Analysis of the functional mechanisms and signaling pathways of RSPO3 in vascular development and angiogenesis

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This article focuses on the molecular characteristics and biological functions of RSPO3 as a core member of the R-spondin family, systematically elucidating its dual mechanisms in regulating angiogenesis through both the canonical Wnt/β-catenin pathway and the non-canonical Gαi1/3-Akt-mTOR pathway.

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Functional Mechanisms and Signaling Pathways of RSPO3 in Vascular Development and Angiogenesis

Overview
This article focuses on the molecular characteristics and biological functions of RSPO3 as a core member of the R-spondin family, systematically elucidating its dual regulatory mechanisms in angiogenesis through the canonical Wnt/β-catenin pathway and the non-canonical Gαi1/3-Akt-mTOR pathway.

I. Molecular Characteristics and Family Positioning of RSPO3

The R-spondin family consists of four secreted glycoproteins, RSPO1 to RSPO4, which are key signaling molecules in embryonic development and tissue homeostasis. RSPO3 is one of the most extensively studied members of this family. Its protein structure includes four characteristic functional domains: an N-terminal signal peptide for secretion, two cysteine-rich furin-like domains (FU1 and FU2) responsible for binding to receptors LGR4/5/6, a thrombospondin type 1 domain (TSP1), and a C-terminal basic region. The full-length RSPO3 protein comprises approximately 272 amino acid residues with a molecular weight of about 30–35 kDa.

In terms of tissue distribution, RSPO3 is expressed in the embryonic vascular system and endothelial cells of adult organs such as the heart, lungs, and kidneys. Its expression levels are closely associated with the development and remodeling states of vascular beds.

II. RSPO3 Regulates Angiogenesis via the Canonical Wnt/β-catenin Pathway

The most well-known molecular function of RSPO3 is its enhancement of Wnt signaling through the ligand LRP6. In the canonical Wnt pathway, RSPO3 binds to receptors LGR4/5/6 and leucine-rich repeat-containing G protein-coupled receptors (LGRs), promoting the clearance of E3 ubiquitin ligases RNF43 and ZNRF3, thereby relieving their inhibitory effects on Wnt receptors and amplifying Wnt/β-catenin signaling. Activated β-catenin translocates to the nucleus and binds to TCF/LEF transcription factors, driving the expression of downstream target genes, including vascular endothelial growth factor (VEGF). As a central regulator of angiogenesis, VEGF promotes endothelial cell proliferation, migration, and lumen formation, ultimately driving the formation of new blood vessels. Additionally, RSPO3 maintains cellular lineage balance during vascular development by inhibiting hematopoietic cell differentiation.

III. RSPO3 Regulates Angiogenesis via the Non-canonical Gαi1/3-Akt-mTOR Pathway

Although the Wnt/β-catenin pathway is a crucial mechanism for RSPO3-mediated angiogenesis, recent studies have revealed a novel molecular mechanism independent of canonical Wnt signaling. A 2022 study published in *Protein & Cell* first demonstrated the pivotal role of Gαi1/3 in RSPO3-induced angiogenesis.

Gαi proteins belong to the heterotrimeric G protein α-subunit family, traditionally believed to bind only to G protein-coupled receptors. The study found that upon RSPO3 stimulation, receptor LGR4 forms a signaling complex with Gαi1/3, recruiting the adaptor protein Gab1 to initiate the downstream Akt-mTOR signaling cascade. This regulatory pathway is entirely independent of the Wnt/β-catenin pathway: silencing Gαi1/3 does not affect active β-catenin accumulation, and knocking down β-catenin does not alter Gαi1/3 expression levels or Akt-mTOR pathway activation.

Functional validation showed that Gαi1/3 silencing significantly inhibited RSPO3-induced endothelial cell migration, invasion, proliferation, and in vitro vessel formation, while Gαi1/3 overexpression enhanced these responses. In vivo experiments demonstrated that endothelial cell-specific knockdown of Gαi1/3 in mice markedly suppressed RSPO3 overexpression-induced Akt-mTOR activation and retinal angiogenesis, whereas Gαi1/3 overexpression promoted retinal neovascularization.

IV. Synergistic Significance of RSPO3's Dual Signaling Pathways

The dual regulation of angiogenesis by RSPO3 through the Wnt/β-catenin-VEGF and Gαi1/3-Akt-mTOR pathways holds significant biological and translational implications. The Wnt/β-catenin pathway primarily regulates VEGF expression at the transcriptional level, providing key growth factor signals for angiogenesis as a long feedback mechanism. In contrast, the Gαi1/3-Akt-mTOR pathway directly drives angiogenesis by rapidly activating endothelial cell survival, proliferation, and migration effectors, serving as a rapid response mechanism. The temporal and spatial coordination of these two pathways enables RSPO3 to finely regulate different stages of vascular development.

This discovery also offers new therapeutic targets for angiogenesis-related diseases. In pathological neovascularization (e.g., tumor angiogenesis, diabetic retinopathy, age-related macular degeneration), selectively targeting the Gαi1/3 downstream signaling pathway may precisely inhibit pathological angiogenesis without disrupting Wnt/β-catenin-mediated tissue homeostasis.

V. Conclusion

As a core member of the R-spondin family, RSPO3 plays an irreplaceable role in vascular development and pathological angiogenesis through its dual regulation of angiogenesis via the canonical Wnt/β-catenin and non-canonical Gαi1/3-Akt-mTOR pathways. Recombinant human RSPO3 protein, as a vital tool for basic research and drug development, will continue to provide critical support for elucidating angiogenesis mechanisms and exploring therapeutic strategies for related diseases.

In RSPO3-related basic research and drug screening, high-quality recombinant human RSPO3 protein is essential for receptor binding analysis, signaling pathway exploration, and functional validation. To meet this research demand, Uni offers RSPO3 Protein, Human, suitable for applications such as RSPO3-LGR4/5/6 receptor binding analysis, investigation of Wnt/β-catenin and Gαi1/3-Akt-mTOR signaling pathways, and in vitro activity evaluation of anti-RSPO3 antibody drugs.

This article is reviewed and published by the technical expert team of UA

Disclaimer: This article partially utilizes artificial intelligence assistance in its creation. If any content involves copyright or intellectual property issues, please let us know and we promise to verify and remove it as soon as possible.

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