Epigenetic mechanisms regulate sex differences in cardiac reparative functions of bone marrow progenitor cells

Historically, a lower incidence of cardiovascular diseases (CVD) and related deaths in women as compared with men of the same age has been attributed to female sex hormones, particularly estrogen and its receptors. Autologous bone marrow stem cell (BMSC) clinical trials for cardiac cell therapy overwhelmingly included male patients. However, meta-analysis data from these trials suggest a better functional outcome in postmenopausal women as compared with aged-matched men. Mechanisms governing sex-specific cardiac reparative activity in BMSCs, with and without the influence of sex hormones, remain unexplored. To discover these mechanisms, Male (M), female (F), and ovariectomized female (OVX) mice-derived EPCs were subjected to a series of molecular and epigenetic analyses followed by in vivo functional assessments of cardiac repair. F-EPCs and OVX EPCs show a lower inflammatory profile and promote enhanced cardiac reparative activity after intra-cardiac injections in a male mouse model of myocardial infarction (MI). Epigenetic sequencing revealed a marked difference in the occupancy of the gene repressive H3K9me3 mark, particularly at transcription start sites of key angiogenic and proinflammatory genes in M-EPCs compared with F-EPCs and OVX-EPCs. Our study unveiled that functional sex differences in EPCs are, in part, mediated by differential epigenetic regulation of the proinflammatory and anti-angiogenic gene CCL3, orchestrated by the control of H3K9me3 by histone methyltransferase, G9a/Ehmt2. Our research highlights the importance of considering the sex of donor cells for progenitor-based tissue repair.

Role of circular RNA cdr1as in modulation of macrophage phenotype

AIMS

Macrophages are crucial for the initiation and resolution of an inflammatory response. Non-coding circular RNAs are ubiquitously expressed in mammalian tissue, highly conserved among species, and recently implicated in the regulation of macrophage activation. We sought to determine whether circRNAs modulate monocyte/macrophage biology and function.

MATERIALS AND METHODS

We performed circRNA microarray analyses to assess transcriptome changes using RNA isolated from bone marrow derived macrophages polarized to a pro-inflammatory phenotype (INFγ + TNFα) or an anti-inflammatory phenotype (IL-10, IL-4, and TGF-β). Among differentially expressed circRNAs, circ-Cdr1as was chosen for further investigation. Additionally, we performed loss or gain of function studies to investigate if circ-Cdr1as is involved in phenotypic switching. For gain of function, we overexpressed circ-Cdr1as using pc3.1 plasmid with laccase2 flanking regions to promote circularization. For loss of function, we used a lentiviral short hairpin RNA targeting the circ-Cdr1as splicing junction.

KEY FINDINGS

Among circRNAs that are highly conserved and differentially expressed in pro- and anti-inflammatory lineages, circ-Cdr1as was one of the most downregulated in pro-inflammatory macrophages and significantly upregulated in anti-inflammatory macrophages in vitro. Overexpression of circ-Cdr1as increased transcription of anti-inflammatory markers and percentage of CD206+ cells in naïve and pro-inflammatory macrophages in vitro. Meanwhile, knockdown decreased transcription of anti-inflammatory markers and increased the percentage of CD86+ cells in naïve and anti-inflammatory macrophages in vitro.

SIGNIFICANCE

This study suggests that circ-Cdr1as plays a key role in regulating anti-inflammatory phenotype of macrophages and may potentially be developed as an anti-inflammatory regulator in tissue inflammation.

Abstract P2022: Tipifarnib Mediated Protection By Reduction Of Circulating Exosomes In Pressure Overloaded Cardiac Hypertrophy

Hypertrophic cardiomyopathy (HCM) in response to pathophysiological stress is one of the leading causes of heart failure. A growing body of evidence emphasizes the crucial role of exosomes and their modulated content in aggravating cardiac damage due to their inherent intercellular cross-talk abilities during cardiac remodeling. However, the role of circulating exosomes in HCM for the trafficking of pathogenic factors and remodeling the cardiac microenvironment is yet unclear. We investigated the effect of systemic exosome inhibition during cardiac dysfunction in a transverse aortic constriction (TAC) model of heart failure using a recently identified exosome biogenesis inhibitor, Tipifarnib initially developed as Farnesyl transferase inhibitor. In this study, 10-week-old C57BL6J male mice were randomized into three groups i.e., Sham, TAC and Tipifarnib treated (10 mg/kg) TAC. The untreated TAC mice gradually developed hypertrophy and had reduced cardiac functions with a significant increase in heart weight/body weight ratio, cardiomyocyte size and upregulation of hypertrophy and fibrosis associated genes expression by 8 weeks. On the contrary, Tipifarnib treated TAC mice showed remarkably improved cardiac left ventricular functions, reduced cardiac hypertrophy and fibrosis. Notably, Nanosight analysis indicated significantly higher serum exosomes concentration in TAC mice which were substantially suppressed with Tipifarnib treatment. The molecular analysis of the heart tissue revealed Tipifarnib treated TAC mice had reduced expression of the proteins involved in exosome biogenesis in comparison to untreated TAC mice. To gain insight into the cargo of these circulating exosomes, we performed the serum cytokine array and serum exosomes miRNA sequencing in untreated and Tipifarnib treated TAC mice. There was a marked reduction in inflammatory cytokines in serum and differentially expressed exosomal miRNAs with Tipifarnib treatment in comparison to the untreated TAC mice. Overall, our studies suggest the promising potential of Tipifarnib that effectively protects against pressure overload-induced cardiac remodeling and dysfunction by suppressing exosome secretion and altering hypertrophic and fibrotic gene expression.

Abstract P2053: Role Of Podoplanin Positive Cells Exosomes In Cardiac Inflammation And Amyloidosis

The extra-cellular-matrix (ECM) composition of scar tissue after myocardial infarction (MI)has been largely investigated. Although fibronectin and collagen are favorable for newmyocyte formation, other components that may increase the scar stiffness and reducethe remodeling of the ischemic area, remain to be identified. Our preliminary studiesidentified primary Serum Amyloid A3 (SAA3) extracellular accumulation that maycontribute to the chronic alteration of the ischemic myocardium’s scar. Specifichistological staining such as thioflavin and Congo red, showed amyloid deposition inmouse hearts 1 month after MI; furthermore, immunohistochemistry for SAA3 detectedthe deposition of the misfolded protein alongside fibronectin and collagen. Serum amyloidamyloidosis (AA) is characterized by deposition of hepatic misfolded protein and SAA3 isthe only amyloid protein that is released locally after inflammation, mostly bymesenchymal progenitor cells. We have reported earlier that two days after MI, a cohortof mesenchymal cells begin to de novo express Podoplanin (PDPN), a plateletaggregation-inducing type I transmembrane glycoprotein, as a signal of activation.PDPN+ cells, in addition to cytokines, release extracellular vesicles including exosomes(Exo) as major paracrine entities driving intercellular communications in homeostasis anddisease. Exo derived from activated PDPN+ cells isolated from MI hearts highly expressSAA3 and injection of activated PDPN+ cell Exo in uninjured healthy mouse hearts leadsto recruitment of immune cells, an extended epicardial fibrosis and amyloidosis with asubsequent impairment in the contractility and increase of the end systolic volumes anddiameters. SAA3 binds Toll-like receptors, and in vitro treatment of bone marrow derivedmonocytes either with PDPN+ cells derived Exo or recombinant SAA3, activated themtowards pro-inflammatory phenotype on contrary these stimuli failed to activate TLR2knocked out monocytes showing an impairment in the expression of major cytokine,chemokine and pro inflammatory markers. Thus, PDPN+ cells in the ischemic heartrelease SAA3 through Exo prolonging inflammation and macrophage recruitment viaTLR2 and contribute to amyloidosis after MI.

Abstract P2065: Ischemic Injury Aggravated Muscle-specific Mir-499-5p-impaired Angiogenic Property Of Endothelial Cell In Hindlimb Of Diabetic Db/db Mice: Role Of Small Extracellular Vesicles

Background: Recently, skeletal muscle cells (SKMCs) have been reported to be critical for regulation of EC function in limbs. miR-499, a muscle specific microRNA (miR), was found to be modulated in diabetes and ischemic injury. Here, we studied the role of miR-499 in EC dysfunction in diabetic ischemic limb injury.

Methods: ECs and SKMCs were isolated from ischemic or non-ischemic hindlimb (IHL) of male db/+ and db/db mice. Serum- and SKMC-derived small extracellular vesicles/exosomes (EV/Exo) were isolated by gradient ultracentrifugation. Ischemic hindlimb (IHL) surgery was conducted by unilateral ligation of formal artery.

Results: miR-499-5p level was increased in SKMCs and ECs of db/db mice which was synergistically increased by ischemic injury. Overexpression of miR-499-5p impaired tube formation and migratory activity of ECs. Intramuscular injection of anti-miR-499-5p lentivirus improved blood prefusion and neovascularization in IHL of db/db mice. Mechanistically, miR-499-5p level was enhanced in serum- and SKMC-derived EV/Exo from db/db mice which was synergistically increased by ischemic injury. Diabetic SKMC-EV/Exo impaired blood perfusion in wildtype mice. Anti-miR-499-5p rescued diabetic SKMC-EV/Exo-impaired EC function. Co-culture of diabetic SKMCs with wildtype ECs increased miR-499-5p expression in ECs which was inhibited by EV/Exo inhibitor GW4869. Sex-determining region Y-box 6 (SOX6), the most attractive gene targeted by miR-499-5p, was decreased in ECs from db/db mice which was synergistically reduced by ischemic injury. SOX6 siRNA impaired pro-angiogenic factor secretion and function of ECs. Anti-miR-499-5p significantly enhanced SOX6 level in SKMs from IHL of db/db mice. Finally, overexpression of SOX6 by transduction of lentivirus improved EC function of db/db mice.

Conclusions: Enhanced miR-499-5p expression in ECs of SKMs from hindlimb of db/db mice is synergistically increased by ischemic injury. EV/Exo transfer miR-499-5p from SKMCs to ECs. miR-499-5p impairs angiogenic property of EC via, at least partially, SOX6/proangiogenic factors axis. miR-499-5p may be a novel target for treatment of critical limb ischemia in diabetic patients.

Abstract P3093: Gender-specific Functional Dimorphism Of Bone Marrow Endothelial Progenitor Cells: Estrogen Independent Epigenetic Mechanisms

Introduction: Several studies, including our labs, have previously determined the role of estrogen in augmenting EPC-based cardiac repair; however, a direct comparison of therapeutic efficacy of gender-specific stem cells or estrogen-independent mechanisms of gender-specific dimorphism in the reparative properties of BM-EPCs, has not been established.

Hypothesis: We hypothesized that epigenetic mechanisms contribute to the sex-specific functional dimorphism of Sca-1+/CD31+ BM-EPCs in regulating cell-homing, pro-angiogenic and anti-inflammatory functions in the ischemic myocardium leading to the enhanced reparative function of female EPCs.

Methods: To evaluate our hypothesis, we sorted the male, female and ovariectomized (OVX) mice derived Sca-1+/CD31+ BM-EPCs using MACS multi-sort method. We then subjected the BM-EPCs through a series of cytokine quantifications and epigenetic screening followed by assessment of their therapeutic function in vitro and in vivo .

Results: Female and ovariectomized (OVX) female BM-EPCs secrete high levels of pro-angiogenic factors and low levels of pro-inflammatory cytokines compared to male BM-EPCs. Further evaluation of the secretome showed that the male EPCs secreted high levels of interleukins and chemokines compared to female and OVX EPCs. We found that male EPCs exclusively secreted CCL3/Mip-1α. Functional in vitro angiogenic evaluation of the EPC secretome showed higher propensity of female and OVX EPCs than the male EPCs. Post-MI injection of BM-EPCs resulted in remarkable preservation of cardiac structure and functions in both female BM-EPC groups compared to the male EPCs. Male EPC injection resulted in high inflammation in the heart tissue. Epigenetic sequencing of the BM-EPCs for the H3K9me3 mark showed high methylation in male EPCs compared to female and OVX EPCs. The inhibition of histone methyltransferase, Ehmt2/G9a using BIX-01294 upregulated the secretion of inflammatory factors in all EPCs. The conditioned medium from all EPCs with high levels of CCL3 inhibited angiogenesis in vitro . Neutralizing CCL3 in the same medium restored in vitro angiogenesis.

Conclusion: Estrogen-independent epigenetic mechanisms govern the enhanced cardiac reparative properties of female BM-EPC.

Abstract P3081: Glypican 3 Regulates Diabetes Induced Mesenchymal Stromal Cells Dysfunctions

Mesenchymal stromal cells (MSC) based therapies are considered as an ideal stem cell-based treatment for cardiovascular diseases due to their immunosuppressive characteristics, anti-inflammatory properties, and differentiation potential. Diabetic microenvironment encompassing high glucose, inflammation, hypoxic conditions, and reactive oxygen species content has deleterious effects on the functionality of MSCs. The purpose of this study was to understand the molecular basis of diabetes-induced MSC dysfunction and potentially reversing these dysfunctions to enhance cell-based therapeutics for myocardial repair in diabetic patients. we isolated MSCs from bone marrow of mice from db/+ non-diabetic (WT-MSC) and diabetic mice (db/db-MSC) and examined the effect of diabetes on MSC differentiation, proliferation, angiogenesis, and immunomodulation in vitro, and their reparative functions on myocardial injury repair post-MI in mice. Compared to WT-MSC, MSCs isolated from bone marrow of diabetic mice showed impaired differentiation, decreased proliferation, reduced immunomodulatory activities and impairment to promote endothelial cell tubulogenesis. Our data also shows diminished functional activity of diabetic MSCs to improve post-MI cardiac functions. Furthermore, we found that glypican-3 (GPC3), a heparan sulfate proteoglycan, is highly upregulated in diabetic MSCs when compared to WT-MSC. GPC3 overexpression in WT-MSC showed decreased proliferation, lowers the immunosuppression activity, and reduced vascular tube formation. Interestingly, GPC3 knockdown in WT-MSC showed increased proliferation, improved the immunosuppression activity, and enhanced vascular tube formation. Our data also showed that, knockdown of GPC3 in diabetic MSCs restore their functions. In conclusion, these data suggest that diabetes increases GPC3 expression in MSC thereby impairs MSC functions under diabetic condition and knockdown of GPC3 in diabetic MSC rescued diabetes-induced dysfunctions. Ongoing studies are testing whether ex vivo GPC3 knockdown in db/db MSCs will rescue their defective cardiac reparative activities, post-MI.

STK35 Gene Therapy Attenuates Endothelial Dysfunction and Improves Cardiac Function in Diabetes

Diabetic cardiomyopathy (DCM) is characterized by microvascular pathology and interstitial fibrosis that leads to progressive heart failure. The mechanisms underlying DCM pathogenesis remain obscure, and no effective treatments for the disease have been available. In the present study, we observed that STK35, a novel kinase, is decreased in the diabetic human heart. High glucose treatment, mimicking hyperglycemia in diabetes, downregulated STK35 expression in mouse cardiac endothelial cells (MCEC). Knockdown of STK35 attenuated MCEC proliferation, migration, and tube formation, whereas STK35 overexpression restored the high glucose-suppressed MCEC migration and tube formation. Angiogenesis gene PCR array analysis revealed that HG downregulated the expression of several angiogenic genes, and this suppression was fully restored by STK35 overexpression. Intravenous injection of AAV9-STK35 viral particles successfully overexpressed STK35 in diabetic mouse hearts, leading to increased vascular density, suppression of fibrosis in the heart, and amelioration of left ventricular function. Altogether, our results suggest that hyperglycemia downregulates endothelial STK35 expression, leading to microvascular dysfunction in diabetic hearts, representing a novel mechanism underlying DCM pathogenesis. Our study also emerges STK35 is a novel gene therapeutic target for preventing and treating DCM.

Diabetes impairs cardioprotective function of endothelial progenitor cell-derived extracellular vesicles via H3K9Ac inhibition

Background and Purpose: Myocardial infarction (MI) in diabetic patients results in higher mortality and morbidity. We and others have previously shown that bone marrow-endothelial progenitor cells (EPCs) promote cardiac neovascularization and attenuate ischemic injury. Lately, small extracellular vesicles (EVs) have emerged as major paracrine effectors mediating the benefits of stem cell therapy. Modest clinical outcomes of autologous cell-based therapies suggest diabetes-induced EPC dysfunction and may also reflect their EV derivatives. Moreover, studies suggest that post-translational histone modifications promote diabetes-induced vascular dysfunctions. Therefore, we tested the hypothesis that diabetic EPC-EVs may lose their post-injury cardiac reparative function by modulating histone modification in endothelial cells (ECs).

Methods: We collected EVs from the culture medium of EPCs isolated from non-diabetic (db/+) and diabetic (db/db) mice and examined their effects on recipient ECs and cardiomyocytes in vitro, and their reparative function in permanent ligation of left anterior descending (LAD) coronary artery and ischemia/reperfusion (I/R) myocardial ischemic injuries in vivo.

Results: Compared to db/+ EPC-EVs, db/db EPC-EVs promoted EC and cardiomyocyte apoptosis and repressed tube-forming capacity of ECs. In vivo, db/db EPC-EVs depressed cardiac function, reduced capillary density, and increased fibrosis compared to db/+ EPC-EV treatments after MI. Moreover, in the I/R MI model, db/+ EPC-EV-mediated acute cardio-protection was lost with db/db EPC-EVs, and db/db EPC-EVs increased immune cell infiltration, infarct area, and plasma cardiac troponin-I. Mechanistically, histone 3 lysine 9 acetylation (H3K9Ac) was significantly decreased in cardiac ECs treated with db/db EPC-EVs compared to db/+ EPC-EVs. The H3K9Ac chromatin immunoprecipitation sequencing (ChIP-Seq) results further revealed that db/db EPC-EVs reduced H3K9Ac level on angiogenic, cell survival, and proliferative genes in cardiac ECs. We found that the histone deacetylase (HDAC) inhibitor, valproic acid (VPA), partly restored diabetic EPC-EV-impaired H3K9Ac levels, tube formation and viability of ECs, and enhanced cell survival and proliferative genes, Pdgfd and Sox12, expression. Moreover, we observed that VPA treatment improved db/db EPC-mediated post-MI cardiac repair and functions.

Conclusions: Our findings unravel that diabetes impairs EPC-EV reparative function in the ischemic heart, at least partially, through HDACs-mediated H3K9Ac downregulation leading to transcriptional suppression of angiogenic, proliferative and cell survival genes in recipient cardiac ECs. Thus, HDAC inhibitors may potentially be used to restore the function of diabetic EPC and other stem cells for autologous cell therapy applications.

Abstract P313: Over-expression Of Serine Threonine Kinase 35 Improves Cardiac Function In Streptozotocin Induced Diabetic Mice

Diabetic cardiomyopathy is a common complication in patients with diabetes and is associatedwith impaired responsiveness of ischemic myocardium to proangiogenic factors, subsequentlyleading to heart failure. STK35, a novel kinase that binds to nuclear actin, has been shown toregulate important cellular functions such as cell migration, proliferation, survival, andangiogenesis. Currently, the contribution of altered STK35 expression in human diseases remainsunexplored. In initial studies, we observed that human cardiac biopsies from diabetic patientsshowed a significant decrease in STK35 expression as compared to non-diabetic control hearts.Intriguingly, in a STZ-induced mouse model of diabetes, i.v . injection of rAAV9-STK35 to expressconstitutive STK35 in heart in FVB/N male mice promoted neovascularization and lowered cardiacfibrosis, leading to improved cardiac function of diabetic heart. Our in vitro studies observed highglucose decreased STK35 expression in mouse cardiac endothelial cells (MCEC), whereasSTK35 overexpression increased MCEC migration and vascular tube formation, and upregulatedMCEC to expression of multiple pro-angiogenic proteins. Taken together, our results demonstratethat cardiac-targeted STK35 gene therapy exerts a marked beneficial action by attenuating bothcardiac remodeling and cardiac function in a mouse model of diabetes mellitus. Mechanistically,the beneficial effect may be attributed, at least partially, to enhanced neovascularization in heart.

Abstract P375: Gender-based Cardio-protective Functional Dimorphism Of Bone Marrow Endothelial Progenitor Cells And Their Exosomes: Estrogen-independent Epigenetic Mechanisms

Introduction: Estrogen or estrogen receptor-dependent mechanisms in enhancing the cardioprotective efficacy of bone marrow endothelial progenitor cells (BM-EPC) is well-established in preclinical studies. However, the efficacy of estrogen does not reflect in the data from randomized cardiovascular clinical trials, suggesting an estrogen-independent role of female BM-EPC in eliciting enhanced cardiac protection compared to males.

Hypothesis: Epigenetic mechanisms may contribute to the sex-specific dimorphism of Sca-1 + /CD31 + BM-EPC in regulating cell-homing, pro-angiogenic and anti-inflammatory functions in the ischemic myocardium leading to enhanced reparative function of female progenitor cells.

Methods & Results: Transplantation of GFP-BM-mononuclear cells from male and female GFP transgenic mice into the BM of lethally irradiated recipient male C57BL/6 mice resulted in the enhanced mobilization of female Sca-1 + CD31 + /GFP + BM-EPC into circulation post-MI. A higher number of female BM-EPC homed to the ischemic myocardium and significantly improved LV functions and capillary density post-MI compared to male BM-EPC. Female BM-EPC showed increased expression of bFGF, VEGFR2, SDF-1α, and IL-10 genes, thereby efficiently promoted endothelial tube formation in vitro compared to male BM-EPC. Transplantation of female BM-EPC and their exosomes into post-MI male mice improved LV cardiac function, reduced scar size, and improved capillary density compared to male BM-EPC and exosomes. Male BM-EPC showed an increased expression of G9a/Ehmt2, an H3K9me3 methyltransferase, and Dnmt3a DNA methyltransferase compared to female BM-EPC. In contrast, Kdm6b/JMJD3, H3K27me3 demethylase was highly expressed in female BM-EPC compared to males. Treatment of BM-EPC of both sexes with 17-β-estradiol did not alter the expression of Kdm6b/JMJD3. Male BM-EPC highly expressed repressive gene marks, H3K9me3, and H3K27me3 compared to females. Compared to the male, BM-EPC from female and ovariectomized (OXV) female mice showed equally high expression of angiogenic genes ANGPT-1, MDK, PLAU, Tie-2, and VEGFR2 and lower levels of inflammatory cytokines, TNFα, IFNγ, IL-1β, and CCL3. Conditioned medium from female and OVX BM-EPC equally promoted enhanced migration and tube formation of HUVEC in vitro, compared to male BM-EPC.

Conclusions: An estrogen-independent epigenetic mechanism likely governs the enhanced cardiac reparative properties of female BM-EPC.

Abstract P329: Exosomes Derived From Podoplanin Positive Cells Alter The Cellular Composition Of Healthy Mouse Hearts

Fibrosis and blood hypoperfusion stimulated by paracrine signals enhances the ventricular dysfunctionafter myocardial infarction (MI). We have earlier reported that within 2 days post-MI a cohort ofpodoplanin (PDPN) positive cells populate injured heart and enhance inflammatory response by physicalinteractions with monocytes. Here we explored whether exosomes from these cells could independentlyalter healthy heart physiology and structure. PDPN+ cells were isolated 2 days after MI, culture expandedand activated with TNFα and Angiotensin II. Exosomes derived from activated PDPN+cells conditionedmedia (PDPN+exo) were used in vitro for the treatment of mouse cardiac endothelial cells (mCECs) andmouse fibroblast (3T3) and in vivo for the treatment of healthy mouse hearts. In vitro, PDPN+exoinfluenced the phenotype of mCECs, stimulating their lineage into lymphatic endothelial cells andfacilitated fibroblasts transition to myofibroblast. Characterization of the protein content of PDPN+exoshowed high concentration of Notch receptors and γ-Secretase, suggesting these cellular transitions maydepend on exosome-mediated Notch translocation and cleavage. In fact, after exosomes treatmentcleaved notch (NICD) translocated in the nuclei of mCECs and 3T3 as early as 1h of treatment and eitherHes-1 or Hey-1, major transcription factors activated by NICD were enhanced within 2d of treatment.Using DAPT, a γSecretase inhibitor, notch cleavage was inhibited, and no phenotype switching in responseto exosome treatment was observed. In vivo, PDPN+exo were injected into the left ventricle of healthymouse hearts followed by boosters delivered by retro-orbital vein injection. Treated mice developed anextended epicardial fibrosis with a subsequent impairment in the contractility and increase of the enddiastolic and systolic volumes. The fibrotic area was characterized by vessels double positive toendothelial and lymphatic endothelial markers, and infiltrating CD45+ cells. Podoplanin positive cellsrepresent 80% of the scar’s cells of a chronic infarcted myocardium and the specific exosomes cargo highlyinfluence the lineage of cardiac cells altering the biology of endothelial cells and fibroblasts which mayfacilitate adverse remodeling.

Abstract P358: Cardiac Innervation Remodeling And Impaired Brain Derived Neurotrophic Factor (bdnf) Levels In Physiological Aging Vivo Model

Aging is a multifactorial process associated with gradual loss of function and decay involving several neurohormonal systems, such as the autonomic nervous system (ANS). Progressive remodeling of ANS, induces a circulating catecholamines spillover and cardiac autonomic fibers depletion with raising both morbidities and mortality risk. Neurotrophic factors (NF) play a pivotal role in modulating neuronal function and are impaired in cardiovascular disorders. Whether and how physiological aging impacts these neurobiomarkers and cardiac innervation remains still unclear. Therefore, we investigated the impact of aging on neurotrophins (such as BDNF and NGF) production and secretion and its consequences, on cardiac nervous system homeostasis. In vivo, we used young (age: 3 months; n=10) and old (age: 24 months; n=11) male Fisher rats. In vitro, human neuroblastoma cells (SH-SY5Y) were stimulated with serum withdrawn from both experimental groups. Old rats showed a significant reduction in overall ANS fiber density, sympathetic (marked by dopamine β-hydroxylase, dβh) and cholinergic compartment (evidenced by vesicular acetylcholine transporter, VaChT) compared to the young group, assessed by immunohistochemical staining. In addition, we observed a marked downregulation of GAP-43 and BDNF protein levels in left ventricle total lysates via immunoblot analysis, in aged hearts as opposed to young ones. Conversely, no changes were observed in NGF protein expression. To further investigate the autocrine effect of aging on autonomic nerve fibers, we treated SH-SY5Y cells in vitro, with blood serum obtained by young or old rats. Both stimuli induced a remarkable increase in neuronal sprouting, as evidenced via crystal violet assay. Nevertheless, we found a bulky drop in the neuronal function of cells stimulated with old rat serum. Interestingly, this effect was accompanied by a sizeable blunt in GAP-43 and BDNF protein levels, compared to cells treated with young rat serum. Taken together, our data suggest that neuronal function impairment aging-induced associated with significant BDNF impoverishment, might favor maladaptive remodeling of cardiac ANS.

Abstract 110: Human-Induced Pluripotent Stem Cell Derived Exosomal Protein Induce Cardiac Regeneration

Introduction: Cardiovascular diseases are the leading causes of death worldwide. After myocardial infarction (MI), there is a permanent loss of cardiomyocytes (CMs), and as the mammalian heart has limited regenerative capacity, it leads to Heart Failure. Recent studies from zebrafish and 1-day old mice showed that they could regenerate their heart through inducing existing CM proliferation. Attempts have been made to transiently reconstitute embryonic signaling in adult hearts, including overexpression of cell cycle activating genes with limited success. iPSC-derived extracellular vesicles (EV)/exosomes have been shown to improve cardiac function and some degree of CM renewal. However, the iPSC-EVs-mediated cardiac regeneration mechanism remains unclear and largely pertains to microRNAs and other RNAs, with a little elucidation of the role of iPSC-exosome proteins.

Hypothesis: The myocardial delivery of iPSC-EV-specific protein improves cardiac function and remodeling post-MI by activating pro-proliferative and anti-oxidative stress molecular pathways.

Methods and Results: Our preliminary studies showed that hiPSC-EVs induced the CM cell cycle in mice post-MI, and by employing a proteomic approach, we found a novel protein exclusively expressed in iPSC-EVs. The overexpression of hiPSC-EV enriched protein in the form of modRNA (modified mRNA) induced a robust CM cell cycle in rat neonatal CMs and in adult hearts post-MI. This increase in the CMs cell cycle by the modRNA was associated with reduced scar size, improved cardiac function (%EF 49.76 ± 5.8 vs. 27.47 ± 6.9 (control, Luc modRNA), respectively), and mice survival 28 days post-MI. Furthermore, using the siRNA and modRNA (inhibition and over-expression) approach, we found that the protein-induced Yap1-β-catenin molecular pathway stimulates CM proliferation. Furthermore, the overexpression protein post-MI inhibited the CM apoptosis (TUNEL + CMs, 1.3% ± 0.1 vs. 2.1% ± 0.11 (control)) by reducing oxidative stress and DNA damage response.

Conclusion: The myocardial injection of iPSC-EV specific protein through a highly therapeutic modRNA tool improve cardiac function by inducing CMs proliferation, inhibiting oxidative stress, and reactivating cardiac regeneration post-injury.

Aging is associated with cardiac autonomic nerve fiber depletion and reduced cardiac and circulating BDNF levels

BACKGROUND

Aging is a multifactorial process associated with an impairment of autonomic nervous system (ANS) function. Progressive ANS remodeling includes upregulation of expression of circulating catecholamines and depletion of cardiac autonomic nerve fibers, and it is responsible, in part, for the increased susceptibility to cardiac diseases observed in elderly subjects. Neurotrophic factors, such as brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), are involved in synaptogenesis and neurite outgrowth processes, supporting neuronal cell differentiation and maturation. However, whether and how these factors and their downstream signaling are involved in cardiac aging remains unclear. Here, we tested whether, in the aged heart, the overall extent of autonomic fibers is reduced, owing to lower production of trophic factors such as BDNF and NGF.

METHODS

In vivo, we used young (age: 3 months; n = 10) and old (age: 24 months; n = 11) male Fisher rats, whereas, we used human neuroblastoma (SH-SY5Y) cells in vitro.

RESULTS

Compared to the young rats, old rats displayed a marked reduction in the overall ANS fiber density, affecting both sympathetic and cholinergic compartments, as indicated by dopamine β-hydroxylase (dβh) and vesicular acetylcholine transporter (VaChT) immunohistochemical staining. In addition, a marked downregulation of GAP-43 and BDNF protein was observed in the left ventricular lysates of old rats compared to those of young rats. Interestingly, we did not find any significant difference in cardiac NGF levels between the young and old groups. To further explore the impact of aging on ANS fibers, we treated SH-SY5Y cells in vitro with serum obtained from young and old rats. Sera from both groups induced a remarkable increase in neuronal sprouting, as evidenced by a crystal violet assay. However, this effect was blunted in cells cultured with old rat serum and was accompanied by a marked reduction in GAP-43 and BDNF protein levels.

CONCLUSIONS

Our data indicate that physiological aging is associated with an impairment of ANS structure and function and that reduced BDNF levels are responsible, at least in part, for these phenomena.

Serum-Derived Small Extracellular Vesicles From Diabetic Mice Impair Angiogenic Property of Microvascular Endothelial Cells: Role of EZH2

Background

Impaired angiogenic abilities of the microvascular endothelial cell (MVEC) play a crucial role in diabetes mellitus–impaired ischemic tissue repair. However, the underlying mechanisms of diabetes mellitus–impaired MVEC function remain unclear. We studied the role of serum‐derived small extracellular vesicles (ssEVs) in diabetes mellitus–impaired MVEC function.

Methods and Results

ssEVs were isolated from 8‐week‐old male db/db and db/+ mice by ultracentrifugation and size/number were determined by the Nano‐sight tracking system. Diabetic ssEVs significantly impaired tube formation and migration abilities of human MVECs. Furthermore, local transplantation of diabetic ssEVs strikingly reduced blood perfusion and capillary/arteriole density in ischemic hind limb of wildtype C57BL/6J mice. Diabetic ssEVs decreased secretion/expression of several pro‐angiogenic factors in human MVECs. Mechanistically, expression of enhancer of zest homolog 2 (EZH2), the major methyltransferase responsible for catalyzing H3K27me3 (a transcription repressive maker), and H3K27me3 was increased in MVECs from db/db mice. Diabetic ssEVs increased EZH2 and H3K27me3 expression/activity in human MVECs. Expression of EZH2 mRNA was increased in diabetic ssEVs. EZH2‐specific inhibitor significantly reversed diabetic ssEVs‐enhanced expression of EZH2 and H3K27me3, impaired expression of angiogenic factors, and improved blood perfusion and vessel density in ischemic hind limb of C57BL/6J mice. Finally, EZH2 inactivation repressed diabetic ssEVs‐induced H3K27me3 expression at promoter of pro‐angiogenic genes.

Conclusions

Diabetic ssEVs impair the angiogenic property of MVECs via, at least partially, transferring EZH2 mRNA to MVECs, thus inducing the epigenetic mechanism involving EZH2‐enhanced expression of H3K27me3 and consequent silencing of pro‐angiogenic genes. Our findings unravel the cellular mechanism and expand the scope of bloodborne substances that impair MVEC function in diabetes mellitus.

Role of Podoplanin-Positive Cells in Cardiac Fibrosis and Angiogenesis After Ischemia

New insights into the cellular and extra-cellular composition of scar tissue after myocardial infarction (MI) have been identified. Recently, a heterogeneous podoplanin-expressing cell population has been associated with fibrogenic and inflammatory responses and lymphatic vessel growth during scar formation. Podoplanin is a mucin-like transmembrane glycoprotein that plays an important role in heart development, cell motility, tumorigenesis, and metastasis. In the adult mouse heart, podoplanin is expressed only by cardiac lymphatic endothelial cells; after MI, it is acquired with an unexpected heterogeneity by PDGFRα-, PDGFRβ-, and CD34-positive cells. Podoplanin may therefore represent a sign of activation of a cohort of progenitor cells during different phases of post-ischemic myocardial wound repair. Podoplanin binds to C-type lectin-like receptor 2 (CLEC-2) which is exclusively expressed by platelets and a variety of immune cells. CLEC-2 is upregulated in CD11b^high cells, including monocytes and macrophages, following inflammatory stimuli. We recently published that inhibition of the interaction between podoplanin-expressing cells and podoplanin-binding cells using podoplanin-neutralizing antibodies reduces but does not fully suppress inflammation post-MI while improving heart function and scar composition after ischemic injury. These data support an emerging and alternative mechanism of interactome in the heart that, when neutralized, leads to altered inflammatory response and preservation of cardiac function and structure. The overarching objective of this review is to assimilate and discuss the available evidence on the functional role of podoplanin-positive cells on cardiac fibrosis and remodeling. A detailed characterization of cell-to-cell interactions and paracrine signals between podoplanin-expressing cells and the other type of cells that compose the heart tissue is needed to open a new line of investigation extending beyond the known function of these cells. This review attempts to discuss the role and biology of podoplanin-positive cells in the context of cardiac injury, repair, and remodeling.

Long-Term Effects of Very Low Dose Particle Radiation on Gene Expression in the Heart: Degenerative Disease Risks

Compared to low doses of gamma irradiation (γ-IR), high-charge-and-energy (HZE) particle IR may have different biological response thresholds in cardiac tissue at lower doses, and these effects may be IR type and dose dependent. Three- to four-month-old female CB6F1/Hsd mice were exposed once to one of four different doses of the following types of radiation: γ-IR ¹³⁷Cs (40-160 cGy, 0.662 MeV), ¹⁴Si-IR (4-32 cGy, 260 MeV/n), or ²²Ti-IR (3-26 cGy, 1 GeV/n). At 16 months post-exposure, animals were sacrificed and hearts were harvested and archived as part of the NASA Space Radiation Tissue Sharing Forum. These heart tissue samples were used in our study for RNA isolation and microarray hybridization. Functional annotation of twofold up/down differentially expressed genes (DEGs) and bioinformatics analyses revealed the following: (i) there were no clear lower IR thresholds for HZE- or γ-IR; (ii) there were 12 common DEGs across all 3 IR types; (iii) these 12 overlapping genes predicted various degrees of cardiovascular, pulmonary, and metabolic diseases, cancer, and aging; and (iv) these 12 genes revealed an exclusive non-linear DEG pattern in ¹⁴Si- and ²²Ti-IR-exposed hearts, whereas two-thirds of γ-IR-exposed hearts revealed a linear pattern of DEGs. Thus, our study may provide experimental evidence of excess relative risk (ERR) quantification of low/very low doses of full-body space-type IR-associated degenerative disease development.

Cardiomyocyte Krüppel-Like Factor 5 Promotes De Novo Ceramide Biosynthesis and Contributes to Eccentric Remodeling in Ischemic Cardiomyopathy

BACKGROUND

We previously showed that cardiomyocyte Krϋppel-like factor (KLF) 5 regulates cardiac fatty acid oxidation. As heart failure has been associated with altered fatty acid oxidation, we investigated the role of cardiomyocyte KLF5 in lipid metabolism and pathophysiology of ischemic heart failure.

METHODS

Using real-time polymerase chain reaction and Western blot, we investigated the KLF5 expression changes in a myocardial infarction (MI) mouse model and heart tissue from patients with ischemic heart failure. Using 2D echocardiography, we evaluated the effect of KLF5 inhibition after MI using pharmacological KLF5 inhibitor ML264 and mice with cardiomyocyte-specific KLF5 deletion (αMHC [α-myosin heavy chain]-KLF5^-/-). We identified the involvement of KLF5 in regulating lipid metabolism and ceramide accumulation after MI using liquid chromatography-tandem mass spectrometry, and Western blot and real-time polymerase chain reaction analysis of ceramide metabolism-related genes. We lastly evaluated the effect of cardiomyocyte-specific KLF5 overexpression (αMHC-rtTA [reverse tetracycline-controlled transactivator]-KLF5) on cardiac function and ceramide metabolism, and rescued the phenotype using myriocin to inhibit ceramide biosynthesis.

RESULTS

KLF5 mRNA and protein levels were higher in human ischemic heart failure samples and in rodent models at 24 hours, 2 weeks, and 4 weeks post-permanent left coronary artery ligation. αMHC-KLF5^-/- mice and mice treated with ML264 had higher ejection fraction and lower ventricular volume and heart weight after MI. Lipidomic analysis showed that αMHC-KLF5^-/- mice with MI had lower myocardial ceramide levels compared with littermate control mice with MI, although basal ceramide content of αMHC-KLF5^-/- mice was not different in control mice. KLF5 ablation suppressed the expression of SPTLC1 and SPTLC2 (serine palmitoyltransferase [SPT] long-chain base subunit ()1 2, respectively), which regulate de novo ceramide biosynthesis. We confirmed our previous findings that myocardial SPTLC1 and SPTLC2 levels are increased in heart failure patients. Consistently, αMHC-rtTA-KLF5 mice showed increased SPTLC1 and SPTLC2 expression, higher myocardial ceramide levels, and systolic dysfunction beginning 2 weeks after KLF5 induction. Treatment of αMHC-rtTA-KLF5 mice with myriocin that inhibits SPT, suppressed myocardial ceramide levels and alleviated systolic dysfunction.

CONCLUSIONS

KLF5 is induced during the development of ischemic heart failure in humans and mice and stimulates ceramide biosynthesis. Genetic or pharmacological inhibition of KLF5 in mice with MI prevents ceramide accumulation, alleviates eccentric remodeling, and increases ejection fraction. Thus, KLF5 emerges as a novel therapeutic target for the treatment of ischemic heart failure.

Abstract 272: Epigenetic Regulation Involved in Diabetes-induced Impairment in Myocardial Reparative Function of Endothelial Progenitor Cell-derived Exosomes

Myocardial infarction (MI) occurs frequently in patients with diabetes resulting in higher mortality and morbidity than non-diabetic patients. We and others have shown that bone marrow-derived endothelial progenitor cells (EPCs) promote cardiac neovascularization and attenuate ischemic injury in animal models. Moreover, emerging evidence supports that exosomes (Exo) mediate stem cell therapy by carrying cell-specific biological signatures and by inducing signaling via transfer of bioactive molecules to target cells. However, autologous cell-based therapies yielded modest clinical results, suggesting that cellular/Exo reparative function may be compromised on a background of disease such as diabetes. In addition, recent studies suggest epigenetic mechanisms, such as histone methylation for gene silencing, promotes diabetes-induced vascular complication. Therefore, we hypothesized that diabetic EPCs produce exosomes of altered and dysfunctional content which compromise EPC reparative function in ischemic heart disease via epigenetic alterations. We collected EPC-Exo from non-diabetic mice (Lepr db/+ ) and diabetic mice (Lepr db/db ) and examined their effect on tube formation and cardiomyocyte/endothelial cell survival in vitro as well as their reparative effects on permanent and acute ischemia/reperfusion (I/R) myocardial ischemic injuries in vivo . Diabetic EPC-Exo promoted neonatal rat cardiomyocyte cell apoptosis under hypoxic stress and repressed endothelial tube formation and cell survival compared to cells treated with WT EPC-Exo. In vivo studies revealed diabetic EPC-Exo significantly attenuated cardiac function, reduced capillary density, increased fibrosis and infarct size in permanent LAD ligation and I/R MI models. Mechanistically,H3K9Me3 was increased in mouse cardiac endothelial cells treated with diabetic EPC-exo, suggesting inhibition of angiogenic genes. Our results provide evidence that diabetic EPC-derived exosomes lose their cardiac reparative activities. Specific angiogenic genes will be examined by CHIP analysis of H3K9Me3. Reversing EPC-Exo function by manipulating H3K9Me3 expression will augment autologous therapies in regenerative medicine.

Abstract 249: Plasma Exosomes Impair Angiogenesis in Ischemic Hind Limb of Diabetic Mice- Role of Histone Methylation

Background: Critical limb ischemia (CLI) is one of most prevenient cardiovascular disease in diabetic patients. Recent evidence suggests that altered cargo and function of plasma exosomes (plasma-Exo) may play an important role in diabetes-induced cardiovascular complications. Here, we tested the hypotheses that inhibition of exosome biosynthesis/release improves ischemic hind limb (IHL) repair in db/db mice.

Methods: Plasma-Exo from db/+ and db/db mice were isolated by density-gradient ultracentrifugation. Unilateral IHL in mice was conducted by ligation of left femoral artery. Blood perfusion in IHL was measured by Laser Doppler Imager.

Results: Diabetic plasma-Exo impaired tube formation/migration of human microvascular endothelial cells (HMVECs) and blood perfusion in IHL of C57BL/6J mice. Exosome inhibitor GW4869 improved blood flow, capillary density, cell survival, and rescued necrosis of toe/toenail and fibrosis in IHL muscle of db/db mice. Mechanistically, diabetic plasma-Exo decreased secretion of pro-angiogenic factor Ang I&II, artemin, FGF2 and IGFBP1&2, and increased repressive transcriptional mark H3K27me3 and its methylase enhancer of zest homolog-2 (EZH2) in HMVECs. EZH2 inhibitor GSK343 rescued diabetic plasma-Exo-impaired tube formation and secretion of FGF2/artemin from HMVECs. Moreover, GW4869 reduced EZH2 and H3K27me3 protein expression in lung microvascular ECs of IHL db/db mice. Finally, diabetic plasma-Exo increased H3K27me3 level at promoter of artemin and FGF2.

Conclusions: Diabetic plasma-Exo impair angiogenesis and IHL injury repair. Diabetic plasma-Exo impair reparative property of ECs via, at least in part, enhancement of EZH2/H3K27me3/artemin and FGF2 cascade. Inhibition of plasma-Exo biosynthesis/secretion improve IHL repair in db/db mice. Plasma-Exo may be a novel target for prevention/treatment of CLI in diabetic patients.

Abstract 467: Exosomes Derived From Podoplanin Positive Cells Alter Physiology and Structure of Healthy Mouse Heart

Superseding fibrosis through paracrine signals enhances the ventricular dysfunction aftermyocardial infarction (MI). We have earlier reported that within 2 days post-MI a cohort ofpodoplanin (PDPN), a platelet aggregation-inducing type I transmembrane glycoprotein,positive cells populate injured heart and enhance inflammatory response by physicalinteractions with monocytes. Here we explored whether exosomes from these cells couldindependently alter healthy heart physiology and structure. PDPN+ cells were isolated 2 daysafter MI, cultured expanded and activated with TNFα and AngiotensinII. Exosomes derivedfrom activated PDPN+ cells conditioned media were used in vitro treatment of mouse cardiacendothelial cells (mCECs), mouse embryonic fibroblast (MEF) and monocytes and in vivo forthe treatment of healthy mouse hearts. PDPN+ cells derived exosomes (PDPN-exo)reprogramed mCECs to the lymphatic phenotype enhancing the expression of the majorlymphatic lineage markers and upregulated the expression of fibrotic markers suggesting anendothelial-mesenchymal transition. Furthermore, PDPN-exo drove the MEF to myo-fibroblastphenotype and monocytes toward pro-inflammatory phenotype. Proteomic analysis of PDPN-exo suggest these transitions may depend on NOTCH cleavage trough β-γSecretase andSerum Amyloid A3 protein accumulation/mis-folding. In vivo, PDPN-exo were initially injectedinto the left ventricle of healthy mouse hearts followed with exosomes boosters delivered byretro-orbital vein injection. Treated mice developed an extended epicardial fibrosis andamyloidosis with a subsequent impairment in the contractility and increase of the end diastolicand systolic volumes. The fibrotic area was characterized by vessels double positive toendothelial and lymphatic endothelial markers, and infiltrating CD45+ cells. In conclusionthese data suggest that PDPN-exo alter the biology of mCECs, fibroblast and monocytes andparticipate in adverse remodeling after MI; their specific cargo may represent a cohort oftargets for the treatment of cardiac fibrosis.

Interleukin-10 Deficiency Alters Endothelial Progenitor Cell-Derived Exosome Reparative Effect on Myocardial Repair via Integrin-Linked Kinase Enrichment

Rationale: Systemic inflammation compromises the reparative properties of endothelial progenitor cell (EPC) and their exosomes on myocardial repair, although the underlying mechanism of loss of function of exosomes from inflamed EPCs is still obscure. Objective: To determine the mechanisms of IL-10 (interleukin-10) deficient-EPC-derived exosome dysfunction in myocardial repair and to investigate if modification of specific exosome cargo can rescue reparative activity. Methods and Results: Using IL-10 knockout mice mimicking systemic inflammation condition, we compared therapeutic effect and protein cargo of exosomes isolated from wild-type EPC and IL-10 knockout EPC. In a mouse model of myocardial infarction (MI), wild-type EPC-derived exosome treatment significantly improved left ventricle cardiac function, inhibited cell apoptosis, reduced MI scar size, and promoted post-MI neovascularization, whereas IL-10 knockout EPC-derived exosome treatment showed diminished and opposite effects. Mass spectrometry analysis revealed wild-type EPC-derived exosome and IL-10 knockout EPC-derived exosome contain different protein expression pattern. Among differentially expressed proteins, ILK (integrin-linked kinase) was highly enriched in both IL-10 knockout EPC-derived exosome as well as TNFα (tumor necrosis factor-α)-treated mouse cardiac endothelial cell-derived exosomes (TNFα inflamed mouse cardiac endothelial cell-derived exosome). ILK-enriched exosomes activated NF-κB (nuclear factor κB) pathway and NF-κB-dependent gene transcription in recipient endothelial cells and this effect was partly attenuated through ILK knockdown in exosomes. Intriguingly, ILK knockdown in IL-10 knockout EPC-derived exosome significantly rescued their reparative dysfunction in myocardial repair, improved left ventricle cardiac function, reduced MI scar size, and enhanced post-MI neovascularization in MI mouse model. Conclusions: IL-10 deficiency/inflammation alters EPC-derived exosome function, content and therapeutic effect on myocardial repair by upregulating ILK enrichment in exosomes, and ILK-mediated activation of NF-κB pathway in recipient cells, whereas ILK knockdown in exosomes attenuates NF-κB activation and reduces inflammatory response. Our study provides new understanding of how inflammation may alter stem cell-exosome-mediated cardiac repair and identifies ILK as a target kinase for improving progenitor cell exosome-based cardiac therapies.

Circular RNA CircFndc3b modulates cardiac repair after myocardial infarction via FUS/VEGF-A axis

Circular RNAs are generated from many protein-coding genes, but their role in cardiovascular health and disease states remains unknown. Here we report identification of circRNA transcripts that are differentially expressed in post myocardial infarction (MI) mouse hearts including circFndc3b which is significantly down-regulated in the post-MI hearts. Notably, the human circFndc3b ortholog is also significantly down-regulated in cardiac tissues of ischemic cardiomyopathy patients. Overexpression of circFndc3b in cardiac endothelial cells increases vascular endothelial growth factor-A expression and enhances their angiogenic activity and reduces cardiomyocytes and endothelial cell apoptosis. Adeno-associated virus 9 -mediated cardiac overexpression of circFndc3b in post-MI hearts reduces cardiomyocyte apoptosis, enhances neovascularization and improves left ventricular functions. Mechanistically, circFndc3b interacts with the RNA binding protein Fused in Sarcoma to regulate VEGF expression and signaling. These findings highlight a physiological role for circRNAs in cardiac repair and indicate that modulation of circFndc3b expression may represent a potential strategy to promote cardiac function and remodeling after MI.

Circular RNAs (circRNAs) are non-coding RNAs generated from pre-mRNAs of coding genes by the splicing machinery whose function in the heart is poorly understood. Here the authors show that AAV-mediated delivery of the circRNA circFndc3b prevents cardiomyocyte apoptosis, enhances angiogenesis, and attenuates LV dysfunction post-MI in mice by regulating FUS-VEGF-A signalling.

Abstract 133: Exosomal Transfer of Muscle Specific Mir-499 to Endothelial and Endothelial Progenitor Cells Impairs Angiogenesis in Diabetes

Background: miR-499, a muscle specific-miR, is enhanced in diabetic heart and has been suggested to be a therapeutic target for cardiovascular disease in diabetes. Recent studies provided the evidence that overexpressing miR-499 in ECs inhibits the capillary tube networks. Here, we tested the hypothesis that under diabetic conditions, myocyte-derived exosomes transfer miR-499 to EC/EPCs thereby impairing their angiogenic properties.

Methods and Results: miR-499 expression is abundant and enhanced in heart, skeletal muscle, cardiomyocytes and skeletal muscle cells (SKMCs) of db/db mice. We observed that miR-499 level was also increased in diabetic EC/EPCs. In vitro, high D-glucose (25 mM) increased miR-499 level in SKMCs but not in ECs, suggesting that enhanced miR-499 in diabetic EC/EPCs is not regulated by hyperglycemia. To study whether SKMC-derived exosomes transfer miR-499 from SKMCs to EC/EPCs, we first examined the miR-499 levels in diabetic SKMC-derived exosomes and plasma-derived exosomes from db/db mice. We observed that miR-499 levels were greater in diabetic SKMC- and plasma-derived exosomes. Furthermore, by co-culture, we found that diabetic SKMCs increased miR-499 levels in human microvascular endothelial cells (ECs) and impaired EC tube formation and migration which was blocked by exosome inhibitor GW4869 (GW). We also observed that GW partially rescued diabetic SKMC- and plasma-derived exosome-mediated impairment in tube formation and migration of ECs. Overexpression of miR-499 in ECs decreased angiogenic factors and impaired tube formation/migration. Furthermore, in a hind-limb ischemia model of db/db mice, GW treatment improved ischemic hindlimb blood perfusion and angiogenesis. Our study suggests that diabetes-enhanced miR-499 in myocytes can be transferred to ECs via myocyte-derived exosomes thus impairs EC/EPC function. Mechanistically, Sex-determining region Y-box 6 (SOX6), one of the validated target of miR-499, was significantly decreased in diabetic EC/EPCs. Knockdown of SOX6 impairs tube formation and migration of ECs.

Conclusions: Our results suggest that exosomal transfer of muscle specific miR-499 to EC/EPCs impairs angiogenesis and ischemic tissue injury repair in diabetes via suppression of SOX6.

Abstract 513: Exosomes Derived From Podoplanin Positive Cells Induce Fibrosis and Inflammation in Healthy Mouse Heart

Superseding fibrosis is the leading cause of the adverse remodeling after myocardial infarction (MI); inflammation and paracrine signals enhance the fibrosis and ventricular dysfunction and inhibit the favorable repair. It has been reported that cells expressing Podoplanin (PDPN), a platelet aggregation- inducing type I transmembrane glycoprotein, appear around 2 days after MI as a signal of activation. We hypothesized that exosomes derived from these cells may actively affect the biology of fibrosis and inflammation. PDPN+ cells were isolated from hearts of mice 2 days after MI, expanded in a selective media and treated with TNFα, Angiotensin II or the combination of both. Exosomes derived from activated PDPN+ cells were isolated from the conditioned media and used in vitro for the treatment of mouse cardiac endothelial cells (mCECs), mouse embryonal fibroblast (MEF) and monocytes and in vivo for the treatment of healthy mouse hearts. Data from q-PCR showed that stimulated PDPN+ cells derived exosomes reprogramed mCECs to the endothelial lymphatic phenotype enhancing the expression of the major lymphatic lineage markers and upregulated the expression of fibrotic markers suggesting an endothelial-mesenchymal transition. Furthermore, stimulated PDPN+ cells derived exosomes drove the fibroblast to myo-fibroblast phenotype and activated monocytes toward pro-inflammatory lineage with an increased expression of TNFα and IL- 1β. In vivo, stimulated PDPN+ cells derived exosomes were initially injected in to the left ventricle of healthy mouse hearts followed with additional boosters delivered by retro-orbital vein injection. Treated mice developed an extended epicardial fibrosis with a subsequent impairment in the contractility and increase in the end diastolic and systolic volumes. In conclusion stimulated PDPN+ cells derived exosomes may impair the biology of mCECs, fibroblast and monocytes leading to adverse remodeling after MI.

Podoplanin neutralization improves cardiac remodeling and function after acute myocardial infarction

Podoplanin, a small mucine-type transmembrane glycoprotein, has been recently shown to be expressed by lymphangiogenic, fibrogenic and mesenchymal progenitor cells in the acutely and chronically infarcted myocardium. Podoplanin binds to CLEC-2, a C-type lectin-like receptor 2 highly expressed by CD11bhigh cells following inflammatory stimuli. Why podoplanin expression appears only after organ injury is currently unknown. Here, we characterize the role of podoplanin in different stages of myocardial repair after infarction and propose a podoplanin-mediated mechanism in the resolution of post-MI inflammatory response and cardiac repair. Neutralization of podoplanin led to significant improvements in the left ventricular functions and scar composition in animals treated with podoplanin neutralizing antibody. The inhibition of the interaction between podoplanin and CLEC-2 expressing immune cells in the heart enhances the cardiac performance, regeneration and angiogenesis post MI. Our data indicates that modulating the interaction between podoplanin positive cells with the immune cells after myocardial infarction positively affects immune cell recruitment and may represent a novel therapeutic target to augment post-MI cardiac repair, regeneration and function.

Abstract 460: Diabetes Impairs Reparative Property of Bone Marrow-derived Endothelial Progenitor Cells: Role of Mir-499-mediated Hydrogen Sulfide Deficiency

Background: miR-499 has been considered as a potential biomarker for myocardial infarction. Overexpression of miR-499 impaired heart function and induced cardiac hypertrophy in mice. Recent studies suggested miR-499 suppresses tumor growth through the inhibition of vascular endothelial growth factor (VEGF) mediated angiogenesis. Furthermore, emerging evidences indicate that miR-499 is increased in heart of diabetic rodents and patients. Here, we tested the hypotheses that miR-499 impairs angiogenic ability of endothelial cells (ECs) under diabetic conditions.

Methods and Results: miR-499 levels were examined in endothelial progenitor cells (EPCs), microvascular endothelial cells (MVECs) and plasma in diabetic db/db mice (8-week, male). Gender- and age-matched non-diabetic db/+ mice served as controls. EPCs were isolated from bone marrow density-gradient centrifugation. MVECs were isolated using collagenase. We found that miR-499 levels were significantly increased in EPCs, MVECs as well as plasma of db/db mice. miR-499 antagomiR rescued high glucose (25 mM D-glucose for 48 h)-impaired tube formation and migration of human cardiac microvascular endothelial cells (HCMVECs). Mechanistically, by luciferase assay, we found that miR-499 directly targets cystathionine γ-lyase (CSE), a major hydrogen sulfide (H 2 S)-synthesizing enzyme in cardiovascular cells. Overexpression of miR-499 by transfection of miR-499 mimics decreased CSE protein levels and intracellular H 2 S production in HCMVECs.

Conclusions: Our results suggest that miR-499-induced CSE downregulation/inactivation thus H 2 S reduction may play an important role in diabetes-impaired angiogenic capacity. Silencing miR-499 in diabetic EPCs/ECs may provide a novel tool for the treatment of ischemic tissue injury in patients with diabetes.

Abstract 288: Circular RNA CircFNDC3b Modulates Cardiac Repair After Myocardial Infarction via FUS-1/VEGF-A Axis

Circular RNA (circRNA) is a new addition to the list of growing body of non-coding RNAs.Recent studies highlighted that circRNA are dysregulated in cardiovascular disease. However,knowledge of the role of circRNAs in ischemic cardiac injury is limited. Using global circRNAexpression profiling, we identified several circRNA transcripts that were differentially regulatedpost-MI in mice, including circFNDC3b (derived from 2 and 3 exons of cognate FNDC3b gene)which is significantly down regulated. Cell fractionation experiments revealed that circFNDC3bis highly enriched in endothelial cells of post-MI mice. Notably, we found a circFNDC3b orthologin humans, which was also significantly down regulated in ischemic cardiomyopathy patients.Further, gene profile analysis of circFNDC3b overexpression in cardiac endothelial cellsdemonstrated an increase in angiogenic genes. Among them, vascular endothelial growthfactor-A (VEGF-A) was significantly elevated concomitant with reduced in vitro apoptosis ofcardiomyoblasts and endothelial cells, which also exhibited enhanced tube formation. Forcardiac overexpression of circFNDC3b, we generated AAV9 viral particles and found that in vivoover expression attenuated LV dysfunction post-MI and enhanced neovascularization.Mechanistically, circFNDC3b interacts with its potential target RNA binding protein FUS-1 (fusedin sarcoma) and regulate VEGF signaling, thereby reducing cardiomyocyte apoptosis andenhancing neovascularization and cardiac function post-MI. These results indicatethat circFNDC3b is a novel potential target to prevent cardiac remodeling and highlight theimportance of circRNAs in cardiovascular diseases.

Abstract 333: TNF Receptor Modulation of Progenitor Cells and Exosomes for Myocardial Repair

Our published studies, using TNFR1 and TNFR2 knockout (KO) mice have demonstrated that negative effects of TNF during ischemic tissue repair including enhanced apoptosis and inflammatory cytokines expression and signaling, is largely mediated by TNFR1/p55. Our hypothesis is that inhibition of TNF-TNFR1 signaling inhibits multiple negative effects of TNF after myocardial ischemia by promoting TNF signaling through protective TNFR2 receptor and thereby augmenting EPC-mediated myocardial angiogenesis and repair and this enhanced protective effect of TNFR1 KO EPCs may involve alteration in the cargo and function of TNFR1-KO EPC derived exosomes.

Protective effect of disrupted TNF-TNFR1/p55 signaling in BM-EPCs under stress conditions in WT, p55KO and p75KO EPCs were tested in tube formation assay under hypoxia conditions and H2O2 treatment. In the absence of TNFR1 (p55KO EPCs) - EC function of BM-EPCs is enhanced under normoxia/hypoxia conditions and survival of BM-EPCs is increased under oxidative stress. To test the effect of TNFR1 and TNFR2 loss in the BM-EPCs for recovery after AMI, WT mice were subjected to AMI and WT, p75KO and p55KO BM-EPCs were injected into the myocardium immediately after AMI. Compared to WT and p75KO, injection of p55KO EPCs into WT hosts led to - increased retention of p55KO EPCs in the WT mice hearts; decreased post-MI apoptosis in WT mice; increased vascular network; significantly improved cardiac function; substantially small infarct size; the last three indicating improved cardiac remodeling by day 21 post-AMI. Further, in vitro exosome studies showed that compared to WT and p75KOs, p55KO BM-EPCs-derived exosomes showed positive activities in vitro, including - enhanced angiogenic function in HUVECs and increased survival of H9C2 cells. These effects were mediated via upregulation of miRNA-191-5p as shown by increased levels of angiogenic miR-191-5p in the exosomal cargo of p55KO EPCs and near complete inhibition of HUVEC angiogenic function in vitro by miR-191-5p-antagomiR.

Our findings suggest that decrease/loss of TNFR1 modulates both the content and function of EPC exosomes and enhance reparative and angiogenic capabilities of EPCs and EPC-mediated vascular and anatomical repair in the MI model.

Abstract 387: Lymphatic Endothelial Cells Derived Exosomes Promote Neolymphangiogenesis After Injury

Neolymphangiogenesis after myocardial infarction (MI) has been extensively documented; however the source of new lymphatic vessels (LVs) is still unknown. It has been described that new LVs may derive from resident lymphatic endothelial cells (LECs) or from trans-differentiation of endothelial cells (ECs) and pericytes from veins into LECs. Which signals activate both the spreading and the trans-differentiation needs to be investigated. LECs are known to release transcytotic vesicles and exosomes, thus, we hypnotized that the enriched protein and RNA cargo of LECs derived exosomes may promote the new LVs formation after injury. Exosomes derived from LECs were isolated from LECs cultured conditioned medium and HUVECs were treated with different concentration of exosomes cargo for 10 days. After treatment, q-PCR for the major endothelial and lymphatic endothelial markers was performed on treated HUVECs. In a dose dependent manner we observed a decreased expression of KDR and CD31, endothelial markers that are not expressed by LECs and an increased expression of Prox-1 and VEGFR3. Prox-1 is the major lymphatic endothelial transcription factor that is not activated in ECs and is responsible for the transcription of LYVE-1 and podoplanin. VEGFR3 is the only known vascular endothelial growth factor receptor expressed on LECs which is not displayed by ECs. Next, we evaluated the effect of LECs derived exosomes on in vitro lymphangiogenesis assay by measuring the ability of LECs to organize into capillary-like structures on matrigel. LECs treated with LECs derived exosomes are able to form tubes and branches as early as within 1 hour compared to untreated cells. Our preliminary results show cargo of exosomes from LECs activates the signal transduction and metabolism of LECs and HUVECs promoting the new LVs formation through spreading and trans-differentiation of the targeted cells.

Abstract 216: Interleukin-10 Deficiency Impairs Reparative Properties of Bone Marrow-Derived Endothelial Progenitor Cell Exosomes

EPC based therapy in clinical trials is largely benefited from paracrine effect such as exosomes. Exosomes mirror the behavior of parental cells and their function is dependent on RNAs and proteins packed inside. Systemic inflammation in MI patients greatly compromise the reparative performance of EPCs and relative exosomes. We hypothesized that EPCs under inflammatory stress produce dysfunctional exosomes with altered content, which compromise EPCs reparative benefit in ischemic heart disease. We choose interleukin-10 knockout (IL-10KO) mice as a model mimicking systemic inflammation. After EPC isolation and expansion from IL-10KO and wild-type (WT) mice, we isolated exosomes and compared their reparative properties both in vitro and in vivo . Our in vitro studies showed WT-EPC-Exo treatment enhanced endothelial cell proliferation and tube formation, and inhibited apoptosis, whereas IL-10KO-Exo exhibited impaired or even detrimental effects. We used MI mouse model to compare the in vivo function of two groups of exosomes, we found WT-EPC-Exo treatment significantly improved left ventricle cardiac function, inhibited cell death and promoted angiogenesis; while these benefits were lost in IL-10KO-EPC-Exo treated group. Both in vitro and in vivo studies suggested impaired exosome function under IL-10 deficiency. We checked the alteration of exosomal content using NGS RNAseq and mass spectrometry and found the RNA and protein expression pattern is drastically different in two groups of exosomes. Importantly, IL-10KO-EPC-Exo were highly enriched in microRNAs and proteins that promote inflammation and apoptosis and inhibit angiogenesis. We picked two candidates for further study, mir-375 and integrin linked kinase (ilk), both are highly enriched in IL-10KO-EPC-Exo. Through modulating the expression of mir-375 and ilk in exosomes, we partially rescued IL-10KO-EPC-Exo dysfunction. Thus, our study revealed that even the same type of cells, under different conditions, secrete exosomes with different function. The differences in exosomal function is caused by alteration in exosomal content, and the function can be enhanced or rescued by modulating specific targets in exosomes.

Abstract 330: Systemic Blocking Exosome Formation/Release Improves Ischemic Hindlimb Repair in Diabetic db/db Mice

Background: Recent studies demonstrated that plasma exosomes from diabetic patients and animals lose their ability to maintain physiological properties of cardiomyocytes. Exosome inhibitor GW 4869 (GW) tended to improve heart function in diabetic mice with myocardial infarction. We tested the hypotheses that systemic blocking exosome synthesis/formation improves ischemic hindlimb repair in diabetes.

Methods and Results: Unilateral hindlimb ischemia (HLI) surgery was conducted by ligation of left femoral artery in 12-week male db/db and db/+ mice which were administrated with either GW (2 mg/kg body weight, i.p) or vehicle for 4 weeks starting from one week before HLI. Blood perfusion in ischemic hindlimbs was examined by Laser Doppler at pre-HLI, and 0, 3, 7, 14 and 21 days post-HLI. Plasma exosomes were isolated by standard ultracentrifugation method and counted by NanoSight. GW increased blood concentration of CD31 + /Sca-1 + cell 3-day post-HLI and decreased necrosis and loss of toe/toenail; improved blood flow; enhanced capillary/arterial density determined by CD31 and SMA-α staining and decreased fibrosis in the muscles of ischemic hindlimbs in db/db mice 21-day post-HLI. Plasma exosomes from db/db mice significantly impaired human cardiac microvascular endothelial cells (HCMVECs) tube formation and migration. Mechanistically, hepatocyte growth factor (HGF) expression was decreased in bone marrow-derived endothelial progenitor cells (EPCs) from db/db mice and HCMVECs treated with diabetic plasma exosomes. Administration of GW increased HGF level in diabetic EPCs. Furthermore, diabetic plasma exosomes decreased H3K4me3 (active maker of transcription) whereas increased H3K27me3 (suppressive marker of transcription) at HGF promoter. Finally, treatment of HCMEVs with exogenous HGF rescued diabetic exosomes impaired tube formation of HCMVEC.

Conclusions: Systemic inhibition of exosome synthesis/formation by GW increased ischemic limb repair in diabetic db/db mice, at least partially, via histone methylation mediated suppression of HGF. Our findings suggest that therapeutic targeting of systemic dysfunctional exosomes could represent a new avenue for therapeutics of ischemic tissue injury in patients with diabetes.

Hyperhomocysteinemia potentiates diabetes-impaired EDHF-induced vascular relaxation: Role of insufficient hydrogen sulfide

Insufficient hydrogen sulfide (H₂S) has been implicated in Type 2 diabetic mellitus (T2DM) and hyperhomocysteinemia (HHcy)-related cardiovascular complications. We investigated the role of H₂S in T2DM and HHcy-induced endothelial dysfunction in small mesenteric artery (SMA) of db/db mice fed a high methionine (HM) diet. HM diet (8 weeks) induced HHcy in both T2DM db/db mice and non-diabetic db/+ mice (total plasma Hcy: 48.4 and 31.3 µM, respectively), and aggravated the impaired endothelium-derived hyperpolarization factor (EDHF)-induced endothelium-dependent relaxation to acetylcholine (ACh), determined by the presence of eNOS inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) and prostacyclin (PGI₂) inhibitor indomethacin (INDO), in SMA from db/db mice but not that from db/+ mice. A non-selective Ca²⁺-active potassium channel (K_Ca) opener NS309 rescued T2DM/HHcy-impaired EDHF-mediated vascular relaxation to ACh. EDHF-induced relaxation to ACh was inhibited by a non-selective K_Ca blocker TEA and intermediate-conductance K_Ca blocker (IK_Ca) Tram-34, but not by small-conductance K_Ca (SK_Ca) blocker Apamin. HHcy potentiated the reduction of free sulfide, H₂S and cystathionine γ-lyase protein, which converts L-cysteine to H₂S, in SMA of db/db mice. Importantly, a stable H₂S donor DATS diminished the enhanced O₂^- production in SMAs and lung endothelial cells of T2DM/HHcy mice. Antioxidant PEG-SOD and DATS improved T2DM/HHcy impaired relaxation to ACh. Moreover, HHcy increased hyperglycemia-induced IK_Ca tyrosine nitration in human micro-vascular endothelial cells. EDHF-induced vascular relaxation to L-cysteine was not altered, whereas such relaxation to NaHS was potentiated by HHcy in SMA of db/db mice which was abolished by ATP-sensitive potassium channel blocker Glycolamide but not by K_Ca blockers.

Conclusions

Intermediate HHcy potentiated H₂S reduction via CSE-downregulation in microvasculature of T2DM mice. H₂S is justified as an EDHF. Insufficient H₂S impaired EDHF-induced vascular relaxation via oxidative stress and IK_Ca inactivation in T2DM/HHcy mice. H₂S therapy may be beneficial for prevention and treatment of micro-vascular complications in patients with T2DM and HHcy.

Abstract 298: Circular Rna Mmu_circ_008396 Attenuates Cardiac Remodeling After Myocardial Infarction in Mice

Recent studies highlighted that circular RNAs (circRNA) can play an important role in cardiac hypertrophy. However, the circRNAs in cardiac diseases is still limited. Using global circRNA expression profiling, we identified several circRNA transcripts that were differentially regulated post-MI in mice, including mmu_circ_008396 that is significantly down regulated. Cell fractionation experiments indicated that mmu_circ_008396 is highly enriched in endothelial cells in post-MI mice. Interestingly, we found a mmu_circ_008396 circRNA ortholog in humans, which was also significantly down regulated in ischemic cardiomyopathy patients. Further, overexpression of mmu_circ_008396 significantly enhanced tube formation and reduced apoptosis of human umbilical vein endothelial cells. For cardiac overexpression of mmu_circ_008396 circRNA, we created AAV9 viral particles and found that in vivo over expression attenuated LV dysfunction post-MI and enhanced neovascularization. Mechanistically, mmu_circ_008396 binds to its potential target miRNAs (mmu-miR-93-3p, mmu-miR-412-3p and mmu-miR-298-5p) and regulate hemeoxygenase-1/ VEGF signaling, thereby enhancing neovascularization and cardiac repair post-MI. These results indicate that mmu_circ_008396 circRNA might be a novel potential target to prevent cardiac remodeling and also highlight the significance of circRNAs in cardiovascular diseases.

Abstract 413: Podoplanin Neutralization Improves Cardiac Remodeling and Function After Acute Myocardial Infarction

Variety of cardioprotective and reparative therapeutic approaches have emerged for the treatment of cardiac remodeling after myocardial infarction (MI). Here we propose a novel mechanism using a neutralizing antibody that target Podoplanin (PDPN), a platelet aggregation-inducing type I transmembrane glycoprotein, expressed on a cohort of myocardial cells that migrate to the infarcted area after MI and contribute significantly to scar formation. The PDPN+ cells were isolated from infarcted hearts two days after MI, using magnetic beads sorting. We tested in vitro the effect of PDPN neutralizing antibody (5μg/ml) in a transwell migration assay and the activation of monocytes co-cultured with PDPN+ cells. The neutralizing antibody decreased significantly PDPN+ cells migration. Monocytes co-cultured with PDPN+ cells produced high levels of IL1α and IL12, whereas treatment of co-cultures with podoplanin neutralizing antibody inhibited IL1α and IL12 production and increased IL9 and IL10 production, suggesting a switch form pro-inflammatory to anti-inlammatory phenotype. To tests the effect of podoplanin neutralizing antibody in vivo, C57BL/6 wild type mice were subjected to experimental MI and anti-PDPN antibody (25μg/ml) was injected i.p. on days 1, 2, 7 and 15 after MI and mice were scarified two months after. At 7 days after MI echocardiography revealed comparable ~30% of ejection fraction (EF) in control and antibody-injected mice. After one month EF% remained unchanged in control group and increased up to 45% in antibody-treated group, suggesting improvement in cardiac function. Histologically, in the control group the ischemic area was composed by fibrotic tissue highly positive for fibronectin and αSMA, whereas in the antibody-treated group revealed large number of survived, as well as proliferating myocytes expressing αSARC-actin and Phospho-H3. Further, there was a significant increase in CD31 positive cells in the infarct border-zone of antibody-treated vs. control hearts, suggesting increased angiogenesis. Our findings suggest that inhibition of PDPN during first two weeks after MI intensely enhances cardiac regeneration and angiogenesis. This may represent a new therapeutic support for the tissue renewal after MI.

Abstract 353: Bone Marrow Fibroblast Progenitor Cell-derived Exosomes Activate Resident Fibroblast and Augment Pressure Overload Induced Cardiac Fibrosis in IL10KO Mice

Background: Activated fibroblasts (myoFBs) play critical role in cardiac fibrosis, however, their origin in diseased heart remains uncertain. Previous studies suggest the contribution of bone marrow fibroblasts progenitor cells (FPC) in pressure overload (PO)-induced cardiac fibrosis and inflammation acts as catalyst in this process. Recently others and we have shown that paracrine mediators packaged in exosomes play important role in cardiac pathophysiology. Thus, we hypothesized that exosome-derived from IL10KO-FPC augments PO-induced resident cardiac fibroblast activation and therefore, aggravate cardiac fibrosis.

Methods and Results: Cardiac fibrosis was induced in Wild-type (WT) and IL10-knockout (IL10KO) mice by transverse aortic constriction (TAC). TAC-induced left ventricular (LV) dysfunction and fibrosis were further exaggerated in IL10KO mice. PO-enhanced FPC (Prominin1 + cells) mobilization and homing in IL10KO mice compared to WT mice. To establish the IL10KO-FPC paracrine signaling, exosomes were isolated from WT and IL10KO BM-FPC culture media and characterized for proteins/miRNA. IL10 KO FPC-exosomes showed altered packaging of signature fibrotic miR and proteins. To explore whether FPC-exosomes modulate resident fibroblast activation, adult cardiac fibroblasts were treated with WT and IL10KO FPC-derived exosomes. IL10KO-FPC-derived exosomes exaggerate TGFβ 2 -induced activation of adult fibroblasts. These data suggest that fibrotic remodeling factors (miRs and/or proteins) packaged in IL10KO-FPC exosomes are sufficient to enhance the resident cardiac fibroblast activation and mediate cardiac fibrotic remodeling IL10 treatment significantly inhibits TGFβ 2 -induced FPC to myoFBs transition.

Conclusion: Taken together, our findings suggest that paracrine factors secreted by BM-FPC augment resident cardiac fibroblast activation and fibrosis in pressure overloaded myocardium and IL10 negatively regulates this process. Ongoing investigations using molecular approaches will provide a better understanding on the mechanistic and therapeutic aspects of IL10 on PO-induced cardiac fibrosis and heart failure.

Therapeutic inhibition of miR-375 attenuates post-myocardial infarction inflammatory response and left ventricular dysfunction via PDK-1-AKT signalling axis

AIMS

Increased miR-375 levels has been implicated in rodent models of myocardial infarction (MI) and with patients with heart failure. However, no prior study had established a therapeutic role of miR-375 in ischemic myocardium. Therefore, we assessed whether inhibition of MI-induced miR-375 by LNA anti-miR-375 can improve recovery after acute MI.

METHODS AND RESULTS

Ten weeks old mice were treated with either control or LNA anti miR-375 after induction of MI by LAD ligation. The inflammatory response, cardiomyocyte apoptosis, capillary density and left ventricular (LV) functional, and structural remodelling changes were evaluated. Anti-miR-375 therapy significantly decreased inflammatory response and reduced cardiomyocyte apoptosis in the ischemic myocardium and significantly improved LV function and neovascularization and reduced infarct size. Repression of miR-375 led to the activation of 3-phosphoinositide-dependent protein kinase 1 (PDK-1) and increased AKT phosphorylation on Thr-308 in experimental hearts. In corroboration with our in vivo findings, our in vitro studies demonstrated that knockdown of miR-375 in macrophages modulated their phenotype, enhanced PDK-1 levels, and reduced pro-inflammatory cytokines expression following LPS challenge. Further, miR-375 levels were elevated in failing human heart tissue.

CONCLUSION

Taken together, our studies demonstrate that anti-miR-375 therapy reduced inflammatory response, decreased cardiomyocyte death, improved LV function, and enhanced angiogenesis by targeting multiple cell types mediated at least in part through PDK-1/AKT signalling mechanisms.

Interleukin-10 Inhibits Bone Marrow Fibroblast Progenitor Cell-Mediated Cardiac Fibrosis in Pressure-Overloaded Myocardium

BACKGROUND

Activated fibroblasts (myofibroblasts) play a critical role in cardiac fibrosis; however, their origin in the diseased heart remains unclear, warranting further investigation. Recent studies suggest the contribution of bone marrow fibroblast progenitor cells (BM-FPCs) in pressure overload-induced cardiac fibrosis. We have previously shown that interleukin-10 (IL10) suppresses pressure overload-induced cardiac fibrosis; however, the role of IL10 in inhibition of BM-FPC-mediated cardiac fibrosis is not known. We hypothesized that IL10 inhibits pressure overload-induced homing of BM-FPCs to the heart and their transdifferentiation to myofibroblasts and thus attenuates cardiac fibrosis.

METHODS

Pressure overload was induced in wild-type (WT) and IL10 knockout (IL10KO) mice by transverse aortic constriction. To determine the bone marrow origin, chimeric mice were created with enhanced green fluorescent protein WT mice marrow to the IL10KO mice. For mechanistic studies, FPCs were isolated from mouse bone marrow.

RESULTS

Pressure overload enhanced BM-FPC mobilization and homing in IL10KO mice compared with WT mice. Furthermore, WT bone marrow (from enhanced green fluorescent protein mice) transplantation in bone marrow-depleted IL10KO mice (IL10KO chimeric mice) reduced transverse aortic constriction-induced BM-FPC mobilization compared with IL10KO mice. Green fluorescent protein costaining with α-smooth muscle actin or collagen 1α in left ventricular tissue sections of IL10KO chimeric mice suggests that myofibroblasts were derived from bone marrow after transverse aortic constriction. Finally, WT bone marrow transplantation in IL10KO mice inhibited transverse aortic constriction-induced cardiac fibrosis and improved heart function. At the molecular level, IL10 treatment significantly inhibited transforming growth factor-β-induced transdifferentiation and fibrotic signaling in WT BM-FPCs in vitro. Furthermore, fibrosis-associated microRNA (miRNA) expression was highly upregulated in IL10KO-FPCs compared with WT-FPCs. Polymerase chain reaction-based selective miRNA analysis revealed that transforming growth factor-β-induced enhanced expression of fibrosis-associated miRNAs (miRNA-21, -145, and -208) was significantly inhibited by IL10. Restoration of miRNA-21 levels suppressed the IL10 effects on transforming growth factor-β-induced fibrotic signaling in BM-FPCs.

CONCLUSIONS

Our findings suggest that IL10 inhibits BM-FPC homing and transdifferentiation to myofibroblasts in pressure-overloaded myocardium. Mechanistically, we show for the first time that IL10 suppresses Smad-miRNA-21-mediated activation of BM-FPCs and thus modulates cardiac fibrosis.

Phenotypically heterogeneous podoplanin-expressing cell populations are associated with the lymphatic vessel growth and fibrogenic responses in the acutely and chronically infarcted myocardium

Cardiac lymphatic vasculature undergoes substantial expansion in response to myocardial infarction (MI). However, there is limited information on the cellular mechanisms mediating post-MI lymphangiogenesis and accompanying fibrosis in the infarcted adult heart. Using a mouse model of permanent coronary artery ligation, we examined spatiotemporal changes in the expression of lymphendothelial and mesenchymal markers in the acutely and chronically infarcted myocardium. We found that at the time of wound granulation, a three-fold increase in the frequency of podoplanin-labeled cells occurred in the infarcted hearts compared to non-operated and sham-operated counterparts. Podoplanin immunoreactivity detected LYVE-1-positive lymphatic vessels, as well as masses of LYVE-1-negative cells dispersed between myocytes, predominantly in the vicinity of the infarcted region. Podoplanin-carrying populations displayed a mesenchymal progenitor marker PDGFRα, and intermittently expressed Prox-1, a master regulator of the lymphatic endothelial fate. At the stages of scar formation and maturation, concomitantly with the enlargement of lymphatic network in the injured myocardium, the podoplanin-rich LYVE-1-negative multicellular assemblies were apparent in the fibrotic area, aligned with extracellular matrix deposits, or located in immediate proximity to activated blood vessels with high VEGFR-2 content. Of note, these podoplanin-containing cells acquired the expression of PDGFRβ or a hematoendothelial epitope CD34. Although Prox-1 labeling was abundant in the area affected by MI, the podoplanin-presenting cells were not consistently Prox-1-positive. The concordance of podoplanin with VEGFR-3 similarly varied. Thus, our data reveal previously unknown phenotypic and structural heterogeneity within the podoplanin-positive cell compartment in the infarcted heart, and suggest an alternate ability of podoplanin-presenting cardiac cells to generate lymphatic endothelium and pro-fibrotic cells, contributing to scar development.

Abstract 294: Therapeutic Silencing of miR-375 Attenuates Post-MI Inflammatory Response and Left Ventricular Dysfunction in Mice With Myocardial Infarction

MicroRNAs are known to be dysregulated in the ischemic heart disease and have emerged as potential therapeutic targets for treatment of myocardial infarction (MI). Our preliminary data indicated elevated MicroRNA-375 levels in failing human heart tissue. Therefore, we assessed whether inhibition of the miR-375 using a s.c.-delivered locked nucleic acid (LNA)-modified anti-miR (LNA-antimiR-375) can provide therapeutic benefit in mice with myocardial infarction (MI). After the induction of acute myocardial infarction, mice were treated with either control or LNA based LNA-anti-miR-375, and inflammatory response, cardiomyocyte apoptosis, capillary density and LV functional and structural remodeling changes were evaluated. LNA-anti-miR-375 therapy significantly reduced inflammatory cell infiltration, expression of pro-inflammatory cytokines and cardiomyocyte apoptosis in the myocardium. Further, our cell sorting experiments revealed that within the myocardium, LNA-anti-miR-375 was taken up by cardiomyocytes, endothelial cells and macrophages and repressed miR-375 levels, thereby activating 3-phosphoinositide-dependent protein kinase 1 (PDK-1) and downstream AKT phosphorylation on Thr-308. LNA anti-miR-375 therapy significantly improved LV functions, enhanced neovascularization and reduced infarct size. Corroborating with our in vivo findings, our in vitro studies demonstrated that knock down of miR-375 in macrophages enhanced the expression of PDK-1 and revealed reduced pro-inflammatory cytokines expression following LPS challenge. Taken together, our studies demonstrate that anti miR-375 therapy reduced inflammatory response, cardiomyocyte death, improved LV function and enhanced angiogenesis by targeting multiple cell types via activation of PDK-1/AKT signaling.

Myocyte repolarization modulates myocardial function in aging dogs

Studies of myocardial aging are complex and the mechanisms involved in the deterioration of ventricular performance and decreased functional reserve of the old heart remain to be properly defined. We have studied a colony of beagle dogs from 3 to 14 yr of age kept under a highly regulated environment to define the effects of aging on the myocardium. Ventricular, myocardial, and myocyte function, together with anatomical and structural properties of the organ and cardiomyocytes, were evaluated. Ventricular hypertrophy was not observed with aging and the structural composition of the myocardium was modestly affected. Alterations in the myocyte compartment were identified in aged dogs, and these factors negatively interfere with the contractile reserve typical of the young heart. The duration of the action potential is prolonged in old cardiomyocytes contributing to the slower electrical recovery of the myocardium. Also, the remodeled repolarization of cardiomyocytes with aging provides inotropic support to the senescent muscle but compromises its contractile reserve, rendering the old heart ineffective under conditions of high hemodynamic demand. The defects in the electrical and mechanical properties of cardiomyocytes with aging suggest that this cell population is an important determinant of the cardiac senescent phenotype. Collectively, the delayed electrical repolarization of aging cardiomyocytes may be viewed as a critical variable of the aging myopathy and its propensity to evolve into ventricular decompensation under stressful conditions.

c-Kit-positive cardiac stem cells nested in hypoxic niches are activated by stem cell factor reversing the aging myopathy

RATIONALE

Hypoxia favors stem cell quiescence, whereas normoxia is required for stem cell activation, but whether cardiac stem cell (CSC) function is regulated by the hypoxic/normoxic state of the cell is currently unknown.

OBJECTIVE

A balance between hypoxic and normoxic CSCs may be present in the young heart, although this homeostatic control may be disrupted with aging. Defects in tissue oxygenation occur in the old myocardium, and this phenomenon may expand the pool of hypoxic CSCs, which are no longer involved in myocyte renewal.

METHODS AND RESULTS

Here, we show that the senescent heart is characterized by an increased number of quiescent CSCs with intact telomeres that cannot re-enter the cell cycle and form a differentiated progeny. Conversely, myocyte replacement is controlled only by frequently dividing CSCs with shortened telomeres; these CSCs generate a myocyte population that is chronologically young but phenotypically old. Telomere dysfunction dictates their actual age and mechanical behavior. However, the residual subset of quiescent young CSCs can be stimulated in situ by stem cell factor reversing the aging myopathy.

CONCLUSIONS

Our findings support the notion that strategies targeting CSC activation and growth interfere with the manifestations of myocardial aging in an animal model. Although caution has to be exercised in the translation of animal studies to human beings, our data strongly suggest that a pool of functionally competent CSCs persists in the senescent heart and that this stem cell compartment can promote myocyte regeneration effectively, partly correcting the aging myopathy.

Age-associated defects in EphA2 signaling impair the migration of human cardiac progenitor cells

BACKGROUND

Aging negatively impacts on the function of resident human cardiac progenitor cells (hCPCs). Effective regeneration of the injured heart requires mobilization of hCPCs to the sites of damage. In the young heart, signaling by the guidance receptor EphA2 in response to the ephrin A1 ligand promotes hCPC motility and improves cardiac recovery after infarction.

METHODS AND RESULTS

We report that old hCPCs are characterized by cell-autonomous inhibition of their migratory ability ex vivo and impaired translocation in vivo in the damaged heart. EphA2 expression was not decreased in old hCPCs; however, the elevated level of reactive oxygen species in aged cells induced post-translational modifications of the EphA2 protein. EphA2 oxidation interfered with ephrin A1-stimulated receptor auto-phosphorylation, activation of Src family kinases, and caveolin-1-mediated internalization of the receptor. Cellular aging altered the EphA2 endocytic route, affecting the maturation of EphA2-containing endosomes and causing premature signal termination. Overexpression of functionally intact EphA2 in old hCPCs corrected the defects in endocytosis and downstream signaling, enhancing cell motility. Based on the ability of phenotypically young hCPCs to respond efficiently to ephrin A1, we developed a novel methodology for the prospective isolation of live hCPCs with preserved migratory capacity and growth reserve.

CONCLUSIONS

Our data demonstrate that the ephrin A1/EphA2 pathway may serve as a target to facilitate trafficking of hCPCs in the senescent myocardium. Importantly, EphA2 receptor function can be implemented for the selection of hCPCs with high therapeutic potential, a clinically relevant strategy that does not require genetic manipulation of stem cells.

Abstract 258: Hypoxic and Normoxic Niches Regulate Cardiac Stem Cell Function

In bone marrow niches, hypoxia favors stem cell quiescence and normoxia is required for stem cell proliferation and commitment. The objectives of this work were to determine whether a) differences in O 2 content regulate the function of cardiac stem cells (CSCs); and b) defects in tissue oxygenation with aging affects niche homeostasis. At 3 and 30 months of age, hypoxic and normoxic CSCs were found in the myocardium, but the senescent mouse heart was characterized by a 1.5-fold increase in hypoxic CSCs. At both ages, hypoxic CSCs were quiescent and lineage negative while cycling and early committed cells were restricted to the normoxic pool. Importantly, telomeres were longer in hypoxic than normoxic CSCs and this difference was more apparent in old mice. Telomere length did not change with age in hypoxic CSCs but decreased 40% in normoxic CSCs. As a consequence, at 3 and 30 months, the fraction of normoxic CSCs expressing the senescence-associated marker p16 INK4a was, respectively, 6-fold and 2.7-fold higher than that of hypoxic CSCs. Collectively, these findings indicate that the old heart contains a larger fraction of CSCs, which are forced in a quiescent state and do not participate in myocyte turnover. To define whether hypoxic CSCs can be activated, senescent mice were kept in an atmosphere of 70% O 2 to increase O 2 content in the hypoxic niches. Hyperoxia decreased significantly the fraction of hypoxic CSCs at 1 day and this response persisted at one week, possibly favoring myocyte formation. These in vivo results suggest that O 2 levels in CSCs may be regulated by the capillary network and the degree of tissue oxygenation. The distance between CSCs and the closest capillary was significantly higher for hypoxic than for normoxic CSCs. The numerical density of capillaries per mm 2 of myocardium computed within a radius of 30 μm from hypoxic CSCs decreased markedly with age. Thus, diffusion distance for O 2 to CSCs appears to constitute a major determinant in the maintenance of the hypoxic state of CSCs. Collectively, our data demonstrate that a balance between hypoxic and normoxic niches is present in the young heart but is disrupted later in life when capillary rarefaction expands the pool of hypoxic quiescent CSCs, which are no longer involved in myocyte replacement.

Abstract 125: Genetic Deletion Of Telomerase Promotes Premature Cardiac Aging

Telomeropathies are a group of human diseases characterized by mutations in the telomerase gene, accelerated telomere attrition, and premature organ aging. Manifestations of telomere disease include bone marrow failure, liver cirrhosis, and lung fibrosis. It remains, however, to be documented whether loss of telomerase activity is coupled with alterations in cardiac structure and function. To address this issue, the heart of mice carrying a deletion of the RNA component of telomerase (Terc -/- mice) was studied at 3-13 months of age. This allowed us to define whether defects in telomerase function in cardiac stem cells (CSCs) and their progeny promote ventricular dysfunction independently from chronological age, which is typically associated with significant telomere erosion. For this purpose, the characteristics of the aging cardiomyopathy were defined first in 30-month-old wild-type mice (WT). Deteriorations in systolic and diastolic indices of myocardial contractility were detected in senescent mice by echo-Doppler, MRI, and invasive hemodynamics. Importantly, 6-month-old Terc -/- mice showed severe ventricular dysfunction comparable to that seen in 30 month-old WT. Telomere length in Terc -/- mouse CSCs was ~50% shorter than in age-matched WT cells but was comparable to that found in 30 month-old WT cells. The number of CSCs was 60% lower in Terc -/- than age-matched WT mice, and the fraction of BrdU-positive CSCs decreased 1.4-fold, from 25% to 14%. The absence of Terc led to a 50% reduction in myocyte turnover, which was coupled with myocyte hypertrophy and myocyte loss. BrdU labeling was reduced 60% in Terc -/- myocytes. Old CSCs formed a senescent progeny composed of cardiomyocytes, which carried markedly shortened telomeres and showed a severe depression in cell shortening and re-lengthening. Moreover, the renewal of endothelial cells was 75% lower in Terc -/- mice mimicking the rarefaction in capillary typically seen in the old myocardium. Our findings document that loss of telomerase activity is a critical determinant of cardiac aging with reduced cardiomyogenesis and vasculogenesis. These maladaptive responses may be operative in patients carrying mutations of telomerase.

Use of electron microscopy to classify canine perivascular wall tumors

The histologic classification of canine perivascular wall tumors (PWTs) is controversial. Many PWTs are still classified as hemangiopericytomas (HEPs), and the distinction from peripheral nerve sheath tumors (PNSTs) is still under debate. A recent histologic classification of canine soft tissue sarcomas included most histologic types of PWT but omitted those that were termed undifferentiated. Twelve cases of undifferentiated canine PWTs were evaluated by transmission electron microscopy. The ultrastructural findings supported a perivascular wall origin for all cases with 4 categories of differentiation: myopericytic (n = 4), myofibroblastic (n = 1), fibroblastic (n = 2), and undifferentiated (n = 5). A PNST was considered unlikely in each case based on immunohistochemical expression of desmin and/or the lack of typical ultrastructural features, such as basal lamina. Electron microscopy was pivotal for the subclassification of canine PWTs, and the results support the hypothesis that canine PWTs represent a continuum paralleling the phenotypic plasticity of vascular mural cells. The hypothesis that a subgroup of PWTs could arise from a pluripotent mesenchymal perivascular wall cell was also considered and may explain the diverse differentiation of canine PWTs.

Abstract 52: Impaired Ephrin A1/EphA2 Signaling Results in Defective Migration and Homing of Senescent Human Cardiac Stem Cells

Aging is the major independent risk factor for chronic heart failure. Despite the presence of cardiac stem cells (CSCs), the old human heart undergoes progressive deterioration in ventricular performance, coupled with scattered foci of fibrosis and accumulation of poorly contracting myocytes. We raised the possibility that defects in the translocation of senescent human CSCs (hCSCs) to the sites of damage constitute a key determinant in the manifestation of the aging myopathy. We report that ephrin A1-EphA2 receptor signaling is a critical modulator of hCSC motility. Ephrin A1, a membrane-anchored protein, is expressed on the myocyte sarcolemma and acts as a ligand for the EphA2 receptor on neighboring hCSCs, facilitating their migration. Pre-treatment of young hCSCs with ephrin A1 resulted in enhanced movement of the transplanted cells to the necrotic tissue, with formation of new myocardium and improvement in cardiac function. Whether senescent hCSCs promote a comparable regenerative response remained to be established. Surprisingly, the expression of EphA2 did not differ in young and old hCSCs. With respect to young cells, senescent hCSCs showed a 2-fold increase in intracellular ROS levels. Oxidative stress led to post-translational modifications and functional alterations of the EphA2 receptor. Specifically, the ability of ephrin A1 to induce phosphorylation of the EphA2 receptor was markedly attenuated in senescent hCSCs, resulting in inadequate activation of Src family proteins. As a consequence, the phosphorylation and activity of caveolin-1, a substrate of Src kinases, was reduced. These molecular alterations led to impaired endocytosis of the ligand-receptor complex, a cellular process essential for ephrin A1-EphA2 signaling. Lack of endocytosis precluded rearrangement of the actin cytoskeleton and cell migration. Importantly, ephrin A1-stimulated senescent hCSCs delivered to infarcted rats accumulated in proximity of the site of injection and did not translocate to the ischemic area. Thus, oxidative stress interferes with EphA2 signaling in aging hCSCs, negatively affecting their migration. Restoration of the EphA2 function in old hCSCs may enhance their mobilization and improve cell targeting to the injured area.