High-efficiency system for the construction of adenovirus vectors and its application to the generation of representative adenovirus-based cDNA expression libraries

Combining CRISPR-Cas-mediated terminal resolution with a novel genetic workflow to achieve high-diversity adenoviral libraries

While recombinant adenoviruses (rAds) are widely used in both laboratory and medical gene transfer, library-based applications using this vector platform are not readily available. Recently, we developed a new method, the CRISPR-Cas9 mediated in vivo terminal resolution aiding high-efficiency rescue of rAds from recombinant DNA. Here we report on a genetic workflow that allows construction of bacterial artificial chromosome-based rAd libraries reconstituted using highly efficient terminal resolution. We utilized frequent, pre-existing genomic sequences to allow the insertion of a selection marker, complementing two selected target sites into novel endonuclease recognition sites. In the second step, this selection marker is replaced with a transgene or mutation of interest via Gibson assembly. Our approach does not cause unwanted genomic off-target mutations while providing substantial flexibility for the site and nature of the genetic modification. This new genetic workflow, which we termed half site-directed fragment replacement (HFR) allows the introduction of more than 106 unique modifications into rAd encoding BACs using laboratory scale methodology. To demonstrate the power of HFR, we rescued barcoded viral vector libraries yielding a diversity of approximately 2.5 × 104 unique rAds per cm2 of transfected cell culture.

Early cellular responses of BMSCs genetically modified with bFGF/BMP2 co-cultured with ligament fibroblasts in a three-dimensional model in vitro

Currently, a number of strategies including the implantation of bone marrow-derived mesenchymal stem cells (BMSCs) and growth factors have been developed to regenerate the tendon-to-bone interface after performing anterior cruciate ligament reconstruction. However, the mechanisms behind the interactions of the implanted BMSCs and tendon cells remain to be elucidated. The aim of this study was to evaluate the early cellular responses of BMSCs genetically modified with basic growth factor growth factor (bFGF)/bone morphogenic protein 2 (BMP2) and ligament fibroblasts in a three-dimensional co-culture model. BMSCs and ligament fibroblasts were both isolated from male Wistar rats. The BMSCs were then transfected with an adenoviral vector carrying bFGF or BMP2. The transfected BMSCs and ligament fibroblasts both encapsulated in alginate beads were co-cultured for 6 days in three-dimensional model. On days 0, 3 and 6, cell proliferation was assayed. On day 6, the expression of several tendon-bone related markers was evaluated. In the co-culture system, bFGF and BMP2 were highly expressed at the mRNA and protein level. During the process, bFGF significantly promoted cell proliferation, as well as the expression of scleraxis (SCX) and collagen (COL) type Ⅰ (COL1) in the BMSCs; however, it markedly decreased the expression of phenotype markers in the ligament fibroblasts, including COL1 and COL3. BMP2 markedly increased the expression of alkaline phosphatase and osteocalcin in the BMSCs and ligament fibroblasts, whereas it had no obvious effect on cell proliferation and collagen synthesis in the ligament fibroblasts. The combination of bFGF and BMP2 resulted in the similarly enhanced proliferation of BMSCs and ligament fibroblasts as observed with bFGF alone; however, this combination more potently promoted osteogenic differentiation than did BMP2 alone. The findings of our study demonstrate the superiority of the combined use of growth factors in inducing osteogenic differentiation and provide a theoretical foundation for the regeneration of the tendon-to-bone interface.

AAV-mediated in vivo functional selection of tissue-protective factors against ischaemia

Functional screening of expression libraries in vivo would offer the possibility of identifying novel biotherapeutics without a priori knowledge of their biochemical function. Here we describe a procedure for the functional selection of tissue-protective factors based on the in vivo delivery of arrayed cDNA libraries from the mouse secretome using adeno-associated virus (AAV) vectors. Application of this technique, which we call FunSel, in the context of acute ischaemia, revealed that the peptide ghrelin protects skeletal muscle and heart from ischaemic damage. When delivered to the heart using an AAV9 vector, ghrelin markedly reduces infarct size and preserves cardiac function over time. This protective activity associates with the capacity of ghrelin to sustain autophagy and remove dysfunctional mitochondria after myocardial infarction. Our findings describe an innovative tool to identify biological therapeutics and reveal a novel role of ghrelin as an inducer of myoprotective autophagy.

Cell-based screening assays allow functional testing of chemicals but do not mimic the in vivo situation well. Here, the authors report a method for the discovery of secreted cytoprotective factors in mice and use it to demonstrate that the hormone ghrelin protects cardiac muscle from ischaemic damage.

Cancer cell senescence: a new frontier in drug development

Senescence forms a universal block to tumorigenesis which impacts on all hallmarks of cancer, making it an attractive target for drug discovery. Therefore a strategy must be devised to focus this broad potential into a manageable drug discovery programme. Several issues remain to be addressed including the lack of robust senescence-inducing compounds and causally related biomarkers to measure cellular response. Here, we review the latest progress in translating senescence as a target for cancer therapy and some promising approaches to drug and biomarker discovery. Finally, we discuss the potential application of a senescence-induction therapy in a clinical setting.

Effects of adenovirus-mediated bFGF, IL-1Ra and IGF-1 gene transfer on human osteoarthritic chondrocytes and osteoarthritis in rabbits

The study investigated the effects of adenovirus-mediated gene transfection of basic fibroblast growth factor (bFGF), bFGF combined with interleukin-1 receptor antagonist protein (IL-Ra) and/or insulin-like growth factor-1 (IGF-1) both in human osteoarthritis (OA) chondrocytes and rabbits OA model. Human OA chondrocytes were delivered by adenovirus-mediated bFGF, IL-Ra and IGF-1 vectors, respectively. Chondrocyte proliferation, glycosaminoglycan (GAG) content, expression of type II collagen, ADAMTS-5, MMP-13, MMP-3 and TIMP-1 were determined. Rabbit OA model was induced by anterior cruciate ligament transaction (ACLT) in knees. Adenoviral vectors encoding human bFGF, IL-Ra and IGF-1 were injected intraarticularly into the knee joints after ACLT. The effects of adenovirus-mediated gene transfection on rabbit OA were evaluated. In vitro, the transfected genes were expressed in cell supernatant of human OA chondrocytes. AdbFGF group significantly promoted chondrocyte proliferation, and increased GAG and type II collagen synthesis than in the OA group. As two or three genes were transfected in different combinations, there was significant enhancement on the GAG content, type II collagen synthesis, and TIMP-1 levels, while ADAMTS-5, MMP-13, and MMP-3 levels were reduced. In vivo, the transfected genes were expressed in synovial fluid of rabbits. Intraarticular delivery of bFGF enhanced the expression of type II collagen in cartilage and decreased cartilage Mankin score compared with the OA control group (P=0.047; P<0.01, respectively). Multiple-gene transfection in different combinations showed better results than bFGF transfection alone. This study suggests that bFGF gene transfection is effective in treating experimental OA. Multiple gene transfection has better biologic effects on OA.

A herpes simplex virus vector system for expression of complex cellular cDNA libraries

Viral vector-based gene expression libraries from normal or diseased tissues offer opportunities to interrogate cellular functions that influence or participate directly in specific biological processes. Here we report the creation and characterization of a herpes simplex virus (HSV)-based expression library consisting of cDNAs derived from PC12 pheochromocytoma cells. A replication-defective HSV vector backbone was engineered to contain both a bacterial artificial chromosome (BAC) and the Invitrogen in vitro Gateway recombination system, creating DBAC-GW. A cDNA library was produced and transferred into the DBAC-GW genome by in vitro recombination and selection in bacteria to produce DBAC-L. DBAC-L contained at least 15,000 unique cDNAs, as shown by DNA array analysis of PCR-amplified cDNA inserts, representing a wide range of cancer- and neuron-related cellular functions. Transfection of the recombinant DBAC-L DNA into complementing animal cells produced more than 1 million DBAC-L virus particles representing the library genes. By microarray analysis of vector-infected cells, we observed that individual members of this vector population expressed unique PC12 cDNA-derived mRNA, demonstrating the power of this system to transfer and express a variety of gene activities. We discuss the potential utility of this and similarly derived expression libraries for genome-wide approaches to identify cellular functions that participate in complex host-pathogen interactions or processes related to disease and to cell growth and development.