Poster Topical Area: Aging and Chronic Disease
Poster Board Number: 98
Objectives: Advanced glycation end products (AGEs) form when proteins and lipids reacts with sugars or their metabolites. An accumulation of AGEs causes glycative stress in tissues and organs which has been associated with an increased risk of various ocular diseases such as age-related macular degeneration and cataract.
AGEs can be soluble or become insoluble when in high concentration. Two proteolytic cellular processes participate in the reduction of the levels of AGES: ubiquitin/proteasome system (UPS) which degrades cytosolic proteins and autophagy which primary degrades protein aggregates and cellular organelles.
In this work, we focused on the contribution of autophagy in the degradation of AGEs. We expected that autophagy plays a major role in the removal of insoluble fraction of AGEs, which cannot be efficiently degraded by the UPS.
Methods: We exposed human ARPE-19 retinal pigment epithelial cells to methylglyoxal (MGO), a glycating metabolite of glucose which mimics glycative stress accelerates production and accumulation of AGEs. Cells exposed to glycative stress were treated with chloroquine, a lysosomotropic agent that blocks the degradation of autophagic cargo. To clarify the specific pools, we separate AGEs in two different fractions (insoluble and soluble in 1% Triton) and analyzed which pool is mainly being targeted to the autophagosomes. Furthermore, we evaluated the colocalization of AGEs with LC3, a structural marker of autophagosomes, and p62, an autophagic adaptor that helps bring ubiquitinated cargo to the autophagic compartment.
Results: Biochemical analyses revealed that the insoluble fraction of AGEs is mainly targeted to the autophagosomal compartment for degradation. When the degradation of the autophagosome is blocked using chloroquine, the AGEs are formed but not degraded and there is an accumulation of MG-H1, a MGO-derived AGE, in puncta form positive for LC3 and p62. The lack of p62 increased the formation of AGEs suggesting that p62-selective autophagy plays a role in the removal of the insoluble AGEs population.
Conclusions: Our findings show a role of autophagy in the removal of insoluble AGEs with a significant contribution of p62 as autophagic adaptor. Further experiments will be needed to clarify if the lack of p62 leads to an increased glucotoxicity mediated by AGEs.