach holds substantial potential as a novel immunotherapeutic strategy for the management of infectious diseases.

molecular biology↗