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Autofluorescence (green) of the internal elastic lamina (IEL) of mesenteric first, second, and third order arteries (top), and skeletal muscle popliteal, feed, first and second order arteries (bottom). Note that areas without green demonstrate lack of IEL, indicating fenestration and area of myoendothelial space. Bar = 10 µm.
Source publication
Holes within the internal elastic lamina (IEL) of blood vessels are sites of fenestration allowing for passage of diffusible vasoactive substances and interface of endothelial cell membrane projections with underlying vascular smooth muscle. Endothelial projections are sites of dynamic Ca(2+) events leading to endothelium dependent hyperpolarizatio...
Citations
... Enabled by sulfo-NHS groups on the surface, ahNP can readily and covalently react with the abundant amine groups on ECM proteins to form amide bonds [34] (Fig. 1F), and the ahNP can be simply pen-brushed onto the vessel surface and immobilized on the ECM, to release drug locally and durably (schematized in Fig. 1G and H). Because the elastic laminae in the vessel wall are fenestrated sheets [35,36] that allow small molecules to pass through [37], it is conceivable that the drug released from the immobilized ahNP should readily diffuse into the neighboring medial layer where SMCs reside. To mimic open vascular reconstruction, we opened the neck of the rat and injured the common carotid artery with a balloon catheter. ...
Open vascular reconstructions such as bypass are common treatments for cardiovascular disease. Unfortunately, neointimal hyperplasia (IH) follows, leading to treatment failure for which there is no approved therapy. Here we combined the strengths of tailoring nanoplatforms for open vascular reconstructions and targeting new epigenetic mechanisms. We produced adhesive nanoparticles (ahNP) that could be pen-brushed and immobilized on the adventitia to sustainably release pinometostat, an inhibitor drug selective to the epigenetic writer DOT1L that catalyzes histone-3 lysine-79 dimethylation (H3K79me2). This treatment not only reduced IH by 76.8% in injured arteries mimicking open reconstructions in obese Zucker rats with human-like diseases but also avoided the shortcoming of endothelial impairment in IH management. In mechanistic studies, chromatin immunoprecipitation (ChIP) sequencing revealed co-enrichment of the histone mark H3K27ac(acetyl) and its reader BRD4 at the gene of aurora kinase B (AURKB), where H3K79me2 was also enriched as indicated by ChIP-qPCR. Accordingly, DOT1L co-immunoprecipitated with H3K27ac. Furthermore, the known IH driver BRD4 governed the expression of DOT1L which controlled AURKB's protein level, revealing a BRD4- > DOT1L- > AURKB axis. Consistently, AURKB-selective inhibition reduced IH. Thus, this study presents a prototype nanoformulation suited for open vascular reconstructions, and the new insights into chromatin modulators may aid future translational advances.
... The IEL contains fenestrations that vary dramatically in size, shape and frequency, depending on the location in the arterial tree [28,40,41]. In larger conduit arteries, the IEL is a thick sheet with punctate fenestrations while the branch arteries to skeletal muscle possess a thinner IEL with more numerous and larger fenestrations [42]. We also observed along the arterial tree that more distal branches have diminishing elastic fiber content down to the arteriolar level. ...
When a large artery becomes occluded, hemodynamic changes stimulate remodeling of arterial networks to form collateral arteries in a process termed arteriogenesis. However, the structural changes necessary for collateral remodeling have not been defined. We hypothesize that deconstruction of the extracellular matrix is essential to remodel smaller arteries into effective collaterals. Using multiphoton microscopy, we analyzed collagen and elastin structure in maturing collateral arteries isolated from ischemic rat hindlimbs. Collateral arteries harvested at different timepoints showed progressive diameter expansion associated with striking rearrangement of internal elastic lamina (IEL) into a loose fibrous mesh, a pattern persisting at 8 weeks. Despite a 2.5-fold increase in luminal diameter, total elastin content remained unchanged in collaterals compared with control arteries. Among the collateral midzones, baseline elastic fiber content was low. Outward remodeling of these vessels with a 10–20 fold diameter increase was associated with fractures of the elastic fibers and evidence of increased wall tension, as demonstrated by the straightening of the adventitial collagen. Inhibition of lysyl oxidase (LOX) function with β-aminopropionitrile resulted in severe fragmentation or complete loss of continuity of the IEL in developing collaterals. Collateral artery development is associated with permanent redistribution of existing elastic fibers to accommodate diameter growth. We found no evidence of new elastic fiber formation. Stabilization of the arterial wall during outward remodeling is necessary and dependent on LOX activity.
... The IEL contains fenestrations that vary dramatically in size, shape and frequency depending on the location in the arterial tree (28,40,41). In larger conduit arteries, the IEL is a thick sheet with punctate fenestrations while the branch arteries to skeletal muscle possess a thinner IEL with more numerous and larger fenestrations (42). We also observed along the arterial tree that more distal branches have diminishing elastic fiber content down to the arteriolar level. ...
When a large artery becomes occluded, hemodynamic changes stimulate remodeling of arterial networks to form collateral arteries in a process termed arteriogenesis. However, the structural changes necessary for collateral remodeling have not been defined. We hypothesize that decon-struction of the extracellular matrix is essential to the remodeling of smaller arteries into effective collaterals. Using multiphoton microscopy, we analyzed collagen and elastin structure in maturing collateral arteries isolated from ischemic rat hindlimbs. Collateral arteries harvested at different timepoints showed progressive diameter expansion associated with striking rearrangement of in-ternal elastic lamina (IEL) into a loose fibrous mesh, a pattern persisting at 8 weeks. Despite a 2.5-fold increase in luminal diameter, total elastin content remained unchanged in collaterals compared with control arteries. Among the collateral midzones, baseline elastic fiber content is low. Outward remodeling of these vessels with a 10-20 fold diameter increase was associated with fractures of the elastic fibers and evidence of increased wall tension as demonstrated by straight-ening of the adventitial collagen. Inhibition of lysyl oxidase (LOX) function with β-aminopropionitrile resulted in severe fragmentation or complete loss of continuity of the IEL in developing collaterals. Collateral artery development is associated with permanent redistribution of existing elastic fibers to accommodate diameter growth. We found no evidence of new elastic fiber formation. Stabilization of the arterial wall during outward remodeling is necessary and dependent on LOX activity.
... Between the tunica intima and media, a prominent lamina underpins the endothelium and is better known as the internal elastic lamina (IEL). These elastic lamellae contain fenestrations which vary in size and frequency depending on the arterial branch order, and allow for cellular communication, diffusion, and molecular transport (36)(37)(38)(39). More importantly, these lamellae become active sites of arterial remodeling during postnatal growth of arterial structures and arteriogenesis (40,41). ...
Lower extremity arterial occlusive disease (AOD) results in significant morbidity and mortality for the population, with up to 10% of patients ultimately requiring amputation. An alternative method for non-surgical revascularization which is yet to be fully understood is the optimization of the body's own natural collateral arterial network in a process known as arteriogenesis. Under conditions of conductance vessel stenosis or occlusion resulting in increased flow, shear forces, and pressure gradients within collaterals, positive remodeling occurs to increase the diameter and capacity of these vessels. The creation of a distal arteriovenous fistula (AVF) will drive increased arteriogenesis as compared to collateral formation with the occlusion of a conductance vessel alone by further increasing flow through these arterioles, demonstrating the capacity for arteriogenesis to form larger, more efficient collaterals beyond what is spontaneously achieved after arterial occlusion. Arteries rely on an extracellular matrix (ECM) composed of elastic fibers and collagens that provide stability under hemodynamic stress, and ECM remodeling is necessary to allow for increased diameter and flow conductance in mature arterial structures. When positive remodeling occurs, digestion of lamella and the internal elastic lamina (IEL) by matrix metalloproteinases (MMPs) and other elastases results in the rearrangement and thinning of elastic structures and may be replaced with disordered elastin synthesis without recovery of elastic function. This results in transmission of wall strain to collagen and potential for aneurysmal degeneration along collateral networks, as is seen in the pancreaticoduodenal artery (PDA) after celiac occlusion and inferior mesenteric artery (IMA) with concurrent celiac and superior mesenteric artery (SMA) occlusions. Further understanding into the development of collaterals is required to both better understand aneurysmal degeneration and optimize collateral formation in AOD.
... 6 Elastic lamellae such as the IEL are frequently interrupted by fenestrations, which serve as windows for small molecule transport and cellecell communication. [7][8][9][10] Collagen fibers have a short half-life compared with that of elastic fibers, especially under strain, such as occurs in hypertension, and require continual synthesis for replacement. 11 Adventitial collagen fibers are oriented in a double helical pattern around the axis of the vessel, with the waviness dependent on the applied tension. ...
Objective
To understand arterial remodeling and the pathophysiology of arterial diseases, it is necessary to understand the baseline qualities and variations in arterial structure. Arteries could differ in wall thickness, laminar structure, and laminar fenestration depending on their position within the arterial tree. We endeavored to evaluate and compare the extracellular matrix structure of different arteries throughout the arterial tree, from the aorta to the adductor muscle arteriole, with a particular focus on the internal elastic lamina (IEL).
Methods
Arterial segments were harvested from male Sprague-Dawley rats and imaged using multiple modalities. En face scans by multiphoton microscopy were used to compare native-state adventitial collagen undulation and IEL fenestration.
Results
Collagen undulation was similar across most examined arteries but straighter in the skeletal muscle arterioles (P < .05). The elastic lamellae showed several differences. The IEL fenestrae were similar in average size among abdominal aorta and celiac, renal, common iliac, and common femoral arteries (range, 14-24 μm2), with wide within-vessel variance (square of the standard deviation, 462-1904 μm4). However, they tended to be smaller (9.08 μm2) and less variable (square of the standard deviation, 88.3 μm4) in the popliteal artery. Fenestrae were greater in number in the superior mesenteric artery (SMA; 6686/mm2; P < .05) and profunda femoris artery (PFA; 11,042/mm2; P < .05) compared with the other examined vessels, which ranged in surface density from 3143/mm2 to 4362/mm2. The SMA and PFA also showed greater total fenestration as a proportion of the IEL surface area (SMA, 15.04%; P < .05; PFA, 24.11%; P < .001) than the other examined arteries (range of means, 4.7%-9.4%). The arteriolar IEL was structurally distinct, comparable to a low-density wireframe. Other structural differences were also noted, including differences in the number of medial lamellae along the arterial tree.
Conclusions
We found that vessels at different locations along the arterial tree differ in structure. The SMA, PFA, and intramuscular arterioles have fundamental differences in the extracellular matrix structure compared with other arteries. Location-specific features such as the medial lamellae number and elastic laminar structure might have relevance to physiology and confer vulnerabilities to the development of pathology.
... Especially in distal arterioles, the IEL forms alternatively a fibrillary, meshwork-like structure. Such an architecture has been described in rat muscle and cremaster arterioles or in human and porcine myocardial arterioles (202,242) and may allow easier and less spatially ordered myoendothelial contact. However, potential functional consequences have not been studied to date. ...
Of the 21 members of the connexin family, 4 (Cx37, Cx40, Cx43, and Cx45) are expressed in the endothelium and/or smooth muscle of intact blood vessels to a variable and dynamically regulated degree. Full-length connexins oligomerize and form channel structures connecting the cytosol of adjacent cells (gap junctions) or the cytosol with the extracellular space (hemichannels). The different connexins vary mainly with regard to length and sequence of their cytosolic COOH-terminal tails. These COOH-terminal parts, which in the case of Cx43 are also translated as independent short isoforms, are involved in various cellular signaling cascades and regulate cell functions. This review focuses on channel-dependent and -independent effects of connexins in vascular cells. Channels play an essential role in coordinating and synchronizing endothelial and smooth muscle activity and in their interplay, in the control of vasomotor actions of blood vessels including endothelial cell reactivity to agonist stimulation, nitric oxide-dependent dilation, and endothelial-derived hyperpolarizing factor-type responses. Further channel-dependent and -independent roles of connexins in blood vessel function range from basic processes of vascular remodeling and angiogenesis to vascular permeability and interactions with leukocytes with the vessel wall. Together, these connexin functions constitute an often underestimated basis for the enormous plasticity of vascular morphology and function enabling the required dynamic adaptation of the vascular system to varying tissue demands.
... Interestingly, in GMA, the vasodilatory effect of BA was reduced by the ANT whereas the ANT did not affect significantly the BA-induced vasodilation in MA, suggesting that the mechanisms of relaxation to BA in these two vessels differ. Although both MA and GMA are resistance vessels, they differ in the structure of the internal elastic lamina [16] and in the response to TRP agonists [30]. Our findings suggest that BA-induced vasorelaxation is dependent on GPR41/43 receptors in GMA but not in MA. ...
Butyric acid (BA) is a short-chain fatty acid (SCFA) produced by gut bacteria in the colon. We hypothesized that colon-derived BA may affect hemodynamics. Arterial blood pressure (BP) and heart rate (HR) were recorded in anesthetized, male, 14-week-old Wistar rats. A vehicle, BA, or 3-hydroxybutyrate, an antagonist of SCFA receptors GPR41/43 (ANT) were administered intravenously (IV) or into the colon (IC). Reactivity of mesenteric (MA) and gracilis muscle (GMA) arteries was tested ex vivo. The concentration of BA in stools, urine, portal, and systemic blood was measured with liquid chromatography coupled with mass spectrometry. BA administered IV decreased BP with no significant effect on HR. The ANT reduced, whereas L-NAME, a nitric oxide synthase inhibitor, did not affect the hypotensive effect of BA. In comparison to BA administered intravenously, BA administered into the colon produced a significantly longer decrease in BP and a decrease in HR, which was associated with a 2–3-fold increase in BA colon content. Subphrenic vagotomy and IC pretreatment with the ANT significantly reduced the hypotensive effect. Ex vivo, BA dilated MA and GMA. In conclusion, an increase in the concentration of BA in the colon produces a significant hypotensive effect which depends on the afferent colonic vagus nerve signaling and GPR41/43 receptors. BA seems to be one of mediators between gut microbiota and the circulatory system.
... A subsequent study by the Sandow laboratory demonstrated that ∼70% of TRPC3 channels in the endothelium of rat mesenteric arteries are localized to MEPs, and that inhibition of these channels with Pyr3 attenuated ACh-induced endothelial cell hyperpolarization and arterial relaxation (240). A report from Kirby et al. further supported localization of TRPC3 to MEPs in distinct microdomains that also contain SK and IK channels in rat popliteal and first-order skeletal muscle arteries from the gastrocnemius muscle (138). Collectively, these data suggest that TRPC3 channel stimulation produces EDH responses following muscarinic receptor activation. ...
The vascular endothelium is a broadly distributed and highly specialized organ. The endothelium has a number of functions including the control of blood vessels diameter through the production and release of potent vasoactive substances or direct electrical communication with underlying smooth muscle cells, regulates the permeability of the vascular barrier, stimulates the formation of new blood vessels, and influences inflammatory and thrombotic processes. Endothelial cells that make up the endothelium express a variety of cell‐surface receptors and ion channels on the plasma membrane that are capable of detecting circulating hormones, neurotransmitters, oxygen tension, and shear stress across the vascular wall. Changes in these stimuli activate signaling cascades that initiate an appropriate physiological response. Increases in the global intracellular Ca2+ concentration and localized Ca2+ signals that occur within specialized subcellular microdomains are fundamentally important components of many signaling pathways in the endothelium. The transient receptor potential (TRP) channels are a superfamily of cation‐permeable ion channels that act as a primary means of increasing cytosolic Ca2+ in endothelial cells. Consequently, TRP channels are vitally important for the major functions of the endothelium. In this review, we provide an in‐depth discussion of Ca2+‐permeable TRP channels in the endothelium and their role in vascular regulation. © 2019 American Physiological Society. Compr Physiol 9:1249‐1277, 2019.
... Our work focused specifically on thirdand fourth-order resistance arteries (~150 μm diameter), vessels commonly used in myoendothelial feedback studies and where projections are presumed to be abundant. 22 Briefly, plastic-embedded arterial sections (200-300 nm thick) were prepared and subjected to automated dual-axis electron tomography, an approach that generates digital, serial z-slices throughout the entire specimen. ...
... The sections were then incubated overnight at 4°with rabbit polyclonal anti-VE-cadherin (1/200; Abcam; Ref: ab33168) in 1% BSA-PBS. The next day sections were washed several times in PBS and incubated for 90 min at room temperature with 4′,6′-diamidino-2-phenylindole (DAPI) for cell nuclei counterstaining and with the donkey anti-rabbit Alexa fluor 488 secondary antibody (1:200; Ref: A21206; Life Technologies).Elastic lamina labeling was obtained by auto-fluorescence after excitation at 488 nm as described previously[30]. ...
Increased oxidative stress and advanced glycation end-product (AGE) formation are major contributors to the development of type 2 diabetes. Here plasma proteins e.g. albumin can undergo glycoxidation and play a key role in diabetes onset and related pathologies. However, despite recent progress linking albumin-AGE to increased oxidative stress and downstream effects, its action in metabolic organs such as the liver remains to be elucidated. The current study therefore investigated links between oxidative perturbations and biochemical/structural modifications of plasma albumin, and subsequent downstream effects in transgenic db/db mouse livers and HepG2 cells, respectively. Our data reveal increased oxidative stress biomarkers and lipid accumulation in plasma and livers of diabetic mice, together with albumin glycoxidation. Purified mouse albumin modifications resembled those typically found in diabetic patients, i.e. degree of glycation, carbonylation, AGE levels and in terms of chemical composition. Receptor for AGE expression and reactive oxygen species production were upregulated in db/db mouse livers, together with impaired proteolytic, antioxidant and mitochondrial respiratory activities. In parallel, acute exposure of HepG2 cells to glycated albumin also elicited intracellular free radical formation. Together this study demonstrates that AGE-modified albumin can trigger damaging effects on the liver, i.e. by increasing oxidative stress, attenuating antioxidant capacity, and by impairment of hepatic proteolytic and respiratory chain enzyme activities.
