Background and Aims:
The co-stimulatory CD40-CD40L axis is a major driver of atherosclerosis. Both platelets and T-cells express CD40L, but its cell-specific role in atherosclerosis remains unresolved. We hypothesize both a platelet- and T cell-specific CD40L deficiency may attenuate maladaptive inflammatory and thrombotic responses while reducing plaque progression.

Methods:
We generated mice carrying a mutated allele of the CD40L gene flanked by loxP-sites sensitive to cre-mediated inactivation. Mice were backcrossed to Apoe-/- mice expressing Cre specifically in platelets (Pf4Cre) or T cells (Cd4Cre) to generate hypercholesterolemic Cd40lgfl/fl-PF4cre-Apoe-/- and Cd40lgfl/fl-Cd4cre-Apoe-/- mice. First, Cd40lgfl/fl-PF4cre platelets were phenotyped via whole blood perfusion microspot experiments. Additionally, atherosclerotic lesion progression from both models was investigated following a 28 week chow diet. Finally, we investigated neointima formation using a wire injury model as well as immune cell activation via histology and flow cytometry.

Results:
In Cd40lgfl/fl-PF4cre platelets, we observed significant reductions in platelet deposition (brightfield – p=0.036 and DiOC6-stained – p=0.014) as well as fibrinogen content (p=0.018). Although no effect on plaque lesion size was observed in Cd40lgfl/fl-PF4cre-Apoe-/- mice, significant reductions in aortic root plaque size (p=0.013) were observed in Cd40lgfl/fl-Cd4cre-Apoe-/- mice when compared to their WT littermates. However, Cd40lgfl/fl-PF4cre mice showed a significant reduction in neointima volume (p=0.039). No differences were observed in cholesterol levels, body weight, or leukocyte counts.

Conclusions:
Our data demonstrates differing roles for platelet and T cell CD40L in atherosclerosis. Interestingly platelet CD40L does not mediate atherogenesis, but plays a crucial role in neointima growth after injury, which suggests platelet CD40L plays a key role in atherothrombosis.

04 - PLATELET CD40L DOES NOT AFFECT ATHEROGENESIS, BUT IS A KEY PLAYER IN ATHEROTHROMBOSIS