This work sits off to the side: nearby in the archive are studies on the quantum rotor, the cellular scaffold, magnetic resonance in chromium oxide and gene delivery into cells. Our text deals with the molecular biology of blood vessels and comes closest to the topic of cell mechanics, but it differs in scale: we are not looking at individual molecules or cellular structures, but at an entire signaling pathway in smooth muscle cells. Plenty of data have already accumulated on how cells sense magnetic fields, twist their scaffold and swallow particles, yet the role of NOTCH3 in mature vascular cells remained poorly described. Our work fills that gap by showing that NOTCH3 acts as a regulator of homeostasis rather than a simple phenotype switch.
The researchers took a culture of human aortic smooth muscle cells (HAoSMC) and switched off the NOTCH3 gene in them using small interfering RNAs (siRNA). The cells were compared with controls treated with scrambled siRNA under three conditions: no stimulation, with the growth factor PDGF, and with TGF-β. Changes were assessed at several levels: gene expression was measured by quantitative PCR, proteins were analyzed by mass spectrometry and western blotting, metabolism was checked with a Seahorse assay, and the structure of the actin cytoskeleton and collagen was visualized by microscopy. To find protein partners of NOTCH3, the team ran immunoprecipitation followed by mass spectrometry.
After NOTCH3 was switched off, gene expression dropped by 83–87% under all conditions. The cells remained viable, and the division rate did not change. The main shift: production of type III collagen (COL3A1) rose under all conditions, and with TGF-β stimulation the output of other collagens (COL1A1, COL4A1) increased as well. Proteomic analysis showed a decrease in glycolysis enzymes, especially ENO2, and an increase in proteins linked to the actin cytoskeleton, including cortactin (CTTN). Functionally, this showed up as greater F-actin intensity and a lower rate of glycolysis, but cell migration and the formation of vascular networks with endothelial cells were unaffected. Immunoprecipitation revealed that NOTCH3 physically binds to collagens, CTTN and cytoskeleton regulators.
This work stands apart from neighboring studies in that it is the first to systematically describe the consequences of acute NOTCH3 suppression specifically in mature, healthy human smooth muscle cells, rather than in models of development or disease. The neighbors study the mechanical and magnetic properties of cells, while we show how a single signaling receptor coordinates several programs at once: matrix, cytoskeleton and metabolism. This is not the discovery of a new physical phenomenon but a refinement of the biological role of a known protein. The results underscore that losing NOTCH3 is not the same as a NOTCH3 mutation: in CADASIL, what most likely dominates is the toxic accumulation of the mutant protein, not merely a shortage of signal.
The topic could move toward testing combined approaches: temporary suppression of mutant NOTCH3 together with delivery of a healthy copy of the gene. It would also be promising to study how cells with different NOTCH3 mutations respond to the same treatments and to compare them with the results of acute knockdown. Perhaps it will be possible to find molecular markers that distinguish the consequences of loss of function from the toxic effect of aggregates.
The results matter for vascular biology, CADASIL research and the development of RNA therapy against NOTCH3. They also provide a basis for studying the link between NOTCH3, fibrosis and the metabolic flexibility of cells.
The next step is to test the effect of siRNA in multicellular models, for example in co-culture with endothelium or in vascular organoids. It is also worth studying how cells with CADASIL mutations respond to knockdown and to replacement with healthy NOTCH3.
The work speaks directly to an unresolved question in vascular biology: is CADASIL a disease of NOTCH3 loss of function or of toxic accumulation of the mutant protein. Our data show that acute loss of NOTCH3 by itself alters the matrix and metabolism but does not reproduce all the defects characteristic of mutant cells. This supports a model in which the mutant protein, rather than simply the absence of signal, plays the key role. Another open question concerns the compensatory mechanisms that allow cells to preserve their functions when NOTCH3 is almost completely suppressed.
The NOTCH3 protein got its name from a mutation in Drosophila: flies with a defect in this gene had wings with a jagged edge resembling a notch. In humans, the same protein turned out to be key for blood vessel walls, and when it breaks down it causes hereditary strokes.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.