The PPAR-gamma agonist pioglitazone protects cortical neurons from inflammatory mediators via improvement in peroxisomal function

<p>Abstract</p> <p>Background</p> <p>Inflammation is known to play a pivotal role in mediating neuronal damage and axonal injury in a variety of neurodegenerative disorders. Among the range of inflammatory mediators, nitric oxide and hydrogen peroxide are potent neurotoxic agents. Recent evidence has suggested that oligodendrocyte peroxisomes may play an important role in protecting neurons from inflammatory damage.</p> <p>Methods</p> <p>To assess the influence of peroxisomal activation on nitric oxide mediated neurotoxicity, we investigated the effects of the peroxisomal proliferator activated receptor (PPAR) gamma agonist, pioglitazone in primary cortical neurons that were either exposed to a nitric oxide donor or co-cultured with activated microglia.</p> <p>Results</p> <p>Pioglitazone protected neurons and axons against both nitric-oxide donor-induced and microglia-derived nitric oxide-induced toxicity. Moreover, cortical neurons treated with this compound showed a significant increase in the protein and gene expression of PPAR-gamma, which was associated with a concomitant increase in the enzymatic activity of catalase. In addition, the protection of neurons and axons against hydrogen peroxide-induced toxicity afforded by pioglitazone appeared to be dependent on catalase.</p> <p>Conclusions</p> <p>Collectively, these observations provide evidence that modulation of PPAR-gamma activity and peroxisomal function by pioglitazone attenuates both NO and hydrogen peroxide-mediated neuronal and axonal damage suggesting a new therapeutic approach to protect against neurodegenerative changes associated with neuroinflammation.</p

S-[F-18] THK-5117-PET and [C-11] PIB-PET Imaging in Idiopathic Normal Pressure Hydrocephalus in Relation to Confirmed Amyloid-beta Plaques and Tau in Brain Biopsies

BACKGROUND: Detection of pathological tau aggregates could facilitate clinical diagnosis of Alzheimer’s disease (AD) and monitor drug effects in clinical trials. S-[18F]THK-5117 could be a potential tracer to detect pathological tau deposits in brain. However, no previous study have correlated S-[18F]THK-5117 uptake in PET with brain biopsy verified tau pathology in vivo. OBJECTIVE: Here we aim to evaluate the association between cerebrospinal fluid (CSF) AD biomarkers, S-[18F]THK-5117, and [11C]PIB PET against tau and amyloid lesions in brain biopsy. METHODS: Fourteen patients with idiopathic normal pressure hydrocephalus (iNPH) with previous shunt surgery including right frontal cortical brain biopsy and CSF Aβ1 - 42, total tau, and P-tau181 measures, underwent brain MRI, [11C]PIB PET, and S-[18F]THK-5117 PET imaging. RESULTS: Seven patients had amyloid-β (Aβ, 4G8) plaques, two both Aβ and phosphorylated tau (Pτ, AT8) and one only Pτ in biopsy. As expected, increased brain biopsy Aβ was well associated with higher [11C]PIB uptake in PET. However, S-[18F]THK-5117 uptake did not show any statistically significant correlation with either brain biopsy Pτ or CSF P-tau181 or total tau. CONCLUSION: S-[18F]THK-5117 lacked clear association with neuropathologically verified tau pathology in brain biopsy probably, at least partially, due to off-target binding. Further studies with larger samples of patients with different tau tracers are urgently needed. The detection of simultaneous Aβ and tau pathology in iNPH is important since that may indicate poorer and especially shorter response for CSF shunt surgery compared with no pathology

Absence of functional peroxisomes from mouse CNS causes dysmyelination and axon degeneration

Peroxisomal metabolism is essential for normal brain development both in men and in mice. Using conditional knock-out mice, we recently showed that peroxisome deficiency in liver has a severe and persistent impact on the formation of cortex and cerebellum, whereas absence of functional peroxisomes from the CNS only causes developmental delays without obvious alteration of brain architecture. We now report that a substantial fraction of the latter Nes-Pex5 knock-out mice survive into adulthood but develop progressive motoric and coordination problems, impaired exploration, and a deficit in cognition and die before the age of 6 months. Histopathologically, both the white and gray matter of the CNS displayed a region-specific accumulation of neutral lipids, astrogliosis and microgliosis, upregulation of catalase, and scattered cell death. Nes-Pex5 knock-out mice featured a dramatic reduction of myelin staining in corpus callosum, whereas cerebellum and other white matter tracts were less affected or unchanged. This was accompanied by a depletion of alkenylphospholipids in myelin and differentially reduced immunoreactivity of myelin proteins. EM analysis revealed that myelin wrappings around axons did still form, but they showed a reduction in thickness relative to axon diameters. Remarkably, multifocal axonal damage occurred in the corpus callosum. Thereby, debris accumulated between axolemma and inner myelin surface and axons collapsed, although myelin sheaths remained present. These anomalies of myelinated axons were already present in juvenile mice but aggravated in adulthood. Together, loss of CNS peroxisomal metabolism both affects myelin sheaths and axonal integrity possibly via independent pathways

Emergence of early alterations in network oscillations and functional connectivity in a tau seeding mouse model of Alzheimer’s disease pathology

Abstract Synaptic dysfunction and disconnectivity are core deficits in Alzheimer’s disease (AD), preceding clear changes in histopathology and cognitive functioning. Here, the early and late effects of tau pathology induction on functional network connectivity were investigated in P301L mice. Multichannel EEG oscillations were used to compute (1) coherent activity between the prefrontal cortex (PFC) and hippocampus (HPC) CA1-CA3 networks; (2) phase-amplitude cross frequency coupling (PAC) between theta and gamma oscillations, which is instrumental in adequate cognitive functioning; (3) information processing as assessed by auditory evoked potentials and oscillations in the passive oddball mismatch negativity-like (MMN) paradigm. At the end, the density of tau aggregation and GABA parvalbumin (PV+) interneurons were quantified by immunohistochemistry. Early weakening of EEG theta oscillations and coherent activity were revealed between the PFC and HPC CA1 and drastic impairments in theta–gamma oscillations PAC from week 2 onwards, while PV+ interneurons count was not altered. Moreover, the tau pathology disrupted the MMN complex amplitude and evoked gamma oscillations to standard and deviant stimuli suggesting altered memory formation and recall. The induction of intracellular tau aggregation by tau seed injection results in early altered connectivity and strong theta–gamma oscillations uncoupling, which may be exploited as an early electrophysiological signature of dysfunctional neuronal networks

Discovery of N-(4-[F-18]Fluoro-5-methylpyridin-2-yl)isoquinolin-6-amine (JNJ-64326067), a New Promising Tau Positron Emission Tomography Imaging Tracer (vol 62, pg 2974, 2019)

status: publishe

Intracerebral injection of preformed synthetic tau fibrils initiates widespread tauopathy and neuronal loss in the brains of tau transgenic mice

Neurofibrillary tangles composed of hyperphosphorylated fibrillized tau are found in numerous tauopathies including Alzheimer's disease. Increasing evidence suggests that tau pathology can be transmitted from cell-to-cell; however the mechanisms involved in the initiation of tau fibrillization and spreading of disease linked to progression of tau pathology are poorly understood. We show here that intracerebral injections of preformed synthetic tau fibrils into the hippocampus or frontal cortex of young tau transgenic mice expressing mutant human P301L tau induces tau hyperphosphorylation and aggregation around the site of injection, as well as a time-dependent propagation of tau pathology to interconnected brain areas distant from the injection site. Furthermore, we show that the tau pathology as a consequence of injection of tau preformed fibrils into the hippocampus induces selective loss of CA1 neurons. Together, our data confirm previous studies on the seeded induction and the spreading of tau pathology in a different tau transgenic mouse model and reveals neuronal loss associated with seeded tau pathology in tau transgenic mouse brain. These results further validate the utility of the tau seeding model in studying disease transmission, and provide a more complete in vivo tauopathy model with associated neurodegeneration which can be used to investigate the mechanisms involved in tau aggregation and spreading, as well as aid in the search for disease modifying treatments for Alzheimer's disease and related tauopathies