Local DIO2 Elevation Is an Adaption in Malformed Cerebrovasculature

Cerebrovascular malformations are a pivotal cause of hemorrhage and neurological disability alongside lacking effective medication. Thyroid hormones (THs), including thyroxine and triiodothyronine, are essential for vascular development, yet whether they participate in malformed cerebrovascular pathology remains elusive.

Single-cell transcriptome analysis characterized human cerebral cavernous malformations and brain arteriovenous malformations, 2 typical cerebrovascular malformation diseases. Adeno-associated virus-mediated Dio2 (iodothyronine deiodinase 2; an enzyme that converts thyroxine to active triiodothyronine) overexpression/knockdown or triiodothyronine/methimazole (an antithyroid drug) treatment was applied to mouse models of cerebral cavernous malformations (endothelial-specific Pdcd10 knockout mice, Pdcd10 endothelial-specific knockout [KO]) and brain arteriovenous malformations (endothelial-specific Kras mutant mice, Kras) to evaluate the involvement of DIO2 and TH signaling in cerebrovascular malformations.

TH signaling was markedly activated in fibroblasts of human cerebral cavernous malformation and arteriovenous malformation single-cell samples, accompanied by elevated DIO2 expression. Similar DIO2 upregulation was observed in cerebrovascular fibroblasts of Pdcd10 KO/Kras mice and patient brain sections. Exogenous Dio2 or triiodothyronine replenishment effectively reduced brain hemorrhage, excessive ECM (extracellular matrix) remodeling, and vascular leakage in juvenile and adult male and female Pdcd10 KO/Kras mice. In contrast, Dio2 silencing or TH inhibition deteriorated vascular anomalies. Mechanistically, transcription factor FOXK1 (forkhead box K1) was determined to interact with the DIO2 promoter region. The activation of fibroblast PI3K (phosphoinositide 3-kinase)-Akt (protein kinase B)-mTOR (mammalian target of rapamycin) signaling in Pdcd10 KO/Kras mice triggered Foxk1 nuclear translocation to promote Dio2 transcription. Triiodothyronine treatment mitigated inflammatory infiltration, normalized mitochondrial morphology, and restored mitochondrial biogenesis in malformed brain vessels by activating the Pgc1a (peroxisome proliferator-activated receptor gamma coactivator 1-alpha)-Sod2 (superoxide dismutase 2)/Prdx3 (peroxiredoxin 3)/Gpx1 (glutathione peroxidase 1) axis to reduce reactive oxygen species accumulation. We also determined that the vascular repair effects of triiodothyronine were Pgc1a-dependent.

We delineate a novel DIO2-mediated adaption in malformed cerebrovasculature and conclude that targeting TH signaling may represent a potential therapy for cerebrovascular disorders.