Epigenetic Induction of Smooth Muscle Cell Phenotypic Alterations in Aortic Aneurysms and Dissections

BACKGROUND

Smooth muscle cell (SMC) phenotypic switching has been increasingly detected in aortic aneurysm and dissection (AAD) tissues. However, the diverse SMC phenotypes in AAD tissues and the mechanisms driving SMC phenotypic alterations remain to be identified.

METHODS

We examined the transcriptomic and epigenomic dynamics of aortic SMC phenotypic changes in mice with angiotensin II-induced AAD by using single-cell RNA sequencing and single-cell sequencing assay for transposase-accessible chromatin. SMC phenotypic alteration in aortas from patients with ascending thoracic AAD was examined by using single-cell RNA sequencing analysis.

RESULTS

Single-cell RNA sequencing analysis revealed that aortic stress induced the transition of SMCs from a primary contractile phenotype to proliferative, extracellular matrix-producing, and inflammatory phenotypes. Lineage tracing showed the complete transformation of SMCs to fibroblasts and macrophages. Single-cell sequencing assay for transposase-accessible chromatin analysis indicated that these phenotypic alterations were controlled by chromatin remodeling marked by the reduced chromatin accessibility of contractile genes and the induced chromatin accessibility of genes involved in proliferation, extracellular matrix, and inflammation. IRF3 (interferon regulatory factor 3), a proinflammatory transcription factor activated by cytosolic DNA, was identified as a key driver of the transition of aortic SMCs from a contractile phenotype to an inflammatory phenotype. In cultured SMCs, cytosolic DNA signaled through its sensor STING (stimulator of interferon genes)-TBK1 (tank-binding kinase 1) to activate IRF3, which bound and recruited EZH2 (enhancer of zeste homolog 2) to contractile genes to induce repressive H3K27me3 modification and gene suppression. In contrast, double-stranded DNA-STING-IRF3 signaling induced inflammatory gene expression in SMCs. In Sting-/- mice, the aortic stress-induced transition of SMCs into an inflammatory phenotype was prevented, and SMC populations were preserved. Finally, profound SMC phenotypic alterations toward diverse directions were detected in human ascending thoracic AAD tissues.

CONCLUSIONS

Our study reveals the dynamic epigenetic induction of SMC phenotypic alterations in AAD. DNA damage and cytosolic leakage drive SMCs from a contractile phenotype to an inflammatory phenotype.

Single-Cell Analysis of Aneurysmal Aortic Tissue in Patients with Marfan Syndrome Reveals Dysfunctional TGF-β Signaling

The molecular and cellular processes leading to aortic aneurysm development in Marfan syndrome (MFS) remain poorly understood. In this study, we examined the changes of aortic cell populations and gene expression in MFS by performing single-cell RNA sequencing (scRNA seq) on ascending aortic aneurysm tissues from patients with MFS (n = 3) and age-matched non-aneurysmal control tissues from cardiac donors and recipients (n = 4). The expression of key molecules was confirmed by immunostaining. We detected diverse populations of smooth muscle cells (SMCs), fibroblasts, and endothelial cells (ECs) in the aortic wall. Aortic tissues from MFS showed alterations of cell populations with increased de-differentiated proliferative SMCs compared to controls. Furthermore, there was a downregulation of MYOCD and MYH11 in SMCs, and an upregulation of COL1A1/2 in fibroblasts in MFS samples compared to controls. We also examined TGF-β signaling, an important pathway in aortic homeostasis. We found that TGFB1 was significantly upregulated in two fibroblast clusters in MFS tissues. However, TGF-β receptor genes (predominantly TGFBR2) and SMAD genes were downregulated in SMCs, fibroblasts, and ECs in MFS, indicating impairment in TGF-β signaling. In conclusion, despite upregulation of TGFB1, the rest of the canonical TGF-β pathway and mature SMCs were consistently downregulated in MFS, indicating a potential compromise of TGF-β signaling and lack of stimulus for SMC differentiation.

Metabolic remodeling precedes mTORC1-mediated cardiac hypertrophy

RATIONALE

The nutrient sensing mechanistic target of rapamycin complex 1 (mTORC1) and its primary inhibitor, tuberin (TSC2), are cues for the development of cardiac hypertrophy. The phenotype of mTORC1 induced hypertrophy is unknown.

OBJECTIVE

To examine the impact of sustained mTORC1 activation on metabolism, function, and structure of the adult heart.

METHODS AND RESULTS

We developed a mouse model of inducible, cardiac-specific sustained mTORC1 activation (mTORC1^iSA) through deletion of Tsc2. Prior to hypertrophy, rates of glucose uptake and oxidation, as well as protein and enzymatic activity of glucose 6-phosphate isomerase (GPI) were decreased, while intracellular levels of glucose 6-phosphate (G6P) were increased. Subsequently, hypertrophy developed. Transcript levels of the fetal gene program and pathways of exercise-induced hypertrophy increased, while hypertrophy did not progress to heart failure. We therefore examined the hearts of wild-type mice subjected to voluntary physical activity and observed early changes in GPI, followed by hypertrophy. Rapamycin prevented these changes in both models.

CONCLUSION

Activation of mTORC1 in the adult heart triggers the development of a non-specific form of hypertrophy which is preceded by changes in cardiac glucose metabolism.

Single-Cell Transcriptome Analysis Reveals Dynamic Cell Populations and Differential Gene Expression Patterns in Control and Aneurysmal Human Aortic Tissue

BACKGROUND

Ascending thoracic aortic aneurysm (ATAA) is caused by the progressive weakening and dilatation of the aortic wall and can lead to aortic dissection, rupture, and other life-threatening complications. To improve our understanding of ATAA pathogenesis, we aimed to comprehensively characterize the cellular composition of the ascending aortic wall and to identify molecular alterations in each cell population of human ATAA tissues.

METHODS

We performed single-cell RNA sequencing analysis of ascending aortic tissues from 11 study participants, including 8 patients with ATAA (4 women and 4 men) and 3 control subjects (2 women and 1 man). Cells extracted from aortic tissue were analyzed and categorized with single-cell RNA sequencing data to perform cluster identification. ATAA-related changes were then examined by comparing the proportions of each cell type and the gene expression profiles between ATAA and control tissues. We also examined which genes may be critical for ATAA by performing the integrative analysis of our single-cell RNA sequencing data with publicly available data from genome-wide association studies.

RESULTS

We identified 11 major cell types in human ascending aortic tissue; the high-resolution reclustering of these cells further divided them into 40 subtypes. Multiple subtypes were observed for smooth muscle cells, macrophages, and T lymphocytes, suggesting that these cells have multiple functional populations in the aortic wall. In general, ATAA tissues had fewer nonimmune cells and more immune cells, especially T lymphocytes, than control tissues did. Differential gene expression data suggested the presence of extensive mitochondrial dysfunction in ATAA tissues. In addition, integrative analysis of our single-cell RNA sequencing data with public genome-wide association study data and promoter capture Hi-C data suggested that the erythroblast transformation-specific related gene(ERG) exerts an important role in maintaining normal aortic wall function.

CONCLUSIONS

Our study provides a comprehensive evaluation of the cellular composition of the ascending aortic wall and reveals how the gene expression landscape is altered in human ATAA tissue. The information from this study makes important contributions to our understanding of ATAA formation and progression.

Glucose regulates the intrinsic inflammatory response of the heart to surgically induced hypothermic ischemic arrest and reperfusion

We investigated the isolated working rat heart as a model to study early transcriptional remodeling induced in the setting of open heart surgery and stress hyperglycemia. Hearts of male Sprague Dawley rats were cold-arrested in Krebs-Henseleit buffer and subjected to 60 min normothermic reperfusion in the working mode with buffer supplemented with noncarbohydrate substrates plus glucose (25 mM) or mannitol (25 mM; osmotic control). Gene expression profiles were determined by microarray analysis and compared with those of nonperfused hearts. Perfused hearts displayed a transcriptional signature independent from the presence of glucose showing a more than twofold increase in expression of 71 genes connected to inflammation, cell proliferation, and apoptosis. These transcriptional alterations were very similar to the ones taking place in the hearts of open heart surgery patients. Prominent among those alterations was the upregulation of the three master regulators of metabolic reprogramming, MYC, NR4A1, and NR4A2. Targeted pathway analysis revealed an upregulation of metabolic processes associated with the proliferation and activation of macrophages and fibroblasts. Glucose potentiated the upregulation of a subset of genes associated with polarization of tissue reparative M2-like macrophages, an effect that was lost in perfused hearts from rats rendered insulin resistant by high-sucrose feeding. The results expose the heart as a significant source of proinflammatory mediators released in response to stress associated with cardiac surgery with cardiopulmonary bypass, and suggest a major role for glucose as a signal in the determination of resident cardiac macrophage polarization.

Clodronate inhibits tumor angiogenesis in mouse models of ovarian cancer

PURPOSE

Bisphosphonates have been shown to inhibit and deplete macrophages. The effects of bisphosphonates on other cell types in the tumor microenvironment have been insufficiently studied. Here, we sought to determine the effects of bisphosphonates on ovarian cancer angiogenesis and growth via their effect on the microenvironment, including macrophage, endothelial and tumor cell populations.

EXPERIMENTAL DESIGN

Using in vitro and in vivo models, we examined the effects of clodronate on angiogenesis and macrophage density, and the overall effect of clodronate on tumor size and metastasis.

RESULTS

Clodronate inhibited the secretion of pro-angiogenic cytokines by endothelial cells and macrophages, and decreased endothelial migration and capillary tube formation. In treated mice, clodronate significantly decreased tumor size, number of tumor nodules, number of tumor-associated macrophages and tumor capillary density.

CONCLUSIONS

Clodronate is a potent inhibitor of tumor angiogenesis. These results highlight clodronate as a potential therapeutic for cancer.

Autocrine effects of tumor-derived complement

We describe a role for the complement system in enhancing cancer growth. Cancer cells secrete complement proteins that stimulate tumor growth upon activation. Complement promotes tumor growth via a direct autocrine effect that is partially independent of tumor-infiltrating cytotoxic T cells. Activated C5aR and C3aR signal through the PI3K/AKT pathway in cancer cells, and silencing the PI3K or AKT gene in cancer cells eliminates the progrowth effects of C5aR and C3aR stimulation. In patients with ovarian or lung cancer, higher tumoral C3 or C5aR mRNA levels were associated with decreased overall survival. These data identify a role for tumor-derived complement proteins in promoting tumor growth, and they therefore have substantial clinical and therapeutic implications.

Decreased long-chain fatty acid oxidation impairs postischemic recovery of the insulin-resistant rat heart

Diabetic patients with acute myocardial infarction are more likely to die than nondiabetic patients. In the present study we examined the effect of insulin resistance on myocardial ischemia tolerance. Hearts of rats, rendered insulin resistant by high-sucrose feeding, were subjected to ischemia/reperfusion ex vivo. Cardiac power of control hearts from chow-fed rats recovered to 93%, while insulin-resistant hearts recovered only to 80% (P<0.001 vs. control). Unexpectedly, impaired contractile recovery did not result from an impairment of glucose oxidation (576±36 vs. 593±42 nmol/min/g dry weight; not significant), but from a failure to increase and to sustain oxidation of the long-chain fatty acid oleate on reperfusion (1878±56 vs. 2070±67 nmol/min/g dry weight; P<0.05). This phenomenon was due to a reduced ability to transport oleate into mitochondria and associated with a 38-58% decrease in the mitochondrial uncoupling protein 3 (UCP3) levels. Contractile function was rescued by replacing oleate with a medium-chain fatty acid or by restoring UCP3 levels with 24 h of food withdrawal. Lastly, the knockdown of UCP3 in rat L6 myocytes also decreased oleate oxidation by 13-18% following ischemia. Together the results expose UCP3 as a critical regulator of long-chain fatty acid oxidation in the stressed heart postischemia and identify octanoate as an intervention by which myocardial metabolism can be manipulated to improve function of the insulin-resistant heart.

Abstract 4990: Complement promotes growth of ovarian cancer

Objective: The complement system is a component of innate immunity against invading pathogens, but also mediates the cell-cell communication in organ regeneration, angiogenesis, epithelial-mesenchymal transition (EMT) and cell migration. We studied whether the complement system affect tumor growth in ovarian cancer.

Materials & Methods: Complement C3 mRNA level was quantified using qRT-PCR in ovarian cancer cell lines and in tumor specimens from patients with ovarian cancer. Small interfering RNA (siRNA) was used to investigate the consequences of C3 gene silencing in vitro and in vivo.

Results: C3 was expressed in ovarian cancer cell lines and tumor tissues from patients. Silencing of the C3 gene decreased ovarian cancer cell proliferation, migration and invasion in vitro. In orthotopic murine models of ovarian cancer, C3 siRNA reduced growth of implanted tumors by 60% as was evident by lower number and smaller size of tumor nodules in C3-siRNA treated mice in comparison to those in scrambled siRNA treated control mice (average tumor weight of 0.19 g in C3 siRNA vs. 0.61 g in scrambled siRNA, n=8 in each group, p=0.017; average nodule number of 4.4 in C3 siRNA vs. 11.4 in scrambled siRNA, n=8 in each group, p=0.05; t-test). Consistent with our in vitro and animal studies, ovarian cancer patients with a higher C3 mRNA level in their tumors had a worse prognosis with overall survival rates compared to those with a lower C3 mRNA level (n=75, p=0.03).

Conclusion: Our studies revealed a novel role for complement in cancer biology. Cancer cell-derived C3 promotes tumor growth and progression. Our studies might identify the complement system as a new target for the development of new anti-tumor reagents.

Citation Format: Min Soon Cho, Hernan G. Vasquez, Hee Dong Han, Sunila Pradeep, Rajesh Rupaimoole, Behrouz Zand, Michael Kroll, Anil K. Sood, Vahid Afshar-Kharghan. Complement promotes growth of ovarian cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4990. doi:10.1158/1538-7445.AM2013-4990

Paraneoplastic thrombocytosis in ovarian cancer

BACKGROUND

The mechanisms of paraneoplastic thrombocytosis in ovarian cancer and the role that platelets play in abetting cancer growth are unclear.

METHODS

We analyzed clinical data on 619 patients with epithelial ovarian cancer to test associations between platelet counts and disease outcome. Human samples and mouse models of epithelial ovarian cancer were used to explore the underlying mechanisms of paraneoplastic thrombocytosis. The effects of platelets on tumor growth and angiogenesis were ascertained.

RESULTS

Thrombocytosis was significantly associated with advanced disease and shortened survival. Plasma levels of thrombopoietin and interleukin-6 were significantly elevated in patients who had thrombocytosis as compared with those who did not. In mouse models, increased hepatic thrombopoietin synthesis in response to tumor-derived interleukin-6 was an underlying mechanism of paraneoplastic thrombocytosis. Tumor-derived interleukin-6 and hepatic thrombopoietin were also linked to thrombocytosis in patients. Silencing thrombopoietin and interleukin-6 abrogated thrombocytosis in tumor-bearing mice. Anti-interleukin-6 antibody treatment significantly reduced platelet counts in tumor-bearing mice and in patients with epithelial ovarian cancer. In addition, neutralizing interleukin-6 significantly enhanced the therapeutic efficacy of paclitaxel in mouse models of epithelial ovarian cancer. The use of an antiplatelet antibody to halve platelet counts in tumor-bearing mice significantly reduced tumor growth and angiogenesis.

CONCLUSIONS

These findings support the existence of a paracrine circuit wherein increased production of thrombopoietic cytokines in tumor and host tissue leads to paraneoplastic thrombocytosis, which fuels tumor growth. We speculate that countering paraneoplastic thrombocytosis either directly or indirectly by targeting these cytokines may have therapeutic potential. (Funded by the National Cancer Institute and others.).

Abstract 3436: Mechanisms of paraneoplastic thrombocytosis in ovarian carcinoma

Objective: The observation that thrombocytosis (platelet count &gt;450,000/μL) occurs in patients with solid malignancies was made over 100 years ago. However, the underlying mechanisms and clinical implications of paraneoplastic thrombocytosis in epithelial malignancies such as ovarian carcinoma are poorly understood and are the focus of the current study.

Methods: Following IRB approval, clinical parameters and initial complete blood counts (CBC) were evaluated in 608 epithelial ovarian cancer patients. Plasma levels of key megakaryopoietic factors thrombopoietin, IL-1α, IL-3, IL-4, IL-6, IL-11, G-CSF, GM-CSF, stem cell factor, and FLT-3 ligand were assayed in a subset of 150 patients at the time of initial diagnosis with advanced stage, high grade epithelial ovarian cancer using a Luminex immunobead-based cytokine profiling platform. For animal studies, CBCs were measured in control mice as well as syngeneic (2 cell lines) and orthotopic (3 cell lines) mouse models of ovarian cancer. Megakaryocytes in spleen and bone marrow were quantified by bright-field microscopy.

Results: Human study: Thirty-two percent of patients had thrombocytosis at initial diagnosis. Compared to patients with normal platelet counts, women presenting with thrombocytosis were significantly more likely to have advanced stage disease (p=0.013) and poor mean progression-free (1.29 vs 2.73 years, p&lt;0.001) and overall survival (3.01 vs 6.05 years, p&lt;0.001). On multivariate analysis, thrombocytosis remained an independent predictor of decreased overall survival. Plasma levels of megakaryopoietic factors IL-6 and G-CSF significantly correlated with platelet counts (r=0.33, p&lt;0.01 and r=0.18, p=0.03). Animal study: Paraneoplastic thrombocytosis was recapitulated in both syngeneic and orthotopic mouse models of ovarian cancer. Platelet counts were increased by 27-200% in mice bearing invasive ovarian tumors compared to controls (p&lt;0.01) and platelet counts significantly correlated with tumor burden (r=0.61, p&lt;0.05). Thrombocytosis was accompanied by a non-significant increase in leukocytes and decrease in red blood cells. Mean platelet count in the peripheral blood strongly correlated with mean megakaryocyte counts in spleen and bone marrow (r=0.95, p&lt;0.05).

Conclusions: Our data provide additional insight into the clinical significance and etiology of paraneoplastic thrombocytosis in ovarian cancer patients. In vivo studies evaluating the effect of silencing tumor cell production of IL-6 and G-CSF on paraneoplastic thrombocytosis using human-specific siRNA sequences are ongoing. Paraneoplastic thrombocytosis and the interaction between platelets and cancer cells could be targets for developing novel therapeutic strategies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3436.

Identification of cytochrome P450s in human glioma cell line

Five different isoforms of cytochrome P450 including 1A1, 1A2, 2E1, 2A and 2B6 have been identified in human glioma Hs 683 cell line using RT-PCR reaction. These isoforms belong to four distinct subfamilies. The effect of benzanthracene (Ba) as inducer was tested on the mRNA level of cytochrome P450 1A1. Northern blot analysis clearly showed an induction response from these cells to Ba in a proportion that is comparable to the induction seen in rat glioma cells.