Characterisation of the microtubule-interacting protein, tau, in pancreatic beta cells

Abstract

Background: Alterations in the microtubule associated protein Tau are associated with neurodegenerative disorders, such as Alzheimer’s Disease (AD). Neuronal Tau can be hyperphosphorylated (pTau) to yield aggregates of poorly-soluble paired helical filaments (PHFs) which have been associated with disease pathology. Tau expression has also been reported outside the brain, and alterations in Tau have been implicated in Type 2 diabetes. This study explores the expression of Tau in the pancreas, with a focus on β cells. Aim: The aim of this project was to characterise the expression and phosphorylation signature of Tau and explore the expression of relevant Tau modifiers in human islets. Methods: A panel of 35 anti-Tau antibodies were validated by Western blot (WB) and immunohistochemistry (IHC). Antibodies that met the validation criteria were used to stain human pancreas sections from the EADB and nPOD collections. Signal intensity quantification analysis and statistical analyses were performed. Results: This study presents the validation of antibodies against Tau, generating a toolbox of reagents for the careful evaluation of Tau protein expression in formalin-fixed paraffin-embedded tissue. It further demonstrates that Tau is present in the pancreatic β cells and that Tau is phosphorylated at several residues in human β cells, including some that are considered pathological in human brain. Interestingly, some pTau forms are present in the nuclei of β cells in young donors, but pTau forms increase in the cytoplasm with age. Preliminary work suggests that the expression of a selection of Tau modifiers found in β cells may be altered with age and disease states. Conclusion: Pancreatic Tau has a differential phosphorylation signature compared to neuronal Tau highlighting that its regulation is cell-dependent. Distinct Tau forms are localised in different subcellular compartments in β cells and this could be related to distinct physiological roles of Tau. Furthermore, the translocation of some pTau forms with age suggests that Tau may be dysregulated with age, potentially influencing insulin secretion. Significance: This study introduces a visualisation system that provides crucial information about the specificity and efficacy of widely used antibodies and is the first study to suggest the expression of at least two Tau forms in the human pancreas.