Laurie Laboratory

UVa Cell Biology

 
 

    Our focus is on the epithelial-specific prosecretory mitogen ‘lacritin’.  We discovered lacritin out of a screen for factors capable of stimulating tear protein secretion by lacrimal acinar cells (Sanghi et al, J. Mol. Biol. '01).  When added topically to dry eye mouse (Vijmasi et al, 14) or normal rabbit (Samudre et al, ‘11) eyes, lacritin stimulates basal tearing .  Several have reported that lacritin monomer is downregulated in dry eye disease - the most common eye disease.  It therefore may offer promise as a natural tear generation therapy for dry eye.


     Via its C-terminal amphipathic alpha helix (top left), lacritin targets the N-terminus of syndecan-1 in a heparanase-dependent manner (middle left) (Ma et al, J. Cell Biol.'06) that both generates and exposes a three pronged binding site: 1) GAGAL in the core protein, 2) cleaved and now apparently exposed 3-O-sulfated heparan sulfate, and 3) an N-terminal chondroitin sulfate chain (Zhang et al, ‘13).  Ligation stimulates mitogenic and prosecretory signaling that is biphasic and cell type selective. 


    Ligation also promotes cell survival of stressed eye epithelia via a rapid FOXO3 dependent mechanism that temporarily accelerates autophagy and restores oxidative phosphorylation.  Normal human tears immunodepleted of lacritin are not protective.  However protective activity is restored to human dry eye tears by spiking in lacritin (top right) (Wang et al, ’13).  A slow release mechanism has been developed by Andrew MacKay’s (Wang et al, ’15).  The same lab has discovered that lacritin promotes corneal wound healing (Wang et al, ’14).


    As a negative control, we use the lacritin truncation mutant ‘C-25’ (bottom left, top right).  C-25 lacks lacritin’s C-terminal 25 amino acids containing the syndecan-1 targeting amphipathic alpha helix.


Lacritin C-terminal fragment is bactericidal



    A C-terminal fragment of lacritin is a normal resident of tears.  This fragment is potently bactericidal for both gram negative and positive bacteria in vitro.  Tears immunodepleted of this fragment and lacritin display little bactericidal activity (McKown et al, ’14).








A panel of lacritin constructs are now available via Addgene.






 

Lacritin in epithelial cell biology and dry eye disease

Epithelial Renewal

Epithelial Differentiation

Epithelial Secretion

Epithelial Cytoprotection

Eye Tearing