sirolimus and Tauopathies

Neurofibrillary tangles are intracellular inclusions made of tau protein that accumulates in neurons in Alzheimer's disease (AD) and in other tauopathies. We have investigated the ability of the rapamycin ester CCI-779/Temsilorimus, a mTOR inhibitor with better stability and pharmacological properties compared to rapamycin, to interfere with the development of a motor phenotype and tau pathology in a mutant tau mouse model developing neurofibrillary tangles, by stimulation of mTOR dependent macroautophagy. Mutant tau mice (Tg30) were treated with CCI-779 before onset of motor signs for 7 months (from 5 to 12 months of age) or after the onset of motor signs for 2 months (from 10 to 12 months of age). End-point motor deficits were 50% lower in the group of Tg30 mice treated for 7 months. Inhibition of mTOR signaling and stimulation of macroautophagy in the brain of CCI-779 treated Tg30 mice was suggested by decreased phosphorylation of mTOR downstream signaling molecules p70S6 kinase and Akt and increased level of the autophagy markers Rab7 and LC3-II. CCI-779 treatment decreased the brain levels of Sarkosyl-insoluble tau and phosphotau inTg30 mice both after 2 months or 7 months of treatment. The density of neurofibrillary tangles was significantly decreased when treatment was started prior onset of motor signs. These results indicate that stimulation of mTOR dependent autophagy by CCI-779 compound is efficient to counteract the accumulation of abnormal tau when administered early or late in a tauopathy model and to improve a motor deficit when started before onset of motor signs.

Topics: Analysis of Variance; Animals; Brain; Gene Expression Regulation; Humans; Liver; Mice; Mice, Transgenic; Motor Activity; Movement Disorders; Mutation; Protein Kinase Inhibitors; rab GTP-Binding Proteins; rab7 GTP-Binding Proteins; Rotarod Performance Test; Signal Transduction; Sirolimus; tau Proteins; Tauopathies; TOR Serine-Threonine Kinases

The perforant pathway projection from layer II of the entorhinal cortex to the hippocampal dentate gyrus is especially important for long-term memory formation, and is preferentially vulnerable to developing a degenerative tauopathy early in Alzheimer's disease (AD) that may spread over time trans-synaptically. Despite the importance of the perforant pathway to the clinical onset and progression of AD, a therapeutic has not been identified yet that protects it from tau-mediated toxicity. Here, we used an adeno-associated viral vector-based mouse model of early-stage AD-type tauopathy to investigate effects of the mTOR inhibitor and autophagy stimulator rapamycin on the tau-driven loss of perforant pathway neurons and synapses. Focal expression of human tau carrying a P301L mutation but not eGFP as a control in layer II of the lateral entorhinal cortex triggered rapid degeneration of these neurons, loss of lateral perforant pathway synapses in the dentate gyrus outer molecular layer, and activation of neuroinflammatory microglia and astroglia in the two locations. Chronic systemic rapamycin treatment partially inhibited phosphorylation of a mechanistic target of rapamycin substrate in brain and stimulated LC3 cleavage, a marker of autophagic flux. Compared with vehicle-treated controls, rapamycin protected against the tau-induced neuronal loss, synaptotoxicity, reactive microgliosis and astrogliosis, and activation of innate neuroimmunity. It did not alter human tau mRNA or total protein levels. Finally, rapamycin inhibited trans-synaptic transfer of human tau expression to the dentate granule neuron targets for the perforant pathway, likely by preventing the synaptic spread of the AAV vector in response to pathway degeneration. These results identify systemic rapamycin as a treatment that protects the entorhinal cortex and perforant pathway projection from tau-mediated neurodegeneration, axonal and synapse loss, and neuroinflammatory reactive gliosis. The findings support the potential for slowing the progression of AD by abrogating tau-mediated neurotoxicity at its earliest neuropathological stages.

Topics: Alzheimer Disease; Animals; Axons; Dentate Gyrus; Disease Models, Animal; Entorhinal Cortex; Hippocampus; Humans; Male; Memory, Long-Term; Mice; Microglia; Neurodegenerative Diseases; Neurons; Perforant Pathway; Phosphorylation; Sirolimus; Synapses; tau Proteins; Tauopathies; TOR Serine-Threonine Kinases

In a variety of neurodegenerative tauopathies including Alzheimer's disease, frontotemporal dementia and some types of Parkinson's disease, tau protein is abnormally hyperphosphorylated by several kinases and eventually aggregates to form neurofibrillary tangles, a neurotoxic pathological characteristic that closely correlates with cognitive impairments. Hence, targeting hyperphosphorylated tau protein has now been considered as a valid therapeutic approach for these neurodegenerative tauopathies. As a newly developed analog of rapamycin, temsirolimus was approved by the U.S. Food and Drug Administration and the European Medicines Agency for the treatment of renal cell carcinoma. Recent findings suggested that temsirolimus also provided beneficial effects in animal models of Huntington's disease and spinocerebellar ataxia type 3, two neurodegenerative diseases caused by accumulation of aberrant proteins within brain. To date, the therapeutic potentials of temsirolimus in neurodegenerative tauopathies have not been determined. Herein, we demonstrated for the first time that temsirolimus treatment effectively enhanced autophagic clearance of hyperphosphorylated tau in okadaic acid-incubated SH-SY5Y cells and in brain of P301S transgenic mice. Meanwhile, we showed that inactivation of glycogen synthase kinase-3β, the most important tau kinase, might contribute to the temsirolimus-induced reduction of tau hyperphosphorylation in these two tauopathy models. More importantly, temsirolimus administration rescued spatial learning and memory impairments in P301S transgenic mice. These findings highlight temsirolimus administration as a potential therapeutic strategy for neurodegenerative tauopathies.

Topics: Animals; Autophagy; Brain; Cell Line, Tumor; Disease Models, Animal; Enzyme Inhibitors; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Male; Memory Disorders; Mice, Inbred C57BL; Mice, Transgenic; Neuroprotective Agents; Okadaic Acid; Phosphorylation; Sirolimus; Spatial Learning; Spatial Memory; tau Proteins; Tauopathies

Accumulation of tau is a critical event in several neurodegenerative disorders, collectively known as tauopathies, which include Alzheimer's disease and frontotemporal dementia. Pathological tau is hyperphosphorylated and aggregates to form neurofibrillary tangles. The molecular mechanisms leading to tau accumulation remain unclear and more needs to be done to elucidate them. Age is a major risk factor for all tauopathies, suggesting that molecular changes contributing to the aging process may facilitate tau accumulation and represent common mechanisms across different tauopathies. Here, we use multiple animal models and complementary genetic and pharmacological approaches to show that the mammalian target of rapamycin (mTOR) regulates tau phosphorylation and degradation. Specifically, we show that genetically increasing mTOR activity elevates endogenous mouse tau levels and phosphorylation. Complementary to it, we further demonstrate that pharmacologically reducing mTOR signaling with rapamycin ameliorates tau pathology and the associated behavioral deficits in a mouse model overexpressing mutant human tau. Mechanistically, we provide compelling evidence that the association between mTOR and tau is linked to GSK3β and autophagy function. In summary, we show that increasing mTOR signaling facilitates tau pathology, while reducing mTOR signaling ameliorates tau pathology. Given the overwhelming evidence that reducing mTOR signaling increases lifespan and healthspan, the data presented here have profound clinical implications for aging and tauopathies and provide the molecular basis for how aging may contribute to tau pathology. Additionally, these results provide preclinical data indicating that reducing mTOR signaling may be a valid therapeutic approach for tauopathies.

Topics: Alzheimer Disease; Amyloid beta-Peptides; Animals; Autophagy; Disease Models, Animal; Frontotemporal Dementia; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Humans; Immunosuppressive Agents; Mice; Mice, Transgenic; Microtubules; Neurofibrillary Tangles; Phosphorylation; Sirolimus; tau Proteins; Tauopathies; TOR Serine-Threonine Kinases; Tuberous Sclerosis Complex 1 Protein; Tuberous Sclerosis Complex 2 Protein; Tumor Suppressor Proteins; Up-Regulation

Altered autophagy contributes to the pathogenesis of Alzheimer's disease and other tauopathies, for which curative treatment options are still lacking. We have recently shown that trehalose reduces tau pathology in a tauopathy mouse model by stimulation of autophagy. Here, we studied the effect of the autophagy inducing drug rapamycin on the progression of tau pathology in P301S mutant tau transgenic mice. Rapamycin treatment resulted in a significant reduction in cortical tau tangles, less tau hyperphosphorylation, and lowered levels of insoluble tau in the forebrain. The favourable effect of rapamycin on tau pathology was paralleled by a qualitative reduction in astrogliosis. These effects were visible with early preventive or late treatment. We further noted an accumulation of the autophagy associated proteins p62 and LC3 in aged tangle bearing P301S mice that was lowered upon rapamycin treatment. Thus, rapamycin treatment defers the progression of tau pathology in a tauopathy animal model and autophagy stimulation may constitute a therapeutic approach for patients suffering from tauopathies.

Topics: Animals; Astrocytes; Disease Progression; Humans; Mice; Mice, Transgenic; Phosphorylation; Sirolimus; Solubility; tau Proteins; Tauopathies; Time Factors