YAP Inhibition Halts Mechanotransductive Regulation of Lens Growth

Abstract

Purpose : The lens grows continuously throughout life, leading to various age-related vision problems (i.e. presbyopia); however, little is known of the factors driving lens growth. In previous studies we have observed that mechanical strains, such as those induced in the lens capsule during disaccommodation, increase the mitotic index (MI) of the lens epithelial cells (LECs). We tested the hypothesis that the mechanotransduction of those forces are mediated by the Yes-associated protein (YAP) and that the inhibition of YAP would prevent the increase in LEC proliferation that occurs in response to mechanical stimulation.

Methods : Paired porcine lenses were dissected such that the ciliary body and a ring of sclera were still attached. The lenses were mounted to a lens stretching device and stretched at the equator to various strain regimes: 0%, 6%, and 12% static strain (defined as the % change from the initial equatorial diameter) in culture. One of the lenses was cultured with the YAP inhibitor verteporfin, and the paired lens was the control. After culturing for 24 hours, the LECs were isolated and stained to quantify the fraction of proliferating cells, or MI, using a flow cytometer.

Results : Linear regression of both treatment groups was used to determine if the LEC mitotic index could be predicted by strain amplitude. A significant correlation was found for the control group (MI = 1.28 + 0.39 * % Strain Amplitude, R² = 0.975, p<0.0001), while no significant relationship was found for the group treated with verteporfin (MI = 0.99 + 0.02 * % Strain Amplitude, R² = 0.292, p = 0.107) (Fig. 1). To confirm the difference between the treatment groups, analysis of covariance (ANCOVA) was used to determine whether there was a significant difference between groups, and a significant difference was observed (F=282.34, p<0.0001). A post-hoc Tukey’s HSD test indicated a significant difference between verteporfin and control groups (p <0.0001).

Conclusions : These data indicate that stretching the lens increased the proliferation of LECs in the control group but lenses treated with the YAP inhibitor did not exhibit such behavior. This implies that YAP plays an essential role in transducing mechanical cues into an increased rate of lens growth.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Figure 1. The Variation of LEC Proliferation in Treatment and Control Lenses in Relation to Strain Amplitude