Laurie Laboratory

UVa Cell Biology

 
 

    Our focus is on the epithelial-specific prosecretory mitogen ‘lacritin’.  We serendipitously 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 rabbit eyes, lacritin stimulates basal tearing (bottom left figure; Samudre et al, Inv. Ophthal. Vis. Sci. ’11), and appears to be downregulated in dry eye disease - the most common eye disease.


    How lacritin works is novel and intriguing.  Recently, lacritin successfully treated a mouse model of dry eye (ARVO’13; Vijmasi et al, #2667), and thus offers promise as a natural replacement 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 but 3-O-sulfated heparan sulfate, and 3) chondroitin sulfate (short N-terminal chain; Zhang et al, J. Biol. Chem. ’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, J. Biol. Chem. ‘13).


    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.


    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