Knockout mice reveal a role for P2Y6 receptor in macrophages, endothelial cells, and vascular smooth muscle cells

P2Y receptors are G-protein-coupled receptors activated by extracellular nucleotides. The P2Y(6) receptor is selectively activated by UDP, and its transcript has been detected in numerous organs, including the spleen, thymus, intestine, blood leukocytes, and aorta. To investigate the biological functions of this receptor, we generated P2Y(6)-null mice by gene targeting. The P2Y(6) knockout (KO) mice are viable and are not distinguishable from the wild-type (WT) mice in terms of growth or fertility. In thioglycollate-elicited macrophages, the production of inositol phosphate in response to UDP stimulation was lost, indicating that P2Y(6) is the unique UDP-responsive receptor expressed by mouse macrophages. Furthermore, the amount of interleukin-6 and macrophage-inflammatory protein-2, but not tumor necrosis factor-alpha, released in response to lipopolysaccharide stimulation was significantly enhanced in the presence of UDP, and this effect was lost in the P2Y(6) KO macrophages. The endothelium-dependent relaxation of the aorta by UDP was abolished in KO P2Y(6) mice. The contractile effect of UDP on the aorta, observed when endothelial nitric-oxide synthase is blocked, was also abolished in P2Y(6)-null mice. In conclusion, we generated P2Y(6)-deficient mice and have shown that these mice have a defective response to UDP in macrophages, endothelial cells, and vascular smooth muscle cells. These observations might be relevant to several physiopathological conditions such as atherosclerosis or hypertension.

Diffusion kurtosis imaging allows the early detection and longitudinal follow-up of amyloid-β-induced pathology

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia in the elderly population. In this study, we used the APP/PS1 transgenic mouse model to explore the feasibility of using diffusion kurtosis imaging (DKI) as a tool for the early detection of microstructural changes in the brain due to amyloid-β (Aβ) plaque deposition.

METHODS

We longitudinally acquired DKI data of wild-type (WT) and APP/PS1 mice at 2, 4, 6 and 8 months of age, after which these mice were sacrificed for histological examination. Three additional cohorts of mice were also included at 2, 4 and 6 months of age to allow voxel-based co-registration between diffusion tensor and diffusion kurtosis  metrics and immunohistochemistry.

RESULTS

Changes were observed in diffusion tensor (DT) and diffusion kurtosis (DK) metrics in many of the 23 regions of interest that were analysed. Mean and axial kurtosis were greatly increased owing to Aβ-induced pathological changes in the motor cortex of APP/PS1 mice at 4, 6 and 8 months of age. Additionally, fractional anisotropy (FA) was decreased in APP/PS1 mice at these respective ages. Linear discriminant analysis of the motor cortex data indicated that combining diffusion tensor and diffusion kurtosis metrics permits improved separation of WT from APP/PS1 mice compared with either diffusion tensor or diffusion kurtosis metrics alone. We observed that mean kurtosis and FA are the critical metrics for a correct genotype classification. Furthermore, using a newly developed platform to co-register the in vivo diffusion-weighted magnetic resonance imaging with multiple 3D histological stacks, we found high correlations between DK metrics and anti-Aβ (clone 4G8) antibody, glial fibrillary acidic protein, ionised calcium-binding adapter molecule 1 and myelin basic protein immunohistochemistry. Finally, we observed reduced FA in the septal nuclei of APP/PS1 mice at all ages investigated. The latter was at least partially also observed by voxel-based statistical parametric mapping, which showed significantly reduced FA in the septal nuclei, as well as in the corpus callosum, of 8-month-old APP/PS1 mice compared with WT mice.

CONCLUSIONS

Our results indicate that DKI metrics hold tremendous potential for the early detection and longitudinal follow-up of Aβ-induced pathology.

Harmonization of Brain Diffusion MRI: Concepts and Methods

MRI diffusion data suffers from significant inter- and intra-site variability, which hinders multi-site and/or longitudinal diffusion studies. This variability may arise from a range of factors, such as hardware, reconstruction algorithms and acquisition settings. To allow a reliable comparison and joint analysis of diffusion data across sites and over time, there is a clear need for robust data harmonization methods. This review article provides a comprehensive overview of diffusion data harmonization concepts and methods, and their limitations. Overall, the methods for the harmonization of multi-site diffusion images can be categorized in two main groups: diffusion parametric map harmonization (DPMH) and diffusion weighted image harmonization (DWIH). Whereas DPMH harmonizes the diffusion parametric maps (e.g., FA, MD, and MK), DWIH harmonizes the diffusion-weighted images. Defining a gold standard harmonization technique for dMRI data is still an ongoing challenge. Nevertheless, in this paper we provide two classification tools, namely a feature table and a flowchart, which aim to guide the readers in selecting an appropriate harmonization method for their study.

Pharmacological characterization of nucleotide P2Y receptors on endothelial cells of the mouse aorta

Nucleotides regulate various effects including vascular tone. This study was aimed to characterize P2Y receptors on endothelial cells of the aorta of C57BL6 mice. Five adjacent segments (width 2 mm) of the thoracic aorta were mounted in organ baths to measure isometric force development. Nucleotides evoked complete (adenosine 5' triphosphate (ATP), uridine 5' triphosphate (UTP), uridine 5' diphosphate (UDP); >90%) or partial (adenosine 5' diphosphate (ADP)) relaxation of phenylephrine precontracted thoracic aortic rings of C57BL6 mice. Relaxation was abolished by removal of the endothelium and was strongly suppressed (>90%) by inhibitors of nitric oxide synthesis. The rank order of potency was: UDP approximately UTP approximately ADP>adenosine 5'-[gamma-thio] triphosphate (ATPgammaS)>ATP, with respective pD2 values of 6.31, 6.24, 6.22, 5.82 and 5.40. These results are compatible with the presence of P2Y1 (ADP>ATP), P2Y2 or P2Y4 (ATP and UTP) and P2Y6 (UDP) receptors. P2Y4 receptors were not involved, since P2Y4-deficient mice displayed unaltered responses to ATP and UTP. The purinergic receptor antagonist suramin exerted surmountable antagonism for all agonists. Its apparent pKb for ATP (4.53+/-0.07) was compatible with literature, but the pKb for UTP (5.19+/-0.03) was significantly higher. This discrepancy suggests that UTP activates supplementary non-P2Y2 receptor subtype(s). Further, pyridoxal-phosphate-6-azophenyl-2'-4'-disulphonic acid (PPADS) showed surmountable (UTP, UDP), nonsurmountable (ADP) or no antagonism (ATP). Finally, 2'-deoxy-N6-methyladenosine3',5'-bisphosphate (MRS2179) inhibited ADP-evoked relaxation only. Taken together, these results point to the presence of functional P2Y1 (ADP), P2Y2 (ATP, UTP) and P2Y6 (UDP) receptors on murine aorta endothelial cells. The identity of the receptor(s) mediating the action of UTP is not fully clear and other P2Y subtypes might be involved in UTP-evoked vasodilatation.

Endothelium-dependent relaxation evoked by ATP and UTP in the aorta of P2Y2-deficient mice

Based on pharmacological criteria, we previously suggested that in the mouse aorta, endothelium-dependent relaxation by nucleotides is mediated by P2Y1 (adenosine diphosphate (ADP)), P2Y2 (adenosine triphosphate (ATP)) and P2Y6 (uridine diphosphate (UDP)) receptors. For UTP, it was unclear whether P2Y2, P2Y6 or yet another subtype was involved. Therefore, in view of the lack of selective purinergic agonists and antagonists, we used P2Y2-deficient mice to clarify the action of UTP. Thoracic aorta segments (width 2 mm) of P2Y2-deficient and wild-type (WT) mice were mounted in organ baths to measure isometric force development and intracellular calcium signalling. Relaxations evoked by ADP, UDP and acetylcholine were identical in knockout and WT mice, indicating that the receptors for these agonists function normally. P2Y2-deficient mice showed impaired ATP- and adenosine 5'[gamma-thio] triphosphate (ATPgammaS)-evoked relaxation, suggesting that in WT mice, ATP and ATPgammaS activate predominantly the P2Y2 subtype. The ATP/ATPgammaS-evoked relaxation and calcium signals in the knockout mice were partially rescued by P2Y1, as they were sensitive to 2'-deoxy-N6-methyladenosine 3',5'-bisphosphate (MRS2179), a P2Y1-selective antagonist. In contrast to ATP, the UTP-evoked relaxation was not different between knockout and WT mice. Moreover, the action of UTP was not sensitive to MRS2179. Therefore, the action of UTP is probably mediated mainly by a P2Y6(like) receptor subtype. In conclusion, we demonstrated that ATP-evoked relaxation of the murine aorta is mainly mediated by P2Y2. But this P2Y2 receptor has apparently no major role in UTP-evoked relaxation. The vasodilator effect of UTP is probably mediated mainly by a P2Y6(like) receptor.

Partial Inhibition of Glycolysis Reduces Atherogenesis Independent of Intraplaque Neovascularization in Mice

OBJECTIVE

Intraplaque neovascularization is an important feature of unstable human atherosclerotic plaques. However, its impact on plaque formation and stability is poorly studied. Because proliferating endothelial cells generate up to 85% of their ATP from glycolysis, we investigated whether pharmacological inhibition of glycolytic flux by the small-molecule 3PO (3-[3-pyridinyl]-1-[4-pyridinyl]-2-propen-1-one) could have beneficial effects on plaque formation and composition. Approach and Results: ApoE-/- (apolipoprotein E deficient) mice treated with 3PO (50 µg/g, ip; 4×/wk, 4 weeks) showed a metabolic switch toward ketone body formation. Treatment of ApoE-/-Fbn1C1039G+/- mice with 3PO (50 µg/g, ip) either after 4 (preventive, twice/wk, 10 weeks) or 16 weeks of Western diet (curative, 4×/wk, 4 weeks) inhibited intraplaque neovascularization by 50% and 38%, respectively. Plaque formation was significantly reduced in all 3PO-treated animals. This effect was independent of intraplaque neovascularization. In vitro experiments showed that 3PO favors an anti-inflammatory M2 macrophage subtype and suppresses an M1 proinflammatory phenotype. Moreover, 3PO induced autophagy, which in turn impaired NF-κB (nuclear factor-kappa B) signaling and inhibited TNF-α (tumor necrosis factor-alpha)-mediated VCAM-1 (vascular cell adhesion molecule-1) and ICAM-1 (intercellular adhesion molecule-1) upregulation. Consistently, a preventive 3PO regimen reduced endothelial VCAM-1 expression in vivo. Furthermore, 3PO improved cardiac function in ApoE-/-Fbn1C1039G+/- mice after 10 weeks of treatment.

CONCLUSIONS

Partial inhibition of glycolysis restrained intraplaque angiogenesis without affecting plaque composition. However, less plaques were formed, which was accompanied by downregulation of endothelial adhesion molecules-an event that depends on autophagy induction. Inhibition of coronary plaque formation by 3PO resulted in an overall improved cardiac function.

Neuregulin-1 attenuates stress-induced vascular senescence

Aims

Cardiovascular ageing is a key determinant of life expectancy. Cellular senescence, a state of irreversible cell cycle arrest, is an important contributor to ageing due to the accumulation of damaged cells. Targeting cellular senescence could prevent age-related cardiovascular diseases. In this study, we investigated the effects of neuregulin-1 (NRG-1), an epidermal growth factor with cardioprotective and anti-atherosclerotic effects, on cellular senescence.

Methods and results

Senescence was induced in cultured rat aortic endothelial cells (ECs) and aortic smooth muscle cells (SMCs) by 2 h exposure to 30 µM hydrogen peroxide (H2O2). Cellular senescence was confirmed after 72 h using senescence-associated-β-galactosidase staining (SA-β-gal), cell surface area, and western blot analyses of SA pathways (acetyl-p53, p21). Recombinant human NRG-1 (rhNRG-1, 20 ng/mL) significantly reduced H2O2-induced senescence, as shown by a lower number of SA-β-gal positive cells, smaller surface area and lower expression of acetyl-p53. In C57BL/6 male mice rendered diabetic with streptozotocin (STZ), rhNRG-1 attenuated cellular senescence in aortic ECs and SMCs. Next, we created mice with SMC-specific knockdown of the NRG-1 receptor ErbB4. Aortic SMCs isolated from SMC-specific ErbB4 deficient mice (ErbB4f/+ SM22α-Cre+) showed earlier cellular senescence in vitro compared with wild-type (ErbB4+/+ SM22α-Cre+) SMCs. Furthermore, when rendered diabetic with STZ, ErbB4f/+ SM22α-Cre+ male mice showed significantly more vascular senescence than their diabetic wild-type littermates and had increased mortality.

Conclusions

This study is the first to explore the role of NRG-1 in vascular senescence. Our data demonstrate that NRG-1 markedly inhibits stress-induced premature senescence in vascular cells in vitro and in the aorta of diabetic mice in vivo. Consistently, deficiency in the NRG-1 receptor ErbB4 provokes cellular senescence in vitro as well as in vivo.

P2Y receptors and atherosclerosis in apolipoprotein E-deficient mice

BACKGROUND AND PURPOSE

P2Y nucleotide receptors are involved in the regulation of vascular tone, smooth muscle cell (SMC) proliferation and inflammatory responses. The present study investigated whether they are involved in atherosclerosis.

EXPERIMENTAL APPROACH

mRNA of P2Y receptors was quantified (RT-PCR) in atherosclerotic and plaque-free aorta segments of apolipoprotein E-deficient (apoE(-/-)) mice. Macrophage activation was assessed in J774 macrophages, and effects of non-selective purinoceptor antagonists on atherosclerosis were evaluated in cholesterol-fed apoE(-/-) mice.

KEY RESULTS

P2Y(6) receptor mRNA was consistently elevated in segments with atherosclerosis, whereas P2Y(2) receptor expression remained unchanged. Expression of P2Y(1) or P2Y(4) receptor mRNA was low or undetectable, and not influenced by atherosclerosis. P2Y(6) mRNA expression was higher in cultured J774 macrophages than in cultured aortic SMCs. Furthermore, immunohistochemical staining of plaques demonstrated P2Y(6)-positive macrophages, but few SMCs, suggesting that macrophage recruitment accounted for the increase in P2Y(6) receptor mRNA during atherosclerosis. In contrast to ATP, the P2Y(6)-selective agonist UDP increased mRNA expression and activity of inducible nitric oxide synthase and interleukin-6 in J774 macrophages; this effect was blocked by suramin (100-300 microM) or pyridoxal-phosphate-6-azophenyl-2'-4'-disulphonic acid (PPADS, 10-30 microM). Finally, 4-week treatment of cholesterol-fed apoE(-/-) mice with suramin or PPADS (50 and 25 mg.kg(-1).day(-1) respectively) reduced plaque size, without changing plaque composition (relative SMC and macrophage content) or cell replication.

CONCLUSIONS AND IMPLICATIONS

These results suggest involvement of nucleotide receptors, particularly P2Y(6) receptors, during atherosclerosis, and warrant further research with selective purinoceptor antagonists or P2Y(6) receptor-deficient mice.

Acute modulation of the cholinergic system in the mouse brain detected by pharmacological resting-state functional MRI

INTRODUCTION

The cholinergic system is involved in learning and memory and is affected in neurodegenerative disorders such as Alzheimer's disease. The possibility of non-invasively detecting alterations of neurotransmitter systems in the mouse brain would greatly improve early diagnosis and treatment strategies. The hypothesis of this study is that acute modulation of the cholinergic system might be reflected as altered functional connectivity (FC) and can be measured using pharmacological resting-state functional MRI (rsfMRI).

MATERIAL AND METHODS

Pharmacological rsfMRI was performed on a 9.4T MRI scanner (Bruker BioSpec, Germany) using a gradient echo EPI sequence. All mice were sedated with medetomidine. C57BL/6 mice (N = 15/group) were injected with either saline, the cholinergic antagonist scopolamine, or methyl-scopolamine, after which rsfMRI was acquired. For an additional group (N = 8), rsfMRI scans of the same mouse were acquired first at baseline, then after the administration of scopolamine and finally after the additional injection of the cholinergic agonist milameline. Contextual memory was evaluated with the same setup as the pharmacological rsfMRI using the passive avoidance behavior test.

RESULTS

Scopolamine induced a dose-dependent decrease of FC between brain regions involved in memory. Scopolamine-induced FC deficits could be recovered completely by milameline for FC between the hippocampus-thalamus, cingulate-retrosplenial, and visual-retrosplenial cortex. FC between the cingulate-rhinal, cingulate-visual and visual-rhinal cortex could not be completely recovered by milameline. This is consistent with the behavioral outcome, where milameline only partially recovered scopolamine-induced contextual memory deficits. Methyl-scopolamine administered at the same dose as scopolamine did not affect FC in the brain.

CONCLUSION

The results of the current study are important for future studies in mouse models of neurodegenerative disorders, where pharmacological rsfMRI may possibly be used as a non-invasive read-out tool to detect alterations of neurotransmitter systems induced by pathology or treatment.

Gasdermin D Deficiency Limits the Transition of Atherosclerotic Plaques to an Inflammatory Phenotype in ApoE Knock-Out Mice

Gasdermin D (GSDMD) is the key executor of pyroptotic cell death. Recent studies suggest that GSDMD-mediated pyroptosis is involved in atherosclerotic plaque destabilization. We report that cleaved GSDMD is expressed in macrophage- and smooth muscle cell-rich areas of human plaques. To determine the effects of GSDMD deficiency on atherogenesis, ApoE^−/− Gsdmd^−/− (n = 16) and ApoE^−/−Gsdmd^+/+ (n = 18) mice were fed a western-type diet for 16 weeks. Plaque initiation and formation of stable proximal aortic plaques were not altered. However, plaques in the brachiocephalic artery (representing more advanced lesions compared to aortic plaques) of ApoE^−/− Gsdmd^−/− mice were significantly smaller (115 ± 18 vs. 186 ± 16 × 10³ µm², p = 0.006) and showed features of increased stability, such as decreased necrotic core area (19 ± 4 vs. 37 ± 7 × 10³ µm², p = 0.03) and increased αSMA/MAC3 ratio (1.6 ± 0.3 vs. 0.7 ± 0.1, p = 0.01), which was also observed in proximal aortic plaques. Interestingly, a significant increase in TUNEL positive cells was observed in brachiocephalic artery plaques from ApoE^−/− Gsdmd^−/− mice (141 ± 25 vs. 62 ± 8 cells/mm², p = 0.005), indicating a switch to apoptosis. This switch from pyroptosis to apoptosis was also observed in vitro in Gsdmd^−/− macrophages. In conclusion, targeting GSDMD appears to be a promising approach for limiting the transition to an inflammatory, vulnerable plaque phenotype.

Endothelial function in aorta segments of apolipoprotein E-deficient mice before development of atherosclerotic lesions

Acetylcholine (ACh)-induced relaxation declines in apolipoprotein E-deficient (apoE-/-) mouse aortas, but only after atherosclerotic plaque formation. This study investigated intracellular calcium concentrations [Ca2+]i and changes in phenylephrine-induced contractions as index of baseline nitric oxide (NO) bioavailability before plaque development. Isometric contractions of thoracic aorta rings of young (4 months) apoE-/- and C57BL/6J (WT) mice were evoked by phenylephrine (3x10(-9)-3x10(-5) M) in the presence and absence of endothelial cells (ECs) or NO synthase (NOS) inhibitors. [Ca2+]i (Fura-2 AM) and endothelium-dependent relaxation were measured at baseline and after ACh stimulation. Segments of apoE-/- mice were significantly more sensitive and developed more tension than WT segments in response to phenylephrine. The differences disappeared after NOS inhibition or EC removal or upon increasing [Ca2+]i in apoE-/- strips with 10(-6) M cyclopiazonic acid or 10(-7) M Ca2+-ionophore A23187. Expression of endothelial NOS (eNOS) mRNA was similar in apoE-/- and WT aorta segments. Basal [Ca2+]i was significantly lower in apoE-/- than in WT strips. Relaxation by ACh (3x10(-9)-10(-5) M) was time- and dose-dependently related to [Ca2+]i, but neither ACh-induced relaxation nor Ca2+ mobilization were diminished in apoE-/- strips. In conclusion, basal, but not ACh-induced NO bioavailability, was compromised in lesion-free aorta of apoE-/- mice. Decreased basal NO bioavailability was not related to lower eNOS expression, but most likely related to lower basal [Ca2+]i. These findings further point to important differences between basal and stimulated eNOS activity.

Doxorubicin induces arterial stiffness: A comprehensive in vivo and ex vivo evaluation of vascular toxicity in mice

Arterial stiffness is an important predictor of cardiovascular risk. Clinical studies have demonstrated that arterial stiffness increases in cancer patients treated with the chemotherapeutic doxorubicin (DOX). However, the mechanisms of DOX-induced arterial stiffness remain largely unknown. This study aimed to evaluate artery stiffening in DOX-treated mice using in vivo and ex vivo techniques. Male C57BL/6J mice were treated for 2 weeks with 2 mg/kg (low dose) or 4 mg/kg (high dose) of DOX weekly. Arterial stiffness was assessed in vivo with ultrasound imaging (abdominal aorta pulse wave velocity (aaPWV)) and applanation tonometry (carotid-femoral PWV) combined with ex vivo vascular stiffness and reactivity evaluation. The high dose increased aaPWV, while cfPWV did not reach statistical significance. Phenylephrine (PE)-contracted aortic segments showed a higher Peterson's modulus (Ep) in the high dose group, while Ep did not differ when vascular smooth muscle cells (VSMCs) were relaxed by a NO donor (DEANO). In addition, aortic rings of DOX-treated mice showed increased PE contraction, decreased basal nitric oxide (NO) index and impaired acetylcholine-induced endothelium-dependent relaxation. DOX treatment contributed to endothelial cell loss and reduced endothelial nitric oxide synthase (eNOS) expression in the aorta. In conclusion, we have replicated DOX-induced arterial stiffness in a murine model and this aortic stiffness is driven by impaired endothelial function, contributing to increased vascular tone.

Effect of erythrophagocytosis-induced ferroptosis during angiogenesis in atherosclerotic plaques

Intraplaque (IP) angiogenesis is a key feature of advanced atherosclerotic plaques. Because IP vessels are fragile and leaky, erythrocytes are released and phagocytosed by macrophages (erythrophagocytosis), which leads to high intracellular iron content, lipid peroxidation and cell death. In vitro experiments showed that erythrophagocytosis by macrophages induced non-canonical ferroptosis, an emerging type of regulated necrosis that may contribute to plaque destabilization. Erythrophagocytosis-induced ferroptosis was accompanied by increased expression of heme-oxygenase 1 and ferritin, and could be blocked by co-treatment with third generation ferroptosis inhibitor UAMC-3203. Both heme-oxygenase 1 and ferritin were also expressed in erythrocyte-rich regions of carotid plaques from ApoE-/- Fbn1C1039G+/- mice, a model of advanced atherosclerosis with IP angiogenesis. The effect of UAMC-3203 (12.35 mg/kg/day) on atherosclerosis was evaluated in ApoE-/- Fbn1C1039G+/- mice fed a western-type diet (WD) for 12 weeks (n = 13 mice/group) or 20 weeks (n = 16-21 mice/group) to distinguish between plaques without and with established IP angiogenesis, respectively. A significant decrease in carotid plaque thickness was observed after 20 weeks WD (87 ± 19 μm vs. 166 ± 20 μm, p = 0.006), particularly in plaques with confirmed IP angiogenesis or hemorrhage (108 ± 35 μm vs. 322 ± 40 μm, p = 0.004). This effect was accompanied by decreased IP heme-oxygenase 1 and ferritin expression. UAMC-3203 did not affect carotid plaques after 12 weeks WD or plaques in the aorta, which typically do not develop IP angiogenesis. Altogether, erythrophagocytosis-induced ferroptosis during IP angiogenesis leads to larger atherosclerotic plaques, an effect that can be prevented by ferroptosis inhibitor UAMC-3203.

Attenuated atherogenesis in apolipoprotein E-deficient mice lacking amyloid precursor protein

OBJECTIVE

Recent evidence suggests that amyloid precursor protein (APP) is overexpressed in atherosclerosis-prone regions of mouse aorta. We therefore investigated in the present study whether APP has a role in the progression and composition of atherosclerotic plaques.

METHODS AND RESULTS

Apolipoprotein E-deficient (apoE(-/-)) mice were crossbred with animals lacking APP (APP(-/-)). After 16 weeks on a Western-type diet, apoE(-/-) and APP(-/-)/apoE(-/-) mice showed similar cholesterol levels. However, atherosclerotic plaque size was significantly reduced in the distal thoracic aorta (90% reduction) and abdominal aorta (75% reduction) of APP(-/-)/apoE(-/-) mice as compared to apoE(-/-). Plaques at the level of the aortic valves were not different in size, but showed a more stable phenotype in APP(-/-)/apoE(-/-) mice, as indicated by a reduced macrophage content, an increased amount of collagen and a thicker fibrous cap.

CONCLUSION

Our findings provide evidence that lack of APP attenuates atherogenesis and leads to plaque stability.

Transcription profiles of aortic smooth muscle cells from atherosclerosis-prone and -resistant regions in young apolipoprotein E-deficient mice before plaque development

BACKGROUND/AIMS

Site-specific atherosclerosis is generally attributed to differential gene expression in endothelial cells. We investigated whether the transcriptome of smooth muscle cells is different between atherosclerosis-prone and atherosclerosis-resistant regions in apolipoprotein E-deficient (apoE-/-) mice before plaque development, and in C57Bl/6 mice.

METHODS

De-endothelialized aortas (both strains: 3 males, 3 females, age 4 months) were divided into atherosclerosis-prone (AA: ascending aorta, aortic arch and proximal 2 mm of thoracic aorta) and -resistant (CTA: central thoracic aorta, i.e. 6 mm distal from the proximal 2 mm) regions. The transcriptome of these two regions was compared using whole-genome mouse microarrays.

RESULTS

Microarray analysis revealed differential expression (>2-fold difference) of 70 and 244 genes in C57Bl/6 and apoE-/- mice. This was confirmed for 6 genes using the real-time quantitative polymerase chain reaction. Up- or downregulation in the AA was observed for 33 and 37 genes in C57Bl/6, and for 186 and 58 genes in apoE-/- mice, respectively. The 201 genes that showed exclusively differential expression in apoE-/- mice were related to atherosclerotic processes, such as cell adhesion, proliferation, differentiation, motility, cell death, lipid metabolism and immune responses.

CONCLUSION

Our findings indicate that smooth muscle cells display an altered transcriptome at atherosclerosis-prone locations before actual lesion development.

Doxorubicin-induced cardiovascular toxicity: a longitudinal evaluation of functional and molecular markers

AIMS

Apart from cardiotoxicity, the chemotherapeutic doxorubicin (DOX) induces vascular toxicity, represented by arterial stiffness and endothelial dysfunction. Both parameters are of interest for cardiovascular risk stratification as they are independent predictors of future cardiovascular events in the general population. However, the time course of DOX-induced cardiovascular toxicity remains unclear. Moreover, current biomarkers for cardiovascular toxicity prove insufficient. Here, we longitudinally evaluated functional and molecular markers of DOX-induced cardiovascular toxicity in a murine model. Molecular markers were further validated in patient plasma.

METHODS AND RESULTS

DOX (4 mg/kg) or saline (vehicle) was administered intra-peritoneally to young, male mice weekly for 6 weeks. In vivo cardiovascular function and ex vivo arterial stiffness and vascular reactivity were evaluated at baseline, during DOX therapy (Weeks 2 and 4) and after therapy cessation (Weeks 6, 9, and 15). Left ventricular ejection fraction (LVEF) declined from Week 4 in the DOX group. DOX increased arterial stiffness in vivo and ex vivo at Week 2, which reverted thereafter. Importantly, DOX-induced arterial stiffness preceded reduced LVEF. Further, DOX impaired endothelium-dependent vasodilation at Weeks 2 and 6, which recovered at Weeks 9 and 15. Conversely, contraction with phenylephrine was consistently higher in the DOX-treated group. Furthermore, proteomic analysis on aortic tissue identified increased thrombospondin-1 (THBS1) and alpha-1-antichymotrypsin (SERPINA3) at Weeks 2 and 6. Up-regulated THBS1 and SERPINA3 persisted during follow-up. Finally, THBS1 and SERPINA3 were quantified in plasma of patients. Cancer survivors with anthracycline-induced cardiotoxicity (AICT; LVEF < 50%) showed elevated THBS1 and SERPINA3 levels compared with age-matched control patients (LVEF ≥ 60%).

CONCLUSIONS

DOX increased arterial stiffness and impaired endothelial function, which both preceded reduced LVEF. Vascular dysfunction restored after DOX therapy cessation, whereas cardiac dysfunction persisted. Further, we identified SERPINA3 and THBS1 as promising biomarkers of DOX-induced cardiovascular toxicity, which were confirmed in AICT patients.

Monitoring Blood-Brain Barrier Integrity Following Amyloid-β Immunotherapy Using Gadolinium-Enhanced MRI in a PDAPP Mouse Model

BACKGROUND

Amyloid-related imaging abnormalities (ARIA) have been reported with some anti-amyloid-β (Aβ) immunotherapy trials. They are detected with magnetic resonance imaging (MRI) and thought to represent transient accumulation of fluid/edema (ARIA-E) or microhemorrhages (ARIA-H). Although the clinical significance and pathophysiology are unknown, it has been proposed that anti-Aβimmunotherapy may affect blood-brain barrier (BBB) integrity.

OBJECTIVE

To examine vascular integrity in aged (12-16 months) PDAPP and wild type mice (WT), we performed a series of longitudinal in vivo MRI studies.

METHODS

Mice were treated on a weekly basis using anti-Aβimmunotherapy (3D6) and follow up was done longitudinally from 1-12 weeks after treatment. BBB-integrity was assessed using both visual assessment of T1-weighted scans and repeated T1 mapping in combination with gadolinium (Gd-DOTA).

RESULTS

A subset of 3D6 treated PDAPP mice displayed numerous BBB disruptions, whereas WT and saline-treated PDAPP mice showed intact BBB integrity under the conditions tested. In addition, the contrast induced decrease in T1 value was observed in the meningeal and midline area. BBB disruption events occurred early during treatment (between 1 and 5 weeks), were transient, and resolved quickly. Finally, BBB-leakages associated with microhemorrhages were confirmed by Perls'Prussian blue histopathological analysis.

CONCLUSION

Our preclinical findings support the hypothesis that 3D6 leads to transient leakage from amyloid-positive vessels. The current study has provided valuable insights on the time course of vascular alterations during immunization treatment and supports further research in relation to the nature of ARIA and the utility of in vivo repeated T1 MRI as a translational tool.

A human importin-β-related disorder: Syndromic thoracic aortic aneurysm caused by bi-allelic loss-of-function variants in IPO8

Importin 8, encoded by IPO8, is a ubiquitously expressed member of the importin-β protein family that translocates cargo molecules such as proteins, RNAs, and ribonucleoprotein complexes into the nucleus in a RanGTP-dependent manner. Current knowledge of the cargoes of importin 8 is limited, but TGF-β signaling components such as SMAD1-4 have been suggested to be among them. Here, we report that bi-allelic loss-of-function variants in IPO8 cause a syndromic form of thoracic aortic aneurysm (TAA) with clinical overlap with Loeys-Dietz and Shprintzen-Goldberg syndromes. Seven individuals from six unrelated families showed a consistent phenotype with early-onset TAA, motor developmental delay, connective tissue findings, and craniofacial dysmorphic features. A C57BL/6N Ipo8 knockout mouse model recapitulates TAA development from 8-12 weeks onward in both sexes but most prominently shows ascending aorta dilatation with a propensity for dissection in males. Compliance assays suggest augmented passive stiffness of the ascending aorta in male Ipo8^-/- mice throughout life. Immunohistological investigation of mutant aortic walls reveals elastic fiber disorganization and fragmentation along with a signature of increased TGF-β signaling, as evidenced by nuclear pSmad2 accumulation. RT-qPCR assays of the aortic wall in male Ipo8^-/- mice demonstrate decreased Smad6/7 and increased Mmp2 and Ccn2 (Ctgf) expression, reinforcing a role for dysregulation of the TGF-β signaling pathway in TAA development. Because importin 8 is the most downstream TGF-β-related effector implicated in TAA pathogenesis so far, it offers opportunities for future mechanistic studies and represents a candidate drug target for TAA.

Contractile Behavior of Mouse Aorta Depends on SERCA2 Isoform Distribution: Effects of Replacing SERCA2a by SERCA2b

The Sarco(endo)plasmic reticulum Ca²⁺ ATPase (SERCA) actively pumps Ca²⁺ into the sarco/endoplasmic reticulum, thereby regulating intracellular Ca²⁺ concentrations and associated physiological processes. Different SERCA isoforms have been described (SERCA1, 2, and 3) with SERCA2 playing a pivotal role in Ca²⁺ homeostasis in cardiovascular tissues. In the heart, SERCA2a is the dominant isoform and has been proposed as therapeutic target in patients with heart failure. In the vasculature, both SERCA2a and SERCA2b are expressed with SERCA2b being the predominant isoform. The physiological role of SERCA2a in the vasculature, however, remains incompletely understood. In the present study, we used gene-modified mice in which the alternative splicing of the SERCA2-encoding gene (Atp2a2), underlying the expression of SERCA2a, is prevented and SERCA2a is replaced by SERCA2b. The resulting SERCA2^b/b mice provide a unique opportunity to investigate the specific contribution of SERCA2a versus SERCA2b to vascular physiology. Aortic segments of SERCA2^b/b (SERCA2a-deficient) and SERCA2^a/b (control) mice were mounted in organ baths to evaluate vascular reactivity. SERCA2^b/b aortic rings displayed higher contractions induced by phenylephrine (1 μM). Surprisingly, the initial inositol-3-phosphate mediated phasic contraction showed a faster decay of force in SERCA2^b/b mice, while the subsequent tonic contraction was larger in SERCA2^b/b segments. Moreover, in the presence of the calcium channel blocker diltiazem (35 μM) SERCA2^b/b aortic rings showed higher contractions compared to SERCA2^a/b, suggesting that SERCA2a (deficiency) modulates the activity of non-selective cation channels. Additionally, in endothelial cell (EC)-denuded aortic segments, the SERCA-inhibitor cyclopiazonic acid (CPA) caused markedly larger contractions in SERCA2^b/b mice, while the increases of cytosolic Ca²⁺ were similar in both strains. Hence, aortas of SERCA2^b/b mice appear to have a stronger coupling of intracellular Ca²⁺ to contraction, which may be in agreement with the reported difference in intracellular localization of SERCA2a versus SERCA2b. Finally, EC-mediated relaxation by acetylcholine and ATP was assessed. Concentration-response-curves for ATP showed a higher sensitivity of aortic segments of SERCA2^b/b mice, while no difference in potency between strains were observed for acetylcholine. In summary, despite the relative low expression of SERCA2a in the murine aorta, our results point toward a distinct role in vascular physiology.

High Pulsatile Load Decreases Arterial Stiffness: An ex vivo Study

Measuring arterial stiffness has recently gained a lot of interest because it is a strong predictor for cardiovascular events and all-cause mortality. However, assessing blood vessel stiffness is not easy and the in vivo measurements currently used provide only limited information. Ex vivo experiments allow for a more thorough investigation of (altered) arterial biomechanical properties. Such experiments can be performed either statically or dynamically, where the latter better corresponds to physiological conditions. In a dynamic setup, arterial segments oscillate between two predefined forces, mimicking the diastolic and systolic pressures from an in vivo setting. Consequently, these oscillations result in a pulsatile load (i.e., the pulse pressure). The importance of pulse pressure on the ex vivo measurement of arterial stiffness is not completely understood. Here, we demonstrate that pulsatile load modulates the overall stiffness of the aortic tissue in an ex vivo setup. More specifically, increasing pulsatile load softens the aortic tissue. Moreover, vascular smooth muscle cell (VSMC) function was affected by pulse pressure. VSMC contraction and basal tonus showed a dependence on the amplitude of the applied pulse pressure. In addition, two distinct regions of the aorta, namely the thoracic descending aorta (TDA) and the abdominal infrarenal aorta (AIA), responded differently to changes in pulse pressure. Our data indicate that pulse pressure alters ex vivo measurements of arterial stiffness and should be considered as an important variable in future experiments. More research should be conducted in order to determine which biomechanical properties are affected due to changes in pulse pressure. The elucidation of the underlying pulse pressure-sensitive properties would improve our understanding of blood vessel biomechanics and could potentially yield new therapeutic insights.

Cardiac electrophysiology studies in mice via the transjugular route: a comprehensive practical guide

Cardiac arrhythmias are associated with cardiovascular morbidity and mortality. Cardiac electrophysiology studies (EPS) use intracardiac catheter recording and stimulation for profound evaluation of the heart's electrical properties. The main clinical application is investigation and treatment of rhythm disorders. These techniques have been translated to the murine setting to open opportunities for detailed evaluation of the impact of different characteristics (including genetics) and interventions on cardiac electrophysiology and -pathology. Currently, a detailed description of the technique of murine transjugular EPS (which is the standard route of catheter introduction) is lacking. This article provides detailed information on EPS in mice via the transjugular route. This includes catheter placement, stimulation protocols, intracardiac tracing interpretation, artefact reduction and surface ECG recording. In addition, reference values as obtained in C57BL/6N mice are presented for common electrophysiological parameters. This detailed methodological description aims to increase accessibility and standardisation of EPS in mice. Ultimately, also human research and patient care may benefit from translation of the knowledge obtained in preclinical models using this technique.

The Protective Effects of the Autophagic and Lysosomal Machinery in Vascular and Valvular Calcification: A Systematic Review

BACKGROUND

Autophagy is a highly conserved catabolic homeostatic process, crucial for cell survival. It has been shown that autophagy can modulate different cardiovascular pathologies, including vascular calcification (VCN).

OBJECTIVE

To assess how modulation of autophagy, either through induction or inhibition, affects vascular and valvular calcification and to determine the therapeutic applicability of inducing autophagy.

DATA SOURCES

A systematic review of English language articles using MEDLINE/PubMed, Web of Science (WoS) and the Cochrane library. The search terms included autophagy, autolysosome, mitophagy, endoplasmic reticulum (ER)-phagy, lysosomal, calcification and calcinosis. Study characteristics: Thirty-seven articles were selected based on pre-defined eligibility criteria. Thirty-three studies (89%) studied vascular smooth muscle cell (VSMC) calcification of which 27 (82%) studies investigated autophagy and six (18%) studies lysosomal function in VCN. Four studies (11%) studied aortic valve calcification (AVCN). Thirty-four studies were published in the time period 2015-2020 (92%).

CONCLUSION

There is compelling evidence that both autophagy and lysosomal function are critical regulators of VCN, which opens new perspectives for treatment strategies. However, there are still challenges to overcome, such as the development of more selective pharmacological agents and standardization of methods to measure autophagic flux.

B-cell lymphoblastic lymphoma following intravenous BNT162b2 mRNA booster in a BALB/c mouse: A case report

Unprecedented immunization campaigns have been rolled out worldwide in an attempt to contain the ongoing COVID-19 pandemic. Multiple vaccines were brought to the market, among two utilizing novel messenger ribonucleic acid technology. Despite their undisputed success in decreasing COVID-19-associated hospitalizations and mortality, various adverse events have been reported. The emergence of malignant lymphoma is one of such rare adverse events that has raised concern, although an understanding of the mechanisms potentially involved remains lacking. Herein, we present the first case of B-cell lymphoblastic lymphoma following intravenous high-dose mRNA COVID-19 vaccination (BNT162b2) in a BALB/c mouse. Two days following booster vaccination (i.e., 16 days after prime), at only 14 weeks of age, our animal suffered spontaneous death with marked organomegaly and diffuse malignant infiltration of multiple extranodal organs (heart, lung, liver, kidney, spleen) by lymphoid neoplasm. Immunohistochemical examination revealed organ sections positive for CD19, terminal deoxynucleotidyl transferase, and c-MYC, compatible with a B-cell lymphoblastic lymphoma immunophenotype. Our murine case adds to previous clinical reports on malignant lymphoma development following novel mRNA COVID-19 vaccination, although a demonstration of direct causality remains difficult. Extra vigilance is required, with conscientious reporting of similar cases and a further investigation of the mechanisms of action explaining the aforementioned association.

Neuregulin-1 compensates for endothelial nitric oxide synthase deficiency

Endothelial cells (ECs) secrete different paracrine signals that modulate the function of adjacent cells; two examples of these paracrine signals are nitric oxide (NO) and neuregulin-1 (NRG1), a cardioprotective growth factor. Currently, it is undetermined whether one paracrine factor can compensate for the loss of another. Herein, we hypothesized that NRG1 can compensate for endothelial NO synthase (eNOS) deficiency. We characterized eNOS null and wild-type (WT) mice by cardiac ultrasound and histology and we determined circulating NRG1 levels. In a separate experiment, eight groups of mice were divided into four groups of eNOS null mice and WT mice; half of the mice received angiotensin II (ANG II) to induce a more severe phenotype. Mice were randomized to daily injections with NRG1 or vehicle for 28 days. eNOS deficiency increased NRG1 plasma levels, indicating that ECs increase their NRG1 expression when NO production is deleted. eNOS deficiency also increased blood pressure, lowered heart rate, induced cardiac fibrosis, and affected diastolic function. In eNOS null mice, ANG II administration not only increased cardiac fibrosis but also induced cardiac hypertrophy and renal fibrosis. NRG1 administration prevented cardiac and renal hypertrophy and fibrosis caused by ANG II infusion and eNOS deficiency. Moreover, Nrg1 expression in the myocardium is shown to be regulated by miR-134. This study indicates that administration of endothelium-derived NRG1 can compensate for eNOS deficiency in the heart and kidneys.NEW & NOTEWORTHY ECs compensate for eNOS deficiency by increasing the secretion of NRG1. NRG1 administration prevents cardiac and renal hypertrophy and fibrosis caused by ANG II infusion and eNOS deficiency. NRG1 expression is regulated by miR-134.