GRK2–YAP Signaling in Pulmonary Arterial Hypertension Development
Pulmonary arterial hypertension (PAH) is a severe and progressive disease characterized by increased pulmonary vascular resistance (PVR), leading to right heart failure and premature death. The pathogenesis of PAH involves sustained vasoconstriction, abnormal vascular remodeling, endothelial dysfunction, and activation of fibroblasts and smooth muscle cells (SMCs). Despite advancements in treatment targeting key signaling pathways, the long-term benefits of current therapies remain uncertain due to incomplete understanding of PAH pathobiology. This study explores the role of G protein-coupled receptor kinase 2 (GRK2) and its interaction with Yes-associated protein (YAP) in the development of PAH, providing new insights into potential therapeutic targets.
GRK2 and PAH: A Critical Link
GRK2, a member of the G protein-coupled receptor kinase family, is known for its role in regulating GPCR signaling. It is involved in various cardiovascular diseases, including heart failure, atherosclerosis, and inflammatory diseases. However, its role in PAH has not been fully elucidated. This study demonstrates that GRK2 expression is significantly upregulated in the pulmonary arteries of PAH patients and in lung tissues of mice with hypoxia-induced PAH. The increased GRK2 levels correlate with disease severity, suggesting a critical role in PAH pathogenesis.
Experimental Models and Methods
To investigate the role of GRK2 in PAH, the study utilized several experimental models. Human lung tissues from healthy donors and PAH patients were analyzed for GRK2 expression. In mice, PAH was induced by chronic hypoxia combined with SU5416 injection (cHx/SU). GRK2 levels were measured in pulmonary arteries and pulmonary arterial smooth muscle cells (PASMCs) using Western blotting and immunofluorescence staining. The proliferation and migration of PASMCs were assessed through wound-healing assays, MTT assays, and EdU staining. Additionally, the interaction between GRK2 and YAP was examined using immunoprecipitation assays.
GRK2 Upregulation in PAH
The study found that GRK2 protein levels were significantly higher in the pulmonary arteries of PAH patients compared to healthy donors. Similarly, GRK2 expression was elevated in lung tissues of mice with hypoxia-induced PAH. In vitro experiments with human PASMCs exposed to hypoxia also showed a time-dependent increase in GRK2 protein levels. These findings indicate that GRK2 upregulation is a consistent feature in PAH, both in humans and animal models.
GRK2 Downregulation Ameliorates PAH
To determine the functional significance of GRK2 in PAH, the study employed GRK2 knockdown in mice using adeno-associated virus (AAV) carrying GRK2 short hairpin RNA (shRNA). GRK2 downregulation significantly reduced right ventricular systolic pressure (RVSP) and right ventricle hypertrophy index (RVHI) in hypoxic mice. Pulmonary angiography revealed improved vascular patency, and histological analysis showed reduced muscularization and wall thickness in small pulmonary arteries. These results suggest that GRK2 downregulation attenuates hypoxia-induced PAH by reducing pulmonary vascular remodeling.
GRK2 Overexpression Exacerbates PAH
Conversely, smooth muscle cell-specific GRK2 overexpression in mice exacerbated hypoxia-induced PAH. GRK2 overexpression led to increased RVSP and RVHI, along with more severe small vessel occlusion and muscularization. The mRNA levels of genes involved in vascular remodeling, such as SM22α, SMMHC, MCP-1, MMP2, MMP9, CTGF, Collagen I, Collagen III, and Vimentin, were significantly elevated in GRK2-overexpressing mice. These findings highlight the detrimental effects of GRK2 overexpression on PAH development.
SMC-Specific GRK2 Knockout Mice Resist PAH
To further confirm the role of GRK2 in PAH, the study generated smooth muscle cell-specific GRK2 knockout mice (Grk2∆SM22). These mice exhibited resistance to hypoxia-induced PAH, with reduced RVSP, RVHI, and pulmonary vascular remodeling compared to wild-type mice. The mRNA levels of vascular remodeling genes were also lower in Grk2∆SM22 mice. These results provide strong evidence that GRK2 deletion in smooth muscle cells protects against PAH development.
GRK2 Promotes PASMCs Proliferation and Migration
The proliferation and migration of PASMCs are key factors in vascular remodeling during PAH. The study found that GRK2 knockdown significantly inhibited hypoxia-induced PASMCs proliferation and migration, while GRK2 overexpression exacerbated these effects. Wound-healing assays, MTT assays, and EdU staining confirmed that GRK2 promotes PASMCs proliferation and migration, contributing to pulmonary vascular remodeling.
GRK2–YAP Signaling Pathway
The study identified the GRK2–YAP signaling pathway as a critical mechanism in PAH development. YAP, a downstream effector of the HIPPO pathway, is involved in cell proliferation, migration, and survival. The study found that GRK2 promotes YAP expression and nuclear translocation in PASMCs, leading to excessive proliferation and migration. Hypoxia-induced upregulation of GRK2 resulted in increased YAP protein levels and AKT-Ser473 phosphorylation. GRK2 knockdown reduced YAP expression and nuclear translocation, while GRK2 overexpression had the opposite effect. These findings suggest that GRK2 regulates YAP activity, contributing to PAH pathogenesis.
Hypoxia Inhibits GRK2 Ubiquitination Degradation
The study also explored the mechanisms underlying GRK2 upregulation in hypoxia. Hypoxia inhibited the ubiquitination degradation of GRK2, leading to increased protein stability. GRK2 phosphorylation at Tyr86 was reduced under hypoxic conditions, suggesting that hypoxia stabilizes GRK2 by inhibiting its phosphorylation and subsequent ubiquitination. This mechanism provides insight into how hypoxia upregulates GRK2 in PAH.
Conclusion
This study demonstrates that GRK2 plays a critical role in PAH development by promoting PASMCs proliferation and migration through the GRK2–YAP signaling pathway. GRK2 upregulation in PAH patients and hypoxia-induced PAH models correlates with disease severity. GRK2 downregulation or deletion attenuates PAH features, while GRK2 overexpression exacerbates them. The findings highlight the potential of GRK2 as a novel therapeutic target for PAH treatment. By targeting GRK2, it may be possible to reduce pulmonary vascular remodeling and improve outcomes for PAH patients.
doi.org/10.1097/CM9.0000000000002946
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