Abstract
Purpose :
As a near-primate mammalian model associated with low cost, a rapid aging profile, and large eyes, the tree shrew may be an attractive pre-clinical animal model for tear-related conditions. Interested in the feasibility of tree shrews for evaporative dry eye studies, which involve the tear film lipid layer and lipid-binding proteins, we performed top-down proteomics to identify if lipocalin is present in tree shrew tears.
Methods :
Tears (0.6-2.5 µL) were collected with microcapillary glass tubes from each eye of 2 anesthetized tree shrews (1 male (M) & 1 female (F) of 6.3 and 7.8 years old, respectively). Proteins were extracted from each tear sample and then detected and identified with mass spectrometry (MS) and tandem MS (MS/MS). Sequences predicted from gene data, along with potential post-translational modifications (PTMs), were utilized for the identification. The identification was manually verified by examining the MS/MS spectra.
Results :
Many protein peaks were detected for the tree shrew tears. The molecular masses of high-intensity peaks were 11,663 Da (F), 11,785 Da (M), 12,056 Da (M), 12,209 Da (M & F), 15,249 Da (M & F), 17,429 Da (M & F), 21,485 Da (M), and 21,647 Da (M). The 17,429 Da peak, identified as lipocalin with PTMs of signal peptide removal and pyroglutamate formation, is abundant for the male tree shrew but significantly decreased in the older female. The observation is consistent with the trend of the amount of lipocalin detected in human tears with age and sex, as well as the high prevalence of dry eye in older women. Lipocalin binds a wide array of tear lipids. We believe that these lipids are detrimental to an ordered lipid layer and thus need to be scavenged via binding to lipocalin to prevent evaporative dry eye. The observed differences in some of the other proteins between male and female tree shrews are likely related to the binding of sex-dependent pheromones.
Conclusions :
We have previously reported that meibomian gland secretions from tree shrews are consistent with humans. In this study, the highly abundant lipocalin, known to bind many lipids in human tears, is also found in tree shrew tears. Taken together, the tree shrew represents a promising near-primate model for pre-clinical evaporative dry eye studies.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.