Genipin Cross-Linked Decellularized Nucleus Pulposus Hydrogel-Like Cell Delivery System Induces Differentiation of ADSCs and Retards Intervertebral Disc Degeneration

Modulation of Decellularized Lacrimal Gland Hydrogel Biodegradation by Genipin Crosslinking

Purpose

Hydrogels derived from decellularized tissues are promising biomaterials in tissue engineering, but their rapid biodegradation can hinder in vitro cultivation. This study aimed to retard biodegradation of a hydrogel derived from porcine decellularized lacrimal glands (dLG-HG) by crosslinking with genipin to increase the mechanical stability without affecting the function and viability of lacrimal gland (LG)-associated cells.

Methods

The effect of different genipin concentrations on dLG-HG stiffness was measured rheologically. Cell-dependent biodegradation was quantified over 10 days, and the impact on matrix metalloproteinase (MMP) activity was quantified by gelatin and collagen zymography. The viability of LG epithelial cells (EpCs), mesenchymal stem cells (MSCs), and endothelial cells (ECs) cultured on genipin-crosslinked dLG-HG was assessed after 10 days, and EpC secretory activity was analyzed by β-hexosaminidase assay.

Results

The 0.5-mM genipin increased the stiffness of dLG-HG by about 46%, and concentrations > 0.25 mM caused delayed cell-dependent biodegradation and reduced MMP activity. The viability of EpCs, MSCs, and ECs was not affected by genipin concentrations of up to 0.5 mM after 10 days. Moreover, up to 0.5-mM genipin did not negatively affect EpC secretory activity compared to control groups.

Conclusions

A concentration of 0.5-mM genipin increased dLG-HG stiffness, and 0.25-mM genipin was sufficient to prevent MMP-dependent degradation. Importantly, concentrations of up to 0.5-mM genipin did not compromise the viability of LG-associated cells or the secretory activity of EpCs. Thus, crosslinking with genipin improves the properties of dLG-HG for use as a substrate in LG tissue engineering.

A new strategy for intervertebral disc regeneration: The synergistic potential of mesenchymal stem cells and their extracellular vesicles with hydrogel scaffolds

Intervertebral disc degeneration (IDD) is a disease that severely affects spinal health and is prevalent worldwide. Mesenchymal stem cells (MSCs) and their derived extracellular vesicles (EVs) have regenerative potential and have emerged as promising therapeutic tools for treating degenerative discs. However, challenges such as the harsh microenvironment of degenerated intervertebral discs and EVs' limited stability and efficacy have hindered their clinical application. In recent years, hydrogels have attracted much attention in the field of IDD therapy because they can mimic the physiologic microenvironment of the disc and provide a potential solution by providing a suitable growth environment for MSCs and EVs. This review introduced the biological properties of MSCs and their derived EVs, summarized the research on the application of MSCs and EVs in IDD, summarized the current clinical trial studies of MSCs and EVs, and also explored the mechanism of action of MSCs and EVs in intervertebral discs. In addition, plenty of research elaborated on the mechanism of action of different classified hydrogels in tissue engineering, the synergistic effect of MSCs and EVs in promoting intervertebral disc regeneration, and their wide application in treating IDD. Finally, the challenges and problems still faced by hydrogel-loaded MSCs and EVs in the treatment of IDD are summarized, and potential solutions are proposed. This paper outlines the synergistic effects of MSCs and EVs in treating IDD in combination with hydrogels and aims to provide theoretical references for future related studies.

Decellularized extracellular matrix biomaterials for regenerative therapies: Advances, challenges and clinical prospects

Tissue engineering and regenerative medicine have shown potential in the repair and regeneration of tissues and organs via the use of engineered biomaterials and scaffolds. However, current constructs face limitations in replicating the intricate native microenvironment and achieving optimal regenerative capacity and functional recovery. To address these challenges, the utilization of decellularized tissues and cell-derived extracellular matrix (ECM) has emerged as a promising approach. These biocompatible and bioactive biomaterials can be engineered into porous scaffolds and grafts that mimic the structural and compositional aspects of the native tissue or organ microenvironment, both in vitro and in vivo. Bioactive dECM materials provide a unique tissue-specific microenvironment that can regulate and guide cellular processes, thereby enhancing regenerative therapies. In this review, we explore the emerging frontiers of decellularized tissue-derived and cell-derived biomaterials and bio-inks in the field of tissue engineering and regenerative medicine. We discuss the need for further improvements in decellularization methods and techniques to retain structural, biological, and physicochemical characteristics of the dECM products in a way to mimic native tissues and organs. This article underscores the potential of dECM biomaterials to stimulate in situ tissue repair through chemotactic effects for the development of growth factor and cell-free tissue engineering strategies. The article also identifies the challenges and opportunities in developing sterilization and preservation methods applicable for decellularized biomaterials and grafts and their translation into clinical products.

How to enhance the ability of mesenchymal stem cells to alleviate intervertebral disc degeneration

Intervertebral disc (ID) degeneration (IDD) is one of the main causes of chronic low back pain, and degenerative lesions are usually caused by an imbalance between catabolic and anabolic processes in the ID. The environment in which the ID is located is harsh, with almost no vascular distribution within the disc, and the nutrient supply relies mainly on the diffusion of oxygen and nutrients from the blood vessels located under the endplate. The stability of its internal environment also plays an important role in preventing IDD. The main feature of disc degeneration is a decrease in the number of cells. Mesenchymal stem cells have been used in the treatment of disc lesions due to their ability to differentiate into nucleus pulposus cells in a nonspecific anti-inflammatory manner. The main purpose is to promote their regeneration. The current aim of stem cell therapy is to replace the aged and metamorphosed cells in the ID and to increase the content of the extracellular matrix. The treatment of disc degeneration with stem cells has achieved good efficacy, and the current challenge is how to improve this efficacy. Here, we reviewed current treatments for disc degeneration and summarize studies on stem cell vesicles, enhancement of therapeutic effects when stem cells are mixed with related substances, and improvements in the efficacy of stem cell therapy by adjuvants under adverse conditions. We reviewed the new approaches and ideas for stem cell treatment of disc degeneration in order to contribute to the development of new therapeutic approaches to meet current challenges.

Multifunctional injectable hydrogels with controlled delivery of bioactive factors for efficient repair of intervertebral disc degeneration

Millions of people worldwide suffer from intervertebral disc degeneration (IVDD), which imposes a significant socioeconomic burden on society. There is an urgent clinical demand for more effective treatments for IVDD because conventional treatments can only alleviate the symptoms rather than preventing the progression of IVDD. Hydrogels, a class of elastic biomaterials with good biocompatibility, are promising candidates for intervertebral disc repair and regeneration. In recent years, various hydrogels have been investigated in vitro and in vivo for the repair of intervertebral discs, some of which are ready for clinical testing. This review summarizes the latest findings and developments in using bioactive factors-released bioactive injectable hydrogels for the repair and regeneration of intervertebral discs. It focuses on the analysis and summary of the use of multifunctional injectable hydrogels to delivery bioactive factors (cells, exosomes, growth factors, genes, drugs) for disc regeneration, providing guidance for future study. Finally, we discussed and analyzed the optimal timing for the application of controlled-release hydrogels in the treatment of IVDD to meet the high standards required for intervertebral disc regeneration and precision medicine.

A Review: Methodologies to Promote the Differentiation of Mesenchymal Stem Cells for the Regeneration of Intervertebral Disc Cells Following Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration (IDD), a highly prevalent pathological condition worldwide, is widely associated with back pain. Treatments available compensate for the impaired function of the degenerated IVD but typically have incomplete resolutions because of their adverse complications. Therefore, fundamental regenerative treatments need exploration. Mesenchymal stem cell (MSC) therapy has been recognized as a mainstream research objective by the World Health Organization and was consequently studied by various research groups. Implanted MSCs exert anti-inflammatory, anti-apoptotic, and anti-pyroptotic effects and promote extracellular component production, as well as differentiation into IVD cells themselves. Hence, the ultimate goal of MSC therapy is to recover IVD cells and consequently regenerate the extracellular matrix of degenerated IVDs. Notably, in addition to MSC implantation, healthy nucleus pulposus (NP) cells (NPCs) have been implanted to regenerate NP, which is currently undergoing clinical trials. NPC-derived exosomes have been investigated for their ability to differentiate MSCs from NPC-like phenotypes. A stable and economical source of IVD cells may include allogeneic MSCs from the cell bank for differentiation into IVD cells. Therefore, multiple alternative therapeutic options should be considered if a refined protocol for the differentiation of MSCs into IVD cells is established. In this study, we comprehensively reviewed the molecules, scaffolds, and environmental factors that facilitate the differentiation of MSCs into IVD cells for regenerative therapies for IDD.

Hypoxia regulates adipose mesenchymal stem cells proliferation, migration, and nucleus pulposus-like differentiation by regulating endoplasmic reticulum stress via the HIF-1α pathway

OBJECTIVE

Hypoxia can promote stem cell proliferation and migration through HIF-1α. Hypoxia can regulate cellular endoplasmic reticulum (ER) stress. Some studies have reported the relationship among hypoxia, HIF-α, and ER stress, however, while little is known about HIF-α and ER stress in ADSCs under hypoxic conditions. The purpose of the study was to investigate the role and relationship of hypoxic conditions, HIF-1α and ER stress in regulating adipose mesenchymal stem cells (ADSCs) proliferation, migration, and NPC-like differentiation.

METHOD

ADSCs were pretreated with hypoxia, HIF-1α gene transfection, and HIF-1α gene silence. The ADSCs proliferation, migration, and NPC-like differentiation were assessed. The expression of HIF-1α in ADSCs was regulated; then, the changes of ER stress level in ADSCs were observed to investigate the relationship between ER stress and HIF-1α in ADSCs under hypoxic conditions.

RESULT

The cell proliferation and migration assay results show that hypoxia and HIF-1α overexpression can significantly increase the ADSCs proliferation and migration, while HIF-1α inhibition can significantly decrease the ADSCs proliferation and migration. The HIF-1α and co-cultured with NPCs played an important role in the directional differentiation of ADSCs into NPCs. The hypoxia-regulated ER stress in ADSCs through the HIF-1α pathway, thereby regulating the cellular state of ADSCs, was also observed.

CONCLUSION

Hypoxia and HIF-1α play important roles in proliferation, migration, and NPC-like differentiation of ADSCs. This study provides preliminary evidence that HIF-1α-regulated ER stress thus affects ADSCs proliferation, migration, and differentiation. Therefore, HIF-1α and ER may serve as key points to improve the efficacy of ADSCs in treating disc degeneration.

Kartogenin-loaded hydrogel promotes intervertebral disc repair via protecting MSCs against reactive oxygen species microenvironment by Nrf2/TXNIP/NLRP3 axis

Intervertebral disc (IVD) degeneration (IDD) and the consequent low back pain present a major medical challenge. Stem cell-based tissue engineering is promising for the treatment of IDD. However, stem cell-based treatment is severely impaired by the increased generation of reactive oxygen species (ROS) in degenerative disc, which can lead to a high level of cell dysfunction and even death. In this study, a kartogenin (KGN)@PLGA-GelMA/PRP composite hydrogel was designed and used as a carrier of ADSCs-based therapies in disc repair. Injectable composite hydrogel act as a carrier for controlled release of KGN and deliver ADSCs to the degenerative disc. The released KGN can stimulate the differentiation of ADSCs into a nucleus pulposus (NP) -like phenotype and boost antioxidant capacity of ADSCs via activating Nrf2/TXNIP/NLRP3 axis. Furthermore, the composite hydrogel combined with ADSCs attenuated the in vivo degeneration of rat IVDs, maintained IVD tissue integrity and accelerated the synthesis of NP-like extracellular matrix. Therefore, the KGN@PLGA-GelMA/PRP composite hydrogel is a promising strategy for stem cell-based therapies of IDD.

Research progress in decellularized extracellular matrix hydrogels for intervertebral disc degeneration

As one of the most common clinical disorders, low back pain (LBP) influences patient quality of life and causes substantial social and economic burdens. Many factors can result in LBP, the most common of which is intervertebral disc degeneration (IDD). The progression of IDD cannot be alleviated by conservative or surgical treatments, and gene therapy, growth factor therapy, and cell therapy have their own limitations. Recently, research on the use of hydrogel biomaterials for the treatment of IDD has garnered great interest, and satisfactory treatment results have been achieved. This article describes the classification of hydrogels, the methods of decellularized extracellular matrix (dECM) production and the various types of gel formation. The current research on dECM hydrogels for the treatment of IDD is described in detail in this article. First, an overview of the material sources, decellularization methods, and gel formation methods is given. The focus is on research performed over the last three years, which mainly consists of bovine and porcine NP tissues, while for decellularization methods, combinations of several approaches are primarily used. dECM hydrogels have significantly improved mechanical properties after the polymers are cross-linked. The main effects of these gels include induction of stem cell differentiation to intervertebral disc (IVD) cells, good mechanical properties to restore IVD height after polymer cross-linking, and slow release of exosomes. Finally, the challenges and problems still faced by dECM hydrogels for the treatment of IDD are summarised, and potential solutions are proposed. This paper is the first to summarise the research on dECM hydrogels for the treatment of IDD and aims to provide a theoretical reference for subsequent studies.

Mechanical stimulation promotes MSCs healing the lesion of intervertebral disc annulus fibrosus

Mesenchymal stem cells (MSCs) and scaffolds offer promising perspectives for annulus fibrosus (AF) repair. The repair effect was linked to features of the local mechanical environment related to the differentiation of MSCs. In this study, we established a Fibrinogen-Thrombin-Genipin (Fib-T-G) gel which is sticky and could transfer strain force from AF tissue to the human mesenchymal stem cells (hMSCs) embedded in the gel. After the Fib-T-G biological gel was injected into the AF fissures, the histology scores of intervertebral disc (IVD) and AF tissue showed that Fib-T-G gel could better repair the AF fissure in caudal IVD of rats, and increase the expression of AF-related proteins including Collagen 1 (COL1), Collagen 2 (COL2) as well as mechanotransduction-related proteins including RhoA and ROCK1. To clarify the mechanism that sticky Fib-T-G gel induces the healing of AF fissures and the differentiation of hMSCs, we further investigated the differentiation of hMSCs under mechanical strain in vitro. It was demonstrated that both AF-specific genes, including Mohawk and SOX-9, and ECM markers (COL1, COL2, aggrecan) of hMSCs were up-regulated in the environment of strain force. Moreover, RhoA/ROCK1 proteins were also found to be significantly up-regulated. In addition, we further -demonstrated that the fibrochondroinductive effect of the mechanical microenvironment process could be significantly blocked or up-regulated by inhibiting the RhoA/ROCK1 pathway or overexpressing RhoA in MSCs, respectively. Summarily, this study will provide a therapeutic alternative to repair AF tears and provide evidence that RhoA/ROCK1 is vital for hMSCs response to mechanical strain and AF-like differentiation.

Decellularized matrix for repairing intervertebral disc degeneration: Fabrication methods, applications and animal models

Intervertebral disc degeneration (IDD)-induced low back pain significantly influences the quality of life, placing a burden on public health systems worldwide. Currently available therapeutic strategies, such as conservative or operative treatment, cannot effectively restore intervertebral disc (IVD) function. Decellularized matrix (DCM) is a tissue-engineered biomaterial fabricated using physical, chemical, and enzymatic technologies to eliminate cells and antigens. By contrast, the extracellular matrix (ECM), including collagen and glycosaminoglycans, which are well retained, have been extensively studied in IVD regeneration. DCM inherits the native architecture and specific-differentiation induction ability of IVD and has demonstrated effectiveness in IVD regeneration in vitro and in vivo. Moreover, significant improvements have been achieved in the preparation process, mechanistic insights, and application of DCM for IDD repair. Herein, we comprehensively summarize and provide an overview of the roles and applications of DCM for IDD repair based on the existing evidence to shed a novel light on the clinical treatment of IDD.

Cross-Linking Agents for Electrospinning-Based Bone Tissue Engineering

Electrospun nanofibers are promising bone tissue scaffolds that support bone healing due to the body’s structural similarity to the extracellular matrix (ECM). However, the insufficient mechanical properties often limit their potential in bone tissue regeneration. Cross-linking agents that chemically interconnect as-spun electrospun nanofibers are a simple but effective strategy for improving electrospun nanofibers’ mechanical, biological, and degradation properties. To improve the mechanical characteristic of the nanofibrous bone scaffolds, two of the most common types of cross-linking agents are used to chemically crosslink electrospun nanofibers: synthetic and natural. Glutaraldehyde (GTA) is a typical synthetic agent for electrospun nanofibers, while genipin (GP) is a natural cross-linking agent isolated from gardenia fruit extracts. GP has gradually gained attention since GP has superior biocompatibility to synthetic ones. In recent studies, much more progress has been made in utilizing crosslinking strategies, including citric acid (CA), a natural cross-linking agent. This review summarizes both cross-linking agents commonly used to improve electrospun-based scaffolds in bone tissue engineering, explains recent progress, and attempts to expand the potential of this straightforward method for electrospinning-based bone tissue engineering.