Cell secretome based approaches in Parkinson’s disease regenerative medicine

Mesenchymal stem cell secretome for regenerative medicine: Where do we stand?

BACKGROUND

Mesenchymal stem cell (MSC)-based therapies have yielded beneficial effects in a broad range of preclinical models and clinical trials for human diseases. In the context of MSC transplantation, it is widely recognized that the main mechanism for the regenerative potential of MSCs is not their differentiation, with in vivo data revealing transient and low engraftment rates. Instead, MSCs therapeutic effects are mainly attributed to its secretome, i.e., paracrine factors secreted by these cells, further offering a more attractive and innovative approach due to the effectiveness and safety of a cell-free product.

AIM OF REVIEW

In this review, we will discuss the potential benefits of MSC-derived secretome in regenerative medicine with particular focus on respiratory, hepatic, and neurological diseases. Both free and vesicular factors of MSC secretome will be detailed. We will also address novel potential strategies capable of improving their healing potential, namely by delivering important regenerative molecules according to specific diseases and tissue needs, as well as non-clinical and clinical studies that allow us to dissect their mechanisms of action.

KEY SCIENTIFIC CONCEPTS OF REVIEW

MSC-derived secretome includes both soluble and non-soluble factors, organized in extracellular vesicles (EVs). Importantly, besides depending on the cell origin, the characteristics and therapeutic potential of MSC secretome is deeply influenced by external stimuli, highlighting the possibility of optimizing their characteristics through preconditioning approaches. Nevertheless, the clarity around their mechanisms of action remains ambiguous, whereas the need for standardized procedures for the successful translation of those products to the clinics urges.

Paracrine activity of Smurf1-silenced mesenchymal stem cells enhances bone regeneration and reduces bone loss in postmenopausal osteoporosis

BACKGROUND

Osteoporosis (OP), characterized by reduced bone mass and mineral density, is a global metabolic disorder that severely impacts the quality of life in affected individuals. Although current pharmacological treatments are effective, their long-term use is often associated with adverse effects, highlighting the need for safer, more sustainable therapeutic strategies. This study investigates the pro-osteogenic and anti-resorptive potential of the secretome from Smurf1-silenced mesenchymal stem cells (MSCs) as a promising cell-free therapy for bone regeneration.

METHODS

Conditioned media (CM) from Smurf1-silenced rat (rCM-Smur1) and human MSCs (hCM-Smurf1) was collected and analyzed. Pro-osteogenic potential was assessed by measuring in vitro mineralization in human and rat MSCs cultures. In vivo, studies were conducted using a rat ectopic bone formation model and a post-menopausal osteoporotic mouse model. Additionally, primary human osteoporotic MSCs were preconditioned with hCM-Smurf1, and their osteogenic capacity was compared to that induced by BMP2 treatment. Ex vivo, human bone explants were treated with hCM-Smurf1 to assess anti-resorptive effects. Proteomic analysis of the soluble and vesicular CM fractions identified key proteins involved in bone regeneration.

RESULTS

CM from Smurf1-silenced MSCs significantly enhanced mineralization in vitro and bone formation in vivo. Preconditioning human osteoporotic MSCs with hCM-Smurf1 significantly increases in vitro mineralization, with levels comparable to those achieved with BMP2 treatment. Additionally, in ex vivo human bone cultures, treatment with hCM-Smurf1 significantly reduced RANKL expression without affecting OPG levels, indicating an anti-resorptive effect. In vivo, CM from Smurf1-silenced MSCs significantly increased bone formation in a rat ectopic model, and its local administration reduced trabecular bone loss by 50% in a post-menopausal osteoporotic mouse model after a single administration within just four weeks. Proteomic analysis revealed both soluble and vesicular fractions of hCM-Smurf1 were enriched with proteins essential for ossification and extracellular matrix organization, enhancing osteogenic differentiation.

CONCLUSIONS

The Smurf1-silenced MSCs' secretome shows potent osteogenic and anti-resorptive effects, significantly enhancing bone formation and reducing bone loss. This study provides compelling evidence for the therapeutic potential of Smurf1-silenced MSC-derived secretome as a non-toxic and targeted treatment for osteoporosis. These findings warrant further in vivo studies and clinical trials to validate its therapeutic efficacy and safety.

Engineered exosome therapeutics for neurodegenerative diseases

An increase in life expectancy comes with a higher risk for age-related neurological and cognitive dysfunctions. Given the psycho-socioeconomic burden due to unhealthy aging in the coming decades, the United Nations has declared 2021-2030 as a decade of healthy aging. In this line, multipotent mesenchymal stromal cell-based therapeutics received special interest from the research community. Based on decades of research on cell therapy, a consensus has emerged that the therapeutic effects of cell therapy are due to the paracrine mechanisms rather than cell replacement. Exosomes, a constituent of the secretome, are nano-sized vesicles that have been a focus of intense research in recent years as a possible therapeutic agent or as a cargo to deliver drugs of interest into the central nervous system to induce neurogenesis, reduce neuroinflammation, confer neuroregeneration/neuroprotection, and improve cognitive and motor functions. In this review, we have discussed the neuroprotective properties of exosomes derived from adult mesenchymal stem cells, with a special focus on the role of exosomal miRNAs. We also reviewed various strategies to improve exosome production and their content for better therapeutic effects. Further, we discussed the utilization of ectomesenchymal stem cells like dental pulp stem cells and their exosomes in treating neurodegenerative diseases.

The prospective role of mesenchymal stem cells in Parkinson's disease

Parkinson's disease (PD) is a stressful neurodegenerative disorder affecting millions worldwide. PD leads to debilitating motor and cognitive symptoms such as tremors, rigidity, and difficulty walking. Current therapies for PD are symptomatic and don't address the root cause. Therefore, there is an urgent need for better management and intensive research into alternative therapies. Mesenchymal stem cell (MSC) therapy is among the leading contenders among these promising avenues. We examined preclinical and clinical evidence demonstrating the neuroprotective, anti-inflammatory, and regenerative properties of the MSCs. This review focuses on the complex pathophysiological mechanisms of PD, as well as the perspectives of MSCs and their derivatives, such as secretomes and exosomes, in the clinical management of PD. We also analyzed the challenges and limitations of each approach, including delivery methods, timing of administration, and long-term safety considerations.

Secretome of bone marrow mesenchymal stromal cells cultured in a dynamic system induces neuroprotection and modulates microglial responsiveness in an α-synuclein overexpression rat model

BACKGROUND AIMS

Parkinson's disease (PD) is the second most common neurodegenerative disorder. The etiology of the disease remains largely unknown, but evidence have suggested that the overexpression and aggregation of alpha-synuclein (α-syn) play key roles in the pathogenesis and progression of PD. Mesenchymal stromal cells (MSCs) have been earning attention in this field, mainly due to their paracrine capacity. The bioactive molecules secreted by MSCs, i.e. their secretome, have been associated with enhanced neuronal survival as well as a strong modulatory capacity of the microenvironments where the disease develops. The selection of the appropriate animal model is crucial in studies of efficacy assessment. Given the involvement of α-syn in the pathogenesis of PD, the evidence generated from the use of animal models that develop a pathologic phenotype due to the action of this protein is extremely valuable. Therefore, in this work, we established an animal model based on the viral vector-mediated overexpression of A53T α-syn and studied the impact of the secretome of bone marrow mesenchymal stromal cells MSC(M) as a therapeutic strategy.

METHODS

Adult male rats were subjected to α-syn over expression in the nigrostriatal pathway to model dopaminergic neurodegeneration. The impact of locally administered secretome treatment from MSC(M) was studied. Motor impairments were assessed throughout the study coupled with whole-region (striatum and substantia nigra) confocal microscopy evaluation of histopathological changes associated with dopaminergic neurodegeneration and glial cell reactivity.

RESULTS

Ten weeks after lesion induction, the animals received secretome injections in the substantia nigra pars compacta (SNpc) and striatum (STR). The secretome used was produced from bone marrow mesenchymal stromal cells MSC(M) expanded in a spinner flask (SP) system. Nine weeks later, animals that received the viral vector containing the gene for A53T α-syn and treated with vehicle (Neurobasal-A medium) presented dopaminergic cell loss in the SNpc and denervation in the STR. The treatment with secretome significantly reduced the levels of α-syn in the SNpc and protected the dopaminergic neurons (DAn) within the SNpc and STR.

CONCLUSIONS

Our results are aligned with previous studies in both α-syn Caenorhabditis elegans models, as well as 6-OHDA rodent model, revealing that secretome exerted a neuroprotective effect. Moreover, these effects were associated with a modulation of microglial reactivity supporting an immunomodulatory role for the factors contained within the secretome. This further supports the development of new studies exploring the effects and the mechanism of action of secretome from MSC(M) against α-syn-induced neurotoxicity.

Treating Parkinson's Disease with Human Bone Marrow Mesenchymal Stem Cell Secretome: A Translational Investigation Using Human Brain Organoids and Different Routes of In Vivo Administration

Parkinson's disease (PD) is the most common movement disorder, characterized by the progressive loss of dopaminergic neurons from the nigrostriatal system. Currently, there is no treatment that retards disease progression or reverses damage prior to the time of clinical diagnosis. Mesenchymal stem cells (MSCs) are one of the most extensively studied cell sources for regenerative medicine applications, particularly due to the release of soluble factors and vesicles, known as secretome. The main goal of this work was to address the therapeutic potential of the secretome collected from bone-marrow-derived MSCs (BM-MSCs) using different models of the disease. Firstly, we took advantage of an optimized human midbrain-specific organoid system to model PD in vitro using a neurotoxin-induced model through 6-hydroxydopamine (6-OHDA) exposure. In vivo, we evaluated the effects of BM-MSC secretome comparing two different routes of secretome administration: intracerebral injections (a two-site single administration) against multiple systemic administration. The secretome of BM-MSCs was able to protect from dopaminergic neuronal loss, these effects being more evident in vivo. The BM-MSC secretome led to motor function recovery and dopaminergic loss protection; however, multiple systemic administrations resulted in larger therapeutic effects, making this result extremely relevant for potential future clinical applications.

Therapeutic potential of extracellular vesicles in neurodegenerative disorders

Neurodegenerative disorders are characterized by complex multifactorial pathogeneses, thus posing a challenge for standard therapeutic approaches that tend to focus only on one underlying disease aspect. For systemically administered drugs, the blood-brain barrier (BBB) is yet another major obstacle to overcome. In this context, naturally occurring extracellular vesicles (EVs) with intrinsic ability to cross the BBB have been investigated as therapeutics for various diseases, including Alzheimer's and Parkinson's diseases. EVs are cell-derived, lipid membrane-enclosed vesicles carrying a broad spectrum of biologically active molecules, which play a crucial role in intercellular communication. In a therapeutic context, mesenchymal stem cell (MSC)-derived EVs are in the spotlight because they reflect the therapeutic properties of their parental cells and, thus, hold promise as independent cell-free therapeutics. On the other hand, EVs can be used as drug delivery vehicles by modifying their surface or content, e.g., by decorating the surface with brain-specific ligands or loading the EVs with therapeutic RNAs or proteins, thus further enhancing the EV's targeting and therapeutic potency, respectively. Although EVs have been deemed safe for use in humans, some obstacles remain that prevent their progression into clinics. This review scrutinizes the promises and challenges of EV-based treatments for neurodegenerative disorders.

Cell-based therapeutic strategies for treatment of spinocerebellar ataxias: an update

Spinocerebellar ataxias are heritable neurodegenerative diseases caused by a cytosine-adenine-guanine expansion, which encodes a long glutamine tract (polyglutamine) in the respective wild-type protein causing misfolding and protein aggregation. Clinical features of polyglutamine spinocerebellar ataxias include neuronal aggregation, mitochondrial dysfunction, decreased proteasomal activity, and autophagy impairment. Mutant polyglutamine protein aggregates accumulate within neurons and cause neural dysfunction and death in specific regions of the central nervous system. Spinocerebellar ataxias are mostly characterized by progressive ataxia, speech and swallowing problems, loss of coordination and gait deficits. Over the past decade, efforts have been made to ameliorate disease symptoms in patients, yet no cure is available. Previous studies have been proposing the use of stem cells as promising tools for central nervous system tissue regeneration. So far, pre-clinical trials have shown improvement in various models of neurodegenerative diseases following stem cell transplantation, including animal models of spinocerebellar ataxia types 1, 2, and 3. However, contrasting results can be found in the literature, depending on the animal model, cell type, and route of administration used. Nonetheless, clinical trials using cellular implants into degenerated brain regions have already been applied, with the expectation that these cells would be able to differentiate into the specific neuronal subtypes and re-populate these regions, reconstructing the affected neural network. Meanwhile, the question of how feasible it is to continue such treatments remains unanswered, with long-lasting effects being still unknown. To establish the value of these advanced therapeutic tools, it is important to predict the actions of the transplanted cells as well as to understand which cell type can induce the best outcomes for each disease. Further studies are needed to determine the best route of administration, without neglecting the possible risks of repetitive transplantation that these approaches so far appear to demand. Despite the challenges ahead of us, cell-transplantation therapies are reported to have transient but beneficial outcomes in spinocerebellar ataxias, which encourages efforts towards their improvement in the future.

Applying stem cell therapy in intractable diseases: a narrative review of decades of progress and challenges

Background and Objective

Stem cell therapy (SCT) is one of the vastly researched branches of regenerative medicine as a therapeutic tool to treat incurable diseases. With the use of human stem cells such as embryonic stem cells (ESCs), adult stem cells (ASCs) and induced pluripotent stem cells (iPSCs), stem cell therapy aims to regenerate or repair damaged tissues and congenital defects. As stem cells are able to undergo infinite self-renewal, differentiate into various types of cells and secrete protective paracrine factors, many researchers have investigated the potential of SCT in regenerative medicine. Therefore, this review aims to provide a comprehensive review on the recent application of SCT in various intractable diseases, namely, haematological diseases, neurological diseases, diabetes mellitus, retinal degenerative disorders and COVID-19 infections along with the challenges faced in the clinical translation of SCT.

Methods

An extensive search was conducted on Google scholar, PubMed and Clinicaltrials.gov using related keywords. Latest articles on stem cell therapy application in selected diseases along with their challenges in clinical applications were selected.

Key content and findings

In vitro and in vivo studies involving SCT are shown to be safe and efficacious in treating various diseases covered in this review. There are also a number of small-scale clinical trials that validated the positive therapeutic outcomes of SCT. Nevertheless, the effectiveness of SCT are highly variable as some SCT works best in patients with early-stage diseases while in other diseases, SCT is more likely to work in patients in late stages of illnesses. Among the challenges identified in SCT translation are uncertainty in the underlying stem cell mechanism, ethical issues, genetic instability and immune rejection.

Conclusions

SCT will be a revolutionary treatment in the future that will provide hope to patients with intractable diseases. Therefore, studies ought to be done to ascertain the long-term effects of SCT while addressing the challenges faced in validating SCT for clinical use. Moreover, as there are many studies investigating the safety and efficacy of SCT, future studies should look into elucidating the regenerative and reparative capabilities of stem cells which largely remains unknown.

Cell Therapy for Neurological Disorders: The Perspective of Promising Cells

Neurological disorders are big public health challenges that are afflicting hundreds of millions of people around the world. Although many conventional pharmacological therapies have been tested in patients, their therapeutic efficacies to alleviate their symptoms and slow down the course of the diseases are usually limited. Cell therapy has attracted the interest of many researchers in the last several decades and has brought new hope for treating neurological disorders. Moreover, numerous studies have shown promising results. However, none of the studies has led to a promising therapy for patients with neurological disorders, despite the ongoing and completed clinical trials. There are many factors that may affect the outcome of cell therapy for neurological disorders due to the complexity of the nervous system, especially cell types for transplantation and the specific disease for treatment. This paper provides a review of the various cell types from humans that may be clinically used for neurological disorders, based on their characteristics and current progress in related studies.

View Point: Disease Modification and Cell Secretome Based Approaches in Parkinson's Disease: Are We on the Right Track?

The term idiopathic Parkinson's disease describes an entity of various not well-characterized disorders resembling each other. They are characterized by chronic neuronal dying originating from various disease mechanisms. They result in the onset of motor and related non-motor features, both of which respond to administration of personalized drug combinations and surgical therapies. The unmet need is beneficial disease course modification with repair and neurogenesis. Objectives are to discuss the value of cell secretome based treatments including neuronal graft transplantation and to suggest as an alternative the stimulation of an endogenous available approach for neuronal repair. Chronic neurodegenerative processes result from different heterogeneous, but complementing metabolic, pathological cascade sequences. Accumulated evidence from experimental research suggested neuron transplantation, stem cell application and cell secretome-based therapies as a promising future treatment with cure as an ultimate goal. To date, clinical testing of disease-modifying treatments has focused on substitution or repair of the remaining dopamine synthesizing neurons following diagnosis. At diagnosis, many of the still surviving and functioning, but already affected neurons have lost most of their axons and are primed for cell death. A more promising therapeutic concept may be the stimulation of an existing, endogenous repair system in the peripheral and central nervous systems. The abundant protein repulsive guidance molecule A blocks restoration and neurogenesis, both of which are mediated via the neogenin receptor. Inhibition of the physiological effects of repulsive guidance molecule A is an endogenous available repair pathway in chronic neurodegeneration. Antagonism of this protein with antibodies or stimulation of the neogenin receptor should be considered as an initial repair step. It is an alternative to cell replacement, stem cell or associated cell secretome concepts.

Endothelial Progenitor Cell-Derived Factors Exert Neuroprotection in Cultured Cortical Neuronal Progenitor Cells

There is substantial evidence that stem and progenitor cells secrete trophic factors that have potential for repairing injured tissues. We have previously reported that the conditioned medium (CM) obtained from endothelial progenitor cells (EPC) cultures protects striatal neurons against 3-nitropropionic acid-induced toxicity. In the present study we tested the hypothesis that EPC-CM may support cortical neuronal cell function and/or survival. EPC were isolated from the peripheral blood of healthy human donors and cultured in hypoxic conditions (1.5% O₂) to stimulate the secretion of growth factors. The supernatant or conditioned medium (EPC-CM) was then collected and used for the various experiments. Primary cultures of cerebral cortex from fetal rat embryonic day 14 were treated with EPC-CM and challenged by glucose and serum deprivation. We observed that EPC-CM treatment significantly increased total cell number and cell viability in the cultures. Similarly, the number of lba1-expressing cells was significantly upregulated by EPC-CM, while western blot analyses for the astroglial marker glial fibrillary acidic protein did not show a marked difference. Importantly, the number of beta-lll-tubulin-positive neurons in the cultures was significantly augmented after EPC-CM treatment. Similarly, western blot analyses for beta-III-tubulin showed significant higher signal intensities. Furthermore, EPC-CM administration protected neurons against glucose- and serum deprivation-induced cell loss.

In sum, our findings identified EPC-CM as a means to promote viability and/or differentiation of cortical neurons and suggest that EPC-CM might be useful for neurorestorative approaches.

Neuroprotective effects of human amniotic fluid stem cells-derived secretome in an ischemia/reperfusion model

Stem cells offer the basis for the promotion of robust new therapeutic approaches for a variety of human disorders. There are still many limitations to be overcome before clinical therapeutic application, including a better understanding of the mechanism by which stem cell therapies may lead to enhanced recovery. In vitro investigations are necessary to dissect the mechanisms involved and to support the potential development in stem cell-based therapies. In spite of growing interest in human amniotic fluid stem cells, not much is known about the characteristics of their secretome and regarding the potential neuroprotective mechanism in different pathologies, including stroke. To get more insight on amniotic fluid cells therapeutic potential, signal transduction pathways activated by human amniotic fluid stem cells (hAFSCs)-derived secretome in a stroke in vitro model (ischemia/reperfusion [I/R] model) were investigated by Western blot. Moreover, miRNA expression in the exosomal fraction of the conditioned medium was analyzed. hAFSCs-derived secretome was able to activate pro-survival and anti-apoptotic pathways. MicroRNA analysis in the exosomal component revealed a panel of 16 overexpressed miRNAs involved in the regulation of coherent signaling pathways. In particular, the pathways of relevance in ischemia/reperfusion, such as neurotrophin signaling, and those related to neuroprotection and neuronal cell death, were analyzed. The results obtained strongly point toward the neuroprotective effects of the hAFSCs-conditioned medium in the in vitro stroke model here analyzed. This can be achieved by the modulation and activation of pro-survival processes, at least in part, due to the activity of secreted miRNAs.

Therapeutic Effects of Conditioned Medium of Neural Differentiated Human Bone Marrow-Derived Stem Cells on Rotenone-Induced Alpha-Synuclein Aggregation and Apoptosis

Mesenchymal stem cells (MSCs) have been used against several diseases. Their potential mainly appears from its secreted biomolecules. Human bone marrow-derived stem cells (hBMSC) displayed neuronal functional characteristics after differentiation by basic fibroblast growth factor (bFGF) and forskolin. PD is a chronic age-related neurodegenerative disease (NDD) characterized by loss of dopaminergic neurons in the substantia nigra (SN) and abnormal accumulation of α-synuclein (α-syn) aggregations. In this present study, we evaluated the therapeutic effects of neural differentiated hBMSC (NI-hBMSC) conditioned medium (NI-hBMSC-CM) to a rotenone- (ROT-) induced Parkinson's disease (PD) model in SH-SY5Y cells. NI-hBMSC-CM treatment (50% diluted) in the last 24 h of 48 h ROT (0.5 μM) toxicity showed a significant increase in cell survival. The decreased tyrosine hydroxylase (TH) expression as a hallmark of PD was increased by NI-hBMSC-CM. The Triton X-100-soluble and Triton X-100-insoluble cell lysate fractions were used in Western blotting. The oligomeric, dimeric, and monomeric phosphorylated serine129 (p-S129) α-syn and total monomeric α-syn were decreased during ROT toxicity in the Triton X-100-soluble fraction. The Triton X-100-insoluble fraction revealed that ROT toxicity significantly increased the oligomeric but decreased the dimeric and monomeric p-S129 α-syn expressions while all forms of total α-syn were increased in SH-SY5Y cells. NI-hBMSC-CM stabilized the physiological α-syn monomers and reduced aggregated insoluble p-S129 α-syn against ROT. The cytoskeletal proteins, neurofilament-H (NF-H), β3-tubulin (Tuj1), neuronal nuclei (NeuN), and synaptophysin (SYP) were significantly decreased during ROT toxicity. In addition, proapoptotic Bax was increased by ROT with decreased antiapoptotic Bcl-2 and Mcl-1 as well as proforms of caspase-9, caspase-3, caspase-7, and PARP-1. NI-hBMSC-CM ameliorated the neurotrophic protein expressions, controlled the Bax/Bcl-2 ratio, upregulated procaspases, and inactivated PARP-1. From our results, we conclude that NI-hBMSC-CM containing released biomolecules during neural differentiation employs regenerative effects on the ROT model of PD in SH-SY5Y cells.

Stem cell secretome derived from human amniotic fluid affords neuroprotection in an ischemic model

Human amniotic fluid stem cells (hAFSCs) are growing in interest; yet, little is understood about their secretome and neuroprotective actions in different diseases, including stroke. When stem cells are grown in vitro, they release an array of cytokines and growth factors that can stimulate neuroprotective processes. Furthermore, administering secretome rather than cells may be a safer route for patients who are at risk for rejection, promoting innate restorative processes. Current literature implicates that the miRNA contents of such secretome, more specifically exosomes, may regulate the effectiveness of secretome administration. In this review, we explore what factors may promote pro-survival and pro-apoptotic pathways after the administration of hAFSCs-derived secretome in ischemic models.

Insights into the Effects of Mesenchymal Stem Cell-Derived Secretome in Parkinson's Disease

Mesenchymal stem cell (MSC)-derived secretome demonstrated therapeutic effects like those reported after MSCs transplantation. MSC-derived secretome may avoid various side effects of MSC-based therapy, comprising undesirable differentiation of engrafted MSCs and potential activation of the allogeneic immune response. MSC-derived secretome comprises soluble factors and encapsulated extravesicles (EVs). MSC-derived EVs comprise microvesicles, apoptotic bodies, and exosomes. In this review, we focus on the recent insights into the effects of MSC-derived secretome in Parkinson’s disease (PD). In particular, MSC-derived secretome and exosomal components counteracted neuroinflammation and enhanced antioxidant capacity and neurotrophic factors expression. In light of the insights reported in this review, MSC-derived secretome or their released exosomes may be used as a potential therapeutic approach or as adjuvant therapy to counteract the disease progression and improve PD symptoms. Also, MSC-derived secretome may be used as a vehicle in cell transplantation approaches to enhance the viability and survival of engrafted cells. Furthermore, since exosomes can cross the blood–brain barrier, they may be used as biomarkers of neural dysfunction. Further studies are necessary to fully characterize the bioactive molecules present in the secretome and to create a new, effective, cell-free therapeutic approach towards a robust clinical outcome for PD patients.

Multilayer Injectable Hydrogel System Sequentially Delivers Bioactive Substances for Each Wound Healing Stage

Wound healing is a dynamic and complex process that contains several sequential phases. However, most of the current drug delivery systems were designed to treat only one certain phase of wound repair, ignoring the fact that every stage plays critical roles in the wound healing process and those critical stages coordinately work to ensure optimal tissue regeneration. Therefore, a delivery system that can precisely meet the requirements of each wound healing stage is desired to enhance tissue regeneration. In this study, an injectable sodium alginate/bioglass (SA/BG) composite hydrogel was used to carry SA microparticles containing a conditioned medium (CM) of cells (SA_CM). Inside the SA_CM microparticles, poly(lactic-co-glycolic acid) (PLGA) microspheres containing pirfenidone (PFD) were encapsulated (PLGA_PFD). This multilayer injectable hydrogel system (SA/BG-SA_CM-PLGA_PFD) was designed to sequentially deliver bioactive molecules for meeting the bioactivity requirement and timeline of each wound healing stage. First, SA/BG hydrogels could rapidly release BG ionic products in the first 1-3 days to regulate the inflammatory response of the host and initiate the subsequent tissue regeneration. Then, SA_CM hydrogel microparticles could release CM of RAW 264.7 cells stimulated with BG ionic products in 2-7 days to facilitate the formation of the vascularized granulation tissue. Finally, PLGA_PFD microspheres released PFD in 8-20 days to prevent the fibrosis and scar formation in the regenerated skin. Thus, this SA/BG-SA_CM-PLGA_PFD delivery system could restrain host inflammation, accelerate wound healing, and inhibit the fibrosis formation in a diabetic mouse skin damage model, enhancing skin regeneration. As the bioactive components in each layer of the system can be adjusted according to the requirements of different tissue regeneration, this three-layered injectable biomaterial system has a wide application potential in the regenerative medicine field.

Restoring Function to Dopaminergic Neurons: Progress in the Development of Cell-Based Therapies for Parkinson's Disease

There is escalating interest in cell-based therapies to restore lost dopamine inputs in Parkinson's disease. This is based upon the rationale that implanting dopamine progenitors into the striatum can potentially improve dopamine-responsive motor symptoms. A rich body of data describing clinical trials of previous cell transplantation exists. These have included multiple cell sources for transplantation including allogeneic (human embryonic mesencephalic tissue, retinal pigment epithelial cells) and autologous (carotid body, adrenal medullary tissue) cells, as well as xenotransplantation. However, there are multiple limitations related to these cell sources, including availability of adequate numbers of cells for transplant, heterogeneity within cells transplanted, imprecisely defined mechanisms of action, and poor cell survival after transplantation in some cases. Nonetheless, evidence has accrued from a subset of trials to support the rationale for such a regenerative approach. Recent rapid advances in stem cell technology may now overcome these prior limitations. For example, dopamine neuron precursor cells for transplant can be generated from induced pluripotent cells and human embryonic stem cells. The benefits of these innovative approaches include: the possibility of scalability; a high degree of quality control; and improved understanding of mechanisms of action with rigorous preclinical testing. In this review, we focus on the potential for cell-based therapies in Parkinson's disease to restore the function of dopaminergic neurons, we critically review previous attempts to harness such strategies, we discuss potential benefits and predicted limitations, and we address how previous roadblocks may be overcome to bring a cell-based approach to the clinic.

Exosomes derived from mesenchymal stem cells repair a Parkinson's disease model by inducing autophagy

Parkinson's disease (PD) is a progressively debilitating neurodegenerative condition that leads to motor and cognitive dysfunction. At present, clinical treatment can only improve symptoms, but cannot effectively protect dopaminergic neurons. Several reports have demonstrated that human umbilical cord mesenchymal stem cells (hucMSCs) afford neuroprotection, while their application is limited because of their uncontrollable differentiation and other reasons. Stem cells communicate with cells through secreted exosomes (Exos), the present study aimed to explore whether Exos secreted by hucMSCs could function instead of hucMSCs. hucMSCs were successfully isolated and characterized, and shown to contribute to 6-hydroxydopamine (6-OHDA)-stimulated SH-SY5Y cell proliferation; hucMSC-derived Exos were also involved in this process. The Exos were purified and identified, and then labeled with PKH 26, it was found that the Exos could be efficiently taken up by SH-SY5Y cells after 12 h of incubation. Pretreatment with Exos promoted 6-OHDA-stimulated SH-SY5Y cells to proliferate and inhibited apoptosis by inducing autophagy. Furthermore, Exos reached the substantia nigra through the blood-brain barrier (BBB) in vivo, relieved apomorphine-induced asymmetric rotation, reduced substantia nigra dopaminergic neuron loss and apoptosis, and upregulated the level of dopamine in the striatum. These results demonstrate that hucMSCs-Exos have a treatment capability for PD and can traverse the BBB, indicating their potential for the effective treatment of PD.

Clinical potential and current progress of mesenchymal stem cells for Parkinson's disease: a systematic review

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease characterized by severe dyskinesia due to a progressive loss of dopaminergic neurons along the nigro-striatal pathway. The current focus of treatment is to relieve symptoms through administration of levodopa, such as L-3,4-dihydroxy phenylalanine replacement therapy, dopaminergic agonist administration, functional neurosurgery, and gene therapy, rather than preventing dopaminergic neuronal damage. Hence, the application and development of neuroprotective/disease modification strategies is absolutely necessary. Currently, stem cell therapy has been considered for PD treatment. As for the stem cells, mesenchymal stem cells (MSCs) seem to be the most promising. In this review, we analyze the mechanisms of action of MSCs in Parkinson's disease, including growth factor secretion, exocytosis, and attenuation of neuroinflammation. To determine efficacy and protect patients from possible adverse effects, ongoing rigorous and controlled studies of MSC treatment will be critical.

Bone Marrow Mesenchymal Stem Cells' Secretome Exerts Neuroprotective Effects in a Parkinson's Disease Rat Model

Parkinson's disease (PD) is characterized by a selective loss of dopamine (DA) neurons in the human midbrain causing motor dysfunctions. The exact mechanism behind dopaminergic cell death is still not completely understood and, so far, no cure or neuroprotective treatment for PD is available. Recent studies have brought attention to the variety of bioactive molecules produced by mesenchymal stem cells (MSCs), generally referred to as the secretome. Herein, we evaluated whether human MSCs-bone marrow derived (hBMSCs) secretome would be beneficial in a PD pre-clinical model, when compared directly with cell transplantation of hBMSCs alone. We used a 6-hydroxydpomanie (6-OHDA) rat PD model, and motor behavior was evaluated at different time points after treatments (1, 4, and 7 weeks). The impact of the treatments in the recovery of DA neurons was estimated by determining TH-positive neuronal densities in the substantia nigra and fibers in the striatum, respectively, at the end of the behavioral characterization. Furthermore, we determined the effect of the hBMSCs secretome on the neuronal survival of human neural progenitors in vitro, and characterized the secretome through proteomic-based approaches. This work demonstrates that the injection of hBMSCs secretome led to the rescue of DA neurons, when compared to transplantation of hBMSCs themselves, which can explain the recovery of secretome-injected animals' behavioral performance in the staircase test. Moreover, we observed that hBMSCs secretome induces higher levels of in vitro neuronal differentiation. Finally, the proteomic analysis revealed that hBMSCs secrete important exosome-related molecules, such as those related with the ubiquitin-proteasome and histone systems. Overall, this work provided important insights on the potential use of hBMSCs secretome as a therapeutic tool for PD, and further confirms the importance of the secreted molecules rather than the transplantation of hBMSCs for the observed positive effects. These could be likely through normalization of defective processes in PD, namely proteostasis or altered gene transcription, which lately can lead to neuroprotective effects.

Conditioned medium from Endothelial Progenitor Cells promotes number of dopaminergic neurons and exerts neuroprotection in cultured ventral mesencephalic neuronal progenitor cells

Transplantation of stem and progenitor cells offers a promising tool for brain repair in the context of neuropathological disorders including Parkinson's disease. There is growing proof that the capacity of adult stem and progenitor cells for tissue regeneration relies rather on the release of paracrine factors than on their cell replacement properties. In line with this notion, we have previously reported that conditioned medium (CM) collected from cultured Endothelial Progenitor Cells (EPC) stimulated survival of striatal neurons. In the present study we investigated whether EPC-CM promotes survival of cultured midbrain progenitor cells. For that purpose primary cultures from fetal rat embryonic ventral mesencephalon (VM) were prepared and grown for 7 days in vitro (DIV). EPC-CM was administered from DIV5-7. First, we found that EPC-CM treatment resulted in significantly increased cell densities of TH-ir neurons. Interestingly, this effect was no longer seen after proteolytic digestion of the EPC-CM. EPC-CM also significantly increased densities of beta-III-tubulin positive neurons and lba-1-ir microglial cells. The effect on dopaminergic neurons was not due to higher cell proliferation as no incorporation of EdU was observed in TH-ir cells. Importantly, EPC-CM exerted neuroprotection against MPP+ induced toxicity as in vitro model of Parkinson's disease. Taken together, our findings identified EPC-CM as a powerful tool to promote survival of cultured VM neurons and further support the importance of paracrine factors in the actions of stem and progenitor cells for brain repair.