Author ORCID Identifier
Date of Graduation
Biochemistry and Molecular Biology
Doctor of Philosophy (PhD)
Dianna M. Milewicz, M.D., Ph.D.
Sean P. Marrelli, Ph.D.
Ketankumar Ghaghada, Ph.D.
Heinrich T. Taegtmeyer, M.D., Ph.D.
Louise D. McCullough, M.D., Ph.D.
Jiaqian Wu, Ph.D.
Yong-Jian Geng, M.D., Ph.D.
Heterozygous pathogenic variants in ACTA2, encoding smooth muscle α-actin (α-SMA), predispose to thoracic aortic aneurysms and dissections. De novo missense variants disrupting ACTA2 arginine 179 (p.Arg179) cause a multisystemic disease termed smooth muscle dysfunction syndrome (SMDS), which is characterized by early onset thoracic aortic disease and moyamoya disease-like (MMD) cerebrovascular disease. The MMD-like cerebrovascular disease in SMDS patients is marked by bilateral steno-occlusive lesions in the distal internal carotid arteries (ICAs) and their branches. To study the molecular mechanisms that underlie the ACTA2 p.Arg179 variants, a smooth muscle-specific Cre-lox knock-in mouse model of the heterozygous Acta2 R179C variant, termed the Acta2SMC-R179C/+ mouse model, was generated. Acta2SMC-R179C/+ mice exhibit mild hypotension, but do not have spontaneous aortic disease, strokes, or death up to two years of age. In the Acta2SMC-R179C/+ mouse model, 67% of the smooth muscle cells (SMCs) in the vasculature express the heterozygous Acta2 R179C mutation. However, when SMCs are explanted from Acta2SMC-R179C/+ mouse aortas, the population is completely heterozygous for the mutation. Here, I show that Acta2SMC-R179C/+ SMCs are not fully differentiated and proliferate and migrate faster than wild-type (WT) SMCs. Metabolic profiling identified that the Acta2SMC-R179C/+ SMCs have increased glycolytic flux and decreased oxidative phosphorylation (OXPHOS), which is associated with reduced mitochondrial DNA and complex I activity, reflecting decreased electron transport chain activity. Nicotinamide riboside (NR), a NAD+ analogue, altered this metabolic profile. NR decreased glycolysis and increased OXPHOS by enhancing complex I activity without altering mitochondrial mass in Acta2SMC-R179C/+ SMCs. Furthermore, NR increased differentiation and decreased migration in Acta2SMC-R179C/+ SMCs.
To determine how phenotypic changes in Acta2SMC-R179C/+ SMCs contribute to cerebrovascular disease, left carotid artery ligation (LCAL) was performed in these mice. One-fifth of Acta2SMC-R179C/+ mice die immediately post-ligation due to ischemic strokes, whereas no WT mice died. The surviving mutant mice have persistent intraluminal lesions containing SMCs that resemble MMD lesions, which is consistent with increased migration observed in mutant SMCs, along with medial thinning and an enlarged lumen area proximal to the ligation site. In contrast, the WT mice show nearly patent lumens with medial thickening. Additionally, Acta2SMC-R179C/+ mice display aberrant vascular remodeling consisting of increased neovascularization surrounding the left carotid artery, augmented leptomeningeal collateral remodeling, and greater post-occlusion stenosis in the large intracranial arteries when compared to the WT mice.
To establish whether NR treatment alters outcomes in LCAL-injured Acta2SMC-R179C/+ mice, mice were administered NR every other day beginning five days prior to the ligation injury. NR treatment prevented deaths post-ligation and improved the vascular remodeling in the mutant mice. Specifically, NR partially resolved the intraluminal left carotid artery lesions, reduced neovascularization surrounding the left carotid artery, attenuated leptomeningeal collateral remodeling, and increased patency of the large intracranial arteries distal to the ligation. Together, these results establish a novel role for glycolytic metabolism in driving vascular occlusive disease. These results also highlight the potential of increasing mitochondrial metabolism in SMCs to restore a differentiated and quiescent phenotype and attenuate MMD-like cerebrovascular occlusive lesions to prevent ischemic strokes in patients with SMDS.
genetics, mouse, models, stroke, cerebrovascular, acta2, moyamoya, pediatric, vascular, smooth, muscle
Available for download on Wednesday, April 03, 2024
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