Enhancement of Subcutaneously Transplanted β Cell Survival Using 3D Stem Cell Spheroids with Proangiogenic and Prosurvival Potential

Injectable Glucose-Releasing Microgels Enhance the Survival and Therapeutic Potential of Transplanted MSCs Under Ischemic Conditions

Mesenchymal stem cell (MSC)-based therapies show potential to treat ischemic diseases owing to their versatile functions. However, sustaining MSC viability and therapeutic efficacy in ischemic tissues postengraftment remains a significant challenge. This is because, although MSCs are metabolically flexible, they fail to adapt to hypoxic conditions in the absence of glucose, leading to cell death. To overcome these issues, it is aimed to establish an injectable glucose delivery system using starch and amyloglucosidase embedded in alginate microgels. Here, starch/amyloglucosidase (S/A) microgels are engineered to continuously release glucose for seven days via enzymatic hydrolysis, thereby supporting MSC functions under ischemic conditions. In vitro tests under oxygen/glucose-deprived conditions revealed that the S/A microgels not only maintained the viability and intracellular energy but also enhanced the pro-angiogenic and immunomodulatory functions of MSCs. In vivo data further confirmed the pro-survival and pro-angiogenic effects of S/A microgels on MSCs following subcutaneous engraftment in mice. Overall, the developed S/A microgel significantly enhanced the survival and therapeutic potential of MSCs via sustained glucose delivery, highlighting its potential use in advancing MSC-based therapies for ischemic conditions.

In Vivo Imaging of Immune Rejection of MIN6 Cells Transplanted in C3H Mice

Recently, we successfully utilized noninvasive magnetic resonance and bioluminescence imaging to track MIN6 cells subcutaneously transplanted in immunocompromised nude mice for up to 64 days. In this study, we further used bioluminescence imaging to investigate the immune rejection of MIN6 cells in immunocompetent C3H mice. A total of 5 × 106 luciferase-transfected MIN6 cells were implanted into the subcutaneous space of each nude or C3H mouse. After transplantation, hypoglycemia and persistent bioluminescence signals were observed in eight of eight (100%) nude mice and five of nine (56%) C3H mice (p < 0.05). We then presensitized a group of C3H mice with C57BL/6 spleen cells just prior to transplantation (n = 14). Interestingly, none of them had hypoglycemia or persistent bioluminescence signals (p < 0.01 vs. C3H mice without presensitization). Histological examination of the grafts revealed a lack or minimal presence of insulin-positive cells in recipients without hypoglycemia and persistent bioluminescence signals. In contrast, recipients with hypoglycemia and persistent bioluminescence signals showed a significant presence of insulin-positive cells in their grafts. Our results indicate that rejection of MIN6 cells occurred in C3H mice and could be enhanced by presensitization with C57BL/6 spleen cells and that bioluminescence imaging is a useful noninvasive tool for detecting rejection of subcutaneously transplanted MIN6 cells.

Schwann cells acquire a repair phenotype after assembling into spheroids and show enhanced in vivo therapeutic potential for promoting peripheral nerve repair

The prognosis for postinjury peripheral nerve regeneration remains suboptimal. Although transplantation of exogenous Schwann cells (SCs) has been considered a promising treatment to promote nerve repair, this strategy has been hampered in practice by the limited availability of SC sources and an insufficient postengraftment cell retention rate. In this study, to address these challenges, SCs were aggregated into spheroids before being delivered to an injured rat sciatic nerve. We found that the three-dimensional aggregation of SCs induced their acquisition of a repair phenotype, as indicated by enhanced levels of c-Jun expression/activation and decreased expression of myelin sheath protein. Furthermore, our in vitro results demonstrated the superior potential of the SC spheroid-derived secretome in promoting neurite outgrowth of dorsal root ganglion neurons, enhancing the proliferation and migration of endogenous SCs, and recruiting macrophages. Moreover, transplantation of SC spheroids into rats after sciatic nerve transection effectively increased the postinjury nerve structure restoration and motor functional recovery rates, demonstrating the therapeutic potential of SC spheroids. In summary, transplantation of preassembled SC spheroids may hold great potential for enhancing the cell delivery efficiency and the resultant therapeutic outcome, thereby improving SC-based transplantation approaches for promoting peripheral nerve regeneration.

The Transplantation of 3-Dimensional Spheroids of Adipose-Derived Stem Cells Promotes Achilles Tendon Healing in Rabbits by Enhancing the Proliferation of Tenocytes and Suppressing M1 Macrophages

BACKGROUND

Tendons have limited regenerative potential, so healing of ruptured tendon tissue requires a prolonged period, and the prognosis is suboptimal. Although stem cell transplantation-based approaches show promise for accelerating tendon repair, the resultant therapeutic efficacy remains unsatisfactory.

HYPOTHESIS

The transplantation of stem cells preassembled as 3-dimensional spheroids achieves a superior therapeutic outcome compared with the transplantation of single-cell suspensions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Adipose-derived stem cells (ADSCs) were assembled as spheroids using a methylcellulose hydrogel system. The secretome of ADSC suspensions or spheroids was collected and utilized to treat tenocytes and macrophages to evaluate their therapeutic potential and investigate the mechanisms underlying their effects. RNA sequencing was performed to investigate the global difference in gene expression between ADSC suspensions and spheroids in an in vitro inflammatory microenvironment. For the in vivo experiment, rabbits that underwent Achilles tendon transection, followed by stump suturing, were randomly assigned to 1 of 3 groups: intratendinous injection of saline, rabbit ADSCs as conventional single-cell suspensions, or preassembled ADSC spheroids. The tendons were harvested for biomechanical testing and histological analysis at 4 weeks postoperatively.

RESULTS

Our in vitro results demonstrated that the secretome of ADSCs assembled as spheroids exhibited enhanced modulatory activity in (1) tenocyte proliferation (P = .015) and migration (P = .001) by activating extracellular signal-regulated kinase (ERK) signaling and (2) the suppression of the secretion of interleukin-6 (P = .005) and interleukin-1α (P = .042) by M1 macrophages via the COX-2/PGE2/EP4 signaling axis. Gene expression profiling of cells exposed to an inflammatory milieu revealed significantly enriched terms that were associated with the immune response, cytokines, and tissue remodeling in preassembled ADSC spheroids. Ex vivo fluorescence imaging revealed that the engraftment efficiency of ADSCs in the form of spheroids was higher than that of ADSCs in single-cell suspensions (P = .003). Furthermore, the transplantation of ADSC spheroids showed superior therapeutic effects in promoting the healing of sutured stumps, as evidenced by improvements in the tensile strength (P = .019) and fiber alignment (P < .001) of the repaired tendons.

CONCLUSION

The assembly of ADSCs as spheroids significantly advanced their potential to harness tenocytes and macrophages. As a proof of concept, this study clearly demonstrates the effectiveness of using ADSC spheroids to promote tendon regeneration.

CLINICAL RELEVANCE

The present study lays a foundation for future clinical applications of stem cell spheroid-based therapy for the management of tendon injuries.

Subcutaneous device-free islet transplantation

Diabetes mellitus is a chronic metabolic disease, characterized by high blood sugar levels; it affects more than 500 million individuals worldwide. Type 1 diabetes mellitus (T1DM) is results from insufficient insulin secretion by islets; its treatment requires lifelong use of insulin injections, which leads to a large economic burden on patients. Islet transplantation may be a promising effective treatment for T1DM. Clinically, this process currently involves directly infusing islet cells into the hepatic portal vein; however, transplantation at this site often elicits immediate blood-mediated inflammatory and acute immune responses. Subcutaneous islet transplantation is an attractive alternative to islet transplantation because it is simpler, demonstrates lower surgical complication risks, and enables graft monitoring and removal. In this article, we review the current methods of subcutaneous device-free islet transplantation. Recent subcutaneous islet transplantation techniques with high success rate have involved the use of bioengineering technology and biomaterial cotransplantation-including cell and cell growth factor co-transplantation and hydrogel- or simulated extracellular matrix-wrapped subcutaneous co-transplantation. In general, current subcutaneous device-free islet transplantation modalities can simplify the surgical process and improve the posttransplantation graft survival rate, thus aiding effective T1DM management.

The Image-Histology Correlation of Subcutaneous mPEG-poly(Ala) Hydrogel-Embedded MIN6 Cell Grafts in Nude Mice

Previously, we have successfully used noninvasive magnetic resonance (MR) and bioluminescence imaging to detect and monitor mPEG-poly(Ala) hydrogel-embedded MIN6 cells at the subcutaneous space for up to 64 days. In this study, we further explored the histological evolution of MIN6 cell grafts and correlated it with image findings. MIN6 cells were incubated overnight with chitosan-coated superparamagnetic iron oxide (CSPIO) and then 5 × 10⁶ cells in the 100 μL hydrogel solution were injected subcutaneously into each nude mouse. Grafts were removed and examined the vascularization, cell growth and proliferation with anti-CD31, SMA, insulin and ki67 antibodies, respectively, at 8, 14, 21, 29 and 36 days after transplantation. All grafts were well-vascularized with prominent CD31 and SMA staining at all time points. Interestingly, insulin-positive cells and iron-positive cells were scattered in the graft at 8 and 14 days; while clusters of insulin-positive cells without iron-positive cells appeared in the grafts at 21 days and persisted thereafter, indicating neogrowth of MIN6 cells. Moreover, proliferating MIN6 cells with strong ki67 staining was observed in 21-, 29- and 36-day grafts. Our results indicate that the originally transplanted MIN6 cells proliferated from 21 days that presented distinctive bioluminescence and MR images.

Newly Generated 3D Schwann-Like Cell Spheroids From Human Adipose-Derived Stem Cells Using a Modified Protocol

Peripheral nerve injury (PNI) is a relatively frequent type of trauma that results in the suffering of many patients worldwide every year. Schwann cells (SCs) are expected to be applied in cell therapy because of their ability to promote peripheral nerve regeneration. However, the lack of clinically renewable sources of SCs hinders the application of SC-based therapies. Adipose-derived stem cells (ADSCs) have generated great interest in recent years because of their multipotency and ease of harvest, and they have already been verified to differentiate into Schwann-like cells (SLCs) in vitro. However, the efficiency of differentiation and the functions of SLCs remain unsatisfactory. We newly generated three-dimensional (3D) SLC spheroids from ADSCs using a modified protocol with human recombinant peptide (RCP) petaloid μ-piece. Morphological analysis, gene expression analysis by qRT-PCR, ELISA measurement of the secretion capabilities of neurotrophic factors, and neurite formation assay were performed to evaluate the functions of these 3D SLCs in vitro. Motor function recovery was measured in a sciatic nerve injury mouse model to analyze the nerve regeneration-promoting effect of 3D SLCs in vivo. The differentiation efficiency and the secretion of neurotrophic factors were enhanced in 3D SLCs compared with conventional SLCs. 3D SLCs could more effectively promote neurite growth and longer neurite extension in a neuron-like SH-SY5Y model. Additionally, 3D SLCs had a better therapeutic effect on nerve regeneration after transplantation into the sciatic nerve injury mouse model. These findings demonstrated that the potential of ADSC-derived SLCs to promote nerve regeneration could be significantly increased using our modified differentiation protocol and by assembling cells into a 3D sphere conformation. Therefore, these cells have great potential and can be used in the clinical treatment of PNI.

Effective in vitro differentiation of adipose-derived stem cells into Schwann-like cells with folic acid supplementation

Peripheral nerve injury (PNI) after pelvic surgery is a common issue with a significant impact on patients. Autologous nerve grafting is the gold standard treatment for PNI, but this technique cannot be applied to fine nerve fibers in the pelvis. Schwann-like cell (SLC) differentiation is a novel therapeutic strategy for this clinical condition. However, the efficiency of SLC differentiation remains unsatisfactory. We modified an SLC differentiation protocol using adipose-derived stem cells (ADSCs) and folic acid. Morphology, gene expression and secretion of neurotrophic factors were examined to assess the differentiation quality and phenotypic characteristics. Our new modified protocol effectively induced a Schwann cell (SC) phenotype in ADSCs as assessed by morphology and expression of SC markers [S100 calcium-binding protein B (S100B), P < 0.01 ; p75 neurotrophic receptor (p75NTR), P < 0.05]. SLCs produced by the new protocol displayed a repair phenotype with decreased expression of ERBB2 and early growth response protein 2 (EGR2) / KROX20 (P < 0.01). Furthermore, our new protocol enhanced both mRNA expression and secretion of nerve growth factors by SLCs (P < 0.01). This protocol enhanced the SC characteristics and functions of ADSC-derived SLCs. This promising protocol requires further research and may contribute to SC-based nerve regeneration. J. Med. Invest. 68 : 347-353, August, 2021.

Modulation of Inherent Niches in 3D Multicellular MSC Spheroids Reconfigures Metabolism and Enhances Therapeutic Potential

Multicellular spheroids show three-dimensional (3D) organization with extensive cell–cell and cell–extracellular matrix interactions. Owing to their native tissue-mimicking characteristics, mesenchymal stem cell (MSC) spheroids are considered promising as implantable therapeutics for stem cell therapy. Herein, we aim to further enhance their therapeutic potential by tuning the cultivation parameters and thus the inherent niche of 3D MSC spheroids. Significantly increased expression of multiple pro-regenerative paracrine signaling molecules and immunomodulatory factors by MSCs was observed after optimizing the conditions for spheroid culture. Moreover, these alterations in cellular behaviors may be associated with not only the hypoxic niche developed in the spheroid core but also with the metabolic reconfiguration of MSCs. The present study provides efficient methods for manipulating the therapeutic capacity of 3D MSC spheroids, thus laying solid foundations for future development and clinical application of spheroid-based MSC therapy for regenerative medicine.

Bioactive Decellularized Extracellular Matrix Derived from 3D Stem Cell Spheroids under Macromolecular Crowding Serves as a Scaffold for Tissue Engineering

Scaffolds for tissue engineering aim to mimic the native extracellular matrix (ECM) that provides physical support and biochemical signals to modulate multiple cell behaviors. However, the majority of currently used biomaterials are oversimplified and therefore fail to provide a niche required for the stimulation of tissue regeneration. In the present study, 3D decellularized ECM (dECM) scaffolds derived from mesenchymal stem cell (MSC) spheroids and with intricate matrix composition are developed. Specifically, application of macromolecular crowding (MMC) to MSC spheroid cultures facilitate ECM assembly in a 3D configuration, resulting in the accumulation of ECM and associated bioactive components. Decellularized 3D dECM constructs produced under MMC are able to adequately preserve the microarchitecture of structural ECM components and are characterized by higher retention of growth factors. This results in a stronger proangiogenic bioactivity as compared to constructs produced under uncrowded conditions. These dECM scaffolds can be homogenously populated by endothelial cells, which direct the macroassembly of the structures into larger cell-carrying constructs. Application of empty scaffolds enhances intrinsic revascularization in vivo, indicating that the 3D dECM scaffolds represent optimal proangiogenic bioactive blocks for the construction of larger engineered tissue constructs.

Injection of hybrid 3D spheroids composed of podocytes, mesenchymal stem cells, and vascular endothelial cells into the renal cortex improves kidney function and replenishes glomerular podocytes

Podocytes are highly differentiated epithelial cells that are crucial for maintaining the glomerular filtration barrier in the kidney. Podocyte injury followed by depletion is the major cause of pathological progression of kidney diseases. Although cell therapy has been considered a promising alternative approach to kidney transplantation for the treatment of kidney injury, the resultant therapeutic efficacy in terms of improved renal function is limited, possibly owing to significant loss of engrafted cells. Herein, hybrid three-dimensional (3D) cell spheroids composed of podocytes, mesenchymal stem cells, and vascular endothelial cells were designed to mimic the glomerular microenvironment and as a cell delivery vehicle to replenish the podocyte population by cell transplantation. After creating a native glomerulus-like condition, the expression of multiple genes encoding growth factors and basement membrane factors that are strongly associated with podocyte maturation and functionality was significantly enhanced. Our in vivo results demonstrated that intrarenal transplantation of podocytes in the form of hybrid 3D cell spheroids improved engraftment efficiency and replenished glomerular podocytes. Moreover, the proteinuria of the experimental mice with hypertensive nephropathy was effectively reduced. These data clearly demonstrated the potential of hybrid 3D cell spheroids for repairing injured kidneys.

Transplantation of 3D MSC/HUVEC spheroids with neuroprotective and proangiogenic potentials ameliorates ischemic stroke brain injury

Ischemic stroke, and the consequent brain cell death, is a common cause of death and disability worldwide. Current treatments that primarily aim to relieve symptoms are relatively inefficient in achieving brain tissue regeneration and functional recovery, and thus novel therapeutic options are urgently needed. Although cell-based therapies have shown promise for treating the infarcted brain, a recurring challenge is the inadequate retention and engraftment of transplanted cells at the target tissue, thereby limiting the ultimate therapeutic efficacy. Here, we show that transplantation of preassembled three-dimensional (3D) spheroids of mesenchymal stem cells (MSCs) and vascular endothelial cells (ECs) results in significantly improved cell retention and survival compared with conventional mixed-cell suspensions. The transplanted 3D spheroids exhibit notable neuroprotective, proneurogenic, proangiogenic and anti-scarring potential as evidenced by clear extracellular matrix structure formation and paracrine factor expression and secretion; this ultimately results in increased structural and motor function recovery in the brain of an ischemic stroke mouse model. Therefore, transplantation of MSCs and ECs using the 3D cell spheroid configuration not only reduces cell loss during cell harvesting/administration but also enhances the resultant therapeutic benefit, thus providing important proof-of-concept for future clinical translation.

Noninvasive Tracking of mPEG-poly(Ala) Hydrogel-Embedded MIN6 Cells after Subcutaneous Transplantation in Mice

Recently, we demonstrated the feasibility of subcutaneous transplantation of MIN6 cells embedded in a scaffold with poly(ethylene glycol) methyl ether (mPEG)-poly(Ala) hydrogels. In this study, we further tracked these grafts using magnetic resonance (MR) and bioluminescence imaging. After being incubated overnight with chitosan-coated superparamagnetic iron oxide (CSPIO) nanoparticles and then mixed with mPEG-poly(Ala) hydrogels, MIN6 cells appeared as dark spots on MR scans. For in vivo experiments, we transfected MIN6 cells with luciferase and/or incubated them overnight with CSPIO overnight; 5 × 10⁶ MIN6 cells embedded in mPEG-poly(Ala) hydrogels were transplanted into the subcutaneous space of each nude mouse. The graft of CSPIO-labeled MIN6 cells was visualized as a distinct hypointense area on MR images located at the implantation site before day 21. However, this area became hyperintense on MR scans for up to 64 days. In addition, positive bioluminescence images were also observed for up to 64 days after transplantation. The histology of removed grafts showed positive insulin and iron staining. These results indicate mPEG-poly(Ala) is a suitable scaffold for β-cell encapsulation and transplantation. Moreover, MR and bioluminescence imaging are useful noninvasive tools for detecting and monitoring mPEG-poly(Ala) hydrogel-embedded MIN6 cells at a subcutaneous site.

In Vivo Imaging of Pancreatic Islet Grafts in Diabetes Treatment

Transplantation of pancreatic islets has potential to offer life-long blood glucose management in type I diabetes and severe type II diabetes without the need of exogenous insulin administration. However, islet cell therapy suffers from autoimmune and allogeneic rejection as well as non-immune related factors. Non-invasive techniques to monitor and evaluate the fate of cell implants in vivo are essential to understand the underlying causes of graft failure, and hence to improve the precision and efficacy of islet therapy. This review describes how imaging technology has been employed to interrogate the distribution, number or volume, viability, and function of islet implants in vivo. To date, fluorescence imaging, PET, SPECT, BLI, MRI, MPI, and ultrasonography are the many imaging modalities being developed to fulfill this endeavor. We outline here the advantages, limitations, and clinical utility of each particular imaging approach.

3D Spheroids of Umbilical Cord Blood MSC-Derived Schwann Cells Promote Peripheral Nerve Regeneration

Schwann cells (SCs) are promising candidates for cell therapy due to their ability to promote peripheral nerve regeneration. However, SC-based therapies are hindered by the lack of a clinically renewable source of SCs. In this study, using a well-defined non-genetic approach, umbilical cord blood mesenchymal stem cells (cbMSCs), a clinically applicable cell type, were phenotypically, epigenetically, and functionally converted into SC-like cells (SCLCs) that stimulated effective sprouting of neuritic processes from neuronal cells. To further enhance their therapeutic capability, the cbMSC-derived SCLCs were assembled into three-dimensional (3D) cell spheroids by using a methylcellulose hydrogel system. The cell-cell and cell-extracellular matrix interactions were well-preserved within the formed 3D SCLC spheroids, and marked increases in neurotrophic, proangiogenic and anti-apoptotic factors were detected compared with cells that were harvested using conventional trypsin-based methods, demonstrating the superior advantage of SCLCs assembled into 3D spheroids. Transplantation of 3D SCLC spheroids into crush-injured rat sciatic nerves effectively promoted the recovery of motor function and enhanced nerve structure regeneration. In summary, by simply assembling cells into a 3D-spheroid conformation, the therapeutic potential of SCLCs derived from clinically available cbMSCs for promoting nerve regeneration was enhanced significantly. Thus, these cells hold great potential for translation to clinical applications for treating peripheral nerve injury.

Development of a Novel Hanging Drop Platform for Engineering Controllable 3D Microenvironments

Conventional biomedical research is mostly performed by utilizing a two-dimensional monolayer culture, which fails to recapitulate the three-dimensional (3D) organization and microenvironment of native tissues. To overcome this limitation, several methods are developed to fabricate microtissues with the desired 3D microenvironment. However, they tend to be time-consuming, labor-intensive, or costly, thus hindering the application of 3D microtissues as models in a wide variety of research fields. In the present study, we have developed a pressure-assisted network for droplet accumulation (PANDA) system, an easy-to-use chip that comprises a multichannel fluidic system and a hanging drop cell culture module for uniform 3D microtissue formation. This system can control the desired artificial niches for modulating the fate of the stem cells to form the different sizes of microtissue by adjusting the seeding density. Furthermore, a large number of highly consistent 3D glomerulus-like heterogeneous microtissues that are composed of kidney glomerular podocytes and mesenchymal stem cells have been formed successfully. These data suggest that the developed PANDA system can be employed as a rapid and economical platform to fabricate microtissues with tunable 3D microenvironment and cellular heterogeneity, thus can be employed as tissue-mimicking models in various biomedical research.