Somatostatin-like immunoreactivity (SLIR) in rat harderian and meibomian glands and glands of Zeis

Immunohistochemical study on the expressions of neuropeptides in the superficial and deep gland of the third eyelid of pigs

The superficial gland of the third eyelid (SGTE) and deep gland of the third eyelid (DGTE) are classified as accessory lacrimal glands. The aim of the present study was to immunohistochemically investigate the expression of vasoactive intestinal peptide (VIP), dopamine beta-hydroxylase (DβH), substance P (SP), galanin, neuropeptide Y (NPY), pituitary adenylate cyclase-activating peptide (PACAP), somatostatin and calcitonin gene-related peptide (CGRP) in the porcine SGTE and DGTE. We demonstrated the distribution patterns of VIP, DβH, SP, NPY and galanin in the nerve fibres in the SGTE and DGTE. None of somatostatin-, PACAP- and CGRP-immunoreactive (IR) nerve fibres were found in the SGTE and DGTE. The majority of VIP- and DβH-IR nerves fibres were found near to glandular acini, tubules, secretory ducts and blood vessels in the SGTE and DGTE. VIP-IR nerve fibres were found in external connective tissue in SGTE and DGTE and only in interlobular connective tissue in the SGTE. DβH-IR nerve fibres were found in interlobular and external connective tissue in the DGTE but not in the SGTE. Single galanin-, SP- and NPY-IR nerve fibres were observed in close proximity to acini and tubules in the SGTE and DGTE. Single galanin-, SP-, NPY-IR nerve fibres were found in close proximity to the secretory ducts in the DGTE, however only SP-IR nerve fibres were found near to the secretory ducts in SGTE. In conclusion, our research aims to highlight some aspects of SGTE and DGTE innervation in pigs and may also be a source of basic knowledge for further studies.

Neurotransmitter influence on human meibomian gland epithelial cells

PURPOSE

A striking characteristic of the human meibomian gland is its rich sensory, sympathetic, and parasympathetic innervation, yet the functional relevance of these nerve fibers remains unknown. Acting on the hypothesis that neurotransmitters are released in the vicinity of the gland, act on glandular receptors, and influence the production, secretion, and/or delivery of meibomian gland secretions to the ocular surface, the goal in this study was to begin to determine whether neurotransmitters influence the meibomian gland.

METHODS

Immortalized human meibomian gland epithelial (SLHMG) cells were examined for the presence of vasoactive intestinal peptide (VIP) and muscarinic acetylcholine (mACh) receptor transcripts and proteins. Cells were also exposed to VIP, carbachol, forskolin, and/or 3-isobutyl-1-methylxanthine (IBMX) to determine whether these agents, alone or in combination, modulate the adenylyl cyclase pathway, the accumulation of intracellular free calcium ([Ca2+]i), or cell proliferation.

RESULTS

Results demonstrate that SLHMG cells transcribe and translate VIP and mACh receptors; VIP, with either IBMX or forskolin, activates the adenylyl cyclase pathway, and the effect of VIP and forskolin together is synergistic; both VIP and carbachol increase intracellular [Ca2+] in SLHMG cells; and VIP with forskolin stimulates SLHMG cell proliferation.

CONCLUSIONS

This study shows that parasympathetic neurotransmitters and their agonists influence the function of human meibomian gland epithelial cells. It remains to be determined whether this action alters the production, secretion, and/or delivery of meibum to the ocular surface.

Proteomic analysis of human meibomian gland secretions

BACKGROUND/AIM

Human tears contain hundreds of proteins that may exert a significant influence on tear film stability, ocular surface integrity, and visual function. The authors hypothesise that many of these proteins originate from the meibomian gland. This study's aim was to begin to develop the proteomic methodology to permit the testing of their hypothesis.

METHODS

Meibomian gland secretions were collected from the lower eyelids of adult volunteers and placed in a chloroform-methanol mixture. Samples were partitioned in a biphasic system and non-lipid phase materials were reduced, alkylated, and trypsin digested to obtain peptides for protein identification. This peptide mixture was separated by micro-capillary reverse phase chromatography and the effluent examined by nano-electrospray MS and data dependent MS/MS. SEQUEST software was used to identify proteins from the MS/MS spectra.

RESULTS

The methodological approach to date has permitted the identification of more than 90 proteins in human meibomian gland secretions. Proteins include the alpha2-macroglobulin receptor, IgA alpha chain, farnesoid X activated receptor, interferon regulatory factor 3, lacritin precursor, lactotransferrin, lipocalin 1, lysozyme C precursor, potential phospholipid transporting ATPase IK, seven transmembrane helix receptor (also termed somatostatin receptor type 4), testes development related NYD-SP21 (also termed high affinity IgE receptor beta subunit), and TrkC tyrosine kinase.

CONCLUSIONS

These findings indicate that the meibomian gland secretes a number of proteins into the tear film. It is quite possible that these proteins contribute to the dynamics of the tear film in both health and disease.

Mucosal Immunity and Self-Tolerance in the Ocular Surface System

This paper articulates a new working hypothesis that explains many of the pathophysiological conditions described under the common rubric "dry eye" as altered states of mucosal immune regulation. A central principle of mucosal immune physiology is that the parenchymal tissues at the effector sites, i.e., the sites at which secretory antibodies are produced, maintain local signaling milieus that support differentiation of IgA+ plasmablasts and survival of IgA+ plasmacytes. These local signaling milieus also support robust regulatory networks that maintain tolerance to commensual microbes, benign antigens, and parenchymal autoantigens. The regulatory networks are mediated by cycles of interactions between successive generations of dendritic cells, which normally mature with tolerogenic functions, and regulatory T cells, which normally reinforce the system's ability to generate new tolerogenic dendritic cells. The systemic endocrine environment controls expression of the local signaling milieu in the mammary gland and in the prostate and male urethral glands. Emerging evidence indicates that the local signaling milieu in the lacrimal gland also is determined, in part, by the systemic endocrine environment. This working hypothesis suggests explanations for the excess incidence of Sjogren syndrome among women and for the mechanisms of several different immunophysiological states in addition to Sjogren syndrome that, like Sjogren syndrome, are associated with the classical symptoms and signs of dry eye. It also comprises a promising rationale for specific new approaches to therapy.

Changes in the tear film and ocular surface from dry eye syndrome

Dry eye syndrome (DES) refers to a spectrum of ocular surface diseases with diverse and frequently multiple aetiologies. The common feature of the various manifestations of DES is an abnormal tear film. Tear film abnormalities associated with DES are tear deficiency, owing to insufficient supply or excessive loss, and anomalous tear composition. These categorizations are artificial, as in reality both often coexist. DES disrupts the homeostasis of the tear film with its adjacent structures, and adversely affects its ability to perform essential functions such as supporting the ocular surface epithelium and preventing microbial invasion. In addition, whatever the initial trigger, moderate and severe DES is characterized by ocular surface inflammation, which in turn becomes the cause and consequence of cell damage, creating a self-perpetuating cycle of deterioration. Progress has been made in our understanding of the aetiology and pathogenesis of DES, and these advances have encouraged a proliferation of therapeutic options. This article aims to amalgamate prevailing ideas of DES development, and to assist in that, relevant aspects of the structure, function, and production of the tear film are reviewed. Additionally, a synopsis of therapeutic strategies for DES is presented, detailing treatments currently available, and those in development.