Gene expression profiling reveals insight into the role of MMP-9 in transforming growth factor β (TGFβ)-induced epithelial-mesenchymal transition (EMT) in the lens.

Abstract

Purpose: Previous studies from our lab have shown that reduced expression of Matrix Metalloproteinase 9 (MMP9) prevents TGFβ-induced EMT and subsequent anterior subcapsular cataract (ASC) formation. However, the mechanism by which this occurs is not well understood. To further understand this we have studied the variations in gene expression following TGFβ-induced EMT in the lens in the presence and absence of MMP9 utilizing a novel gene expression analysis tool, NanoString.

Methods: Wild-type (WT) (N=12), TGFβ overexpressing transgenic (TGFβ^tg) (N= 12) or TGFβ^tg mice on the MMP9 knock out background (TG;M9KO) (N=8), at 1.5 - 2 months of age were sacrificed and their eyes removed. RNA was isolated from the lenses and expression profiling was done using a 184-gene probe-set custom designed array on NanoString nCounter gene expression system, which captures and counts individual mRNA transcripts. The data was normalized and the ratios of expression were calculated using one set of WT as the reference. Genes that showed at least an average of two-fold increase or decrease were further processed for constructing a heat map and graphs.

Results: A 7-fold and 5-fold decrease in expression of e-cadherin was observed in TGFβ^tg (p<0.01) and TG;M9KO (p<0.01) lenses, respectively when compared to WT. In contrast, the expression of α-smooth muscle actin, acta2, was increased by approximately 1.5 and 2 -fold in TGFβ^tg (p<0.01) and TG;M9KO (p<0.01) lenses, respectively. Interestingly, wnt8a and slug were observed to be decreased by 2.3 and 2.4 -fold, respectively, in TGFβ^tg (p<0.01) lenses but was increased by 1-fold (p=0.04) and 1.4-fold (p=0.06), respectively, in TG;M9KO lenses, when compared to WT lenses.

Conclusions: Our results are consistent with previous reports that show a decrease in e-cadherin and an increase in acta2 during TGFβ-induced EMT of LEC. However, data for wnt8a and slug shows that these genes are differentially expressed in the TGFβ^tg versus TG;M9KO lenses. Further molecular investigation is required to determine the mechanism by which MMP-9 regulates the expression of these genes during TGFβ-induced EMT in the lens.