S14G-humanin improves cognitive deficits and reduces amyloid pathology in the middle-aged APPswe/PS1dE9 mice

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by clinical cognitive decline and pathological deposition of amyloid-beta protein (Aβ) in the brain. So far, there has been no causative therapy for this devastating disease. S14G-Humanin (HNG), a synthetic derivative of Humanin (HN), has been shown to have strong neuroprotective ability against AD-related insults in vitro and prevent cognitive impairments in Aβ-infused animal models. In addition, a recent study has reported a beneficial effect of intranasal HNG treatment on memory deficit and Aβ accumulation in triple transgenic (3xTg-AD) mice at the early plaque-bearing stage. However, whether HNG treatment has the disease-modifying efficacy on AD with pre-existing well-established amyloid plaque pathology remains unclear. In this study, we employed 9-month-old APPswe/PS1dE9 mice with pre-existing robust amyloid plaque pathology to investigate the effects of chronic HNG treatment on the progression of cognitive dysfunction and Aβ-associated neuropathology. We found that vehicle-treated APPswe/PS1dE9 mice showed impaired spatial learning and memory compared with vehicle- and HNG-treated wild-type mice, while intraperitoneal HNG treatment for 3 months significantly improved spatial learning and memory deficits in APPswe/PS1dE9 mice compared with vehicle control treatment. Coincidental with this, HNG treatment significantly reduced cerebral Aβ plaque deposition, insoluble Aβ levels, and neuroinflammatory responses in APPswe/PS1dE9 mice compared with control treatment. Cumulatively, these findings demonstrate that chronic administration of HNG is able to attenuate cognitive deficits and reduce Aβ loads as well as neuroinflammation in the middle-aged APPswe/PS1dE9 mice even with pre-existing substantial Aβ neuropathology, indicating that HNG has potential as a pharmacotherapeutic intervention in the development of cognitive deficits and neuropathology seen in the cases of established AD.