Stem cell therapies in the treatment of diabetic retinopathy and keratopathy

Extracellular vesicles derived from mouse adipose-derived mesenchymal stem cells promote diabetic corneal epithelial wound healing through NGF/TrkA pathway activation involving dendritic cells

Diabetic keratopathy (DK) is a common ocular complication of diabetes in which the dendritic cells (DCs)-mediated inflammatory response plays an important role. Nerve growth factor (NGF)/Tropomyosin receptor kinase A (TrkA)-mediated inhibition of the nuclear factor kappa B (NF-κB) pathway can reduce inflammatory cytokine production. Extracellular vesicles (EVs) derived from mouse adipose-derived mesenchymal stem cells (mADSC-EVs) have been explored extensively as treatments for degenerative eye disease. However, mADSC-EVs is poorly studied in the DK models. In this study, we investigated the anti-inflammatory effects of mADSC-EVs and explored the underlying mechanisms in vitro and in vivo DK models. Our results showed that mADSC-EVs have significant therapeutic effects including increasing tear volume and the ratio of lacrimal gland/body weight, promoting corneal nerve regeneration, and sensation recovery in streptozotocin (STZ)-induced DK mice. In addition, mADSC-EVs significantly reduced the inflammatory response involving DCs, consistently up-regulated protein expression of the NGF/TrkA pathway, and importantly, reduced lipopolysaccharide (LPS)-mediated IL-6 and TNF-α expression and directly dependent on TrkA in the induced culture of bone marrow-derived DCs (BMDCs). Taken together, our findings revealed that mADSC-EVs promoted diabetic corneal epithelial wound healing through NGF/TrkA pathway activation involving DCs. Given the significant therapeutic efficacy of mADSC-EVs and its clinical application, mADSC-EVs appears to be a promising new therapy for DK.

Genetic Modification as a New Approach to Ameliorate the Therapeutic Efficacy of Stem Cells in Diabetic Retinopathy

Over the last decades, the strategy of using stem cells has gained a lot of attention in treating many diseases. Recently, DR was identified as one of the common complications experienced by diabetic patients around the world. The current treatment strategy needs to be addressed since the active progression of DR may lead to permanent blindness. Interestingly, varieties of stem cells have emerged to optimize the therapeutic effects. It is also known that stem cells possess multilineage properties and are capable of differentiating, expanding in vitro and undergoing genetic modification. Moreover, modified stem cells have shown to be an ideal resource to prevent the degenerative disease and exhibit promising effects in conferring the migratory, anti-apoptotic, anti-inflammatory and provide better homing for cells into the damaged tissue or organ as well promoting healing properties. Therefore, the understanding of the functional properties of the stem cells may provide the comprehensive guidance to understand the manipulation of stem cells making them useful for long-term therapeutic applications. Hence in this review the potential use and current challenges of genetically modified stem cells to treat DR will be discussed along with its future perspectives.

Programmed cell death in stem cell-based therapy: Mechanisms and clinical applications

Stem cell-based therapy raises hopes for a better approach to promoting tissue repair and functional recovery. However, transplanted stem cells show a high death percentage, creating challenges to successful transplantation and prognosis. Thus, it is necessary to investigate the mechanisms underlying stem cell death, such as apoptotic cascade activation, excessive autophagy, inflammatory response, reactive oxygen species, excitotoxicity, and ischemia/hypoxia. Targeting the molecular pathways involved may be an efficient strategy to enhance stem cell viability and maximize transplantation success. Notably, a more complex network of cell death receives more attention than one crucial pathway in determining stem cell fate, highlighting the challenges in exploring mechanisms and therapeutic targets. In this review, we focus on programmed cell death in transplanted stem cells. We also discuss some promising strategies and challenges in promoting survival for further study.

Neurovascular unit in diabetic retinopathy: pathophysiological roles and potential therapeutical targets

Diabetic retinopathy (DR), one of the common complications of diabetes, is the leading cause of visual loss in working-age individuals in many industrialized countries. It has been traditionally regarded as a purely microvascular disease in the retina. However, an increasing number of studies have shown that DR is a complex neurovascular disorder that affects not only vascular structure but also neural tissue of the retina. Deterioration of neural retina could precede microvascular abnormalities in the DR, leading to microvascular changes. Furthermore, disruption of interactions among neurons, vascular cells, glia and local immune cells, which collectively form the neurovascular unit, is considered to be associated with the progression of DR early on in the disease. Therefore, it makes sense to develop new therapeutic strategies to prevent or reverse retinal neurodegeneration, neuroinflammation and impaired cell-cell interactions of the neurovascular unit in early stage DR. Here, we present current perspectives on the pathophysiology of DR as a neurovascular disease, especially at the early stage. Potential novel treatments for preventing or reversing neurovascular injuries in DR are discussed as well.

Nuclear translocation of β-catenin induced by E-cadherin endocytosis causes recurrent erosion of diabetic cornea

Recurrent epithelial erosion and refractory corneal ulcer are the clinical features of diabetic keratopathy (DK), which eventually lead to corneal scar and visual disturbance. In this study, we sought to determine the abnormalities of cell junction in diabetic corneal epithelial cells and the effect of high glucose on the β-catenin/E-cadherin complex. Corneal histology showed that corneal epithelial cells of high glucose mice were loosely arranged, and the immunohistochemistry showed that the expression of E-cadherin decreased, the levels of β-catenin increased in nuclear. High glucose-induced degradation and endocytosis of E-cadherin of corneal epithelial cells reduce the formation of β-catenin/E-cadherin complex and promote the nuclear translocation of β-catenin. Moreover, high glucose also activated the transcription and expression of matrix metallopeptidase and snail, which interfered with the adhesion of corneal epithelial cells to the basement membrane. These findings reveal that DK is associated with the dissociation of cell junctions. The maintenance of the stability of the β-catenin/E-cadherin complex may be a potential therapeutic target of refractory corneal ulcers in patients with diabetes.

Combined Transplantation of Mesenchymal Stem Cells and Endothelial Colony-Forming Cells Accelerates Refractory Diabetic Foot Ulcer Healing

Background

This study is aimed at investigating the effect of combined transplantation of umbilical cord mesenchymal stem cells (UCMSCs) and umbilical cord blood-derived endothelial colony-forming cells (ECFCs) on diabetic foot ulcer healing and at providing a novel therapy for chronic diabetic foot ulcer.

Methods

We reported the treatment of refractory diabetic foot ulcers in twelve patients. Among them, five patients had two or more wounds; thus, one wound in the same patient was treated with cell injection, and other wounds were regarded as self-controls. The remaining seven patients had only one wound; therefore, the difference between the area of wound before and after treatment was estimated. The UCMSCs and ECFCs were injected into the wound along with topically applied hyaluronic acid (HA).

Results

In this report, we compared the healing rate of multiple separate wounds in the same foot of the same patient: one treated with cell injection combined with topically applied HA-based hydrogel and was later covered by the hydrocolloid dressings, while the self-control wounds were only treated with conventional therapy and covered by the hydrocolloid dressings. The wound underwent cell injection showed accelerated healing in comparison to control wound within the first week after treatment. In other diabetic patients with only one refractory wound, the healing rate after cell transplantation was significantly faster than that before injection. Two large wounds healed without needing skin grafts after combination therapy of cell injection and HA. After four weeks of combination treatment, wound closure was reached in six patients, and the wounds of the other six patients were significantly reduced in size.

Conclusions

Our study suggests that the combination of UCMSCs, ECFCs, and HA can safely synergize the accelerated healing of refractory diabetic foot ulcers.

Diabetic keratopathy: Insights and challenges

Ocular complications from diabetes mellitus are common. Diabetic keratopathy, the most frequent clinical condition affecting the human cornea, is a potentially sight-threatening condition caused mostly by epithelial disturbances that are of clinical and research attention because of their severity. Diabetic keratopathy exhibits several clinical manifestations, including persistent corneal epithelial erosion, superficial punctate keratopathy, delayed epithelial regeneration, and decreased corneal sensitivity, that may lead to compromised visual acuity or permanent vision loss. The limited amount of clinical studies makes it difficult to fully understand the pathobiology of diabetic keratopathy. Effective therapeutic approaches are elusive. We summarize the clinical manifestations of diabetic keratopathy and discuss available treatments and up-to-date research studies in an attempt to provide a thorough overview of the disorder.

A novel tissue culture model for evaluating the effect of aging on stem cell fate in adult microvascular networks

In vitro models of angiogenesis are valuable tools for understanding the underlying mechanisms of pathological conditions and for the preclinical evaluation of therapies. Our laboratory developed the rat mesentery culture model as a new tool for investigating mechanistic cell-cell interactions at specific locations across intact blood and lymphatic microvascular networks ex vivo. The objective of this study was to report a method for evaluating the effect of aging on human stem cell differentiation into pericytes during angiogenesis in cultured microvascular networks. DiI labeled exogenous stem cells were seeded onto harvested adult Wistar rat mesenteric tissues and cultured in alpha-MEM + 1% serum for up to 5 days according to four experimental groups: (1) adult human adipose-derived stem cells (hASCs), (2) aged hASCs, (3) adult human bone marrow-derived stem cells (hBMSCs), and (4) aged hBMSCs. Angiogenesis per experimental group was supported by observation of increased vessel density and capillary sprouting. For each tissue per experimental group, a subset of cells was observed in typical pericyte location wrapped along blood vessels. Stem cell differentiation into pericytes was supported by the adoption of elongated pericyte morphology along endothelial cells and positive NG2 labeling. The percentage of cells in pericyte locations was not significantly different across the experimental groups, suggesting that aged mesenchymal stem cells are able to retain their differentiation capacity. Our results showcase an application of the rat mesentery culture model for aging research and the evaluation of stem cell fate within intact microvascular networks.

Retinal cell regeneration using tissue engineered polymeric scaffolds

Degenerative retinal diseases, such as age-related macular degeneration (AMD), can lead to permanent sight loss. Although intravitreal anti-vascular endothelial growth factor (VEGF) and steroid injections are effective for the management of early stages of wet and/or neovascular AMD (nAMD), no proven treatments currently exist for dry AMD or for the advanced geographic atrophy of the retina that follows. Tissue engineering (TE) has recently emerged as a promising alternative to repair retinal damaged and restore its functions. Here, we review recent advances in TE, with a particular emphasis on retinal regeneration. We provide an overview of retinal diseases, followed by a comprehensive review of TE techniques, cells, and polymers used in the fabrication of scaffolds for retinal cell regenerations, in particular the retinal pigment epithelium (RPE).

Myocardial Infarction-Related Transcripts (MIAT) Participate in Diabetic Optic Nerve Injury by Regulating Heart Shock Protein 5 (HSPA5) via Competitively Binding to MicroRNA-379

Background

The aim of this study was to explore the role of MIAT (myocardial infarction related transcripts) in diabetic optic neuropathy and its underlying mechanism.

Material/Methods

QRT-PCR (quantitative real-time polymerase chain reaction) was performed to detect the mRNA levels of MIAT and HSPA5 (heart shock protein 5) in diabetic rat model and high-glucose cultured Müller cells. After the intracellular MIAT level was increased by lentivirus transfection, the proliferation, cell cycle, and apoptosis of Müller cells were measured using the CCK-8 (Cell Counting Kit-8) assay, flow cytometry, and TUNEL (terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling) assay, respectively. Mechanisms underlying the MIAT-related apoptosis were explored by Western blot analysis. The binding condition of microRNA-379 to MIAT and HSPA5 was confirmed by luciferase reporter gene assay.

Results

Both MIAT and HSPA5 levels were remarkably increased in high-glucose cultured Müller cells. After transfected with LV (lentivirus)-MIAT, Müller cells showed a decreased proliferation and an enhanced apoptosis with the increased expressions of pro-apoptotic proteins. However, no remarkable changes were observed in cell cycle. Further mechanistic studies found that MIAT regulated HSPA5 expression by directly binding to microRNA-379.

Conclusions

MIAT was overexpressed in the diabetic optic nerve. MIAT overexpression remarkably promoted the apoptosis of Müller cells by adsorbing microRNA-379 and thus regulating HSPA5, which was a direct target of microRNA-379.

Novel stem cell and gene therapy in diabetic retinopathy, age related macular degeneration, and retinitis pigmentosa

Degenerative retinal disease leads to significant visual morbidity worldwide. Diabetic retinopathy and macular degeneration are leading causes of blindness in the developed world. While current therapies for these diseases slow disease progression, stem cell and gene therapy may also reverse the effects of these, and other, degenerative retinal conditions. Novel therapies being investigated include the use of various types of stem cells in the regeneration of atrophic or damaged retinal tissue, the prolonged administration of neurotrophic factors and/or drug delivery, immunomodulation, as well as the replacement of mutant genes, and immunomodulation through viral vector delivery. This review will update the reader on aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa and other less common inherited retinal dystrophies. These therapies include the use of adeno-associated viral vector-based therapies for treatment of various types of retinitis pigmentosa and dry age-related macular degeneration. Other potential therapies reviewed include the use of mesenchymal stem cells in local immunomodulation, and the use of stem cells in generating structures like three-dimensional retinal sheets for transplantation into degenerative retinas. Finally, aspects of stem cell and gene therapy in diabetic retinopathy, age-related macular degeneration, retinitis pigmentosa, and other less common inherited retinal dystrophies will be reviewed.

Lymphatic Vascular Structures: A New Aspect in Proliferative Diabetic Retinopathy

Diabetic retinopathy (DR) is the most common diabetic microvascular complication and major cause of blindness in working-age adults. According to the level of microvascular degeneration and ischemic damage, DR is classified into non-proliferative DR (NPDR), and end-stage, proliferative DR (PDR). Despite advances in the disease etiology and pathogenesis, molecular understanding of end-stage PDR, characterized by ischemia- and inflammation-associated neovascularization and fibrosis, remains incomplete due to the limited availability of ideal clinical samples and experimental research models. Since a great portion of patients do not benefit from current treatments, improved therapies are essential. DR is known to be a complex and multifactorial disease featuring the interplay of microvascular, neurodegenerative, metabolic, genetic/epigenetic, immunological, and inflammation-related factors. Particularly, deeper knowledge on the mechanisms and pathophysiology of most advanced PDR is critical. Lymphatic-like vessel formation coupled with abnormal endothelial differentiation and progenitor cell involvement in the neovascularization associated with PDR are novel recent findings which hold potential for improved DR treatment. Understanding the underlying mechanisms of PDR pathogenesis is therefore crucial. To this goal, multidisciplinary approaches and new ex vivo models have been developed for a more comprehensive molecular, cellular and tissue-level understanding of the disease. This is the first step to gain the needed information on how PDR can be better evaluated, stratified, and treated.

Bone Marrow CD133+ Stem Cells Ameliorate Visual Dysfunction in Streptozotocin-induced Diabetic Mice with Early Diabetic Retinopathy

Diabetic retinopathy (DR), one of the leading causes of vision loss worldwide, is characterized by neurovascular disorders. Emerging evidence has demonstrated retinal neurodegeneration in the early pathogenesis of DR, and no treatment has been developed to prevent the early neurodegenerative changes that precede detectable microvascular disorders. Bone marrow CD133+ stem cells with revascularization properties exhibit neuroregenerative potential. However, whether CD133+ cells can ameliorate the neurodegeneration at the early stage of DR remains unclear. In this study, mouse bone marrow CD133+ stem cells were immunomagnetically isolated and analyzed for the phenotypic characteristics, capacity for neural differentiation, and gene expression of neurotrophic factors. After being labeled with enhanced green fluorescent protein, CD133+ cells were intravitreally transplanted into streptozotocin (STZ)-induced diabetic mice to assess the outcomes of visual function and retina structure and the mechanism underlying the therapeutic effect. We found that CD133+ cells co-expressed typical hematopoietic/endothelial stem/progenitor phenotypes, could differentiate to neural lineage cells, and expressed genes of robust neurotrophic factors in vitro. Functional analysis demonstrated that the transplantation of CD133+ cells prevented visual dysfunction for 56 days. Histological analysis confirmed such a functional improvement and showed that transplanted CD133+ cells survived, migrated into the inner retina (IR) over time and preserved IR degeneration, including retina ganglion cells (RGCs) and rod-on bipolar cells. In addition, a subset of transplanted CD133+ cells in the ganglion cell layer differentiated to express RGC markers in STZ-induced diabetic retina. Moreover, transplanted CD133+ cells expressed brain-derived neurotrophic factors (BDNFs) in vivo and increased the BDNF level in STZ-induced diabetic retina to support the survival of retinal cells. Based on these findings, we suggest that transplantation of bone marrow CD133+ stem cells represents a novel approach to ameliorate visual dysfunction and the underlying IR neurodegeneration at the early stage of DR.

Diabetic corneal neuropathy: clinical perspectives

Diabetic keratopathy is characterized by impaired innervation of the cornea that leads to decreased sensitivity, with resultant difficulties with epithelial wound healing. These difficulties in wound healing put patients at risk for ocular complications such as surface irregularities, corneal infections, and stromal opacification. Pathological changes in corneal innervations in diabetic patients are an important early indicator of diabetic neuropathy. The decrease in corneal sensitivity is strongly correlated with the duration of diabetes as well as the severity of the neuropathy. This review presents recent findings in assessing the ocular surface as well as the recent therapeutic strategies for optimal management of individuals with diabetes who are susceptible to developing diabetic neuropathy.

Cigarette Smoking Impairs Adipose Stromal Cell Vasculogenic Activity and Abrogates Potency to Ameliorate Ischemia

Cigarette smoking (CS) adversely affects the physiologic function of endothelial progenitor, hematopoietic stem and progenitor cells. However, the effect of CS on the ability of adipose stem/stromal cells (ASC) to promote vasculogenesis and rescue perfusion in the context of ischemia is unknown. To evaluate this, ASC from nonsmokers (nCS-ASC) and smokers (CS-ASC), and their activity to promote perfusion in hindlimb ischemia models, as well as endothelial cell (EC) survival and vascular morphogenesis in vitro were assessed. While nCS-ASC improved perfusion in ischemic limbs, CS-ASC completely lost this therapeutic effect. In vitro vasculogenesis assays revealed that human CS-ASC and ASC from CS-exposed mice showed compromised support of EC morphogenesis into vascular tubes, and the CS-ASC secretome was less potent in supporting EC survival/proliferation. Comparative secretome analysis revealed that CS-ASC produced lower amounts of hepatocyte growth factor (HGF) and stromal cell-derived growth factor 1 (SDF-1). Conversely, CS-ASC secreted the angiostatic/pro-inflammatory factor Activin A, which was not detected in nCS-ASC conditioned media (CM). Furthermore, higher Activin A levels were measured in EC/CS-ASC cocultures than in EC/nCS-ASC cocultures. CS-ASC also responded to inflammatory cytokines with 5.2-fold increase in Activin A secretion, whereas nCS-ASC showed minimal Activin A induction. Supplementation of EC/CS-ASC cocultures with nCS-ASC CM or with recombinant vascular endothelial growth factor, HGF, or SDF-1 did not rescue vasculogenesis, whereas inhibition of Activin A expression or activity improved network formation up to the level found in EC/nCS-ASC cocultures. In conclusion, ASC of CS individuals manifest compromised in vitro vasculogenic activity as well as in vivo therapeutic activity. Stem Cells 2018;36:856-867.

Diabetic complications in the cornea

Diabetic corneal alterations, such as delayed epithelial wound healing, edema, recurrent erosions, neuropathy/loss of sensitivity, and tear film changes are frequent but underdiagnosed complications of both type 1 (insulin-dependent) and type 2 (non-insulin-dependent) diabetes mellitus. The disease affects corneal epithelium, corneal nerves, tear film, and to a lesser extent, endothelium, and also conjunctiva. These abnormalities may appear or become exacerbated following trauma, as well as various surgeries including retinal, cataract or refractive. The focus of the review is on mechanisms of diabetic corneal abnormalities, available animal, tissue and organ culture models, and emerging treatments. Changes of basement membrane structure and wound healing rates, the role of various proteinases, advanced glycation end products (AGEs), abnormal growth and motility factors (including opioid, epidermal, and hepatocyte growth factors) are analyzed. Experimental therapeutics under development, including topical naltrexone, insulin, inhibitors of aldose reductase, and AGEs, as well as emerging gene and cell therapies are discussed in detail.

Mesenchymal Stem and Progenitor Cells in Regeneration: Tissue Specificity and Regenerative Potential

It has always been an ambitious goal in medicine to repair or replace morbid tissues for regaining the organ functionality. This challenge has recently gained momentum through considerable progress in understanding the biological concept of the regenerative potential of stem cells. Routine therapeutic procedures are about to shift towards the use of biological and molecular armamentarium. The potential use of embryonic stem cells and invention of induced pluripotent stem cells raised hope for clinical regenerative purposes; however, the use of these interventions for regenerative therapy showed its dark side, as many health concerns and ethical issues arose in terms of using these cells in clinical applications. In this regard, adult stem cells climbed up to the top list of regenerative tools and mesenchymal stem cells (MSC) showed promise for regenerative cell therapy with a rather limited level of risk. MSC have been successfully isolated from various human tissues and they have been shown to offer the possibility to establish novel therapeutic interventions for a variety of hard-to-noncurable diseases. There have been many elegant studies investigating the impact of MSC in regenerative medicine. This review provides compact information on the role of stem cells, in particular, MSC in regeneration.

Advances in bone marrow stem cell therapy for retinal dysfunction

The most common cause of untreatable vision loss is dysfunction of the retina. Conditions, such as age-related macular degeneration, diabetic retinopathy and glaucoma remain leading causes of untreatable blindness worldwide. Various stem cell approaches are being explored for treatment of retinal regeneration. The rationale for using bone marrow stem cells to treat retinal dysfunction is based on preclinical evidence showing that bone marrow stem cells can rescue degenerating and ischemic retina. These stem cells have primarily paracrine trophic effects although some cells can directly incorporate into damaged tissue. Since the paracrine trophic effects can have regenerative effects on multiple cells in the retina, the use of this cell therapy is not limited to a particular retinal condition. Autologous bone marrow-derived stem cells are being explored in early clinical trials as therapy for various retinal conditions. These bone marrow stem cells include mesenchymal stem cells, mononuclear cells and CD34+ cells. Autologous therapy requires no systemic immunosuppression or donor matching. Intravitreal delivery of CD34+ cells and mononuclear cells appears to be tolerated and is being explored since some of these cells can home into the damaged retina after intravitreal administration. The safety of intravitreal delivery of mesenchymal stem cells has not been well established. This review provides an update of the current evidence in support of the use of bone marrow stem cells as treatment for retinal dysfunction. The potential limitations and complications of using certain forms of bone marrow stem cells as therapy are discussed. Future directions of research include methods to optimize the therapeutic potential of these stem cells, non-cellular alternatives using extracellular vesicles, and in vivo high-resolution retinal imaging to detect cellular changes in the retina following cell therapy.

Mesenchymal Stem Cells Improve Healing of Diabetic Foot Ulcer

Mesenchymal stem cells (MSCs), an ideal cell source for regenerative therapy with no ethical issues, play an important role in diabetic foot ulcer (DFU). Growing evidence has demonstrated that MSCs transplantation can accelerate wound closure, ameliorate clinical parameters, and avoid amputation. In this review, we clarify the mechanism of preclinical studies, as well as safety and efficacy of clinical trials in the treatment of DFU. Bone marrow-derived mesenchymal stem cells (BM-MSCs), compared with MSCs derived from other tissues, may be a suitable cell type that can provide easy, effective, and cost-efficient transplantation to treat DFU and protect patients from amputation.