(721f) Elucidating TGF? and TNF? Crosstalk Mechanisms in Valve Interstitial Cells

Background

Calcific aortic valve disease (CAVD) is the most common valvular heart disease in developed countries and has increased 4.4-fold over the last 20 years [1]. There are no pharmaceutical treatments that delay or halt the progression of CAVD and current treatment options are restricted to valve replacement procedures with either mechanical or bioprosthetic heart valves. Mechanical valves restrict patients to lifelong anticoagulation therapy to prevent blood clot formation, while bioprosthetic valves have a limited lifespan due to structural degradation. Minimally invasive procedures like transcatheter aortic valve replacement (TAVR) are increasingly utilized, but concerns arise regarding long-term durability and freedom from structural valve degeneration [2]. There is a clear need for non-invasive, medication-based strategies to combat CAVD that avoid issues associated with valve replacement.

Valvular interstitial cells (VICs) are the main cell type residing in heart valves and are responsible for extracellular matrix maintenance and repair. VICs undergo phenotypic transitions from a quiescent phenotype (qVICs) that maintains normal valve physiology, an activated myofibroblast phenotype (aVICs) that regulates (patho-)physiological fibrotic responses, and an osteoblastic-like phenotype (oVICs) that contribute to calcification [3]. VIC phenotypic transitions are driven by several chemokines and growth factors including transforming growth factor β (TGFβ) and tumor necrosis factor α (TNFα) which are upregulated in end-stage disease [4]. TGFβ promotes the qVIC to aVIC transition and TNFα promotes the qVIC to oVIC transition. However, mutual inhibition between TGFβ and TNFα signaling pathways create regulatory motifs that could lead to bistability. Using a mechanistic systems biology framework, we seek to elucidate bistability mechanisms that contribute to complex crosstalk between TGFβ and TNFα signaling in VICs.

Methods

TGFβ and TNFα signaling pathways were modeled with a mechanistic framework that describes protein/gene synthesis, degradation, and interactions using mass action and Michaelis-Menten kinetic mechanisms. The model was parameterized by a combination of literature searches and parameter estimation with Western blotting and proteomics data of porcine VICs stimulated with TGFβ or TNFα. Simulations were carried out in the Julia language, with packages Catalyst.jl, DifferentialEquations.jl, and Optimization.jl extensively utilized for software implementation and analysis. This combined approach facilitated a comprehensive understanding of the dynamics underlying the response of VICs to TGFβ and TNFα stimulation, bridging theoretical predictions with experimental observations.

Results

Our model can exhibit bistability due to double-negative feedback loops caused by interactions between TNFα and TGFβ pathways as presented in Figure 1. If not accounted for, hypothetical drugs that inhibit TGFβ-driven fibrosis may exacerbate TNFα-driven calcification and vice versa.

Discussion

This study emphasizes the critical need for evaluating crosstalk mechanisms in computational drug target identification platforms. Future work will incorporate non-canonical signaling pathways, expanding the complexity of regulatory mechanisms underlying TNFα and TGFβ crosstalk. Additionally, we plan to extend the investigation to longer time frames, recognizing the pivotal role of receptor dynamics in governing cellular behaviors over extended periods.

References

[1] S. S. Martin et al., ‘2024 Heart Disease and Stroke Statistics: A Report of US and Global Data From the American Heart Association’, Circulation, vol. 149, no. 8, Feb. 2024, doi: 10.1161/CIR.0000000000001209.

[2] M. A. Rezvova, K. Y. Klyshnikov, A. A. Gritskevich, and E. A. Ovcharenko, ‘Polymeric Heart Valves Will Displace Mechanical and Tissue Heart Valves: A New Era for the Medical Devices’, IJMS, vol. 24, no. 4, p. 3963, Feb. 2023, doi: 10.3390/ijms24043963.

[3] A. C. Liu, V. R. Joag, and A. I. Gotlieb, ‘The Emerging Role of Valve Interstitial Cell Phenotypes in Regulating Heart Valve Pathobiology’, The American Journal of Pathology, vol. 171, no. 5, pp. 1407–1418, Nov. 2007, doi: 10.2353/ajpath.2007.070251.

[4] A. Galeone, D. Paparella, S. Colucci, M. Grano, and G. Brunetti, ‘The Role of TNF- α and TNF Superfamily Members in the Pathogenesis of Calcific Aortic Valvular Disease’, The Scientific World Journal, vol. 2013, pp. 1–10, 2013, doi: 10.1155/2013/875363.