The Role of BMP9-Induced SEMA3G in Pulmonary Vascular Stability

The progressive disease, pulmonary arterial hypertension (PAH), occurs when the pulmonary vasculature pathologically remodels and constricts, causing increased pulmonary arterial pressure eventually leading to right heart failure. Loss of function mutations in the bone morphogenetic protein (BMP) pathway are known to be causative for PAH. Mutations in the type II receptor BMPR-II are the main cause of familial PAH and are also found in sporadic idiopathic PAH patients. BMP9 therapy is being investigated in PAH, as it increases *BMPR2* expression, inhibits endothelial cell permeability, and reverses vessel remodeling in PAH preclinical models. The exact mechanism by which BMP9 regulates vessel stability is unknown, but BMP9 is known to inhibit pro-angiogenic VEGF signalling. A microarray study conducted by the Morrell group in pulmonary artery endothelial cells after treatment with BMP9 revealed Semaphorin 3G (SEMA3G) as a potential BMP9-regulated gene. Class 3 semaphorins have been implicated in angiogenesis and endothelial cell migration, with several family members, including SEMA3G, inhibiting VEGF signalling via competition for the neuropilin co-receptors. Furthermore, SEMA3G was shown to prevent pathological vascular remodelling in diabetic and oxygen-induced retinopathies. These findings suggest that SEMA3G could play an important role in maintaining the stability and integrity of the vasculature. The work presented in this thesis confirms that BMP9 and BMP10 treatment of pulmonary microvascular endothelial cells (PMECs) increases *SEMA3G* expression 5-10-fold. Knockdown of BMP signalling pathway components revealed that BMP9/10 regulated *SEMA3G* expression via the canonical Smad signalling pathway. Involvement of SOX17 in *SEMA3G* upregulation was also observed. Additionally, *Sema3g* expression was reduced in *Bmp9* knockout mice and in an experimental animal model of PAH. Interestingly, VEGF treatment inhibited the BMP9-mediated increase of *SEMA3G* expression. Conversely, I found that SEMA3G could inhibit VEGF-mediated phosphorylation of VEGFR2. *In vitro* endothelial cell assays were used to examine the functional consequence of BMP9-mediated *SEMA3G* expression. This work confirmed that BMP9 inhibits VEGF-induced endothelial cell migration and tube network formation in PMECs, and subsequently demonstrated that *SEMA3G* is essential for BMP9-mediated inhibition of migration and tube network formation. Therefore, the work presented here suggests that SEMA3G plays an important role in balancing pro-angiogenic VEGF and anti-angiogenic BMP9 signalling. This study further elucidates the mechanism by which BMP9 functions as a vascular quiescence factor in healthy vasculature and elucidates mechanisms by which BMP9 might act therapeutically in PAH.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Mirza, Sarah

Advisor dc:contributor.advisor

• Morrell, Nicholas

• BMP9
• PAH
• Pulmonary Arterial Hypertension
• SEMA3G
• Semaphorin
• Vascular
• VEGF

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/371ab1bd-b12a-433b-9414-4fa701e2e6ac/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.111343

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/372477