Elastic Laminar Reorganization Occurs with Outward Diameter Oxidase for Stabilization

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.

Morphological Subtypes of Intracranial Internal Carotid Artery Arteriosclerosis and the Risk of Stroke

Background and Purpose: Accumulating evidence highlights the existence of distinct morphological subtypes of intracranial carotid arteriosclerosis. So far, little is known on the prevalence of these subtypes and subsequent stroke risk in the general population. We determined the prevalence of morphological subtypes of intracranial arteriosclerosis and assessed the risk of stroke associated with these subtypes. Methods: Between 2003 and 2006, 2391 stroke-free participants (mean age 69.6, 51.7% women) from the population-based Rotterdam Study underwent noncontrast computed tomography to visualize calcification in the intracranial carotid arteries as a proxy for intracranial arteriosclerosis. Calcification morphology was evaluated according to a validated grading scale and categorized into intimal, internal elastic lamina (IEL), or mixed subtype. Follow-up for stroke was complete until January 1, 2016. We used multivariable Cox regression to assess associations of each subtype with incident stroke. Results: The prevalence of calcification was 82% of which 39% had the intimal subtype, 48% IEL subtype, and 13% a mixed subtype. During a median follow-up of 10.4 years, 155 participants had a stroke. All 3 subtypes were associated with a higher risk of stroke (adjusted hazard ratio [95% CI] for intimal: 2.11 [1.07–4.13], IEL: 2.66 [1.39–5.11], and mixed subtype 2.57 [1.18–5.61]). The association of the IEL subtype with stroke was strongest among older participants. The association of the intimal subtype with stroke was noticeably stronger in women than in men. Conclusions: Calcification of the IEL was the most prevalent subtype of intracranial arteriosclerosis. All 3 subtypes were associated with an increased risk of stroke, with noticeable age and sex-specific differences.

Structural Remodeling of the Extracellular Matrix in Arteriogenesis: A Review

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.

Immunoreactivity and a new staining method of monocarboxylate transporter 1 located in endothelial cells of cerebral vessels of human brain in distinguishing cerebral venules from arterioles

Distinguishing brain venules from arterioles with arteriolosclerosis is less reliable using traditional staining methods. We aimed to immunohistochemically assess the monocarboxylate transporter 1 (MCT1), a specific marker of venous endothelium found in rodent studies, in different caliber vessels in human brains. Both largeand small-caliber cerebral vessels were dissected from four autopsy donors. Immunoreactivity for MCT1 was examined in all autopsied human brain tissues, and then each vessel was identified by neuropathologists using hematoxylin and eosin stain, the Verhoeff’s Van Gieson stain, immunohistochemical stain with antibodies for α-smooth muscle actin and MCT1 in sequence. A total of 61 cerebral vessels, including 29 arteries and 32 veins were assessed. Immunoreactivity for MCT1 was observed in the endothelial cells of various caliber veins as well as the capillaries, whereas that was immunenegative in the endothelium of arteries. The different labeling patterns for MCT1 could aid in distinguishing various caliber veins from arteries, whereas assessment using the vessel shape, the internal elastic lamina, and the pattern of smooth muscle fibers failed to make the distinction between small-caliber veins and sclerotic arterioles. In conclusion, MCT1 immunohistochemical staining is a sensitive and reliable method to distinguish cerebral veins from arteries.

Vascular Smooth Muscle Cell Subpopulations and Neointimal Formation in Mouse Models of Elastin Insufficiency

Objective: Using a mouse model of Eln (elastin) insufficiency that spontaneously develops neointima in the ascending aorta, we sought to understand the origin and phenotypic heterogeneity of smooth muscle cells (SMCs) contributing to intimal hyperplasia. We were also interested in exploring how vascular cells adapt to the absence of Eln. Approach and Results: We used single-cell sequencing together with lineage-specific cell labeling to identify neointimal cell populations in a noninjury, genetic model of neointimal formation. Inactivating Eln production in vascular SMCs results in rapid intimal hyperplasia around breaks in the ascending aorta’s internal elastic lamina. Using lineage-specific Cre drivers to both lineage mark and inactivate Eln expression in the secondary heart field and neural crest aortic SMCs, we found that cells with a secondary heart field lineage are significant contributors to neointima formation. We also identified a small population of secondary heart field-derived SMCs underneath and adjacent to the internal elastic lamina. Within the neointima of SMC-Eln knockout mice, 2 unique SMC populations were identified that are transcriptionally different from other SMCs. While these cells had a distinct gene signature, they expressed several genes identified in other studies of neointimal lesions, suggesting that some mechanisms underlying neointima formation in Eln insufficiency are shared with adult vessel injury models. Conclusions: These results highlight the unique developmental origin and transcriptional signature of cells contributing to neointima in the ascending aorta. Our findings also show that the absence of Eln, or changes in elastic fiber integrity, influences the SMC biological niche in ways that lead to altered cell phenotypes.

Microstructural Characterization of Resistance Artery Remodelling in Diabetes Mellitus

<b><i>Introduction:</i></b> Microvascular remodelling is a symptom of cardiovascular disease. Despite the mechanical environment being recognized as a major contributor to the remodelling process, it is currently only understood in a rudimentary way. <b><i>Objective:</i></b> A morphological and mechanical evaluation of the resistance vasculature in health and diabetes mellitus. <b><i>Methods:</i></b> The cells and extracellular matrix of human subcutaneous resistance arteries from abdominal fat biopsies were imaged using two-photon fluorescence and second harmonic generation at varying transmural pressure. The results informed a two-layer mechanical model. <b><i>Results:</i></b> Diabetic resistance arteries reduced in wall area as pressure was increased. This was attributed to the presence of thick, straight collagen fibre bundles that braced the outer wall. The abnormal mechanical environment caused the internal elastic lamina and endothelial and vascular smooth muscle cell arrangements to twist. <b><i>Conclusions:</i></b> Our results suggest diabetic microvascular remodelling is likely to be stress-driven, comprising at least 2 stages: (1) Laying down of adventitial bracing fibres that limit outward distension, and (2) Deposition of additional collagen in the media, likely due to the significantly altered mechanical environment. This work represents a step towards elucidating the local stress environment of cells, which is crucial to build accurate models of mechanotransduction in disease.

Pathophysiology of Vascular Stenosis and Remodeling in Moyamoya Disease

Moyamoya disease (MMD) and moyamoya syndrome (MMS) are progressive vascular pathologies unique to the cerebrovasculature that are important causes of stroke in both children and adults. The natural history of MMD is characterized by primary progressive stenosis of the supraclinoid internal carotid artery, followed by the formation of fragile collateral vascular networks. In MMS, stenosis and collateralization occur in patients with an associated disease or condition. The pathological features of the stenosis associated with MMD include neointimal hyperplasia, disruption of the internal elastic lamina, and medial attenuation, which ultimately lead to progressive decreases in both luminal and external arterial diameter. Several molecular pathways have been implicated in the pathophysiology of stenosis in MMD with functions in cellular proliferation and migration, extracellular matrix remodeling, apoptosis, and vascular inflammation. Importantly, several of these molecular pathways overlap with those known to contribute to diseases of systemic arterial stenosis, such as atherosclerosis and fibromuscular dysplasia (FMD). Despite these possible shared mechanisms of stenosis, the contrast of MMD with other stenotic pathologies highlights the central questions underlying its pathogenesis. These questions include why the stenosis that is associated with MMD occurs in such a specific and limited anatomic location and what process initiates this stenosis. Further investigation of these questions is critical to developing an understanding of MMD that may lead to disease-modifying medical therapies. This review may be of interest to scientists, neurosurgeons, and neurologists involved in both moyamoya research and treatment and provides a review of pathophysiologic processes relevant to diseases of arterial stenosis on a broader scale.

Cerebral large artery stenosis and occlusion in POEMS syndrome

Background This study aimed to investigate the frequency and risk factors for cerebral artery stenosis and occlusion in patients with polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome. Methods We reviewed results of magnetic resonance angiography (MRA) or computed tomography angiography (CTA) in 61 patients with POEMS syndrome seen between 2010 and 2017. Stenosis or occlusion was assessed in the initial MRA/CTA. Multivariate analysis was used to identify risk factors for artery stenosis/occlusion. In an autopsy case, pathologic examination was conducted of the occluded middle cerebral arteries. Results Stenosis (> 50 %) or occlusion of the major cerebral arteries was found in 29 (47.5 %) patients on the initial MRA/CTA. The internal carotid artery was involved most frequently (32.8 %), followed by the anterior (21.3 %) and middle (16.4 %) cerebral arteries. The basilar (1.3 %) and vertebral (3.6 %) arteries were rarely affected. Cerebral infarction developed in eight (13.1 %) patients. The serum vascular endothelial growth factor (VEGF) level was an independent predictor for stenosis/occlusion (odds ratio, 1.228; 95 % confidence interval, 1.042–1.447; P = 0.014). An autopsy study showed occluded middle cerebral arteries by fibrous and myxomatous thickening of intima with splitting of the internal elastic lamina. Follow-up MRA in 23 patients showed improved, worsened, and unchanged stenosis in 20.7 %, 8.7 %, and 69.6 %, respectively. Conclusions Cerebral large-vessel stenosis or occlusion is frequently seen in approximately half of patients with POEMS syndrome. Vasculopathy was related to serum VEGF levels and thereby disease activity. Assessment of cerebral vessels is recommended in these patients to improve management.

Generalized Arterial Calcification of Infancy Type 1 (GACI1): Identification of a Novel Pathogenic Variant (c.1715T>C (p.Leu572Ser))

Generalized Arterial Calcification of Infancy (GACI) is a rare disease inherited in a recessive manner, with severe and diffuse early onset of calcifications along the internal elastic lamina in large and medium size arteries. The diagnosis results are from clinical manifestations, imaging, histopathologic exams, and genetic tests. GACI is predominantly caused by biallelic pathogenic variant in the ENPP1 gene (GACI1, OMIM#208000) and, to a lesser extent, by pathogenic variants in the ABCC6 gene (GACI2, OMIM#614473). We present a novel variation in the ENPP1 gene identified in a patient clinically diagnosed with GACI and confirmed by genetic investigation and autopsy as GACI type 1. The sequence analysis of the patient’s ENPP1 gene detected two heterozygous variants c.1412A>G (p.Tyr471Cys) and c.1715T>C (p.Leu572Ser). The variant c.1715T>C (p.Leu572Ser) has not been described yet in the literature and in mutation databases. A genetic analysis was also carried out for the parents of the newborn; the heterozygous pathogenic variant c.1412A>G (p.Tyr471Cys) was detected in the mother’s ENPP1 gene, and a sequence analysis of the father’s ENPP1 gene revealed the novel heterozygous variant c.1715T>C (p.Leu572Ser). Our results showed that the variant c.1715T>C (p.Leu572Ser) may have a pathogenic role in the development of GACI type1 (GACI1, OMIM#208000), at least when associated with the pathogenic c.1412A>G (p.Tyr471Cys) variant. The identification of novel mutations potentially enabled genotype/phenotype associations that will ultimately have an impact on clinical management and prognosis for the disease.

Contributions of the Endothelium to Vascular Calcification

Vascular calcification (VC) increases morbidity and mortality and constitutes a significant obstacle during percutaneous interventions and surgeries. On a cellular and molecular level, VC is a highly regulated process that involves abnormal cell transitions and osteogenic differentiation, re-purposing of signaling pathways normally used in bone, and even formation of osteoclast-like cells. Endothelial cells have been shown to contribute to VC through a variety of means. This includes direct contributions of osteoprogenitor cells generated through endothelial-mesenchymal transitions in activated endothelium, with subsequent migration into the vessel wall. The endothelium also secretes pro-osteogenic growth factors, such as bone morphogenetic proteins, inflammatory mediators and cytokines in conditions like hyperlipidemia, diabetes, and renal failure. High phosphate levels caused by renal disease have deleterious effects on the endothelium, and induction of tissue non-specific alkaline phosphatase adds to the calcific process. Furthermore, endothelial activation promotes proteolytic destruction of the internal elastic lamina that serves, among other things, as a stabilizer of the endothelium. Appropriate bone mineralization is highly dependent on active angiogenesis, but it is unclear whether the same relationship exists in VC. Through its location facing the vascular lumen, the endothelium is the first to encounter circulating factor and bone marrow-derived cells that might contribute to osteoclast-like versus osteoblast-like cells in the vascular wall. In the same way, the endothelium may be the easiest target to reach with treatments aimed at limiting calcification. This review provides a brief summary of the contributions of the endothelium to VC as we currently know them.