Three-dimensional (3D) cultures, so-called organoids, have emerged as an attractive tool for disease modeling and therapeutic innovations. Here, we aim to determine if boundary cap neural crest stem cells (BC) can survive and differentiate in gelatin-based 3D bioprinted bioink scaffolds in order to establish an enabling technology for the fabrication of spinal cord organoids on a chip. BC previously demonstrated the ability to support survival and differentiation of co-implanted or co-cultured cells and supported motor neuron survival in excitotoxically challenged spinal cord slice cultures. We tested different combinations of bioink and cross-linked material, analyzed the survival of BC on the surface and inside the scaffolds, and then tested if human iPSC-derived neural cells (motor neuron precursors and astrocytes) can be printed with the same protocol, which was developed for BC. We showed that this protocol is applicable for human cells. Neural differentiation was more prominent in the peripheral compared to central parts of the printed construct, presumably because of easier access to differentiation-promoting factors in the medium. These findings show that the gelatin-based and enzymatically cross-linked hydrogel is a suitable bioink for building a multicellular, bioprinted spinal cord organoid, but that further measures are still required to achieve uniform neural differentiation.

Exposure to microgravity (μg) results in a range of systemic changes in the organism, but may also have beneficial cellular effects. In a previous study we detected increased proliferation capacity and upregulation of genes related to proliferation and survival in boundary cap neural crest stem cells (BC) after MASER14 sounding rocket flight compared to ground-based controls. However, whether these changes were due to μg or hypergravity was not clarified. In the current MASER15 experiment BCs were exposed simultaneously to μg and 1 g conditions provided by an onboard centrifuge. BCs exposed to μg displayed a markedly increased proliferation capacity compared to 1 g on board controls, and genetic analysis of BCs harvested 5 h after flight revealed an upregulation, specifically in μg-exposed BCs, of Zfp462 transcription factor, a key regulator of cell pluripotency and neuronal fate. This was associated with alterations in exosome microRNA content between μg and 1 g exposed MASER15 specimens. Since the specimens from MASER14 were obtained for analysis with 1 week’s delay, we examined whether gene expression and exosome content were different compared to the current MASER15 experiments, in which specimens were harvested 5 h after flight. The overall pattern of gene expression was different and Zfp462 expression was down-regulated in MASER14 BC μg compared to directly harvested specimens (MASER15). MicroRNA exosome content was markedly altered in medium harvested with delay compared to directly collected samples. In conclusion, our analysis indicates that even short exposure to μg alters gene expression, leading to increased BC capacity for proliferation and survival, lasting for a long time after μg exposure. With delayed harvest of specimens, a situation which may occur due to special post-flight circumstances, the exosome microRNA content is modified compared to fast specimen harvest, and the direct effects from μg exposure may be partially attenuated, whereas other effects can last for a long time after return to ground conditions.

We previously demonstrated that boundary cap neural crest stem cells (BCs) induce the proliferation of beta-cells in vitro, increase survival of pancreatic islets (PIs) in vivo after transplantation, and themselves strongly increase their proliferation capacity after exposure to space conditions. Therefore, we asked if space conditions can induce the proliferation of beta-cells when PIs are alone or together with BCs in free-floating or 3D-printed form. During the MASER 15 sounding rocket experiment, half of the cells were exposed to 6 min of microgravity (µg), whereas another group of cells were kept in 1 g conditions in a centrifuge onboard. The proliferation marker EdU was added to the cells just before the rocket reached µg conditions. The morphological assessment revealed that PIs successfully survived and strongly proliferated, particularly in the free-floating condition, though the fusion of PIs hampered statistical analysis. Proliferation of beta-cells was displayed in 3D-printed islets two weeks after µg exposure, suggesting that the effects of µg may be delayed. Thus, PIs in 3D-printed scaffolds did not fuse, and this preparation is more suitable than free-floating specimens for morphological analysis in µg studies. PIs maintained their increased proliferation capacity for weeks after µg exposure, an effect that may not appear directly, but can emerge after a delay.

Translational medicine for neurodegenerative diseases can advance through the use of in vitro models incorporating human neural cells derived from patient-specific induced pluripotent stem cells (iPSCs). Previously, we investigated whether motor neuron (MN) progenitors derived from human iPSCs could differentiate to MNs within 3D-printed scaffolds. While extensive neurite arborization was observed on the scaffold surface, no neurite outgrowth occurred within the scaffold interior. Here we show the extensive growth of the neurites from iPSC-derived neural progenitors, imbedded into the gelatin scaffolds during 30 days of experimental time. We present a bioink formulation that softens the scaffold while preserving its 3D structure, thereby facilitating neurite outgrowth throughout the scaffold. MN differentiation, evidenced by extensive neurite arborization and the expression of choline acetyltransferase (ChAT) was verified in 3D images deep within the scaffold structure. Notably, the degree of MN differentiation appeared to depend on two factors: the delivery of MN differentiation factors via mesoporous silica particles (MSPs) embedded in the bioink and the method used to generate MN progenitors prior to 3D printing. We provide a detailed protocol for 3D printing human iPSC-derived MN progenitors, enabling their differentiation and survival within gelatin scaffolds. This protocol could be expanded to incorporate additional cell types, allowing the creation of more complex and standardized 3D neural tissues. Such advancements could facilitate investigations into the pathophysiology of motor neuron diseases and the development of new therapeutic strategies.

Dorsal root avulsion injuries lead to loss of sensation and to reorganization of blood vessels (BVs) in the injured area. The inability of injured sensory axons to re-enter the spinal cord results in permanent loss of sensation, and often also leads to the development of neuropathic pain. Approaches that restore connection between peripheral sensory axons and their CNS targets are thus urgently need. Previous research has shown that sensory axons from peripherally grafted human sensory neurons are able to enter the spinal cord by growing along BVs which penetrate the CNS from the spinal cord surface. In this study we analysed the distribution of BVs after avulsion injury and how their pattern is affected by implantation at the injury site of boundary cap neural crest stem cells (bNCSCs), a transient cluster of cells, which are located at the boundary between the spinal cord and peripheral system and assist the growth of sensory axons from periphery into the spinal cord during development. The superficial dorsal spinal cord vasculature was examined using intravital microscopy and intravascular BV labelling. bNCSC transplantation increased vascular volume in a non-dose responsive manner, whereas dorsal root avulsion alone did not decrease the vascular volume. To determine whether bNCSC are endowed with angiogenic properties we prepared 3D printed scaffolds, containing bNCSCs together with rings prepared from mouse aorta. We show that bNCSC do induce migration and assembly of endothelial cells in this system. These findings suggest that bNCSC transplant can promote vascularization in vivo and contribute to BV formation in 3D printed scaffolds.

Boundary cap neural crest stem cells (BCs) previously demonstrated resilience during short-term microgravity exposure. In this study, BCs were sent to the International Space Station aboard Axiom Mission 3. Owing to launch regulations and weather delays, cells remained outside controlled culture conditions longer than anticipated, exceeding expected survival limits. Three BC populations were included: naive BCs (NBC), once-flown BCs (V15), and twice-flown BCs (V1415), cultured as neurospheres or within 3D-printed scaffolds. Corresponding ground controls were maintained under matched conditions. Only V1415 cells survived in both flight and ground groups, while NBC cells survived exclusively after spaceflight. V15 cells did not survive. All surviving cells exhibited reduced proliferation, contrasting with the enhanced proliferation reported after short-term microgravity exposure. Following 1 month of post-flight expansion, surviving cells retained the capacity to differentiate into neurons and glial cells without detectable electrophysiological impairment. Space-exposed NBC cultures showed increased glial differentiation, whereas V1415 flight cultures displayed a higher neuronal proportion than ground controls. BCs cultured in 3D-printed scaffolds exhibited robust survival and significantly increased proliferation after space exposure. Exosome analysis identified miRNAs associated with enhanced proliferation in flight samples. These findings demonstrate the remarkable stress resistance, developmental plasticity, and adaptability of BCs during prolonged spaceflight conditions.