Vascular endothelial cells (ECs) play important roles in the physiological maintenance of organ blood flow and in the development of renal and cardiovascular diseases. Tissue-specific EC dysfunction can contribute to several different diseases including hypertension. Recent transcriptomic studies identified many EC subtypes in multiple organs including the brain and the kidneys, however, their functions are incompletely understood. The present study aimed to explore physiological functional significance and cardiovascular disease and hypertension relevance of a newly discovered minority subtype of scattered ECs expressing neuronal nitric oxide synthase (Nos1).
Design and method:
A comprehensive research toolbox was applied in this study including transgenic mouse models (Nos1-GFP, GCaMP6, mTORgof/lof), intravital multiphoton imaging of calcium dynamics of Nos1+ endothelial cells in the brain and the kidney, genetic cell fate tracking, two-kidney one-clip (2K1C) model of renovascular (Goldblatt) hypertension (RVHT), whole mount organ imaging for 3D vascular density measurements, and single-cell transcriptomic analysis.
Our studies identified and characterized, for the first time, a new endothelial cell type expressing both endothelial and neuron-like functional and gene transcriptomic signatures, therefore we named them neuroendothelial cells (NECs). NECs exhibit a well-defined arteriovenous zonal localization exclusively to small resistance arterioles. NECs are found only in the three organs that exhibit the best blood flow autoregulation capacity, with the highest density in the brain>kidney>heart (NEC/EC (%) 8.42+/-0.79, 3.21+/−0.33, 1.73+/−0.07, respectively). NEC density is reduced with aging in the brain and the kidney (NEC/EC (%) 4.675, and 1.850, respectively, p < 0.01, 2.5 years old compared to 2-month-old). The number of NECs increased significantly in the hypo-perfused, hypoxic clipped (CK) kidney, but reduced in the hyperperfused non-clipped (NCK) kidney in RVHT. Intravital multiphoton microscopy (MPM) of intact brain and kidney arterioles in vivo revealed regular, autonomous NEC calcium transients with blood pressure-dependent frequency alterations. Newly established NEC gain-of-function mouse models exhibited increased endothelium-dependent vasodilation and diminished agonist-induced vascular contractility in brain and kidney resistance arterioles compared to controls.
In addition, preliminary single-cell RNA sequencing and transcriptomic analyses showed that, in contrast to other ECs, NECs highly express several traditional (e.g., Nos1, Klotho) and novel (e.g., Aard) tissue trophic factors that are known to play important roles in angiogenesis, aging, vascular (dys)function, and chronic vascular diseases.
These new vascular anatomy and hemodynamic findings strongly suggest sensory, blood flow and/or baroreceptor functions of NECs as well as a role in the autoregulation of organ blood flow and hypertension pathogenesis.