Engineering Mesoscopic 3D Tumor Models with a Self-Organizing Vascularized Matrix

Exosomes derived from fibroblasts enhance skin wound angiogenesis by regulating HIF-1α/VEGF/VEGFR pathway

Background

Angiogenesis is vital for tissue repair but insufficient in chronic wounds due to paradoxical growth factor overexpression yet reduced neovascularization. Therapeutics physiologically promoting revascularization remain lacking. This study aims to investigate the molecular mechanisms underlying fibroblast-derived exosome-mediated angiogenesis during wound repair.

Methods

To assess the effects of fibroblasts derived exosomes on wound healing and angiogenesis, a full-thickness mouse skin injury model was established, followed by pharmacological inhibition of exosome secretion. The number and state of blood vessels in wounds were assessed by immunofluorescence, immunohistochemistry, hematoxylin-eosin staining, and laser Doppler imaging system. The high-throughput miRNA sequencing was carried out to detect the miRNA profiles of fibroblast-derived exosomes. The roles of candidate miRNAs, their target genes, and relevant pathways were predicted by bioinformatic online software. The knockdown and overexpression of candidate miRNAs, co-culture system, matrigel assay, pharmacological blockade, cell migration, EdU incorporation assay, and cell apoptosis were employed to investigate their contribution to angiogenesis mediated by fibroblast-derived exosomes. The expression of vascular endothelial growth factor A (VEGFA), vascular endothelial growth factor receptor 2 (VEGFR2), hypoxia-inducible factor 1α (HIF-1α), von Hippel-Lindau (VHL), and proline hydroxylases 2 was detected by western blot, co-immunoprecipitation, immunofluorescence, real-time quantitative polymerase chain reaction, flow cytometry, and immunohistochemistry. Furthermore, a full-thickness mouse skin injury model based on type I diabetes mellitus induced by streptozotocin was established for estimating the effect of fibroblast-derived exosomes on chronic wound healing.

Results

Pharmacological inhibition of exosome biogenesis markedly reduces neovascularization and delays murine cutaneous wound closure. Topical administration of fibroblast-secreted exosomes rescues these defects. Mechanistically, exosomal microRNA-24-3p suppresses VHL E3 ubiquitin ligase levels in endothelial cells to stabilize hypoxia-inducible factor-1α and heighten vascular endothelial growth factor signaling. MicroRNA-24-3p-deficient exosomes exhibit attenuated pro-angiogenic effects. Strikingly, topical application of exosomes derived from fibroblasts onto chronic wounds in diabetic mice improves neovascularization and healing dynamics.

Conclusions

Overall, we demonstrate central roles for exosomal miR-24-3p in stimulating endothelial HIF-VEGF signaling by inhibiting VHL-mediated degradation. The findings establish fibroblast-derived exosomes as promising acellular therapeutic candidates to treat vascular insufficiency underlying recalcitrant wounds.

Engineering in vitro vascular microsystems

Blood vessels are hierarchical microchannels that transport nutrients and oxygen to different tissues and organs, while also eliminating metabolic waste from the body. Disorders of the vascular system impact both physiological and pathological processes. Conventional animal vascular models are complex, high-cost, time-consuming, and low-validity, which have limited the exploration of effective in vitro vascular microsystems. The morphologies of micro-scaled tubular structures and physiological properties of vascular tissues, including mechanical strength, thrombogenicity, and immunogenicity, can be mimicked in vitro by engineering strategies. This review highlights the state-of-the-art and advanced engineering strategies for in vitro vascular microsystems, covering the domains related to rational designs, manufacturing approaches, supporting materials, and organ-specific cell types. A broad range of biomedical applications of in vitro vascular microsystems are also summarized, including the recent advances in engineered vascularized tissues and organs for physiological and pathological study, drug screening, and personalized medicine. Moreover, the commercialization of in vitro vascular microsystems, the feasibility and limitations of current strategies and commercially available products, as well as perspectives on future directions for exploration, are elaborated. The in vitro modeling of vascular microsystems will facilitate rapid, robust, and efficient analysis in tissue engineering and broader regenerative medicine towards the development of personalized treatment approaches.

Advancing tissue engineering through vascularized cell spheroids: building blocks of the future

Vascularization is a crucial aspect of biofabrication, as the development of vascular networks is essential for tissue survival and the optimization of cellular functions. Spheroids have emerged as versatile units for vascularization, demonstrating significant potential in angiogenesis and prevascularization for tissue engineering and regenerative medicine. However, a major challenge in creating customized vascularized spheroids is the construction of a biomimetic extracellular matrix (ECM) microenvironment. This process requires careful regulation of environmental factors, including the modulation of growth factors, the selection of culture media, and the co-culture of diverse cell types. Recent advancements in biofabrication have expanded the potential applications of vascularized spheroids. The integration of microfluidic technology with bioprinting offers promising solutions to existing challenges in regenerative medicine. Spheroids have been widely studied for their ability to promote vascularization in in vitro models. This review highlights the latest developments in vascularized biofabrication, and systematically explores strategies for constructing vascularized spheroids. We provide a comprehensive analysis of spheroid applications in specific tissues, including skin, liver, bone, cardiac, and tumor models. Finally, the review addresses the major challenges and future directions in the field.

Synergizing bioprinting and 3D cell culture to enhance tissue formation in printed synthetic constructs

Bioprinting is currently the most promising method to biofabricate complex tissuesin vitrowith the potential to transform the future of organ transplantation and drug discovery. Efforts to create such tissues are, however, almost exclusively based on animal-derived materials, such as gelatin methacryloyl, which have demonstrated efficacy in bioprinting of complex tissues. While these materials are already used in clinical applications, uncertainty about their safety still remains due to their animal origin. Alternatively, synthetic bioinks have been developed that match the printability of natural bioinks but lack their biological complexity, and thereby often fail to support cell growth and facilitate tissue formation. Additionally, most synthetic materials do not meet the mechanical demands of bioprint stable constructs while providing a suitable environment for cells to grow, limiting the number of available bioinks. To bridge this gap and synergize bioprinting and 3D cell culture, we developed a polyethylene glycol-based bioink system to promote the growth and spreading of cell spheroids that consist of human primary endothelial cells and fibroblasts. The 3D bioprinted centimeter-scale constructs have a high shape fidelity and accelerated softening to provide sufficient space for cells to grow. Adjusting the rate of degradability, induced by the integration of ester-functionalized crosslinkers in addition to protease cleavable crosslinkers into the hydrogel network, improves the growth of spheroids in larger printed hydrogel constructs containing an interconnected channel structure. The perfusable constructs enable extensive spheroid sprouting and the formation of a cellular network upon fusion of sprouts as initial steps toward tissue formation with the potential for clinical translation.

Dual Enzyme-Driven Cascade Reactions Modulate Immunosuppressive Tumor Microenvironment for Catalytic Therapy and Immune Activation

Lactate-enriched tumor microenvironment (TME) fosters an immunosuppressive milieu to hamper the functionality of tumor-associated macrophages (TAMs). However, tackling the immunosuppressive effects wrought by lactate accumulation is still a big challenge. Herein, we construct a dual enzyme-driven cascade reaction platform (ILH) with immunosuppressive TME modulation for photoacoustic (PA) imaging-guided catalytic therapy and immune activation. The ILH is composed of iridium (Ir) metallene nanozyme, lactate oxidase (LOx), and hyaluronic acid (HA). The combination of Ir nanozyme and LOx can not only efficiently consume lactate to reverse the immunosuppressive TME into an immunoreactive one by promoting the polarization of TAMs from the M2 to M1 phenotype, thus enhancing antitumor defense, but also alleviate tumor hypoxia as well as induce strong oxidative stress, thus triggering immunogenic cell death (ICD) and activating antitumor immunity. Furthermore, the photothermal performance of Ir nanozyme can strengthen the cascade catalytic ability and endow ILH with a PA response. Based on the changes in PA signals from endogenous molecules, three-dimensional multispectral PA imaging was utilized to track the process of cascade catalytic therapy in vivo. This work provides a nanoplatform for dual enzyme-driven cascade catalytic therapy and immune activation by regulating the immunosuppressive TME.

RGD-coated polymeric microbubbles promote ultrasound-mediated drug delivery in an inflamed endothelium-pericyte co-culture model of the blood-brain barrier

Drug delivery to central nervous pathologies is compromised by the blood-brain barrier (BBB). A clinically explored strategy to promote drug delivery across the BBB is sonopermeation, which relies on the combined use of ultrasound (US) and microbubbles (MB) to induce temporally and spatially controlled opening of the BBB. We developed an advanced in vitro BBB model to study the impact of sonopermeation on the delivery of the prototypic polymeric drug carrier pHPMA as a larger molecule and the small molecule antiviral drug ribavirin. This was done under standard and under inflammatory conditions, employing both untargeted and RGD peptide-coated MB. The BBB model is based on human cerebral capillary endothelial cells and human placental pericytes, which are co-cultivated in transwell inserts and which present with proper transendothelial electrical resistance (TEER). Sonopermeation induced a significant decrease in TEER values and facilitated the trans-BBB delivery of fluorescently labeled pHPMA (Atto488-pHPMA). To study drug delivery under inflamed endothelial conditions, which are typical for e.g. tumors, neurodegenerative diseases and CNS infections, tumor necrosis factor (TNF) was employed to induce inflammation in the BBB model. RGD-coated MB bound to and permeabilized the inflamed endothelium-pericyte co-culture model, and potently improved Atto488-pHPMA and ribavirin delivery. Taken together, our work combines in vitro BBB bioengineering with MB-mediated drug delivery enhancement, thereby providing a framework for future studies on optimization of US-mediated drug delivery to the brain.

High-Scale 3D-Bioprinting Platform for the Automated Production of Vascularized Organs-on-a-Chip

3D bioprinting possesses the potential to revolutionize contemporary methodologies for fabricating tissue models employed in pharmaceutical research and experimental investigations. This is enhanced by combining bioprinting with advanced organs-on-a-chip (OOCs), which includes a complex arrangement of multiple cell types representing organ-specific cells, connective tissue, and vasculature. However, both OOCs and bioprinting so far demand a high degree of manual intervention, thereby impeding efficiency and inhibiting scalability to meet technological requirements. Through the combination of drop-on-demand bioprinting with robotic handling of microfluidic chips, a print procedure is achieved that is proficient in managing three distinct tissue models on a chip within only a minute, as well as capable of consecutively processing numerous OOCs without manual intervention. This process rests upon the development of a post-printing sealable microfluidic chip, that is compatible with different types of 3D-bioprinters and easily connected to a perfusion system. The capabilities of the automized bioprint process are showcased through the creation of a multicellular and vascularized liver carcinoma model on the chip. The process achieves full vascularization and stable microvascular network formation over 14 days of culture time, with pronounced spheroidal cell growth and albumin secretion of HepG2 serving as a representative cell model.