ROLES FOR NETRIN-4 AND LAMININS CONTAINING THE β2 OR γ3 SUBUNITS IN CORNEAL DEVELOPMENT AND WOUND HEALING

Abstract

Corneal diseases are among the top preventable causes of vision loss in the developed world. Injuries, infections, age-related diseases and congenital diseases are typically accompanied by defects in the extracellular matrix (ECM) or its remodeling. Laminins and laminin-related molecules, netrins, are ECM proteins that play an important yet not fully characterized role in corneal development, disease and wound recovery. With regulatory roles in cell proliferation, migration and neural guidance, the main research question addressed here is how netrin-4 and specific laminin subunits, i.e. the laminin β2 and γ3 chains, are involved in corneal development and wound recovery. A reverse genetics approach was employed to characterize the corneal phenotype in mice lacking the Ntn4, Lamb2, or Lamc3genes during development and wound healing.Immunohistochemistry data showed that netrin-4 and the laminin β2 and γ3 chains are components of corneal basement membranes. Genetic ablation of Lamb2, Lamc3or both genes led to hypo-proliferation of epithelial progenitors and hypo-innervation of the corneal surface, indicating regulatory roles in corneal development and possibly wound recovery. In addition to these effects at the surface, in the deep cornea, Descemet’s Membrane (DM) was thinner and endothelial cells displayed disruptions in tight-junction formation, likely resulting from an altered molecular composition of DM.On the other hand, deletion of Ntn4led to hyper-innervation of the corneal surface during development. When further characterizedin the context of wound recovery, adult Ntn4-/-mice showed a slightlyearlier reepithelialization, upregulated cell proliferation and reinnervation of wound area compared to wild-type littermates. Altogether, these data indicate that netrin-4 is likely a negative regulator of proliferative events in the cornea.Hownetrin-4 and laminin heterotrimers containing the laminin β2or γ3 subunits affect nerve-cell interactions in the cornea merits further inquiry. Given the observations presented herein, these molecules are important for corneal maintenance and have applications potential in strategies aimed toward treatment of corneal injuries, such as development of fully characterized, synthetic pro-regenerative membranes, or incorporation into implantable biomimetic scaffolds which can also mitigate current donor tissue shortages.