Abdominal Aortic Aneurysm Rupture is not Associated with an Up-regulation of Inflammation within the Aneurysm Wall

Completing the view - histologic insights from circular AAA specimen including 3D imaging : A methodologic approach towards histologic analysis of circumferential AAA samples

Abdominal aortic aneurysm (AAA) is a pathologic enlargement of the infrarenal aorta with an associated risk of rupture. However, the responsible mechanisms are only partially understood. Based on murine and human samples, a heterogeneous distribution of characteristic pathologic features across the aneurysm circumference is expected. Yet, complete histologic workup of the aneurysm sac is scarcely reported. Here, samples from five AAAs covering the complete circumference partially as aortic rings are investigated by histologic means (HE, EvG, immunohistochemistry) and a new method embedding the complete ring. Additionally, two different methods of serial histologic section alignment are applied to create a 3D view. The typical histopathologic features of AAA, elastic fiber degradation, matrix remodeling with collagen deposition, calcification, inflammatory cell infiltration and thrombus coverage were distributed without recognizable pattern across the aneurysm sac in all five patients. Analysis of digitally scanned entire aortic rings facilitates the visualization of these observations. Immunohistochemistry is feasible in such specimen, however, tricky due to tissue disintegration. 3D image stacks were created using open-source and non-generic software correcting for non-rigid warping between consecutive sections. Secondly, 3D image viewers allowed visualization of in-depth changes of the investigated pathologic hallmarks. In conclusion, this exploratory descriptive study demonstrates a heterogeneous histomorphology around the AAA circumference. Warranting an increased sample size, these results might need to be considered in future mechanistic research, especially in reference to intraluminal thrombus coverage. 3D histology of such circular specimen could be a valuable visualization tool for further analysis.

Gene Expression Profiling in Abdominal Aortic Aneurysms

Gene expression profiling of abdominal aortic aneurysms (AAA) indicates that chronic inflammatory responses, active matrix metalloproteinases, and degradation of the extracellular matrix components are involved in disease development and progression. This study investigates intra- and interpersonal RNA genome-wide expression profiling differences (Illumina HumanHT-12, BeadCHIP expression) of 24 AAA biopsies from 12 patients using a single gene and pathway (GeneOntology, GO enrichment) analysis. Biopsies were collected during open surgical AAA repair and according to prior finite element analysis (FEA) from regions with the highest and lowest wall stress. Single gene analysis revealed a strong heterogeneity of RNA expression parameters within the same and different AAA biopsies. The pathway analysis of all samples showed significant enrichment of genes from three different signaling pathways (integrin signaling pathway: fold change FC 1.63, p = 0.001; cholecystokinin receptor pathway: FC 1.60, p = 0.011; inflammation mediated by chemokine signaling pathway: FC 1.45, p = 0.028). These results indicate heterogeneous gene expression patterns within the AAA vascular wall. Single biopsy investigations do not permit a comprehensive characterization of activated molecular processes in AAA disease.

Interleukin 12p40 Deficiency Promotes Abdominal Aortic Aneurysm by Activating CCN2/MMP2 Pathways

Background Development of abdominal aortic aneurysm (AAA) is associated with proinflammatory cytokines including interleukin-12 (IL12). Deficiency of interleukin 12p40 (IL12p40) increases localized fibrotic events by promoting TGFβ2 (transforming growth factor β)-dependent anti-inflammatory response. Here, we determined whether IL12p40 deficiency in apolipoprotein E-/- mice attenuates the development of AAA by antagonizing proinflammatory response. Methods and Results Double knockout (DKO) mice were generated by crossbreeding IL12p40-/- mice with apolipoprotein E-/- mice (n=12). Aneurysmal studies were performed using angiotensin II (1 µg/kg/min; subcutaneous). Surprisingly, DKO mice did not prevent the development of AAA with angiotensin II infusion. Immunohistological analysis, however, showed distinct pathological features between apolipoprotein E-/- and DKO mice. Polymerase chain reaction (7 day) and cytokine arrays (28 day) of the aortic tissues from DKO mice showed significantly increased expression of cytokines related to anti-inflammatory response (interleukin 5 and interleukin 13), synthetic vascular smooth muscle cell phenotype (Activin receptor-like kinase-1 (ALK-1), artemin, and betacellulin) and T helper 17-associated response (4-1BB, interleukin-17e (Il17e) and Cd40 ligand (Cd-40L)). Indeed, DKO mice exhibited increased expression of the fibro-proteolytic pathway in the medial layer of aortae induced by cellular communication network factor 2 (CCN2) and Cd3+IL17+ cells compared with apolipoprotein E-/- mice. Laser capture microdissection showed predominant expression of CCN2/TGFβ2 in the medial layer of human AAA. Finally, Ccn2 haploinsufficiency in the mice showed decreased AAA incidence in response to elastase infusion, associated with decreased matrix metalloproteinase-2 expression. Conclusions Our study reveals novel roles for IL12p40 deficiency in inducing fibro-proteolytic activities in the aneurysmal mouse model. Mechanistically, these effects of IL12p40 deficiency are mediated by CCN2/matrix metalloproteinase-2 crosstalk in the medial layer of aneurysmal aortae.

Smooth muscle cell-specific Notch1 haploinsufficiency restricts the progression of abdominal aortic aneurysm by modulating CTGF expression

Aims

Infiltration of macrophages and apoptosis of vascular smooth muscle cells (VSMCs) promote the development of abdominal aortic aneurysm (AAA). Previously, we demonstrated that global Notch1 deficiency prevents the formation of AAA in a mouse model. Herein, we sought to explore the cell-specific roles of Notch1 in AAA development.

Methods and results

Cell-specific Notch1 haploinsufficient mice, generated on Apoe^-/- background using Cre-lox technology, were infused with angiotensin II (1000 ng/min/kg) for 28 days. Notch1 haploinsufficiency in myeloid cells (n = 9) prevented the formation of AAA attributed to decreased inflammation. Haploinsufficiency of Notch1 in SMCs (n = 14) per se did not prevent AAA formation, but histoarchitectural traits of AAA including elastin degradation and aortic remodeling, were minimal in SMC-Notch1^+/-;Apoe^-/- mice compared to Apoe^-/- mice (n = 33). Increased immunostaining of the contractile SMC-phenotype markers and concomitant decreased expression of synthetic SMC-phenotype markers were observed in the aortae of SMC-Notch1^+/-;Apoe^-/- mice. Expression of connective tissue growth factor (CTGF), a matrix-associated protein that modulates the synthetic VSMC phenotype, increased in the abdominal aorta of Apoe^-/- mice and in the adventitial region of the abdominal aorta in human AAA. Notch1 haploinsufficiency decreased the expression of Ctgf in the aorta and in vitro cell culture system. In vitro studies on SMCs using the Notch1 intracellular domain (NICD) plasmid, dominant negative mastermind-like (dnMAML), or specific siRNA suggest that Notch1, not Notch3, directly modulates the expression of CTGF.

Conclusions

Our data suggest that lack of Notch1 in SMCs limits dilation of the abdominal aorta by maintaining contractile SMC-phenotype and preventing matrix-remodeling.

Histone acetylation and histone acetyltransferases show significant alterations in human abdominal aortic aneurysm

Background

Epigenetic modifications may play a relevant role in the pathogenesis of human abdominal aortic aneurysm (AAA). The aim of the study was therefore to investigate histone acetylation and expression of corresponding lysine [K] histone acetyltransferases (KATs) in AAA.

Results

A comparative study of AAA tissue samples (n = 37, open surgical intervention) and healthy aortae (n = 12, trauma surgery) was performed using quantitative PCR, immunohistochemistry (IHC), and Western blot. Expression of the KAT families GNAT (KAT2A, KAT2B), p300/CBP (KAT3A, KAT3B), and MYST (KAT5, KAT6A, KAT6B, KAT7, KAT8) was significantly higher in AAA than in controls (P ≤ 0.019). Highest expression was observed for KAT2B, KAT3A, KAT3B, and KAT6B (P ≤ 0.007). Expression of KAT2B significantly correlated with KAT3A, KAT3B, and KAT6B (r = 0.705, 0.564, and 0.528, respectively, P < 0.001), and KAT6B with KAT3A, KAT3B, and KAT6A (r = 0.407, 0.500, and 0.531, respectively, P < 0.05). Localization of highly expressed KAT2B, KAT3B, and KAT6B was further characterized by immunostaining. Significant correlations were observed between KAT2B with endothelial cells (ECs) (r = 0.486, P < 0.01), KAT3B with T cells and macrophages, (r = 0.421 and r = 0.351, respectively, P < 0.05), KAT6A with intramural ECs (r = 0.541, P < 0.001) and with a contractile phenotype of smooth muscle cells (SMCs) (r = 0.425, P < 0.01), and KAT6B with T cells (r = 0.553, P < 0.001). Furthermore, KAT2B was associated with AAA diameter (r = 0.382, P < 0.05), and KAT3B, KAT6A, and KAT6B correlated negatively with blood urea nitrogen (r = −0.403, −0.408, −0.478, P < 0.05). In addtion, acetylation of the histone substrates H3K9, H3K18 and H3K14 was increased in AAA compared to control aortae.

Conclusions

Our results demonstrate that aberrant epigenetic modifications such as changes in the expression of KATs and acetylation of corresponding histones are present in AAA. These findings may provide new insight in the pathomechanism of AAA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0169-6) contains supplementary material, which is available to authorized users.

Vascular effects of glycoprotein130 ligands--part II: biomarkers and therapeutic targets

Glycoprotein130 (gp130) ligands are defined by the use of the common receptor subunit gp130 and comprise interleukin (IL)-6, oncostatin M (OSM), IL-11, leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), cardiotrophin-like cytokine (CLC), ciliary neurotrophic factor (CNTF), IL-27 and neuropoietin (NP). In part I of this review we addressed the pathophysiological functions of gp130 ligands with respect to the vascular wall. In part II of this review on the vascular effects of gp130 ligands we will discuss data about possible use of these molecules as biomarkers to predict development or progression of cardiovascular diseases. Furthermore, the possibility to modulate circulating levels of gp130 ligands or their tissue expression by specific antibodies, soluble gp130 protein, renin-angiotensin-aldosterone system (RASS) inhibitors, statins, agonists of peroxisome proliferator-activated receptors (PPAR), hormone replacement therapy, nonsteroidal anti-inflammatory drugs (NSAID) or lifestyle modulating strategies are presented. Recent knowledge about the application of recombinant cytokines from the gp130 cytokine family as therapeutic agents in obesity or atherosclerosis is also summarized. Thus the purpose of this review is to cover a possible usefulness of gp130 ligands as biomarkers and targets for therapy in cardiovascular pathologies.