Mesenchymal stromal/stem cells as potential therapy in diabetic retinopathy

Photobiomodulation inhibits retinal degeneration in diabetic mice through modulation of stem cell mobilization and gene expression

The number of people suffering from type 2 diabetes (DM2) is increasing and over 30 percent of DM2 patients will develop diabetic retinopathy (DR). Available therapeutic approaches for DR have their limitations. It is of great significance to search for other effective alternate therapeutic approaches. The present study aimed to explore the beneficial effects of photobiomodulation (PBM) on the diabetic retinopathy and underlying mechanisms. Streptozotocin was administered to male mice to establish diabetic model. The mice in the diabetic group (DM) received no treatment, and the mice in DM + PBM group received LED illumination (wavelength 670 nm) once a day for 20 consecutive weeks. Retinal vessel degenerate changes, the expression levels of E-Cadherin, N-Cadherin and the mRNA levels of c-kit, CXCR4, MYPT1, SCF, SDF1-α in retina, the levels of SDF-1α and SCF in the peripheral blood and the number of LSK cells expressing c-kit and sca-1 were determined. PBM could significantly inhibit the degenerative change of diabetic retinal vessels, decrease the expression levels of E-Cadherin and N-Cadherin and the mRNA levels of c-kit, CXCR4, MYPT1, SCF, SDF1-α and increase VEGF mRNA levels in retina. PBM could also increase the levels of SDF-1α and SCF in the peripheral blood and the number of LSK cells expressing c-kit and sca-1 in diabetic mice. PBM at 4 min/day for 20 consecutive weeks significantly inhibit the degenerative change of diabetic retinal vessels, and PBM is likely to produce its beneficial effects on the retina through promoting the migration of bone marrow stem cells to circulation and diabetic retinal tissue. The present study provides a new therapeutic direction and experimental foundation for the treatment of diabetic retinopathy.

HucMSCs can alleviate abnormal vasculogenesis induced by high glucose through the MAPK signaling pathway

Vascular complications caused by diabetes mellitus contribute a major threat to increased disability and mortality of diabetic patients, which are characterized by damaged endothelial cells and angiogenesis. Human umbilical cord-derived mesenchymal stem cells (hucMSCs) have been demonstrated to alleviate endothelial cell damage and improve angiogenesis. However, these investigations overlooked the pivotal role of vasculogenesis. In this study, we utilized blood vessel organoids (BVOs) to investigate the impact of high glucose on vasculogenesis and subsequent angiogenesis. We found that BVOs in the vascular lineage induction stage were more sensitive to high glucose and more susceptible to affect endothelial cell differentiation and function. Moreover, hucMSCs can alleviate the high glucose-induced inhibition of endothelial cell differentiation and dysfunction through MAPK signaling pathway downregulation, with the MAPK activator dimethyl fumarate further illustrating the results. Thereby, we demonstrated that high glucose can lead to abnormal vasculogenesis and impact subsequent angiogenesis, and hucMSCs can alleviate this effect.

Exosomes derived from umbilical cord-derived mesenchymal stem cells exposed to diabetic microenvironment enhance M2 macrophage polarization and protect against diabetic nephropathy

The role of mesenchymal-stem-cell-derived exosomes (MSCs-Exo) in the regulation of macrophage polarization has been recognized in several diseases. There is emerging evidence that MSCs-Exo partially prevent the progression of diabetic nephropathy (DN). This study aimed to investigate whether exosomes secreted by MSCs pre-treated with a diabetic environment (Exo-pre) have a more pronounced protective effect against DN by regulating the balance of macrophages. Exo-pre and Exo-Con were isolated from the culture medium of UC-MSCs pre-treated with a diabetic mimic environment and natural UC-MSCs, respectively. Exo-pre and Exo-Con were injected into the tail veins of db/db mice three times a week for 6 weeks. Serum creatinine and serum urea nitrogen levels, the urinary protein/creatinine ratio, and histological staining were used to determine renal function and morphology. Macrophage phenotypes were analyzed by immunofluorescence, western blotting, and quantitative reverse transcription polymerase chain reaction. In vitro, lipopolysaccharide-induced M1 macrophages were incubated separately with Exo-Con and Exo-pre. We performed microRNA (miRNA) sequencing to identify candidate miRNAs and predict their target genes. An miRNA inhibitor was used to confirm the role of miRNAs in macrophage modulation. Exo-pre were more potent than Exo-Con at alleviating DN. Exo-pre administration significantly reduced the number of M1 macrophages and increased the number of M2 macrophages in the kidney compared to Exo-Con administration. Parallel outcomes were observed in the co-culture experiments. Moreover, miR-486-5p was distinctly expressed in Exo-Con and Exo-pre groups, and it played an important role in macrophage polarization by targeting PIK3R1 through the PI3K/Akt pathway. Reducing miR-486-5p levels in Exo-pre abolished macrophage polarization modulation. Exo-pre administration exhibited a superior effect on DN by remodeling the macrophage balance by shuttling miR-486-5p, which targets PIK3R1.

Clinical-grade human embryonic stem cell-derived mesenchymal stromal cells ameliorate diabetic retinopathy in db/db mice

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) hold great promise in the treatment of diabetic retinopathy (DR), as evidenced by increasing preclinical and clinical studies. However, the absence of standardized and industrialized clinical-grade donor cells hampers the continued development and large-scale clinical application of MSCs-based therapies for DR. Previously, we have identified a unique population of MSCs generated from a clinical-grade human embryonic stem cell (hESC) line under Good Manufacturing Practice conditions that could be a potential source to address the issues. Here, we investigated the therapeutic potential of the clinical-grade hESC line-derived MSCs (hESC-MSCs) on db/db mice with DR.

METHODS

hESC-MSCs were initially characterized by morphological assessment, flow cytometry analysis and trilineage differentiation assays. These cells (5 × 106 cells) were then transplanted intravenously into 12-week-old db/db mice via tail vein, with phosphate-buffered saline transplantation and untreated groups used as controls. The retinal alterations in neural functions and microvascular perfusions, and inflammatory responses in peripheral blood and retina were evaluated at 4 and 6 weeks after transplantation using electroretinography, optical coherence tomography angiography and flow cytometry, respectively. Body weight and fasting blood glucose (FBG) levels were also measured to investigate their systemic implications.

RESULTS

Compared with controls, intravenous transplantation of hESC-MSCs could significantly: (i) enhance impaired retinal electroretinography functions (including amplitudes of a-, b-wave and oscillatory potentials) at 4 weeks after transplantation; (ii) alleviate microvascular dysfunctions, especially in the inner retina with significance (including reducing non-perfusion area and increasing vascular area density) at 4 weeks after transplantation; (iii) decrease FBG levels at 4 weeks after transplantation and induce weight loss up to 6 weeks after transplantation and (iv) increase both peripheral blood and retinal interleukin-10 levels at 4 weeks after transplantation and modulate peripheral blood inflammatory cytokines and chemokines levels, such as monocyte chemotactic protein-1, up to 6 weeks after transplantation.

CONCLUSIONS

The findings of our study indicated that intravenous transplantation of hESC-MSCs ameliorated retinal neural and microvascular dysfunctions, regulated body weight and FBG and modulated peripheral blood and retinal inflammation responses in a mouse model of DR. These results suggest that hESC-MSCs could be a potentially effective clinical-grade cell source for the treatment of DR.

Pericyte in retinal vascular diseases: A multifunctional regulator and potential therapeutic target

Retinal vascular diseases (RVDs), in particular diabetic retinopathy, retinal vein occlusion, and retinopathy of prematurity, are leading contributors to blindness. The pathogenesis of RVD involves vessel dilatation, leakage, and occlusion; however, the specific underlying mechanisms remain unclear. Recent findings have indicated that pericytes (PCs), as critical members of the vascular mural cells, significantly contribute to the progression of RVDs, including detachment from microvessels, alteration of contractile and secretory properties, and excessive production of the extracellular matrix. Moreover, PCs are believed to have mesenchymal stem properties and, therefore, might contribute to regenerative therapy. Here, we review novel ideas concerning PC characteristics and functions in RVDs and discuss potential therapeutic strategies based on PCs, including the targeting of pathological signals and cell-based regenerative treatments.

Combined Light and Thermal Stimulation of Bone Marrow Stem Cells

Introduction: The purpose of this study is to achieve a significant increase in the proliferative activity of mesenchymal stem cells (MSCs) of the bone marrow (BM) at early passages after laser exposure to a suspension of these cells and to estimate the effect of light and heat components of laser radiation on the proliferation of BM MSCs. Methods: The studies were performed on rats BM MSCs. MSC suspension was placed into the wells and heated by using laser radiation (980 nm wavelength) or a water bath at 70 °C providing similar temperature dynamics. The studies were carried out in 3 comparison groups: (1) control suspension of MSCs, which was not subjected to heating in a water bath or laser exposure; (2) MSC suspension, which was heated for in a water bath; and (3) suspension of MSCs, which was subjected to laser exposure. The exposure times for the 2nd and 3rd experimental groups were 10- 50 seconds. Results: Under optimal parameters of laser action on the suspension of BM MSCs, a six-fold increase in the number of BM MSCs colonies was registered compared to the control. The role of the light and heat components of laser exposure to MSCs was determined by comparable heating of a suspension of BM MSCs in a water bath, at which only a twofold increase in the number of colonies was maximally obtained. Conclusion: The increase in the MSC proliferation activity occurs due to their Thermo-Photobiomodulation. The result obtained is important for practical use in cell transplantation in the treatment of traumatic injuries of bone, cartilage, and tendon tissues when a rapid and multiple increase in the initial number of autologous BM MSCs is required.

Beneficial Effect of Sirolimus-Pretreated Mesenchymal Stem Cell Implantation on Diabetic Retinopathy in Rats

BACKGROUND

Diabetic retinopathy (DR) is a vision-threatening complication that affects virtually all diabetic patients. Various treatments have been attempted, but they have many side effects and limitations. Alternatively, stem cell therapy is being actively researched, but it faces challenges due to a low cell survival rate. In this study, stem cells were pretreated with sirolimus, which is known to promote cell differentiation and enhance the survival rate. Additionally, the subconjunctival route was employed to reduce complications following intravitreal injections.

METHODS

Diabetes mellitus was induced by intraperitoneal injection of 55 mg/kg of streptozotocin (STZ), and DR was confirmed at 10 weeks after DM induction through electroretinogram (ERG). The rats were divided into four groups: intact control group (INT), diabetic retinopathy group (DR), DR group with subconjunctival MSC injection (DR-MSC), and DR group with subconjunctival sirolimus-pretreated MSC injection (DR-MSC-S). The effects of transplantation were evaluated using ERG and histological examinations.

RESULTS

The ERG results showed that the DR-MSC-S group did not significantly differ from the INT in b-wave amplitude and exhibited significantly higher values than the DR-MSC and DR groups (p < 0.01). The flicker amplitude results showed that the DR-MSC and DR-MSC-S groups had significantly higher values than the DR group (p < 0.01). Histological examination revealed that the retinal layers were thinner in the DR-induced groups compared to the INT group, with the DR-MSC-S group showing the thickest retinal layers among them.

CONCLUSIONS

Subconjunctival injection of sirolimus-pretreated MSCs can enhance retinal function and mitigate histological changes in the STZ-induced DR rat model.

Stem cells as a regenerative medicine approach in treatment of microvascular diabetic complications

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by high blood glucose and is associated with high morbidity and mortality among the diabetic population. Uncontrolled chronic hyperglycaemia causes increased formation and accumulation of different oxidative and nitrosative stress markers, resulting in microvascular and macrovascular complications, which might seriously affect the quality of a patient's life. Conventional treatment strategies are confined to controlling blood glucose by regulating the insulin level and are not involved in attenuating the life-threatening complications of diabetes mellitus. Thus, there is an unmet need to develop a viable treatment strategy that could target the multi-etiological factors involved in the pathogenesis of diabetic complications. Stem cell therapy, a regenerative medicine approach, has been investigated in diabetic complications owing to their unique characteristic features of self-renewal, multilineage differentiation and regeneration potential. The present review is focused on potential therapeutic applications of stem cells in the treatment of microvascular diabetic complications such as nephropathy, retinopathy, and polyneuropathy.

Safety evaluation of human umbilical cord-mesenchymal stem cells in type 2 diabetes mellitus treatment: A phase 2 clinical trial

BACKGROUND

Progressive pancreatic β cell dysfunction is a fundamental aspect of the pathology underlying type 2 diabetes mellitus (T2DM). Recently, mesenchymal stem cell (MSC) transplantation has emerged as a new therapeutic method due to its ability to promote the regeneration of pancreatic β cells. However, current studies have focused on its efficacy, and there are few clinical studies on its safety.

AIM

To evaluate the safety of human umbilical cord (hUC)-MSC infusion in T2DM treatment.

METHODS

An open-label and randomized phase 2 clinical trial was designed to evaluate the safety of hUC-MSC transplantation in T2DM in a Class A hospital. Ten patients in the placebo group received acellular saline intravenously once per week for 3 wk. Twenty-four patients in the hUC-MSC group received hUC-MSCs (1 × 106 cells/kg) intravenously once per week for 3 wk. Diabetic clinical symptoms and signs, laboratory findings, and imaging findings were evaluated weekly for the 1st mo and then at weeks 12 and 24 post-treatment.

RESULTS

No serious adverse events were observed during the 24-wk follow-up. Four patients (16.7%) in the hUC-MSC group experienced transient fever, which occurred within 24 h after the second or third infusion; this did not occur in any patients in the placebo group. One patient from the hUC-MSC group experienced hypoglycemic attacks within 1 mo after transplantation. Significantly lower lymphocyte levels (weeks 2 and 3) and thrombin coagulation time (week 2) were observed in the hUC-MSC group compared to those in the placebo group (all P < 0.05). Significantly higher platelet levels (week 3), immunoglobulin levels (weeks 1, 2, 3, and 4), fibrinogen levels (weeks 2 and 3), D-dimer levels (weeks 1, 2, 3, 4, 12, and 24), and neutrophil-to-lymphocyte ratios (weeks 2 and 3) were observed in the hUC-MSC group compared to those in the placebo group (all P < 0.05). There were no significant differences between the two groups for tumor markers (alpha-fetoprotein, carcinoembryonic antigen, and carbohydrate antigen 199) or blood fat. No liver damage or other side effects were observed on chest X-ray.

CONCLUSION

Our study suggested that hUC-MSC transplantation has good tolerance and high safety in the treatment of T2DM. It can improve human immunity and inhibit lymphocytes. Coagulation function should be monitored vigilantly for abnormalities.

Stem cells and diabetic retinopathy: From models to treatment

Diabetic retinopathy is a common yet complex microvascular disease, caused as a complication of diabetes mellitus. Associated with hyperglycemia and subsequent metabolic abnormalities, advanced stages of the disease lead to fibrosis, subsequent visual impairment and blindness. Though clinical postmortems, animal and cell models provide information about the progression and prognosis of diabetic retinopathy, its underlying pathophysiology still needs a better understanding. In addition to it, the loss of pericytes, immature retinal angiogenesis and neuronal apoptosis portray the disease treatment to be challenging. Indulged with cell loss of both vascular and neuronal type cells, novel therapies like cell replacement strategies by various types of stem cells have been sightseen as a possible treatment of the disease. This review provides insight into the pathophysiology of diabetic retinopathy, current models used in modelling the disease, as well as the varied aspects of stem cells in generating three-dimensional retinal models. Further outlook on stem cell therapy and the future directions of stem cell treatment in diabetic retinopathy have also been contemplated.

Mesenchymal-Stem-Cell-Based Strategies for Retinal Diseases

Retinal diseases are major causes of irreversible vision loss and blindness. Despite extensive research into their pathophysiology and etiology, pharmacotherapy effectiveness and surgical outcomes remain poor. Based largely on numerous preclinical studies, administration of mesenchymal stem cells (MSCs) as a therapeutic strategy for retinal diseases holds great promise, and various approaches have been applied to the therapies. However, hindered by the retinal barriers, the initial vision for the stem cell replacement strategy fails to achieve the anticipated effect and has now been questioned. Accumulating evidence now suggests that the paracrine effect may play a dominant role in MSC-based treatment, and MSC-derived extracellular vesicles emerge as a novel compelling alternative for cell-free therapy. This review summarizes the therapeutic potential and current strategies of this fascinating class of cells in retinal degeneration and other retinal dysfunctions.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

Diabetic macular ischaemia- a new therapeutic target?

Diabetic macular ischaemia (DMI) is traditionally defined and graded based on the angiographic evidence of an enlarged and irregular foveal avascular zone. However, these anatomical changes are not surrogate markers for visual impairment. We postulate that there are vascular phenotypes of DMI based on the relative perfusion deficits of various retinal capillary plexuses and choriocapillaris. This review highlights several mechanistic pathways, including the role of hypoxia and the complex relation between neurons, glia, and microvasculature. The current animal models are reviewed, with shortcomings noted. Therefore, utilising the advancing technology of optical coherence tomography angiography (OCTA) to identify the reversible DMI phenotypes may be the key to successful therapeutic interventions for DMI. However, there is a need to standardise the nomenclature of OCTA perfusion status. Visual acuity is not an ideal endpoint for DMI clinical trials. New trial endpoints that represent disease progression need to be developed before irreversible vision loss in patients with DMI. Natural history studies are required to determine the course of each vascular and neuronal parameter to define the DMI phenotypes. These DMI phenotypes may also partly explain the development and recurrence of diabetic macular oedema. It is also currently unclear where and how DMI fits into the diabetic retinopathy severity scales, further highlighting the need to better define the progression of diabetic retinopathy and DMI based on both multimodal imaging and visual function. Finally, we discuss a complete set of proposed therapeutic pathways for DMI, including cell-based therapies that may provide restorative potential.

Human umbilical cord-derived mesenchymal stem cells not only ameliorate blood glucose but also protect vascular endothelium from diabetic damage through a paracrine mechanism mediated by MAPK/ERK signaling

BACKGROUND

Endothelial damage is an initial step of macro- and micro-vasculature dysfunctions in diabetic patients, accounting for a high incidence of diabetic vascular complications, such as atherosclerosis, nephropathy, retinopathy, and neuropathy. However, clinic lacks effective therapeutics targeting diabetic vascular complications. In field of regenerative medicine, mesenchymal stem cells, such as human umbilical cord-derived MSCs (hucMSCs), have great potential in treating tissue damage.

METHODS

To determine whether hucMSCs infusion could repair diabetic vascular endothelial damage and how it works, this study conducted in vivo experiment on streptozotocin-induced diabetic rat model to test body weight, fasting blood glucose (FBG), serum ICAM-1 and VCAM-1 levels, histopathology and immunohistochemical staining of aorta segments. In vitro experiment was further conducted to determine the effects of hucMSCs on diabetic vascular endothelial damage, applying assays of resazurin staining, MTT cell viability, wound healing, transwell migration, and matrigel tube formation on human umbilical vein endothelial cells (HUVECs). RNA sequencing (RNAseq) and molecular experiment were conducted to clarify the mechanism of hucMSCs.

RESULTS

The in vivo data revealed that hucMSCs partially restore the alterations of body weight, FBG, serum ICAM-1 and VCAM-1 levels, histopathology of aorta and reversed the abnormal phosphorylation of ERK in diabetic rats. By using the conditioned medium of hucMSCs (MSC-CM), the in vitro data revealed that hucMSCs improved cell viability, wound healing, migration and angiogenesis of the high glucose-damaged HUVECs through a paracrine action mode, and the altered gene expressions of IL-6, TNF-α, ICAM-1, VCAM-1, BAX, P16, P53 and ET-1 were significantly restored by MSC-CM. RNAseq incorporated with real-time PCR and Western blot results clarified that high glucose activated MAPK/ERK signaling in HUVECs, while MSC-CM reversed the abnormal phosphorylation of ERK and overexpressions of MKNK2, ERBB3, MYC and DUSP5 in MAPK/ERK signaling pathway.

CONCLUSIONS

HucMSCs not only ameliorated blood glucose but also protected vascular endothelium from diabetic damage, in which MAPK/ERK signaling mediated its molecular mechanism of paracrine action. Our findings provided novel knowledge of hucMSCs in the treatment of diabetes and suggested a prospective strategy for the clinical treatment of diabetic vascular complications.

Administration of Melatonin in Diabetic Retinopathy Is Effective and Improves the Efficacy of Mesenchymal Stem Cell Treatment

Stem cell transplantation is a promising therapeutic technique for the treatment of a variety of diseases; nevertheless, stem cell therapy may not always work as well as it could. The goal of this study was to test the hypothesis that employing a powerful antioxidant like melatonin improves stem cell transplantation success and potentiates stem cell function in the therapy of diabetic retinopathy. For this purpose, 50 adult male rats were divided into the following: control group: this group received 0.5 ml of 0.1 M of sodium citrate buffer (pH = 4.5) (intraperitoneal (I.P.)). The confirmed diabetic rats were divided into 4 groups: diabetic group: confirmed diabetic rats received no treatments with a regular follow of the blood glucose profile for 8 weeks; melatonin group: confirmed diabetic rats received melatonin (5 mg/kg/day); stem cell group: the confirmed diabetic rats were given intravitreal injection of stem cells (2 μl cell suspension of stem cells (3 × 10⁴ cells/μl)); and melatonin+stem cell group: confirmed diabetic rats received melatonin (5 mg/kg/day), orally once daily for 8 weeks, and 2 μl cell suspension of stem cells (3 × 10⁴ cells/μl) was carefully injected into the vitreous cavity. Our results showed that administration of melatonin and/or stem cell restored the retinal oxidative/antioxidant redox and reduced retinal inflammatory mediators. Coadministration of melatonin and stem cells enhanced the number of transplanted stem cells in the retinal tissue and significantly reduced retinal BDEF, VEGF, APOA1, and RBP4 levels as compared to melatonin and/or stem alone. We may conclude that rats treated with melatonin and stem cells had their retinal oxidative/antioxidant redox values restored to normal and their histological abnormalities reduced. These findings support the hypothesis that interactions with the BDEF, VEGF, APOA1, and RBP4 signaling pathways are responsible for these effects.

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.

Protective effects of umbilical cord mesenchymal stem cell exosomes in a diabetic rat model through live retinal imaging

AIM

To assess the protective effect of human umbilical cord mesenchymal stem cell exosomes (hucMSC-Exs) in a diabetic rat model by using a variety of retinal bioassays.

METHODS

hucMSCs were subjected to differential ultracentrifugation for the collection of exosomes, and transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA) using a NanoSight analysis system and Western blotting (WB) were used to analyze the expression of surface marker proteins such as CD63, CD9 and Calnexin. Streptozotocin (STZ) was injected into the intraperitoneal cavity to establish a diabetic model. Rats were divided into a normal group, diabetic group and hucMSC-Ex group. Fundus fluorescein angiography (FFA), optical coherence tomography (OCT) and other live imaging methods were used to observe the fundus of the rats. Finally, the eyeballs of rats from each group were collected for hematoxylin-eosin (HE) staining to further analyze the retinal structure.

RESULTS

Through TEM, NTA and WB, we successfully isolated hucMSC-Exs. Subsequent FFA and OCT confirmed that hucMSC-Exs effectively prevented early retinal vascular damage and thickening of the retina. Finally, HE staining of rat retinal sections revealed that exosomes effectively alleviated retinal structure disruption caused by diabetes.

CONCLUSION

hucMSC-Exs have a protective effect on the retina in diabetic rat through FFA, OCT and HE staining.

Mesenchymal Stem Cells Enhance Vascular Endothelial Growth Factor-A, Endothelial Nitric Oxide Synthetase, and HSP70 Expression in Improving Erectile Dysfunction in Streptozotocin-induced Diabetic Rats

This study investigated the therapeutic role of mesenchymal stem cells (MSCs) on erectile function in a diabetes mellitus erectile dysfunction (DMED) rat model by analyzing the expression of endothelial nitric oxide synthetase (eNOS), vascular endothelial growth factor (VEGF), and the 70 kilodalton heat shock proteins (HSP70). MSCs were isolated from umbilical cords (UCs), and their characteristics identified by flow cytometry and osteogenic differentiation analysis. Thirty 8-week-old rats were divided into four groups: sham, control, T1, and T2. After a 16 h fast, 24 rats were randomly selected and intraperitoneally injected with streptozotocin (STZ) to induce DM. At 8 weeks after STZ injection, rats with DMED were classified into four groups, sham, control group [DMED rats received 500 μL phosphate buffer saline (PBS)]; T1 [DMED rats treated with 500 μL PBS containing 1 × 106 UC-MSCs]; T2 [DMED rats treated with 500 μL PBS containing 2 × 106 UC-MSCs]. Eight weeks after MSCs administration, the rats’ erectile function was measured by cavernous nerve stimulation. The blinded histological and gene expression assessment were used to analyze the eNOS, HSP70 content, and VEGF expression on the penile tissues. MSCs administration, rats in T1 and T2 groups showed a significant enhancement of erectile response that showed a trend of increase of VEGF mRNA level expression was 2.2 ± 0.61 in T2 Group supported with the optimum recovery of eNOS, in which the value of eNOS expression was 20.66% ± 2.32%. While optimum decrease of HSP70 content, the value of HSP70 expression was 15.50% ± 0.90%. IHC results showed that the DMED induction in rats caused a significant decrease of eNOS content in corpus cavernosum tissue. MSCs could ameliorate DMED in rats by increasing VEGF and decreasing HSP70 and eNOS, indicating these cells offer a potential application for DMED patients’ treatment.

Lysophosphatidylcholine Offsets the Protective Effects of Bone Marrow Mesenchymal Stem Cells on Inflammatory Response and Oxidative Stress Injury of Retinal Endothelial Cells via TLR4/NF-κB Signaling

Diabetic retinopathy (DR), as a major cause of blindness worldwide, is one common complication of diabetes mellitus. Inflammatory response and oxidative stress injury of endothelial cells play significant roles in the pathogenesis of DR. The study is aimed at investigating the effects of lysophosphatidylcholine (LPC) on the dysfunction of high glucose- (HG-) treated human retinal microvascular endothelial cells (HRMECs) after being cocultured with bone marrow mesenchymal stem cells (BMSCs) and the underlying regulatory mechanism. Coculture of BMSCs and HRMECs was performed in transwell chambers. The activities of antioxidant-related enzymes and molecules of oxidative stress injury and the contents of inflammatory cytokines were measured by ELISA. Flow cytometry analyzed the apoptosis of treated HRMECs. HRMECs were further treated with 10-50 μg/ml LPC to investigate the effect of LPC on the dysfunction of HRMECs. Western blotting was conducted to evaluate levels of TLR4 and p-NF-κB proteins. We found that BMSCs alleviated HG-induced inflammatory response and oxidative stress injury of HRMECs. Importantly, LPC offsets the protective effects of BMSCs on inflammatory response and oxidative stress injury of HRMECs. Furthermore, LPC upregulated the protein levels of TLR4 and p-NF-κB, activating the TLR4/NF-κB signaling pathway. Overall, our study demonstrated that LPC offsets the protective effects of BMSCs on inflammatory response and oxidative stress injury of HRMECs via TLR4/NF-κB signaling.

Protective effect of LIF-huMSCs on the retina of diabetic model rats

AIM

To investigate the protective effect of human umbilical cord mesenchymal stem cells (hUCMSCs) modified by the LIF gene on the retinal function of diabetic model rats and preliminarily explore the possible mechanism.

METHODS

A stably transfected cell line of hUCMSCs overexpressing leukemia inhibitory factor (LIF) was constructed. Overexpression was verified by fluorescent quantitative polymerase chain reaction (qPCR). Forty-eight adult Sprague-Dawley rats were randomly divided into a normal control group (group A), streptozotocin-induced diabetic control group (group B), diabetic rats at 3mo injected with empty vector-transfected hUCMSCs (group C) or injected with LIF-hUCMSCs (group D). Four weeks after the intravitreal injection, analyses in all groups included retinal function using flash electroretinogram (F-ERG), retinal blood vessel examination of retinal flat mounts perfused with fluorescein isothiocyanate-dextran (FITC-dextran), and retinal structure examination of sections using hematoxylin and eosin staining. Expression levels of adiponectin (APN), high-sensitivity C-reactive protein (hs-CRP), and neurotrophin-4 (NT-4) in each group was detected using immunohistochemistry, PCR, Western blotting, and ELISA, respectively.

RESULTS

A stable transgenic cell line of LIF-hUCMSCs was constructed. F-ERG and FITC-dextran examinations revealed no abnormalities of retinal structure and function in group A, severe damage of the retinal blood vessels and function in group B, and improved retinal structure and function in group C and especially group D. qPCR, ELISA, and Western blot analyses revealed progressively higher APN and NT-4 expression levels in groups B, C, and D than in group A. hs-CRP expression was significantly higher in group B than in groups A, C, and D, and was significantly higher in group C than in group D (P<0.05).

CONCLUSION

LIF-hUCMSCs protect the retina of diabetic rats by upregulating APN and NT-4 expression and downregulating hs-CRP expression in the retina.

A Review on Mesenchymal Stem Cells for Treatment of Retinal Diseases

Mesenchymal Stem Cells (MSCs) have been studied extensively for the treatment of several retinal diseases. The therapeutic potential of MSCs lies in its ability to differentiate into multiple lineages and secretome enriched with immunomodulatory, anti-angiogenic and neurotrophic factors. Several studies have reported the role of MSCs in repair and regeneration of the damaged retina where the secreted factors from MSCs prevent retinal degeneration, improve retinal morphology and function. MSCs also donate mitochondria to rescue the function of retinal cells and exosomes secreted by MSCs were found to have anti-apoptotic and anti-inflammatory effects. Based on several promising results obtained from the preclinical studies, several clinical trials were initiated to explore the potential advantages of MSCs for the treatment of retinal diseases. This review summarizes the various properties of MSCs that help to repair and restore the damaged retinal cells and its potential for the treatment of retinal degenerative diseases.

Bone marrow mesenchymal stem cells-induced exosomal microRNA-486-3p protects against diabetic retinopathy through TLR4/NF-κB axis repression

AIM

Diabetic retinopathy (DR) is a chronic disease causing health and economic burdens on individuals and society. Thus, this study is conducted to figure out the mechanisms of bone marrow mesenchymal stem cells (BMSCs)-induced exosomal microRNA-486-3p (miR-486-3p) in DR.

METHODS

The putative miR-486-3p binding sites to 3'untranslated region of Toll-like receptor 4 (TLR4) was verified by luciferase reporter assay. High glucose (HG)-treated Muller cells were transfected with miR-486-3p or TLR4-related oligonucleotides and plasmids to explore theirs functions in DR. Additionally, HG-treated Muller cells were co-cultured with BMSC-derived exosomes, exosomes collected from BMSCs that had been transfected with miR-486-3p or TLR4-related oligonucleotides and plasmids to explore their functions in DR. MiR-486-3p, TLR4 and nuclear factor-kappaB (NF-κB) expression, angiogenesis-related factors, oxidative stress factors, viability and apoptosis in HG-treated Muller cells were detected by RT-qPCR, western blot analysis, ELISA, MTT assay and flow cytometry, respectively.

RESULTS

MiR-486-3p was poorly expressed while TLR4 and NF-κB were highly expressed in HG-treated Muller cells. TLR4 was a target of miR-486-3p. Upregulating miR-486-3p or down-regulating TLR4 inhibited oxidative stress, inflammation and apoptosis, and promoted proliferation of HG-treated Muller cells. Meanwhile, BMSC-derived exosomes inhibited oxidative stress, inflammation and apoptosis, and promoted proliferation of HG-treated Muller cells. Restoring miR-486-3p further enhanced, while up-regulating TLR4 reversed, the improvement of exosomes treatment.

CONCLUSION

Our study highlights that up-regulation of miR-486-3p induced by BMSC-derived exosomes played a protective role in DR mice via TLR4/NF-κB axis repression.

Human umbilical cord mesenchymal stem cells in type 2 diabetes mellitus: the emerging therapeutic approach

The umbilical cord has been proved to be an easy-access, reliable, and useful source of mesenchymal stem cells (MSC) for clinical applications due to its primitive, immunomodulatory, non-immunogenic, secretory and paracrine, migratory, proliferative, and multipotent properties. This set of characteristics has recently attracted great research interest in the fields of nanotechnology and regenerative medicine and cellular therapy. Accumulating evidence supports a pronounced therapeutic potential of MSC in many different pathologies, from hematology to immunology, wound-healing, tissue regeneration, and oncology. Diabetes mellitus, branded the epidemic of the century, is considered a chronic metabolic disorder, representing a major burden for health system sustainability and an important public health challenge to modern societies. The available treatments for type 2 diabetes mellitus (T2DM) still rely mainly on combinations of oral antidiabetic agents with lifestyle and nutritional adjustments. Despite the continuous development of novel and better hypoglycemic drugs, their efficacy is limited in the installment and progression of silent T2DM complications. T2DM comorbidities and mortality rates still make it a serious, common, costly, and long-term manageable disease. Recently, experimental models, preclinical observations, and clinical studies have provided some insights and preliminary promising results using umbilical cord MSCs to treat and manage diabetes. This review focuses on the latest research and applications of human-derived umbilical cord MSC in the treatment and management of T2DM, exploring and systematizing the key effects of both umbilical cord MSC and its factor-rich secretome accordingly with the major complications associated to T2DM.

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.

Effects of High Glucose Concentration on Pericyte-Like Differentiated Human Adipose-Derived Mesenchymal Stem Cells

A pericyte-like differentiation of human adipose-derived mesenchymal stem cells (ASCs) was tested in in vitro experiments for possible therapeutic applications in cases of diabetic retinopathy (DR) to replace irreversibly lost pericytes. For this purpose, pericyte-like ASCs were obtained after their growth in a specific pericyte medium. They were then cultured in high glucose conditions to mimic the altered microenvironment of a diabetic eye. Several parameters were monitored, especially those particularly affected by disease progression: cell proliferation, viability and migration ability; reactive oxygen species (ROS) production; inflammation-related cytokines and angiogenic factors. Overall, encouraging results were obtained. In fact, even after glucose addition, ASCs pre-cultured in the pericyte medium (pmASCs) showed high proliferation rate, viability and migration ability. A considerable increase in mRNA expression levels of the anti-inflammatory cytokines transforming growth factor-β1 (TGF-β1) and interleukin-10 (IL-10) was observed, associated with reduction in ROS production, and mRNA expression of pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), and angiogenic factors. Finally, a pmASC-induced better organization of tube-like formation by retinal endothelial cells was observed in three-dimensional co-culture. The pericyte-like ASCs obtained in these experiments represent a valuable tool for the treatment of retinal damages occurring in diabetic patients.

Mesenchymal Stem Cell-Based Therapy for Retinal Degenerative Diseases: Experimental Models and Clinical Trials

Retinal degenerative diseases, such as age-related macular degeneration, retinitis pigmentosa, diabetic retinopathy or glaucoma, represent the main causes of a decreased quality of vision or even blindness worldwide. However, despite considerable efforts, the treatment possibilities for these disorders remain very limited. A perspective is offered by cell therapy using mesenchymal stem cells (MSCs). These cells can be obtained from the bone marrow or adipose tissue of a particular patient, expanded in vitro and used as the autologous cells. MSCs possess potent immunoregulatory properties and can inhibit a harmful inflammatory reaction in the diseased retina. By the production of numerous growth and neurotrophic factors, they support the survival and growth of retinal cells. In addition, MSCs can protect retinal cells by antiapoptotic properties and could contribute to the regeneration of the diseased retina by their ability to differentiate into various cell types, including the cells of the retina. All of these properties indicate the potential of MSCs for the therapy of diseased retinas. This view is supported by the recent results of numerous experimental studies in different preclinical models. Here we provide an overview of the therapeutic properties of MSCs, and their use in experimental models of retinal diseases and in clinical trials.

Insights into stem cell therapy for diabetic retinopathy: a bibliometric and visual analysis

Stem cells have been confirmed to be involved in the occurrence and development of diabetic retinopathy; however, the underlying mechanisms remain unclear. In this study, we used Citespace software to visually analyze 552 articles exploring the stem cell-based treatment of diabetic retinopathy over the past 20 years, which were included in the Web of Science Core Collection. We found the following: (1) a co-citation analysis of the references cited by all 552 articles indicated 15 clusters. In cluster #0, representing the stem cell field, some highly cited landmark studies emerged between 2009–2013. For example, endothelial progenitor cells and diabetic retinopathy gradually received the full attention of scholars, in terms of their relationship and therapeutic prospects. Some researchers also verified the potential of adipose-derived stem cells to differentiate into stable retinal perivascular cells, using a variety of animal models of retinal vascular disease. All of these achievements provided references for the subsequent stem cell research. (2) An analysis of popular keywords among the 552 articles revealed that, during the past 20 years, a relative increase in basic research articles examining stem cells and endothelial progenitor cells for the treatment of diabetic retinopathy was observed. The contents of these articles primarily involved the expression of vascular endothelial growth factor, vascular regeneration, oxidative stress, and inflammatory response. (3) A burst analysis of keywords used in the 552 articles indicated that genetic and cytological research regarding the promotion of angiogenesis was an issue of concern from 2001 to 2012, including several studies addressing the expression of various growth factor genes; from 2014 to 2020, mouse models of diabetic retinopathy were recognized as mature animal models, and the most recent research has focused on macular degeneration, macular edema, neurodegeneration, and inflammatory changes in diabetic animal models. (4) Globally, the current authoritative studies have focused on basic research towards the stem cell treatment of diabetic retinopathy. Existing clinical studies are of low quality and have insufficient evidence levels, and their findings have not yet been widely accepted in clinical practice. Major challenges during stem cell transplantation remain, including stem cell heterogeneity, cell delivery, and the effective homing of stem cells to damaged tissue. However, clinical trials examining potential stem cell-based treatments of diabetic retinopathy, including the use of pluripotent stem cells, retinal pigment epithelial cells, bone marrow mesenchymal stem cells, and endothelial progenitor cells, are currently ongoing, and high-quality clinical evidence is likely to appear in the future, to promote clinical transformation.

The Role of Mesenchymal Stromal Cells-Derived Small Extracellular Vesicles in Diabetes and Its Chronic Complications

Mesenchymal stromal cells (MSCs) are applied in regenerative medicine of several tissues and organs nowadays by virtue of their self-renewal capabilities, multiple differentiation capacity, potent immunomodulatory properties, and their ability to be favourably cultured and manipulated. With the continuous development of "cell-free therapy" research, MSC-derived small extracellular vesicles (MSC-sEVs) have increasingly become a research hotspot in the treatment of various diseases. Small extracellular vesicles (SEVs) are membrane vesicles with diameters of 30 to 150 nm that mediate signal transduction between adjacent or distal cells or organs by delivering non-coding RNA, protein, and DNA. The contents and effects of sEVs vary depending on the properties of the originating cell. In recent years, MSC-sEVs have been found to play an important role in the occurrence and development of diabetes mellitus as a new way of communication between cells. Diabetes mellitus is a common metabolic disease in clinic. Its complications of the heart, brain, kidney, eyes, and peripheral nerves are a serious threat to human health and has been a hot issue for clinicians. MSC-sEVs could be applied to repair or prevent damage from the complications of diabetes mellitus through anti-inflammatory effects, reduction of endoplasmic reticulum-related protein stress, polarization of M2 macrophages, and increasing autophagy. Therefore, we highly recommend that MSC-sEVs-based therapies to treat diabetes mellitus and its chronic complication be further explored. The analysis of the role and molecular mechanisms of MSC-sEVs in diabetes and its related complications will provide new idea and insights for the prevention and treatment of diabetes.

Human Fetal Pigmented Ciliary Epithelium Stem Cells have Regenerative Capacity in the Murine Retinal Degeneration Model of Laser Injury

BACKGROUND

Retinal degeneration and related eye disorders have limited treatment interventions. Since stem cell therapy has shown promising results, ciliary epithelium (CE) derived stem cells could be a better choice given the fact that cells from eye niche can better integrate with the degenerating retina, rewiring the synaptic damage.

OBJECTIVE

To test the effect of human fetal pigmented ciliary epithelium-derived neurospheres in the mouse model of laser-induced retinal degeneration.

METHODS

C57 male mice were subjected to retinal injury by Laser photocoagulation. Human fetal pigmented ciliary epithelium was obtained from post-aborted human eyeballs and cultured with epidermal growth factor (rhEGF) and fibroblast growth factor (rhFGF). The six day neurospheres were isolated, dissociated and transplanted into the subretinal space of the laser injured mice at the closest proximity to Laser shots. Mice were analyzed for functional vision through electroretinogram (ERG) and sacrificed at 1 week and 12 week time points. Retinal, Neurotropic, Apoptotic and proliferation markers were analysed using real-time polymerase chain reaction (PCR).

RESULTS

The CE neurospheres showed an increase in the expression of candidate genes analyzed in the study at 1 week time point, which sustained for longer time point of 12 weeks.

CONCLUSION

We showed the efficacy of human CE cells in the regeneration of retinal degeneration in murine model for the first time. CE cells need to be explored comprehensively both in disease and degeneration.

Management of retinitis pigmentosa by Wharton's jelly-derived mesenchymal stem cells: prospective analysis of 1-year results

PURPOSE

The aim of the study was to investigate annual structural and functional results, and their correlation with inheritance pattern of retinitis pigmentosa (RP) patients who were treated with Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs).

MATERIAL AND METHODS

This prospective, sequential, open-label phase-3 clinical study was conducted at Ankara University Faculty of Medicine, Department of Ophthalmology, between April 2019 and May 2020. The study included 34 eyes from 32 retinitis pigmentosa patients of various genotypes who were enrolled in the stem cells clinical trial. The patients were followed for 12 months after the WJ-MSCs transplantation into subtenon space and evaluated with consecutive examinations. Genetic mutations were investigated using a retinitis pigmentosa panel sequencing method consisting of 90 genes. All patients underwent a complete routine ophthalmic examination with best corrected visual acuity, optical coherence tomography angiography, visual field, and full-field electroretinography. Quantitative data obtained from baseline (T0), 6th month (T1), and 12th month (T2) examinations were compared.

RESULTS

According to timepoints at T0, T1, and T2: The mean outer retinal thickness was 100.3 μm, 119.1 μm, and 118.0 μm, respectively (p = 0.01; T0 < T1, T2). The mean horizontal ellipsoid zone width were 2.65 mm, 2.70 mm, and 2.69 mm respectively (p = 0.01; T0 < T1, T2). The mean best corrected visual acuity (BCVA) were 70.5 letters, 80.6 letters, and 79.9 letters, respectively (p = 0.01; T0 < T1, T2). The mean fundus perimetry deviation index (FPDI) was 8.0%, 11.4%, and 11.6%, respectively (p = 0.01; T0 < T1, T2). The mean full-field flicker ERG parameters at T0, T1, and T2: amplitudes were 2.4 mV, 5.0 mV, and 4.6 mV, respectively (p = 0.01; T0 < T1, T2). Implicit time were 43.3 ms, 37.9 ms, and 38.6 ms, respectively (p = 0.01; T0 > T1, T2). According to inheritance pattern, BCVA, FPDI, ERG amplitude, and implicit time data improved significantly in autosomal dominant (AD) and in autosomal recessive (AR) RP at 1 year follow-up (pAD = 0.01, pAR = 0.01; pAD = pAR > pX-linked). No ocular or systemic adverse events related to the surgical methods and/or WJ-MSCs were observed during the 1 year follow-up period.

CONCLUSION

Subtenon transplantation of WJ-MSCs was found to be effective and safe in the treatment of RP during the first year, similar to the sixth month's results. In autosomal dominant and autosomal recessive inheritance of RP, regardless of the genetic mutations, subtenon administration of WJ-MSCs can be considered an effective and safe option without any adverse effect for slowing or stopping the disease progression.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04224207 . Registered 8 January 2020.

Human umbilical cord-derived mesenchymal stem cells prevent the progression of early diabetic nephropathy through inhibiting inflammation and fibrosis

Background

Diabetic nephropathy (DN) is one of the most serious complications of diabetes and the leading cause of end-stage chronic kidney disease. Currently, there are no effective drugs for treating DN. Therefore, novel and effective strategies to ameliorate DN at the early stage should be identified. This study aimed to explore the effectiveness and underlying mechanisms of human umbilical cord mesenchymal stem cells (UC-MSCs) in DN.

Methods

We identified the basic biological properties and examined the multilineage differentiation potential of UC-MSCs. Streptozotocin (STZ)-induced DN rats were infused with 2 × 10⁶ UC-MSCs via the tail vein at week 6. After 2 weeks, we measured blood glucose level, levels of renal function parameters in the blood and urine, and cytokine levels in the kidney and blood, and analyzed renal pathological changes after UC-MSC treatment. We also determined the colonization of UC-MSCs in the kidney with or without STZ injection. Moreover, in vitro experiments were performed to analyze cytokine levels of renal tubular epithelial cell lines (NRK-52E, HK2) and human renal glomerular endothelial cell line (hrGECs).

Results

UC-MSCs significantly ameliorated functional parameters, such as 24-h urinary protein, creatinine clearance rate, serum creatinine, urea nitrogen, and renal hypertrophy index. Pathological changes in the kidney were manifested by significant reductions in renal vacuole degeneration, inflammatory cell infiltration, and renal interstitial fibrosis after UC-MSC treatment. We observed that the number of UC-MSCs recruited to the injured kidneys was increased compared with the controls. UC-MSCs apparently reduced the levels of pro-inflammatory cytokines (IL-6, IL-1β, and TNF-α) and pro-fibrotic factor (TGF-β) in the kidney and blood of DN rats. In vitro experiments showed that UC-MSC conditioned medium and UC-MSC-derived exosomes decreased the production of these cytokines in high glucose-injured renal tubular epithelial cells, and renal glomerular endothelial cells. Moreover, UC-MSCs secreted large amounts of growth factors including epidermal growth factor, fibroblast growth factor, hepatocyte growth factor, and vascular endothelial growth factor.

Conclusion

UC-MSCs can effectively improve the renal function, inhibit inflammation and fibrosis, and prevent its progression in a model of diabetes-induced chronic renal injury, indicating that UC-MSCs could be a promising treatment strategy for DN.

Pro-angiogenic Activity Discriminates Human Adipose-Derived Stromal Cells From Retinal Pericytes: Considerations for Cell-Based Therapy of Diabetic Retinopathy

Diabetic retinopathy (DR) is a frequent diabetes-associated complication. Pericyte dropout can cause increased vascular permeability and contribute to vascular occlusion. Adipose-derived stromal cells (ASC) have been suggested to replace pericytes and restore microvascular support as potential therapy of DR. In models of DR, ASC not only generated a cytoprotective and reparative environment by the secretion of trophic factors but also engrafted and integrated into the retina in a pericyte-like fashion. The aim of this study was to compare the pro-angiogenic features of human ASC and human retinal microvascular pericytes (HRMVPC) in vitro. The proliferation and the expression of ASC and HRMVPC markers were compared. Adhesion to high glucose-conditioned endothelial extracellular matrix, mimicking the diabetic microenvironment, was measured. The angiogenesis-promoting features of both cell types and their conditioned media on human retinal endothelial cells (EC) were assessed. To identify a molecular basis for the observed differences, gene expression profiling was performed using whole-genome microarrays, and data were validated using PCR arrays and flow cytometry. Based on multiplex cytokine results, functional studies on selected growth factors were performed to assess their role in angiogenic support. Despite a distinct heterogeneity in ASC and HRMVPC cultures with an overlap of expressed markers, ASC differed functionally from HRMVPC. Most importantly, the pro-angiogenic activity was solely featured by ASC, whereas HRMVPC actively suppressed vascular network formation. HRMVPC, in contrast to ASC, showed impaired adhesion and proliferation on the high glucose-conditioned endothelial extracellular matrix. These data were supported by gene expression profiles with differentially expressed genes. The vessel-stabilizing factors were more highly expressed in HRMVPC, and the angiogenesis-promoting factors were more highly expressed in ASC. The vascular endothelial growth factor receptor-2 inhibition efficiently abolished the ASC angiogenic supportive capacities, whereas the addition of angiopoietin-1 and angiopoietin-2 did not alter these effects. Our results clearly show that ASC are pro-angiogenic, whereas HRMVPC are marked by anti-angiogenic/EC-stabilizing features. These data support ASC as pericyte replacement in DR but also suggest a careful risk-to-benefit analysis to take full advantage of the ASC therapeutic features.

Preliminary research on the effects and mechanisms of umbilical cord‑derived mesenchymal stem cells in streptozotocin‑induced diabetic retinopathy

Diabetic retinopathy (DR) is one of the most prevalent microvascular complications of diabetes, and a common cause of blindness in working‑age individuals. Mesenchymal stem cell (MSC) transplantation has been considered a promising intervention therapy for DR, wherein the differentiation of MSCs into nerve cells plays an essential role. However, research into the role of MSCs in DR treatment remains incomplete, and the mechanisms of retinal repair at the molecular level have yet to be clarified. In the present study, all‑trans retinoic acid (ATRA) was used to promote the proliferation of rat umbilical cord (UC)‑derived MSCs and their differentiation into nerve cells. Furthermore, the effects and mechanisms of UC‑MSCs with or without ATRA treatment were investigated in rats subjected to streptozocin (STZ)‑induced DR. The results demonstrated that the transplantation of UC‑MSCs treated with or without ATRA attenuated DR in rats, and alleviated retinal tissue damage and apoptosis. In addition, the transplantation of UC‑MSCs treated with or without ATRA attenuated angiogenesis and inflammation in the retina by regulating the levels of relevant cytokines. UC‑MSCs treated with ATRA exerted a more prominent therapeutic effect than the untreated UC‑MSCs. On the whole, these findings indicate that UC‑MSCs alleviate STZ‑induced DR in rats by regulating angiogenesis and the inflammatory response at the molecular level. Thus, the findings of the present study may provide a theoretical basis for the application of MSCs in the treatment of DR.

Adipose-derived mesenchymal stromal cells reverse high glucose-induced reduction of angiogenesis in human retinal microvascular endothelial cells

BACKGROUND AIMS

Diabetic retinopathy (DR) is characterized by a progressive alteration of the retinal microvasculature, arising from microaneurysms to leaky vessels and finally abnormal neovascularization. The hyperglycemia-mediated loss of pericytes is a key event in vessel degeneration causing vascular destabilization. To overcome this, mesenchymal stromal cells (MSCs) have been tested as pericyte replacement in several animal models showing repair and regeneration of DR-damaged vasculature.

METHODS

We hypothesized that adipose-derived mesenchymal stromal cells (ASCs) resist high glucose-induced challenges and protect human retinal microvascular endothelial cells (HRMVECs) from glucose-mediated injury. ASCs and HRMVECs were cultured under normal-glucose (NG; 1 g/L) and high-glucose (HG; 4.5 g/L) conditions comparing their phenotype and angiogenic potential.

RESULTS

Whereas ASCs were generally unaffected by HG, HG caused a reduction of the angiogenic potential in HRMVEC. Indeed, HG-treated HRMVECs formed fewer vascular tube structures in a basement membrane angiogenesis assay. However, this was not observed in a direct ASC and HRMVEC coculture angiogenesis assay. Increased oxidative stress levels appeared to be linked to the HG-induced reduction of angiogenesis, which could be restored by ASC-conditioned medium and antioxidant treatment.

CONCLUSIONS

These findings suggest that ASC resist HG-stress whereas endothelial cell angiogenic capacity is reduced. Thus, ASC may be potentially therapeutically active in DR by restoring angiogenic deficits in retinal endothelial cells by the secretion of proangiogenic factors. However, these data also inquire for a thorough risk assessment about the timing of the ASC-based cell therapy, which can be considered advantageous at early stage of DR, but possibly detrimental at the late neo-angiogenic stage of DR.

Recent advances in understanding mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are among of the most studied cell type for cellular therapy thanks to the ease of isolation, cultivation, and the high ex vivo expansion potential. In 2018, the European Medicines Agency finally granted the first marketing authorization for an MSC product. Despite the numerous promising results in preclinical studies, translation into routine practice still lags behind: therapeutic benefits of MSCs are not as satisfactory in clinical trial settings as they appear to be in preclinical models. The bench-to-bedside-and-back approach and careful evaluation of discrepancies between preclinical and clinical results have provided valuable insights into critical components of MSC manufacturing, their mechanisms of action, and how to evaluate and quality-control them. We sum up these past developments in the introductory section (“Mesenchymal stromal cells: name follows function”). From the huge amount of information, we then selected a few examples to illustrate challenges and opportunities to improve MSCs for clinical purposes. These include tissue origin of MSCs, MSC culture conditions, immune compatibility, and route of application and dosing. Finally, we add some information on MSC mechanisms of action and translation into potency assays and give an outlook on future perspectives raising the question of whether the future clinical product may be cell-based or cell-derived.

Mesenchymal Stem Cells Attenuate Diabetic Lung Fibrosis via Adjusting Sirt3-Mediated Stress Responses in Rats

Diabetes affects a variety of organs such as the kidneys, eyes, and liver, and there is increasing evidence that the lung is also one of the target organs of diabetes and imbalance of Sirt3-mediated stress responses such as inflammation, oxidative stress, apoptosis, autophagy, and ER stress may contribute to diabetic lung fibrosis. Although previous studies have reported that mesenchymal stem cells (MSCs) have beneficial effects on various diabetic complications, the effect and mechanisms of MSCs on diabetes-induced lung injury are not clear. In this study, the STZ-induced diabetes model was constructed in rats, and the effect and potential mechanisms of bone marrow MSCs on diabetic lung fibrosis were investigated. The results revealed that fibrotic changes in the lung were successfully induced in the diabetic rats, while MSCs significantly inhibited or even reversed the changes. Specifically, MSCs upregulated the expression levels of Sirt3 and SOD2 and then activated the Nrf2/ARE signaling pathway, thereby controlling MDA, GSH content, and iNOS and NADPH oxidase subunit p22phox expression levels in the lung tissue. Meanwhile, high levels of Sirt3 and SOD2 induced by MSCs reduced the expression levels of IL-1β, TNF-α, ICAM-1, and MMP9 by suppressing the NF-κB/HMGB1/NLRP3/caspase-1 signaling pathway, as well as regulating the expression levels of cleaved caspasese-3, Bax, and Bcl2 by upregulating the expression level of P-Akt, thereby inhibiting the apoptosis of the lung tissue. In addition, MSCs also regulated the expression levels of LC3, P62, BiP, Chop, and PERK, thereby enhancing autophagy and attenuating endoplasmic reticulum stress. Taken together, our results suggest that MSCs effectively attenuate diabetic lung fibrosis via adjusting Sirt3-mediated responses, including inflammation, oxidative stress, apoptosis, autophagy, and endoplasmic reticulum stress, providing a theoretical foundation for further exploration of MSC-based diabetic therapeutics.

Glucose-induced oxidative stress and accelerated aging in endothelial cells are mediated by the depletion of mitochondrial SIRTs

Diabetic complications cause significant morbidity and mortality. Dysfunction of vascular endothelial cells (ECs), caused by oxidative stress, is a main mechanism of cellular damage. Oxidative stress accelerates EC senescence and DNA damage. In this study, we examined the role of mitochondrial sirtuins (SIRTs) in glucose-induced oxidative stress, EC senescence, and their regulation by miRNAs. Human retinal microvascular endothelial cells (HRECs) were exposed to 5 mmol/L (normoglycemia; NG) or 25 mmol/L glucose (hyperglycemia; HG) with or without transfection of miRNA antagomirs (miRNA-1, miRNA-19b, and miRNA-320; specific SIRT-targeting miRNAs). Expressions of SIRT3, 4 and 5 and their targeting miRNAs were examined using qRT-PCR and ELISAs were used to study SIRT proteins. Cellular senescence was investigated using senescence-associated β-gal stain; while, oxidative stress and mitochondrial alterations were examined using 8-OHdG staining and cytochrome B expressions, respectively. A streptozotocin-induced diabetic mouse model was also used and animal retinas and hearts were collected at 2 months of diabetes. In HRECs, HG downregulated the mRNAs of SIRTs, while SIRT-targeting miRNAs were upregulated. ELISA analyses confirmed such downregulation of SIRTs at the protein level. HG additionally caused early senescence, endothelial-to-mesenchymal transition and oxidative DNA damage in ECs. These changes were prevented by the transfection of specific miRNA antagomirs and by resveratrol. Retinal and cardiac tissues from diabetic mice also showed similar reductions of mitochondrial SIRTs. Collectively, these findings demonstrate a novel mechanism in which mitochondrial SIRTs regulate glucose-induced cellular aging through oxidative stress and how these SIRTs are regulated by specific miRNAs. Identifying such mechanisms may lead to the discovery of novel treatments for diabetic complications.

Management of retinitis pigmentosa by Wharton's jelly derived mesenchymal stem cells: preliminary clinical results

PURPOSE

The aim of this study is to determine if umbilical cord Wharton's jelly derived mesenchymal stem cells implanted in sub-tenon space have beneficial effects on visual functions in retinitis pigmentosa patients by reactivating the degenerated photoreceptors in dormant phase.

MATERIAL AND METHODS

This prospective, open-label, phase-3 clinical trial was conducted between April of 2019 and October of 2019 at Ankara University Faculty of Medicine, Department of Ophthalmology. 32 RP patients (34 eyes) were included in the study. The patients were followed for 6 months after the Wharton's jelly derived mesenchymal stem cell administration, and evaluated with consecutive examinations. All patients underwent a complete routine ophthalmic examination, and best corrected visual acuity, optical coherens tomography angiography, visual field, multifocal and full-field electroretinography were performed. The quantitative results were obtained from a comparison of the pre-injection and final examination (6th month) values.

RESULTS

The mean best corrected visual acuity was 70.5 letters prior to Wharton's jelly derived mesenchymal stem cell application and 80.6 letters at the 6th month (p = 0.01). The mean visual field median deviation value was 27.3 dB before the treatment and 24.7 dB at the 6th month (p = 0.01). The mean outer retinal thickness was 100.3 μm before the treatment and 119.1 μm at 6th month (p = 0.01). In the multifocal electroretinography results, P1 amplitudes improved in ring1 from 24.8 to 39.8 nv/deg2 (p = 0.01), in ring2 from 6.8 to 13.6 nv/deg2 (p = 0.01), and in ring3 from 3.1 to 5.7 nv/deg2 (p = 0.02). P1 implicit times improved in ring1 from 44.2 to 32.4 ms (p = 0.01), in ring2 from 45.2 to 33.2 ms (p = 0.02), and in ring3 from 41.9 to 32.4 ms (p = 0.01). The mean amplitude improved in 16 Tds from 2.4 to 5.0 nv/deg2 (p = 0.01) and in 32 Tds from 2.4 to 4.8 nv/deg2 (p = 0.01) in the full-field flicker electroretinography results. Full field flicker electroretinography mean implicit time also improved in 16 Tds from 43.3 to 37.9 ms (p = 0.01). No ocular or systemic adverse events related to the two types of surgical methods and/or Wharton's jelly derived mesenchymal stem cells itself were observed during the follow-up period.

CONCLUSION

RP is a genetic disorder that can result in blindness with outer retinal degeneration. Regardless of the type of genetic mutation, sub-tenon Wharton's jelly derived mesenchymal stem cell administration appears to be an effective and safe option. There are no serious adverse events or ophthalmic / systemic side effects for 6 months follow-up. Although the long-term adverse effects are still unknown, as an extraocular approach, subtenon implantation of the stem cells seems to be a reasonable way to avoid the devastating side effects of intravitreal/submacular injection. Further studies that include long-term follow-up are needed to determine the duration of efficacy and the frequency of application.

TRIAL REGISTRATION

SHGM56733164. Redistered 28 January 2019 https://shgm.saglik.gov.tr/organ-ve-doku-nakli-koordinatorlugu/56733164/203 E.507.

Pericytes in Microvessels: From "Mural" Function to Brain and Retina Regeneration

Pericytes are branched cells located in the wall of capillary blood vessels that are found throughout the body, embedded within the microvascular basement membrane and wrapping endothelial cells, with which they establish a strong physical contact. Pericytes regulate angiogenesis, vessel stabilization, and contribute to the formation of both the blood-brain and blood-retina barriers by Angiopoietin-1/Tie-2, platelet derived growth factor (PDGF) and transforming growth factor (TGF) signaling pathways, regulating pericyte-endothelial cell communication. Human pericytes that have been cultured for a long period give rise to multilineage progenitor cells and exhibit mesenchymal stem cell (MSC) features. We focused our attention on the roles of pericytes in brain and ocular diseases. In particular, pericyte involvement in brain ischemia, brain tumors, diabetic retinopathy, and uveal melanoma is described. Several molecules, such as adenosine and nitric oxide, are responsible for pericyte shrinkage during ischemia-reperfusion. Anti-inflammatory molecules, such as IL-10, TGFβ, and MHC-II, which are increased in glioblastoma-activated pericytes, are responsible for tumor growth. As regards the eye, pericytes play a role not only in ocular vessel stabilization, but also as a stem cell niche that contributes to regenerative processes in diabetic retinopathy. Moreover, pericytes participate in melanoma cell extravasation and the genetic ablation of the PDGF receptor reduces the number of pericytes and aberrant tumor microvessel formation with important implications for therapy efficacy. Thanks to their MSC features, pericytes could be considered excellent candidates to promote nervous tissue repair and for regenerative medicine.

Adult Stem Cell Therapeutics in Diabetic Retinopathy

Diabetic retinopathy (DR), a complication of diabetes, is one of the leading causes of blindness in working-age adults. The pathology of the disease prevents the endogenous stem cells from participating in the natural repair of the diseased retina. Current treatments, specifically stem cell therapeutics, have shown variable efficacy in preclinical models due to the multi-faceted nature of the disease. Among the various adult stem cells, mesenchymal stem cells, especially those derived from adipose tissue and bone marrow, have been explored as a possible treatment for DR. This review summarizes the current literature around the various adult stem cell treatments for the disease and outlines the benefits and limitations of the therapeutics that are being explored in the field. The paracrine nature of adipose stem cells, in particular, has been highlighted as a potential solution to the lack of a homing and conducive environment that poses a challenge to the implantation of exogenous stem cells in the target tissue. Various methods of mesenchymal stem cell priming to adapt to a hostile retinal microenvironment have been discussed. Current clinical trials and potential safety concerns have been examined, and the future directions of stem cell therapeutics in DR have also been contemplated.

Therapeutic effect of lutein supplement on non-proliferative diabetic retinopathy: A retrospective study

This study retrospectively evaluated the effect of lutein supplement (LS) on patients with non-proliferative diabetic retinopathy (NPDR).A total of 72 patients with NPDR were included in this study. All patients received Zeaxanthin during the study period. In addition, 36 patients also received LS and were assigned to the treatment group, while the other 36 patients did not receive LS and were assigned to the control group. All patients were treated for a total of 4 months. The endpoints included visual acuity (VA), contrast sensitivity (CS), and glare sensitivity (GS). In addition, any adverse events were also assessed. All endpoints were measured before and after 4-month treatment.Before treatment, there were no significant differences in VA (P = .75), CS (P = .71), and GS (P = .73) between two groups. After 4-month treatment, there were still no significant differences in all endpoints of VA (P = .66), CS (P = .58), and GS (P = .61) between two groups. No adverse events were recorded in either group.The results of this retrospective study showed that LS may not benefit for patients with NPDR after 4-month treatment. More high quality randomized controlled trials should still be needed to warrant the results of this study.

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.

Human adipose tissue-derived stromal cells act as functional pericytes in mice and suppress high-glucose-induced proinflammatory activation of bovine retinal endothelial cells

AIMS/HYPOTHESIS

The immunomodulatory capacity of adipose tissue-derived stromal cells (ASCs) is relevant for next-generation cell therapies that aim to reverse tissue dysfunction such as that caused by diabetes. Pericyte dropout from retinal capillaries underlies diabetic retinopathy and the subsequent aberrant angiogenesis.

METHODS

We investigated the pericytic function of ASCs after intravitreal injection of ASCs in mice with retinopathy of prematurity as a model for clinical diabetic retinopathy. In addition, ASCs influence their environment by paracrine signalling. For this, we assessed the immunomodulatory capacity of conditioned medium from cultured ASCs (ASC-Cme) on high glucose (HG)-stimulated bovine retinal endothelial cells (BRECs).

RESULTS

ASCs augmented and stabilised retinal angiogenesis and co-localised with capillaries at a pericyte-specific position. This indicates that cultured ASCs exert juxtacrine signalling in retinal microvessels. ASC-Cme alleviated HG-induced oxidative stress and its subsequent upregulation of downstream targets in an NF-κB dependent fashion in cultured BRECs. Functionally, monocyte adhesion to the monolayers of activated BRECs was also decreased by treatment with ASC-Cme and correlated with a decline in expression of adhesion-related genes such as SELE, ICAM1 and VCAM1.

CONCLUSIONS/INTERPRETATION

The ability of ASC-Cme to immunomodulate HG-challenged BRECs is related to the length of time for which ASCs were preconditioned in HG medium. Conditioned medium from ASCs that had been chronically exposed to HG medium was able to normalise the HG-challenged BRECs to normal glucose levels. In contrast, conditioned medium from ASCs that had been exposed to HG medium for a shorter time did not have this effect. Our results show that the manner of HG preconditioning of ASCs dictates their immunoregulatory properties and thus the potential outcome of treatment of diabetic retinopathy.

The role of the retinal pigment epithelium and Müller cells secretome in neovascular retinal pathologies

Secreted trophic factors are key to maintain the structural and functional integrity of the retina, as they regulate cellular pathways responsible for survival, function, and response to injury. Nevertheless, these same factors can also be involved in retinal pathologies, as a consequence of the impairment of the secretory function of cells. The cells considered as major contributors to the retinal secretome are the retinal pigmented epithelium (RPE) and Müller cells. Their role in the pathophysiology of the most common neovascular pathologies in the retina - Age-related Macular Degeneration (AMD), Diabetic Retinopathy (DR), and Retinopathy of Prematurity (ROP) - is highlighted in this short review, together with current trophic factor-based therapies, which are mainly focused on controlling inflammation, cell survival, and angiogenesis.