Soluble lymphocyte activation gene-3 contributes to α-synucleinopathy and related therapeutic development

Pathogenetic α-synuclein (α-Syn) misfolded preformed fibrils (PFF) in Parkinson’s disease (PD) spreads from cell-to-cell in a prion-like manner has been evident in many studies. However, the spreading mechanism remains unclear. We have determined that α-Syn PFF but not α-Syn monomer, can specifically bind with transmembrane Lag3 (lymphocyte-activation gene 3), and the binding domain is the extracellular domain 1 (D1). Depletion of Lag3 can significantly inhibit pathogenic α-Syn cell-to-cell transmission. Membrane-bound Lag3 can be cleaved and soluble Lag3 (sLag3) can shed from the Lag3-expressing cell. Abundant sLag3 can be found in the plasma, however, the role of sLag3 in mediating α-synucleinopathy is completely unknown. Here, we used sLag3 lacking mice (membrane-bound Lag3 still exists) can reduce α-Syn pathology spreading from the gut to the brain, following by the discovery of facilitation of α-Syn PFF uptake in primary neuron by sLag3, which indicates the promoting role of sLag3 in the pathogenic α-Syn spreading. Moreover, we investigated the interaction of sLag3 to the immune system, in which we found both in vivo and in vitro that sLag3 facilitates the immune response. To explore the underlying molecular mechanism, we have identified several sLag3 binding receptors, which needs further validation. Insighted by the specific interaction between Lag3-D1 and α-Syn PFF, we further apply proteolysis targeting chimeric (PROTAC) technology to link a E3 ligase with the extracellular domain 1 (D1) of Lag3. The new agent, D1-E3 can significantly reduce α-Syn pathology induced by α-Syn PFF. In these studies, we determine that depletion of sLag3 can inhibit α-Syn gut-to-brain spreading and explored the underlying mechanism. By using the specific interaction with prion-like α-Syn, we show the efficacy of D1-E3 in clearance of α-Syn pathology, which provide new agents for therapeutic development against PD and related α-synucleinopathies