Rapid and Efficient Production of Coronary Artery Ligation and Myocardial Infarction in Mice Using Surgical Clips

Injection of Matrix Metalloproteinase-9 Leads to Ventricular Remodeling

OBJECTIVE

Previous studies have found that some ventricular remodeling is accompanied by increased matrix metalloproteinase-9 (MMP-9) in vivo, and MMP-9 inhibitors can reduce ventricular remodeling. However, there is still no direct evidence that MMP-9 causes ventricular remodeling. In this study, MMP-9 was injected into rats to observe whether MMP-9 caused ventricular remodeling, thereby providing direct evidence of MMP-9-induced ventricular remodeling.

METHODS

Forty-eight eight-week-old male Wistar rats were randomly divided, by weight, into control, low-, medium-, and high-dose MMP-9 groups and were administered normal saline or recombinant rat MMP-9 0.7, 1.4, or 2.1 ng/g, respectively, via intraperitoneal injection, twice per week. On the 28th day, six rats were randomly selected from each group (Stage I). The remaining rats continued receiving injections until the 56th day (Stage II). Echocardiography was performed to observe cardiac structure and function, and the left ventricular mass index (LVWI) was calculated. Myocardial pathological changes and the collagen volume fraction (CVF) were observed by HE and VG staining in myocardial tissue. MMP-9 levels in serum were tested using ELISA. Myocardial MMP-9 levels were measured using Western blots, and the myocardial expression levels of MMP-9 mRNA were assessed using RT-PCR.

RESULTS

During Stage I, serum MMP-9 and myocardial MMP-9 mRNA levels are increased; hypertrophic cardiomyocytes, disorderly arrangement of fibers, and endochylema dissolution are observed in the medium- and high-dose groups. The left ventricular weight index (LVWI) and myocardial MMP-9 increased, and the collagen volume fraction (CVF) reduced in the high-dose group. In Stage II, the left ventricular end-diastolic volume (LVEDV) and diameter (LVIDd) are higher, and CVF decreased in the medium- and high-dose groups. Myocardial pathological lesions intensified. Serum MMP-9 in the model groups and myocardial MMP-9 in the medium- and high-dose groups are increased.

CONCLUSIONS

Injection of MMP-9 can lead to ventricular remodeling.

Novel PET/CT tracers for targeted imaging of membrane receptors to evaluate cardiomyocyte apoptosis and tissue repair process in a rat model of myocardial infarction

The purpose of this study was to employ novel tracers PET imaging approach to define the time course and intensity of myocardial repair after apoptosis and to correlate the imaging signal to immunohistochemical staining in myocardial infarction (MI). We designed novel α_Vβ₃-targeted and radio-functionalized tracers for detection of apoptosis in H9C2 cells and myocardial tissue. MI rats were imaged with [¹⁸F]FDG, [¹⁸F]ANP-Cin or [¹⁸F]ANP-RGD₂ using a small-animal PET/CT device. Rats were sacrificed, and tissue samples from viable and injured myocardial areas were sectioned for TUNEL assay and histology. The uncorrected radiochemical yield of [¹⁸F]ANP-Cin and [¹⁸F]ANP-RGD₂ were 41.3 ± 5.4% and 21.17 ± 4.7%, respectively. Two tracers meet many criteria for cardiac imaging, including high stability, high binding, no toxicity, fast renal clearance and excellent biodistribution in rat models. The uptake of [¹⁸F]ANP-Cin was significantly higher on the 1st and 3rd day than the 7th or 28th day after MI induction, a timeframe associated with increased cardiomyocyte apoptosis. Higher uptake of [¹⁸F]ANP-Cin was observed in MI rats than in N-acetylcysteine (NAC)-treated rats on the 3rd days. In contrast with [¹⁸F]ANP-Cin, no hot-spots was observed with [¹⁸F]ANP-RGD₂ on the 1st day and more hot-spots was observed from the 3rd day to the 7th day, then less on the 28th days in the high apoptotic site. There was no uptake of [¹⁸F]FDG in or around the apoptotic region. On the 7th day the uptake of [¹⁸F]ANP-RGD₂ was higher in NAC-treated rats than MI rats. [¹⁸F]ANP-Cin and [¹⁸F]ANP-RGD₂ are superior to [¹⁸F]FDG for PET/CT imaging for evaluation of cardiomyocyte apoptosis and tissue repair processes in the MI rats.

The Prominin-1-Derived Peptide Improves Cardiac Function Following Ischemia

Myocardial infarction (MI) remains the leading cause of death in the western world. Despite advancements in interventional revascularization technologies, many patients are not candidates for them due to comorbidities or lack of local resources. Non-invasive approaches to accelerate revascularization within ischemic tissues through angiogenesis by providing Vascular Endothelial Growth Factor (VEGF) in protein or gene form has been effective in animal models but not in humans likely due to its short half-life and systemic toxicity. Here, we tested the hypothesis that PR1P, a small VEGF binding peptide that we developed, which stabilizes and upregulates endogenous VEGF, could be used to improve outcome from MI in rodents. To test this hypothesis, we induced MI in mice and rats via left coronary artery ligation and then treated animals with every other day intraperitoneal PR1P or scrambled peptide for 14 days. Hemodynamic monitoring and echocardiography in mice and echocardiography in rats at 14 days showed PR1P significantly improved multiple functional markers of heart function, including stroke volume and cardiac output. Furthermore, molecular biology and histological analyses of tissue samples showed that systemic PR1P targeted, stabilized and upregulated endogenous VEGF within ischemic myocardium. We conclude that PR1P is a potential non-invasive candidate therapeutic for MI.

NIPAM-based Microgel Microenvironment Regulates the Therapeutic Function of Cardiac Stromal Cells

To tune the chemical, physical, and mechanical microenvironment for cardiac stromal cells to treat acute myocardial infarction (MI), we prepared a series of thermally responsive microgels with different surface charges (positive, negative, and neutral) and different degrees of hydrophilicity, as well as functional groups (carboxyl, hydroxyl, amino, and methyl). These microgels were used as injectable hydrogels to create an optimized microenvironment for cardiac stromal cells (CSCs). Our results indicated that a hydrophilic and negatively charged microenvironment created from poly( N-isopropylacrylamide- co-itaconic acid) was favorable for maintaining high viability of CSCs, promoting CSC proliferation and facilitating the formation of CSC spheroids. A large number of growth factors, such as vascular endothelial growth factor (VEGF), insulin-like growth factor I (IGF-1), and stromal-derived factor-1 (SDF-1) were released from the spheroids, promoting neonatal rat cardiomyocyte activation and survival. After injecting the poly( N-isopropylacrylamide- co-itaconic acid) microgel into mice, we examined their acute inflammation and T-cell immune reactions. The microgel itself did not elicit obvious immune response. We then injected the same microgel-encapsulated with CSCs into MI mice. The result revealed the treatment-promoted MI heart repair through angiogenesis and inhibition of apoptosis with an improved cell retention rate. This study will open a door for tailoring poly( N-isopropylacrylamide)-based microgel as a delivery vehicle for CSC therapy.

Ataxia telangiectasia mutated kinase deficiency impairs the autophagic response early during myocardial infarction

Ataxia telangiectasia mutated kinase (ATM) is activated in response to DNA damage. We have previously shown that ATM plays a critical role in myocyte apoptosis and cardiac remodeling after myocardial infarction (MI). Here, we tested the hypothesis that ATM deficiency results in autophagic impairment in the heart early during MI. MI was induced in wild-type (WT) and ATM heterozygous knockout (hKO) mice by ligation of the left anterior descending artery. Structural and biochemical parameters of the heart were measured 4 h after left anterior descending artery ligation. M-mode echocardiography revealed that MI worsens heart function, as evidenced by reduced percent ejection fraction and fractional shortening in both groups. However, MI-induced increase in left ventricular end-diastolic and end-systolic diameters and volumes were significantly lower in hKO hearts. ATM deficiency resulted in autophagic impairment during MI, as evidenced by decreased microtubule-associated protein light chain 3-II increased p62, decreased cathepsin D protein levels, and increased aggresome accumulation. ERK1/2 activation was only observed in WT-MI hearts. Activation of Akt and AMP-activated protein kinase (AMPK) was lower, whereas activation of glycogen synthase kinase (GSK)-3β and mammalian target of rapamycin (mTOR) was higher in hKO-MI hearts. Inhibition of ATM using KU-55933 resulted in autophagic impairment in cardiac fibroblasts, as evidenced by decreased light chain 3-II protein levels and formation of acidic vesicular organelles. This impairment was associated with decreased activation of Akt and AMPK but enhanced activation of GSK-3β and mTOR in KU-55933-treated fibroblasts. Thus, ATM deficiency results in autophagic impairment in the heart during MI and cardiac fibroblasts. This autophagic impairment may occur via the activation of GSK-3β and mTOR and inactivation of Akt and AMPK. NEW & NOTEWORTHY Ataxia telangiectasia mutated kinase (ATM) plays a critical role in myocyte apoptosis and cardiac remodeling after myocardial infarction (MI). Here, we provide evidence that ATM deficiency results in autophagic impairment during MI. Further investigation of the role of ATM in autophagy post-MI may provide novel therapeutic targets for patients with ataxia telangiectasia suffering from heart disease.

Sphingomyelin phosphodiesterase 1 (SMPD1) mediates the attenuation of myocardial infarction-induced cardiac fibrosis by astaxanthin

Uncontrolled cardiac fibrosis following myocardial infarction (MI) is a critical pathological change leading to heart failure. Current pharmacotherapies are limited by unsatisfactory efficacy and undesired systemic side effects. Astaxanthin (ASX) is a natural carotenoid with strong antioxidant and anti-inflammatory activities. The effects of ASX on MI-induced cardiac fibrosis and the underlying mechanisms remain largely unknown. In this study, after the establishment of MI model, mice were administrated with ASX (200 mg/kg⋅d) for 4 weeks. We found that ASX treatment attenuated cardiac fibrosis and improved heart function following MI, as evidenced by reduced collagen I/III ratio, hydroxyproline content and left ventricular end diastolic pressure (LVEDP). Lipidomic analysis revealed the overaccumulation of myocardial ceramides in mice with cardiac fibrosis, which was normalized by ASX treatment. Molecular docking analysis showed that ASX produced a tight fit in the pocket of sphingomyelin phosphodiesterase 1 (SMPD1), a key enzyme in the production of ceramides. Western blot analysis confirmed the significant inhibition of SMPD1 expression by ASX. Furthermore, MI-induced overexpression of transforming growth factor β1 (TGF-β1) and phosphorylated SMAD2/3 were attenuated by ASX administration. SMPD1 knockout (KO) abrogated the beneficial effect of ASX. Taken together, our results suggest that the cardioprotective effects of ASX are mediated by SMPD1 through the indirection inhibition of TGF- β1/SMAD signaling cascade.

Heart Repair Using Nanogel-Encapsulated Human Cardiac Stem Cells in Mice and Pigs with Myocardial Infarction

Stem cell transplantation is currently implemented clinically but is limited by low retention and engraftment of transplanted cells and the adverse effects of inflammation and immunoreaction when allogeneic or xenogeneic cells are used. Here, we demonstrate the safety and efficacy of encapsulating human cardiac stem cells (hCSCs) in thermosensitive poly(N-isopropylacrylamine-co-acrylic acid) or P(NIPAM-AA) nanogel in mouse and pig models of myocardial infarction (MI). Unlike xenogeneic hCSCs injected in saline, injection of nanogel-encapsulated hCSCs does not elicit systemic inflammation or local T cell infiltrations in immunocompetent mice. In mice and pigs with acute MI, injection of encapsulated hCSCs preserves cardiac function and reduces scar sizes, whereas injection of hCSCs in saline has an adverse effect on heart healing. In conclusion, thermosensitive nanogels can be used as a stem cell carrier: the porous and convoluted inner structure allows nutrient, oxygen, and secretion diffusion but can prevent the stem cells from being attacked by immune cells.

Integrin β-3 is required for the attachment, retention and therapeutic benefits of human cardiospheres in myocardial infarction

Cardiovascular diseases remain the leading causes of death worldwide. Stem cell therapy offers a promising option to regenerate injured myocardium. Among the various types of stem cells, cardiosphere cells represent a mixture of intrinsic heart stem cells and supporting cells. The safety and efficacy of cardiosphere cells have been demonstrated in recent clinical trials. Cell–matrix interaction plays an important role in mediating the engraftment of injected stem cells. Here, we studied the role of integrin β‐3 in cardiosphere‐mediated cell therapy in a mouse model of myocardial infarction. Our results indicated that inhibiting integrin β‐3 reduced attachment, retention and therapeutic benefits of human cardiospheres in mice with acute myocardial infarction. This suggests integrin β‐3 plays an important role in cardiosphere‐mediated heart regeneration.

A Regenerative Cardiac Patch Formed by Spray Painting of Biomaterials onto the Heart

Layering a regenerative polymer scaffold on the surface of the heart, termed as a cardiac patch, has been proven to be effective in preserving cardiac function after myocardial infarction (MI). However, the placement of such a patch on the heart usually needs open-chest surgery, which is traumatic, therefore prevents the translation of this strategy into the clinic. We sought to device a way to apply a cardiac patch by spray painting in situ polymerizable biomaterials onto the heart with a minimally invasive procedure. To prove the concept, we used platelet fibrin gel as the "paint" material in a mouse model of MI. The use of the spraying system allowed for placement of a uniform cardiac patch on the heart in a mini-invasive manner without the need for sutures or glue. The spray treatment promoted cardiac repair and attenuated cardiac dysfunction after MI.

Therapeutic microparticles functionalized with biomimetic cardiac stem cell membranes and secretome

Stem cell therapy represents a promising strategy in regenerative medicine. However, cells need to be carefully preserved and processed before usage. In addition, cell transplantation carries immunogenicity and/or tumourigenicity risks. Mounting lines of evidence indicate that stem cells exert their beneficial effects mainly through secretion (of regenerative factors) and membrane-based cell–cell interaction with the injured cells. Here, we fabricate a synthetic cell-mimicking microparticle (CMMP) that recapitulates stem cell functions in tissue repair. CMMPs carry similar secreted proteins and membranes as genuine cardiac stem cells do. In a mouse model of myocardial infarction, injection of CMMPs leads to the preservation of viable myocardium and augmentation of cardiac functions similar to cardiac stem cell therapy. CMMPs (derived from human cells) do not stimulate T-cell infiltration in immuno-competent mice. In conclusion, CMMPs act as ‘synthetic stem cells’ which mimic the paracrine and biointerfacing activities of natural stem cells in therapeutic cardiac regeneration.

Stem cells exert their beneficial effects through secretion of regenerative factors. Here, the authors take the membranes and secreted factors from cardiac stem cells and generate a synthetic cell-mimicking microparticle, which, on injection in a mouse model of myocardial infarction, improves cardiac function.

Animal models of cardiac cachexia

Cachexia is the loss of body weight associated with several chronic diseases including chronic heart failure (CHF). The cachectic condition is mainly due to loss of skeletal muscle mass and adipose tissue depletion. The majority of experimental in vivo studies on cachexia rely on animal models of cancer cachexia while a reliable and appropriate model for cardiac cachexia has not yet been established. A critical issue in generating a cardiac cachexia model is that genetic modifications or pharmacological treatments impairing the heart functionality and used to obtain the heart failure model might likely impair the skeletal muscle, this also being a striated muscle and sharing with the myocardium several molecular and physiological mechanisms. On the other hand, often, the induction of heart damage in the several existing models of heart failure does not necessarily lead to skeletal muscle loss and cachexia. Here we describe the main features of cardiac cachexia and illustrate some animal models proposed for cardiac cachexia studies; they include the genetic calsequestrin and Dahl salt-sensitive models, the monocrotaline model and the surgical models obtained by left anterior descending (LAD) ligation, transverse aortic constriction (TAC) and ascending aortic banding. The availability of a specific animal model for cardiac cachexia is a crucial issue since, besides the common aspects of cachexia in the different syndromes, each disease has some peculiarities in its etiology and pathophysiology leading to cachexia. Such peculiarities need to be unraveled in order to find new targets for effective therapies.