Resolvin E1 Reduces Leukotriene B4-Induced Intracellular Calcium Increase and Mucin Secretion in Rat Conjunctival Goblet Cells

Anti-Inflammatory and Pro-Resolving Actions of the N-Terminal Peptides Ac2-26, Ac2-12, and Ac9-25 of Annexin A1 on Conjunctival Goblet Cell Function

Annexin A1 (AnxA1) is the primary mediator of the anti-inflammatory actions of glucocorticoids. AnxA1 functions as a pro-resolving mediator in cultured rat conjunctival goblet cells to ensure tissue homeostasis through stimulation of intracellular [Ca2+] ([Ca2+]i) and mucin secretion. AnxA1 has several N-terminal peptides with anti-inflammatory properties of their own, including Ac2-26, Ac2-12, and Ac9-25. The increase in [Ca2+]i caused by AnxA1 and its N-terminal peptides in goblet cells was measured to determine the formyl peptide receptors used by the compounds and the action of the peptides on histamine stimulation. Changes in [Ca2+]i were determined by using a fluorescent Ca2+ indicator. AnxA1 and its peptides each activated formyl peptide receptors in goblet cells. AnxA1 and Ac2-26 at 10-12 mol/L and Ac2-12 at 10-9 mol/L inhibited the histamine-stimulated increase in [Ca2+]i, as did resolvin D1 and lipoxin A4 at 10-12 mol/L, whereas Ac9-25 did not. AnxA1 and Ac2-26 counter-regulated the H1 receptor through the p42/p44 mitogen-activated protein kinase/extracellular regulated kinase 1/2, β-adrenergic receptor kinase, and protein kinase C pathways, whereas Ac2-12 counter-regulated only through β-adrenergic receptor kinase. In conclusion, current data show that the N-terminal peptides Ac2-26 and Ac2-12, but not Ac9-25, share multiple functions with the full-length AnxA1 in goblet cells, including inhibition of histamine-stimulated increase in [Ca2+]i and counter-regulation of the H1 receptor. These actions suggest a potential pharmaceutical application of the AnxA1 N-terminal peptides Ac2-26 and Ac2-12 in homeostasis and ocular inflammatory diseases.

Inflammation resolution and specialized pro-resolving lipid mediators in chronic rhinosinusitis

INTRODUCTION

In chronic rhinosinusitis (CRS), a complex pathophysiology results from varied pro-inflammatory stimuli but is consistently characterized by classic cellular, molecular, and microbial alterations. Normally, endogenous specialized pro-resolving mediators (SPM) actively promote resolution of inflammation through numerous pathways, including those involved in host antimicrobial defense. However, these pathways appear to be disrupted in CRS.

AREAS COVERED

This paper describes features of CRS in the context of chronic tissue inflammation, and potential mechanisms by which specialized pro-resolving mediators promote active resolution of tissue inflammation.

EXPERT OPINION

Temporal phases of resolution must be tightly regulated to successfully resolve inflammation in CRS while preserving tissue functions such as barrier maintenance and special sensory function. Dysregulation of SPM enzymatic pathways has been recently shown in CRS and is associated with disease phenotypes and microbial colonization patterns. Current research in animal models and in vitro human cell culture, as well as human dietary studies, demonstrate relevant changes in cell signaling with lipid mediator bioavailability. Further clinical research may provide insight into the therapeutic value of this approach in CRS.

View from the Biological Property: Insight into the Functional Diversity and Complexity of the Gut Mucus

Due to mucin's important protective effect on epithelial tissue, it has garnered extensive attention. The role played by mucus in the digestive tract is undeniable. On the one hand, mucus forms "biofilm" structures that insulate harmful substances from direct contact with epithelial cells. On the other hand, a variety of immune molecules in mucus play a crucial role in the immune regulation of the digestive tract. Due to the enormous number of microorganisms in the gut, the biological properties of mucus and its protective actions are more complicated. Numerous pieces of research have hinted that the aberrant expression of intestinal mucus is closely related to impaired intestinal function. Therefore, this purposeful review aims to provide the highlights of the biological characteristics and functional categorization of mucus synthesis and secretion. In addition, we highlight a variety of the regulatory factors for mucus. Most importantly, we also summarize some of the changes and possible molecular mechanisms of mucus during certain disease processes. All these are beneficial to clinical practice, diagnosis, and treatment and can provide some potential theoretical bases. Admittedly, there are still some deficiencies or contradictory results in the current research on mucus, but none of this diminishes the importance of mucus in protective impacts.

Omega-3 polyunsaturated fatty acids and corneal nerve health: Current evidence and future directions

Corneal nerves play a key role in maintaining ocular surface integrity. Corneal nerve damage, from local or systemic conditions, can lead to ocular discomfort, pain, and, if poorly managed, neurotrophic keratopathy. Omega-3 polyunsaturated fatty acids (PUFAs) are essential dietary components that play a key role in neural development, maintenance, and function. Their potential application in modulating ocular and systemic inflammation has been widely reported. Omega-3 PUFAs and their metabolites also have neuroprotective properties and can confer benefit in neurodegenerative disease. Several preclinical studies have shown that topical administration of omega-3 PUFA-derived lipid mediators promote corneal nerve recovery following corneal surgery. Dietary omega-3 PUFA supplementation can also reduce corneal epithelial nerve loss and promote corneal nerve regeneration in diabetes. Omega-3 PUFAs and their lipid mediators thus show promise as therapeutic approaches to modulate corneal nerve health in ocular and systemic disease. This review discusses the role of dietary omega-3 PUFAs in maintaining ocular surface health and summarizes the possible applications of omega-3 PUFAs in the management of ocular and systemic conditions that cause corneal nerve damage. In examining the current evidence, this review also highlights relatively underexplored applications of omega-3 PUFAs in conferring neuroprotection and addresses their therapeutic potential in mediating corneal nerve regeneration.

Association of Polyunsaturated Fatty Acid Intake on Inflammatory Gene Expression and Multiple Sclerosis: A Systematic Review and Meta-Analysis

The health benefits of omega-3 fatty acid (FA) supplementation on inflammatory gene expression (IGE) and multiple sclerosis (MS) are becoming more evident. However, an overview of the results from randomized controlled trials is lacking. This study aimed to conduct a meta-analysis to evaluate the effect of omega-3 fatty acid intake on MS (based on the criteria of the Expanded Disability Status Scale (EDSS)) and inflammatory gene expression (IGE). A search was conducted of PubMed, EMBASE, and Web of Science for cohort studies published from the inception of the database up to May 2022 that assessed the associations of omega-3 polyunsaturated fatty acids (n-3 PUFAs), docosahexaenoic acid (DHA), α-linolenic acid (ALA), and eicosapentaenoic acid (EPA) with EDSS and inflammatory gene expression (peroxisome proliferator-activated receptor gamma (PPAR-γ), tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), interleukin-6 (IL-6), and interleukin-8 (IL-8)) outcomes. For the highest vs. lowest comparison, the relative risk (RR) estimates with a 95% confidence interval (CI) were pooled using the random-effect model. In total, 13 cohort studies with 1353 participants were included in the meta-analysis during periods of 3 to 144 weeks. A significant inverse relationship was found between DHA and EDSS scores (RR: 1.05; 95% CI: 0.62, 1.48; p < 0.00001). Our results also showed that omega-3 FAs significantly upregulated the gene expression of PPAR-γ (RR: 0.95; 95% CI: 0.52, 1.38; p < 0.03) and downregulated the expression of TNF-α (RR: −0.15; 95% CI: −0.99, 0.70; p < 0.00001) and IL-1 (RR: −0.60; 95% CI: −1.02, −0.18; p < 0.003). There was no clear evidence of publication bias with Egger’s tests for inflammatory gene expression (p = 0.266). Moreover, n-3 PUFAs and EPA were not significantly associated with EDSS scores (p > 0.05). In this meta-analysis of cohort studies, blood omega-3 FA concentrations were inversely related to inflammatory gene expression (IGE) and EDSS score, which indicates that they may hold great potential markers for the diagnosis, prognosis, and management of MS. However, further clinical trials are required to confirm the potential effects of the omega-3 FAs on MS disease management.

Sex-based differences in conjunctival goblet cell responses to pro-inflammatory and pro-resolving mediators

Many conjunctival inflammatory diseases differ between the sexes and altered conjunctival goblet cells (CGCs) response is often involved. Inflammation is initiated by the release of pro-inflammatory mediators and terminated by the biosynthesis of specialized pro-resolution mediators (SPMs). Herein, we determined the sex-based difference in the responses of CGCs to inflammatory stimuli or pro-resolving lipid SPMs and their interaction with sex hormones. GCs were cultured from pieces of human conjunctiva in RPMI media. CGCs were transferred 24 h before the start of experiments to phenol red-free and FBS-free media to minimize exogenous hormones. RT-PCR, immunofluorescence microscopy (IF), and Western Blot (WB) were performed to determine the presence of sex hormone receptors. Cellular response to pro-inflammatory stimuli or SPMs was studied by measuring the increase in intracellular [Ca²⁺] ([Ca²⁺]_i) using fura 2/AM microscopy. Use of RT-PCR demonstrated estrogen receptor (ER) α in 4/5 males and 3/3 females; ERβ in 2/4 males and 2/3 females; and androgen receptors (AR) in 3/3 male and 3/3 female CGCs. Positive immunoreactivity by IF and protein expression by WB was detected using antibodies for the ERα and ERβ in 3/3 males and 3/3 females, while AR were only present in males. Significantly different Ca²⁺ responses between sexes were found with carbachol only at 10^–3 M, but not with histamine or leukotriene (LT) B₄ at any concentration used. Incubation with dihydrotestosterone (DHT), estrone (E1), or estradiol (E2) at 10^–7 M for 30 min significantly inhibited the LTB₄-stimulated [Ca²⁺]_i increase in male and female CGCs. Incubation with DHT, E1, and E2 overnight significantly inhibited the LTB₄ response in females, while DHT and E2 significantly inhibited the LTB₄ response in males. The SPM lipoxin A₄ (LXA₄) (10^–9–10⁻⁸ M), but not the resolvins D1 or D2, induced an [Ca²⁺]_i increase that was significantly higher in males compared to females. We conclude that male and female CGCs showed differences in the expression of sex hormone receptors. Treatment with sex hormones altered pro-inflammatory mediator LTB₄-induced response. Males compared to females have a higher response to the ω-6-fatty acid derived SPM LXA₄, indicating males may terminate inflammation in conjunctival goblet cells faster than females.

Signaling Pathways Used by the Specialized Pro-Resolving Mediator Maresin 2 Regulate Goblet Cell Function: Comparison with Maresin 1

Specialized pro-resolving mediators (SPMs), including Maresins (MaR)-1 and 2, contribute to tear film homeostasis and resolve conjunctival inflammation. We investigated MaR2's signaling pathways in goblet cells (GC) from rat conjunctiva. Agonist-induced [Ca2+]i and high-molecular weight glycoconjugate secretion were measured. MaR2 increased [Ca2+]i and stimulated secretion. MaR2 and MaR1 stimulate conjunctival goblet cell function, especially secretion, by activating different but overlapping GPCR and signaling pathways, and furthermore counter-regulate histamine stimulated increase in [Ca2+]i. Thus, MaR2 and MaR1 play a role in maintaining the ocular surface and tear film homeostasis in health and disease. As MaR2 and MaR1 modulate conjunctival goblet cell function, they each may have potential as novel, but differing, options for the treatment of ocular surface inflammatory diseases including allergic conjunctivitis and dry eye disease. We conclude that in conjunctival GC MaR2 and MaR1, both increase the [Ca2+]i and stimulate secretion to maintain homeostasis by using one set of different, but overlapping, signaling pathways to increase [Ca2+]i and another set to stimulate secretion. MaR2 also resolves ocular allergy.