SYP and Alzheimer disease: Synaptic impairment and attrition are key characteristics of AD, closely linked with the deterioration of cognitive function.[43, 44] Therapeutic strategies aimed at the rehabilitation of synaptic health and stability hold significant promise for influencing and regulating the activity of neural circuits.[45, 46] Consequently, both mRNA and protein levels of postsynaptic density protein 95 (PSD95, encoded by Dlg4) and synaptophysin (SYP) were elevated after PQQ administration in AD mice (Figure 5b,c).