Signaling pathways activated by resolvin E1 to stimulate mucin secretion and increase intracellular Ca2+ in cultured rat conjunctival goblet cells

Purinergic agonists increase [Ca2+]i in rat conjunctival goblet cells through ryanodine receptor type 3

ATP and benzoylbenzoyl-ATP (BzATP) increase free cytosolic Ca2+ concentration ([Ca2+]i) in conjunctival goblet cells (CGCs) resulting in mucin secretion. The purpose of this study was to investigate the source of the Ca2+i mobilized by ATP and BzATP. First-passage cultured rat CGCs were incubated with Fura-2/AM, and [Ca2+]i was measured under several conditions with ATP and BzATP stimulation. The following conditions were used: 1) preincubation with the Ca2+ chelator EGTA, 2) preincubation with the SERCA inhibitor thapsigargin (10-6 M), which depletes ER Ca2+ stores, 3) preincubation with phospholipase C (PLC) or protein kinase A (PKA) inhibitor, or 4) preincubation with the voltage-gated calcium channel antagonist nifedipine (10-5 M) and the ryanodine receptor (RyR) antagonist dantrolene (10-5 M). Immunofluorescence microscopy (IF) and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to investigate RyR presence in rat and human CGCs. ATP-stimulated peak [Ca2+]i was significantly lower after chelating Ca2+i with 2 mM EGTA in Ca2+-free buffer. The peak [Ca2+]i increase in CGCs preincubated with thapsigargin, the PKA inhibitor H89, nifedipine, and dantrolene, but not the PLC inhibitor, was reduced for ATP at 10-5 M and BzATP at 10-4 M. Incubating CGCs with dantrolene alone decreased [Ca2+]i and induced CGC cell death at a high concentration. RyR3 was detected in rat and human CGCs with IF and RT-qPCR. We conclude that ATP- and BzATP-induced Ca2+i increases originate from the ER and that RyR3 may be an essential regulator of CGC [Ca2+]i. This study contributes to the understanding of diseases arising from defective Ca2+ signaling in nonexcitable cells.NEW & NOTEWORTHY ATP and benzoylbenzoyl-ATP (BzATP) induce mucin secretion through an increase in free cytosolic calcium concentration ([Ca2+]i) in conjunctival goblet cells (CGCs). The mechanisms through which ATP and BzATP increase [Ca2+]i in CGCs are unclear. Ryanodine receptors (RyRs) are fundamental in [Ca2+]i regulation in excitable cells. Herein, we find that ATP and BzATP increase [Ca2+]i through the activation of protein kinase A, voltage-gated calcium channels, and RyRs, and that RyRs are crucial for nonexcitable CGCs' Ca2+i homeostasis.

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.

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.

Early life stage transient aristolochic acid exposure induces behavioral hyperactivity but not nephrotoxicity in larval zebrafish

Aristolochic acids (AA) are nitrophenanthrene carboxylic acids found in plants of the Aristolochiaceae family. Humans are exposed to AA by deliberately taking herbal medicines or unintentionally as a result of environmental contamination. AA is notorious for its nephrotoxicity, however, fewer studies explore potential neurotoxicity associated with AA exposure. The developing nervous system is vulnerable to xenobiotics, and pregnant women exposed to AA may put their fetuses at risk. In the present study, we used the embryonic zebrafish model to evaluate the developmental neurotoxicity associated with AA exposure. At non-teratogenic concentrations (≤ 4 µM), continuous AA exposure from 8 to 120 hours post fertilization (hpf) resulted in larval hyperactivity that was characterized by increased moving distance, elevated activity and faster swimming speeds in several behavioral assays. Further analysis revealed that 8-24 hpf is the most sensitive exposure window for AA-induced hyperactivity. AA exposures specifically increased motor neuron proliferation, increased apoptosis in the eye, and resulted in cellular oxidative stress. In addition, AA exposures increased larval eye size and perturbed the expression of vision genes. Our study, for the first time, demonstrates that AA is neurotoxic to the developmental zebrafish with a sensitive window distinct from its well-documented nephrotoxicity.

Pro-Resolving Mediator Annexin A1 Regulates Intracellular Ca2+ and Mucin Secretion in Cultured Goblet Cells Suggesting a New Use in Inflammatory Conjunctival Diseases

The amount of mucin secreted by conjunctival goblet cells is regulated to ensure the optimal level for protection of the ocular surface. Under physiological conditions lipid specialized pro-resolving mediators (SPM) are essential for maintaining tissue homeostasis including the conjunctiva. The protein Annexin A1 (AnxA1) can act as an SPM. We used cultured rat conjunctival goblet cells to determine if AnxA1 stimulates an increase in intracellular [Ca²⁺] ([Ca²⁺]_i) and mucin secretion and to identify the signaling pathways. The increase in [Ca²⁺]_i was determined using fura2/AM and mucin secretion was measured using an enzyme-linked lectin assay. AnxA1 stimulated an increase in [Ca²⁺]_i and mucin secretion that was blocked by the cell-permeant Ca²⁺ chelator BAPTA/AM and the ALX/FPR2 receptor inhibitor BOC2. AnxA1 increased [Ca²⁺]_i to a similar extent as the SPMs lipoxin A₄ and Resolvin (Rv) D1 and histamine. The AnxA1 increase in [Ca²⁺]_i and mucin secretion were inhibited by blocking the phospholipase C (PLC) pathway including PLC, the IP₃ receptor, the Ca²⁺/ATPase that causes the intracellular Ca²⁺ stores to empty, and blockade of Ca²⁺ influx. Inhibition of protein kinase C (PKC) and Ca²⁺/calmodulin-dependent protein kinase also decreased the AnxA1-stimulated increase in [Ca²⁺]_i and mucin secretion. In contrast inhibitors of ERK 1/2, phospholipase A₂ (PLA₂), and phospholipase D (PLD) did not alter AnxA1-stimulated increase in [Ca²⁺]_i, but did inhibit mucin secretion. Activation of protein kinase A did not decrease either the AnxA1-stimulated rise in [Ca²⁺]_i or secretion. We conclude that in health, AnxA1 contributes to the mucin layer of the tear film and ocular surface homeostasis by activating the PLC signaling pathway to increase [Ca²⁺]_i and stimulate mucin secretion and ERK1/2, PLA₂, and PLD to stimulate mucin secretion from conjunctival goblet cells.

D-series Resolvins activate Phospholipase D in phagocytes during inflammation and resolution

A successful acute inflammatory response results in the elimination of infectious agents by neutrophils and monocytes, followed by resolution and repair through tissue-resident and recruited macrophages. Resolvins (D-series and E-series) are pro-resolving lipid mediators involved in resolution and tissue repair, whose intracellular signaling remains of interest. Here, we report that D-series resolvins (RvD1- RvD5) activate phospholipase D (PLD), a ubiquitously expressed membrane lipase enzyme activity in modulating phagocyte functions. The mechanism for PLD-mediated actions of Resolvin-D5 (RvD5) in polarizing macrophages (M1-like toward M2-like) was found to be two-pronged: (a) RvD5 inhibits post-transcriptional modifications, by miRs and 3'exonucleases that process PLD2 mRNA, thus increasing PLD2 expression and activity; and (b) RvD5 enhances PLD2-S6Kinase signaling required for membrane expansion and efferocytosis. In an in vivo model of second organ reflow injury, we found that RvD5 did not reduce lung neutrophil myeloperoxidase levels in PLD2^-/- mice compared to WT and PLD1^-/- mice, confirming a novel role of PLD2 as the isoform in RvD5-mediated resolution processes. These results demonstrate that RvD5-PLD2 are attractive targets for therapeutic interventions in vascular inflammation such as ischemia-reperfusion injury and cardiovascular diseases.

The Role of Specialized Pro-Resolving Mediators in Cystic Fibrosis Airways Disease

Cystic Fibrosis (CF) is a recessive genetic disease due to mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene encoding the CFTR chloride channel. The ion transport abnormalities related to CFTR mutation generate a dehydrated airway surface liquid (ASL) layer, which is responsible for an altered mucociliary clearance, favors infections and persistent inflammation that lead to progressive lung destruction and respiratory failure. The inflammatory response is normally followed by an active resolution phase to return to tissue homeostasis, which involves specialized pro-resolving mediators (SPMs). SPMs promote resolution of inflammation, clearance of microbes, tissue regeneration and reduce pain, but do not evoke unwanted immunosuppression. The airways of CF patients showed a decreased production of SPMs even in the absence of pathogens. SPMs levels in the airway correlated with CF patients' lung function. The prognosis for CF has greatly improved but there remains a critical need for more effective treatments that prevent excessive inflammation, lung damage, and declining pulmonary function for all CF patients. This review aims to highlight the recent understanding of CF airway inflammation and the possible impact of SPMs on functions that are altered in CF airways.

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

Leukotriene B4 (LTB4) is a major proinflammatory mediator important in host defense, whereas resolvins (Rvs) are produced during the resolution phase of inflammation. The authors determined the actions of both RvE1 and RvD1 on LTB4-induced responses of goblet cells cultured from rat conjunctiva. The responses measured were an increase in the intracellular [Ca²⁺] ([Ca²⁺]_i) and high-molecular-weight glycoprotein secretion. Treatment with RvE1 or RvD1 for 30 minutes significantly blocked the LTB4-induced [Ca²⁺]_i increase. The actions of RvE1 on LTB4-induced [Ca²⁺]_i increase were reversed by siRNA for the RvE1 receptor, and the actions of RvD1 were reversed by an RvD1 receptor inhibitor. The RvE1 and RvD1 block of LTB4-stimulated increase in [Ca²⁺]_i was also reversed by an inhibitory peptide to β-adrenergic receptor kinase. LTB4 and block of the LTB4-stimulated increase in [Ca²⁺]_i by RvE1 and RvD1 were partially mediated by the depletion of intracellular Ca²⁺ stores. RvE1, but not RvD1, counterregulated the LTB4-induced high-molecular-weight glycoprotein secretion. Thus, both RvE1 and RvD1 receptors directly inhibit LTB4 by phosphorylating the LTB4 receptor using β adrenergic receptor kinase. RvE1 receptor counterregulates the LTB4-induced increase in [Ca²⁺]_i and secretion, whereas RvD1 receptor only counterregulates LTB4-induced [Ca²⁺]_i increase.

Maresin 1, a specialized proresolving mediator, stimulates intracellular [Ca2+ ] and secretion in conjunctival goblet cells

Mucin secretion from conjunctival goblet cells forms the tear film mucin layer and requires regulation to function properly. Maresin 1 (MaR1) is a specialized proresolving mediator produced during the resolution of inflammation. We determined if MaR1 stimulates mucin secretion and signaling pathways used. Cultured rat conjunctival goblet cells were used to measure the increase in intracellular Ca²⁺ ([Ca^{2 +} ]_i ) concentration and mucin secretion. MaR1-increased [Ca²⁺ ]_i and secretion were blocked by inhibitors of phospholipase C, protein kinase C, Ca²⁺ /calmodulin-dependent protein kinase II, and extracellular-regulated kinase 1/2. MaR1 added before addition of histamine counterregulated histamine-stimulated increase in [Ca²⁺ ]_i and secretion. We conclude that MaR1 likely has two actions in conjunctival goblet cells: first, maintaining optimal tear film mucin levels by increasing [Ca²⁺ ]_i and stimulating mucin secretion in health and, second, attenuating the increase in [Ca²⁺ ]_i and overproduction of mucin secretion by counterregulating the effect of histamine as occurs in ocular allergy.

RvE1 uses the LTB4 receptor BLT1 to increase [Ca2+]i and stimulate mucin secretion in cultured rat and human conjunctival goblet cells

PURPOSE

Specialized pro-resolving lipid mediator resolvin (Rv) E1 stimulates secretion including mucins from conjunctival goblet cells. RvE1 can use both its ChemR23 receptor and the LTB₄ receptor BLT1 to increase [Ca²⁺]_i. The purpose of this study was to determine the expression of ChemR23 and BLT1 and receptors on conjunctival goblet cells and the respective roles these two receptors play in goblet cell responses to RvE1.

METHODS

Goblet cells were cultured from male rat or human conjunctiva from both sexes. Western blotting analysis, reverse transcription PCR and immunofluorescence microscopy were used to demonstrate the expression of ChemR23 and BLT1 in conjunctival goblet cells. High molecular weight glycoprotein secretion was determined using an enzyme-linked lectin assay. Signaling pathways were studied by measuring the increase in [Ca²⁺]_i using fura 2/AM.

RESULTS

ChemR23 and BLT1 and receptors were present on both rat and human conjunctival goblet cells. The BLT1 inhibitors LY293111 and U75302 significantly blocked RvE1-and LTB₄-stimulated [Ca²⁺]_i increase. RvE1-and LTB₄-stimulated [Ca²⁺]_i and secretion increases were blocked by BLT1-targeted siRNA. RvE1-stimulated [Ca²⁺]_i and secretion increases were also blocked by ChemR23-targeted siRNA. Addition of RvE1 2 min before or simultaneously with LTB₄ desensitized the LTB₄ [Ca²⁺]_i response. Addition of RvE1 and LTB₄ simultaneously caused secretion that was decreased compared to either response alone.

CONCLUSION

RvE1, in addition to the ChemR23 receptor, uses the BLT1 receptor to increase [Ca²⁺]_i and stimulate secretion in both rat and human cultured conjunctival goblet cells.

Exoproteome profiling of Trypanosoma cruzi during amastigogenesis early stages

Chagas disease is caused by the protozoan Trypanosoma cruzi, affecting around 8 million people worldwide. After host cell invasion, the infective trypomastigote form remains 2–4 hours inside acidic phagolysosomes to differentiate into replicative amastigote form. In vitro acidic-pH-induced axenic amastigogenesis was used here to study this step of the parasite life cycle. After three hours of trypomastigote incubation in amastigogenesis promoting acidic medium (pH 5.0) or control physiological pH (7.4) medium samples were subjected to three rounds of centrifugation followed by ultrafiltration of the supernatants. The resulting exoproteome samples were trypsin digested and analysed by nano flow liquid chromatography coupled to tandem mass spectrometry. Computational protein identification searches yielded 271 and 483 protein groups in the exoproteome at pH 7.4 and pH 5.0, respectively, with 180 common proteins between both conditions. The total amount and diversity of proteins released by parasites almost doubled upon acidic incubation compared to control. Overall, 76.5% of proteins were predicted to be secreted by classical or non-classical pathways and 35.1% of these proteins have predicted transmembrane domains. Classical secretory pathway analysis showed an increased number of mucins and mucin-associated surface proteins after acidic incubation. However, the number of released trans-sialidases and surface GP63 peptidases was higher at pH 7.4. Trans-sialidases and mucins are anchored to the membrane and exhibit an enzyme-substrate relationship. In general, mucins are glycoproteins with immunomodulatory functions in Chagas disease, present mainly in the epimastigote and trypomastigote surfaces and could be enzymatically cleaved and released in the phagolysosome during amastigogenesis. Moreover, evidence for flagella discard during amastigogenesis are addressed. This study provides the first comparative analysis of the exoproteome during amastigogenesis, and the presented data evidence the dynamism of its profile in response to acidic pH-induced differentiation.

Resolvin D2 elevates cAMP to increase intracellular [Ca2+] and stimulate secretion from conjunctival goblet cells

Under physiologic conditions, conjunctival goblet cells (CGCs) secrete mucins into the tear film to preserve ocular surface homeostasis. Specialized proresolving mediators (SPMs), like resolvins (Rvs), regulate secretion from CGCs and actively terminate inflammation. The purpose of this study was to determine if RvD2 stimulated mucin secretion and to investigate the cellular signaling components. Goblet cells were cultured from rat conjunctiva. Secretion was measured by an enzyme-linked lectin assay, change in intracellular [Ca²⁺] ([Ca²⁺]_i) using Fura-2, and cellular cAMP levels by ELISA. RvD2 (10^-11-10^-8 M) stimulated secretion, increased cellular cAMP levels and the [Ca²⁺]_i. RvD2-stimulated increase in [Ca²⁺]_i and secretion was blocked by Ca²⁺ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis and the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride but not by the cAMP exchange protein inhibitor α-[2-(3-chlorophenyl)hydrazinylidene]-5-(1,1-dimethylethyl)-b-oxo-3-isoxazolepropanenitrile. Forskolin, 3-isobutyl-1-methylxanthine, and 8-bromo-cAMP (8-Br-cAMP) increased [Ca²⁺]_i. Increasing cAMP with 8-Br-cAMP inhibited the increase in [Ca²⁺]_i stimulated by the cAMP-independent agonist cholinergic agonist carbachol. In conclusion, RvD2 uses both cellular cAMP and [Ca²⁺]_i to stimulate glycoconjugate secretion from CGCs, but the interaction of cAMP and [Ca²⁺]_i is context dependent. Thus RvD2 likely assists in the maintenance of the mucous layer of the tear film to sustain ocular surface homeostasis and has potential as a novel treatment for dry eye disease.-Botten, N., Hodges, R. R., Li, D., Bair, J. A., Shatos, M. A., Utheim, T. P., Serhan, C. N., Dartt, D. A. Resolvin D2 elevates cAMP to increase intracellular [Ca²⁺] and stimulate secretion from conjunctival goblet cells.

Resolvin D1, but not resolvin E1, transactivates the epidermal growth factor receptor to increase intracellular calcium and glycoconjugate secretion in rat and human conjunctival goblet cells

PURPOSE

To identify interactions of the epidermal growth factor receptor (EGFR) with the pro-resolving mediator receptors for RvD1 and RvE1 to stimulate an increase in intracellular [Ca²⁺] ([Ca²⁺]_i) and mucin secretion from cultured human and rat conjunctival goblet cells.

METHODS

Goblet cells from human and rat conjunctiva were grown in culture using RPMI media. Cultured goblet cells were pre-incubated with inhibitors, and then stimulated with RvD1, RvE1, EGF or the cholinergic agonist carbachol (Cch). Increase in [Ca²⁺]_i was measured using fura-2/AM. Goblet cell secretion was measured using an enzyme-linked lectin assay with UEA-1. Western blot analysis was performed with antibodies against AKT and ERK 1/2.

RESULTS

In cultured human conjunctival goblet cells RvE1 -stimulated an increase in [Ca²⁺]_i. RvD1-, but not the RvE1-, stimulated increase in [Ca²⁺]_i and mucin secretion was blocked by the EGFR inhibitor AG1478 and siRNA for the EGFR. RvD1-, but not RvE1-stimulated an increase in [Ca²⁺]_i that was also inhibited by TAPI-1, an inhibitor of the matrix metalloprotease ADAM 17. Inhibition of the EGFR also blocked RvD1-stimulated increase in AKT activity and both RvD1-and RvE1-stimulated increase in ERK 1/2 activity. Pretreatment with either RvD1 or RvE1 did not block the EGFR-stimulated increase in [Ca²⁺]_i.

CONCLUSIONS

We conclude that in cultured rat and human conjunctival goblet cells, RvD1 activates the EGFR, increases [Ca²⁺]_i, activates AKT and ERK1/2 to stimulate mucin secretion. RvE1 does not transactivate the EGFR to increase [Ca²⁺]_I and stimulate mucin secretion, but does interact with the receptor to increase ERK 1/2 activity.

Activation of the EGF Receptor by Histamine Receptor Subtypes Stimulates Mucin Secretion in Conjunctival Goblet Cells

Purpose

The purpose of this study was to determine if histamine receptors interact with the epidermal growth factor receptor (EGFR) in cultured rat conjunctival goblet cells.

Methods

Goblet cells from rat conjunctiva were grown in organ culture. First-passage goblet cells were used in all experiments. Phosphorylated (active) and total EGFR, AKT, and extracellular signal-regulated kinase (ERK)1/2 were measured by Western blot analysis. Cells were preincubated with the EGFR antagonist AG1478 for 30 minutes or small interfering RNA specific to the EGFR for 3 days prior to stimulation with histamine or agonists specific for histamine receptor subtypes for 2 hours. Goblet cell secretion was measured using an enzyme-linked lectin assay. Goblet cells were incubated for 1 hour with the calcium indicator molecule fura-2/AM, and intracellular [Ca2+] ([Ca2+]i) was determined. Data were collected in real time and presented as the actual [Ca2+]i with time and as the change in peak [Ca2+]i.

Results

Histamine increased the phosphorylation of the EGFR. Mucin secretion and increase in [Ca2+]i stimulated by histamine, and agonists specific for each histamine receptor subtype were blocked by inhibition of the EGFR. Increase in [Ca2+]i stimulated by histamine and specific agonists for each histamine receptor was also inhibited by TAPI-1, a matrix metalloproteinase (MMP) inhibitor. The histamine-stimulated increase in activation of AKT, but not ERK1/2, was blocked by AG1478.

Conclusions

In conjunctival goblet cells, histamine, using all four receptor subtypes, transactivates the EGFR via an MMP. This in turn phosphorylates AKT to increase [Ca2+]i and stimulate mucin secretion.