Mast cells directly promote proliferation and tube formation of vascular endothelial cells (VECs) by secreting high levels of vascular endothelial growth factor A (VEGF-A), researchers report in a study published in The Ocular Surface.
The investigation sought to determine how non-immunoglobulin E (IgE) mediated activation of mast cells promote neovascularization. Most research on mast cells in pathological angiogenesis has been limited to tumors, the study explains.
They induced corneal neovascularization in BALB/c, C57BL/6 wild-type (WT) and mast cell-deficient cKitw-sh mice by intrastromally placing a suture on the nasal side of the cornea. The corneas were harvested 6 hours postsuture placement, and VEGF-A, β-hexosaminidase enzyme, and tryptase enzyme levels were measured. The researchers evaluated corneal neovascularization using slit-lamp biomicroscopy on day 4 post-suture.
Using flow cytometric quantification analysis, the researchers found that cKit+FCεR+ mast cells’ frequencies increased after suture placement. There was a 5-fold increase (P =.008) of tryptase and a 2.5-fold increase of β-hexosaminidase (P =.004). VEGF-A expression after suture placement substantially increased relative to naïve controls (P =.0001). Significantly less corneal neovascularization was observed in cKitw-sh mice on day 4 post-suture compared with WT mice (P =.0003).
To investigate whether the increase of VEGF-A expression following suture placement is due to mast cells, the researchers stimulated bone marrow-derived mast cells and compared them with corneal epithelial cells, which did not indicate protein levels of VEGF-A and thereby were used as controls.
VECs co-cultured with mast cells resulted in significantly more branch and node formation (P =.002 and P =.007, respectively) as well as higher total branch length (P =.01; measures of tube formation). VECs showed significant increase in proliferation when co-cultured with mast cells (P ≤.0001).
Cromolyn treatment to inhibit mast cell activation resulted in significantly less neovascularization compared with the PBS treatment on day 4 (P =.04). When corneas were harvested on day 4 for immunohistochemistry analyses, cromolyn-treated corneas showed significantly smaller vessel area relative to PBS-treated controls (P =.005).
“In summary, our data provide novel insights on the role of ocular surface mast cells in corneal neovascularization,” according to investigators. “Mast cells, which secrete high levels of VEGF-A, induce vascular endothelial cell proliferation and new vessel formation. Finally, we report that pharmacological inhibition of ocular surface mast cells suppresses corneal neovascularization, suggesting mast cells could be a potential therapeutic target for treating corneal neovascularization.”
Cho W, Mittal SK, Elbasiony E, Chauhan SK. Activation of ocular surface mast cells promotes corneal neovascularization. Ocul Surf. Published online September 8, 2020. doi:10.1016/j.jtos.2020.09.002