Platelet-activating factor causes goblet cell depletion in the conjunctiva

Functional morphology of mucosal goblet cells based on spatial separation of orifice openings to the surface--application to the rabbit bulbar conjunctiva

The purpose of the study was to assess spatial separation of goblet cell orifices observed at the surface of the rabbit bulbar conjunctiva by scanning electron microscopy (SEM) specimens of the bulbar conjunctiva from 8 healthy pigmented rabbits were obtained using a special preparation technique by which the tissue was carefully stretched out during glutaraldehyde fixation. On high magnification prints of SEM images of the conjunctival surface, the locations of goblet cell openings (orifices) to the apical surface were marked and the centre-to-centre spacing between all such orifices measured. Across the regions of interest (ROI), with averaged dimensions of 322 μm × 230 μm (adjusted for tissue shrinkage), the averaged value for the distances between all orifices was 196 μm (range 141-241 μm), with the calculated density of orifices being 412 mm(-2). A sequential order-based analysis of the spatial separation between orifices indicated a predictable value of 6 μm, a separation that showed a nearly linear inter-dependence over distances of at least 200 μm. The openings of goblet cells to the surface of unstimulated bulbar conjunctiva have a organized spatial distribution that is consistent with there being an organized control of goblet cell secretion.

Role of histamine and its receptor subtypes in stimulation of conjunctival goblet cell secretion

PURPOSE

The purpose of this study was to determine the effect of histamine and its receptors on goblet cell secretion.

METHODS

Cultured rat and human goblet cells were grown in RPMI 1640. Goblet cell secretion of high molecular weight glycoconjugate was measured by an enzyme-linked lectin assay. Cultured rat goblet cells were homogenized and either RNA was isolated for RT-PCR or proteins were isolated for Western blot analysis for presence of histamine receptors subtypes H₁ through H₄. The localization of these receptors was determined in rat and human goblet cells by immunofluorescence microscopy.

RESULTS

Histamine stimulated goblet cell secretion in a concentration- and time-dependent manner. All four histamine receptors were present in cultured rat and human goblet cells. Use of agonists specific to individual histamine receptor subtypes indicated that the rank order of agonist stimulation was H₁ = H₃ > H₄ > H₂. Using antagonists specific to individual histamine receptor subtypes determined that H₂ and H₃, but not the H₁ and H₄, antagonists, inhibited histamine-stimulated conjunctival goblet cell secretion.

CONCLUSIONS

Rat and human conjunctival goblet cells are a direct target of histamine, which induces secretion. All four histamine receptors are present in rat and human conjunctiva and are active in rat conjunctival goblet cells. These findings suggest that all four histamine receptor subtypes are important for conjunctival goblet cell secretion. Blockage of histamine receptor subtypes could prevent the excess mucus production associated with ocular allergy.

Conjunctival goblet cell secretion stimulated by leukotrienes is reduced by resolvins D1 and E1 to promote resolution of inflammation

The conjunctiva is a mucous membrane that covers the sclera and lines the inside of the eyelids. Throughout the conjunctiva are goblet cells that secrete mucins to protect the eye. Chronic inflammatory diseases such as allergic conjunctivitis and early dry eye lead to increased goblet cell mucin secretion into tears and ocular surface disease. The purpose of this study was to determine the actions of the inflammatory mediators, the leukotrienes and the proresolution resolvins, on secretion from cultured rat and human conjunctival goblet cells. We found that both cysteinyl leukotriene (CysLT) receptors, CysLT(1) and CysLT(2,) were present in rat conjunctiva and in rat and human cultured conjunctival goblet cells. All leukotrienes LTB(4), LTC(4), LTD(4), and LTE(4), as well as PGD(2), stimulated goblet cell secretion in rat goblet cells. LTD(4) and LTE(4) increased the intracellular Ca(2+) concentration ([Ca(2+)](i)), and LTD(4) activated ERK1/2. The CysLT(1) receptor antagonist MK571 significantly decreased LTD(4)-stimulated rat goblet cell secretion and the increase in [Ca(2+)](i). Resolvins D1 (RvD1) and E1 (RvE1) completely reduced LTD(4)-stimulated goblet cell secretion in cultured rat goblet cells. LTD(4)-induced secretion from human goblet cells was blocked by RvD1. RvD1 and RvE1 prevented LTD(4)- and LTE(4)-stimulated increases in [Ca(2+)](i), as well as LTD(4) activation of ERK1/2. We conclude that cysteinyl leukotrienes stimulate conjunctival goblet cell mucous secretion with LTD(4) using the CysLT(1) receptor. Stimulated secretion is terminated by preventing the increase in [Ca(2+)](i) and activation of ERK1/2 by RvD1 and RvE1.

PAF mediates cigarette smoke-induced goblet cell metaplasia in guinea pig airways

Goblet cell metaplasia is an important morphological feature in the airways of patients with chronic airway diseases; however, the precise mechanisms that cause this feature are unknown. We investigated the role of endogenous platelet-activating factor (PAF) in airway goblet cell metaplasia induced by cigarette smoke in vivo. Guinea pigs were exposed repeatedly to cigarette smoke for 14 consecutive days. The number of goblet cells in each trachea was determined with Alcian blue-periodic acid-Schiff staining. Differential cell counts and PAF levels in bronchoalveolar lavage fluid were also evaluated. Cigarette smoke exposure significantly increased the number of goblet cells. Eosinophils, neutrophils, and PAF levels in bronchoalveolar lavage fluid were also significantly increased after cigarette smoke. Treatment with a specific PAF receptor antagonist, E-6123, significantly attenuated the increases in the number of airway goblet cells, eosinophils, and neutrophils observed after cigarette smoke exposure. These results suggest that endogenous PAF may play a key role in goblet cell metaplasia induced by cigarette smoke and that potential roles exist for inhibitors of PAF receptor in the treatment of hypersecretory airway diseases.

Morphological and morphometric analysis on the rabbit conjunctival goblet cells in different hormonal conditions

An altered conjunctival mucous secretion was reported in pregnancy or oral contraceptive use. Four groups of rabbits (males, dioestrous females, oestrous females, pregnant) were studied to determine whether sex and/or different physiological conditions could influence conjunctival goblet cells structure and ultrastructure. Light microscopy, transmission electron microscopy, and morphometry were performed. In males and in oestrous females the intracytoplasmic secretory granules were filled with granular material, whilst in pregnant and dioestrous females the granules were formed by a more homogenous and dense secretory material. The number of goblet cells was not statistically different in the groups studied, whilst pregnant animals showed the largest mean diameter. As to the secretory granules, their mean area was larger in dioestrous females, whilst their optical density was highest in pregnant animals. These observations indicate that the morphology of conjunctival goblet cell may vary according to sex and to different physiological conditions: this may account for the peculiar mucous secretion demonstrated during pregnancy.

Dry eye with only decreased tear break-up time is sometimes associated with allergic conjunctivitis

PURPOSE

The authors' clinical experience has suggested that there is a form of dry eye with only decreased tear break-up time, which is associated with allergic conjunctivitis. The current study was performed to verify this hypothesis.

METHOD

The authors recruited patients with two types of dry eye syndrome, those with only decreased tear break-up (BUT type) and those with positive vital staining (staining type). Individuals without any symptoms or signs served as controls. All subjects were compared regarding symptoms, Schirmer and tear clearance test results, conjunctival papillary formation, antigen-specific serum-IgE level (s-IgE), and goblet cell density of the palpebral conjunctiva. Antigen-induced allergic conjunctivitis was produced in guinea pigs, and histopathologic changes of the conjunctiva were examined.

RESULTS

Patients with the BUT-type dry eye syndrome were younger and their symptoms were as severe as the staining type. The Schirmer and tear clearance test results were better, and the papillary formation and s-IgE were observed more than in the BUT type. The average goblet cell density in the BUT-type syndrome was 625.4 +/- 193.2/mm2, which was significantly less than 1005.6 +/- 294.5/mm2 in the controls (P < 0.01). The average goblet cell density was significantly decreased in the allergic animals (10.40 +/- 1.11/0.2 mm) compared with that of the controls (16.21 +/- 0.26/0.2 mm) or the anti-allergic drug-treated group (13.69 +/- 0.30/0.2 mm) (P < 0.01).

CONCLUSION

These results support the authors' hypothesis that decreased break-up time is in part associated with the decreased goblet cell density caused by allergic conjunctivitis.

Effect of platelet activating factor on formation and composition of airway fluid in the guinea-pig trachea

1. We studied the effect of platelet activating factor (PAF) on leakage of albumin, and secretion of fucose (a marker for mucus glycoprotein) and protein into the tracheal lumen of the guinea-pig isolated in situ, and on bioelectric properties and fluxes of mannitol in vitro. We also studied the effect of PAF on mucus secretion in human bronchi in vitro. 2. In guinea-pig, intravenous PAF markedly increased the luminal concentration of protein but did not significantly increase fucose concentrations. Increased albumin leakage (274% above controls at a dose of 50 ng/kg PAF) was associated with the increased luminal content of protein (248% above controls at the same dose of PAF). 3. Leakage of albumin was maximal 10 min after PAF, was significantly reduced by 20 min and had returned to baseline by 30 min. This pattern of leakage could be repeated with successive administrations of PAF. 4. PAF induced small but significant biphasic changes in bioelectric properties in vitro. The initial response was rapid in onset and characterized by maximal increases in short-circuit current (Isc) of 6.5% above controls at 7.5 min and in conductance (G) of 7% at 20 min. Both responses were blocked by the PAF receptor antagonist WEB 2086. Amiloride blocked the increase in Isc. Permeability of the tissue to mannitol (Pmann) was unaltered. The delayed response was characterized by maximal increases in Isc and G of 10% above controls at 60-90 min which were not significantly affected by WEB 2086 or amiloride. Pmann was increased by 38% at 90 min. 5. PAF increased fucose secretion in human bronchi in vitro. 6. Lyso-PAF in vitro caused changes similar to those induced by PAF on bioelectric properties and mucus secretion, but had no significant effects in vivo. 7. Light microscopy showed no evidence of epithelial disruption in animals given intravenous PAF at a dose causing significant albumin transudation. 8. We conclude that PAF increases the protein content of guinea-pig tracheal fluid principally by inducing plasma leakage rather than mucus secretion and that the small changes in ion transport and epithelial conductance may reduce the tendency to epithelial disruption during plasma leakage.