Effect of the blockade of the IL-23-Th17-IL-17A pathway on streptozotocin-induced diabetic retinopathy in rats

Interleukin-17A in diabetic retinopathy: The crosstalk of inflammation and angiogenesis

Diabetic retinopathy (DR) is a severe ocular complication of diabetes which can leads to irreversible vision loss in its late-stage. Chronic inflammation results from long-term hyperglycemia contributes to the pathogenesis and progression of DR. In recent years, the interleukin-17 (IL-17) family have attracted the interest of researchers. IL-17A is the most widely explored cytokine in IL-17 family, involved in various acute and chronic inflammatory diseases. Growing body of evidence indicate the role of IL-17A in the pathogenesis of DR. However, the pro-inflammatory and pro-angiogenic effect of IL-17A in DR have not hitherto been reviewed. Gaining an understanding of the pro-inflammatory role of IL-17A, and how IL-17A control/impact angiogenesis pathways in the eye will deepen our understanding of how IL-17A contributes to DR pathogenesis. Herein, we aimed to thoroughly review the pro-inflammatory role of IL-17A in DR, with focus in how IL-17A impact inflammation and angiogenesis crosstalk.

Berberine alleviates diabetic retinopathy by regulating the Th17/Treg ratio

BACKGROUND

Diabetic retinopathy (DR) stands as a prominent complication of diabetes. Berberine (BBR) has reported to be effective to ameliorate the retinal damage of DR. Studying the potential immunological mechanisms of BBR on the streptozotocin (STZ) induced DR mouse model will explain the therapeutic mechanisms of BBR and provide theoretical basis for the clinical application of this drug.

METHODS

C57BL/6 J mice were induced into a diabetic state using a 50 mg/(kg·d) dose of STZ over a 5-day period. Subsequently, they were subjected to a high-fat diet (HFD) for one month. Following a 5-week treatment with 100 mg/(kg·d) BBR, the concentrations of inflammatory factors in the mice's peripheral blood were determined using an enzyme-linked immunosorbent assay (ELISA). Hematoxylin-eosin staining was employed to scrutinize pathological changes in the mice's retinas, while flow cytometry assessed the proportions of T-lymphocyte subsets and the activation status of dendritic cells (DCs) in the spleen and lymph nodes. CD4+T cells and DC2.4 cell lines were utilized to investigate the direct and indirect effects of BBR on T cells under high glucose conditions in vitro.

RESULTS

Following 5 weeks of BBR treatment in the streptozotocin (STZ) mouse model of DR, we observed alleviation of retinal lesions and a down-regulation in the secretion of inflammatory cytokines, namely TNF-α, IL-1β, and IL-6, in the serum of these mice. And in the spleen and lymph nodes of these mice, BBR inhibited the proportion of Th17 cells and promoted the proportion of Treg cells, thereby down-regulating the Th17/Treg ratio. Additionally, in vitro experiments, BBR directly inhibited the expression of the transcription factor RORγt and promoted the expression of the transcription factor Foxp3 in T cells, resulting in a down-regulation of the Th17/Treg ratio. Furthermore, BBR indirectly modulated the Th17/Treg ratio by suppressing the secretion of TNF-α, IL-1β, and IL-6 by DCs and enhancing the secretion of indoleamine 2,3-dioxygenase (IDO) and transforming growth factor-beta (TGF-β) by DCs. This dual action inhibited Th17 cell differentiation while promoting Treg cells.

CONCLUSION

Our findings indicate that BBR regulate T cell subpopulation differentiation, reducing the Th17/Treg ratio by directly or indirectly pathway. This represents a potential therapeutic avenue of BBR for improving diabetic retinopathy.

Gut microbiome in diabetic retinopathy: A systematic review and meta-analysis

CONTEXT

Changes in the gut microbiome are linked with Type 2diabetes mellitus (T2DM) development, but alterations in patients with diabetic retinopathy (DR) are still being debated.

OBJECTIVE

To investigate the differences in biodiversity and relative abundance of gut microbiome between patients with DR and T2DM.

METHODS

A comprehensive search was performed in five electronic databases (PubMed, EMBASE, Cochrane Central Register of Controlled Trials, Web of Science, and CNKI) from the inception of each database through to August 2023. The standardized mean difference (SMD) and its 95% confidence interval (CI) were estimated using Stata 15.1. Furthermore, the alpha diversity index and relative abundance of the gut microbiome were calculated. The Egger test determined publication bias in the literature.

RESULTS

Seven case-control studies were included in the final dataset, comprising 195 patients with DR and 211 patients with T2DM. Compared to T2DM patients, patients in the DR group had a reduced but not significantly different α-diversity. The analysis of microbial composition at the phylum level revealed a marked increase in the relative abundance of Bacteroidetes(ES = 23.27, 95%CI[8.30, 38.23], P = 0.000) and a decline in Firmicutes(ES = 47.05, 95%CI[36.58, 57.52], P = 0.000), Proteobacteria (ES = 11.08, 95%CI[6.08, 16.07], P = 0.000) and Actinobacteria (ES = 10.43, 95%CI[1.64, 19.22], P = 0.001) in patients with DR when compared to those with T2DM.

CONCLUSIONS

An association exists between alterations in the gut microbiome of T2DM and the development and progression of DR. This suggests that re-establishing homeostasis of the gut microbiome could be a potential way to prevent or treat DR and requires further confirmation in future studies.

REGISTRATION DATABASE

Prospero.

REGISTRATION NUMBER

CRD42023455280.

Targeting IL-12 family cytokines: A potential strategy for type 1 and type 2 diabetes mellitus

Diabetes is a common metabolic disease characterized by an imbalance in blood glucose levels. The pathogenesis of diabetes involves the essential role of cytokines, particularly the IL-12 family cytokines. These cytokines, which have a similar structure, play multiple roles in regulating the immune response. Recent studies have emphasized the importance of IL-12 family cytokines in the development of both type 1 and type 2 diabetes mellitus. As a result, they hold promise as potential therapeutic targets for the treatment of these conditions. This review focuses on the potential of targeting IL-12 family cytokines for diabetes therapy based on their roles in the pathogenesis of both types of diabetes. We have summarized various therapies that target IL-12 family cytokines, including drug therapy, combination therapy, cell therapy, gene therapy, cytokine engineering therapy, and gut microbiota modulation. By analyzing the advantages and disadvantages of these therapies, we have evaluated their feasibility for clinical application and proposed possible solutions to overcome any challenges. In conclusion, targeting IL-12 family cytokines for diabetes therapy provides updated insights into their potential benefits, such as controlling inflammation, preserving islet β cells, reversing the onset of diabetes, and impeding the development of diabetic complications.

Alteration of intestinal microbiota is associated with diabetic retinopathy and its severity: Samples collected from southeast coast Chinese

BACKGROUND

Current approaches for the therapy of diabetic retinopathy (DR), which was one of leading causes of visual impairment, have their limitations. Animal experiments revealed that restructuring of intestinal microbiota can prevent retinopathy.

AIM

To explore the relationship between intestinal microbiota and DR among patients in the southeast coast of China, and provide clues for novel ways to prevention and treatment methods of DR.

METHODS

The fecal samples of non-diabetics (Group C, n = 15) and diabetics (Group DM, n = 30), including 15 samples with DR (Group DR) and 15 samples without DR (Group D), were analyzed by 16S rRNA sequencing. Intestinal microbiota compositions were compared between Group C and Group DM, Group DR and Group D, as well as patients with proliferative diabetic retinopathy (PDR) (Group PDR, n = 8) and patients without PDR (Group NPDR, n = 7). Spearman correlation analyses were performed to explore the associations between intestinal microbiota and clinical indicators.

RESULTS

The alpha and beta diversity did not differ significantly between Group DR and Group D as well as Group PDR and Group NPDR. At the family level, Fusobacteriaceae, Desulfovibrionaceae and Pseudomonadaceae were significantly increased in Group DR than in Group D (P < 0.05, respectively). At the genera level, Fusobacterium, Pseudomonas, and Adlercreutzia were increased in Group DR than Group D while Senegalimassilia was decreased (P < 0.05, respectively). Pseudomonas was negatively correlated with NK cell count (r = -0.39, P = 0.03). Further, the abundance of genera Eubacterium (P < 0.01), Peptococcus, Desulfovibrio, Acetanaerobacterium and Negativibacillus (P < 0.05, respectively) were higher in Group PDR compared to Group NPDR, while Pseudomonas, Alloprevotella and Tyzzerella (P < 0.05, respectively) were lower. Acetanaerobacterium and Desulfovibrio were positively correlated with fasting insulin (r = 0.53 and 0.61, respectively, P < 0.05), when Negativibacillus was negatively correlated with B cell count (r = -0.67, P < 0.01).

CONCLUSION

Our findings indicated that the alteration of gut microbiota was associated with DR and its severity among patients in the southeast coast of China, probably by multiple mechanisms such as producing short-chain fatty acids, influencing permeability of blood vessels, affecting levels of vascular cell adhesion molecule-1, hypoxia-inducible factor-1, B cell and insulin. Modulating gut microbiota composition might be a novel strategy for prevention of DR, particularly PDR in population above.

Th22 cells induce Müller cell activation via the Act1/TRAF6 pathway in diabetic retinopathy

T helper 22 (Th22) cells have been implicated in diabetic retinopathy (DR), but it remains unclear whether Th22 cells involve in the pathogenesis of DR. To investigate the role of Th22 cells in DR mice, the animal models were established by intraperitoneal injection of STZ and confirmed by fundus fluorescein angiography and retinal haematoxylin-eosin staining. IL-22BP was administered by intravitreal injection. IL-22 level was measured by ELISA in vivo and in vitro. The expression of IL-22Rα1 in the retina was assessed by immunofluorescence. We assessed GFAP, VEGF, ICAM-1, inflammatory-associated factors and the integrity of blood-retinal barrier in control, DR, IL-22BP, and sham group. Müller cells were co-cultured with Th22 cells, and the expression of the above proteins was measured by immunoblotting. Plasmid transfection technique was used to silence Act1 gene in Müller cells. Results in vivo and in vitro indicated that Th22 cells infiltrated into the DR retinal and IL-22Rα1 expressed in Müller cells. Th22 cells promoted Müller cells activation and inflammatory factor secretion by secreting IL-22 compared with high-glucose stimulation alone. In addition, IL-22BP ameliorated the pathological alterations of the retina in DR. Inhibition of the inflammatory signalling cascade through Act1 knockdown alleviated DR-like pathology. All in all, the results suggested that Th22 cells infiltrated into the retina and secreted IL-22 in DR, and then IL-22 binding with IL-22Rα1 activated the Act1/TRAF6 signal pathway, and promoted the inflammatory of Müller cells and involved the pathogenesis of DR.

Aqueous Humor Factors' Predictive Effects in Treating Refractor Macular Edema: An Overview

The refractory macular edema (RME) seriously affects the patient's vision due to its repetition and ineffective drug response. RME is mainly related to the inflammatory pathway and angiogenesis pathway. At present, microglia activation and angiogenesis have also been widely focused on. With the promotion of the concept of precision diagnosis and treatment, intraocular fluid is becoming a popular evidence-based method. The detection and evaluation of aqueous humor factors can provide more accurate evidences and guidance for the treatment of RME. The purpose of this article is to review the treatment prediction and assessment progress of aqueous humor cytokines for the RME, giving evidence to provide a basis for expanding the diagnosis and treatment ideas of RME and guiding the development of personalized medical treatment.

Melatonin prevents experimental central serous chorioretinopathy in rats

Central serous chorioretinopathy (CSC) is a vision-threatening disease with no validated treatment and unclear pathogenesis. It is characterized by dilation and leakage of choroidal vasculature, resulting in the accumulation of subretinal fluid, and serous detachment of the neurosensory retina. Numerous studies have demonstrated that melatonin had multiple protective effects against endothelial dysfunction, vascular inflammation, and blood-retinal barrier (BRB) breakdown. However, the effect of melatonin on CSC, and its exact pathogenesis, is not well understood thus far. In this study, an experimental model was established by intravitreal injection of aldosterone in rats, which mimicked the features of CSC. Our results found that melatonin administration in advance significantly inhibited aldosterone-induced choroidal thickening and vasodilation by reducing the expression of calcium-activated potassium channel KCa2.3, and attenuated tortuosity of choroid vessels. Moreover, melatonin protected the BRB integrity and prevented the decrease in tight junction protein (ZO-1, occludin, and claudin-1) levels in the rat model induced by aldosterone. Additionally, the data also showed that intraperitoneal injection of melatonin in advance inhibited aldosterone-induced macrophage/microglia infiltration, and remarkably diminished the levels of inflammatory cytokines (interleukin-6 [IL-6], IL-1β, and cyclooxygenase-2), chemokines (chemokine C-C motif ligand 3, and C-X-C motif ligand 1), and matrix metalloproteinases (MMP-2 and MMP-9). Luzindole, as the nonselective MT1 and MT2 antagonist, and 4-phenyl-2-propionamidotetraline, as the selective MT2 antagonist, neutralized the melatonin-induced inhibition of choroidal thickening and choroidal vasodilation, indicating that melatonin might exert the effects via binding to its receptors. Furthermore, the IL-17A/nuclear factor-κB signaling pathway was activated by intravitreal administration of aldosterone, while it was suppressed in melatonin-treated in advance rat eyes. This study indicates that melatonin could serve as a promising safe therapeutic strategy for CSC patients.

Contribution of Interleukin-17A to Retinal Degenerative Diseases

Retinal degenerative diseases are a leading cause of vision loss and blindness throughout the world, characterized by chronic and progressive loss of neurons and/or myelin. One of the common features of retinal degenerative diseases and central neurodegenerative diseases is chronic neuroinflammation. Interleukin-17A (IL-17A) is the cytokine most closely related to disease in its family. Accumulating evidence suggests that IL-17A plays a key role in human retinal degenerative diseases, including age-related macular degeneration, diabetic retinopathy and glaucoma. This review aims to provide an overview of the role of IL-17A participating in the pathogenesis of retinal degenerative diseases, which may open new avenues for potential therapeutic interventions.

IL-17A Damages the Blood-Retinal Barrier through Activating the Janus Kinase 1 Pathway

Blood-retinal barrier (BRB) dysfunction underlies macular oedema in many sight-threatening conditions, including diabetic macular oedema, neovascular age-related macular degeneration and uveoretinitis. Inflammation plays an important role in BRB dysfunction. This study aimed to understand the role of the inflammatory cytokine IL-17A in BRB dysfunction and the mechanism involved. Human retinal pigment epithelial (RPE) cell line ARPE19 and murine brain endothelial line bEnd.3 were cultured on transwell membranes to model the outer BRB and inner BRB, respectively. IL-17A treatment (3 days in bEnd.3 cells and 6 days in ARPE19 cells) disrupted the distribution of claudin-5 in bEnd.3 cells and ZO-1 in ARPE19 cells, reduced the transepithelial/transendothelial electrical resistance (TEER) and increased permeability to FITC-tracers in vitro. Intravitreal (20 ng/1 μL/eye) or intravenous (20 ng/g) injection of recombinant IL-17A induced retinal albumin leakage within 48 h in C57BL/6J mice. Mechanistically, IL-17A induced Janus kinase 1 (JAK1) phosphorylation in bEnd.3 but not ARPE19 cells. Blocking JAK1 with Tofacitinib prevented IL-17A-mediated claudin-5 dysmorphia in bEnd.3 cells and reduced albumin leakage in IL-17A-treated mice. Our results suggest that IL-17A can damage the BRB through the activating the JAK1 signaling pathway, and targeting this pathway may be a novel approach to treat inflammation-induced macular oedema.

Comparison of inflammatory cytokines levels in the aqueous humor with diabetic retinopathy

PURPOSE

Evidence has accumulated suggesting that various inflammatory cytokines are involved in the progress of diabetic retinopathy (DR), but there are few studies concerning the relationship between individual cytokines levels in the aqueous humor (AH) and the severity of DR. This study aimed to explore the differences of interleukin (IL)-23, IL-17, IL-10 and transforming growth factor (TGF)-β in AH form patients with different proliferative stages of DR.

METHODS

From June 2016 to June 2019, patients for senile cataract surgery were enrolled with the informed consent. All cases were graded into 4 groups: the control group (patients without diabetes), non-retinopathy (NDR) group (diabetic patients without retinopathy), non-proliferative diabetic retinopathy (NPDR) group, and proliferative diabetic retinopathy (PDR) group. The concentrations of IL-23, IL-17, IL-10, and TGF-β in AH were measured using ELISA and compared them within four groups by ANOVA.

RESULTS

In this study, 20 (28.57%), 18 (25.71%), 17 (24.29%), and 15 (21.43%) patients were included in the control, NDR, NPDR, and PDR groups, respectively. There had no significant differences in demographic characteristics (P > 0.05). Comparison of these cytokines within four groups revealed: the IL-23 level was increased in NDR group initially and raised along with the progression of DR (P < 0.01). The IL-17 level was significantly higher in NPDR and PDR groups compared to NDR and the control groups, and positively correlated with more-severe DR (P < 0.01). By contrast, The IL-10 level was significantly lower in diabetic patients than in non-diabetic controls, and decreased as the severity of DR increased (P < 0.05). In addition, TGF-β was also elevated in diabetic patients, but showed no differences based on the presence or severity of DR (P > 0.05).

CONCLUSIONS

The over-expression of IL-23 and IL-17 in AH might have a synergistic effect on the pathogenesis well before the proliferative stage, and was typical positively correlated with the severity of DR. These results offer a novel early therapeutic target for DR.

Could IL-17A Be a Novel Therapeutic Target in Diabetic Nephropathy?

Chronic kidney disease has become a major medical issue in recent years due to its high prevalence worldwide, its association with premature mortality, and its social and economic implications. A number of patients gradually progress to end-stage renal disease (ESRD), requiring then dialysis and kidney transplantation. Currently, approximately 40% of patients with diabetes develop kidney disease, making it the most prevalent cause of ESRD. Thus, more effective therapies for diabetic nephropathy are needed. In preclinical studies of diabetes, anti-inflammatory therapeutic strategies have been used to protect the kidneys. Recent evidence supports that immune cells play an active role in the pathogenesis of diabetic nephropathy. Th17 immune cells and their effector cytokine IL-17A have recently emerged as promising targets in several clinical conditions, including renal diseases. Here, we review current knowledge regarding the involvement of Th17/IL-17A in the genesis of diabetic renal injury, as well as the rationale behind targeting IL-17A as an additional therapy in patients with diabetic nephropathy.

Curcumin Alleviates Oxaliplatin-Induced Peripheral Neuropathic Pain through Inhibiting Oxidative Stress-Mediated Activation of NF-κB and Mitigating Inflammation

Oxaliplatin is a first-line clinical drug in cancer treatment and its side effects of peripheral neuropathic pain have also attracted much attention. Neuroinflammation induced by oxidative stress-mediated activation of nuclear factor-kappa B (NF-κB) plays an important role in the course. Current studies have shown that curcumin has various biological activities like antioxidant, anti-inflammatory, antitumor and so on, while few studies were conducted about its role in oxaliplatin-induced peripheral neuropathic pain. The aim of this study is to verify the mechanism of curcumin alleviating oxaliplatin-induced peripheral neuropathic pain. Intraperitoneal injection with oxaliplatin (4 mg/kg body weight) was given to the rats twice a week and last for four weeks to establish the model rats. Gavage administration of curcumin (12.5, 25, and 50 mg/kg body weight, respectively) was conducted for consecutive 28 d to explore the effects and potential mechanism. Our results showed that curcumin administration could increase mechanical withdrawal threshold and decrease the paw-withdrawal times of cold allodynia significantly; meanwhile, motor nerve conduction velocity (MNCV) and sense nerve conduction velocity (SNCV) were both increased and the injured neurons of the spinal cord were repaired. In addition, curcumin administration increased superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and reduced malondialdehyde (MDA). Moreover, the curcumin operation inhibited the activated of NF-κB and level of inflammatory factors like tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6). In conclusion, these findings suggested that curcumin could alleviate oxaliplatin-induced peripheral neuropathic pain; the mechanism might be inhibiting oxidative stress-mediated activation of NF-κB and mitigating neuroinflammation.

Interleukin-17: The Role for Pathological Angiogenesis in Ocular Neovascular Diseases

Ocular neovascular diseases are featured by abnormal angiogenesis in the eye, and they seriously threaten the human visual health. These diseases include proliferative diabetic retinopathy (PDR), age-related macular degeneration (AMD), retinopathy of prematurity (ROP), and retinal vein occlusion (RVO). In fact, ocular neovascular diseases represent the leading causes of vision impairment and blindness worldwide. Ocular neovascularization, the process of pathological vessel formation in eye, underlies ocular neovascular diseases. Cytokines have important regulatory roles in neovascularization through immunological networks. Interleukin (IL)-17, the signature cytokine produced by T helper 17 (Th17) cells, has proven to be involved in ocular neovascularization. However, roles of IL-17 in ocular neovascular diseases still remain controversial. This review provides an overview of the functional roles of IL-17 in ocular neovascular diseases from basic research to clinical evidence by focusing on PDR, AMD, ROP, and RVO. The possible roles of IL-17 in neovascularization are achieved through a regulatory network of cytoskeleton remodeling, vascular endothelial growth factor (VEGF), VEGF-related cytokines, and complement components. Current applications as well as potential therapies targeting IL-17 with genome editing systems are also outlined and discussed. Targeting IL-17 might be a promising therapeutic strategy against ocular neovascular diseases.

Interleukin-17A blockade reduces albuminuria and kidney injury in an accelerated model of diabetic nephropathy

Diabetic nephropathy (DN) is one of the most common complications of diabetes, and currently the first end-stage renal disease worldwide. New strategies to treat DN using agents that target inflammatory pathways have attracted special interest. Recent pieces of evidences suggest a promising effect of IL-17A, the Th17 effector cytokine. Among experimental DN models, mouse strain BTBR ob/ob (leptin deficiency mutation) develops histological features similar to human DN, which means an opportunity to study mechanisms and novel therapies aimed at DN regression. We found that BTBR ob/ob mice presented renal activation of the factors controlling Th17 differentiation. The presence of IL-17A-expressing cells, mainly CD4⁺ and γδ lymphocytes, was associated with upregulation of proinflammatory factors, macrophage infiltration and the beginning of renal damage. To study IL-17A involvement in experimental DN pathogenesis, treatment with an IL-17A neutralizing antibody was carried out starting when the renal damage had already appeared. IL-17A blockade ameliorated renal dysfunction and disease progression in BTBR ob/ob mice. These beneficial effects correlated to podocyte number restoration and inhibition of NF-κB/proinflammatory factors linked to a decrease in renal inflammatory-cell infiltration. These data demonstrate that IL-17A takes part in diabetes-mediated renal damage and could be a promising therapeutic target to improve DN.

Interleukin 17A promotes diabetic kidney injury

The role of the pro-inflammatory cytokine IL-17 in the pathogenesis of numerous inflammatory disorders is well-documented, but conflicting results are reported for its role in diabetic nephropathy. Here we examined the role of IL-17 signalling in a model of streptozotocin-induced diabetic nephropathy through IL-17 knockout mice, administration of neutralising monoclonal anti-IL-17 antibody and in vitro examination of gene expression of renal tubular cells and podocytes under high glucose conditions with or without recombinant IL-17. IL-17 deficient mice were protected against progression of diabetic nephropathy, exhibiting reduced albuminuria, glomerular damage, macrophage accumulation and renal fibrosis at 12 weeks and 24 weeks. Administration of anti-IL-17 monoclonal antibody to diabetic wild-type mice was similarly protective. IL-17 deficiency also attenuated up-regulation of pro-inflammatory and pro-fibrotic genes including IL-6, TNF-α, CCL2, CXCL10 and TGF-β in diabetic kidneys. In vitro co-stimulation with recombinant IL-17 and high glucose were synergistic in increasing the expression of pro-inflammatory genes in both cultured renal tubular cells and podocytes. We conclude that absence of IL-17 signalling is protective against streptozotocin-induced diabetic nephropathy, thus implying a pro-inflammatory role of IL-17 in its pathogenesis. Targeting the IL-17 axis may represent a novel therapeutic approach in the treatment of this disorder.

A complex auxiliary: IL-17/Th17 signaling during type 1 diabetes progression

Type 1 diabetes (T1D) is an autoimmune disease centered around the loss of the beta cells of the islets of Langerhans, and consequent inability of the islets to produce the insulin necessary to maintain glycemic control. While most therapeutic approaches have been centered on insulin replacement, newer approaches to target the underlying immune response have become an area of focus. However, the immune landscape in T1D is extremely complex, and the roles played by individual cytokines during disease progression are incompletely understood, making the development of immunotherapies very difficult. In this review, we discuss the complex auxiliary role played by IL-17, both around the islet and in peripheral tissues such as the gut and kidney, which might influence T1D progression. Through our re-analysis of the key factors involved IL-17 signaling in recently published single-cell sequencing and sorted-cell bulk sequencing datasets, we find supporting evidence for the general existence of the signaling apparatus in islet endocrine cells. We also explore the emerging evidence of IL-17 serving as an influential factor in diabetic complications that affect distal tissues. While anti-IL-17 therapies are emerging as an option for psoriasis and other autoimmune disorders, we highlight here a number of questions that would need to be addressed before their potential applicability to treating T1D can be fully evaluated.

Mesenchymal stromal/stem cells as potential therapy in diabetic retinopathy

Diabetic retinopathy (DR) is a multifactorial microvascular disease induced by hyperglycemia and subsequent metabolic abnormalities. The resulting cell stress causes a sequela of events that ultimately can lead to severe vision impairment and blindness. The early stages are characterized by activation of glia and loss of pericytes, endothelial cells (EC) and neuronal cells. The integrity of the retinal microvasculature becomes affected, and, as a possible late response, macular edema may develop as a common reason for vision loss in patients with non-proliferative DR. Moreover, the local ischemia can trigger vasoproliferation leading to vision-threating proliferative DR (PDR) in humans. Available treatment options include control of metabolic and hemodynamic factors. Timely intervention of advanced DR stages with laser photocoagulation, intraocular anti-vascular endothelial growth factor (VEGF) or glucocorticoid drugs can reduce vision loss. As the pathology involves cell loss of both the vascular and neuroglial compartments, cell replacement strategies by stem and progenitor cells have gained considerable interest in the past years. Compared to other disease entities, so far little is known about the efficacy and potential mode of action of cell therapy in treatment of DR. In preclinical models of DR different cell types have been applied ranging from embryonic or induced pluripotent stem cells, hematopoietic stem cells, and endothelial progenitor cells to mesenchymal stromal cells (MSC). The latter cell population can combine various modes of action (MoA), thus they are among the most intensely tested cell types in cell therapy. The aim of this review is to discuss the rationale for using MSC as potential cell therapy to treat DR. Accordingly, we will revise identified MoA of MSCs and speculate how these may support the repair of the damaged retina.

Association between aqueous humor and vitreous fluid levels of Th17 cell-related cytokines in patients with proliferative diabetic retinopathy

Inflammation is known to be involved in the progression of diabetic retinopathy. We have recently reported that vitreous levels of IL-4, IL-17A, IL-22, IL-31, and TNFα are higher than the respective serum levels in proliferative diabetic retinopathy (PDR) patients, and that vitreous levels of these cytokines are higher in PDR than in other non-inflammatory vitreoretinal diseases or uveitis associated with sarcoidosis. In the present study, we investigated inflammatory cytokines including Th17 cell-related cytokines in aqueous humor samples obtained from eyes with PDR, and analyzed the association between the aqueous humor and vitreous fluid levels of individual cytokines. The study group consisted of 31 consecutive type 2 diabetic patients with PDR who underwent cataract surgery and vitrectomy for vitreous hemorrhage and/or tractional retinal detachment. Undiluted aqueous humor was collected during cataract surgery, and then vitreous fluid was obtained using a 25G vitreous cutter inserted into the mid-vitreous cavity at the beginning of vitrectomy. IL-1β, IL-4, IL-6, IL-10, IL-17A, IL-17F, IL-21, IL-22, IL-23, IL-25, IL-31, IL-33, IFN-γ, soluble CD40 ligand (sCD40L), and TNFα levels in the aqueous humor and vitreous fluid were measured using a beads-array system. Although IL-17A was detected in the aqueous humor of eyes with PDR and the level correlated with IL-17A level in the vitreous fluid, both percent detectable and level of IL-17A in the aqueous humor were significantly lower than those in the vitreous fluid. Vitreous IL-17A level was related significantly to IL-10, IL-22, and TNFα levels in aqueous humor as well as in vitreous fluid, On the other hand, aqueous IL-17A level was not related significantly to aqueous or vitreous levels of IL-10, IL-22 or TNFα level. The present study demonstrated that IL-17A level and detectable rate in the aqueous humor of patients with PDR are markedly lower than those in the vitreous fluid and aqueous IL-17A does not correlate with vitreous levels of other cytokines, and hence should not be used as a surrogate for IL-17A in the vitreous fluid.

Levels of Interleukin 27 and Interleukin 35 in the Serum and Vitreous of Patients with Proliferative Diabetic Retinopathy

PURPOSE

To examine the role of interleukin 27(IL-27) and interleukin 35 (IL-35) in diabetic retinopathy (DR).

METHODS

Patients with diabetes mellitus were divided into three groups: diabetes without retinopathy (DWR), non-proliferative diabetic retinopathy (NPDR), and proliferative diabetic retinopathy (PDR). Patients with idiopathic macular epiretinal membrane (IMEM) were included as a control group. The serum and vitreous levels of IL-27 and IL-35 were measured using ELISA.

RESULTS

The serum levels of IL-27 (median 240.900 pg/mL, range 42.224 - 617.810 pg/mL; p < 0.001) and IL-35 (median 11.875 ng/mL, range 8.640 - 19.340 ng/mL; p < 0.001) were significantly decreased in PDR patients compared to controls (median 2712.310 pg/mL, range 1005.375-5786.877 pg/mL and median 25.185 ng/mL, range 22.845 - 29.590 ng/mL, respectively). The vitreous levels of IL-35 were significantly decreased in PDR patients (16.32 ± 3.24 ng/mL) compared to controls (24.54 ± 5.86 ng/mL, p < 0.001).

CONCLUSIONS

Serum and vitreous levels of IL-35 and serum level of IL-27 may be associated with the pathogenesis of PDR.

Association of Complement C5 Gene Polymorphisms with Proliferative Diabetic Retinopathy of Type 2 Diabetes in a Chinese Han Population

Purpose

To investigate the association of C5 SNPs with proliferative diabetic retinopathy (PDR) of type 2 diabetes (T2D).

Methods

A total of four C5 SNPs including rs2269067, rs7040033, rs1017119 and rs7027797 were genotyped in 400 PDR patients with T2D (cases) and 600 non- proliferative diabetic retinopathy PDR (NPDR) with T2D patients (controls) by using PCR-RFLP method. mRNA expression was examined by real-time PCR. Cytokine production was detected by ELISA.

Results

The frequency of GG genotype of C5 rs2269067 was significantly increased in cases compared with controls (Pc = 3.4×10⁻⁵, OR = 1.87). And C5 mRNA expression was significantly increased in rs2269067 GG cases as compared with CG or CC cases (P = 0.003, P = 0.001, respectively). Moreover, the production of IL-6 was significantly increased in rs2269067 GG cases compared to CG cases or CC cases (P = 0.002, P = 0.001, respectively).

Conclusions

C5 rs2269067 GG genotype confers risk for PDR of T2D in Chinese han population and is associated with an elevated C5 mRNA expression and an increased IL-6 production.

Protective effects of SIRT1 in patients with proliferative diabetic retinopathy via the inhibition of IL-17 expression

Diabetic retinopathy (DR) is a chronic microvascular complication of diabetes that may lead to loss of vision. The pathogenesis of DR is complex and elevated expression levels of T helper (Th)17 cells and interleukin (IL)-17 have been suggested to be associated with the development and progression of DR. Sirtuin 1 (SIRT1) is a nicotinamide-adenine dinucleotide⁺-dependent histone deacetylase that is downregulated in patients with DR. Previous studies have demonstrated that SIRT1 is capable of inhibiting the production of IL-17. In the present study, 19 patients with proliferative diabetic retinopathy (PDR) and 20 non-diabetic controls with idiopathic macular epiretinal membranes were recruited and the SIRT1 expression levels of excised specimens were analyzed using immunohistochemistry. IL-17 expression levels in the sera from patients with PDR and controls were determined by enzyme-linked immunosorbent assay (ELISA). Furthermore, SIRT1 mRNA and protein expression levels in peripheral blood mononuclear cells (PBMCs) from the two groups were analyzed following culture with or without a SIRT1 activator, resveratrol. IL-17 expression levels in the supernatants of PBMCs were determined using ELISA and the results demonstrated that IL-17 expression levels were increased in the sera of patients with PDR, as compared with the controls. Furthermore, increased expression levels of SIRT1 and IL-17 were detected in fibrovascular membranes and PBMCs harvested from patients with PDR, respectively. Notably, SIRT1 mRNA and protein expression levels were decreased in the PBMCs of patients with PDR and IL-17 production was inhibited following SIRT1 activation. The results of the present study indicated that imbalanced IL-17 and SIRT1 expression levels may contribute to the pathogenesis of DR, and SIRT1 may have a protective role in PDR by inhibiting the production of IL-17.