GPI anchoring and MMP-mediated shedding of the endogenous Nogo receptor antagonist LOTUS (CRTAC1B)

Nogo receptor-1 (NgR1) is a common receptor for Nogo and other axonal growth inhibitors that suppress neural regeneration following central nervous system injury and contribute to axonal degeneration in neurological disorders. We previously identified lateral olfactory tract usher substance (LOTUS) as an endogenous NgR1 antagonist that promotes neuronal regeneration and showed that reduced LOTUS levels in human cerebrospinal fluid are associated with axonal degeneration. However, the molecular basis of its potent antagonistic activity and its regulatory dynamics remain unclear. Here, we investigated the molecular characteristics and dynamics of LOTUS using mass spectrometry and molecular biological approaches. We found that extracellular phosphatidylinositol-specific phospholipase C cleaved LOTUS and generated ethanolamine-linked LOTUS-specific peptides, demonstrating that LOTUS is a glycosylphosphatidylinositol (GPI)-anchored protein, similar to NgR1. This structural similarity suggests that LOTUS localizes to the cell surface, where it can effectively antagonize NgR1 signaling. Furthermore LOTUS was released into the extracellular space through cleavage by matrix metalloproteinase (MMP)-3 and MMP-9. These findings reveal distinct modes of NgR1 inhibition mediated by membrane-bound GPI-anchored and soluble forms of LOTUS and support LOTUS as a potential therapeutic target and biomarker for neurodegenerative disorders.