Enhancement of engineered cardiac tissues by promotion of hiPSC-cardiomyocyte proliferation

Background/Introduction

Cardiac tissue engineering is a promising strategy to generate human cardiac tissues for modelling cardiac diseases, screening for therapeutic drugs, and repairing the injured heart. Yet, several issues remain to be resolved including the generation of tissues with high cardiomyocyte density.

Purpose

Determining the effects of the induction of human-induced pluripotent stem cell-derived (hiPSC) cardiomyocyte proliferation post-fabrication.

Methods

hiPSCs were differentiated into cardiomyocytes, embedded with or without CHIR990121 at three concentrations in a collagen pre-gel, and cast. The engineered cardiac tissues were then cultured in the absence or presence of CHIR99021 for up to 35 days. Hydrogels and engineered cardiac tissues were analysed utilizing rheology and assays to determine viability, proliferation, calcium flow, and contractility.

Results

Here, we show that the integration of CHIR99021 in collagen I hydrogels promotes proliferation of hiPSC-cardiomyocytes post-fabrication improving contractility of and calcium flow in engineered cardiac tissues. Presence of CHIR99021 has no effect on the gelation kinetic or the mechanical properties of collagen I hydrogels. Analysis of cell density and proliferation based on Ki-67 staining indicates that integration of CHIR99021 together with external CHIR99021 stimulation increases hiPSC-cardiomyocyte number by ∼2-fold within 7 days post-fabrication. Analysis of the contractility of engineered cardiac tissues after another 3 days in the absence of external CHIR99021 shows that CHIR99021-induced hiPSC-cardiomyocyte proliferation results in synchronized calcium flow, rhythmic beating, increases speed of contraction and contraction amplitude, and reduces peak-to-peak time. The CHIR99021-stimulated engineered cardiac tissues exhibited spontaneous rhythmic contractions for at least 35 days.

Conclusion

Collectively, our data demonstrate the potential of induced cardiomyocyte proliferation to enhance engineered cardiac tissues by increasing cardiomyocyte density and reducing arrhythmia.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft

Direct 3D printing of hiPSC-cardiomyocytes in collagen-based bioinks

Background

Cardiac tissue engineering is an effective strategy to generate tissues for drug testing and disease modelling as well as for cardiac repair. Tissues produced by casting show good functionality and advanced maturation, but do not replicate the native tissue architecture and hierarchy. Additive manufacturing technologies, such as 3D bioprinting, enable the generation of hierarchically structured tissues with complex geometries. This technology has been used previously to generate models of the heart. However, these approaches either showed limited tissue functionality or required a two-step procedure using a structural and a cell-laden bioink.

Purpose

Here, we aimed to develop a collagen-based bioink, which enables direct 3D-bioprinting of hiPSC-derived cardiomyocytes and supports the formation of functional cardiac tissue.

Methods

To generate cardiac tissues, a commercial pneumatic extrusion bioprinter with custom modifications to enable passive cooling of the bioink was used. Gelatin/gum arabic microparticles were obtained through complex coacervation, compacted by centrifugation and utilized as support bath. Cardiomyocytes were differentiated in 2D monolayer and expanded by CHIR99021-treatment and regular passaging. Cells were encapsulated in a rat collagen-I based bioink and printed into support bath prior to gelation. After bioink gelation at 37°C, support bath was removed, and constructs cultivated free-floating for up to 30 days.

Results

We printed ring-shaped cardiac tissues measuring 5 x 5 x 1 mm, which remained stable over the course of cultivation. First contractions were observed after three days, which increased in magnitude and synchronized across the tissue with prolonged culture. HiPSC-cardiomyocytes displayed striated sarcomeres and were responsive to pharmacological stimulation. In addition, using two distinct bioinks, multi-layered constructs were generated.

Conclusion

3D-bioprinting is a promising tool to generate engineered cardiac tissues with complex geometries and improved functionality through designed hierarchy. Our collagen-based bioink and associated printing strategy enables the fabrication of Collagen-based contractile cardiac tissues in a direct manner.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft (DFG) Contractions of printed cardiac tissue

Transcription factor TAp73 and microRNA-449 complement each other to support multiciliogenesis

Motile cilia serve vital functions in development, homeostasis, and regeneration. We recently demonstrated that TAp73 is an essential transcriptional regulator of respiratory multiciliogenesis. Here, we show that TAp73 is expressed in multiciliated cells (MCCs) of diverse tissues. Analysis of TAp73 mutant animals revealed that TAp73 regulates Foxj1, Rfx2, Rfx3, axonemal dyneins Dnali1 and Dnai1, plays a pivotal role in the generation of MCCs in male and female reproductive ducts, and contributes to fertility. However, the function of MCCs in the brain appears to be preserved despite the loss of TAp73, and robust activity of cilia-related networks is maintained in the absence of TAp73. Notably, TAp73 loss leads to distinct changes in ciliogenic microRNAs: miR34bc expression is reduced, whereas the miR449 cluster is induced in diverse multiciliated epithelia. Among different MCCs, choroid plexus (CP) epithelial cells in the brain display prominent miR449 expression, whereas brain ventricles exhibit significant increase in miR449 levels along with an increase in the activity of ciliogenic E2F4/MCIDAS circuit in TAp73 mutant animals. Conversely, E2F4 induces robust transcriptional response from miR449 genomic regions. To address whether increased miR449 levels in the brain maintain the multiciliogenesis program in the absence of TAp73, we deleted both TAp73 and miR449 in mice. Although loss of miR449 alone led to a mild ciliary defect in the CP, more pronounced ciliary defects and hydrocephalus were observed in the brain lacking both TAp73 and miR449. In contrast, miR449 loss in other MCCs failed to enhance ciliary defects associated with TAp73 loss. Together, our study shows that, in addition to the airways, TAp73 is essential for generation of MCCs in male and female reproductive ducts, whereas miR449 and TAp73 complement each other to support multiciliogenesis and CP development in the brain.