Allogeneic Mesenchymal Stem Cells Restore Endothelial Function in Heart Failure by Stimulating Endothelial Progenitor Cells

BACKGROUND

Endothelial dysfunction, characterized by diminished endothelial progenitor cell (EPC) function and flow-mediated vasodilation (FMD), is a clinically significant feature of heart failure (HF). Mesenchymal stem cells (MSCs), which have pro-angiogenic properties, have the potential to restore endothelial function. Accordingly, we tested the hypothesis that MSCs increase EPC function and restore flow-mediated vasodilation (FMD).

METHODS

Idiopathic dilated and ischemic cardiomyopathy patients were randomly assigned to receive autologous (n = 7) or allogeneic (n = 15) MSCs. We assessed EPC-colony forming units (EPC-CFUs), FMD, and circulating levels of vascular endothelial growth factor (VEGF) in patients before and three months after MSC transendocardial injection (n = 22) and in healthy controls (n = 10).

FINDINGS

EPC-colony forming units (CFUs) were markedly reduced in HF compared to healthy controls (4 ± 3 vs. 25 ± 16 CFUs, P < 0.0001). Similarly, FMD% was impaired in HF (5.6 ± 3.2% vs. 9.0 ± 3.3%, P = 0.01). Allogeneic, but not autologous, MSCs improved endothelial function three months after treatment (Δ10 ± 5 vs. Δ1 ± 3 CFUs, P = 0.0067; Δ3.7 ± 3% vs. Δ-0.46 ± 3% FMD, P = 0.005). Patients who received allogeneic MSCs had a reduction in serum VEGF levels three months after treatment, while patients who received autologous MSCs had an increase (P = 0.0012), and these changes correlated with the change in EPC-CFUs (P < 0.0001). Lastly, human umbilical vein endothelial cells (HUVECs) with impaired vasculogenesis due to pharmacologic nitric oxide synthase inhibition, were rescued by allogeneic MSC conditioned medium (P = 0.006).

INTERPRETATION

These findings reveal a novel mechanism whereby allogeneic, but not autologous, MSC administration results in the proliferation of functional EPCs and improvement in vascular reactivity, which in turn restores endothelial function towards normal in patients with HF. These findings have significant clinical and biological implications for the use of MSCs in HF and other disorders associated with endothelial dysfunction.

Zika virus impairs the development of blood vessels in a mouse model of congenital infection

Zika virus (ZIKV) is associated with brain development abnormalities such as primary microcephaly, a severe reduction in brain growth. Here we demonstrated in vivo the impact of congenital ZIKV infection in blood vessel development, a crucial step in organogenesis. ZIKV was injected intravenously in the pregnant type 2 interferon (IFN)-deficient mouse at embryonic day (E) 12.5. The embryos were collected at E15.5 and postnatal day (P)2. Immunohistochemistry for cortical progenitors and neuronal markers at E15.5 showed the reduction of both populations as a result of ZIKV infection. Using confocal 3D imaging, we found that ZIKV infected brain sections displayed a reduction in the vasculature density and vessel branching compared to mocks at E15.5; altogether, cortical vessels presented a comparatively immature pattern in the infected tissue. These impaired vascular patterns were also apparent in the placenta and retina. Moreover, proteomic analysis has shown that angiogenesis proteins are deregulated in the infected brains compared to controls. At P2, the cortical size and brain weight were reduced in comparison to mock-infected animals. In sum, our results indicate that ZIKV impairs angiogenesis in addition to neurogenesis during development. The vasculature defects represent a limitation for general brain growth but also could regulate neurogenesis directly.

S-Nitrosoglutathione Reductase Deficiency Enhances the Proliferative Expansion of Adult Heart Progenitors and Myocytes Post Myocardial Infarction

Background

Mammalian heart regenerative activity is lost before adulthood but increases after cardiac injury. Cardiac repair mechanisms, which involve both endogenous cardiac stem cells (CSCs) and cardiomyocyte cell-cycle reentry, are inadequate to achieve full recovery after myocardial infarction (MI). Mice deficient in S-nitrosoglutathione reductase (GSNOR^−⁄−), an enzyme regulating S-nitrosothiol turnover, have preserved cardiac function after MI. Here, we tested the hypothesis that GSNOR activity modulates cardiac cell proliferation in the post-MI adult heart.

Methods and Results

GSNOR^−⁄− and C57Bl6/J (wild-type [WT]) mice were subjected to sham operation (n=3 GSNOR^−⁄−; n=3 WT) or MI (n=41 GSNOR^−⁄−; n=65 WT). Compared with WT,GSNOR^−⁄− mice exhibited improved survival, cardiac performance, and architecture after MI, as demonstrated by higher ejection fraction (P<0.05), lower endocardial volumes (P<0.001), and diminished scar size (P<0.05). In addition, cardiomyocytes from post-MI GSNOR^−⁄− hearts exhibited faster calcium decay and sarcomeric relaxation times (P<0.001). Immunophenotypic analysis illustrated that post-MI GSNOR^−⁄− hearts demonstrated enhanced neovascularization (P<0.001), c-kit⁺ CSC abundance (P=0.013), and a ≈3-fold increase in proliferation of adult cardiomyocytes and c-kit⁺/CD45⁻ CSCs (P<0.0001 and P=0.023, respectively) as measured by using 5-bromodeoxyuridine.

Conclusions

Loss of GSNOR confers enhanced post-MI cardiac regenerative activity, characterized by enhanced turnover of cardiomyocytes and CSCs. Endogenous denitrosylases exert an inhibitory effect over cardiac repair mechanisms and therefore represents a potential novel therapeutic target.

Case Report: Administration of Amniotic Fluid-Derived Nanoparticles in Three Severely Ill COVID-19 Patients

Rationale/Objectives: A human coronavirus (HCoV-19) has caused the novel coronavirus disease (COVID-19) outbreak worldwide. There is an urgent need to develop new interventions to suppress the excessive immune response, protect alveolar function, and repair lung and systemic organ damage. Zofin (previously known as Organicell Flow) is a novel therapeutic that is derived from the soluble and nanoparticle fraction (extracellular vesicles and exosomes) of human amniotic fluid. Here within, we present the clinical outcomes after Zofin treatment in three critically ill patients suffering from severe, multi-organ complications induced by COVID-19 infection. All patients were diagnosed with COVID-19, developed respiratory failure, and were hospitalized for more than 40 days.

Methods: Zofin was administered to patients concurrently with ongoing medical care who were monitored for 28-days post-therapy. SOFA score assessment, chest X-rays, and inflammatory biomarker testing was performed.

Main Results: There were no adverse events associated with the therapy. The patients showed improvements in ICU clinical status and experienced respiratory improvements. Acute delirium experienced by patients completely resolved and inflammatory biomarkers improved.

Conclusions: Primary outcomes demonstrate the therapy was safe, accessible, and feasible. This is the first demonstration of human amniotic fluid-derived nanoparticles as a safe and potentially efficacious therapeutic treatment for respiratory failure induced by COVID-19 infection.

Tumor Suppressors RB1 and CDKN2a Cooperatively Regulate Cell-Cycle Progression and Differentiation During Cardiomyocyte Development and Repair

RATIONALE

Although rare cardiomyogenesis is reported in the adult mammalian heart, whether this results from differentiation or proliferation of cardiomyogenic cells remains controversial. The tumor suppressor genes RB1 (retinoblastoma) and CDKN2a (cyclin-dependent kinase inhibitor 2a) are critical cell-cycle regulators, but their roles in human cardiomyogenesis remains unclear.

OBJECTIVE

We hypothesized that developmental activation of RB1 and CDKN2a cooperatively cause permanent cell-cycle withdrawal of human cardiac precursors (CPCs) driving terminal differentiation into mature cardiomyocytes, and that dual inactivation of these tumor suppressor genes promotes myocyte cell-cycle reentry.

METHODS AND RESULTS

Directed differentiation of human pluripotent stem cells (hPSCs) into cardiomyocytes revealed that RB1 and CDKN2a are upregulated at the onset of cardiac precursor specification, simultaneously with GATA4 (GATA-binding protein 4) homeobox genes PBX1 (pre-B-cell leukemia transcription factor 1) and MEIS1 (myeloid ecotropic viral integration site 1 homolog), and remain so until terminal cardiomyocyte differentiation. In both GATA4+ hPSC cardiac precursors and postmitotic hPSC-cardiomyocytes, RB1 is hyperphosphorylated and inactivated. Transient, stage-specific, depletion of RB1 during hPSC differentiation enhances cardiomyogenesis at the cardiac precursors stage, but not in terminally differentiated hPSC-cardiomyocytes, by transiently upregulating GATA4 expression through a cell-cycle regulatory pathway involving CDKN2a. Importantly, cytokinesis in postmitotic hPSC-cardiomyocytes can be induced with transient, dual RB1, and CDKN2a silencing. The relevance of this pathway in vivo was suggested by findings in a porcine model of cardiac cell therapy post-MI, whereby dual RB1 and CDKN2a inactivation in adult GATA4+ cells correlates with the degree of scar size reduction and endogenous cardiomyocyte mitosis, particularly in response to combined transendocardial injection of adult human hMSCs (bone marrow-derived mesenchymal stromal cells) and cKit+ cardiac cells.

CONCLUSIONS

Together these findings reveal an important and coordinated role for RB1 and CDKN2a in regulating cell-cycle progression and differentiation during human cardiomyogenesis. Moreover, transient, dual inactivation of RB1 and CDKN2a in endogenous adult GATA4+ cells and cardiomyocytes mediates, at least in part, the beneficial effects of cell-based therapy in a post-MI large mammalian model, a finding with potential clinical implications.

The V beta complementarity determining region 1 of a major histocompatibility complex (MHC) class I-restricted T cell receptor is involved in the recognition of peptide/MHC I and superantigen/MHC II complex

We investigated the role of the complementarity determining region 1 (CDR1) of T cell receptor (TCR) beta chain both in antigen/major histocompatibility complex I (MHC I) and in superantigen (SAg)/MHC II complex recognition. Residues 26 to 31 of the V beta 10 domain of a TCR derived from an H-2Kd-restricted cytotoxic clone were individually changed to alanine, using site-directed mutagenesis, and the mutated TCR beta chains were transfected along with the wild-type TCR alpha chain into a TCR alpha-beta-T hydridoma. These mutations affected antigen/H-2Kd complex recognition, although to a different extent, as estimated by interleukin 2 production. Certain mutations also affected differently the recognition of two Staphylococcal toxins, exfoliative toxin and Staphylococcal enterotoxin C2, presented by HLA-DR1. Whereas mutation of residues D30 or T31 affect the recognition of both toxins, residues T26, L27, and H29 are critical for the recognition of only one of the SAgs. These observations demonstrate the participation of the CDR1 region in the recognition of peptide/MHC class I as well as SAg/MHC II complexes.

Anti-fibrotic effects of different sources of MSC in bleomycin-induced lung fibrosis in C57BL6 male mice

BACKGROUND AND OBJECTIVE

IPF is a fatal and debilitating lung disorder increasing in incidence worldwide. To date, two approved treatments only slow disease progression, have multiple side effects and do not provide a cure. MSC have promising therapeutic potential as a cell-based therapy for many lung disorders based on the anti-fibrotic properties of the MSC.

METHODS

Critical questions remain surrounding the optimal source, timing and efficacy of cell-based therapies. The present study examines the most effective sources of MSC. Human MSC were derived from adipose, WJ, chorionic membrane (CSC) and chorionic villi (CVC). MSC were injected into the ageing mouse model of BLM-induced lung fibrosis.

RESULTS

All sources decreased Aschroft and hydroxyproline levels when injected into BLM-treated mice at day 10 with the exception of CSC cells that did not change hydroxyproline levels. There were also decreases in mRNA expression of αv -integrin and TNFα in all sources except CSC. Only ASC- and WJ-derived cells reduced AKT and MMP-2 activation, while Cav-1 was increased by ASC treatment as previously reported. BLM-induced miR dysregulation of miR-29 and miR-199 was restored only by ASC treatment.

CONCLUSION

Our data suggest that sources of MSC may differ in the pathway(s) involved in repair.

Mesenchymal Stem Cell-derived Extracellular Vesicles Prevent Experimental Bronchopulmonary Dysplasia Complicated By Pulmonary Hypertension

Mesenchymal stem cell (MSC) extracellular vesicles (EVs) have beneficial effects in preclinical bronchopulmonary dysplasia and pulmonary hypertension (BPD-PH) models. The optimal source, dosing, route, and duration of effects are however unknown. The objectives of this study were to (a) compare the efficacy of GMP-grade EVs obtained from Wharton’s Jelly MSCs (WJ-MSCs) and bone marrow (BM-MSCs), (b) determine the optimal dosing and route of administration, (c) evaluate its long-term effects, and (d) determine how MSC EVs alter the lung transcriptome. Newborn rats exposed to normoxia or hyperoxia (85% O₂) from postnatal day (P)1-P14 were given (a) intra-tracheal (IT) BM or WJ-MSC EVs or placebo, (b) varying doses of IT WJ-MSC EVs, or (c) IT or intravenous (IV) WJ-MSC EVs on P3. Rats were evaluated at P14 or 3 months. Early administration of IT BM-MSC or WJ-MSC EVs had similar beneficial effects on lung structure and PH in hyperoxia-exposed rats. WJ-MSC EVs however had superior effects on cardiac remodeling. Low, medium, and high dose WJ-MSC EVs had similar cardiopulmonary regenerative effects. IT and IV WJ-MSC EVs similarly improved vascular density and reduced PH in hyperoxic rats. Gene-set enrichment analysis of transcripts differentially expressed in WJ-MSC EV-treated rats showed that induced transcripts were associated with angiogenesis. Long-term studies demonstrated that a single early MSC EV dose has pulmonary vascular protective effects 3 months after administration. Together, our findings have significant translational implications as it provides critical insight into the optimal source, dosing, route, mechanisms of action, and duration of effects of MSC-EVs for BPD-PH.

Amniotic fluid-derived extracellular vesicles: characterization and therapeutic efficacy in an experimental model of bronchopulmonary dysplasia

BACKGROUND AIMS

Extracellular vesicles (EVs) are being tested for their use as novel therapeutics. However, the optimal source of EVs is currently under investigation. Amniotic fluid (AF) is a natural source of EVs that can be easily obtained for use in regenerative medicine, yet AF-EV characterization has not been fully explored.

METHODS

Here the authors demonstrate AF as a rich source of EVs and identify the microRNA and proteomic cargo. Bioinformatics analysis of this cargo revealed multiple pathway targets, including immunomodulatory, anti-inflammatory and free radical scavenging networks. The authors further demonstrated the therapeutic potential of this EV product as a novel preventative agent for bronchopulmonary dysplasia (BPD).

RESULTS

Intra-tracheal administration of AF-EVs preserved alveolar development, attenuated vascular remodeling and pulmonary hypertension, decreased lung pro-inflammatory cytokine expression and reduced macrophage infiltration in an experimental BPD model.

CONCLUSIONS

The authors' results suggest that AF is a viable biological fluid for EV harvest and that AF-EVs have strong therapeutic potential for pulmonary diseases, such as BPD, warranting further development to transition this novel EV product into the clinic.

Physiological and hypoxic oxygen concentration differentially regulates human c-Kit+ cardiac stem cell proliferation and migration

Cardiac stem cells (CSCs) are being evaluated for their efficacy in the treatment of heart failure. However, numerous factors impair the exogenously delivered cells' regenerative capabilities. Hypoxia is one stress that contributes to inadequate tissue repair. Here, we tested the hypothesis that hypoxia impairs cell proliferation, survival, and migration of human CSCs relative to physiological and room air oxygen concentrations. Human endomyocardial biopsy-derived CSCs were isolated, selected for c-Kit expression, and expanded in vitro at room air (21% O2). To assess the effect on proliferation, survival, and migration, CSCs were transferred to physiological (5%) or hypoxic (0.5%) O2 concentrations. Physiological O2 levels increased proliferation (P < 0.05) but did not affect survival of CSCs. Although similar growth rates were observed in room air and hypoxia, a significant reduction of β-galactosidase activity (-4,203 fluorescent units, P < 0.05), p16 protein expression (0.58-fold, P < 0.001), and mitochondrial content (0.18-fold, P < 0.001) in hypoxia suggests that transition from high (21%) to low (0.5%) O2 reduces senescence and promotes quiescence. Furthermore, physiological O2 levels increased migration (P < 0.05) compared with room air and hypoxia, and treatment with mesenchymal stem cell-conditioned media rescued CSC migration under hypoxia to levels comparable to physiological O2 migration (2-fold, P < 0.05 relative to CSC media control). Our finding that physiological O2 concentration is optimal for in vitro parameters of CSC biology suggests that standard room air may diminish cell regenerative potential. This study provides novel insights into the modulatory effects of O2 concentration on CSC biology and has important implications for refining stem cell therapies.

Treatment of a COVID-19 long hauler with an amniotic fluid-derived extracellular vesicle biologic

Post-COVID-19 infection symptoms such as mental fog, tachycardia, and extreme fatigue are just a few of the symptoms wreaking havoc on patients’ lives. Patients with long-term symptoms following COVID-19 are being called long haulers. To date, long haulers are receiving little to no guidance from physicians on their lingering COVID-19 symptoms with limited treatment options available. Zofin is an acellular biologic that contains the extracellular vesicle (EV) fraction of human amniotic fluid and is under investigation for use as a COVID-19 therapeutic. We obtained FDA and IRB approval to investigate the therapeutic use of Zofin in a single long hauler patient case experiencing prolonged shortness of breath and respiratory impairment. Administration of the EV product was shown to be safe. Furthermore, demonstrated respiratory improvements through chest X ray images and oxygen saturation measurement. The single patient IND studies were completed without any reported adverse events or safety concerns. Furthermore, these completed studies demonstrate the feasibility and a therapeutic potential of amniotic fluid-derived EVs for COVID-19 long hauler intervention.

Costimulatory action of glycoinositolphospholipids from Trypanosoma cruzi: increased interleukin 2 secretion and induction of nuclear translocation of the nuclear factor of activated T cells 1

The effects of the glycoinositolphospholipids (GIPLs) fromTrypanosoma cruzi on T lymphocyte activation were investigated in a mouse T cell hybridoma (DO-11.10). Purified GIPLs from T. cruzi strains Y and G markedly increased IL-2 mRNA transcripts and IL-2 secretion induced by mitogenic anti-CD3 and anti-Thy1 mAbs. This costimulatory function was also revealed by the induction of IL-2 secretion after the simultaneous addition of the T. cruzi GIPLs and either the calcium ionophore A23187 or phorbol ester. The capacity of the GIPL molecule to induce an increase in cytoplasmic calcium levels was also demonstrated. After exposure of T cell hybridoma to GIPL, the nuclear transcription factor NFAT1 became partially dephosphorylated, and its nuclear localization was demonstrated both in the T cell hybridoma and in Balb/c CD3(+) cells. These results demonstrate that T. cruzi GIPL molecules are capable of signaling to T cells and therefore could be valuable tools for the study of T cell activation, besides playing a potential role in subverting the T lymphocyte immune response during T. cruzi infection.

Proof-of-concept trial of an amniotic fluid-derived extracellular vesicle biologic for treating high risk patients with mild-to-moderate acute COVID-19 infection

A pandemic brought on by COVID-19 has created a scalable health crisis. The search to help alleviate COVID-19-related complications through therapeutics has become a necessity. Zofin is an investigational, acellular biologic derived from full-term perinatal amniotic fluid that contains extracellular vesicles. Extracellular nanoparticles as such have been studied for their immunomodulatory benefits via cellular therapeutics and, if applied to COVID-19-related inflammation, could benefit patient outcome. Subjects (n = 8) experiencing mild-to-moderate COVID-19 symptoms were treated with the experimental intervention. Complete blood count, complete metabolic panel, inflammatory biomarkers, and absolute lymphocyte counts were recorded prior to and on days 4, 8, 14, 21, and 30 as markers of disease progression. Additionally, chest x-rays were taken of the patients prior to and on days 8 and 30. Patients experienced no serious adverse events. All COVID-19-associated symptoms resolved or became stable with no indication of disease worsening as found by patient and chest x-ray reports. Inflammatory biomarkers (CRP, IL-6, TNF- α ) and absolute lymphocyte counts improved throughout the study period. Findings from a proof-of-concept, expanded access trial for COVID-19 patients prove the acellular biologic is safe and potentially effective to prevent disease progression in a high-risk COVID-19 population with mild-to-moderate symptoms.

Characterization of extracellular vesicle miRNA identified in peripheral blood of chronic pancreatitis patients

Plasma-derived extracellular vesicles (EV) can serve as markers of cell damage/disease but can also have therapeutic utility depending on the nature of their cargo, such as miRNA. Currently, there are challenges and lack of innovations regarding early diagnosis and therapeutic options within different aspects of management of patients suffering from chronic pancreatitis (CP). Use of EV as biomarkers for pancreatic health and/or as adjuvant therapy would make a difference in management of these patients. The aim of this study was to characterize the miRNA cargo of EV purified from the plasma of CP patients and compared to those of healthy participants. EVs were isolated from plasma of 15 CP patients and 10 healthy controls. Nanoparticle tracking analysis was used to determine frequency and size, while NanoString technology was used to characterize the miRNA cargo. Relevant clinical parameters were correlated with EV miRNA cargo. ~ 30 miRNA species were identified to have significantly (p < 0.05) different expression in EV from individuals with CP compared to healthy individuals; ~ 40 miRNA were differentially expressed in EV from pre-diabetic versus non-diabetic CP patients. miR-579-3p, while exhibiting significantly lower (~ 16-fold) expression in CP compared to healthy and lower (~ 24-fold) in CP narcotic users compared to the non-users, is actually enriched (~ 32-fold) within EV in pre-diabetic CP patients compared to non-diabetic CP patients. A unique pattern was identified in female CP patients. These data support the prospect of using a plasma-derived EV cargo to assess pancreatic health and its therapeutic potential in CP patients.

OUP accepted manuscript

Bronchopulmonary dysplasia (BPD) is a life-threatening condition in preterm infants with few effective therapies. Mesenchymal stem or stromal cells (MSCs) are a promising therapeutic strategy for BPD. The ideal MSC source for BPD prevention is however unknown. The objective of this study was to compare the regenerative effects of MSC obtained from bone marrow (BM) and umbilical cord tissue (UCT) in an experimental BPD model. In vitro, UCT-MSC demonstrated greater proliferation and expression of anti-inflammatory cytokines as compared to BM-MSC. Lung epithelial cells incubated with UCT-MSC conditioned media (CM) had better-wound healing following scratch injury. UCT-MSC CM and BM-MSC CM had similar pro-angiogenic effects on hyperoxia-exposed pulmonary microvascular endothelial cells. In vivo, newborn rats exposed to normoxia or hyperoxia (85% O₂) from postnatal day (P) 1 to 21 were given intra-tracheal (IT) BM or UCT-MSC (1 × 10⁶ cells/50 μL), or placebo (PL) on P3. Hyperoxia PL-treated rats had marked alveolar simplification, reduced lung vascular density, pulmonary vascular remodeling, and lung inflammation. In contrast, administration of both BM-MSC and UCT-MSC significantly improved alveolar structure, lung angiogenesis, pulmonary vascular remodeling, and lung inflammation. UCT-MSC hyperoxia-exposed rats however had greater improvement in some morphometric measures of alveolarization and less lung macrophage infiltration as compared to the BM-MSC-treated group. Together, these findings suggest that BM-MSC and UCT-MSC have significant lung regenerative effects in experimental BPD but UCT-MSC suppresses lung macrophage infiltration and promotes lung epithelial cell healing to a greater degree.

Human amniotic fluid derived extracellular vesicles attenuate T cell immune response

Introduction

Extracellular vesicles isolated from human amniotic fluid (AF-EVs) have previously been found to modulate inflammation and macrophage infiltration in a mouse model. However, the effects of acellular amniotic fluid (acAF) or AF-EVs on the T-Cell immune response have not been explored.

Methods

In this study, we investigated the effects of acAF and AF-EVs on the T cell immune response in an in vitro cell culture model. Peripheral Blood Mononuclear Cells (PBMCs) were stimulated with Phytohemagglutinin (PHA) to induce the immune response and were subsequently treated with either serum-free media (vehicle), acAF, or concentrated AF-EVs.

Results

Both acAF and AF-EV treatment suppressed PHA-induced T cell proliferation and PHA-induced T cell activation; however, treatment with concentrated AF-EVs had a greater effect. Additionally, both acAF and AF-EVs reduced PBMC pro-inflammatory cytokine release. AF-EVs were found to be taken up by both CD4+ and CD8+ effector T cell subsets.

Conclusion

Overall, this data demonstrates that AF-EVs have a robust immunomodulatory effect on T cells and suggests AF-EVs could be used as an immunotherapeutic tool.

Role of the CDR1 region of the TCR beta chain in the binding to purified MHC-peptide complex

Single alanine substitutions were introduced into the CDR1 region of the beta chain of a Kd-restricted TCR. Mutants and wild-type TCR were attached to the zeta chain of the CD3 complex and expressed at the surface of a rat basophil cell line. Transfectants were tested for the binding of purified soluble Kd-peptide complexes. With this experimental system, accessory molecules are unlikely to play a major role and the contribution of each residue to the interaction can be addressed. Results show that all positions in the CDR1 region are involved in the binding to the Kd-peptide complex but at varying degrees. These effects are discussed in relation to a molecular model of the TCR. Comparison of these results with previous data obtained in a T cell hybridoma system suggests the existence of a threshold in the TCR affinity necessary for mature T cell activation.

Genetic control of the B cell response to LPS: opposing effects in peritoneal versus splenic B cell populations

Lipopolysaccharide (LPS) from gram-negative bacteria activates B cells, enabling them to proliferate and differentiate into plasma cells. This response is critically dependent on the expression of TLR4; but other genes, such as RP105 and MHC class II, have also been shown to contribute to B cell LPS response. Here, we have evaluated the role of genetic control of the B cell response to LPS at the single cell level. We compared the response to LPS of peritoneal cavity (PEC) and splenic B cells on the BALB/c genetic background (LPS-low responder) to those on the C57BL/6J background (LPS-high responder) and their F1 progeny (CB6F1). Both PEC and splenic B cells from B6 exhibited 100% clonal growth in the presence of LPS; whereas, BALB/c PEC and splenic B cells achieved only 50% and 23% clonal growth, respectively. Adding CpG to the LPS stimulus pushed PEC B cell clonal growth in the low responder strain BALB/c up to 90%, showing that the nonresponse to LPS is a specific effect. Surprisingly, PEC B cells on the F1 background behaved as high responders, while splenic B cells behaved as low responders to LPS. The data presented here reveals a previous unsuspected behavior in the genetic control of the B cell response to LPS with an opposing impact in splenic versus peritoneal cavity B cells. These results suggest the existence of an, as yet, unidentified genetic factor exclusively expressed by coelomic B cells that contributes to the control of the LPS signaling pathway in the B lymphocyte.

A rapid and quantitative method for the evaluation of V gene usage, specificities and the clonal size of B cell repertoires

The quantitative simultaneous description of both variable region gene usage and antigen specificity of immunoglobulin repertoires is a major goal in immunology. Current quantitative assays are labor intensive and depend on extensive gene expression cloning prior to screening for antigen specificity. Here we describe an alternative method based on high efficiency single B cell cultures coupled with RT-PCR that can be used for rapid characterization of immunoglobulin gene segment usage, clonal size and antigen specificity. This simplified approach should facilitate the study of antibody repertoires expressed by defined B cell subpopulations, the analysis of immune responses to self and nonself-antigens, the development and screening of synthetic antibodies and the accelerated study and screening of neutralizing antibodies to pathogenic threats.

Hypoxic Stress Decreases c-Myc Protein Stability in Cardiac Progenitor Cells Inducing Quiescence and Compromising Their Proliferative and Vasculogenic Potential

Cardiac progenitor cells (CPCs) have been shown to promote cardiac regeneration and improve heart function. However, evidence suggests that their regenerative capacity may be limited in conditions of severe hypoxia. Elucidating the mechanisms involved in CPC protection against hypoxic stress is essential to maximize their cardioprotective and therapeutic potential. We investigated the effects of hypoxic stress on CPCs and found significant reduction in proliferation and impairment of vasculogenesis, which were associated with induction of quiescence, as indicated by accumulation of cells in the G0-phase of the cell cycle and growth recovery when cells were returned to normoxia. Induction of quiescence was associated with a decrease in the expression of c-Myc through mechanisms involving protein degradation and upregulation of p21. Inhibition of c-Myc mimicked the effects of severe hypoxia on CPC proliferation, also triggering quiescence. Surprisingly, these effects did not involve changes in p21 expression, indicating that other hypoxia-activated factors may induce p21 in CPCs. Our results suggest that hypoxic stress compromises CPC function by inducing quiescence in part through downregulation of c-Myc. In addition, we found that c-Myc is required to preserve CPC growth, suggesting that modulation of pathways downstream of it may re-activate CPC regenerative potential under ischemic conditions.

Interactions between CD3 and Thy1 T cell activation pathways: blockade of CD3-mediated T lymphocyte activation induced by immobilized anti-Thy1 antibodies

Resting murine T cell activation induced by either CD3 complexes or Thy1 molecules was investigated in vitro, using surface-bound anti-CD3 mAb as the stimulus. One mitogenic anti-Thy 1 mAb (G7) lost mitogenicity when presented to T cells immobilized on a plastic surface, even in the presence of phorbol ester. Moreover, T cell activation induced by immobilized anti-CD3 was potently blocked by coimmobilized anti-Thy 1 mAb. Nonmitogenic anti-Thy 1 mAb also blocked CD3-induced activation when coimmobilized with anti-CD3. Control experiments showed that anti-Thy 1 specifically blocked T cell activation, even in the presence of measurable and functional concentrations of plastic-bound anti-CD3. Coimmobilized anti-Thy 1 potently blocked IL2 secretion stimulated by anti-CD3. Addition of exogenous rIL2 completely prevented anti-Thy 1-mediated blockade. On the other hand, while completely blocking T cell proliferation, immobilized anti-Thy 1 only partially blocked secretion of IL3-like activity by the T cells. One IgM anti-Thy 1 mAb (2A3) induced secretion of IL3-like activity by T cells when immobilized in the absence of bound anti-CD3. These results indicate that extensive aggregation of Thy 1 molecules delivers a potent negative signal which antagonizes CD3-mediated T cell activation and growth.

S-Nitrosoglutathione Reductase Deficiency Causes Aberrant Placental S-Nitrosylation and Preeclampsia

Background Preeclampsia, a leading cause of maternal and fetal mortality and morbidity, is characterized by an increase in S-nitrosylated proteins and reactive oxygen species, suggesting a pathophysiologic role for dysregulation in nitrosylation and nitrosative stress. Methods and Results Here, we show that mice lacking S-nitrosoglutathione reductase (GSNOR-⁄-), a denitrosylase regulating protein S-nitrosylation, exhibit a preeclampsia phenotype, including hypertension, proteinuria, renal pathology, cardiac concentric hypertrophy, decreased placental vascularization, and fetal growth retardation. Reactive oxygen species, NO, and peroxynitrite levels are elevated. Importantly, mass spectrometry reveals elevated placental S-nitrosylated amino acid residues in GSNOR-⁄- mice. Ascorbate reverses the phenotype except for fetal weight, reduces the difference in the S-nitrosoproteome, and identifies a unique set of S-nitrosylated proteins in GSNOR-⁄- mice. Importantly, human preeclamptic placentas exhibit decreased GSNOR activity and increased nitrosative stress. Conclusions Therefore, deficiency of GSNOR creates dysregulation of placental S-nitrosylation and preeclampsia in mice, which can be rescued by ascorbate. Coupled with similar findings in human placentas, these findings offer valuable insights and therapeutic implications for preeclampsia.

HIV Promotes Atherosclerosis via Circulating Extracellular Vesicle MicroRNAs

People living with HIV (PLHIV) are at a higher risk of having cerebrocardiovascular diseases (CVD) compared to HIV negative (HIVneg) individuals. The mechanisms underlying this elevated risk remains elusive. We hypothesize that HIV infection results in modified microRNA (miR) content in plasma extracellular vesicles (EVs), which modulates the functionality of vascular repairing cells, i.e., endothelial colony-forming cells (ECFCs) in humans or lineage negative bone marrow cells (lin- BMCs) in mice, and vascular wall cells. PLHIV (N = 74) have increased atherosclerosis and fewer ECFCs than HIVneg individuals (N = 23). Plasma from PLHIV was fractionated into EVs (HIVposEVs) and plasma depleted of EVs (HIV PLdepEVs). HIVposEVs, but not HIV PLdepEVs or HIVnegEVs (EVs from HIVneg individuals), increased atherosclerosis in apoE-/- mice, which was accompanied by elevated senescence and impaired functionality of arterial cells and lin- BMCs. Small RNA-seq identified EV-miRs overrepresented in HIVposEVs, including let-7b-5p. MSC (mesenchymal stromal cell)-derived tailored EVs (TEVs) loaded with the antagomir for let-7b-5p (miRZip-let-7b) counteracted, while TEVs loaded with let-7b-5p recapitulated the effects of HIVposEVs in vivo. Lin- BMCs overexpressing Hmga2 (a let-7b-5p target gene) lacking the 3'UTR and as such is resistant to miR-mediated regulation showed protection against HIVposEVs-induced changes in lin- BMCs in vitro. Our data provide a mechanism to explain, at least in part, the increased CVD risk seen in PLHIV.

Abstract 259: Role of Connexin 43 in Human Bone Marrow Derived Mesenchymal Stem Cell Cardiac Integration and Cardiac Stem cell Niche Formation

Introduction: Bone marrow-derived mesenchymal stem cells (MSCs) and cardiac progenitor cells (CPCs) have been used successfully as a cell-based approach for cardiac regeneration after myocardial infarction. While MSCs and CPCs are effective, in part due to differentiation, paracrine effect, and integration into the heart, the mechanism underlying these effects remains controversial.

Objective: We hypothesized that functional connexin 43 (Cx43) gap junctions are crucial for MSC and CPCs interaction and integration into cardiac tissue and cardiac stem cell niche formation.

Methods and Results: Human MSCs were co-cultured with neonatal rat ventricular cardiomyocytes (NRVMs). The ability of MSCs to form gap junctions was modulated using lentiviral constructs to either knockdown (Cx43KD) or overexpress (Cx43OE) Cx43. Co-culture of Cx43OE or control MSCs with NRVMs led to the formation of beating, three-dimensional tubes whereas Cx43KD MSCs failed to form tubes (n=5, p<0.05). Furthermore, we replicated the cardiac stem cell niche by combining human CPCs and MSCs in an in vitro model (the same lentiviral constructs were used). As a result, Cx43 expressing MSCs and CPCs formed organotypic three-dimensional structures similar to human MSCs and NRVMs, whereas the lack of Cx43 significantly affected the structure formation (n=6, p<0.05). Cx43KD significantly increased proliferation (n=5, p<0.05) and changed culture phenotype (n=4, p<0.05) of MSCs or CPCs cultured separately. The angiogenic tube length, assessed by a Matrigel assay in vitro, was significantly reduced in MSCs and HUVEC Cx43 KD groups compared to control (n=5, p<0.05). The change/onset of endothelial (KDR, PECAM-1, VE-cadherin), and cardiomyocyte (Nkx2.5, Gata4, Troponin I, Na+ channel, K+ channel, Ca2+ channel, Na+-Ca2+ exchanger) gene expression was investigated in co-culture of MSCs and CPCs. Only voltage ion channel gene expression was upregulated in control and Cx43OE groups by co-culture (n=5, p<0.05), but not affected in Cx43KD group.

Conclusion: These findings reveal that cell−cell contact mediated by Cx43 gap junctions enables MSCs to interact with CPCs, integrate and reconstitute cardiac stem cell niches.