The importance of maintaining contractile function in aortic smooth muscle cells (SMCs) is evident by the fact that heterozygous mutations in the major structural proteins or kinases controlling ...contraction lead to the formation of aneurysms of the ascending thoracic aorta that predispose to life-threatening aortic dissections. Force generation by SMC requires ATP-dependent cyclic interactions between filaments composed of SMC-specific isoforms of α-actin (encoded by ACTA2) and myosin heavy chain (MYH11). ACTA2 and MYH11 mutations are predicted or have been shown to disrupt this cyclic interaction predispose to thoracic aortic disease. Movement of the myosin motor domain is controlled by phosphorylation of the regulatory light chain on the myosin filament, and loss-of-function mutations in the dedicated kinase for this phosphorylation, myosin light chain kinase (MYLK) also predispose to thoracic aortic disease. Finally, a mutation in the cGMP-activated protein kinase (PRKG1) results in constitutive activation of the kinase in the absence of cGMP, thus driving SMC relaxation in part through increased dephosphorylation of the regulatory light chain and predisposes to thoracic aortic disease. Furthermore, SMCs cannot generate force without connections to the extracellular matrix through focal adhesions, and mutations in the major protein in the extracellular matrix, fibrillin-1, linking SMCs to the matrix also cause thoracic aortic disease in individuals with Marfan syndrome. Thus, disruption of the ability of the aortic SMC to generate force through the elastin-contractile units in response to pulsatile blood flow may be a primary driver for thoracic aortic aneurysms and dissections.
Abstract
Melatonin plays an important role in stress tolerance in plants. In this study, exogenous melatonin significantly alleviated the dwarf phenotype and inhibited the decrease of plant fresh ...weight induced by excess copper (Cu2+). Our results indicated that melatonin alleviated Cu2+ toxicity by improving Cu2+ sequestration, carbon metabolism and ROS (reactive oxygen species) scavenging, rather than by influencing the Cu2+ uptake under excess Cu2+ conditions. Transcriptome analysis showed that melatonin broadly altered gene expression under Cu2+ stress. Melatonin increased the levels of glutathione and phytochelatin to chelate excess Cu2+ and promoted cell wall trapping, thus keeping more Cu2+ in the cell wall and vacuole. Melatonin inhibited ROS production and enhanced antioxidant systems at the transcriptional level and enzyme activities, thus building a line of defense in response to excess Cu2+. The distribution of nutrient elements was recovered by melatonin which was disturbed by Cu2+. In addition, melatonin activated carbon metabolism, especially glycolysis and the pentose phosphate pathway, to generate more ATP, an intermediate for biosynthesis. Taken together, melatonin alleviated Cu2+ toxicity in cucumber via multiple mechanisms. These results will help to resolve the toxic effects of Cu2+ stress on plant growth and development. These results can be used for new strategies to solve problems associated with Cu2+ stress.
Vascular inflammation contributes to cardiovascular diseases such as aortic aneurysm and dissection. However, the precise inflammatory pathways involved have not been clearly defined. We have shown ...here that subcutaneous infusion of Ang II, a vasopressor known to promote vascular inflammation, into older C57BL/6J mice induced aortic production of the proinflammatory cytokine IL-6 and the monocyte chemoattractant MCP-1. Production of these factors occurred predominantly in the tunica adventitia, along with macrophage recruitment, adventitial expansion, and development of thoracic and suprarenal aortic dissections. In contrast, a reduced incidence of dissections was observed after Ang II infusion into mice lacking either IL-6 or the MCP-1 receptor CCR2. Further analysis revealed that Ang II induced CCR2+CD14hiCD11bhiF4/80- macrophage accumulation selectively in aortic dissections and not in aortas from Il6-/- mice. Adoptive transfer of Ccr2+/+ monocytes into Ccr2-/- mice resulted in selective monocyte uptake into the ascending and suprarenal aorta in regions of enhanced ROS stress, with restoration of IL-6 secretion and increased incidence of dissection. In vitro, coculture of monocytes and aortic adventitial fibroblasts produced MCP-1- and IL-6-enriched conditioned medium that promoted differentiation of monocytes into macrophages, induced CD14 and CD11b upregulation, and induced MCP-1 and MMP-9 expression. These results suggest that leukocyte-fibroblast interactions in the aortic adventitia potentiate IL-6 production, inducing local monocyte recruitment and activation, thereby promoting MCP-1 secretion, vascular inflammation, ECM remodeling, and aortic destabilization.
Exome sequencing of genes associated with heritable thoracic aortic disease (HTAD) failed to identify a pathogenic variant in a large family with Marfan syndrome (MFS). A genome‐wide linkage analysis ...for thoracic aortic disease identified a peak at 15q21.1, and genome sequencing identified a novel deep intronic FBN1 variant that segregated with thoracic aortic disease in the family (LOD score 2.7) and was predicted to alter splicing. RT‐PCR and bulk RNA sequencing of RNA harvested from fibroblasts explanted from the affected proband revealed an insertion of a pseudoexon between exons 13 and 14 of the FBN1 transcript, predicted to lead to nonsense mediated decay (NMD). Treating the fibroblasts with an NMD inhibitor, cycloheximide, greatly improved the detection of the pseudoexon‐containing transcript. Family members with the FBN1 variant had later onset aortic events and fewer MFS systemic features than typical for individuals with haploinsufficiency of FBN1. Variable penetrance of the phenotype and negative genetic testing in MFS families should raise the possibility of deep intronic FBN1 variants and the need for additional molecular studies.
These results indicate that families with decreased penetrance of features of MFS and negative genetic testing should be assessed for deep intronic variants that lead to the insertion of a pseudoexon, and detection of these pseudoexons may be improved when the cells are treated with inhibitors of nonsense mediated decay.
: The major disease processes affecting the aorta are aortic aneurysms and dissections. Aneurysms are usually described in terms of their anatomic location, with thoracic aortic aneurysms (TAAs) ...involving the ascending and descending aorta in the thoracic cavity and abdominal aortic aneurysms (AAAs) involving the infrarenal abdominal aorta. Both thoracic and abdominal aortas are elastic arteries, and share similarities in their physical structures and cellular components. However, thoracic and abdominal aortas differ in their biochemical properties and the origin of their vascular smooth muscle cells (VSMCs). These similarities and differences between thoracic and abdominal aortas provide the basis for the various pathologic mechanisms observed in this disease. This review focuses on the comparison of the pathologic mechanisms involved in TAA and AAA.
Heritable thoracic aortic disease can result from null variants in MYLK, which encodes myosin light-chain kinase (MLCK). Data on which MYLK missense variants are pathogenic and information to guide ...aortic disease management are limited.
Clinical data from 60 cases with MYLK pathogenic variants were analyzed (five null and two missense variants), and the effect of missense variants on kinase activity was assessed.
Twenty-three individuals (39%) experienced an aortic event (defined as aneurysm repair or dissection); the majority of these events (87%) were aortic dissections. Aortic diameters were minimally enlarged at the time of dissection in many cases. Time-to-aortic-event curves showed that missense pathogenic variant (PV) carriers have earlier-onset aortic events than null PV carriers. An MYLK missense variant segregated with aortic disease over five generations but decreases MYLK kinase acitivity marginally. Functional Assays fail to identify all pathogenic variants in MYLK.
These data further define the aortic phenotype associated with MYLK pathogenic variants. Given minimal aortic enlargement before dissection, an alternative approach to guide the timing of aortic repair is proposed based on the probability of a dissection at a given age.
Gene mutations that lead to decreased contraction of vascular smooth-muscle cells (SMCs) can cause inherited thoracic aortic aneurysms and dissections. Exome sequencing of distant relatives affected ...by thoracic aortic disease and subsequent Sanger sequencing of additional probands with familial thoracic aortic disease identified the same rare variant, PRKG1 c.530G>A (p.Arg177Gln), in four families. This mutation segregated with aortic disease in these families with a combined two-point LOD score of 7.88. The majority of affected individuals presented with acute aortic dissections (63%) at relatively young ages (mean 31 years, range 17–51 years). PRKG1 encodes type I cGMP-dependent protein kinase (PKG-1), which is activated upon binding of cGMP and controls SMC relaxation. Although the p.Arg177Gln alteration disrupts binding to the high-affinity cGMP binding site within the regulatory domain, the altered PKG-1 is constitutively active even in the absence of cGMP. The increased PKG-1 activity leads to decreased phosphorylation of the myosin regulatory light chain in fibroblasts and is predicted to cause decreased contraction of vascular SMCs. Thus, identification of a gain-of-function mutation in PRKG1 as a cause of thoracic aortic disease provides further evidence that proper SMC contractile function is critical for maintaining the integrity of the thoracic aorta throughout a lifetime.
Pathogenic variants in
cause thoracic aortic aneurysms and dissections, along with aneurysms and rupture of other arteries. Here, we examined differences in clinical presentation of aortic events ...(dissection or surgical repair of an aneurysm) with respect to age and variant type in an international cohort of individuals with
variants.
Aortic status and events, vital status and clinical features were abstracted through retrospective review of medical records of 212 individuals with 51 unique
variants, including haploinsufficiency (HI) and missense substitutions in the MH2 domain, as well as novel in-frame deletions and missense variants in the MH1 domain.
Aortic events were documented in 37% of cases, with dissections accounting for 70% of events. The median age at first aortic event was significantly lower in individuals with
MH2 missense variants than those with HI variants (42years vs 49 years; p=0.003), but there was no difference in frequency of aortic events by variant type. The cumulative risk of an aortic event was 50% at 54 years of age. No aortic events in childhood were observed.
pathogenic variants cause thoracic aortic aneurysms and dissections in the majority of individuals with variable age of onset and reduced penetrance. Of the covariates examined, the type of underlying
variant was responsible for some of this variation. Later onset of aortic events and the absence of aortic events in children associated with
variants support gene-specific management of this disorder.
Rare variants were classified as pathogenic based on the American College of Medical Genetics guidelines and the following rules (2): 1) variants that cause nonsense-mediated decay or gene deletions ...occurring in genes for which haploinsufficiency is known to cause disease; 2) FBN1 variants that disrupt amino acids in the epidermal growth factor-like calcium-binding domains and COL3A1 variants that alter glycine residues in the helical domain; 3) variants previously reported to cause thoracic aortic disease and validated by genetic or functional data; and 4) rare missense variants recurrent in HTAD patients, not present in the Exome Aggregation Consortium database and located at protein domains where disease-causing mutations are reported. Pathogenic variants are located in the following protein domains: the cytoplasmic domains of transforming growth factor (TGF)-β type I and II receptors (TGFBR1 and TGFBR2), MH2 domain of SMAD3, proteolytic cleavage site for the production of active TGF-β2 (TGFB2), 130-kDa isoform (short form) of MYLK, and procollagen C-proteinase cleaved active enzyme of lysyl oxidase (LOX). ESTAD-EA (n = 231) ESP-EA (n = 4,300) OR (95% CI) p Value VUSs in ESTAD-EA versus ESP-EA HTAD genes VUSs 74 712 2.42 (1.78-3.17) 2.0 x 10−8 HTAD genes missense VUSs 70 708 2.21 (1.65-2.95) 3.9 x 10−7 HTAD genes synonymous variants∗ 40 839 0.86 (0.61-1.23) 0.44 HCM genes VUSs† 23 350 0.80 (0.51-1.25) 0.33 VUSs in HTAD genes in ESTAD-EA versus ESP-EA ACTA2 2 2 18.77 (2.63-133.85) 0.01 TGFBR2 7 10 13.41 (5.06-35.55) 1.0 x 10−5 TGFBR1 7 32 4.17 (1.82-9.55) 3.1 x 10−3 LOX 3 19 2.97 (0.87-10.09) 0.10 MYLK 8 54 2.82 (1.33-6.00) 0.01 SMAD3 1 7 2.67 (0.33-21.76) 0.34 COL3A1 12 112 2.05 (1.11-3.77) 0.03 TGFB2 6 58 1.95 (0.83-4.57) 0.14 MYH11 18 233 1.48 (0.90-2.43) 0.14 FBN1 10 183 1.02 (0.53-1.95) 0.87 1 D.M. Milewicz, K.M. Trybus, D.C. Guo, Altered smooth muscle cell force generation as a driver of thoracic aortic aneurysms and dissections, Arterioscler Thromb Vasc Biol, Vol. 37, 2017, 26-34 2 S. Richards, N. Aziz, S. Bale, Standards and guidelines for the interpretation of sequence variants: a joint consensus recommendation of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology, Genet Med, Vol. 17, 2015, 405-424 3 University of Texas McGovern Medical School.
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