Lacritin

Lacritin is a common glycoprotein of the human tear film. It is mainly produced by the lacrimal gland. Some lacritin also is produced by the meibomian gland, and also by epithelial cells of the conjunctiva and cornea. The lacritin gene LACRT is one of the most highly transcriptionally regulated genes in the human eye. Functional studies suggest a role in epithelial renewal of some nongermative epithelia. By flowing downstream through ducts, it may generate a 'proliferative field'. Lacritin also promotes secretion. This raises the possibility that lacritin may have clinical applications in the treatment of dry eye, the most common eye disease. Recent studies suggest that lacritin is differentially deregulated in blepharitis.

One particularly remarkable feature about lacritin is its cell targeting specificity. New studies suggest that the cell surface proteoglycan syndecan-1 is partly responsible. Syndecan-1 binds many growth factors through its heparan sulfate side chains. It also binds lacritin, but interestingly heparan sulfate interferes with lacritin binding. Since syndecan-1's appear to be always decorated with heparan sulfate, this means that heparanase must be available to partially or completely cleave off heparan sulfate allowing lacritin to bind. Thus heparanase regulates lacritin function.

Lacritin consists of 119 amino acids after cleavage of the N-terminal signal peptide. It displays several predicted alpha helices. One near the C-terminus is a predicted amphipathic alpha helix. This alpha helix appears to bind a domain in the N-terminus of syndecan-1.

Genomic sequencing assembled by Ensembl reveals the existence of putative lacritin orthologues in other species  including: Dasypus novemcinctus (nine-banded armadillo),  Echinops telfairi (lesser hedgehog), Felis silvestris catus (house cat), Macaca mulatta (rhesus macaque or monkey), Myotis lucifugus (little brown bat), Pan troglodytes (chimpanzee), Sorex araneus (common shrew) and Tupaia belangeri (northern tree shrew).

Category: Tears