Polymeric alkylpyridinium salts permit intracellular delivery of human Tau in rat hippocampal neurons: requirement of Tau phosphorylation for functional deficits

Abstract

Patients suffering from tauopathies including frontotemporal dementia (FTD) and Alzheimer's disease (AD) present with intra-neuronal aggregation of microtubule-associated protein Tau. During the disease process, Tau undergoes excessive phosphorylation, dissociates from microtubules and aggregates into insoluble neurofibrillary tangles (NFTs), accumulating in the soma. While many aspects of the disease pathology have been replicated in transgenic mouse models, a region-specific non-transgenic expression model is missing. Complementing existing models, we here report a novel region-specific approach to modelling Tau pathology. Local co-administration of the pore-former polymeric 1,3-alkylpyridinium salts (Poly-APS) extracted from marine sponges, and synthetic full-length 4R recombinant human Tau (hTau) was performed in vitro and in vivo. At low doses, Poly-APS was non-toxic and cultured cells exposed to Poly-APS (0.5 µg/ml) and hTau (1 µg/ml; ~22 µM) had normal input resistance, resting-state membrane potentials and Ca(2+) transients induced either by glutamate or KCl, as did cells exposed to a low concentration of the phosphatase inhibitor Okadaic acid (OA; 1 nM, 24 h). Combined hTau loading and phosphatase inhibition resulted in a collapse of the membrane potential, suppressed excitation and diminished glutamate and KCl-stimulated Ca(2+) transients. Stereotaxic infusions of Poly-APS (0.005 µg/ml) and hTau (1 µg/ml) bilaterally into the dorsal hippocampus at multiple sites resulted in hTau loading of neurons in rats. A separate cohort received an additional 7-day minipump infusion of OA (1.2 nM) intrahippocampally. When tested 2 weeks after surgery, rats treated with Poly-APS+hTau+OA presented with subtle learning deficits, but were also impaired in cognitive flexibility and recall. Hippocampal plasticity recorded from slices ex vivo was diminished in Poly-APS+hTau+OA subjects, but not in other treatment groups. Histological sections confirmed the intracellular accumulation of hTau in CA1 pyramidal cells and along their processes; phosphorylated Tau was present only within somata. This study demonstrates that cognitive, physiological and pathological symptoms reminiscent of tauopathies can be induced following non-mutant hTau delivery into CA1 in rats, but functional consequences hinge on increased Tau phosphorylation. Collectively, these data validate a novel model of locally infused recombinant hTau protein as an inducer of Tau pathology in the hippocampus of normal rats; future studies will provide insights into the pathological spread and maturation of Tau pathology.

Soluble pre-fibrillar tau and β-amyloid species emerge in early human Alzheimer’s disease and track disease progression and cognitive decline

“…Overall, our data lend direct support to the patho-physiological relevance of non-filamentous, oligomeric tau. Nevertheless, strong correlations with cognitive decline were also observed for conformational and phospho-tau as previously reported in humans [25, 30] and animal models [43, 44, 83]. Our data expand on the suggested disruptive role of monomeric phospho-tau [41], and suggest oligomerization caused by pathological modification of monomeric tau to play a key role.…”

Functional Alterations in the Olfactory Neuronal Circuit Occur before Hippocampal Plasticity Deficits in the P301S Mouse Model of Tauopathy: Implications for Early Diagnosis and Translational Research in Alzheimer’s Disease

“…To our knowledge, this is the first study that describes the age-dependent disturbance in olfactory network oscillations in this mouse model of tauopathy. Tau deposition may occur gradually and may be dissociated from functional and behavioral alterations, while it may be correlated with the appearance of soluble phosphorylated tau as it was found in other transgenic tau models [40][41][42][43]. Thus, the disruption of neuronal function could be related to soluble tau species but not neurofibrillary aggregates.…”

Molecular Factors Mediating Neural Cell Plasticity Changes in Dementia Brain Diseases

“…Pore-forming polymeric 1,3-alkylpyridinium salts (Poly-APS) may be effective in tauopathies such as AD and FTD [162]. Another drug used in cholinergic degeneration of cortical neurons and synaptic plasticity decline, ladostigil (TV-3326 (N-propargyl-3R-aminoindan-5-yl) methylmethylcarbamate), appears to be effective in AD and DLB.…”