Abnormal tau induces cognitive impairment through two different mechanisms: synaptic dysfunction and neuronal loss

Area of Science:

• Neuroscience
• Molecular Biology
• Genetics

Background:

• Hyperphosphorylated tau protein is implicated in neurodegenerative diseases, but its direct causal role is unclear.
• Existing mouse models often do not adequately replicate tau phosphorylation observed in human conditions like Alzheimer's disease.

Purpose of the Study:

• To develop and characterize an inducible mouse model expressing pseudophosphorylated tau (Pathological Human Tau, PH-Tau) to investigate its in vivo effects.
• To determine the impact of varying PH-Tau levels on cognitive function, synaptic integrity, and neuronal survival.

Main Methods:

• Creation of an inducible mouse model with controlled expression of pseudophosphorylated human tau (PH-Tau).
• Assessment of cognitive deficits using behavioral tests.
• Evaluation of synaptic changes via electron microscopy (EM) and synaptic protein analysis.
• Quantification of neuronal death and glial response (astrocytosis).

Main Results:

• Low basal PH-Tau levels (4%) unexpectedly caused significant cognitive deficits, reduced synaptic density and proteins, and nuclear tau localization.
• Induced high PH-Tau levels (14%) led to substantial neuronal death (60% in CA3), astrogliosis, and dendritic process loss in CA1.
• The study demonstrated distinct neurodegenerative outcomes correlating with different PH-Tau expression levels.

Conclusions:

• Phosphorylated tau is sufficient to induce neurodegeneration and cognitive impairment.
• The level of PH-Tau expression dictates the specific mechanisms and severity of cognitive deficits and neuronal damage.
• This PH-Tau mouse model provides a valuable tool for studying tauopathies and developing targeted therapies.