Reelin is a glycoprotein that is essential for the correct cytoarchitectonic organization of the developing CNS. Its function in the adult brain is less understood, although it has been proposed that Reelin is involved in signaling pathways linked to neurodegeneration. Here we analyzed Reelin expression in brains and cerebrospinal fluid (CSF) from Alzheimer's disease (AD) patients and nondemented controls. We found a 40% increase in the Reelin protein levels in the cortex of AD patients compared with controls. Similar increases were detected at the Reelin mRNA transcriptional level. This expression correlates with parallel increases in CSF but not in plasma samples. Next, we examined whether CSF Reelin levels were also altered in neurological diseases, including frontotemporal dementia, progressive supranuclear palsy, and Parkinson's disease. The Reelin 180-kDa band increased in all of the neurodegenerative disorders analyzed. Moreover, the 180-kDa Reelin levels correlated positively with Tau protein in CSF. Finally, we studied the pattern of Reelin glycosylation by using several lectins and the anti-HNK-1 antibody. Glycosylation differed in plasma and CSF. Furthermore, the pattern of Reelin lectin binding differed between the CSF of controls and in AD. Our results show that Reelin is up-regulated in the brain and CSF in several neurodegenerative diseases and that CSF and plasma Reelin have distinct cellular origins, thereby supporting that Reelin is involved in the pathogenesis of a number of neurodegenerative diseases.eelin is an extracellular 420-kDa glycoprotein that binds to the transmembrane receptors apolipoprotein receptor 2 and very-low-density lipoprotein receptor (1, 2), which transduce the Reelin signal through the intracellular adapter disabled-1 (3-5). Reelin signaling triggers a disabled-1-dependent signaling cascade involving several kinases, which ultimately controls proper neuronal migration and positioning during CNS development (for review see ref. 6).The complex pattern of Reelin expression is consistent with evidence that this protein has multiple roles in brain development and adult brain function (7-9). In the adult mammalian brain, Reelin has been proposed to influence synaptogenesis and neural plasticity and to favor memory formation (8)(9)(10)(11)(12). Reelin is also expressed in peripheral tissues, including the liver, and is detected in blood (10, 13). However, whether brain and other tissues contribute to the pool of Reelin in blood remains to be elucidated. In this context, we recently reported the presence of detectable levels of Reelin in adult cerebrospinal fluid (CSF) (14).Furthermore, the involvement of the Reelin signaling pathway in neurodegeneration has also been proposed (1,6,9,(15)(16)(17). First, Reelin binds to apolipoprotein E (ApoE) receptors, and some ApoE gene polymorphisms are considered risk factors for Alzheimer's disease (AD). Moreover, the lack of Reelin is associated with increased phosphorylation of Tau (1, 2, 18), whose hyperphosphorylation leads to intracel...

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Reelin is a signaling protein increasingly associated with the pathogenesis of Alzheimer’s disease that relevantly modulates tau phosphorylation. We have previously demonstrated that β-amyloid peptide (Aβ) alters reelin expression. We have now attempted to determine whether abnormal reelin triggered by Aβ will result in signaling malfunction, contributing to the pathogenic process. Here, we show that reelin forms induced by β-amyloid are less capable of down-regulating tau phosphorylation via disabled-1 and GSK3β kinase. We also demonstrate that the scaffold protein 14-3-3 that increases tau phosphorylation by modulating GSK3β activity, is up-regulated during defective reelin signaling. Binding of reelin to its receptor, mainly ApoER2 in the brain, relays the signal into the cell. We associate the impaired reelin signaling with inefficiency of reelin in forming active homodimers and decreased ability to bind efficiently to its receptor, ApoER2. More remarkably, reelin from Alzheimer cortex shows a tendency to form large complexes instead of homodimers, the active form for signaling. Our results suggest that reelin expression is altered by Aβ leading to impaired reelin signaling.