Hameetha B. Rajamohamedsait

Tau pathology induces loss of GABAergic interneurons leading to altered synaptic plasticity and behavioral impairments

BackgroundTau is a microtubule stabilizing protein and is mainly expressed in neurons. Tau aggregation into oligomers and tangles is considered an important pathological event in tauopathies, such as frontotemporal dementia (FTD) and Alzheimer’s disease (AD). Tauopathies are also associated with deficits in synaptic plasticity such as long-term potentiation (LTP), but the specific role of tau in the manifestation of these deficiencies is not well-understood. We examined long lasting forms of synaptic plasticity in JNPL3 (BL6) mice expressing mutant tau that is identified in some inherited FTDs.ResultsWe found that aged (>12 months) JNPL3 (BL6) mice exhibit enhanced hippocampal late-phase (L-LTP), while young JNPL3 (BL6) mice (age 6 months) displayed normal L-LTP. This enhanced L-LTP in aged JNPL3 (BL6) mice was rescued with the GABAAR agonist, zolpidem, suggesting a loss of GABAergic function. Indeed, we found that mutant mice displayed a reduction in hippocampal GABAergic interneurons. Finally, we also found that expression of mutant tau led to severe sensorimotor-gating and hippocampus-dependent memory deficits in the aged JNPL3 (BL6) mice.ConclusionsWe show for the first time that hippocampal GABAergic function is impaired by pathological tau protein, leading to altered synaptic plasticity and severe memory deficits. Increased understanding of the molecular mechanisms underlying the synaptic failure in AD and FTD is critical to identifying targets for therapies to restore cognitive deficiencies associated with tauopathies.

Antibody-Derived In Vivo Imaging of Tau Pathology

Antibodies or their derivatives as imaging probes for pathological tau protein have great potential, but have not been well studied. In particular, smaller, single-chain-variable antibody fragments (scFvs) are attractive for detecting tau lesions in live subjects. Here, we generated libraries of scFvs and identified numerous phospho-tau-selective scFvs. Peripheral injection of one of these scFvs consistently resulted in a strong in vivo brain signal in transgenic tauopathy mice, but not in wild-type or amyloid-β plaque mice. The parent tau antibody provided similar results, albeit with a weaker signal intensity. The imaging signal correlated very well with colocalization of the probe with intraneuronal tau aggregates. Both were associated with markers of endosomes, autophagosomes, and lysosomes, suggesting their interaction in these degradation pathways. Such specific antibody-derived imaging probes have great potential as diagnostic markers for Alzheimers disease and related tauopathies.

Histological Staining of Amyloid and Pre-amyloid Peptides and Proteins in Mouse Tissue

The increased availability of transgenic mouse models for studying human diseases has shifted the focus of many laboratories from in vitro to in vivo assays. Herein, methods are described to allow investigators to obtain well-preserved mouse tissue to be stained with the standard histological dyes for amyloid, Congo Red, and Thioflavin S. These sections can as well be used for immunohistological procedures that allow detection of tissue amyloid and pre-amyloid, such as those composed of the amyloid-β peptide, the tau protein, and the islet amyloid polypeptide.

Affinity of Tau antibodies for solubilized pathological Tau species but not their immunogen or insoluble Tau aggregates predicts in vivo and ex vivo efficacy

BackgroundA few tau immunotherapies are now in clinical trials with several more likely to be initiated in the near future. A priori, it can be anticipated that an antibody which broadly recognizes various pathological tau aggregates with high affinity would have the ideal therapeutic properties. Tau antibodies 4E6 and 6B2, raised against the same epitope region but of varying specificity and affinity, were tested for acutely improving cognition and reducing tau pathology in transgenic tauopathy mice and neuronal cultures.ResultsSurprisingly, we here show that one antibody, 4E6, which has low affinity for most forms of tau acutely improved cognition and reduced soluble phospho-tau, whereas another antibody, 6B2, which has high affinity for various tau species was ineffective. Concurrently, we confirmed and clarified these efficacy differences in an ex vivo model of tauopathy. Alzheimer’s paired helical filaments (PHF) were toxic to the neurons and increased tau levels in remaining neurons. Both toxicity and tau seeding were prevented by 4E6 but not by 6B2. Furthermore, 4E6 reduced PHF spreading between neurons. Interestingly, 4E6’s efficacy relates to its high affinity binding to solubilized PHF, whereas the ineffective 6B2 binds mainly to aggregated PHF. Blocking 4E6s uptake into neurons prevented its protective effects if the antibody was administered after PHF had been internalized. When 4E6 and PHF were administered at the same time, the antibody was protective extracellularly.ConclusionsOverall, these findings indicate that high antibody affinity for solubilized PHF predicts efficacy, and that acute antibody-mediated improvement in cognition relates to clearance of soluble phospho-tau. Importantly, both intra- and extracellular clearance pathways are in play. Together, these results have major implications for understanding the pathogenesis of tauopathies and for development of immunotherapies.

Prophylactic Active Tau Immunization Leads to Sustained Reduction in Both Tau and Amyloid-β Pathologies in 3xTg Mice

Amyloid-β (Aβ) and tau pathologies are intertwined in Alzheimer’s disease, and various immunotherapies targeting these hallmarks are in clinical trials. To determine if tau pathology influences Aβ burden and to assess prophylactic benefits, 3xTg and wild-type mice received tau immunization from 2–6 months of age. The mice developed a high IgG titer that was maintained at 22 months of age. Pronounced tau and Aβ pathologies were primarily detected in the subiculum/CA1 region, which was therefore the focus of analysis. The therapy reduced histopathological tau aggregates by 70–74% overall (68% in males and 78–86% in females), compared to 3xTg controls. Likewise, western blot analysis revealed a 41% clearance of soluble tau (38–76% in males and 48% in females) and 42–47% clearance of insoluble tau (47–58% in males and 49% in females) in the immunized mice. Furthermore, Aβ burden was reduced by 84% overall (61% in males and 97% in females). These benefits were associated with reductions in microgliosis and microhemorrhages. In summary, prophylactic tau immunization not only prevents tau pathology but also Aβ deposition and related pathologies in a sustained manner, indicating that tau pathology can promote Aβ deposition, and that a short immunization regimen can have a long-lasting beneficial effect.

Tau immunotherapy improves axonal transport as detected in vivo by manganese-enhanced magnetic resonance imaging

Background: Immunotherapy targeting hyperphosphorylated tau is a promising prospect to mitigate the neurodegenerative effects of tauopathies. Assessing the effectiveness of such immunotherapies often involves sacrifice of the animal. However, Manganese-Enhanced Magnetic Resonance Imaging (MEMRI) permits the longitudinal study of neuronal function with minimal risk to the animal. We hypothesize that tract-tracing MEMRI in a mouse model of tau pathology should enable non-invasive monitoring of various tau targeting therapies aimed at improving neuronal integrity. Methods: Twenty-five homozygous JNPL3 tangle transgenic mice underwent MEMRI at 6 months of age. Thirteen of the mice received tau immunotherapy with Tau379-408[P-Ser396,404] in alum adjuvant from 3 months of age, and twelve controls received an adjuvant alone. Imaging studies were performed on a 7-T micro-MRI. Mice were imaged pre-injection, then injected in one nostril with a solution of 2.5 M MnCl 2, under isoflurane anesthesia. Image sets were acquired at 1, 4, 8, 12, 24, 36 and 48 hours, and finally at 7 days (Fig 1). The datasets were processed using ImageJ. Normalized measurements for each mouse were plotted and fitted to a tract tracing bolus model using MATLAB. Fitting enabled the estimation of the timing (Pt) and intensity (Pv) of the bolus peak of Mn, and maximal slope of uptake (Sv).Results:A significant increase in maximal slope of manganese uptake, Sv, was observed in the mitral cell layer (35%, P <.005) and glomerular layer (36%, P<0.02) in treated JNPL3mice compared to identical controls. There was also a significant increase in bolus peak value, Pv, in the mitral layer in the treated group (7%, P 1⁄4 0.02). Furthermore, in the immunized mice, there was a strong trend for a decrease in the time to peak value, Pt (-9%P 1⁄4 0.10), in the mitral cell layer, compared to the controls. Conclusions:UtilizingMEMRI’s non-invasive, longitudinal measurements from 1 hour to 7 days, allowed us to detect substantial improvements in neuronal transport following tau immunotherapy. We are analyzing tau pathology in olfactory sections from these mice to assess the correlation of these benefits with clearance of tau lesions, which we have shown previously to occur with this treatment.

In Vivo Imaging of Tauopathy in Mice

Alzheimers disease is characterized by amyloid-β plaques and neurofibrillary tangles composed of tau aggregates. Several β-sheet dyes are already in clinical use to detect amyloid-β plaques by in vivo positron emission tomography (PET), and related dye compounds are being developed for targeting pathological tau aggregates. In contrast to β-sheet binders, antibody-derived ligands should provide greater specificity for detecting tau lesions, and can be tailored to detect various pathological tau epitopes.For preclinical in vivo evaluation of these ligands prior to PET development, we have established an in vivo imaging system (IVIS) protocol to detect tauopathy in live mice. Antibodies and their derivatives are conjugated with a near infrared fluorescent dye and injected intravenously into anesthetized mice, which subsequently are imaged at various intervals to assess their pathological tau burden, and clearance of the ligand from the brain. The in vivo signal obtained through the skull correlates well with the degree of tau pathology in the mice, and the injected ligand can be found intraneuronally within the brain bound to tau aggregates. Control IgG and injections of the tau antibodies/fragments into wild-type mice or mice with amyloid-β plaques lead to minimal or no signal, confirming the specificity of the approach.

Sex and Immunogen-Specific Benefits of Immunotherapy Targeting Islet Amyloid Polypeptide in Transgenic and Wild-Type Mice

Type 2 diabetes mellitus is characterized by the deposition of islet amyloid polypeptide (IAPP) as amyloid in islets, a process thought to be toxic to β-cells. To determine the feasibility of targeting these aggregates therapeutically, we vaccinated transgenic (Tg) mice that overexpress human IAPP and were fed a high-fat diet to promote their diabetic phenotype. Our findings indicate that prophylactic vaccination with IAPP and its derivative IAPP7-19-TT, protects wild-type female mice, but not males, from obesity-induced early mortality, and the derivative showed a strong trend for prolonging the lifespan of Tg females but not males. Furthermore, IAPP7-19-TT-immunized Tg females cleared a glucose bolus more efficiently than controls, while IAPP-immunized Tg females showed an impaired ability to clear a glucose bolus compared to their adjuvant injected Tg controls. Interestingly, IAPP or IAPP7-19-TT treatments had no effect on glucose clearance in Tg males. Overall, these beneficial effects of IAPP targeted immunization depend on Tg status, sex, and immunogen. Hence, future studies in this field should carefully consider these variables that clearly affect the therapeutic outcome. In conclusion, IAPP targeting immunotherapy may have benefits in patients with type 2 diabetes.

The postsynaptic density protein, PSD-95, coexists with neuropathological changes in 5XFAD and P301L transgenic mice

Background: Impairment of synaptic plasticity is believed to underlie memory dysfunction in Alzheimer’s and other dementing illnesses. Molecules involved in synaptic plasticity may, therefore, play important roles in pathogenesis and offer clues for treatment. PSD-95 is the major scaffold protein that controls NMDA and AMPA receptors at excitatory synapses and is essential for long term potentiation (LTP) and long term depression (LTD). Surprisingly, the role of PSD-95 in neurodegenerative diseases has not been extensively investigated. Methods: We examined brain tissue from two transgenic mouse models: 5XFAD for amyloidopathy and JNPL3 P301L for tauopathy using double-labeling immunofluorescence and confocal microscopy. Results: In 5XFAD mice, PSD-95 colocalized with amyloid-b (Ab), primarily within the center of plaque cores. A similar staining was noted for MAP-2, another dendritic protein. In addition, PSD-95 immunopositivity increased in neuronal soma adjacent to Ab plaques. In JNPL3 mice, both PSD-95 and tau accumulated in neuronal cell bodies, especially in hippocampal pyramidal neurons. Interestingly, PSD-95 and tau were located in disparate neurons in close proximity to one another. MAP-2, on the other hand, did not colocalize with either PSD-95 or tau in this model. In wild-type animals, PSD-95 had a typical synaptic pattern without any build-up within soma. Conclusions: Accumulation of PSD-95 in plaques and neuronal cell bodies in 5XFAD mice may represent an Ab-induced degenerative change. Similarly, build-up of PSD-95 in subsets of neurons in JNPL3 mice may be indicative of tauopathy-related toxicity. Taken together, the abnormal redistribution of PSD-95 to neuronal soma may lead to synaptic dysfunction at dendritic spines and thus could impede memory function in both amyloidopathy and tauopathy.