MMP9 and fragile X syndrome: Moreover, metformin treatment also rescues dendritic overgrowth, elevated matrix metalloproteinase 9 (MMP-9) secretion levels, upregulated extracellular-signal-regulated kinase (ERK) signaling, and hyperphosphorylated eukaryotic translation initiation factor 4E (eIF4E) in adult FXS male mice.