The insulin receptor (IR) is a tyrosine kinase receptor present in cell membranes. It is highly expressed in hepatocytes (where it promotes glycogenesis and inhibits gluconeogenesis) , and skeletal muscle and fat (where it facilitates glucose uptake by translocation of the glucose transporter GLUT4) . IR expression is also found throughout the brain, both in neurons and all glial cell types, and for decades impaired insulin signaling has been implicated in the onset and development of Alzheimer’s disease. IR expression pattern in the brain parenchyma is heterogeneous, with highest levels of expression found in olfactory bulb, hypothalamus, and hippocampus. However, the choroid plexus (CP) , a structure present in all 4 ventricles of the brain and responsible for the secretion of cerebrospinal fluid, has the highest affinity for insulin binding compared to any other brain region. This work aims to characterize the insulin signaling in the epithelial cells of the choroid plexus (EChP) and its possible implications in diseases of the brain. Relative expression levels of specific splicing variants of the Insr gene in dissected CP of adult mice were evaluated by qPCR and revealed predominant expression of the variant coding for isoform IR-A when compared to isoform IR-B. In vitro stimulation of EChP with insulin elicits a classical tyrosine kinase cascade, with activation of both the mitogenic (ERK) and metabolic (Akt) arms of the insulin signaling pathway, in a time-and concentration-dependent manner. Using pharmacological (S961, an insulin receptor antagonist) and genetic (insulin receptor shRNA, and Insr cre-loxP) approaches, we show that downregulation of IR in these cells not only impairs insulin signaling, but it also decreases IGF2’s ability to activate ERK and Akt, even when IGF1R levels are unaltered. Finally, using a viral vector coding for an IR shRNA, we show that downregulation of Insr expression in CP of adult mice has a profound effect on its structure, as demonstrated by MRI and histological technique.
C.Mazucanti: None. V.L.Kennedy: None. A.Cho: None. Q.Liu: None. J.F.O’connell: None. S.Camandola: None. J.M.Egan: None.