Platelet to Lymphocyte Ratio (PLR) As a Marker for Aortic Stenosis Development in a Mouse Model: Relationship to Platelet TGFβ1

Objective: Aortic stenosis (AS) is an age-related degenerative valvular disease that can lead to heart failure and sudden death. There is no biomarker for early detection of AS. However, an elevated neutrophil-to-lymphocyte ratio (NLR), reflective of systemic inflammation, is associated with higher mortality in cardiovascular disease, including AS and, recently, the platelet-to-lymphocyte ratio (PLR) was proposed as an additional inflammatory biomarker linked to AS. We have shown that platelet-derived TGF-β1 contributes to AS progression in LDLR^-/-ApoB^100/100 (LA100) mice, a model that simulates human AS valve pathology. We now evaluate PLR, along with NLR and plasma TGF-β1 levels, as possible correlates of AS progression in this model.

Methods: PLR, NLR, and plasma TGF-β1 were measured in control C57Bl/6 mice and LA100 mice before AS development (2-3 months of age), at the point of moderate AS (10 months of age), and upon development of severe AS (22 months of age). LA100 mice with depletion of TGF-β1 in platelets (LA100-PF4CreTgfb1^flox/flox) and LA100 mice treated with low dose galunisertib, an inhibitor of the TGFβ-I receptor kinase, were similarly assessed at 22 months of age.

Results: PLR was significantly higher in mice with severe and moderate AS vs. control LA100 mice (192 ± 49, p<0.01, 249 ± 63 vs. 503 ±139, p=0.009, respectively). NLR was also increased in LA100 vs. control mice (n=12; p<0.01). Total TGF-β1 plasma levels were significantly higher in aged LA100 mice (n=21; 22 months) than in age-matched control C57Bl/6 mice (22 months; p<0.0001). Plasma TGF-β1 levels correlated with both PLR (R=0.26; p=0.020) and NLR (R=0.6, p=<0.001) in LA100 mice, but not in C57Bl/6 mice. Increased PLR and NLR negatively correlated with decreased fractional valve opening, a measure of AS progression, in LA100 mice (p<0.05 for both). To assess the role of platelet-derived TGF-β1 in influencing PLR, we utilized LA100 mice deficient in platelet TGF-β1 (LA100-PF4CreTgfb1^flox/flox). They were partially protected from developing AS at 22 months, despite having higher PLR than control LA100 mice at 22 months of age (735 ± 245 vs. 503 ± 139). Moreover, treatment of LA100 mice with low dose galunisertib, was associated with a higher PLR (192 ± 49 vs. 671 ± 290; p<0.05), but a reduced NLR (p=0.03), compared to vehicle-treated control mice.

Conclusions: 1. Increased PLR, NLR, and plasma TGF-β1 levels are surrogate markers of AS progression in a robust mouse model that simulates human AS pathology. 2. Demonstration of higher PLR in mice with altered TGF-β1, via either platelet-specific TGF-β1 depletion or treatment with galunisertib, along with finding a lower NLR in the latter, warrants further study into the mechanism by which PLR may serve as a prognostic marker for AS progression apart from inflammation.

No relevant conflicts of interest to declare.