GCG and Parkinson disease: To date, numerous ageing-regulating pathways, including the IIS, glucagon-like peptide-1 (GLP-1), AMPK, sirtuin, mTOR and NAD+ pathways, have been identified.126,396,397 The expression of the transcription factor C/EBPβ has been found to increase with age, resulting in the activation of AEP (also known as δ-secretase) transcription and ultimately leading to excitatory neurotoxicity and a shortened lifespan.398 This pathway has also been implicated in AD and PD.399,400