The importance of Ca2+/Zn2+ signaling S100 proteins and RAGE in translational medicine

Proinflammatory S100A9 Regulates Differentiation and Aggregation of Neural Stem Cells

Inflammation is the primary pathological feature of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease. Proinflammatory molecules (e.g., S100A9) play important roles during the progression of the diseases by regulating behavior and fate of multiple cell types in the nervous system. Our earlier studies reveal that S100A9 is toxic to neurons, and its interaction with Aβ peptides leads to the formation of large nontoxic amyloidogenic aggregates, suggesting a protective role of coaggregation with Aβ amyloids. We herein demonstrate that S100A9 interacts with neural stem cells (NSCs) and causes NSC differentiation. In the brain of transgenic AD mouse models, we found large quantities of proinflammatory S100A9, which colocalizes with the differentiated NSCs. NSC sphere formation, which is a representative character of NSC stemness, is also substantially inhibited by S100A9. These results suggest that S100A9 is a representative marker for the inflammatory conditions in AD, and it promotes NSC differentiation. Intriguingly, in contrast to the death of both stem and differentiated NSCs caused by high S100A9 doses, S100A9 at a moderate concentration is toxic only to the early differentiated NSCs but not the stem cells. We therefore postulate that, at the early stage of AD, the expression of S100A9 leads to NSC differentiation, which remedies the neuron damage. The application of drugs, which help maintain NSC stemness (e.g., the platelet-derived growth factor, PDGF), may help overcome the acute inflammatory conditions and improve the efficacy of NSC transplantation therapy.

S100B as an Antagonist To Interfere with the Interface Area Flanked by S100A11 and RAGE V Domain

The Ca²⁺-sensing protein S100A11 of the S100 family is an important mediator of numerous biological functions and pathological conditions including cancer. The receptor for advanced glycation end products (RAGE) has been well accepted as the major receptor for several S100 family members. Here, we take the S100B protein as an antagonist to interfere with the interaction flanked by S100A11 and the RAGE V domain. We employed NMR spectroscopy to describe the interactions between the S100A11 and S100B proteins. ¹H-¹⁵N heteronuclear single-quantum correlation-NMR titrations showed the potential binding dynamics of S100A11 and S100B interactions. In the HADDOCK program, we constructed the S100A11-S100B heterodimer complex that was then superimposed with the S100A11-S100B complex structure in the same orientation as the S100A11-RAGE V domain complex. This overlay analysis showed that S100B could interfere in the binding section of S100A11 and the RAGE V domain. Additionally, water-soluble tetrazolium-1 assay provided a functional read-out of the effects of these proteins in an in vitro cancer model. Our study establishes that the development of an S100B antagonist could perform a vital part in the treatment of S100- and RAGE-dependent human diseases.