An Evolving Understanding of the Genetic Causes of Abdominal Aortic Aneurysm Disease

Aneurysms of the abdominal aorta (AAA) are relatively common - affecting as many as 8% of men and 1% of women over the age of 65. AAAs are characterized by a 50% increase in the diameter of the aneurysmal aorta compared with the normal vessel. Degeneration of structural components of the aortic wall is believed to be central in the pathogenesis of AAAs. The exact mechanism of degeneration is not well characterized, although degradation of elastin and collagen has been clearly shown. At least six genetic variants have been associated with AAA in genome-wide association studies: CDKN2BAS1, DAB2IP, LDLR, LRP1, SORT1, and IL6R. These variants reach genome-wide significance; however, they have not been replicated in multiple cohorts, nor have they been clearly shown to be disease causative. AAA is a challenging disease for investigation because it is most often asymptomatic and generally has a late disease onset, making it difficult to diagnose. Determination of the genetic mechanism behind aneurysm formation, progression, and rupture crosses disciplines requiring input from multiple fields of study, larger patient cohorts, and the evolving modalities of genetic testing.

Abstract 652: Coronary Capillaries in Ischemic Congestive Heart Failure in Rats Exhibit Significant Morphological Disorder

In ischemic congestive heart failure (CHF), the heart is damaged and undergoes compensatory remodeling, a pathological process associated with harmful effects. The goal of this study is to explore the manifestation of CHF by examining the morphological changes occurring in the coronary microvasculature in CHF versus normal rat hearts. We tested the hypothesis that coronary capillaries in rats with CHF exhibit significantly more morphological disorder than those in control rats. Methods: CHF was induced by aortic banding, ischemia/reperfusion injury two months post-banding (left coronary artery ligation for 30 minutes) and aortic debanding one month post-injury. Resin polymer containing fluorescent dye was injected into coronary vasculature of excised hearts. Muscle tissue was digested using NaOH to reveal vascular casts that were sputter coated with gold for imaging under a Scanning Electron Microscope (SEM). A total of 93 SEM images from 14 rats (7 control, 7 CHF) were analyzed for structural alignment using an automated gradient detection algorithm and circular statistics implemented using MATLAB software; Mean Vector Length (MVL) was calculated for each image as a measure of capillary organization (0<MVL<0. MVL->1 perfect alignment, MVL->0 random disarray). Results: CHF capillaries exhibit significantly more structural disorder than control (MVL 0.35±0.02 for 61 CHF, 0.58±0.02 for 32 control. p<0.01). Conclusions: Coronary capillaries in CHF rats exhibit significant abnormal morphological disarray that may impair blood flow hemodynamics and material and oxygen exchange in myocytes. Such disordered capillary remodeling could have detrimental consequences for the progression and prognosis of heart failure.

Phospholamban as a crucial determinant of the inotropic response of human pluripotent stem cell-derived ventricular cardiomyocytes and engineered 3-dimensional tissue constructs

BACKGROUND

Human (h) embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) serve as a potential unlimited ex vivo source of cardiomyocytes (CMs). However, a well-accepted roadblock has been their immature phenotype. hESC/iPSC-derived ventricular (v) CMs and their engineered cardiac microtissues (hvCMTs) similarly displayed positive chronotropic but null inotropic responses to β-adrenergic stimulation. Given that phospholamban (PLB) is robustly present in adult but poorly expressed in hESC/iPSC-vCMs and its defined biological role in β-adrenergic signaling, we investigated the functional consequences of PLB expression in hESC/iPSC-vCMs and hvCMTs.

METHODS AND RESULTS

First, we confirmed that PLB protein was differentially expressed in hESC (HES2, H9)- and iPSC-derived and adult vCMs. We then transduced hES2-vCMs with the recombinant adenoviruses (Ad) Ad-PLB or Ad-S16E-PLB to overexpress wild-type PLB or the pseudophosphorylated point-mutated variant, respectively. As anticipated from the inhibitory effect of unphosphorylated PLB on sarco/endoplasmic reticulum Ca2+-ATPase, Ad-PLB transduction significantly attenuated electrically evoked Ca2+ transient amplitude and prolonged the 50% decay time. Importantly, Ad-PLB-transduced hES2-vCMs uniquely responded to isoproterenol. Ad-S16E-PLB-transduced hES2-vCMs displayed an intermediate phenotype. The same trends were observed with H9- and iPSC-vCMs. Directionally, similar results were also seen with Ad-PLB-transduced and Ad-S16E-transduced hvCMTs. However, Ad-PLB altered neither the global transcriptome nor ICa,L, implicating a PLB-specific effect.

CONCLUSIONS

Engineered upregulation of PLB expression in hESC/iPSC-vCMs restores a positive inotropic response to β-adrenergic stimulation. These results not only provide a better mechanistic understanding of the immaturity of hESC/iPSC-vCMs but will also lead to improved disease models and transplantable prototypes with adult-like physiological responses.

Stem cell factor gene transfer improves cardiac function after myocardial infarction in swine

BACKGROUND

Stem cell factor (SCF), a ligand of the c-kit receptor, is a critical cytokine, which contributes to cell migration, proliferation, and survival. It has been shown that SCF expression increases after myocardial infarction (MI) and may be involved in cardiac repair. The aim of this study was to determine whether gene transfer of membrane-bound human SCF improves cardiac function in a large animal model of MI.

METHODS AND RESULTS

A transmural MI was created by implanting an embolic coil in the left anterior descending artery in Yorkshire pigs. One week after the MI, the pigs received direct intramyocardial injections of either a recombinant adenovirus encoding for SCF (Ad.SCF, n=9) or β-gal (Ad.β-gal, n=6) into the infarct border area. At 3 months post-MI, ejection fraction increased by 12% relative to baseline after Ad.SCF therapy, whereas it decreased by 4.2% (P=0.004) in pigs treated with Ad.β-gal. Preload-recruitable stroke work was significantly higher in pigs after SCF treatment (Ad.SCF, 55.5±11.6 mm Hg versus Ad.β-gal, 31.6±12.6 mm Hg, P=0.005), indicating enhanced cardiac function. Histological analyses confirmed the recruitment of c-kit(+) cells as well as a reduced degree of apoptosis 1 week after Ad.SCF injection. In addition, increased capillary density compared with pigs treated with Ad.β-gal was found at 3 months and suggests an angiogenic role of SCF.

CONCLUSIONS

Local overexpression of SCF post-MI induces the recruitment of c-kit(+) cells at the infarct border area acutely. In the chronic stages, SCF gene transfer was associated with improved cardiac function in a preclinical model of ischemic cardiomyopathy.

Physical developmental cues for the maturation of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are the most promising source of cardiomyocytes (CMs) for experimental and clinical applications, but their use is largely limited by a structurally and functionally immature phenotype that most closely resembles embryonic or fetal heart cells. The application of physical stimuli to influence hPSC-CMs through mechanical and bioelectrical transduction offers a powerful strategy for promoting more developmentally mature CMs. Here we summarize the major events associated with in vivo heart maturation and structural development. We then review the developmental state of in vitro derived hPSC-CMs, while focusing on physical (electrical and mechanical) stimuli and contributory (metabolic and hypertrophic) factors that are actively involved in structural and functional adaptations of hPSC-CMs. Finally, we highlight areas for possible future investigation that should provide a better understanding of how physical stimuli may promote in vitro development and lead to mechanistic insights. Advances in the use of physical stimuli to promote developmental maturation will be required to overcome current limitations and significantly advance research of hPSC-CMs for cardiac disease modeling, in vitro drug screening, cardiotoxicity analysis and therapeutic applications.

Abstract 230: Regional Variation in Intrinsic Mechanics of Arterial Vascular Smooth Muscle Cells in Spontaneously Hypertensive Rats

Aims: An increased aortic stiffness is a fundamental manifestation of hypertension (HT). Our previous study showed that intrinsic mechanical properties of aortic vascular smooth muscle cells (VSMC) are an important contributor to the increased large artery stiffness in HT. However, whether VSMC mechanics of smaller arteries is also altered in HT remains unknown. The goal of this study is to test our hypothesis that the VSMC elastic and adhesive properties vary along the arterial tree reflecting the regional heterogeneities of physiological loading and geometric properties of the artery wall.

Methods and Results: Primary VSMCs were isolated from the thoracic aorta (TA) and renal artery (RA) of adult spontaneously hypertensive rats (SHR) (16 weeks old, male) and age-matched Wistar-Kyoto normotensive (WKY) rats. Atomic force microscopy (AFM) was used to measure mechanical properties of individual VSMC at 37°C. Local apparent elastic modulus (Eap) was determined using Hertz contact analysis for a cone to model the indentation force curve, and maximum adhesion force (Fad) was obtained from the retraction force curve; results were shown as mean (±SD) (n=10 cells per condition) and compared using two way ANOVA. Eap of VSMCs from the TA was significantly higher in SHR (7.0± 1.3 kPa) vs. WKY (5.3 ± 1.5 kPa; p < 0.001) and Fad was significantly larger in SHR (39.9 7.2 pN) vs. WKY (30.6 10.9 pN; p < 0.01). No difference was found between SHR and WKY in VSMCs from renal artery in terms of Eap (4.5 0.8 kPa vs. 4.8 0.9 kPa; p = 0.59) and Fad (23.1 5.2 pN vs. 28.0 7.0 pN; p = 0.17). Although no difference was observed in cell shape represented by the cellular length:width ratio (p > 0.25), stiffness and adhesion of VSMC from TA were significantly higher vs. RA in SHR (p<0.0001) but not in WKY (P>0.35), indicating that the altered mechanics of VSMC in hypertension is more prominent in the large conduction vessel compared to the small artery.

Conclusion: Intrinsic stiffness and adhesion of isolated VSMC are elevated preferentially in the thoracic aorta of SHR rats; the regional variations may associate mechanistically with increased aortic tissue stiffness in hypertension.

Synthesis and in vitro evaluation of a multifunctional and surface-switchable nanoemulsion platform

We present a multifunctional nanoparticle platform that has targeting moieties shielded by a matrix metalloproteinase-2 (MMP2) cleavable PEG coating. Upon incubation with MMP2 this surface-switchable coating is removed and the targeting ligands become available for binding. The concept was evaluated in vitro using biotin and αvβ3-integrin-specific RGD-peptide functionalized nanoparticles.

Abnormal muscle mechanosignaling triggers cardiomyopathy in mice with Marfan syndrome

Patients with Marfan syndrome (MFS), a multisystem disorder caused by mutations in the gene encoding the extracellular matrix (ECM) protein fibrillin 1, are unusually vulnerable to stress-induced cardiac dysfunction. The prevailing view is that MFS-associated cardiac dysfunction is the result of aortic and/or valvular disease. Here, we determined that dilated cardiomyopathy (DCM) in fibrillin 1-deficient mice is a primary manifestation resulting from ECM-induced abnormal mechanosignaling by cardiomyocytes. MFS mice displayed spontaneous emergence of an enlarged and dysfunctional heart, altered physical properties of myocardial tissue, and biochemical evidence of chronic mechanical stress, including increased angiotensin II type I receptor (AT1R) signaling and abated focal adhesion kinase (FAK) activity. Partial fibrillin 1 gene inactivation in cardiomyocytes was sufficient to precipitate DCM in otherwise phenotypically normal mice. Consistent with abnormal mechanosignaling, normal cardiac size and function were restored in MFS mice treated with an AT1R antagonist and in MFS mice lacking AT1R or β-arrestin 2, but not in MFS mice treated with an angiotensin-converting enzyme inhibitor or lacking angiotensinogen. Conversely, DCM associated with abnormal AT1R and FAK signaling was the sole abnormality in mice that were haploinsufficient for both fibrillin 1 and β1 integrin. Collectively, these findings implicate fibrillin 1 in the physiological adaptation of cardiac muscle to elevated workload.

Advancing functional engineered cardiac tissues toward a preclinical model of human myocardium

Cardiac experimental biology and translational research would benefit from an in vitro surrogate for human heart muscle. This study investigated structural and functional properties and interventional responses of human engineered cardiac tissues (hECTs) compared to human myocardium. Human embryonic stem cell-derived cardiomyocytes (hESC-CMs, >90% troponin-positive) were mixed with collagen and cultured on force-sensing elastomer devices. hECTs resembled trabecular muscle and beat spontaneously (1.18 ± 0.48 Hz). Microstructural features and mRNA expression of cardiac-specific genes (α-MHC, SERCA2a, and ACTC1) were comparable to human myocardium. Optical mapping revealed cardiac refractoriness with loss of 1:1 capture above 3 Hz, and cycle length dependence of the action potential duration, recapitulating key features of cardiac electrophysiology. hECTs reconstituted the Frank-Starling mechanism, generating an average maximum twitch stress of 660 μN/mm(2) at Lmax, approaching values in newborn human myocardium. Dose-response curves followed exponential pharmacodynamics models for calcium chloride (EC50 1.8 mM) and verapamil (IC50 0.61 μM); isoproterenol elicited a positive chronotropic but negligible inotropic response, suggesting sarcoplasmic reticulum immaturity. hECTs were amenable to gene transfer, demonstrated by successful transduction with Ad.GFP. Such 3-D hECTs recapitulate an early developmental stage of human myocardium and promise to offer an alternative preclinical model for cardiology research.

Effect of engineered anisotropy on the susceptibility of human pluripotent stem cell-derived ventricular cardiomyocytes to arrhythmias

Human (h) pluripotent stem cells (PSC) such as embryonic stem cells (ESC) can be directed into cardiomyocytes (CMs), representing a potential unlimited cell source for disease modeling, cardiotoxicity screening and myocardial repair. Although the electrophysiology of single hESC-CMs is now better defined, their multi-cellular arrhythmogenicity has not been thoroughly assessed due to the lack of a suitable experimental platform. Indeed, the generation of ventricular (V) fibrillation requires single-cell triggers as well as sustained multi-cellular reentrant events. Although native VCMs are aligned in a highly organized fashion such that electrical conduction is anisotropic for coordinated contractions, hESC-derived CM (hESC-CM) clusters are heterogenous and randomly organized, and therefore not representative of native conditions. Here, we reported that engineered alignment of hESC-VCMs on biomimetic grooves uniquely led to physiologically relevant responses. Aligned but not isotropic control preparations showed distinct longitudinal (L) and transverse (T) conduction velocities (CV), resembling the native human V anisotropic ratio (AR = LCV/TCV = 1.8-2.0). Importantly, the total incidence of spontaneous and inducible arrhythmias significantly reduced from 57% in controls to 17-23% of aligned preparations, thereby providing a physiological baseline for assessing arrhythmogenicity. As such, promotion of pro-arrhythmic effect (e.g., spatial dispersion by β adrenergic stimulation) could be better predicted. Mechanistically, such anisotropy-induced electrical stability was not due to maturation of the cellular properties of hESC-VCMs but their physical arrangement. In conclusion, not only do functional anisotropic hESC-VCMs engineered by multi-scale topography represent a more accurate model for efficacious drug discovery and development as well as arrhythmogenicity screening (of pharmacological and genetic factors), but our approach may also lead to future transplantable prototypes with improved efficacy and safety against arrhythmias.

Abstract 130: Secretion of Angiogenic and Anti-apoptotic Factors Accompanies Mesenchymal Stem Cell-mediated Enhancement of Contractile Function in Engineered Cardiac Tissues

Previous studies using three-dimensional engineered cardiac tissues (ECT) demonstrated beneficial effects of mesenchymal stem cells (MSC) on contractile function, recapitulating findings in animal studies and in clinical trials. But the mechanisms by which MSC effect this functional enhancement remain unclear. This study tested the hypothesis that MSC-mediated enhancement of ECT function involves paracrine signaling, independent of direct cell-cell interaction with cardiomyocytes (CM).

To create ECT, CM were isolated from neonatal rat ventricles, mixed with 2.0 mg/ml bovine type I collagen and 0.9 mg/ml Matrigel, and pipetted into a custom elastomeric mold with integrated force sensing end-posts. Two types of ECT were created: one containing 1.5 million CM (“CM-only”) and the other containing 1.5 million CM supplemented with 150,000 MSC (“MSC-CM hybrid”). Contractile function of CM-only ECT was then assessed during 2-Hz pacing either in the presence or absence of hybrid tissues sharing the same media. Media surrounding the tissues was also collected and analyzed via protein microarray (RayBiotech) combined with Ingenuity Pathway Analysis software.

CM-only ECT cultured for 5 days showed aligned and compacted structure with a cross-sectional area of 0.39 ± 0.03 mm 2 and a twitch force of 4.7 ± 0.7 N (mean ± SD; n = 6). In CM-only tissues co-cultured for 5 days in shared media alongside hybrid tissues, cross-sectional area was unchanged (0.42 ± 0.02 mm 2 , p = 0.17, n=3), but twitch force increased two-fold to 9.8 ± 6.5 N (p = 0.08). Threshold voltage for electrical pacing of CM-only ECT also decreased from 0.54 ± 0.12 V/mm to 0.39 ± 0.07 V/mm when co-cultured with hybrid ECT (p = 0.097). Protein microarray analysis of the shared co-culture conditioned media showed enrichment (relative to CM-only conditioned media) of the angiogenic factors VEGF (1240x) and IL-1 (8.6x) as well as the cardiac anti-apoptotic/pro-survival factors TNF (194x), bFGF (55x), and bNGF (14.9x).

In conclusion, these findings support paracrine signaling, independent of direct cell-cell contact, as one mechanism of MSC-mediated enhancement of CM function in rat ECT. Identification and isolation of defined cardiotropic factors may lead to novel molecular therapies for cardiac repair.

Abstract 256: mRNA-based Nanoparticles Are Highly Effective Agents For Cardiac Gene Therapy

Gene therapy holds promise for repair and regeneration of damaged myocardium after infarction. Viral vectors used in most studies, while highly effective, carry concerns of safety and immunogenicity. Nanoparticle (NP)-enabled transfection using polymeric and lipidoid reagents mitigates some of the concerns related to the use of viral vectors. However, these agents have been less effective in transfecting cardiac myocytes, which are primarily post-mitotic and only weakly facilitate DNA entry to the nucleus. Because translation occurs in the cytosol, transfection with RNA obviates the need for nuclear entry. Recent work has shown that synthetic alterations to messenger RNA (mRNA) can prolong its half-life in the cytosol and diminish the host’s immune response. We hypothesized that transfection of cardiac myocytes with lipidoid NPs formed using modified mRNA would lead to high levels of protein expression. Neonatal rat (NRCM), adult rat (ARCM) and human embryonic stem cell-derived (hES-CM) cardiac myocytes were transfected with modified GFP-mRNA NPs using a lipidoid vehicle (Stemfect TM , Stemgent, Cambridge, MA) or Lipofectamine2000 (LF, Invitrogen) and GFP expression was assessed after 24 hours. Average transfection efficiency in NRCM was significantly higher using Stemfect versus LF as measured by flow cytometry (48.5% vs. 6.6% at 20ng mRNA; 47.4% vs. 11.8% at 40ng mRNA, 48.1% vs. 18.6% at 80ng mRNA; 48.1% vs. 28% at 160ng mRNA; n=3, p<0.01 for each pair). In hES-CM transfection was also more robust with Stemfect NPs versus LF (91.6% vs. 62.2%, p<0.05 at 40ng mRNA; 96.1 vs. 87.8%, p<0.01 at 160ng mRNA; n=3). GFP expression was noted by fluorescence microscopy to be higher in ARCMs transfected with Stemfect NPs versus LF. In conclusion, we have shown that difficult-to-transfect cardiac myocytes are readily transfected with mRNA-based NPs in vitro and with significantly higher efficiency when using Stemfect rather than Lipofectamine. Gene therapy with mRNA represents a novel approach to cardiac repair and may be preferable to DNA because of the transient window of protein expression and lower side effect profile.

Abstract 129: Human Mesenchymal Stem Cells Augment Contractile Function of Human Engineered Cardiac Tissues

Mesenchymal stem cells (MSC) have demonstrated efficacy for improving cardiomyocyte (CM) function in vitro, in vivo and in clinical trials, but the mechanism of this enhancement remains elusive. The objective of this study was to test the hypothesis that human engineered cardiac tissues (hECT) offer a viable model system to investigate the effects of human MSC on CM contractile function.

Human CM (hCM) were produced from embryonic stem cells (hESC, H7 line) using a small-molecule based differentiation approach. Blebbistatin and BMP4 were added to hESC suspended in StemPro34 differentiation media for 24 h, followed by BMP4 and Activin A to day 4.5, followed by addition of IWR-1 Wnt inhibitor for at least 4 days. To create hECT, approximately 1 million hCM were mixed with 2.0 mg/ml bovine type I collagen and 0.9 mg/ml Matrigel, and pipetted into a mold fabricated from polydimethylsiloxane with integrated cantilever end-posts. To model hMSC cell therapy, two types of hECT were created: hCM-only control hECT, and hMSC-CM hybrid hECT containing hCM mixed with 5-10% of human bone marrow-derived MSC. Over several days in culture, the hECT self-assembled and started beating; end-post deflection was tracked in real time to compute twitch force using beam theory.

Human CMs were produced with high efficiency (>70% cTnT+) with a predominantly ventricular phenotype (MLC2v+). Resulting hECTs exhibited spontaneous beating (1.3±0.4 Hz), cellular alignment, registered sarcomeres, and expression of cardiac specific genes cTnT, α-MHC, β-MHC and SERCA2a. After 11±2 days in culture, developed stress (force/area) was over 10-fold higher in hMSC-CM hybrid tissues (0.27±0.048 mN/mm 2 ) compared to hCM-only controls (0.02±0.006 mN/mm 2 ; p=0.04, n=5 per group). This reflected significantly greater twitch force (0.11±0.004 mN vs 0.033±0.016 mN, p=0.016) and smaller cross-sectional area (0.19±0.12 mm 2 vs 0.49±0.10 mm 2 ; p=0.003) in hMSC-CM hybrid vs hCM-only hECT.

In conclusion, human ECT offer a novel system to study MSC-CM interactions. The findings suggest hMSC supplementation improves contractility compared to CM-only hECT. Investigating the mechanisms of hMSC-mediated enhancement of hECT function may yield insights into MSC-based therapies for cardiac regeneration.

Engineered human pluripotent stem cell-derived cardiac cells and tissues for electrophysiological studies

Human cardiomyocytes (CMs) do not proliferate in culture and are difficult to obtain for practical reasons. As such, our understanding of the mechanisms that underlie the physiological and pathophysiological development of the human heart is mostly extrapolated from studies of the mouse and other animal models or heterologus expression of defective gene product(s) in non-human cells. Although these studies provided numerous important insights, much of the exact behavior in human cells remains unexplored given that significant species differences exist. With the derivation of human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSCs) from patients with underlying heart disease, a source of human CMs for disease modeling, cardiotoxicity screening and drug discovery is now available. In this review, we focus our discussion on the use of hESC/ iPSC-derived cardiac cells and tissues for studying various heart rhythm disorders and the associated pro-arrhythmogenic properties in relation to advancements in electrophysiology and tissue engineering.

Myocyte-depleted engineered cardiac tissues support therapeutic potential of mesenchymal stem cells

The therapeutic potential of mesenchymal stem cells (MSCs) for restoring cardiac function after cardiomyocyte loss remains controversial. Engineered cardiac tissues (ECTs) offer a simplified three-dimensional in vitro model system to evaluate stem cell therapies. We hypothesized that contractile properties of dysfunctional ECTs would be enhanced by MSC treatment. ECTs were created from neonatal rat cardiomyocytes with and without bone marrow-derived adult rat MSCs in a type-I collagen and Matrigel scaffold using custom elastomer molds with integrated cantilever force sensors. Three experimental groups included the following: (1) baseline condition ECT consisting only of myocytes, (2) 50% myocyte-depleted ECT, modeling a dysfunctional state, and (3) 50% myocyte-depleted ECT plus 10% MSC, modeling dysfunctional myocardium with intervention. Developed stress (DS) and pacing threshold voltage (VT) were measured using 2-Hz field stimulation at 37°C on culture days 5, 10, 15, and 20. By day 5, DS of myocyte-depleted ECTs was significantly lower than baseline, and VT was elevated. In MSC-supplemented ECTs, DS and VT were significantly better than myocyte-depleted values, approaching baseline ECTs. Findings were similar through culture day 15, but lost significance at day 20. Trends in DS were partly explained by changes in the cell number and alignment with time. Thus, supplementing myocyte-depleted ECTs with MSCs transiently improved contractile function and compensated for a 50% loss of cardiomyocytes, mimicking recent animal studies and clinical trials and supporting the potential of MSCs for myocardial therapy.

Cardiac tissue engineering using human stem cell-derived cardiomyocytes for disease modeling and drug discovery

Cardiovascular disease (CVD) is the most prevalent health problem in the world, and the high mortality rate associated with irreversibly injured heart muscle motivates an urgent need for the development of novel therapies to treat damaged myocardium. Recently, human engineered cardiac tissues (hECT) have been created using cardiomyocytes derived from human embryonic stem cells and human induced pluripotent stem cells. Although a healthy adult phenotype remains elusive, such hECT display structural and functional properties that recapitulate key aspects of natural human myocardium, including dose related responses to compounds with known chronotropic, inotropic and arrhythmogenic effects. Thus, hECT offer the advantage over traditional in vitro culture models of providing a biomimetic 3D environment for the study of myocardial physiopathology, and may be used to generate preclinical models for the development and screening of therapies for CVD.

Enhanced cell sorting and manipulation with combined optical tweezer and microfluidic chip technologies

Sorting (or isolation) and manipulation of rare cells with high recovery rate and purity are of critical importance to a wide range of physiological applications. In the current paper, we report on a generic single cell manipulation tool that integrates optical tweezers and microfluidic chip technologies for handling small cell population sorting with high accuracy. The laminar flow nature of microfluidics enables the targeted cells to be focused on a desired area for cell isolation. To recognize the target cells, we develop an image processing methodology with a recognition capability of multiple features, e.g., cell size and fluorescence label. The target cells can be moved precisely by optical tweezers to the desired destination in a noninvasive manner. The unique advantages of this sorter are its high recovery rate and purity in small cell population sorting. The design is based on dynamic fluid and dynamic light pattern, in which single as well as multiple laser traps are employed for cell transportation, and a recognition capability of multiple cell features. Experiments of sorting yeast cells and human embryonic stem cells are performed to demonstrate the effectiveness of the proposed cell sorting approach.

Biomedical model fitting and error analysis

This Teaching Resource introduces students to curve fitting and error analysis; it is the second of two lectures on developing mathematical models of biomedical systems. The first focused on identifying, extracting, and converting required constants--such as kinetic rate constants--from experimental literature. To understand how such constants are determined from experimental data, this lecture introduces the principles and practice of fitting a mathematical model to a series of measurements. We emphasize using nonlinear models for fitting nonlinear data, avoiding problems associated with linearization schemes that can distort and misrepresent the data. To help ensure proper interpretation of model parameters estimated by inverse modeling, we describe a rigorous six-step process: (i) selecting an appropriate mathematical model; (ii) defining a "figure-of-merit" function that quantifies the error between the model and data; (iii) adjusting model parameters to get a "best fit" to the data; (iv) examining the "goodness of fit" to the data; (v) determining whether a much better fit is possible; and (vi) evaluating the accuracy of the best-fit parameter values. Implementation of the computational methods is based on MATLAB, with example programs provided that can be modified for particular applications. The problem set allows students to use these programs to develop practical experience with the inverse-modeling process in the context of determining the rates of cell proliferation and death for B lymphocytes using data from BrdU-labeling experiments.

Aortic implantation of mesenchymal stem cells after aneurysm injury in a porcine model

BACKGROUND

Cell-based therapies are being evaluated in the setting of degenerative pathophysiologic conditions. The search for the ideal method of delivery and improvement in cell engraftment continue to pose a challenge. This study explores the feasibility of introducing mesenchymal stem cells (MSC) following aortic injury in a porcine model.

METHODS

Bone marrow-derived MSC were obtained from eight pigs, characterized for the MSC markers CD13 and CD 29, labeled with green fluorescent protein (GFP), and collected for autologous injection in a porcine model of abdominal aortic aneurysm (AAA). The pigs were euthanized (1-7 d) after the procedure to assess the histologic characteristics and presence of MSC in the aortic tissue. Negative controls included noninjured aorta. Tracking of the MSC was conducted by the identification of the GFP-labeled cells using immunofluorescence.

RESULTS

AAA sections stained with hematoxylin and eosin showed disorganization of the aortic tissue; collagen-muscle-elastin stain demonstrated fragmentation of elastin fibers. The presence of the implanted MSC in the aortic wall was evidenced by fluorescent microscopy showing GFP labeled cells. Engraftment of MSC up to 7 d after introduction was observed.

CONCLUSION

Autologous implantation of bone marrow-derived MSC following aortic injury in a porcine model may be successfully accomplished. The long-term impact and therapeutic value of such cell-based therapy will require further investigation.

Atomic force microscopy in mechanobiology: measuring microelastic heterogeneity of living cells

Recent findings clearly demonstrate that cells feel mechanical forces, and respond by altering their -phenotype and modulating their mechanical environment. Atomic force microscope (AFM) indentation can be used to mechanically stimulate cells and quantitatively characterize their elastic properties, providing critical information for understanding their mechanobiological behavior. This review focuses on the experimental and computational aspects of AFM indentation in relation to cell biomechanics and pathophysiology. Key aspects of the indentation protocol (including preparation of substrates, selection of indentation parameters, methods for contact point detection, and further post-processing of data) are covered. Historical perspectives on AFM as a mechanical testing tool as well as studies of cell mechanics and physiology are also highlighted.

Dynamic AFM elastography reveals phase dependent mechanical heterogeneity of beating cardiac myocytes

We developed a novel atomic force microscope (AFM) indentation technique for mapping spatiotemporal stiffness of spontaneously beating neonatal rat cardiac myocytes. Cells were indented at a rate close but unequal to their contractile frequency. Resultant apparent elastic modulus cycled at a predictable envelope frequency between a systolic value of 26.2 +/- 5.1 kPa and a diastolic value of 7.8 +/- 4.1 kPa. In cells probed along their axis, spatial heterogeneity of systolic stiffness correlated with the sarcomeric structure of underlying myofibrils. Treatment with blebbistatin eliminated contractile activity and resulted in a uniform modulus of 6.5 +/- 4.8 kPa. The technique provides a unique means of probing the mechanical effects of disease processes and pharmacological treatments on beating cardiomyocytes at the subcellular level, providing new insights relating myocardial structure and function.