Proteomic analysis of human meibomian gland secretions

P Tsai

J Evans

K Green

R Sullivan

P S Tsai, R M Sullivan, D A Schaumberg, S M Richards, M R Dana, D A Sullivan, Schepens Eye Research Institute, Boston, MA, USA

P S Tsai, D A Schaumberg, M R Dana, Massachusetts Eye and Ear Infirmary, Boston, MA, USA

P S Tsai, D A Schaumberg, S M Richards, M R Dana, D A Sullivan, Harvard Medical School, MA, USA

D A Schaumberg, Brigham and Women's Hospital, Boston, MA, USA

J E Evans, K M Green, University of Massachusetts Medical School, Worcester, MA, USA, USA

Correspondence to: David A Sullivan
PhD, Schepens Eye Research Institute, 20 Staniford Street, Boston, MA 02114, USA; sullivan@vision.eri.harvard.edu

P S Tsai, R M Sullivan, D A Schaumberg, S M Richards, M R Dana, D A Sullivan, Schepens Eye Research Institute, Boston, MA, USAP S Tsai, D A Schaumberg, M R Dana, Massachusetts Eye and Ear Infirmary, Boston, MA, USAP S Tsai, D A Schaumberg, S M Richards, M R Dana, D A Sullivan, Harvard Medical School, MA, USAD A Schaumberg, Brigham and Women's Hospital, Boston, MA, USAJ E Evans, K M Green, University of Massachusetts Medical School, Worcester, MA, USA, USACorrespondence to: David A Sullivan
PhD, Schepens Eye Research Institute, 20 Staniford Street, Boston, MA 02114, USA; sullivan@vision.eri.harvard.edu

Accepted 2005 Nov 2.

Abstract

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 µ‐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 α2‐macroglobulin receptor, IgA α 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 β 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.

Keywords: meibomian gland, protein, tear film, proteomics

Abstract

Human tears contain a complex array of proteins that exert a tremendous influence on tear film stability and ocular surface integrity.¹² To date, at least 500 proteins have been identified in the tear film.³ These proteins, in turn, possess a vast range of functions, including bactericidal, virucidal, and fungicidal activities, specific and non‐specific immune capabilities, and lipid transport abilities.¹ Human tear proteins may also minimise autolytic damage, attenuate ultraviolet B radiation induced effects, inhibit serine and cysteine proteases, promote ocular surface wound healing, and modulate the proliferation, motility, and differentiation of corneal and/or conjunctival epithelial cells.¹ The source of these proteins is traditionally thought to be the main and accessory lacrimal glands, the ocular surface epithelium, and the conjunctival blood vessels.⁴

However, we hypothesise that many of these proteins also originate from the meibomian gland. The rationale for our hypothesis is twofold. Firstly, the meibomian gland is a large sebaceous gland, and sebaceous glands are known to secrete a variety of proteins, such as IgA and pro‐inflammatory cytokines (for example, TNF‐α and IL‐1α) in non‐ocular sites.⁵⁶⁷⁸⁹¹⁰ Secondly, the meibomian gland secretes through a holocrine mechanism. Secretion occurs when mature epithelial cells lining the meibomian ducts disintegrate and release their proteinaceous lipid contents into the ducts and onto the ocular surface.⁴ These meibomian gland proteins may represent a significant source of tear film proteins.

The aim of this study was to begin to develop the proteomic methodology to permit the testing of our hypothesis.

Acknowledgements

The authors express their appreciation to Dr Malcolm Pluskal (Acton, MA, USA) and Ms Barbara Evans (Worcester, MA, USA) for their technical assistance and advice. This research was supported by research grants from Allergan, NIH[EY05612], the Schepens Eye Research Institute/ Massachusetts Eye and Ear Infirmary (MEEI) Joint Clinical Research Center, and the MEEI Cornea Service.

Acknowledgements

Abbreviations

IL - interleukin

MS - mass spectrometry

TNF - tissue necrosis factor

Abbreviations

Footnotes

These studies were approved by the human studies committee of the Schepens Eye Research Institute (Boston, MA, USA) and were performed in accordance with guidelines established by the Declaration of Helsinki.

Competing interests: none declared

Footnotes

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