Platelet-derived growth factor-AB improves scar mechanics and vascularity after myocardial infarction.

Therapies that target scar formation after myocardial infarction (MI) could prevent ensuing heart failure or death from ventricular arrhythmias. We have previously shown that recombinant human platelet-derived growth factor-AB (rhPDGF-AB) improves cardiac function in a rodent model of MI. To progress clinical translation, we evaluated rhPDGF-AB treatment in a clinically relevant porcine model of myocardial ischemia-reperfusion. Thirty-six pigs were randomized to sham procedure or balloon occlusion of the proximal left anterior descending coronary artery with 7-day intravenous infusion of rhPDGF-AB or vehicle. One month after MI, rhPDGF-AB improved survival by 40% compared with vehicle, and cardiac magnetic resonance imaging showed left ventricular (LV) ejection fraction improved by 11.5%, driven by reduced LV end-systolic volumes. Pressure volume loop analyses revealed improved myocardial contractility and energetics after rhPDGF-AB treatment with minimal effect on ventricular compliance. rhPDGF-AB enhanced angiogenesis and increased scar anisotropy (high fiber alignment) without affecting overall scar size or stiffness. rhPDGF-AB reduced inducible ventricular tachycardia by decreasing heterogeneity of the ventricular scar that provides a substrate for reentrant circuits. In summary, we demonstrated that rhPDGF-AB promotes post-MI cardiac wound repair by altering the mechanics of the infarct scar, resulting in robust cardiac functional improvement, decreased ventricular arrhythmias, and improved survival. Our findings suggest a strong translational potential for rhPDGF-AB as an adjunct to current MI treatment and possibly to modulate scar in other organs.

Theranostic α-Lactalbumin-Polymer-Based Nanocomposite as a Drug Delivery Carrier for Cancer Therapy.

A nanotheranostic system was developed using α-lactalbumin along with Fe3O4 nanoparticles as an magnetic resonance imaging (MRI) contrast agent for medical imaging and doxorubicin as the therapeutic agent. α-lactalbumin was precipitated and cross-linked using poly(ethylene glycol) and glutaraldehyde. Besides, polyethylenimine was applied to increase the number of amine groups during cross-linking between α-lactalbumin and Fe3O4 nanoparticles. Interestingly, 90% of the initial protein used for the coaggregation process was incorporated in the prepared 130 nm nanocomposites, which facilitated the 85% doxorubicin loading. Formation of pH-sensitive imine bonds between glutaraldehyde and amine groups on α-lactalbumin and polyethylenimine resulted in higher release of doxorubicin at acidic pHs and consequently development of a pH-sensitive nanocarrier. The designed nanocomposite was less immunogenic owing to stimulating the production of less amounts of C3a, C5a, platelet factor 4, glycoprotein IIb/IIIa, platelet-derived ß-thromboglobulin, interleukin-6, and interleukin-1ß compared to the free doxorubicin. Furthermore, 1000 µg/mL nanocomposite led to 0.2% hemolytic activity, much less than the 5% standard limit. The void nanocarrier induced no significant level of cytotoxicity in breast cancer and normal cells following 96 h incubation. The doxorubicin-loaded nanocomposite presented higher cytotoxicity, apoptosis induction, and doxorubicin uptake in cancer cells than free doxorubicin. Conversely, lower cytotoxicity, apoptosis induction, and doxorubicin uptake were observed in normal cells treated with the doxorubicin-loaded nanocarrier compared to free doxorubicin. In line with the results of in vitro experiments, in vivo studies on tumor-bearing mice showed more suppression of tumor growth by the doxorubicin-loaded nanocomposite compared to the free drug. Moreover, the pharmacokinetic study revealed slow release of doxorubicin from the nanocomposite. Besides, in vitro and in vivo MRI studies presented a higher r2/r1 ratio and comparable contrast to the commercially available DOTAREM, respectively. Our findings suggest that this new nanocomposite is a promising nanotheranostic system with promising potential for cancer therapy and diagnosis.

Hox-Mediated Spatial and Temporal Coding of Stem Cells in Homeostasis and Neoplasia.

Hox genes are fundamental components of embryonic patterning and morphogenesis with expression persisting into adulthood. They are also implicated in the development of diseases, particularly neoplastic transformations. The tight spatio-temporal regulation of Hox genes in concordance with embryonic patterning is an outstanding feature of these genes. In this review we have systematically analyzed Hox functions within the stem/progenitor cell compartments and asked whether their temporo-spatial topography is retained within the stem cell domain throughout development and adulthood. In brief, evidence support involvement of Hox genes at several levels along the stem cell hierarchy, including positional identity, stem cell self-renewal, and differentiation. There is also strong evidence to suggest a role for Hox genes during neoplasia. Although fundamental questions are yet to be addressed through more targeted and high- throughput approaches, existing evidence suggests a central role for Hox genes within a continuum along the developmental axes persisting into adult homeostasis and disease.

Epithelial to mesenchymal transition as a portal to stem cell characters embedded in gene networks.

Cells can transit between a range of stable epithelial and mesenchymal states and this has allowed the evolution of complex body forms. Epithelial to mesenchymal transition (EMT) and its reverse, mesenchymal to epithelial transition (MET), occur sequentially in development and organogenesis. EMT often accompanies transitions between stem-like cells and their more differentiated progeny, as occurs at gastrulation, although the relevance of this had not been clarified. New findings from the cancer and cell reprogramming fields suggest that EMT and MET can act as essential portals to stem cell character. Here, we review these findings in the broader context of EMT and MET with emphasis on stem cell biology. Using the heart as an example, we also explore the potential role of EMT/MET in organ regeneration. Understanding EMT and MET at a network level will give us new tools to probe stem cell character and enhance tissue repair.

Adult cardiac-resident MSC-like stem cells with a proepicardial origin.

Colony-forming units - fibroblast (CFU-Fs), analogous to those giving rise to bone marrow (BM) mesenchymal stem cells (MSCs), are present in many organs, although the relationship between BM and organ-specific CFU-Fs in homeostasis and tissue repair is unknown. Here we describe a population of adult cardiac-resident CFU-Fs (cCFU-Fs) that occupy a perivascular, adventitial niche and show broad trans-germ layer potency in vitro and in vivo. CRE lineage tracing and embryo analysis demonstrated a proepicardial origin for cCFU-Fs. Furthermore, in BM transplantation chimeras, we found no interchange between BM and cCFU-Fs after aging, myocardial infarction, or BM stem cell mobilization. BM and cardiac and aortic CFU-Fs had distinct CRE lineage signatures, indicating that they arise from different progenitor beds during development. These diverse origins for CFU-Fs suggest an underlying basis for differentiation biases seen in different CFU-F populations, and could also influence their capacity for participating in tissue repair.

Spatiotemporally restricted regulation of generic motor neuron programs by miR-196-mediated repression of Hoxb8.

Hox transcription factors are key determinants of antero-posterior identity and have been implicated in assigning positionally appropriate neuron subtypes in the neural tube. These roles inherently necessitate stringent control mechanisms that confine Hox protein activities to discrete spatiotemporal domains. Here, we provide evidence that the timing and rostro-caudal extent of Hoxb8 activity in the neural tube is tightly regulated by miR-196, a microRNA species encoded within three Hox gene clusters. In vitro and in vivo sensor-tracer analysis and transcription assays revealed that miR-196 activity restricts the caudal extent of Hoxb8 expression to the thoracic-lumbar intersect via 3' UTR-dependent negative regulation. Spatio-temporally inappropriate Hoxb8 activity, through relief of miR-196-mediated repression or direct misexpression, affected normal progression of motor neuron genesis by affecting generic motor neuron differentiation programs. In addition to uncovering a role for microRNA-dependent restriction of caudal Hox activities, these data thus indicate novel aspects of Hox-dependent neural tube patterning by revealing a requirement of temporal regulation of a generic neuronal specification program.

MicroRNAs in organogenesis and disease.

Large numbers and quantities of different, small RNA molecules are present in the cytoplasm of animal and plant cells. One subclass of these molecules is represented by the noncoding microRNAs. Since their discovery in the 1990s a multitude of basic information has accumulated, which has identified their function in post-transcriptional control, either via degradation or translational inhibition of target mRNAs. This function is in most of the cases a finetuning of gene expression, working in parallel with transcriptional regulatory processes. MicroRNA expression profiles are highly dynamic during embryonic development and in adulthood. Misexpression of microRNAs can perturb embryogenesis, organogenesis, tissue homeostasis and the cell cycle. Evidence from gain- and loss-of function studies indicates roles for microRNAs in pathophysiologic states including cardiac hypertrophy, muscle dystrophy, hepatitis infection, diabetes, Parkinson syndrome, hematological malignancies and other types of cancer. In this review, we focus on studies addressing the role of various microRNAs in heart, muscle, liver, pancreas, central nervous system, and hematopoiesis.

Regulation of geminin functions by cell cycle-dependent nuclear-cytoplasmic shuttling.

The geminin protein functions both as a DNA rereplication inhibitor through association with Cdt1 and as a repressor of Hox gene transcription through the polycomb pathway. Here, we report that the functions of avian geminin are coordinated with and regulated by cell cycle-dependent nuclear-cytoplasmic shuttling. In S phase, geminin enters nuclei and inhibits both loading of the minichromosome maintenance (MCM) complex onto chromatin and Hox gene transcription. At the end of mitosis, geminin is exported from nuclei by the exportin protein Crm1 and is unavailable in the nucleus during the next G(1) phase, thus ensuring proper chromatin loading of the MCM complex and Hox gene transcription. This mechanism for regulating the functions of geminin adds to distinct mechanisms, such as protein degradation and ubiquitination, applied in other vertebrates.