Dysregulation of tau phosphorylation is a hypothesized point of convergence in the pathogenesis of Alzheimer's disease, frontotemporal dementia and schizophrenia with therapeutic implications

Two members of the family of low-density lipoprotein receptors (i.e., very low-density lipoprotein [VLDL] receptor and apolipoprotein E [apoE] type 2 receptor) are expressed in brain, where, they bind and transduce reelin, a secreted glycoprotein that shares structural analogies with extracellular matrix proteins. In the developing fetal brain, reelin-signal transduction is critical for the correct positioning of neurons and the formation of appropriate synaptic connections, whereas in the mature brain, reelin participates in the mediation of experience-dependent synaptic plasticity. An important "downstream" consequence of the reelin-signal transduction cascade is inhibition of the phosphorylation of tau, a protein that regulates microtubule assembly and stability. Importantly, hyperphospborylated tau comprises the paired helical filament, whose pathological deposition as neurofibrillary tangles is implicated in Alzheimer's disease; hyperphosphorylated tau is also implicated in the pathogenesis of other neurodegenerative disorders. Isoforms of apoE may affect the binding of reelin to its cell surface receptors and, thereby, influence tau phosphorylation, whereas insulin, insulin-like growth factor-1, and the lithium ion have actions within the cell at the level of the specific tyrosine kinases involved in the phosphorylation of tau. These data support the exploration of pharmacotherapeutic interventions designed to prevent or reduce the burden of hyperphosphorylated tau. Impaired reelin-signal transduction due to an actual deficiency of reelin expression may occur in at least some patients with psychotic disorders, especially schizophrenia; conceivably, hyperphosphorylation of tau would result from deficient transduction of reelin in schizophrenia. Schizophrenia has been conceptualized as a neurodevelopmental disorder of impaired synaptic "connectivity", whose consequence does not become fully apparent until late adolescence or early adulthood. In summary, hyperphosphorylation of tau may be an underlying point of pathological convergence for several neuropsychiatric disorders, and prevention of tau hyperphosphorylation may be an important therapeutic target. Published by Elsevier Inc.