IL-20 promotes epithelial healing of the injured mouse cornea

CsIL-20, a tongue sole interleukin-20, negatively mediates leucocyte activity and antibacterial defense

Interleukin-20 (IL-20), as an essential member of IL-10 family, plays vital roles in mammalian immunological response such as antimicrobial, inflammation, hematopoiesis, and immune diseases. In teleost, the study about immune antimicrobial function of IL-20 is largely scarce. In this article, we revealed the expression profiles and the immunological functions of the IL-20 (CsIL-20) in tongue sole Cynoglossus semilaevis. CsIL-20 is composed of 183 amino acid residues, with seven cysteine residues and a typical IL-10 domain which comprises six α-helices and two β-sheets, and shares 34.4-71.2 % identities with other teleost IL-20. CsIL-20 was constitutively expressed in a variety of tissues and regulated by bacterial invasion, and the recombinant CsIL-20 (rCsIL-20) could bind to different bacteria. In vitro rCsIL-20 could interact with the membrane of peripheral blood leukocytes (PBLs), leading to the attenuation of reactive oxygen species (ROS) production and acid phosphatase activity in PBLs. In line with In vitro results, In vivo rCsIL-20 could obviously suppressed the host immune against bacterial infection. Furthermore, knockdown of CsIL-20 in vivo could markedly enhance the host antibacterial immunity. Collectively, these observations offer new insights into the negative effect of CsIL-20 on antibacterial immunity.

A Method for Real-Time Assessment of Mitochondrial Respiration Using Murine Corneal Biopsy

Purpose

To develop and optimize a method to monitor real-time mitochondrial function by measuring the oxygen consumption rate (OCR) in murine corneal biopsy punches with a Seahorse extracellular flux analyzer.

Methods

Murine corneal biopsies were obtained using a biopsy punch immediately after euthanasia. The corneal metabolic profile was assessed using a Seahorse XFe96 pro analyzer, and mitochondrial respiration was analyzed with specific settings.

Results

Real-time adenosine triphosphate rate assay showed that mitochondrial oxidative phosphorylation is a major source of adenosine triphosphate production in ex vivo live murine corneal biopsies. Euthanasia methods (carbon dioxide asphyxiation vs. overdosing on anesthetic drugs) did not affect corneal OCR values. Mouse corneal biopsy punches in 1.5-mm diameter generated higher and more reproducible OCR values than those in 1.0-mm diameter. The biopsy punches from the central and off-central cornea did not show significant differences in OCR values. There was no difference in OCR reading by the tissue orientations (the epithelium side up vs. the endothelium side up). No significant differences were found in corneal OCR levels between sexes, strains (C57BL/6J vs. BALB/cJ), or ages (4, 8, and 32 weeks). Using this method, we showed that the wound healing process in the mouse cornea affected mitochondrial activity.

Conclusions

The present study validated a new strategy to measure real-time mitochondrial function in fresh mouse corneal tissues. This procedure should be helpful for studies of the ex vivo live corneal metabolism in response to genetic manipulations, disease conditions, or pharmacological treatments in mouse models.

Effects of Topical 1,25 and 24,25 Vitamin D on Diabetic, Vitamin D Deficient and Vitamin D Receptor Knockout Mouse Corneal Wound Healing

Delayed or prolonged corneal wound healing and non-healing corneas put patients at risk for ocular surface infections and subsequent stromal opacification, resulting in discomfort or visual loss. It is important to enhance corneal wound healing efficiency and quality. Vitamin D (Vit D) is both a hormone and a vitamin, and its insufficiency has been linked to immune disorders and diabetes. For this study, wound healing and recruitment of CD45+ cells into the wound area of normoglycemic and diabetic mice were examined following corneal epithelial debridement and treatment with 1,25-dihyroxyvitamin D (1,25 Vit D) or 24,25-dihydroxyvitamin D (24,25 Vit D). Treatment with topical 1,25-dihyroxyvitamin D (1,25 Vit D) resulted in significantly increased corneal wound healing rates of normoglycemic, diabetic and diabetic Vit D deficient mice. Furthermore, 24,25-dihydroxyvitamin D (24,25 Vit D) significantly increased corneal wound healing of diabetic Vit D deficient and Vit D receptor knockout (VDR KO) mice. In addition, CD45+ cell numbers were reduced in diabetic and VDR KO mouse corneas compared to normoglycemic mice, and 24,25 Vit D increased the recruitment of CD45+ cells to diabetic mouse corneas after epithelial debridement. CD45+ cells were found to infiltrate into the corneal basal epithelial layer after corneal epithelial debridement. Our data indicate that topical Vit D promotes corneal wound healing and further supports previous work that the Vit D corneal wound healing effect is not totally VDR-dependent.

Dual Role of Interleukin-20 in Different Stages of Osteoclast Differentiation and Its Osteoimmune Regulation during Alveolar Bone Remodeling

Osteoimmunology mediators are critical to balance osteoblastogenesis and osteoclastogenesis to maintain bone homeostasis. A lot of the osteoimmunology mediators are regulated by interleukin-20 (IL-20). However, little is known about the role of IL-20 in bone remodeling. Here, we showed that IL-20 expression was correlated with osteoclast (OC) activity in remodeled alveolar bone during orthodontic tooth movement (OTM). Ovariectomize (OVX) in rats promoted OC activity and enhanced IL-20 expression, while blocking OC inhibited IL-20 expression in osteoclasts. In vitro, IL-20 treatment promoted survival, inhibited apoptosis of the preosteoclast at the early stages of osteoclast differentiation, and boosted the formation of osteoclasts and their bone resorption function at the late stages. More importantly, anti-IL-20 antibody treatment blocked IL-20-induced osteoclastogenesis and the subsequent bone resorption function. Mechanistically, we showed that IL-20 synergistically acts with RANKL to activate the NF-κB signaling pathway to promote the expression of c-Fos and NFATc1 to promote osteoclastogenesis. Moreover, we found that local injection of IL-20 or anti-IL-20 antibody enhanced osteoclast activity and accelerated OTM in rats, while blocking IL-20 reversed this phenomenon. This study revealed a previously unknown role of IL-20 in regulating alveolar bone remodeling and implies the application of IL-20 to accelerated OTM.

Tear inflammation related indexes after cataract surgery in elderly patients with type 2 diabetes mellitus

BACKGROUND

Quantitative studies on the changes in inflammation-related content in tears, especially the effect of diabetes, are lacking. In this study, we measured the preoperative and postoperative tear inflammatory mediator levels in cataract patients, focusing on the expression of inflammatory factors in postoperative cataracts in the diabetic, and investigated the effect of drugs on the control of postoperative inflammation.

AIM

To study the expression of inflammatory factors in elderly people with type 2 diabetes after cataract surgery.

METHODS

Patients with a mean age of 70.3 ± 6.3 years were divided into group A (composed of elderly patients with cataracts and type 2 diabetes, n = 20 eyes) and group B (patients with age-related cataract, n = 20 eyes). Their tears were collected before each operation and on days 1 and 3, and weeks 1, 2, 3, and 4 post-surgery. Saline (150 μL) was dropped into the conjunctival sac of the surgical eye, followed by oculogyration in four directions. The fluid in the conjunctival sac was extracted using a sterile syringe and stored in Eppendorf tubes at -80 °C until measurement. The expression levels of matrix metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), TIMP-2, interleukin-6 (IL-6), and IL-20 in tear fluid were measured using enzyme-linked immunosorbent assays.

RESULTS

The postoperative expression levels of MMP-2, MMP-9, TIMP-2, IL-6, and IL-20 in group A were significantly higher than those in group B, whereas the concentration of TIMP-1 in group A remained lower than that in group B. The levels of MMP-2 and IL-6 in both groups continuously increased until the peak in the first postoperative week, and then gradually decreased over the next three weeks. Ultimately, MMP-2 declined to a lower level than that preoperatively at week 4, but IL-6 decreased to the same level as that preoperatively. The level of MMP-9 peaked in the first two weeks postoperative and then returned to the same level as 1-day post-operation. The concentration of TIMP-1 post-operation remained constant at a lower level than before surgery, and TIMP-2 Levels remained stable in both groups. IL-20 content started to increase in the third week after surgery.

CONCLUSION

Inflammatory factor levels in tears fluctuated before and post-operation, which indicated more severe postoperative inflammation in the first two weeks.

IL-20 Activates ERK1/2 and Suppresses Splicing of X-Box Protein-1 in Intestinal Epithelial Cells but Does Not Improve Pathology in Acute or Chronic Models of Colitis

The cytokine Interleukin (IL)-20 belongs to the IL-10 superfamily. IL-20 levels are reported to increase in the intestines of Ulcerative Colitis (UC) patients, however not much is known about its effects on intestinal epithelial cells. Here, we investigated the influence of IL-20 on intestinal epithelial cell lines and primary intestinal organoid cultures. By using chemical-induced (dextran sodium sulphate; DSS) colitis and a spontaneous model of colitis (Winnie mice), we assess whether recombinant IL-20 treatment is beneficial in reducing/improving pathology. Following stimulation with IL-20, intestinal primary organoids from wild-type and Winnie mice increased the expression of ERK1/2. However, this was lost when cells were differentiated into secretory goblet cells. Importantly, IL-20 treatment significantly reduced endoplasmic reticulum (ER) stress, as measured by spliced-XBP1 in epithelial cells, and this effect was lost in the goblet cells. IL-20 treatment in vivo in the DSS and Winnie models had minimal effects on pathology, but a decrease in macrophage activation was noted. Taken together, these data suggest a possible, but subtle role of IL-20 on epithelial cells in vivo. The therapeutic potential of IL-20 could be harnessed by the development of a targeted therapy or combination therapy to improve the healing of the mucosal barrier.

Collagen as a Biomaterial for Skin and Corneal Wound Healing

The cornea and the skin are two organs that form the outer barrier of the human body. When either is injured (e.g., from surgery, physical trauma, or chemical burns), wound healing is initiated to restore integrity. Many cells are activated during wound healing. In particular, fibroblasts that are stimulated often transition into repair fibroblasts or myofibroblasts that synthesize extracellular matrix (ECM) components into the wound area. Control of wound ECM deposition is critical, as a disorganized ECM can block restoration of function. One of the most abundant structural proteins in the mammalian ECM is collagen. Collagen type I is the main component in connective tissues. It can be readily obtained and purified, and short analogs have also been developed for tissue engineering applications, including modulating the wound healing response. This review discusses the effect of several current collagen implants on the stimulation of corneal and skin wound healing. These range from collagen sponges and hydrogels to films and membranes.

Neuroimmune crosstalk in the cornea: The role of immune cells in corneal nerve maintenance during homeostasis and inflammation

In the cornea, resident immune cells are in close proximity to sensory nerves, consistent with their important roles in the maintenance of nerves in both homeostasis and inflammation. Using in vivo confocal microscopy in humans, and ex vivo immunostaining and fluorescent reporter mice to visualize corneal sensory nerves and immune cells, remarkable progress has been made to advance our understanding of the physical and functional interactions between corneal nerves and immune cells. In this review, we summarize and discuss recent studies relating to corneal immune cells and sensory nerves, and their interactions in health and disease. In particular, we consider how disrupted corneal nerve axons can induce immune cell activity, including in dendritic cells, macrophages and other infiltrating cells, directly and/or indirectly by releasing neuropeptides such as substance P and calcitonin gene-related peptide. We summarize growing evidence that the role of corneal intraepithelial immune cells is likely different in corneal wound healing versus other inflammatory-dominated conditions. The role of different types of macrophages is also discussed, including how stromal macrophages with anti-inflammatory phenotypes communicate with corneal nerves to provide neuroprotection, while macrophages with pro-inflammatory phenotypes, along with other infiltrating cells including neutrophils and CD4⁺ T cells, can be inhibitory to corneal re-innervation. Finally, this review considers the bidirectional interactions between corneal immune cells and corneal nerves, and how leveraging this interaction could represent a potential therapeutic approach for corneal neuropathy.

Regulatory role of miR-146a in corneal epithelial wound healing via its inflammatory targets in human diabetic cornea

PURPOSE

MiR-146a upregulated in limbus vs. central cornea and in diabetic vs. non-diabetic limbus has emerged as an important immune and inflammatory signaling mediator in corneal epithelial wound healing. Our aim was to investigate the potential inflammation-related miR-146a target genes and their roles in normal and impaired diabetic corneal epithelial wound healing.

METHODS

Our previous data from RNA-seq combined with quantitative proteomics of limbal epithelial cells (LECs) transfected with miR-146a mimic vs. mimic control were analyzed. Western blot and immunostaining were used to confirm the expression of miR-146a inflammatory target proteins in LECs and organ-cultured corneas. Luminex assay was performed on conditioned media at 6- and 20-h post-wounding in miR-146a mimic/inhibitor transfected normal and diabetic cultured LECs.

RESULTS

Overexpression of miR-146a decreased the expression of pro-inflammatory TRAF6 and IRAK1 and downstream target NF-κB after challenge with lipopolysaccharide (LPS) or wounding. Additionally, miR-146a overexpression suppressed the production of downstream inflammatory mediators including secreted cytokines IL-1α, IL-1β, IL-6 and IL-8, and chemokines CXCL1, CXCL2 and CXCL5. These cytokines and chemokines were upregulated in normal but not in diabetic LEC during wounding. Furthermore, we achieved normalized levels of altered secreted cytokines and chemokines in diabetic wounded LEC via specific inhibition of miR-146a.

CONCLUSION

Our study documented significant impact of miR-146a on the expression of inflammatory mediators at the mRNA and protein levels during acute inflammatory responses and wound healing, providing insights into the regulatory role of miR-146a in corneal epithelial homeostasis in normal and diabetic conditions.

Immune responses to injury and their links to eye disease

The eye is regarded as an immune privileged site. Since the presence of a vasculature would impair vision, the vasculature of the eye is located outside of the central light path. As a result, many regions of the eye evolved mechanisms to deliver immune cells to sites of dysgenesis, injury, or in response to the many age-related pathologies. While the purpose of these immune responses is reparative or protective, cytokines released by immune cells compromise visual acuity by inducing inflammation and fibrosis. The response to traumatic or pathological injury is distinct in different regions of the eye. Age-related diseases impact both the anterior and posterior segment and lead to reduced quality of life and blindness. Here we focus attention on the role that inflammation and fibrosis play in the progression of age-related pathologies of the cornea and the lens as well as in glaucoma, the formation of epiretinal membranes, and in proliferative vitreoretinopathy.

Expression of IL-20 Receptor Subunit β Is Linked to EAE Neuropathology and CNS Neuroinflammation

Considerable clinical evidence supports that increased blood-brain barrier (BBB) permeability is linked to immune extravasation of CNS parenchyma during neuroinflammation. Although BBB permeability and immune extravasation are known to be provoked by vascular endothelial growth factor-A (i.e., VEGF-A) and C-X-C motif chemokine ligand 12 (CXCL12), respectively, the mechanisms that link both processes are still elusive. The interleukin-20 (i.e., IL-20) cytokine signaling pathway was previously implicated in VEGF-mediated angiogenesis and is known to induce cellular response by way of signaling through IL-20 receptor subunit β (i.e., IL-20RB). Dysregulated IL-20 signaling is implicated in many inflammatory pathologies, but it's contribution to neuroinflammation has yet to be reported. We hypothesize that the IL-20 cytokine, and the IL cytokine subfamily more broadly, play a key role in CNS neuroinflammation by signaling through IL-20RB, induce VEGF activity, and enhance both BBB-permeability and CXCL12-mediated immune extravasation. To address this hypothesis, we actively immunized IL-20RB^-/- mice and wild-type mice to induce experimental autoimmune encephalomyelitis (EAE) and found that IL-20RB^-/- mice showed amelioration of disease progression compared to wild-type mice. Similarly, we passively immunized IL-20RB^-/- mice and wild-type mice with myelin-reactive Th1 cells from either IL-20RB^-/- and wild-type genotype. Host IL-20RB^-/- mice showed lesser disease progression than wild-type mice, regardless of the myelin-reactive Th1 cells genotype. Using multianalyte bead-based immunoassay and ELISA, we found distinctive changes in levels of pro-inflammatory cytokines between IL-20RB^-/- mice and wild-type mice at peak of EAE. We also found detectable levels of all cytokines of the IL-20 subfamily within CNS tissues and specific alteration to IL-20 subfamily cytokines IL-19, IL-20, and IL-24, expression levels. Immunolabeling of CNS region-specific microvessels confirmed IL-20RB protein at the spinal cord microvasculature and upregulation during EAE. Microvessels isolated from macaques CNS tissues also expressed IL-20RB. Moreover, we identified the expression of all IL-20 receptor subunits: IL-22 receptor subunit α-1 (IL-22RA1), IL-20RB, and IL-20 receptor subunit α (IL-20RA) in human CNS microvessels. Notably, human cerebral microvasculature endothelial cells (HCMEC/D3) treated with IL-1β showed augmented expression of the IL-20 receptor. Lastly, IL-20-treated HCMEC/D3 showed alterations on CXCL12 apicobasal polarity consistent with a neuroinflammatory status. This evidence suggests that IL-20 subfamily cytokines may signal at the BBB via IL-20RB, triggering neuroinflammation.

Investigation of Possible Role of Chlamydia in Pseudoexfoliation Syndrome

Background: Pseudoexfoliation syndrome (PES) is a systemic disease characterized by the aggregation of fibrillar extracellular material in intraocular and extraocular tissues with unknown etiology. Clarifying the etiopathogenesis of PES would be important for public health. Objectives: We aimed to investigate the possible role of Chlamydia in the etiology of PES. Methods: This cross-sectional study was carried out in the ophthalmology clinic of a tertiary hospital. The study included two groups, including the patient group (PES patients with nuclear cataracts) and the control group (patients with nuclear cataracts). Patients with other ophthalmic problems and systemic diseases were excluded. Blood samples and conjunctival swabs taken from 49 patients and 42 controls were used in the study. Anti-Chlamydia trachomatis IgG and IgM, anti-C. pneumoniae IgG and IgM, Interleukin (IL)-6, and IL-20 were studied in the serum samples. The PCR study was performed with conjunctival swab samples and sequence analysis of PCR-positive samples was performed. Results: According to the results of the study, there was no statistically significant difference between the groups in terms of anti-C. trachmatis IgG, anti-C. trachmatis IgM, anti-C. pneumoniae IgM, IL-6, and PCR results. There was a statistically significant difference between patient and control groups in terms of anti-C. pneumoniae IgG and IL-20 levels. The DNA sequencing of all PCR products was found to be compatible with C. pneumoniae. Conclusions: It seems that C. pneumoniae might have an important role in the etiology and development of PES. However, further studies in larger groups are needed to clarify these results.

Functional characterization of an interleukin 20 like homologue in grass carp Ctenopharyngodon idella

IL-20 is a pleiotropic cytokine that belongs to the IL-10 family and plays an important biological role in tissue homeostasis and regulation of host immune defenses. IL-20 homologues have recently been discovered in fish, but their functions have not been studied. In this study, an IL-20 like (IL-20L) cytokine was cloned in grass carp (Ctenopharyngodon idella) and its bioactivities were investigated. Expression analysis showed that the CiIL-20L gene was constitutively expressed in tissues with the highest expression detected in the head kidney. It was upregulated in the head kidney after infection with Flavobactrium columnare (F. cloumnare) and grass carp reovirus II (GCRV II). The recombinant CiIL-20L produced in E. coli cells was shown to be effective in inducing the expression of Th cytokine genes (IFN-γ, IL-4/13A, IL-4/13B and IL-10), macrophage marker genes (arginase 2, IRF4, KLF4 and SOCS3) and inflammatory genes (IL-1β, IL-6, IL-8 and TNFα) in the head kidney leukocytes when stimulated at 12 h. Long term culture (6 days) of head kidney macrophages in the presence of CiIL-20L leads to high expression of IRF4, TGFβ1 and arginase 2. Our data suggest that IL-20 may play regulatory roles in promoting Th responses, macrophage differentiation and inflammation.

Platelet and Erythrocyte Extravasation across Inflamed Corneal Venules Depend on CD18, Neutrophils, and Mast Cell Degranulation

Platelet extravasation during inflammation is under-appreciated. In wild-type (WT) mice, a central corneal epithelial abrasion initiates neutrophil (PMN) and platelet extravasation from peripheral limbal venules. The same injury in mice expressing low levels of the β₂-integrin, CD18 (CD18_hypo mice) shows reduced platelet extravasation with PMN extravasation apparently unaffected. To better define the role of CD18 on platelet extravasation, we focused on two relevant cell types expressing CD18: PMNs and mast cells. Following corneal abrasion in WT mice, we observed not only extravasated PMNs and platelets but also extravasated erythrocytes (RBCs). Ultrastructural observations of engorged limbal venules showed platelets and RBCs passing through endothelial pores. In contrast, injured CD18_hypo mice showed significantly less venule engorgement and markedly reduced platelet and RBC extravasation; mast cell degranulation was also reduced compared to WT mice. Corneal abrasion in mast cell-deficient (Kit^W-sh/W-sh) mice showed less venule engorgement, delayed PMN extravasation, reduced platelet and RBC extravasation and delayed wound healing compared to WT mice. Finally, antibody-induced depletion of circulating PMNs prior to corneal abrasion reduced mast cell degranulation, venule engorgement, and extravasation of PMNs, platelets, and RBCs. In summary, in the injured cornea, platelet and RBC extravasation depends on CD18, PMNs, and mast cell degranulation.

Interleukin-20 Acts as a Promotor of Osteoclastogenesis and Orthodontic Tooth Movement

Objectives

Bones constitute organs that are engaged in constant self-remodelling. Osteoblast and osteoclast homeostasis during remodelling contribute to overall skeletal status. Orthodontics is a clinical discipline that involves the investigation and implementation of moving teeth through the bone. The application of mechanical force to the teeth causes an imbalance between osteogenesis and osteogenesis in alveolar bone, leading to tooth movement. Osteoimmunology comprises the crosstalk between the immune and skeletal systems that regulate osteoclast–osteoblast homeostasis. Interleukin- (IL-) 20, an IL-10 family member, is regarded as a proinflammatory factor for autoimmune diseases and has been implicated in bone loss disease. However, the mechanism by which IL-20 regulates osteoclast differentiation and osteoclastogenesis activation remains unclear. This study investigated the effects of IL-20 on osteoclast differentiation in a rat model; it explored the underlying molecular mechanism in vitro and the specific effects on orthodontic tooth movement in vivo.

Methods

For in vitro analyses, primary rat bone marrow-derived macrophages (BMMs) were prepared from Sprague–Dawley rats for osteoclast induction. After BMMs had been treated with combinations of recombinant IL-20 protein, siRNA, and plasmids, the expression levels of osteoclast-specific factors and signalling pathway proteins were detected through real-time polymerase chain reaction, western blotting, and immunofluorescence staining. For in vivo analyses, IL-20 was injected into the rat intraperitoneal cavity after the establishment of a rat orthodontic tooth movement (OTM) model. OTM distance was detected by Micro-CT and HE staining; the expression levels of protein were detected through immunofluorescence staining.

Results

In vitro analyses showed that a low concentration of IL-20 promoted preosteoclast proliferation and osteoclastogenesis. However, a high concentration of IL-20 inhibited BMM proliferation and osteoclastogenesis. IL-20 knockdown decreased the expression of osteoclast specific-markers, while IL-20 overexpression increased the expression of osteoclast specific-markers. Furthermore, IL-20 regulated osteoclast differentiation through the OPG/RANKL/RANK pathway. Overexpression of IL-20 could significantly upregulate RANKL-mediated osteoclast differentiation and osteoclast specific-marker expression; moreover, RANKL/NF-κB/NFATc1 acted as downstream signalling molecule for IL-20. In vivo analysis showed that OTM speed was significantly increased after intraperitoneal injection of IL-20; additionally, mechanical stress sensing proteins were markedly activated.

Conclusions

IL-20 augments osteoclastogenesis and osteoclast-mediated bone erosion through the RANKL/NF-κB/NFATc1 signalling pathway. IL-20 inhibition can effectively reduce osteoclast differentiation and diminish bone resorption. Furthermore, IL-20 can accelerate orthodontic tooth movement and activate mechanical stress sensing proteins.

Interleukin-20 inhibits the osteogenic differentiation of MC3T3-E1 cells via the GSK3β/β-catenin signalling pathway

OBJECTIVE

To investigate the effects of interleukin-20 (IL-20) on the osteogenic differentiation of MC3T3-E1 cells.

METHODS

The pre-osteoblast line MC3T3-E1 was treated with different concentrations of IL-20 (0, 2, 20 and 100 ng/mL), and the cell viability was detected by the CCK8 assay. To assess the influence of IL-20 on osteogenic differentiation, alkaline phosphatase (ALP) activity and Alizarin red staining were performed at predetermined times. The expression levels of Runt-related transcription factor 2 (RUNX2), Osterix (Osx), glycogen synthase kinase-3β (GSK-3β) and β-catenin were detected by qRT-PCR and Western blotting analyses. 5 nmol/L lithium chloride (LiCl) was used as GSK-3β inhibitor.

RESULTS

IL-20 promoted cell proliferation but decreased ALP activity and mineralization. Moreover, IL-20 downregulated the expression of RUNX2, Osx and β-catenin but upregulated the level of GSK-3β.

CONCLUSIONS

The results suggest that IL-20 could inhibit the osteogenic differentiation of MC3T3-E1 cells via the GSK3β/β-catenin signalling pathway.

Epithelial Cell Migration and Proliferation Patterns During Initial Wound Closure in Normal Mice and an Experimental Model of Limbal Stem Cell Deficiency

Purpose

Establishing the dynamics of corneal wound healing is of vital importance to better understand corneal inflammation, pathology, and corneal regeneration. Numerous studies have made great strides in investigating multiple aspects of corneal wound healing; however, some aspects remain to be elucidated. This study worked toward establishing (1) if epithelial limbal stem cells (LSCs) are necessary for healing all corneal wounds, (2) the mechanism by which epithelial cells migrate toward the wound, and (3) if centrifugal epithelial cell movement exists.

Methods

To establish different aspects of corneal epithelial wound healing we subjected mice lacking hyaluronan synthase 2 (previously shown to lack LSCs) and wild-type mice to different corneal debridement injury models.

Results

Our data show that both LSCs and corneal epithelial cells contribute toward closure of corneal wounds. In wild-type mice, removal of the limbal rim delayed closure of 1.5-mm wounds, and not of 0.75-mm wounds, indicating that smaller wounds do not rely on LSCs as do larger wounds. In mice shown to lack LSCs, removal of the limbal rim did not affect wound healing, irrespective of the wound size. Finally, transient amplifying cells and central epithelial cells move toward a central corneal wound in a centripetal manner, whereas central epithelial cells may move in a centrifugal manner to resurface peripheral corneal wounds.

Conclusions

Our findings show the dimensions of the corneal wound dictate involvement of LSCs. Our data suggest that divergent findings by different groups on the dynamics of wound healing can be in part owing to differences in the wounding models used.

Corneal dysfunction precedes the onset of hyperglycemia in a mouse model of diet-induced obesity

PURPOSE

The purpose of this study was to use a mouse model of diet-induced obesity to determine if corneal dysfunction begins prior to the onset of sustained hyperglycemia and if the dysfunction is ameliorated by diet reversal.

METHODS

Six-week-old male C57BL/6 mice were fed a high fat diet (HFD) or a normal diet (ND) for 5-15 weeks. Diet reversal (DiR) mice were fed a HFD for 5 weeks, followed by a ND for 5 or 10 weeks. Corneal sensitivity was determined using aesthesiometry. Corneal cytokine expression was analyzed using a 32-plex Luminex assay. Excised corneas were prepared for immunofluorescence microscopy to evaluate diet-induced changes and wound healing. For wounding studies, mice were fed a HFD or a ND for 10 days prior to receiving a central 2mm corneal abrasion.

RESULTS

After 10 days of HFD consumption, corneal sensitivity declined. By 10 weeks, expression of corneal inflammatory mediators increased and nerve density declined. While diet reversal restored nerve density and sensitivity, the corneas remained in a heightened inflammatory state. After 10 days on the HFD, corneal circadian rhythms (limbal neutrophil accumulation, epithelial cell division and Rev-erbα expression) were blunted. Similarly, leukocyte recruitment after wounding was dysregulated and accompanied by delays in wound closure and nerve recovery.

CONCLUSION

In the mouse, obesogenic diet consumption results in corneal dysfunction that precedes the onset of sustained hyperglycemia. Diet reversal only partially ameliorated this dysfunction, suggesting a HFD diet may have a lasting negative impact on corneal health that is resistant to dietary therapeutic intervention.

Interleukin-20 differentially regulates bone mesenchymal stem cell activities in RANKL-induced osteoclastogenesis through the OPG/RANKL/RANK axis and the NF-κB, MAPK and AKT signalling pathways

The immune and skeletal systems share common mechanisms, and the crosstalk between the two has been termed osteoimmunology. Osteoimmunology mainly focuses on diseases between the immune and bone systems including bone loss diseases, and imbalances in osteoimmune regulation affect skeletal homeostasis between osteoclasts and osteoblasts. The immune mediator interleukin-20 (IL-20), a member of the IL-10 family, enhances inflammation, chemotaxis and angiogenesis in diseases related to bone loss. However, it is unclear how IL-20 regulates the balance between osteoclastogenesis and osteoblastogenesis; therefore, we explored the mechanisms by which IL-20 affects bone mesenchymal stem cells (BMSCs) in osteoclastogenesis in primary cells during differentiation, proliferation, apoptosis and signalling. We initially found that IL-20 differentially regulated preosteoclast proliferation and apoptosis; BMSC-conditioned medium (CM) significantly enhanced osteoclast formation and bone resorption, which was dose-dependently regulated by IL-20; IL-20 inhibited OPG expression and promoted M-CSF, RANKL and RANKL/OPG expression; and IL-20 differentially regulated the expression of osteoclast-specific gene and transcription factors through the OPG/RANKL/RANK axis and the NF-kB, MAPK and AKT pathways. Therefore, IL-20 differentially regulates BMSCs in osteoclastogenesis and exerts its function by activating the OPG/RANKL/RANK axis and the NF-κB, MAPK and AKT pathways, which make targeting IL-20 a promising direction for targeted regulation in diseases related to bone loss.

Sirt6 deficiency impairs corneal epithelial wound healing

Corneal transparency, dependent on the integrity of epithelial cells, is essential for vision. Corneal epithelial damage is one of the most commonly observed ocular conditions and proper wound healing is necessary for corneal transparency. Sirt6, a histone deacetylase, has been shown to regulate many cellular events including aging and inflammation. However, its specific role in corneal epithelial wound healing remains unknown. Here we demonstrated that Sirt6 was expressed in corneal epithelial cells and its expression decreased with age. In an in vivo corneal epithelial wound healing model, Sirt6 deficiency resulted in delayed and incomplete wound healing and was associated excessive inflammation in the corneal stroma and dysfunction of Notch signaling, leading to keratinization of the corneal epithelium and corneal opacity. Aging Sirt6-deficient mice spontaneously developed corneal keratitis with extensive infiltration of inflammatory cells into the cornea. In vitro experiments demonstrated that primary corneal epithelial cells with Sirt6 downregulation expressed increased basal levels of inflammatory genes and exhibited hyper-inflammatory reactivity to IL-1β and TNFα treatment. These results provide compelling evidence that Sirt6 is a critical regulator of inflammation in the cornea, and is responsible for corneal epithelial wound healing, thus contributing to the maintenance of epithelial integrity and corneal transparency.

Nanotechnology in regenerative ophthalmology

In recent years, regenerative medicine is gaining momentum and is giving hopes for restoring function of diseased, damaged, and aged tissues and organs and nanotechnology is serving as a catalyst. In the ophthalmology field, various types of allogenic and autologous stem cells have been investigated to treat some ocular diseases due to age-related macular degeneration, glaucoma, retinitis pigmentosa, diabetic retinopathy, and corneal and lens traumas. Nanomaterials have been utilized directly as nanoscaffolds for these stem cells to promote their adhesion, proliferation and differentiation or indirectly as vectors for various genes, tissue growth factors, cytokines and immunosuppressants to facilitate cell reprogramming or ocular tissue regeneration. In this review, we reviewed various nanomaterials used for retina, cornea, and lens regenerations, and discussed the current status and future perspectives of nanotechnology in tracking cells in the eye and personalized regenerative ophthalmology. The purpose of this review is to provide comprehensive and timely insights on the emerging field of nanotechnology for ocular tissue engineering and regeneration.

Biomaterials: Foreign Bodies or Tuners for the Immune Response?

The perspectives of regenerative medicine are still severely hampered by the host response to biomaterial implantation, despite the robustness of technologies that hold the promise to recover the functionality of damaged organs and tissues. In this scenario, the cellular and molecular events that decide on implant success and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. To avoid adverse events, rather than the use of inert scaffolds, current state of the art points to the use of immunomodulatory biomaterials and their knowledge-based use to reduce neutrophil activation, and optimize M1 to M2 macrophage polarization, Th1 to Th2 lymphocyte switch, and Treg induction. Despite the fact that the field is still evolving and much remains to be accomplished, recent research breakthroughs have provided a broader insight on the correct choice of biomaterial physicochemical modifications to tune the reaction of the host immune system to implanted biomaterial and to favor integration and healing.

Wound-Healing Markers Revealed by Proximity Extension Assay in Tears of Patients following Glaucoma Surgery

Tears are a constantly available and highly valuable body fluid collectable by non-invasive techniques. Although it can give information on ocular status and be used for follow-ups, tear analysis is challenging due to the low amount of sample that is available. Proximity extension assay (PEA) allows for a sensitive and scalable analysis of multiple proteins in a single run from a one-µL sample, so we applied this technique and examined the amount of 184 proteins in tears collected at different time points after trabeculectomy. The success rate of this surgical intervention highly depends on proper wound healing; therefore, information on the process is indispensable. We observed significantly higher levels of IL-6 and MMP1 at the early time points (day one, two, and four) following trabeculectomy, and the protein amounts went back to the level observed before the surgery three months after the intervention. Patients with or without complications were tested, and proteins that have roles in the immune response and wound healing could be observed with altered frequency and amounts in the cases of patients with complications. Our results highlight the importance of inflammation in wound-healing complications, and at the same time, indicate the utility of PEA in tear analysis.

Soluble Fas ligand blocks destructive corneal inflammation in mouse models of corneal epithelial debridement and LPS induced keratitis

Neutrophil-mediated inflammation plays a critical role in corneal damage following injury or infection. Previous studies demonstrated that membrane-bound FasL (mFasL) induces neutrophil chemokine production. However, the extracellular domain of mFasL is normally cleaved by matrix metalloproteinases to release a soluble form of FasL (sFasL) and sFasL antagonizes mFasL-mediated chemokine production. Therefore, we hypothesized that sFasL could be used to prevent neutrophil-mediated corneal inflammation associated with injury and bacterial keratitis. To test this hypothesis, GFP-only, sFasL-GFP, or mFasL-GFP were expressed in the corneal stroma of C57BL/6 mice, using intra-stromal injections of plasmid DNA or adenoviral vectors (AV) and the role of mFasL and sFasL in corneal inflammation was examined in models of corneal injury and LPS-induced keratitis. Our work addresses an important area of disagreement in the field of FasL, with regard to the mechanism by which sFasL regulates ocular inflammation. Herein, we demonstrate that an intrastromal injection of GFP-only, sFasL-GFP, or mFasL-GFP plasmid DNA resulted in GFP expression throughout the corneal stroma for up to two weeks with little to no evidence of inflammation in the GFP-only and sFasL-GFP groups and mild corneal inflammation in the mFasL-GFP group. Similarly, following epithelial debridement, corneas expressing GFP-only or sFasL-GFP showed no significant signs of corneal inflammation, with clear corneas at 15 days post debridement. By contrast, epithelial debridement of corneas expressing mFasL-GFP triggered persistent corneal inflammation and the development of central corneal opacities that was blocked by sFasL. Similar to the mFasL-GFP plasmid DNA, intrastromal injection of mFasL-GFP AV triggered mild corneal inflammation, but it was transient and resolved by day 10 with corneas remaining clear out to 30 days post injection. Nevertheless, intrastromal expression of mFasL-GFP AV exacerbated LPS-induced keratitis, corneal opacity, and neovascularization, while sFasL-GFP AV expression prevented LPS-induced keratitis, resulting in a clear cornea. Histological analysis of corneas with LPS-induced keratitis revealed a robust infiltration of macrophages and neutrophils and sFasL expression specifically blocked the neutrophil influx. Overall, our data demonstrate that stromal expression of mFasL is inflammatory, while sFasL is non-inflammatory, and opposes the effects of mFasL in mouse models of epithelial debridement and LPS-induced keratitis. These data demonstrate that a delicate balance between sFasL and mFasL regulates ocular inflammation. This study further identifies sFasL as a potent inhibitor of neutrophil-mediated corneal damage, and supports the potential use of sFasL in the treatment of neutrophil-mediated keratitis. These results strongly support the hypothesis that, in the immune privileged environment of the eye, the isoform of FasL regulates immune privilege and determines the extent of inflammation: mFasL promotes inflammation and sFasL blocks inflammation.

Neprilysin inhibition promotes corneal wound healing

Neprilysin (NEP), an ectoenzyme that modulates inflammation by degrading neuropeptides, was recently identified in the human corneal epithelium. The cornea expresses many NEP substrates, but the function of NEP in homeostatic maintenance and wound healing of the cornea is unknown. We therefore investigated the role of this enzyme under naive and injured conditions using NEP-deficient (NEP-/-) and wild type (WT) control mice. In vivo ocular surface imaging and histological analysis of corneal tissue showed no differences in limbal vasculature or corneal anatomy between naive NEP-/- and WT mice. Histological examination revealed increased corneal innervation in NEP-/- mice. In an alkali burn model of corneal injury, corneal wound healing was significantly accelerated in NEP-/- mice compared to WT controls 3 days after injury. Daily intraperitoneal administration of the NEP inhibitor thiorphan also accelerated corneal wound healing after alkali injury in WT mice. Collectively, our data identify a previously unknown role of NEP in the cornea, in which pharmacologic inhibition of its activity may provide a novel therapeutic option for patients with corneal injury.

The mouse autonomic nervous system modulates inflammation and epithelial renewal after corneal abrasion through the activation of distinct local macrophages

Inflammation and reepithelialization after corneal abrasion are critical for the rapid restoration of vision and the prevention of microbial infections. However, the endogenous regulatory mechanisms are not completely understood. Here we report that the manipulation of autonomic nervous system (ANS) regulates the inflammation and healing processes. The activation of sympathetic nerves inhibited reepithelialization after corneal abrasion but increased the influx of neutrophils and the release of inflammatory cytokines. Conversely, the activation of parasympathetic nerves promoted reepithelialization and inhibited the influx of neutrophils and the release of inflammatory cytokines. Furthermore, we observed that CD64⁺CCR2⁺ macrophages in the cornea preferentially expressed the β-2 adrenergic receptor (AR), whereas CD64⁺CCR2^- macrophages preferentially expressed the α-7 nicotinic acetylcholine receptor (α7nAChR). After abrasion, the topical administration of a β2AR agonist further enhanced the expression of the proinflammatory genes in the CD64⁺CCR2⁺ cell subset sorted from injured corneas. In contrast, the topical administration of an α7nAChR agonist further enhanced the expression of the anti-inflammatory genes in the CD64⁺CCR2^- subset. Thus crosstalk between the ANS and local macrophage populations is necessary for the progress of corneal wound repair. Manipulation of ANS inputs to the wounded cornea may represent an alternative approach to the treatment of impaired wound healing.

Role of negative regulation of immune signaling pathways in neutrophil function

Polymorphonuclear neutrophils (PMNs) play a critical role in host defense against infection and in the resolution of inflammation. However, immune responses mediated by PMN must be tightly regulated to facilitate elimination of invading pathogens without inducing detrimental inflammation and host tissue damage. Specific engagement of cell surface immunoreceptors by a diverse range of extracellular signals regulates PMN effector functions through differential activation of intracellular signaling cascades. Although mechanisms of PMN activation mediated via cell signaling pathways have been well described, less is known about negative regulation of PMN function by immune signaling cascades. Here, we provide an overview of immunoreceptor-mediated negative regulation of key PMN effector functions including maturation, migration, phagocytosis, reactive oxygen species release, degranulation, apoptosis, and NET formation. Increased understanding of mechanisms of suppression of PMN effector functions may point to possible future therapeutic targets for the amelioration of PMN-mediated autoimmune and inflammatory diseases.

Ell3 Modulates the Wound Healing Activity of Conditioned Medium of Adipose-derived Stem Cells

While adipose-derived stem cell-conditioned medium (ADSC-CM) has been demonstrated to promote skin wound healing, the mechanism regulating this effect remains unelucidated. In this study, we aimed to investigate the role of Ell3 in the wound healing activity of ADSC-CM. In vitro analysis revealed that Ell3 suppression in ADSCs impairs the promotive activity of ADSC-CM on the proliferation and migration of mouse embryonic fibroblasts (MEF) and normal human dermal fibroblasts (NHDF). Consistently, the expression of MMP family genes, which regulate cell proliferation and migration, was significantly suppressed in MEF and NHDF treated with siEll3-transfected ADSC-CM. Proinflammatory cytokines, such as interleukin-1 and interleukin-6, were highly expressed in MEF treated with siEll3-transfected ADSC-CM. The wound healing activity of siEll3-transfected ADSC-CM was significantly lower than that of the control in vivo. Our results suggest that Ell3 may contribute to the inhibition of inflammatory response during skin wound healing.

Limbal and corneal epithelial homeostasis

PURPOSE OF REVIEW

The aim of this review is to describe the underlying mechanisms of corneal epithelial homeostasis in addition to illustrating the vital role of the limbal epithelial stem cells (LESCs) and the limbal niche in epithelial regeneration and wound healing.

RECENT FINDINGS

The shedded corneal epithelial cells are constantly replenished by the LESCs which give rise to epithelial cells that proliferate, differentiate, and migrate centripetally. While some recent studies have proposed that epithelial stem cells may also be present in the central cornea, the predominant location for the stem cells is the limbus. The limbal niche is the specialized microenvironment consisting of cells, extracellular matrix, and signaling molecules that are essential for the function of LESCs. Disturbances to limbal niche can result in LESC dysfunction; therefore, limbal stem cell deficiency should also be considered a limbal niche deficiency. Current and in-development therapeutic strategies are aimed at restoring the limbal niche, by medical and/or surgical treatments, administration of trophic factors, and cell based therapies.

SUMMARY

The corneal epithelium is constantly replenished by LESCs that are housed within the limbal niche. The limbal niche is the primary determinant of the LESC function and novel therapeutic approaches should be focused on regeneration of this microenvironment.

Key players in the immune response to biomaterial scaffolds for regenerative medicine

The compatibility of biomaterials is critical to their structural and biological function in medical applications. The immune system is the first responder to tissue trauma and to a biomaterial implant. The innate immune effector cells, most notably macrophages, play a significant role in the defense against foreign bodies and the formation of a fibrous capsule around synthetic implants. Alternatively, macrophages participate in the pro-regenerative capacity of tissue-derived biological scaffolds. Research is now elucidating the role of the adaptive immune system, and T cells in particular, in directing macrophage response to synthetic and biological materials. Here, we review basic immune cell types and discuss recent research on the role of the immune system in tissue repair and its potential relevance to scaffold design. We will also discuss new emerging immune cell types relevant to biomaterial responses and tissue repair. Finally, prospects for specifically targeting and modulating the immune response to biomaterial scaffolds for enhancing tissue repair and regeneration will be presented.

IL-20 Signaling in Activated Human Neutrophils Inhibits Neutrophil Migration and Function

Neutrophils possess multiple antimicrobial mechanisms that are critical for protection of the host against infection with extracellular microbes, such as the bacterial pathogen Staphylococcus aureus Recruitment and activation of neutrophils at sites of infection are driven by cytokine and chemokine signals that directly target neutrophils via specific cell surface receptors. The IL-20 subfamily of cytokines has been reported to act at epithelial sites and contribute to psoriasis, wound healing, and anti-inflammatory effects during S. aureus infection. However, the ability of these cytokines to directly affect neutrophil function remains incompletely understood. In this article, we show that human neutrophils altered their expression of IL-20R chains upon migration and activation in vivo and in vitro. Such activation of neutrophils under conditions mimicking infection with S. aureus conferred responsiveness to IL-20 that manifested as modification of actin polymerization and inhibition of a broad range of actin-dependent functions, including phagocytosis, granule exocytosis, and migration. Consistent with the previously described homeostatic and anti-inflammatory properties of IL-20 on epithelial cells, the current study provides evidence that IL-20 directly targets and inhibits key inflammatory functions of neutrophils during infection with S. aureus.