Abstract
Purpose: :
Tear film lipids play a critical role in terrestrial mammals, by promoting tear film stability and visual acuity, providing lubrication during blinking, interfering with bacterial colonization, and preventing tear film evaporation. Lipid loss leads to tear film instability, evaporative dry eye, and reduced visual acuity. In striking contrast to terrestrial mammals, our previous research indicates that marine mammals may have no tear film lipid layer. This finding is quite significant, and suggests that sea mammals may use an alternative approach to stabilize their tear film. We hypothesize that tear film proteins, and specifically mucins, provide such stability. Our goals in this study were two-fold: first, to determine whether the tears of sea mammals, including the Pinnipedia (sea lions, seals) and Cetacea (dolphins), contain similar levels and types of proteins; and second, to examine whether mucins exist in these tears.
Methods: :
Ocular surface secretions (gifts from Sam Ridgway, Dolphin Quest, Ed Latson and the Niagra Falls Aquarium) were collected from California sea lions, Pacific and Atlantic harbor seals, Atlantic bottlenose dolphins and humans. Tear protein concentrations were determined with a BCA assay, whereas protein profiles were evaluated by polyacrylamide gel electrophoresis and silver staining. For mucin detection, native or sialidase-treated tears were electrophoresed on SDS-agarose gels, then transferred to nitrocellulose membranes for the analysis of peanut agglutinin (PNA) and Sambucus nigra (SNA) binding. These lectins associate with different mucin moieties.
Results: :
Our studies demonstrate that: (1) protein concentrations are comparable in tears of sea lions, dolphins and humans, but lower in seals; (2) tear protein profiles of sea lions, seals, dolphins and humans show many similarities, and all feature a prominent protein migrating between 60 and 70 kDa; and (3) dolphin tears contain PNA- and SNA-reactive mucins.
Conclusions: :
Our findings demonstrate that the tears of sea mammals contain a variety of proteins, including mucins. These mucins, in lieu of lipids, may serve to promote the stability and prevent the evaporation of their tear film.
Keywords: cornea: tears/tear film/dry eye • cornea: surface mucins