Generation of hiPSC-Derived Functional Dopaminergic Neurons in Alginate-Based 3D Culture

Dopamine‑iron homeostasis interaction rescues mitochondrial fitness in Parkinson's disease

Imbalances of iron and dopamine metabolism along with mitochondrial dysfunction have been linked to the pathogenesis of Parkinson's disease (PD). We have previously suggested a direct link between iron homeostasis and dopamine metabolism, as dopamine can increase cellular uptake of iron into macrophages thereby promoting oxidative stress responses. In this study, we investigated the interplay between iron, dopamine, and mitochondrial activity in neuroblastoma SH-SY5Y cells and human induced pluripotent stem cell (hiPSC)-derived dopaminergic neurons differentiated from a healthy control and a PD patient with a mutation in the α-synuclein (SNCA) gene. In SH-SY5Y cells, dopamine treatment resulted in increased expression of the transmembrane iron transporters transferrin receptor 1 (TFR1), ferroportin (FPN), and mitoferrin2 (MFRN2) and intracellular iron accumulation, suggesting that dopamine may promote iron uptake. Furthermore, dopamine supplementation led to reduced mitochondrial fitness including decreased mitochondrial respiration, increased cytochrome c control efficiency, reduced mtDNA copy number and citrate synthase activity, increased oxidative stress and impaired aconitase activity. In dopaminergic neurons derived from a healthy control individual, dopamine showed comparable effects as observed in SH-SY5Y cells. The hiPSC-derived PD neurons harboring an endogenous SNCA mutation demonstrated altered mitochondrial iron homeostasis, reduced mitochondrial capacity along with increased oxidative stress and alterations of tricarboxylic acid cycle linked metabolic pathways compared with control neurons. Importantly, dopamine treatment of PD neurons promoted a rescue effect by increasing mitochondrial respiration, activating antioxidant stress response, and normalizing altered metabolite levels linked to mitochondrial function. These observations provide evidence that dopamine affects iron homeostasis, intracellular stress responses and mitochondrial function in healthy cells, while dopamine supplementation can restore the disturbed regulatory network in PD cells.

SinCMat: A single-cell-based method for predicting functional maturation transcription factors

A major goal of regenerative medicine is to generate tissue-specific mature and functional cells. However, current cell engineering protocols are still unable to systematically produce fully mature functional cells. While existing computational approaches aim at predicting transcription factors (TFs) for cell differentiation/reprogramming, no method currently exists that specifically considers functional cell maturation processes. To address this challenge, here, we develop SinCMat, a single-cell RNA sequencing (RNA-seq)-based computational method for predicting cell maturation TFs. Based on a model of cell maturation, SinCMat identifies pairs of identity TFs and signal-dependent TFs that co-target genes driving functional maturation. A large-scale application of SinCMat to the Mouse Cell Atlas and Tabula Sapiens accurately recapitulates known maturation TFs and predicts novel candidates. We expect SinCMat to be an important resource, complementary to preexisting computational methods, for studies aiming at producing functionally mature cells.

Intracellular delivery of Parkin-RING0-based fragments corrects Parkin-induced mitochondrial dysfunction through interaction with SLP-2

BACKGROUND

Loss-of-function mutations in the PRKN gene, encoding Parkin, are the most common cause of autosomal recessive Parkinson's disease (PD). We have previously identified mitoch ondrial Stomatin-like protein 2 (SLP-2), which functions in the assembly of respiratory chain proteins, as a Parkin-binding protein. Selective knockdown of either Parkin or SLP-2 led to reduced mitochondrial and neuronal function in neuronal cells and Drosophila, where a double knockdown led to a further worsening of Parkin-deficiency phenotypes. Here, we investigated the minimal Parkin region involved in the Parkin-SLP-2 interaction and explored the ability of Parkin-fragments and peptides from this minimal region to restore mitochondrial function.

METHODS

In fibroblasts, human induced pluripotent stem cell (hiPSC)-derived neurons, and neuroblastoma cells the interaction between Parkin and SLP-2 was investigated, and the Parkin domain responsible for the binding to SLP-2 was mapped. High resolution respirometry, immunofluorescence analysis and live imaging were used to analyze mitochondrial function.

RESULTS

Using a proximity ligation assay, we quantitatively assessed the Parkin-SLP-2 interaction in skin fibroblasts and hiPSC-derived neurons. When PD-associated PRKN mutations were present, we detected a significantly reduced interaction between the two proteins. We found a preferential binding of SLP-2 to the N-terminal part of Parkin, with a highest affinity for the RING0 domain. Computational modeling based on the crystal structure of Parkin protein predicted several potential binding sites for SLP-2 within the Parkin RING0 domain. Amongst these, three binding sites were observed to overlap with natural PD-causing missense mutations, which we demonstrated interfere substantially with the binding of Parkin to SLP-2. Finally, delivery of the isolated Parkin RING0 domain and a Parkin mini-peptide, conjugated to cell-permeant and mitochondrial transporters, rescued compromised mitochondrial function in Parkin-deficient neuroblastoma cells and hiPSC-derived neurons with endogenous, disease causing PRKN mutations.

CONCLUSIONS

These findings place further emphasis on the importance of the protein-protein interaction between Parkin and SLP-2 for the maintenance of optimal mitochondrial function. The possibility of restoring an abolished binding to SLP-2 by delivering the Parkin RING0 domain or the Parkin mini-peptide involved in this specific protein-protein interaction into cells might represent a novel organelle-specific therapeutic approach for correcting mitochondrial dysfunction in Parkin-linked PD.

A novel perfusion bioreactor promotes the expansion of pluripotent stem cells in a 3D-bioprinted tissue chamber

While the field of tissue engineering has progressed rapidly with the advent of 3D bioprinting and human induced pluripotent stem cells (hiPSCs), impact is limited by a lack of functional, thick tissues. One way around this limitation is to 3D bioprint tissues laden with hiPSCs. In this way, the iPSCs can proliferate to populate the thick tissue mass prior to parenchymal cell specification. Here we design a perfusion bioreactor for an hiPSC-laden, 3D-bioprinted chamber with the goal of proliferating the hiPSCs throughout the structure prior to differentiation to generate a thick tissue model. The bioreactor, fabricated with digital light projection, was optimized to perfuse the interior of the hydrogel chamber without leaks and to provide fluid flow around the exterior as well, maximizing nutrient delivery throughout the chamber wall. After 7 days of culture, we found that intermittent perfusion (15 s every 15 min) at 3 ml min-1provides a 1.9-fold increase in the density of stem cell colonies in the engineered tissue relative to analogous chambers cultured under static conditions. We also observed a more uniform distribution of colonies within the tissue wall of perfused structures relative to static controls, reflecting a homogeneous distribution of nutrients from the culture media. hiPSCs remained pluripotent and proliferative with application of fluid flow, which generated wall shear stresses averaging ∼1.0 dyn cm-2. Overall, these promising outcomes following perfusion of a stem cell-laden hydrogel support the production of multiple tissue types with improved thickness, and therefore increased function and utility.

Long-termin vitroculture of 3D brain tissue model based on chitosan thermogel

Methods for studying brain function and disease heavily rely onin vivoanimal models,ex-vivotissue slices, and 2D cell culture platforms. These methods all have limitations that significantly impact the clinical translatability of results. Consequently, models able to better recapitulate some aspects ofin vivohuman brain are needed as additional preclinical tools. In this context, 3D hydrogel-basedin vitromodels of the brain are considered promising tools. To create a 3D brain-on-a-chip model, a hydrogel capable of sustaining neuronal maturation over extended culture periods is required. Among biopolymeric hydrogels, chitosan-β-glycerophosphate (CHITO-β-GP) thermogels have demonstrated their versatility and applicability in the biomedical field over the years. In this study, we investigated the ability of this thermogel to encapsulate neuronal cells and support the functional maturation of a 3D neuronal network in long-term cultures. To the best of our knowledge, we demonstrated for the first time that CHITO-β-GP thermogel possesses optimal characteristics for promoting neuronal growth and the development of an electrophysiologically functional neuronal network derived from both primary rat neurons and neurons differentiated from human induced pluripotent stem cells (h-iPSCs) co-cultured with astrocytes. Specifically, two different formulations were firstly characterized by rheological, mechanical and injectability tests. Primary nervous cells and neurons differentiated from h-iPSCs were embedded into the two thermogel formulations. The 3D cultures were then deeply characterized by immunocytochemistry, confocal microscopy, and electrophysiological recordings, employing both 2D and 3D micro-electrode arrays. The thermogels supported the long-term culture of neuronal networks for up to 100 d. In conclusion, CHITO-β-GP thermogels exhibit excellent mechanical properties, stability over time under culture conditions, and bioactivity toward nervous cells. Therefore, they are excellent candidates as artificial extracellular matrices in brain-on-a-chip models, with applications in neurodegenerative disease modeling, drug screening, and neurotoxicity evaluation.

Organ-Chips Enhance the Maturation of Human iPSC-Derived Dopamine Neurons

While cells in the human body function in an environment where the blood supply constantly delivers nutrients and removes waste, cells in conventional tissue culture well platforms are grown with a static pool of media above them and often lack maturity, limiting their utility to study cell biology in health and disease. In contrast, organ-chip microfluidic systems allow the growth of cells under constant flow, more akin to the in vivo situation. Here, we differentiated human induced pluripotent stem cells into dopamine neurons and assessed cellular properties in conventional multi-well cultures and organ-chips. We show that organ-chip cultures, compared to multi-well cultures, provide an overall greater proportion and homogeneity of dopaminergic neurons as well as increased levels of maturation markers. These organ-chips are an ideal platform to study mature dopamine neurons to better understand their biology in health and ultimately in neurological disorders.

OCT4 protein and gene expression analysis in the differentiation of spermatogonia stem cells into neurons by immunohistochemistry, immunocytochemistry, and bioinformatics analysis

BACKGROUND

Spermatogonia Stem Cells (SSCs) are potential candidates for reprogramming and regeneration. Recent studies have revealed that differentiated cells can be reverted to pluripotent by overexpressing a set of pluripotent transcription factors. OCT4 (encoded by pou5f1), a POU transcription factor family member, is essential to the potential that controls pluripotency, and it is widely expressed in pluripotent stem cells, although it decreased or suppressed after differentiation.

METHODS

In this investigated research, we examined the OCT4 expression during the differentiation of SSCs into neurons (involving four stages in the following order: SSCs in vivo and in-vitro, embryonic Stem Cell-like (ES-like), Embryonic Bodies (EBs), and finally Neurons) by Immunocytochemistry (ICC), Immunohistochemistry (IMH), and Fluidigm Real-Time polymerase chain reaction. In addition, we use some databases like STRING to predict protein-protein interaction and enrichment analysis.

RESULTS

We evaluated the expression of OCT4 in this process, and we observed that it is expressed in SSCs, ES-like, and EBs during the differentiation of spermatogonia stem cells into adult neurons. We show that by adding RA to EBs, the expression of OCT4 is reduced and is not expressed in the neuron cells. We observed that the expression of OCT4 is linked and interacts with the differentiation of spermatogonia stem cells into neuron cells, and it has been shown to be biologically functional, like stem cell maintenance and somatic cell reprogramming.

CONCLUSION

Our findings can help us better understand the process of differentiation of spermatogonia stem cells into neurons, and it can be effective in finding new and more efficient treatments for neurogenesis and repair of neurons. We examined the OCT4 expression during the differentiation of SSCs into neurons (involving four stages in the following order: SSCs in vivo and in-vitro, embryonic Stem Cell-like (ES-like), Embryonic Bodies (EBs), and finally Neurons) by Immunocytochemistry (ICC), Immunohistochemistry (IMH), and Fluidigm Real-Time polymerase chain reaction. In addition, we use some databases like STRING to predict protein-protein interaction and enrichment analysis. We evaluated the expression of OCT4 in this process, and we observed that it is expressed in SSCs, ES-like, and EBs during the differentiation of spermatogonia stem cells into adult neurons. We show that by adding RA to EBs, the expression of OCT4 is reduced and is not expressed in the neuron cells. We observed that the expression of OCT4 is linked and interacts with the differentiation of spermatogonia stem cells into neuron cells, and it has been shown to be biologically functional, like stem cell maintenance and somatic cell reprogramming.

Xeno-free culture and proliferation of hPSCs on 2D biomaterials

Human pluripotent stem cells (human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs)) have unlimited proliferative potential, whereas adult stem cells such as bone marrow-derived stem cells and adipose-derived stem cells have problems with aging. When hPSCs are intended to be cultured on feeder-free or xeno-free conditions without utilizing mouse embryonic fibroblasts or human fibroblasts, they cannot be cultured on conventional tissue culture polystyrene dishes, as adult stem cells can be cultured but should be cultivated on material surfaces grafted or coated with (a) natural or recombinant extracellular matrix (ECM) proteins, (b) ECM protein-derived peptides and specific synthetic polymer surfaces in xeno-free and/or chemically defined conditions. This review describes current developing cell culture biomaterials for the proliferation of hPSCs while maintaining the pluripotency and differentiation potential of the cells into 3 germ layers. Biomaterials for the cultivation of hPSCs without utilizing a feeder layer are essential to decrease the risk of xenogenic molecules, which contributes to the potential clinical usage of hPSCs. ECM proteins such as human recombinant vitronectin, laminin-511 and laminin-521 have been utilized instead of Matrigel for the feeder-free cultivation of hPSCs. The following biomaterials are also discussed for hPSC cultivation: (a) decellularized ECM, (b) peptide-grafted biomaterials derived from ECM proteins, (c) recombinant E-cadherin-coated surface, (d) polysaccharide-immobilized surface, (e) synthetic polymer surfaces with and without bioactive sites, (f) thermoresponsive polymer surfaces with and without bioactive sites, and (g) synthetic microfibrous scaffolds.

Susceptibility of Ovine Bone Marrow-Derived Mesenchymal Stem Cell Spheroids to Scrapie Prion Infection

In neurodegenerative diseases, including prion diseases, cellular in vitro models appear as fundamental tools for the study of pathogenic mechanisms and potential therapeutic compounds. Two-dimensional (2D) monolayer cell culture systems are the most used cell-based assays, but these platforms are not able to reproduce the microenvironment of in vivo cells. This limitation can be surpassed using three-dimensional (3D) culture systems such as spheroids that more effectively mimic in vivo cell interactions. Herein, we evaluated the effect of scrapie prion infection in monolayer-cultured ovine bone marrow-derived mesenchymal stem cells (oBM-MSCs) and oBM-MSC-derived spheroids in growth and neurogenic conditions, analyzing their cell viability and their ability to maintain prion infection. An MTT assay was performed in oBM-MSCs and spheroids subjected to three conditions: inoculated with brain homogenate from scrapie-infected sheep, inoculated with brain homogenate from healthy sheep, and non-inoculated controls. The 3D conditions improved the cell viability in most cases, although in scrapie-infected spheroids in growth conditions, a decrease in cell viability was observed. The levels of pathological prion protein (PrPSc) in scrapie-infected oBM-MSCs and spheroids were measured by ELISA. In neurogenic conditions, monolayer cells and spheroids maintained the levels of PrPSc over time. In growth conditions, however, oBM-MSCs showed decreasing levels of PrPSc throughout time, whereas spheroids were able to maintain stable PrPSc levels. The presence of PrPSc in spheroids was also confirmed by immunocytochemistry. Altogether, these results show that a 3D culture microenvironment improves the permissiveness of oBM-MSCs to scrapie infection in growth conditions and maintains the infection ability in neurogenic conditions, making this model of potential use for prion studies.

Message in a Scaffold: Natural Biomaterials for Three-Dimensional (3D) Bioprinting of Human Brain Organoids

Brain organoids are invaluable tools for pathophysiological studies or drug screening, but there are still challenges to overcome in making them more reproducible and relevant. Recent advances in three-dimensional (3D) bioprinting of human neural organoids is an emerging approach that may overcome the limitations of self-organized organoids. It requires the development of optimal hydrogels, and a wealth of research has improved our knowledge about biomaterials both in terms of their intrinsic properties and their relevance on 3D culture of brain cells and tissue. Although biomaterials are rarely biologically neutral, few articles have reviewed their roles on neural cells. We here review the current knowledge on unmodified biomaterials amenable to support 3D bioprinting of neural organoids with a particular interest in their impact on cell homeostasis. Alginate is a particularly suitable bioink base for cell encapsulation. Gelatine is a valuable helper agent for 3D bioprinting due to its viscosity. Collagen, fibrin, hyaluronic acid and laminin provide biological support to adhesion, motility, differentiation or synaptogenesis and optimize the 3D culture of neural cells. Optimization of specialized hydrogels to direct differentiation of stem cells together with an increased resolution in phenotype analysis will further extend the spectrum of possible bioprinted brain disease models.

Biomaterial-based strategies for in vitro neural models

In vitro models have been used as a complementary tool to animal studies in understanding the nervous system's physiological mechanisms and pathological disorders, while also serving as platforms to evaluate the safety and efficiency of therapeutic candidates. Following recent advances in materials science, micro- and nanofabrication techniques and cell culture systems, in vitro technologies have been rapidly gaining the potential to bridge the gap between animal and clinical studies by providing more sophisticated models that recapitulate key aspects of the structure, biochemistry, biomechanics, and functions of human tissues. This was made possible, in large part, by the development of biomaterials that provide cells with physicochemical features that closely mimic the cellular microenvironment of native tissues. Due to the well-known material-driven cellular response and the importance of mimicking the environment of the target tissue, the selection of optimal biomaterials represents an important early step in the design of biomimetic systems to investigate brain structures and functions. This review provides a comprehensive compendium of commonly used biomaterials as well as the different fabrication techniques employed for the design of neural tissue models. Furthermore, the authors discuss the main parameters that need to be considered to develop functional platforms not only for the study of brain physiological functions and pathological processes but also for drug discovery/development and the optimization of biomaterials for neural tissue engineering.

Fibronectin-Enriched Biomaterials, Biofunctionalization, and Proactivity: A Review

Modern innovation in reconstructive medicine implies the proposition of material-based strategies suitable for tissue repair and regeneration. The development of such systems necessitates the design of advanced materials and the control of their interactions with their surrounding cellular and molecular microenvironments. Biomaterials must actively engage cellular matter to direct and modulate biological responses at implant sites and beyond. Indeed, it is essential that a true dialogue exists between the implanted device and the cells. Biomaterial engineering implies the knowledge and control of cell fate considering the globality of the adhesion process, from initial cell attachment to differentiation. The extracellular matrix (ECM) represents a complex microenvironment able to meet these essential needs to establish a relationship between the material and the contacting cells. The ECM exhibits specific physical, chemical, and biochemical characteristics. Considering the complexity, heterogeneity, and versatility of ECM actors, fibronectin (Fn) has emerged among the ECM protagonists as the most pertinent representative key actor. The following review focuses on and synthesizes the research supporting the potential to use Fn in biomaterial functionalization to mimic the ECM and enhance cell–material interactions.