The Pathogenesis and Impact of Arterial Stiffening in Hypertension: The 2023 John H. Laragh Research Award

Fifty years ago, Dr. John Laragh brought forward the "vasoconstriction-volume hypothesis" of hypertension. This is Ohm's Law in blood pressure regulation, explicating hypertension as a consequence of increased peripheral vascular resistance, cardiac output, or both. Resistance vessels, those of a diameter less than 200 μm, determines mean arterial pressure by controlling peripheral vascular resistance. In comparison, large capacitance arteries, particularly the aorta, confines the systolic and diastolic blood pressure in physiological range through the "windkessel effect." Loss of this cushioning function results in aortic stiffening and isolated systolic hypertension, both of which are independently associated with increased risk for coronary, cerebral, and renal diseases. Aortic stiffening is both a cause and a consequence of hypertension. On one hand, aortic stiffness precedes the onset of hypertension in populations and experimental models, and hemodynamic derangements related to aortic stiffening contributes to the development of hypertension by promoting renal dysfunction. On the other hand, the vasculature itself is a hypertensive target organ and hypertensive mechanical stretch directly induces the pathogenesis of aortic adventitial remodeling. Various cell types, including bone marrow-derived circulating fibrocytes, vascular stem cell antigen-1 positive progenitors, and endothelial to mesenchymal transition, and to a lesser extent resident fibroblasts, contribute to adventitial matrix deposition and aortic stiffening in hypertension. Vascular smooth muscle stiffness is another important contributor of aortic stiffening. Understanding the roles of immune components and specific signal pathways in the pathogenesis aortic stiffening paves the path to novel antihypertensive and anti-fibrosis therapies.

Heart of glass anchors Rasip1 at endothelial cell-cell junctions to support vascular integrity

Heart of Glass (HEG1), a transmembrane receptor, and Rasip1, an endothelial-specific Rap1-binding protein, are both essential for cardiovascular development. Here we performed a proteomic screen for novel HEG1 interactors and report that HEG1 binds directly to Rasip1. Rasip1 localizes to forming endothelial cell (EC) cell-cell junctions and silencing HEG1 prevents this localization. Conversely, mitochondria-targeted HEG1 relocalizes Rasip1 to mitochondria in cells. The Rasip1-binding site in HEG1 contains a 9 residue sequence, deletion of which abrogates HEG1’s ability to recruit Rasip1. HEG1 binds to a central region of Rasip1 and deletion of this domain eliminates Rasip1’s ability to bind HEG1, to translocate to EC junctions, to inhibit ROCK activity, and to maintain EC junctional integrity. These studies establish that the binding of HEG1 to Rasip1 mediates Rap1-dependent recruitment of Rasip1 to and stabilization of EC cell-cell junctions.

DOI:http://dx.doi.org/10.7554/eLife.11394.001

Blood vessels are lined with cells known as vascular endothelial cells. These cells are connected to each other at junctions that consist of several different proteins. The junctions help to control how the blood vessel develops and provide a barrier that controls the movement of water and certain other molecules through the vessel wall. This barrier becomes weakened in diseases like sepsis and atherosclerosis.

Two proteins that are essential for the heart and blood vessels to develop correctly are called “Heart of Glass” (HEG1) and Rasip1. Although a protein has been identified that binds to HEG1 at the cell junctions, this binding only involves a small region of HEG1. This led de Kreuk, Gingras et al. to look for other proteins that interact with HEG1 and that might be important for controlling the development of the blood vessels. This revealed that HEG1 binds directly to Rasip1.

Further experiments revealed that HEG1 is essential for targeting Rasip1 to the junctions between the endothelial cells, and that this helps to stabilize the cell junctions. Mutant forms of Rasip1 that lacked a particular sequence in the middle of the protein were unable to bind to HEG1 and did not localize to the cell junctions. These studies open the door to future work to define how the interaction of Rasip1 and HEG1 is controlled and how Rasip1 stabilizes blood vessels.

DOI:http://dx.doi.org/10.7554/eLife.11394.002

Force production and mechanical accommodation during convergent extension

Forces generated within the embryo during convergent extension (CE) must overcome mechanical resistance to push the head away from the rear. As mechanical resistance increases more than eightfold during CE and can vary twofold from individual to individual, we have proposed that developmental programs must include mechanical accommodation in order to maintain robust morphogenesis. To test this idea and investigate the processes that generate forces within early embryos, we developed a novel gel-based sensor to report force production as a tissue changes shape; we find that the mean stress produced by CE is 5.0±1.6 Pascal (Pa). Experiments with the gel-based force sensor resulted in three findings. (1) Force production and mechanical resistance can be coupled through myosin contractility. The coupling of these processes can be hidden unless affected tissues are challenged by physical constraints. (2) CE is mechanically adaptive; dorsal tissues can increase force production up to threefold to overcome a stiffer microenvironment. These findings demonstrate that mechanical accommodation can ensure robust morphogenetic movements against environmental and genetic variation that might otherwise perturb development and growth. (3) Force production is distributed between neural and mesodermal tissues in the dorsal isolate, and the notochord, a central structure involved in patterning vertebrate morphogenesis, is not required for force production during late gastrulation and early neurulation. Our findings suggest that genetic factors that coordinately alter force production and mechanical resistance are common during morphogenesis, and that their cryptic roles can be revealed when tissues are challenged by controlled biophysical constraints.

Neuroendocrine signaling via the serotonin transporter regulates clearance of apoptotic cells

Serotonin (5-hydroxytryptamine; 5-HT) is a CNS neurotransmitter increasingly recognized to exert immunomodulatory effects outside the CNS that contribute to the pathogenesis of autoimmune and chronic inflammatory diseases. 5-HT signals to activate the RhoA/Rho kinase (ROCK) pathway, a pathway known for its ability to regulate phagocytosis. The clearance of apoptotic cells (i.e. efferocytosis) is a key modulator of the immune response that is inhibited by the RhoA/ROCK pathway. Because efferocytosis is defective in many of the same illnesses where 5-HT has been implicated in disease pathogenesis, we hypothesized that 5-HT would suppress efferocytosis via activation of RhoA/ROCK. The effect of 5-HT on efferocytosis was examined in murine peritoneal and human alveolar macrophages, and its mechanisms were investigated using pharmacologic blockade and genetic deletion. 5-HT impaired efferocytosis by murine peritoneal macrophages and human alveolar macrophages. 5-HT increased phosphorylation of myosin phosphatase subunit 1 (Mypt-1), a known ROCK target, and inhibitors of RhoA and ROCK reversed the suppressive effect of 5-HT on efferocytosis. Peritoneal macrophages expressed the 5-HT transporter and 5-HT receptors (R) 2a, 2b, but not 2c. Inhibition of 5-HTR2a and 5-HTR2b had no effect on efferocytosis, but blockade of the 5-HT transporter prevented 5-HT-impaired efferocytosis. Genetic deletion of the 5-HT transporter inhibited 5-HT uptake into peritoneal macrophages, prevented 5-HT-induced phosphorylation of Mypt-1, reversed the inhibitory effect of 5-HT on efferocytosis, and decreased cellular peritoneal inflammation. These results suggest a novel mechanism by which 5-HT might disrupt efferocytosis and contribute to the pathogenesis of autoimmune and chronic inflammatory diseases.

Intravitreal fasudil combined with bevacizumab for treatment of refractory diabetic macular edema; a pilot study

PURPOSE

To evaluate the effect of intravitreal injection of a Rho-associated protein kinase (ROCK) inhibitor (Fasudil, Asahi Kasei Pharma Corporation, Tokyo, Japan) combined with intravitreal bevacizumab (IVB) on refractory diabetic macular edema (DME).

METHODS

This prospective, interventional case series included 15 eyes of 15 patients with DME unresponsive to previous IVB injections. Eligible eyes underwent intravitreal injection of 0.025 mg Fasudil and 1.25 mg bevacizumab. Best corrected visual acuity (BCVA) and central macular thickness (CMT) were evaluated before and 4 weeks after treatment.

RESULTS

Mean age was 64.6±7.3 (range, 49-79) years and mean number of previous IVB injections was 2.8. Mean pre-injection BCVA was 0.84±0.35 LogMAR, which was improved to 0.49±0.29 LogMAR four weeks after intervention (P=0.003). Mean CMT was decreased from 448±123 µm before treatment, to 347±76 µm at four weeks (P=0.001); no adverse event was observed during the study period.

CONCLUSION

Intravitreal ROCK inhibitors seem to entail structural and visual benefits in eyes with DME refractory to IVB monotherapy.