Infection of receptor-bearing cells by coronaviruses is mediated by their spike (S) proteins. The coronavirus (SARS-CoV) that causes severe acute respiratory syndrome (SARS) infects cells expressing the receptor angiotensin-converting enzyme 2 (ACE2).Here we show that codon optimization of the SARS-CoV S-protein gene substantially enhanced S-protein expression. We also found that two retroviruses, simian immunodeficiency virus (SIV) and murine leukemia virus, both expressing green fluorescent protein and pseudotyped with SARS-CoV S protein or S-protein variants, efficiently infected HEK293T cells stably expressing ACE2. Infection mediated by an S-protein variant whose cytoplasmic domain had been truncated and altered to include a fragment of the cytoplasmic tail of the human immunodeficiency virus type 1 envelope glycoprotein was, in both cases, substantially more efficient than that mediated by wild-type S protein. Using S-protein-pseudotyped SIV, we found that the enzymatic activity of ACE2 made no contribution to S-protein-mediated infection. Finally, we show that a soluble and catalytically inactive form of ACE2 potently blocked infection by S-proteinpseudotyped retrovirus and by SARS-CoV. These results permit studies of SARS-CoV entry inhibitors without the use of live virus and suggest a candidate therapy for SARS.A distinct coronavirus (SARS-CoV) has been identified as the etiological agent of severe acute respiratory syndrome (SARS), an acute pulmonary syndrome characterized by an atypical pneumonia that results in progressive respiratory failure and death in close to 10% of infected individuals (8,11,14,15). SARS-CoV is not closely related to any of the three previously defined genetic and serological coronavirus groups, although it may be distantly related to group 2 coronaviruses (21); the SARS-CoV spike (S) protein, a surface glycoprotein that mediates coronavirus entry into receptor-bearing cells, is also distinct from those of other coronaviruses (18,20). Reflecting this difference, SARS-CoV does not utilize any previously identified coronavirus receptors to infect cells. Rather, as our group have recently demonstrated, angiotensin-converting enzyme 2 (ACE2) serves as a functional receptor for this coronavirus (16,24,25).A quantitative system utilizing a well-characterized retroviral vector (1) for measuring SARS-CoV S-protein-mediated infection would obviate the need for specialized biosafety facilities for many studies, including those assessing humoral responses to potential vaccines. Here we show that simian immunodeficiency virus (SIV) pseudotyped with several codon-optimized S-protein variants could efficiently infect Vero E6 cells and HEK293T cells transiently or stably expressing ACE2. One such variant, truncated at its cytoplasmic tail and bearing instead a region of the tail of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (17), was especially efficient at mediating infection. Murine leukemia virus (MLV) pseudotyped with this S-protein variant also infected ACE2-ex...

Mesenchymal stem cell (MSC)-derived exosomes have been recognized as new candidates for cell-free treatment of various diseases. However, maintaining the retention and stability of exosomes over time in vivo after transplantation is a major challenge in the clinical application of MSC-derived exosomes. Here, we investigated if human placenta-derived MSC-derived exosomes incorporated with chitosan hydrogel could boost the retention and stability of exosomes and further enhance their therapeutic effects. Our results demonstrated that chitosan hydrogel notably increased the stability of proteins and microRNAs in exosomes, as well as augmented the retention of exosomes in vivo as confirmed by Gaussia luciferase imaging. In addition, we assessed endothelium-protective and proangiogenesis abilities of hydrogel-incorporated exosomes in vitro. Meanwhile, we evaluated the therapeutic function of hydrogel-incorporated exosomes in a murine model of hindlimb ischemia. Our data demonstrated that chitosan hydrogel could enhance the retention and stability of exosomes and further augment the therapeutic effects for hindlimb ischemia as revealed by firefly luciferase imaging of angiogenesis. The strategy used in this study may facilitate the development of easy and effective approaches for assessing and enhancing the therapeutic effects of stem cell-derived exosomes.

Mesenchymal stem cells (MSCs) represent a heterogenous population of adult,fibroblast-like multi-potent cells. MSCs have drawn much attention during the last decade in the field of regenerative medicine, mainly due to their capacity to differentiate into specific cell types, abundant production of soluble growth factors and cytokines, and hematopoiesis supporting properties. In addition, MSCs can migrate to the sites of inflammation and hold potent of immunomodulatory and anti-inflammatory effects through cell and cell interactions between MSCs and lymphocytes or production of soluble factors. Therefore, the application of MSCs in many disease situations is full of possibilities for future clinical treatment. Phase III clinical trials have been run using

The Cre-loxP recombination system is the most widely used technology for in vivo tracing of stem or progenitor cell lineages. The precision of this genetic system largely depends on the specificity of Cre recombinase expression in targeted stem or progenitor cells. However, Cre expression in nontargeted cell types can complicate the interpretation of lineage-tracing studies and has caused controversy in many previous studies. Here we describe a new genetic lineage tracing system that incorporates the Dre-rox recombination system to enhance the precision of conventional Cre-loxP-mediated lineage tracing. The Dre-rox system permits rigorous control of Cre-loxP recombination in lineage tracing, effectively circumventing potential uncertainty of the cell-type specificity of Cre expression. Using this new system we investigated two topics of recent debates-the contribution of c-Kit cardiac stem cells to cardiomyocytes in the heart and the contribution of Sox9 hepatic progenitor cells to hepatocytes in the liver. By overcoming the technical hurdle of nonspecific Cre-loxP-mediated recombination, this new technology provides more precise analysis of cell lineage and fate decisions and facilitates the in vivo study of stem and progenitor cell plasticity in disease and regeneration.

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Bone Tissue engineering (BTE) has recently been introduced as an alternative to conventional treatments for large non-healing bone defects. BTE approaches mimic autologous bone grafts, by combining cells, scaffold, and growth factors, and have the added benefit of being able to manipulate these constituents to optimize healing. Electrical stimulation (ES) has long been used to successfully treat non-healing fractures and has recently been shown to stimulate bone cells to migrate, proliferate, align, differentiate, and adhere to bio compatible scaffolds, all cell behaviors that could improve BTE treatment outcomes. With the above in mind we performed in vitro experiments and demonstrated that exposing Mesenchymal Stem Cells (MSC) + scaffold to ES for 3 weeks resulted in significant increases in osteogenic differentiation. Then in in vivo experiments, for the first time, we demonstrated that exposing BTE treated rat femur large defects to ES for 8 weeks, caused improved healing, as indicated by increased bone formation, strength, vessel density, and osteogenic gene expression. Our results demonstrate that ES significantly increases osteogenic differentiation in vitro and that this effect is translated into improved healing in vivo. These findings support the use of ES to help BTE treatments achieve their full therapeutic potential.

Wound healing is regulated by a complex series of events and overlapping phases. A delicate balance of cytokines and mediators in tissue repair is required for optimal therapy in clinical applications. Molecular imaging technologies, with their versatility in monitoring cellular and molecular events in living organisms, offer tangible options to better guide tissue repair by regulating the balance of cytokines and mediators at injured sites.Methods: A murine cutaneous wound healing model was developed to investigate if incorporation of prostaglandin E2 (PGE2) into chitosan (CS) hydrogel (CS+PGE2 hydrogel) could enhance its therapeutic effects. Bioluminescence imaging (BLI) was used to noninvasively monitor the inflammation and angiogenesis processes at injured sites during wound healing. We also investigated the M1 and M2 paradigm of macrophage activation during wound healing.Results: CS hydrogel could prolong the release of PGE2, thereby improving its tissue repair and regeneration capabilities. Molecular imaging results showed that the prolonged release of PGE2 could ameliorate inflammation by promoting the M2 phenotypic transformation of macrophages. Also, CS+PGE2 hydrogel could augment angiogenesis at the injured sites during the early phase of tissue repair, as revealed by BLI. Furthermore, our results demonstrated that CS+PGE2 hydrogel could regulate the balance among the three overlapping phases—inflammation, regeneration (angiogenesis), and remodeling (fibrosis)—during cutaneous wound healing.Conclusion: Our findings highlight the potential of the CS+PGE2 hydrogel as a novel therapeutic strategy for promoting tissue regeneration via M2 macrophage polarization. Moreover, molecular imaging provides a platform for monitoring cellular and molecular events in real-time during tissue repair and facilitates the discovery of optimal therapeutics for injury repair by regulating the balance of cytokines and mediators at injured sites.

Background: Mesenchymal stem cells are heterogenous populations with hematopoietic supporting and immunomodulating capacities. Enormous studies have focused on their preclinical or clinical therapeutic effects, yet the systematic study of continuous in vitro passages on signatures and functions of UC-MSCs at both the cellular and molecular levels is still lacking. Methods: In this study, to systematically evaluate the biological properties of MSCs at various passages, we analyzed biomarker expression, cell proliferation and apoptosis, chromosome karyotype, and tri-lineage differentiation potential. Subsequently, we took advantage of whole-exome sequencing to compare the somatic hypermutation of hUC-MSCs at P3, P6, and P15 including SNV and INDEL mutations. In addition, to explore the safety of the abovementioned hUC-MSCs, we performed metabolic pathway enrichment analysis and in vivo transplantation analysis. Furthermore, we cocultured the abovementioned hUC-MSCs with UCB-CD34 + HSCs to evaluate their hematopoietic supporting capacity in vitro. Finally, we transplanted the cells into acute graft-versushost disease (aGVHD) mice to further evaluate their therapeutic effect in vivo. Results: The hUC-MSCs at P3, P6, and P15 showed similar morphology, biomarker expression, and cytokine secretion. hUC-MSCs at P15 had advantages on adipogenic differentiation and some cytokine secretion such as IL-6 and VEGF, with disadvantages on cell proliferation, apoptosis, and osteogenic and chondrogenic differentiation potential. Based on the SNP data of 334,378 exons and bioinformatic analyses, we found the somatic point mutations could be divided into 96 subsets and formed 30 kinds of signatures but did not show correlation with risk of tumorigenesis, which was confirmed by the in vivo transplantation experiments. However, hUC-MSCs at P15 showed impaired hematologic supporting effect in vitro and declined therapeutic effect on aGVHD in vivo.