Jourd'heuil, F. L. | bioRxiv Science

bioRxiv2026

Smooth Muscle Cell Cytoglobin is a Negative Regulator of Atherosclerotic Fibrous Cap Development

Rupture of the fibrous cap is the primary cause of clinical complications from atherosclerosis. Smooth muscle cells (SMCs) are a major contributor to fibrous cap development and stability through de-differentiation to extracellular matrix-producing cells. We previously showed that the antioxidant enzyme cytoglobin (CYGB) is expressed in vascular SMCs and regulates SMC dependent vascular remodeling and gene expression. In the present study, we investigated the function of SMC-CYGB in atherosclerosis. To this end, we generated a mouse line with SMC-specific deletion of Cygb and simultaneous SMC-lineage tracing. We found that SMC specific deletion of CYGB increased fibrous cap thickness in a 17-week PCSK9-AAV8 gain of function combined with Western diet mouse model of atherosclerosis. SMC specific deletion of CYGB increased collagen deposition and SMC cellularity of the fibrous cap in the absence of changes in total plaque and necrotic core sizes. CYGB expression in SMCs was associated with transdifferentiation towards a fibroblast-like, matrix remodeling phenotype. Finally, CYGB was expressed in the fibrous cap of human coronary atherosclerotic lesions and was associated with ACTA2 positive cells. These results provide first-time evidence that SMC-CYGB reduces plaque stability by decreasing cap thickness, collagen deposition, and SMC cellularity.

physiology↗

bioRxiv2023

A role for cytoglobin in regulating intracellular hydrogen peroxide and redox signals in the vasculature

The oxidant hydrogen peroxide serves as a signaling molecule that alters many aspects of cardiovascular functions. Recent studies suggest that cytoglobin - a hemoglobin expressed in the vasculature - may promote electron transfer reactions with proposed functions in hydrogen peroxide decomposition. Here, we determined the extent to which cytoglobin regulates intracellular hydrogen peroxide and established mechanisms. We found that cytoglobin decreased the hyperoxidation of peroxiredoxins and maintained the activity of peroxiredoxin 2 following challenge with exogenous hydrogen peroxide. Cytoglobin promoted a reduced intracellular environment and facilitated the reduction of the thiol-based hydrogen peroxide sensor Hyper7 after bolus addition of hydrogen peroxide. Cytoglobin also limited the inhibitory effect of hydrogen peroxide on glycolysis and reversed the oxidative inactivation of the glycolytic enzyme GAPDH. Our results indicate that cytoglobin in cells exists primarily as oxyferrous cytoglobin (CygbFe2+-O2) with its cysteine residues in the reduced form. We found that the specific substitution of one of two cysteine residues on cytoglobin (C83A) inhibited the reductive activity of cytoglobin on Hyper7 and GAPDH. Carotid arteries from cytoglobin knockout mice were more sensitive to glycolytic inhibition by hydrogen peroxide than arteries from wildtype mice. Together, these results support a role for cytoglobin in regulating intracellular redox signals associated with hydrogen peroxide through oxidation of its cysteine residues, independent of hydrogen peroxide reaction at its heme center.

biochemistry↗