Spatial distributions of phosphorylated membrane proteins aquaporin 0 and MP20 across young and aged human lenses

- Distributions of pAQP0 and pMP20 change with age and across human lens regions.
- MP20 pSer170 peaks in the cortex and decreases with lens age in the nucleus.
- AQP0 pSer235 peaks in the inner cortex and declines with lens age in the nucleus.
- A decrease in AQP0 pSer235 in aged lenses correlates with the permeability barrier.
- AQP0 pSer229 is minor, but levels remain steady into the nucleus and with lens age.

In the human ocular lens it is now realized that post-translational modifications can alter protein function and/or localization in fiber cells that no longer synthesize proteins. The specific sites of post-translational modification to the abundant ocular lens membrane proteins AQP0 and MP20 have been previously identified and their functional effects are emerging. To further understand how changes in protein function and/or localization induced by these modifications alter lens homeostasis, it is necessary to determine the spatial distributions of these modifications across the lens. In this study, a quantitative LC-MS approach was used to determine the spatial distributions of phosphorylated AQP0 and MP20 peptides from manually dissected, concentric layers of fiber cells from young and aged human lenses. The absolute amounts of phosphorylation were determined for AQP0 Ser235 and Ser229 and for MP20 Ser170 in fiber cells from the lens periphery to the lens center. Phosphorylation of AQP0 Ser229 represented a minor portion of the total phosphorylated AQP0. Changes in spatial distributions of phosphorylated APQ0 Ser235 and MP20 Ser170 correlated with regions of physiological interest in aged lenses, specifically, where barriers to water transport and extracellular diffusion form.