Harnessing the chondroitin sulfate-binding characteristics of human lactoferrin to neutralize neurite outgrowth inhibition

Human lactoferrin (hLF) is a glycosaminoglycan (GAG)-binding protein involved in various biological functions. It consists of two globular functional domains, referred to as the N- and C-lobes. Both heparin (HP) and heparan sulfate (HS) bind to the N-lobe domain of hLF. Although some biological functions of hLF such as neuroprotective effects and cancer growth inhibition are regulated by its binding to HS, the binding characteristics of hLF with other GAG subtypes, and their effects on biological activities are still poorly understood. Here, we report that hLF binds to chondroitin sulfate (CS)-E, a GAG subtype involved in various neurodegenerative diseases. The α-helical content of hLF, which is an indicator of changes in the secondary structure of hLF, increased in the presence of CS-C, CS-D, or CS-E, but not in the presence of HP, HS, CS-A, or CS-B. This structural change was also observed in the N-lobe, the N-terminal half region of the hLF. Additionally, the thermal stability of the N-lobe showed a dose-dependent improvement in the presence of CS-E, but not in the presence of HP. This indicates that the binding mode of hLF/N-lobe to CS-E may differ from that of HP. hLF was also found to neutralize CS-E-induced inhibition of neurite outgrowth and neuronal growth cone collapse, which are neurodegenerative responses to spinal cord injury, in cultured dorsal root ganglion neurons. Thus, hLF is a promising drug candidate for the treatment of CS-E-induced neurodegenerative diseases such as spinal cord injury.