Somatic PDGFRB activating variants promote smooth muscle cell phenotype modulation in intracranial fusiform aneurysm.

BACKGROUND: The fusiform aneurysm is a nonsaccular dilatation affecting the entire vessel wall over a short distance. Although PDGFRB somatic variants have been identified in fusiform intracranial aneurysms, the molecular and cellular mechanisms driving fusiform intracranial aneurysms due to PDGFRB somatic variants remain poorly understood. METHODS: In this study, single-cell sequencing and immunofluorescence were employed to investigate the phenotypic changes in smooth muscle cells within fusiform intracranial aneurysms. Whole-exome sequencing revealed the presence of PDGFRB gene mutations in fusiform intracranial aneurysms. Subsequent immunoprecipitation experiments further explored the functional alterations of these mutated PDGFRB proteins. For the common c.1684 mutation site of PDGFRß, we established mutant smooth muscle cell lines and zebrafish models. These models allowed us to simulate the effects of PDGFRB mutations. We explored the major downstream cellular pathways affected by PDGFRBY562D mutations and evaluated the potential therapeutic effects of Ruxolitinib. RESULTS: Single-cell sequencing of two fusiform intracranial aneurysms sample revealed downregulated smooth muscle cell markers and overexpression of inflammation-related markers in vascular smooth muscle cells, which was validated by immunofluorescence staining, indicating smooth muscle cell phenotype modulation is involved in fusiform aneurysm. Whole-exome sequencing was performed on seven intracranial aneurysms (six fusiform and one saccular) and PDGFRB somatic mutations were detected in four fusiform aneurysms. Laser microdissection and Sanger sequencing results indicated that the PDGFRB mutations were present in smooth muscle layer. For the c.1684 (chr5: 149505131) site mutation reported many times, further cell experiments showed that PDGFRBY562D mutations promoted inflammatory-related vascular smooth muscle cell phenotype and JAK-STAT pathway played a crucial role in the process. Notably, transfection of PDGFRBY562D in zebrafish embryos resulted in cerebral vascular anomalies. Ruxolitinib, the JAK inhibitor, could reversed the smooth muscle cells phenotype modulation in vitro and inhibit the vascular anomalies in zebrafish induced by PDGFRB mutation. CONCLUSION: Our findings suggested that PDGFRB somatic variants played a role in regulating smooth muscle cells phenotype modulation in fusiform aneurysms and offered a potential therapeutic option for fusiform aneurysms.

Genetic testing and surveillance in infantile myofibromatosis: a report from the SIOPE Host Genome Working Group.

Infantile myofibromatosis (IM), which is typically diagnosed in young children, comprises a wide clinical spectrum ranging from inconspicuous solitary soft tissue nodules to multiple disseminated tumors resulting in life-threatening complications. Familial IM follows an autosomal dominant mode of inheritance and is linked to PDGFRB germline variants. Somatic PDGFRB variants were also detected in solitary and multifocal IM lesions. PDGFRB variants associated with IM constitutively activate PDGFRB kinase activity in the absence of its ligand. Germline variants have lower activating capabilities than somatic variants and, thus, require a second cis-acting hit for full receptor activation. Typically, these mutant receptors remain sensitive to tyrosine kinase inhibitors such as imatinib. The SIOPE Host Genome Working Group, consisting of pediatric oncologists, clinical geneticists and scientists, met in January 2020 to discuss recommendations for genetic testing and surveillance for patients who are diagnosed with IM or have a family history of IM/PDGFRB germline variants. This report provides a brief review of the clinical manifestations and genetics of IM and summarizes our interdisciplinary recommendations.