Distinct phenotypes induced by acute hypoxia and TGF-beta1 in human adult cardiac fibroblasts.
Publication Year:
2024
PubMed ID:
39329164
Funding Grants:
Public Summary:
This study examines how two key signals—low oxygen (hypoxia) and TGF-β1, both present after a heart attack—differently affect human cardiac fibroblasts, the cells that build scar tissue in the heart. Researchers exposed adult cardiac fibroblasts to either hypoxia or TGF-β1 and analyzed how their behavior and protein expression changed. They found that under hypoxia, fibroblasts activated HIF-1, a protein that helps cells adapt to low oxygen, and increased expression of VEGFA, which promotes blood vessel growth. However, hypoxia also reduced protein synthesis, including collagen production. In contrast, TGF-β1 strongly activated fibrotic pathways, pushing fibroblasts toward a myofibroblast state that produces more extracellular matrix. Both treatments slowed cell proliferation, but only TGF-β1 triggered a robust fibrotic response. Overall, the results show that while both signals influence fibroblast behavior, TGF-β1—not acute hypoxia—is the main driver of fibrosis after heart injury, offering insight into how post–heart attack scarring might be controlled therapeutically.
Scientific Abstract:
Myocardial infarction (MI) causes hypoxic injury to downstream myocardial tissue, which initiates a wound healing response that replaces injured myocardial tissue with a scar. Wound healing is a complex process that consists of multiple phases, in which many different stimuli induce cardiac fibroblasts to differentiate into myofibroblasts and deposit new matrix. While this process is necessary to replace necrotic tissue, excessive and unresolved fibrosis is common post-MI and correlated with heart failure. Therefore, defining how cardiac fibroblast phenotypes are distinctly regulated by stimuli that are prevalent in the post-MI microenvironment, such as hypoxia and transforming growth factor-beta (TGF-beta), is essential for understanding and ultimately mitigating pathological fibrosis. In this study, we acutely treated primary human adult cardiac fibroblasts with TGF-beta1 or hypoxia and then characterized their phenotype through immunofluorescence, quantitative RT-PCR, and proteomic analysis. We found that fibroblasts responded to low oxygen with increased localization of hypoxia inducible factor 1 (HIF-1) to the nuclei after 4h, which was followed by increased gene expression of vascular endothelial growth factor A (VEGFA), a known target of HIF-1, by 24h. Both TGF-beta1 and hypoxia inhibited proliferation after 24h. TGF-beta1 treatment also upregulated various fibrotic pathways. In contrast, hypoxia caused a reduction in several protein synthesis pathways, including collagen biosynthesis. Collectively, these data suggest that TGF-beta1, but not acute hypoxia, robustly induces the differentiation of human cardiac fibroblasts into myofibroblasts. Discerning the overlapping and distinctive outcomes of TGF-beta1 and hypoxia treatment is important for elucidating their roles in fibrotic remodeling post-MI and provides insight into potential therapeutic targets.