Aggrelyte-2 promotes protein solubility and decreases lens stiffness through lysine acetylation and disulfide reduction: Implications for treating presbyopia

Aging Cell. 2023 Apr;22(4):e13797. doi: 10.1111/acel.13797. Epub 2023 Feb 23.

Abstract

Aging proteins in the lens become increasingly aggregated and insoluble, contributing to presbyopia. In this study, we investigated the ability of aggrelyte-2 (N,S-diacetyl-L-cysteine methyl ester) to reverse the water insolubility of aged human lens proteins and to decrease stiffness in cultured human and mouse lenses. Water-insoluble proteins (WI) of aged human lenses (65-75 years) were incubated with aggrelyte-2 (500 μM) for 24 or 48 h. A control compound that lacked the S-acetyl group (aggrelyte-2C) was also tested. We observed 19%-30% solubility of WI upon treatment with aggrelyte-2. Aggrelyte-2C also increased protein solubility, but its effect was approximately 1.4-fold lower than that of aggrelyte-2. The protein thiol contents were 1.9- to 4.9-fold higher in the aggrelyte-2- and aggrelyte-2C-treated samples than in the untreated samples. The LC-MS/MS results showed Nε -acetyllysine (AcK) levels of 1.5 to 2.1 nmol/mg protein and 0.6 to 0.9 nmol/mg protein in the aggrelyte-2- and aggrelyte-2C-treated samples. Mouse (C57BL/6J) lenses (incubated for 24 h) and human lenses (incubated for 72 h) with 1.0 mM aggrelyte-2 showed significant decreases in stiffness with simultaneous increases in soluble proteins (human lenses) and protein-AcK levels, and such changes were not observed in aggrelyte-2C-treated lenses. Mass spectrometry of the solubilized protein revealed AcK in all crystallins, but more was observed in α-crystallins. These results suggest that aggrelyte-2 increases protein solubility and decreases lens stiffness through acetylation and disulfide reduction. Aggrelyte-2 might be useful in treating presbyopia in humans.

Keywords: Nε-acetyllysine; acetylation; disulfides; lens; presbyopia; stiffness.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, N.I.H., Extramural

MeSH terms

  • Acetylation
  • Aged
  • Animals
  • Chromatography, Liquid
  • Crystallins* / analysis
  • Crystallins* / metabolism
  • Disulfides / analysis
  • Disulfides / metabolism
  • Humans
  • Lens, Crystalline* / metabolism
  • Lysine / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Presbyopia* / metabolism
  • Solubility
  • Tandem Mass Spectrometry
  • Water / analysis
  • Water / metabolism

Substances

  • Lysine
  • Crystallins
  • Water
  • Disulfides