Prep1 enhances neuronal activity by increasing insulin-like growth factor 1 pro-survival signalling

Background and aims: Several studies show a strong association between alterations of insulin and/or insulin-like growth factor 1 (IGF1) signaling and the onset of neurodegenerative disorders, such as Parkinson disease or Alzheimer disease. Diabetic patients dis- play an increased risk of developing neurological alterations. On the other hand, about 80% of subjects with neurodegenerative dis- eases show impaired glucose tolerance or diabetes mellitus. Indeed, insulin and IGF1 may regulate neuronal metabolism and survival in specific brain areas. Previous studies have identified the transcrip- tional factor Prep1 as a key regulator of insulin signaling. Prep1 hypomorphic mice (Prep1i/+), which express about 55-57% of pro- tein, show a better insulin sensitivity and are protected from streptozotocin-induced diabetes. In addition, Prep1 has an essential role during embryonic development of the hindbrain. Morphological data, reported on web-based atlas, revealed that Prep1 expression is kept also in adult mouse brain and, in partic- ular, in the olfactory bulbs (OBs). OBs represent the central ner- vous system area with the highest density of insulin and IGF1 receptors. Moreover, olfactory impairments have been associated to a wide range of neurological disorders, both in mouse and in human. Thus, in our study we investigated the role of Prep1 in insulin/IGF1 signaling in OBs and the possibility that Prep1 may be involved in neurodegenerative events linked to insulin/IGF1 pathways dysfunction. Materials and methods: OBs of WT and Prep1i/+ mice have been ana- lyzed by cytocrome C oxidase (COX) and Hemalum histological staining. Western blot experiments have been used to measure protein phosphory- lation levels. Growth-curves and Sulphorodamine B assays have been performed on mouse neuroblastoma cell lines (N2A) to assess cell growth and viability. Results: Histological analysis of OBs sections obtained from Prep1i/+ mice revealed a significant (p<0.05) 20% decrease of COX activity and cell density in glomerular and granular cell layers, compared to WT mice. Moreover, Western blot analysis showed 30% reduction of phosphorylation levels of the main kinases involved in cell prolifer- ation and metabolism (Akt/PKB and ERK). Consistently, N2A stably transfected with Prep1 cDNA show a 35% increase of cell growth and viability, with 50% higher phosphorylation levels of ERK and Akt/ PKB kinases, both in basal growth conditions and after IGF1 stimulation. Conclusion: Our data suggest that Prep1 has a role in IGF1-mediated neuro-survival signalling pathway, and give a rationale to further investi- gate Prep1 as possible candidate in neurodegenerative disorders linked to insulin/IGF1-resistance.