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.