Heart in a dish - choosing the right in vitro model

The heart is the first functional organ established during embryogenesis. Investigating heart development and disease is a fascinating and crucial field of research because cardiovascular diseases remain the leading cause of morbidity and mortality worldwide. Therefore, there is great interest in establishing in vitro models for recapitulating both physiological and pathological aspects of human heart development, tissue function and malfunction. Derived from pluripotent stem cells, a large variety of three-dimensional cardiac in vitro models have been introduced in recent years. In this At a Glance article, we discuss the available methods to generate such models, grouped according to the following classification: cardiac organoids, cardiac microtissues and engineered cardiac tissues. For these models, we provide a systematic overview of their applications for disease modeling and therapeutic development, as well as their advantages and limitations to assist scientists in choosing the most suitable model for their research purpose.

Microstructured soft devices for the growth and analysis of populations of homogenous multicellular tumor spheroids

Multicellular tumor spheroids are rapidly emerging as an improved in vitro model with respect to more traditional 2D culturing. Microwell culturing is a simple and accessible method for generating a large number of uniformly sized spheroids, but commercially available systems often do not enable researchers to perform complete culturing and analysis pipelines and the mechanical properties of their culture environment are not commonly matching those of the target tissue. We herein report a simple method to obtain custom-designed self-built microwell arrays made of polydimethylsiloxane or agarose for uniform 3D cell structure generation. Such materials can provide an environment of tunable mechanical flexibility. We developed protocols to culture a variety of cancer and non-cancer cell lines in such devices and to perform molecular and imaging characterizations of the spheroid growth, viability, and response to pharmacological treatments. Hundreds of tumor spheroids grow (in scaffolded or scaffold-free conditions) at homogeneous rates and can be harvested at will. Microscopy imaging can be performed in situ during or at the end of the culture. Fluorescence (confocal) microscopy can be performed after in situ staining while retaining the geographic arrangement of spheroids in the plate wells. This platform can enable statistically robust investigations on cancer biology and screening of drug treatments.

Peripheral nerve defects repaired with autogenous vein grafts filled with platelet-rich plasma and active nerve microtissues and evaluated by novel multimodal ultrasound techniques

BACKGROUND

Developing biocompatible nerve conduits that accelerate peripheral nerve regeneration, lengthening and functional recovery remains a challenge. The combined application of nerve microtissues and platelet-rich plasma (PRP) provides abundant Schwann cells (SCs) and various natural growth factors and can compensate for the deficiency of SCs in the nerve bridge, as well as the limitations of applying a single type of growth factor. Multimodal ultrasound evaluation can provide additional information on the stiffness and microvascular flow perfusion of the tissue. This study was designed to investigate the effectiveness of a novel tissue-engineered nerve graft composed of an autogenous vein, nerve microtissues and PRP in reconstructing a 12-mm tibial nerve defect and to explore the value of multimodal ultrasound techniques in evaluating the prognosis of nerve repair.

METHODS

In vitro, nerve microtissue activity was first investigated, and the effects on SC proliferation, migration, factor secretion, and axonal regeneration of dorsal root ganglia (DRG) were evaluated by coculture with nerve microtissues and PRP. In vivo, seventy-five rabbits were equally and randomly divided into Hollow, PRP, Micro-T (Microtissues), Micro-T + PRP and Autograft groups. By analysing the neurological function, electrophysiological recovery, and the comparative results of multimodal ultrasound and histological evaluation, we investigated the effect of these new nerve grafts in repairing tibial nerve defects.

RESULTS

Our results showed that the combined application of nerve microtissues and PRP could significantly promote the proliferation, secretion and migration of SCs and the regeneration of axons in the early stage. The Micro-T + PRP group and Autograft groups exhibited the best nerve repair 12 weeks postoperatively. In addition, the changes in target tissue stiffness and microvascular perfusion on multimodal ultrasound (shear wave elastography; contrast-enhanced ultrasonography; Angio PlaneWave UltrasenSitive, AngioPLUS) were significantly correlated with the histological results, such as collagen area percentage and VEGF expression, respectively.

CONCLUSION

Our novel tissue-engineered nerve graft shows excellent efficacy in repairing 12-mm defects of the tibial nerve in rabbits. Moreover, multimodal ultrasound may provide a clinical reference for prognosis by quantitatively evaluating the stiffness and microvescular flow of nerve grafts and targeted muscles.

Microtissues from mesenchymal stem cells and siRNA-loaded cross-linked gelatin microparticles for bone regeneration

The aim of this study was the evaluation of cross-linked gelatin microparticles (cGM) as substrates for osteogenic cell culture to assemble 3D microtissues and their use as delivery system for siRNA to cells in these assemblies.

In a 2D transwell cultivation system, we found that cGM are capable to accumulate calcium ions from the surrounding medium. Such a separation of cGM and SaOS-2 ​cells consequently led to a suppressed matrix mineral formation in the SaOS-2 culture on the well bottom of the transwell system. Thus, we decided to use cGM as component in 3D microtissues and get a close contact between calcium ion accumulating microparticles and cells to improve matrix mineralization.

Gelatin microparticles were cross-linked with a N,N-diethylethylenediamine-derivatized (DEED) maleic anhydride (MA) containing oligo (pentaerythritol diacrylate monostearate-co-N-isopropylacrylamide-co-MA) (oPNMA) and aggregated with SaOS-2 or human mesenchymal stem cells (hMSC) to microtissue spheroids. We systematically varied the content of cGM in microtissues and observed cell differentiation and tissue formation. Microtissues were characterized by gene expression, ALP activity and matrix mineralization. Mineralization was detectable in microtissues with SaOS-2 ​cells after 7 days and with hMSC after 24–28 days in osteogenic culture. When we transfected hMSC via cGM loaded with Lipofectamine complexed chordin siRNA, we found increased ALP activity and accelerated mineral formation in microtissues in presence of BMP-2. As a model for positive paracrine effects that indicate promising in vivo effects of these microtissues, we incubated pre-differentiated microtissues with freshly seeded hMSC monolayers and found improved mineral formation all over the well in the co-culture model. These findings may support the concept of microtissues from hMSC and siRNA-loaded cGM for bone regeneration.

Arrhythmia Assessment in Heterotypic Human Cardiac Myocyte-Fibroblast Microtissues

Risk assessment assays for chemically induced arrhythmia are critical, but significant limitations exist with current cardiotoxicity testing, including a focus on single select ion channels, the use of non-human species in vitro and in vivo, and limited direct physiological translation. To be predictive of actual adverse clinical arrhythmic risk, arrhythmia assessment models for chemicals and drugs should be fit-for-purpose and suited for evaluating compounds in which the mechanism of action may not be entirely known. Here, we describe methods for efficient and reliable screening for arrhythmogenic cardiotoxicity with a 3D human cardiac microtissue model using purified human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and human cardiac fibroblasts. Applying optical mapping of voltage and calcium-sensitive dyes-an established approach to evaluate cardiac action potentials and calcium transients-to 3D heterotypic cardiac myocyte-fibroblast tissues allows for the generation and functional analysis of a large number of individual microtissues to provide greater throughput and high statistical power in analyses. Hundreds of microtissues in standard cell culture plates can be produced with low variability beat-to-beat, microtissue-to-microtissue, and across hiPSC-cardiomyocyte differentiation batches, reducing the number of microtissues required per condition for predictive outputs. The platform described here can be used as a sensitive, efficient, and predictive preclinical model validated for the purpose of assessing human pro-arrhythmic risk.

Biofabrication and bioprinting using cellular aggregates, microtissues and organoids for the engineering of musculoskeletal tissues

The modest clinical impact of musculoskeletal tissue engineering (TE) can be attributed, at least in part, to a failure to recapitulate the structure, composition and functional properties of the target tissue. This has motivated increased interest in developmentally inspired TE strategies, which seek to recapitulate key events that occur during embryonic and post-natal development, as a means of generating truly biomimetic grafts to replace or regenerate damaged tissues and organs. Such TE strategies can be substantially enabled by emerging biofabrication and bioprinting strategies, and in particular the use of cellular aggregates, microtissues and organoids as 'building blocks' for the development of larger tissues and/or organ precursors. Here, the application of such biological building blocks for the engineering of musculoskeletal tissues, from vascularised bone to zonally organised articular cartilage, will be reviewed. The importance of first scaling-down to later scale-up will be discussed, as this is viewed as a key component of engineering functional grafts using cellular aggregates or microtissues. In the context of engineering anatomically accurate tissues of scale suitable for tissue engineering and regenerative medicine applications, novel bioprinting modalities and their application in controlling the process by which cellular aggregates or microtissues fuse and self-organise will be reviewed. Throughout the paper, we will highlight some of the key challenges facing this emerging field. STATEMENT OF SIGNIFICANCE: The field of bioprinting has grown substantially in recent years, but despite the hype and excitement it has generated, there are relatively few examples of bioprinting strategies producing implants with superior regenerative potential to that achievable with more traditional tissue engineering approaches. This paper provides an up-to-date review of emerging biofabrication and bioprinting strategies which use cellular aggregates and microtissues as 'building blocks' for the development of larger musculoskeletal tissues and/or organ precursors - a field of research that can potentially enable functional regeneration of damaged and diseased tissues. The application of cellular aggregates and microtissues for the engineering of musculoskeletal tissues, from vascularised bone to zonally organised articular cartilage, will be reviewed. In the context of engineering anatomically accurate tissues of scale, novel bioprinting modalities and their application in controlling the process by which cellular aggregates or microtissues self-organise is addressed, as well as key challenges facing this emerging field.

Force sensors for measuring microenvironmental forces during mesenchymal condensation

Mechanical forces are an essential element to early tissue formation. However, few techniques exist that can quantify the mechanical microenvironment present within cell-dense neotissues and organoid structures. Here is a versatile approach to measure microscale, cellular forces during mesenchymal condensation using specially tailored, hyper-compliant microparticles (HCMPs). Through monitoring of HCMP deformation over both space and time, measurements of the mechanical forces that cells exert, and have exerted on them, during tissue formation are acquired. The current study uses this technology to track changes in the mechanical microenvironment as mesenchymal stem cells self-assemble into spheroids and condense into cohesive units. An array analysis approach, using a high-content imaging system, shows that cells exert a wide range of tensile and compressive forces during the first few hours of self-assembly, followed by a period of relative equilibrium. Cellular interactions with HCMPs are further examined by applying collagen coating, which allows for increased tensile forces to be exerted compared to non-coated HCMPs. Importantly, the hyper-compliant nature of our force sensors allows for increased precision over less compliant versions of the same particle. This sensitivity resolves small changes in the microenvironment even at the earliest stages of development and morphogenesis. The overall experimental platform provides a versatile means for measuring direct and indirect spatiotemporal forces in cell-dense biological systems.

Rat multicellular 3D liver microtissues to explore TGF-β1 induced effects

Chronic liver damage can lead to fibrosis, encompassing hepatocellular injury, activation of Kupffer cells (KC), and activation of hepatic stellate cells (HSC). Inflammation and TGF-β1 are known mediators in the liver fibrosis adverse outcome pathway (AOP). The aim of this project was to develop a suitable rodent cell culture model for the investigation of key events involved in the development of liver fibrosis, specifically the responses to pathophysiological stimuli such as TGF-β1 and LPS-triggered inflammation. We optimized a single step protocol to purify rat primary hepatocytes (Hep), HSC and KC cells to generate 3D co-cultures based on the hanging drop method. This primary multicellular model responded to the profibrotic cytokine TGF-β1 (1 ng/mL) with signs of hepatocellular damage, inflammation and ultimately HSC activation (increase in αSMA expression). LPS elicited an inflammatory response characterized by increased expression of cytokines. 3D-monocultures comprising only Hep displayed different responses, underlying that parenchymal and non-parenchymal cells need to be present in the system to recapitulate fibrosis. The data also suggest that pre-activated HSC may reverse to a quiescent phenotype in 3D, probably due to the more physiological conditions.

Injectable osteogenic microtissues containing mesenchymal stromal cells conformally fill and repair critical-size defects

Repair of complex fractures with bone loss requires a potent, space-filling intervention to promote regeneration of bone. We present a biomaterials-based strategy combining mesenchymal stromal cells (MSC) with a chitosan-collagen matrix to form modular microtissues designed for delivery through a needle to conformally fill cavital defects. Implantation of microtissues into a calvarial defect in the mouse showed that osteogenically pre-differentiated MSC resulted in complete bridging of the cavity, while undifferentiated MSC produced mineralized tissue only in apposition to native bone. Decreasing the implant volume reduced bone regeneration, while increasing the MSC concentration also attenuated bone formation, suggesting that the cell-matrix ratio is important in achieving a robust response. Conformal filling of the defect with microtissues in a carrier gel resulted in complete healing. Taken together, these results show that modular microtissues can be used to augment the differentiated function of MSC and provide an extracellular environment that potentiates bone repair.

High-throughput scaffold-free microtissues through 3D printing

BACKGROUND

Three-dimensional (3D) cell cultures and 3D bioprinting have recently gained attention based on their multiple advantages over two-dimensional (2D) cell cultures, which have less translational potential to recapitulate human physiology. 3D scaffold supports, cell aggregate systems and hydrogels have been shown to accurately mimic native tissues and support more relevant cell-cell interactions for studying effects of drugs and bioactive agents on cells in 3D. The development of cost-effective, high-throughput and scaffold-free microtissue assays remains challenging. In the present study, consumer grade 3D printing was examined as a fabrication method for creation of high-throughput scaffold-free 3D spheroidal microtissues.

RESULTS

Consumer grade 3D printing was capable of forming 96-well cell culture inserts to create scaffold-free microtissues in liquid suspensions. The inserts were seeded with human glioblastoma, placental-derived mesenchymal stem cells, and intestinal smooth muscle cells. These inserts allowed for consistent formation of cell density-controllable microtissues that permit screening of bioactive agents.

CONCLUSION

A variety of different cell types, co-cultures, and drugs may be evaluated with this 3D printed microtissue insert. It is suggested that the microtissue inserts may benefit 3D cell culture researchers as an economical assay solution with applications in pharmaceuticals, disease modeling, and tissue-engineering.

Cellular self-assembly into 3D microtissues enhances the angiogenic activity and functional neovascularization capacity of human cardiopoietic stem cells

While cell therapy has been proposed as next-generation therapy to treat the diseased heart, current strategies display only limited clinical efficacy. Besides the ongoing quest for the ideal cell type, in particular the very low retention rate of single-cell (SC) suspensions after delivery remains a major problem. To improve cellular retention, cellular self-assembly into 3D microtissues (MTs) prior to transplantation has emerged as an encouraging alternative. Importantly, 3D-MTs have also been reported to enhance the angiogenic activity and neovascularization potential of stem cells. Therefore, here using the chorioallantoic membrane (CAM) assay we comprehensively evaluate the impact of cell format (SCs versus 3D-MTs) on the angiogenic potential of human cardiopoietic stem cells, a promising second-generation cell type for cardiac repair. Biodegradable collagen scaffolds were seeded with human cardiopoietic stem cells, either as SCs or as 3D-MTs generated by using a modified hanging drop method. Thereafter, seeded scaffolds were placed on the CAM of living chicken embryos and analyzed for their perfusion capacity in vivo using magnetic resonance imaging assessment which was then linked to a longitudinal histomorphometric ex vivo analysis comprising blood vessel density and characteristics such as shape and size. Cellular self-assembly into 3D-MTs led to a significant increase of vessel density mainly driven by a higher number of neo-capillary formation. In contrast, SC-seeded scaffolds displayed a higher frequency of larger neo-vessels resulting in an overall 1.76-fold higher total vessel area (TVA). Importantly, despite that larger TVA in SC-seeded group, the mean perfusion capacity (MPC) was comparable between groups, therefore suggesting functional superiority together with an enhanced perfusion efficacy of the neo-vessels in 3D-MT-seeded scaffolds. This was further underlined by a 1.64-fold higher perfusion ratio when relating MPC to TVA. Our study shows that cellular self-assembly of human cardiopoietic stem cells into 3D-MTs substantially enhances their overall angiogenic potential and their functional neovascularization capacity. Hence, the concept of 3D-MTs may be considered to increase the therapeutic efficacy of future cell therapy concepts.

3D breast cancer microtissue reveals the role of tumor microenvironment on the transport and efficacy of free-doxorubicin in vitro

The use of 3D cancer models will have both ethical and economic impact in drug screening and development, to promote the reduction of the animals employed in preclinical studies. Nevertheless, to be effective, such cancer surrogates must preserve the physiological relevance of the in vivo models in order to provide realistic information on drugs' efficacy. To figure out the role of the architecture and composition of 3D cancer models on their tumor-mimicking capability, here we studied the efficacy of doxorubicin (DOX), a well-known anticancer molecule in two different 3D cancer models: our 3D breast cancer microtissue (3D-μTP) versus the golden standard represented by spheroid model (sph). Both models were obtained by using cancer associated fibroblast (CAF) and breast cancer cells (MCF-7) as cellular component. Unlike spheroid model, 3D-μTP was engineered in order to induce the production of endogenous extracellular matrix by CAF. 3D-μTP have been compared to spheroid in mono- (MCF-7 alone) and co-culture (MCF-7/CAF), after the treatment with DOX in order to study cytotoxicity effect, diffusional transport and expression of proteins related to cancer progression. Compared to the spheroid model, 3D-μTP showed higher diffusion coefficient of DOX and lower cell viability. Also, the expression of some tumoral biomarkers related to cell junctions were different in the two models.

STATEMENTS OF SIGNIFICANCE

Cancer biology has made progress in unraveling the mechanism of cancer progression, anyway the most of the results are still obtained by 2D cell cultures or animal models, that do not faithfully copycat the tumor microenvironment. The lack of correlation between preclinical models and in vivo organisms negatively influences the clinical efficacy of chemotherapeutic drugs. Consequently, even if a huge amount of new drugs has been developed in the last decades, still people are dying because of cancer. Pharmaceutical companies are interested in 3D tumor model as valid alternative in drug screening in preclinical studies. However, a 3D tumor model that completely mimics tumor heterogeneity is still far to achieve. In our work we compare 3D human breast cancer microtissues and spheroids in terms of response to doxorubicin and drug diffusion. We believe that our results are interesting because they highlight the potential role of the proposed tumor model in the attempts to improve efficacy tests.

Wharton's jelly-derived mesenchymal cells as a new source for the generation of microtissues for tissue engineering applications

Microtissues (MT) are currently considered as a promising alternative for the fabrication of natural, 3D biomimetic functional units for the construction of bio-artificial substitutes by tissue engineering (TE). The aim of this study was to evaluate the possibility of generating mesenchymal cell-based MT using human umbilical cord Wharton's jelly stromal cells (WJSC-MT). MT were generated using agarose microchips and evaluated ex vivo during 28 days. Fibroblasts MT (FIB-MT) were used as control. Morphometry, cell viability and metabolism, MT-formation process and ECM synthesis were assessed by phase-contrast microscopy, functional biochemical assays, and histological analyses. Morphometry revealed a time-course compaction process in both MT, but WJSC-MT resulted to be larger than FIB-MT in all days analyzed. Cell viability and functionality evaluation demonstrated that both MT were composed by viable and metabolically active cells, especially the WJSC during 4-21 days ex vivo. Histology showed that WJSC acquired a peripheral pattern and synthesized an extracellular matrix-rich core over the time, what differed from the homogeneous pattern observed in FIB-MT. This study demonstrates the possibility of using WJSC to create MT containing viable and functional cells and abundant extracellular matrix. We hypothesize that WJSC-MT could be a promising alternative in TE protocols. However, future cell differentiation and in vivo studies are still needed to demonstrate the potential usefulness of WJSC-MT in regenerative medicine.

Comparison of biophysical properties characterized for microtissues cultured using microencapsulation and liquid crystal based 3D cell culture techniques

Growing three dimensional (3D) cells is an emerging research in tissue engineering. Biophysical properties of the 3D cells regulate the cells growth, drug diffusion dynamics and gene expressions. Scaffold based or scaffoldless techniques for 3D cell cultures are rarely being compared in terms of the physical features of the microtissues produced. The biophysical properties of the microtissues cultured using scaffold based microencapsulation by flicking and scaffoldless liquid crystal (LC) based techniques were characterized. Flicking technique produced high yield and highly reproducible microtissues of keratinocyte cell lines in alginate microcapsules at approximately 350 ± 12 pieces per culture. However, microtissues grown on the LC substrates yielded at lower quantity of 58 ± 21 pieces per culture. The sizes of the microtissues produced using alginate microcapsules and LC substrates were 250 ± 25 μm and 141 ± 70 μm, respectively. In both techniques, cells remodeled into microtissues via different growth phases and showed good integrity of cells in field-emission scanning microscopy (FE-SEM). Microencapsulation packed the cells in alginate scaffolds of polysaccharides with limited spaces for motility. Whereas, LC substrates allowed the cells to migrate and self-stacking into multilayered structures as revealed by the nuclei stainings. The cells cultured using both techniques were found viable based on the live and dead cell stainings. Stained histological sections showed that both techniques produced cell models that closely replicate the intrinsic physiological conditions. Alginate microcapsulation and LC based techniques produced microtissues containing similar bio-macromolecules but they did not alter the main absorption bands of microtissues as revealed by the Fourier transform infrared spectroscopy. Cell growth, structural organization, morphology and surface structures for 3D microtissues cultured using both techniques appeared to be different and might be suitable for different applications.

L-mimosine and hypoxia enhance angiopoietin-like 4 production involving hypoxia-inducible factor-1alpha: Insights from monolayer and spheroid cultures of dental pulp-derived cells and tooth slice cultures

OBJECTIVE

Angiopoietin-like 4 (Angptl4) is an angiogenesis modulating signaling factor and as such involved in blood vessel formation but also in hard tissue resorption. Here we hypothesized that the hypoxia mimetic agent L-mimosine (L-MIM) and hypoxia stimulate the production of Angptl4 in the dental pulp.

MATERIAL AND METHODS

Monolayer and spheroid cultures of primary human dental pulp-derived cells (DPC) were treated with L-MIM or hypoxia. Furthermore, tooth slice cultures were performed. The production of Angptl4 was assessed at mRNA and protein levels using reverse transcription qPCR and immunoassays, respectively. To assess the involvement of hypoxia inducible factor (HIF)-1α (HIF-1signaling, inhibitor studies with echinomycin and Western Blot analysis for HIF-1α were performed in DPC monolayer cultures.(HIF-1 RESULTS: L-MIM and hypoxia increased production of Angptl4 at mRNA and protein levels in monolayer cultures of DPC. The increase of Angptl4 was paralleled by an increase of HIF-1α and inhibited by echinomycin. Angptl4 protein levels were also elevated in spheroid cultures. In tooth slice cultures, the pulp tissue expressed and released Angptl4 under normoxic and hypoxic conditions and in the presence of L-MIM. There was a trend for an increase in Angptl4 mRNA levels and a trend for a decrease in the protein levels of the supernatants.

CONCLUSIONS

Our results suggest that the hypoxia mimetic agent L-MIM and hypoxia can increase Angptl4 production in DPC involving HIF-1α. However, the increase in the cell culture supernatants does not translate in an increased release in tooth slice organ cultures.

Quick and easy microfabrication of T-shaped cantilevers to generate arrays of microtissues

Over the past decade, a major effort was made to miniaturize engineered tissues, as to further improve the throughput of such approach. Most existing methods for generating microtissues thus rely on T-shaped cantilevers made by soft lithography and based on the use of negative SU-8 photoresist. However, photopatterning T-shaped microstructures with these negative photoresists is fastidious and time-consuming. Here we introduce a novel method to quickly generate T-shaped cantilevers dedicated to generation of cellular microtissues, based on the use of positive photoresist. With only two layers of photoresist and one photomask, we were able to fabricate arrays of microwells in less than 3 h, each containing two T-shaped cantilevers presenting either a rectangular or a circular geometry. As a proof of concept, these arrays were then replicated in poly(dimethylsiloxane) and microtissues composed of NIH 3T3 fibroblasts encapsulated in collagen I were generated, while the two cantilevers simultaneously constrain and report forces generated by the microtissues. Immunostainings showed longitudinally aligned and elongated fibroblasts over the whole microtissue after 8 days of culture. The method described here opens the potential to quick prototyping platforms for high-throughput, low-volume screening applications.

Bottom-up assembly of salivary gland microtissues for assessing myoepithelial cell function

Myoepithelial cells are flat, stellate cells present in exocrine tissues including the salivary glands. While myoepithelial cells have been studied extensively in mammary and lacrimal gland tissues, less is known of the function of myoepithelial cells derived from human salivary glands. Several groups have isolated tumorigenic myoepithelial cells from cancer specimens, however, only one report has demonstrated isolation of normal human salivary myoepithelial cells needed for use in salivary gland tissue engineering applications. Establishing a functional organoid model consisting of myoepithelial and secretory acinar cells is therefore necessary for understanding the coordinated action of these two cell types in unidirectional fluid secretion. Here, we developed a bottom-up approach for generating salivary gland microtissues using primary human salivary myoepithelial cells (hSMECs) and stem/progenitor cells (hS/PCs) isolated from normal salivary gland tissues. Phenotypic characterization of isolated hSMECs confirmed that a myoepithelial cell phenotype consistent with that from other exocrine tissues was maintained over multiple passages of culture. Additionally, hSMECs secreted basement membrane proteins, expressed adrenergic and cholinergic neurotransmitter receptors, and released intracellular calcium [Ca²⁺_i] in response to parasympathetic agonists. In a collagen I contractility assay, activation of contractile machinery was observed in isolated hSMECs treated with parasympathetic agonists. Recombination of hSMECs with assembled hS/PC spheroids in a microwell system was used to create microtissues resembling secretory complexes of the salivary gland. We conclude that the engineered salivary gland microtissue complexes provide a physiologically relevant model for both mechanistic studies and as a building block for the successful engineering of the salivary gland for restoration of salivary function in patients suffering from hyposalivation.

L-mimosine and hypoxia can increase angiogenin production in dental pulp-derived cells

Background

Angiogenin is a key molecule in the healing process which has been successfully applied in the field of regenerative medicine. The role of angiogenin in dental pulp regeneration is unclear. Here we aimed to reveal the impact of the hypoxia mimetic agent L-mimosine (L-MIM) and hypoxia on angiogenin in the dental pulp.

Methods

Human dental pulp-derived cells (DPC) were cultured in monolayer and spheroid cultures and treated with L-MIM or hypoxia. In addition, tooth slice organ cultures were applied to mimic the pulp-dentin complex. We measured angiogenin mRNA and protein levels using qPCR and ELISA, respectively. Inhibitor studies with echinomycin were performed to reveal the role of hypoxia-inducible factor (HIF)-1 signaling.

Results

Both, L-MIM and hypoxia increased the production of angiogenin at the protein level in monolayer cultures of DPC, while the increase at the mRNA level did not reach the level of significance. The increase of angiogenin in response to treatment with L-MIM or hypoxia was reduced by echinomycin. In spheroid cultures, L-MIM increased angiogenin at protein levels while the effect of hypoxia was not significant. Angiogenin was also expressed and released in tooth slice organ cultures under normoxic and hypoxic conditions and in the presence of L-MIM.

Conclusions

L-MIM and hypoxia modulate production of angiogenin via HIF-1 differentially and the response depends on the culture model. Given the role of angiogenin in regeneration the here presented results are of high relevance for pre-conditioning approaches for cell therapy and tissue engineering in the field of regenerative endodontics.