Alzheimer's disease brain-derived extracellular vesicles reveal altered synapse-related proteome and induce cognitive impairment in mice.

INTRODUCTION: Extracellular vesicles (EVs) have been implicated in the spread of neuropathology in Alzheimer's disease (AD), but their involvement in behavioral outcomes linked to AD remains to be determined. METHODS: EVs isolated from post mortem brain tissue from control, AD, or frontotemporal dementia (FTD) donors, as well as from APP/PS1 mice, were injected into the hippocampi of wild-type (WT) or a humanized Tau mouse model (hTau/mTauKO). Memory tests were carried out. Differentially expressed proteins in EVs were assessed by proteomics. RESULTS: Both AD-EVs and APP/PS1-EVs trigger memory impairment in WT mice. We further demonstrate that AD-EVs and FTD-EVs carry Tau protein, present altered protein composition associated with synapse regulation and transmission, and trigger memory impairment in hTau/mTauKO mice. DISCUSSION: Results demonstrate that AD-EVs and FTD-EVs have negative impacts on memory in mice and suggest that, in addition to spreading pathology, EVs may contribute to memory impairment in AD and FTD. HIGHLIGHTS: Aß was detected in EVs from post mortem AD brain tissue and APP/PS1 mice. Tau was enriched in EVs from post mortem AD, PSP and FTD brain tissue. AD-derived EVs and APP/PS1-EVs induce cognitive impairment in wild-type (WT) mice. AD- and FTD-derived EVs induce cognitive impairment in humanized Tau mice. Proteomics findings associate EVs with synapse dysregulation in tauopathies.

α-Synuclein Regulates Peripheral Insulin Secretion and Glucose Transport.

AIM: Population based studies indicate a positive association between type 2 diabetes (T2D) and Parkinson's disease (PD) where there is an increased risk of developing PD in patients with T2D. PD is characterized by the abnormal accumulation of intraneuronal aggregated α-synuclein (α-syn) in Lewy bodies, which negatively impact neuronal viability. α-syn is also expressed in both pancreatic islets and skeletal muscle, key players in glucose regulation. Therefore, we examined the functional role of α-syn in these tissues. METHODS: Using mice lacking, overexpressing or transiently injected with α-syn, effects on glucose and insulin tolerance and insulin secretion were determined, with further characterization of the effects on GLUT4 translocation using GLUT4myc myotubes. RESULTS: Mice genetically ablated for α-syn became glucose intolerant and insulin resistant with hyperinsulinemia and reduced glucose-stimulated insulin secretion (GSIS). Mice overexpressing human α-syn are more insulin senstive and glucose tolerant compared to controls with increased GSIS. Injection of purified α-syn monomers also led to improved glucose tolerance and insulin sensitivity with hightened GSIS. α-syn monomer treatments increased surface GLUT4 levels in myotubes but without any significant change in Akt phosphorylation. The increase in cell surface GLUT4 was largely due to a large reduction in GLUT4 endocytosis, however, with a compensatory reduction in GLUT4 exocytosis. CONCLUSION: Cumulatively, this data suggests that α-syn modulates both pancreatic beta cell function and glucose transport in peripheral tissues, thereby playing a pivitol role in the maintenance of normal glucose homeostasis.

Combination of human tau and islet amyloid polypeptide exacerbates metabolic dysfunction in transgenic mice.

Amyloid plaques and neurofibrillary tangles composed of hyperphosphorylated tau are important contributors to Alzheimer's disease (AD). Tau also impacts pancreatic beta cell function and glucose homeostasis. Amyloid deposits composed of islet amyloid polypeptide (IAPP) are a pathological feature of type 2 diabetes (T2D). The current study investigates the role of human tau (hTau) in combination with human IAPP (hIAPP) as a potential mechanism connecting AD and T2D. Transgenic mice expressing hTau and hIAPP in the absence of murine tau were generated to determine the impact of these pathological factors on glucose metabolism. Co-expression of hIAPP and hTau resulted in mice with increased hyperglycaemia, insulin resistance, and glucose intolerance. The hTau-hIAPP mice also exhibited reduced beta cell area, increased amyloid deposition, impaired insulin processing, and reduced insulin content in islets. Tau phosphorylation also increased after stimulation with high glucose. In addition, brain insulin content and signalling were reduced, and tau phosphorylation was increased in these animals. These data support a link between tau and IAPP amyloid, which seems to act co-ordinately to impair beta cell function and glucose homeostasis, and suggest that the combined pathological actions of these proteins may be a potential mechanism connecting AD and T2D. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Longitudinal evaluation of Tau-P301L transgenic mice reveals no cognitive impairments at 17 months of age.

Introduction: Tau is a microtubule-associated binding protein implicated in neurodegenerative tauopathies, including frontotemporal dementia (FTD) and Alzheimer's disease (AD). These diseases result in the intracellular accumulation of hyperphosphorylated tau in the form of neurofibrillary tangles, the presence of which is associated with cognitive deficits. Methods: We conducted a longitudinal behavioral study to provide a profile of the TgTau(P301L)23027 transgenic mouse in multiple cognitive domains across multiple ages. P301L is the tau mutation most frequently observed in patients with frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) and this mouse model recapitulates the progressive development of glial and neurofibrillary tangles, and associated cerebral atrophy observed in patients. We examined frontal cortex-dependent executive function and attention with the touchscreen 5-choice serial reaction time test (5-CSRTT) and assessed the function of temporal cortical structures using novel object recognition (OR). Results: Despite using sensitive tasks, there were no apparent changes in executive function, attention, or recognition memory in the transgenic mice from 5 to 17 months of age. Conclusions: This study represents the first comprehensive longitudinal analysis of cognition in the TgTauP301L mouse model and suggests that this model is not ideal for studying early attention and recognition memory impairments associated with tauopathy. However, spatial and object recognition memory impairments were observed during follow-up assessments when the mice were 18 and 21 months, respectively. These impairments are consistent with previous publications, and with a dementia-like phenotype in these mice when aged.

Tau ablation in mice leads to pancreatic ß cell dysfunction and glucose intolerance.

The microtubule-associated protein tau is highly expressed in pancreatic islets. Abnormally phosphorylated tau aggregates assemble into neurofibrillary tangles linked to Alzheimer's disease pathology and has also been found in islets of patients with type 2 diabetes. However, the significance of tau in islet function remains relatively unexplored. Therefore, we investigated the role of tau on ß cell function and glucose homeostasis using tau knockout (tauKO) mice. TauKO mice were hyperglycemic and glucose intolerant at an early age. Islet insulin content was reduced and proinsulin levels were significantly elevated in tauKO mice, resulting in impaired glucose-stimulated insulin secretion. Loss of tau also resulted in increased epididymal fat mass and leptin levels, reduced glucose production, and insulin resistance at later ages, leading to complete onset of diabetes. Transgenic expression of human tau in islets was unable to rescue those defects in glucose regulation, indicating structural and/or functional differences between mouse and human tau. Cumulatively, these results suggest an important role for tau in the proper maintenance of pancreatic ß cell function and glucose homeostasis.-Wijesekara, N., Gonçalves, R. A., Ahrens, R., De Felice, F. G., Fraser, P. E. Tau ablation in mice leads to pancreatic ß cell dysfunction and glucose intolerance.

Amyloid-ß and islet amyloid pathologies link Alzheimer's disease and type 2 diabetes in a transgenic model.

Alzheimer's disease (AD) and type 2 diabetes (T2D) present a significant risk to each other. AD and T2D are characterized by deposition of cerebral amyloid-ß (Aß) and pancreatic human islet amyloid polypeptide (hIAPP), respectively. We investigated the role of amyloidogenic proteins in the interplay between these diseases. A novel double transgenic mouse model combining T2D and AD was generated and characterized. AD-related amyloid transgenic mice coexpressing hIAPP displayed peripheral insulin resistance, hyperglycemia, and glucose intolerance. Aß and IAPP amyloid co-deposition increased tau phosphorylation, and a reduction in pancreatic ß-cell mass was detected in islets. Increased brain Aß deposition and tau phosphorylation and reduced insulin levels and signaling were accompanied by extensive synaptic loss and decreased neuronal counts. Aß immunization rescued the peripheral insulin resistance and hyperglycemia, suggesting a role for Aß in T2D pathogenesis for individuals predisposed to AD. These findings demonstrate that Aß and IAPP are key factors in the overlapping pathologies of AD and T2D.-Wijesekara, N., Ahrens, R., Sabale, M., Wu, L., Ha, K., Verdile, G., Fraser, P. E. Amyloid-ß and islet amyloid pathologies link Alzheimer's disease and type 2 diabetes in a transgenic model.

1α,25-Dihydroxyvitamin D3 reduces cerebral amyloid-ß accumulation and improves cognition in mouse models of Alzheimer's disease.

We demonstrate a role of the vitamin D receptor (VDR) in reducing cerebral soluble and insoluble amyloid-ß (Aß) peptides. Short-term treatment of two human amyloid precursor protein-expressing models, Tg2576 and TgCRND8 mice, with 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], the endogenous active ligand of VDR, resulted in higher brain P-glycoprotein (P-gp) and lower soluble Aß levels, effects negated with coadministration of elacridar, a P-gp inhibitor. Long-term treatment of TgCRND8 mice with 1,25(OH)2D3 during the period of plaque formation reduced soluble and insoluble plaque-associated Aß, particularly in the hippocampus in which the VDR is abundant and P-gp induction is greatest after 1,25(OH)2D3 treatment, and this led to improved conditioned fear memory. In mice fed a vitamin D-deficient diet, lower cerebral P-gp expression was observed, but levels were restored on replenishment with VDR ligands. The composite data suggest that the VDR is an important therapeutic target in the prevention and treatment of Alzheimer's disease.

The adult mouse and human pancreas contain rare multipotent stem cells that express insulin.

The search for putative precursor cells within the pancreas has been the focus of extensive research. Previously, we identified rare pancreas-derived multipotent precursor (PMP) cells in the mouse with the intriguing capacity to generate progeny in the pancreatic and neural lineages. Here, we establish the embryonic pancreas as the developmental source of PMPs through lineage-labeling experiments. We also show that PMPs express insulin and can contribute to multiple pancreatic and neural cell types in vivo. In addition, we have isolated PMPs from adult human islet tissue that are also capable of extensive proliferation, self-renewal, and generation of multiple differentiated pancreatic and neural cell types. Finally, both mouse and human PMP-derived cells ameliorated diabetes in transplanted mice. These findings demonstrate that the adult mammalian pancreas contains a population of insulin(+) multipotent stem cells and suggest that these cells may provide a promising line of investigation toward potential therapeutic benefit.

Genetic mapping of activity determinants within cellular prion proteins: N-terminal modules in PrPC offset pro-apoptotic activity of the Doppel helix B/B' region.

The PrP-like Doppel (Dpl) protein causes apoptotic death of cerebellar neurons in transgenic mice, a process prevented by expression of the wild type (wt) cellular prion protein, PrP(C). Internally deleted forms of PrP(C) resembling Dpl such as PrPDelta32-121 produce a similar PrP(C)-sensitive pro-apoptotic phenotype in transgenic mice. Here we demonstrate that these phenotypic attributes of wt Dpl, wt PrP(C), and PrPDelta132-121 can be accurately recapitulated by transfected mouse cerebellar granule cell cultures. This system was then explored by mutagenesis of the co-expressed prion proteins to reveal functional determinants. By this means, neuroprotective activity of wt PrP(C) was shown to be nullified by a deletion of the N-terminal charged region implicated in endocytosis and retrograde axonal transport (PrPDelta23-28), by deletion of all five octarepeats (PrPDelta51-90), or by glycine replacement of four octarepeat histidine residues required for selective binding of copper ions (Prnp"H/G"). In the case of Dpl, overlapping deletions defined a requirement for the gene interval encoding helices B and B' (DplDelta101-125). These data suggest contributions of copper binding and neuronal trafficking to wt PrP(C) function in vivo and place constraints upon current hypotheses to explain Dpl/PrP(C) antagonism by competitive ligand binding. Further implementation of this assay should provide a fuller understanding of the attributes and subcellular localizations required for activity of these enigmatic proteins.