A synthetic NCAM-derived mimetic peptide, FGL, exerts anti-inflammatory properties via IGF-1 and interferon-γ modulation

Microglial cell activity increases in the rat hippocampus during normal brain aging. The neural cell adhesion molecule (NCAM)-derived mimetic peptide, FG loop (FGL), acts as an anti-inflammatory agent in the hippocampus of the aged rat, promoting CD200 ligand expression while attenuating glial cell activation and subsequent pro-inflammatory cytokine production. The aim of the current study was to determine if FGL corrects the age-related imbalance in hippocampal levels of insulin-like growth factor-1 (IGF-1) and pro-inflammatory interferon-gamma (IFN gamma), and subsequently attenuates the glial reactivity associated with aging. Administration of FGL reversed the age-related decline in IGF-1 in hippocampus, while abrogating the age-related increase in IFN gamma. FGL robustly promotes IGF-1 release from primary neurons and IGF-1 is pivotal in FGL induction of neuronal Akt phosphorylation and subsequent CD200 ligand expression in vitro. In addition, FGL abrogates both age- and IFN gamma-induced increases in markers of glial cell activation, including major histocompatibility complex class II (MHCII) and CD40. Finally, the proclivity of FGL to attenuate IFN gamma-induced glial cell activation in vitro is IGF-1-dependent. Overall, these findings suggest that FGL, by correcting the age-related imbalance in hippocampal levels of IGF-1 and IFN gamma, attenuates glial cell activation associated with aging. These findings also highlight a novel mechanism by which FGL can impact on neuronal CD200 ligand expression and subsequently on glial cell activation status.